CN112654664A

CN112654664A - Copolyester film

Info

Publication number: CN112654664A
Application number: CN201980057594.0A
Authority: CN
Inventors: 铃木智博; 西河博以
Original assignee: Mitsubishi Chemical Corp
Current assignee: Mitsubishi Chemical Corp
Priority date: 2018-09-13
Filing date: 2019-09-05
Publication date: 2021-04-13
Anticipated expiration: 2039-09-05
Also published as: JPWO2020054576A1; KR20210057011A; WO2020054576A1; TW202024171A; JP7192869B2; TWI813769B; CN112654664B

Abstract

A novel copolyester film which is more flexible, more flexible and has elongation, strength and heat resistance is proposed, which comprises a copolyester layer (layer I) containing a copolyester A as a main component resin, wherein the copolyester A is a copolymer of terephthalic acid and a "second dicarboxylic acid component", ethylene glycol and a "second alcohol component", the proportion of the "second dicarboxylic acid component" in the copolyester is 5 to 20 mol% inclusive of the dicarboxylic acid component, the proportion of the "second alcohol component" in the alcohol component is 1 to 25 mol% inclusive, and the copolyester film has a storage modulus at 25 ℃ of 2500MPa or less and a storage modulus at 120 ℃ of 10MPa or more.

Description

Copolyester film

Technical Field

The present invention relates to a copolyester film having a copolyester layer containing a copolyester as a main component resin.

Background

A polyethylene terephthalate (PET) film, which is a representative polyester film, particularly a biaxially stretched PET film, is used in various fields such as industrial materials, optical materials, electronic component materials, and battery packaging materials because of its excellent transparency, mechanical strength, heat resistance, flexibility, and the like.

As for such a polyester film, for example, patent document 1 proposes a flexible polyester film which exhibits flexibility not possessed by conventional polyester films and is excellent in moldability at a relatively low temperature and a low pressure, characterized in that the elastic modulus E' of the film is 20MPa or less at 120 ℃ and 5MPa or less at 180 ℃ and the haze of the film is 1.0% or less, 1, 4-cyclohexanedimethanol units are contained in an amount of 29 to 32 mol% as a diol component, and isophthalic acid units are not contained as a dicarboxylic acid component.

Patent document 2 proposes a thermal transfer image receiving sheet in which a developing layer formed of a copolyester film having a copolymerization percentage of 5 to 30 mol% is laminated on at least one surface of a polyester film.

Further, patent document 3 proposes a polyester film for metal plate lamination molding, which is characterized by containing a polyester film having an average particle diameter of 0.1 to 2.5 μm, a pore volume of 0.05 to 2.5ml/g, and a specific surface area of 50 to 600m²A copolyester having an intrinsic viscosity of 0.50 to 0.80dl/g and a glass transition temperature of 0.05 to 5.0 wt% based on the total weight of the biaxially oriented film and a lubricant having a compression resistance of 1 to 100MPaThe lubricant has a melting point of 210 to 250 ℃ and a temperature of 70 ℃ or higher, and the biaxially oriented film contains only up to 10 coarse particles/mm of the lubricant having a particle size of 20 μm or more²。

Further, patent document 4 proposes a biaxially stretched polyester film for molding, which is formed from a copolyester containing 1 to 20 mol% of an aliphatic dicarboxylic acid component relative to the total acid component, and which has a film strength F at 100% elongation in an atmosphere of 150 ℃₁₀₀0.5 to 5kg/mm²And the thickness of the film is not 40% or less.

Patent document 5 proposes a laminated polyester film in which a polyester (B) layer containing a polyester (B) as a main component is laminated on at least one surface of a polyester (a) layer containing a polyester (a) as a main component, and the laminated film has an elastic modulus of 20 to 1000MPa in an atmosphere at 23 ℃ and an elastic modulus of 10 to 200MPa in an atmosphere at 120 ℃ and is substantially non-oriented.

In recent years, as an image display apparatus, a computer (wearable computer) that is miniaturized to a size that can be worn on the body due to miniaturization and high performance of a portable terminal has been attracting attention.

An electronic device (wearable terminal) used in a wearable computer is preferably provided around a human body like a watch (patent document 6).

In addition, a flexible display which can be freely flexed attracts attention as a next-generation image display device. The flexible display mainly uses an organic electroluminescent (organic EL) display.

Since the flexible display uses a thin glass substrate or plastic substrate, the polyester film used for the members for the image display device is required not only to have optical characteristics and durability required for the conventional flat display panel but also to have no breakage or the like even when subjected to a bending test.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2014-1699371

Patent document 2: japanese laid-open patent publication No. H04-086293

Patent document 3: japanese patent laid-open No. 2000-001552

Patent document 4: japanese laid-open patent publication No. H03-067629

Patent document 5: international publication No. 09/078304

Patent document 6: japanese patent laid-open No. 2014-134903

Disclosure of Invention

Problems to be solved by the invention

As described above, when considering the use of polyester films for wearable terminals, flexible displays, and the like, it is necessary to develop polyester films that are not only soft but also more flexible and have elongation and strength than those of polyester films that have been generally used. In addition, heat resistance that does not shrink when heated is also required.

Accordingly, an object of the present invention is to provide: a novel copolyester film which is softer and more flexible than conventionally used polyester films and further has elongation, strength and heat resistance.

Means for solving the problems

The present invention provides a copolyester film, which is characterized in that the copolyester film comprises a copolyester layer (layer I) containing copolyester A as a main component resin,

the copolyester A is a copolymer of terephthalic acid and "other dicarboxylic acid component", and ethylene glycol and "other alcohol component", wherein the proportion of the "other dicarboxylic acid component" in the dicarboxylic acid component in the copolyester is 5 mol% or more and 20 mol% or less, and the proportion of the "other alcohol component" in the alcohol component is 1 mol% or more and less than 25 mol%,

the copolyester film has a storage modulus at 25 ℃ of 2500MPa or less and a storage modulus at 120 ℃ of 10MPa or more.

The present invention also provides a copolyester film, which is characterized by comprising a copolyester layer (layer I) containing 1 or 2 or more polyesters,

the total content of the "other dicarboxylic acid components" in the total content of the dicarboxylic acid components in the total polyester contained in the copolyester layer (layer I) is 5 mol% or more and 20 mol% or less, the total content of the "other alcohol components" in the total content of the alcohol components is 1 mol% or more and less than 25 mol%,

ADVANTAGEOUS EFFECTS OF INVENTION

The copolyester film provided by the invention has excellent flexibility at normal temperature, is soft and more flexible, further has elongation and strength, and further can have practically sufficient heat resistance. Thus, the copolyester film proposed by the present invention can be suitably used as a packaging material for batteries, an image display member, and particularly a constituent member of a flexible display, a wearable terminal, or the like, for example.

Drawings

Fig. 1 is a diagram schematically illustrating a method of the deflection measurement method performed in the example.

Detailed Description

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

< the present copolyester film >

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

The copolyester 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. In particular, a biaxially stretched film is preferable in terms of excellent balance of mechanical properties and flatness. When the copolyester film is such a stretched film, the storage modulus at 120 ℃ tends to be easily set to 10MPa or more.

< copolyester layer (I layer) >)

The copolyester layer (I layer) is a layer containing a copolyester a as a main component resin.

Here, the "main component resin" refers to a resin having the largest content ratio among the resins constituting the copolyester layer (I layer). The main component resin may be contained in the resin constituting the copolyester layer (I layer) in an amount of 30 mass% or more, particularly 50 mass% or more, particularly 80 mass% or more (including 100 mass%).

The copolyester layer (I layer) may be composed of only the copolyester a, or may further contain a resin B other than the copolyester a.

In this case, the resin B is preferably a resin compatible with the copolyester a.

The case where the copolyester layer (I layer) contains the copolyester a and the resin B compatible therewith is as described later.

(copolyester A)

The copolyester A is preferably a copolymer of terephthalic acid and other dicarboxylic acid components, and ethylene glycol and other alcohol components, i.e., a copolyester.

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), more specifically, a polyester resin having a melting point observed in Differential Scanning Calorimetry (DSC) according to JIS K7121(1987), and includes a so-called semicrystalline state. Conversely, a thermoplastic resin in which a melting point is not observed in the DSC is referred to as "non-crystalline". The crystalline polyester generally refers to a polyester having a crystal melting peak temperature (melting point). More specifically, the polyester having a melting point observed in Differential Scanning Calorimetry (DSC) in accordance with JIS K7121(1987) includes a so-called semicrystalline state.

Conversely, a thermoplastic resin in which a melting point is not observed in the DSC is referred to as "non-crystalline".

Examples of the "other dicarboxylic acid component" include aromatic dicarboxylic acids, alicyclic dicarboxylic acids, aliphatic dicarboxylic acids, polyfunctional acids, and the like. The "other dicarboxylic acid component" may be used in combination of 2 or more. By using 2 or more kinds in combination, the copolyester film can be softened more effectively, and the heat resistance can be maintained in some cases.

Among these, from the viewpoint of easily softening the copolyester film, the "other dicarboxylic acid component" is preferably an aromatic dicarboxylic acid such as isophthalic acid, 2, 6-naphthalenedicarboxylic acid, or diphenyldicarboxylic acid, an aliphatic dicarboxylic acid such as adipic acid, sebacic acid, dodecanedioic acid, eicosanoic acid, or derivatives thereof, an alicyclic dicarboxylic acid such as 1, 4-cyclohexanedicarboxylic acid, 1, 2-cyclopentanedicarboxylic acid, or cyclooctanedicarboxylic acid, or a dimer acid. Among them, aliphatic dicarboxylic acids or dimer acids are preferably contained.

Among the aliphatic dicarboxylic acids, aliphatic dicarboxylic acids having 20 to 80 carbon atoms, 30 or more and 60 or less, and 36 or more and 48 or less are particularly preferable from the viewpoint of further lowering the glass transition temperature.

The dimer acid is preferably a dicarboxylic acid composed of a dimer of unsaturated fatty acids, and the number of carbon atoms in the unsaturated fatty acids is 18 or more. Examples of such dimer acids include dimer acids obtained by dimerization using unsaturated fatty acids different from or the same as each other selected from oleic acid, elaidic acid, cetoleic acid, erucic acid, brassidic acid, linoleic acid, linolenic acid, and the like. Further, a dimer acid obtained by hydrogenating such dimerization may be used. The dimer acid may contain an aromatic ring, an alicyclic monocyclic ring, and an alicyclic polycyclic ring.

Among such dimer acids, dimer acids having 20 to 80 carbon atoms, particularly 26 or more and 60 or less, and particularly 30 or more and 50 or less are preferable from the viewpoint of further lowering the glass transition temperature.

As described above, the "other dicarboxylic acid component" may be arbitrarily selected. Among them, it is preferable to use 1 or more selected from aromatic dicarboxylic acids, and 1 or more selected from aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, and dimer acids in combination. Among them, 2 or more species of isophthalic acid, aliphatic dicarboxylic acid, and dimer acid are particularly preferably contained, and 2 or more species of isophthalic acid, aliphatic dicarboxylic acid having 20 to 80 carbon atoms, and dimer acid are particularly preferably contained.

When an aromatic dicarboxylic acid is used as the "other dicarboxylic acid component", the film tends to be softened while maintaining strength and heat resistance. On the other hand, if the "other dicarboxylic acid component" is selected from aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, and dimer acids, the film tends to soften with a smaller content ratio while maintaining the elongation (elongation at break), and among these, dimer acids are most effectively used. Therefore, by combining and using "other dicarboxylic acid components" as described above, a film having good strength, heat resistance, elongation, and flexibility can be formed.

In the copolyester A, the ratio of the "other dicarboxylic acid component" to the dicarboxylic acid component, i.e., the total of terephthalic acid and the "other dicarboxylic acid component", is preferably 5 to 20 mol%, more preferably, particularly, 8 mol% or more or 18 mol% or less, and particularly, 10 mol% or more or 15 mol% or less. When 2 or more "other dicarboxylic acid components" are used in combination herein, the total amount thereof is meant.

When the ratio of the "other dicarboxylic acid component" is in the above range, the copolyester film tends to have good elongation, strength and heat resistance and to be effectively softened.

Examples of the "other alcohol component (diol component)" include 1, 4-butanediol, 1, 6-hexanediol, diethylene glycol, 1, 3-propanediol, neopentyl glycol, 1, 4-cyclohexanedimethanol, bisphenol, and derivatives thereof. 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 (polycondensation) polyester is produced using ethylene glycol as one of raw materials, a part of ethylene glycol is modified into diethylene glycol and introduced into a polyester skeleton. This diethylene glycol is referred to as a by-product diethylene glycol, and the amount of the by-product is about 1 to 5 mol% in ethylene glycol, although it varies depending on the type of polycondensation (transesterification method, direct polycondensation) and the like. In the present invention, diethylene glycol by-produced from ethylene glycol in this manner is also considered as a copolymerization component, and is included in the "other alcohol component".

In the copolyester a, the ratio of the "other alcohol component (glycol component)" to the alcohol component (glycol component), that is, the total of ethylene glycol and the "other alcohol component" is preferably 1 mol% or more and less than 25 mol%, more preferably 2 mol% or more or 20 mol% or less, particularly 3 mol% or more or 18 mol% or less. When 2 or more "other alcohol components" are used in combination herein, the total amount thereof is meant.

When the ratio of the "other alcohol component" is in the above range, the copolyester film tends to have good elongation, strength and heat resistance and to be effectively softened.

The "other alcohol component" may be used in combination of 2 or more. By using 2 or more kinds in combination, the copolyester film may be softened more effectively.

In addition, preferably "other two carboxylic acid components" and "other alcohol components" total, combined use of 3 or more. By using a combination of a plurality of copolymerization components, the film tends to be softened at a smaller content ratio. Since it may be difficult to stabilize the film properties if the copolymerization component is excessively selected, the total of the "other dicarboxylic acid component" and the "other alcohol component" is preferably 3 to 5, more preferably 3 or 4.

Particularly preferred copolyesters a include the following crystalline copolyesters Aa: the copolymer is a copolymer of terephthalic acid, isophthalic acid and aliphatic dicarboxylic acid or dimer acid, and ethylene glycol and diethylene glycol, wherein the ratio of isophthalic acid, aliphatic dicarboxylic acid or dimer acid in the dicarboxylic acid component constituting the copolyester is 5 mol% or more and 20 mol% or less, and the ratio of diethylene glycol in the alcohol component constituting the copolyester is 1 mol% or more and less than 25 mol%.

In general, when the ratio of the copolymerization component is increased in order to decrease the elastic modulus, the crystallinity is decreased, and when the ratio is increased, the copolyester becomes amorphous. The copolyester Aa has a high ratio of copolymerized components and can realize a low elastic modulus, but can be heat-set by heat treatment after stretching in order to maintain crystallinity. As a result, the copolyester Aa is flexible, and further has good elongation and strength, and further can suppress heat shrinkage.

(resin B)

As described above, the copolyester layer (I layer) may be a layer comprising the copolyester a and the resin B compatible therewith.

In the present invention, "compatible" means that 2 or more resins to be mixed are completely mixed at a molecular level. In this case, the amorphous region mixed at a molecular level may be regarded as a single phase, and the micro brownian motion is also generated at a single temperature. Therefore, when 2 or more resins are compatible, the melting point or glass transition temperature of the mixed resin of the 2 or more resins is single, and the main dispersion peak is also single. Therefore, conversely, the resin compatible with the copolyester A can be defined as a resin which can change the melting point or glass transition temperature of the copolyester A when blended with the copolyester A.

The glass transition temperature in this case is, for example, a peak temperature of main dispersion of loss tangent (tan δ) when a temperature dispersion measurement of dynamic viscoelasticity (dynamic viscoelasticity measurement according to JIS K7244 method) is performed under conditions of a strain of 0.1%, a frequency of 10Hz, and a temperature rise rate of 3 ℃/min.

When the copolyester layer (I layer) is a layer comprising a copolyester a and a resin B, the resin B is preferably a resin compatible with the copolyester a and having a melting point of 270 ℃ or less or a non-crystalline glass transition temperature of 30 to 120 ℃. By selecting such a resin B, the glass transition temperature of the copolyester layer (I layer) can be increased, and the heat resistance can be improved. As the resin B, for example, a polyester such as polyethylene terephthalate (PET) is selected, and dimensional stability and heat resistance can be imparted.

From the viewpoint of achieving both flexibility and heat resistance, the resin B contains 1 or 2 or more types of polyesters (including 1 or 2 or more types of polyesters) containing terephthalic acid and "other dicarboxylic acid components" as dicarboxylic acid components and ethylene glycol and "other alcohol components" as alcohol components, and the ratio of the total content of the other dicarboxylic acid components "to the total content of the dicarboxylic acid components (in the case where 2 or more types of polyesters are contained, the total content of the dicarboxylic acid components contained in each polyester) is 5 mol% or more and 20 mol% or less, preferably 8 mol% or more or 18 mol% or less, more preferably 10 mol% or 15 mol% or less, and the ratio of the total content of the other alcohol components" to the total content of the alcohol components (in the case where 2 or more types of polyesters are contained, the total content of the alcohol components contained in each polyester) is preferably 1 mol% or more and less than 25 mol%, Among them, 2 mol% or more or 20 mol% or less, and among them, 3 mol% or more or 18 mol% or less are preferable.

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

In the copolyester layer (I layer), the mass ratio of the copolyester a to the resin B is preferably 98: 2-50: 50. further preferred are especially 95: 5-60: 40. in particular 90: 10-65: 35.

it is considered that the same effect as that obtained when the copolyester a is contained as the main component resin can be obtained, as long as the component ratio of the entire polyester contained in the copolyester layer (I layer) is the same as that of the copolyester a.

Thus, when the copolyester layer (I layer) contains 1 or 2 or more kinds of polyesters, the same effect as in the case of containing the copolyester a as the main component resin can be obtained as long as 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 ratio of the total content of the "other alcohol components" to the total content of the alcohol components is 1 mol% or more and less than 25 mol% in the total content of all the polyesters contained in the copolyester layer (I layer).

In this case, the preferable range of the ratio of the total content of the "other dicarboxylic acid component" to the total content of the dicarboxylic acid components is the same as the preferable range of the ratio of the "other dicarboxylic acid component" to the dicarboxylic acid component in the copolyester A. The preferable 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 preferable range of the ratio of the "other alcohol components" to the alcohol components in the copolymerized polyester A.

< case of laminated construction >

As described above, the present copolyester film may be a laminated film including a copolyester layer (I layer) and other layers.

For example, a laminated film having the following structure is exemplified: a polyester layer (layer II) containing a polyester C as a main component resin was laminated on both the front and back sides of the copolyester layer (layer I).

In this case, when the copolyester a is crystalline, the polyester C is preferably a polyester having a melting point higher than that of the copolyester a, and when the copolyester a is amorphous, the polyester C is preferably a polyester having a melting point higher than the glass transition temperature of the copolyester a.

In such a laminated film having a structure in which a polyester layer (II layer) containing a polyester C as a main component resin is laminated, a raw material resin composition is laminated by coextrusion or the like so as to form a polyester layer (II layer)/copolyester layer (I layer)/polyester layer (II layer) and then stretched, and then heat-setting treatment can be performed at a higher temperature than in the case of a single layer of the copolyester layer (I layer), and therefore, softening to a level that cannot be achieved in a single layer of the copolyester layer (I layer), improvement in heat resistance, or further prevention of heat shrinkage can be achieved.

Specifically, the copolyester film can have a storage modulus at 25 ℃ of 300 to 2500MPa, wherein the storage modulus is 500MPa or more or 2000MPa or less.

In the laminated film, the thickness of each polyester layer (layer II) is preferably 1 to 20% of the thickness of the copolyester layer (layer I).

The thickness of each polyester layer (II layer) is preferably 1% or more of the thickness of the copolyester layer (I layer) because film formation can be performed without significantly impairing the productivity, and 20% or less because the required flexibility can be sufficiently secured.

From the above-mentioned viewpoint, the thickness of each layer of the polyester layer (II layer) is preferably 1 to 20%, more preferably 3% or more or 15% or less, particularly 5% or more or 12% or less of the thickness of the copolyester layer (I layer).

The thickness of the polyester layer (II layer) present on both the front and back sides of the copolyester layer (I layer) may be different or the same on the front and back sides.

When the copolyester A is crystalline, the polyester C is preferably a polyester having a melting point higher than that of the copolyester A by 10 to 100 ℃, 20 ℃ or 90 ℃ or lower, or 40 ℃ or higher or 70 ℃ or lower, and when the copolyester A is amorphous, the polyester C is preferably a polyester having a melting point higher than that of the copolyester A by 120 to 260 ℃, 140 ℃ or higher or 230 ℃ or lower, or 160 ℃ or higher or 200 ℃ or lower.

The polyester C which is the main component of the polyester layer (layer II) present on both the front and back sides of the copolyester layer (layer I) may be different or the same on the front and back sides. Among them, it is preferable that the melting points of the polyester C on the front and back surfaces are not greatly different. Specifically, the difference between the melting points of the polyester layers (layer II) present on both the front and back sides is preferably 80 ℃ or lower, more preferably 60 ℃ or lower, and more preferably 40 ℃ or lower.

The polyester C present in the polyester layers (layer II) on both the front and back sides of the copolyester layer a, if the same, can realize coextrusion of 2 kinds of 3 layers, and therefore, 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. But is not limited thereto.

When the polyester C is a copolyester, examples of the dicarboxylic acid component other than terephthalic acid include aromatic dicarboxylic acids, alicyclic dicarboxylic acids, aliphatic dicarboxylic acids, polyfunctional acids, and the like.

In the polyester C, the proportion of the "dicarboxylic acid component other than terephthalic acid" in the dicarboxylic acid component is preferably 1 to 30 mol%, more preferably 5 mol% or more or 25 mol% or less, particularly 10 mol% or more or 20 mol% or less.

When the polyester C is a copolyester, examples of the alcohol component other than ethylene glycol include 1, 4-butanediol, 1, 6-hexanediol, diethylene glycol, 1, 3-propanediol, neopentyl glycol, 1, 4-cyclohexanedimethanol, bisphenol, and derivatives thereof.

In the polyester C, the proportion of the "alcohol component other than ethylene glycol" in the alcohol component is preferably 1 to 100 mol%, more preferably 5 mol% or more or 95 mol% or less, particularly 10 mol% or more or 90 mol% or less.

Thickness of the copolyester film

The thickness of the copolyester film is not particularly limited, and an appropriate thickness can be selected according to the application.

Among them, from the viewpoint of further developing the characteristics of the present copolyester film, the total thickness of the film is preferably more than 20 μm.

It can be said that the strength of the stiffness of the film is proportional to the cube of the thickness. However, the copolyester film may have a thickness of more than 20 μm and also has characteristics of weak rigidity and flexibility, and can further enjoy the advantages of the present invention.

From the above-mentioned viewpoints, the total thickness of the copolyester film is preferably more than 20 μm, more preferably 23 μm or more, and particularly 30 μm or more.

On the other hand, the upper limit of the total thickness of the present copolyester film is not particularly limited. Preferably 1000 μm or less, more preferably especially 500 μm or less, especially 250 μm or less, especially 100 μm or less.

< Property of the copolyester film >

The copolyester film preferably has a storage modulus at 25 ℃ of 2500MPa or less.

By setting the storage modulus at 25 ℃, that is, at room temperature, to 2500MPa or less, it is possible to sufficiently follow the skin when the wearable terminal is worn, for example.

From the above-mentioned viewpoints, the copolyester film preferably has a storage modulus at 25 ℃ of 2500MPa or less, more preferably 2000MPa or less, particularly 1200MPa or less.

From the viewpoint of workability in the process, the storage modulus at 25 ℃ is preferably 300MPa or more, more preferably particularly 500MPa or more, and particularly 700MPa or more.

The storage modulus at 25 ℃ is a value obtained by the measurement method described in the examples described later.

In the present copolyester film, the storage modulus at 25 ℃ can be adjusted to the above range by adjusting the kind and content of the copolymerization component of the copolyester a, for example.

As described above, the adjustment can also be made by forming a laminate film having a structure in which a polyester layer (layer II) containing a polyester C as a main component resin is laminated on both the front and back surfaces of a copolyester layer (layer I).

Further, the stretching conditions in the production of the copolyester film of the present invention and the subsequent heat-setting conditions may be adjusted.

But is not limited to these methods.

In addition, the copolyester film preferably has a storage modulus of 10MPa or more at 120 ℃.

By setting the storage modulus at high temperature to 10MPa or more in this way, sufficient heat resistance is obtained and wrinkles can be suppressed from occurring during processing.

From the above-mentioned viewpoints, the copolyester film of the present invention preferably has a storage modulus at 120 ℃ of 10MPa or more, more preferably 30MPa or more, particularly 50MPa or more.

In view of suppressing the amount of heat required for processing, the copolyester film of the present invention preferably has a storage modulus at 120 ℃ of 500MPa or less, more preferably 400MPa or less, particularly 300MPa or less.

The storage modulus at 120 ℃ is a value obtained by the measurement method described in the examples described later.

In the present copolyester film, a method for adjusting the storage modulus at 120 ℃ to the above range may be the same as the method for adjusting the storage modulus at 25 ℃. Among these methods, a method of adjusting particularly the stretching conditions and the subsequent heat-setting conditions is particularly effective. But is not limited to this method.

The copolyester film preferably has a loss tangent (tan. delta.) at 25 ℃ of 0.02 or more.

By setting the loss tangent at 25 ℃, that is, at room temperature, to 0.02 or more, it is possible to sufficiently follow the skin when the wearable terminal is worn, for example.

From the above-mentioned viewpoints, the loss tangent at 25 ℃ of the copolyester film is preferably 0.05 or more, more preferably 0.08 or more, particularly 0.10 or more.

From the viewpoint of workability in the process, the loss tangent (tan δ) at 25 ℃ is preferably 1.5 or less, more preferably 1.0 or less, and particularly 0.5 or less.

In the present copolyester film, a method for adjusting the loss tangent at 25 ℃ to the above range may be the same as the method for adjusting the storage modulus at 25 ℃. Among these, a method of adjusting the kind and content of the copolymerization component of the copolyester A is particularly effective. But is not limited to this method.

In the present copolyester film, when the copolyester A is crystalline, the crystal melting enthalpy DeltaHm is preferably 3.0J/g or more, more preferably particularly 5.0J/g or more, and particularly 7.0J/g or more. Δ Hm is an index of crystallinity, and when it is 3.0J/g or more, sufficient heat resistance can be obtained and heat shrinkability can be suppressed.

The present copolyester film preferably has a ratio ((a)/(b)) of (a) to (b) of 0.3 or more, more preferably 0.5 or more, particularly 1.0 or more, when the "flexibility (rigidity)" measured by the deflection measuring method described in the examples described later, that is, when the length of the film which is lowered in the vertical direction is (a) and the length of the film which is projected in the horizontal direction is (b).

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 the (a)/(b) is not particularly limited, but is preferably 15.0 or less, more preferably particularly 10.0 or less, and particularly 6.0 or less, from the viewpoint of workability in the process.

In the present copolyester film, in order to adjust (a)/(b) to the above range, it is important to adjust the film thickness first and then to adjust the kind and content of the copolymerization component of the copolyester A for the same film thickness. But is not limited to this method.

From the above-mentioned viewpoint, the "other dicarboxylic acid component" in the copolymerized component of the copolyester a is preferably an aliphatic dicarboxylic acid or dimer acid, and the content thereof is preferably 5 mol% or more and 20 mol% or less. On the other hand, the "other alcohol component" is preferably diethylene glycol, and the content thereof is preferably 1 mol% or more and less than 25 mol%.

< method for producing copolyester film of the present invention >

As an example of the method for producing the copolyester film, a case where the copolyester film is a biaxially stretched film will be described. But is not limited to the manufacturing method described herein.

First, a raw material such as a polyester chip is supplied to a melt extrusion device by a known method, heated to a temperature equal to or higher than the melting point of each polymer, and extruded from a die to form a molten polymer, and cooled and solidified on a rotary cooling drum to a temperature equal to or lower than the glass transition temperature of the polymer, thereby obtaining a substantially amorphous unoriented sheet.

Next, the unoriented sheet is stretched in one direction by a roller or tenter type stretching machine. In this case, the stretching temperature is usually 25 to 120 ℃ and preferably 35 to 100 ℃, and the stretching ratio is usually 2.5 to 7 times and preferably 2.8 to 6 times.

Then, the film is stretched in a direction orthogonal to the stretching direction in the first stage. In this case, the stretching temperature is usually 50 to 140 ℃ and the stretching ratio is usually 3.0 to 7 times, preferably 3.5 to 6 times.

Further, the copolyester film can be obtained as a biaxially oriented film by heat-fixing the film under tension or under 30% relaxation at 130 to 270 ℃.

In addition, the above-described stretching may be performed in one direction in two or more stages.

In the case of a single layer of the copolyester layer (I layer), the heat-setting treatment (also referred to as "heat treatment") is preferably performed at a temperature 10 to 70 ℃ lower than the melting point of the copolyester a.

When the 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) may be co-extruded and then stretched and heat-set as an integral film as described above.

The heat-setting treatment in this case is preferably performed by heating to a temperature lower than the melting point of the polyester C. Further, when the copolyester a is crystalline, it is preferable to perform the 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, the copolyester layer (I layer) can be softened to a level that cannot be achieved in the case of a single layer.

The reason for this is that: the heat-setting is performed at a temperature lower than the melting point of the polyester C to fix the stretch orientation of the surface layer, thereby improving the elongation, strength and heat resistance (heat shrinkability), while the heat-setting is performed at a temperature higher than the melting point of the copolyester a to relax the stretch orientation and strain of the intermediate layer, thereby making it possible to produce a film further flexible.

Use of the copolyester film

As described above, the copolyester film of the present invention is excellent in flexibility at room temperature, has a characteristic of being flexible and having almost no rigidity, and can exhibit practically sufficient heat resistance. Therefore, the resin composition can be suitably used as a constituent member of, for example, a battery packaging material, a surface protective film, an image display member, particularly a flexible display, a wearable terminal, or the like.

The use of the copolyester film is not limited to the above, and the copolyester film can be used for various packaging materials, building materials, stationery, automobile members, other structural members, and the like.

< statement of sentence etc. >

In the present invention, the term "film" also includes the case of "sheet", and the term "sheet" also includes the case of "film".

In addition, when a "panel" is expressed as an image display panel, a protective panel, or the like, a plate body, a sheet, and a film are included.

In the present invention, unless otherwise specified, the term "X to Y" (X, Y is an arbitrary number) includes the meaning of "X or more and Y or less" and also includes the meaning of "preferably more than X" or "preferably less than Y".

In addition, when "X" or more (X is an arbitrary number) is described, the meaning of "preferably more than X" is included unless otherwise specified, and when "Y" or less (Y is an arbitrary number), the meaning of "preferably less than Y" is included unless otherwise specified.

Examples

Next, the present invention will be described in further detail by way of examples. The present invention is not limited to the examples described below.

< evaluation method >

Hereinafter, measurement and evaluation of various physical properties and the like were performed as follows.

(1) Storage modulus E', loss tangent tan delta

Based on JIS K7244, the storage modulus E' at 25 ℃ and 120 ℃ and the loss tangent tan. delta at 25 ℃ were obtained based on the data obtained by measuring the width direction (TD) of the copolyester film (sample) at a vibration frequency of 10Hz, a strain of 0.1%, and a temperature rise rate of 1 ℃/min from-100 ℃ to 200 ℃ using a Measurement & Control technology Co., Ltd.

(2) Crystal melting enthalpy Δ Hm

Differential Scanning Calorimeter (DSC) measurements of the measurement samples were performed based on JIS K7141-2 (2006). The temperature was raised from 30 ℃ to 280 ℃ at 10 ℃/min for 1 minute, then lowered from 280 ℃ to 30 ℃ at 10 ℃/min for 1 minute, and further raised from 30 ℃ to 280 ℃ at 10 ℃/min. The crystal melting enthalpy (. DELTA.hm) was calculated based on the crystal melting peak area during the reheating at that time.

In the case of single layer, the copolyester film was used as a measurement sample, and in the case of lamination, the intermediate layer was used as a measurement sample.

(3) Young's modulus

The copolyester films (samples) obtained in examples and comparative examples were stretched at a strain rate of 10%/min in a chamber adjusted to a temperature of 23 ℃ and a humidity of 50% RH using a tensile tester (manufactured by Intesco Corporation, Intesco model 2001), and the initial linear portion of the tensile stress-strain curve was used to calculate the tensile stress-strain curve according to the following formula.

E＝Δσ/Δε

(in the above formula, E is Young's modulus (GPa), Δ σ is the stress difference (GPa) based on the original average cross-sectional area between 2 points on the straight line, and Δ ε is the strain difference/initial length between the same 2 points.)

(4) Tensile breaking strength

The copolyester films (samples) obtained in examples and comparative examples were mounted on a tensile tester (model Intesco model 2001, manufactured by Intesco Corporation) in a chamber adjusted to a temperature of 23 ℃ and a humidity of 50% RH such that the chuck pitch of the copolyester film (sample) having a width of 15mm was 50mm, and the copolyester film was stretched at a strain rate of 200 mm/min in the longitudinal direction (MD) or the width direction (TD) of the film to obtain the tensile breaking strength according to the following formula.

Tensile breaking strength (MPa) ═ F/A

Wherein in the above formula, F is the load (N) at the time of fracture, and A is the original cross-sectional area (mm) of the test piece²)。

(5) Elongation at tensile break

The same test as the tensile break strength was carried out, and the tensile break elongation of the copolyester films (samples) obtained in examples and comparative examples was determined according to the following formula.

Tensile elongation at break (%) (100 × (L-L0)/L0

Wherein, in the formula, L is the gauge length (mm) at the time of fracture, and L0 is the original gauge length (mm).

(6) Heat shrinkage rate

The copolyester films (samples) obtained in examples and comparative examples were left to stand in a drying machine maintained at 120 ℃ for 5 minutes in a tensionless state, the lengths of the samples before and after the treatment were measured, and the respective heat shrinkage rates in the longitudinal direction (MD) and the width direction (TD) of the films were calculated by the following formulas.

Heat shrinkage (%) of { (L0-L1)/L0} × 100

(in the above formula, L0 represents the sample length before heat treatment, and L1 represents the sample length after heat treatment.)

The film was measured at 5 points in the longitudinal direction (MD) and the width direction (TD), and the average values were obtained.

(7) Evaluation of flexibility (rigidity) (Flex measurement method)

The copolyester films (samples) obtained in examples and comparative examples were allowed to stand at 23 ℃ for 24 hours in an atmosphere of 50% RH, and then cut into a size of 150mm in length and 50mm in width.

As shown in fig. 1, the copolyester film (sample) was placed on a table at 23 ℃ so as to protrude from the edge of the table by a length of 50mm, a 200g weight was placed on the copolyester film (sample) on the table and fixed, and the front end side of the sample protruding from the edge of the table was bent downward by its own weight. After 3 minutes, the length (a) of the front end portion of the sample protruding from the edge of the table, which droops in a curve vertically downward, and the length (b) of the front end portion protruding from the edge of the table in the horizontal direction were measured.

The ratio ((a)/(b)) of the length (a) of the bending sag to the length (b) of the protrusion in the horizontal direction was calculated, and the evaluation was "good" when the ratio was 0.30 or more, and "bad" when the ratio was less than 0.30.

(raw materials)

The following raw materials were used in examples and comparative examples.

Copolyester 1 ("co-PS 1"): a crystalline copolyester having an acid component comprising 88 mol% of terephthalic acid, 7 mol% of a hydrogenated dimer acid having 36 carbon atoms and 5 mol% of isophthalic acid, and a glycol component comprising 90 mol% of ethylene glycol and 10 mol% of diethylene glycol. Melting point 208 deg.C, and intrinsic viscosity 0.68 dl/g.

Copolyester 2 ("co-PS 2"): a crystalline copolyester having an acid component comprising 88 mol% of terephthalic acid and 12 mol% of a hydrogenated dimer acid having 36 carbon atoms and a diol component comprising 67 mol% of ethylene glycol and 33 mol% of 1, 4-butanediol (the amount of diethylene glycol by-produced is less than 0.1 mol%). Melting point 200 deg.C, and intrinsic viscosity 0.72 dl/g.

Copolyester 3 ("co-PS 3"): a crystalline copolyester having an acid component comprising 78 mol% of terephthalic acid and 22 mol% of isophthalic acid and a glycol component comprising 98 mol% of ethylene glycol and 2 mol% of diethylene glycol as a by-product. Melting point 198 deg.C, and intrinsic viscosity 0.70 dl/g.

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

[ example 1]

As the surface layer and the intermediate layer, chips of copolyester 1 (Co-PS 1) were fed into an extruder with vent holes set at 280 ℃ and extruded from the tip of the extruder via a gear pump and a filter, and then subjected to a static charge method to be rapidly cooled and solidified on a cooling roll having a surface temperature set at 30 ℃ to obtain an unstretched sheet.

Subsequently, the obtained unstretched sheet was stretched at 50 ℃ for 3.3 times in the longitudinal direction (MD), introduced into a tenter, stretched at 80 ℃ for 4.2 times in the width direction (TD), and subjected to heat treatment at 200 ℃ for 10 seconds to relax by 10% in the width direction (TD), thereby obtaining a biaxially stretched copolyester film (sample) substantially composed of a single layer and having a thickness of 25 μm.

[ example 2]

As the intermediate layer, chips of copolyester 1 (Co-PS 1) were fed into a twin-screw extruder with a main vent set at 280 ℃.

Further, as the skin layer, chips of Polyester (PET) were fed into a twin-screw extruder with a vent hole set at 280 ℃.

2 types of 3 layers (surface layer/intermediate layer/surface layer) were co-extruded from a pipe head so that the polymer from the main extruder became an intermediate layer and the polymer from the sub-extruder became a surface layer by means of a gear pump and a filter, and the resultant was quenched and solidified on a cooling roll having a surface temperature of 30 ℃ by an electrostatic precipitation method to obtain an unstretched sheet.

Subsequently, the obtained unstretched sheet was stretched at 80 ℃ for 3.2 times in the longitudinal direction (MD), introduced into a tenter, stretched at 100 ℃ to 4.0 times in the width direction (TD), and subjected to heat treatment at 200 ℃ for 10 seconds to relax by 10% in the width direction (TD), thereby obtaining a biaxially stretched copolyester film (sample) having a thickness of 25 μm and formed in a thickness composition of 1 μm (surface layer)/23 μm (intermediate layer)/1 μm (surface layer).

[ 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, "total PS1/PET 80/20" in example 3 means that 180 parts by mass of total PS is mixed with 20 parts by mass of PET, and the mass ratio is similarly expressed for other examples.

Comparative example 1

Polyester (PET) chips were fed into an extruder having an exhaust hole and set at 280 ℃ and extruded from the tip of the extruder through a gear pump and a filter, and then subjected to a static charge method to be rapidly cooled and solidified on a cooling roll having a surface temperature set at 30 ℃ to obtain an unstretched sheet.

Subsequently, the obtained unstretched sheet was stretched at 86 ℃ for 3.5 times in the longitudinal direction (MD), introduced into a tenter, stretched at 110 ℃ for 4.3 times in the width direction (TD), and subjected to heat treatment at 235 ℃ for 10 seconds to relax by 10% in the width direction (TD), thereby obtaining a biaxially stretched copolyester film (sample) having a thickness of 50 μm.

Comparative example 2

An undrawn sheet was obtained by feeding 85 parts by mass of chips of co-PS 3 and 15 parts by mass of chips of PET into an extruder with an exhaust port set at 280 ℃, extruding the mixture from the tip of the extruder through a gear pump and a filter, and subjecting the mixture to an electrostatic charge method to rapidly cool and solidify the mixture on a cooling roll having a surface temperature set at 30 ℃.

Subsequently, the obtained unstretched sheet was stretched at 80 ℃ for 3.4 times in the longitudinal direction (MD), introduced into a tenter, stretched at 145 ℃ for 3.9 times in the width direction (TD), and subjected to heat treatment at 186 ℃ for 10 seconds to relax by 10% in the width direction (TD), to obtain a biaxially stretched copolyester film (sample) having a thickness of 50 μm.

Comparative example 3

The chips of copolyester 2 (Co-PS 2) were fed into an extruder having a vent hole and set at 280 ℃ and extruded from the tip of the extruder via a gear pump and a filter, and then quenched and solidified on a chill roll having a surface temperature of 30 ℃ by an electrostatic charge method to obtain an unstretched copolyester film (sample) having a thickness of 200. mu.m.

[ Table 1]

From the foregoing examples and the results of experiments that the inventors have conducted, it is known that: the copolyester film having the copolyester layer (I layer) containing the copolyester a as a main component resin has excellent flexibility at room temperature, is not only flexible but also more flexible, and can have elongation and strength by having a storage modulus at 25 ℃ of 2500MPa or less. And it is known that: the storage modulus at 120 ℃ is 10MPa or more, whereby practically sufficient heat resistance can be obtained.

As shown in examples 2 to 5, it was confirmed that: when the main component resin of the intermediate layer is a crystalline copolyester, and 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 copolyester, the heat treatment (heat setting) temperature after stretching can be further increased as compared with the case of a single layer composed of only the intermediate layer, and the heat shrinkage can be further suppressed.

It should be noted that: when the main component resin of the intermediate layer is an amorphous copolyester, and the polyester as the main component resin of the surface layer is a polyester having a melting point higher than the glass transition temperature of the copolyester, the heat treatment (heat fixation) temperature after stretching can be further increased as compared with the case of a single layer composed only of the intermediate layer, and therefore the heat shrinkability can be further suppressed.

Claims

1. A copolyester film characterized by comprising a copolyester layer (layer I) containing a copolyester A as a main component resin,

the copolyester A is a copolymer of terephthalic acid and other dicarboxylic acid component, and ethylene glycol and other alcohol component, wherein the proportion of other dicarboxylic acid component in the dicarboxylic acid component is 5 mol% or more and 20 mol% or less, the proportion of other alcohol component in the alcohol component is 1 mol% or more and less than 25 mol%,

2. The copolyester film according to claim 1, wherein the copolyester layer (I layer) is a layer comprising the copolyester a and a resin B compatible therewith.

3. The copolyester film according to claim 1 or 2, wherein the resin B comprises 1 or 2 or more polyesters, and the ratio of the total content of the "other dicarboxylic acid components" to the total content of the dicarboxylic acid components in the polyester is 5 mol% or more and 20 mol% or less, and the ratio of the total content of the "other alcohol components" to the total content of the alcohol components is 1 mol% or more and less than 25 mol%.

4. A copolyester film characterized by comprising a copolyester layer (layer I) containing 1 or 2 or more polyesters,

5. The copolyester film according to any of claims 1 to 4, wherein the "other dicarboxylic acid component" comprises an aliphatic dicarboxylic acid or a dimer acid.

6. The copolyester film according to any of claims 1 to 5, wherein the "other dicarboxylic acid component" comprises 2 or more of isophthalic acid, aliphatic dicarboxylic acid and dimer acid.

7. The copolyester film according to any one of claims 1 to 5, wherein the "other dicarboxylic acid component" comprises 2 or more of isophthalic acid, aliphatic dicarboxylic acid having 20 to 80 carbon atoms, and dimer acid.

8. The copolyester film according to any of claims 1 to 7, wherein the "other alcohol component" comprises diethylene glycol.

9. The copolyester film according to any one of claims 1 to 8, which has a constitution in which a polyester layer (layer II) containing a polyester C as a main component resin is laminated on both front and back sides of a copolyester layer (layer I),

when the copolyester a is crystalline, the polyester C is a polyester having a melting point higher than that of the copolyester a, and when the copolyester a is amorphous, the polyester C is a polyester having a melting point higher than the glass transition temperature of the copolyester a.

10. The copolyester film according to claim 9 wherein the thickness of each of the polyester layers (II) is 1 to 20% of the thickness of the copolyester layer (I).

11. The copolyester film according to any one of claims 1 to 10, wherein the loss tangent (tan δ) at 25 ℃ is 0.02 or more.

12. The copolyester film according to any of claims 1 to 11 wherein the total thickness of the film is more than 20 μm.

13. A surface protective film comprising the copolyester film according to any one of claims 1 to 12.

14. An optical member comprising the copolyester film according to any one of claims 1 to 12.