Multilayer film, packaging material, and package

Abstract

To provide a polypropylene-based multilayer film capable of achieving a high level of heat resistance, a low-temperature sealing property, heat shrinkage resistance, cold impact resistance, and rigidity in a well-balanced manner.SOLUTION: There is provided a multilayer film, comprising a first layer that is a heat seal layer, and a second layer, wherein: the first layer contains, based on a total amount of the first layer, 10 to 30 mass% of a propylene homopolymer (A) and 70 to 90 mass% of a propylene-ethylene random copolymer (B); the second layer contains, based on a total amount of the second layer, 60 to 91 mass% of a propylene-ethylene block copolymer (C) and 9 to 40 mass% of an ethylene-propylene copolymer elastomer (D); and the multilayer film contains, based on a total amount of the multilayer film, 0.10 to 0.19 mass% of a crystal nucleating agent.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a multilayer film, a packaging material, and a package. More specifically, the present invention 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. [Background technology]

[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 flexible polypropylene resin, and a high melt tension polypropylene resin.

[0005] Patent Document 3 proposes a laminated polypropylene-based non-oriented film that simultaneously satisfies multiple 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 composite film consisting of three layers, characterized in that the middle layer is made of a layer mainly composed of a propylene-ethylene block copolymer, and both surface layers are made of layers mainly composed of a propylene-based random copolymer. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 8-283423 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-105162 [Patent Document 3] Japanese Patent Application Laid-Open No. 2007-237641 [Patent Document 4] Japanese Patent Application Laid-Open No. 2017-132186 Summary of the Invention [Problem to be solved by the invention]

[0008] Polypropylene-based films have traditionally been required to have heat resistance to withstand retort processes, which involve high-temperature pressure treatment for sterilization and sterilization. In addition, in recent years, biaxially oriented polypropylene (OPP) films have been used as base films to improve the recyclability of packaging materials. Because biaxially oriented polypropylene films have a lower melting point than the conventionally used biaxially oriented polyamide (ONy) and biaxially oriented polyester (PET) films, they cannot be heat-sealed at high temperatures during bag-making, raising concerns about reduced productivity and distortion due to heat-induced film shrinkage. Therefore, low-temperature sealing capabilities are now required for polypropylene-based films. Furthermore, the use of OPP as a base film raises concerns about thermal shrinkage during high-temperature retort processing, leading to the need 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 invention has been made in view of the above circumstances, and an object of the present invention is 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 object of the present invention is to provide a packaging material and a package obtained using the polypropylene-based multilayer film. [Means for solving the problem]

[0011] As a result of intensive investigations to solve the above problems, the inventors have found that it is important to mix and incorporate 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 incorporate a nucleating agent in an amount of 0.10 to 0.19 mass % based on the total amount of the multilayer film, which has led to the completion of the present invention.

[0012] That is, the present invention provides the following multilayer film, packaging material, and packaging body. [1] A multilayer film comprising a first layer which is a heat-sealable 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 [1] above, 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). [3] The multilayer film according to [1] or [2] above, wherein the nucleating agent comprises a sorbitol-based compound. [4] A packaging material comprising the multilayer film according to any one of [1] to [3] above and a biaxially stretched polypropylene film. [5] The packaging material according to [4] above, wherein the polypropylene biaxially oriented 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. [6] A package made from the packaging material described in [4] or [5] 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. This allows the multilayer film to exhibit excellent low-temperature sealability while maintaining heat resistance and heat shrinkage resistance, and to achieve both low-temperature impact resistance and rigidity. Such an effect cannot be obtained when a resin composition containing a propylene-based resin and a compound having a specific structure is used (for example, Patent Document 1), when a polypropylene-based resin composition containing a block copolymer polypropylene resin, a flexible polypropylene-based resin, and a high melt tension polypropylene resin is used (for example, Patent Document 2), when a laminated polypropylene-based non-oriented film is used that is composed of two layers: 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 (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). This effect is particularly suitable for use in large retort pouch packaging made of the same polypropylene material.

[0014] In the multilayer film described in [2] 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 [5] above comprises 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. [Effects of the Invention]

[0016] According to the present invention, 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 invention, 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 the bag 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 invention, it is possible to provide packaging materials and packages obtained using the multilayer film. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a cross-sectional view of a multilayer film according to one embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view of a multilayer film according to one embodiment of the present invention. [Figure 3] FIG. 3 is a cross-sectional view of a packaging material according to one embodiment of the present invention. [Figure 4] FIG. 4 is a cross-sectional view of a packaging material according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] <Multilayer film> Fig. 1 is a cross-sectional view of a multilayer film according to one embodiment of the present invention. Multilayer film 10 comprises a first layer 1, which is a heat-sealable layer, and a second layer 2, in this order. Fig. 2 is a cross-sectional view of a multilayer film according to another embodiment of the present invention. Multilayer film 20 comprises a first layer 1, which is a heat-sealable layer, a second layer 2, and a third layer 3, in this order. 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 mass %, and the content of the propylene-ethylene random copolymer (B) is 70 to 90 mass %. The propylene homopolymer (A) has a high melting point. By combining the propylene homopolymer (A) with the propylene-ethylene random copolymer (B) having a moderately lower melting point, in the above-mentioned amounts, excellent heat resistance and low-temperature sealability can be achieved. The first layer is a heat-sealable layer (sealing layer), and the first layers of the multilayer film are heat-sealed together to form a package.

[0020] (Propylene homopolymer (A)) The propylene homopolymer (A) can be produced by any method, including homopolymerizing propylene using a Ziegler-Natta catalyst, a metallocene catalyst, or a half-metallocene catalyst. The inclusion of the propylene homopolymer (A) in the first layer provides the first layer with excellent heat resistance. This reduces the likelihood of fusion on the inner surface of the packaging bag after high-temperature pressure and 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 endowed with superior heat resistance. This makes it more unlikely that fusion will occur on the inner surface of the packaging bag after high-temperature heat and pressure treatment. In this specification, the conditions for differential scanning calorimetry are as follows:

[0022] [Differential scanning calorimetry conditions] When the temperature is increased from 25°C to 230°C at a rate of 10°C / min, the melting onset temperature is determined as the point where a line extending the low-temperature baseline of the DSC curve to the high-temperature side intersects with a tangent drawn to the low-temperature side curve of the melting peak so that the slope is maximum, and the temperature at the top 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. 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 propylene-ethylene random copolymer (B) can be produced 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.

[0025] 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 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 an ethylene content equal to or less than the above upper limit, low-temperature sealability is maintained while heat resistance is unlikely to decrease excessively. 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 from the viewpoint of low-temperature sealability, it can be 3% by mass.

[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 the Polymer Analysis Handbook (May 10, 2013, 3rd printing), edited by the Polymer Analysis Discussion Group of the Japan Analytical Society.

[0028] 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. When the content of the propylene homopolymer (A) is 10 mass% or more, excellent heat resistance can be exhibited. From this viewpoint, the content may be 15 mass% or more, or may be 20 mass% or more. When the content of the propylene homopolymer (A) is 30 mass% or less, that is, when the content of the propylene-ethylene random copolymer (B) is 70 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 mass% or less, or may be 25 mass% or less. From the above viewpoint, the content of the propylene-ethylene random copolymer (B) may be 75 to 85 mass%.

[0029] The total content of the propylene homopolymer (A) and the propylene-ethylene random copolymer (B) in the first layer may be 90 mass % or more, 95 mass % or more, or 99 mass % or more based on the total amount of the second layer, from the viewpoint of achieving both excellent heat resistance and low-temperature sealability, and from the same viewpoint, may be 100 mass % based on the total amount of components other than the 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 weight 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) has excellent rigidity, heat shrinkage resistance, and cold impact resistance, while the ethylene-propylene copolymer elastomer (D) has particularly excellent cold impact resistance. By combining the propylene-ethylene block copolymer (C) and the ethylene-propylene copolymer elastomer (D) in the above-mentioned amounts, 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 obtained by producing a propylene polymer (C1) in the first step, followed by gas-phase polymerization to produce an ethylene-propylene copolymer (C2) in the 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 rather a type of blend copolymer. The inclusion of the propylene-ethylene block copolymer (C) in the second layer facilitates the attainment of excellent rigidity, heat shrink resistance, and cold impact resistance.

[0032] The propylene-ethylene block copolymer (C) can 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. A melt flow rate above the lower limit reduces the load on the extruder during molding, making it difficult for the processing speed to decrease and facilitating the maintenance of excellent productivity. A melt flow rate below the upper limit facilitates the second layer's excellent cold impact resistance.

[0033] The propylene-ethylene block copolymer (C) may contain 90 to 60 mass% of the propylene polymer (C1) and 10 to 40 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 mass% of the propylene polymer (C1) and 12.5 to 35 mass% of the ethylene-propylene copolymer (C2), or 85 to 70 mass% of the propylene polymer (C1) and 15 to 30 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% by 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)) Ethylene-propylene copolymer elastomer (D) can be obtained by, for example, slurry polymerization in the presence of an inert hydrocarbon solvent such as hexane, heptane, or kerosene, or a liquefied α-olefin solvent such as propylene, or by gas-phase polymerization without a solvent. Specifically, ethylene-propylene copolymer elastomer (D) can be obtained using a known multi-stage polymerization method. That is, propylene and / or propylene-α-olefin polymers are polymerized in the first reactor, followed by copolymerization of propylene with α-olefins in the second reactor. This polymerized polypropylene-based resin with a high rubber content can be obtained. The inclusion of ethylene-propylene copolymer elastomer (D) in the second layer facilitates obtaining even better cold impact resistance.

[0036] The ethylene-propylene copolymer elastomer (D) can 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. A melt flow rate above the lower limit reduces the load on the extruder during molding, making it difficult for the processing speed to decrease and making it easier to maintain excellent productivity. A melt flow rate below the upper limit ensures good compatibility between the propylene-ethylene block copolymer (C) and the ethylene-propylene copolymer elastomer (D), making it easier to achieve impact resistance.

[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 propylene-ethylene block copolymer (C) content is 60% by mass or more, excellent heat shrink 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 propylene-ethylene block copolymer (C) content is 91% by mass or less, i.e., when the ethylene-propylene copolymer elastomer (D) content is 9% by mass or more, excellent cold impact resistance can be achieved. From this perspective, the propylene-ethylene block copolymer (C) content may be 87.5% by mass or less, or 85% by mass or less. From the above perspective, the ethylene-propylene copolymer elastomer (D) content 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 a high level 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 nucleating agent contained in the second layer.

[0040] (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 that promotes the crystallization of a polymer compound and adjusts its physical properties 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; metal benzoates; alkyl fatty acid salts; and talc. Among these, it is preferable that the crystal nucleating agent contains a sorbitol-based compound, as this facilitates the formation of finer and more uniform crystals in the polypropylene-based resin and facilitates 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 perspective, 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 into which the nucleating agent is to be incorporated is not particularly limited, and it may be incorporated into at least one of the layers constituting the multilayer film. However, to more fully obtain the effects of the nucleating agent described above, the nucleating agent may be incorporated into at least one of the first layer, second layer, and third layer described below, and may be incorporated into at least the second layer. By including 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 incorporated can be more fully obtained. Furthermore, from the viewpoint of heat shrinkage resistance, the nucleating agent may be incorporated into 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, it is preferable to use the same resins as those used in the first layer in the same or similar ratios as those 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] Measurement equipment: X-ray diffraction equipment (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) End angle: 40° (approx.) Sampling width: 0.02° Scan speed: 30° / min Voltage: 50kV Current: 300mA 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, 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. To achieve 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, relative to 100 parts by mass of the total polypropylene resin. To achieve 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, relative to 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-intensive. 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, excellent heat seal strength is easily achieved, and when the thickness ratio is equal to or less than the upper limit, the film is likely to have good cold impact resistance.

[0052] The thickness of the second layer may be 30 μm or more. This makes it easier for the film to have cold impact resistance and to be less likely to break even when dropped repeatedly. From this perspective, 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 it 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] <Multilayer film manufacturing method> The method for producing the multilayer film is not particularly limited, and known methods can be used. For example, thermoforming methods include melt-kneading methods using common mixers such as single-screw extruders, twin-screw extruders, and multi-screw extruders, and methods in which the components are dissolved or dispersed and mixed and then the solvent is removed by heating. Considering workability, single-screw extruders or twin-screw extruders can be used. When using a single-screw extruder, 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. 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-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, 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 oriented polypropylene film (OPP) is composed of one or more of propylene homopolymer, propylene-ethylene random copolymer, or propylene-ethylene block copolymer, and can also be used by laminating multiple resins.

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

[0061] The biaxially oriented polypropylene film (OPP) may have a melting point of 168°C or higher, which corresponds to 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, making it difficult for the packaging material to deform during heat sealing. From the same perspective, the melting point of the biaxially oriented 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, and 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] <Packaging material composition> FIG. 3 is a cross-sectional view of a packaging material according to one embodiment of the present invention. 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-deposited layer. FIG. 4 is a cross-sectional view of a packaging material according to another embodiment of the present invention. 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-deposited 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 produced 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 used.

[0065] The laminate structure of the laminate can be adjusted as needed to suit the required properties of the packaging, such as barrier properties that meet the shelf life of the packaged food, size and impact resistance to accommodate the weight of the contents, and visibility of the contents.

[0066] <Package> The packaging body may be made into a bag from the above-mentioned packaging material, and there are no particular restrictions on the bag-making style. For example, the above-mentioned packaging material (laminate) can be used to make flat bags, three-sided bags, palm-shaped bags, gusseted bags, standing pouches, pouches with spouts, pouches with beaks, etc., using the multilayer film 10 as a sealing material. [Example]

[0067] 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.

[0068] <Preparing 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 with 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 according to the ethylene content determination method (IR method) described on pages 412-413 of the Polymer Analysis Handbook (May 10, 2013, 3rd printing), edited by the Polymer Analysis Discussion Group of the Japan Analytical Society.

[0072] (Propylene-ethylene block copolymer (C)) A propylene-ethylene block copolymer with a melt flow rate (MFR: ISO 1133) of 1.8 g / 10 min (temperature 230°C, load 2.16 kg), containing 81.5 mass% propylene polymer and 18.5 mass% ethylene-propylene copolymer, with the ethylene content of the ethylene-propylene copolymer being 36.2 mass%.

[0073] (Ethylene-propylene copolymer elastomer (D)) The ethylene-propylene copolymer elastomer (D) used was Cattalloy Q100F (trade name, manufactured by LyondellBasell). 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-mentioned propylene-ethylene block copolymer (C) using a co-rotating twin-screw extruder, extruding the mixture into strands, and pelletizing the mixture.

[0075] <Preparation of multilayer film> Example 1 For forming 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 the form of pellets. For forming 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 nucleating agent masterbatch (E) in pellet form. Each resin mixture was fed into an extruder whose temperature was 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 The 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 nucleating agent masterbatch (E) blended in the resin mixture for forming the second layer were changed as shown in Table 1.

[0078] (Examples 4 to 5) The 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 forming 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 the form of pellets. For forming 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 nucleating agent masterbatch (E) in pellet form. For forming the third layer, a resin mixture was prepared by mixing 20 parts by mass of a propylene homopolymer (A) and 80 parts by mass of a propylene-ethylene random copolymer (B) in the form of pellets. Each resin mixture was fed into an extruder whose temperature was 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 was 7 μm thick, the second layer was 46 μm thick, and the third layer was 7 μm thick, 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 nucleating agent masterbatch (E) in the resin mixture for forming the second layer were changed as shown in Table 2.

[0082] Example 9 The 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) The 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 to 6) The films of Comparative Examples 5 and 6 were prepared 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 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, and the results are shown in Tables 1 to 3.

[0088] [Low temperature sealing evaluation] For the low-temperature sealability evaluation, the films obtained in each example were heat-sealed with the first layers facing each other 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, varying in 2°C increments. The heat-sealed films were cut into 15 mm wide x 80 mm pieces and subjected to T-peel testing at a tensile speed of 300 mm / min using a tensile tester manufactured by Shimadzu Corporation. The heat-seal strength of the heat-sealed portions was measured. The lowest sealing temperature at which a heat-seal strength of 15 N / 15 mm or more was obtained was defined as the heat-seal initiation temperature. The lower the heat-seal initiation temperature, the better the low-temperature sealability was determined to be.

[0089] [Heat resistance evaluation] For the heat resistance evaluation, the films obtained in each example were heat-sealed with the first layers facing each other 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 films were 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. The heat-sealed portions were measured for heat-seal strength. In this measurement, a heat-seal strength of 2.0 N / 15 mm or less was considered to have good heat resistance.

[0090] [Heat shrinkage resistance evaluation] The films obtained in each example were cut into 120 mm squares, a 100 mm square mark was drawn in the center of the film, and the film was heat-treated in an oven at 128°C for 30 minutes. The dimensional change rates in the machine direction (MD) and 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 length after heating - gauge length before heating) / gauge length before heating x 100

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

[0092] [Rigidity evaluation] The films obtained in each example were cut into strips of 300 mm in the machine direction (MD) and 20 mm in the transverse direction (TD), and were stretched using a tensile tester manufactured by Shimadzu Corporation at a chuck distance of 250 mm and a pulling speed of 5 mm / min, and 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 higher was considered to have good rigidity.

[0093] [Table 1]

[0094] [Table 2]

[0095] [Table 3] [Industrial Applicability]

[0096] The polypropylene-based multilayer film of the present invention 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. [Explanation of symbols]

[0097] 10, 20... multilayer film, 100, 200... packaging material, 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.

Claims

1. A multilayer film comprising a first layer, which is a heat seal layer, and a second layer, the first layer contains, based on the total amount of the first layer, 10 to 30 mass% of a propylene homopolymer (A) and 70 to 90 mass% of a propylene-ethylene random copolymer (B); the second layer contains, based on the total amount 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); The multilayer film contains a crystal nucleating agent in an amount of 0.10 to 0.19 mass % based on the total amount of the multilayer film.

2. 2. The multilayer film according to claim 1, 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).

3. The multilayer film of claim 1 , wherein the nucleating agent comprises a sorbitol-based compound.

4. A packaging material comprising the multilayer film according to any one of claims 1 to 3 and a biaxially stretched polypropylene film.

5. 5. The packaging material according to claim 4, wherein the biaxially stretched polypropylene film has a melting point of 168°C or higher, which corresponds to 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.

6. A package produced from the packaging material according to claim 4.

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