Multilayer film, packaging material and packaging body

Abstract

The multilayer film of the present invention comprises, in order: a first outer layer, which contains 70 to 30% by mass of a propylene homopolymer (A) and 30 to 70% by mass of a propylene-ethylene random copolymer (B) having an ethylene content of less than 5% by mass; an inner layer, which contains a propylene-ethylene block copolymer (C) and an ethylene-propylene copolymer elastomer (D); and a second outer layer, which contains 70 to 30% by mass of a propylene homopolymer (A) and 30 to 70% by mass of a propylene-ethylene random copolymer (B) having an ethylene content of less than 5% by mass.

Description

Technical Field

[0001] The present invention relates to a multilayer film, a packaging material and a packaging body. Specifically, the present invention relates to a polypropylene multilayer film having excellent heat resistance and transparency and being preferably used as a sealing film for packaging bags even in harsh treatments such as boiling water treatment or high-temperature retorting treatment, and a packaging material and a packaging body obtained by using the polypropylene multilayer film. Background Art

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

[0003] Patent Document 1 proposes a polypropylene composite film consisting of three layers, wherein the middle layer is formed of a propylene-ethylene block copolymer and both surface layers are formed of propylene random copolymers.

[0004] Patent Document 2 proposes a multilayer film composed of two surface layers containing an ethylene-α-olefin copolymer and a propylene-based polymer, and an intermediate layer containing a propylene polymer and an ethylene-propylene copolymer.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2017-132186

[0008] Patent Document 2: Japanese Patent Application Publication No. 2017-105174 Summary of the invention

[0009] Technical problem to be solved by the invention

[0010] Polypropylene multilayer films are required to have heat resistance, such as being able to withstand pressure treatment at high temperatures of 120 to 135°C, high-temperature retort treatment for sterilization and disinfection, and transparency that allows visibility of the contents. However, it is currently difficult to achieve both excellent heat resistance and transparency in existing polypropylene multilayer films.

[0011] 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 both excellent heat resistance and transparency. Another object of the present invention is to provide a packaging material and a packaging body obtained by using the multilayer film.

[0012] Means for solving technical problems

[0013] As a result of intensive studies to solve the above-mentioned technical problems, the present inventors have found that it is important to mix different propylene-based polymers in predetermined amounts in the outer layer of a polypropylene-based multilayer film, thereby completing the present invention.

[0014] The multilayer film of one aspect of the present invention comprises, in sequence: a first outer layer, which contains 70 to 30% by mass of a propylene homopolymer (A) and 30 to 70% by mass of a propylene-ethylene random copolymer (B) having an ethylene content of less than 5% by mass; an inner layer, which contains a propylene-ethylene block copolymer (C) and an ethylene-propylene copolymer elastomer (D); and a second outer layer, which contains 70 to 30% by mass of a propylene homopolymer (A) and 30 to 70% by mass of a propylene-ethylene random copolymer (B) having an ethylene content of less than 5% by mass.

[0015] In the above-mentioned multilayer film, the outer layer contains a propylene homopolymer (A) and a propylene-ethylene random copolymer (B) having a specified ethylene content in a specified quantitative ratio. As a result, it is possible to suppress surface irregularities that are a factor in reducing the transparency of the film while maintaining heat resistance. This effect cannot be obtained when a propylene-based random copolymer is used in the outer layer (for example, the above-mentioned patent document 1) or when an ethylene-α-olefin copolymer and a propylene-based polymer are used (for example, the above-mentioned patent document 2), and is particularly preferred in high-temperature retort treatment applications.

[0016] In one embodiment, the ratio Mw(EPR) / Mw(PP) of the weight average molecular weight Mw(EPR) of the ethylene-propylene copolymer in the propylene-ethylene block copolymer (C) to the weight average molecular weight Mw(PP) of the propylene polymer can be 1.5 or less. At this time, the outer layer contains a propylene homopolymer (A) and a propylene-ethylene random copolymer (B) in a specific amount ratio, and the ratio of the weight average molecular weight of the propylene polymer and the ethylene-propylene copolymer in the propylene-ethylene block copolymer (C) contained in the inner layer is below a specific value. Thus, the refractive index difference in the film, which is a factor that reduces the transparency of the film, can be further reduced while maintaining heat resistance. This effect cannot be obtained in existing multilayer films (such as the above-mentioned patent documents 1 and patent document 2), and is a preferred effect in particular in high temperature steaming treatment applications.

[0017] In one embodiment, the inner layer may further contain 90-50% by weight of a propylene-ethylene block copolymer (C) and 10-50% by weight of an ethylene-propylene copolymer elastomer (D). Thus, the film can maintain its flexibility, and after high-temperature retorting, the edge folding of the heat-sealed portion can be suppressed, making it easy to obtain excellent heat-sealing properties.

[0018] In one embodiment, the total thickness of the first outer layer and the second outer layer may be 16 to 42% based on the thickness of the multilayer film. This makes it easier to achieve both transparency and heat sealability.

[0019] In one embodiment, the thickness of the inner layer may be 20 μm or more, thereby making it easier to maintain the flexibility of the film.

[0020] In one embodiment, the thickness of the ethylene-propylene copolymer present as a dispersion in the inner layer in the lamination direction may be 1.5 μm or less. This makes it easy to maintain the transparency of the film.

[0021] A packaging material according to one aspect of the present invention comprises the multilayer film described above and a substrate.

[0022] A packaging body according to one aspect of the present invention is formed from the above-mentioned packaging material.

[0023] Effects of the Invention

[0024] According to the present invention, a polypropylene-based multilayer film having both excellent heat resistance and transparency can be provided. In addition, according to the present invention, a packaging material and a packaging body obtained by using the multilayer film can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a cross-sectional view of a multilayer film according to one embodiment of the present invention.

[0026] Figure 2 This is a graph showing the total heat of fusion of the propylene-ethylene random copolymer (B) used in Example 1 and the result of dividing the heat of fusion at 135°C.

[0027] Figure 3 This is a graph showing the total heat of fusion of the propylene-ethylene random copolymer (E) used in Comparative Example 2 and the result of dividing the heat of fusion at 135°C.

[0028] Figure 4 This is a cross-sectional photograph of the inner layer of Example 1.

[0029] Figure 5 This is a cross-sectional photograph of the inner layer of Example 10. DETAILED DESCRIPTION

[0030] <Multilayer Film>

[0031] Figure 1 This is a cross-sectional view of a multilayer film according to one embodiment of the present invention. The multilayer film 10 includes a first outer layer 1a, an inner layer 2, and a second outer layer 1b in this order. The multilayer film can be used as a polypropylene-based non-stretch sealant film.

[0032] [First outer layer and second outer layer]

[0033] The first outer layer and the second outer layer contain a propylene homopolymer (A) and a propylene-ethylene random copolymer (B). The first outer layer and the second outer layer are sometimes collectively referred to as simply an outer layer. The first outer layer and the second outer layer may have the same composition or different compositions.

[0034] (Propylene homopolymer (A))

[0035] The propylene homopolymer (A) can be obtained, for example, by homopolymerizing propylene using a Ziegler-Natta catalyst or a metallocene catalyst. When the outer layer contains the propylene homopolymer (A), excellent heat resistance can be imparted to the outer layer.

[0036] As the propylene homopolymer (A), a propylene homopolymer having a melting start temperature of 150° C. or higher and a melting peak temperature of 155° C. or higher when subjected to differential scanning calorimetry (JIS K 7121) can be used. A propylene homopolymer having a melting start temperature and a melting peak temperature both within these ranges has excellent heat resistance and, for example, is unlikely to be melt-bonded to the inner surface of a packaging bag after being subjected to a high-temperature retort treatment at a high temperature.

[0037] As the propylene homopolymer (A), a propylene homopolymer having 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 minutes can be used. When the melt flow rate is at least the lower limit, the extruder load during the molding process is reduced, the processing speed is unlikely to be reduced, and excellent productivity is easily maintained. In addition, when the melt flow rate is at most the upper limit, the outer layer is likely to have excellent impact resistance.

[0038] (Propylene-ethylene random copolymer (B))

[0039] The propylene-ethylene random copolymer (B) can be obtained, for example, by copolymerizing ethylene as a comonomer in a main monomer consisting of propylene using a Ziegler-Natta catalyst or a metallocene catalyst. By containing the propylene-ethylene random copolymer (B) in the outer layer, a multilayer film having excellent transparency can be obtained.

[0040] As the propylene-ethylene random copolymer (B), a propylene-ethylene random copolymer having a melting onset temperature of 140° C. or higher and a melting peak temperature of 145° C. or higher when subjected to differential scanning calorimetry (JIS K 7121) can be used. A propylene-ethylene random copolymer having a melting onset temperature and a melting peak temperature both within this range has excellent heat resistance and is unlikely to be melt-bonded to the inner surface of a packaging bag after, for example, a high-temperature retort treatment at a high temperature.

[0041] As the propylene-ethylene random copolymer (B), the heat of fusion ΔH at a higher temperature than the measurement temperature of 135° C. in differential scanning calorimetry (JIS K 7121) can be used. h The melting heat ΔH on the lower temperature side l The ratio ΔH h / ΔH lThe propylene-ethylene random copolymer is in the range of 1.5 to 2.5. When the above ratio is below the upper limit, the flexibility of the film can be maintained, the edge folding of the heat-sealed portion can be suppressed after high-temperature cooking, and the heat-sealing strength is unlikely to decrease. The lower limit of the above ratio can be 1.5 from the viewpoint that melt bonding is unlikely to occur on the inner surface of the packaging bag after high-temperature cooking.

[0042] The ethylene content of the propylene-ethylene random copolymer (B) is 5% by mass or less. When the ethylene content is below the upper limit, the heat resistance can be maintained while the transparency is maintained, and the melt adhesion on the inner surface of the packaging bag after high-temperature boiling treatment can be suppressed. From this point of view, the ethylene content can be 4.5% by mass or less, and can also be 4% by mass or less. The lower limit of the ethylene content is not particularly limited, and can be 2% by mass from the viewpoint of maintaining the softness of the film, suppressing the edge fold at the heat-sealed portion after high-temperature boiling treatment, and making it difficult for the heat-sealing strength to decrease.

[0043] The ethylene content of the propylene-ethylene random copolymer (B) can be measured according to the quantitative method (IR method) for ethylene content described in the Polymer Analysis Handbook edited by the Japan Society for Analytical Analysis (Japan Society for Analytical Analysis Polymer Analysis Forum) (May 10, 2013, third edition), pages 412 to 413.

[0044] The outer layer contains 70 to 30% by mass of a propylene homopolymer (A) and 30 to 70% by mass of a propylene-ethylene random copolymer (B) having an ethylene content of 5% or less. Excellent heat resistance can be maintained by having a propylene homopolymer (A) content of 30% or more by mass. From this point of view, the content can be 35% or more by mass, or even 40% or more by mass. Excellent transparency and heat sealing properties can be exhibited by having a propylene homopolymer (A) content of 70% or less, that is, by having a propylene-ethylene random copolymer (B) content of 5% or less by mass of at least 30% or more by mass. From this point of view, the content of the propylene homopolymer (A) can be 65% or less by mass, or even 60% or less by mass. From the above viewpoints, the content of the propylene-ethylene random copolymer (B) having an ethylene content of 5% or less by mass can be 35 to 65% by mass, or even 40 to 60% by mass.

[0045] [Inner layer]

[0046] The inner layer contains a propylene-ethylene block copolymer (C) and an ethylene-propylene copolymer elastomer (D).

[0047] (Propylene-ethylene block copolymer (C))

[0048] The propylene-ethylene block copolymer (C) is a copolymer that can be obtained by manufacturing a propylene polymer (C1) in a first step and then manufacturing an ethylene-propylene copolymer (C2) by gas phase polymerization in a second step. The propylene-ethylene block copolymer (C) is not a block copolymer formed by bonding the propylene polymer end to the ethylene-propylene copolymer end, but a mixed copolymer. By containing the propylene-ethylene block copolymer (C) in the inner layer, the flexibility of the film can be maintained, the edge folding of the heat-sealed portion can be suppressed after high-temperature boiling treatment, and excellent heat sealing properties can be easily obtained.

[0049] The propylene-ethylene block copolymer (C) comprises a propylene polymer component (C1) and an ethylene-propylene copolymer component (C2) as constituent components as described above. The ratio Mw(EPR) / Mw(PP) of the weight average molecular weight Mw(EPR) of the ethylene-propylene copolymer in the propylene-ethylene block copolymer (C) to the weight average molecular weight Mw(PP) of the propylene polymer may be 1.5 or less. Thus, the inner layer may have more preferred transparency. From this viewpoint, the ratio may be 1.3 or less, or 1.2 or less. The lower limit of Mw(EPR) / Mw(PP) is not particularly limited, and may be 0.9 from the viewpoint of impact resistance.

[0050] The weight average molecular weight ratio can be measured as follows. First, add 200 ml of n-decane to 5 g of propylene-ethylene block copolymer (C) and completely dissolve it at 145°C. After that, cool it to room temperature and separate the precipitate by filtration. The filtered substance is used as the propylene polymer component (propylene resin component), and the remaining solution is completely freed of the solvent in a dryer to obtain the ethylene-propylene copolymer component. Add 20 ml of mobile phase for GPC measurement to each of the obtained components, dissolve it at 145°C, and then perform hot filtration using a sintered filter with a pore size of 1.0 μm to prepare the filtrate as a measurement liquid. As a measuring device, a Tosoh HLC-8321GPC / HT high temperature gel permeation chromatograph is used. Under the conditions of a chromatographic column size of 7.5 mm in inner diameter, 300 mm in length, 140°C in temperature, o-dichlorobenzene (stabilizer; containing 0.025 wt% BHT) as the mobile phase, and a flow rate of 1.0 ml, the molecular weight is measured using a simple PS conversion method. Regarding the obtained results, the ratio of the weight average molecular weight Mw(EPR) of the ethylene-propylene copolymer component to the weight average molecular weight Mw(PP) of the propylene polymer component was taken as the weight average molecular weight ratio Mw(EPR) / Mw(PP).

[0051] The thickness of the ethylene-propylene copolymer in the stacking direction as a dispersion in the inner layer can be 1.5 μm or less. Ethylene-propylene copolymer is a so-called elastomer component, and the thickness in the stacking direction is within this range, which is easy to suppress the rise of the internal haze value. Thus, the blurriness of the entire film can be suppressed, and the contents can be easily seen. From this point of view, the thickness can be 1.25 μm or less, and can also be 1.0 μm or less.

[0052] As the propylene-ethylene block copolymer (C), a propylene-ethylene block copolymer having a melt flow rate (MFR: ISO1133) (temperature: 230°C, load: 2.16 kg) in the range of 0.5 to 2.5 g / 10 minutes can be used. When the melt flow rate is above the lower limit, the extruder load during the molding process becomes smaller, the processing speed is difficult to decrease, and it is easy to maintain excellent productivity. When the melt flow rate is below the upper limit, the inner layer is easy to have excellent softness, the edge folding of the heat-sealed portion can be suppressed, and it is easy to obtain excellent heat sealing properties.

[0053] The propylene-ethylene block copolymer (C) may contain 90 to 60% by mass of the above-mentioned propylene polymer (C1) and 10 to 40% by mass of ethylene-propylene copolymer (C2). By making each component in this range, it is easy to obtain excellent heat sealability. From this viewpoint, 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), and may also contain 85 to 70% by mass of the propylene polymer (C1) and 15 to 30% by mass of the ethylene-propylene copolymer (C2).

[0054] The ethylene content of the ethylene-propylene copolymer (C2) contained in the propylene-ethylene block copolymer (C) is not particularly limited and may be in the range of 20 to 40% by mass. When the ethylene content is below the upper limit, the stickiness of the product can be suppressed, and contamination caused by the stickiness of the product is unlikely to occur during manufacture, making it easy to maintain excellent productivity. When the ethylene content is above the lower limit, the softness of the film can be maintained, and the folding of the heat-sealed portion can be suppressed after high-temperature steaming treatment, making it easy to obtain excellent heat sealing properties.

[0055] (Ethylene-propylene copolymer elastomer (D))

[0056] Ethylene-propylene copolymer elastomer (D) can be obtained, for example, by a slurry polymerization method carried out in the presence of an inactive hydrocarbon such as hexane, heptane, kerosene, or a liquefied α-olefin solvent such as propylene, a gas phase polymerization method in the absence of a solvent, etc. Specifically, ethylene-propylene copolymer elastomer (D) can be obtained using a known multi-stage polymerization method. That is, after polymerizing propylene and / or propylene-α-olefin polymer in a reactor of the first stage, a polymerized high-rubber polypropylene resin can be obtained by copolymerizing propylene and α-olefin through a reaction in the second stage. By containing ethylene-propylene copolymer elastomer (D) in the inner layer, it is easy to impart flexibility to the film, the edge folding of the heat-sealed portion can be suppressed, and excellent heat-sealing properties can be easily obtained.

[0057] As the ethylene-propylene copolymer elastomer (D), an ethylene-propylene copolymer elastomer having a melt flow rate (MFR: ISO1133) (temperature: 230°C, load: 2.16 kg) in the range of 0.5 to 3.5 g / 10 minutes can be used. When the melt flow rate is above the lower limit, the extruder load during the molding process is reduced, the processing speed is difficult to decrease, and it is easy to maintain excellent productivity. When the melt flow rate is below the upper limit, the compatibility of the propylene-ethylene block copolymer (C) and the ethylene-propylene copolymer elastomer (D) becomes good, and the transparency or impact resistance is difficult to decrease.

[0058] As the ethylene-propylene copolymer elastomer (D), an ethylene-propylene copolymer elastomer having a ratio of propylene content to ethylene content (propylene content / ethylene content) in the range of 1.5 to 4 can be used. When the above ratio is above the lower limit, the flexibility of the film can be maintained, the edge folding of the heat-sealed portion can be suppressed after high-temperature boiling treatment, and excellent heat sealing properties can be easily obtained. When the above ratio is below the upper limit, the compatibility of the propylene-ethylene block copolymer (C) and the ethylene-propylene copolymer elastomer (D) becomes good, and the transparency is unlikely to decrease.

[0059] The inner layer may contain 90 to 50% by mass of a propylene-ethylene block copolymer (C) and 10 to 50% by mass of an ethylene-propylene copolymer elastomer (D). By having a content of 50% by mass or more of a propylene-ethylene block copolymer (C), it is easy to maintain excellent heat sealing properties. From this viewpoint, the content may be 60% by mass or more, or 70% by mass or more. By having a content of 90% by mass or less of a propylene-ethylene block copolymer (C), that is, having a content of at least 10% by mass of an ethylene-propylene copolymer elastomer (D), more excellent heat sealing properties may be exhibited. From this viewpoint, the content of a propylene-ethylene block copolymer (C) may be 87.5% by mass or less, or 85% by mass or less. From the above viewpoints, the content of an ethylene-propylene copolymer elastomer (D) may be 12.5 to 40% by mass, or 15 to 30% by mass.

[0060] When only the resin used for the inner layer is formed into a film having a thickness of 60 μm using an extruder at 250° C., the internal haze value measured as follows may be 5% or less, or may be 4% or less.

[0061] [Internal haze measurement]

[0062] The produced film was cut into 70 mm×70 mm, and silicone oil was applied to both surfaces of the film in the light receiving area to obtain a smooth film with uniform thickness, which was measured using a haze meter (model HM-150) manufactured by Murakami Color Research Laboratory in accordance with JIS K 7136.

[0063] The thickness of the multilayer film is not particularly limited as long as it is within a range that allows the film to be used as a packaging material. If the film is too thick, it will lead to cost disadvantages. Therefore, the thickness of the multilayer film may be 100 μm or less, and may be 50 to 70 μm.

[0064] The thickness of the outer layer (i.e., the total thickness of the first outer layer and the second outer layer) can be 16 to 42% based on the thickness of the multilayer film. When the ratio of the thickness of the outer layer is above the lower limit, it is easy to obtain excellent transparency, and when it is below the upper limit, the reduction of the heat sealability of the film can be suppressed, and it is easy to obtain practicality. From this viewpoint, the ratio of the thickness of the outer layer can be 20 to 35%.

[0065] The thickness of the inner layer can be 20 μm or more. Thus, the flexibility of the film can be maintained, the film becomes difficult to break after high-temperature boiling treatment, and the heat seal strength is difficult to decrease. From this point of view, the thickness of the inner layer can be 25 μm or more, and can also be 30 μm or more. The upper limit of the thickness of the inner layer is not particularly limited, but it can be 50 μm because it will cause cost disadvantages.

[0066] <Characteristics of multilayer films>

[0067] The surface roughness of the multilayer film, i.e., the arithmetic mean roughness Ra (JIS B 0601-2001) of the outer layer constituting the multilayer film, can be 0.05 to 0.15 μm. When Ra is above the lower limit, the sliding property of the multilayer film is easy to become good, and it is easy to maintain excellent processability. When Ra is below the upper limit, it is difficult to cause random reflections caused by the unevenness of the film surface, and it is easy to obtain excellent transparency.

[0068] The haze value of the multilayer film having a thickness of 60 μm measured in accordance with JIS K 7136 may be 18% or less, or may be 15% or less. A haze value of 18% or less means that visibility of the contents is easily maintained.

[0069] The multilayer film may have a melt bonding strength of 2.0 N / 15 mm or less in a melt bonding test conducted as described below. A melt bonding strength of 2.0 N / 15 mm or less means that the films are unlikely to be melt bonded to each other when subjected to a high temperature retort treatment at 135°C.

[0070] [Melt bonding test]

[0071] The multilayer films were heat-sealed using a heat sealer manufactured by Tester Sangyo Co., Ltd. under the conditions of a sealing pressure of 0.03 MPa, a sealing time of 30 seconds, a sealing width of 10 mm, and a sealing temperature of 135° C. Thereafter, the heat-sealed multilayer film was cut into pieces of 15 mm wide by 80 mm, and T-peeling was performed at a tensile speed of 300 mm / min using a tensile testing machine manufactured by Shimadzu Corporation to measure the melt adhesion strength of the heat-sealed portion.

[0072] <Method for producing multilayer film>

[0073] The method for manufacturing multilayer film is not particularly limited, and known methods can be used. For example, as the method for hot forming processing, the melt mixing method using the general mixers such as single-axis screw extruder, twin-axis screw extruder, multi-axis screw extruder can be enumerated, and the method of removing the solvent by heating after each component is dissolved or dispersed and mixed, etc. can be enumerated. When considering operability, a single-axis screw extruder or a twin-axis screw extruder can be used. When using a single-axis extruder, a full-length screw, a screw with a mixing element, a separation type screw, a grooved screw, etc. can be enumerated as a screw, and they can be used without particular restrictions. As a twin-axis mixing device, a twin-axis screw extruder rotating in the same direction, a twin-axis screw extruder rotating in different directions, etc. can be used, and in addition, as a screw shape, a full-length screw, a kneading disc type, etc. can be used without particular restrictions.

[0074] Among the above methods, a method in which a multilayer film is melted by a single-screw extruder or a twin-screw extruder and then formed into a film by a T-die via an oil supply sleeve or a multi-manifold may be used.

[0075] The obtained multilayer film may be subjected to a surface modification treatment to improve the adaptability to subsequent processes as required. For example, in order to improve the printing adaptability when using a single film or the lamination adaptability when using a layered film, the printed surface or the surface in contact with the substrate may be subjected to a surface modification treatment. Examples of surface modification treatments include treatments such as corona discharge treatment, plasma treatment, and flame treatment that generate functional groups by oxidizing the film surface; and modification treatments using a wet process that forms an easy-adhesion layer by coating.

[0076] <Packaging Materials>

[0077] The multilayer film may be used as a single film or may be used after being laminated with a substrate, and the method of using the multilayer film as a packaging material is not particularly limited.

[0078] When a multilayer film is laminated with a substrate and then used, the packaging material may include the multilayer film and the substrate. Specifically, the packaging material may be obtained by laminating at least one layer of a biaxially stretched polyamide film (ONy), a biaxially stretched polyester film (PET), a printed paper, a metal foil (AL foil), a transparent vapor-deposited film or other substrate on the multilayer film to form a laminate. The manufacturing method of the laminate may preferably adopt a conventional dry lamination method in which an adhesive is used to adhere the laminate to a film constituting the laminate, but may also adopt a method of directly extruding and laminating the multilayer film on the substrate as required.

[0079] The stacking structure of the laminate can be appropriately adjusted according to the required characteristics of the package, such as barrier properties during the quality maintenance period of the food to be packaged, size or impact resistance corresponding to the weight of the contents, visibility of the contents, etc.

[0080] <Packaging>

[0081] The packaging body can be made of the above packaging material, and there is no particular limitation on the bag making style. For example, the above packaging material (laminated body) can be used in a flat bag, a three-side sealed bag, a gas-seal bag, an accordion bag, a stand-up bag, a bag with a nozzle, a bag with a flap, etc., which uses a multilayer film as a sealing material.

[0082] Example

[0083] The present invention will be described in detail below using examples, but the present invention is not limited to the following examples.

[0084] <Production of Laminated Film>

[0085] (Example 1)

[0086] A propylene homopolymer (A), a propylene-ethylene random copolymer (B), a propylene-ethylene block copolymer (C), and an ethylene-propylene copolymer elastomer (D) shown below were prepared.

[0087] (Propylene homopolymer (A))

[0088] 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) (temperature: 230°C, load: 2.16 kg) of 3.0 g / 10 min when subjected to differential scanning calorimetry (JIS K 7121).

[0089] (Propylene-ethylene random copolymer (B))

[0090] The melting start temperature was 142°C, the melting peak temperature was 147°C, and the ΔH h / ΔH l A propylene-ethylene random copolymer having a molecular weight of 1.84 and an ethylene content of 3.4% by mass.

[0091] The ethylene content was measured according to the quantitative method for ethylene content (IR method) described in the Polymer Analysis Handbook edited by the Japan Society for Analytical Studies (Japan Society for Analytical Studies, Polymer Analysis Forum) (May 10, 2013, third edition), pages 412-413.

[0092] ΔH h / ΔH l The heat of fusion ΔH at a higher temperature than the measurement temperature of 135°C when performing differential scanning calorimetry (JIS K 7121) h The melting heat ΔH on the lower temperature side l ratio. Figure 2 This is a graph showing the total heat of fusion of the propylene-ethylene random copolymer (B) and the result of dividing the heat of fusion at 135°C.

[0093] (Propylene-ethylene block copolymer (C))

[0094] A propylene-ethylene block copolymer having a melt flow rate (MFR: ISO 1133) (temperature: 230°C, load: 2.16 kg) of 2.0 g / 10 min, containing 77.1% by mass of a propylene polymer and 22.9% by mass of an ethylene-propylene copolymer, the ethylene content of the ethylene-propylene copolymer being 28.7% by mass, and a ratio of the weight average molecular weight Mw(EPR) of the ethylene-propylene copolymer to the weight average molecular weight Mw(PP) of the propylene polymer, Mw(EPR) / Mw(PP), of 1.25.

[0095] The weight average molecular weight ratio is measured as follows. 200 ml of n-decane is added to 5 g of propylene-ethylene block copolymer (C), and the mixture is completely dissolved at 145°C. After cooling to room temperature, the precipitate is separated by filtration. The filtered substance is used as the propylene polymer component, and the remaining solution is completely freed of the solvent in a dryer to obtain the ethylene-propylene copolymer component. 20 ml of mobile phase for GPC measurement is added to each of the obtained components, and after dissolving at 145°C, hot filtration is performed using a sintered filter with a pore size of 1.0 μm, and the filtrate is prepared as a measurement liquid. As a measuring device, a HLC-8321GPC / HT high temperature gel permeation chromatograph made by Tosoh is used, and the molecular weight is measured using a simple PS conversion method under the conditions that the column size has an inner diameter of 7.5 mm, a length of 300 mm, a temperature of 140°C, o-dichlorobenzene (stabilizer; containing 0.025 wt% BHT) as the mobile phase, and a flow rate of 1.0 ml. Regarding the obtained results, the ratio of the weight average molecular weight Mw(EPR) of the ethylene-propylene copolymer component to the weight average molecular weight Mw(PP) of the propylene polymer component was taken as the weight average molecular weight ratio Mw(EPR) / Mw(PP).

[0096] (Ethylene-propylene copolymer elastomer (D))

[0097] An ethylene-propylene copolymer elastomer having a melt flow rate (MFR: ISO 1133) (temperature: 230°C, load: 2.16 kg) of 0.6 g / 10 min and a propylene content / ethylene content of 2.7.

[0098] For the outer layer, a resin mixture in which 70% by mass of a propylene homopolymer (A) and 30% by mass of a propylene-ethylene random copolymer (B) were mixed in a pellet state was used, and for the inner layer, a resin mixture in which 83% by mass of a propylene-ethylene block copolymer (C) and 17% by mass of an ethylene-propylene copolymer elastomer (D) were mixed in a pellet state was used. The respective raw materials were supplied to an extruder whose temperature was adjusted to 250° C., kneaded in a molten state, and laminated using a T-die extruder with an oil supply sleeve so that the thickness of the first outer layer and the second outer layer were 10 μm, respectively, and the thickness of the inner layer was 40 μm, to produce the film of Example 1.

[0099] (Example 2)

[0100] Except having changed the mixing ratio of the propylene homopolymer (A) and the propylene-ethylene random copolymer (B) as shown in Table 1, the same procedure as in Example 1 was carried out to produce a film of Example 2.

[0101] (Example 3)

[0102] Except having changed the mixing ratio of the propylene homopolymer (A) and the propylene-ethylene random copolymer (B) as shown in Table 1, the same procedure as in Example 1 was carried out to produce a film of Example 3.

[0103] (Example 4)

[0104] A film of Example 4 was prepared in the same manner as in Example 2 except that the thicknesses of the outer layer and the inner layer were changed as shown in Table 1.

[0105] (Example 5)

[0106] A film of Example 5 was prepared in the same manner as in Example 2 except that the mixing ratio of the propylene-ethylene block copolymer (C) and the ethylene-propylene copolymer elastomer (D) was changed as shown in Table 1.

[0107] (Example 6)

[0108] A film of Example 6 was prepared in the same manner as in Example 2 except that the mixing ratio of the propylene-ethylene block copolymer (C) and the ethylene-propylene copolymer elastomer (D) was changed as shown in Table 1.

[0109] (Example 7)

[0110] The film of Example 7 was prepared in the same manner as in Example 2, except that the following propylene-ethylene block copolymer (C′) was used instead of the propylene-ethylene block copolymer (C) and the mixing ratio of the propylene-ethylene block copolymer (C′) and the ethylene-propylene copolymer elastomer (D) was changed as shown in Table 1.

[0111] (Propylene-ethylene block copolymer (C'))

[0112] 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% by mass of a propylene polymer and 18.5% by mass of an ethylene-propylene copolymer, the ethylene content of the ethylene-propylene copolymer being 36.2% by mass, and a ratio of the weight average molecular weight Mw(EPR) of the ethylene-propylene copolymer to the weight average molecular weight Mw(PP) of the propylene polymer, Mw(EPR) / Mw(PP), of 1.16.

[0113] (Example 8)

[0114] A film of Example 8 was prepared in the same manner as in Example 2 except that the mixing ratio of the propylene-ethylene block copolymer (C′) and the ethylene-propylene copolymer elastomer (D) was changed as shown in Table 1.

[0115] (Example 9)

[0116] A film of Example 9 was prepared in the same manner as in Example 2 except that the mixing ratio of the propylene-ethylene block copolymer (C′) and the ethylene-propylene copolymer elastomer (D) was changed as shown in Table 1.

[0117] (Comparative Example 1)

[0118] A film of Comparative Example 1 was produced in the same manner as in Example 1 except that only the propylene-ethylene random copolymer (B) was used to form the outer layer.

[0119] (Comparative Example 2)

[0120] A film of Comparative Example 2 was prepared in the same manner as in Example 1 except that the following propylene-ethylene random copolymer (E) was used instead of the propylene-ethylene random copolymer (B) and the mixing ratio of the propylene homopolymer (A) and the propylene-ethylene random copolymer (E) was changed as shown in Table 2.

[0121] (Propylene-ethylene random copolymer (E))

[0122] The melting start temperature was 122°C, the melting peak temperature was 133°C, and the ΔH h / ΔH l A propylene-ethylene random copolymer having a molecular weight of 0.275 and an ethylene content of 5.8% by mass.

[0123] Figure 3 This is a graph showing the total heat of fusion of the propylene-ethylene random copolymer (E) and the result of dividing the heat of fusion at 135°C.

[0124] (Comparative Example 3)

[0125] A film of Comparative Example 3 was prepared in the same manner as in Example 1 except that the following elastomer resin was used instead of the propylene-ethylene random copolymer (B) and the mixing ratio of the propylene homopolymer (A) and the elastomer resin was changed as shown in Table 2.

[0126] (Elastomer resin)

[0127] This is an olefin elastomer obtained by using a metallocene catalyst, ethylene as a main monomer and butene-1 as a comonomer, and has a melt flow rate (MFR: ISO 1133) (temperature 190°C, load 2.16 kg) of 3.6 g / 10 minutes.

[0128] (Comparative Example 4)

[0129] A film of Comparative Example 4 having a thickness of 60 μm and consisting only of the material for the inner layer was prepared using a resin mixture in which 83% by mass of the propylene-ethylene block copolymer (C) and 17% by mass of the ethylene-propylene copolymer elastomer (D) were mixed in a pelletized state.

[0130] (Example 10)

[0131] A film of Example 10 was produced in the same manner as in Example 1 except that the following propylene-ethylene block copolymer (C") was used in place of the propylene-ethylene block copolymer (C).

[0132] (propylene-ethylene block copolymer (C″))

[0133] A propylene-ethylene block copolymer having a melt flow rate (MFR: ISO 1133) (temperature: 230°C, load: 2.16 kg) of 2.5 g / 10 min, containing 81.0% by mass of a propylene polymer and 19.0% by mass of an ethylene-propylene copolymer, the ethylene content of the ethylene-propylene copolymer being 36.7% by mass, and a ratio of the weight average molecular weight Mw(EPR) of the ethylene-propylene copolymer to the weight average molecular weight Mw(PP) of the propylene polymer, Mw(EPR) / Mw(PP), of 1.65.

[0134] (Example 11)

[0135] A film of Example 11 was produced in the same manner as in Example 2 except that a propylene-ethylene block copolymer (C") was used instead of the propylene-ethylene block copolymer (C).

[0136] (Example 12)

[0137] A film of Example 12 was produced in the same manner as in Example 3 except that a propylene-ethylene block copolymer (C") was used instead of the propylene-ethylene block copolymer (C).

[0138] <Various Reviews>

[0139] The following evaluations were performed on the films obtained in each example. The results are shown in Tables 1 and 2.

[0140] [Dispersion thickness measurement method]

[0141] After the multilayer film obtained in each example was cured by photocurable resin, a cross section was cut out using an ultrathin slicer made by Leica, and the ethylene-propylene copolymer component was dyed using ruthenium tetroxide. Further, a scanning electron microscope (model S-4800) made by Hitachi Hightechnologies Co., Ltd. was used to magnify the film cross section to 10,000 times for cross-sectional observation, and the thickness of the ethylene-propylene copolymer component as a dispersion was measured. The flow direction (MD) when the measurement was made along the film was implemented. Figure 4 This is a cross-sectional photograph of the inner layer of Example 1. Figure 5 This is a cross-sectional photograph of the inner layer of Example 10.

[0142] [Internal haze measurement]

[0143] Only the resin used in the inner layer was formed into a film with a thickness of 60 μm using an extruder at 250° C. The film was cut into 70 mm×70 mm pieces, and silicone oil was applied to both surfaces of the film in the light-receiving range to form a smooth film with uniform thickness. The internal haze was measured in accordance with JIS K 7136 using a haze meter (model HM-150) manufactured by Murakami Color Research Laboratory.

[0144] [Surface roughness measurement]

[0145] The surface roughness of the film obtained in each example (surface roughness of the outer layer) was measured. As a measuring device, a small surface roughness measuring machine SURFTEST manufactured by Mitutoyo Co., Ltd. was used. The arithmetic mean roughness Ra (JIS B 0601-2001) was measured with a cutoff value λc of 0.25.

[0146] [Haze measurement]

[0147] Evaluation was performed using a haze meter (model HM-150) manufactured by Murakami Color Research Laboratory in accordance with the haze measuring method described in JIS K7136.

[0148] [Heat sealability evaluation]

[0149] A 12 μm thick biaxially stretched polyester film (PET), a 15 μm thick biaxially stretched polyamide film (ONy), a 9 μm thick AL foil and the film obtained in each example (polypropylene film) were bonded together using a urethane adhesive by a conventional dry lamination method to form a laminate having the following structure.

[0150] Laminated structure: PET / adhesive / ONy / adhesive / AL foil / adhesive / polypropylene film

[0151] The polypropylene films of the laminate were placed facing each other and heat-sealed using a heat sealer manufactured by Tester Sangyo Co., Ltd. under the 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 200° C. Thereafter, a high-temperature boiling treatment was performed at 135° C. for 40 minutes. The film subjected to the high-temperature boiling treatment was cut into a 15 mm wide × 80 mm piece, and a T-shaped peeling was performed at a tensile speed of 300 mm / min using a tensile testing machine manufactured by Shimadzu Corporation to measure the heat seal strength.

[0152] [Measuring melt adhesion strength]

[0153] The films obtained in each example were heat-sealed with each other using a heat sealer manufactured by Tester Sangyo Co., Ltd. under the conditions of a sealing pressure of 0.03 MPa, a sealing time of 30 seconds, a sealing width of 10 mm, and a sealing temperature of 135° C. Thereafter, the heat-sealed film was cut into pieces of 15 mm wide by 80 mm, and T-peeling was performed at a tensile speed of 300 mm / min using a tensile testing machine manufactured by Shimadzu Corporation to measure the melt adhesion strength of the heat-sealed portion.

[0154]

[0155]

[0156] Industrial Applicability

[0157] The polypropylene-based multilayer film of the present invention has both high levels of heat resistance and transparency and can be preferably used as a sealant film for retort packaging.

[0158] Explanation of symbols

[0159] 10 polypropylene multilayer film, 1a first outer layer, 1b second outer layer, 2 inner layer.

Claims

1. A multilayer film, comprising: A first outer layer, the first outer layer comprising 70 to 30% by mass of a propylene homopolymer A and 30 to 70% by mass of a propylene-ethylene random copolymer B having an ethylene content of 5% or less by mass; an inner layer comprising a propylene-ethylene block copolymer C and an ethylene-propylene copolymer elastomer D; and a second outer layer comprising 70 to 30% by mass of a propylene homopolymer A and 30 to 70% by mass of a propylene-ethylene random copolymer B having an ethylene content of 5% or less by mass, The multilayer film is a sealant film composed of the first outer layer, the inner layer and the second outer layer, The ratio Mw(EPR) / Mw(PP) of the weight average molecular weight Mw(EPR) of the ethylene-propylene copolymer to the weight average molecular weight Mw(PP) of the propylene polymer in the propylene-ethylene block copolymer C is 1.5 or less.

2. The multilayer film according to claim 1, wherein The inner layer contains 90 to 50% by mass of the propylene-ethylene block copolymer C and 10 to 50% by mass of the ethylene-propylene copolymer elastomer D.

3. The multilayer film according to claim 1 or 2, wherein The total thickness of the first outer layer and the second outer layer is 16 to 42% based on the thickness of the multilayer film.

4. The multilayer film according to claim 1 or 2, wherein The inner layer has a thickness of 20 μm or more.

5. The multilayer film according to claim 1, wherein The thickness of the ethylene-propylene copolymer present as a dispersion in the inner layer in the lamination direction is 1.5 μm or less. 6 . A packaging material comprising the multilayer film according to claim 1 and a substrate.

7. A packaging body made from the packaging material according to claim 6.

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