polyester film

Abstract

To provide an environment consideration type polyester film having excellent dimensional stability which is suitable for producing a gas barrier film with an inorganic thin film.SOLUTION: There is provided a polyester film having a laminate structure comprising at least two layers, wherein the laminate structure has a polyester layer (X) containing a chemical-recycled polyester and the shrinkage rate after hot water treatment at 125°C for 30 minutes is 0.7% or less both in the longitudinal direction (MD) and transverse direction (TD).SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a polyester film.

Background Art

[0002] Polyester films typified by polyethylene terephthalate films and polyethylene naphthalate films have excellent properties such as mechanical properties, dimensional stability, flatness, heat resistance, chemical resistance, and optical properties, and are used in various applications because of their excellent cost performance.

[0003] Due to the recent increase in environmental problems, in order to reduce environmental burdens such as carbon dioxide emissions, instead of polyester produced from petroleum, which is a fossil fuel (hereinafter also referred to as "fossil fuel polyester"), recycled polyester obtained by recycling the polyester contained in used products is being used. As the above recycling methods, methods such as material recycling, chemical recycling, and thermal recycling are known.

[0004] As a starting material for recycled polyester, for example, PET bottles are used, and in the polyester used for PET bottles, the crystallinity may be controlled in order to improve the bottle appearance.

[0005] For example, Patent Documents 1 and 2 disclose a polyester film containing chemically recycled polyester as a base material for a vapor deposition resin film or a printed resin film, which enables the production of a packaging container with reduced environmental burden and extremely excellent hygiene.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

[0007] Patent documents 1 and 2 state that chemically recycled polyester is obtained by decomposing polyester contained in used packaging containers to the monomer level, removing contaminants, and then repolymerizing it, and therefore is more hygienic. However, while the films described in Patent Documents 1 and 2 have been shown to reduce environmental impact and have excellent hygiene due to the inclusion of chemically recycled polyester, they have not explored ways to adjust other physical properties.

[0008] Therefore, the present invention has been made in view of the above circumstances, and its problem to be solved is to provide an environmentally friendly polyester film with excellent dimensional stability that is suitable for the manufacture of a gas barrier film comprising an inorganic thin film. [Means for solving the problem]

[0009] As a result of diligent research, the inventors have found that the above problem can be solved by having the following configuration. The present invention has the following aspects.

[0010] [1] A polyester film having a laminated structure consisting of at least two layers, wherein the laminated structure has a polyester layer (X) containing chemically recycled polyester, and the shrinkage rate when treated with hot water at 125°C for 30 minutes is 0.7% or less in both the longitudinal direction (MD) and the width direction (TD). [2] The polyester film according to [1] above, wherein the content of isophthalic acid in the total dicarboxylic acid components in the total polyester is 0.1 to 1.2 mol%. [3] The polyester film according to [1] or [2] above, wherein the chemically recycled polyester is derived from bottles and / or film. [4] A polyester film according to any of [1] to [3] above, wherein the tensile breaking strength in both the longitudinal direction (MD) and the width direction (TD) is 90 MPa or more. [5] A polyester film according to any of [1] to [4] above, wherein the tensile elongation at break in both the longitudinal direction (MD) and the width direction (TD) is 70% or more. [6] A polyester film according to any of [1] to [5] above, wherein the intrinsic viscosity (IV) of the film is 0.5 to 0.8 dL / g. [7] The polyester film according to any one of [1] to [6] above, wherein the content of the chemically recycled polyester is 50% by mass or less relative to the total polyester. [8] The polyester film according to any one of [1] to [7] above, wherein the laminated structure has three layers: a surface layer, an intermediate layer, and a surface layer in that order. [9] The polyester film according to [8] above, wherein the intermediate layer is a polyester layer (X) containing chemically recycled polyester.

[10] The polyester film according to [8] or [9] above, wherein each of the surface layers contains fossil fuel polyester as the main component.

[11] The polyester film according to any one of [8] to

[10] above, wherein the thickness of each of the surface layers is 10 to 30% of the thickness of the intermediate layer.

[12] A laminated polyester film having a resin layer formed of a resin composition on at least one surface of the polyester film described in any of [1] to

[11] above.

[13] The laminated polyester film according to

[12] above, wherein the resin composition comprises the following compounds (A) and (B). (A) One or more resins selected from the group consisting of (meth)acrylic resin, polyester resin, and polyurethane resin. (B) Oxazoline compounds

[14] A gas barrier film comprising an inorganic thin film on the resin layer of the laminated polyester film described in

[12] or

[13] above.

[15] The gas barrier film according to

[14] above, wherein the inorganic thin film is formed from an inorganic substance selected from the group consisting of silicon, aluminum, magnesium, zinc, tin, nickel, titanium, or oxides, carbides, nitrides, or mixtures thereof of these. [Advantages of the Invention]

[0011] According to the present invention, there is provided an environmentally friendly polyester film having excellent dimensional stability, which is suitable for the production of a gas barrier film provided with an inorganic thin film. [Brief Description of the Drawings]

[0012] [Figure 1] It is a cross-sectional view schematically showing the structure of a gas barrier film according to an embodiment of the present invention. [Modes for Carrying Out the Invention]

[0013] Next, an example of an embodiment of the present invention will be described. However, the present invention is not limited to the embodiments described below.

[0014] [<Polyester Film>] The polyester film of the present invention (hereinafter also referred to as "the present film") has a laminated structure composed of at least two layers, and the laminated structure has a polyester layer (X) containing a chemically recyclable polyester, and the shrinkage rate when heat-treated in hot water at 125°C for 30 minutes is 0.7% or less in both the longitudinal direction (MD) and the width direction (TD).

[0015] As described above, this film has a laminated structure composed of at least two layers. The laminated structure may be a two-layer structure, a three-layer structure, etc., and may be a four-layer or more multi-layer as long as it does not depart from the gist of the present invention. The number of laminated layers is not particularly limited, but it is preferably 10 layers or less. If it is 10 layers or less, the thickness of each layer is sufficient, so the lamination property during film formation is sufficient, flow marks and the like are less likely to occur, and the quality of the film is sufficiently maintained. Among them, the laminated structure is preferably a three-layer structure of two types or a three-layer structure of three types, and more preferably a three-layer structure of two types.

[0016] In addition, this film may be an unstretched film (sheet) or a stretched film. Among them, it is preferably a stretched film stretched in a uniaxial direction or a biaxial direction. Among them, in terms of excellent balance of mechanical properties and flatness, it is more preferably a biaxially stretched film.

[0017] <Chemical recycled polyester> This film needs to have a polyester layer (X) containing chemical recycled polyester. Therefore, it is necessary to contain chemical recycled polyester in any of the polyester layers constituting the laminated structure.

[0018] In this specification, "chemical recycled polyester" means that used polyester products are recovered, appropriately pulverized, washed, foreign matter separated, etc., and then flakes and / or the flakes are chipped, for example, and it is depolymerized using ethylene glycol to decompose it to bis-β-hydroxyethyl terephthalate (BHET), and polyester is polymerized again using BHET as a raw material. Note that the decomposition method etc. are not limited to this, and conventionally known methods can be used. Also, the polyester contained in the used polyester product is not particularly limited, but it is preferably at least one polyester selected from the group consisting of fossil fuel polyester, biomass polyester, chemical recycled polyester and mechanical recycled polyester.

[0019] Thus, chemically recycled polyester is obtained by decomposing the polyester contained in used polyester products to the monomer level, removing foreign substances, and then repolymerizing it. As a result, it tends to contain fewer foreign substances compared to polyester obtained by other recycling methods. Therefore, in applications where the inclusion of foreign matter is a problem, such as packaging in the food and medical fields, it is preferable to use chemically recycled polyester.

[0020] In chemically recycled polyesters, polyester refers to a polymer compound having ester bonds continuously in its main chain, and may be either a homopolyester or a copolymer polyester. Specifically, polyesters obtained by polycondensation reaction of a dicarboxylic acid component and a diol component can be mentioned. Furthermore, it is preferable to use a polyester that contains more than 50 mol% of aromatic dicarboxylic acid or aliphatic dicarboxylic acid when the dicarboxylic acid component is 100 mol%.

[0021] Examples of the dicarboxylic acid component include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, and 4,4'-diphenylsulfondicarboxylic acid, as well as aliphatic dicarboxylic acids such as adipic acid, suberic acid, sebacic acid, dimer acid, dodecanedionic acid, cyclohexanedicarboxylic acid, and their ester derivatives.

[0022] Examples of the diol component include ethylene glycol, 1,2-propanediol, 1,3-propanediol, neopentyl glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-hexanedimethanol, diethylene glycol, triethylene glycol, polyalkylene glycol, 2,2-bis(4-hydroxyethoxyphenyl)propane, isosorbate, and spiroglycol.

[0023] In particular, polyethylene terephthalate is preferred as the polyester used in chemically recycled polyester, from the viewpoint of transparency and ease of recovery of used polyester products. The above polyethylene terephthalate contains at least terephthalic acid as a dicarboxylic acid component and at least ethylene glycol as a diol component. Furthermore, polyethylene terephthalate may be homopolyethylene terephthalate that does not contain the third component, or it may be a copolymer containing 30 mol% or less of the third component. The third component refers to the copolymerization component, and more specifically, it is a component other than the compound that is the main component (i.e., the component with the highest content) of the dicarboxylic acid component that constitutes the polyester, and the compound that is the main component of the diol component, and in copolymerized polyethylene, it is a component other than terephthalic acid and ethylene glycol.

[0024] Normally, when polyester is produced (polycondensed) using ethylene glycol as one of the raw materials, diethylene glycol is produced as a by-product from ethylene glycol. In this specification, this diethylene glycol is referred to as by-product diethylene glycol. The amount of diethylene glycol produced as a by-product from ethylene glycol varies depending on the type of polycondensation, but it is approximately 5 mol% or less of the ethylene glycol. In the present invention, 5 mol% or less of diethylene glycol is considered as by-product diethylene glycol, and this by-product diethylene glycol is also included in ethylene glycol and distinguished from copolymer components.

[0025] Furthermore, the used polyester products mentioned above may be bottles such as PET bottles, or films such as polyethylene terephthalate film. In other words, the chemically recycled polyester is preferably derived from bottles and / or films, and more preferably from bottles. The polyester used in PET bottles undergoes crystallinity control to improve the bottle's appearance, and as a result, polyester containing 10 mol% or less of isophthalic acid is sometimes used. Therefore, when chemically recycled polyester is derived from bottles, polyester containing isophthalic acid will be used. In such cases, it is preferable to use a chemically recycled polyester that contains 10 mol% or less, more preferably 5 mol% or less, and even more preferably 3 mol% or less of isophthalic acid in the total dicarboxylic acid component of the polyester. Polyethylene terephthalate is also preferred as the polyester in this case.

[0026] In the present invention, the content of the chemically recycled polyester is preferably 5 to 50% by mass relative to the total polyester in the laminated structure of the film, more preferably 10 to 50% by mass, even more preferably 20 to 50% by mass, and particularly preferably 30 to 50% by mass. If the chemically recycled polyester content is 5% by mass or more, it can contribute to reducing environmental impact. On the other hand, if the chemically recycled polyester content is 50% by mass or less, it is possible to suppress the deterioration of the basic physical properties of the film (e.g., dimensional stability and mechanical properties) due to the effects of isophthalic acid contained in the chemically recycled polyester. Furthermore, since the content of polyesters other than chemically recycled polyester (e.g., fossil fuel polyester) can be ensured, it becomes easier to adjust the dimensional change rate before and after hot water treatment to the desired value.

[0027] <Polyester> This film may further contain polyesters other than the chemically recycled polyester mentioned above. In this context, "polyester other than chemically recycled polyester" refers to both the polyester layer (X) and the polyester layers other than the polyester layer (X).

[0028] There are no particular restrictions on the polyesters mentioned above, but polyesters obtained by polycondensation reaction of a dicarboxylic acid component and a diol component are preferred, and it is more preferable to use a polyester that contains more than 50 mol% of aromatic dicarboxylic acid or aliphatic dicarboxylic acid when the dicarboxylic acid component is 100 mol%.

[0029] Examples of the dicarboxylic acid component include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, and 4,4'-diphenylsulfondicarboxylic acid, as well as aliphatic dicarboxylic acids such as adipic acid, suberic acid, sebacic acid, dimer acid, dodecanedionic acid, cyclohexanedicarboxylic acid, and their ester derivatives.

[0030] Examples of the diol component include ethylene glycol, 1,2-propanediol, 1,3-propanediol, neopentyl glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-hexanedimethanol, diethylene glycol, triethylene glycol, polyalkylene glycol, 2,2-bis(4-hydroxyethoxyphenyl)propane, isosorbate, and spiroglycol.

[0031] When the above polyester is a homopolyester, it is preferable to obtain one obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic diol. Preferred aromatic dicarboxylic acids include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and preferred aliphatic diols include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. Representative homopolyesters include polyethylene terephthalate (PET) and polyethylene-2,6-naphthalenedicarboxylate (PEN), with polyethylene terephthalate being preferred.

[0032] On the other hand, the copolymerized polyester is preferably a polycondensation polymer of a dicarboxylic acid component and an aliphatic diol. The dicarboxylic acid component is preferably one or more of isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, and oxycarboxylic acids (e.g., p-oxybenzoic acid). The aliphatic diol is preferably one or more of ethylene glycol, diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, and neopentyl glycol. The copolymerized polyester preferably contains terephthalic acid as the dicarboxylic acid component and ethylene glycol as the aliphatic diol.

[0033] If the above polyester is a copolymerized polyester, it is preferable that it is a copolymer containing 30 mol% or less of a third component. The third component is a component other than the compound that is the main component (i.e., the component with the highest content) of the dicarboxylic acid component constituting the polyester and the compound that is the main component of the diol component. For example, in copolymerized polyethylene terephthalate, it is a component other than terephthalic acid and ethylene glycol.

[0034] Furthermore, the copolymerized polyester may also contain structural units derived from difunctional compounds other than dicarboxylic acid components and aliphatic diols. The structural units derived from difunctional compounds other than dicarboxylic acid components and aliphatic diols are preferably 20 mol% or less, more preferably 10 mol% or less, relative to the total moles of all structural units constituting the polyester. Examples of difunctional compounds include various hydroxycarboxylic acids and aromatic diols.

[0035] In particular, from the viewpoint of easily obtaining desired basic physical properties (e.g., dimensional stability and mechanical properties) of this film, it is especially preferable to use homopolyethylene terephthalate as the polyester other than chemically recycled polyester. By using homopolyethylene terephthalate, high crystallinity can be maintained, thus enabling sufficient mechanical properties and heat resistance. Furthermore, it is also preferable from the viewpoint of compatibility with chemically recycled polyethylene terephthalate, which is particularly preferred as a chemically recycled polyester.

[0036] Normally, when polyester is produced (polycondensed) using ethylene glycol as one of the raw materials, diethylene glycol is produced as a by-product from ethylene glycol. In this specification, this diethylene glycol is referred to as by-product diethylene glycol. The amount of diethylene glycol produced as a by-product from ethylene glycol varies depending on the type of polycondensation, but it is approximately 5 mol% or less of the ethylene glycol. In this invention, diethylene glycol of 5 mol% or less is considered by-product diethylene glycol, and this by-product diethylene glycol is also included in ethylene glycol and distinguished from copolymer components. On the other hand, depending on the content of diethylene glycol, more specifically, if the content of diethylene glycol exceeds 5 mol%, the diethylene glycol is treated as a copolymer component rather than as by-product diethylene glycol.

[0037] <Preferred embodiment> A preferred form of the film 10 is a laminated structure consisting of three layers, with a surface layer 2, an intermediate layer 1, and a surface layer 3 in that order (see Figure 1). In addition to the laminated structure consisting of the three layers described above, it is preferable that each of the surface layers (i.e., surface layer 2 and surface layer 3) contains fossil fuel polyester as its main component, and it is more preferable that the fossil fuel polyester is homopolyethylene terephthalate. Furthermore, it is preferable that the intermediate layer 1 is a polyester layer (X) containing chemically recycled polyester. By adopting this configuration, the basic physical properties of the film (e.g., dimensional stability and mechanical properties) can be improved. Moreover, since it is possible to reduce foreign matter in the surface layer, which tends to affect adhesion and barrier properties when an inorganic thin film is provided, it is possible to suppress to the greatest extent possible the decrease in adhesion and barrier properties due to the influence of foreign matter. The chemical polyester content in the intermediate layer should be such that it satisfies the chemical recycled polyester content relative to the total polyester in the laminated structure of the film described above. More specifically, it is preferably 10 to 80% by mass, more preferably 20 to 78% by mass, even more preferably 30 to 76% by mass, and particularly preferably 45 to 75% by mass.

[0038] Furthermore, the thickness of each surface layer is preferably 10 to 30% of the thickness of the intermediate layer, more preferably 15 to 28%, and even more preferably 20 to 25%. By making each layer of the surface 10% or more thick, the basic physical properties of the film (e.g., dimensional stability and mechanical properties) can be improved. Furthermore, when an inorganic thin film is applied, the amount of foreign matter in the surface layer, which tends to affect adhesion and barrier properties, can be reduced, thereby minimizing the reduction in adhesion and barrier properties due to the influence of foreign matter. On the other hand, by making each layer of the surface 30% or less thick, the thickness of the intermediate layer can be secured, making it easier to increase the amount of chemically recycled polyester contained in the intermediate layer, thereby enhancing the effect of reducing environmental impact. In addition, when particles are contained in the surface layer, good transparency can be maintained while providing good handling properties. The layer structure and thickness of each layer of this film can be determined, for example, by observing a cross-section obtained by cryogenic fracture using an ultramicrotome, magnifying it 3,000 to 200,000 times using a transmission electron microscope, and taking a cross-sectional photograph.

[0039] The isophthalic acid content in the total dicarboxylic acid component of the total polyester in the laminated structure of this film is preferably 0.1 to 1.2 mol%, more preferably 0.2 to 1.2 mol%, even more preferably 0.3 to 1.1 mol%, particularly preferably 0.4 to 1.0 mol%, and especially preferably 0.5 to 0.9 mol%. If the isophthalic acid content is 0.1 mol% or more, it is estimated that the crystallization of the film will proceed mainly in the thickness direction due to hot water treatment, i.e., the intervention of moisture, resulting in shrinkage in the thickness direction but slight expansion in the area direction, thus mitigating the shrinkage. Furthermore, mitigating shrinkage in the area direction has the advantage of improving gas barrier properties. On the other hand, if the isophthalic acid content is 1.2 mol% or less, the significant progression of crystallization of the film in the area direction can be suppressed, thereby suppressing shrinkage in the area direction that would lead to a deterioration of gas barrier properties.

[0040] As mentioned above, it is preferable to use a polyester containing 10 mol% or less, more preferably 5 mol% or less, and even more preferably 3 mol% or less of isophthalic acid as the chemically recycled polyester, so that the isophthalic acid content in the total dicarboxylic acid component of the total polyester in the laminated structure of this film is within this range. The content of ester units derived from terephthalic acid and isophthalic acid contained in the polyester raw material and the polyester constituting this film can be determined by preparing a sample solution by dissolving the sample in a mixed solution of deuterated chloroform and trifluoroacetic acid (volume ratio 9 / 1), measuring the NMR of protons, calculating the peak intensity of a predetermined proton, and then calculating the content (mol%) of ester units derived from terephthalic acid and isophthalic acid in 100 mol% of ester units.

[0041] <Polycondensation catalyst> There are no particular restrictions on the polycondensation catalyst used when polycondensing the above polyesters; conventionally known compounds can be used, such as titanium compounds, germanium compounds, antimony compounds, manganese compounds, aluminum compounds, magnesium compounds, and calcium compounds. In addition to the above, chemically recycled polyester may also contain cobalt compounds and other substances.

[0042] <Intrinsic viscosity> The intrinsic viscosity (IV) of the laminated structure of this film is preferably 0.5 to 0.8 dL / g, more preferably 0.5 to 0.7 dL / g, and even more preferably 0.6 to 0.7 dL / g, from the viewpoint of film-forming properties and productivity.

[0043] <particle> This film can also contain particles. By containing particles, the polyester film is given slipperiness and prevents scratches during each process, resulting in improved handling. The type of particles to be contained in this film is not particularly limited as long as they can impart slipperiness. Specific examples include inorganic particles such as silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, magnesium phosphate, kaolin, aluminum oxide, and titanium oxide, as well as crosslinked polymers such as crosslinked silicone resin particles, crosslinked acrylic resin particles, crosslinked styrene-acrylic resin particles, and crosslinked polyester particles, and organic particles such as calcium oxalate and ion exchange resins. Among these, silica is preferred from the viewpoint of transparency and other factors. Furthermore, during the polyester manufacturing process, precipitated particles obtained by precipitating and finely dispersing a portion of metal compounds such as catalysts can also be used.

[0044] There are no particular restrictions on the shape of the particles used; spherical, lumpy, rod-shaped, flattened, or any other shape may be used. Furthermore, there are no particular restrictions on their hardness, specific gravity, color, etc. Two or more types of these particles may be used in combination as needed.

[0045] Furthermore, the average particle size of the particles used is usually 5 μm or less, preferably 0.5 to 4 μm, more preferably 1.0 to 3 μm, and even more preferably 2 to 2.8 μm. Within this range of average particle size, both the handling properties and transparency of the film can be achieved. Furthermore, if the particles are in powder form, the average particle size can be determined by using a centrifugal sedimentation particle size distribution analyzer (e.g., Shimadzu Corporation's "SA-CP3" model) to measure the particle size distribution at 50% of the cumulative volume fraction (d50). For particles in films, layers, or resins, the average particle size can be determined by observing 10 or more particles with a scanning electron microscope (SEM), measuring the diameter of each particle, and taking the average value. In the case of non-spherical particles, the average of the longest and shortest diameters can be used as the diameter of each particle.

[0046] When incorporating particles into this film, it is preferable to provide a surface layer and an intermediate layer, with the particles being incorporated into the surface layer. Furthermore, in the case of a three-layer structure with different designs on the front and back, it is possible to incorporate particles into at least one of the surface layers. Therefore, it is preferable to incorporate particles into at least one of the surface layers, and from the viewpoint of handling ease, it is more preferable to incorporate particles into both surface layers. The particle content, although it also depends on the average particle size, is preferably 5000 ppm or less by mass in the particle-containing layer, more preferably 4000 ppm or less, and even more preferably 3000 ppm or less. Within this range, the transparency of the film can be made good. If there are no particles or if the particle content is low, the slipperiness may be insufficient, so the content is preferably 50 ppm or more, and more preferably 100 ppm or more.

[0047] The method for adding particles to this film is not particularly limited, and conventionally known methods can be employed. For example, in the case of a laminated polyester film, the particles can be added at any stage in the production of the polyester constituting each layer, but it is preferable to add them after the esterification or transesterification reaction is completed.

[0048] <Other> To suppress the precipitation of oligomer components, the film may be manufactured using polyester with a low oligomer content as the raw material. Various known methods can be used to manufacture polyester with a low oligomer content, such as a method of solid-phase polymerization after polyester production. Furthermore, the film may be constructed with three or more layers, and the surface layer of the film may be made of a polyester raw material with a low oligomer content to suppress the amount of oligomer component precipitated. Alternatively, polyester may be obtained by esterification or transesterification, followed by further increasing the reaction temperature and melt polycondensation under reduced pressure.

[0049] In addition to the particles mentioned above, conventionally known ultraviolet absorbers, antioxidants, antistatic agents, heat stabilizers, lubricants, dyes, pigments, etc., may be added to this film as needed.

[0050] The total thickness of this film is not particularly limited as long as it is within the range that can be formed as a film, but from the viewpoint of suitability as a substrate for gas barrier films, it is preferably 25 μm or less, more preferably 20 μm or less, even more preferably 18 μm or less, and particularly preferably 15 μm or less. On the other hand, from the viewpoint of mechanical strength, handling and productivity, it is preferably 1 μm or more, more preferably 5 μm or more, even more preferably 8 μm or more, and particularly preferably 10 μm or more. The total thickness of this film can be obtained, for example, by cutting out a roughly square sample piece with sides of 40 mm, measuring the thickness at five arbitrary points on the film surface using a dial gauge with a scale of 1 / 1000 mm, and calculating the average value.

[0051] <Method for manufacturing polyester film> Next, we will specifically describe examples of the manufacturing of this film, but the manufacturing examples are not limited to those listed below. For example, when manufacturing a biaxially oriented film, it is preferable to extrude the dried pellets of the polyester raw material (including recycled raw material) mentioned above as a molten sheet from a die using a melt extrusion device such as an extruder, and then cool and solidify them on a cooling roll such as a rotating cooling drum to obtain an unstretched sheet. Here, cooling is carried out to a temperature below the glass transition point of the polymer, for example, to obtain a substantially amorphous, unoriented sheet (unstretched sheet). Furthermore, in order to improve the flatness of the sheet, it is preferable to increase the adhesion between the sheet and the cooling roll, and electrostatic application adhesion and / or liquid coating adhesion methods are preferably employed.

[0052] Next, the obtained unstretched sheet is stretched in two axial directions. In this case, first, the unstretched sheet is stretched in one direction using a roll or tenter type stretcher. The stretching temperature is usually 70 to 120°C, preferably 80 to 110°C, and the stretching ratio is usually 2.5 to 7.0 times, preferably 2.8 to 6.0 times.

[0053] Next, the material is stretched in a direction perpendicular to the stretching direction of the first stage. In this case, the stretching temperature is usually 70 to 170°C, and the stretching ratio is usually 3.0 to 7.0 times, preferably 3.5 to 6.0 times, and more preferably 4.0 to 5.0 times.

[0054] Next, a heat treatment is performed at a temperature of typically 180-270°C, under tension or with a relaxation of up to 30%, to obtain a biaxially oriented film. This heat treatment is also called the heat setting process. The heat treatment may be carried out in two or more stages at different temperatures. Furthermore, cooling may be performed in a cooling zone after the heat treatment. The cooling temperature is preferably higher than the glass transition temperature (Tg) of the polyester constituting the film, and more specifically, it is preferably in the range of 100 to 160°C. This cooling may be carried out in two or more stages at different temperatures. In the stretching described above, a method can be adopted in which stretching is performed in two or more stages in one direction. In that case, it is preferable to perform the stretching so that the final stretching ratios in both directions fall within the above ranges.

[0055] Furthermore, simultaneous biaxial stretching can also be used in the manufacture of this film. Simultaneous biaxial stretching is a method of simultaneously stretching and oriented the aforementioned unstretched sheet in the machine direction (longitudinal direction) and width direction (transverse direction) while the temperature is controlled, usually at 70 to 120°C, preferably 80 to 110°C. The stretching ratio is preferably 4 to 50 times, more preferably 7 to 35 times, and even more preferably 10 to 25 times in terms of area. Then, heat treatment is carried out at a temperature of typically 180-270°C under tension or under relaxation of 30% or less to obtain a stretched and oriented film. For the simultaneous biaxial stretching apparatus employing the above stretching method, conventional known stretching methods such as screw type, pantograph type, and linear drive type can be used.

[0056] The longitudinal direction (MD) of the film refers to the direction in which the film progresses during the film manufacturing process, i.e., the winding direction of the film roll, and is also called the machine direction or vertical direction. The width direction (TD) of the film refers to the direction parallel to the film surface and perpendicular to the longitudinal direction; in other words, when the film is in a roll, it refers to the direction parallel to the central axis of the roll, and is also called the transverse direction.

[0057] <Physical properties of polyester film> The shrinkage rate of this film (laminated structure) after hot water treatment at 125°C for 30 minutes is 0.7% or less in both the longitudinal direction (MD) and the width direction (TD). If the shrinkage rate exceeds 0.7%, the inorganic thin film cannot follow the shrinkage (deformation) of the polyester film, resulting in a sparse structure or the formation of microcracks in the inorganic thin film, which reduces its gas barrier properties. From this viewpoint, the shrinkage rate is more preferably 0.6% or less, and even more preferably 0.5% or less. The lower limit of the shrinkage rate is not particularly limited, but is approximately 0.01%. The shrinkage rate after hot water treatment can be adjusted depending on the type and content of polyester used in this film (laminated structure), the film manufacturing and stretching conditions, etc.

[0058] The shrinkage rate of this film (laminated structure) when heat-treated at 125°C for 30 minutes is preferably 1.0% or less in both the longitudinal direction (MD) and the width direction (TD), more preferably 0.9% or less, even more preferably 0.8% or less, and particularly preferably 0.7% or less. If the shrinkage rate is 1.0% or less, the load on the inorganic thin film due to the shrinkage (deformation) of the polyester film is small, and the decrease in gas barrier properties can be suppressed. On the other hand, there is no particular lower limit to the shrinkage rate, and it is approximately 0.01%. The shrinkage rate after heat treatment can be adjusted depending on the type and content of polyester used in the film, as well as the film manufacturing and stretching conditions.

[0059] The tensile breaking strength of this film (laminated structure) is preferably 90 MPa or more in both the longitudinal direction (MD) and the width direction (TD), more preferably 93 MPa or more, and even more preferably 96 MPa or more. It may also be 250 MPa or less, 240 MPa or less, or 230 MPa or less. Furthermore, the tensile elongation at break of this film (laminated structure) is preferably 70% or more in both the longitudinal direction (MD) and the width direction (TD), more preferably 75% or more, and even more preferably 80% or more. It may also be 250% or less, 240% or less, or 230% or less. If the tensile breaking strength and tensile breaking elongation of this film are within this range, the decrease in gas barrier properties against external forces applied during processing, when wound on a roll, during transportation, etc., can be suppressed. Furthermore, the tensile breaking strength and tensile breaking elongation can be adjusted depending on the type and content of polyester used in this film, the film manufacturing and stretching conditions, etc.

[0060] <<Laminated polyester film>> The laminated polyester film (hereinafter also referred to as "the laminated film") 20 of the present invention may have a resin layer (hereinafter also referred to as "the resin layer") 4 formed of a resin composition on at least one surface of the film 10 (see Figure 1). The presence of this resin layer 4 improves the adhesion between the film 10 and the inorganic thin film 5 when the film 10 is used as a substrate for the gas barrier film 30 described later. In this case, the resin layer 4 plays a role known as an anchor coat layer. Here, the polyester film 10 having the resin layer 4 is referred to as the laminated polyester film 20 and is distinguished from the polyester film. Furthermore, other layers may be present between the polyester film 10 and the resin layer 4.

[0061] <Resin layer> As described above, this resin layer is formed from a resin composition (hereinafter also referred to as "this composition"). From the viewpoint of adhesion to inorganic thin films, it is preferable that this composition contains a binder resin and a crosslinking agent.

[0062] <Binder resin> The aforementioned binder resin is defined as a polymer compound having a number-average molecular weight (Mn) of 1000 or more, as measured by gel permeation chromatography (GPC), and possessing film-forming properties, in accordance with the "Flow Scheme for Safety Evaluation of Polymer Compounds" (November 1985, sponsored by the Chemical Substances Council). There are no particular restrictions on such binder resins, and conventionally known binder resins such as (meth)acrylic resins, polyester resins, polyurethane resins, polyvinyl resins (polyvinyl alcohol, vinyl chloride vinyl acetate copolymer, etc.), polyalkylene glycols, polyalkyleneimines, methylcellulose, hydroxycellulose, and starches can be used. One type of binder resin may be used alone, or two or more types may be used in combination.

[0063] <Crosslinking agent> There are no particular restrictions on the crosslinking agent, and conventionally known crosslinking agents can be used. Examples include oxazoline compounds, melamine compounds, epoxy compounds, carbodiimide compounds, isocyanate compounds, silane coupling compounds, etc. One crosslinking agent may be used alone, or two or more may be used in combination.

[0064] <Preferred embodiment> This composition preferably contains the following compound (A) as a binder resin and the following compound (B) as a crosslinking agent. In other words, this composition preferably contains the following compounds (A) and (B). (A) One or more resins selected from the group consisting of (meth)acrylic resin, polyester resin, and polyurethane resin. (B) Oxazoline compounds

[0065] ((meth)acrylic resin) (Meth)acrylic resin is a polymer composed of polymerizable monomers, including acrylic and methacrylic monomers. These may be homopolymers, copolymers, or copolymers with polymerizable monomers other than acrylic and methacrylic monomers. Furthermore, copolymers of these polymers with other polymers (e.g., polyester, polyurethane, etc.) are also included. Examples include block copolymers and graft copolymers. In other words, the (meth)acrylic resin may be a (meth)acrylic-modified polyester resin or a (meth)acrylic-modified polyurethane resin. In addition, polymers (and sometimes mixtures of polymers) obtained by polymerizing polymerizable monomers having carbon-carbon double bonds in polyester solutions or dispersions are also included. Similarly, polymers (and sometimes mixtures of polymers) obtained by polymerizing polymerizable monomers having carbon-carbon double bonds in polyurethane solutions or dispersions are also included. In the same manner, polymers (and sometimes mixtures of polymers) obtained by polymerizing polymerizable monomers having carbon-carbon double bonds in other polymer solutions or dispersions are also included. Furthermore, the (meth)acrylic resin may contain hydroxyl groups and amino groups to further improve its adhesion to the film.

[0066] The polymerizable monomers having carbon-carbon double bonds mentioned above are not particularly limited, but some representative compounds include various carboxyl group-containing monomers such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, fumaric acid, maleic acid, and citraconic acid, and their salts; various hydroxyl group-containing monomers such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, monobutyl hydroxyfumarate, and monobutyl hydroxyitaconate; methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, and lauryl (meth)acrylate. Examples include various alkyl(meth)acrylic acid esters such as (meth)acrylamide, diacetone acrylamide, or (meth)acrylonitrile; hydroxyl group-containing nitrogen-containing compounds such as N-methylol(meth)acrylamide; various styrene derivatives such as styrene, α-methylstyrene, divinylbenzene, and vinyltoluene; various vinyl esters such as vinyl propionate; various silicon-containing polymerizable monomers such as γ-methacryloxypropyltrimethoxysilane and vinyltrimethoxysilane; phosphorus-containing vinyl monomers; various vinyl halides such as vinyl chloride and vinylidene chloride; and various conjugated dienes such as butadiene.

[0067] Among the above, polymers obtained by polymerizing polymerizable monomers including acrylic and methacrylic monomers are preferred, and polymers that include alkyl (meth)acrylic acid esters are more preferred. Furthermore, when the coating solution is aqueous, it is preferable that the polymerizable monomer has hydrophilic groups such as hydroxyl groups and carboxyl groups, from the viewpoint of facilitating the dissolution or dispersion of the binder resin. Therefore, (meth)acrylic resins are also preferable polymers obtained by polymerizing alkyl (meth)acrylic acid esters with polymerizable monomers that include hydrophilic group-containing monomers such as hydroxyl group-containing monomers and carboxyl group-containing monomers. Furthermore, the (meth)acrylic resin may also be an emulsion polymer obtained by polymerizing polymerizable monomers in the presence of a surfactant, for example.

[0068] (Polyester resin) Polyester resins are primarily composed of polycarboxylic acids and polyhydroxy compounds, such as those listed below. In other words, as polycarboxylic acids, terephthalic acid, isophthalic acid, orthophthalic acid, phthalic acid, 4,4'-diphenyldicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, and 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 2-potassium sulfoterephthalic acid, 5-sodium sulfisoisophthalic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, glutaric acid, succinic acid, trimellitic acid, trimesic acid, pyromellitic acid, trimellitic anhydride, phthalic anhydride, p-hydroxybenzoic acid, monopotassium salt of trimellitic acid, and their ester-forming derivatives can be used. Examples of polyvalent hydroxy compounds that can be used include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 2-methyl-1,5-pentanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, p-xylylene glycol, bisphenol A-ethylene glycol adduct, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polytetramethylene oxide glycol, dimethylolpropionic acid, glycerin, trimethylolpropane, sodium dimethylolethylsulfonate, potassium dimethylolpropionate, etc. One or more of these polyvalent carboxylic acids and polyvalent hydroxy compounds can be appropriately selected, and a polyester resin can be synthesized by a conventional polycondensation reaction.

[0069] Furthermore, in order to impart water dispersibility or water solubility, a method is also preferably used in which sulfoisophthalic acid is used as a copolymer component as part of the polycarboxylic acid to introduce sulfonic acid groups into the polyester skeleton, and then neutralized with a basic compound to make the polyester resin hydrophilic. The amount copolymerized is usually 1 to 10 mol%, preferably 2 to 8 mol%, relative to the total polycarboxylic acid. By introducing an appropriate amount of sulfonic acid groups, the water dispersion stability can be further improved.

[0070] (Polyurethane resin) Polyurethane resin is a polymer compound having urethane bonds within its molecule, and is preferably water-dispersible or water-soluble. Polyurethane resin may be used individually or in combination of two or more types.

[0071] To impart water dispersibility or water solubility, it is common and preferable to introduce hydrophilic groups such as hydroxyl groups, carboxyl groups, sulfonic acid groups, sulfonyl groups, phosphate groups, and ether groups into the urethane resin. Among these hydrophilic groups, carboxyl groups or sulfonic acid groups are particularly preferred from the viewpoint of improving adhesion.

[0072] One method for producing polyurethane resin involves the reaction of a hydroxyl group-containing compound with an isocyanate compound. Polyols are preferably used as the hydroxyl group-containing compound, such as polyether polyols, polyester polyols, polycarbonate polyols, polyolefin polyols, and acrylic polyols. These compounds may be used individually or in combination.

[0073] Examples of polyether polyols include polyethylene glycol, polypropylene glycol, polyethylene propylene glycol, polytetramethylene ether glycol, and polyhexamethylene ether glycol.

[0074] Polyester polyols include, for example, polycarboxylic acids (malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, sebacic acid, fumaric acid, maleic acid, terephthalic acid, isophthalic acid, etc.) or their acid anhydrides, and polyhydric alcohols (ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 2-methyl-1,3-propanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 2- Examples include those obtained from reactions with methyl-2,4-pentanediol, 2-methyl-2-propyl-1,3-propanediol, 1,8-octanediol, 2,2,4-trimethyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol, 2,5-dimethyl-2,5-hexanediol, 1,9-nonanediol, 2-methyl-1,8-octanediol, 2-butyl-2-ethyl-1,3-propanediol, 2-butyl-2-hexyl-1,3-propanediol, cyclohexanediol, bishydroxymethylcyclohexane, dimethanolbenzene, bishydroxyethoxybenzene, alkyldialkanolamine, lactonediol, etc.

[0075] Examples of polycarbonate-based polyols include polycarbonate diols obtained by de-alcoholization reactions of polyhydric alcohols with dimethyl carbonate, diethyl carbonate, diphenyl carbonate, ethylene carbonate, etc., such as poly(1,6-hexylene) carbonate and poly(3-methyl-1,5-pentylene) carbonate.

[0076] Among the hydroxyl group-containing compounds used to obtain polyurethane resins, polyester polyols are preferred.

[0077] Examples of polyisocyanate compounds used to obtain polyurethane resins include aromatic diisocyanates such as tolylene diisocyanate, xylylene diisocyanate, methylenediphenyl diisocyanate, phenylene diisocyanate, naphthalene diisocyanate, and tolidine diisocyanate; aliphatic diisocyanates having aromatic rings such as α,α,α',α'-tetramethylxylylene diisocyanate; aliphatic diisocyanates such as methylene diisocyanate, propylene diisocyanate, lysine diisocyanate, trimethylhexamethylene diisocyanate, and hexamethylene diisocyanate; and alicyclic diisocyanates such as cyclohexane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, and isopropylidene dicyclohexyl diisocyanate. These may be used individually or in combination of multiple types.

[0078] Chain extenders may be used when synthesizing polyurethane resins. There are no particular restrictions on the chain extender as long as it has two or more active groups that react with isocyanate groups. Generally, chain extenders having two hydroxyl groups or amino groups can be used.

[0079] Examples of chain extenders having two hydroxyl groups include aliphatic glycols such as ethylene glycol, propylene glycol, and butanediol; aromatic glycols such as xylylene glycol and bishydroxyethoxybenzene; and ester glycols such as neopentyl glycol hydroxypivalate.

[0080] Examples of chain extenders having two amino groups include aromatic diamines such as tolylenediamine, xylylenediamine, and diphenylmethanediamine; aliphatic diamines such as ethylenediamine, propylenediamine, hexanediamine, 2,2-dimethyl-1,3-propanediamine, 2-methyl-1,5-pentanediamine, trimethylhexanediamine, 2-butyl-2-ethyl-1,5-pentanediamine, 1,8-octanediamine, 1,9-nonanediamine, and 1,10-decanediamine; and alicyclic diamines such as 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane, dicyclohexylmethanediamine, 1,4-diaminocyclohexane, and 1,3-bisaminomethylcyclohexane.

[0081] Furthermore, in order to impart water dispersibility or water solubility, a method is also preferably used in which carboxyl groups are introduced into the urethane skeleton using dimethylolpropionic acid, dimethylolbutanoic acid, etc., and then neutralized with a basic compound to make the urethane resin hydrophilic.

[0082] (Oxazoline compounds) Oxazoline compounds are compounds having an oxazoline group in their molecule, and polymers containing an oxazoline group are particularly preferred. They can be produced by polymerization of an addition-polymerizable oxazoline group-containing monomer alone or with other monomers. Examples of addition-polymerizable oxazoline group-containing monomers include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, and 2-isopropenyl-5-ethyl-2-oxazoline. One or more of these can be used. Among these, 2-isopropenyl-2-oxazoline is preferred because it is readily available industrially. Other monomers are not limited as long as they are copolymerizable with addition-polymerizable oxazoline group-containing monomers, for example (meth)acrylic acid esters such as alkyl (meth)acrylates (alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, 2-ethylhexyl, and cyclohexyl groups); unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, styrenesulfonic acid and their salts (sodium salt, potassium salt, ammonium salt, tertiary amine salt, etc.); unsaturated nitriles such as acrylonitrile and methacrylonitrile; (meth)acrylamide, N-alkyl(meth) Examples of unsaturated amides such as acrylamide and N,N-dialkyl(meth)acrylamide (alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, 2-ethylhexyl, and cyclohexyl groups); vinyl esters such as vinyl acetate and vinyl propionate; vinyl ethers such as methyl vinyl ether and ethyl vinyl ether; α-olefins such as ethylene and propylene; halogen-containing α,β-unsaturated monomers such as vinyl chloride and vinylidene chloride; and α,β-unsaturated aromatic monomers such as styrene and α-methylstyrene. One or more of these monomers can be used. Furthermore, the oxazoline compound may have a polyalkylene oxide chain, such as a polyethylene oxide chain, and for example, a (meth)acrylate having a polyalkylene oxide chain may be used as another monomer.

[0083] The content of compound (A) in this composition is preferably 10 to 90% by mass, more preferably 20 to 85% by mass, and even more preferably 30 to 80% by mass, as a percentage of the total nonvolatile components of this composition. The content of compound (B) in this composition is preferably 10 to 90% by mass, more preferably 15 to 80% by mass, and even more preferably 20 to 70% by mass, as a percentage of the total nonvolatile components of this composition. Within this range, adhesion to inorganic thin films can be sufficiently improved, and as a result, a gas barrier film with good barrier properties can be obtained.

[0084] <Other> Furthermore, to the extent that the spirit of the present invention is not impaired, additives such as crosslinking catalysts, defoaming agents, coating properties improvers, surfactants, thickeners, organic lubricants, ultraviolet absorbers, antioxidants, foaming agents, dyes, and pigments may be further added as appropriate, in addition to the above-mentioned compounds.

[0085] <Solvent> This composition may be diluted with a solvent to form a coating solution. That is, this composition may be applied as a liquid coating solution to, for example, this film, and then dried and cured as necessary to form a resin layer. Furthermore, each component of this composition (binder resin, crosslinking agent, and other components) may be dissolved in a solvent or dispersed in a solvent. When used as a coating solution, the concentration of the total non-volatile components of this composition in the coating solution is preferably 0.1 to 50% by mass. If it is 0.1% by mass or more, a resin layer of the desired thickness can be efficiently formed. On the other hand, if it is 50% by mass or less, the viscosity during coating can be suppressed, thereby improving the appearance of the resin layer and increasing the stability in the coating solution.

[0086] There are no particular restrictions on the solvent, and either water or an organic solvent can be used. From the viewpoint of environmental protection and impact on the human body, it is preferable to use an aqueous coating solution with water as the main solvent (50% by mass or more of the total solvent). The water content is preferably 60% by mass or more, more preferably 70% by mass or more. The aqueous coating solution may contain a small amount of organic solvent. The specific amount of organic solvent should be less than or equal to the amount of water by mass, for example, 50% by mass or less, preferably 40% by mass or less, and more preferably 30% by mass or less of the solvent. Examples of organic solvents used in combination with water include alcohols such as ethanol, isopropanol, ethylene glycol, and glycerin; ethers such as ethyl cellosolve, t-butyl cellosolve, propylene glycol monomethyl ether, and tetrahydrofuran; ketones such as acetone and methyl ethyl ketone; esters such as ethyl acetate; and amines such as dimethylethanolamine. These can be used individually or in combination. By appropriately selecting and including these organic solvents in the aqueous coating solution as needed, the stability and coating properties of the coating solution can be improved.

[0087] Furthermore, when using only organic solvents as the solvent, examples of such organic solvents include aromatic hydrocarbons such as toluene; aliphatic hydrocarbons such as hexane, heptane, and isooctane; esters such as ethyl acetate and butyl acetate; ketones such as ethyl methyl ketone and isobutyl methyl ketone; alcohols such as ethanol and 2-propanol; and ethers such as diisopropyl ether and dibutyl ether. These may be used individually or in combination, taking into consideration their solubility, coating properties, boiling point, etc.

[0088] It can be inferred that the resin layer contains unreacted substances, reacted compounds, or mixtures thereof of each component constituting this composition (binder resin, crosslinking agent, and other components). Furthermore, the individual components in the resin layer can be analyzed using methods such as TOF-SIMS, ESCA, and X-ray fluorescence.

[0089] <Method for forming a resin layer> Next, the method for forming the resin layer that constitutes this laminated film will be described. The method for forming this resin layer is not particularly limited, and conventionally known coating methods such as reverse gravure coating, direct gravure coating, roll coating, die coating, bar coating, and curtain coating can be used. Furthermore, methods for forming the resin layer include in-line coating and off-line coating. The method for heat-treating the applied resin composition is not particularly limited. For example, when providing a resin layer by off-line coating, it is generally preferable to heat-treat at 80-200°C for 3-40 seconds, preferably at 100-180°C for 3-40 seconds. On the other hand, when providing a resin layer by in-line coating, it is generally preferable to heat-treat at 70-280°C for 3-200 seconds.

[0090] In the present invention, the resin layer is preferably formed by in-line coating, which treats the film surface during the polyester film manufacturing process. In-line coating is a method of coating within the polyester film manufacturing process. Specifically, it involves coating at any stage from melt extrusion of polyester to stretching, heat fixing, and winding. Typically, the coating is applied to an unstretched sheet obtained by melting and rapid cooling, a stretched uniaxially oriented film, a biaxially oriented film before heat fixing, or a film after heat fixing but before winding.

[0091] While not limited to the following, for example, in sequential biaxial stretching, a method in which a uniaxially stretched film stretched in the longitudinal direction (vertical direction) is coated and then stretched in the width direction (lateral direction) is particularly superior. With this method, film formation and resin layer formation can be performed simultaneously, which has advantages in terms of manufacturing costs. Furthermore, because stretching is performed after coating, the thickness of the resin layer can be changed according to the stretching ratio, making thin-film coating easier compared to offline coated films.

[0092] Furthermore, by providing a resin layer on the film before stretching, the resin layer can be stretched together with the polyester film, thereby allowing the resin layer to adhere firmly to the polyester film.

[0093] Furthermore, in the manufacturing of biaxially oriented polyester film, the film can be restrained in both the longitudinal and transverse directions by gripping the film edges with clips or the like while stretching it. This allows for high temperatures to be applied during subsequent heat treatment (heat setting process) without wrinkles or other defects, while maintaining flatness. Therefore, because the heat treatment applied after coating can reach temperatures that cannot be achieved by other methods, the film-forming properties of the resin layer are improved, and the resin layer and polyester film can be bonded more firmly. Furthermore, a strong resin layer can be created, improving properties such as resistance to migration and resistance to humid heat to various functional layers that may be formed on the resin layer.

[0094] Furthermore, regardless of whether it is offline coating or in-line coating, heat treatment and active energy ray irradiation such as ultraviolet irradiation may be used in combination as needed. The polyester film constituting this laminated polyester film may be subjected to surface treatment such as corona treatment or plasma treatment in advance.

[0095] The thickness of this resin layer, as the thickness of the resin layer in the final laminated polyester film, is preferably 0.005 μm or more, more preferably 0.007 μm or more, and even more preferably 0.01 μm or more. Furthermore, the thickness of the resin layer is preferably 1 μm or less, more preferably 0.5 μm or less, and even more preferably 0.1 μm or less. Within this range of resin layer thickness, the adhesion to the inorganic thin film can be sufficiently improved. The thickness of the resin layer can be measured by the method described in the examples.

[0096] <<Gas barrier film>> The gas barrier film 30 of the present invention (hereinafter also referred to as "this gas barrier film") comprises an inorganic thin film 5 on the resin layer 4 of the laminated film 20 (see Figure 1). In other words, the gas barrier film 30 has a resin layer (anchor coat layer) 4 and an inorganic thin film 5 in this order on at least one surface of the polyester film 10 which is the base material.

[0097] <Inorganic Thin Film> The inorganic material constituting the inorganic thin film is preferably formed from an inorganic material selected from the group consisting of silicon, aluminum, magnesium, zinc, tin, nickel, titanium, or oxides, carbides, nitrides, or mixtures thereof. Among these, the inorganic material is preferably silicon oxide, silicon nitride, silicon oxidized nitride, silicon carbide oxide, silicon carbide oxidized nitride, aluminum oxide, or diamond-like carbon. In particular, silicon oxide, silicon nitride, silicon oxidized nitride, silicon carbide oxide, silicon carbide oxidized nitride, and aluminum oxide are preferred because they can stably maintain high gas barrier properties.

[0098] While methods such as vapor deposition and coating can be used to form inorganic thin films, vapor deposition is preferred from the viewpoint of obtaining a uniform inorganic thin film with high gas barrier properties. Vapor deposition methods include PVD (physical vapor deposition) such as vacuum deposition, ion plating, and sputtering, or CVD (chemical vapor deposition) such as plasma CVD using plasma, and catalytic chemical vapor deposition (Cat-CVD) which uses a heated catalyst to catalytically decompose the material gas.

[0099] The thickness of the inorganic thin film is generally around 0.1 to 500 nm, but preferably 1 to 150 nm, and more preferably 5 to 70 nm. Within this range, sufficient gas barrier properties can be obtained, and the inorganic thin film will not develop cracks or delamination, and will also have excellent transparency. The inorganic thin film may consist of a single layer or two or more layers. Furthermore, if the inorganic thin film consists of two or more layers, they may be the same layer or different layers.

[0100] A topcoat layer (not shown) may be formed on the inorganic thin film 5 to improve adhesion with the plastic film laminated thereon. Examples of this topcoat agent include solvent-soluble or water-soluble polyester resins, isocyanate resins, urethane resins, acrylic resins, vinyl alcohol resins, ethylene vinyl alcohol resins, vinyl-modified resins, epoxy resins, oxazoline group-containing resins, modified styrene resins, modified silicone resins, alkyl titanates, and the like. These can be used individually or in combination of two or more.

[0101] This gas barrier film 30 is typically used in various applications as a gas barrier laminate in which a plastic film 6 is provided on top of an inorganic thin film 5 (Figure 1). The thickness of the plastic film is typically selected from a range of 5 to 500 μm, preferably 10 to 200 μm, depending on the application, considering factors such as mechanical strength, flexibility, and transparency. The width and length of the film are not particularly limited and can be selected as appropriate for the application.

[0102] As for the plastic films mentioned above, polyolefin films are preferred as films or sheets that can withstand hot water treatment and are heat-sealable. Furthermore, biaxially oriented polyester films and biaxially oriented nylon films are preferred as films with excellent mechanical strength.

[0103] The known dry lamination method and extrusion lamination method are used for laminating the plastic film. In this case, conventionally known adhesives such as urethane-based, polyester-based, and acrylic-based adhesives can be used.

[0104] <<Applications>> This film is suitable for manufacturing gas barrier films with an inorganic thin film due to its excellent dimensional stability, and more specifically, its low shrinkage rate after hot water treatment. Therefore, the laminated film and gas barrier film based on this film are particularly suitable as packaging substrates for contents that undergo hot water treatment (such as retort processing or sterilization) in the food and medical fields. Furthermore, since this film has a polyester layer (X) containing chemically recycled polyester, it is an environmentally friendly film that can be applied to current environmental issues. In the present invention, no deterioration in properties is observed due to the inclusion of chemically recycled polyester, and it can be used without any practical problems.

[0105] <<Explanation of terms>> In this invention, the term "film" includes "sheets," and the term "sheet" includes "film." In this invention, the term "film" is used to mean not only a single layer but also a laminated structure of multiple layers. In this invention, unless otherwise specified, the term "film" refers to a laminated structure. In this invention, when "X~Y" (where X and Y are any numbers) is written, unless otherwise specified, it means "X or greater and Y or less," and also includes the meaning of "preferably greater than X" or "preferably less than Y." Furthermore, when "X or greater" (where X is any number) is written, unless otherwise specified, it includes the meaning of "preferably greater than X," and when "Y or less" (where Y is any number) is written, unless otherwise specified, it also includes the meaning of "preferably less than Y." [Examples]

[0106] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following embodiments, unless it exceeds the gist of the invention.

[0107] <Evaluation Method> (1) Intrinsic viscosity (IV) To measure the intrinsic viscosity of polyester raw materials, 1 g of polyester, from which incompatible components have been removed, was accurately weighed, dissolved in 100 mL of a phenol / tetrachloroethane mixed solvent (50 / 50 by mass ratio), and measured at 30°C using a viscosity measuring device "VMS-022UPC·F10" (manufactured by Rigosha Co., Ltd.). To measure the intrinsic viscosity of polyester film, 0.30 g of sample film was accurately weighed, dissolved in 30 mL of a phenol / tetrachloroethane mixed solvent (50 / 50 mass ratio), and measured at 30°C using a viscosity measuring device "VMS-022UPC·F10" (manufactured by Rigosha Co., Ltd.).

[0108] (2) Average particle size For the average particle size of the particles contained in the polyester, the particle size at which the cumulative volume fraction of 50% of the equivalent spherical distribution was measured using a centrifugal sedimentation particle size distribution analyzer (SA-CP3 type) manufactured by Shimadzu Corporation was defined as the average particle size d50.

[0109] (3) Shrinkage rate (heat treatment) A 1.5 cm x 15 cm sample film was heat-treated for 30 minutes in a hot-air oven maintained at a predetermined temperature (125°C) in a tension-free state. The length of the sample film was measured before and after the treatment, and the length was calculated using the following formula. Measurements were taken in both the longitudinal direction (MD) and the width direction (TD) of the film. Thermal shrinkage rate (%) = {(Sample length before heat treatment) - (Sample length after heat treatment)} ÷ (Sample length before heat treatment) × 100

[0110] (4) Shrinkage rate (hot water treatment) A sample film with a 10cm x 10cm border drawn on it was subjected to hot water treatment (water inclusion and pressurization) in an autoclave at 125°C for 30 minutes. The moisture adhering to the sample film was allowed to air dry at room temperature for at least half a day, and the length of the sample film was measured before and after the treatment. The length was then calculated using the following formula. Measurements were taken in both the longitudinal direction (MD) and the width direction (TD) of the film. Thermal shrinkage rate (%) = {(Sample length before heat treatment) - (Sample length after heat treatment)} ÷ (Sample length before heat treatment) × 100

[0111] (5) Tensile breaking strength and tensile breaking elongation Sample pieces measuring 15 mm in width and 150 mm in length were taken from designated locations on the polyester film, and the tensile breaking strength and tensile elongation were measured using an Autograph AGX-V manufactured by Shimadzu Corporation. Gauge marks were marked at 50 mm intervals in the center of each test piece, and a tensile test was performed using a tensile testing machine with a gripping distance of 50 mm and a tensile speed of 200 mm / min. The load and elongation at the time of breakage were measured, and the tensile breaking strength and tensile elongation were determined.

[0112] (6) Size exclusion chromatography The sample film was dissolved in HFIP solution (with 5 mM sodium trifluoroacetate added, at 40°C), and after preparing a 0.1 wt% solution in the mobile phase, it was allowed to stand overnight. The solution was then filtered through a 0.45 μm PTFE filter and measured using size exclusion chromatography (Tosoh HLC-8320, manufactured by Tosoh Techno Systems Co., Ltd.). The molecular weight was converted to PMMA equivalent, and the weight-average molecular weight (Mw) and number-average molecular weight (Mn) of the main peak, as well as the peak area (%) corresponding to molecular weights of 1000 or less, were calculated as the LMWOs ratio.

[0113] (7) Thickness of the resin layer The surface of the resin layer was stained with RuO4 and embedded in epoxy resin. Subsequently, sections prepared by the ultrathin sectioning method were stained with RuO4, and the cross-section of the resin layer was measured using a transmission electron microscope (TEM) (Hitachi High-Tech Corporation, H-7650, accelerating voltage 100kV).

[0114] <Materials used> [Polyester raw material] Raw material A: Homopolyethylene terephthalate (intrinsic viscosity = 0.64 dL / g) Raw material B: A masterbatch containing 0.6% by mass of silica particles with an average particle size of 2.7 μm, made from homopolyethylene terephthalate (intrinsic viscosity = 0.61 dL / g). Raw material C: Chemically recycled polyester (intrinsic viscosity = 0.62 dL / g)

[0115] The raw material C is polyethylene terephthalate with a dicarboxylic acid component of terephthalic acid / isophthalic acid = 98.2 / 1.8 (mol%) and a diol component of ethylene glycol = 100 (mol%), and was derived from the bottle. Furthermore, raw materials A and B are fossil fuel polyester (virgin raw materials).

[0116] [Resin layer] The following resin composition was used to form the resin layer. (A1): Polyurethane resin (A2): (Meth)acrylic resin (A3): Polyester resin (B1): Epocross (manufactured by Nippon Shokubai Co., Ltd.), an oxazoline compound.

[0117] The coating solutions used in the examples and comparative examples were prepared by diluting a resin composition obtained by stirring and mixing the above compounds with water.

[0118] (Example 1) Mixed raw materials A and B were prepared in proportions of 75% by mass and 25% by mass, respectively, to form the raw materials for both surface layers. Mixed raw materials A and C were prepared in proportions of 55% by mass and 45% by mass, respectively, to form the raw material for the intermediate layer. Each of the raw materials for the surface and intermediate layers was supplied to two extruders, melted at 280°C, and then co-extruded onto a cooling roll set at 25°C in a layer configuration of 2 types and 3 layers (surface layer / intermediate layer / surface layer = 1 / 4 / 1 discharge volume) and cooled and solidified to obtain an unstretched sheet. Next, the obtained unstretched sheet was stretched 2.95 times in the longitudinal direction (MD) at 85°C using a roll stretcher. Furthermore, after preheating at 85°C in a tenter, it was stretched 4.60 times in the width direction (TD) at 110°C. Finally, it was heat-treated at 250°C to obtain a biaxially oriented polyester film with a thickness of 12 μm (each surface layer: 2 μm, intermediate layer: 8 μm). The properties of the obtained polyester film were evaluated using the method described above. The evaluation results are shown in Table 2.

[0119] In the production of the polyester film described above, after stretching in the longitudinal direction (MD) and before stretching in the width direction (TD), a coating solution of the resin composition that forms the resin layer described above was applied to both sides of one side of the uniaxially oriented polyester film so that the film thickness (after drying) was 0.03 to 0.04 μm. Then, stretching in the width direction and heat treatment were performed under the conditions described above to obtain a laminated polyester film.

[0120] (Example 2) The procedure was the same as in Example 1, except that the composition and film formation conditions were as described in Table 1 below. The evaluation results are shown in Table 2.

[0121] (Comparative Example 1) The procedure was the same as in Example 1, except that the composition and film formation conditions were as described in Table 1 below. The evaluation results are shown in Table 2.

[0122] [Table 1]

[0123] [Table 2]

[0124] As shown in the above examples, the polyester film of the present invention is an environmentally friendly film having a polyester layer (X) containing chemically recycled polyester, and having a shrinkage rate of 0.7% or less in both the longitudinal direction (MD) and the width direction (TD) after hot water treatment. Because the shrinkage rate is 0.7% or less, the inorganic thin film can follow the shrinkage (deformation) of the polyester film, and it is expected that a decrease in gas barrier properties caused by the inorganic thin film becoming loosely structured or by the occurrence of microcracks can be suppressed. Although the shrinkage rates of the films in the examples and comparative examples were not significantly different after heat treatment, differences were observed in the shrinkage rates after hot water treatment. Therefore, the polyester film of the present invention can be suitably used as a packaging base material for contents that undergo hot water treatment (such as retort treatment or sterilization treatment) in the food and medical fields, and thus its range of application is wider than that of conventional films (Comparative Example 1).

[0125] Furthermore, in the evaluation of low molecular weight organic substances (hereinafter also referred to as "LMWOs") by size exclusion chromatography, the films of the examples and comparative examples showed similar area percentages of LMWOs. Here, "LMWOs" includes cyclic oligomers, linear oligomers, residual monomers, etc., and the smaller the area percentage of LMWOs, the more effectively the contamination of the contents with low molecular weight organic substances can be suppressed when used for packaging purposes. In addition, when used as a gas barrier film, the reduction in adhesion of the inorganic thin film can also be suppressed. Furthermore, the films of the examples and comparative examples were equivalent in terms of the molecular weight of the main peak measured by size exclusion chromatography, more specifically, the weight-average molecular weight (Mw) and number-average molecular weight (Mn). Therefore, in size exclusion chromatography measurements, no degradation in properties due to the inclusion of chemically recycled polyester was observed, and it can be said that it can be used without practical problems for packaging applications. [Industrial applicability]

[0126] The polyester film of the present invention is suitable for the manufacture of gas barrier films with an inorganic thin film due to its excellent dimensional stability, and more specifically, its low shrinkage rate after hot water treatment. Therefore, the embodiments of this disclosure are suitable as packaging materials for contents that undergo hot water treatment (such as retort processing or sterilization) in the food and medical fields, and are also environmentally friendly films that can be applied to current environmental issues, thus possessing high industrial value. [Explanation of symbols]

[0127] 1. Intermediate layer (polyester layer (X)) 2 Surface layer 3 Surface layer 4. Resin layer (anchor coat layer) 5. Inorganic Thin Films 6 Plastic film 10. Polyester film (laminated structure) 20 Laminated polyester film 30 Gas barrier film

Claims

1. It is a laminated structure consisting of at least three layers having a surface layer, an intermediate layer, and another surface layer in that order. The laminated structure has a polyester layer (X) containing chemically recycled polyester as the intermediate layer, Each of the aforementioned surface layers contains fossil fuel polyester as a constituent component, The thickness of each of the aforementioned surface layers is 10 to 30% of the thickness of the aforementioned intermediate layer. The content of the aforementioned chemically recycled polyester is 5% by mass or more and 50% by mass or less relative to the total polyester. The shrinkage rate after hot water treatment at 125°C for 30 minutes is 0.7% or less in both the longitudinal direction (MD) and the width direction (TD). The total thickness of the film is between 1 μm and 25 μm. The aforementioned chemically recycled polyester is a polyester film obtained by decomposing the polyester contained in a polyester product to the monomer level and then repolymerizing it.

2. A laminated structure comprising at least three layers having a surface layer, an intermediate layer, and a surface layer in this order, The laminated structure has a polyester layer (X) containing chemically recycled polyester as the intermediate layer, Each of the aforementioned surface layers contains fossil fuel polyester as a constituent component, The thickness of each of the aforementioned surface layers is 10 to 30% of the thickness of the aforementioned intermediate layer. The content of the aforementioned chemically recycled polyester is 5% by mass or more and 50% by mass or less relative to the total polyester. The shrinkage rate after hot water treatment at 125°C for 30 minutes is 0.7% or less in both the longitudinal direction (MD) and the width direction (TD). The isophthalic acid content in the total dicarboxylic acid components of the total polyester is 0.1 to 1.2 mol%, The aforementioned chemically recycled polyester is a polyester film obtained by decomposing the polyester contained in a polyester product to the monomer level and then repolymerizing it.

3. The polyester film according to claim 1 or 2, wherein the polyester product in the chemically recycled polyester is a bottle and / or a film.

4. The polyester film according to claim 1 or 2, wherein the tensile breaking strength in the longitudinal direction (MD) and the width direction (TD) is 90 MPa or more in both directions.

5. The polyester film according to claim 1 or 2, wherein the tensile elongation at break in both the longitudinal direction (MD) and the width direction (TD) is 70% or more.

6. The polyester film according to claim 1 or 2, wherein the intrinsic viscosity (IV) of the film is 0.5 to 0.8 dL / g.

7. The polyester film according to claim 1 or 2, wherein the content of the chemically recycled polyester in the intermediate layer is 10 to 80% by mass.

8. The polyester film according to claim 1 or 2, wherein the chemically recycled polyester contains 10 mol% or less of isophthalic acid in the total dicarboxylic acid components of the polyester.

9. The polyester film according to claim 1 or 2, wherein the chemically recycled polyester is polyethylene terephthalate.

10. The polyester film according to claim 1 or 2, wherein the fossil fuel polyester is homopolyethylene terephthalate.

11. A gas barrier film comprising a polyester film, a resin layer formed of a resin composition on at least one surface of the polyester film, and an inorganic thin film on the resin layer, The aforementioned polyester film is It is a laminated structure consisting of at least three layers having a surface layer, an intermediate layer, and another surface layer in that order. The laminated structure has a polyester layer (X) containing chemically recycled polyester as the intermediate layer, Each of the aforementioned surface layers contains fossil fuel polyester as a constituent component, The thickness of each of the aforementioned surface layers is 10 to 30% of the thickness of the aforementioned intermediate layer. The content of the aforementioned chemically recycled polyester is 5% by mass or more and 50% by mass or less relative to the total polyester. The shrinkage rate after hot water treatment at 125°C for 30 minutes is 0.7% or less in both the longitudinal direction (MD) and the width direction (TD). The aforementioned chemically recycled polyester is a gas barrier film obtained by decomposing the polyester contained in a polyester product to the monomer level and then repolymerizing it.

12. A laminated polyester film comprising a polyester film and a resin layer formed of a resin composition on at least one surface of the polyester film, The aforementioned polyester film is It is a laminated structure consisting of at least three layers having a surface layer, an intermediate layer, and another surface layer in that order. The laminated structure has a polyester layer (X) containing chemically recycled polyester as the intermediate layer, Each of the aforementioned surface layers contains fossil fuel polyester as a constituent component, The thickness of each of the aforementioned surface layers is 10 to 30% of the thickness of the aforementioned intermediate layer. The content of the aforementioned chemically recycled polyester is 5% by mass or more and 50% by mass or less relative to the total polyester. The shrinkage rate after hot water treatment at 125°C for 30 minutes is 0.7% or less in both the longitudinal direction (MD) and the width direction (TD). The aforementioned chemically recycled polyester is a polyester obtained by decomposing the polyester contained in a polyester product to the monomer level and then repolymerizing it. A laminated polyester film wherein the resin composition comprises the following compounds (A) and (B). (A) One or more resins selected from the group consisting of (meth)acrylic resin, polyester resin, and polyurethane resin. (B) Oxazoline compounds

13. A gas barrier film comprising an inorganic thin film on the resin layer of a laminated polyester film according to claim 12.

14. The gas barrier film according to claim 11 or 13, wherein the inorganic thin film is formed from an inorganic substance selected from the group consisting of silicon, aluminum, magnesium, zinc, tin, nickel, titanium, or oxides, carbides, nitrides, or mixtures thereof.

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