Polyester sealant film and package using same

Abstract

The present invention provides a polyester sealant which has excellent heat seal strength between heat seal surfaces, and is capable of maintaining the excellent heat seal strength even after storage. Disclosed is a polyester sealant film which is characterized by being composed of a polyester resin that contains ethylene terephthalate as a main constituent component, and which is also characterized by having at least one heat seal layer and satisfying the following requirements (1) and (2). (1) A heat seal strength reduction rate \{(A-B / A) × 100\} calculated from the maximum heat seal strength A before aging and the maximum heat seal strength B after aging is 0% to 25% inclusive. Meanwhile, A is the value of the maximum heat seal strength when the heat seal layers of the sealant film are heat-sealed in the temperature range of 100°C to 200°C at a pitch of 10°C under 2 kg / cm2 for 2 seconds. B is the value of heat seal strength obtained by evaluating the sealant film under the same conditions as A after 96 hours of aging in an atmosphere at 50°C. (2) The average wavelength Sλa of the surface of the heat seal layer is 43 μm or less.

Description

Polyester sealant film and packaging using the same

[0001] The present invention relates to a polyester sealant film. More specifically, the present invention relates to a polyester sealant film that has excellent heat seal strength between heat seal surfaces and can maintain the excellent heat seal strength even after storage, and to a package using the same.

[0002] Containers made of molded plastic films or sheets are used as packaging materials for foods such as vegetables and prepared dishes. Among these, containers made of polyester materials such as polyethylene terephthalate are widely used, not only because of their beautiful appearance, such as transparency and gloss, but also because they are recyclable. For example, when a container is made of a polyester material, a polyester film is often used as the lid material, and heat sealing is a common method for bonding the lid to the polyester container. Furthermore, polyester films are sometimes used as sealants to be laminated to general-purpose polyester films, and heat sealing performance is important.

[0003] Patent Document 1 discloses a polyester sealant film made from an amorphous polyester raw material. While the film has excellent heat sealing performance, the present inventors have found that the heat sealing strength decreases over time.

[0004] Patent Document 2 discloses a film with a specified enthalpy relaxation amount and good heat sealability. However, since laser irradiation is required, a process of unwinding the film from a roll, irradiating the film with the laser, and then rewinding the film is necessary, resulting in poor productivity. Furthermore, the need for laser irradiation equipment poses the problem of the equipment being large-scale. Furthermore, Patent Document 2 does not disclose any means for controlling the enthalpy relaxation amount. Furthermore, Patent Document 2 does not mention the problem of a decrease in heat seal strength over time.

[0005] International Publication No. WO2020 / 213471 Japanese Patent Application Laid-Open No. 2017-19894

[0006] The present invention aims to solve the above-mentioned problems of the prior art, that is, to provide a polyester sealant that has excellent heat-seal strength between heat-sealable surfaces and can maintain the excellent heat-seal strength even after storage.

[0007] The present invention has the following configuration: [1] A polyester sealant film made of a polyester resin containing ethylene terephthalate as a main component, having at least one heat seal layer, and satisfying the following (1) and (2): (1) The heat seal strength reduction rate after aging {(A-B / A) x 100} calculated from the maximum heat seal strength A before aging and the maximum heat seal strength B after aging is 0% or more and 25% or less. The maximum heat seal strength A before aging is 2 kg / cm2 at 10°C intervals in the temperature range of 100°C to 200°C. ２The maximum heat seal strength B after aging is the value of the maximum heat seal strength when the sealant film is heat-sealed for 2 seconds. The maximum heat seal strength B after aging is the value of the heat seal strength evaluated under the same conditions as the maximum heat seal strength A before aging after 96 hours of aging in a 50°C atmosphere. (2) The average wavelength Sλa of the heat seal layer surface is 43 μm or less. [2] The polyester sealant film according to [1], characterized in that the maximum heat seal strength A before aging is 5 N / 15 mm or more and 50 N / 15 mm or less. [3] The polyester sealant film according to [1] or [2], characterized in that the crystallization temperature of the heat seal layer is 90°C or more and 150°C or less, the melting point of the heat seal layer is 193°C or more and 230°C or less, and the enthalpy relaxation amount ΔH of the heat seal layer after aging under the above conditions is 1.50 J / g or less. [4] The polyester sealant film according to any of [1] to [3], characterized in that the number of initial breaks of the sealant after aging under the above conditions is 2 or less out of 10 samples. [5] The polyester sealant film according to any one of [1] to [4], characterized in that the planar orientation degree ΔP of the heat seal layer surface is 0.010 or more and 0.038 or less. [6] The polyester sealant film according to any one of [1] to [5], characterized in that it comprises a heat seal layer and another layer. [7] The polyester sealant film according to [6], wherein the other layer is a heat-resistant layer. [8] The polyester sealant film according to any one of [1] to [7], characterized in that it is laminated with a gas barrier layer. [9] The polyester sealant film according to any one of [1] to [8], wherein the main constituent component is ethylene terephthalate units in an amount of 50 mol % or more, when the total amount of all constituent components of the polyester resin is taken as 100 mol %.

[10] The polyester sealant film according to any one of [1] to [9], wherein the polyester resin contains at least one monomer other than ethylene terephthalate, selected from the group consisting of neopentyl glycol, 1,4-cyclohexanedimethanol, 1,4-butanediol, and diethylene glycol.

[11] The polyester sealant film according to

[10] , wherein the content of a monomer other than ethylene terephthalate in the heat seal layer is 10 to 50 mol %.

[12] The polyester sealant film according to [7], wherein the content of a monomer other than ethylene terephthalate in the heat-resistant layer is 9 to 20 mol %.

[13] A package, at least in part, comprising the polyester sealant film according to any one of [1] to

[12] .

[0008] The polyester sealant of the present invention has excellent heat seal strength when heat seal surfaces are heat sealed together, and maintains excellent heat seal strength even after a long storage period.

[0009] The polyester sealant film of the present invention will be described below. The polyester sealant film of the present invention has at least one heat seal layer and also has the following preferred properties and configuration.

[0010] 1. Properties of the Sealant Film 1.1 Maximum Heat Seal Strength A Before Aging The maximum heat seal strength A (hereinafter sometimes simply referred to as "sealant") between the heat seal layers of the polyester sealant film of the present invention (hereinafter sometimes simply referred to as "sealant") before aging is preferably 5 N / 15 mm or more and 50 N / 15 mm or less. The maximum heat seal strength A before aging is the maximum heat seal strength at each temperature when the heat seal surfaces are heat sealed at a sealing temperature ranging from 100°C to 200°C (10°C increments from 100°C), a seal bar pressure of 0.2 MPa, and a sealing time of 2 seconds. If the maximum heat seal strength A before aging is less than 5 N / 15 mm, the sealed portion may easily peel, making it impossible to use as a package. The maximum heat seal strength A before aging is more preferably 6 N / 15 mm or more, and even more preferably 7 N / 15 mm or more. A high maximum heat seal strength before aging is preferable, but the currently achievable upper limit is approximately 50 N / 15 mm. In practice, a value of 49 N / 15 mm is considered to be sufficiently preferable. That is, the maximum heat seal strength A before aging is preferably 5 to 50 N / 15 mm, more preferably 6 to 49 N / 15 mm, and even more preferably 7 to 49 N / 15 mm.

[0011] 1.2 Heat Seal Strength Reduction Rate After Aging The heat seal strength reduction rate of the sealant of the present invention after aging must be between 0% and 25%. The heat seal strength reduction rate after aging is calculated using the following formula (1), where the aging conditions are 96 hours in a 50°C atmosphere, the seal strength before aging is A (N / 15 mm), and the seal strength after aging is B (N / 15 mm): Heat Seal Strength Reduction Rate After Aging (%) = (A - B) / A x 100 ... (1) If the heat seal strength reduction rate after aging is greater than 25%, the heat seal strength of the package before and after storage of the polyester film will differ, impairing the stability of the heat seal. Furthermore, the sealed portion will easily peel off or heat sealing will become impossible, making it unusable as a package. A heat seal strength reduction rate after aging of less than 0% indicates an increase in seal strength after aging, resulting in excellent heat sealability, but no increase is observed, and is therefore considered to be in the range of 0% or more under current technology. The rate of decrease in heat seal strength after aging is preferably 0% to 24%, more preferably 0% to 23%. That is, the rate of decrease in heat seal strength after aging is 0 to 25%, preferably 0 to 24%, and even more preferably 0 to 23%.

[0012] 1.3 Planar orientation degree ΔP The planar orientation degree ΔP of the heat seal layer surface of the sealant of the present invention is preferably 0.010 or more and 0.038 or less. The planar orientation ΔP is a value calculated from the refractive index nx in the longitudinal direction, the refractive index ny in the width direction, and the refractive index nz in the thickness direction of the heat seal layer of the sealant, measured with an Abbe refractometer, using the following formula (2): Planar orientation degree ΔP=(nx+ny) / 2-nz (2)

[0013] If ΔP is less than 0.010, the rate of decrease in heat seal strength after aging described above increases, resulting in the problem of insufficient heat seal strength after aging. The reason for this will be explained. First, ΔP indicates the degree of orientation of the polymer chains that make up the heat seal layer of the sealant, and the larger ΔP, the more regularly the polymer main chains are aligned. Since intermolecular forces act between molecular chains, the larger ΔP, the more energy is required to move the molecular chains. Therefore, it is thought that if ΔP is small, the molecular chains will move with less energy.

[0014] Regarding the storage conditions of sealants during actual processing, they are not immediately processed and processed into bags after receipt, but are generally stored for several days, or even several months. The temperature of the storage environment may be controlled at a constant temperature, or it may be affected by the external air and change from low to high temperatures, applying thermal energy to the sealant. This energy causes the molecular chains of sealants with a small ΔP to move, resulting in molecular densification due to enthalpy relaxation and a decrease in heat seal strength after aging. During heat sealing, the polymer undergoes glass transition or melting, causing molecular chain movement, which is thought to cause the polymers on the heat seal surface to bite into or become entangled with each other, completing the heat seal. If the molecular chains are mobile during storage, the amorphous portions may densify due to the energy generated during storage, making the molecular chains less mobile during heat sealing and resulting in a decrease in heat sealability.

[0015] If ΔP is less than 0.010, the molecular chains are prone to movement, which tends to densify the amorphous portion of the heat-sealable layer during storage, resulting in a large decrease in heat-seal strength after aging, which is undesirable. If ΔP is greater than 0.038, the molecular chains are highly aligned, which suppresses the mobility of the molecular chains during heat-sealing, resulting in a decrease in seal strength before aging, which is undesirable. ΔP is more preferably 0.0105 or more and 0.0375 or less, and even more preferably 0.011 or more and 0.037 or less. That is, ΔP is preferably 0.010 to 0.038, more preferably 0.0105 to 0.0375, and even more preferably 0.011 to 0.037.

[0016] 1.4 Enthalpy Relaxation Amount After Aging The enthalpy relaxation amount after aging of the heat seal layer of the sealant of the present invention is preferably 1.50 J / g or less. The enthalpy relaxation amount after aging is the endothermic peak area obtained from the endothermic peak observed on the higher side of the glass transition temperature in differential scanning calorimetry (DSC) of the heat seal layer after 96 hours of aging treatment in a 50°C atmosphere. The enthalpy relaxation amount is considered to be the amount of densification of the amorphous portion in a glassy state over a given period of time (as manifested as an endothermic peak in DSC, it is presumed that the molecular chains are more aligned than before aging). The heat equivalent to this endothermic peak is consumed during heat sealing, resulting in a reduction in the amount of heat applied to the film, and thus a decrease in the heat seal strength after aging. If the enthalpy relaxation amount after aging is greater than 1.50 J / g, the molecular chains are more likely to move during storage, resulting in a large decrease in the heat seal strength after aging, which is undesirable. It is more preferably 1.45 J / g or less, and even more preferably 1.40 J / g or less.

[0017] 1.5 Mean wavelength Sλa of the surface roughness element of the heat seal layer The mean wavelength Sλa of the heat seal layer of the present invention must be 43 μm or less. Sλa is one of the three-dimensional surface roughness parameters of the surface roughness of the heat seal layer when measured with a cutoff of 0.08 mm and a measurement speed of 0.1 mm / sec, and is calculated by the following formula (3) by assuming the two-dimensional arithmetic mean wavelength λa as a three-dimensional surface. Mean wavelength Sλa = 2π × SRa / SΔa (3)

[0018] These parameters, such as SRa (center surface average roughness), SΔa (calculated as a three-dimensional surface from a two-dimensional arithmetic mean slope Δa), and Sλa, are standard data processing parameters and are incorporated into the data processing software of general surface roughness measuring instruments, allowing for automatic calculation and output. The average wavelength Sλa is the average period when the uneven surface structure is calculated as a periodic irregularity. Therefore, a larger Sλa indicates a longer average period (less irregularity) and a smoother surface, while a smaller Sλa indicates a shorter average period and a more irregular surface. The irregularities in the surface shape of the heat-seal layer of a sealant are thought to be significantly influenced by the lubricant and manufacturing conditions. A large amount of lubricant on the surface leads to the formation of irregularities, resulting in a smaller average wavelength, while the lubricant settling into the film leads to a smoother surface and a larger Sλa. The relationship between Sλa and ΔP is explained below. The sealant of the present invention exhibits heat-seal strength by melting the heat-seal layer in the final heat treatment described below. It is believed that this final heat treatment step promotes surface melting, causing the lubricant to settle into the film, smoothing the surface and increasing Sλa. It is believed that a high heat treatment temperature causes the lubricant on the heat-sealed surface to settle, smoothing the surface (increasing Sλa), and causing aligned molecular chains to lose their orientation (decreasing planar orientation ΔP). If Sλa is greater than 43 μm, ΔP is small and molecular chains are more likely to move during storage, resulting in a large amount of enthalpy relaxation after aging and a large rate of decrease in heat-seal strength after aging, which is undesirable. Furthermore, since the surface irregularities are reduced (smoothed), the contact area between films tends to increase when they are overlapped, which is undesirable because it reduces slippage. The average wavelength Sλa is more preferably 42 μm or less, and even more preferably 41 μm or less. The lower limit of Sλa is not particularly limited, and even if Sλa is small, i.e., the surface irregularities are formed, there are no problems with heat-sealability or film transportability. However, when Sλa is small, it is considered that the heat seal layer is not melted sufficiently.Therefore, the molecular chains of the heat seal layer are highly aligned, and the mobility of the molecular chains during heat sealing is suppressed, which may result in a decrease in the seal strength before aging, which is undesirable. A wavelength of 10 μm or more is more preferable, and 11 μm or more is even more preferable. That is, the average wavelength Sλa is 43 μm or less, preferably 10 to 42 μm, and more preferably 11 to 41 μm.

[0019] 1.6 Dynamic Friction Coefficient of Heat-Seal Layer The heat-seal layer of the present invention preferably has a dynamic friction coefficient of 0.1 or more and 0.9 or less. If the dynamic friction coefficient is less than 0.1, the film will be too slippery, and there is a risk of it easily shifting position, for example, when heat-sealing overlapping heat-sealing layers or when stacking films. On the other hand, if the dynamic friction coefficient exceeds 0.9, the film will be less slippery, and problems such as slippage, unevenness, and blocking will easily occur when the film is wound into a roll. The dynamic friction coefficient is more preferably 0.2 or more and 0.8 or less, and even more preferably 0.3 or more and 0.7 or less. That is, the dynamic friction coefficient is preferably 0.1 to 0.9, more preferably 0.2 to 0.8, and even more preferably 0.3 to 0.7.

[0020] 1.7 Number of Initial Breaks After Aging The number of initial breaks after aging for the sealant of the present invention is preferably two or less. The number of initial breaks after aging refers to the number of samples for which the longitudinal breaking elongation is 5% when the breaking elongation is measured 10 times using a tensile tester after 96 hours of heat treatment in a 50°C atmosphere. The reason for the occurrence of initial breaks is thought to be that if the film contains a large amount of crystalline portions (including densification after aging), the stress caused by pulling the film during measurement causes breakage in the crystalline portions, making the film brittle. If the number of initial breaks is three or more samples, the film's tear resistance deteriorates. In polyester-based sealants, the heat seal strength also depends on the tensile strength of the film. Poor tear resistance leads to easy tearing near the heat-sealed portion, resulting in a decrease in seal strength. In addition, it is thought that the amorphous portions become denser due to aging, which can cause a problem of a decrease in heat seal strength. The number of initial breaks is more preferably one or less samples.

[0021] 1.8 Crystallization Temperature and Melting Point The heat seal layer of the sealant of the present invention preferably has a melting point of 193°C or higher and 230°C or lower, as measured by differential scanning calorimetry (DSC), and a crystallization temperature of 90°C or higher and 150°C or lower. If the crystallization temperature exceeds 150°C or is not observed, the heat seal layer of the sealant is considered to be highly amorphous, resulting in a large amount of enthalpy relaxation after aging and a large rate of decrease in heat seal strength after aging, which is undesirable. If the crystallization temperature is not observed, the degree of molecular chain alignment, i.e., ΔP, is considered to be small due to high amorphousness. If the crystallization temperature is lower than 90°C, the crystallization is high, resulting in a large ΔP, which is undesirable because it reduces the seal strength before aging. The crystallization temperature is more preferably 95°C or higher and 145°C or lower, and even more preferably 100°C or higher and 140°C or lower. That is, the crystallization temperature is preferably 90 to 150°C, more preferably 95 to 145°C, and even more preferably 100 to 140°C. A melting point below 193°C or absent entirely is considered to be highly amorphous in the heat-seal layer of the sealant, resulting in a large enthalpy relaxation after aging and a large decrease in heat-seal strength after aging, which is undesirable. A melting point above 230°C is undesirable because it is highly crystalline and reduces the seal strength before aging. The melting point is more preferably 195°C or higher and 225°C or lower, and even more preferably 197°C or higher and 220°C or lower. That is, the melting point is preferably 193 to 230°C, more preferably 195 to 225°C, and even more preferably 197 to 220°C. In the present invention, it is preferable that the crystallization temperature of the heat-seal layer, the melting point of the heat-seal layer, and the enthalpy relaxation ΔH of the heat-seal layer after aging fall within the above-mentioned ranges, and the synergistic effect of these factors allows the above-mentioned effects to be optimally achieved. Control of the amorphous nature of the heat-seal layer will be described in detail in relation to the temperature of the final heat treatment step, which is the final step in the sealant film formation process, as well as the extrusion conditions and raw material composition.

[0022] 1.9 Maximum Heat Seal Strength After Additional Aging The maximum heat seal strength of the sealant of the present invention after additional aging is preferably 5 N / 15 mm or more and 50 N / 15 mm or less. The heat seal strength after additional aging is the maximum heat seal strength at each temperature when a sealant aged under conditions of 192 hours in a 50°C atmosphere is heat-sealed at a temperature range of 100°C to 200°C (in 10°C increments from 100°C), with a sealing bar pressure of 0.2 MPa and a sealing time of 2 seconds, and the heat seal surfaces are heat-sealed together. If the heat seal strength after additional aging is less than 5 N / 15 mm, the sealed portion may easily peel, making it impossible to use as a package. The heat seal strength after additional aging is more preferably 6 N / 15 mm or more, and even more preferably 7 N / 15 mm or more. Although a high heat seal strength after additional aging is preferable, the currently achievable upper limit is approximately 50 N / 15 mm. In practice, even 49 N / 15 mm is considered to be sufficiently preferable. That is, the maximum heat seal strength after additional aging is preferably 5 to 50 N / 15 mm, more preferably 6 to 49 N / 15 mm, and even more preferably 7 to 49 N / 15 mm.

[0023] 2. Layer Structure and Layer Ratio of the Sealant The sealant of the present invention preferably has at least one heat-sealing layer and one heat-resistant layer. Considering that heat sealing is performed using a heated sealing bar (heat jaw) or the like, the sealant of the present invention preferably has a two-layer structure with one heat-sealing layer and one heat-resistant layer to achieve both heat-sealing properties and heat resistance. The structural requirements for each layer will be described later, but the layer with the highest ethylene terephthalate content will be the heat-resistant layer. The sealant layer structure may also include a third layer other than the sealing layer and the heat-resistant layer, but the heat-sealing layer must be located as the outermost layer of at least one of them. The ratio of the heat-sealing layer to the overall thickness of the sealant film is preferably 20% to 80%. A ratio of the heat-sealing layer less than 20% is undesirable because it reduces heat-sealing strength. A ratio of the heat-sealing layer greater than 80% is undesirable because it improves heat-sealing strength but reduces heat resistance and mechanical strength. The ratio of the heat seal layer is more preferably 30% or more and 70% or less.

[0024] Furthermore, the outermost layer (including the heat seal layer) of the sealant of the present invention may be provided with a layer that has been subjected to corona treatment, coating treatment, flame treatment, or the like in order to improve the printability and slipperiness of the film surface, and such a layer may be provided as desired within the scope of the present invention.

[0025] 3. Constituent Materials of the Sealant The following description will be made assuming a two-layer structure consisting of a heat seal layer and a heat resistant layer, which is a preferred embodiment of the present invention.

[0026] 3.1. Types of Polyester Raw Materials The polyester raw materials constituting the sealant of the present invention are those containing ethylene terephthalate units as the main component in each layer described below, for example, the heat-seal layer and heat-resistant layer of the present invention. Here, "main component" refers to a content of 50 mol% or more when the total amount of components is 100 mol%. Furthermore, in the present invention, when the sealant film is a laminate consisting of two layers, a heat-seal layer and a heat-resistant layer, or even a gas barrier layer, it is also a preferred embodiment that the content of ethylene terephthalate units in the heat-resistant layer is greater than the content of ethylene terephthalate units in the heat-seal layer. The ethylene terephthalate units in the heat-seal layer are preferably 50 to 80 mol%, more preferably 55 to 75 mol%. The ethylene terephthalate units in the heat-resistant layer are preferably 80 mol% or more. Furthermore, it is preferable that the polyester used in the polyester-based resin layer of the present invention, for example, the heat-seal layer and heat-resistant layer of the present invention, contains at least one component other than ethylene terephthalate. This is because the presence of components other than ethylene terephthalate improves the heat-seal strength of the heat-seal layer. In the heat-resistant layer, the amount of components other than ethylene terephthalate is preferably small. However, the inclusion of components other than ethylene terephthalate can reduce the difference in shrinkage rate with the heat-seal layer, thereby reducing curling of the laminate. The content of each component differs between the heat-seal layer and the heat-resistant layer, as described below. Examples of dicarboxylic acid monomers that can be components other than terephthalic acid that constitute ethylene terephthalate include aromatic dicarboxylic acids such as isophthalic acid, 1,4-cyclohexanedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and orthophthalic acid; aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, and decanedicarboxylic acid; and alicyclic dicarboxylic acids. However, it is preferable not to include trivalent or higher polycarboxylic acids (e.g., trimellitic acid, pyromellitic acid, and anhydrides thereof) in the polyester. Among the above carboxylic acid components, isophthalic acid is preferred because it facilitates achieving a seal strength of 5 N / 15 mm or more between the heat-seal layers.

[0027] Examples of diol monomers that can be components other than ethylene glycol that constitute ethylene terephthalate include long-chain diols such as neopentyl glycol, 1,4-cyclohexanedimethanol, diethylene glycol, 2,2-diethyl-1,3-propanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 2,2-isopropyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol, hexanediol, and 1,4-butanediol; aliphatic diols such as hexanediol; and aromatic diols such as bisphenol A. These may be used alone or in combination of two or more. However, it is preferable that the polyester does not contain diols having 8 or more carbon atoms (e.g., octanediol, etc.) or polyhydric alcohols having a valence of 3 or more (e.g., trimethylolpropane, trimethylolethane, glycerin, diglycerin, etc.).

[0028] Among these, the use of at least one, more preferably two or more, selected from the group consisting of neopentyl glycol, 1,4-cyclohexanedimethanol, 1,4-butanediol, and diethylene glycol is preferred, as this facilitates achieving a seal strength of 8 N / 15 mm or more between the heat seal layers. It is more preferred to use at least one selected from the group consisting of neopentyl glycol, 1,4-cyclohexanedimethanol, and 1,4-butanediol, and a more preferred embodiment is to use two or more. For example, neopentyl glycol is preferred as a single type, and 1,4-butanediol and neopentyl glycol, or 1,4-butanediol and 1,4-cyclohexanedimethanol are preferred as two types.

[0029] Furthermore, the polyester may contain a polyester elastomer containing ε-caprolactone, tetramethylene glycol, etc. The polyester elastomer has the effect of lowering the melting point of the polyester resin layer, and is therefore particularly suitable for use in the heat seal layer.

[0030] Various additives, such as waxes, antioxidants, antistatic agents, crystal nucleating agents, viscosity reducers, heat stabilizers, coloring pigments, coloring inhibitors, and UV absorbers, can be added to the polyester resin layer constituting the sealant of the present invention as needed. Furthermore, it is preferable to add fine particles as a lubricant to at least the outermost layer of the film to improve the film's slipperiness. Any fine particles can be selected. For example, inorganic fine particles include silica, alumina, titanium dioxide, calcium carbonate, kaolin, and barium sulfate, while organic fine particles include acrylic resin particles, melamine resin particles, silicone resin particles, and cross-linked polystyrene particles. The average particle size of the fine particles can be appropriately selected as needed within the range of 0.05 to 3.0 μm as measured with a Coulter counter.

[0031] As a method for incorporating particles into the polyester resin layer constituting the sealant of the present invention, for example, they can be added at any stage of producing the polyester resin (resin), but it is preferable to add them as a slurry dispersed in ethylene glycol or the like at the stage of esterification or after the completion of the transesterification reaction and before the start of the polycondensation reaction, and then proceed with the polycondensation reaction. Other examples include a method of blending a slurry of particles dispersed in ethylene glycol, water, or other solvent with a polyester resin raw material using a vented kneading extruder, and a method of blending dried particles with a polyester resin raw material using a kneading extruder.

[0032] 3.2. Amount of Polyester Raw Material Component in Heat-Seal Layer The polyester used in the heat-seal layer preferably contains 10 mol% or more and 50 mol% or less of dicarboxylic acid monomers and / or diol monomers (hereinafter sometimes referred to as "monomers other than ethylene terephthalate"), which are components other than terephthalic acid and ethylene glycol that constitute ethylene terephthalate. This is believed to enable adjustment of ΔP and the amount of enthalpy relaxation after aging within a predetermined range. A content of 10 mol% or more is preferred, more preferably 12 mol% or more, even more preferably 14 mol% or more, and even more preferably 25 mol% or more. The upper limit of the content of the monomers other than ethylene terephthalate is 50 mol%. If the content of the monomers other than ethylene terephthalate contained in the heat-seal layer is less than 10 mol%, even if the molten resin is rapidly cooled and solidified after extrusion through the die, it will crystallize during the subsequent stretching and heat-setting steps, making it difficult to achieve a heat-seal strength of 5 N / 15 mm or more, which is undesirable. On the other hand, if the content of the monomers other than ethylene terephthalate in the heat-seal layer is greater than 50 mol%, the increased amorphousness increases the amount of enthalpy relaxation after aging, which is thought to increase the rate of decrease in heat-seal strength after aging, which is undesirable. The heat-seal layer's heat resistance is extremely low, which can lead to blocking around the heat-sealed area during heat-sealing (a phenomenon in which a wider area than intended is sealed due to heat conduction from the heating element), making proper heat-sealing difficult. The content of the monomers other than ethylene terephthalate is preferably 48 mol% or less, even more preferably 46% or less, and even more preferably 45 mol% or less. That is, the content of the monomers other than ethylene terephthalate in the heat-seal layer is preferably 10 to 50 mol%, more preferably 12 to 48 mol%, even more preferably 14 to 46 mol%, and even more preferably 25 to 45 mol%.

[0033] 3.3. Amount of Polyester Raw Material Component in Heat-Resistant Layer The polyester used in the heat-resistant layer preferably contains 9 mol% or more of dicarboxylic acid monomers and / or diol monomers (monomers other than ethylene terephthalate) that constitute the components other than terephthalic acid and ethylene glycol of ethylene terephthalate, more preferably 10 mol% or more, and particularly preferably 11 mol% or more. The upper limit of the content of the monomers other than ethylene terephthalate is 20 mol%. If the content of the monomers other than ethylene terephthalate contained in the heat-resistant layer is less than 9 mol%, the difference in heat shrinkage rate between the heat-sealable layer and the heat-resistant layer becomes large, which may result in significant curling of the sealant. If the difference in the content of the monomers other than ethylene terephthalate contained in the heat-resistant layer and the sealable layer becomes large, the difference in heat shrinkage rate between the layers during heat setting becomes large. Even if cooling after heat setting is strengthened, shrinkage toward the sealable layer may become large, resulting in significant curling. On the other hand, if the content of the monomers other than ethylene terephthalate in the heat-resistant layer is 20 mol % or more, the heat resistance of the sealant may be reduced, such as holes being formed due to the heat applied during heat sealing, which is undesirable. The content of the monomers other than ethylene terephthalate is more preferably 19 mol % or less, and particularly preferably 18 mol % or less. That is, the content of the monomers other than ethylene terephthalate in the heat-resistant layer is preferably 9 to 20 mol %, more preferably 10 to 19 mol %, and even more preferably 11 to 18 mol %. The content of the monomers other than ethylene terephthalate in the heat-resistant layer is preferably lower than the content of the monomers other than ethylene terephthalate in the heat-sealable layer.

[0034] 4. Sealant Production Conditions The sealant film of the present invention not only satisfies the above-mentioned raw material composition, but can also satisfy each of the above requirements by being produced under appropriate conditions. 4.1. Melt Extrusion The sealant of the present invention can be obtained by melt-extruding the polyester raw material described above in 3.1. "Types of Polyester Raw Materials" using an extruder to form an unstretched film, which is then stretched using the specified method described below. Note that if the sealant includes a heat-sealable layer and a heat-resistant layer, or other layers, the timing of laminating the layers may be either before or after stretching. When laminating before stretching, it is preferable to employ a method in which the resins that form the raw materials for each layer are melt-extruded using separate extruders and then joined using a feed block or the like midway through the resin flow path. When laminating after stretching, it is preferable to employ lamination, in which separately produced films are bonded together with an adhesive, or extrusion lamination, in which a molten polyester resin is poured onto the surface layer of a single or laminated film to laminate it. Among these, the method of laminating the layers before stretching is preferred. As described above, the polyester resin can be obtained by polycondensation of a dicarboxylic acid component and a diol component, selecting their types and amounts so as to contain an appropriate amount of a monomer other than ethylene terephthalate. Alternatively, two or more types of polyester chips can be mixed and used as a raw material for the polyester-based resin layer.

[0035] When the raw material resin is melt-extruded, it is preferable to dry the polyester raw material of each layer using a dryer such as a hopper dryer or a paddle dryer, or a vacuum dryer. After drying the polyester raw material of each layer in this way, it is melted and extruded into a laminated film using an extruder.

[0036] As polyester resins are melt-mixed in an extruder, transesterification progresses, resulting in a randomly copolymerized polyester, which increases amorphousity and influences heat-seal strength after aging. Transesterification is affected by factors such as the mixing condition, temperature, and time of the resins in the extruder. In the present invention, the authors discovered that suppressing excessive transesterification through the extruder conditions and raw material composition maintains crystallinity and reduces the amount of enthalpy relaxation after aging, thereby contributing to the suppression of the rate of decline in heat-seal strength after storage. In other words, suppressing densification of the amorphous portion during storage is believed to maintain the mobility of molecular chains before and after aging, i.e., maintain the entanglement of polymer chains during heat-sealing, thereby suppressing the rate of decline in heat-seal strength after aging.

[0037] The resin temperature in the extruder is preferably 200°C or higher and 300°C or lower. At temperatures below 200°C, not only does the transesterification reaction not proceed sufficiently, but the melt viscosity of the polyester resin becomes too high, increasing the extrusion pressure and placing a load on the melt line, which is undesirable. At temperatures above 300°C, transesterification is promoted (amorphism increases), which is preferable because it increases the maximum heat seal strength before aging, but is undesirable because it increases the amount of enthalpy relaxation after aging. The resin temperature range is more preferably 210°C or higher and 290°C or lower, and even more preferably 220°C or higher and 280°C or lower.

[0038] The melt extruder is mainly composed of a cylinder and a screw, but it is preferable that the number of screws is two or less. In order to prevent a decrease in heat seal strength after aging (to minimize the rate of decrease in heat seal strength after aging), it is preferable to suppress transesterification. The authors have found that the transesterification can be adjusted by the extrusion temperature, filling rate, extrusion line length, and extrusion residence time. If the number of screws is three or more, the degree of kneading increases and transesterification proceeds, which is not preferable. It is more preferable that the number of screws is one, i.e., a single screw.

[0039] The filling ratio (Q / N), which is the ratio of the extruder's output rate Q to the screw rotation speed N, is preferably 1.5 or more and 5.0 or less. The filling ratio is given by the following formula (4): Filling ratio = Output rate (kg / h) ÷ Screw rotation speed (rpm) ... formula (4). A filling ratio of more than 5.0 is undesirable because it causes unstable discharge and poor sealant thickness accuracy. Insufficient mixing of the resins prevents the transesterification necessary for achieving seal strength, making it difficult to reduce crystallinity. A filling ratio of less than 1.5 is undesirable because it increases the pressure inside the extruder, potentially causing filter deformation. Furthermore, the high amorphous nature of the resin increases the amount of enthalpy relaxation after aging, causing a decrease in seal strength. A filling ratio of less than 1.5 is more preferable because it is 1.6 or more and 4.8 or less, and even more preferable because it is 1.7 or more and 4.6 or less.

[0040] The residence time in the extruder is preferably 5 to 20 minutes. Residence times exceeding 20 minutes are undesirable because they accelerate transesterification, increase the amount of enthalpy relaxation after aging, and increase the rate of decrease in heat seal strength after aging, as well as lower the intrinsic viscosity and increase the number of initial breaks in the sealant. Residence times less than 5 minutes are undesirable because they make it difficult for the raw materials to be sufficiently melted, and the extrusion pressure increases, potentially causing filter deformation. A more preferable residence time is 6 to 19 minutes, and even more preferable is 7 to 18 minutes.

[0041] Any existing method such as a T-die method or a tubular method can be used for extrusion.

[0042] The film melted by extrusion is then quenched to obtain an unstretched film. As a method for quenching the molten resin, a method in which the molten resin is cast from a die onto a rotating drum and rapidly cooled and solidified to obtain a substantially unoriented resin sheet can be suitably employed.

[0043] The film may be produced by any of the following methods: non-stretching, uniaxial stretching (stretching in at least one of the longitudinal (length) direction and the transverse (width) direction), and biaxial stretching. From the viewpoint of the mechanical strength and productivity of the laminate of the present invention, uniaxial stretching is preferred, and biaxial stretching is more preferred. The following description will focus on a sequential biaxial stretching method of longitudinal stretching-transverse stretching, in which longitudinal stretching is carried out first and then transverse stretching is carried out, but the reverse order of transverse stretching-longitudinal stretching is also acceptable, as it only changes the main orientation direction. A simultaneous biaxial stretching method in which stretching is carried out simultaneously in the longitudinal and transverse directions is also acceptable.

[0044] 4.2. First (Longitudinal) Stretching Stretching in the first direction (longitudinal or longitudinal direction) can be performed by introducing the unstretched film into a longitudinal stretching machine with multiple roll groups arranged in series. For longitudinal stretching, it is preferable to preheat the film using preheating rolls until the film temperature reaches 65°C to 90°C. A film temperature lower than 65°C during stretching is undesirable because it becomes difficult to stretch in the longitudinal direction and is prone to breakage. Temperatures higher than 90°C are also undesirable because the film tends to stick to the rolls, causing the film to wrap around the rolls and contaminate the rolls during continuous production. Once the film temperature reaches 65°C to 90°C, longitudinal stretching is performed. The longitudinal stretching ratio is preferably 1x or more and 5x or less. Because a 1x stretch is not performed longitudinally, a longitudinal stretching ratio of 1x results in a uniaxially stretched film, while a longitudinal stretching ratio of greater than 1.1x results in a biaxially stretched film. By setting the longitudinal stretching ratio to 1.1 times or more, molecular orientation can be imparted to the film in the longitudinal direction, increasing its mechanical strength, making it easier to keep the heat deformation rate when tension is applied to 10% or less. Furthermore, by setting the longitudinal stretching ratio to 1.1 times or more and imparting molecular orientation to the film in the longitudinal direction, it is easier to bring the cooling deformation rate when tension is applied close to 0%. Furthermore, although the upper limit of the longitudinal stretching ratio may be any number of times, a stretching ratio that is too high makes transverse stretching difficult and increases the likelihood of stretching breakage, so it is preferably 5 times or less.

[0045] 4.3. Intermediate Heat Treatment After the first (longitudinal) stretching, a step of heating the film (intermediate heat treatment) is preferably performed to reduce the shrinkage of the film caused by the stretching. This intermediate heat treatment can be performed using a constant length heating method, in which the film is heated while maintaining a constant length, or a relaxation treatment, in which the film is heated while relaxing in the longitudinal direction. Among these, relaxation treatment is a preferred embodiment for reducing the shrinkage of the film in the longitudinal direction caused by the longitudinal stretching.

[0046] Relaxation in the longitudinal direction not only reduces the shrinkage rate of the film in the longitudinal direction, but also reduces the bowing phenomenon (distortion) that occurs in the tenter. This is because, during the subsequent second (transverse) stretching and final heat treatment, the film is heated while both ends in the width direction are held, causing only the center portion of the film to shrink in the longitudinal direction. The longitudinal relaxation rate is preferably 0% to 70% (a relaxation rate of 0% indicates no relaxation). The upper limit of the longitudinal relaxation rate is determined by the raw materials used and the longitudinal stretching conditions, and relaxation cannot be performed beyond this limit. In the polyester-based sealant of the present invention, the upper limit of the longitudinal relaxation rate is 70%. Relaxation in the longitudinal direction can be achieved by heating the film after longitudinal stretching at a temperature of 65°C to 100°C and adjusting the roll speed difference (slowing the roll speed on the downstream side) or shortening the distance between the clips (slowing the moving speed on the downstream side). Any heating means, such as a roll, near infrared rays, far infrared rays, or a hot air heater, can be used. Furthermore, relaxation in the longitudinal direction does not have to be performed immediately after longitudinal stretching; for example, it can be performed during transverse stretching (including the preheating zone) or final heat treatment by narrowing the clip interval in the longitudinal direction (in this case, both ends in the width direction of the film are also relaxed in the longitudinal direction, thereby reducing bowing strain), and can be performed at any timing. After relaxation in the longitudinal direction (or longitudinal stretching if relaxation is not performed), it is preferable to cool the film once, and cooling is preferably performed with a cooling roll having a surface temperature of 20 to 40°C.

[0047] 4.4. Second (Transverse) Stretching After the first (longitudinal) stretching, the film is preferably transversely stretched in a tenter at a stretch ratio of about 1.5 to 5 times, more preferably about 2 to 5 times, and even more preferably about 3 to 5 times, while both edges of the film in the width direction (the direction perpendicular to the longitudinal direction) are held with clips at 65°C to 130°C. Preheating is preferably performed before transverse stretching, and preheating is preferably performed until the film surface temperature reaches 75°C to 120°C. After transverse stretching, the film is preferably passed through an intermediate zone where no active heating operation is performed. Because the temperature in the final heat treatment zone following the tenter's transverse stretching zone is higher than that in the transverse stretching zone, if an intermediate zone is not provided, heat from the final heat treatment zone (hot air itself or radiant heat) will flow into the transverse stretching process. In this case, the temperature in the transverse stretching zone is unstable, resulting in poor film thickness accuracy and variations in heat seal strength. Therefore, it is preferable to pass the transversely stretched film through an intermediate zone for a predetermined time before carrying out final heat treatment. In this intermediate zone, it is important to block the accompanying flow caused by the running of the film and the hot air from the transverse stretching zone and the final heat treatment zone so that when a strip of paper is hung down without the film passing through, the paper hangs down almost completely vertically. A passage time through the intermediate zone of about 1 to 5 seconds is sufficient. If it is shorter than 1 second, the length of the intermediate zone will be insufficient and the heat blocking effect will be insufficient. On the other hand, a longer intermediate zone is preferable, but if it is too long, the equipment will become large, so about 5 seconds is sufficient.

[0048] 4.5. Final Heat Treatment After passing through the intermediate zone, heat treatment is preferably performed in the final heat treatment zone to melt the heat-seal layer and develop heat-seal strength. The degree of melting can be determined by the difference between the heat treatment temperature and the melting point of the heat-seal layer. The difference between the melting point Tm of the heat-seal layer and the heat treatment temperature T (the melting point Tm of the heat-seal layer minus the heat treatment temperature T) is preferably between 0°C and 22°C. As mentioned above, crystallinity is important for suppressing the rate of heat-seal strength loss after aging. If the difference between the melting point and the heat treatment temperature is less than 0°C (i.e., a negative value), the heat-seal layer is excessively melted, increasing amorphousness, decreasing the degree of planar orientation ΔP, reducing the amount of enthalpy relaxation after aging, and increasing the rate of heat-seal strength loss after aging, which is undesirable. Furthermore, excessive melting is undesirable because the film may melt during the heat treatment process and fall into the tenter. If the difference between the melting point and the heat treatment temperature exceeds 22°C, the heat seal layer will not melt sufficiently, resulting in high crystallinity and a decrease in seal strength before aging, which is undesirable. The difference between the melting point and the heat treatment temperature is preferably 1°C to 20°C, more preferably 2°C to 18°C, and even more preferably 3°C to 16°C. The difference between the melting point and the heat treatment temperature is also affected by the melting point of the heat seal layer. If the amorphous nature of the material is high due to the raw material composition or extrusion conditions, the melting point will decrease or even disappear, resulting in a large decrease in heat seal strength after aging, which is undesirable. During the final heat treatment, the shrinkage rate in the width direction can be reduced by shortening the distance between the tenter clips by a desired factor (relaxation in the width direction). Therefore, it is preferable to perform relaxation in the width direction in the final heat treatment within a range of 0% to 10% (a relaxation rate of 0% means no relaxation). Although the higher the relaxation rate in the width direction, the lower the shrinkage rate in the width direction, the upper limit of the relaxation rate (the shrinkage rate in the width direction of the film immediately after transverse stretching) is determined by the raw materials used, the stretching conditions in the width direction, and the heat treatment temperature, and therefore relaxation cannot be performed beyond this limit. In the sealant of the present invention, the upper limit of the relaxation rate in the width direction is 20%.Furthermore, during the final heat treatment, as described above, the distance between the clips of the tenter can be reduced by any desired factor in the longitudinal direction (relaxation in the longitudinal direction).

[0049] 4.6. Cooling After passing through the final heat treatment zone, the film is preferably cooled in the cooling zone with cooling air at 10°C to 30°C. In this case, it is preferable to improve the cooling efficiency by lowering the temperature of the cooling air or increasing the air speed so that the actual temperature of the film at the tenter exit is lower than the glass transition temperature of either the sealing layer or the heat-resistant layer, whichever is lower. The actual temperature refers to the film surface temperature measured with a non-contact radiation thermometer. If the actual temperature of the film at the tenter exit exceeds the glass transition temperature, the film will thermally shrink when both ends of the film held by the clips are released. This is undesirable because the film will curl toward the sealing layer, which has a large thermal shrinkage rate. The film is then wound up while cutting and removing both ends to obtain a film roll.

[0050] 5. Gas Barrier Layer The sealant of the present invention may be provided with a gas barrier layer, if necessary. In the following description, the sealant of the present invention provided with a gas barrier layer will be simply referred to as a "laminate" or a "gas barrier layer laminate."

[0051] 5.1. Properties of Gas Barrier Layer Laminate 5.1.1. Water Vapor Permeability A laminate in which a gas barrier layer is further laminated using the sealant of the present invention has a water vapor permeability of 0.05 [g / (m ２ ・d)] or more 4 [g / (m ２ It is preferable that the water vapor permeability is 4 [g / (m ２ If the water vapor permeability exceeds 0.05 [g / (m ２ If the gas barrier property is less than 0.05 [g / (m ２ The lower limit of the water vapor permeability is 0.05 [g / (m ２d)] is sufficient for practical use. The upper limit of water vapor permeability is 3.8 [g / (m ２ d)], and 3.6 [g / (m ２ It is more preferable that the water vapor permeability is 0.05 to 4 [g / (m ２ d)], more preferably 0.05 to 3.8 [g / (m ２ ·d)], more preferably 0.05 to 3.6 [g / (m ２ ・d)].

[0052] 5.1.2. Oxygen Permeability A laminate obtained by laminating a gas barrier layer using the sealant of the present invention has an oxygen permeability of 0.05 [cc / (m ２ ・d・atm)] or more 4 [cc / (m ２ It is preferable that the oxygen permeability is 4 [cc / (m ２ If the oxygen permeability exceeds 0.05 [cc / (m ２ If the oxygen permeability is less than 0.05 [cc / (m ２ The lower limit of oxygen permeability is 0.05 [cc / (m ２ The upper limit of oxygen permeability is 3.8 [cc / (m ２ .d.atm)], and 3.6 [cc / (m ２ It is more preferable that the oxygen permeability is 0.05 to 4 [cc / (m ２ · d · atm)], more preferably 0.05 to 3.8 [cc / (m ２ ·d·atm)], more preferably 0.05 to 3.6 [cc / (m ２ ·d·atm)].

[0053] 5.2. Raw Material Types and Composition of the Gas Barrier Layer The raw material types of the gas barrier layer are not particularly limited, and conventionally known materials can be used. These raw materials can be appropriately selected to achieve the desired gas barrier properties, etc., depending on the purpose. Examples of raw material types for the gas barrier layer include metals such as silicon, aluminum, tin, zinc, iron, and manganese, as well as inorganic compounds containing one or more of these metals. Examples of such inorganic compounds include oxides, nitrides, carbides, and fluorides. These inorganic substances or inorganic compounds may be used alone or in combination. In particular, the use of silicon oxide (SiOx) or aluminum oxide (AlOx) alone (as a single component) or in combination (as a binary component) is preferred because it can improve the transparency of a sealant provided with a gas barrier layer. When the inorganic compound components are a binary component of silicon oxide and aluminum oxide, the aluminum oxide content is preferably 20% by mass or more and 80% by mass or less, and more preferably 25% by mass or more and 70% by mass or less. An aluminum oxide content of 20% by mass or less is undesirable because it may reduce the density of the gas barrier layer and degrade the gas barrier properties. Furthermore, an aluminum oxide content of 80% by mass or more is undesirable because it reduces the flexibility of the gas barrier layer, making it more susceptible to cracking, and as a result, it may degrade the gas barrier properties. It is preferable for the oxygen / metal element ratio of the metal oxide used in the gas barrier layer to be 1.3 or more and less than 1.8, because this reduces the variation in gas barrier properties and consistently achieves excellent gas barrier properties. The oxygen / metal element ratio can be determined by measuring the amounts of oxygen and metal elements by X-ray photoelectron spectroscopy (XPS) and calculating the oxygen / metal element ratio.

[0054] 5.3. Gas Barrier Layer Formation Method The gas barrier layer formation method is not particularly limited, and any known manufacturing method can be used as long as it does not impair the objectives of the present invention. However, vapor deposition is preferred. Examples include PVD (physical vapor deposition) methods such as vacuum deposition, sputtering, and ion plating, as well as CVD (chemical vapor deposition). Physical vapor deposition is preferred, with vacuum deposition being particularly preferred in terms of production speed and stability. Heating methods used in vacuum deposition include resistance heating, high-frequency induction heating, and electron beam heating. Reactive vapor deposition may also be used, such as introducing oxygen, nitrogen, or water vapor as a reactive gas, or using ozone addition or ion-assisted deposition. The deposition conditions may also be changed, as long as they do not impair the objectives of the present invention, by applying a bias to the substrate, increasing or cooling the substrate temperature, or the like. The gas barrier layer may be directly laminated onto the sealant of the present invention, or another film laminated with a gas barrier layer may be laminated onto the sealant of the present invention.

[0055] The following describes a method for forming a gas barrier layer using vacuum deposition. When forming a gas barrier layer, the sealant (film) of the present invention is transported via a metal roll to a gas barrier layer manufacturing apparatus. An example of the gas barrier layer manufacturing apparatus includes a feed roll, a coating drum, a take-up roll, an electron beam gun, a crucible, and a vacuum pump. The film is placed on the feed roll, passes through the coating drum, and is then wound up on the take-up roll. The film path (within the gas barrier layer manufacturing apparatus) is depressurized by a vacuum pump, and the inorganic material placed in the crucible is evaporated by a beam emitted from the electron gun and deposited onto the film as it passes through the coating drum. During the deposition of the inorganic material, the film is heated and tension is applied between the feed roll and the take-up roll. Excessively high temperatures on the film not only increase the film's thermal shrinkage but also promote softening, making it more susceptible to elongation and deformation due to tension. Furthermore, the temperature drop (cooling) of the film after leaving the vapor deposition process becomes large, and the amount of shrinkage (different from thermal shrinkage) after expansion becomes large, which is undesirable because cracks occur in the gas barrier layer and it becomes difficult to achieve the desired gas barrier properties. On the other hand, a lower temperature applied to the film is preferable because deformation of the film is suppressed, but the amount of evaporation of the inorganic material decreases, which reduces the thickness of the gas barrier layer, raising concerns that the desired gas barrier properties may not be achieved. The temperature applied to the film is preferably 100°C or higher and 180°C or lower, more preferably 110°C or higher and 170°C or lower, and even more preferably 120°C or higher and 160°C or lower.

[0056] 6. Overcoat Layer 6.1. Types of Overcoat Layer The sealant of the present invention may have an overcoat layer formed on top of the gas barrier layer described above in "5. Gas Barrier Layer" for the purpose of improving scratch resistance and further gas barrier properties. The type of overcoat layer is not particularly limited, and conventionally known materials such as a composition consisting of a urethane resin and a silane coupling agent, a compound consisting of an organosilicon and its hydrolyzate, and a water-soluble polymer having a hydroxyl group or a carboxyl group can be used. These materials can be appropriately selected according to the purpose to achieve the desired gas barrier properties, etc. Furthermore, the overcoat layer may contain one or more additives for the purpose of imparting antistatic properties, UV absorption, coloring, thermal stability, slip properties, etc., within a range that does not impair the purpose of the present invention. The type and amount of each additive can be appropriately selected according to the desired purpose.

[0057] 6.2. Method for Forming an Overcoat Layer When forming an overcoat layer, the sealant of the present invention or a laminate comprising the sealant of the present invention and a gas barrier layer (hereinafter collectively referred to as the substrate film) is transported to a coating facility via a metal roll. Examples of the facility configuration include an unwinding roll, a coating process, a drying process, and a winding process. During overcoating, the laminate set on the unwinding roll passes through a metal roll and undergoes a coating process and a drying process before finally being guided to a winding roll. The coating method is not particularly limited, and conventionally known methods such as gravure coating, reverse coating, dipping, low coating, air knife coating, comma coating, screen printing, spray coating, gravure offset, die coating, and bar coating can be used and can be appropriately selected depending on the desired purpose. Among these, gravure coating, reverse coating, and bar coating are preferred from the viewpoint of productivity. As the drying method, one or a combination of two or more heating methods such as hot air drying, hot roll drying, high frequency irradiation, infrared irradiation, and UV irradiation can be used.

[0058] In the drying process, the substrate film is heated and tension is applied between metal rolls. If the temperature to which the substrate film is heated in the drying process is too high, not only will the substrate film experience significant thermal shrinkage, but softening will also occur, making extensional deformation due to tension more likely, and cracks will likely occur in the gas barrier layer of the substrate film. Furthermore, the temperature drop (cooling) of the laminate after the drying process will be significant, which will increase the amount of shrinkage (different from thermal shrinkage) after expansion, causing cracks in the gas barrier layer and overcoat layer, making it difficult to achieve the desired gas barrier properties, which is undesirable. On the other hand, a lower temperature to which the substrate film is heated is preferable because it suppresses deformation of the substrate film, but it will make it difficult to dry the solvent in the coating liquid, raising concerns that the desired gas barrier properties will not be achieved. The temperature to which the substrate film is heated is preferably 60°C or higher and 200°C or lower, more preferably 80°C or higher and 180°C or lower, and even more preferably 100°C or higher and 160°C or lower.

[0059] 7. Packaging Structure and Bag-Making Method A sealant having the above properties, a sealant provided with a gas barrier layer as described in "5. Gas Barrier Layer," or a sealant provided with an overcoat layer as described in "6. Overcoat Layer" can be suitably used as a packaging structure. The sealant of the present invention can be used alone to form a bag, or it may be laminated with other materials. Examples of other layers constituting the sealant include, but are not limited to, unstretched films containing polyethylene terephthalate as a constituent component, unstretched, uniaxially or biaxially oriented films containing other amorphous polyesters as constituent components, unstretched, uniaxially or biaxially oriented films containing nylon as a constituent component, and unstretched, uniaxially or biaxially oriented films containing polypropylene as a constituent component. The method for using the sealant in a packaging structure is not particularly limited, and conventionally known manufacturing methods such as coating, lamination, and heat sealing can be used.

[0060] At least a portion of the package may be made of the sealant of the present invention, but a configuration in which the sealant is present throughout the entire package is preferred because it improves the gas barrier properties of the package. The sealant of the present invention may be present in any layer of the package, but considering the anti-fogging properties of the inner surface of the package and the heat-sealing strength when manufacturing the bag, a configuration in which the heat-sealing layer of the sealant of the present invention is the innermost layer of the bag is preferred. The method for manufacturing a package containing the sealant of the present invention is not particularly limited, and conventional manufacturing methods such as heat sealing using a heat bar (heat jaw), adhesion using hot melt, and center sealing using a solvent can be used. Packages containing the sealant of the present invention can be suitably used as packaging materials for various items such as food, pharmaceuticals, and industrial products.

[0061] This application claims priority based on Japanese Patent Application No. 2023-125647, filed on August 1, 2023. The entire contents of the specification of Japanese Patent Application No. 2023-125647, filed on August 1, 2023, are incorporated herein by reference.

[0062] Next, the present invention will be specifically explained using examples and comparative examples, but the present invention is not limited to the embodiments of these examples and can be appropriately modified within the scope of the present invention.

[0063] <Preparation of Polyester Raw Materials> [Synthesis Example 1] A stainless steel autoclave equipped with a stirrer, thermometer, and partial reflux condenser was charged with 100 mol% dimethyl terephthalate (DMT) as a dicarboxylic acid component and 100 mol% ethylene glycol (EG) as a polyhydric alcohol component, with the ethylene glycol being 2.2 times the molar ratio of dimethyl terephthalate. Using 0.05 mol% (relative to the acid component) of zinc acetate as a transesterification catalyst, a transesterification reaction was carried out while distilling off the resulting methanol. Subsequently, 0.225 mol% (relative to the acid component) of antimony trioxide was added as a polycondensation catalyst, and a polycondensation reaction was carried out at 280°C under reduced pressure of 26.7 Pa to obtain a polyester (A) with an intrinsic viscosity of 0.75 dl / g. This polyester (A) was polyethylene terephthalate. The composition of polyester (A) is shown in Table 1.

[0064] Synthesis Example 2 Polyesters (B) to (F) were obtained by changing the monomers using the same procedure as in Synthesis Example 1. The composition of each polyester is shown in Table 1. In Table 1, TPA is terephthalic acid, IPA is isophthalic acid, BD is 1,4-butanediol, NPG is neopentyl glycol, CHDM is 1,4-cyclohexanedimethanol, and DEG is diethylene glycol. In addition, when producing polyester (F), SiO ２ (Sylysia 266 manufactured by Fuji Silysia Ltd.) was added at a ratio of 20,000 ppm to the polyester. Each polyester was appropriately cut into chips. The compositions of polyesters (B) to (F) are shown in Table 1.

[0065]

[0066] <Method of manufacturing polyester sealant film>

[0067] Example 1: The raw materials for the heat-sealable layer (Layer A) were a mixture of polyester A, polyester B, polyester E, and polyester F in a mass ratio of 9:60:24:7. The raw materials for the heat-resistant layer (Layer B) were a mixture of polyester A, polyester B, polyester E, and polyester F in a mass ratio of 50:37:6:7. The mixed raw materials for Layer A and Layer B were each fed into separate screw extruders and melted at 280°C. The molten resins were joined by a feed block midway through the flow path, extruded from a T-die, and cooled on a chill roll set at a surface temperature of 30°C to obtain an unstretched laminated film. The flow path for the molten resin was set so that one side of the laminated film was Layer A and the other side was Layer B (a two-layer structure consisting of Layer A and Layer B). The extrusion rate was adjusted so that the thickness ratio of Layer A to Layer B was 44 / 56. The unstretched laminated film obtained by cooling and solidifying was introduced into a longitudinal stretching machine equipped with a series of rolls, preheated on a preheating roll until the film temperature reached 87°C, and then stretched 3.8 times. Immediately after longitudinal stretching, the film was passed through a heating furnace set at 90°C using a hot air heater, and subjected to a 20% relaxation treatment in the longitudinal direction by utilizing the speed difference between the rolls at the entrance and exit of the heating furnace. The longitudinally stretched film was then forcibly cooled by a cooling roll set at a surface temperature of 25°C.

[0068] The relaxed film was introduced into a transverse stretching machine (tenter) and preheated for 5 seconds until the surface temperature reached 105°C, after which it was stretched 4.0 times in the width direction (transverse direction). The transversely stretched film was then introduced directly into the intermediate zone and passed through in 1.0 second. In the intermediate zone of the tenter, the hot air from the final heat treatment zone and the hot air from the transverse stretching zone were blocked so that when a strip of paper was hung down without the film passing through, the paper would hang down almost completely vertically. The film then passed through the intermediate zone and was introduced into the final heat treatment zone and heat-treated at 205°C for 5 seconds. Simultaneously with the heat treatment, the clip spacing in the film width direction was narrowed to perform a 3% relaxation treatment in the width direction. After passing through the final heat treatment zone, the film was cooled with 30°C cooling air for 5 seconds. The actual film temperature at the tenter exit was 40°C. Both edges were cut off and the resulting film was wound into a roll with a width of 600 mm, thereby continuously producing a biaxially stretched sealant with a thickness of 30 μm over a predetermined length. The properties of the resulting sealant were evaluated using the methods described above. The production conditions and evaluation results are shown in Table 2.

[0069] [Examples 2 to 7] In Examples 2 to 7, polyester sealant films were continuously produced by arbitrarily changing the blending ratio of raw materials, extrusion output rate, extrusion ratio of raw material resin, final heat treatment conditions, and sealant thickness compared to Example 1. The production conditions and evaluation results for each sealant are shown in Table 2.

[0070] Example 8: Polyester A and polyester F were mixed at a mass ratio of 93:7 to form the heat-sealable layer (Layer A), and polyester A and polyester F were mixed at a mass ratio of 93:7 to form the heat-resistant layer (Layer B). The mixed materials for Layer A and Layer B were each fed into separate screw extruders and melted at 270°C. The molten resins were joined by a feed block midway through the flow path, extruded from a T-die, and cooled on a chill roll set at a surface temperature of 30°C to obtain an unstretched laminated film. The flow path for the molten resin was set so that one side of the laminated film was Layer A and the other side was Layer B (a two-layer structure consisting of Layer A and Layer B), and the extrusion rate was adjusted so that the thickness ratio of Layer A to Layer B was 50 / 50. The unstretched laminated film obtained after cooling and solidification was introduced into a longitudinal stretching machine equipped with multiple roll groups arranged in series, preheated on a preheating roll until the film temperature reached 87°C, and then stretched 1.5 times. Thereafter, the longitudinally stretched film was forcibly cooled by a cooling roll set at a surface temperature of 25°C.

[0071] The longitudinally stretched film was introduced into a transverse stretching machine (tenter) and preheated for 5 seconds until the surface temperature reached 105°C, after which it was stretched 1.5 times in the width direction (transverse direction). The transversely stretched film was then introduced directly into the intermediate zone and passed through in 1.0 second. In the intermediate zone of the tenter, the hot air from the final heat treatment zone and the hot air from the transverse stretching zone were blocked so that when a strip of paper was hung down without the film passing through, the paper would hang down almost completely vertically. The film then passed through the intermediate zone and was introduced into the final heat treatment zone and heat-treated at 200°C for 5 seconds. After passing through the final heat treatment zone, the film was cooled with cooling air at 30°C for 5 seconds. At this time, the actual film temperature at the tenter exit was 40°C. Both edges were cut and removed, and the film was wound into a roll with a width of 600 mm, thereby continuously producing a biaxially stretched sealant with a thickness of 30 μm over a predetermined length. The properties of the resulting sealant were evaluated using the above-mentioned method. The production conditions and evaluation results are shown in Table 2.

[0072] [Example 9] A sealant was produced in the same manner as in Example 8, except that the raw material composition of Layer A and Layer B, the longitudinal stretch ratio, and the widthwise stretch ratio were changed. The properties of the resulting sealant were evaluated by the methods described above. The production conditions and evaluation results are shown in Table 2.

[0073] [Examples 10 and 11] Sealant was obtained in the same manner as in Example 3, except that a gas barrier layer was provided as explained below. The sealant was unwound from the roll, and a gas barrier layer was continuously provided on the opposite side of the heat seal layer. Using the materials shown in Table 2 as the deposition source, a film was formed by vacuum deposition using a vacuum deposition machine, introducing oxygen gas as needed. The production conditions and evaluation results for each sealant are shown in Table 2.

[0074] Example 12 A sealant was obtained in the same manner as in Example 3, except that a gas barrier layer was provided, as explained below. The side opposite the gas barrier layer of Ecosyar VE100-12 μm (manufactured by Toyobo Co., Ltd.) was laminated to the side opposite the heat seal side of the sealant obtained in Example 3, to obtain the sealant of Example 12. The evaluation results are shown in Table 2.

[0075] Comparative Examples 1 to 7 Each sealant was obtained by the manufacturing method shown in Table 2. The evaluation results are shown in Table 2.

[0076]

[0077]

[0078]

[0079] <Method for Evaluating Sealants> The method for evaluating sealants is as follows.

[0080] [Maximum Heat-Seal Strength Before Aging] The heat-seal strength was measured in accordance with JIS Z1707. Specific procedures are as follows: The heat-sealed surfaces of the samples were bonded together using a heat sealer. The heat-sealing conditions were an upper bar temperature ranging from 100°C to 200°C (in 10°C increments from 100°C), a pressure of 0.2 MPa, and a time of 2 seconds. The heat-sealed sample was cut out to a seal width of 15 mm. The peel strength was measured using a universal tensile tester "DSS-100" (manufactured by Shimadzu Corporation) at a tensile speed of 200 mm / min. The peel strength is expressed as the strength per 15 mm (N / 15 mm). The seal strength was measured in a temperature range from 100°C to 200°C, and the maximum seal strength was taken as the maximum heat-seal seal strength.

[0081] [Reduction rate of heat seal strength after aging] The aging conditions were such that the sealant was stored in an incubator in an atmosphere of 50°C for 96 hours, with the heat seal strength before aging being designated A and the heat seal strength after aging being designated B. The evaluation method for the heat seal strength B after aging was the same as the evaluation method for the heat seal strength A before aging, except that no aging treatment was performed. The reduction rate of heat seal strength after aging was calculated using the following formula (1): Reduction rate of heat seal strength after aging (%) = (A - B) / A x 100 (1)

[0082] [Plane Orientation Degree ΔP] The refractive index was measured in accordance with JIS K7105. A sample was prepared by cutting the sealant to a width of 2 cm and a length of 3 cm. The sample was prepared by cutting the longitudinal direction of the sample parallel to the longitudinal direction of the film. The heat-sealed surface was measured using an Abbe Refractometer 4T manufactured by Atago Optical Co., Ltd., and the plane orientation degree ΔP was calculated from the longitudinal refractive index nx, the width refractive index ny, and the thickness refractive index nz according to the following formula (2): Plane orientation degree ΔP = (nx + ny) / 2 - nz (2) The solvent used for the measurement was diiodomethane, and the measurement conditions were 23°C and 60% RH or less. The number of measurements was n = 3. For a film with two or more layers, the lower values ​​for nx and ny were read, and the higher value for nz was used as the refractive index of the heat-sealed layer.

[0083] [Amount of Enthalpy Relaxation] Using a temperature-modulated differential scanning calorimeter (DSC) "Q100" (manufactured by TA Instruments), 5.0 mg of only the heat seal layer of the sealant was weighed out in a hermetic aluminum pan, and the temperature was raised from 30° C. to 300° C. at a rate of 10° C. / min to measure an endothermic curve. The area of ​​the endothermic peak observed on the high temperature side of the glass transition temperature in the obtained endothermic curve, i.e., the amount of enthalpy relaxation, was measured.

[0084] [Melting Point and Crystallization Temperature] These were determined in accordance with JIS-K7121-1987 using a temperature-modulated differential scanning calorimeter (DSC) "Q100" (manufactured by TA Instruments). 5.0 mg of only the heat seal layer of the sealant was weighed into a hermetic aluminum pan, and the temperature was raised from 30°C to 300°C at a rate of 10°C / min to measure the endothermic curve. The peak temperature appearing in the range of 90°C to 160°C of the obtained endothermic curve was taken as the crystallization temperature Tc1. The peak temperature appearing at 180°C or higher was taken as the melting point Tm. When two melting points appeared, the lowest one was taken as the melting point. For these analyses, analysis software attached to the DSC ("Trios" manufactured by TA Instruments) was used.

[0085] [Number of Initial Breaks] The breaking elongation of 10 sealant films was measured in the longitudinal direction using a tensile tester (Instron 5985, manufactured by Instron Corporation) in accordance with JIS-C-2318, and the number of samples with a breaking elongation of 5% or less was determined. The samples used were cut into a shape of 100 mm in the longitudinal direction and 15 mm in the width direction.

[0086] [Average wavelength Sλa] Using a contact-type three-dimensional surface roughness meter (model ET-4000A) manufactured by Kosaka Laboratory Co., Ltd., the average wavelength (Sλa) of the film surface was measured by the stylus method under the following conditions. The sample was 20 mm long x 20 mm wide, the measurement surface was the heat-sealed surface, and it was set so that the MD direction was at 45° to the left. The measurement conditions were as follows, and the average value of three measurements was used. Stylus tip radius: 0.5 μm Stylus pressure: 50 μN Cutoff value: 80 μm Measurement length: 1000 μm Measurement speed: 0.1 μm / sec Measurement interval: 2 μm Number of measurements: 100

[0087] [Dynamic Friction Coefficient] In accordance with JIS K-7125, a tensile tester (Tensilon RTG-1210 manufactured by A&D Corporation) was used to determine the dynamic friction coefficient when the heat-sealed surfaces of the sealants were joined together under an environment of 23°C and 65% RH. The weight of the sled (weight) around which the upper film was wrapped was 1.5 kg, and the size of the base area of ​​the sled was 63 mm long x 63 mm wide. The pulling speed during friction measurement was 200 mm / min.

[0088] [Maximum Heat-Seal Strength After Additional Aging] The aging conditions involved storing the sealant in an incubator at 50°C for 196 hours, and measuring the heat-seal strength in accordance with JIS Z1707. The specific procedure is as follows: The heat-sealed surfaces of the samples were bonded together using a heat sealer. The heat-sealing conditions were a temperature range of 100°C to 200°C (in 10°C increments from 100°C), a pressure of 0.2 MPa, and a time of 2 seconds. The heat-sealed samples were cut to a seal width of 15 mm. Peel strength was measured at a tensile speed of 200 mm / min using a universal tensile tester "DSS-100" (Shimadzu Corporation). Peel strength is expressed as the strength per 15 mm (N / 15 mm). Seal strength was measured over a temperature range of 100°C to 200°C, and the maximum seal strength was taken as the maximum heat-seal strength.

[0089] [Gas Barrier Properties] Water vapor permeability and oxygen permeability were evaluated as gas barrier properties by the following methods. Water vapor permeability was measured in accordance with JIS K7126 Method B. Using a water vapor permeability measuring device (PERMATRAN-W3 / 33MG, manufactured by MOCON Corporation), water vapor permeability was measured in the direction in which humidity-conditioning gas permeated from the seal layer side of the laminate to the gas barrier layer side under an atmosphere of 40°C temperature and 90% RH. Oxygen permeability was measured in accordance with JIS K7126-2 Method. Using an oxygen transmission rate measuring device (OX-TRAN 2 / 20, manufactured by MOCOM Corporation), oxygen permeability was measured in the direction in which oxygen permeated from the seal layer side of the laminate to the gas barrier layer side under an atmosphere of 23°C temperature and 65% RH. Note that before measuring water vapor permeability and oxygen permeability, the humidity was 65% RH. The sample was left in the atmosphere for 4 hours to condition the humidity.

[0090] [Thickness of inorganic thin film] A sample cut to 1 mm in the longitudinal direction and 10 mm in the width direction was embedded in epoxy resin for electron microscopy, and then fixed in a sample holder of an ultramicrotome. A cross-sectional section parallel to the short side of the embedded sample piece was prepared. Next, a significantly undamaged portion of this thin film slice was observed using a transmission electron microscope (JEOL, JEM2010). After observation at an acceleration voltage of 200 kV and 20,000x magnification, the thickness of each layer was measured at 100 points, and the average was taken as the thickness.

[0091] [Film Evaluation Results] As shown in Table 2, all of the sealants of Examples 1 to 12 satisfied the heat seal strength reduction rate after aging, Sλa, enthalpy relaxation amount after aging, number of initial breaks after aging, and planar orientation ΔP. Therefore, they had excellent seal strength before aging and were able to maintain heat seal performance before and after storage, and had excellent performance as polyester sealant films. On the other hand, Comparative Examples 1 to 7 had a large enthalpy relaxation amount after aging, and therefore showed a large heat seal strength reduction rate after aging. Therefore, they were not suitable as sealant films that can maintain heat seal performance even after storage.

[0092] The polyester sealant of the present invention has excellent heat seal strength between heat seal surfaces, and maintains excellent heat seal strength even after a long storage period.

Claims

1. A polyester sealant film that is composed of a polyester resin whose main component is ethylene terephthalate, has at least one heat seal layer, and satisfies the following (1) and (2): (1) The heat seal strength reduction rate after aging {(A-B / A) x 100} calculated from the maximum heat seal strength A before aging and the maximum heat seal strength B after aging is 0% or more and 25% or less. The maximum heat seal strength A before aging is 2 kg / cm when the heat seal layers of the sealant film are bonded to each other at a temperature range of 100°C to 200°C at 10°C intervals. ２ The maximum heat seal strength B after aging is a value of heat seal strength evaluated under the same conditions as the maximum heat seal strength A before aging after aging the sealant film for 96 hours in an atmosphere of 50° C. (2) The average wavelength Sλa of the heat seal layer surface is 43 μm or less 2. The polyester sealant film according to claim 1, characterized in that the maximum heat seal strength A before aging is 5 N / 15 mm or more and 50 N / 15 mm or less.

3. The polyester sealant film according to claim 1, characterized in that the crystallization temperature of the heat seal layer is 90°C or higher and 150°C or lower, the melting point of the heat seal layer is 193°C or higher and 230°C or lower, and the enthalpy relaxation amount ΔH of the heat seal layer after aging under the above conditions is 1.50 J / g or less.

4. The polyester sealant film according to claim 1, wherein the number of initial breaks of the sealant after aging under the above conditions is 2 or less out of 10 samples.

5. The polyester sealant film according to claim 1, characterized in that the planar orientation degree ΔP of the heat seal layer surface is 0.010 or more and 0.038 or less.

6. The polyester sealant film according to claim 1, comprising a heat seal layer and other layers.

7. The polyester sealant film according to claim 6, wherein the other layer is a heat-resistant layer.

8. The polyester sealant film according to claim 1, characterized in that a gas barrier layer is laminated thereon.

9. A polyester sealant film according to claim 1, wherein the main constituent component is ethylene terephthalate units in an amount of 50 mol % or more when the total amount of the constituent components of the polyester resin is taken as 100 mol %.

10. The polyester sealant film according to claim 1, wherein the polyester resin contains at least one monomer other than ethylene terephthalate selected from the group consisting of neopentyl glycol, 1,4-cyclohexanedimethanol, 1,4-butanediol, and diethylene glycol.

11. The polyester sealant film according to claim 10, wherein the content of monomers other than ethylene terephthalate in the heat seal layer is 10 to 50 mol %.

12. The polyester sealant film according to claim 7, wherein the content of monomers other than ethylene terephthalate in the heat-resistant layer is 9 to 20 mol %.

13. A package, at least a part of which is made of the polyester sealant film according to any one of claims 1 to 12.

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