KR20210057011A - Copolyester film - Google Patents

Abstract

Co-polyester film with a co-polyester layer (layer I) containing co-polyester A as a main component resin as a new co-polyester film that is more flexible, more flexible, and yet has both elongation, strength, and heat resistance. As, the said copolymerized polyester A is a copolymer of terephthalic acid and a "other dicarboxylic acid component", and ethylene glycol and "other alcohol component", and occupied in the dicarboxylic acid component in the said copolymerized polyester The ratio of the "external dicarboxylic acid component" is 5 mol% or more and 20 mol% or less, the ratio of the "other alcohol component" to the alcohol component is 1 mol% or more and less than 25 mol%, and the storage modulus at 25°C is 2500 MPa or less, and It proposes a copolymer polyester film characterized in that the storage modulus at 120° C. is 10 MPa or more.

Description

Copolyester film

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

Polyethylene terephthalate (PET) film, which is a typical polyester film, especially biaxially stretched PET film, has excellent transparency, mechanical strength, heat resistance, flexibility, etc., and thus various fields such as industrial materials, optical materials, electronic parts materials, battery packaging materials, etc. It is being used for.

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

In addition, in Patent Document 2, an image-receiving sheet for thermal transfer is proposed in which an image-receiving layer made of a copolymerized polyester layer having a copolymerization ratio of 5 to 30 mol% is laminated on at least one side of a polyester film. .

In addition, in Patent Document 3, containing 0.05 to 5.0% by weight of a lubricant having an average particle diameter of 0.1 to 2.5 μm, a pore volume of 0.05 to 2.5 ml/g, a specific surface area of 50 to 600 m ^{2 /g, and a compressive strength of 1 to 100 MPa} As a biaxially oriented film composed of a copolymerized polyester, the biaxially oriented film has an intrinsic viscosity of 0.50 to 0.80 dl/g, a glass transition point of 70° C. or higher, and a melting point of 210 to 250° C., A polyester film for metal plate bonding molding processing has been proposed, ^{wherein the lubricant contains only a maximum of 10 particles/mm 2} of the lubricant having a particle diameter of 20 μm or more.

_{In addition, in Patent Document 4, the film strength F 100} at 100% elongation in an atmosphere of 150°C, which is made of a copolymer polyester containing 1 to 20 mol% of an aliphatic dicarboxylic acid component with respect to the total acid component. The biaxially stretched polyester film for molding, characterized in that it is 0.5 to 5 kg/mm ² and the thickness non-uniformity of the film is 40% or less, has been proposed.

In addition, in Patent Document 5, as a laminated film in which a polyester (B) layer containing polyester (B) as a main component is laminated on at least one side of a polyester (A) layer containing polyester (A) as a main component, A laminated polyester film is proposed, wherein the laminated film has an elastic modulus of 20 to 1000 MPa in an atmosphere of 23°C, an elastic modulus of 10 to 200 MPa in an atmosphere of 120°C, and substantially no orientation.

BACKGROUND ART Recently, as an image display device, a computer (wearable computer) miniaturized to a size that can be attached to a body is attracting attention due to miniaturization and high performance of portable terminals.

Ideally, an electronic device (wearable terminal) used in a wearable computer is provided in a personal belongings such as a wrist watch (Patent Document 6).

In addition, as a next-generation image display device, a flexible display capable of flexing freely is attracting attention. For flexible displays, organic electroluminescent (organic EL) displays are mainly used.

Since a thin glass substrate or a plastic substrate is used for a flexible display, in addition to the optical properties and durability required in the conventional flat display panel, the polyester film used for these image display device members is subjected to a bending test. Even if it is, it is required that no breakage or the like occurs.

Japanese Unexamined Patent Application Publication No. 2014-169371 Japanese Unexamined Patent Application Publication No. Hei 04-086293 Japanese Unexamined Patent Application Publication No. 2000-001552 Japanese Unexamined Patent Application Publication No. Hei 03-067629 International Publication No. 09/078304 Japanese Unexamined Patent Application Publication No. 2014-134903

As described above, when considering using a polyester film for a wearable terminal or a flexible display, it is not only flexible, but also bends better, compared to the conventionally generally used polyester film, and yet, elongation and It was necessary to develop a polyester film having strength. In addition, heat resistance that does not shrink when heated was also required.

Accordingly, an object of the present invention is to provide a novel copolymerized polyester film that is more flexible and bends better than a polyester film generally used in the past, and yet has both elongation, strength, and heat resistance.

The present invention is a copolymer polyester film provided with a copolymer polyester layer (layer I) containing copolymer polyester A as a main component resin,

The copolymerized polyester A is a copolymer of terephthalic acid and ``other dicarboxylic acid components'', and ethylene glycol and ``other alcohol components'', and the ``other dicarboxylic acid components'' occupied by the dicarboxylic acid component in the copolymerized polyester The ratio of ``rebonic acid component'' is 5 mol% or more and 20 mol% or less, and the ratio of ``other alcohol components'' to the alcohol component is 1 mol% or more and less than 25 mol%,

It proposes a copolymer polyester film characterized in that the storage elastic modulus at 25°C is 2500 MPa or less, and the storage elastic modulus at 120°C is 10 MPa or more.

The present invention is also a copolymer polyester film provided with a copolymer polyester layer (layer I) containing one or two or more types of polyester,

In all polyesters contained in the copolymerized polyester layer (layer I), the ratio of the total content of ``other dicarboxylic acid components'' to the total content of dicarboxylic acid components is 5 mol% or more and 20 mol% or less. , The ratio of the total content of "other alcohol components" to the total content of alcohol components is 1 mol% or more and less than 25 mol%,

It proposes a copolymer polyester film characterized in that the storage elastic modulus at 25°C is 2500 MPa or less, and the storage elastic modulus at 120°C is 10 MPa or more.

The copolymer polyester film proposed by the present invention is excellent in flexibility at room temperature, is not only flexible, but also bends more easily, yet has elongation and strength, and may further have sufficient heat resistance for practical use. Accordingly, the copolymer polyester film proposed by the present invention can be suitably used as, for example, a battery packaging material, an image display member, and particularly as a constituent member such as a flexible display or a wearable terminal.

1 is a diagram schematically showing a method of a warpage measurement method performed in an example.

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

<This copolymerized polyester film>

Co-polyester film (referred to as ``this co-polyester film'') according to an example of the embodiment of the present invention is a single layer or laminate with a co-polyester layer (layer I) containing co-polyester A as a main component resin It's a film.

This copolymerized polyester film may be a non-stretched film (sheet) or a stretched film. Especially, it is preferable that it is a stretched film stretched in a uniaxial direction or a biaxial direction. Among them, it is preferable that it is a biaxially stretched film from the viewpoint of excellent balance of mechanical properties and flatness. If this copolymerized polyester film is such a stretched film, there exists a tendency for it to become easy to make 120 degreeC storage modulus 10 MPa or more.

<Copolymer polyester layer (I layer)>

The co-polyester layer (I layer) is a layer containing co-polyester A as a main component resin.

Here, the "main component resin" is the meaning of the resin with the largest content ratio among the resins constituting the copolymerized polyester layer (layer I). The said main component resin may occupy 30 mass% or more, especially 50 mass% or more, especially 80 mass% or more (including 100 mass %) of the resin which comprises a copolymerization polyester layer (I layer).

As for the copolymerized polyester layer (layer I), the resin constituting may be only copolymerized polyester A or may include resin B other than copolymerized polyester A.

At this time, as resin B, it is preferable that it is a resin compatible with the copolymerized polyester A.

The case where the copolymerized polyester layer (layer I) contains the copolymerized polyester A and the resin B compatible with it will be described later.

(Copolymer Polyester A)

It is preferable that the copolymerized polyester A is a copolymerized polyester which is a copolymer of terephthalic acid and other dicarboxylic acid components, and ethylene glycol and other alcohol components.

Copolyester A may be crystalline or amorphous.

In addition, in the present invention, further, the crystalline polyester resin refers to a polyester resin that is generally said to have a crystal melting peak temperature (melting point), and more specifically, differential scanning performed in accordance with JIS K7121 (1987). As a polyester resin whose melting point is observed in calorimetry (DSC), a so-called semi-crystalline state is included. Conversely, a thermoplastic resin whose melting point is not observed in DSC is referred to as "amorphous". The crystalline polyester generally refers to a polyester that is said to have a crystal melting peak temperature (melting point). More specifically, as a polyester whose melting point is observed in a differential scanning calorimetry (DSC) performed in accordance with JIS K7121 (1987), a so-called semi-crystalline state is included.

Conversely, a thermoplastic resin whose melting point is not observed in DSC is referred to as "amorphous".

Examples of the "other dicarboxylic acid components" include aromatic dicarboxylic acids, alicyclic dicarboxylic acids, aliphatic dicarboxylic acids, and polyfunctional acids. In addition, two or more types of "other dicarboxylic acid components" may be used in combination. By using two or more kinds in combination in this way, not only can the copolymerized polyester film be more effectively flexible, but also the crystal structure can be retained, and heat resistance may be obtained.

Among them, from the viewpoint of making this copolymerized polyester film easy to soften, examples of "other dicarboxylic acid components" include aromatic dicarboxylic acids such as isophthalic acid, 2,6-naphthalenedicarboxylic acid, and diphenyldicarboxylic acid, and Aliphatic dicarboxylic acids such as dipic acid, sebacic acid, dodecanedioic acid, eiconic acid, and derivatives thereof, alicyclic rings such as 1,4-cyclohexanedicarboxylic acid, 1,2-cyclopentanedicarboxylic acid, and cyclooctanedicarboxylic acid Group dicarboxylic acid or dimer acid is preferable. Among them, it is preferable to contain an aliphatic dicarboxylic acid or dimer acid.

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

As the dimer acid, it is preferable that the unsaturated fatty acid has 18 or more carbon atoms as a dicarboxylic acid composed of a dimer of an unsaturated fatty acid. Examples of such dimer acids include those obtained by dimerization using different or identical unsaturated fatty acids selected from oleic acid, elaidic acid, cetoleic acid, erucic acid, brassidic acid, linoleic acid (CLA), linolenic acid, etc. have. Further, hydrogenated ones after such dimerization can also be used. In addition, the dimer acid may contain an aromatic ring, an alicyclic monocyclic ring, and an alicyclic polycyclic ring.

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

As described above, "other dicarboxylic acid components" can be selected arbitrarily. Especially, it is preferable to select one or more types from aromatic dicarboxylic acids, and to select and use one or more types from aliphatic dicarboxylic acid, alicyclic dicarboxylic acid, and dimer acid. Among them, those containing two or more of isophthalic acid, aliphatic dicarboxylic acid and dimer acid are particularly preferred, and in particular, those containing two or more of isophthalic acid, aliphatic dicarboxylic acid having 20 to 80 carbon atoms, and dimer acid. It is particularly preferred.

When an aromatic dicarboxylic acid is used as the "other dicarboxylic acid component", there is a tendency that the film can be softened while maintaining strength and heat resistance. On the other hand, if the ``other dicarboxylic acid component'' is selected from aliphatic dicarboxylic acid, alicyclic dicarboxylic acid, and dimer acid, the film can be softened with a smaller content ratio while maintaining elongation (elongation at break). There is a tendency to have, and among them, the use of dimer acid is the most effective. Therefore, by combining and using "other dicarboxylic acid components" as described above, it becomes possible to obtain a film having good strength, heat resistance, elongation, and flexibility.

In the copolymerized polyester A, the ratio of the ``other dicarboxylic acid components'' to the total of the dicarboxylic acid component, that is, terephthalic acid and ``other dicarboxylic acid components,'' is preferably 5 to 20 mol%, especially 8 mol. % Or more or 18 mol% or less, more preferably 10 mol% or more or 15 mol% or less. Here, when two or more types of "other dicarboxylic acid components" are used in combination, the total amount thereof is meant.

When the ratio of the "other dicarboxylic acid component" is within the above range, the present copolymer polyester film tends to be effectively flexible 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-cyclohexanedimethanol, bisphenol, and And derivatives. 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 addition, in general, when polyester is produced (polycondensation) using ethylene glycol as one of the raw materials, a part of ethylene glycol is modified to become diethylene glycol, and is introduced into the polyester skeleton. This diethylene glycol is referred to as by-product diethylene glycol, and the amount of by-product varies depending on the mode of polycondensation (transesterification method, direct polycondensation), etc., but is about 1 to 5 mol% in ethylene glycol. In the present invention, diethylene glycol obtained by-producing from ethylene glycol in this way is also treated as a copolymerization component, and is included in "other alcohol components".

In the copolymerized polyester A, the ratio of the ``other alcohol component (diol component)'' to the total of the alcohol component (diol component), that is, ethylene glycol and the ``other alcohol component'' is preferably 1 mol% or more and less than 25 mol%, In particular, it is more preferably 2 mol% or more or 20 mol% or less, and more preferably 3 mol% or more or 18 mol% or less. Here, when two or more types of "other alcohol components" are used in combination, the total amount thereof is meant.

When the ratio of the "other alcohol component" is within the above range, there is a tendency that the present copolymer polyester film can be effectively softened while having good elongation, strength, and heat resistance.

In addition, two or more types of "other alcohol components" may be used in combination. By using two or more types together, the copolymerized polyester film may be more effectively softened.

In addition, it is preferable to combine "other dicarboxylic acid components" and "other alcohol components" and use three or more kinds in combination. By using a plurality of copolymerization components together, there is a tendency that the film can be softened with a smaller content ratio. In addition, when there are too many kinds of copolymerization components, it may be difficult to stabilize the properties of the film, so it is preferable that the ``other dicarboxylic acid components'' and ``other alcohol components'' are 3 to 5 types in total, Among them, it is preferable that it is 3 types or 4 types.

Among the above, particularly preferred copolymerized polyester A is a copolymer of terephthalic acid, isophthalic acid and aliphatic dicarboxylic acid or dimer acid with ethylene glycol and diethylene glycol, and isophthalic acid occupied in the dicarboxylic acid component constituting the copolymerized polyester, The proportion of aliphatic dicarboxylic acid or dimer acid is 5 mol% or more and 20 mol% or less, and the proportion of diethylene glycol in the alcohol component constituting the copolymer polyester is 1 mol% or more and less than 25 mol%, and crystalline copolymer polyester Aa is mentioned. I can.

Usually, in order to lower the modulus of elasticity, the copolyester generally decreases crystallinity when the ratio of the copolymerization component is increased, and becomes amorphous when the ratio is increased. Although the copolymerization polyester Aa has a high copolymerization component ratio and a low elastic modulus can be achieved, since it maintains crystallinity, it can be thermally fixed by heat treatment after stretching. As a result, the copolymer polyester Aa bends well, and yet, elongation and strength are good, and thermal contraction can be suppressed.

(Resin B)

As described above, the copolymer polyester layer (layer I) may be a layer containing a copolymer polyester A and a resin B compatible with it.

In addition, in the present invention, "commercial use" means a state in which two or more kinds of mixed resins are completely mixed with each other at a molecular level. At this time, the amorphous regions mixed with each other at the molecular level can be regarded as a single phase, and micro-Brown motion also occurs at a single temperature. Therefore, when two or more types of resins are compatible, the melting point or glass transition temperature of the mixed resin of the two or more types of resins is single, and the peak of the main dispersion is also single. Therefore, in other words, the resin compatible with the copolymerized polyester A can also be defined as a resin capable of changing the melting point or glass transition temperature of the copolymerized polyester A when mixed with the copolymerized polyester A.

In addition, the glass transition temperature at this time is, for example, when the dynamic viscoelasticity temperature dispersion measurement (dynamic viscoelasticity measurement by JIS K7244 method) is performed under the conditions of 0.1% strain, 10 Hz frequency, and 3°C/min heating rate, It is the temperature of the peak of the main variance of the loss tangent (tanδ).

When the copolymerized polyester layer (layer I) is a layer containing the copolymerized polyester A and the resin B, the resin B is a resin compatible with the copolymerized polyester A, and has a melting point of 270°C or less, or amorphous, and glass A resin having a transition temperature of 30 to 120°C is preferred. By selecting such resin B, the glass transition temperature of the copolymerized polyester layer (I layer) can be made high, and heat resistance can be improved. As resin B, dimensional stability and heat resistance can be imparted by selecting polyester, such as polyethylene terephthalate (PET), for example.

In addition, from the viewpoint of achieving both flexibility and heat resistance, as resin B, one or two or more types of polyester are included, and the polyester (including one or two or more types of polyester) is a dicarboxylic acid component. Terephthalic acid and ``other dicarboxylic acid components'', ethylene glycol as alcohol components and ``other alcohol components'' are included, and the total content of the dicarboxylic acid components (when two or more types of polyester are included, each polyester The ratio of the total content of ``other dicarboxylic acid components'' to the total of the dicarboxylic acid components contained in) is 5 mol% or more and 20 mol% or less, particularly preferably 8 mol% or more or 18 mol% or less, particularly preferably 10 mol% or more or 15 mol% or less, and the ratio of the total content of ``other alcohol components'' to the total content of alcohol components (in the case of containing two or more types of polyester, the sum of alcohol components contained in each polyester) This is 1 mol% or more and less than 25 mol%, particularly preferably 2 mol% or more or 20 mol% or less, particularly preferably 3 mol% or more or 18 mol% or less.

In addition, the copolymerized polyester layer (layer I) may be a layer containing a copolymerized polyester A and a resin D incompatible therewith. As resin D, polyolefin, polystyrene, acrylic resin, urethane resin, etc. are mentioned, for example.

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

In addition, if the component ratio of the whole polyester contained in the copolymerized polyester layer (layer I) is the same as that of the copolymerized polyester A, the same effect as in the case of containing the copolymerized polyester A as the main component resin can be obtained. I think there is.

Therefore, in the case where the copolymerized polyester layer (layer I) contains one type or two or more types of polyester, in the total amount of the components of all polyesters contained in the copolymerized polyester layer (layer I), dicarboxylic acid The ratio of the total content of ``other dicarboxylic acid components'' to the total content of the components is 5 mol% or more and 20 mol% or less, and the ratio of the total content of ``other alcohol components'' to the total content of alcohol components is 1 mol% or more If it is less than 25 mol%, the same effect as in the case of containing the copolymerized polyester A as a main component resin can be obtained.

In this case, the preferred range of the ratio of the total content of the "other dicarboxylic acid components" to the total content of the dicarboxylic acid components is the "other dicarboxylic acids occupied by the dicarboxylic acid component in the copolymerized polyester A" It is the same as the preferable range of the ratio of "component". In addition, the preferable range of the ratio of the total content of the "other alcohol components" occupied by the total content of the alcohol component is the same as the preferable range of the proportion of the "other alcohol components" occupied by the alcohol component in the copolymerized polyester A. to be.

<In the case of a laminated configuration>

This copolymerized polyester film may be a laminated film provided with a layer different from the copolymerized polyester layer (layer I) as described above.

For example, a laminated film having a configuration obtained by laminating a polyester layer (layer II) containing polyester C as a main component resin on both front and back sides of a copolymerized polyester layer (layer I) is exemplified.

At this time, the polyester C is preferably a polyester having a melting point higher than the melting point of the copolymerized polyester A when the copolymerized polyester A is crystalline, and when the copolymerized polyester A is amorphous, the copolymerized polyester It is preferable that it is a polyester which has a melting point of a temperature higher than the glass transition point of A.

If it is a laminated film having a configuration formed by laminating a polyester layer (layer II) containing such polyester C as a main component resin, a polyester layer (II layer)/copolymerized polyester layer (I layer)/polyester layer Since the raw resin composition can be laminated by coextrusion or the like so as to become (layer II), stretched, and then heat-fixed at a higher temperature compared to the case of a single layer of the copolymerized polyester layer (layer I), the copolymer polyester The layer (layer I) can be softened to a level that cannot be achieved with a single layer, or it is possible to increase heat resistance, or to further prevent heat shrinkage.

Specifically, the storage elastic modulus at 25°C of the present copolymerized polyester film can be 300 to 2500 MPa, especially 500 MPa or more or 2000 MPa or less.

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

If the thickness of each layer of the polyester layer (layer II) is 1% or more of the thickness of the copolymerized polyester layer (layer I), film formation is possible without significantly impairing productivity, and if it is less than 20%, the required flexibility will be sufficiently secured. It is desirable because it can.

From this point of view, the thickness of each layer of the polyester layer (layer II) is preferably 1 to 20% of the thickness of the copolymerized polyester layer (layer I), particularly 3% or more or 15% or less, especially 5% It is more preferable that it is more than or 12% or less.

In addition, the thickness of the polyester layer (II layer) present on both the front and back sides of the copolymerized polyester layer (layer I) may be different from the front and back, or may be the same.

Polyester C, when copolymerized polyester A is crystalline, has a melting point 10 to 100°C higher than the melting point of copolymerized polyester A, particularly 20°C or more or 90°C or less, especially 40°C or more or 70°C or less. It is preferable that it is a polyester, on the other hand, when the copolymerized polyester A is amorphous, 120 to 260°C higher than the glass transition point of the copolymerized polyester A, particularly 140°C or more or 230°C or less, especially 160°C or more, or It is preferably a polyester having a high melting point of 200°C or less.

In addition, polyester C serving as the main component of the polyester layer (II layer) present on both the front and back sides of the copolymerized polyester layer (layer I) may be different or the same in the front and back. Especially, it is preferable that the melting point of the polyester C on the front and the back is not significantly different. Specifically, it is preferable that the difference in the melting point of the polyester layer (II layer) present on both sides of the front and back is 80°C or less, particularly 60°C or less, and particularly 40°C or less.

If the polyester C in the polyester layer (II layer) present on both the front and rear sides of the copolymerized polyester layer A is the same, since coextrusion molding of two or three layers is possible, this aspect is also preferable.

As polyester C, for example, a homopolyester or copolymer polyester containing terephthalic acid as a dicarboxylic acid component and ethylene glycol as an alcohol component can be suitably used. However, it is not limited thereto.

When polyester C is a copolymerized polyester, examples of dicarboxylic acid components other than terephthalic acid include aromatic dicarboxylic acids, alicyclic dicarboxylic acids, aliphatic dicarboxylic acids, and polyfunctional acids.

In polyester C, the ratio of the ``dicarboxylic acid component other than terephthalic acid'' to the dicarboxylic acid component is preferably 1 to 30 mol%, particularly 5 mol% or more or 25 mol% or less, particularly 10 mol% or more or 20 mol It is more preferred that it is less than or equal to %.

When polyester C is a copolymerized polyester, examples of alcohol components other than ethylene glycol include 1,4-butanediol, 1,6-hexanediol, diethylene glycol, trimethylene glycol, neopentyl glycol, and 1,4-cyclohexane. Dimethanol, bisphenol, and derivatives thereof.

In polyester C, the ratio of ``an alcohol component other than ethylene glycol'' to the alcohol component is preferably 1 to 100 mol%, particularly 5 mol% or more or 95 mol% or less, particularly 10 mol% or more or 90 mol% or less. More preferable.

<Thickness of this 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 application.

Among them, it is preferable that the total thickness of the film exceeds 20 µm from the viewpoint of more exerting the characteristics of the present copolymerized polyester film.

It is known that the stiffness strength of a film is proportional to the third power of the thickness. However, even if this copolymerized polyester film has a thickness exceeding 20 micrometers, it has the feature of weak rigidity and it is good to bend, and the benefit of this invention can be further enjoyed.

From this point of view, it is preferable that the total thickness of the present copolymerized polyester film exceeds 20 µm, more preferably 23 µm or more, and more preferably 30 µm or more.

In addition, the upper limit of the total thickness of this copolymerized polyester film is not specifically limited. It is preferably 1000 µm or less, particularly 500 µm or less, particularly 250 µm or less, and more preferably 100 µm or less.

<Physical properties of this copolymerized polyester film>

It is preferable that this copolymerized polyester film has a storage elastic modulus at 25 degreeC of 2500 MPa or less.

Since the storage modulus at 25° C., that is, at room temperature is 2500 MPa or less, for example, when a wearable terminal is mounted, it can sufficiently follow the skin.

From such a viewpoint, the storage modulus of the present copolymer polyester film at 25° C. is preferably 2500 MPa or less, more preferably 2000 MPa or less, and more preferably 1200 MPa or less.

The storage modulus at 25°C is preferably 300 MPa or more, particularly 500 MPa or more, and more preferably 700 MPa or more from the viewpoint of handling properties in the process.

In addition, the storage elastic modulus of 25 degreeC is a value obtained by the measurement method described in Examples mentioned later.

In this copolymerized polyester film, in order to make the storage modulus of 25 degreeC into the said range, it can achieve by adjusting the kind and content of the copolymerization component of the copolymerization polyester A, for example.

In addition, as described above, also by forming a laminated film having a configuration formed by laminating a polyester layer (layer II) containing polyester C as a main component resin on both sides of the front and back of the copolymerized polyester layer (layer I), Can be adjusted.

Furthermore, it can also be adjusted by the stretching conditions at the time of manufacturing the copolymer polyester film of this invention, and the heat setting conditions after that.

However, it is not limited to this method.

In addition, it is preferable that the storage elastic modulus of this copolymerized polyester film is 10 MPa or more at 120 degreeC.

As described above, when the storage modulus at high temperature is 10 MPa or more, it has sufficient heat resistance and it is possible to suppress the occurrence of wrinkles during processing.

From such a viewpoint, it is preferable that the storage elastic modulus of this copolymerized polyester film at 120 degreeC is 10 MPa or more, especially 30 MPa or more, Especially, it is more preferable that it is 50 MPa or more.

The present copolymer polyester film preferably has a storage elastic modulus of 500 MPa or less at 120° C., more preferably 400 MPa or less, and more preferably 300 MPa or less, from the viewpoint of suppressing the amount of heat required during processing.

In addition, the storage modulus of 120 degreeC is a value obtained by the measuring method described in Examples mentioned later.

In the present copolymerized polyester film, the method for adjusting the storage elastic modulus at 120°C to the above range is a method for adjusting the storage elastic modulus at 25°C, for example, a method similar to the above-described means. Among these, a method of adjusting the stretching conditions and subsequent heat setting conditions is particularly effective. However, it is not limited to this method.

It is preferable that this copolymerized polyester film has a loss tangent (tan δ) of 0.02 or more at 25°C.

Since the loss tangent at 25°C, that is, at room temperature is 0.02 or more, for example, when a wearable terminal is mounted, it can sufficiently follow the skin.

From such a viewpoint, it is preferable that the loss tangent at 25°C is 0.05 or more, and more preferably 0.08 or more, and more preferably 0.10 or more.

In addition, the 25°C loss tangent (tan?) is preferably 1.5 or less, particularly 1.0 or less, and more preferably 0.5 or less from the viewpoint of handling properties in the process.

In the present copolymer polyester film, the method for adjusting the loss tangent at 25°C to the above range includes a method similar to the above-described means as a method for adjusting the storage modulus at 25°C. Among these, in particular, the method of adjusting by adjusting the kind and content of the copolymerization component of the copolymerized polyester A is effective. However, it is not limited to this method.

In the present copolymerized polyester film, when the copolymerized polyester A is crystalline, the enthalpy of crystal fusion ΔHm is preferably 3.0 J/g or more, more preferably 5.0 J/g or more, and more preferably 7.0 J/g or more. ΔHm serves as an index of the degree 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 is ``good warp (stiffness)'' measured by the warpage measurement method described in Examples to be described later, that is, the length down in the vertical direction (a), and the length protruding in the horizontal direction (b). When set to, the value ((a)/(b)) of the ratio between (a) and (b) is preferably 0.3 or more, more preferably 0.5 or more, and more preferably 1.0 or more.

When (a)/(b) is 0.3 or more, it is suggested that the film has sufficient warpness.

On the other hand, the upper limit of (a)/(b) is not particularly limited, but from the viewpoint of handling properties in the process, it is preferably 15.0 or less, particularly 10.0 or less, and more preferably 6.0 or less.

In this copolymerized polyester film, in order to adjust (a)/(b) to the above range, it is important to first adjust the thickness of the film, and next, in the same film thickness, the copolymerization component of the copolymerized polyester A It can be achieved by adjusting the type and content of. However, it is not limited to this method.

From such a viewpoint, as for the copolymerization component of the copolymerized polyester A, it is preferable that the "other dicarboxylic acid component" is 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, it is preferable that the said "other alcohol component" is diethylene glycol, and it is preferable that the content is 1 mol% or more and less than 25 mol%.

<Production method of this copolymerized polyester film>

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

First, by a known method, a raw material, such as polyester chips, is supplied to a melt-extrusion apparatus, heated above the melting point of each polymer, and extruded the molten polymer from the die, and the glass transfer of the polymer on a rotary cooling drum. It is good to cool and solidify so that it may become a temperature below this point, and to obtain a substantially amorphous unoriented sheet.

Next, the unoriented sheet is stretched in one direction by a stretching machine of a roll or tenter system. In this case, 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.

Subsequently, it stretches in a direction orthogonal to the stretch direction of the 1st stage. At this time, the stretching temperature is usually 50 to 140°C, and the stretching ratio is usually 3.0 to 7 times, preferably 3.5 to 6 times.

Then, heat setting treatment is performed at a temperature of 130 to 270° C. under tension or under 30% relaxation to obtain the present copolymer polyester film as a biaxially oriented film.

Further, in the above stretching, a method of performing stretching in one direction in two or more steps may be employed.

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

When the present copolymerized polyester film has a laminated configuration of a copolymerized polyester layer (I layer) and a polyester layer (II layer), the copolymerized polyester layer (I layer) and polyester layer (II layer) are coextruded. After that, as described above, stretching and heat setting treatment may be performed as an integral film.

The heat setting treatment at this time is preferably heat set by heating to a temperature lower than the melting point of polyester C. In addition, when the copolymerized polyester A is crystalline, it is preferable to perform heat setting treatment at a temperature higher than the melting point of the copolymerized polyester A. By heat setting treatment at such a temperature, it is possible to soften it to a level that cannot be achieved with a single layer of the copolymerized polyester layer (layer I).

This is, by heat fixing at a temperature lower than the melting point of polyester C, since the stretching orientation of the surface layer is fixed, the elongation, strength, and heat resistance (heat shrinkage) become good, while heat fixing at a temperature higher than the melting point of the copolymerized polyester A. By doing so, since the stretching orientation and deformation of the intermediate layer are alleviated, it is possible to obtain a film that can be more easily bent.

<Use of this copolymerized polyester film>

As described above, the present copolymer polyester film is excellent in flexibility at room temperature, and has characteristics that it is not only flexible, but also has almost no rigidity, and yet can exhibit sufficient heat resistance for practical use. Therefore, for example, it can be suitably used as a battery packaging material, a surface protective film, a member for image display, particularly as a constituent member such as a flexible display and a wearable terminal.

In addition, the use of the present copolymerized polyester film is not limited to the above, and can be used, for example, for various packaging materials, building materials, stationery, automobile members, and other structural members.

<Explanation of phrases, etc.>

In the present invention, even when referred to as "film", "sheet" is included, and when referred to as "sheet", "film" is also included.

In addition, when expressing "panel" like an image display panel, a protective panel, etc., it includes a plate body, a sheet, and a film.

In the present invention, when it is described as "X to Y" (X and Y are arbitrary numbers), unless otherwise specified, together with the meaning of "X or more and Y or less", "preferably greater than X" or " It also includes the meaning of "preferably smaller than Y".

In addition, when ``X or more'' (X is an arbitrary number), unless otherwise specified, the meaning of ``preferably greater than X'' is included, and described as ``Y or less'' (Y is an arbitrary number). In one case, it also includes the meaning of "preferably less than Y" unless otherwise noted.

Example

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

<Evaluation method>

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

(1) Storage modulus E', tangent loss tanδ

According to JIS K 7244, using the dynamic viscoelasticity measuring apparatus DVA-200 manufactured by IT Measurement Control Co., Ltd., with respect to the width direction (TD) of the copolymerized polyester film (sample), the vibration frequency is 10 Hz, and the strain is 0.1. % And a temperature increase rate of 1°C/min, from -100°C to 200°C were measured, and from the obtained data, the storage modulus E'at 25°C and 120°C, and tangent loss tanδ at 25°C were obtained.

(2) Crystal melting enthalpy ΔHm

According to JIS K7141-2 (2006), differential scanning calorimeter (DSC) measurement of the measurement sample was performed. After raising the temperature from 30°C to 280°C at 10°C/min, it is held for 1 minute, and then lowered from 280°C to 30°C at 10°C/min, then held for 1 minute, and further 10°C/from 30°C to 280°C It was heated again in minutes. 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, the copolymer polyester 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

For the copolymerized polyester film (sample) obtained in Examples and Comparative Examples, the temperature was controlled at 23°C and humidity 50% RH using a tensile tester (manufactured by Intesco Co., Ltd., Intesco Model 2001 type). In the room, a copolyester film (sample) having a length of 300 mm and a width of 20 mm was stretched at a strain rate of 10%/min, and calculated by the following equation using the first straight portion of the tensile stress-strain curve.

E=Δσ/Δε

(In the above formula, E is the Young's modulus (GPa), Δσ is the stress difference (GPa) based on the original average cross-sectional area between two points of a straight line, and Δε is the deformation difference/initial length between the same two points)

(4) tensile breaking strength

With respect to the copolymerized polyester film (sample) obtained in Examples and Comparative Examples, in a room controlled at a temperature of 23°C and a humidity of 50% RH using a tensile strength tester (manufactured by Intesco Co., Ltd., Intesco Model 2001 type). , A co-polyester film (sample) having a width of 15 mm was set in a tester so that the interchuck was 50 mm, and at a strain rate of 200 mm/min, the film was stretched in the longitudinal direction (MD) or the width direction (TD), and the following Tensile breaking strength was calculated|required by the formula.

Tensile breaking strength (MPa) = F/A

However, in the above formula, F is the load (N) at the time of fracture, and A is the original cross-sectional area (mm ² ) of the test piece.

(5) tensile breaking elongation

The same test as the above tensile breaking strength was performed, and the tensile breaking elongation of the copolymer polyester film (sample) obtained in Examples and Comparative Examples was determined by the following equation.

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

However, in the above formula, L is the distance between gages at the time of fracture (mm), and L0 is the original distance between gages (mm).

(6) heating shrinkage rate

The copolymer polyester film (sample) obtained in Examples and Comparative Examples was allowed to stand for 5 minutes in an oven maintained at 120° C. in a tension-free state, and the length of the sample before and after it was measured, according to the following equation, in the longitudinal direction of the film (MD ) And the respective heating shrinkage rates in the width direction (TD) were calculated.

Heating shrinkage rate (%)={(L0-L1)/L0}×100

(In the above formula, L0 is the sample length before heat treatment, and L1 is the sample length after heat treatment)

Five points were measured in the length direction (MD) and width direction (TD) of the film, and the average value was calculated for each.

(7) Evaluation of good warpage (stiffness) (warpage measurement method)

Samples Samples were prepared by cutting the co-polyester film (sample) obtained in Examples and Comparative Examples into a size of 150 mm in length and 50 mm in width, after standing for 24 hours in an atmosphere of 23°C and 50% RH.

As shown in Fig. 1, a copolymer polyester film (sample) was placed on a table so as to protrude out from the edge of the table 50 mm in length under an environment of 23°C, and a copolymer polyester film (sample) on the table A 200 g weight was placed on the top and fixed, and the tip side of the sample protruding from the edge of the table was bent downward by its own weight. After 3 minutes, the length (a) in which the tip of the sample protruding from the edge of the table was bent vertically downward and stretched downward (a), and the length (b) that the tip of the sample protruded from the edge of the table in the horizontal direction was measured.

Then, calculate the ratio ((a)/(b)) of the length (a) stretched down the bend to the length (b) protruding in the horizontal direction, and if it is 0.30 or more, it is ``passed'', and if it is less than 0.30, it is ``failed''. Evaluated.

(Raw material)

In Examples and Comparative Examples, the following raw materials were used.

Copolyester 1 ("Co-PS1"): The acid component is composed of 88 mol% terephthalic acid, 7 mol% hydrogenated dimer acid having 36 carbon atoms, and 5 mol% isophthalic acid, and the diol component is ethylene glycol Crystalline copolymer polyester comprising 90 mol% and diethylene glycol 10 mol%. Melting point 208°C, intrinsic viscosity 0.68 dl/g.

Copolyester 2 (``Co-PS2''): The acid component is composed of 88 mol% terephthalic acid and 12 mol% of hydrogenated dimer acid having 36 carbon atoms, and the diol component is 67 mol% ethylene glycol and 33 mol% 1,4-butanediol ( Crystalline copolymer polyester comprising less than 0.1 mol% of by-product diethylene glycol). Melting point 200°C, intrinsic viscosity 0.72 dl/g.

Copolyester 3 ("Co-PS3"): A crystalline copolymer polyester composed of 78 mol% terephthalic acid and 22 mol% isophthalic acid as an acid component, and 98 mol% ethylene glycol and 2 mol% by-product diethylene glycol as a diol component. Melting point 198 deg. 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, a chip of copolymerized polyester 1 (coated PS1) is sent to an extruder having a vent set at 280°C, and through a gear pump and a filter, it is extruded from the cap of the extruder, and the electrostatic application adhesion method is performed. It was quenched and solidified on a cooling roll in which the surface temperature was set to 30 degreeC by using, and the unstretched sheet was obtained.

Subsequently, the obtained unstretched sheet was stretched 3.3 times at 50° C. in the longitudinal direction (MD), guided to a tenter, and then stretched 4.2 times at 80° C. in the width direction (TD), and then heated at 200° C. for 10 seconds. The treatment was performed, and 10% relaxation was performed in the width direction (TD) to obtain a 25 µm-thick biaxially stretched copolymer polyester film (sample) substantially composed of a single layer.

[Example 2]

As an intermediate layer, chips of copolymerized polyester 1 (coated PS1) were sent to a twin-screw extruder having a main vent set at 280°C.

In addition, as the surface layer, polyester (PET) chips were sent to a twin-screw extruder having a sub vent set at 280°C.

Through a gear pump and filter, the polymer from the main extruder is the intermediate layer and the polymer from the sub-extruder is co-extruded in a layered configuration of two or three layers (surface layer/intermediate layer/surface layer), extruded from the cleft, and electrostatically applied. By using the method, it was rapidly cooled and solidified on a cooling roll in which the surface temperature was set to 30°C to obtain an unstretched sheet.

Subsequently, the obtained unstretched sheet was 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), and then heated at 200°C for 10 seconds. Treatment was carried out, and it was relaxed by 10% in the width direction (TD), and a biaxially stretched copolymer polyester film having a thickness of 25 μm ( Sample) was obtained.

[Examples 3 to 5]

Except having changed the conditions as shown in Table 1, it carried out similarly to Example 2, and obtained the biaxially stretched copolymer polyester film (sample).

In addition, in the table, for example, "empty PS1/PET=80/20" in Example 3 means that 80 parts by mass of empty PS1 and 20 parts by mass of PET are mixed, and similarly to other examples. It shows the mass ratio.

[Comparative Example 1]

The polyester (PET) chips are sent to an extruder with a vent set at 280°C, extruded from the cap of the extruder through a gear pump and filter, and cooled by setting the surface temperature to 30°C using an electrostatic application adhesion method. It was quenched and solidified on a roll, and the unstretched sheet was obtained.

Subsequently, the obtained unstretched sheet was 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), and then heated at 235° C. for 10 seconds. The treatment was performed, and 10% of relaxation was performed in the width direction (TD) to obtain a 50 µm-thick biaxially stretched copolymer polyester film (sample).

[Comparative Example 2]

The mixture of 85 parts by mass of empty PS3 chips and 15 parts by mass of PET chips is sent to an extruder having a vent set at 280°C, and is extruded from the cap of the extruder through a gear pump and filter, and an electrostatic application is used. Then, it was rapidly cooled and solidified on a cooling roll in which the surface temperature was set at 30°C to obtain an undrawn sheet.

Subsequently, the obtained unstretched sheet was stretched 3.4 times at 80°C in the longitudinal direction (MD), guided to a tenter, and then stretched 3.9 times at 145°C in the width direction (TD), and then heated at 186°C for 10 seconds. The treatment was performed, and 10% of relaxation was performed in the width direction (TD) to obtain a 50 µm-thick biaxially stretched copolymer polyester film (sample).

[Comparative Example 3]

Send the chip of the copolyester 2 (coated PS2) to an extruder having a vent set at 280°C, and extrude it from the cap of the extruder through a gear pump and filter, and the surface temperature to 30°C using an electrostatic application adhesion method. It was quenched and solidified on a set cooling roll, and the unstretched copolymer polyester film (sample) of 200 micrometers in thickness was obtained.

From the above examples and the results of the tests conducted by the inventors so far, as a copolymer polyester film having a copolymer polyester layer (layer I) containing the copolymer polyester A as a main component resin, the storage modulus at 25°C is 2500 MPa or less. By being, it is excellent in flexibility at room temperature, not only is simply flexible, but also bends better, and yet, it can have elongation and strength. In addition, it was found that when the storage modulus at 120°C was 10 MPa or more, it was possible to have sufficient heat resistance for practical use.

As in Examples 2 to 5, when the main component resin of the intermediate layer is a crystalline copolymer polyester, if 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, a single layer consisting of only the intermediate layer Compared with the case of, it was confirmed that the heat treatment (heat fixation) temperature after stretching could be made higher, and the heat shrinkability could be further suppressed.

In addition, when the main component resin of the intermediate layer is amorphous copolymerized polyester, 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, if it is a single layer composed of only the intermediate layer. In contrast, since the heat treatment (heat setting) temperature after stretching can be made higher, it is considered that the heat shrinkability can be further suppressed.

Claims (14)

As a copolymer polyester film provided with a copolymer polyester layer (layer I) 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'' occupied by the dicarboxylic acid component in the copolymerized polyester The ratio of ``rebonic acid component'' is 5 mol% or more and 20 mol% or less, and the ratio of ``other alcohol components'' to the alcohol component is 1 mol% or more and less than 25 mol%,
A copolymer polyester film characterized in that the storage elastic modulus at 25°C is 2500 MPa or less, and the storage elastic modulus at 120°C is 10 MPa or more. The method of claim 1,
The copolymer polyester film (layer I) is a layer containing the copolymer polyester A and a resin B compatible with the copolymer polyester A. The method according to claim 1 or 2,
As the resin B, one or more polyesters are included, and the polyester has a ratio of the total content of ``other dicarboxylic acid components'' to the total content of dicarboxylic acid components of 5 mol% or more and 20 mol% It is the following, and the ratio of the total content of "other alcohol components" with respect to the total content of alcohol components is 1 mol% or more and less than 25 mol%, The copolymer polyester film characterized by the above-mentioned. As a copolymerized polyester film provided with a copolymerized polyester layer (layer I) containing one type or two or more types of polyester,
In all polyesters contained in the copolymerized polyester layer (layer I), the ratio of the total content of ``other dicarboxylic acid components'' to the total content of dicarboxylic acid components is 5 mol% or more and 20 mol% or less, and alcohol component The ratio of the total content of "other alcohol components" to the total content of is 1 mol% or more and less than 25 mol%,
A copolymer polyester film characterized in that the storage elastic modulus at 25°C is 2500 MPa or less, and the storage elastic modulus at 120°C is 10 MPa or more. The method according to any one of claims 1 to 4,
The said "other dicarboxylic acid component" contains an aliphatic dicarboxylic acid or dimer acid, The copolymer polyester film characterized by the above-mentioned. The method according to any one of claims 1 to 5,
The said "other dicarboxylic acid component" contains two or more types of isophthalic acid, aliphatic dicarboxylic acid, and dimer acid, The copolymer polyester film characterized by the above-mentioned. The method according to any one of claims 1 to 5,
The said "other dicarboxylic acid component" contains two or more types of isophthalic acid, C20-C80 aliphatic dicarboxylic acid, and dimer acid, The copolymer polyester film characterized by the above-mentioned. The method according to any one of claims 1 to 7,
The copolymer polyester film, wherein the "other alcohol component" contains diethylene glycol. The method according to any one of claims 1 to 8,
It has a configuration obtained by laminating a polyester layer (II layer) containing polyester C as a main component resin on both front and back sides of the copolymerized polyester layer (layer I),
The said polyester C is polyester which has a melting point higher than the melting point of copolymerized polyester A when the copolymerized polyester A is crystalline, and when the copolymerized polyester A is amorphous, it is more than the glass transition point of the copolymerized polyester A Copolymer polyester film, characterized in that it is a polyester having a high temperature melting point. The method of claim 9,
The thickness of each layer of the polyester layer (layer II) is 1 to 20% of the thickness of the copolymerized polyester layer (layer I). The method according to any one of claims 1 to 10,
A copolymer polyester film having a loss tangent (tanδ) of 0.02 or more at 25°C. The method according to any one of claims 1 to 11,
Copolyester film, characterized in that the total thickness of the film exceeds 20㎛. 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.

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