Polyester-based sealant film

Abstract

To provide a polyester-based sealant film that, while being a monomaterial, offers easy peelability and sufficient sealing strength, and is less likely to tear or break when the heat-sealed film is peeled off a plastic container. [Solution] A polyester sealant film having a heat-sealable sealing layer and a heat-resistant layer laminated on the sealing layer, wherein the film has a tear resistance of 140N or more in the longitudinal and width directions, a tensile breaking strength of 140MPa or more in the longitudinal and width directions at room temperature, and a heat seal strength of 6-15N / 15mm when the A-PET sheet and the sealing layer are overlapped and heat-sealed at 160°C for 1 second under a load of 0.2MPa.

Description

Technical Field

[0001] The present invention relates to a polyester-based sealant film that is a single material but has easy peelability and sufficient seal strength, and is difficult to tear or cut when peeling a film heat-sealed to a plastic container.

Background Art

[0002] Packaging of foods and the like using plastic containers has been widely carried out. As a lid material for such containers, a fitting lid formed by molding a plastic such as A-PET has been used heretofore. Here, A-PET means an amorphous PET (amorphous polyethylene terephthalate) containing ethylene terephthalate units alone or in an amount of 50% by mass or more, and is usually non-oriented and non-crystalline. However, in recent years, in order to make lid materials common, reduce waste, and extend the expiration date, the filmization of lid materials for plastic containers has been promoted. These films for lid materials are required to have easy peelability that can be easily peeled by hand after heat sealing and sufficient seal strength so that the contents do not flow out after heat sealing.

[0003] Further, as a method for obtaining a sealant film capable of exhibiting such easy peelability and sufficient seal strength, there is a technique of laminating a seal layer and a support layer and delaminating the seal layer and the support layer (see, for example, Patent Documents 1 and 2).

[0004] However, in the above method, the seal layer and the support layer need to have different resin compositions in order to have appropriate delaminability (for example, when the seal layer is polyester, the support layer needs to be an olefin-based material such as polyethylene or polypropylene). Therefore, although the sealant film obtained by the above delamination has high functionality, it is not a single material (unifying each layer of a laminated film for packaging in which a plurality of layers are laminated with a single resin material), and thus recycling of the film required in recent years becomes difficult.

[0005] On the other hand, when delaminating a plastic container and film at the interface, a large load is placed on the film when peeling off the heat-sealed film from the plastic container, making the film prone to tearing or ripping. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2001-328221 [Patent Document 2] Japanese Patent Publication No. 2019-171792 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The objective of the present invention is to solve the problems of the prior art described above and to provide a polyester-based sealant film that, while being a monomaterial, provides easy peelability and sufficient sealing strength, and is less likely to tear or break when the film is heat-sealed to a plastic container. [Means for solving the problem]

[0008] The polyester-based sealant film of the present invention, which can solve the above problems, has the following configuration.

[0009] In other words, the present invention consists of the following configuration. 1. A polyester sealant film having a heat-sealable sealing layer and a heat-resistant layer laminated on the sealing layer, wherein the film has a tear resistance of 140 N or more in the longitudinal and width directions, a tensile breaking strength of 140 MPa or more in the longitudinal and width directions at room temperature, and a heat seal strength of 6 to 15 N / 15 mm when the A-PET sheet and the sealing layer are overlapped and heat-sealed at 160°C for 1 second under a load of 0.2 MPa. 2. The polyester-based sealant film described in item 1 above, wherein the haze content is 10% or less. 3. The polyester-based sealant film according to the first or second above, wherein the thermal shrinkage rate at 150°C in both the longitudinal and width directions is 0.01 to 3.0%. 4. The polyester sealant film according to any one of the first to third claims above, wherein the heat-resistant layer contains particles, the average particle size of the particles is 0.01 to 6 μm, and the particle content in the heat-resistant layer is 0.01 to 25% by mass. 5. A polyester sealant film according to any one of the first to fourth claims, wherein the contact angle with water of the surface of the sealing layer is 23° or less. 6. A polyester-based sealant film according to any one of the above 1 to 5, containing chemically recycled polyester. [Effects of the Invention]

[0010] The polyester sealant film of the present invention, while being a monomaterial, provides easy peelability and sufficient sealing strength, and exhibits properties that make it less likely for the film to tear or break when peeling off a heat-sealed film from a plastic container. [Modes for carrying out the invention]

[0011] (Technical meaning and significance of the physical properties described in this invention) In the present invention, the polyester sealant film preferably has a tensile breaking strength in the longitudinal and width directions at room temperature of 140 MPa or more, with a lower limit of 145 MPa more preferably, 150 MPa even more preferably, and 155 MPa particularly preferably. A tensile breaking strength of 140 MPa or more in the longitudinal and width directions at room temperature is preferable because it reduces the likelihood of the film tearing at the edges of the container during the initial stages of peeling after heat sealing the film to a plastic container. A higher tensile breaking strength in the longitudinal and width directions at room temperature is preferable because it makes the film tougher, but in the case of the polyester sealant film of the present invention, a strength of 300 MPa or less is also preferable.

[0012] In the present invention, the polyester sealant film preferably has a tear resistance of 140 N or more in the longitudinal and widthwise directions, with a lower limit of 145 N more preferably, 150 N even more preferably, and 155 N particularly preferably. A tear resistance of 140 N or more is preferable because it makes the film less likely to tear during the peeling process when heat-sealing it to a plastic container. While a higher tear resistance in the longitudinal and widthwise directions is preferable because it makes the film tougher, the polyester sealant film of the present invention is also preferable even if it is 500 N or less, as it can maintain adequate heat-sealability.

[0013] Furthermore, in this invention, it is preferable that the heat seal strength when the A-PET sheet and the seal layer are overlapped and heat-sealed at 160°C for 1 second under a load of 0.2 MPa is 6 to 15 N / 15 mm. The upper limit of the seal strength is more preferably 14 N / 15 mm, even more preferably 13 N / 15 mm, and particularly preferably 12 N / 15 mm. The lower limit of the seal strength is more preferably 7 N / 15 mm, even more preferably 8 N / 15 mm, and particularly preferably 9 N / 15 mm. A seal strength of 15 N / 15 mm or less is preferable because it provides easy opening. Also, a seal strength of 6 N / 15 mm or more is preferable because it provides sufficient seal strength, and after heat-sealing the film onto an A-PET container filled with food, the contents are less likely to leak.

[0014] In the polyester sealant film of the present invention, the haze is preferably 10% or less. The upper limit of the haze is more preferably 8%, even more preferably 6%, and particularly preferably 4%. A haze of 10% or less is preferable because the contents are clearly visible when the film is used as packaging or lid material. A haze as close to 0% as possible is preferable, but it is also preferable to have 0.1% or more, and also preferable to have 0.3% or more.

[0015] In the polyester-based sealant film of the present invention, it is preferable that the biaxial heat shrinkage rates in the longitudinal and width directions at 150 °C are both 0.01 to 3.0%. The lower limit value of the heat shrinkage rate at 150 °C is more preferably 0.1%, still more preferably 0.4%. On the other hand, the upper limit value of the heat shrinkage rate at 150 °C is more preferably 2.6%, still more preferably 2.2%, and particularly preferably 1.8%. Even if a film with a heat shrinkage rate in the longitudinal and width directions of the film at 150 °C less than 0.01% is produced, no significant difference is found in the practical effects, and the productivity is very low. Therefore, it is not necessary to make the heat shrinkage rate at 150 °C less than 0.01%. When the heat shrinkage rate at 150 °C is 3.0% or less, the shrinkage of the film during heat sealing is reduced, and the A-PET container is not deformed, which is preferable.

[0016] In the polyester-based sealant film of the present invention, the contact angle of the sealant layer with respect to water is preferably 23° or less. The upper limit value of the contact angle is more preferably 21°, still more preferably 19°, and particularly preferably 17°. When the contact angle is 23° or less, when the corresponding film is used as a packaging material or a lid material, the film is less likely to become cloudy and the contents look clear, which is preferable. The lower limit value of the contact angle is more preferably 5°, still more preferably 7°, and particularly preferably 9°. Even if a film with a contact angle less than 5° is produced, no significant difference is found in the practical effects, and the productivity may be very low. Therefore, it is preferable that the contact angle is 5° or more.

[0017] (Preferred embodiments of the film) As the film raw material in the present invention, in each layer of the sealant layer and the heat-resistant layer, it is preferable that polyester is contained at 50% by mass or more, and still more preferably 75% by mass or more. It can be any of homopolyester alone, copolyester alone, a blend of one or more homopolyesters or copolyesters, or a combination of homopolyester and copolyester.

[0018] When using a copolyester composed of an aromatic dicarboxylic acid component, ethylene glycol, and diethylene glycol as the copolyester described above, as the aromatic dicarboxylic acid component, terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, or their ester-forming derivatives are suitable. The amount of terephthalic acid and / or naphthalenedicarboxylic acid component relative to the total dicarboxylic acid component is preferably 70 mol% or more, more preferably 85 mol% or more, still more preferably 95 mol% or more, and particularly preferably 100 mol%.

[0019] Using only diethylene glycol as a copolymerization component in the seal layer is suitable for imparting good heat sealability. Furthermore, it is excellent in transparency and heat resistance, and due to its moderate crystallinity, crystallization is promoted during high-temperature heat sealing, so the seal strength does not become too high during high-temperature sealing, and it is also preferable in that an appropriate seal strength can be exhibited in a wide temperature range. Using only diethylene glycol as a copolymerization component in the seal layer described above means that the dicarboxylic acid component is only terephthalic acid, and the diol component is a copolyester composed of two kinds, ethylene glycol and diethylene glycol.

[0020] Also, when using a copolyester composed of an aromatic dicarboxylic acid component and a diol component containing diethylene glycol and ethylene glycol as the copolyester described above, when the diol component constituting the copolyester contained in the seal layer is set to 100 mol%, the ratio of the diethylene glycol component is preferably 14 to 20 mol%. The upper limit value of the diethylene glycol component ratio in the seal layer is more preferably 18.5 mol%, still more preferably 18 mol%, and particularly preferably 17.5 mol%. The lower limit value of the diethylene glycol component ratio in the seal layer is more preferably 14.5 mol%, still more preferably 15 mol%, and particularly preferably 15.5 mol%.

[0021] When the diol component constituting the copolymerized polyester in the seal layer is set to 100 mol%, setting the diethylene glycol component ratio to 14 mol% or more makes it easier to obtain appropriate amorphousness on the surface of the seal layer, resulting in sufficient seal strength. This is preferable because it makes it less likely for the contents to leak after the film is heat-sealed onto an A-PET container filled with food.

[0022] When the diol component constituting the copolymer polyester contained in the seal layer is set to 100 mol%, it is preferable to set the ratio of the diethylene glycol component to 20 mol% or less, as this makes it easier to obtain a moderate amorphousness on the surface of the seal layer and thus easier to peel.

[0023] Furthermore, in the heat-resistant layer, it is preferable that the ethylene glycol component ratio is 70 to 100 mol% when the diol component constituting the polyester contained in the heat-resistant layer is set to 100 mol%. The lower limit of the ethylene glycol component ratio in the heat-resistant layer is more preferably 75 mol%, even more preferably 80 mol%, and particularly preferably 85 mol%. Setting the ethylene glycol component ratio of the heat-resistant layer to 70 to 100 mol% makes it easier to control the melting point of the heat-resistant layer to 200°C or higher, and suppresses the film from sticking to the seal bar during heat sealing, which is therefore preferable. The diol component constituting the polyester contained in the heat-resistant layer may be 100 mol% ethylene glycol, but if it is a copolymer polyester containing other diol components, it is preferable that the other diol components are diethylene glycol.

[0024] In the present invention, examples of catalysts that can be used when producing polyester include alkaline earth metal compounds, manganese compounds, cobalt compounds, aluminum compounds, antimony compounds, titanium compounds, titanium / silicon composite oxides, and germanium compounds. Among these, titanium compounds, antimony compounds, germanium compounds, and aluminum compounds are preferred from the viewpoint of catalytic activity.

[0025] When manufacturing the polyester, it is preferable to add a phosphorus compound as a heat stabilizer. Preferred phosphorus compounds include, for example, phosphoric acid and phosphorous acid.

[0026] The polyester preferably has an intrinsic viscosity of 0.70 dl / g or higher, more preferably 0.73 dl / g or higher, and particularly preferably 0.76 dl / g or higher. Setting the intrinsic viscosity to 0.70 dl / g or higher improves film formation stability while increasing the entanglement of molecular chains in the resulting film, making it easier to control the edge tear resistance in the longitudinal and width directions to 140 N or higher, and the tensile breaking strength in the longitudinal and width directions at room temperature to 140 MPa or higher. Furthermore, if a filter for removing foreign matter is provided in the melt line, it is preferable to set the upper limit of the intrinsic viscosity to 1.0 dl / g from the viewpoint of discharge stability during extrusion of the molten resin.

[0027] Furthermore, this polyester-based sealant film may also contain chemically recycled polyester.

[0028] Chemically recycled polyester is obtained by breaking down the polyester contained in used polyester products to the monomer level and then repolymerizing it. Because chemically recycled polyester is manufactured using polyester contained in used polyester products as raw material, it can reduce the environmental impact. Moreover, because foreign substances (such as catalysts, colorants, different plastics, and metals) are removed during the recycling process, chemically recycled polyester is more hygienic than mechanically recycled polyester.

[0029] Used polyester products can be cited as examples of polyester that can be broken down to the monomer level. Used polyester products may be in the form of bales, flakes, or pellets. Used PET bottles are preferred as examples of used polyester products.

[0030] One method for decomposing polyester to the monomer level is to crush and wash a PET bottle bale, then add at least ethylene glycol (EG) and a catalyst to it and heat it to decompose it to bis-2-hydroxyethyl terephthalate (BHET) (hereinafter sometimes referred to as the "BHET method") (see Japanese Patent Publication No. 2000-169623). Another method for decomposing polyester to the monomer level is, for example, the method described in Japanese Patent Publication No. 2000-302707. Of course, polyester may be decomposed to the monomer level by methods other than those exemplified herein.

[0031] Regarding the BHET method, here is an example of the procedure for obtaining BHET by decomposing polyethylene terephthalate, which makes up used PET bottles. The PET bottle bale is put into a shredder and wet shredded. In wet shredded, washing water (even If necessary, the PET bottle bales can be crushed in tap water or groundwater to which detergent has been added. The washing water may be at room temperature or heated. The washing water is discharged from the crusher along with the PET bottle flakes, and foreign matter (e.g., metal, stone, glass, sand) is removed by specific gravity separation. Next, the flakes are rinsed with deionized water and centrifugal dehydration is performed if necessary. After melting the flakes, a catalyst or excess ethylene glycol is added and heated (i.e., depolymerization is performed). This allows the polyethylene terephthalate constituting the flakes to be depolymerized, and as a result, a depolymerization solution in which BHET is dissolved in ethylene glycol can be obtained. It is preferable to melt the flakes in a state containing moisture (e.g., in a state containing moisture after centrifugal dehydration). Foreign matter (e.g., different plastics, metals, glass) that is suspended or precipitated in the depolymerization solution is removed. Since the melting point of cyclic oligomers in the depolymerization solution is higher than that of polyethylene terephthalate, low molecular weight components such as cyclic oligomers can also be removed by filtration. The depolymerization solution is passed through activated carbon (i.e., liquid-through), and then through an ion exchange resin. Passing the depolymerization solution through activated carbon removes coloring components (e.g., pigments, dyes, compounds produced by the thermal degradation of organic matter). Passing the depolymerization solution through an ion exchange resin removes catalysts (e.g., polymerization catalysts, depolymerization catalysts) and metal ions. Next, the depolymerization solution is cooled to precipitate BHET, and then BHET and ethylene glycol are separated by solid-liquid separation. Vacuum evaporation is performed to remove the ethylene glycol remaining in the BHET (i.e., to concentrate the BHET). Molecular distillation is performed on the concentrated BHET. High-purity BHET can be obtained using this procedure. Although the operation of separating BHET and ethylene glycol by solid-liquid separation followed by vacuum evaporation has been described here, ethylene glycol may be distilled from the depolymerization solution instead.

[0032] Examples of chemically recycled polyesters include chemically recycled polyethylene terephthalate (hereinafter sometimes referred to as "chemically recycled PET"), chemically recycled polybutylene terephthalate, and chemically recycled polyethylene-2,6-naphthalate. Of course, these may also contain copolymer components. Chemically recycled PET is preferred because it is readily available and has excellent mechanical properties and heat resistance. These may be used individually or in combination of two or more.

[0033] Chemically recycled polyester may contain copolymers of other components. Examples of dicarboxylic acid components as copolymers include isophthalic acid, naphthalenedicarboxylic acid, 4,4-diphenyldicarboxylic acid, adipic acid, sebacic acid, and their ester-forming derivatives. On the other hand, examples of diol components as copolymers include diethylene glycol, hexamethylene glycol, neopentyl glycol, and cyclohexanedimethanol. Similarly, polyoxyalkylene glycols such as polyethylene glycol and polypropylene glycol can also be used. These may be used individually or in combination of two or more. Considering that PET, which constitutes PET bottles, generally contains copolymers of isophthalic acid to improve moldability into bottles, it is preferable that chemically recycled PET contains at least an isophthalic acid component as a copolymer.

[0034] When the total number of moles of dicarboxylic acid components in the chemically recycled polyester is taken as 100 mol%, the number of moles of copolymer components is preferably 10 mol% or less, more preferably 8 mol% or less, even more preferably 5 mol% or less, and still more preferably 3 mol% or less. The number of moles of copolymer components is preferably 0.1 mol% or more, more preferably 1 mol% or more, and even more preferably 2 mol% or more. The chemically recycled polyester may contain one or more copolymer components that satisfy these preferred number of moles.

[0035] When the chemically recycled polyester is chemically recycled PET, the number of moles of isophthalic acid components is preferably 10 mol% or less, more preferably 8 mol% or less, even more preferably 5 mol% or less, and still more preferably 3 mol% or less, when the total number of moles of dicarboxylic acid components in the chemically recycled PET is taken as 100 mol%. The number of moles of isophthalic acid components is preferably 0.1 mol% or more, more preferably 1 mol% or more, and even more preferably 2 mol% or more. The chemically recycled PET may contain one or more types of isophthalic acid components that satisfy these preferred number of moles.

[0036] The intrinsic viscosity of the chemically recycled polyester is preferably 0.50 dl / g or higher, more preferably 0.55 dl / g or higher, and even more preferably 0.57 dl / g or higher. A viscosity of 0.50 dl / g or higher allows for limiting the amount of low molecular weight components in the chemically recycled polyester to a certain extent, thereby further reducing the yellowish tint that the polyester film may exhibit. On the other hand, the intrinsic viscosity of the chemically recycled polyester is preferably 0.90 dl / g or lower, more preferably 0.85 dl / g or lower, even more preferably 0.80 dl / g or lower, even more preferably 0.75 dl / g or lower, and even more preferably 0.69 dl / g or lower. A viscosity of 0.90 dl / g or lower allows for limiting the intrinsic viscosity of the polyester film to a certain extent, thereby further preventing excessive stress during stretching (i.e., tensile stress) in the polyester film manufacturing process, and consequently further suppressing or reducing film breakage that may occur during stretching. Furthermore, the chemically recycled polyester may contain one or more types that satisfy such suitable intrinsic viscosity.

[0037] In the molecular weight distribution curve obtained by gel permeation chromatography (GPC) of chemically recycled polyester, the area percentage of the region with a molecular weight of 1000 or less may be 3.5% or less, 3.0% or less, 2.5% or less, 2.2% or less, or 2.0% or less of the total peak area. On the other hand, this area percentage may be 0.8% or more, 1.0% or more, or 1.2% or more.

[0038] The melting resistivity at 285°C in chemically recycled polyester is, for example, 30.0 × 10⁻⁶. 8 It may be less than or equal to Ω ·cm, and 25.0 × 10 8 It may be less than or equal to Ω ·cm, and 20.0 × 10 8 It may be less than or equal to Ω·cm, and 15.0 × 10 8 It may be less than Ω·cm. The melting resistivity at 285°C in chemically recycled polyester is, for example, 0.5 × 10⁻⁶. 8 It may be greater than or equal to Ω·cm, and 1.5 × 10 8 It may be greater than or equal to Ω·cm, and 3.0 × 10 8 It may be greater than or equal to Ω·cm, and 5.0 × 10 8 It may be Ω·cm or greater. Furthermore, the chemically recycled polyester may contain one or more types that satisfy these suitable melting resistivity requirements.

[0039] The magnesium compound content in the chemically recycled polyester may be, for example, less than 30 ppm, 20 ppm or less, 10 ppm or less, 5 ppm or less, 3 ppm or less, or 0 ppm, based on magnesium atoms (i.e., in terms of magnesium atoms). The chemically recycled polyester may contain one or more types of magnesium compounds that satisfy such a suitable magnesium compound content.

[0040] The phosphorus compound content in the chemically recycled polyester may be 10 ppm or more, 15 ppm or more, 20 ppm or more, or 30 ppm or more, based on phosphorus atoms (i.e., in terms of phosphorus atoms). On the other hand, the phosphorus compound content may be 300 ppm or less, 200 ppm or less, or 100 ppm or less, based on phosphorus atoms. Here, the phosphorus compound content is the mass of the phosphorus compound based on phosphorus atoms relative to the mass of the chemically recycled polyester (i.e., mass of the phosphorus compound based on phosphorus atoms / mass of the chemically recycled polyester). The chemically recycled polyester may contain one or more types of phosphorus compounds that satisfy these preferred phosphorus compound content requirements.

[0041] The thickness of the heat-resistant layer is preferably 5 μm or more. The lower limit of the thickness of the heat-resistant layer is more preferably 10 μm, and particularly preferably 15 μm. On the other hand, the upper limit of the thickness of the heat-resistant layer is preferably 70 μm, and more preferably 60 μm. A thickness of 5 μm or more for the heat-resistant layer is preferable because it makes it easier to obtain a film that is less likely to break during film formation or when peeling the film after heat sealing. Furthermore, a thickness of 70 μm or less for the heat-resistant layer is preferable because it makes it easier to obtain a film with excellent thickness accuracy as the stress tends to increase when stretching the film.

[0042] The sealing layer can be formed by coating or co-extrusion. Of these, co-extrusion is preferable because it does not require solvents, thus reducing environmental impact and improving cost-effectiveness.

[0043] The thickness of the seal layer is preferably 5 μm or more. The lower limit of the seal layer thickness is more preferably 7 μm, and particularly preferably 9 μm. On the other hand, the upper limit of the seal layer thickness is preferably 30 μm, more preferably 25 μm, and particularly preferably 20 μm. A seal layer thickness of 5 μm or more is preferable because it makes it less likely for cohesive failure of the seal layer to occur when peeling off the heat-sealed film, and sufficient heat seal strength can be easily obtained. Furthermore, a seal layer thickness of 30 μm or less is preferable because it makes it easier to obtain a film with excellent thickness accuracy because the stress increases when stretching the film.

[0044] The thickness of the laminated film is preferably 30 μm or more. The lower limit of the thickness of the laminated film is more preferably 35 μm, and particularly preferably 40 μm. On the other hand, the upper limit of the thickness of the laminated film is preferably 80 μm, more preferably 75 μm, and particularly preferably 70 μm. A thickness of 30 μm or more is preferable because it makes the film less likely to tear when peeling off the heat-sealed film. Furthermore, a thickness of 80 μm or less is preferable because it allows heat to be easily transferred to the surface of the sealing layer during heat sealing, making it easier to obtain appropriate heat seal strength.

[0045] Furthermore, to improve the handling properties of the film, such as its slipperiness and winding ability, it is preferable to form irregularities on the film surface. A suitable method for forming irregularities on the film surface is to incorporate particles into the film. When incorporating particles into the film, they may be incorporated into the sealing layer, but it is preferable to incorporate them mainly into the heat-resistant layer.

[0046] Examples of the aforementioned particles include internally precipitated particles, inorganic particles, and / or organic particles with an average particle diameter of 0.01 to 6 μm. Using particles with an average particle diameter of 6 μm or less is preferable because it reduces the likelihood of film defects and makes it easier to obtain good design and transparency. Furthermore, setting the average particle diameter of the aforementioned particles to 0.01 μm or more is preferable because it provides good slipperiness and windability of the film, resulting in good handling. From the viewpoint of handling properties such as slipperiness and windability, the lower limit of the average particle diameter of the aforementioned particles is more preferably 0.1 μm, and even more preferably 0.5 μm. On the other hand, from the viewpoint of transparency and reduction of film defects due to coarse protrusions, the upper limit of the average particle diameter of the aforementioned particles is more preferably 5 μm, and even more preferably 2 μm.

[0047] The average particle diameter can be calculated by taking multiple photographs of at least 200 particles using scanning electron microscopy (SEM), tracing the particle contours onto an OHP film, and converting the traced images to an equivalent diameter using an image analysis device.

[0048] As the external particles, for example, inorganic particles such as wet and dry silica, colloidal silica, aluminum silicate, titanium oxide, calcium carbonate, calcium phosphate, barium sulfate, alumina, mica, kaolin, clay, and hydroxyapatite, and organic particles composed of styrene, silicone, acrylic acids, etc., can be used. In particular, inorganic particles such as dry, wet, and dry colloidal silica and alumina, and organic particles composed of styrene, silicone, acrylic acid, methacrylic acid, polyester, divinylbenzene, etc., are preferably used. Two or more of these internal particles, inorganic particles, and / or organic particles may be used in combination within a range that does not impair the properties defined in the present invention.

[0049] Furthermore, the content of the particles in the film is preferably in the range of 0.01 to 25% by mass. A content of 0.01% by mass is preferable because it makes it easier to obtain good slipperiness in the film, improves winding performance, and provides good handling performance. A content of 25% by mass or less is also preferable because it makes it easier to obtain good transparency, makes it less likely for coarse protrusions to form, and makes it easier to obtain good film-forming properties and transparency.

[0050] To obtain high transparency while maintaining the handling properties of the film, it is preferable that the heat-resistant layer is constructed by laminating a base layer and a surface layer, with a sealing layer laminated on the surface of the base layer within the heat-resistant layer, wherein the surface layer has particles and preferably has a thickness of 0.01 to 3 μm. The upper limit of the thickness of the surface layer is more preferably 2.5 μm, and particularly preferably 2 μm. In this case, the particles can be those exemplified above.

[0051] In the present invention, in order to reduce the film haze to 10% or less, it is preferable to have a laminated structure in which the substrate layer is substantially free of particles, and a surface layer with a thickness of 0.01 to 3 μm is formed, with particles contained only in the surface layer.

[0052] Furthermore, the phrase "substantially free of particles in the substrate layer" as used above means, for example, in the case of inorganic particles, that the amount of inorganic elements is below the detection limit when quantified by fluorescence X-ray analysis. This is because even without intentionally adding particles to the substrate layer, contaminants from foreign substances may be mixed in. To obtain a film with low haze and high aesthetic appeal, it is preferable to substantially free of particles in the substrate layer, but it is acceptable to add particles to the substrate layer if the amount is 30 ppm or less.

[0053] On the other hand, when silica particles with an average particle size of 1.5 μm or less are used as the particles to be contained in the surface layer, the cut edges of the film and waste film generated during paper feeding may be melted again and incorporated into the base layer. In this case, it is preferable that the particle content in the base layer be 1500 ppm or less. When using silica particles with an average particle size of 1.5 μm or less, it is preferable to have a particle content of 1500 ppm or less in the base layer because it is easier to obtain a film with low haze and excellent design. By reusing the film in this way, the amount of film discarded is reduced, and environmental adaptability is improved.

[0054] The particles to be contained in the surface layer can be the same as those described above. Among the particles, silica particles, glass fillers, and silica-alumina composite oxide particles are particularly suitable in terms of transparency because their refractive index is relatively close to that of polyester.

[0055] The heat-resistant layer constituting the polyester sealant film of the present invention can be laminated using different types of polyester compositions and known methods to impart other functions. The form of such a laminated film is not particularly limited, but for example, when the layers formed by different extruders are the surface layer X, the base layer Y, and the other layer Z, examples of laminated forms include a two-layer configuration of X / Y, a three-layer configuration of X / Y / X, and a three-layer configuration of X / Y / Z. In the case of a two-layer configuration of X / Y, it is preferable that the seal layer is laminated on the side of the base layer Y that is not laminated with the surface layer X. In the case of a three-layer configuration of X / Y / Z, it is preferable that the seal layer is laminated on the side of the other layer Z that is not laminated with the base layer Y.

[0056] The polyester sealant film of the present invention is preferably a biaxially oriented film. In the present invention, molecular orientation due to biaxial orientation improves the solvent resistance and dimensional stability, which are drawbacks of unoriented sheets.

[0057] The method for producing the biaxially oriented polyester film is not particularly limited, but an example is to dry the polyester resin as needed, then supply it to a known melt extruder, extrude it into a sheet from a slit-shaped die, press it against a casting drum using methods such as electrostatic application, cool and solidify it to obtain an unstretched sheet (raw material), and then biaxially stretch the unstretched sheet. Co-extrusion, in which polyester raw materials for forming the heat-resistant layer and polyester raw materials for forming the seal layer are melt-extruded from separate extruders and laminated, is also preferred, and the heat-resistant layer may further be composed of a surface layer and a base layer that are laminated by co-extruding polyester raw materials separately.

[0058] As a biaxial stretching method, a method is employed in which an unstretched sheet is stretched in the longitudinal direction (MD) and the width direction (TD) of the film, heat-treated, and a biaxially oriented film with the desired degree of in-plane orientation is obtained. Among these methods, in terms of film quality, sequential biaxial stretching methods such as the MD / TD method, where the sheet is stretched in the longitudinal direction first and then in the width direction, or the TD / MD method, where the sheet is stretched in the width direction first and then in the longitudinal direction, or simultaneous biaxial stretching methods, where the sheet is stretched in the longitudinal and width directions almost simultaneously, are desirable. In the case of simultaneous biaxial stretching, a tenter driven by a linear motor may be used. Furthermore, if necessary, a multi-stage stretching method may be used, in which stretching in the same direction is divided into multiple stages.

[0059] When biaxially stretching the film, the stretching ratio is preferably 3.5 to 4.0 times in the longitudinal direction, and particularly preferably 3.6 to 3.9 times. Furthermore, when biaxially stretching the film, the stretching ratio is preferably 3.3 to 4.0 times in the width direction, and particularly preferably 3.4 to 3.9 times. It is preferable to set the stretching ratio within the above range because it facilitates the formation of appropriately oriented crystals in the longitudinal and width directions, making it easier to control the edge tear resistance in the longitudinal and width directions to 140 N or more, and the tensile breaking strength in the longitudinal and width directions at room temperature to 140 MPa or more.

[0060] When manufacturing the polyester sealant film of the present invention, it is preferable to use the following conditions for stretching.

[0061] In longitudinal stretching, it is preferable to set the stretching temperature to 50-150°C and the stretching ratio to 3.5-4.0 times so that transverse stretching, which is usually performed later, can be carried out smoothly.

[0062] Furthermore, after biaxial stretching, the film is further heat-treated in a tenter. The heat treatment is preferably carried out in a temperature range of 220 to 230°C. The lower limit of the heat treatment temperature is more preferably 223°C, and the upper limit of the heat treatment temperature is more preferably 227°C. A heat treatment temperature of 220°C or higher is preferable because it melts the crystals of the seal layer, making it easier to achieve appropriate heat sealability. Also, a heat treatment temperature of 230°C or lower makes it easier to obtain stable film formation, and prevents excessive growth of the oriented crystals of the heat-resistant layer, making it easier to control the edge tear resistance in the longitudinal and width directions to 140 N or higher, and the tensile breaking strength in the longitudinal and width directions at room temperature to 140 MPa or higher. The heat treatment can be either tension heat treatment or relaxation heat treatment. To reduce the thermal shrinkage rate, a relaxation heat treatment of 3 to 10% is preferred.

[0063] Generally, methods for reducing the heat shrinkage rate at 150°C include reducing the stretch ratio and reducing the amount of copolymer components. However, the former method may worsen the thickness unevenness of the film, and the latter method increases the crystallinity of the seal layer, worsening the heat sealability, which is therefore undesirable. In the present invention, it is preferable to perform heat fixing to reduce the heat shrinkage rate of the polyester sealant film at 150°C.

[0064] Furthermore, when using a film as a lid material, a surfactant may be added to the film to prevent condensation and fogging caused by water vapor inside the container. In this case, it is preferable to add the surfactant only to the sealing layer and not to the heat-resistant layer, as this allows for both fogging suppression and film transparency.

[0065] Furthermore, it is preferable that the amount of surfactant added be 0.9% by mass or less of the total weight of the polyester sealant film. The upper limit of the weight ratio of surfactant to the total film is more preferably 0.8% by mass, and particularly preferably 0.7% by mass. It is preferable to keep the weight ratio of surfactant to the total film at 0.9% by mass or less because it makes it easier to control the haze to 10% or less.

[0066] The polyester sealant film of the present invention may be surface-treated to prevent water droplets from adhering to the film and causing fogging due to water vapor inside the container when used as a lid material. Examples of surface treatment methods include corona discharge treatment and plasma treatment, and there are no particular limitations. It is preferable to perform corona discharge treatment or plasma treatment, which can be performed continuously and can be easily carried out before the winding process in the manufacturing process of this film. [Examples]

[0067] The present invention will be described in detail below with reference to examples. The film properties obtained in each example were measured and evaluated by the following methods.

[0068] (1) Intrinsic viscosity A 0.1 g chip sample was accurately weighed and dissolved in 25 ml of a phenol / tetrachloroethane mixed solvent (60 / 40 mass ratio). The viscosity was measured at 30°C using an Ostwald viscometer. Three measurements were performed, and the average value was calculated.

[0069] (2) Haze In accordance with JIS K7136:2000, the haze of the film was measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., 300A). Two measurements were taken, and the average value was calculated.

[0070] (3) Film thickness Using the former Seiko EM Millitron 1202D, we measured 5 points on each of the 3 cards, for a total of 15 points, and calculated the average value.

[0071] (4) Thermal shrinkage rate at 150°C Cut strips of film, 150 mm in length and 20 mm in width, from the longitudinal and width directions, respectively. Mark two points 100 mm apart along the length of each strip and measure the distance A between the two points under no load. Suspend one end of each strip of film in a basket with a clip under no load and place it in a gear oven at 150°C, simultaneously timing the process. After 30 minutes, remove the basket from the gear oven and leave it at room temperature for 30 minutes. Then, for each sample, read the distance B under no load. Calculate the thermal shrinkage rate of each sample at 150°C using the following formula based on the measured distances A and B. Thermal shrinkage rate (%) = {(AB) / A} × 100

[0072] (5) End tear resistance In accordance with JIS C2318:1975, measurements were taken at three points in the longitudinal and widthwise directions of the roll sample: the right end, the center, and the left end. The average value of the three points cut from each position was used as the edge tear resistance.

[0073] (6) Heat seal strength Heat seal strength was measured in accordance with JIS Z1707:2019. The specific procedure is as follows: Using a heat sealer "TYB-300" (manufactured by Seibu Kikai), the seal layer of the film sample was bonded to the A-PET sheet obtained as described below. The heat sealing conditions were a top bar temperature of 160°C, a pressure of 0.2 MPa, and a time of 1 second. The bonded heat-sealed sample was cut to a seal width of 15 mm. Peel strength was measured using a universal tensile testing machine "DSS-100" (manufactured by Shimadzu Corporation) at a tensile speed of 200 mm / min. Peel strength is expressed as strength per 15 mm (N / 15 mm). Furthermore, if the heat-sealed film does not tear when peeled, it is classified as ○ (film tear resistance), and if the heat-sealed film tears when peeled, it is classified as × (film tear resistance).

[0074] (7) Tensile breaking strength Measurements were taken in accordance with JIS K 7127:1999. Samples measuring 10 mm in width and 180 mm in length were cut from the film using a razor blade in both the longitudinal and lateral directions. After being left for 12 hours in an atmosphere of 23°C and 65% RH, measurements were taken under the conditions of 23°C and 65% RH, with a chuck distance of 100 mm and a tensile speed of 200 mm / min. The average of five measurement results was used. A Shimadzu Autograph AG5000A was used as the measuring instrument.

[0075] (8) Film formation of A-PET sheets for evaluation A polyethylene terephthalate chip (A) with an intrinsic viscosity of 0.62 dl / g, comprising 100 mol% terephthalic acid units as the aromatic dicarboxylic acid component and 100 mol% ethylene glycol units as the diol component, was dried. The chip (A) was melt-extruded at 280°C through the slit of a T-die using an extruder, rapidly cooled and solidified on a chill roll with a surface temperature of 20°C, and simultaneously adhered to the chill roll using an electrostatic application method to obtain an A-PET sheet with a thickness of 220 μm.

[0076] (9) Contact angle Under conditions of 25°C and 50% RH, a contact angle meter (Kyowa Interface Science Co., Ltd., fully automatic contact angle meter DM-701) was used to prepare droplets of water (droplet volume 0.9 μL) on the surface of the film's sealing layer, and the contact angle was measured. The contact angle was recorded 30 seconds after droplet placement on the film, and the average of five measurements was used.

[0077] (10) Anti-fogging properties 1) Pour 300cc of 53°C warm water into a 500cc container with an open top. 2) With the sealing layer of the film facing inward, seal the container opening with the film. 3) Leave at 5°C for 30 minutes. 4) The degree of dew adhesion to the film surface was evaluated. Areas with dew covering up to 1 / 10 were rated as ○, while areas with more than 1 / 10 were rated as △.

[0078] Example 1 The separated and collected PET bottle bales were crushed while circulating them in a wet crusher with a washing solution (specifically, a washing solution made by adding 500g of liquid dish soap to 1000 liters of water). A specific gravity separator connected to the wet crusher was used to settle foreign matter with a high specific gravity, such as metal, sand, and glass, and flakes were taken from the upper layer. These flakes were rinsed with pure water and dehydrated by centrifugal force. The recovered flakes were obtained using this procedure. 30 kg of the molten, undried recovered flakes were mixed in a stirring autoclave with a preheated mixture, specifically a mixture of 150 kg of ethylene glycol and 150 g of zinc acetate dihydrate, and then sediments with lower boiling points than ethylene glycol, such as water and acetic acid, were removed. Next, the mixture was reacted for 4 hours at a temperature of 195°C to 200°C using a reflux condenser. After the reaction was complete, the reactor contents were cooled to 97°C-98°C, and then hot filtration was performed using a filter to remove suspended solids and precipitates. The filtrate was further cooled to confirm that the crude BHET was completely dissolved, and then the filtrate was passed through an activated carbon bed at 50°C-51°C, followed by an anion / cation exchange mixed bed, for 30 minutes. In other words, it underwent a pre-purification treatment. The pre-purified liquid was charged into a stirred autoclave and heated to distill off excess ethylene glycol at atmospheric pressure to obtain a molten concentrated BHET. The molten concentrated BHET was allowed to cool naturally while being stirred under a nitrogen gas atmosphere, and then removed from the stirred autoclave to obtain a fragment block of concentrated BHET. The fragment block was heated to 130°C and melted, then supplied to a thin-film vacuum evaporator using a metering pump, evaporated, and cooled and condensed to obtain purified BHET. 2650 kg of this purified BHET was supplied all at once to a dissolution tank purged with nitrogen, and after purging with nitrogen again, dissolution was carried out at a dissolution tank temperature of 150°C. After dissolution was complete, the temperature of the dissolution tank was raised to 230°C over 30 minutes while stirring.2650 kg of the obtained BHET solution was transferred to a polycondensation reactor. To the BHET solution, 300 ppm antimony trioxide, 170 ppm cobalt acetate, 55 ppm phosphoric acid, and 0.3 wt% titanium dioxide were added relative to the amount of PET to be obtained (approximately 2000 kg of PET can be obtained from 265 kg of BHET). The temperature of the polycondensation reactor was gradually increased from 230°C to 290°C while stirring at 10-40 rpm, and the pressure was reduced to 40 Pa. After reaching the predetermined stirring torque, the polycondensation reactor was purged with nitrogen to return to atmospheric pressure and stop the polycondensation reaction. The solution was then discharged in strand form, cooled, and immediately cut to obtain chip-shaped polyester. Following this procedure, chemically recycled polyester, i.e., chip C, with an intrinsic viscosity of 0.59 dl / g was obtained.

[0079] Polyester C (i.e., chemically recycled polyester with an intrinsic viscosity of 0.59 dl / g) was continuously supplied to a crystallization apparatus and crystallized at 150°C. After crystallization, it was supplied to a dryer and dried at 130°C for 10 hours. The dried polyester C was sent to a preheater and heated to 180°C before being supplied to a solid-phase polymerization apparatus. The solid-phase polymerization reaction was carried out at 190°C for 24 hours under nitrogen gas to obtain chemically recycled polyester, i.e., chip B, with an intrinsic viscosity of 0.79 dl / g.

[0080] Chips (D) and (B) of a copolymer polyester with an intrinsic viscosity of 0.68 dl / g, comprising 100 mol% terephthalic acid units as an aromatic dicarboxylic acid component, and 78 mol% ethylene glycol units and 22 mol% diethylene glycol units as diol components, were dried. Chips (E) of polyethylene terephthalate, with an intrinsic viscosity of 0.62 dl / g and containing 0.72 mass% amorphous silica with an average particle size (SEM method) of 2.7 μm, were dried. Chips (F) of Takemoto Oil & Fat Co., Ltd., mainly composed of polyethylene terephthalate and containing 20 mass% surfactant, were also dried. Furthermore, chips (B) and (E) were mixed in a mass ratio of 87.5:12.5 (mixed raw material 1). In addition, chips (D), (B), and (F) were mixed in a mass ratio of 81.8:7.2:11.0 (mixed raw material 2). Next, the chip (B) was melt-extruded at 280°C through a slit in a T-die using an extruder, forming a 57% by mass base layer (base layer Y), an 8% by mass surface layer (surface layer X) on one side of the base layer with mixed raw material 1, and a 35% by mass surface layer (seal layer Z) on the other side of the base layer (a three-layer configuration of surface layer X / base layer Y / seal layer Z). The sheet was then rapidly cooled and solidified on a chill roll at a surface temperature of 20°C, and simultaneously, an amorphous unstretched sheet was obtained by adhering it to the chill roll using an electrostatic application method.

[0081] The obtained unstretched sheet was stretched 3.5 times in the longitudinal direction at 115°C between a heating roll and a cooling roll. Next, the uniaxially oriented film was guided to a tenter, heated at 105°C for 16 seconds, and then transversely stretched 4.0 times at 120°C. Furthermore, after heat treatment at 230°C and a 5% relaxation treatment in the transverse direction, corona discharge treatment was performed on the surface of the sealing layer using a corona discharge treatment machine manufactured by Kasuga Electric Co., Ltd. at an output of 0.3 kW to obtain a biaxially oriented polyester film with a thickness of 30 μm.

[0082] Example 2 A biaxially oriented polyester film was obtained in the same manner as in Example 1, except that a polyethylene terephthalate chip (G) with an intrinsic viscosity of 0.72 dl / g was used instead of chip (C) in Example 1.

[0083] Example 3 A biaxially oriented polyester film was obtained in the same manner as in Example 1, except that the raw materials for the seal layer Z were mixed in a mass ratio of chip (D), chip (B), and chip (F) of 81.8:5.2:13.0.

[0084] Example 4 A biaxially oriented polyester film was obtained in the same manner as in Example 1, except that the raw materials for the seal layer Z were mixed in a mass ratio of chip (D), chip (B), and chip (F) of 81.8:13.2:6.0.

[0085] Example 5 In Example 1, a biaxially oriented polyester film was obtained in the same manner as in Example 1, except that the raw materials for the seal layer Z were mixed with chips (D) and chips (B) in a mass ratio of 81.8:18.2, and the heat treatment temperature after transverse stretching was set to 220°C.

[0086] Example 6 A biaxially oriented polyester film was obtained in the same manner as in Example 1, except that the heat treatment temperature after transverse stretching was set to 225°C.

[0087] Example 7 A biaxially oriented polyester film was obtained in the same manner as in Example 1, except that the raw materials for the seal layer Z were mixed in a mass ratio of chip (D), chip (B), and chip (F) of 63.6:25.4:11.0.

[0088] Example 8 A biaxially oriented polyester film was obtained in the same manner as in Example 1, except that the raw materials for the seal layer Z were mixed with chips (D) and chips (F) in a mass ratio of 89.0:11.0.

[0089] Example 9 A biaxially oriented polyester film was obtained in the same manner as in Example 1, except that the film thickness after biaxial stretching was set to 80 μm.

[0090] Example 10 A biaxially oriented polyester film was obtained in the same manner as in Example 1, except that the transverse stretching ratio was set to 3.3 times.

[0091] Example 11 A biaxially oriented polyester film was obtained in the same manner as in Example 1, except that the longitudinal stretching ratio was set to 4.0 times.

[0092] Example 12 A biaxially oriented polyester film was obtained in the same manner as in Example 1, except that a polyethylene terephthalate chip (H) with an intrinsic viscosity of 0.79 dl / g was used instead of chip (C) in Example 1.

[0093] Comparative Example 1 A biaxially oriented polyester film was obtained in the same manner as in Example 1, except that the raw materials for the seal layer Z were mixed with chips (D) and chips (B) in a mass ratio of 81.8:18.2.

[0094] Comparative Example 2 A biaxially oriented polyester film was obtained in the same manner as in Example 1, except that the heat treatment temperature after transverse stretching was set to 220°C.

[0095] Comparative Example 3 A biaxially oriented polyester film was obtained in the same manner as in Example 1, except that the heat treatment temperature after transverse stretching was set to 235°C.

[0096] Comparative Example 4 A biaxially oriented polyester film was obtained in the same manner as in Example 1, except that the raw materials for the seal layer Z were mixed in a mass ratio of chip (D), chip (B), and chip (F) of 54.5:34.5:11.0.

[0097] Comparative Example 5 A biaxially oriented polyester film was obtained in the same manner as in Example 1, except that the film thickness after biaxial stretching was set to 20 μm.

[0098] Comparative Example 6 A biaxially oriented polyester film was obtained in the same manner as in Example 1, except that the film thickness after biaxial stretching was set to 100 μm.

[0099] Comparative Example 7 A biaxially oriented polyester film was obtained in the same manner as in Example 1, except that a polyethylene terephthalate chip (A) with an intrinsic viscosity of 0.63 dl / g was used instead of chip (B) in Example 1.

[0100] Comparative Example 8 A biaxially oriented polyester film was obtained in the same manner as in Example 1, except that the transverse stretching ratio was set to 3.1 times.

[0101] Comparative Example 9 A biaxially oriented polyester film was obtained in the same manner as in Example 1, except that the longitudinal stretching ratio was set to 3.2 times.

[0102] In each embodiment, sufficient heat sealability and resistance to film tearing and ripping were obtained.

[0103] In Comparative Example 1, the number of chips (F) in the seal layer was reduced compared to Example 4. As a result, the inhibition of heat sealing by surfactants on the surface of the seal layer was reduced, leading to increased heat seal strength and decreased easy-peel properties at high temperatures.

[0104] In Comparative Example 2, the inhibition of heat sealing by the surfactant on the surface of the seal layer was greater than in Example 5, resulting in lower heat seal strength.

[0105] In Comparative Example 3, the heat treatment temperature after transverse stretching was increased compared to Example 1. As a result, crystallization of the substrate layer was promoted, the film strength decreased, and film tearing occurred during sealant removal.

[0106] In Comparative Example 4, the amount of diethylene glycol copolymer component in the seal layer was reduced compared to Example 7. As a result, the amorphous component of the seal layer was reduced, leading to a decrease in heat sealability.

[0107] In Comparative Example 5, the film thickness was reduced compared to Example 1, resulting in decreased film strength and film tearing during sealant removal.

[0108] In Comparative Example 6, increasing the film thickness compared to Example 9 resulted in reduced heat transfer to the surface of the sealing layer during heat sealing, leading to decreased sealing strength.

[0109] In Comparative Example 7, reducing the IV of the substrate layer Y compared to Example 2 resulted in reduced molecular chain entanglement within the substrate layer, decreased film strength, and film tearing during sealant removal.

[0110] In Comparative Example 8, reducing the transverse stretching ratio compared to Example 10 resulted in decreased film orientation, reduced film strength, and film tearing during sealant removal.

[0111] In Comparative Example 9, reducing the longitudinal stretching ratio compared to Example 1 resulted in decreased film orientation, reduced film strength, and film tearing during sealant removal.

[0112] [Table 1] [Industrial applicability]

[0113] According to the present invention, it is possible to provide a polyester-based sealant film that, despite being a monomaterial, offers easy peelability and sufficient sealing strength, and is less likely to tear or break when the heat-sealed film is peeled off a plastic container.

Claims

1. A polyester sealant film having a heat-sealable sealing layer and a heat-resistant layer laminated on the sealing layer, wherein the film has a tear resistance of 140 N or more in the longitudinal and width directions, a tensile breaking strength of 140 MPa or more in the longitudinal and width directions at room temperature, and a heat seal strength of 6 to 15 N / 15 mm when an A-PET sheet and the sealing layer are overlapped and heat-sealed at 160°C for 1 second under a load of 0.2 MPa.

2. The polyester sealant film according to claim 1, wherein the haze content is 10% or less.

3. The polyester sealant film according to claim 1 or 2, wherein the thermal shrinkage rate at 150°C in both the longitudinal and width directions is 0.01 to 3.0%.

4. The polyester sealant film according to any one of claims 1 to 3, wherein the heat-resistant layer contains particles, the average particle size of the particles is 0.01 to 6 μm, and the particle content in the heat-resistant layer is 0.01 to 25% by mass.

5. The polyester sealant film according to any one of claims 1 to 4, wherein the contact angle of the surface of the sealing layer with respect to water is 23° or less.

6. A polyester-based sealant film according to any one of claims 1 to 5, comprising chemically recycled polyester.

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