JP2021024940A - Polyester film - Google Patents

Abstract

To provide a new polyester film which is more flexible, is more pliable, combines elongation, strength and heat resistance, and is excellent in productivity compared to conventional, general-use polyester films.SOLUTION: There is provided a polyester film comprising a polyester layer (I) containing one or two or more kinds of polyesters, wherein the polyester contains a structural unit derived from a dicarboxylic acid component and a diol component. A structural unit derived from the dicarboxylic acid component includes terephthalic acid and a dimer acid, and a structural unit derived from the diol component includes ethylene glycol and polyalkylene glycol.SELECTED DRAWING: None

Description

The present invention relates to a polyester film having a polyester layer containing one or more polyesters.

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 the polyester film, for example, in Patent Document 1, a polyester film composed of at least two types of polyester as a polyester film having excellent moldability and transparency, particularly excellent properties for molding processing applications, is carbon. Polyester A containing 1 to 80 mol% of an aliphatic component having an alkylene group of several 4 or more, and polyester B containing ethylene terephthalate as a main component, and having a temperature rise crystallization temperature of 70 ° C to 140 ° C. Polyester films characterized by a haze of 1-20% have been proposed.

Further, in Patent Document 2, polyester (A) is used as a laminated polyester film which satisfies all of flexibility, solvent resistance, printability, heat resistance, moldability, and aging resistance and is excellent in cost performance. 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 as a main component, and the elasticity of the laminated film in an atmosphere of 23 ° C. A laminated polyester film having an elastic ratio of 20 to 1000 MPa, an elastic coefficient of 10 to 200 MPa in an atmosphere of 120 ° C., and substantially no orientation has been proposed.

Further, Patent Document 3 states that 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 elastic rate E'of the film is 20 MPa at 120 ° C. The following, 5 MPa or less at 180 ° C., 1.0% or less film haze, 29 to 32 mol% of 1,4-cyclohexanedimethanol unit as a diol component, and a dicarboxylic acid component. A softened polyester film characterized by not containing an isophthalic acid unit has been proposed.

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 4).

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 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.

Regarding this type of polyester film, for example, in Patent Document 5, a new copolymerized polyester film that is more flexible and supple than a conventional polyester film, yet has elongation, strength, and heat resistance. A copolymerized polyester film comprising a copolymerized polyester layer A containing the copolymerized polyester A as a main component resin, wherein the copolymerized polyester A contains terephthalic acid and “other dicarboxylic acid components” and ethylene glycol. And "other alcohol components", and the ratio of "other dicarboxylic acid components" to the dicarboxylic acid components in the copolymerized polyester is 5 to 20 mol%, and "other alcohols" to the alcohol components. A copolymerized polyester film characterized in that the ratio of "components" is 25 to 50 mol%, the storage elasticity at 25 ° C. is 2500 MPa or less, and the storage elasticity at 120 ° C. is 10 MPa or more has been proposed. There is.

Japanese Unexamined Patent Publication No. 2006-219509 International Publication WO2009 / 078304 Japanese Unexamined Patent Publication No. 2014-169371 Japanese Unexamined Patent Publication No. 2014-134903 International Publication No. 2019-059322

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 is necessary to develop a polyester film that has elongation and strength, and also has heat resistance that does not shrink when heated.

The present inventor has developed such a novel copolymerized polyester film in Patent Document 5, but there is still room for improvement in terms of productivity.
Therefore, the subject of the present invention is that it is more flexible and more supple than the polyester film generally used in the past, and also has elongation, strength and heat resistance, and is excellent in productivity. The purpose is to provide a new polyester film.

The present inventor is a polyester film provided with a polyester layer (I) containing one or more kinds of polyesters as a means for solving the above-mentioned problems.
The polyester contains a structural unit derived from a dicarboxylic acid and a diol component.
As a constituent unit derived from the dicarboxylic acid component, terephthalic acid and dimer acid are contained.
We propose a polyester film characterized by containing ethylene glycol and polyalkylene glycol as a constituent unit derived from the diol component.

The polyester film of the present invention has excellent flexibility at room temperature, is not only flexible, but also more supple, yet has elongation and strength, and further has sufficient heat resistance for practical use. Can have.
Further, since the polyester film of the present invention has excellent compatibility with a commonly used polyester film (for example, polyethylene terephthalate), it is necessary to change the setup to a general-purpose polyester product after manufacturing the polyester film. Even if it is performed, the replacement work can be easily performed and the productivity is improved.
Therefore, the polyester film of 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 polyester film >>
The polyester film according to an example of the embodiment of the present invention (hereinafter, also referred to as “the present polyester film”) is a single-layer or laminated film including a polyester layer (I) containing one or more kinds of polyesters. is there.

The present 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 polyester film is such a stretched film, the storage elastic modulus at 120 ° C. can be easily set to 10 MPa or more.

<Polyester layer (I layer)>
The polyester layer (I layer) is a layer containing one kind or two or more kinds of polyesters, and is preferably a layer containing one kind of polyester or two or more kinds of polyester blends as a main component resin.

Here, the "main component resin" means the resin having the highest content ratio among the resins constituting the polyester layer (I layer). At this time, when the polyester layer (I layer) contains a polyester blend composed of two or more types of polyester, the total content of the two or more types of polyester is the highest among the resins constituting the polyester layer (I layer). The higher the content ratio, the better.
The content of the main component resin (when two or more kinds of polyesters are contained, the total content of two or more kinds of polyesters) is 30% by mass or more, particularly 50% by mass, of the resins constituting the polyester layer (I layer). % Or more, and 80% by mass or more (including 100% by mass) may be occupied.

The polyester layer (I layer) may be composed of only one type of polyester, or may be, for example, a mixed resin (polymer blend) of two or more types containing polyester A and polyester B. Further, a resin other than these polyesters may be contained.

(Book polyester)
The polyester (also referred to as "the present polyester") as the main component resin of the polyester layer (I layer) preferably contains at least a structural unit derived from a dicarboxylic acid and a diol component.
The structural unit refers to a repeating unit introduced into polyester derived from a compound (monomer) used as a raw material for producing polyester.

Further, the polyester preferably contains terephthalic acid and dimer acid as the structural unit derived from the dicarboxylic acid component, and contains ethylene glycol and polyalkylene glycol as the structural unit derived from the diol component. ..
Further, the present polyester preferably contains the terephthalic acid, dimer acid, ethylene glycol and polyalkylene glycol as a main constituent unit.
The main structural unit refers to a repeating unit that occupies 60% by mass or more, particularly 70 to 100% by mass, of all the structural units constituting polyester.

As described above, the present polyester may be one kind of polyester or may be a blend of two or more kinds of polyesters. Therefore, when the present polyester is made of one kind of polyester, that is, the above polyester layer (I). When the layer) contains one kind of polyester, the polyester contains terephthalic acid and dimer acid as the constituent units derived from the dicarboxylic acid component, and ethylene glycol and poly as the constituent units derived from the diol component. It is preferably "copolymerized polyester I (d2)" containing alkylene glycol.

On the other hand, when the present polyester is composed of two or more kinds of polyesters, that is, when the polyester layer (I layer) contains a polyester blend composed of two or more kinds of polyesters, the polyester blend is derived from the dicarboxylic acid component. It is preferable that the constituent unit contains terephthalic acid and dimeric acid, and the constituent unit derived from the diol component contains ethylene glycol and polyalkylene glycol.
A polyester film having a polyester layer (I layer) containing a polyester having such a structural unit as a main component resin is flexible and supple, and can have elongation, strength, and heat resistance.

At this time, the polyester blend may have the above-mentioned structural unit. For example, when the polyester blend is a mixed resin of a first polyester and a second polyester, the first polyester and the second polyester It is not necessary for each polyester to have all of the above building blocks.

(Dicarboxylic acid component)
Examples of the dimer acid include a dimer of an unsaturated aliphatic carboxylic acid having 16 or more carbon atoms or a hydrogenated product thereof.

The dimer acid is an unsaturated carboxylic acid having 16 or more carbon atoms (for example, an unsaturated aliphatic carboxylic acid containing linoleic acid or oleic acid as a main component) extracted from non-petroleum raw materials such as soybean oil, rapeseed oil, beef fat, and tall oil. A mixture of acids) can be obtained by dimerizing or watering it.
When dimer acid is obtained by using such a production method, an excessively reacted trimer and an unreacted unsaturated aliphatic carboxylic acid are contained as impurities.
The impurities are preferably as small as possible because they cause bleed-out and gelation in polyester.

The dimer acid contains an unsaturated bond, and if used as it is, a branching reaction may proceed during polymerization or the color tone of the polyester resin may be deteriorated. Therefore, the dimer acid is preferably hydrogenated.

Among them, 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 particularly preferable from the viewpoint of being able to further lower the glass transition temperature.

The content of the dimer is 5% by mass or more and 25% by mass with respect to all the constituent units of the polyester contained in the polyester layer (I) (the total mass when two or more kinds of polyesters are contained; the same applies hereinafter). It is preferably contained below, and more preferably 6% by mass or more or 19% by mass or less.
As long as the content of the dimer acid is within such a range, the polyester film can have excellent flexibility and high transparency.

The dicarboxylic acid component of polyester can be quantified by measuring the 1H-NMR spectrum.

The polyester may contain structural units derived from "other dicarboxylic acid components" other than the terephthalic acid and dimer acid.
Examples of the constituent unit derived from the "other dicarboxylic acid component" include a) isophthalic acid, phthalic acid, sodium sulfoisophthalate, phenylenedioxydicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-. Aromatic dicarboxylic acids such as diphenyl ether dicarboxylic acid, 4,4'-diphenylketone dicarboxylic acid, 4,4'-diphenoxyetanedicarboxylic acid, 4,4'-diphenylsulfonedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, b. ) Hexahydroterephthalic acid, hexahydroisophthalic acid and other alicyclic dicarboxylic acids, succinic acid, glutaric acid, adipic acid, pimeric acid, suberic acid, azelaic acid, sebacic acid, undecadicarboxylic acid, dodecadicarboxylic acid, etc. Examples thereof include "aliphatic dicarboxylic acids" of the above, and esters and halides having an alkyl group having about 1 to 4 carbon atoms.
These may contain one kind or a mixture of two or more kinds.

Above all, from the viewpoint of facilitating the softening of the polyester film, the polyester preferably contains isophthalic acid as a constituent unit derived from "another dicarboxylic acid component" other than the terephthalic acid and the dimer acid.

The content of the isophthalic acid is preferably 1% by mass or more and 10% by mass or less, particularly 2% by mass or more or 8% by mass or less, based on all the constituent units of the polyester contained in the polyester layer (I). Is more preferable.
When the content of the isophthalic acid is within such a range, the present polyester film has improved impact resistance without impairing excellent flexibility and high transparency.

Further, among the above-mentioned "aliphatic dicarboxylic acids", from the viewpoint of being able to further lower the glass transition temperature, the aliphatic dicarboxylic acids having 20 to 80 carbon atoms, particularly 30 or more or 60 or less, and 36 or more or 48 or less among them. Especially preferable.

(Diol component)
The polyester may contain a structural unit derived from a diol component other than the polyalkylene glycol.
Examples of the constituent units derived from the diol component include a) ethylene glycol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, and the like. Aliphatic diols such as octamethylene glycol, decamethylene glycol, neopentyl glycol, 2-ethyl-2-butyl-1,3-propanediol, b) 1,2-cyclohexanediol, 1,1-cyclohexanedimethylol, 1 , 4-Cyclohexanedimethanol, alicyclic diols such as 2,5-norbornandimethylol, c) xylylene glycol, 4,4'-dihydroxybiphenyl, 2,2-bis (4'-hydroxyphenyl) propane, 2 , 2-bis (4'-β-hydroxyethoxyphenyl) propane, bis (4-hydroxyphenyl) sulfone, aromatic diols such as bis (4-β-hydroxyethoxyphenyl) sulfonic acid, 2,2-bis (4) '-Hydroxyphenyl) Propane ethylene oxide adduct or propylene oxide adduct, dimerdiol can be mentioned.
These may contain one kind or a mixture of two or more kinds.

The content of the diethylene glycol is preferably 0.5% by mass or more and 5% by mass or less, particularly 0.5% by mass or more and 4% by mass, based on all the constituent units of the polyester contained in the polyester layer (I). More preferably, it is less than%.
When the content of the diethylene glycol is within such a range, the thermal stability of the polyester is improved and the transparency of the polyester film is improved.

The content of 1,4-cyclohexanedimethanol is preferably 1% by mass or more and 12% by mass or less, and more than 2% by mass or more, based on all the constituent units of the polyester contained in the polyester layer (I). Alternatively, it is more preferably 8% by mass or less.
When the content of 1,4-cyclohexanedimethanol is within such a range, the thermal stability of the polyester becomes good, and the present polyester film has good whitening resistance during storage.

Each diol component of the present polyester can be quantified by measuring a 1H-NMR spectrum.

As a method of controlling the amount of diethylene glycol in the present polyester, first, a method of adjusting the amount of diethylene glycol used as a raw material in the production of polyester can be mentioned.
Further, the diethylene glycol in the present polyester may be incorporated into the polyester as a diol component by dehydration bonding of two ethylene glycol molecules used as a raw material in the production of the polyester to form diethylene glycol.

As the above-mentioned control method, a method of increasing the charged molar ratio of the diol component containing ethylene glycol used as a raw material to the dicarboxylic acid component used as a raw material can be mentioned. According to this method, bimolecularization of ethylene glycol is promoted, and the amount of diethylene glycol tends to increase.

Further, when the esterification reaction is carried out in the presence of a metal hydroxide such as sodium hydroxide or an alkaline component such as tetraethylammonium hydroxide, the binarization of ethylene glycol is suppressed and the amount of diethylene glycol tends to decrease.

(Polyalkylene glycol)
In order to impart further flexibility and suppleness, it is conceivable to increase the dimer acid component.
However, when the dimer acid component is increased, the compatibility with other general-purpose polyesters such as polyethylene terephthalate is lost, and the productivity deteriorates due to the setup change work and the like.
Therefore, in the present invention, in order to improve such compatibility, a polyalkylene glycol component is added, and in particular, a polyalkylene glycol component having a long molecular chain is added to impart further flexibility and suppleness. Still, we are getting a polyester film with excellent productivity.

The total content of the dimer acid and the polyalkylene glycol is preferably 6% by mass or more and 45% by mass or less, particularly 9% by mass, with respect to all the constituent units of the polyester contained in the polyester layer (I). It is more preferably% or more or 35% by mass or less, and particularly preferably 12% by mass or more or 25% by mass or less.

As the polyalkylene glycol, polyethylene glycol having a mass average molecular weight of 3000 or less and polytetramethylene glycol having a number average molecular weight of 2000 or less are preferable.
Further, in the case of polyethylene glycol, the mass average molecular weight thereof is preferably 500 or more, particularly preferably 1000 or more, and on the other hand, preferably 2000 or less.
Further, in the case of polytetramethylene glycol, the number average molecular weight thereof is more preferably 1500 or less, and particularly preferably 1000 or less. On the other hand, it is preferably 500 or more, and more preferably 800 or more.
When the molecular weight of the polyalkylene glycol is within such a range, the transparency of the polyester film is improved.
The mass average molecular weight of polyethylene glycol and the number average molecular weight of polytetramethylene glycol are values obtained by size exclusion chromatography (SEC).

The content of the polyalkylene glycol is preferably 1% by mass or more and 20% by mass or less, particularly 2% by mass or more or 12% by mass, based on all the constituent units of the polyester contained in the polyester layer (I). Hereinafter, among them, it is more preferably 11% by mass or less.
As long as the content of the polyalkylene glycol is within such a range, the polyester film can have excellent flexibility and high transparency.

(Polyester blend)
As a preferred embodiment of the polyester blend, a "polyester A" containing a dimer acid as a constituent unit derived from a dicarboxylic acid and a "polyester B" containing a polyalkylene glycol as a constituent unit derived from a diol component are used. Examples include polyester blends containing.
At this time, the polyester A and / or the polyester B may further contain terephthalic acid as a constituent unit derived from the dicarboxylic acid.
Further, the polyester A and / or the polyester B may further contain ethylene glycol as a constituent unit derived from the diol component.

Among them, "polyester A" containing terephthalic acid and dimeric acid as a constituent unit derived from a dicarboxylic acid and containing 1,4-butanediol or ethylene glycol as a constituent unit derived from a diol component, and dicarboxylic acid. The constituent unit derived from the acid contains terephthalic acid, and the constituent unit derived from the diol component includes "polyester B" containing 1,4-butanediol or ethylene glycol, and polyalkylene glycol. Polyester blends are preferred.

In addition to the polyesters A and B, the polyester blend further contains terephthalic acid as a constituent unit derived from the dicarboxylic acid component, and ethylene glycol as a constituent unit derived from the diol component. It preferably contains homopolyester C and / or copolymerized polyester E.
The polyester E is a copolymerized polyester other than the polyester A and the polyester B.

Further, as another example of the polyester blend, "polyester D" containing dimer acid as a constituent unit derived from the dicarboxylic acid component and containing polyalkylene glycol as a constituent unit derived from the diol component, and dicarboxylic acid. Examples of the constituent unit derived from the acid component include a polyester blend containing terephthalic acid and, as a constituent unit derived from the diol component, "polyester C" containing ethylene glycol or "polyester EE". be able to.
The polyester EE is a copolymerized polyester other than the polyester D.

According to the blend of two or more kinds of polyesters as compared with one kind of copolymerized polyester, terephthalic acid and dimer acid as the constituent units derived from the dicarboxylic acid component and ethylene glycol as the constituent units derived from the diol component. In addition, there are advantages such as being able to finely control the ratio of each component of the polyalkylene glycol and the intrinsic viscosity (IV).

(Preferable Embodiment 1: Polyester composition α)
As a particularly preferable embodiment of the polyester blend, "copolymerized polyester a1" containing terephthalic acid and dimer acid as a constituent unit derived from a dicarboxylic acid component and ethylene glycol as a constituent unit derived from a diol component. And "copolymerized polyester b1" containing terephthalic acid as a constituent unit derived from the dicarboxylic acid component and containing 1,4-butanediol and polyalkylene glycol as a constituent unit derived from the diol component. The "polyester composition α" containing the above can be mentioned.
The most typical examples of the polyester composition α are copolymerized polyethylene terephthalate (copolymerized polyester a1) containing dimer acid as a constituent unit derived from a dicarboxylic acid component, and poly as a constituent unit derived from a diol component. Examples thereof include a polyester composition containing a copolymerized polybutylene terephthalate (copolymerized polyester b1) containing an alkylene glycol.

The copolymerized polyester a1 further preferably contains a structural unit derived from other diol components other than ethylene glycol, preferably contains diethylene glycol from the viewpoint of flexibility, and from the viewpoint of heat resistance and strength. It preferably contains 1,4-butanediol.

The copolymerized polyester b1 may contain a structural unit derived from other dicarboxylic acid components other than terephthalic acid.
Further, as described above, the copolymerized polyester b1 preferably contains polytetramethylene glycol or polyethylene glycol as the polyalkylene glycol.

In the polyester layer (I layer), the mass ratio of the copolymerized polyester a1 and the copolymerized polyester b1 is preferably 50:50 to 90:10, and more preferably 55:45 to 85:15. Among them, 60:40 to 80:20 is more preferable.

The polyester composition α further contains terephthalic acid as a constituent unit derived from the dicarboxylic acid component and ethylene glycol as a constituent unit derived from the diol component, homopolyester C and / or "polyester". It is preferable to include "E1".
The polyester E1 is a copolymerized polyester other than the copolymerized polyester a1 and the copolymerized polyester b1.
The composition α preferably contains homopolyester C from the viewpoint of dimensional stability and heat resistance.

The copolymerized polyester E1 is selected from, for example, an aromatic dicarboxylic acid, an alicyclic dicarboxylic acid, an aliphatic dicarboxylic acid, or a polyfunctional acid as a constituent unit derived from a dicarboxylic acid other than terephthalic acid. Alternatively, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, trimethylene glycol, neopentyl glycol, 1,4 are contained as a constituent unit containing two or more kinds and derived from a diol component other than ethylene glycol. -Cycopolymerized polyester containing any one or more selected from cyclohexanedimethanol, bisphenol and derivatives thereof can be mentioned.

Among them, the copolymerized polyester E1 which is compatible with the copolymerized polyester a1 and / or the polyester b1 and has a melting point of 270 ° C. or lower or an amorphous material and a glass transition temperature of 30 to 120 ° C. is particularly preferable.
By selecting such E1, the glass transition temperature of the polyester layer (I layer) can be increased, and the heat resistance can be enhanced.

In the polyester layer (I layer), the total content of the homopolyester C and the copolymerized polyester E1 is preferably 5 to 50% by mass, particularly 10% by mass or more or 45% by mass or less, and 15% by mass or more among them. Alternatively, it is more preferably 40% by mass or less.

It is preferable that the copolymerized polyester E1 does not contain dimer acid as a structural unit derived from the dicarboxylic acid component and does not contain polyalkylene glycol as a structural unit derived from the diol component.

(Preferable Embodiment 2: Polyester composition β)
As another preferred embodiment of the polyester blend, "terephthalic acid and dimer acid are contained as the structural unit derived from the dicarboxylic acid component, and 1,4-butanediol is contained as the structural unit derived from the diol component. "Copolymerized polyester a2" and "copolymerized polyester b2" containing terephthalic acid as a constituent unit derived from a dicarboxylic acid component and containing ethylene glycol and polyalkylene glycol as a constituent unit derived from a diol component. , And "polyester composition β" containing.
The most typical example of the polyester composition β is a copolymerized polybutylene terephthalate (copolymerized polyester a2) containing dimer acid as a constituent unit derived from a dicarboxylic acid component, and a constituent unit derived from a diol component. Examples thereof include a copolymerized polyethylene terephthalate containing a polyalkylene glycol (copolymerized polyester b2) and a polyester composition containing the same.

The copolymerized polyester a2 may further contain a structural unit derived from other diol components other than 1,4-butanediol.

The copolymerized polyester b2 may contain a structural unit derived from other dicarboxylic acid components other than terephthalic acid.

Further, as described above, the copolymerized polyester b2 preferably contains polytetramethylene glycol or polyethylene glycol as the polyalkylene glycol.

In the polyester layer (I layer), the mass ratio of the copolymerized polyester a2 and the copolymerized polyester b2 is preferably 50:50 to 90:10, and more preferably 55:45 to 85:15. Among them, 60:40 to 80:20 is more preferable.

Further, the polyester composition β preferably further contains the homopolyester C and / or "polyester E2".
The polyester E2 is a copolymerized polyester other than the copolymerized polyester a2 and the copolymerized polyester b2.
The composition β preferably contains homopolyester C from the viewpoint of dimensional stability and heat resistance.

As the polyester E2, other than the copolymerized polyester a2 and the copolymerized polyester b2, those exemplified by the polyester E1 can be used.
Of these, the copolymerized polyester E2, which is compatible with the copolymerized polyester a2 and / or the polyester b2, has a melting point of 270 ° C. or lower, or is amorphous, and has a glass transition temperature of 30 to 120 ° C. is preferable.
By selecting such polyester E2, the glass transition temperature of the polyester layer (I layer) can be increased, and the heat resistance can be enhanced.

The preferable range of the contents of the homopolyester C and the copolymerized polyester E2 in the polyester layer (I layer) when the composition β is used is the same as that in the first embodiment.

It is preferable that the copolymerized polyester E2 does not contain dimer acid as a structural unit derived from the dicarboxylic acid component and does not contain polyalkylene glycol as a structural unit derived from the diol component.

(Preferable Embodiment 3: Polyester composition γ)
As a particularly preferable embodiment of the polyester blend, a "polyester composition γ" containing the "copolymerized polyester a1" and the above "copolymerized polyester b2" can be mentioned.
As the most typical example of the polyester composition γ, a copolymerized polyethylene terephthalate (copolymerized polyester a1) containing dimer acid as a constituent unit derived from a dicarboxylic acid component and a polyalkylene as a constituent unit derived from a diol component. Examples thereof include a copolymerized polyethylene terephthalate containing glycol (copolymerized polyester b2) and a polyester composition containing the same.

(Preferable Embodiment 4: Polyester Composition δ)
As a particularly preferable embodiment of the polyester blend, a "polyester composition δ" containing the "copolymerized polyester a2" and the above "copolymerized polyester b1" can be mentioned.
The most typical example of the polyester composition δ is a copolymerized polybutylene terephthalate (copolymerized polyester a2) containing dimer acid as a constituent unit derived from a dicarboxylic acid component, and a constituent unit derived from a diol component. Examples thereof include a copolymer composition containing a copolymerized polybutylene terephthalate (copolymerized polyester b1) containing a polyalkylene glycol and a polyester composition containing the same.

In the above-described embodiments 3 and 4, specific examples and preferred embodiments of the above-mentioned copolymerized polyesters a1, a2, b1 and b2 are the same as those of the above-described embodiments 1 and 2.

Further, the polyester composition γ preferably contains the homopolyester C and / or “polyester E3”.
The polyester E3 is a copolymerized polyester other than the copolymerized polyester a1 and the copolymerized polyester b2.

As the polyester E3, other than the copolymerized polyester a1 and the copolymerized polyester b2, those exemplified by the above-mentioned polyester E1 can be used.
Among them, a copolymerized polyester which is compatible with the copolymerized polyester a1 and / or the polyester b2, has a melting point of 270 ° C. or lower, or is amorphous, and has a glass transition temperature of 30 to 120 ° C. is preferable.
By selecting such a polyester, the glass transition temperature of the polyester layer (I layer) can be increased, and the heat resistance can be enhanced.

Further, the polyester composition δ preferably contains the homopolyester C and / or "polyester E4".
The polyester E4 is a copolymerized polyester other than the copolymerized polyester a2 and the copolymerized polyester b1.

As the polyester E4, those other than the copolymerized polyester a2 and the copolymerized polyester b1 and exemplified by the above-mentioned polyester E1 can be used.
Among them, a copolymerized polyester which is compatible with the copolymerized polyester a2 and / or the polyester b1 and has a melting point of 270 ° C. or lower or an amorphous material and a glass transition temperature of 30 to 120 ° C. is preferable.
By selecting such a polyester, the glass transition temperature of the polyester layer (I layer) can be increased, and the heat resistance can be enhanced.

The polyester compositions γ and δ preferably contain homopolyester C from the viewpoint of dimensional stability and heat resistance.

The preferable range of the contents of the homopolyester C and the copolymerized polyester E3 or E4 in the polyester layer (I layer) when the polyester compositions γ and δ are used is the same as that in the first embodiment.

It is preferable that the copolymerized polyesters E3 and E4 do not contain dimer acid as a structural unit derived from the dicarboxylic acid component and do not contain polyalkylene glycol as a structural unit derived from the diol component.

(Preferable Embodiment 5: Polyester composition ε)
As another preferred embodiment of the polyester blend, "copolymerized polyester D" containing dimer acid as a constituent unit derived from the dicarboxylic acid component and polyalkylene glycol as a constituent unit derived from the diol component. ,
A "copolymerized polyester EE" other than the homopolyester C containing terephthalic acid as a constituent unit derived from the dicarboxylic acid component and ethylene glycol as a constituent unit derived from the diol component and / or the copolymerized polyester D. , And "polyester composition ε" containing.

The copolymerized polyester D contains terephthalic acid and dimer acid as constituent units derived from dicarboxylic acid, and copolymerization containing 1,4-butanediol and polyalkylene glycol as constituent units derived from the diol component. As a preferred embodiment, polyester d1 or a copolymerized polyester d2 containing terephthalic acid and dimer acid as a constituent unit derived from a dicarboxylic acid and containing ethylene glycol and polyalkylene glycol as a constituent unit derived from a diol component is mentioned as a preferable embodiment. Can be done.

Among the above, the polyester composition ε preferably contains homopolyester C from the viewpoint of dimensional stability and heat resistance.

In the polyester layer (I layer), the mass ratio of the copolymerized polyester D to the homopolyester C or the copolymerized polyester E3 is preferably 50:50 to 90:10, particularly 55:45 to 85:15. It is more preferable that the amount is 60:40 to 80:20.

As the copolymerized polyester EE, other than the copolymerized polyester D, those exemplified by the above-mentioned copolymerized polyester E1 can be used.
Of these, a copolymerized polyester that is compatible with the copolymerized polyester D and has a melting point of 270 ° C. or lower, or an amorphous material and a glass transition temperature of 30 to 120 ° C. is preferable.
By selecting such a copolymerized polyester EE, the glass transition temperature of the polyester layer (I layer) can be increased, and the heat resistance can be enhanced.

The preferable range of the content of the homopolyester C or the copolymerized polyester EE in the polyester layer (I layer) when the polyester composition ε is used is the same as that in the first embodiment.

It is preferable that the copolymerized polyester EE does not contain dimer acid as a structural unit derived from the dicarboxylic acid component and does not contain polyalkylene glycol as a structural unit derived from the diol component.

(Intrinsic viscosity of polyester (IV))
The intrinsic viscosity (IV) of the present polyester (as a polyester mixture when two or more kinds of polyesters are used) is preferably 0.40 dL / g to 1.20 dL / g, and more than 0.45 dL / g. Alternatively, it is more preferably 1.15 dL / g or less, particularly 0.48 dL / g or more or 1.10 dL / g or less.
If the intrinsic viscosity of the polyester is within such a range, it is possible to obtain a polyester having excellent molding processability without deteriorating productivity.

(Manufacturing method of this polyester)
The method for producing this polyester is not particularly limited, and a usual method can be applied. For example, a dicarboxylic acid component containing terephthalic acid or an ester-forming derivative thereof, isophthalic acid or an ester-forming derivative thereof and an ethylene glycol, preferably a diol component containing diethylene glycol are mixed at a predetermined ratio under stirring to prepare a raw material slurry. (“Material slurry preparation step”), then the raw material slurry is heated under normal pressure or pressure to undergo an esterification reaction to obtain a polyester low polymer (hereinafter, may be referred to as “oligomer”) (“oligomer”). Preparation step "), then, dimeric acid or an ester-forming derivative thereof and polyalkylene glycol are added to the obtained oligomer, and the pressure is gradually reduced and heated in the presence of an ester exchange catalyst or the like to carry out a melt polycondensation reaction. The polyester may be further subjected to a solid phase polycondensation reaction (“solid phase polycondensation step”), and the obtained polyester may be further subjected to a solid phase polycondensation reaction if necessary.

The dimer acid or its ester-forming derivative or polyalkylene glycol can be added to the raw material slurry or added to the oligomer by either method.

Examples of the ester exchange catalyst include antimony compounds such as diantimon trioxide; germanium compounds such as germanium dioxide and germanium tetroxide; titanium alcoholates such as tetramethyl titanate, tetraisopropyl titanate and tetrabutyl titanate, and titanium such as tetraphenyl titanate. Titanium compounds such as phenolate; dibutyltin oxide, methylphenyltin oxide, tetraethyltin, hexaethylditin oxide, cyclohexahexyl distin oxide, didodecyltin oxide, triethyltin hydrooxide, triphenyltin hydrooxide, triisobutyltin Tin compounds such as acetate, dibutyltin diacetate, diphenyltindilaurate, monobutyltin trichloride, tributyltin chloride, dibutyltin sulfate, butylhydroxytin oxide, methylstannoic acid, ethylstannoic acid, butylstannonic acid; magnesium acetate, magnesium hydroxide , Magnesium compounds such as magnesium carbonate, magnesium oxide, magnesium alcoholide, magnesium hydrogen phosphate, calcium acetate, calcium hydroxide, calcium carbonate, calcium oxide, calcium alcoholides, calcium hydrogen phosphate and the like. it can.
It should be noted that these catalysts can be used alone or in combination of two or more.

Further, in the production of polyester, it is preferable to use a stabilizer together with an ester exchange catalyst, and the stabilizers include orthophosphorous acid, polyphosphoric acid, and trimethylphosphate, triethyl phosphate, tri-n-butyl phosphate, and trioctyl phosphate. , Triphenyl phosphate, tricresyl phosphate, tris (triethylene glycol) phosphate, ethyl diethylphosphonoacetate, methyl acid phosphate, ethyl acid phosphate, isopropyl acid phosphate, butyl acid phosphate, monobutyl phosphate, dibutyl phosphate, dioctyl phosphate, Five-valent phosphorus compounds such as triethylene glycol acid phosphate, phosphorous acid, hypophosphite, and trivalent phosphorus compounds such as diethyl phosphite, trisdodecyl phosphite, trisnonyl decyl phosphite, and triphenyl phosphite. Can be mentioned.
Among them, the trivalent phosphorus compound is generally more reducing than the pentavalent phosphorus compound, and the metal compound added as a polycondensation catalyst may be reduced and precipitated, which may cause foreign matter to be generated. Valuable phosphorus compounds are preferred.

The reaction pressure in the melt polycondensation reaction is preferably 0.001 kPa to 1.33 kPa in absolute pressure.

The reaction temperature is preferably 220 ° C. to 280 ° C., more preferably 230 ° C. or higher or 260 ° C. or lower.

The solid phase polycondensation reaction is carried out under reduced pressure or under an inert gas atmosphere, and the reaction temperature is preferably 180 ° C. to 220 ° C.

The reaction time of the solid phase polycondensation reaction is preferably 5 hours to 100 hours.

A polyester having a desired intrinsic viscosity can be obtained by setting the melt polycondensation reaction conditions and the solid polycondensation reaction conditions.

(Other ingredients)
The polyester layer (I layer) may contain "another resin" other than the polyester.
Examples of the "other resin" include polyolefin, polystyrene, acrylic resin, urethane resin and the like.

In addition to the above, the polyester layer (I layer) further includes a crystal nucleating agent, an antioxidant, an antioxidant, a pigment, a dye, an ultraviolet absorber, a mold release agent, a lubricant, a flame retardant, and an antistatic agent. It can contain various additives such as inorganic and / or organic particles.

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

For example, a laminate having a structure in which another polyester layer (II layer), for example, a polyester layer (II layer) containing "polyester F" as a main component resin is laminated on both the front and back sides of the polyester layer (I layer). The film can be mentioned.

(Polyester F)
When the polyester of the polyester layer (I layer) is crystalline, the polyester F preferably has a melting point higher than the melting point of the polyester, and the polyester of the polyester layer (I layer) is amorphous. In the case, it is preferable that the polyester has a melting point having a temperature higher than the glass transition point of the polyester.

When the polyester of the polyester layer (I layer) is crystalline, the polyester F is 10 to 100 ° C higher than the melting point of the polyester, particularly 20 ° C or higher or 90 ° C or lower, and 40 ° C or higher or 70 ° C or lower. It preferably has a high melting point, while when the polyester of the polyester layer (I layer) is amorphous, it is 120 to 260 ° C. higher than the glass transition point of the polyester, particularly 140 ° C. or higher or 230 ° C. It is preferably one having a melting point higher than that of 160 ° C. or higher or 200 ° C. or lower.

The polyester F, which is the main component of the polyester layer (II layer) existing on both the front and back sides of the 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 F 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 surfaces is preferably 80 ° C. or lower, particularly 60 ° C. or lower, and more preferably 40 ° C. or lower.
If the polyester layers F on both the front and back sides of the polyester layer (I layer) are the same, coextrusion molding of two types and three layers is possible, and this embodiment is also preferable.

As the polyester F, for example, a homopolyester or a copolyester containing terephthalic acid as a dicarboxylic acid component and ethylene glycol as an alcohol component can be preferably used.

When the polyester F is a copolymerized polyester, examples of the dicarboxylic acid component other than terephthalic acid include aromatic dicarboxylic acids, alicyclic dicarboxylic acids, aliphatic dicarboxylic acids, and polyfunctional acids.
In the copolymerized polyester, 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 among them. It is more preferably% or less.

When the polyester F 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 the copolymerized polyester, the ratio of the "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 10 mol% or more or 90 mol% or less among them. Is more preferable.

The polyester layer (II layer) may contain "other resins" other than polyester.
Examples of the "other resin" include polyolefin, polystyrene, acrylic resin, urethane resin and the like.
In addition, the polyester layer (II layer) may further include a crystal nucleating agent, an antioxidant, an antioxidant, a pigment, a dye, an ultraviolet absorber, a mold release agent, an easy lubricant, a flame retardant, and an antistatic agent. It can contain various additives such as agents, inorganic and / or organic particles.

In the case of a laminated film having a structure in which a polyester layer (II layer) containing polyester F as a main component resin is laminated, the polyester layer (II layer) / polyester layer (I layer) / polyester layer ( The raw material resin composition can be laminated by coextrusion or the like so as to form a layer II), stretched, and then heat-fixed at a higher temperature than in the case of a single layer of a copolyester layer (layer I). Therefore, it can be made flexible to a level that cannot be achieved by a single layer of the copolyester layer (I layer), heat resistance can be increased, and heat shrinkage can be further prevented.

In such a laminated film, the thickness of each layer of the polyester layer (II layer) is preferably 1 to 20% of the thickness of the 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 polyester layer (I layer), film formation can be performed without significantly impairing productivity. On the other hand, if it is 20% or less, it is preferable because the required flexibility can be sufficiently secured.
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 polyester layer (I layer), particularly 3% or more or 15% or less, and 5% or more or 12 among them. It is more preferably% or less.

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

<Thickness of this polyester film>
The thickness of the 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 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 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 polyester film is preferably more than 20 μm, more preferably 23 μm or more, and more preferably 25 μm or more.
On the other hand, the upper limit of the total thickness of the 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 polyester film>
The present polyester film can obtain the following physical characteristics.

(Storage modulus at 25 ° C)
The polyester film preferably has a storage elastic modulus at 25 ° C. of 3300 MPa or less.
When the storage elastic modulus at 25 ° C., that is, at room temperature is 3300 MPa or less, it is possible to sufficiently follow the skin, for example, when wearing a wearable terminal.
From this point of view, the polyester film preferably has a storage elastic modulus at 25 ° C. of 3300 MPa or less, more preferably 2500 MPa or less, and more preferably 2000 MPa or less.

On the other hand, the storage elastic modulus at 25 ° C. is preferably 300 MPa or more, more preferably 500 MPa or more, and more preferably 700 MPa or more, from the viewpoint of handleability in the process.
The storage elastic modulus at 25 ° C. is a value obtained by the measuring method described in Examples described later.

In this polyester film, the storage elastic modulus at 25 ° C. can be achieved by using the polyester described above.
Further, as described above, it can also be adjusted by forming a laminated film having a structure in which a polyester layer (II layer) containing polyester F as a main component resin is laminated on both the front and back sides of the polyester layer (I layer). can do.
Furthermore, it can also be adjusted by the stretching conditions when producing the polyester film of the present invention and the subsequent heat fixing conditions.

(Storage modulus at 120 ° C)
The 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 polyester film preferably has a storage elastic modulus at 120 ° C. of 10 MPa or more, more preferably 30 MPa or more, and even more preferably 80 MPa or more.

On the other hand, from the viewpoint of suppressing the amount of heat required for processing, the 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 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.

(25 ° C loss tangent (tan δ))
The 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, for example, when wearing a wearable terminal.
From this point of view, the 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.

On the other hand, 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 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.

(Crystal fusion enthalpy ΔHm)
In this polyester film, when the polyester of the polyester layer (I layer) is crystalline, the crystal melting enthalpy ΔHm of the polyester (polyester composition) is preferably 3.0 J / g or more, and above all, 5.0 J / g. Above all, it is more preferable that it is 7.0 J / g or more.
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.

(Suppleness (Koshi))
This 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 (b) is, the value of the ratio of (a) to (b) ((a) / (b)) is preferably 0.2 or more, particularly 0.5 or more, and 1 among them. It is more preferably 0.0 or more.
When the (a) / (b) is 0.2 or more, it is suggested that the film has sufficient suppleness.

In this 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 polyester layer (I layer). ) Can be achieved by using the specific polyester described above.
From this point of view, it is particularly preferable to adopt any of the first to third embodiments.

<Manufacturing method of this polyester film>
As an example of the manufacturing method of the present polyester film, the manufacturing method when the present 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, for example, a polyester chip, is supplied to a melt extruder by a known method, heated above the melting point of each polymer, extruded from the die, and below the glass transition point of the polymer on a rotary cooling drum. It may be cooled and solidified to a temperature so as to obtain an unaligned sheet in a substantially amorphous state.

Next, the unaligned 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 polyester film as a biaxially oriented film.

In the above 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 polyester layer (I layer), the heat fixing treatment is performed at a temperature 10 to 70 ° C. lower than the melting point of the polyester for forming the polyester layer (I layer). preferable.

When the present polyester film has a laminated structure of a polyester layer (I layer) and a polyester layer (II layer), the polyester layer (I layer) and the polyester layer (II layer) are co-extruded and then integrated as described above. The film may be stretched and heat-fixed.

In this case, the heat fixing treatment is preferably carried out by heating to a temperature lower than the melting point of the polyester F for forming the polyester layer (II layer).
Further, when the polyester for forming the polyester layer (I layer) is crystalline, it is preferable to perform heat fixing treatment at a temperature higher than the melting point of the polyester.
By heat-fixing treatment at such a temperature, it is possible to soften the 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 the polyester F, so that the elongation, strength and heat resistance (heat shrinkage) are improved, while the polyester layer (heat shrinkability) is improved. This is because the stretching orientation and strain of the intermediate layer are alleviated by heat-fixing at a temperature higher than the melting point of the polyester for forming I layer), so that the film can be made even more supple.

<Use of this polyester film>
As described above, this polyester film has excellent flexibility at room temperature, and is not only flexible but also has a feature of having almost no stiffness, yet exhibits sufficient heat resistance for practical use. can do.

Therefore, this polyester film can be suitably used, for example, as a packaging material for batteries, particularly as a constituent member such as a surface protective film, an image display member, an optical member, a flexible display, and a wearable terminal.

The use of this 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".
In addition, when the term "panel" is used, such as an image display panel or a protective panel, it includes a plate, 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", unless otherwise specified. It also includes the meaning of "smaller".

In addition, 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) Tensile storage elastic modulus E', tangent loss (tan δ)
Vibration frequency 10 Hz in the width direction (TD) of the polyester film (sample) obtained in Examples and Comparative Examples using the dynamic viscoelasticity measuring device DVA-200 manufactured by IT Measurement Control Co., Ltd. based on JIS K 7244. , Strain 0.1%, temperature rise rate 1 ° C./min, measured from -100 ° C to 200 ° C, and from the obtained data, tensile storage elastic modulus E'at 25 ° C and 120 ° C and at 25 ° C. A tangent loss (tan δ) was obtained.

(2) Crystal melting enthalpy ΔHm
Differential scanning calorimetry (DSC) measurement of the measurement sample was performed based on JIS K7141-2 (2006). After raising the temperature from 30 ° C. to 280 ° C. at 10 ° C./min, hold for 1 minute, then lower the temperature from 280 ° C. to 30 ° C. at 10 ° C./min, hold for 1 minute, and then hold at 10 ° C. from 30 ° C. to 280 ° 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 polyester film was used as a measurement sample, and in the case of lamination, an intermediate layer was used as a measurement sample.

(3) Using a haze haze meter (NDH2000, manufactured by Nippon Denshoku Kogyo Co., Ltd.), the haze of the polyester film (sample) obtained in Examples and Comparative Examples was measured according to JIS K7136.

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

(5) Tensile breaking strength The polyester film (sample) obtained in Examples and Comparative Examples was subjected to a tensile tester (Intesco Co., Ltd., Intesco Model 2001) at a temperature of 23 ° C and a humidity of 50% RH. In the adjusted room, a polyester film (sample) with a width of 15 mm is set in the testing machine so that the chuck distance is 50 mm, and the film is pulled at a strain rate of 200 mm / min, and the film is subjected to the longitudinal direction (MD) and the film according to the following formula. The tensile breaking strength of each in the width direction (TD) was determined.
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.
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.

(6) Tensile breaking elongation The polyester films (samples) obtained in Examples and Comparative Examples were subjected to the same tests as the above-mentioned tensile breaking strength, and the films were subjected to the following formulas in the longitudinal direction (MD) and the width direction (TD). ) Each tensile elongation at break was calculated.
Tensile breaking elongation (%) = 100 × (L-L0) / L0
However, in the above formula, L is the distance between the gauge points at the time of breakage (mm), and L0 is the original distance between the gauge points (mm).
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) Heat shrinkage rate The polyester film (sample) obtained in Examples and Comparative Examples was treated in an oven maintained at 120 ° C. in a non-tensioned state for 5 minutes, and the length of the sample before and after that was measured and the following formula was used. The heat shrinkage rate in each of the longitudinal direction (MD) and the width direction (TD) of the film was calculated.
Heat shrinkage rate (%) = {(L0-L1) / L0} × 100
(In the above formula, L0 is the sample length before the heat treatment, and L1 is the sample length after the heat treatment).
Five points were measured in the longitudinal direction (MD) and the width direction (TD) of the film, and the average value was calculated for each.

(8) Evaluation of suppleness (flexibility measurement method)
The polyester film (sample) obtained in Examples and Comparative Examples was allowed to stand at 23 ° C. in a 50% RH atmosphere for 24 hours, and then cut into a size of 150 mm in length and 50 mm in width to prepare a measurement sample film.
As shown in FIG. 1, the measurement sample film 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 on the measurement sample film on the desk. A 200 g weight was placed 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, the length (a) of the tip of the measurement sample film protruding from the edge of the desk flexed vertically downward and hung down, and the length of the tip protruding horizontally from the edge of the desk (b). Was measured.
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 0.2 or more, it is "passed (○)". If it is less than 0.2, it is evaluated as "failed (x)".

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

(1) Copolymerized polyester a1
The constituent units derived from the dicarboxylic acid include terephthalic acid, isophthalic acid and dimeric acid (36 carbon atoms), the content of the terephthalic acid is 58.5% by mass, and the content of the dimeric acid is 17. Copolymerized polyester a1 (5% by mass), the content of isophthalic acid is 3.5% by mass, and 18.5% by mass of ethylene glycol and 2% by mass of diethylene glycol are contained as constituent units derived from the diol component. Intrinsic viscosity (IV) 0.68 dl / g) was prepared.

The copolymerized polyester a1 was produced as follows.

The amounts of terephthalic acid and isophthalic acid in the polyester after polymerization are 58.5% by mass and 3.5% by mass, respectively, and ethylene glycol is 1.2 times the molar ratio of the total amount of terephthalic acid and isophthalic acid. The amount was charged in an esterification reaction tank equipped with a stirrer, a temperature raising device and a distillate separation column, and the esterification reaction was carried out at ^{a temperature of 250 ° C. and a pressure of 0.90 kg / cm 2 for 4 hours.} Next, an esterification reaction was carried out at a temperature of 250 ° C. under normal pressure for 4 hours to obtain a polyester low polymer (oligomer).

Next, the oligomer was transferred to a polycondensation reaction tank equipped with a distiller and equipped with a stirrer, and hydrogenated dimer acid having 36 carbon atoms (“Pripol 1009” manufactured by Claude Japan) was added to the polymerized polyester in an amount of 17.5% by mass. As a catalyst, an ethylene glycol solution of germanium dioxide was added, and an ethylene glycol solution of orthophosphate was added.

While maintaining the temperature inside the polycondensation reaction tank at 280 ° C., the pressure was reduced to 0.13 kPa over 2 hours, and then the reaction was carried out at the same pressure for 3 hours, and the reaction system was returned to normal pressure to complete the reaction. .. The obtained polyester was extracted as a strand from the bottom of the polycondensation reaction tank, submerged in water, and then the strand was cut with a cutter to obtain pellets of the copolymerized polyester a1.

(2) Copolymerized polyester a1-2
It contains terephthalic acid and dimeric acid (36 carbon atoms) as constituent units derived from dicarboxylic acid, the content of the terephthalic acid is 51% by mass, the content of the dimeric acid is 29% by mass, and diol. Copolymerized polyester a1-2 (inherent viscosity (IV) 0.72 dl / g) containing 18% by mass of ethylene glycol and 2% by mass of diethylene glycol was prepared as a constituent unit derived from the components.

The copolymerized polyester a1-2 was produced in the same manner as the copolymerized polyester a1 except that dimer acid (“Pripol1009” manufactured by Crowder Japan) was added to the polymerized polyester in an amount of 29% by mass.

(3) Copolymerized polyester b1
The constituent unit derived from the dicarboxylic acid contains terephthalic acid, the content of the terephthalic acid is 47% by mass, and the constituent unit derived from the diol component is 1,4-butanediol and poly having a number average molecular weight of 1000. Copolymerized polyester b1 (inherent viscosity (IV) 1.18 dl / g) containing tetramethylene glycol, the content of the butanediol is 23% by mass, and the content of the polytetramethylene glycol is 30% by mass. I prepared it.

The copolymerized polyester b1 was produced as follows.

A transesterification reaction vessel equipped with a stirrer, a nitrogen inlet, a heating device, a thermometer, and a distillate tube contains 64.1 parts by mass of dimethylterephthalate, 36.8 parts by mass of 1,4-butanediol (BG), and fluorine. 30 parts by mass of polytetramethylene glycol (manufactured by Mitsubishi Chemical, number average molecular weight 1000) having an amount of 190 mass ppm and tetrabutyl titanate as a catalyst were added as a BG solution so as to be 33 ppm with respect to the polymer to be produced in terms of metallic titanium. ..

Next, the temperature of the liquid in the tank was maintained at 150 ° C. for 60 minutes, then raised to 210 ° C. over 90 minutes, and maintained at 210 ° C. for 30 minutes. During this period, the transesterification reaction was carried out for a total of 180 minutes while distilling off the produced methanol.

Fifteen minutes before the end of the transesterification reaction, magnesium acetate / tetrahydrate was dissolved in BG and added, and a hindered phenolic antioxidant [Irganox1010 manufactured by Ciba Geigy Co., Ltd.] was added in a slurry state of BG. Then, after adding tetrabutyl titanate as a solution of BG, it was transferred to a polycondensation reaction tank equipped with a stirrer, a nitrogen inlet, a heating device, a thermometer, a distillate, and a decompression exhaust port to add decompression. The polycondensation reaction was carried out.

The polycondensation reaction was carried out by gradually reducing the pressure in the tank from normal pressure to 0.4 kPa over 85 minutes and continuing at 0.4 KPa or less. The reaction temperature was maintained at 210 ° C. for 15 minutes from the start of depressurization, then raised to the maximum temperature of 240 ° C. for this reaction in 45 minutes, held at this temperature for 1 hour, and then controlled to reach the final temperature of 235 ° C. ..

The final temperature is 235 ° C. The reaction was terminated when a predetermined stirring torque (corresponding to IV = 1.20) was reached. The time required for the polycondensation reaction was 150 minutes. (The polycondensation reaction time was the time from the start of depressurization to the repressurization with nitrogen)

Next, the inside of the tank was decompressed with nitrogen, and then pressurized to extract the polymer. The polymer was extracted from the mouthpiece in a strand shape at a heat medium temperature of the mouthpiece at the time of extraction at 230 ° C., and then the strands were cooled in a cooling water tank and then cut with a strand cutter to obtain pellets of copolymerized polyester b1.

(4) Homopolyester C1
A polyester containing terephthalic acid as a structural unit derived from a carboxylic acid component and ethylene glycol as a structural unit derived from a diol component, having an intrinsic viscosity (IV) of 0.82 dl / g. Homopolyester (homo PET) C1 was prepared.

(5) Homopolyester C2
A polyester containing terephthalic acid as a structural unit derived from a carboxylic acid component and ethylene glycol as a structural unit derived from a diol component, having an intrinsic viscosity (IV) of 0.64 dl / g. A certain homopolyester C2 (homo PET) was prepared.

(6) Particle-containing polyester C3
A polyester containing terephthalic acid as a constituent unit derived from a carboxylic acid component and ethylene glycol as a constituent unit derived from a diol component, having an intrinsic viscosity (IV) of 0.70 dl / g. A particle-containing homopolyester C3 (particle-containing homopet) containing 3.5% by mass of silica particles having an average particle size of 4 μm was prepared.

(7) Particle-containing polyester C4
A polyester containing terephthalic acid as a constituent unit derived from a carboxylic acid component and ethylene glycol as a constituent unit derived from a diol component, having an intrinsic viscosity (IV) of 0.62 dl / g. A particle-containing homopolyester C4 (particle-containing homopet) containing 0.6% by mass of silica particles having an average particle size of 4 μm was prepared.

[Example 1]
As an intermediate layer, a chip of a polyester composition for forming an intermediate layer containing 50% by mass of a copolymerized polyester a1 and 30% by mass of a copolymerized polyester b1 and 20% by mass of a homopolyester C1 is provided with a main vent set at 270 ° C. It was sent to a twin-screw extruder.

Further, as the surface layer, chips of a surface layer forming polyester composition containing 90% by mass of homopolyester C2 and 10% by mass of particle-containing polyester C3 were sent to 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, so that the polymer is co-extruded in a layer structure of 2 types and 3 layers (surface layer / intermediate layer / surface layer) and the base The unstretched sheet was obtained by extruding from

Next, the obtained unstretched sheet was stretched 3.0 times at 80 ° C. in the longitudinal direction (MD), guided to a tenter, and then stretched 4.6 times at 120 ° C. in the width direction (TD). A 25 μm-thick polyester film (sample) 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). Got

[Examples 2 to 5 and Comparative Examples 1 to 2]
A polyester film (sample) was obtained in the same manner as in Example 1 except that the conditions were changed as shown in Table 1.
The polyester film (sample) produced in Example 5 is a biaxially stretched polyester film having a single-layer structure composed of layers formed of the raw materials shown as intermediate layers.

From the results of the above Examples and Comparative Examples and the test results conducted by the inventor so far, the polyester film provided with the polyester layer (I layer) containing a specific polyester is excellent in flexibility at room temperature and is simply flexible. It was found that it is not only more supple, yet has elongation and strength, and also has sufficient heat resistance for practical use.

Based on the above results, it can be considered that the same effect as that of the above embodiment can be further obtained in the following embodiments.

First, a copolymerized polyester containing terephthalic acid as a constituent unit derived from a dicarboxylic acid, ethylene glycol and polyethylene glycol as a constituent unit derived from a diol component, and the content of the polyethylene glycol is 20% by mass. Prepare b1-2.

Then, as the intermediate layer, the chip of the polyester composition for forming the intermediate layer containing 50% by mass of the copolymerized polyester a1, 30% by mass of the copolymerized polyester b1-2 and 20% by mass of the polyester C1 was set at 270 ° C. Feed into a vented twin-screw extruder.
Further, as the surface layer, chips of the surface layer forming polyester composition containing 90% by mass of polyester C2 and 10% by mass of particle-containing polyester C3 are 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, so that the polymer is co-extruded in a layer structure of 2 types and 3 layers (surface layer / intermediate layer / surface layer) from the base. An unstretched sheet is obtained by extruding and quenching and solidifying on a cooling roll whose surface temperature is set to 30 ° C. using an electrostatic application adhesion method.
Next, the obtained unstretched sheet was stretched 3.0 times at 80 ° C. in the longitudinal direction (MD), guided to a tenter, and then stretched 4.6 times at 120 ° 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). Obtain a film (sample).

The copolypolypolymerized polyester b1-2 can be produced as follows.

An ester equipped with a stirrer, a temperature raising device, and a distillate separation column in which terephthalic acid is 61% by mass in the polymerized polyester and ethylene glycol is 1.2 times the molar ratio of terephthalic acid. The esterification reaction is carried out in a chemical reaction tank at a temperature of 250 ° C. and a pressure of 0.90 kg / cm2 for 4 hours.

Next, an esterification reaction is carried out at a temperature of 250 ° C. under normal pressure for 4 hours to obtain a polyester low polymer (oligomer).

Next, the oligomer is transferred to a polycondensation reaction tank equipped with a distiller and equipped with a stirrer, and the ethylene glycol solution of polyethylene glycol having a mass average molecular weight of 2000 is 20% by mass in the polyester after the polymerization of polyethylene glycol. The amount is added, and as a catalyst, an ethylene glycol solution of germanium dioxide is added, and an ethylene glycol solution of orthophosphate is added.
Further, a hindered phenolic antioxidant [Irganox 1330 manufactured by Ciba Geigy Co., Ltd.], which is 0.35 parts by mass with respect to the produced polymer, is added with an ethylene glycol solution.
Further, an ethylene glycol solution of silicon oil KF-54 manufactured by Shin-Etsu Chemical Co., Ltd. is added in order to suppress foaming during polymerization.

While maintaining the temperature inside the polycondensation reaction tank at 280 ° C., the pressure was reduced to 0.13 kPa over 2 hours, then the reaction was carried out at the same pressure for 3 hours, the reaction system was returned to normal pressure, and the reaction was completed. .. The obtained polyester is extracted from the bottom of the polycondensation reaction tank as a strand, submerged in water, and then the strand is cut with a cutter to obtain pellets of the copolymerized polyester b1-2.

The polyester film of the present invention, obtained using a particular polyester, is not only flexible and simply flexible, but also more supple, yet has elongation and strength, and even more. Since it has sufficient heat resistance for practical use, it can be suitably used for applications such as surface protective films, optical members, wearable terminals, and flexible displays.

Claims (15)

A polyester film comprising a polyester layer (I) containing one or more polyesters.
The polyester contains a structural unit derived from a dicarboxylic acid and a diol component.
As a constituent unit derived from the dicarboxylic acid component, terephthalic acid and dimer acid are contained.
A polyester film comprising ethylene glycol and polyalkylene glycol as a constituent unit derived from the diol component. Claimed that the content of the dimer acid is 5 to 25% by mass and the content of the polyalkylene glycol is 1 to 20% by mass with respect to all the constituent units of the polyester contained in the polyester layer (I). Item 1. The polyester film according to Item 1. The polyester film according to claim 1 or 2, which contains isophthalic acid as a constituent unit derived from the dicarboxylic acid. The polyester film according to claim 3, wherein the content of the isophthalic acid is 1% by mass or more and 10% by mass or less with respect to all the constituent units of the polyester contained in the polyester layer (I). The polyester is a copolymerized polyester a that contains terephthalic acid and dimer acid as a constituent unit derived from a dicarboxylic acid component and 1,4-butanediol or ethylene glycol as a constituent unit derived from a diol component. When,
A copolymerized polyester b containing terephthalic acid as a constituent unit derived from the dicarboxylic acid component and 1,4-butanediol or ethylene glycol, and polyalkylene glycol as a constituent unit derived from the diol component.
The polyester film according to any one of claims 1 to 4, which is a polyester composition containing. The polyester composition further contains homopolyester C and / or a copolymerized polyester containing terephthalic acid as a constituent unit derived from the dicarboxylic acid component and ethylene glycol as a constituent unit derived from the diol component. The polyester film according to claim 5, further comprising E, wherein the copolymerized polyester E is a copolymerized polyester other than the copolymerized polyester a and the copolymerized polyester b. The polyester contains a copolymerized polyester D containing dimer acid as a constituent unit derived from a dicarboxylic acid component and polyalkylene glycol as a constituent unit derived from a diol component.
Homopolyester C or a copolymerized polyester EE other than the copolymerized polyester D containing ethylene glycol as a constituent unit derived from the dicarboxylic acid component and containing terephthalic acid as a constituent unit derived from the diol component.
The polyester film according to any one of claims 1 to 4, which is a polyester composition containing. The polyester film according to any one of claims 1 to 7, wherein the polyalkylene glycol is a polytetramethylene glycol having a number average molecular weight of 2000 or less. The polyester film according to any one of claims 1 to 7, wherein the polyalkylene glycol is a polyethylene glycol having a mass average molecular weight of 3000 or less. The polyester comprises 1% by mass or more and 10% by mass or less with respect to all the structural units of the polyester contained in the polyester layer (I) as a structural unit derived from the dicarboxylic acid, claims 5 to 9. The polyester film according to any one of the above. The polyester film according to any one of claims 1 to 10, further comprising a structure in which a polyester layer (II) is laminated on both the front and back sides of the polyester layer (I). A surface protective film using the polyester film according to any one of claims 1 to 11. An optical member using the polyester film according to any one of claims 1 to 11. A wearable terminal using the polyester film according to any one of claims 1 to 11. A flexible display using the polyester film according to any one of claims 1 to 11.

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