Polyester-based sealant film

Abstract

The present invention solves the problems of the prior art and provides a polyester-based sealant film which achieves an appropriate heat seal strength over a wide temperature range even through being a mono-material.　The present invention specifically provides a polyester-based sealant film which has a sealing layer that exhibits heat sealability and a heat-resistant layer that is superposed on the sealing layer. The crystallinity of the surface of the sealing layer on the side not having the heat-resistant layer is 0.90 or less as determined by the ATR method. The crystallization temperature of the sealing layer is 93-118°C as measured by DSC. When an A-PET sheet and the sealing layer are overlapped and heat-sealed for one second under a load of 0.2 MPa, the respective heat seal strengths at a heat seal temperature of 130°C, 150°C, and 180°C are 6-20 N / 15 mm.

Description

Polyester sealant film

[0001] The present invention relates to a polyester sealant film that is a monomaterial but has adequate heat seal strength over a wide temperature range and is highly transparent.

[0002] Plastic containers are widely used for packaging foods and other products. Until now, snap-fit ​​lids molded from plastics such as A-PET have been used as the lid material for these containers. Here, A-PET refers to amorphous PET (amorphous polyethylene terephthalate), which is in a non-crystalline state containing ethylene terephthalate units alone or at least 50% by mass, and is typically unoriented and uncrystallized. However, in recent years, the use of standardized lid materials, waste reduction, and extended shelf lives have led to the shift to film-based lid materials for plastic containers. These lid films are required to have easy releasability, allowing for easy manual peeling after heat sealing, and sufficient seal strength to prevent leakage of contents after heat sealing.

[0003] Furthermore, if the heat-sealing temperature range in which the above-mentioned easy peeling property and sufficient seal strength can be exhibited is wide, heat sealing exhibiting appropriate seal strength can be performed under various conditions and with various machines, resulting in a sealant film with high versatility. As a method for obtaining such a sealant film, there is a method in which a seal layer and a support layer are laminated together and the seal layer and the support layer are delaminated from each other (see, for example, Patent Documents 1 and 2).

[0004] However, in this method, the sealing layer and the support layer must be made of different resin compositions to provide adequate delamination (for example, if the sealing layer is polyester, the support layer must be made of an olefin such as polyethylene or polypropylene.) Therefore, although the sealant film obtained by delamination has high functionality, it is not a mono-material (each layer of a multi-layered packaging laminate film is made of a single resin material), which makes it difficult to recycle films as is now required.

[0005] JP 2001-328221 A JP 2019-171792 A

[0006] The object of the present invention is to solve the problems of the prior art described above, and to provide a polyester sealant film which is a monomaterial and yet has adequate heat seal strength over a wide temperature range.

[0007] The polyester sealant film of the present invention, which can solve the above problems, has the following configuration.

[0008] That is, the present invention has the following configurations. [1] A polyester sealant film having a seal layer exhibiting heat sealability and a heat-resistant layer laminated on the seal layer, wherein the crystallinity of the surface of the seal layer not having the heat-resistant layer measured by ATR method is 0.90 or less, the crystallization temperature of the seal layer measured by DSC is 93 to 118°C, and when an A-PET sheet and the seal layer are overlapped and heat-sealed for 1 second under a load of 0.2 MPa, the heat seal strength at heat sealing temperatures of 130°C, 150°C, and 180°C is 6 to 20 N / 15 mm. [2] The polyester sealant film according to [1], which has a haze of 10.0% or less. [3] The polyester sealant film according to [1] or [2], which has a heat shrinkage of 0.01 to 4.0% at 150°C in both the longitudinal and transverse directions. [4] The polyester sealant film according to any one of [1] to [3], further comprising particles, the particles having an average particle size of 0.01 to 6 μm, and the content of the particles in the polyester sealant film being 0.01 to 25% by mass. [5] The polyester sealant film according to any one of [1] to [4], wherein the mass ratio of the particles contained in the seal layer to the particles contained in the heat-resistant layer (seal layer:heat-resistant layer) is 0:100 to 45:55. [6] The polyester sealant film according to any one of [1] to [5], wherein the contact angle of the seal layer surface with water is 21.0° or less. [7] The polyester sealant film according to any one of [1] to [6], wherein the heat-resistant layer has a thickness of 50 μm or less. [8] The polyester sealant film according to any one of [1] to [7], wherein the seal layer contains 50 to 100% by mass of polyester relative to 100% by mass of the resin constituting the seal layer. [9] The polyester sealant film according to [8], wherein the polyester is a homopolyester and / or a copolymer polyester.

[10] The polyester sealant film according to any one of [1] to [9], wherein the seal layer contains a copolymer polyester and the copolymer polyester contains diethylene glycol as a copolymer component.

[11] The polyester sealant film according to

[10] , wherein the diethylene glycol component ratio is 11.0 to 19.0 mol % when the diol component constituting the copolymer polyester contained in the seal layer is taken as 100 mol %.

[12] The polyester sealant film according to any one of [1] to

[11] , wherein the heat-resistant layer contains 50 to 100 mass % of polyester relative to 100 mass % of the resin constituting the heat-resistant layer.

[13] The polyester sealant film according to

[12] , wherein the polyester is a homopolyester and / or a copolymer polyester.

[14] The polyester sealant film according to

[12] or

[13] , wherein the ethylene glycol component ratio is 70 to 100 mol % when the diol component constituting the polyester contained in the heat-resistant layer is taken as 100 mol %.

[15] The polyester sealant film according to any one of [1] to

[14] , further containing a surfactant.

[16] The polyester sealant film according to

[15] , wherein the ratio of the concentration of the surfactant contained in the heat-resistant layer to the concentration of the surfactant contained in the seal layer (heat-resistant layer:sealing layer) is 0:100 to 45:55.

[17] A lid material comprising the polyester sealant film according to any one of [1] to

[16] .

[18] A packaging material comprising the polyester sealant film according to any one of [1] to

[16] .

[0009] The polyester sealant film of the present invention is a monomaterial, yet it is possible to obtain an appropriate heat seal strength over a wide temperature range.

[0010] (Polyester-Based Sealant Film) The polyester-based sealant film of the present invention is a polyester-based sealant film having a seal layer exhibiting heat-sealability and a heat-resistant layer laminated on the seal layer. The seal layer is preferably a layer having heat-sealability, and more preferably a layer that exhibits a heat-seal strength of 3 N / 15 mm or more at a heat-sealing temperature of 130°C, 150°C, or 180°C when an A-PET sheet and the seal layer are overlapped and heat-sealed for 1 second at a load of 0.2 MPa. On the other hand, the heat-resistant layer is a layer that does not have heat-sealability, and more preferably a layer that exhibits a heat-seal strength of less than 3 N / 15 mm at heat-sealing temperatures of 130°C, 150°C, or 180°C when an A-PET sheet and the seal layer are overlapped and heat-sealed for 1 second at a load of 0.2 MPa. When the polyester-based sealant film is used as a lid material, the lid material is used as a material for sealing the opening of a container, and the seal layer forms an adhesive portion with the container. The heat-resistant layer may have a laminated structure of two or more layers having different compositions.

[0011] (Technical Meaning and Significance of the Physical Properties Described in the Present Invention) In the polyester sealant film of the present invention, the crystallinity of the seal layer surface (the surface of the seal layer on the side not having the heat-resistant layer) measured by the ATR method is 0.90 or less. By controlling the crystallinity of the seal layer surface measured by the ATR method within the above range, a seal strength sufficient for practical use as a sealant film can be obtained.

[0012] The upper limit of the crystallinity of the seal layer surface as measured by the ATR method is more preferably 0.86, even more preferably 0.82, and particularly preferably 0.78. By setting the crystallinity of the seal layer surface as measured by the ATR method to 0.90 or less, sufficient seal strength can be obtained even at low heat-sealing temperatures, which is preferred. On the other hand, while there is no particular lower limit for the crystallinity of the seal layer surface as measured by the ATR method, a value of 0.10 or more is preferred because this makes the heat-sealed film less likely to tear when peeled off, and is more preferably 0.20 or more, and particularly preferably 0.30 or more (i.e., preferably 0.10 to 0.90, 0.20 to 0.86, 0.30 to 0.82, or 0.30 to 0.78).

[0013] The polyester sealant film of the present invention has a crystallization temperature of 93 to 118°C as measured by a DSC (differential scanning calorimeter), with the upper limit of the crystallization temperature being more preferably 116°C, even more preferably 114°C, and particularly preferably 112°C. The crystallization temperature was determined using a differential scanning calorimeter (DSC3100S, manufactured by Mac Science) at a heating rate of 10°C / min. The lower limit of the crystallization temperature is more preferably 95°C, even more preferably 97°C, and particularly preferably 99°C (i.e., preferably 93 to 118°C, 95 to 116°C, 97 to 114°C, or 99 to 112°C). By setting the crystallization temperature of the seal layer to 118°C or less, crystallization of the seal layer is promoted during heat sealing at high temperatures, preventing excessive increases in seal strength and broadening the temperature range over which an appropriate seal strength can be obtained, which is preferred. Furthermore, by setting the crystallization temperature of the seal layer to 93° C. or higher, crystallization is not promoted even at a relatively low heat sealing temperature, and sufficient seal strength can be obtained, which is preferable.

[0014] Furthermore, in the present invention, when the A-PET sheet and the seal layer are overlapped and heat-sealed for 1 second under a load of 0.2 MPa, the seal strength at 130°C, 150°C, and 180°C is 6 to 20 N / 15 mm. The upper limit of the seal strength is more preferably 19 N / 15 mm, even more preferably 18 N / 15 mm, and particularly preferably 17 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 (i.e., preferably 6 to 20 N / 15 mm, 7 to 19 N / 15 mm, 8 to 18 N / 15 mm, or 9 to 17 N / 15 mm). A seal strength of 20 N / 15 mm or less is preferable because it provides easy opening. Furthermore, a seal strength of 6 N / 15 mm or more is preferable because sufficient seal strength is obtained, and the contents are less likely to leak after the film is heat-sealed to an A-PET container filled with food.

[0015] In the polyester sealant film of the present invention, the haze is preferably 10.0% or less. The upper limit of the haze is more preferably 8.0%, even more preferably 6.0%, and particularly preferably 4.0%. By keeping the haze at 10.0% or less, the contents can be clearly seen when the film is used as a packaging material or a lid material, which is preferable. The closer the haze is to 0%, the more preferable it is, but 0.1% or more is also preferable, and 0.3% or more is also preferable (i.e., preferably 0% to 10.0%, 0.1% to 8.0%, 0.1% to 6.0%, or 0.3% to 4.0%).

[0016] In the polyester sealant film of the present invention, the heat shrinkage rate in both the longitudinal and transverse directions at 150°C is preferably 0.01 to 4.0%. The lower limit of the heat shrinkage rate at 150°C is more preferably 0.1%, and even more preferably 0.4%. On the other hand, the upper limit of the heat shrinkage rate at 150°C is preferably 3.0%, more preferably 2.6%, even more preferably 2.2%, and particularly preferably 1.8% (i.e., preferably 0.01 to 4.0%, 0.01 to 3.0%, 0.1 to 2.6%, 0.1 to 2.2%, or 0.4 to 1.8%). Even if a film having a heat shrinkage rate of less than 0.01% in the longitudinal and transverse directions at 150°C is produced, no significant difference is observed in practical effects and productivity is significantly reduced, so there is no need to make the heat shrinkage rate at 150°C less than 0.01%. In particular, a heat shrinkage rate of 3.0% or less at 150°C is preferable because the shrinkage of the film during heat sealing is small and the A-PET container is not deformed. The heat shrinkage rate can be appropriately adjusted by changing the amorphous component (for example, the amount of diethylene glycol) contained in the heat-resistant layer.

[0017] In the polyester sealant film of the present invention, the contact angle of the seal layer surface with water is preferably 21.0° or less. The upper limit of the contact angle is more preferably 19.0°, even more preferably 17.0°, and particularly preferably 15.0°. A contact angle of 21.0° or less is preferable because, when the film is used as a packaging material or a lid material, the film is less likely to cloud and the contents are clearly visible. The lower limit of the contact angle is more preferably 5.0°, even more preferably 7.0°, and particularly preferably 9.0° (i.e., preferably 5.0 to 21.0°, 7.0 to 19.0°, 9.0 to 17.0°, or 9.0 to 15.0°). Producing a film with a contact angle of less than 5.0° may not result in a significant difference in practical effect and may significantly reduce productivity, so a contact angle of 5.0° or more is preferable. The contact angle can be appropriately adjusted by changing the amount of surfactant contained in the seal layer.

[0018] (Preferred Embodiment of Film) From the viewpoint of making the polyester-based sealant film of the present invention a mono-material, the film raw materials in each of the sealing layer and the heat-resistant layer preferably contain polyester in an amount of 50% by mass or more, more preferably 75% by mass or more. Furthermore, in each of the sealing layer and the heat-resistant layer, the polyester content is preferably 50 to 100% by mass, more preferably 75 to 100% by mass, and even more preferably 85 to 100% by mass, based on 100% by mass of the resin constituting each layer. The polyester in the present invention includes homopolyesters and / or copolymer polyesters, and specifically may include any of homopolyesters alone, copolymer polyesters alone, blends of two or more homopolyesters, blends of two or more copolymer polyesters, and blends of one or more homopolyesters and one or more copolymer polyesters.

[0019] The copolymer polyester includes a copolymer polyester composed of an aromatic dicarboxylic acid component, ethylene glycol, and a copolymerization component other than ethylene glycol. The aromatic dicarboxylic acid component is preferably terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, or an ester-forming derivative thereof. The amount of terephthalic acid and / or naphthalenedicarboxylic acid component relative to the total dicarboxylic acid components is preferably 70 mol% or more, more preferably 85 mol% or more, even more preferably 95 mol% or more, and particularly preferably 100 mol%. Examples of the copolymerization component include diethylene glycol, neopentyl glycol, and cyclohexanedimethanol.

[0020] Diethylene glycol is preferred as a copolymerization component in the copolymerized polyester. In particular, it is preferable that the seal layer contains a copolymerized polyester and that the copolymerized polyester contains diethylene glycol as a copolymerization component. Using diethylene glycol (preferably only diethylene glycol) as a copolymerization component in the seal layer is suitable for imparting good heat sealability. Furthermore, it is also preferred in that it has excellent transparency and heat resistance, and its moderate crystallinity promotes crystallization during high-temperature heat sealing, preventing excessively high seal strength during high-temperature sealing and enabling the development of moderate seal strength over a wide temperature range. Using only diethylene glycol as a copolymerization component in the seal layer means that the polyester constituting the seal layer is a copolymerized polyester whose dicarboxylic acid component is terephthalic acid alone and whose diol components are ethylene glycol and diethylene glycol.

[0021] Furthermore, when a copolymerized polyester composed of an aromatic dicarboxylic acid component and a diol component containing diethylene glycol and ethylene glycol is used as the polyester, the diol component constituting the copolymerized polyester contained in the seal layer is taken as 100 mol %, and the diethylene glycol component ratio is, for example, 11.0 to 19.0 mol %, preferably 12.0 to 18.0 mol %. The upper limit of the diethylene glycol component ratio in the seal layer is more preferably 17.5 mol %, even more preferably 17.0 mol %, and particularly preferably 16.5 mol %. The lower limit of the diethylene glycol component ratio in the seal layer is more preferably 12.5 mol %, even more preferably 13.0 mol %, and particularly preferably 13.5 mol % (i.e., preferably 11.0 to 19.0 mol %, 12.0 to 18.0 mol %, 12.5 to 17.5 mol %, 13.0 to 17.0 mol %, or 13.5 to 16.5 mol %). Within the above range, good heat sealability can be imparted to the seal layer.

[0022] When the amount of diethylene glycol is 11.0 mol % or more based on the total diol components, the FT-IR ATR measurement of the sealing layer shows a peak at 1340 cm －１ Around (1330-1350 cm －１ ) the maximum peak intensity at 1410 cm －１ Around (1400-1420 cm －１ ) by the maximum peak intensity at 1000 kJ / min, the crystallization temperature of the seal layer measured by DSC can be easily controlled to 93 to 118°C, and an appropriate seal strength can be easily obtained over a wide range of heat sealing temperatures, which is preferable.

[0023] Furthermore, in the heat-resistant layer, the ethylene glycol component ratio is preferably 70 to 100 mol%, assuming the total diol component of the polyester contained in the heat-resistant layer to be 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%, particularly preferably 85 mol%, and most preferably 90 mol%. A 70 to 100 mol% ethylene glycol component ratio in the heat-resistant layer is preferred because it facilitates controlling the melting point of the heat-resistant layer to 200°C or higher and reduces sticking of the film to the seal bar during heat sealing. The diol component of the polyester contained in the heat-resistant layer may be 100 mol% ethylene glycol, but in the case of a copolymer polyester containing other diol components, it is preferable that the other diol component other than ethylene glycol is diethylene glycol. In the heat-resistant layer, the diethylene glycol component ratio is preferably 0 to 11 mol%, more preferably 0 to 5 mol%, even more preferably 0 to 3 mol%, and most preferably 0 mol%, assuming the total diol component of the polyester contained in the heat-resistant layer to be 100 mol%.

[0024] In the present invention, the catalyst used in producing the polyester may be, for example, an alkaline earth metal compound, a manganese compound, a cobalt compound, an aluminum compound, an antimony compound, a titanium compound, a titanium / silicon composite oxide, a germanium compound, etc. Among these, the titanium compound, the antimony compound, the germanium compound, and the aluminum compound are preferred from the viewpoint of catalytic activity.

[0025] When producing the polyester, it is preferable to add a phosphorus compound as a heat stabilizer, such as phosphoric acid or phosphorous acid.

[0026] The polyester preferably has an intrinsic viscosity of 0.50 dl / g or more, more preferably 0.55 dl / g or more, and particularly preferably 0.60 dl / g or more. An intrinsic viscosity of 0.50 dl / g or more is preferred because it tends to improve film formation stability. Furthermore, when a filter for removing foreign matter is provided in the melt line, the upper limit of the intrinsic viscosity is preferably 1.0 dl / g (i.e., preferably 0.50 to 1.0 dl / g, 0.55 to 1.0 dl / g, or 0.60 to 1.0 dl / g) from the viewpoint of discharge stability during extrusion of the molten resin.

[0027] 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 50 μm, and more preferably 40 μm (i.e., preferably 5 to 50 μm, 10 to 50 μm, or 15 to 40 μm). A thickness of the heat-resistant layer of 5 μm or more is preferable because it results in a film that is less likely to break during film formation or when peeling the film after heat sealing. Furthermore, a thickness of the heat-resistant layer of 50 μm or less is preferable because it is more likely to increase stress when stretching the film, making it easier to obtain a film with excellent thickness precision.

[0028] The sealing layer can be formed by a coating method or a co-extrusion method. Among these, the co-extrusion method is more preferable because it does not require a solvent and therefore reduces the environmental load and improves economic efficiency.

[0029] The thickness of the sealing layer is preferably 5 μm or more. The lower limit of the sealing layer thickness is more preferably 7 μm, and particularly preferably 9 μm. On the other hand, the upper limit of the sealing layer thickness is preferably 25 μm, more preferably 23 μm, and particularly preferably 21 μm (i.e., preferably 5 to 25 μm, 7 to 23 μm, or 9 to 21 μm). A thickness of 5 μm or more is preferred because it facilitates obtaining adequate seal strength during heat sealing. Furthermore, a thickness of 25 μm or less is preferred because it is less likely to cause cohesive failure of the sealing layer when the heat-sealed film is peeled, and therefore, sufficient heat seal strength is easily obtained. The thickness ratio of the sealing layer to the heat-resistant layer is preferably 5:95 to 95:5, more preferably 10:90 to 60:40, and even more preferably 20:80 to 40:60. Within the above ranges, the resulting film has adequate heat seal strength and is less likely to break. In the present disclosure, the thickness of each layer constituting the film of the present invention can be calculated from the thickness of the film and the mass ratio of each layer.

[0030] The thickness of the laminate film, which is the polyester sealant film of the present invention, is preferably 10 μm or more. The lower limit of the thickness of the laminate film is more preferably 15 μm, and particularly preferably 20 μm. On the other hand, the upper limit of the thickness of the laminate film is preferably 70 μm, more preferably 65 μm, and particularly preferably 60 μm (i.e., preferably 10 to 70 μm, 15 to 65 μm, or 20 to 60 μm). A thickness of 10 μm or more is preferable because the film is less likely to tear when peeling off the heat-sealed film. Furthermore, a thickness of 70 μm or less is preferable because heat is easily transferred to the surface of the seal layer during heat sealing, making it easier to obtain appropriate heat seal strength.

[0031] Furthermore, in order to improve the handling properties of the film, such as its slipperiness and winding properties, 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. When the film of the present invention contains particles, the mass ratio of the particles contained in the sealing layer to the particles contained in the heat-resistant layer (sealing layer:heat-resistant layer) is preferably 0:100 to 100:0, more preferably 0:100 to 45:55, even more preferably 0:100 to 20:80, and even more preferably 0:100 to 5:95.

[0032] The particles preferably have an average particle size of 0.01 to 6 μm. Examples of the particles include internally precipitated particles, which are minute particles formed inside the film, and external particles, which are particles formed outside the film, such as inorganic and / or organic particles. External particles are preferred because their physical properties can be easily controlled. Using particles with an average particle size of 6 μm or less is preferred because they are less likely to cause film defects and are more likely to achieve good design and transparency. Furthermore, an average particle size of 0.01 μm or more is preferred because it provides good film lubricity, windability, and other properties, resulting in good handleability. From the perspective of handleability, such as lubricity and windability, the lower limit of the average particle size of the particles is more preferably 0.1 μm, and even more preferably 0.5 μm. On the other hand, from the viewpoint of transparency and reducing film defects due to coarse protrusions, the upper limit of the average particle size of the particles is more preferably 5 μm, even more preferably 3 μm, and still more preferably 2 μm (i.e., preferably 0.01 to 6 μm, 0.1 to 5 μm, 0.1 to 3 μm, or 0.5 to 2 μm).

[0033] The average particle diameter of the particles can be calculated by taking multiple photographs of at least 200 particles using a scanning electron microscope (SEM), tracing the particle contours on an OHP film, and converting the traced images into circle-equivalent diameters using an image analyzer.

[0034] Examples of the internal particles include particles produced by an in situ synthesis method, in which metal ions are introduced into a polymer matrix and then subjected to chemical reduction or heat treatment to precipitate metal nanoparticles within the polymer matrix. Examples of the external particles include inorganic particles such as wet and dry colloidal silica, colloidal silica, aluminum silicate, titanium oxide, calcium carbonate, calcium phosphate, barium sulfate, alumina, mica, kaolin, clay, hydroxyapatite, glass, and silica-alumina composite oxides, as well as organic particles containing styrene, silicone, acrylic acids such as (meth)acrylic acid, polyester, divinylbenzene, and the like. Among these, inorganic particles such as wet and dry colloidal silica and alumina, as well as organic particles containing styrene, silicone, acrylic acid, methacrylic acid, polyester, divinylbenzene, and the like, are preferred. These particles may be used alone, or two or more types may be used in combination within the range that does not impair the properties specified in the present invention.

[0035] Furthermore, the content of the particles in the polyester sealant film according to the present invention is preferably in the range of 0.01 to 25% by mass, more preferably 0.02 to 15% by mass, even more preferably 0.03 to 10% by mass, and even more preferably 0.04 to 5% by mass. A content of 0.01% by mass or more is preferred because it facilitates obtaining good slip properties for the film, improves winding properties, and provides good handleability. Furthermore, a content of 25% by mass or less is preferred because it facilitates obtaining good transparency, further reduces the formation of coarse protrusions, and facilitates obtaining good film-forming properties and transparency.

[0036] The heat-resistant layer constituting the polyester sealant film of the present invention can be formed into a laminate structure by a known method using different polyester compositions to impart other functions. The form of such a laminate film is not particularly limited. 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 laminate structures include a two-type two-layer structure (X / Y), a two-type three-layer structure (X / Y / X), and a three-type three-layer structure (X / Y / Z). In the case of a two-type two-layer structure (X / Y), it is preferable that the seal layer is laminated on the surface of the base layer Y on the side where the surface layer X is not laminated (i.e., a laminate structure in the order of X / Y / seal layer). In the case of a three-type three-layer structure (X / Y / Z), it is preferable that the seal layer is laminated on the surface of the other layer Z on the side where the base layer Y is not laminated (i.e., a laminate structure in the order of X / Y / Z / seal layer).

[0037] To achieve high transparency while maintaining the film's handling properties, the heat-resistant layer preferably has a structure in which a base layer and a surface layer are laminated, and a seal layer is preferably laminated on the surface of the base layer. The surface layer preferably contains particles, and the thickness of each layer is preferably 0.01 to 6.0 μm. The upper limit of the thickness of the surface layer is preferably 5.0 μm, preferably 4.0 μm, more preferably 3.0 μm, even more preferably 2.5 μm, and particularly preferably 2.0 μm (i.e., preferably 0.01 to 6.0 μm, 0.01 to 5.0 μm, 0.01 to 4.0 μm, 0.01 to 3.0 μm, 0.01 to 2.5 μm, or 0.01 to 2.0 μm). In this case, the particles exemplified above can be used.

[0038] In the present invention, in order to make the haze of the film 10% or less, it is preferable to form a laminate structure in which the base layer does not substantially contain particles, and the surface layer has a thickness of 0.01 to 6.0 μm, and contains particles only in the surface layer.

[0039] The above phrase "substantially no particles are contained in the base layer" means, for example, in the case of inorganic particles, that the content is below the detection limit when the inorganic element is quantified by fluorescent X-ray analysis. This is because even if particles are not intentionally added to the base layer, contaminants derived from foreign matter may be mixed in. To obtain a film with low haze and excellent design, it is preferable that the base layer does not substantially contain particles, but particles may be added to the base layer as long as the content is 30 ppm or less.

[0040] On the other hand, when silica particles having an average particle size of 3.0 μm or less (preferably 1.5 μm or less) are used as particles to be contained in the surface layer, the cut edge of the film or waste film generated during paper passing can be remelted and contained in the surface layer. In this case, the particle content in the surface layer is preferably 1500 ppm or less, more preferably 1200 ppm, and even more preferably 1000 ppm. When silica particles having an average particle size of 3.0 μm or less are used, it is preferable to set the particle content in the surface layer to 1500 ppm or less, because this makes it easier to obtain a film with low haze and excellent design. By reusing the film in this way, the amount of film to be discarded is reduced and environmental adaptability is improved.

[0041] The particles contained in the surface layer may be the same as those described above. Among these particles, silica particles, glass filler, and silica-alumina composite oxide particles are particularly suitable from the viewpoint of transparency because their refractive indexes are relatively close to that of polyester.

[0042] The thickness ratio of the surface layer to the base layer is preferably 2:98 to 98:2, more preferably 5:95 to 50:50, and even more preferably 10:90 to 40:60. Within the above ranges, the resulting film has excellent handleability and transparency.

[0043] The polyester sealant film of the present invention may be either a uniaxially stretched film or a biaxially stretched film, but is preferably a biaxially stretched film. In the present invention, the molecular orientation achieved by biaxial stretching improves the solvent resistance and dimensional stability that are drawbacks of unstretched sheets.

[0044] The method for producing the biaxially oriented polyester film is not particularly limited, but for example, a method is exemplified in which a polyester resin is dried as necessary, then fed into a known melt extruder, extruded into a sheet form through a slit die, and adhered to a casting drum by electrostatic application or other means, cooled and solidified to obtain an unstretched sheet (raw sheet), which is then biaxially stretched. Also preferred is a so-called coextrusion method in which the polyester raw materials for forming the heat-resistant layer and the polyester raw materials for forming the seal layer are melt-extruded from separate extruders and laminated. Furthermore, the heat-resistant layer may further comprise a surface layer and a base layer, each of which is formed by coextrusion of separate polyester raw materials.

[0045] As a biaxial stretching method, a method is adopted in which an unstretched sheet is stretched in the longitudinal direction (MD) and width direction (TD) of the film and heat-treated to obtain a biaxially stretched film with the desired in-plane orientation. Among these methods, from the viewpoint of film quality, sequential biaxial stretching methods such as the MD / TD method in which the sheet is stretched in the longitudinal direction and then in the width direction, or the TD / MD method in which the sheet is stretched in the width direction and then in the longitudinal direction, and simultaneous biaxial stretching methods in which the sheet is stretched in the longitudinal direction and the width direction almost simultaneously are desirable. In addition, 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 in which stretching in the same direction is performed in multiple stages may be used.

[0046] The film stretching ratio during biaxial stretching is preferably 2.8 to 3.7 times in the longitudinal direction, more preferably 3.0 to 3.5 times, and particularly preferably 3.1 to 3.4 times. Furthermore, the stretching ratio in the width direction is preferably 3.2 to 4.2 times, more preferably 3.4 to 4.0 times, and particularly preferably 3.5 to 3.9 times. A stretching ratio within the above range is preferred because good film-forming properties and thickness accuracy can be obtained. Furthermore, the stretching temperature during biaxial stretching is preferably 50 to 150°C, more preferably 80 to 130°C, in both the longitudinal and width directions.

[0047] As the stretching conditions when producing the polyester sealant film of the present invention, for example, the following conditions are preferably employed.

[0048] In the longitudinal stretching, the stretching temperature is preferably 50 to 150° C. and the stretching ratio is preferably 3.0 to 3.5 times so that the transverse stretching, which is usually carried out later, can be carried out smoothly.

[0049] Furthermore, after biaxial stretching, the film is subsequently heat-treated in a tenter. The heat treatment is preferably carried out at a temperature range of 215 to 235°C. The lower limit of the heat treatment temperature is more preferably 220°C, and the upper limit of the heat treatment temperature is more preferably 230°C (i.e., preferably 215 to 235°C or 220 to 230°C). A heat treatment temperature of 215°C or higher is preferred because the crystals in the sealing layer melt and appropriate heat-sealing properties are achieved. A heat treatment temperature of 235°C or lower is also preferred because stable film-forming properties are easily achieved. The heat treatment may be either a tension heat treatment or a relaxation heat treatment. To reduce the heat shrinkage rate, a relaxation heat treatment of 3 to 10% is preferred.

[0050] Generally, known means for reducing the heat shrinkage at 150°C are to reduce the stretch ratio and to reduce the amount of copolymerization component, but the former method may worsen the thickness unevenness of the film, and the latter method is not very preferred because it increases the crystallinity of the seal layer and deteriorates the heat sealability. In the present invention, it is preferable to perform heat setting (the above-mentioned heat treatment) in order to reduce the heat shrinkage at 150°C of the polyester sealant film.

[0051] The present application also encompasses packaging materials and lid materials comprising the polyester sealant film of the present invention. When the film of the present invention is used as a lid material, a surfactant may be added to the film to prevent water droplets from adhering to the film due to water vapor inside a container, causing fogging. In this case, if the film contains a surfactant, the surfactant may be contained in either the sealing layer or the heat-resistant layer. However, adding the surfactant only to the sealing layer without adding it to the heat-resistant layer is preferred, as this achieves both fogging suppression and film transparency. When the film of the present invention contains a surfactant, the ratio of the surfactant concentration in the heat-resistant layer to the surfactant concentration in the sealing layer (heat-resistant layer:sealing layer) is preferably 0:100 to 100:0, more preferably 0:100 to 45:55, even more preferably 0:100 to 20:80, and even more preferably 0:100 to 5:95.

[0052] The amount of surfactant added is preferably 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. Setting the weight ratio of surfactant to the total film to 0.9% by mass or less is preferred because it makes it easier to control the haze to 10% or less. The lower limit is not particularly limited, but may be 0.05% by mass, 0.1% by mass, or 0.2% by mass (i.e., preferably 0.05 to 0.9% by mass, 0.1 to 0.8% by mass, or 0.2 to 0.7% by mass).

[0053] The polyester sealant film of the present invention may be surface-treated to prevent water droplets from adhering to the film due to water vapor inside a container when used as a lid material, causing fogging. In the present invention, it is preferable that the surface of the sealing layer is surface-treated. Examples of the surface treatment method include corona discharge treatment and plasma treatment, and there are no particular limitations. Corona discharge treatment and plasma treatment are preferable because they allow continuous treatment and can be easily carried out before the winding step in the film production process.

[0054] This application claims the benefit of priority based on Japanese Patent Application No. 2024-035906, filed on March 8, 2024. The entire contents of the specification of Japanese Patent Application No. 2024-035906, filed on March 8, 2024, are incorporated herein by reference.

[0055] 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.

[0056] (1) Intrinsic Viscosity 0.1 g of a chip sample was precisely weighed and dissolved in 25 ml of a mixed solvent of phenol / tetrachloroethane = 60 / 40 (mass ratio), and the intrinsic viscosity was measured using an Ostwald viscometer at 30° C. The measurement was performed three times, and the average value was calculated.

[0057] (2) Haze The haze of the film was measured using a haze meter (300A, manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K7136: 2000. The measurement was carried out twice, and the average value was calculated.

[0058] (3) Film Thickness Using a former Seiko EM Millitron 1202D, measurements were taken at five points per film, for a total of three films, for a total of 15 points, and the average value was calculated.

[0059] (4) Heat Shrinkage at 150°C Strip samples 150 mm long and 20 mm wide are cut out in the longitudinal and transverse directions of the film. Two marks are made at 100 mm intervals along the length of each sample, and the distance A between the two marks is measured under no load. Next, one side of each strip sample is hung with a clip under no load on a basket, and placed in a gear oven in an atmosphere of 150°C, while the time is measured. After 30 minutes, the basket is removed from the gear oven and left at room temperature for 30 minutes. Next, the distance B is read for each sample under no load. From the read distances A and B, the heat shrinkage of each sample at 150°C is calculated using the following formula: Heat Shrinkage (%) = {(A - B) / A} x 100

[0060] (5) Crystallization temperature (Tc) and melting point (Tm) of raw material (subject) Using a differential scanning calorimeter (Shimadzu Corporation, FC60A), the surface of the sealing layer of each example was scraped off with a razor blade, approximately 5 mg was placed in a sample pan, the pan was covered, and the temperature was increased from room temperature to 300°C at a heating rate of 10°C / min in a nitrogen gas atmosphere. The crystallization temperature and melting point were determined as the peak temperature defined in JIS K7121:1987, Section 9.1.

[0061] (6) Heat Seal Strength Heat seal strength was measured in accordance with JIS Z1707:2019. Specific procedures are as follows: Using a heat sealer "TYB-300" (manufactured by Nishibe Machinery Co., Ltd.), the seal layer of the film sample was bonded to an A-PET sheet obtained as described below. The heat sealing conditions were upper bar temperatures of 130°C, 150°C, and 180°C, pressure of 0.2 MPa, and time of 1 second. The heat-sealed sample was cut to a seal width of 15 mm. Peel strength was measured using a universal tensile tester "DSS-100" (manufactured by Shimadzu Corporation) at a tensile speed of 200 mm / min. Peel strength is expressed as the strength per 15 mm (N / 15 mm).

[0062] (Film production of A-PET sheet for evaluation) Chips (A) of polyethylene terephthalate having an intrinsic viscosity of 0.62 dl / g and consisting of 100 mol% terephthalic acid units as the aromatic dicarboxylic acid component and 100 mol% ethylene glycol units as the diol component were dried. The chips (A) were melt-extruded at 280°C through a slit in a T-die using an extruder, and rapidly solidified on a chill roll with a surface temperature of 20°C. At the same time, the chips were adhered to the chill roll using an electrostatic application method to obtain an A-PET sheet with a thickness of 200 μm.

[0063] (7) Surface Crystallinity (ATR Method) The seal layer was subjected to total reflection infrared absorption measurement (FT-IR ATR measurement) under the following conditions. －１ Absorption that appears near 1410 cm －１ The intensity ratio of the absorption appearing near (1340 cm －１ / 1410cm －１ The crystallinity was calculated by the following equation: －１ is the CH of ethylene glycol ２This absorption is due to the bending vibration of the (trans structure), and is 1410 cm －１ is absorption unrelated to crystallinity and orientation. (Measurement equipment and conditions) FT-IR equipment: "ALPHA" manufactured by BRUKA OPTICS Element: Diamond Incident angle: 45° Resolution: 4 cm －１ Number of times accumulated: 128

[0064] (8) Contact angle A droplet of water (droplet volume 0.9 μL) was prepared on the surface of the sealing layer of the film and the contact angle was measured using a contact angle meter (Kyowa Interface Science Co., Ltd., fully automatic contact angle meter DM-701) under conditions of 25°C and 50% RH. The contact angle was measured 30 seconds after the drop on the film, and the average value of 5 measurements was used.

[0065] (9) Anti-fogging properties 1) 300cc of 53°C hot water was poured into a 500cc open-top container. 2) The opening of the container was sealed with the film, with the sealing layer side of the film facing inward. 3) The film was left to stand for 30 minutes at 5°C. 4) The state of dew adhesion on the film surface was evaluated. Dew adhesion up to 1 / 10 of the surface area was evaluated as ○, and dew adhesion more than 1 / 10 of the surface area was evaluated as △.

[0066] Example 1: Chips (B) of a copolymer polyester having an intrinsic viscosity of 0.68 dL / g, which is composed of 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, chips (A) of polyethylene terephthalate having an intrinsic viscosity of 0.62 dL / g, and chips (C) of polyethylene terephthalate having 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. Furthermore, chips (A) and chips (C) were mixed in a mass ratio of 87.5:12.5 (Mixed Raw Material 1). Furthermore, chips (B) and chips (A) were mixed in a mass ratio of 81.8:18.2 (Mixed Raw Material 2). Next, the chips (A) were melt-extruded at 280°C through a slit in a T-die using an extruder to form a 57% by mass base layer (base layer Y), an 8% by mass surface layer (surface layer X) of the mixed raw material 1 on one side of the base layer, and a 35% by mass seal layer (seal layer Z) on one side of the base layer different from the surface layer (a three-type, three-layer structure consisting of surface layer X / base layer Y / seal layer Z), and the extruded chips were rapidly cooled and solidified on a chill roll with a surface temperature of 20°C, and at the same time, an amorphous unstretched sheet was obtained by adhering the extruded chips to the chill roll using an electrostatic application method.

[0067] The resulting unstretched sheet was stretched 3.5 times in the machine direction between a heating roll and a cooling roll at 115°C. The uniaxially stretched film was then introduced into a tenter, heated at 105°C for 16 seconds, and stretched 4.0 times in the transverse direction at 120°C. Further, the film was heat-treated at 230°C and relaxed 5% in the transverse direction. The surface of the sealing layer was then corona-discharged at 0.3 kW using a corona discharge treatment machine manufactured by Kasuga Electric Co., Ltd., to obtain a biaxially stretched polyester film having a thickness of 30 μm.

[0068] Example 2 A biaxially stretched polyester film was obtained in the same manner as in Example 1, except that the heat setting temperature was changed to 215°C.

[0069] Comparative Example 1 A biaxially stretched polyester film was obtained in the same manner as in Example 1, except that the heat setting temperature was changed to 240°C.

[0070] Comparative Example 2 A biaxially stretched polyester film was obtained in the same manner as in Example 1, except that the heat setting temperature was changed to 210°C.

[0071] Example 3 A biaxially stretched polyester film was obtained in the same manner as in Example 1, except that the raw materials for the sealing layer Z were a mixture of chips (B) and chips (A) in a mass ratio of 54.5:45.5.

[0072] Comparative Example 3 A biaxially stretched polyester film was obtained in the same manner as in Example 1, except that the raw material for the sealing layer Z was changed to only the chips (B).

[0073] 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 sealing layer Z were a mixture of chips (B) and chips (A) in a mass ratio of 45.5:54.5.

[0074] Example 4 A biaxially stretched polyester film was obtained in the same manner as in Example 1, except that the thickness was changed to 20 μm.

[0075] Example 5 A biaxially stretched polyester film was obtained in the same manner as in Example 1, except that the thickness was changed to 50 μm.

[0076] Example 6 A biaxially stretched polyester film was obtained in the same manner as in Example 1, except that the thickness was changed to 70 μm.

[0077] Comparative Example 5 A biaxially stretched polyester film was obtained in the same manner as in Example 1, except that the thickness was changed to 80 μm.

[0078] Example 7 A biaxially stretched polyester film was obtained in the same manner as in Example 1, except that the raw materials for the base layer Y were prepared by drying chips (B) and chips (A) and mixing them in a mass ratio of 81.8:18.2.

[0079] Example 8 A biaxially oriented polyester film was obtained in the same manner as in Example 1, except that the raw materials for the sealing layer Z were a mixture of chips (B), chips (A), and Elecut S-618-A1 (chip D) manufactured by Takemoto Oil & Fat Co., Ltd., which is mainly composed of polyethylene terephthalate and contains 20% by mass of a surfactant, in a mass ratio of 81.8:7.2:11.0.

[0080] Example 9 A biaxially stretched polyester film was obtained in the same manner as in Example 8, except that the transverse stretching ratio was changed to 3.4 times.

[0081] Example 10 A biaxially stretched polyester film was obtained in the same manner as in Example 8, except that the longitudinal stretching ratio was 3.0 times.

[0082] Example 11 A biaxially oriented polyester film was obtained in the same manner as in Example 1, except that the raw materials for the sealing layer Z were a mixture of chips (B), chips (A), and chips (D) in a mass ratio of 81.8:14.2:4.0.

[0083] Comparative Example 6 A biaxially stretched polyester film was obtained in the same manner as in Example 1, except that the raw materials for the surface layer Z were the chips (B), the chips (A), and Elecut S-618-A1 (D) manufactured by Takemoto Oil & Fat Co., Ltd., which were dried and mixed together in a mass ratio of 81.8:5.2:13.0.

[0084] Comparative Example 7: Chips (E), chips (A), chips (C), and chips (D) of a copolymer polyester having an intrinsic viscosity of 0.75 dL / g and comprising 100 mol% terephthalic acid units as an aromatic dicarboxylic acid component and 70 mol% ethylene glycol units and 30 mol% neopentyl glycol units as diol components were dried. Furthermore, chips (A), chips (C), and chips (E) were mixed in a mass ratio of 52.0:8.0:40.0 (mixed raw material 3). Furthermore, chips (A) and chips (E) were mixed in a mass ratio of 60:40 (mixed raw material 4). Furthermore, chips (E), chips (A), chips (C), and chips (D) were mixed in a mass ratio of 68.0:6.0:6.0:20.0 (mixed raw material 5). Next, the mixed raw material 4 was melt-extruded at 280°C through a slit in a T-die using an extruder to form a 44% by mass base layer (base layer Y), a 12% by mass surface layer (surface layer X) on one side of the base layer, and a 44% by mass surface layer (seal layer Z) on one side different from the surface layer of the base layer (a three-type, three-layer structure of surface layer X / base layer Y / seal layer Z).The materials were then 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 amorphous unstretched sheet.

[0085] The resulting unstretched sheet was stretched 3.2 times in the longitudinal direction between a heating roll and a cooling roll at 130°C, and then relaxed 15% in the longitudinal direction. The uniaxially stretched film was then introduced into a tenter, heated at 118°C for 8.6 seconds, and stretched 4.0 times in the transverse direction at 120°C. Further, the film was heat-treated at 225°C and relaxed 3% in the transverse direction. The surface of the sealing layer was then corona-discharged at 0.3 kW using a corona discharge treatment machine manufactured by Kasuga Electric Co., Ltd., to obtain a biaxially stretched polyester film having a thickness of 30 μm.

[0086] In each example, a wide seal range and high transparency were obtained.

[0087] In Comparative Example 1, the heat setting temperature was increased compared to Example 1, resulting in a crystallinity of the sealing layer of less than 0.3 and an increase in the amorphous component, which resulted in an increase in heat seal strength and a decrease in easy peelability at high temperature sealing.

[0088] In Comparative Example 2, the heat setting temperature was low, the crystals in the seal layer melted less, and the crystallinity was greater than 0.9, resulting in low seal strength at 130°C and 150°C.

[0089] In Comparative Example 3, the amount of diethylene glycol copolymer component in the sealing layer was increased compared to Example 1. As a result, the crystallinity of the sealing layer was less than 0.3 and the amount of amorphous component increased, resulting in an increase in heat seal strength and a decrease in easy peelability at high temperature sealing.

[0090] In Comparative Example 4, the amount of diethylene glycol copolymer component in the seal layer was reduced compared to Example 3, resulting in a crystallinity of the seal layer exceeding 0.9 and a decrease in the amorphous component, resulting in a decrease in heat sealability.

[0091] In Comparative Example 5, the film thickness was increased compared to Example 5, and as a result, sufficient heat was not transferred to the surface of the seal layer during heat sealing, and sufficient seal strength was not obtained during heat sealing at low temperatures.

[0092] In Comparative Example 6, the amount of surfactant added to the seal layer was increased compared to Example 10, resulting in an increased amount of bleed-out of the surfactant and a decrease in heat sealability.

[0093] In Comparative Example 7, the copolymerized PET used for the sealing layer was neopentyl glycol copolymerized PET, which has low crystallinity. As a result, the crystallization temperature of the sealing layer was high and the crystallization of the sealing layer was insufficient during high-temperature sealing. As a result, the sealing strength increased too much during high-temperature sealing and the range of appropriate sealing strength became narrower.

[0094]

[0095]

[0096] The polyester sealant film of the present invention is a monomaterial, yet provides an appropriate heat seal strength over a wide temperature range.

Claims

1. A polyester sealant film having a seal layer exhibiting heat sealing properties and a heat-resistant layer laminated on the seal layer, wherein the crystallinity of the surface of the seal layer on the side not having the heat-resistant layer measured by the ATR method is 0.90 or less, the crystallization temperature of the seal layer measured by DSC is 93 to 118°C, and when an A-PET sheet and the seal layer are overlapped and heat-sealed for 1 second under a load of 0.2 MPa, the heat seal strength at heat seal temperatures of 130°C, 150°C, and 180°C is 6 to 20 N / 15 mm.

2. The polyester sealant film according to claim 1, which has a haze of 10.0% or less.

3. The polyester sealant film according to claim 1, which has a heat shrinkage rate of 0.01 to 4.0% at 150°C in both the longitudinal and transverse directions.

4. The polyester sealant film according to claim 1, further comprising particles, the particles having an average particle size of 0.01 to 6 μm, and the content of the particles in the polyester sealant film being 0.01 to 25 mass %.

5. A polyester sealant film according to claim 1, wherein the mass ratio of the particles contained in the sealing layer to the particles contained in the heat-resistant layer (sealing layer:heat-resistant layer) is 0:100 to 45:

55.

6. The polyester sealant film according to claim 1, wherein the contact angle of the surface of the seal layer with water is 21.0° or less.

7. The polyester sealant film according to claim 1, wherein the thickness of the heat-resistant layer is 50 μm or less.

8. A polyester sealant film according to claim 1, wherein the seal layer contains 50 to 100% by mass of polyester relative to 100% by mass of the resin constituting the seal layer.

9. The polyester sealant film according to claim 8, wherein the polyester is a homopolyester and / or a copolymer polyester.

10. The polyester sealant film according to claim 1, wherein the seal layer comprises a copolymer polyester, and the copolymer polyester contains diethylene glycol as a copolymer component.

11. A polyester sealant film according to claim 10, wherein the diethylene glycol component ratio is 11.0 to 19.0 mol % when the diol component constituting the copolymerized polyester contained in the seal layer is taken as 100 mol %.

12. A polyester sealant film according to claim 1, wherein the heat-resistant layer contains 50 to 100% by mass of polyester relative to 100% by mass of the resin constituting the heat-resistant layer.

13. The polyester sealant film according to claim 12, wherein the polyester is a homopolyester and / or a copolymer polyester.

14. A polyester sealant film according to claim 12, wherein the ethylene glycol component ratio is 70 to 100 mol % when the diol component constituting the polyester contained in the heat-resistant layer is taken as 100 mol %.

15. The polyester sealant film according to claim 1, further comprising a surfactant.

16. The polyester sealant film according to claim 15, wherein the ratio of the concentration of the surfactant contained in the heat-resistant layer to the concentration of the surfactant contained in the sealing layer (heat-resistant layer:sealing layer) is 0:100 to 45:

55.

17. A lid material comprising the polyester sealant film according to any one of claims 1 to 16.

18. A packaging material comprising the polyester sealant film according to any one of claims 1 to 16.