Multilayer film, packaging material, and package

Abstract

Disclosed is a multilayer film which comprises a first layer that serves as a heat seal layer, and a second layer, wherein: the first layer contains, based on the total amount of the first layer, 10-30 mass% of a propylene homopolymer (A) and 70-90 mass% of a propylene-ethylene random copolymer (B); the second layer contains, based on the total amount of the second layer, 60-91 mass% of a propylene-ethylene block copolymer (C) and 9-40 mass% of an ethylene-propylene copolymer elastomer (D); and the multilayer film contains, based on the total amount of the multilayer film, 0.10-0.19 mass% of a crystal nucleating agent.

Description

Multilayer film, packaging material and packaging body

[0001] The present disclosure relates to a multilayer film, a packaging material, and a package. Specifically, the present disclosure relates to a multilayer film that has excellent heat resistance, low-temperature sealing properties, and cold impact resistance, and is suitable for use as a sealant film for packaging, even in severe treatments such as boiling water treatment and retort treatment, and is particularly suitable for use in packaging materials made of the same polypropylene material laminated with a polypropylene-based biaxially oriented film, as well as packaging materials and packaging bags obtained using the multilayer film.

[0002] Polypropylene-based 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 thermoformed propylene-based resin container characterized by being made of a resin composition in which a compound having a specific structure is blended with a propylene-based resin.

[0004] Patent Document 2 proposes a polypropylene resin composition comprising a block copolymer polypropylene resin, a soft polypropylene resin, and a high melt tension polypropylene resin.

[0005] Patent Document 3 proposes a laminated polypropylene-based unstretched film that simultaneously satisfies a plurality of specific properties and is composed of two layers: a laminate layer composed of a propylene-α-olefin random copolymer resin and a propylene-α-olefin block copolymer resin and / or a propylene-ethylene block copolymer resin, and a seal layer composed of a propylene-α-olefin random copolymer resin and a propylene-ethylene block copolymer resin.

[0006] Patent Document 4 proposes a polypropylene-based composite film composed of three layers, characterized in that the middle layer is made of a layer containing a propylene-ethylene block copolymer as a main component, and both surface layers are made of layers containing a propylene-based random copolymer as a main component.

[0007] Japanese Patent Laid-Open No. 8-283423 Japanese Patent Laid-Open No. 2003-105162 Japanese Patent Laid-Open No. 2007-237641 Japanese Patent Laid-Open No. 2017-132186

[0008] Polypropylene-based films have traditionally been required to have heat resistance that enables them to withstand retort treatments, which involve high-temperature pressure treatments for sterilization and sterilization. In addition, in recent years, with the aim of improving the recyclability of packaging materials, biaxially oriented polypropylene film (OPP) has been used as a base film, and the use of packaging materials composed of the same polypropylene material has been considered. Because biaxially oriented polypropylene film has a lower melting point than the conventionally used biaxially oriented polyamide film (ONy) and biaxially oriented polyester film (PET), heat sealing cannot be performed at high temperatures during bag manufacturing, raising concerns about reduced productivity and distortion due to heat-induced film shrinkage. Therefore, low-temperature sealing properties have become a requirement for polypropylene-based films. Furthermore, the use of OPP as a base film has raised concerns about thermal shrinkage during high-temperature retort treatment, leading to the requirement for heat-shrinkage resistance in polypropylene-based films.

[0009] In addition to the above-mentioned problems, in recent years, the size of packages has been increasing, and there is a need for a package that will not break even if it is dropped repeatedly after storage at low temperature, and also for a package that has both the strength to break under severe conditions and the rigidity to maintain the self-supporting properties of the package. However, it is currently difficult for conventional polypropylene-based films to achieve excellent heat resistance, low-temperature sealing properties, heat shrinkage resistance, cold impact resistance, and rigidity.

[0010] The present disclosure has been made in view of the above circumstances, and aims to provide a polypropylene-based multilayer film that can achieve a high level of heat resistance, low-temperature sealability, heat shrinkage resistance, cold impact resistance, and rigidity in a well-balanced manner. Another aim of the present disclosure is to provide a packaging material and a package obtained using the polypropylene-based multilayer film.

[0011] As a result of intensive studies to solve the above problems, the inventors have found that it is important to mix and contain a propylene homopolymer (A) and a propylene-ethylene random copolymer (B) in predetermined amounts, laminate this with a layer containing a propylene-ethylene block copolymer (C) and an ethylene-propylene copolymer elastomer (D), and further contain a crystal nucleating agent in an amount of 0.10 to 0.19 mass % based on the total amount of the multilayer film, and have completed the present invention.

[0012] That is, the present disclosure provides the following multilayer films, packaging materials, and packages. [1] A multilayer film including a first layer that is a heat-sealable layer and a second layer, wherein the first layer contains 10 to 30 mass% of a propylene homopolymer (A) and 70 to 90 mass% of a propylene-ethylene random copolymer (B) based on the total amount of the first layer, and the second layer contains 60 to 91 mass% of a propylene-ethylene block copolymer (C) and 9 to 40 mass% of an ethylene-propylene copolymer elastomer (D) based on the total amount of the second layer, and the multilayer film contains 0.10 to 0.19 mass% of a nucleating agent based on the total amount of the multilayer film. [2] The multilayer film according to [1] above, wherein only the second layer of the layers constituting the multilayer film contains the nucleating agent. [3] The multilayer film according to [1] or [2], wherein the propylene-ethylene block copolymer (C) contains 87.5 to 65% by mass of a propylene polymer (C1) and 12.5 to 35% by mass of an ethylene-propylene copolymer (C2). [4] The multilayer film according to any one of [1] to [3], wherein the thickness of the first layer is 10 to 20% of the thickness of the multilayer film. [5] The multilayer film according to any one of [1] to [4], wherein the thickness of the second layer is 30 to 75 μm. [6] The multilayer film according to any one of [1] to [5], 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). [7] The multilayer film according to [6], wherein the total thickness of the first layer and the third layer is 16 to 40% of the thickness of the multilayer film. [8] The multilayer film according to any one of [1] to [7] above, wherein the nucleating agent comprises a sorbitol-based compound. [9] A packaging material comprising the multilayer film according to any one of [1] to [8] above and a biaxially stretched polypropylene film.

[10] The packaging material according to [9] above, wherein the biaxially stretched polypropylene film has a melting point of 168°C or higher, which is the peak top of a melting curve observed when the film is heated from 25°C to 230°C at a heating rate of 10°C / min in differential scanning calorimetry.

[11] A package made from the packaging material according to [9] or

[10] above.

[0013] In the multilayer film described in [1] above, the first layer contains a propylene homopolymer (A) and a propylene-ethylene random copolymer (B) in a specific ratio, the second layer contains a propylene-ethylene block copolymer (C) and an ethylene-propylene copolymer elastomer (D), and the multilayer film contains 0.10 to 0.19 mass% of a nucleating agent based on the total mass of the multilayer film, thereby achieving excellent low-temperature sealability while maintaining heat resistance and heat shrinkage resistance, and achieving both cold impact resistance and rigidity. Such an effect cannot be obtained when a resin composition containing a propylene-based resin and a compound of a specific structure is used (for example, Patent Document 1 above), when a polypropylene-based resin composition containing a block copolymer polypropylene resin, a soft polypropylene-based resin, and a high melt tension polypropylene resin is used (for example, Patent Document 2 above), when a laminated polypropylene-based non-oriented film containing two layers, namely a laminate layer containing a propylene-α-olefin random copolymer resin and a propylene-α-olefin block copolymer resin and / or a propylene-ethylene block copolymer resin, and a seal layer containing a propylene-α-olefin random copolymer resin and a propylene-ethylene block copolymer resin, is used (for example, Patent Document 3), or when a propylene-based random copolymer is used in the outer layer and a propylene-ethylene block copolymer is used in the middle layer (for example, Patent Document 4 above), and is a particularly suitable effect for use in large retort packaging made of the same polypropylene material.

[0014] In the multilayer film described in [6] above, by providing the first layer, the second layer, and the third layer in this order, distortion and warping of the film can be easily suppressed.

[0015] The packaging material described in

[10] above includes the multilayer film and a biaxially oriented polypropylene film having a specific melting point, which makes it easier to suppress shrinkage due to heat when the packaging material is heat-sealed.

[0016] According to the present disclosure, it is possible to provide a polypropylene-based multilayer film that can achieve a high level of heat resistance, low-temperature sealability, heat shrinkage resistance, cold impact resistance, and rigidity in a well-balanced manner. That is, according to the present disclosure, it is possible to provide a polypropylene-based multilayer film that has heat resistance and heat shrinkage resistance that can withstand retort treatment, which involves pressure treatment at high temperatures to perform sterilization and pasteurization, low-temperature sealability that allows good heat sealing even with packaging materials made of the same polypropylene material, cold impact resistance that prevents bags from breaking even when dropped repeatedly after low-temperature storage, and rigidity that allows the packaging material to stand on its own after being filled with contents. Furthermore, according to the present disclosure, it is possible to provide packaging materials and packages obtained using the multilayer film.

[0017] Figure 1 is a cross-sectional view of a multilayer film according to an embodiment of the present disclosure. Figure 2 is a cross-sectional view of a multilayer film according to an embodiment of the present disclosure. Figure 3 is a cross-sectional view of a packaging material according to an embodiment of the present disclosure. Figure 4 is a cross-sectional view of a packaging material according to an embodiment of the present disclosure.

[0018] <Multilayer Film> Fig. 1 is a cross-sectional view of a multilayer film according to one embodiment of the present disclosure. Multilayer film 10 comprises, in this order, a first layer 1 and a second layer 2, which are heat-sealable layers. Fig. 2 is a cross-sectional view of a multilayer film according to another embodiment of the present disclosure. Multilayer film 20 comprises, in this order, a first layer 1, a second layer 2, and a third layer 3, which are heat-sealable layers. Multilayer films 10 and 20 can be used as polypropylene-based unstretched sealant films.

[0019] [First Layer] The first layer contains a propylene homopolymer (A) and a propylene-ethylene random copolymer (B). Based on the total weight of the first layer, the content of the propylene homopolymer (A) is 10 to 30% by mass, and the content of the propylene-ethylene random copolymer (B) is 70 to 90% by mass. The propylene homopolymer (A) has a high melting point, and by combining the propylene homopolymer (A) with a high melting point and the propylene-ethylene random copolymer (B) with a moderately lower melting point, in the amounts specified above, it is possible to achieve both excellent heat resistance and low-temperature sealability. The first layer is a heat-sealable layer (sealing layer), and a package is formed by heat-sealing the first layers of the multilayer film together.

[0020] (Propylene Homopolymer (A)) The production method of the propylene homopolymer (A) is not particularly limited, and it can be obtained, for example, by a method of homopolymerizing propylene using a Ziegler-Natta catalyst, a metallocene catalyst, or a half-metallocene catalyst. By containing the propylene homopolymer (A) in the first layer, 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 high-temperature pressurized heat treatment.

[0021] The propylene homopolymer (A) can be one having a melting onset temperature of 150°C or higher and a melting point (peak melting temperature) of 155°C or higher when measured by differential scanning calorimetry (JIS K 7121). When the melting onset temperature and melting point of the propylene homopolymer (A) are both within these ranges, the first layer can be imparted with superior heat resistance. This makes it more unlikely that fusion will occur on the inner surface of the packaging bag after high-temperature pressurized heat treatment. In this specification, the conditions for differential scanning calorimetry are as follows:

[0022] [Differential scanning calorimetry conditions] When the temperature is raised from 25°C to 230°C at a heating rate of 10°C / min, the melting onset temperature is determined as the point of intersection between a straight line extending the baseline on the low-temperature side of the DSC curve toward the high-temperature side and a tangent line drawn to the curve on the low-temperature side of the melting peak so as to maximize the gradient, and the temperature at the apex of the melting peak is determined as the melting point.

[0023] 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.

[0024] (Propylene-Ethylene Random Copolymer (B)) The production method of the propylene-ethylene random copolymer (B) is not particularly limited, and it can be obtained, for example, by copolymerizing ethylene as a comonomer with propylene as the main monomer using a Ziegler-Natta catalyst, a metallocene catalyst, or a half-metallocene catalyst. By containing the propylene-ethylene random copolymer (B) in the first layer, it is easy to obtain excellent low-temperature sealing properties while maintaining heat resistance.

[0025] The propylene-ethylene random copolymer (B) may have a melting point in the range of 132 to 150°C when measured by differential scanning calorimetry (JIS K 7121). By using a copolymer with a melting point in this range, it is easy to obtain excellent low-temperature sealing properties while maintaining heat resistance. The conditions for differential scanning calorimetry are as described above.

[0026] The ethylene content of the propylene-ethylene random copolymer (B) may be 8% by mass or less. By having the ethylene content be equal to or less than the above 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 high-temperature pressure and heat treatment. From this perspective, the ethylene content may be 6% by mass or less, or may be 4% by mass or less. The lower limit of the ethylene content is not particularly limited, but can be 3% by mass from the viewpoint of low-temperature sealability.

[0027] The ethylene content of the propylene-ethylene random copolymer (B) can be measured, for example, according to 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 Forum, Japan Analytical Society.

[0028] The first layer contains 10 to 30% by mass of a propylene homopolymer (A) and 70 to 90% by mass of a propylene-ethylene random copolymer (B) based on the total amount of the first layer. When the content of the propylene homopolymer (A) is 10% by mass or more, excellent heat resistance can be exhibited. From this viewpoint, the content may be 15% by mass or more, or 20% by mass or more. When the content of the propylene homopolymer (A) is 30% by mass or less, i.e., when the content of the propylene-ethylene random copolymer (B) is 70% by mass or more, low-temperature sealability can be exhibited while maintaining excellent heat resistance. From this viewpoint, the content of the propylene homopolymer (A) may be 28% by mass or less, or 25% by mass or less. From the above viewpoints, the content of the propylene homopolymer (A) may be 10 to 28% by mass or 10 to 25% by mass, and the content of the propylene-ethylene random copolymer (B) may be 75 to 85% by mass.

[0029] From the viewpoint of achieving both excellent heat resistance and low-temperature sealability, the total content of the propylene homopolymer (A) and the propylene-ethylene random copolymer (B) in the first layer may be 90% by mass or more, 95% by mass or more, or 99% by mass or more, based on the total amount of the second layer; from the same viewpoint, the total content may be 100% by mass, based on the total amount of components other than the crystal nucleating agent contained in the first layer.

[0030] [Second Layer] The second layer contains a propylene-ethylene block copolymer (C) and an ethylene-propylene copolymer elastomer (D). Based on the total amount of the second layer, the content of the propylene-ethylene block copolymer (C) is 60 to 91 mass %, and the content of the ethylene-propylene copolymer elastomer (D) is 9 to 40 mass %. The propylene-ethylene block copolymer (C) is excellent in rigidity, heat shrinkage resistance, and cold impact resistance, and the ethylene-propylene copolymer elastomer (D) is particularly excellent in cold impact resistance. By using the propylene-ethylene block copolymer (C) and the ethylene-propylene copolymer elastomer (D) in the above-mentioned amounts, respectively, a high level of rigidity, heat shrinkage resistance, and cold impact resistance can be achieved in a well-balanced manner.

[0031] (Propylene-Ethylene Block Copolymer (C)) The propylene-ethylene block copolymer (C) used in the second layer is a copolymer obtainable by producing a propylene polymer (C1) in a first step and then producing an ethylene-propylene copolymer (C2) 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. By including the propylene-ethylene block copolymer (C) in the second layer, excellent rigidity, heat shrinkage resistance, and cold impact resistance can be easily achieved.

[0032] The propylene-ethylene block copolymer (C) 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 (C) may contain 90 to 60% by mass of the propylene polymer (C1) and 10 to 40% by mass of the ethylene-propylene copolymer (C2). 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 (C) may contain 87.5 to 65% by mass of the propylene polymer (C1) and 12.5 to 35% by mass of the ethylene-propylene copolymer (C2), or may contain 85 to 70% by mass of the propylene polymer (C1) and 15 to 30% by mass of the ethylene-propylene copolymer (C2).

[0034] The ethylene content of the ethylene-propylene copolymer (C2) is not particularly limited, but can be in the range of 20 to 40 mass%. When the ethylene content is equal to or less than the upper limit, the tackiness of the product can be suppressed, contamination due to the tackiness of the product during production is unlikely, and excellent productivity can be easily maintained. When the ethylene content is equal to or more than the lower limit, excellent cold impact resistance can be easily obtained.

[0035] (Ethylene-Propylene Copolymer Elastomer (D)) The ethylene-propylene copolymer elastomer (D) 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 (D) 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 (D), even better cold impact resistance can be easily obtained.

[0036] The ethylene-propylene copolymer elastomer (D) 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 (C) and the ethylene-propylene copolymer elastomer (D) is good, and impact resistance can be easily obtained.

[0037] The ethylene-propylene copolymer elastomer (D) 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, it is easy to obtain even better cold impact resistance.

[0038] The second layer contains 60 to 91% by mass of a propylene-ethylene block copolymer (C) and 9 to 40% by mass of an ethylene-propylene copolymer elastomer (D), based on the total amount of the second layer. When the content of the propylene-ethylene block copolymer (C) is 60% by mass or more, excellent heat shrinkage resistance and rigidity are easily maintained. From this perspective, the content may be 70% by mass or more, or 80% by mass or more. When the content of the propylene-ethylene block copolymer (C) is 91% by mass or less, i.e., when the content of the ethylene-propylene copolymer elastomer (D) is 9% by mass or more, excellent cold impact resistance can be exhibited. From this perspective, the content of the propylene-ethylene block copolymer (C) may be 87.5% by mass or less, or 85% by mass or less. From the above perspectives, the content of the ethylene-propylene copolymer elastomer (D) may be 12.5 to 40% by mass or 15 to 30% by mass.

[0039] The total content of the propylene-ethylene block copolymer (C) and the ethylene-propylene copolymer elastomer (D) in the second layer may be 90% by mass or more, 95% by mass or more, or 99% by mass or more, based on the total amount of the second layer, from the viewpoint of achieving high levels of rigidity, heat shrinkage resistance, and cold impact resistance in a well-balanced manner; and from the same viewpoint, the total content may be 100% by mass, based on the total amount of components other than the crystal nucleating agent contained in the second layer.

[0040] (Crystal Nucleating Agent) The multilayer film contains a crystal nucleating agent. A crystal nucleating agent (also called a nucleating agent or nucleating agent) is an additive for promoting the crystallization of a polymer compound, and is an agent for adjusting the physical properties of a polymer compound by adding a small amount to the polymer compound. The crystal nucleating agent is not particularly limited as long as it exhibits this function. Examples of the crystal nucleating agent include α crystal nucleating agents such as sorbitol-based compounds, organic phosphate ester metal salt compounds, organic carboxylic acid metal salt compounds, and rosin-based compounds, β crystal nucleating agents such as amide-based compounds and quinanacridone-based compounds, benzoic acid metal salts, alkyl fatty acid salts, and talc. Among these, it is preferable that the crystal nucleating agent contains a sorbitol-based compound, from the viewpoint of easily miniaturizing and homogenizing the crystals of the polypropylene-based resin and easily achieving a high level of heat shrinkage resistance, cold impact resistance, and rigidity in a balanced manner.

[0041] It is believed that the incorporation of a nucleating agent into a multilayer film increases the crystalline regions in the multilayer film, minimizing changes in the amount of crystals in the film during retort treatment or heat sealing, improving heat shrinkage resistance. This can suppress distortion of the package after retort treatment and heat shrinkage during heat sealing of the packaging material. Furthermore, the increase in the crystalline regions in the multilayer film by the nucleating agent makes it easier for the film to achieve excellent rigidity.

[0042] The content of the nucleating agent is 0.10 to 0.19% by mass, based on the total amount of the multilayer film. When the content is equal to or greater than the lower limit, the heat shrinkage resistance is improved, and even when the ethylene-propylene copolymer elastomer (D) necessary for improving the cold impact resistance is blended, the rigidity is less likely to decrease. On the other hand, when the content is equal to or less than the upper limit, the flexibility of the film is maintained, and the cold impact resistance is less likely to decrease. From this viewpoint, the content of the nucleating agent may be 0.12 to 0.15% by mass, based on the total amount of the multilayer film.

[0043] The layer to which the nucleating agent is to be blended is not particularly limited, and it may be blended in at least one of the layers constituting the multilayer film. However, from the viewpoint of more fully obtaining the effects of the nucleating agent described above, the nucleating agent may be blended in at least one of the first layer, the second layer, and the third layer described below, and may be blended in at least the second layer. From the same viewpoint as above, the nucleating agent may be blended only in the second layer of the layers constituting the multilayer film. By containing the nucleating agent in the second layer, the effect of preventing a decrease in rigidity even when the ethylene-propylene copolymer elastomer (D) necessary for improving cold impact resistance is blended can be more fully obtained. Furthermore, from the viewpoint of heat shrinkage resistance, the nucleating agent may be blended in two or more of the first layer, second layer, and third layer.

[0044] [Third Layer] The multilayer film may have a third layer as long as the performance of the multilayer film is not impaired. By providing the third layer on the surface of the second layer opposite to the first layer, distortion and warping of the multilayer film can be easily suppressed. There are no particular restrictions on the resin used for the third layer, and any polypropylene-based resin can be used.

[0045] The third layer preferably contains a propylene homopolymer (A) and a propylene-ethylene random copolymer (B) because this helps to suppress distortion and warpage of the multilayer film. Furthermore, the resin used in the third layer is preferably the same as that used in the first layer, and the ratio is preferably the same as or close to that used in the first layer. This helps to suppress film curl after film formation.

[0046] In an X-ray diffraction pattern measured by X-ray diffractometry, the multilayer film may have a peak intensity of 10,000 cps or more and a half-width of 1.0 or less for a peak derived from the (110) plane of the α-crystal, which is the crystalline structure of polypropylene, which makes it easier to suppress thermal shrinkage after high-temperature retort treatment. [Method for measuring X-ray diffraction peaks] Measuring device: X-ray diffractometer (manufactured by Rigaku Corporation, product name: RINT TTR III) Optical system: focusing method (detector: D / teX Ultra) Scanning axis: 2θ / θ Measurement method: continuous Counting unit: cps Starting angle: 10° (approximate) Ending angle: 40° (approximate) Sampling width: 0.02° Scanning speed: 30° / min Voltage: 50 kV Current: 300 mA Divergence slit: 1 / 3 Divergence vertical slit: 10 mm Scattering slit: open Receiving slit: open Offset angle: 0.000

[0047] Additives such as antioxidants, lubricants, antiblocking agents, antistatic agents, neutralizing agents, pigments, dyes, etc. may be added to the multilayer film as needed, provided that they do not affect the performance of the film. The type of additive is appropriately selected depending on the intended use of the film, etc.

[0048] Examples of antioxidants include phenol-based antioxidants, organic phosphite-based antioxidants, thioether-based antioxidants, and hindered amine-based antioxidants. Examples of lubricants include bisamides such as ethylene bisstearamide, higher fatty acid amides such as oleic acid amide and erucic acid amide, higher fatty acid metal salts such as calcium stearate, zinc stearate, and metal montanic acid salts, and polyolefin waxes such as polyethylene wax and polypropylene wax. Examples of antiblocking agents include aluminum oxide, talc, diatomaceous earth, finely powdered silica, polymethyl methacrylate powder, and silicone resins.

[0049] Examples of pigments include titanium oxide, zinc oxide, and carbon black. Titanium oxide is particularly preferred for imparting opacity to packaging materials. 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. To impart opacity, the content of titanium oxide is preferably 0.10 to 30 mass% based on the total amount of the multilayer film. From the viewpoint of achieving superior opacity, the content of titanium oxide imparting opacity may be 1 part by mass or more, 5 parts by mass or more, or 7 parts by mass or more per 100 parts by mass of the total polypropylene resin. From the viewpoint of achieving superior recyclability and cold impact resistance, the content of titanium oxide may be 23 parts by mass or less, 20 parts by mass or less, 15 parts by mass or less, 12 parts by mass or less, or 8 parts by mass or less per 100 parts by mass of the total polypropylene resin.

[0050] The thickness of the multilayer film is not particularly limited as long as it is usable as a film for packaging, for example, but if the film is too thick, it will be cost-deductible. Therefore, the film thickness can be 100 μm or less, and may be 50 to 80 μm.

[0051] The thickness of the first layer may be 10 to 20% of the thickness of the multilayer film. When the thickness ratio of the first layer is equal to or greater than the lower limit, the film is likely to exhibit excellent heat seal strength, and when the thickness ratio is equal to or less than the upper limit, the film is likely to exhibit low-temperature impact resistance.

[0052] The thickness of the second layer may be 30 μm or more. This makes it easier for the film to acquire cold impact resistance and makes it less likely to break even when dropped repeatedly. From this viewpoint, the thickness of the second layer may be 35 μm or more, or 40 μm or more. The upper limit of the thickness of the second layer is not particularly limited, but can be set to 75 μm to avoid cost disadvantages.

[0053] When a third layer is provided, the thickness range of the third layer may be the same as the thickness range of the first layer. Furthermore, when a third layer is provided, the total thickness of the first and third layers may be 16 to 40% of the thickness of the multilayer film. When the thickness ratio of the first and third layers is equal to or greater than the above-mentioned lower limit, excellent heat seal strength is easily achieved, and when the thickness ratio is equal to or less than the above-mentioned upper limit, cold impact resistance of the film is easily achieved. From this perspective, the total thickness ratio of the first and third layers may be 20 to 35%.

[0054] <Method for Producing a Multilayer Film> The method for producing a multilayer film is not particularly limited, and known methods can be used. For example, thermoforming methods include melt-kneading methods 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-flight screw, a screw with a mixing element, a barrier-flight screw, a fluted screw, or the like, and these can be used without particular limitation. The twin-screw kneading device can be a co-rotating twin-screw extruder, a counter-rotating twin-screw extruder, or the like, and the screw shape can be a full-flight screw, a kneading disk type, or the like, without particular limitation.

[0055] In the above method, it is possible to use a method in which the multilayer film is melted in a single-screw extruder or twin-screw extruder, etc., and then passed through a feed block or multi-manifold to form a film in a T-die.

[0056] The obtained multilayer 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. 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.

[0057] <Packaging Material> The multilayer film may be used as a standalone film or may be laminated with a substrate, and the method of use as a packaging material is not particularly limited. The multilayer film is provided in the packaging material so that the first layer, which is the heat seal layer, faces the contents.

[0058] When the multilayer film is laminated with a substrate, the packaging material can include the multilayer film and the substrate. Specifically, such a packaging material can be obtained by laminating at least one layer of biaxially oriented polypropylene film (OPP) onto the multilayer film to form a laminate.

[0059] Biaxially stretched polypropylene film (OPP) is made of at least one of propylene homopolymer, propylene-ethylene random copolymer, and propylene-ethylene block copolymer, and a plurality of resins can also be laminated for use.

[0060] The polypropylene biaxially stretched film (OPP) may have a polypropylene-based resin content of 99.5% by mass or more based on the total amount of the film. The polypropylene biaxially stretched film (OPP) may contain additives such as antistatic agents, ultraviolet absorbers, plasticizers, and lubricants as trace components. The polypropylene biaxially stretched film (OPP) may be subjected to a surface treatment such as plasma treatment to improve adhesion to the laminated layer. Furthermore, the polypropylene biaxially stretched film (OPP) may be provided with a metal oxide vapor deposition layer.

[0061] The biaxially stretched polypropylene film (OPP) may have a melting point of 168°C or higher, which is the peak top of the melting curve observed in differential scanning calorimetry when the temperature is raised from 25°C to 230°C at a heating rate of 10°C / min. A melting point of 168°C or higher provides excellent heat resistance, and the packaging material is less likely to deform during heat sealing. From the same perspective, the melting point of the biaxially stretched polypropylene film (OPP) may be 170°C or higher, or 175°C or higher.

[0062] The thickness of the biaxially stretched polypropylene film (OPP) is not particularly limited, but may be, for example, 0.1 mm or less. In particular, the thickness of the biaxially stretched polypropylene film (OPP) is preferably 40 μm or less, more preferably 35 μm or less, and particularly preferably 30 μm or less. When the thickness of the biaxially stretched polypropylene film (OPP) 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 biaxially stretched polypropylene film (OPP) is preferably 10 μm or more, more preferably 12 μm or more.

[0063] A biaxially oriented polypropylene film (OPP) may be laminated to the multilayer film via an adhesive layer, which may be made of a material such as a polyester-isocyanate resin, a urethane resin, a polyether resin, or an acid-modified polyolefin.

[0064] <Configuration of Packaging Material> Fig. 3 is a cross-sectional view of a packaging material according to one embodiment of the present disclosure. The packaging material 100 shown in the figure comprises, in this order, a multilayer film 10, an adhesive layer 4, and a biaxially stretched polypropylene film 5 having a metal oxide vapor deposition layer. Fig. 4 is a cross-sectional view of a packaging material according to another embodiment of the present disclosure. The packaging material 200 shown in the figure comprises, in this order, a multilayer film 10, an adhesive layer 4, a biaxially stretched polypropylene film 5 having a metal oxide vapor deposition layer, an adhesive layer 6, and a biaxially stretched polypropylene film 7. In this case, the packaging materials 100 and 200 are used with the multilayer film 10 facing the contents. The laminate can be preferably manufactured by a conventional dry lamination method in which the films constituting the laminate are bonded together using an adhesive. However, if necessary, a method in which the multilayer film is directly extrusion laminated onto a substrate can also be employed.

[0065] The laminate structure of the laminate can be adjusted as appropriate according to the required properties of the packaging material, 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, etc.

[0066] <Packaging> The packaging may be made from the above-mentioned packaging material, and the manufacturing style is not particularly limited. For example, the above-mentioned packaging material (laminate) can be used for a flat bag, a three-sided bag, a two-sided bag, a gusseted bag, a standing pouch, a pouch with a spout, a pouch with a beak, etc., using the multilayer film 10 as a sealing material.

[0067] Hereinafter, the present disclosure will be described in detail using examples and comparative examples, but the present disclosure is not limited to only the following examples.

[0068] <Preparation of Various Materials> The following propylene homopolymer (A), propylene-ethylene random copolymer (B), propylene-ethylene block copolymer (C), ethylene-propylene copolymer elastomer (D), and crystal nucleating agent masterbatch (E) were prepared.

[0069] (Propylene homopolymer (A)) A propylene homopolymer having a melting onset temperature of 153°C, a melting peak temperature 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).

[0070] (Propylene-Ethylene Random Copolymer (B)) A propylene-ethylene random copolymer having a melting peak temperature of 143°C and an ethylene content of 7.1% by mass when measured by differential scanning calorimetry (JIS K 7121).

[0071] 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.

[0072] (Propylene-Ethylene Block Copolymer (C)) 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 mass%.

[0073] (Ethylene-propylene copolymer elastomer (D)) Cattalloy Q100F (trade name) (manufactured by LyondellBasell) was used as the ethylene-propylene copolymer elastomer (D). The melt flow rate (MFR: ISO 1133) of Cattalloy Q100F (temperature 230°C, load 2.16 kg) was 0.6 g / 10 min, and the propylene content / ethylene content was 2.7.

[0074] (Nucleating Agent Masterbatch (E)) The nucleating agent masterbatch (E) was prepared by melt-mixing 10% by mass of a sorbitol-based nucleating agent, GEL ALL DXR (manufactured by New Japan Chemical Co., Ltd.), and 90% by mass of the above-described propylene-ethylene block copolymer (C) using a co-rotating twin-screw extruder, followed by extruding the mixture into strands and pelletizing.

[0075] <Preparation of Multilayer Film> (Example 1) For the formation of the first layer, a resin mixture was prepared by mixing 10 parts by mass of a propylene homopolymer (A) and 90 parts by mass of a propylene-ethylene random copolymer (B) in pellet form. For the formation of the second layer, a resin mixture was prepared by mixing 70 parts by mass of a propylene-ethylene block copolymer (C), 30 parts by mass of an ethylene-propylene copolymer elastomer (D), and 1.50 parts by mass of a crystal nucleating agent masterbatch (E) in pellet form. Each resin mixture was fed to 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 7 μm and the second layer had a thickness of 53 μm, thereby producing the film of Example 1.

[0076] (Example 2) A film of Example 2 was produced in the same manner as in Example 1, except that the mixing ratio of the propylene homopolymer (A) and the propylene-ethylene random copolymer (B) in the resin mixture for forming the first layer was changed as shown in Table 1.

[0077] (Example 3) The film of Example 3 was produced in the same manner as in Example 1, except that the mixing ratio of the propylene homopolymer (A) and the propylene-ethylene random copolymer (B) in the resin mixture for forming the first layer and the mixing ratio of the crystal nucleating agent masterbatch (E) to be blended in the resin mixture for forming the second layer were changed as shown in Table 1.

[0078] (Examples 4 to 5) Films of Examples 4 and 5 were produced in the same manner as in Example 3, except that the mixing ratio of the propylene-ethylene block copolymer (C) and the ethylene-propylene copolymer elastomer (D) in the resin mixture for forming the second layer was changed as shown in Table 1.

[0079] Example 6 For the formation of the first layer, a resin mixture was prepared by mixing 10 parts by mass of propylene homopolymer (A) and 90 parts by mass of propylene-ethylene random copolymer (B) in pellet form. For the formation of the second layer, a resin mixture was prepared by mixing 70 parts by mass of propylene-ethylene block copolymer (C), 30 parts by mass of ethylene-propylene copolymer elastomer (D), and 1.50 parts by mass of crystal nucleating agent masterbatch (E) in pellet form. For the formation of the third layer, a resin mixture was prepared by mixing 20 parts by mass of propylene homopolymer (A) and 80 parts by mass of propylene-ethylene random copolymer (B) in pellet form. 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 7 μm, the second layer had a thickness of 46 μm, and the third layer had a thickness of 7 μm, to produce the film of Example 6.

[0080] (Example 7) The film of Example 7 was produced in the same manner as in Example 6, except that the mixing ratio of the propylene homopolymer (A) and the propylene-ethylene random copolymer (B) in the resin mixture for forming the first layer was changed as shown in Table 2.

[0081] (Example 8) The film of Example 8 was produced in the same manner as in Example 6, except that the mixing ratio of the propylene homopolymer (A) and the propylene-ethylene random copolymer (B) in the resin mixture for forming the first layer, and the mixing ratio of the propylene-ethylene block copolymer (C), the ethylene-propylene copolymer elastomer (D), and the crystal nucleating agent masterbatch (E) in the resin mixture for forming the second layer were changed as shown in Table 2.

[0082] (Example 9) A film of Example 9 was produced in the same manner as in Example 8, except that the mixing ratio of the propylene-ethylene block copolymer (C) and the ethylene-propylene copolymer elastomer (D) in the resin mixture for forming the second layer was changed as shown in Table 2.

[0083] Comparative Example 1 A film of Comparative Example 1 was produced in the same manner as in Example 1, except that the first layer was formed using only the propylene-ethylene random copolymer (B).

[0084] (Comparative Example 2) A film of Comparative Example 2 was produced in the same manner as in Example 1, except that the mixing ratio of the propylene homopolymer (A) and the propylene-ethylene random copolymer (B) in the resin mixture for forming the first layer was changed as shown in Table 3.

[0085] (Comparative Examples 3 to 4) Films of Comparative Examples 3 and 4 were produced in the same manner as in Example 3, except that the mixing ratio of the crystal nucleating agent masterbatch (E) in the resin mixture for forming the second layer was changed as shown in Table 3.

[0086] Comparative Examples 5 and 6 Films of Comparative Examples 5 and 6 were produced in the same manner as in Example 3, except that the mixing ratios of the propylene-ethylene block copolymer (C), the ethylene-propylene copolymer elastomer (D), and the crystal nucleating agent masterbatch (E) in the resin mixture for forming the second layer were changed as shown in Table 3.

[0087] <Various Evaluations> The films obtained in each example were evaluated as follows. The results are shown in Tables 1 to 3.

[0088] [Low-Temperature Sealability Evaluation] In the low-temperature sealability evaluation, the films obtained in each example were placed with the first layers 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 140°C to 160°C, which was varied in 2°C increments. The heat-sealed film was 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 lowest sealing temperature at which a heat seal strength of 15 N / 15 mm or more was obtained was taken as the heat seal rise temperature. The lower the heat seal rise temperature, the better the low-temperature sealability was judged to be.

[0089] [Heat Resistance Evaluation] In the heat resistance evaluation, the films obtained in each example were placed with the first layers 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 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 portion's heat-sealing strength. In this measurement, if the heat-sealing strength was 2.0 N / 15 mm or less, it was determined that the heat resistance was good.

[0090] [Evaluation of Heat Shrinkage Resistance] The film obtained in each example was cut into a 120 mm square, a 100 mm square gauge line was drawn in the center of the film, and the film was heated in an oven at 128°C for 30 minutes. The dimensional change rates in the machine direction (MD) and the transverse direction (TD) of the film before and after heating were calculated using the following formula. In this measurement, if the absolute value of the dimensional change rate was within 2.0%, it was determined that the heat shrinkage resistance was good. Dimensional change rate (%) = (gauge line distance after heating - gauge line distance before heating) / gauge line distance before heating x 100

[0091] [Evaluation of cold impact resistance] The fracture energy of the film obtained in each example during low-temperature storage was measured under the conditions of a temperature of -5°C, a weight of 1.5 J, and a bullet size of 1 / 2 inch using a film impact tester manufactured by Toyo Seiki Co., Ltd. In this measurement, if the fracture energy was 10 J / mm or more, it was determined that the cold impact resistance was good.

[0092] [Rigidity Evaluation] The film obtained in each example was cut into a length of 300 mm in the machine direction (MD) and 20 mm in the transverse direction (TD), and pulled using a tensile tester manufactured by Shimadzu Corporation at a chuck distance of 250 mm and a pulling speed of 5 mm / min. The slope of the stress-strain curve at two points where the film strain was 0.05% and 0.25% was calculated as the modulus of elasticity. In this measurement, a modulus of elasticity of 700 MPa or more was considered to have good rigidity.

[0093]

[0094]

[0095]

[0096] The polypropylene-based multilayer film of the present disclosure can achieve a high level of heat resistance, low-temperature sealability, heat shrinkage resistance, cold impact resistance, and rigidity in a well-balanced manner, and can be suitably used as a sealant film for retort packaging or as a packaging material made of the same polypropylene material.

[0097] 1...first layer, 2...second layer, 3...third layer, 4...adhesive layer, 5...biaxially stretched polypropylene film provided with a metal oxide vapor-deposited layer, 6...adhesive layer, 7...biaxially stretched polypropylene film, 10, 20...multilayer film, 100, 200...packaging material.

Claims

1. A multilayer film comprising a first layer which is a heat seal layer and a second layer, wherein the first layer contains, based on the total weight of the first layer, 10 to 30% by mass of a propylene homopolymer (A) and 70 to 90% by mass of a propylene-ethylene random copolymer (B), the second layer contains, based on the total weight of the second layer, 60 to 91% by mass of a propylene-ethylene block copolymer (C) and 9 to 40% by mass of an ethylene-propylene copolymer elastomer (D), and the multilayer film contains, based on the total weight of the multilayer film, 0.10 to 0.19% by mass of a nucleating agent.

2. The multilayer film according to claim 1, wherein only the second layer of the layers constituting the multilayer film contains the nucleating agent.

3. The multilayer film according to claim 1 or 2, wherein the propylene-ethylene block copolymer (C) contains 87.5 to 65 mass% of a propylene polymer (C1) and 12.5 to 35 mass% of an ethylene-propylene copolymer (C2).

4. The multilayer film according to any one of claims 1 to 3, wherein the thickness of the first layer is 10 to 20% of the thickness of the multilayer film.

5. The multilayer film according to any one of claims 1 to 4, wherein the thickness of the second layer is 30 to 75 µm.

6. The multilayer film according to any one of claims 1 to 5, 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).

7. The multilayer film according to claim 6, wherein the total thickness of the first layer and the third layer is 16 to 40% of the thickness of the multilayer film.

8. The multilayer film according to any one of claims 1 to 7, wherein the nucleating agent comprises a sorbitol-based compound.

9. A packaging material comprising the multilayer film according to any one of claims 1 to 8 and a biaxially oriented polypropylene film.

10. The packaging material according to claim 9, wherein the biaxially oriented polypropylene film has a melting point of 168°C or higher, which corresponds to the peak top of the melting curve observed when the film is heated from 25°C to 230°C at a heating rate of 10°C / min in differential scanning calorimetry.

11. A package made from the packaging material according to claim 9 or 10.

Images