JP7708925B2 - Laminated films and packaging containers - Google Patents

Description

The present invention relates to a laminated film for use in a packaging bag 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 contents such as liquid or solid foods, beverages, cosmetics, and medicines. For example, packaging bags are used as packaging containers for storing contents such as shampoo, detergent, cooked or semi-cooked foods, and are formed into a bag shape by thermally bonding the outer periphery of a laminated film having a sealant layer laminated on a base layer, with the sealant layers facing each other while being stacked, and the contents are stored in the inner storage section (see, for example, Patent Document 1). Also, an example of a cup container with a lid attached is one in which the sealant layer of a laminated film is thermally bonded to the edge flange of a cup-shaped container body for storing contents such as yogurt, jelly, and pudding, and sealed (see, for example, Patent Document 2).

Meanwhile, in recent years, with regard to packaging containers, efforts have been made to reduce the amount of plastic used and to recycle plastics from the standpoint of environmental burden, such as resource conservation and environmental protection.
One way to reduce the amount of plastic used is to make the laminate film thinner. However, for example, making the sealant layer thinner does not provide sufficient heat seal strength, 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 crystallized polypropylene (CPP) have been widely used as materials for sealant layers. However, 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.

JP 2015-150807 A JP 2014-46983 A

The present invention aims to solve the above problems and provide a laminated film and packaging container that has good heat sealability despite being thin and has a reduced environmental impact.

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 has a polytetramethylene ether glycol content of 41% by mass or more and an isophthalic acid content of 8% by mass or less , thereby solving the above-mentioned problems.
The packaging container of the present invention is characterized by using the above-mentioned laminate film.

According to the laminated film of the present invention, the sealant layer is formed from a thermoplastic polyester-based resin, so that although it is a thin layer, it has good heat sealing properties, and as a result, it is possible to obtain a packaging container in which leakage of the contents is prevented while reducing the environmental load.
Furthermore, by making the sealant layer contain a thermoplastic polyester-based resin as the main material and further forming the base layers other than the sealant layer with a polyester-based resin, the entire laminate film is constructed with a polyester-based resin as the main material, and therefore it can be easily recycled into high-quality polyester-based materials and polyester-based products, resulting in high recyclability and further reducing the environmental burden.

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.
Thermoplastic polyester resins contain a heat sealability reinforcing component. Specifically, thermoplastic polyester resins are polyester copolymers containing structural units derived from the heat sealability reinforcing component (hereinafter also referred to as "specific polyester copolymers"), resins in which a heat sealability reinforcing component is dispersed and mixed in a polyester polymer not containing structural units derived from the heat sealability reinforcing component (hereinafter also referred to as "other polyester polymers") (hereinafter also referred to as "resin mixed with heat sealability reinforcing component"), and mixtures of these resins are the main materials.

The specific polyester copolymer includes other polyester polymers described below that contain a structural unit derived from polyoxyalkylene glycol as a heat sealability reinforcing component. Examples of polyoxyalkylene glycol include polytetramethylene ether glycol (PTMG) and polyethylene glycol (PEG). The specific polyester copolymer is preferably a polybutylene terephthalate copolymer containing a structural unit 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 polyester thermoplastic elastomers (TPC). In particular, polyethylene terephthalate and polybutylene terephthalate are more preferably used from the viewpoints of mechanical properties, heat resistance, and economic rationality due to their large distribution volume and low cost. These resins may 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 sealability reinforcing component mixed resin is mainly composed of the above other polyester resins.
When the thermoplastic polyester resin is mainly composed of a specific polyester copolymer, the above-mentioned other polyester polymers not containing a heat sealability enhancing component may be further mixed in. 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. When the mixing ratio of the specific polyester copolymer in the thermoplastic polyester resin is too low, the content of the specific polyester copolymer is not sufficiently secured, and there is a risk that the thinned sealant layer 150 does not have sufficient heat sealability.
The sealant layer 150 may be formed from a mixed resin of the above 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 needs to be kept to a small amount at the additive level. Furthermore, the above thermoplastic polyester resin may contain various additives such as a lubricant (antiblocking agent), a light stabilizer, a compatibilizer, a plasticizer, an antistatic agent, a reaction catalyst, a coloring inhibitor, a radical inhibitor, an antistatic agent, an end blocking agent, an antioxidant, a heat stabilizer, a release agent, a flame retardant, an antibacterial agent, and an antifungal agent, as necessary.

[Heat sealability enhancing component]
The heat sealability enhancing component contained in the thermoplastic polyester-based resin refers to a component of a resin composition that is highly dispersed in the thermoplastic polyester-based resin, that is itself made of an aliphatic compound, that 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 by short-time heat bonding, the low melting point component is preferably one having a melting point of 170°C or less. In addition, 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 materials for the sealant layer, show high heat seal strength by short-time heat bonding of 0.1 seconds to several seconds. In addition, it is necessary for the low melting point component to be highly dispersed in the thermoplastic polyester resin in order to exhibit stable physical properties. High dispersion of the low melting point component in the thermoplastic polyester resin can be achieved by a method of copolymerizing the low melting point component when polymerizing the thermoplastic polyester resin (specific polyester copolymer), or by a method of melt-kneading the low melting point component with other polyester polymers. From the viewpoint of the above melting point and high dispersion, preferred examples of the low melting point component include polyether polyols that can also be copolymerized as a specific polyester copolymer, 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 a by-product produced during the production of polybutylene terephthalate, a type of polyester, and is therefore more economically rational and preferable to use as the low melting point component.
The crystallization inhibitor is a component that is copolymerized when a specific polyester copolymer is polymerized, and examples of the crystallization inhibitor include isophthalic acid, adipic acid, sebacic acid, dimer acid, 1,4-cyclohexanedicarboxylic acid, fumaric acid, maleic acid, sodium 5-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 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 the structural unit derived from the low melting point component in the specific polyester copolymer in the thermoplastic polyester resin and the content of the low melting point component in the heat sealability reinforcing component mixed resin.
If the content of the low melting point component 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 it as a soft packaging material such as a packaging bag or a lid material.
The crystallization inhibitor has the property that, by using it together with the low melting point component, high heat seal strength can be obtained by short-time heat adhesion even if the content ratio of the low melting point component is suppressed. The content ratio of the crystallization inhibitor in the thermoplastic polyester resin varies depending on the type and the content ratio of the low melting point component, but is generally preferably less than 30 mass% in order not to decrystallize the thermoplastic polyester resin. In addition, when the thermoplastic polyester resin contains a sufficient amount of the low melting point 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 which has a low melting point itself and a crystallization inhibiting component which inhibits crystallization in a highly dispersed and moderate amount.

The PTMG-containing PBT copolymer will now be described.
The PTMG-containing PBT copolymer is obtained by subjecting a dicarboxylic acid component mainly composed of terephthalic acid to an esterification reaction and/or an ester exchange reaction between a diol component containing 1,4-butanediol and PTMG, and other components used as necessary, 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, it is preferable to contain isophthalic acid 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. The dicarboxylic acid component is not limited to one type, and two or more types may be mixed and used.
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 consideration.

The diol component for forming the PTMG-containing PBT copolymer contains 1,4-butanediol and PTMG. In the diol component, it is preferable that the structural units derived from 1,4-butanediol and the 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 PTMG in the diol component is, for example, from 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 raw materials such as isosorbide, isomannide, isoidet, and erythritan. These diol components are not limited to one type, and two or more types may be mixed and used.
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 consideration.

Other components that may be used as necessary 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 one type, and two or more types may be mixed together.

The polyester copolymer may be modified with maleic acid. When 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 be a multi-layer structure of two or more layers. However, when the sealant layer 150 is a multi-layer structure, at least the outermost layer to be heat-sealed must be made mainly of a thermoplastic polyester resin containing the heat-sealability enhancing component described above in detail.

[Sealant layer thickness]
The thickness of the sealant layer 150 (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 is too large, and the effect of reducing the environmental load is not sufficiently obtained. On the other hand, if the sealant layer 150 is too thin, there is a risk that the heat seal strength required for sealing the packaging container cannot be ensured.

[Other layers]
The base layer 110 constituting the laminated film 100 together with the sealant layer 150 may be configured as a single layer film or may be configured with multiple layers. The laminated film 100 of the example in Fig. 1 is configured from a surface layer 111 and an intermediate layer 112 interposed between the surface layer 111 and the sealant layer 150. When the base layer 110 is configured as a single layer film, it may be, for example, composed of only the surface layer 111 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.
In addition, each layer constituting the base layer 110 is preferably made of a material mainly composed of a polyester-based resin. The term "mainly composed of a polyester-based resin" means that 80% by mass or more of all materials forming the layer is a polyester-based resin, and it is preferable that all materials (100% by mass) forming the layer are polyester-based resins. Since each layer constituting the base layer 110 is made of a material mainly composed of a polyester-based resin, the entire laminate film 100 including the sealant layer 150 is mainly composed of a polyester-based resin, so that high-quality recycled pellets can be obtained by generating a compatibilizing component by ester exchange during heating and kneading (re-pelletization) during recycling, and therefore high recyclability can be obtained and the environmental load can be reduced.

The surface layer 111 may be made of, for example, polyethylene terephthalate (PET), polytrimethylene terephthalate, polybutylene terephthalate not containing a structural unit derived from PTMG, polyethylene naphthalate, polytrimethylene naphthalate, polybutylene naphthalate, polyethylene furanoate, etc. 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 process (uniaxial stretching, biaxial stretching), but may also be a non-stretched product or a copolymer product. In addition, these may be used alone or in combination of two or more types.
The thickness of the surface layer 111 may be, for example, about 10 to 50 μm.

The intermediate layer 112 may be, for example, a barrier layer provided with gas barrier properties or moisture barrier properties. The barrier layer may be a vapor deposition film of a metal oxide such as alumina or silicon oxide formed on the surface layer 111, or an MXD6 nylon layer having high barrier properties and similar molding conditions to polyester.
The thickness of the intermediate layer 112 may vary depending on the intended use, but may be, for example, about 0.05 to 100 μm.

[Method of producing laminated film]
The laminated film 100 of the present invention can be manufactured by adopting a known method such as a dry lamination method, an extrusion lamination method, or a co-extrusion method depending on the layer structure. 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 a sealant layer 150 is laminated on an intermediate layer 112 formed on a base layer 110, the sealant layer 150 and the intermediate layer 112 can be bonded 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. Also, for example, when adjacent layers are laminated using an extrusion lamination method, the adjacent layers can be laminated via an anchor coat layer as necessary. The thickness of the anchor coat layer is thinner than the adhesive layer and is 10 μm or less. Furthermore, for example, when the sealant layer 150 has a multi-layer structure, the sealant layer 150 having a multi-layer structure can be formed by using a co-extrusion method.

The heat seal strength of the laminated 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.

[Packaging container]
The packaging container of the present invention is a container having a sealability using the above-mentioned laminate film 100. Specifically, examples of the packaging container include a packaging bag (pouch) and a sealed container using the laminate 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 may 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 laminated film 100 as a lid is configured such that the laminated 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-bonded to adhere the laminated 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 shape or a tray shape.

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 changes can be made without departing from the invention described 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 Examples 1 to 3, Reference Examples 1 to 4 ]
Laminated films A to L were prepared in which a sealant layer (innermost layer) shown in Table 1 was laminated on a biaxially oriented PET layer (outermost layer) having a thickness of 38 μm via an adhesive layer by a conventional dry lamination method. The laminated films A to L differ in the material and thickness of the sealant layer. The sealant layer of each of the laminated films A to L is formed from a PTMG-containing PBT copolymer, linear short-chain branched polyethylene (methacerone-catalyzed LLDPE) and high-pressure low-density polyethylene (LDPE), or non-oriented polypropylene (CPP) as shown in Table 1. The polyethylene and polypropylene used in the reference examples are general commercially available products used for standing pouches and retort pouches. Table 1 shows the resin composition of the PTMG-containing PBT copolymer.
The content ratio of structural units derived from isophthalic acid and PTMG in the sealant layer of each of the laminate films A to L 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 A to L was evaluated by a heat seal strength test according to the following method. The results are shown in Table 1.
In the present invention, a heat seal strength of 40 (N/15 mm) or more was evaluated as being suitable for practical use.

<Heat seal strength test>
The laminated films A to L were stacked with the sealant layers facing each other, and heat-sealed using a heat seal tester (manufactured by Tester Sangyo Co., Ltd.) under the 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, to prepare test pieces A to L each having a length of 80 mm (including the seal width of 10 mm) and a width of 15 mm. Then, a tensile test was performed on the test pieces A to L in accordance with JIS-Z1707 using a Tensilon universal testing machine (manufactured by A&D Co., Ltd.) under an environment of 23°C and 50% RH. In the tensile test, the test piece was opened 180° around the heat seal part, both ends were attached to the universal testing machine, and the maximum load (N) was obtained by pulling at a speed 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).

The results in Table 1 confirm that, in the laminate films A to F of Examples 1 to 6, high heat seal strength can be ensured even with a relatively thin sealant layer.

REFERENCE SIGNS LIST 100: laminated film 110: base material layer 111: surface layer 112: intermediate layer 150: sealant layer

Claims (7)

A laminated film having a sealant layer on one side of a base layer,
the sealant layer is formed from a thermoplastic polyester resin,
A laminated film , characterized in that the thermoplastic polyester resin has a polytetramethylene ether glycol content of 41 mass % or more and an isophthalic acid content of 8 mass % or less . The laminated film according to claim 1, characterized in that the heat seal strength of the laminated film is 40 N/15 mm or more. The laminated film according to claim 1 or 2, characterized in that the thickness of the substrate layer is 10 to 50 μm. The laminated film according to any one of claims 1 to 3, characterized in that the base layer is made of a material whose main component is a polyester resin. The laminated film according to any one of claims 1 to 4, characterized in that the thickness of the sealant layer is 40 μm or less. A packaging container using the laminated film according to any one of claims 1 to 5. The packaging container according to claim 6, characterized in that the packaging container is a packaging bag or a sealed container using a lid material made of the laminated film.