JP7727482B2 - Laminated films and packaging containers - Google Patents

Description

The present invention relates to a laminated film for use in packaging bags formed into a bag shape by thermally bonding the laminated film, a laminated film for use as a lid material that is thermally bonded to a container body, and a packaging container.

Currently, packaging bags (pouches) and cup containers with lids attached are used as packaging containers for packaging and storing liquid or solid foods, beverages, cosmetics, medicines, and other contents. For example, packaging bags are used as packaging containers for storing contents such as shampoo, detergent, and cooked or semi-cooked foods. A laminated film, consisting of a base layer and a sealant layer, is stacked with the sealant layers facing each other and heat-sealed around the periphery to form a bag-like shape, with the contents stored in the inner storage compartment (see, for example, Patent Document 1). Another example of a cup container with a lid attached is one in which the sealant layer of a laminated film is heat-sealed to the edge flange of a cup-shaped container body for storing contents such as yogurt, jelly, or pudding, and sealed (see, for example, Patent Document 2).

Meanwhile, in recent years, in the area of packaging containers, efforts have been made to reduce the amount of plastic used and to recycle plastics from the perspective of resource conservation, environmental protection, and other environmental impacts.
One way to reduce the amount of plastic used is to make the laminated film thinner, but if the sealant layer is made thinner, sufficient heat seal strength cannot be obtained, which reduces the sealability and may result in leakage of the contents.
Furthermore, conventionally, olefin resins such as linear short-chain branched polyethylene (LLDPE), high-pressure low-density polyethylene (LDPE), or cast polypropylene (CPP) have been widely used as materials for sealant layers, but depending on the type of material used to form the base layer, it may not be possible to obtain high-quality recycled pellets from the laminated film, resulting in extremely low recyclability.
Furthermore, laminated films for forming packaging bags are required to have puncture resistance. High puncture resistance is required from the viewpoint of external contact, which prevents the packaging bag from tearing when it comes into contact with a sharp object with a pointed tip, and from the viewpoint of internal contact, which prevents the packaging bag from tearing when it is filled with not only liquids but also solids with corners. In addition to bag tearing, films with low puncture strength are also brittle, so they require great care in handling during film formation and processing, and are undesirable because they can cause breakage due to, for example, tension fluctuations or film misalignment during slitting or addition.

JP 2015-150807 A JP 2014-46983 A

The present invention aims to solve the above-mentioned problems by providing a laminated film and packaging container that, despite being thin, has good heat sealing properties, reduces environmental impact, and exhibits high puncture strength both before and after retort processing.

The laminated film of the present invention is a laminated film having a sealant layer provided on one side of a base layer,
the sealant layer is formed from a thermoplastic polyester resin,
The thermoplastic polyester resin contains a heat-sealing property enhancing component,
The content of the heat-sealability enhancing component in the thermoplastic polyester resin is 21% by mass or more,
The puncture strength is 4N or more,
The above problem is solved by making the thickness of the sealant layer 25 μm or less and the heat seal strength of the laminated film 30 N/15 mm or more .
The packaging container of the present invention is characterized by using the above laminated film.

According to the laminated film of the present invention, the sealant layer is formed from a thermoplastic polyester resin, and thus good heat sealing properties are obtained despite the thin layer, and as a result, a packaging container that prevents leakage of contents while reducing the environmental load can be obtained. Furthermore, when the base layer is formed from a material containing polybutylene terephthalate resin as a main component, when this laminated film is used as a material for packaging bags for retort use, high puncture strength is obtained both before and after retort treatment.
Furthermore, by including a thermoplastic polyester resin as the primary material in the sealant layer and further forming the base layers other than the sealant layer from a polyester resin, the entire laminated film is constructed primarily from a polyester resin, which means that it can be easily recycled into high-quality polyester materials and polyester products, resulting in high recyclability and further reducing the environmental impact.

1 is a cross-sectional view showing an outline of a laminated film according to one embodiment of the present invention.

[Laminated film]
As shown in FIG. 1, the laminated film according to one embodiment of the present invention has a sealant layer 150 provided on one side (the upper side in FIG. 1) of a base layer 110 .

[Main constituent materials of sealant layer]
The sealant layer 150 is made of a thermoplastic polyester resin.
The thermoplastic polyester resin contains a heat-sealability enhancing component. Specifically, the thermoplastic polyester resin is a polyester copolymer containing structural units derived from the heat-sealability enhancing component (hereinafter also referred to as a "specific polyester copolymer"), a resin in which a heat-sealability enhancing component is dispersed and mixed in a polyester polymer (hereinafter also referred to as an "other polyester polymer") that does not contain structural units derived from the heat-sealability enhancing component (hereinafter also referred to as a "heat-sealability enhancing component mixed resin"), or a mixture of these as the main material. Because the sealant layer 150 is formed from a thermoplastic polyester resin containing a heat-sealability enhancing component, the heat-seal strength of the laminate film 100 can be 30 N/15 mm or more even when the thickness of the sealant layer 150 is thin, for example, 25 μm or less.

The specific polyester copolymers include those containing structural units derived from polyoxyalkylene glycol as a heat-sealing reinforcing component in other polyester polymers described below. Examples of polyoxyalkylene glycols include polytetramethylene ether glycol (PTMG) and polyethylene glycol (PEG). As the specific polyester copolymer, it is preferable to use a polybutylene terephthalate copolymer containing structural units derived from PTMG (PTMG-containing PBT copolymer). These specific polyester copolymers can be used alone or in combination of two or more.
Examples of other polyester polymers include polyethylene naphthalate, polytrimethylene terephthalate, polytrimethylene naphthalate, polybutylene naphthalate, polyethylene furanoate, and thermoplastic polyester elastomers (TPCs). In particular, polyethylene terephthalate and polybutylene terephthalate are more preferable from the viewpoints of mechanical properties, heat resistance, and economic rationality due to their widespread availability and low cost. These resins may also be copolymers containing copolymerization components such as dicarboxylic acids such as isophthalic acid, diols such as 1,4-cyclohexanedimethanol and neopentyl glycol, and polyfunctional compounds such as trimellitic acid and pentaerythritol. These other polyester polymers may be used alone or in combination of two or more.
The heat-sealing property reinforcing component mixed resin is mainly composed of the above other polyester resins.
When the thermoplastic polyester resin is primarily composed of a specific polyester copolymer, the resin may further contain the above-mentioned other polyester polymers that do not contain a heat-sealability enhancing component. In this case, the mixing ratio of the specific polyester copolymer in the thermoplastic polyester resin is preferably 50% by mass or more, more preferably 70% by mass or more, and particularly preferably 100% by mass. If the mixing ratio of the specific polyester copolymer in the thermoplastic polyester resin is too low, the content of the specific polyester copolymer may not be sufficiently ensured, and the thinned sealant layer 150 may not have sufficient heat-sealability.
The sealant layer 150 may be formed from a mixed resin of the thermoplastic polyester resin and a thermoplastic resin other than polyester. However, from the viewpoint of recyclability, the amount of the thermoplastic resin other than polyester must be kept to a trace amount, equivalent to the amount of additives. Furthermore, the thermoplastic polyester resin may contain various additives, such as lubricants (antiblocking agents), light stabilizers, compatibilizers, plasticizers, antistatic agents, reaction catalysts, color inhibitors, radical inhibitors, antistatic agents, end-capping agents, antioxidants, heat stabilizers, release agents, flame retardants, antibacterial agents, and antifungal agents, as needed.

[Heat sealability enhancing component]
The heat-sealing property-reinforcing component contained in the thermoplastic polyester-based resin is a resin composition component that is highly dispersed in the thermoplastic polyester-based resin and that is itself made of an aliphatic compound, has high flexibility, and a low melting point, and that is composed of a crystallization-inhibiting component that inhibits the crystallization of the thermoplastic polyester-based resin.
From the viewpoint of obtaining high heat seal strength in a short thermal bonding time, it is preferable that the low-melting point component itself has a melting point of 170°C or less. Note that polyethylene (LDPE: melting point 105-115°C, LLDPE: melting point 115-125°C) and polypropylene (melting point 160-170°C), which are commonly used as sealant layer materials, exhibit high heat seal strength in a short thermal bonding time of 0.1 seconds to several seconds. Furthermore, the low-melting point component must be highly dispersed in the thermoplastic polyester-based resin to achieve stable physical properties. High dispersion of the low-melting point component in the thermoplastic polyester-based resin can be achieved by copolymerizing the low-melting point component during polymerization of the thermoplastic polyester-based resin (specific polyester-based copolymer), or by melt-kneading the low-melting point component with another polyester-based polymer. From the viewpoints of the melting point and high dispersion described above, preferred examples of the low-melting component include polyether polyols that can be copolymerized to form specific polyester copolymers, such as polyacetal, polyethylene glycol, polypropylene glycol, polyethylene propylene glycol, polytetramethylene ether glycol, and methoxypolyethylene glycol. Among these, polytetramethylene ether glycol (PTMG) can be made from tetrahydrofuran (THF), which is generated as a by-product in the production of polybutylene terephthalate, a type of polyester, and therefore it is more preferable to use PTMG as the low-melting component because of its excellent economic rationality.
The crystallization inhibitor is a component that is copolymerized when polymerizing a specific polyester copolymer, and examples thereof include isophthalic acid, adipic acid, sebacic acid, dimer acid, 1,4-cyclohexanedicarboxylic acid, fumaric acid, maleic acid, 5-sodium sulfoisophthalate, 5-hydroxyisophthalic acid, succinic acid, azelaic acid, dodecanedioic acid, orthophthalic acid, diphenic acid, itaconic acid, 1,4-cyclohexanedimethanol, neopentyl glycol, isosorbide, etc. As the crystallization inhibitor, it is particularly preferable to use isophthalic acid, which is widely used as a material for resins for PET bottles, is inexpensive, and is therefore economically rational.

The content of the low-melting point component in the thermoplastic polyester resin is preferably 5% by mass or more, more preferably 40 to 80% by mass, even more preferably 50 to 80% by mass, and particularly preferably 50 to 60% by mass. The content of the low-melting point component in the thermoplastic polyester resin refers to the sum of the content of structural units derived from the low-melting point component in a specific polyester copolymer and the content of the low-melting point component in the heat-sealable reinforcing component mixed resin in the thermoplastic polyester resin.
If the content of low-melting point components in the thermoplastic polyester resin is less than 5% by mass, the effect of softening the sealant layer 150 may be insufficient, making it difficult to use as a flexible packaging material such as a packaging bag or lid material.
The crystallization inhibitor has the property that, when used together with the low-melting component, high heat seal strength can be obtained in a short time of thermal bonding even if the content of the low-melting component is suppressed. The content of the crystallization inhibitor in the thermoplastic polyester resin varies depending on the type and the content of the low-melting component, but it is generally preferable that it is less than 30% by mass so as not to cause the thermoplastic polyester resin to become amorphous. Furthermore, if the thermoplastic polyester resin contains a sufficient amount of the low-melting component, the crystallization inhibitor may not be contained.
The content of the heat-sealability enhancing component in the thermoplastic polyester resin, i.e., the total content of the low-melting point component and the crystallization inhibiting component in the thermoplastic polyester resin, is preferably 21% by mass or more, more preferably 30 to 80% by mass, even more preferably 40 to 80% by mass, and particularly preferably 50 to 60% by mass.
When the content ratio of the structural unit derived from the heat-sealability enhancing component in the thermoplastic polyester resin is within the above range, sufficient heat-seal strength is obtained in the sealant layer 150. This is presumably because the thermoplastic polyester resin is made easy to melt and flexible due to the presence of a low-melting point component that itself has a low melting point and a crystallization-inhibiting component that inhibits crystallization in a highly dispersed and moderate amount.

The PTMG-containing PBT copolymer will be described below.
The PTMG-containing PBT copolymer is obtained by subjecting a dicarboxylic acid component containing terephthalic acid as the main component, a diol component containing 1,4-butanediol and PTMG, and other components used as needed, to an esterification reaction and/or transesterification reaction, followed by a polycondensation reaction, and has structural units derived from the dicarboxylic acid component and structural units derived from the diol component.

The dicarboxylic acid component for forming the PTMG-containing PBT copolymer contains terephthalic acid as a main component, and the content of terephthalic acid in all dicarboxylic acid components is preferably 70 mol% or more, and more preferably 85 mol% or more, from the viewpoint of obtaining appropriate heat resistance and economic rationality.
As the other dicarboxylic acid component, isophthalic acid is preferably contained from the viewpoint of suppressing the heat resistance of the sealant layer 150 at low cost.

Specific examples of the dicarboxylic acid component other than terephthalic acid and isophthalic acid include aliphatic chain dicarboxylic acids and ester-forming derivatives thereof, such as oxalic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedicarboxylic acid, and dodecanedicarboxylic acid; alicyclic dicarboxylic acids and ester-forming derivatives thereof, such as hexahydroterephthalic acid and hexahydroisophthalic acid; aromatic dicarboxylic acids and ester-forming derivatives thereof, such as phthalic acid, dibromoisophthalic acid, sodium sulfoisophthalate, phenylenedioxydicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 4,4'-diphenylketonedicarboxylic acid, 4,4'-diphenoxyethanedicarboxylic acid, 4,4'-diphenylsulfonedicarboxylic acid, and 2,6-naphthalenedicarboxylic acid; and 2,5-furandicarboxylic acid and ester-forming derivatives thereof. These dicarboxylic acid components are not limited to one type, and two or more types may be used in combination.
Among these dicarboxylic acid components, terephthalic acid and 2,5-furandicarboxylic acid can be synthesized from plant raw materials, and are preferably used from the viewpoint of environmental considerations.

The diol component for forming the PTMG-containing PBT copolymer contains 1,4-butanediol and PTMG. In the diol component, it is preferable that structural units derived from 1,4-butanediol and structural units derived from PTMG constitute the main components as a whole. Specifically, the total content of 1,4-butanediol and PTMG in the entire diol component is preferably 70 mol% or more, more preferably 80 mol% or more, and particularly preferably 90 mol% or more.
The molecular weight of the PTMG in the diol component is, for example, 500 to 3000. Usually, the molecular weight of the structural unit derived from PTMG in the PTMG-containing PBT copolymer is maintained based on the molecular weight of the PTMG used as a raw material.

Specific examples of diol components other than 1,4-butanediol and PTMG include linear aliphatic diols such as ethylene glycol, diethylene glycol, polyethylene glycol, 1,2-propanediol, 1,3-propanediol, polypropylene glycol, dibutylene glycol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, and 1,8-octanediol; cyclic aliphatic diols such as 1,2-cyclohexanediol, 1,4-cyclohexanediol, 1,1-cyclohexanedimethylol, and 1,4-cyclohexanedimethylol; aromatic diols such as xylylene glycol, 4,4'-dihydroxybiphenyl, 2,2-bis(4-hydroxyphenyl)propane, and bis(4-hydroxyphenyl)sulfone; and diols derived from plant materials such as isosorbide, isomannide, isoidet, and erythritane. These diol components are not limited to one type, and two or more types may be used in combination.
Among these diol components, ethylene glycol, 1,3-propanediol, 1,4-butanediol, polyethylene glycol, polypropylene glycol, and PTMG can also be synthesized and polymerized from plant raw materials, and are preferably used actively from the viewpoint of environmental considerations.

Other components that may be used as needed when forming the PTMG-containing PBT copolymer include hydroxycarboxylic acids such as glycolic acid, p-hydroxybenzoic acid, and p-β-hydroxyethoxybenzoic acid; trifunctional or higher polyfunctional carboxylic acids such as tricarballylic acid, trimellitic acid, trimesic acid, pyromellitic acid, and naphthalenetetracarboxylic acid; and trifunctional or higher polyfunctional alcohols such as trimethylolethane, trimethylolpropane, glycerol, pentaerythritol, and sugar esters. These other components are not limited to a single type, and two or more types may be mixed together.

The polyester copolymer may be modified with maleic acid. If the polyester copolymer is modified with maleic acid, the content of structural units derived from maleic acid in the polyester copolymer is preferably 3.0% by mass or less.

[Layer structure of sealant layer]
The sealant layer 150 may be a single layer or may have a multi-layer structure of two or more layers. However, if the sealant layer 150 has a multi-layer structure, at least the outermost layer to be heat-sealed must be made primarily of a thermoplastic polyester resin containing the heat-sealability-reinforcing component described above.

[Sealant layer thickness]
The thickness of the sealant layer 150 (or the outermost layer if it has a multi-layer structure) is, for example, 40 μm or less, preferably 5 to 35 μm, more preferably 5 to 30 μm, and particularly preferably 5 to 25 μm.
If the sealant layer 150 is too thick, the amount of plastic used will be too large and the effect of reducing the environmental impact will not be sufficient, whereas if the sealant layer 150 is too thin, the heat seal strength required to seal the packaging container may not be ensured.

[Other layers]
The substrate layer 110, which together with the sealant layer 150 constitutes the laminate film 100, may be constructed as a single layer film or may be constructed from multiple layers. The laminate film 100 of the example in Fig. 1 is constructed from a surface layer 111 and an intermediate layer 112 interposed between the surface layer 111 and the sealant layer 150. When the substrate layer 110 is constructed as a single layer film, it may consist of, for example, only the surface layer 111, which will be described in detail below.
Of the layers constituting the base layer 110, at least the surface layer 111 is preferably made of a material having a melting point of, for example, 200° C. or higher so as not to melt when heat-sealed.
Furthermore, each layer constituting the base layer 110 is preferably made of a material primarily composed of a polyester-based resin. "Mainly composed of a polyester-based resin" means that 80% by mass or more of all materials constituting the layer are polyester-based resins, and it is preferable that all materials (100% by mass) constituting the layer are polyester-based resins. By making each layer constituting the base layer 110 out of a material primarily composed of a polyester-based resin, the entire laminate film 100, including the sealant layer 150, is primarily composed of polyester-based resins. This allows high-quality recycled pellets to be obtained by, for example, generating a compatibilizing component through ester exchange during heating and kneading (re-pelletization) during recycling, thereby achieving high recyclability and reducing the environmental impact.

The surface layer 111 can be made of, for example, polyethylene terephthalate (PET), polytrimethylene terephthalate, polybutylene terephthalate not containing structural units derived from PTMG, polyethylene naphthalate, polytrimethylene naphthalate, polybutylene naphthalate, polyethylene furanoate, etc. In particular, from the viewpoint of improving the mechanical strength, such as the puncture resistance, of the laminate film 100, it is preferable to use a polybutylene terephthalate-based resin such as polybutylene terephthalate not containing structural units derived from PTMG, particularly a homopolymer polybutylene terephthalate. Since the surface layer 111 (or the substrate layer 110) is formed from a material primarily composed of a polybutylene terephthalate-based resin, high puncture strength can be obtained both before and after retort treatment. From the viewpoint of mechanical properties and heat resistance, the material forming the surface layer 111 is preferably a homopolymer that has been subjected to a stretching treatment (uniaxial stretching or biaxial stretching), but it may also be an unstretched product or a copolymer product. In particular, by forming the surface layer 111 from a material containing polybutylene terephthalate resin as a main component, the laminate film 100 can have a puncture strength of 4 N or more regardless of whether it is before or after retort treatment.
The thickness of the surface layer 111 can be, for example, about 10 to 50 μm, preferably 25 to 50 μm, and particularly preferably 40 to 50 μm. By making the surface layer 111 have such a thickness, the above-mentioned puncture strength can be reliably imparted to the laminated film 100.

The intermediate layer 112 may be, for example, a barrier layer provided with gas barrier properties or moisture barrier properties. Examples of the barrier layer include a vapor-deposited film of a metal oxide such as alumina or silicon oxide formed on the surface layer 111, or an MXD6 nylon layer that has high barrier properties and is similar in molding processing conditions to polyester. The intermediate layer 112 may be provided in various positions as long as it is in contact with the surface layer 111. For example, the intermediate layer 112 may be provided on one or both sides of the surface layer 111, or between multiple surface layers 111.
The thickness of the intermediate layer 112 may be, for example, about 0.05 to 100 μm, depending on the intended use.

The laminated film 100 may further include an anti-blocking layer on the surface of the sealant layer 150 opposite the substrate layer 110 (inner surface) to prevent blocking between the films.

The laminated film 100 has a puncture strength of 4N or more, preferably 5N or more, and more preferably 6N or more before retort treatment.
Furthermore, the puncture strength of the laminated film 100 after retort treatment is preferably 4N or more, more preferably 5N or more, and even more preferably 6N or more.
It is particularly preferable that the laminate film 100 have a puncture strength of 5N or more, regardless of whether it is before or after retort processing. For example, non-oriented polypropylene (CPP) is used as a material for forming a sealant layer that is also applicable to general retort applications. However, a laminate film having a CPP sealant layer would not be applicable to a wide range of applications unless the sealant layer alone has a thickness of, for example, 70 μm or more in order to achieve a puncture strength of 5N or more. If the CPP sealant layer is, for example, 50 μm thick, the laminate film would be applicable to retort applications, but its applications would be limited due to the need to consider the amount of contents, the size of the packaging bag, and whether it must be placed in a separate box. As described above, from the perspective of being applicable to a wide range of applications, it is preferable that the laminate film 100 have a puncture strength equal to or greater than that of a laminate film having a 70 μm thick CPP sealant layer. That is, it is preferable that the laminate film 100 of the present invention have a puncture strength of 5N or more, regardless of whether it is before or after retort processing. The laminate film 100 of the present invention can be widely used as a substitute for a CPP sealant layer. Furthermore, if the laminated film 100 has a puncture strength of 6N or more regardless of whether it is before or after retort treatment, when this laminated film 100 is used as a substitute for a sealant layer made of CPP, a packaging bag with even better puncture strength can be obtained.

Furthermore, the rate of change in puncture strength of this laminate film 100 before and after retort treatment is preferably within ±20%, more preferably within ±17%, and even more preferably within ±11%. When the rate of change in puncture strength before and after retort treatment is within the above range, high puncture strength can be obtained despite the thinness of the base material layer 110, and as a result, the environmental load can be reduced. The rate of change in puncture strength is a negative value when the puncture strength after retort treatment is smaller than the puncture strength before retort treatment.
Retort treatment is often carried out in the temperature range of 120 to 135° C. The treatment time is often 20 to 30 minutes at 120° C. and 5 to 10 minutes at 135° C. In the present invention, the retort treatment conditions were 127° C. and 30 minutes of heating.
The puncture strength of the laminated film 100 is measured by stretching the film tightly around a ring with a diameter of 40 mm, and using a needle with a tip angle of 60 degrees and a tip radius of 0.5 mm, piercing the center of the circle at a speed of 50 mm/min, and measuring the load (N) when the needle penetrates (in accordance with JIS-Z1707:2019).

[Method for producing laminated film]
The laminated film 100 of the present invention can be produced by employing a known method such as dry lamination, extrusion lamination, or co-extrusion depending on the layer structure.
For example, when adjacent layers are laminated using a coextrusion method, a coextruded film portion can be obtained by coextruding and laminating the materials of each layer. When the base layer 110 of the laminated film 100 is configured as a single-layer film (surface layer 111), the laminated film 100, in which the coextruded film portion consists only of the sealant layer 150 and the base layer 110, can be obtained in a single process. Further appropriate layers may be laminated on the coextruded film portion obtained by coextrusion, for example, using a dry lamination adhesive.
Furthermore, for example, when adjacent layers are laminated using a dry lamination method, the adjacent layers can be laminated using a dry lamination adhesive such as a urethane adhesive or an epoxy adhesive. For example, when the sealant layer 150 is laminated on the intermediate layer 112 formed on the base layer 110, the sealant layer 150 and the intermediate layer 112 can be bonded together using a dry lamination adhesive, and in this case, an adhesive layer is interposed between the sealant layer 150 and the intermediate layer 112. The thickness of the adhesive layer is 100 μm or less.
For example, when adjacent layers are laminated using an extrusion lamination method, the adjacent layers can be laminated via an anchor coat layer as needed. The thickness of the anchor coat layer is thinner than that of the adhesive layer, 10 μm or less. For example, when the sealant layer 150 has a multilayer structure, the sealant layer 150 can also be formed using a co-extrusion method.
Among the above methods, the co-extrusion method, which does not require a solvent or adhesive and does not require a film lamination step, is particularly preferred from the viewpoint of low environmental impact and high production efficiency. Furthermore, when the co-extrusion method is used, if a material containing a polybutylene terephthalate resin as a main component is used as the material for forming the base layer, the base layer is crystallized by co-extrusion with a thermoplastic polyester resin containing a heat-sealing reinforcing component for forming the sealant layer, and then cooled and wound up as is, thereby forming a film having excellent heat resistance and mechanical strength, which is even more preferred.

The heat seal strength of the laminate film 100 of the present invention varies depending on the material, layer structure, and thickness of the sealant layer 150 and the material and thickness of the base layer 110, but is preferably 40 N/15 mm or more, and more preferably 60 N/15 mm or more. In particular, when the thickness of the sealant layer 150 of the laminate film 100 is 25 μm or less, it is preferable that the heat seal strength of this laminate film 100 be 30 N/15 mm or more.

[Packaging container]
The packaging container of the present invention is a container having a sealability using the above-mentioned laminated film 100. Specific examples include a packaging bag (pouch) and a sealed container using the laminated film 100 as a lid material.
The packaging bag (pouch) is formed by stacking laminated films 100 so that the sealant layers 150 face each other and heat-sealing the periphery to form a bag shape. The packaging bag is not limited to a flat pouch having a rectangular outer shape in a plan view and heat-sealed on all four sides, but can be applied to various types of pouches such as a standing pouch, a three-sided sealed type, a pillow type, a gusset type, etc. The shape of the packaging bag may be any shape other than a rectangular shape in a plan view, such as a trapezoid or an irregular shape with some unevenness.
A sealed container using the laminate film 100 as a lid is configured such that the laminate film 100 is placed on the edge flange of a container body that contains the contents, with the sealant layer 150 in contact with the edge flange, and then heat-sealed to adhere the laminate film 100. From the viewpoint of recyclability, the container body of such a sealed container is preferably made of, for example, polyethylene terephthalate (PET). The container body of the sealed container may be in any shape, such as a cup or tray.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various design modifications can be made without departing from the scope of the present invention as set forth in the claims.

Specific examples of the present invention are described below, but the present invention is not limited to these.

[Examples 1 to 5, Comparative Example 1]
PTMG-containing PBT copolymer 1 (or PTMG-containing PBT copolymer 2) and a resin composition (denoted as "MB" in the table) prepared by mixing 5% by mass of hydrophilic silica with PBT were mixed to the mass percentages shown in Table 2, and the resulting mixture was fed from the hopper of twin-screw extruder A and melted at 240-245°C. Furthermore, polybutylene terephthalate (PBT) containing no structural units derived from PTMG was fed from the hopper of twin-screw extruder B and melt-kneaded at 260-270°C. The resins extruded from these twin-screw extruders A and B were fed into a multi-manifold T-die, extruded into a film, and cooled and solidified on a cast roll (50°C) to produce laminate films A to E with the thicknesses shown in Table 2. The resin composition of the PTMG-containing PBT copolymer used (denoted as "copolymer" in the table) is shown in Table 1. The thicknesses of the layers (sealant layers) of the PTMG-containing PBT copolymer and MB and the thicknesses of the layers (base layers) of PBT in the laminated films A to E are shown in Table 2.
Furthermore, PTMG-containing PBT copolymer 3 was fed from the hopper of twin-screw extruder A and melted at 240-245°C. Furthermore, polybutylene terephthalate (PBT) containing no structural units derived from PTMG was fed from the hopper of twin-screw extruder B and melt-kneaded at 260-270°C. The resins extruded from these twin-screw extruders A and B were fed into a multi-manifold T-die, extruded into a film, and cooled and solidified with a cast roll (50°C) to produce laminate film F having the thickness shown in Table 2. The resin composition of the PTMG-containing PBT copolymer 3 used is shown in Table 1. Furthermore, the thicknesses of the PTMG-containing PBT copolymer layer (sealant layer) and the PBT layer (substrate layer) of laminate film F were as shown in Table 2.

The puncture strength of these laminate films A to F was measured as follows. Specifically, the film was stretched tightly around a 40 mm diameter ring, and a needle with a 60-degree tip angle and a 0.5 mm tip radius was used to pierce the center of the circle at a rate of 50 mm/min. The load (N) at which the needle penetrated was recorded as the puncture strength (in accordance with JIS-Z1707:2019). The puncture strength was measured from both the base layer side and the sealant layer side. Each measurement was performed five times for each type of laminate film, and the average of the three measurements, excluding the minimum and maximum values, was recorded as the puncture strength. The puncture strength was measured for both the laminate films before and after retort treatment. The results are shown in Table 2.
Furthermore, to evaluate the heat seal strength of the laminate films A to F, laminate films A' to F' for evaluation were separately prepared, and heat seal strength tests were conducted using these films according to the following method to evaluate the heat seal strength. The laminate films A' to F' for evaluation were formed by laminating films each having a sealant layer for each of the laminate films A to F formed as a single layer on a 12 μm-thick biaxially oriented PET layer (substrate layer) via an adhesive layer using a conventional dry lamination method. The results are shown in Table 2.
In the present invention, a heat seal strength of 30 (N/15 mm) or more was evaluated as being suitable for practical use.

<Heat seal strength test>
For the laminate films A' to F', each laminate film was stacked with the sealant layers facing each other, and heat-sealed using a heat-sealing tester (manufactured by Tester Sangyo Co., Ltd.) under conditions of a seal width of 10 mm, a seal temperature of 210°C (one side), a seal pressure of 0.3 MPa, and a seal time of 1.0 second. Test pieces A to F were then prepared, each measuring 80 mm in length (including the 10 mm seal width) and 15 mm in width. Then, tensile tests were performed on test pieces A to F using a Tensilon universal testing machine (manufactured by A&D Co., Ltd.) in accordance with JIS-Z1707 at 23°C and 50% RH. In the tensile test, the test piece was opened 180° around the heat-sealed portion, and both ends were attached to the universal testing machine. The maximum load (N) was measured at a rate of 300 mm/min. The maximum load relative to the width of the test piece was measured as the heat-seal strength (N/15 mm).
Measurement was carried out five times for each type of laminated film, and the average value of the three measurements excluding the minimum and maximum values was taken as the heat seal strength of the laminated film.

The results in Table 2 confirm that the laminate films A to E of Examples 1 to 5 had high heat seal strength and high puncture strength both before and after retort treatment, and that the rate of change in puncture strength before and after retort treatment was small. In particular, Examples 1 to 4, in which the base layer had a thickness of 30 μm or more, had a puncture strength of 5 N or more both before and after retort treatment, and further, Examples 1, 3, and 4, in which the base layer had a thickness of 40 μm or more, had a puncture strength of 6 N or more both before and after retort treatment.
On the other hand, in the laminated film F according to Comparative Example 1, although high puncture strength was obtained, it was confirmed that the thin sealant layer did not provide sufficient heat seal strength.

[Reference Examples 1 to 6, Comparative Reference Examples 1 to 3]
Laminate films G to O were prepared in which a sealant layer (innermost layer) shown in Table 3 was laminated on a 38 μm-thick biaxially oriented PET layer (outermost layer) via an adhesive layer using a conventional dry lamination method. Each laminate film G to O differs in the material and thickness of the sealant layer. The sealant layer of each laminate film G to O is formed from a PTMG-containing PBT copolymer as shown in Table 3. Table 3 shows the resin composition of the PTMG-containing PBT copolymer.
The content of structural units derived from isophthalic acid and PTMG in the sealant layer of each of the laminate films G to O was calculated by analyzing the resin composition by proton NMR measurement using a nuclear magnetic resonance analyzer (manufactured by JEOL Ltd.).
The heat seal strength of each of the laminated films G to O was measured by a heat seal strength test in the same manner as in Example 1. The results are shown in Table 3.

The results in Table 3 confirm that, in laminate films G to L of Reference Examples 1 to 6, in which the content of the heat-sealability enhancing component in the PTMG-containing PBT copolymer constituting the sealant layer was 21% by mass or more, high heat-seal strength could be ensured even with a relatively thin sealant layer.

[Reference Example 7, Comparative Reference Examples 4 to 9]
Substrate layers having the materials and thicknesses shown in Table 4 were prepared as monolayer films, and the puncture strength of each was measured before and after retort treatment in the same manner as described above. The retort treatment of the monolayer films was as follows: A piece of monolayer film was fixed to a glass plate, placed in a retort bottle, filled with water, and sealed. The retort bottle was heated in an autoclave at 127°C for 30 minutes. The results are shown in Table 4.
In Table 4, "IA-modified PET" is polyethylene terephthalate copolymerized with isophthalic acid, "block PP" is block polypropylene, "PE composition" is a composition consisting of linear short-chain branched polyethylene (methacelon-catalyzed LLDPE) and high-pressure low-density polyethylene (LDPE), and "Modic" is a polyester resin: trade name "Modic QC430" (manufactured by Mitsubishi Chemical Corporation).

As shown in Table 4, when the base layer was PBT, the puncture strength was high both before and after retort treatment, and it was confirmed that the rate of change in puncture strength before and after retort treatment was small.

100: Laminated film 110: Base material layer 111: Surface layer 112: Intermediate layer 150: Sealant layer

Claims (9)

A laminated film having a sealant layer on one side of a base layer,
the sealant layer is formed from a thermoplastic polyester resin,
The thermoplastic polyester resin contains a heat-sealing property enhancing component,
The content of the heat-sealability enhancing component in the thermoplastic polyester resin is 21% by mass or more,
The puncture strength is 4N or more,
A laminated film characterized in that the thickness of the sealant layer is 25 μm or less, and the heat seal strength of the laminated film is 30 N/15 mm or more . The laminate film according to claim 1, characterized in that the laminate film includes a coextruded film portion in which the sealant layer is laminated on one side of the base layer by a coextrusion method. 2. The laminated film according to claim 1, wherein the change in puncture strength of the laminated film before and after retort treatment is within ±20%. 4. The laminated film according to claim 1, wherein the base layer of the laminated film is formed from a material containing polybutylene terephthalate resin as a main component. 5. The laminated film according to claim 1, wherein at least one of the heat-sealing property-reinforcing components is a polyoxyalkylene glycol, and the content of the polyoxyalkylene glycol in the thermoplastic polyester resin is 5% by mass or more. 6. The laminated film according to claim 1, wherein the thickness of the substrate layer is 10 to 50 μm. 7. The laminated film according to claim 1, further comprising an anti-blocking layer provided on the surface of the sealant layer opposite to the substrate layer. A packaging container comprising the laminated film according to any one of claims 1 to 7. 9. The packaging container according to claim 8, wherein the packaging container is a packaging bag or a sealed container using a lid material made of the laminated film.