JPWO2020054576A1 - Copolymerized polyester film - Google Patents

Abstract

As a new copolymerized polyester film that is more flexible, more supple, and yet has elongation, strength, and heat resistance, a copolymerized polyester layer (I layer) containing copolymerized polyester A as a main component resin is provided. The copolymerized polyester film provided is a copolymer of terephthalic acid and "other dicarboxylic acid components", ethylene glycol and "other alcohol components", and the copolymerized polyester. The ratio of "other dicarboxylic acid components" to the dicarboxylic acid components is 5 mol% or more and 20 mol% or less, and the ratio of "other alcohol components" to the alcohol components is 1 mol% or more and less than 25 mol%, at 25 ° C. We propose a copolymerized polyester film characterized by having a storage elasticity of 2500 MPa or less and a storage elasticity of 120 ° C. of 10 MPa or more.

Description

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

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

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

Further, Patent Document 2 proposes a heat-sensitive transfer image receiving sheet in which an image receiving layer made of a copolymerized polyester layer having a copolymerization rate of 5 to 30 mol% is laminated on at least one surface of a polyester film.
Further, in Patent Document 3, the average particle size is 0.1 to 2.5 μm, the pore volume is 0.05 to 2.5 ml / g, the specific surface area is 50 to 600 m ² / g, and the compressive force is 1 to 100 MPa. A biaxially oriented film made of a copolymerized polyester containing 0.05 to 5.0% by weight of a lubricant, the biaxially oriented film having an intrinsic viscosity of 0.50 to 0.80 dl / g and a glass transition point. A metal plate bonding characterized by having a melting point of 70 ° C. or higher and a melting point of 210 to 250 ° C., and containing at most 10 coarse particles of the lubricant having a particle size of 20 μm or higher in the biaxially oriented film / mm ^2. Polyester films for molding have been proposed.

In addition, in Patent Document 4, it is made of a copolymerized polyester containing an aliphatic dicarboxylic acid component in an amount of 1 to 20 mol% with respect to the total acid component, and the film strength F ₁₀₀ at 100% elongation in an atmosphere of 150 ° C. is 0. A biaxially stretched polyester film for molding has been proposed, which is 5 to 5 kg / mm ^{2 and has a thickness unevenness of 40% or less.}
Further, in Patent Document 5, a laminated film in which a polyester (B) layer containing polyester (B) as a main component is laminated on at least one surface of a polyester (A) layer containing polyester (A) as a main component. A laminated polyester film characterized in that the elastic coefficient of the laminated film in an atmosphere of 23 ° C. is 20 to 1000 MPa, the elastic coefficient in an atmosphere of 120 ° C. is 10 to 200 MPa, and is substantially non-oriented has been proposed. There is.

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

In addition, as a next-generation image display device, a flexible display that can be freely bent is drawing attention. Organic electroluminescence (organic EL) displays are mainly used for flexible displays.
Since a thin glass substrate or a plastic substrate is used for the flexible display, the polyester film used for these image display device members has in addition to the optical characteristics and durability required for the conventional flat display panel. , It is required that no breakage occurs even if a bending test is performed.

Japanese Unexamined Patent Publication No. 2014-169371 Japanese Unexamined Patent Publication No. 04-086293 Japanese Unexamined Patent Publication No. 2000-001552 Japanese Unexamined Patent Publication No. 03-07629 International Publication No. 09/078304 Japanese Unexamined Patent Publication No. 2014-134903

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

Therefore, the subject of the present invention is to obtain a new copolymerized polyester film that is more flexible and supple than a polyester film that is generally used in the past, yet has elongation, strength, and heat resistance. To provide.

The present invention is a copolymerized polyester film provided with a copolymerized polyester layer (I layer) containing the copolymerized 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 "other dicarboxylic acids" among the dicarboxylic acid components in the copolymerized polyester. The ratio of "acid component" is 5 mol% or more and 20 mol% or less, and the ratio of "other alcohol component" to the alcohol component is 1 mol% or more and less than 25 mol%.
We propose a copolymerized 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 copolymerized polyester film provided with a copolymerized polyester layer (I layer) containing one or more kinds of polyesters.
In all polyesters contained in the copolymerized polyester layer (I layer), the ratio of the total content of "other dicarboxylic acid components" to the total content of dicarboxylic acid components is 5 mol% or more and 20 mol% or less, and the alcohol component. The ratio of the total content of "other alcohol components" to the total content is 1 mol% or more and less than 25 mol%.
We propose a copolymerized 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 copolyester film proposed by the present invention has excellent flexibility at room temperature, is not only flexible, but also more supple, yet has elongation and strength, and is sufficient for practical use. Can have high heat resistance. Therefore, the copolymerized polyester film proposed by the present invention can be suitably used as, for example, a packaging material for a battery, an image display member, and particularly a constituent member such as a flexible display or a wearable terminal.

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

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

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

The present copolymerized polyester film may be a non-stretched film (sheet) or a stretched film. Of these, a stretched film stretched in the uniaxial direction or the biaxial direction is preferable. Among them, a biaxially stretched film is preferable because it is excellent in balance of mechanical properties and flatness. If the present copolymerized polyester film is such a stretched film, it tends to be easy to set the storage elastic modulus at 120 ° C. to 10 MPa or more.

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

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

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

(Copolymerized polyester A)
The copolymerized polyester A is preferably a copolymerized polyester which is a copolymer of terephthalic acid and other dicarboxylic acid components and ethylene glycol and other alcohol components.

The copolymerized polyester A may be crystalline or amorphous.
In the present invention, the crystalline polyester resin generally refers to a polyester resin having a crystal melting peak temperature (melting point), and more specifically, a differential carried out in accordance with JIS K7121 (1987). It includes polyester resins whose melting point is observed in differential scanning calorimetry (DSC), which are in a so-called semi-crystalline state. 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 having a crystal melting peak temperature (melting point). More specifically, it includes polyesters whose melting points are observed in differential scanning calorimetry (DSC) performed in accordance with JIS K7121 (1987), and which are in a so-called semi-crystalline state.
Conversely, a thermoplastic resin whose melting point is not observed in DSC is referred to as "amorphous".

Examples of the "other dicarboxylic acid component" include aromatic dicarboxylic acids, alicyclic dicarboxylic acids, aliphatic dicarboxylic acids, and polyfunctional acids. In addition, 2 or more types of "other dicarboxylic acid components" may be used in combination. By using two or more of them in combination in this way, not only can the copolymerized polyester film be more effectively softened, but also the crystal structure can be retained, and the copolymer may have heat resistance.
Among them, from the viewpoint of facilitating the softening of this copolymerized polyester film, "other dicarboxylic acid components" include aromatic dicarboxylic acids such as isophthalic acid, 2,6-naphthalenedicarboxylic acid and diphenyldicarboxylic acid, adipic acid and sebacine. An aliphatic dicarboxylic acid such as an acid, dodecanedioic acid, ecoic acid and derivatives thereof, an alicyclic dicarboxylic acid such as 1,4-cyclohexanedicarboxylic acid, 1,2-cyclopentanedicarboxylic acid and cyclooctanedicarboxylic acid, or Dimeric acid is preferred. Among them, it is preferable to contain an aliphatic dicarboxylic acid or a dimer acid.
Among the aliphatic dicarboxylic acids, an aliphatic dicarboxylic acid having 20 to 80 carbon atoms, particularly 30 or more or 60 or less, and particularly 36 or more or 48 or less is particularly preferable, from the viewpoint of being able to further lower the glass transition temperature.

The dimer acid is preferably a dicarboxylic acid composed of a dimer of an unsaturated fatty acid and having 18 or more carbon atoms in the unsaturated fatty acid. Examples of such dimer acids are those quantified using different or identical unsaturated fatty acids selected from oleic acid, elaidic acid, setreic acid, erucic acid, brushzic acid, linolenic acid, linolenic acid and the like. Can be mentioned. Further, those hydrogenated after such dimerization can also 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 or 60 or less, and particularly 30 or more or 50 or less are preferable from the viewpoint of being able to further lower the glass transition temperature.

As described above, the "other dicarboxylic acid component" can be arbitrarily selected. Among them, it is preferable to select one or more from aromatic dicarboxylic acids and select one or more from aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, and dimer acids and use them in combination. Among them, it is particularly preferable to contain two or more of isophthalic acid, an aliphatic dicarboxylic acid and a dimer acid, and in particular, two or more of isophthalic acid, an aliphatic dicarboxylic acid having 20 to 80 carbon atoms and a dimer acid. Is particularly preferable.
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, when selected from aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, and dimer acids as "other dicarboxylic acid components", the film can be obtained in a smaller content ratio while maintaining the elongation (breaking elongation). It tends to be flexible, and among them, the use of dimer acid is the most effective. Therefore, by using "other dicarboxylic acid components" in combination as described above, it is possible to obtain a film having good strength, heat resistance, elongation, and flexibility.

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

Examples of the "other alcohol component (diol component)" include 1,4-butanediol, 1,6-hexanediol, diethylene glycol, trimethylene glycol, neopentyl glycol, 1,4-cyclohexanedimethanol, bisphenol and their respective substances. Derivatives and the like can be mentioned. Of these, diethylene glycol is preferable from the viewpoint of flexibility, and 1,4-butanediol is preferable from the viewpoint of heat resistance and strength.
Normally, when polyester is produced (polycondensed) using ethylene glycol as one of the raw materials, a part of ethylene glycol is modified to become diethylene glycol and introduced into the polyester skeleton. This diethylene glycol is referred to as by-product diethylene glycol, and the amount of the by-product is about 1 to 5 mol% of the ethylene glycol, although it varies depending on the mode of polycondensation (transesterification method, direct polycondensation) and the like. In the present invention, diethylene glycol thus produced as a by-product from ethylene glycol is also treated as a copolymerization component and is included in "other alcohol components".

In the copolymerized polyester A, the ratio of the alcohol component (diol component), that is, the ratio of the "other alcohol component (diol component)" to the total of ethylene glycol and the "other alcohol component" is 1 mol% or more and less than 25 mol%. It is preferable, and 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 kinds of "other alcohol components" are used in combination, it means the total amount thereof.
When the ratio of the "other alcohol component" is in the above range, the copolymerized polyester film tends to be effectively softened while having good elongation, strength and heat resistance.
Two or more kinds of "other alcohol components" may be used in combination. By using two or more kinds in combination, the copolymerized polyester film may be more effectively softened.

Further, it is preferable to add up "other dicarboxylic acid components" and "other alcohol components" and use three or more kinds in combination. By using a plurality of copolymerization components in combination, the film tends to be softened with a smaller content ratio. If there are too many types of copolymerization components, it may be difficult to stabilize the characteristics of the film. Therefore, the total of "other dicarboxylic acid components" and "other alcohol components" is 3 to 5. It is preferably a species, and more preferably 3 or 4 species.

Among the above, particularly preferable copolymerized polyester A is isophthalic acid, isophthalic acid, a copolymer of aliphatic dicarboxylic acid or dimeric acid, ethylene glycol and diethylene glycol, and isophthal in the dicarboxylic acid component constituting the copolymerized polyester. The ratio of acid, aliphatic dicarboxylic acid or dimeric acid is 5 mol% or more and 20 mol% or less, the ratio of diethylene glycol in the alcohol component constituting the copolymerized polyester is 1 mol% or more and less than 25 mol%, and the crystalline copolymerized polyester. Aa can be mentioned.
Generally, when the ratio of the copolymerization component is increased in order to reduce the elastic modulus, the copolymerization polyester is lowered in crystallinity, and when the ratio is further increased, it becomes amorphous. Although the copolymerized polyester Aa has a high proportion of copolymerization components and can achieve a low elastic modulus, it maintains crystallinity and can be heat-fixed by heat treatment after stretching. As a result, the copolyester Aa is supple, yet has good elongation and strength, and can suppress heat shrinkage.

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

When the copolymerized polyester layer (I layer) 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 lower or is not. A resin that is crystalline and has a glass transition temperature of 30 to 120 ° C. is preferable. By selecting such a resin B, the glass transition temperature of the copolymerized polyester layer (I layer) can be increased, and the heat resistance can be enhanced. By selecting polyester such as polyethylene terephthalate (PET) as the resin B, dimensional stability and heat resistance can be imparted.

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

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

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

If the component ratio of the entire polyester contained in the copolymerized polyester layer (I layer) is the same as that of the copolymerized polyester A, the same effect as when the copolymerized polyester A is contained as the main component resin can be obtained. It is thought that it can be done.
Therefore, when the copolymerized polyester layer (I layer) contains one or more types of polyester, the total amount of the components of all polyesters contained in the copolymerized polyester layer (I layer) contains the dicarboxylic acid component. The ratio of the total content of "other dicarboxylic acid components" to the total amount is 5 mol% or more and 20 mol% or less, and the ratio of the total content of "other alcohol components" to the total content of alcohol components is 1 mol%. If it is more than 25 mol% or more, the same effect as when the copolymerized polyester A is contained as the main component resin can be obtained.
At this time, the preferable range of the ratio of the total content of "other dicarboxylic acid components" to the total content of dicarboxylic acid components is the ratio of "other dicarboxylic acid components" to the dicarboxylic acid components in the copolymerized polyester A. It is the same as the preferable range of. Further, the preferable range of the ratio of the total content of "other alcohol components" to the total content of alcohol components is the same as the preferable range of the ratio of "other alcohol components" to the alcohol components in the copolymerized polyester A. Is.

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

For example, a laminated film having a structure in which a polyester layer (II layer) containing polyester C as a main component resin is laminated on both the front and back sides of the copolymerized polyester layer (I layer) can be mentioned.
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 polyester C is preferably a polyester having a melting point higher than that of the copolymerized polyester A. A polyester having a melting point of a temperature higher than the glass transition point of the copolymerized polyester A is preferable.

In the case of a laminated film having such a structure in which a polyester layer (II layer) containing polyester C as a main component resin is laminated, the polyester layer (II layer) / copolymerized polyester layer (I layer) / polyester The raw material resin composition is laminated by coextrusion or the like so as to form a layer (II layer), stretched, and then heat-fixed at a higher temperature than in the case of a single layer of a copolymerized polyester layer (I layer). Therefore, it is possible to soften to a level that cannot be achieved by a single layer of the copolyester layer (I layer), increase heat resistance, and further prevent heat shrinkage.
Specifically, the storage elastic modulus of the copolymerized polyester film at 25 ° C. can be set to 300 to 2500 MPa, particularly 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 (I layer).
If the thickness of each layer of the polyester layer (II layer) is 1% or more of the thickness of the copolymerized polyester layer (I layer), film formation is possible without significantly impairing productivity, and if it is 20% or less, it is required. It is preferable because it can sufficiently secure the flexibility.
From this point of view, the thickness of each layer of the polyester layer (II layer) is preferably 1 to 20% of the thickness of the copolymerized polyester layer (I layer), particularly 3% or more or 15% or less, and 5% or more among them. Alternatively, it is more preferably 12% or less.
The thickness of the polyester layer (II layer) existing on both the front and back sides of the copolymerized polyester layer (I layer) may be different or the same on the front and back sides.

When the copolymerized polyester A is crystalline, the polyester C has a melting point that is 10 to 100 ° C. higher than the melting point of the copolymerized polyester A, particularly 20 ° C. or higher or 90 ° C. or lower, and 40 ° C. or higher or 70 ° C. or lower. On the other hand, when the copolymerized polyester A is amorphous, it is 120 to 260 ° C. higher than the glass transition point of the copolymerized polyester A, particularly 140 ° C. or higher or 230 ° C. or lower, among them. A polyester having a high melting point of 160 ° C. or higher or 200 ° C. or lower is preferable.
The polyester C, which is the main component of the polyester layer (II layer) existing on both the front and back sides of the copolymerized polyester layer (I layer), may be different or the same on the front and back sides. Above all, it is preferable that the melting points of the polyester C on the front and back do not differ significantly. Specifically, the difference in melting point between the polyester layers (II layers) existing on both the front and back sides is preferably 80 ° C. or lower, particularly 60 ° C. or lower, and more preferably 40 ° C. or lower.
If the polyester C in the polyester layer (II layer) existing on both the front and back sides of the copolymerized polyester layer A is the same, coextrusion molding of 2 types and 3 layers becomes possible, so this embodiment is also preferable.

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

When the polyester C is a copolymerized polyester, examples of the dicarboxylic acid component other than terephthalic acid include aromatic dicarboxylic acid, alicyclic dicarboxylic acid, aliphatic dicarboxylic acid, and polyfunctional acid.
In polyester C, the ratio of "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, and 10 mol% or more or 20 mol% or less among them. Is more preferable.

When the polyester C is a copolymerized polyester, the alcohol components other than ethylene glycol include 1,4-butanediol, 1,6-hexanediol, diethylene glycol, trimethylene glycol, neopentyl glycol, and 1,4-cyclohexane. Examples thereof include dimethanol, bisphenol and derivatives thereof.
In polyester C, the ratio of "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, and among them, 10 mol% or more or 90 mol% or less. Is even 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 intended use.
Above all, from the viewpoint of further exhibiting the characteristics of the present copolymerized polyester film, it is preferable that the total thickness of the film exceeds 20 μm.
The firmness of the film is said to be proportional to the cube of the thickness. However, the present copolymerized polyester film has a characteristic that it is weak and supple even if it has a thickness of more than 20 μm, and the benefits of the present invention can be further enjoyed.
From this point of view, the total thickness of the copolymerized polyester film is preferably more than 20 μm, more preferably 23 μm or more, and more preferably 30 μm or more.
On the other hand, the upper limit of the total thickness of the copolymerized polyester film is not particularly limited. It is preferably 1000 μm or less, more preferably 500 μm or less, particularly 250 μm or less, and even more preferably 100 μm or less.

<Physical characteristics of this copolymerized polyester film>
The copolymerized polyester film preferably has a storage elastic modulus at 25 ° C. of 2500 MPa or less.
When the storage elastic modulus at 25 ° C., that is, at room temperature is 2500 MPa or less, it is possible to sufficiently follow the skin, for example, when wearing a wearable terminal.
From this point of view, the copolymerized polyester film preferably has a storage elastic modulus at 25 ° C. of 2500 MPa or less, more preferably 2000 MPa or less, and more preferably 1200 MPa or less.
The storage elastic modulus at 25 ° C. is preferably 300 MPa or more, more preferably 500 MPa or more, and even more preferably 700 MPa or more, from the viewpoint of handleability in the process.
The storage elastic modulus at 25 ° C. is a value obtained by the measuring method described in Examples described later.

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

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

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

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

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

This copolymerized polyester film has "flexibility" measured by the deflection measuring method described in Examples described later, that is, the length lowered in the vertical direction (a) and the length protruding in the horizontal direction. When the value is (b), the value of the ratio of (a) to (b) ((a) / (b)) is preferably 0.3 or more, particularly 0.5 or more, and 1 among them. It is more preferably 0.0 or more.
When the (a) / (b) is 0.3 or more, it is suggested that the film has sufficient suppleness.
On the other hand, the upper limit of (a) / (b) is not particularly limited, but is preferably 15.0 or less, particularly 10.0 or less, and 6.0 or less, among them, from the viewpoint of handleability in the process. Is even more preferable.

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

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

First, a raw material such as a polyester chip is supplied to a melt extruder by a known method, heated above the melting point of each polymer, the molten polymer is extruded from a die, and the temperature is below the glass transition point of the polymer on a rotary cooling drum. It may be cooled and solidified so as to obtain an unaligned sheet in a substantially amorphous state.
Next, the unoriented sheet is stretched in one direction by a roll or tenter type stretching machine. At this time, the stretching temperature is usually 25 to 120 ° C., preferably 35 to 100 ° C., and the stretching ratio is usually 2.5 to 7 times, preferably 2.8 to 6 times.
Then, it is stretched in a direction orthogonal to the stretching direction of the first stage. At this time, the stretching temperature is usually 50 to 140 ° C., and the stretching ratio is usually 3.0 to 7 times, preferably 3.5 to 6 times.
Then, the heat-fixing treatment is subsequently carried out at a temperature of 130 to 270 ° C. under tension or relaxation within 30% to obtain the present copolymerized polyester film as a biaxially oriented film.
In the above-mentioned stretching, a method of stretching in one direction in two or more steps can also be adopted.

When the heat fixing treatment (also referred to as "heat treatment") is composed of a single layer of the copolymerized polyester layer (I layer), it is preferably performed at a temperature lower than the melting point of the copolymerized polyester A by 10 to 70 ° C.

When the copolymerized polyester film has a laminated structure of a copolymerized polyester layer (I layer) and a polyester layer (II layer), the copolymerized polyester layer (I layer) and the polyester layer (II layer) are co-extruded and then co-extruded. As described above, the film may be stretched and heat-fixed as an integral film.
In this case, the heat fixing treatment is preferably carried out by heating to a temperature lower than the melting point of the polyester C. Further, when the copolymerized polyester A is crystalline, it is preferable to heat-fix it at a temperature higher than the melting point of the copolymerized polyester A. By heat-fixing treatment at such a temperature, it is possible to soften the copolymerized polyester layer (I layer) to a level that cannot be achieved by a single layer.
This is because the stretching orientation of the surface layer is fixed by heat-fixing at a temperature lower than the melting point of polyester C, so that the elongation, strength and heat resistance (heat shrinkage) are improved, while the copolymerized polyester A By heat-fixing at a temperature higher than the melting point of, the stretching orientation and strain of the intermediate layer are alleviated, so that the film can be made even more supple.

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

<Explanation of words and phrases>
In the present invention, the term "film" shall include the "sheet", and the term "sheet" shall include the "film".
Further, when the term "panel" is used as in the case of an image display panel, a protective panel, etc., it includes a plate body, a sheet, and a film.

In the present invention, when "X to Y" (X, Y are arbitrary numbers) is described, it means "X or more and Y or less" and "preferably larger than X" or "preferably Y". It also includes the meaning of "smaller".
Further, when "X or more" (X is an arbitrary number) is described, it includes the meaning of "preferably larger than X" and is described as "Y or less" (Y is an arbitrary number) unless otherwise specified. In this case, unless otherwise specified, it also includes the meaning of "preferably smaller than Y".

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

<Evaluation method>
In the following, the measurement and evaluation of various physical properties were carried out as follows.

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

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

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

(4) Tensile breaking strength The copolymerized polyester film (sample) obtained in Examples and Comparative Examples was used with a tensile tester (Intesco Co., Ltd., Intesco Model 2001) at a temperature of 23 ° C. and a humidity of 50% RH. A copolymerized polyester film (sample) having a width of 15 mm was set in a testing machine so that the chuck distance was 50 mm, and the strain rate was 200 mm / min in the longitudinal direction (MD) or the width direction of the film. (TD) was pulled, and the tensile breaking strength was determined by the following formula.
Tensile breaking strength (MPa) = F / A
However, in the above formula, F is the load (N) at the time of breaking, and A is the original cross-sectional area (mm ² ) of the test piece.

(5) Tensile breaking elongation The same test as the above-mentioned tensile breaking strength was carried out, and the tensile breaking elongation was determined by the following formula for the copolymerized polyester film (sample) obtained in Examples and Comparative Examples.
Tensile elongation at break (%) = 100 × (L-L0) / L0
However, in the above formula, L is the distance between the gauge points at the time of fracture (mm), and L0 is the original distance between the gauge points (mm).

(6) Heat shrinkage rate The copolymerized polyester film (sample) obtained in Examples and Comparative Examples was allowed to stand in an oven maintained at 120 ° C. in a non-tensioned state for 5 minutes, and the lengths of the samples before and after that were measured. The heat shrinkage rate in each of the longitudinal direction (MD) and the width direction (TD) of the film was calculated by the following equation.
Heat 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 longitudinal direction (MD) and the width direction (TD) of the film, and the average value was calculated for each.

(7) Evaluation of suppleness (flexibility measurement method)
Sample The sample was prepared by allowing the copolymerized polyester film (sample) obtained in Examples and Comparative Examples to stand at 23 ° C. and a 50% RH atmosphere for 24 hours, and then cutting it into a size of 150 mm in length and 50 mm in width.
As shown in FIG. 1, the copolymerized polyester film (sample) is placed on the desk so as to protrude 50 mm in length from the edge of the desk in an environment of 23 ° C., and the copolymerized polyester on the desk. A 200 g weight was placed on the film (sample) and fixed, and the tip side of the sample protruding from the edge of the desk was bent downward by its own weight. After 3 minutes, measure the length (a) at which the tip of the sample protruding from the edge of the desk bends vertically downward and hangs down, and the length (b) at which the tip protrudes horizontally from the edge of the desk. bottom.
Then, the ratio ((a) / (b)) of the length (a) that bends and hangs down to the length (b) that protrudes in the horizontal direction is calculated, and if it is 0.30 or more, it is "passed", 0. If it was less than 30, it was evaluated as "failed".

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

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

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

Copolymerized polyester 3 (“Co-PS3”): A crystalline copolymer polyester in which the acid component is 78 mol% of terephthalic acid and 22 mol% of isophthalic acid, and the diol component is 98 mol% of ethylene glycol and 2 mol% of by-product diethylene glycol. Melting point 198 ° C., intrinsic viscosity 0.70 dl / g.

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

[Example 1]
As a surface layer and an intermediate layer, a chip of copolymerized polyester 1 (co-PS1) is sent to an extruder with a vent set at 280 ° C., extruded from the mouthpiece of the extruder via a gear pump and a filter, and an electrostatic application adhesion method is used. The unstretched sheet was obtained by quenching and solidifying on a cooling roll whose surface temperature was set to 30 ° C.
Next, 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). It was heat-treated at 200 ° C. for 10 seconds and relaxed by 10% in the width direction (TD) to obtain a biaxially stretched copolymer polyester film (sample) having a thickness of 25 μm, which was substantially composed of a single layer.

[Example 2]
As an intermediate layer, a chip of copolymerized polyester 1 (co-PS1) was fed into a main vented twin-screw extruder set at 280 ° C.
As a surface layer, polyester (PET) chips were fed into a sub-vented twin-screw extruder set at 280 ° C.
Through a gear pump and a filter, the polymer from the main extruder is the intermediate layer, and the polymer from the sub extruder is the surface layer. An unstretched sheet was obtained by extruding and quenching and solidifying on a cooling roll whose surface temperature was set to 30 ° C. using an electrostatic application adhesion method.
Next, 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). A 25 μm-thick biaxially stretched copolymerized polyester having a thickness structure of 1 μm (surface layer) / 23 μm (intermediate layer) / 1 μm (surface layer) after being heat-treated at 200 ° C. for 10 seconds and relaxed by 10% in the width direction (TD). A film (sample) was obtained.

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

[Comparative Example 1]
Polyester (PET) chips are fed into a vented extruder set at 280 ° C, extruded from the extruder mouthpiece via a gear pump and filter, and cooled with a surface temperature set to 30 ° C using the electrostatic application adhesion method. It was rapidly cooled and solidified on a roll to obtain an unstretched sheet.
Next, 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). It was heat-treated at 235 ° C. for 10 seconds and relaxed by 10% in the width direction (TD) to obtain a biaxially stretched copolymer polyester film (sample) having a thickness of 50 μm.

[Comparative Example 2]
A mixture of 85 parts by mass of the PS3 tip and 15 parts by mass of the PET tip is sent to an extruder with a vent set at 280 ° C., extruded from the mouthpiece of the extruder via a gear pump and a filter, and electrostatically applied. An unstretched sheet was obtained by quenching and solidifying on a cooling roll whose surface temperature was set to 30 ° C. using the adhesion method.
Next, 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). It was heat-treated at 186 ° C. for 10 seconds and relaxed by 10% in the width direction (TD) to obtain a biaxially stretched copolymer polyester film (sample) having a thickness of 50 μm.

[Comparative Example 3]
A chip of copolymerized polyester 2 (co-PS2) is sent to an extruder with a vent set at 280 ° C., extruded from the mouthpiece of the extruder via a gear pump and a filter, and the surface temperature is raised to 30 ° C. using an electrostatic application adhesion method. The unstretched copolymerized polyester film (sample) having a thickness of 200 μm was obtained by quenching and solidifying on the cooling roll set in 1.

Based on the above examples and the test results conducted by the inventor so far, it is a copolymerized polyester film provided with a copolymerized polyester layer (I layer) containing the copolymerized polyester A as a main component resin at 25 ° C. When the storage elasticity is 2500 MPa or less, it is excellent in flexibility at room temperature, and it is not only flexible but also more supple, yet it can have elongation and strength. Moreover, it was found that when the storage elastic modulus at 120 ° C. is 10 MPa or more, it is possible to have sufficient heat resistance for practical use.

When the main component resin of the intermediate layer is a crystalline copolymerized polyester as in Examples 2 to 5, the polyester as the main component resin of the surface layer is a polyester having a melting point higher than the melting point of the copolymerized polyester. If there is, it was confirmed that the heat treatment (heat fixing) temperature after stretching can be made higher and the heat shrinkage can be further suppressed as compared with the case of the single layer consisting of only the intermediate layer.
When the main component resin of the intermediate layer is an 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. Compared with the case of a single layer composed of only the intermediate layer, the heat treatment (heat fixing) temperature after stretching can be made higher, so that it is considered that the heat shrinkage can be further suppressed.

Claims (14)

A copolymerized polyester film provided with a copolymerized polyester layer (I layer) containing the copolymerized 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 "other dicarboxylic acids" among the dicarboxylic acid components in the copolymerized polyester. The ratio of "acid component" is 5 mol% or more and 20 mol% or less, and the ratio of "other alcohol component" to the alcohol component is 1 mol% or more and less than 25 mol%.
A copolymerized polyester film having a storage elastic modulus at 25 ° C. of 2500 MPa or less and a storage elastic modulus of 120 ° C. of 10 MPa or more. The copolymerized polyester film according to claim 1, wherein the copolymerized polyester layer (layer I) is a layer containing the copolymerized polyester A and a resin B compatible with the copolymerized polyester A. The resin B contains one or more polyesters, 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% or less. The copolymerized polyester film according to claim 1 or 2, wherein the ratio of the total content of "other alcohol components" to the total content of alcohol components is 1 mol% or more and less than 25 mol%. A copolymerized polyester film provided with a copolymerized polyester layer (I layer) containing one or more kinds of polyesters.
In all polyesters contained in the copolymerized polyester layer (I layer), the ratio of the total content of "other dicarboxylic acid components" to the total content of dicarboxylic acid components is 5 mol% or more and 20 mol% or less, and the alcohol component. The ratio of the total content of "other alcohol components" to the total content is 1 mol% or more and less than 25 mol%.
A copolymerized polyester film having a storage elastic modulus at 25 ° C. of 2500 MPa or less and a storage elastic modulus of 120 ° C. of 10 MPa or more. The copolymerized polyester film according to any one of claims 1 to 4, wherein the "other dicarboxylic acid component" contains an aliphatic dicarboxylic acid or a dimer acid. The copolymerized polyester film according to any one of claims 1 to 5, wherein the "other dicarboxylic acid component" contains two or more of isophthalic acid, an aliphatic dicarboxylic acid, and a dimer acid. .. Any of claims 1 to 5, wherein the "other dicarboxylic acid component" contains two or more of isophthalic acid, an aliphatic dicarboxylic acid having 20 to 80 carbon atoms, and a dimer acid. The copolymerized polyester film according to. The copolymerized polyester film according to any one of claims 1 to 7, wherein the "other alcohol component" contains diethylene glycol. It has a structure in which a polyester layer (II layer) containing polyester C as a main component resin is laminated on both the front and back sides of the copolymerized polyester layer (I layer).
The polyester C is a polyester having a melting point higher than the melting point of the copolymerized polyester A when the copolymerized polyester A is crystalline, and is a glass of the copolymerized polyester A when the copolymerized polyester A is amorphous. The copolymerized polyester film according to any one of claims 1 to 8, wherein the polyester has a melting point having a temperature higher than the transition point. The copolymerized polyester film according to claim 9, wherein the thickness of each layer of the polyester layer (II layer) is 1 to 20% of the thickness of the copolymerized polyester layer (I layer). The copolymerized polyester film according to any one of claims 1 to 10, wherein the loss tangent (tan δ) at 25 ° C. is 0.02 or more. The copolymerized polyester film according to any one of claims 1 to 11, wherein the total thickness of the film exceeds 20 μm. A surface protective film using the copolymerized polyester film according to any one of claims 1 to 12. An optical member using the copolymerized polyester film according to any one of claims 1 to 12.

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