Sealant film, packaging material, and package

Abstract

A sealant film comprising a first layer, the first layer comprising a propylene homopolymer (A), a propylene / ethylene random copolymer (B) and an ethylene-α-olefin copolymer elastomer (C), and the content of the ethylene-α-olefin copolymer elastomer (C) being 17.5 parts by mass or more relative to the total 100 parts by mass of the propylene homopolymer (A) and the propylene / ethylene random copolymer (B).

Description

Sealant film, packaging material and packaging body

[0001] The present invention relates to a sealant film, a packaging material, and a package. More specifically, the present invention relates to a sealant film that is a polypropylene-based film that has excellent low-temperature sealing properties and excellent resistance to bag drop during low-temperature storage, and that can be suitably used as a packaging material even in harsh treatments such as boiling water treatment and retort treatment, as well as to packaging materials and packaging bags obtained using the sealant film.

[0002] Polypropylene-based unstretched films are sometimes used as sealant films in various packaging materials such as food packaging because they have excellent rigidity and heat resistance and are inexpensive.

[0003] Patent Document 1 proposes a polypropylene-based film containing a crystalline propylene polymer having a melting point of 120 to 165°C, an ethylene-α-olefin copolymer, and a copolymer of ethylene and at least one selected from an α-olefin having 3 to 20 carbon atoms, a cyclic olefin, or a cyclic polyene.

[0004] Japanese Patent Application Laid-Open No. 2003-119298

[0005] In recent years, with the aim of improving the recyclability of packaging materials, mono-material packaging materials using a biaxially oriented polypropylene film (OPP) substrate and a non-oriented polypropylene film have been studied. However, since OPP film has a lower melting point than biaxially oriented polyamide film (ONy film) and biaxially oriented polyester film (PET film), which have traditionally been used as substrates, heat sealing at high temperatures during bag manufacturing is not possible. Therefore, low-temperature sealing properties have been required for non-oriented polypropylene films so that appropriate heat sealing can be performed even at lower heat sealing temperatures.

[0006] Furthermore, packaging materials using OPP base materials tend to have poorer resistance to bag drop during low-temperature storage than those using ONy film or PET film. Therefore, in order to create a more practical mono-material packaging material, it is necessary to impart excellent resistance to bag drop to other layers constituting the packaging material, particularly to the polypropylene-based unstretched film used as the sealant film.

[0007] However, with conventional unstretched polypropylene films, it is currently difficult to achieve both excellent low-temperature sealing properties and excellent resistance to dropping during low-temperature storage.

[0008] The present invention has been made in view of the above circumstances, and aims to provide a sealant film that is a polypropylene film and yet has excellent low-temperature sealing properties and excellent resistance to bag drop during low-temperature storage. Another aim of the present invention is to provide a packaging material and a package obtained using the sealant film.

[0009] One aspect of the present invention includes, for example, the following embodiments. [1] A sealant film comprising a first layer containing a propylene homopolymer (A), a propylene-ethylene random copolymer (B), and an ethylene-α-olefin copolymer elastomer (C), wherein the content of the ethylene-α-olefin copolymer elastomer (C) is 17.5 parts by mass or more relative to 100 parts by mass of the total amount of the propylene homopolymer (A) and the propylene-ethylene random copolymer (B). [2] The sealant film according to [1], comprising the first layer and a second layer containing a propylene-ethylene block copolymer (D) and an ethylene-propylene copolymer elastomer (E). [3] The sealant film according to [1], comprising the first layer and a second layer containing a propylene-based polymer and titanium oxide. [4] The sealant film according to [2], comprising, in this order, the first layer, the second layer, and a third layer containing the propylene homopolymer (A) and the propylene-ethylene random copolymer (B). [5] The sealant film according to [3], which comprises, in this order: the first layer, the second layer, and a third layer containing a propylene homopolymer (A) and a propylene-ethylene random copolymer (B). [6] The sealant film according to any one of [1] to [5], wherein the content of the ethylene-α-olefin copolymer elastomer (C) is 17.5 to 43 parts by mass per 100 parts by mass of the total amount of the propylene homopolymer (A) and the propylene-ethylene random copolymer (B). [7] A packaging material comprising the sealant film according to any one of [1] to [6], and a base film containing a propylene-based polymer. [8] The packaging material according to [7], wherein the base film has an inorganic oxide layer on at least one surface. [9] A packaging material comprising, in this order, the sealant film according to any one of [1] to [6], a first base film containing a propylene-based polymer, and a second base film containing a propylene-based polymer, wherein the first base film has an inorganic oxide layer on at least one surface.

[10] A package produced from the packaging material according to [7].

[0010] According to the present invention, it is possible to provide a sealant film that is a polypropylene-based film and yet is capable of achieving a high level of balance between excellent low-temperature sealing properties and excellent bag drop resistance during low-temperature storage. Furthermore, according to the present invention, it is possible to provide a packaging material and a package obtained using the sealant film.

[0011] The sealant film of the present invention also has heat resistance that enables it to withstand retort treatment, which involves pasteurization and sterilization under retort conditions, for example, at 128°C.

[0012] Fig. 1 is a cross-sectional view of a sealant film according to one embodiment of the present invention. Fig. 2 is a cross-sectional view of a sealant film according to one embodiment of the present invention. Fig. 3 is a cross-sectional view of a sealant film according to one embodiment of the present invention. Fig. 4 is a cross-sectional view of a packaging material according to one embodiment of the present invention. Fig. 5 is a cross-sectional view of a packaging material according to one embodiment of the present invention. Fig. 6 is a cross-sectional view of a packaging material according to one embodiment of the present invention.

[0013] 1 is a cross-sectional view of a sealant film 100 according to one embodiment of the present invention. The sealant film 100 comprises a first layer 10 containing a propylene homopolymer (A), a propylene-ethylene random copolymer (B), and an ethylene-α-olefin copolymer elastomer (C).

[0014] (Propylene Homopolymer (A)) The propylene homopolymer (A) can be obtained by homopolymerizing propylene using, for example, a Ziegler-Natta catalyst, a metallocene catalyst, or a half-metallocene catalyst. By including the propylene homopolymer (A) in the sealant film, excellent heat resistance can be imparted to the first layer. As a result, fusion is less likely to occur on the inner surface of the packaging bag after pressure and heat treatment under retort conditions at, for example, 128°C.

[0015] The propylene homopolymer (A) can be one having a melting onset temperature of 150°C or higher and a melting point of 155°C or higher when measured by differential scanning calorimetry (JIS K 7121). Having both the melting onset temperature and melting point within these ranges can impart superior heat resistance to the first layer. This makes it less likely for fusion to occur on the inner surface of the packaging bag after, for example, pressure and heat treatment under retort conditions at 128°C. The conditions for differential scanning calorimetry are as follows. [Differential scanning calorimetry conditions] When the temperature is raised from 25°C to 230°C at a rate of 10°C / min, the melting onset temperature is determined as the intersection of a straight line extending the low-temperature baseline of the DSC curve toward the higher temperature side and a tangent line drawn to the low-temperature side curve of the melting peak so as to maximize the gradient. The temperature at the peak of the melting peak is determined as the melting point.

[0016] The propylene homopolymer (A) may have a melt flow rate (MFR: ISO 1133) (temperature 230°C, load 2.16 kg) in the range of 2.0 to 7.0 g / 10 min. When the melt flow rate is equal to or greater than the lower limit, the load on the extruder during molding is reduced, the processing speed is less likely to decrease, and excellent productivity can be easily maintained. Furthermore, when the melt flow rate is equal to or less than the upper limit, the first layer is likely to have excellent impact resistance.

[0017] (Propylene-ethylene random copolymer (B)) The propylene-ethylene random copolymer (B) can be obtained by copolymerizing ethylene as a comonomer with propylene as the main monomer using, for example, a Ziegler-Natta catalyst, a metallocene catalyst, or a half-metallocene catalyst. By including the propylene-ethylene random copolymer (B) in the first layer, it is easy to obtain excellent low-temperature sealing properties while maintaining heat resistance.

[0018] The propylene-ethylene random copolymer (B) can be one having a melting point in the range of 132 to 150°C when measured by differential scanning calorimetry (JIS K 7121). By using one having a melting point within this range, it is easy to obtain excellent low-temperature sealing properties while maintaining heat resistance. The conditions for differential scanning calorimetry are as follows. [Differential scanning calorimetry conditions] The melting point is the temperature at the apex of the melting peak on the DSC curve when the temperature is raised from 25°C to 230°C at a rate of 10°C / min.

[0019] The ethylene content of the propylene-ethylene random copolymer (B) may be 6% by mass or less. By having the ethylene content be equal to or less than the upper limit, heat resistance is unlikely to decrease excessively while maintaining low-temperature sealability. This makes it easier to suppress fusion on the inner surface of the packaging bag after pressure and heat treatment under retort conditions of, for example, 128°C. From this perspective, the ethylene content may be 5.5% by mass or less, or may be 4.5% by mass or less. The lower limit of the ethylene content is not particularly limited, but from the viewpoint of low-temperature sealability, it can be 3% by mass.

[0020] The ethylene content of the propylene-ethylene random copolymer (B) can be measured according to the ethylene content determination method (IR method) described on pages 412-413 of Polymer Analysis Handbook (May 10, 2013, 3rd edition), edited by the Polymer Analysis Forum, Japan Analytical Society.

[0021] (Ethylene-α-olefin copolymer elastomer (C)) The ethylene-α-olefin copolymer elastomer (C) can be obtained by copolymerizing ethylene and an α-olefin using, for example, a Ziegler-Natta catalyst, a metallocene catalyst, or a half-metallocene catalyst. When the first layer contains the ethylene-α-olefin copolymer elastomer (C), excellent low-temperature sealing properties can be obtained. Furthermore, when the first layer contains the ethylene-α-olefin copolymer elastomer (C), excellent bag drop resistance and pinhole resistance during low-temperature storage can be easily obtained.

[0022] The ethylene-α-olefin copolymer elastomer (C) may be an ethylene-α-olefin copolymer elastomer having structural units derived from ethylene and structural units derived from an α-olefin having 4 to 20 carbon atoms. This makes it easier to obtain excellent low-temperature sealing properties. The ethylene-α-olefin copolymer elastomer (C) may be a random copolymer.

[0023] Examples of the α-olefin having 4 to 20 carbon atoms include 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-hexadecene, 1-eicosene, 4-methyl-1-pentene, and 4-methyl-1-hexene. The α-olefin having 4 to 20 carbon atoms is preferably 1-butene or 1-hexene. The ethylene-α-olefin copolymer elastomer (C) may have two or more structural units derived from these α-olefins having 4 to 20 carbon atoms.

[0024] The ethylene-α-olefin copolymer elastomer (C) may have a content of structural units derived from ethylene in the range of 75 to 97% by mass, preferably 80 to 95% by mass, based on 100% by mass of the total amount of the ethylene-α-olefin copolymer elastomer (C) (total amount of structural units). By having the content of structural units derived from ethylene equal to or greater than the lower limit, excellent heat resistance is easily maintained. Furthermore, by having the content of structural units derived from ethylene equal to or less than the upper limit, excellent low-temperature sealing properties are easily obtained.

[0025] The ethylene-α-olefin copolymer elastomer (C) has a density (JIS K 7112) of 860 to 950 kg / m ３ When the density is equal to or higher than the lower limit, the tackiness of the film can be suppressed. When the density is equal to or lower than the upper limit, low-temperature sealing properties can be easily obtained.

[0026] The ethylene-α-olefin copolymer elastomer (C) may have a melt flow rate (MFR: ISO 1133) (temperature 190°C, load 2.16 kg) of 0.5 to 15 g / 10 min, preferably 0.5 to 10 g / 10 min or 0.5 to 5 g / 10 min. When the melt flow rate is equal to or greater than the lower limit, the load on the extruder during molding is reduced, the processing speed is less likely to decrease, and excellent productivity can be easily maintained. Furthermore, when the melt flow rate is equal to or less than the upper limit, compatibility with the propylene homopolymer (A) and the propylene-ethylene random copolymer (B) is improved, making it easier to maintain heat resistance.

[0027] The first layer contains 17.5 parts by mass or more of ethylene-α-olefin copolymer elastomer (C) per 100 parts by mass of the total amount of propylene homopolymer (A) and propylene-ethylene random copolymer (B). When the content of ethylene-α-olefin copolymer elastomer (C) is equal to or greater than the above-mentioned lower limit, both excellent low-temperature sealability and excellent bag drop resistance during low-temperature storage can be achieved, compared to when the content is less than the above-mentioned lower limit. The upper limit of the content of ethylene-α-olefin copolymer elastomer (C) may be set as appropriate, but from the viewpoint of heat resistance, it can be set to 43 parts by mass or less. From the above viewpoints, the lower limit of the content may be 20 parts by mass, 22 parts by mass, or 24 parts by mass, and the upper limit may be 40 parts by mass, 33 parts by mass, or 26 parts by mass.

[0028] In the first layer, the mass ratio (A) / (B) of the content of the propylene homopolymer (A) to the content of the propylene-ethylene random copolymer (B) may be in the range of 0.05 to 0.30. When the mass ratio (A) / (B) is equal to or greater than the lower limit, excellent heat resistance is easily maintained. Furthermore, when the mass ratio (A) / (B) is equal to or less than the upper limit, excellent low-temperature sealing properties are easily obtained. From this viewpoint, the mass ratio (A) / (B) may be 0.07 to 0.25, or 0.10 to 0.20.

[0029] From the viewpoint of achieving both excellent low-temperature sealing properties and excellent bag drop resistance during low-temperature storage, the content of the propylene homopolymer (A), the propylene-ethylene random copolymer (B), and the ethylene-α-olefin copolymer elastomer (C) in the first layer may be 95% by mass or more, or may be 100% by mass (consisting essentially of these components), based on the total mass of the first layer.

[0030] <Sealant film 101> Figure 2 is a cross-sectional view of a sealant film 101 according to one embodiment of the present invention. The sealant film 101 comprises a first layer 10, which is a heat-sealable layer, and a second layer 1 containing a propylene-ethylene block copolymer (D) and an ethylene-propylene copolymer elastomer (E). The provision of the second layer facilitates the sealant film to obtain excellent cold impact resistance. In this embodiment, the second layer does not have any opacifying properties (it is a non-opacifying layer), as compared to when it contains titanium oxide (described below) (opacifying layer).

[0031] (Propylene-Ethylene Block Copolymer (D)) The propylene-ethylene block copolymer (D) is a copolymer that can be obtained by producing a propylene polymer (D1) in a first step and then producing an ethylene-propylene copolymer (D2) by gas phase polymerization in a second step. The propylene-ethylene block copolymer (D) is not a block copolymer in which a propylene polymer end and an ethylene-propylene copolymer end are bonded, but is a type of blend copolymer. When the second layer contains the propylene-ethylene block copolymer (D), excellent cold impact resistance is easily obtained.

[0032] The propylene-ethylene block copolymer (D) may have a melt flow rate (MFR: ISO 1133) (temperature 230°C, load 2.16 kg) in the range of 0.5 to 2.5 g / 10 min. When the melt flow rate is equal to or greater than the lower limit, the load on the extruder during molding is reduced, the processing speed is less likely to decrease, and excellent productivity can be easily maintained. When the melt flow rate is equal to or less than the upper limit, the second layer can easily achieve excellent cold impact resistance.

[0033] The propylene-ethylene block copolymer (D) may contain 90 to 60% by mass of the propylene polymer (D1) and 10 to 40% by mass of the ethylene-propylene copolymer (D2). When the contents of each component are within these ranges, excellent cold impact resistance is easily obtained. From this perspective, the propylene-ethylene block copolymer (D) may contain 87.5 to 65% by mass of the propylene polymer (D1) and 12.5 to 35% by mass of the ethylene-propylene copolymer (D2), or may contain 85 to 70% by mass of the propylene polymer (D1) and 15 to 30% by mass of the ethylene-propylene copolymer (D2).

[0034] The ethylene content of the ethylene-propylene copolymer (D2) is not particularly limited, but can be in the range of 20 to 40% by mass. When the ethylene content is equal to or less than the upper limit, the tackiness of the product can be suppressed, and contamination due to the tackiness of the product during production is less likely to occur, making it easier to maintain excellent productivity. When the ethylene content is equal to or more than the lower limit, it is easier to obtain excellent cold impact resistance.

[0035] (Ethylene-Propylene Copolymer Elastomer (E)) The ethylene-propylene copolymer elastomer (E) can be obtained by, for example, a slurry polymerization method carried out in the presence of an inert hydrocarbon such as hexane, heptane, kerosene, or a liquefied α-olefin solvent such as propylene, or a gas-phase polymerization method in the absence of a solvent. Specifically, the ethylene-propylene copolymer elastomer (E) can be obtained using a known multi-stage polymerization method. That is, it is a polymerized polypropylene-based resin with a high rubber content, which can be obtained by polymerizing propylene and / or a propylene-α-olefin polymer in a first-stage reactor and then copolymerizing propylene with an α-olefin in a second-stage reaction. When the second layer contains the ethylene-propylene copolymer elastomer (E), even better cold impact resistance can be easily obtained.

[0036] The ethylene-propylene copolymer elastomer (E) may have a melt flow rate (MFR: ISO 1133) (temperature 230°C, load 2.16 kg) in the range of 0.5 to 3.5 g / 10 min. When the melt flow rate is equal to or greater than the lower limit, the load on the extruder during molding is reduced, the processing speed is less likely to decrease, and excellent productivity can be easily maintained. When the melt flow rate is equal to or less than the upper limit, the compatibility between the propylene-ethylene block copolymer (D) and the ethylene-propylene copolymer elastomer (E) is good, and low-temperature impact resistance can be easily obtained.

[0037] The ethylene-propylene copolymer elastomer (E) can be one having a mass ratio of the propylene content to the ethylene content (propylene content / ethylene content) in the range of 1.5 to 4. When the mass ratio is in the above range, even better cold impact resistance can be easily obtained.

[0038] The second layer may contain 90 to 50% by mass of a propylene-ethylene block copolymer (D) and 10 to 50% by mass of an ethylene-propylene copolymer elastomer (E). When the content of the propylene-ethylene block copolymer (D) is 50% by mass or more, excellent heat resistance is easily maintained. From this viewpoint, the content may be 60% by mass or more, or 70% by mass or more. When the content of the propylene-ethylene block copolymer (D) is 90% by mass or less, that is, when the content of the ethylene-propylene copolymer elastomer (E) is at least 10% by mass or more, excellent cold impact resistance can be exhibited. From this viewpoint, the content of the propylene-ethylene block copolymer (D) may be 87.5% by mass or less, or 85% by mass or less. From the above viewpoints, the content of the ethylene-propylene copolymer elastomer (E) may be 12.5 to 40% by mass or 15 to 30% by mass.

[0039] The mass ratio (E) / (D) of the content of the ethylene-propylene copolymer elastomer (E) to the content of the propylene-ethylene block copolymer resin (D) in the second layer is preferably 0.10 to 1.00 from the viewpoint of better heat resistance and cold impact resistance. The mass ratio (E) / (D) may be 0.20 or more, 0.30 or more, or 0.40 or more from the viewpoint of better cold impact resistance. The mass ratio (E) / (D) may be 0.80 or less, 0.60 or less, or 0.50 or less from the viewpoint of better heat resistance.

[0040] In the sealant film 101 shown in Fig. 2, the second layer 1 may be a layer containing a propylene-based polymer and titanium oxide (F). By including titanium oxide (F) in the second layer, it is possible to impart hiding properties to the sealant film. Such a second layer can be referred to as a hiding layer.

[0041] (Titanium oxide (F)) Titanium oxide (F) is, for example, in the form of particles and is dispersed in the second layer. The average particle size of titanium oxide may be 0.10 to 0.50 μm, or may be 0.15 to 0.40 μm, or 0.20 to 0.30 μm. The average particle size of titanium oxide is a value measured by a laser diffraction / scattering method.

[0042] The content of titanium oxide (F) in the hiding layer is preferably 0.10 to 30% by mass. From the viewpoint of more excellent hiding properties, the content of titanium oxide (F) in the hiding layer may be 1% by mass or more, 5% by mass or more, or 7% by mass or more, based on the total mass of the hiding layer. From the viewpoint of more excellent recyclability and cold impact resistance, the content of titanium oxide (F) in the hiding layer may be 23% by mass or less, 20% by mass or less, 15% by mass or less, 12% by mass or less, or 8% by mass or less, based on the total mass of the hiding layer.

[0043] From the viewpoints of opacity, recyclability, and cold impact resistance, the content of the propylene-based resin in the concealing layer is preferably 70 to 99.9 mass% or more based on the total mass of the concealing layer. The content of the propylene-based resin in the concealing layer can be measured by Raman spectroscopy.

[0044] Examples of the propylene-based polymer in the concealing layer include the above-mentioned propylene homopolymer (A), propylene-ethylene random copolymer (B), propylene-ethylene block copolymer (D), and ethylene-propylene copolymer elastomer (E), and these can be used in combination depending on the properties of the concealing layer. The concealing layer may also contain an ethylene-α-olefin copolymer elastomer (C).

[0045] For example, from the viewpoint of excellent cold impact resistance, the propylene-based polymer in the concealing layer preferably contains a propylene-ethylene block copolymer (D), and more preferably contains a propylene-ethylene block copolymer (D) and an ethylene-propylene copolymer elastomer (E).

[0046] From the viewpoint of achieving better heat resistance, the content of the propylene-ethylene block copolymer resin (D) in the concealing layer may be 35% by mass or more, 50% by mass or more, or 60% by mass or more, based on the total mass of the propylene polymer. From the viewpoint of achieving better cold impact resistance, the content of the propylene-ethylene block copolymer resin (D) in the concealing layer may be 90% by mass or less, 80% by mass or less, or 70% by mass or less, based on the total mass of the propylene polymer.

[0047] From the viewpoint of achieving better cold impact resistance, the content of the ethylene-propylene copolymer elastomer (E) in the concealing layer may be 10% by mass or more, 15% by mass or more, or 20% by mass or more, based on the total mass of the propylene polymer. From the viewpoint of achieving better heat resistance, the content of the ethylene-propylene copolymer elastomer (E) in the concealing layer may be 50% by mass or less, 40% by mass or less, or 30% by mass or less, based on the total mass of the propylene polymer.

[0048] The mass ratio (E) / (D) of the content of the ethylene-propylene copolymer elastomer (E) to the content of the propylene-ethylene block copolymer resin (D) in the concealing layer is preferably 0.10 to 1.00 from the viewpoint of better heat resistance and cold impact resistance. From the viewpoint of better cold impact resistance, the mass ratio (E) / (D) may be 0.20 or more, 0.30 or more, or 0.40 or more. From the viewpoint of better heat resistance, the mass ratio (E) / (D) may be 0.80 or less, 0.60 or less, or 0.50 or less.

[0049] <Sealant film 102> Figure 3 is a cross-sectional view of a sealant film 102 according to one embodiment of the present invention. The sealant film 102 comprises, in this order, a first layer 10 which is a heat-sealable layer, a second layer 1, and a third layer 2 which contains a propylene homopolymer (A) and a propylene-ethylene random copolymer (B). The provision of the third layer makes it easier to suppress distortion and curling of the film.

[0050] The mixing ratio (mass ratio) of the propylene homopolymer (A) and the propylene-ethylene random copolymer (B) in the third layer is not particularly limited, but is preferably the same as that of the first layer from the viewpoint of suppressing film curl after film formation. From the same viewpoint, the third layer may contain the propylene homopolymer (A), the propylene-ethylene random copolymer (B), and the ethylene-α-olefin copolymer elastomer (C), and may have the same configuration as the first layer.

[0051] The sealant film is a non-stretched film and can be mainly made of polypropylene-based materials, so it can be called a polypropylene-based non-stretched film.

[0052] The thickness of the sealant film is not particularly limited as long as it is usable as a film for packaging material, for example. However, since a film that is too thick is cost-intensive, the film thickness can be 100 μm or less, and may be 50 to 70 μm. The thickness of the sealant film may be the thickness of the first layer 10 in the sealant film 100.

[0053] The thickness ratio of the first layer in the sealant films 101 and 102 may be 8 to 30% of the thickness of the sealant film. When the thickness ratio of the first layer is equal to or greater than the lower limit, excellent heat seal strength is easily achieved, and when the thickness ratio is equal to or less than the upper limit, the film is easily able to achieve low-temperature impact resistance and practicality. From this perspective, the thickness ratio of the first layer may be 10 to 25%.

[0054] The thickness of the second layer in the sealant films 101 and 102 may be 20 μm or more. This maintains the cold impact resistance of the film and makes it less likely to break even during low-temperature storage. From this perspective, the thickness of the second layer may be 25 μm or more, or 30 μm or more. The upper limit of the thickness of the second layer is not particularly limited, but can be 50 μm or 40 μm to avoid cost disadvantages.

[0055] The ratio of the total thickness of the first layer and the third layer in the sealant film 102 may be 16 to 42% of the thickness of the sealant film. When the ratio of the total thickness of the first layer and the third layer is equal to or greater than the lower limit, excellent heat seal strength is easily achieved, and when it is equal to or less than the upper limit, the film is more likely to have low-temperature impact resistance and be practical. From this perspective, the ratio of the total thickness of the first layer and the third layer may be 20 to 35%.

[0056] <Method for Producing Sealant Film> The method for producing the sealant film is not particularly limited, and known methods can be used. For example, methods for thermoforming the first to third layers include melt-kneading using a general mixer such as a single-screw extruder, twin-screw extruder, or multi-screw extruder, and methods in which the components are dissolved or dispersed and mixed and then the solvent is removed by heating. Considering workability, a single-screw extruder or twin-screw extruder can be used. When a single-screw extruder is used, the screw can be a full-flighted screw, a screw with a mixing element, a barrier-flighted screw, a fluted screw, or the like, and these can be used without particular limitation. Examples of twin-screw kneading devices that can be used include co-rotating twin-screw extruders and counter-rotating twin-screw extruders, and the screw shape can be a full-flighted screw, a kneading disk type, or the like, without particular limitation.

[0057] In the above method, the raw materials for each layer are melted, and then the melted materials are passed through a feed block or a multi-manifold and formed into a film in a T-die, thereby forming and laminating each layer.

[0058] The obtained sealant film may be subjected to a surface modification treatment as needed to improve suitability for subsequent processes. For example, to improve printability when used as a single film or lamination suitability when used in a laminated state, a surface modification treatment may be performed on the printing surface or the surface that comes into contact with the substrate film. Examples of surface modification treatments include treatments that generate functional groups by oxidizing the film surface, such as corona discharge treatment, plasma treatment, and flame treatment, and modification treatments using a wet process that forms an easy-adhesion layer by coating.

[0059] <Packaging Material> The packaging material includes the sealant film. The packaging material may include only the sealant film, or may further include other layers such as a base film. The sealant film is provided in the packaging material so that the first layer, which is a heat seal layer, faces the contents.

[0060] 4 to 6 are cross-sectional views of packaging materials according to one embodiment of the present invention. Packaging material 200 is formed by laminating a sealant film 100 and a base film 4 with an adhesive layer 3 interposed therebetween. Packaging material 201 is formed by laminating a sealant film 101 and a base film 4 with an adhesive layer 3 interposed therebetween. Packaging material 202 is formed by laminating a sealant film 102 and a base film 4 with an adhesive layer 3 interposed therebetween.

[0061] (Base Film) The base film contains a propylene-based polymer and may be made of a propylene-based polymer. Examples of the propylene-based polymer include homopolypropylene and propylene copolymer. Examples of the propylene copolymer include a propylene-ethylene random copolymer, a propylene-ethylene block copolymer, and a propylene-α-olefin copolymer.

[0062] The content of the propylene polymer in the substrate film may be 99.5% by mass or more based on the total amount of the substrate film. The substrate film may contain additives such as antistatic agents, ultraviolet absorbers, plasticizers, and lubricants as trace components. The substrate film may be subjected to a surface treatment such as plasma treatment to improve adhesion to a layer to be laminated. The substrate film may also have an inorganic oxide layer (e.g., a metal oxide vapor-deposited layer) on at least one surface.

[0063] The base film may be a stretched film or a non-stretched film, but is preferably a stretched film from the viewpoint of gas barrier properties. Examples of stretched films include uniaxially stretched films and biaxially stretched films, and biaxially stretched films are preferred because they improve the heat resistance of the packaging material.

[0064] The thickness of the base film is not particularly limited, but may be, for example, 0.1 mm or less. In particular, the thickness of the base film is preferably 40 μm or less, more preferably 35 μm or less, and particularly preferably 30 μm or less. When the thickness of the base film is 0.1 mm or less, the flexibility of the packaging material can be further improved, thereby further improving its durability. Furthermore, from the viewpoint of improving strength, the thickness of the base film is preferably 10 μm or more, and more preferably 12 μm or more.

[0065] (Adhesive Layer) As the material for the adhesive layer, for example, polyester-isocyanate resin, urethane resin, polyether resin, acid-modified polyolefin, etc. can be used.

[0066] The packaging material can be produced by a conventional dry lamination method in which a sealant film and a base film are bonded together via an adhesive layer. However, the packaging material may also be produced by a method in which the sealant film is directly extruded onto the base film and laminated thereon.

[0067] The configuration of the packaging material can be adjusted as appropriate depending on the required properties of the package, such as barrier properties that meet the shelf life of the packaged food, size and impact resistance that can accommodate the weight of the contents, visibility of the contents, recyclability, etc. Such other packaging materials will be described below.

[0068] <Other Packaging Materials> The packaging material may include the sealant film, a first base film containing a propylene-based polymer, and a second base film containing a propylene-based polymer, in this order. The first base film (i.e., the base film on the sealant film side) may have an inorganic oxide layer on at least one surface.

[0069] (First Base Film and Second Base Film) As the first base film and the second base film, the films described above as the base film can be used.

[0070] (Adhesion Layer) An adhesion layer (anchor coat layer) may be provided on the surface of the first base film on which the inorganic oxide layer is laminated. The adhesion layer is provided on the first base film, and can achieve two effects: improving the adhesion performance between the first base film and the inorganic oxide layer, and improving the smoothness of the surface of the first base film. The improved smoothness makes it easier to form the inorganic oxide layer uniformly without defects, and makes it easier to exhibit high barrier properties. The adhesion layer can be formed using an anchor coat agent.

[0071] Examples of anchor coating agents include polyester-based polyurethane resins, polyether-based polyurethane resins, etc. As the anchor coating agent, polyester-based polyurethane resins are preferred from the viewpoints of heat resistance and interlayer adhesive strength.

[0072] The thickness of the adhesive layer is not particularly limited, but is preferably in the range of 0.01 to 5 μm, more preferably in the range of 0.03 to 3 μm, and particularly preferably in the range of 0.05 to 2 μm. When the thickness of the adhesive layer is equal to or greater than the lower limit, more sufficient interlayer adhesive strength tends to be obtained, while when the thickness is equal to or less than the upper limit, desired gas barrier properties tend to be easily exhibited.

[0073] The method for applying the adhesive layer to the first substrate film can be any known application method without any particular limitation, and examples thereof include an immersion method (dipping method), and methods using a spray, a coater, a printer, a brush, etc. In addition, examples of the types of coaters and printers used in these methods and the application methods thereof include gravure coaters such as direct gravure, reverse gravure, kiss reverse gravure, and offset gravure, reverse roll coaters, microgravure coaters, coaters combined with a chamber doctor, air knife coaters, dip coaters, bar coaters, comma coaters, and die coaters.

[0074] The amount of adhesive layer applied is 1 m after applying and drying the anchor coating agent. ２ Mass per unit is 0.01 to 5 g / m ２ It is preferable that the density is 0.03 to 3 g / m ２It is more preferable that the thickness of the anchor coating agent is 1 m after it is applied and dried. ２ When the mass per unit area is equal to or greater than the lower limit, film formation tends to be sufficient, whereas when the mass per unit area is equal to or less than the upper limit, the film tends to be sufficiently dried and the solvent tends not to remain.

[0075] The method for drying the adhesive layer is not particularly limited, but examples thereof include a method of natural drying, a method of drying in an oven set at a predetermined temperature, and a method using a dryer attached to the coater, such as an arch dryer, a floating dryer, a drum dryer, an infrared dryer, etc. Furthermore, the drying conditions can be appropriately selected depending on the drying method, and for example, in a method of drying in an oven, it is preferable to dry at a temperature of 60 to 100°C for about 1 second to 2 minutes.

[0076] Instead of the polyurethane resin, a polyvinyl alcohol resin may be used for the adhesive layer. The polyvinyl alcohol resin may be any resin having a vinyl alcohol unit formed by saponifying a vinyl ester unit, such as polyvinyl alcohol (PVA) or ethylene-vinyl alcohol copolymer (EVOH).

[0077] Examples of PVA include resins obtained by homopolymerizing vinyl esters such as vinyl acetate, vinyl formate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl pivalate, and vinyl versatate, followed by saponification. The PVA may also be a modified PVA that has been copolymerized or post-modified. The modified PVA can be obtained, for example, by copolymerizing a vinyl ester with an unsaturated monomer copolymerizable with the vinyl ester, followed by saponification. Examples of unsaturated monomers copolymerizable with vinyl esters include olefins such as ethylene, propylene, isobutylene, α-octene, α-dodecene, and α-octadecene; hydroxy group-containing α-olefins such as 3-buten-1-ol, 4-pentyn-1-ol, and 5-hexen-1-ol; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, itaconic acid, and undecylenic acid; nitriles such as acrylonitrile and methacrylonitrile; diacetone acrylamide, acrylic acid, and the like. olefin sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid, and methallyl sulfonic acid; vinyl compounds such as alkyl vinyl ethers, dimethyl allyl vinyl ketone, N-vinyl pyrrolidone, vinyl chloride, vinyl ethylene carbonate, 2,2-dialkyl-4-vinyl-1,3-dioxane, glycerin monoallyl ether, and 3,4-diacetoxy-1-butene; vinylidene chloride, 1,4-diacetoxy-2-butene, and vinylene carbonate.

[0078] The degree of polymerization of PVA is preferably 300 to 3000. If the degree of polymerization is less than 300, the barrier properties tend to decrease, while if it exceeds 3000, the viscosity becomes too high and the coatability tends to decrease. The saponification degree of PVA is preferably 90 mol% or more, more preferably 95 mol% or more, and even more preferably 99 mol% or more. The saponification degree of PVA may be 100 mol% or less, or may be 99.9 mol% or less. The polymerization degree and saponification degree of PVA can be measured in accordance with the method described in JIS K 6726 (1994).

[0079] EVOH is generally obtained by saponifying a copolymer of ethylene and an acid vinyl ester such as vinyl acetate, vinyl formate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl pivalate, or vinyl versatate.

[0080] The degree of polymerization of EVOH is preferably 300 to 3,000. If the degree of polymerization is less than 300, the barrier properties tend to decrease, while if it exceeds 3,000, the viscosity becomes too high and the coatability tends to decrease. The degree of saponification of the vinyl ester component of EVOH is preferably 90 mol% or more, more preferably 95 mol% or more, and even more preferably 99 mol% or more. The degree of saponification of EVOH may be 100 mol% or less, or 99.9 mol% or less. The degree of saponification of EVOH is determined by nuclear magnetic resonance (1H-NMR) measurement, from the peak area of ​​hydrogen atoms contained in the vinyl ester structure and the peak area of ​​hydrogen atoms contained in the vinyl alcohol structure.

[0081] The ethylene unit content of EVOH is 10 mol% or more, more preferably 15 mol% or more, even more preferably 20 mol% or more, and particularly preferably 25 mol% or more. The ethylene unit content of EVOH is preferably 65 mol% or less, more preferably 55 mol% or less, and even more preferably 50 mol% or less. When the ethylene unit content is 10 mol% or more, good gas barrier properties or dimensional stability can be maintained under high humidity conditions. On the other hand, when the ethylene unit content is 65 mol% or less, good gas barrier properties can be achieved. The ethylene unit content of EVOH can be determined by NMR.

[0082] When a polyvinyl alcohol resin is used as the adhesive layer, the adhesive layer may be formed by coating a polyvinyl alcohol resin solution or by multi-layer extrusion.

[0083] (Inorganic oxide layer) Examples of inorganic oxides contained in the inorganic oxide layer include aluminum oxide, silicon oxide, magnesium oxide, and tin oxide. From the viewpoint of transparency and barrier properties, the inorganic oxide may be selected from the group consisting of aluminum oxide, silicon oxide, and magnesium oxide. Furthermore, from the viewpoint of excellent tensile stretchability during processing, it is preferable that the inorganic oxide layer is a layer using silicon oxide. By using an inorganic oxide layer, high barrier properties can be obtained with a very thin layer that does not affect the recyclability of the laminate.

[0084] The O / Si ratio of the inorganic oxide layer is desirably 1.7 or more. When the O / Si ratio is 1.7 or more, the content of metallic Si is suppressed, making it easy to obtain good transparency. Furthermore, the O / Si ratio is preferably 2.0 or less. When the O / Si ratio is 2.0 or less, the crystallinity of SiO is high, preventing the inorganic oxide layer from becoming too hard and obtaining good tensile strength. This makes it possible to suppress the occurrence of cracks in the inorganic oxide layer when laminating a gas barrier coating layer. Furthermore, even after forming into a packaging bag, the first base film may shrink due to heat during boiling or retort treatment. However, when the O / Si ratio is 2.0 or less, the inorganic oxide layer easily follows this shrinkage, making it possible to suppress a decrease in barrier properties. From the viewpoint of more fully obtaining these effects, the O / Si ratio of the inorganic oxide layer is preferably 1.75 to 1.9, more preferably 1.8 to 1.85.

[0085] The O / Si ratio of the inorganic oxide layer can be determined by X-ray photoelectron spectroscopy (XPS). For example, the measurement can be performed using an X-ray photoelectron spectrometer (manufactured by JEOL Ltd., product name: JPS-90MXV) with a non-monochromated MgKα (1253.6 eV) X-ray source and an X-ray output of 100 W (10 kV-10 mA). For quantitative analysis to determine the O / Si ratio, relative sensitivity factors of 2.28 for O1s and 0.9 for Si2p can be used.

[0086] The thickness of the inorganic oxide layer is preferably 10 nm or more and 50 nm or less. A thickness of 10 nm or more can provide sufficient water vapor barrier properties. Furthermore, a thickness of 50 nm or less can prevent cracks from occurring due to deformation caused by internal stress in the thin film, thereby preventing a decrease in water vapor barrier properties. Note that a thickness exceeding 50 nm is undesirable from an economic standpoint, as it increases costs due to an increase in the amount of material used and a longer film formation time. From the same viewpoint as above, the thickness of the inorganic oxide layer is more preferably 20 nm or more and 40 nm or less.

[0087] The inorganic oxide layer can be formed by, for example, vacuum film formation. In vacuum film formation, physical vapor deposition or chemical vapor deposition can be used. Examples of physical vapor deposition include, but are not limited to, vacuum deposition, sputtering, and ion plating. Examples of chemical vapor deposition include, but are not limited to, thermal CVD, plasma CVD, and photo CVD.

[0088] In the vacuum film formation, resistance heating vacuum deposition, EB (Electron Beam) heating vacuum deposition, induction heating vacuum deposition, sputtering, reactive sputtering, dual magnetron sputtering, plasma enhanced chemical vapor deposition (PECVD), and the like are particularly preferably used. However, in terms of productivity, vacuum deposition is currently the most superior. As a heating means for vacuum deposition, it is preferable to use any of the electron beam heating method, resistance heating method, and induction heating method.

[0089] (Gas barrier coating layer) The first base film may further have a gas barrier coating layer on the inorganic oxide layer. The gas barrier coating layer is a layer formed using a gas barrier coating layer-forming composition containing at least one selected from the group consisting of a hydroxyl group-containing polymer compound, a metal alkoxide, a silane coupling agent, and a hydrolyzate thereof.

[0090] The gas barrier coating layer is a coating layer having gas barrier properties and is formed using a gas barrier coating layer-forming composition (hereinafter also referred to as a coating agent) whose main component is an aqueous solution or a water / alcohol mixed solution containing at least one selected from the group consisting of a hydroxyl-containing polymer compound, a metal alkoxide, a silane coupling agent, and their hydrolysates. From the viewpoint of more adequately maintaining gas barrier properties after hot water treatment such as retort treatment, the coating agent preferably contains at least a silane coupling agent or its hydrolysate, more preferably at least one selected from the group consisting of a hydroxyl-containing polymer compound, a metal alkoxide, and their hydrolysates, and a silane coupling agent or its hydrolysate, and even more preferably a hydroxyl-containing polymer compound or its hydrolysate, a metal alkoxide or its hydrolysate, and a silane coupling agent or its hydrolysate. The coating agent can be prepared, for example, by mixing a metal alkoxide and a silane coupling agent directly, or after prior hydrolysis, with a solution of a hydroxyl-containing polymer compound, which is a water-soluble polymer, dissolved in an aqueous solvent (water or a water / alcohol mixture).

[0091] Each component contained in the coating agent for forming the gas barrier coating layer will be described in detail. Examples of hydroxyl group-containing polymer compounds used in the coating agent include polyvinyl alcohol, polyvinylpyrrolidone, starch, methyl cellulose, carboxymethyl cellulose, sodium alginate, etc. Among these, polyvinyl alcohol (PVA) is preferably used in the coating agent for the gas barrier coating layer because it has particularly excellent gas barrier properties.

[0092] From the viewpoint of obtaining excellent gas barrier properties, the gas barrier coating layer is preferably formed from a composition containing at least one selected from the group consisting of metal alkoxides represented by the following general formula (I) and hydrolysates thereof: M(OR １ ) ｍ (R ２ ) ｎ－ｍ ...(I) In the above general formula (I), R １ and R ２are each independently a monovalent organic group having 1 to 8 carbon atoms, and are preferably an alkyl group such as a methyl group or an ethyl group. M represents an n-valent metal atom such as Si, Ti, Al, or Zr. m is an integer from 1 to n. １ or R ２ If there are multiple １ Comrades or R ２ They may be the same or different.

[0093] Specific examples of metal alkoxides include tetraethoxysilane [Si(OC ２ H ５ ) ４ ], triisopropoxyaluminum [Al(O-2'-C ３ H ７ ) ３ Tetraethoxysilane and triisopropoxyaluminum are preferred because they are relatively stable in aqueous solvents after hydrolysis.

[0094] Examples of the silane coupling agent include compounds represented by the following general formula (II): Si(OR １１ ) ｐ (R １２ ) ３－ｐ R １３ ... (II) In the above general formula (II), R １１ represents an alkyl group such as a methyl group or an ethyl group, and R １２ represents a monovalent organic group such as an alkyl group, an aralkyl group, an aryl group, an alkenyl group, an alkyl group substituted with an acryloxy group, or an alkyl group substituted with a methacryloxy group, and R １３ represents a monovalent organic functional group, and p represents an integer of 1 to 3. １１ or R １２ If there are multiple １１ Comrades or R １２ R may be the same or different. １３ Examples of the monovalent organic functional group represented by the formula (I) include a monovalent organic functional group containing a glycidyloxy group, an epoxy group, a mercapto group, a hydroxyl group, an amino group, an alkyl group substituted with a halogen atom, or an isocyanate group.

[0095] Specific examples of the silane coupling agent include vinyltrimethoxysilane, γ-chloropropylmethyldimethoxysilane, γ-chloropropyltrimethoxysilane, glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, and γ-methacryloxypropylmethyldimethoxysilane.

[0096] The silane coupling agent may also be a polymer formed by polymerization of the compound represented by the general formula (II). A trimer is preferred as the polymer, and 1,3,5-tris(3-trialkoxysilylalkyl)isocyanurate is more preferred. This is a condensation polymer of 3-isocyanatoalkylalkoxysilane. It is known that 1,3,5-tris(3-trialkoxysilylalkyl)isocyanurate loses chemical reactivity in the isocyanate moiety, but the reactivity is ensured by the polarity of the nurate moiety. It is generally added to adhesives, similar to 3-isocyanatoalkylalkoxysilane, and is known as an adhesion improver. Therefore, adding 1,3,5-tris(3-trialkoxysilylalkyl)isocyanurate to a hydroxyl group-containing polymer compound can improve the water resistance of a gas barrier coating layer through hydrogen bonding. While 3-isocyanate alkyl alkoxysilanes have high reactivity and low liquid stability, 1,3,5-tris(3-trialkoxysilylalkyl) isocyanurates are not water-soluble due to the polarity of the nurate moiety, but are easily dispersed in aqueous solutions and can maintain stable liquid viscosity. Furthermore, the water resistance of 3-isocyanate alkyl alkoxysilanes and 1,3,5-tris(3-trialkoxysilylalkyl) isocyanurates is equivalent.

[0097] Some 1,3,5-tris(3-trialkoxysilylalkyl)isocyanurates are produced by thermal condensation of 3-isocyanatepropylalkoxysilane, and may contain the raw material 3-isocyanatepropylalkoxysilane, but this does not pose any particular problems. 1,3,5-tris(3-trialkoxysilylpropyl)isocyanurate is more preferred, and 1,3,5-tris(3-trimethoxysilylpropyl)isocyanurate is even more preferred. 1,3,5-tris(3-trimethoxysilylpropyl)isocyanurate is practically advantageous because the methoxy group has a fast hydrolysis rate and those containing a propyl group are available relatively inexpensively.

[0098] Furthermore, known additives such as an isocyanate compound, a dispersant, a stabilizer, a viscosity adjuster, and a colorant can be added to the coating agent as needed, provided that the gas barrier properties are not impaired.

[0099] The thickness of the gas barrier coating layer is preferably 50 to 1,000 nm, and more preferably 100 to 500 nm. When the thickness of the gas barrier coating layer is 50 nm or more, more sufficient gas barrier properties tend to be obtained, and when it is 1,000 nm or less, sufficient flexibility tends to be maintained.

[0100] The coating liquid for forming the gas barrier coating layer can be applied by, for example, dipping, roll coating, gravure coating, reverse gravure coating, air knife coating, comma coating, die coating, screen printing, spray coating, gravure offset, etc. The coating film obtained by applying this coating liquid can be dried by, for example, hot air drying, heat roll drying, high frequency irradiation, infrared irradiation, UV irradiation, or a combination thereof.

[0101] The temperature at which the coating film is dried can be, for example, 50 to 150° C., and preferably 70 to 100° C. By keeping the drying temperature within the above range, the occurrence of cracks in the inorganic oxide layer and the gas barrier coating layer can be further suppressed, and excellent barrier properties can be achieved.

[0102] The gas barrier coating layer may be formed using a coating agent containing a polyvinyl alcohol resin and a silane compound. The coating agent may contain an acid catalyst, an alkali catalyst, a photopolymerization initiator, etc., as needed.

[0103] The polyvinyl alcohol resin is as described above. Examples of the silane compound include a silane coupling agent, polysilazane, and siloxane, and specific examples thereof include tetramethoxysilane, tetraethoxysilane, glycidoxypropyltrimethoxysilane, acryloxypropyltrimethoxysilane, and hexamethyldisilazane.

[0104] (Printed Layer) A printed layer can be provided on the first base film side of the second base film. The printed layer is provided in a position visible from the outside of the laminate for the purpose of displaying information about the contents, identifying the contents, or improving the design of the packaging bag. The printing method and printing ink are not particularly limited, and are appropriately selected from known printing methods and printing inks taking into consideration printability on the film, design such as color tone, adhesion, safety as a food container, etc. Examples of printing methods that can be used include gravure printing, offset printing, gravure offset printing, flexographic printing, and inkjet printing. Among these, gravure printing is preferably used from the viewpoints of productivity and high resolution of the image.

[0105] In order to improve adhesion to the printed layer, the surface of the second substrate film facing the first substrate film may be subjected to various pretreatments such as corona treatment, plasma treatment, and flame treatment, or a coating layer such as an easy-adhesion layer may be provided.

[0106] <Packaging> The packaging is made from the packaging material, and there are no particular limitations on the manufacturing style. For example, the packaging material (laminate) can be used for flat bags, three-sided bags, palm-shaped bags, gusseted bags, standing pouches, pouches with spouts, pouches with beaks, etc., using a sealant film as a sealing material.

[0107] EXAMPLES The present invention will be described in detail below using examples and comparative examples, but the present invention is not limited to the following examples.

[0108] <Preparation of Sealant Film> As materials to be used for the first layer and the third layer, the following propylene homopolymer (A), propylene-ethylene random copolymer (B), and ethylene-α-olefin copolymer elastomer (C) were prepared.

[0109] (Propylene homopolymer (A)) A propylene homopolymer having a melting onset temperature of 153°C, a melting point of 159°C, and a melt flow rate (MFR: ISO 1133) of 3.0 g / 10 min (temperature 230°C, load 2.16 kg) when measured by differential scanning calorimetry (JIS K 7121).

[0110] (Propylene-Ethylene Random Copolymer (B)) A propylene-ethylene random copolymer having a melting point of 147° C. and an ethylene content of 3.4% by mass as measured by differential scanning calorimetry (JIS K 7121).

[0111] The ethylene content was measured in accordance with the ethylene content determination method (IR method) described on pages 412-413 of Polymer Analysis Handbook (May 10, 2013, 3rd printing), edited by the Polymer Analysis Roundtable of the Japan Analytical Society.

[0112] (Ethylene-α-olefin copolymer elastomer (C)) Tafmer A-1085S (trade name, manufactured by Mitsui Chemicals, Inc.), an ethylene-1-butene copolymer elastomer, was used. The melt flow rate (MFR: ISO 1133) (temperature 190°C, load 2.16 kg) was 1.2 g / 10 min, and the density was 885 kg / m ３ The content of structural units derived from ethylene was 84% ​​by mass.

[0113] As materials for the second layer (hiding layer), the following propylene-ethylene block copolymer (D), ethylene-propylene copolymer elastomer (E), and titanium oxide (F) were prepared.

[0114] (Propylene-Ethylene Block Copolymer (D)) A propylene-ethylene block copolymer having a melt flow rate (MFR: ISO 1133) (temperature 230°C, load 2.16 kg) of 1.8 g / 10 min, containing 81.5 mass % of a propylene polymer and 18.5 mass % of an ethylene-propylene copolymer, with the ethylene content in the ethylene-propylene copolymer being 36.2 wt %.

[0115] (Ethylene-Propylene Copolymer Elastomer (E)) An ethylene-propylene copolymer elastomer having a melt flow rate (MFR: ISO 1133) (temperature 230°C, load 2.16 kg) of 0.6 g / 10 min and a mass ratio of propylene content / ethylene content of 2.7.

[0116] (Titanium oxide (F)) Titanium oxide PEONY HP WHITE series manufactured by DIC Corporation, model number: L-11232-MPT.

[0117] Example 1 For the formation of the first layer, a resin mixture was prepared by mixing 20.0 parts by mass of a propylene homopolymer (A) and 80.0 parts by mass of a propylene-ethylene random copolymer (B) in pellet form. To this resin mixture, 17.6 parts by mass of an ethylene-α-olefin copolymer elastomer (C) was added relative to a total of 100 parts by mass of the propylene homopolymer (A) and the propylene-ethylene random copolymer (B). The resin mixture was fed to an extruder controlled at 250°C, kneaded in a molten state, and extruded in a T-die extruder equipped with a feed block to produce the sealant film of Example 1 so that the thickness of the first layer was 60 μm.

[0118] Examples 2 to 4 and Comparative Examples 1 and 2 Films were produced in the same manner as in Example 1, except that the mixing ratio of each raw material compound was changed as shown in Table 1.

[0119] Example 5 For the formation of the first layer, a resin mixture was prepared by mixing 20.0 parts by mass of a propylene homopolymer (A) and 80.0 parts by mass of a propylene-ethylene random copolymer (B) in pellet form. To this resin mixture, 17.6 parts by mass of an ethylene-α-olefin copolymer elastomer (C) was added relative to a total of 100 parts by mass of the propylene homopolymer (A) and the propylene-ethylene random copolymer (B). For the formation of the second layer, a resin mixture was prepared by mixing the ethylene-propylene copolymer elastomer (E) to the propylene-ethylene block copolymer (D) in pellet form so that the mass ratio (E) / (D) of the ethylene-propylene copolymer elastomer (E) to the propylene-ethylene block copolymer (D) was 0.43. Each resin mixture was fed into an extruder controlled at 250°C, kneaded in a molten state, and laminated in a T-die extruder equipped with a feed block so that the first layer had a thickness of 10 μm and the second layer had a thickness of 50 μm, producing the sealant film of Example 5.

[0120] Examples 6 to 8 and Comparative Examples 3 and 4 Films were produced in the same manner as in Example 5, except that the mixing ratio of each raw material compound was changed as shown in Table 2.

[0121] Example 9 For the formation of the first layer, a resin mixture was prepared by mixing 20.0 parts by mass of a propylene homopolymer (A) and 80.0 parts by mass of a propylene-ethylene random copolymer (B) in pellet form. To this resin mixture, 17.6 parts by mass of an ethylene-α-olefin copolymer elastomer (C) was added relative to a total of 100 parts by mass of the propylene homopolymer (A) and the propylene-ethylene random copolymer (B). For the formation of the second layer, a resin mixture was prepared by mixing the ethylene-propylene copolymer elastomer (E) to the propylene-ethylene block copolymer (D) in pellet form so that the mass ratio (E) / (D) of the ethylene-propylene copolymer elastomer (E) was 0.43. Titanium oxide (F) was added to this resin mixture so that the amount was 7.5% by mass, based on the total mass of the second layer. Each resin mixture was fed into an extruder whose temperature was controlled to 250°C, kneaded in a molten state, and laminated in a T-die extruder with a feed block so that the first layer was 10 μm thick and the second layer was 50 μm thick, thereby producing the sealant film of Example 9.

[0122] Examples 10 to 12 and Comparative Examples 5 to 6 Films were produced in the same manner as in Example 9, except that the mixing ratio of each raw material mixture was changed as shown in Table 3.

[0123] Example 13 A resin mixture was prepared for forming the first and third layers by mixing 11.8 parts by mass of propylene homopolymer (A) and 88.2 parts by mass of propylene-ethylene random copolymer (B) in pellet form. To this resin mixture, 17.6 parts by mass of ethylene-α-olefin copolymer elastomer (C) was added relative to 100 parts by mass of the total amount of propylene homopolymer (A) and propylene-ethylene random copolymer (B). To form the second layer, a resin mixture was prepared by mixing the ethylene-propylene copolymer elastomer (E) and propylene-ethylene block copolymer (D) in pellet form so that the mass ratio (E) / (D) of the ethylene-propylene copolymer elastomer (E) to the propylene-ethylene block copolymer (D) was 0.43. Titanium oxide (F) was added to this resin mixture in an amount of 7.5% by mass, based on the total mass of the second layer. Each resin mixture was fed into an extruder whose temperature was controlled to 250°C, kneaded in a molten state, and laminated in a T-die extruder with a feed block so that the first and third layers were each 10 μm thick, and the second layer was 40 μm thick, thereby producing the sealant film of Example 1.

[0124] Examples 14 to 16 and Comparative Examples 7 to 8 Films were produced in the same manner as in Example 13, except that the mixing ratio of each raw material compound was changed as shown in Table 4.

[0125] <Various Evaluations> The films obtained in each example were evaluated as follows. The results are shown in Tables 1 to 4.

[0126] [Evaluation of Drop Bag Resistance] The first layers of the films obtained in each example were placed facing each other and heat-sealed using a heat sealer manufactured by Tester Sangyo Co., Ltd. under conditions of a sealing pressure of 0.2 MPa, a sealing time of 1 second, a sealing width of 5 mm, and a sealing temperature of 150°C. A packaging bag was produced in which three sides, excluding one short side, were heat-sealed. The size of the packaging bag was 180 mm x 130 mm. The resulting packaging bag was filled with 150 mL of water, and the unsealed side was heat-sealed to produce a water-filled bag. This water-filled bag was retorted at 127°C for 50 minutes and stored at a low temperature of 5°C for 72 hours. The water-filled bag was then dropped 100 times from a height of 100 cm onto the floor while standing vertically, with the first heat-sealed short side landing on the floor. A total of 10 bags were tested, and the percentage of unbroken bags (survival rate) was evaluated. If the remaining rate was 60% or more, the bag drop resistance during low-temperature storage was evaluated as good.

[0127] [Evaluation of Low-Temperature Sealability] The first layers of the films obtained in each example were placed facing each other and heat-sealed using a heat sealer manufactured by Tester Sangyo Co., Ltd. under conditions of a sealing pressure of 0.2 MPa, a sealing time of 1 second, and a seal width of 5 mm. The sealing temperature was adjusted in 2°C increments between 140°C and 160°C. The films heat-sealed at each temperature were then cut into 15 mm wide x 80 mm pieces and subjected to T-peel at a tensile speed of 300 mm / min using a tensile tester manufactured by Shimadzu Corporation, to measure the heat seal strength of the heat-sealed portion. The temperature at which the heat seal strength reached 15 N / 15 mm or more was taken as the heat seal initiation temperature, and it was determined that the lower the heat seal initiation temperature, the better the low-temperature sealability.

[0128] [Heat Resistance Evaluation] The first layers of the films obtained in each example were placed facing each other and heat-sealed using a heat sealer manufactured by Tester Sangyo Co., Ltd. under the following conditions: sealing pressure 0.05 MPa, sealing time 30 seconds, sealing width 10 mm, and sealing temperature 128°C. The heat-sealed film was then cut into a 15 mm wide x 80 mm piece and subjected to T-peel at a tensile speed of 300 mm / min using a tensile tester manufactured by Shimadzu Corporation, to measure the heat-sealed strength of the heat-sealed portion. The lower the heat-sealing strength, the better the heat resistance was judged to be.

[0129] [Evaluation of Concealing Ability] Of the films obtained in each example, the films prepared by adding titanium oxide to the second layer were subjected to measurement of transmission density using a portable transmission densitometer (Model No. 341C) manufactured by X-RITE Corporation. Here, the transmission density is expressed as -log １０ The value is defined as (I / I0), and the higher the whiteness of the film, the larger the value. If the transmission density value was 0.2 or more, the film was judged to have good hiding power.

[0130] <Evaluation Results> (Examples 1 to 4 and Comparative Examples 1 and 2) The films of Examples 1 to 4 and Comparative Examples 1 and 2, which had only the first layer, were evaluated for bag drop resistance, low-temperature sealability, and heat resistance. As shown in Table 1, all films were confirmed to have good low-temperature sealability and heat resistance. The films of Examples 1 to 4 were also confirmed to have good bag drop resistance. In comparison, the films of Comparative Examples 1 and 2 did not exhibit good bag drop resistance due to the low amount of ethylene-α-olefin copolymer elastomer added. Furthermore, the film of Example 4 exhibited a relatively high heat seal strength due to the high amount of ethylene-α-olefin copolymer elastomer added. From the perspective of more easily suppressing fusion on the inner surface of the packaging bag after pressure and heat treatment under retort conditions at 128°C, it was determined that a heat seal strength of less than 5 N is more preferable. Therefore, from the viewpoint of heat resistance, it is considered more preferable to set the amount of ethylene-α-olefin copolymer elastomer to 43 parts by mass or less relative to 100 parts by mass of the total amount of propylene homopolymer and propylene-ethylene random copolymer. On the other hand, this is not the only option, since sufficient heat resistance to suppress fusion on the inner surface of the packaging bag is exhibited under lower temperature retort conditions.

[0131] (Examples 5 to 8 and Comparative Examples 3 to 4) Evaluations of bag drop resistance, low-temperature sealability, and heat resistance were carried out for the films of Examples 5 to 8 and Comparative Examples 3 to 4, which had a first layer and a second layer. As shown in Table 2, it was confirmed that all of the films had good low-temperature sealability. It was also confirmed that the films of Examples 5 to 8 had good bag drop resistance and heat resistance. In comparison, the films of Comparative Examples 3 to 4 did not exhibit good bag drop resistance due to the low amount of ethylene-α-olefin copolymer elastomer added.

[0132] (Examples 9 to 12 and Comparative Examples 5 to 6) The films of Examples 9 to 12 and Comparative Examples 5 to 6, which had a first layer and a second layer and contained titanium oxide in the second layer, were evaluated for bag drop resistance, low-temperature sealability, heat resistance, and opacity. As shown in Table 3, all of the films were confirmed to have good low-temperature sealability and opacity. The films of Examples 9 to 12 were also confirmed to have good bag drop resistance and heat resistance. In comparison, the films of Comparative Examples 5 and 6 did not exhibit good bag drop resistance due to the low amount of ethylene-α-olefin copolymer elastomer added.

[0133] (Examples 13 to 16 and Comparative Examples 7 to 8) The films of Examples 13 to 16 and Comparative Examples 7 to 8, which had a first layer, a second layer, and a third layer and contained titanium oxide in the second layer, were evaluated for drop bag resistance, low-temperature sealability, heat resistance, and opacity. As shown in Table 4, it was confirmed that all of the films had good low-temperature sealability and opacity. It was also confirmed that the films of Examples 13 to 16 had good drop bag resistance and heat resistance. In comparison, the films of Comparative Examples 7 to 8 did not exhibit good drop bag resistance due to the low amount of ethylene-α-olefin copolymer elastomer added.

[0134]

[0135]

[0136]

[0137]

[0138] The sealant film of the present invention is a polypropylene-based film that can achieve high levels of both low-temperature sealing properties and resistance to bag drop during low-temperature storage. Therefore, the sealant film of the present invention can be suitably used in polypropylene-based mono-material packaging materials (retort packaging materials).

[0139] 1... second layer, 2... third layer, 3... adhesive layer, 4... base film, 10... first layer, 100 to 102... sealant films, 200 to 202... packaging material.

Claims

1. A sealant film having a first layer containing a propylene homopolymer (A), a propylene-ethylene random copolymer (B), and an ethylene-α-olefin copolymer elastomer (C), wherein the content of the ethylene-α-olefin copolymer elastomer (C) is 17.5 parts by mass or more per 100 parts by mass of the total amount of the propylene homopolymer (A) and the propylene-ethylene random copolymer (B).

2. The sealant film according to claim 1, comprising: the first layer; and a second layer containing a propylene-ethylene block copolymer (D) and an ethylene-propylene copolymer elastomer (E).

3. The sealant film according to claim 1, comprising: the first layer; and a second layer containing a propylene-based polymer and titanium oxide.

4. The sealant film according to claim 2, comprising, in this order, the first layer, the second layer, and a third layer containing a propylene homopolymer (A) and a propylene-ethylene random copolymer (B).

5. The sealant film according to claim 3, comprising, in this order, the first layer, the second layer, and a third layer containing a propylene homopolymer (A) and a propylene-ethylene random copolymer (B).

6. The sealant film according to claim 1, wherein the content of the ethylene-α-olefin copolymer elastomer (C) is 17.5 to 43 parts by mass per 100 parts by mass of the total amount of the propylene homopolymer (A) and the propylene-ethylene random copolymer (B).

7. A packaging material comprising the sealant film according to any one of claims 1 to 6 and a base film containing a propylene-based polymer.

8. The packaging material according to claim 7, wherein the base film has an inorganic oxide layer on at least one surface.

9. A packaging material comprising, in this order, the sealant film according to any one of claims 1 to 6, a first base film containing a propylene-based polymer, and a second base film containing a propylene-based polymer, the first base film having an inorganic oxide layer on at least one surface.

10. A package made from the packaging material according to claim 7.

Images