Multilayer film, packaging material and package

Abstract

The present disclosure relates to a multilayer film, which successively has: a first outer layer containing a propylene homopolymer (A) and a propylene-ethylene random copolymer (B) as a heat-seal layer; an inner layer containing a propylene-ethylene block copolymer (C) and an ethylene-propylene copolymer elastomer (D); and a second outer layer containing the propylene homopolymer (A) and the propylene-ethylene random copolymer (B), wherein at least any one of the first outer layer, the inner layer, and the second outer layer further contains a polyphenol compound.

Description

Technical Field

[0001] This disclosure relates to multilayer films, packaging materials, and packaging bodies. More specifically, this disclosure relates to polypropylene multilayer films used as sealing films for packaging bodies, which are also preferably suitable for harsh treatments such as boiling water treatment or high-temperature cooking, and packaging materials and packaging bodies obtained using said polypropylene multilayer films. Background Technology

[0002] Polypropylene films are sometimes used as sealant films in various packaging materials, such as food packaging, due to their excellent rigidity, heat resistance, and low cost. One of the main applications of polypropylene films is in packaging for retortable foods, where sterilization or sterilization is performed under high temperature and pressure.

[0003] In packaged foods that undergo high-temperature sterilization or sterilization processes, such as high-temperature cooking, the contents may sometimes deteriorate or modify due to heat sterilization during manufacturing or long-term storage, producing modified odors. The sources of these modified odors are carbohydrates, fats, and proteins, with the modified odors primarily originating from proteins found in meat, fish, soybeans, and eggs. Sulfur odors, particularly those derived from sulfur compounds, can be problematic.

[0004] Patent document 1 discloses a packaging body characterized by coating an oxygen barrier material formed on a substrate film as a film composed of a resin layer containing a polycarboxylic acid polymer, with a coating agent formed of a zinc compound and a solvent or dispersion medium.

[0005] Patent document 2 discloses a laminate for heat sterilization treatment, which includes a sealant layer comprising a heat-sealing resin and a hydrophobic zeolite with a SiO2 / Al2O3 molar ratio of 30 / 1 to 8000 / 1.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2013-018551

[0009] Patent Document 2: Japanese Patent Application Publication No. 2019-177521 Summary of the Invention

[0010] The technical problem that the invention aims to solve

[0011] While the packaging described in Patent Documents 1 and 2 demonstrates deodorization against sulfur odor, there is still room for improvement in the visibility of the contents.

[0012] This disclosure was made in view of the foregoing facts, and its object is to provide a multilayer film with excellent deodorization properties against sulfurous odors generated by the contents, as well as excellent visibility of the contents. A further object of this disclosure is to provide packaging materials and packaging bodies obtained using said multilayer film.

[0013] Means for solving technical problems

[0014] As a result of in-depth research to solve the above-mentioned technical problems, the inventors discovered that it is important to incorporate polyphenolic compounds in at least one of the multiple polypropylene layers constituting the polypropylene-based multilayer film, thereby completing the following multilayer film.

[0015] One aspect of the multilayer film of this disclosure comprises: a first outer layer containing propylene homopolymer (A) and propylene-ethylene random copolymer (B) as a heat-sealing layer; an inner layer containing propylene-ethylene block copolymer (C) and ethylene-propylene copolymer elastomer (D); and a second outer layer containing propylene homopolymer (A) and propylene-ethylene random copolymer (B), wherein at least any one of the first outer layer, the inner layer and the second outer layer further contains a polyphenol compound.

[0016] In the aforementioned multilayer membranes, by incorporating polyphenolic compounds into the polypropylene membrane, the strong reducing power of the hydroxyl groups in the polyphenolic compounds provides excellent deodorization of sulfurous odors originating from sulfur compounds. Furthermore, by using polyphenolic compounds, which are organic compounds, as the material imparting the deodorizing effect, compared to the case of incorporating inorganic compounds, random light reflection within the membrane can be suppressed, resulting in excellent transparency. Compared to cases using coating agents containing zinc oxide particles (e.g., Patent Document 1) or sealing layers containing hydrophobic zeolites (e.g., Patent Document 2), this membrane can further improve the visibility of the contents while achieving a deodorizing effect. This effect is particularly advantageous for applications involving high-temperature cooking of foods prone to sulfurous odors. Additionally, polyphenolic compounds have the advantage of having fewer environmental or human health impacts compared to other organic or inorganic deodorants that are not naturally derived.

[0017] In one approach, the content of polyphenolic compounds can be 1.5 to 8.0% by mass, based on the total amount of the multilayer film. This allows for a balance between superior deodorization and visibility.

[0018] One approach involves an inner layer containing 90-50 parts by weight of a propylene-ethylene block copolymer (C) and 10-50 parts by weight of an ethylene-propylene copolymer elastomer (D), and further containing a polyphenol compound. By containing 90-50 parts by weight of the propylene-ethylene block copolymer (C) and 10-50 parts by weight of the ethylene-propylene copolymer elastomer (D) in the inner layer, the membrane's flexibility is easily maintained, and excellent cold-impact resistance is readily achieved. Furthermore, by containing a polyphenol compound in the inner layer, deodorization functionality can be imparted to the multilayer membrane. In particular, by containing a polyphenol compound in the inner layer, which tends to be thicker than the outer layer, the apparent amount is reduced, and transparency is easily ensured.

[0019] One embodiment may contain 70-30 parts by weight of propylene homopolymer (A) and 30-70 parts by weight of propylene-ethylene random copolymer (B), and further contain polyphenolic compounds. By using the highly smooth propylene homopolymer (A) and propylene-ethylene random copolymer (B), surface unevenness, a factor that reduces the transparency of the membrane, is easily suppressed. This allows for a balance between superior heat resistance and transparency. Furthermore, by containing polyphenolic compounds in the outer layers, the multilayer membrane can be endowed with deodorizing properties.

[0020] In one approach, the polyphenolic compound can be a condensed tannin. This allows for a balance between superior deodorization and improved visibility.

[0021] In one approach, the total thickness of the first and second outer layers can be 25% to 42% of the thickness of the multilayer film. This makes it easier to balance transparency and heat-sealing properties.

[0022] In one approach, the thickness of the inner layer can be 30 μm or more. This allows for easy maintenance of the membrane's flexibility and easy attainment of excellent cold-impact resistance.

[0023] One aspect of the packaging material disclosed herein includes the aforementioned multilayer film and substrate.

[0024] One aspect of the packaging body disclosed herein is made of the aforementioned packaging materials into bags.

[0025] Invention Effects

[0026] According to this disclosure, a multilayer film can be provided that exhibits excellent deodorization properties against sulfurous odors generated by the contents, as well as excellent visibility of the contents. This disclosure also provides packaging materials and packaging bodies obtained using said multilayer film. According to this disclosure, compared to using, for example, an equal amount of inorganic particles instead of polyphenolic compounds, a multilayer film can be provided that significantly improves transparency while maintaining a high hydrogen sulfide reduction rate. Attached Figure Description

[0027] Figure 1This is a cross-sectional view of a multilayer film according to one embodiment of the present disclosure.

[0028] Figure 2 This is a cross-sectional view of a packaging material according to one embodiment of the present disclosure.

[0029] Figure 3 The graph illustrates the total heat of fusion of the propylene-ethylene random copolymer (B) used in the examples and the results of dividing the heat of fusion at 135°C. Detailed Implementation

[0030] Multilayer film

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

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

[0033] The first and second outer layers contain propylene homopolymer (A) and propylene-ethylene random copolymer (B). The first and second outer layers can be formed from propylene homopolymer (A) and propylene-ethylene random copolymer (B). Sometimes, the first and second outer layers are simply referred to as the outer layers. The first and second outer layers can have the same composition or different compositions. When used as packaging material, the first outer layer functions as a heat-sealing layer and is configured to contact the contents.

[0034] (propylene homopolymer (A))

[0035] There are no particular limitations on the method of manufacturing propylene homopolymer (A). For example, it can be obtained by homopolymerizing propylene using a Ziegler-Natta catalyst, a metallocene catalyst, or a semi-metallocene catalyst. The outer layer, by containing propylene homopolymer (A), can be endowed with excellent heat resistance.

[0036] As a propylene homopolymer (A), those with 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. Those with both melting start temperature and melting peak temperature within this range have excellent heat resistance, for example, after high-temperature cooking treatment at high temperatures, it is difficult for melt adhesion to occur on the inner surface of the packaging.

[0037] As a propylene homopolymer (A), a melt flow rate (MFR: ISO 1133) of 2.0–7.0 g / 10 min (temperature 230°C, load 2.16 kg) can be used. Melt flow rate is a parameter indicating the fluidity of a polymer material during melting; it can also be a parameter indicating molecular weight. Therefore, if the melt flow rate is too high, the impact resistance of the polymer material is easily reduced, while if it is too low, the extruder load during molding increases, the processing speed decreases, and productivity easily decreases. Based on these considerations, the melt flow rate can be 2.0–6.0 g / 10 min, or even 2.0–5.0 g / 10 min.

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

[0039] There are no particular limitations on the manufacturing method of propylene-ethylene random copolymer (B). For example, it can be obtained by copolymerizing ethylene as a comonomer with a main monomer formed from propylene using a Ziegler-Natta type catalyst, a metallocene catalyst, or a semi-metallocene catalyst. A multilayer film with excellent transparency and flexibility can be obtained by containing propylene-ethylene random copolymer (B) in the outer layer.

[0040] As a random copolymer of propylene and ethylene (B), those with a melting start 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. Those with both melting start temperature and melting peak temperature within this range exhibit excellent heat resistance; for example, after a severe high-temperature cooking treatment at 135°C for 40 minutes, it is difficult for melt adhesion to occur on the inner surface of the packaging.

[0041] As a random copolymer of propylene and ethylene (B), the heat of fusion ΔH at a higher temperature than the measurement temperature of 135°C can be used when performing differential scanning calorimetry (JIS K 7121). h The heat of fusion ΔH at a lower temperature l The proportion ΔH h / ΔH l The ratio should be between 1.5 and 2.5. By using a ratio below the upper limit, the film's flexibility can be maintained, edge cracking 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 is 1.5, based on the viewpoint that melt adhesion is unlikely to occur on the inner surface of the packaging after high-temperature cooking.

[0042] The ethylene content of the propylene-ethylene random copolymer (B) can be 5.0% by mass or less. By keeping the ethylene content below the upper limit, transparency can be maintained without excessively reducing heat resistance, and melt adhesion on the inner surface of the packaging can be easily suppressed after high-temperature retort treatment. From this perspective, the ethylene content can be 4.5% by mass or less, or even 4.0% by mass or less. There is no particular limitation on the lower limit of the ethylene content; from the viewpoint of maintaining the film's flexibility, suppressing edge cracking at the heat-sealed portion after high-temperature retort treatment, and minimizing the reduction in heat-sealing strength, it can be 2.0% by mass.

[0043] The ethylene content of the propylene-ethylene random copolymer (B) can be determined by the quantitative method (IR method) for ethylene content described on pages 412-413 of the Handbook of Polymer Analysis (3rd printing, May 10, 2013) compiled by the Polymer Analysis Conference of the Japan Society for Analysis.

[0044] The outer layer may contain 70-30 parts by mass of propylene homopolymer (A) and 30-70 parts by mass of propylene-ethylene random copolymer (B). By containing 30 parts by mass or more of propylene homopolymer (A), excellent heat resistance is easily maintained. Furthermore, by containing 70 parts by mass or less of propylene homopolymer (A), i.e., the content of propylene-ethylene random copolymer (B) is at least 30 parts by mass, excellent transparency and heat-sealing properties are easily achieved. From these perspectives, the outer layer may contain 60-40 parts by mass of propylene homopolymer (A) and 40-60 parts by mass of propylene-ethylene random copolymer (B).

[0045] [Inner layer]

[0046] The inner layer contains a propylene-ethylene block copolymer (C) and an ethylene-propylene copolymer elastomer (D). The inner layer can be formed from 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) can be a copolymer 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 with bonded propylene polymer ends and ethylene-propylene copolymer ends, but rather a blended copolymer. By containing the propylene-ethylene block copolymer (C) in the inner layer, the film's flexibility can be maintained, edge cracking of the heat-sealed portion can be suppressed after high-temperature cooking, excellent heat-sealing properties can be easily obtained, and excellent cold-impact resistance can be easily achieved.

[0049] As a propylene-ethylene block copolymer (C), a melt flow rate (MFR: ISO 1133) (temperature 230°C, load 2.16 kg) of 0.5–2.5 g / 10 min can be used. If the melt flow rate is too high, the impact resistance of the film is easily reduced; if it is too low, the extruder load during molding increases, the processing speed decreases, and productivity is easily reduced. Based on these considerations, the melt flow rate can be 1.0–2.5 g / 10 min, or even 1.0–2.0 g / 10 min.

[0050] The propylene-ethylene block copolymer (C) may contain 90-60% by mass of the aforementioned propylene polymer (C1) and 10-40% by mass of the ethylene-propylene copolymer (C2). With each component in this range, excellent heat-sealing properties and excellent cold-impact resistance can be easily obtained.

[0051] There is no particular limitation on the ethylene content of the ethylene-propylene copolymer (C2) contained in the propylene-ethylene block copolymer (C), which can be 20-40% by mass. By keeping the ethylene content below the upper limit, the stickiness of the product can be suppressed, making it less likely to cause contamination during manufacturing due to stickiness, and facilitating the maintenance of excellent productivity. By keeping the ethylene content above the lower limit, the film's flexibility can be maintained, edge cracking of the heat-sealed portion can be suppressed after high-temperature cooking, excellent heat-sealing properties can be easily obtained, and excellent cold-impact resistance can be easily achieved.

[0052] (Ethylene-propylene copolymer elastomer (D))

[0053] Ethylene-propylene copolymer elastomers (D) can be obtained, for example, through slurry polymerization in the presence of inert hydrocarbons such as hexane, heptane, kerosene, or liquefied α-olefin solvents such as propylene, or through solvent-free gas-phase polymerization. Specifically, ethylene-propylene copolymer elastomers (D) can be obtained using a known multi-stage polymerization method. That is, a polymeric high-rubber polypropylene resin containing polypropylene can be obtained by polymerizing propylene and / or propylene-α-olefin polymers in the first stage reaction and then copolymerizing propylene and α-olefins in the second stage reaction. By containing ethylene-propylene copolymer elastomers (D) in the inner layer, the film is easily given flexibility, edge cracking at the heat-sealing section can be suppressed, excellent heat-sealing properties are easily obtained, and excellent cold-impact resistance is easily achieved.

[0054] As an ethylene-propylene copolymer elastomer (D), a melt flow rate (MFR: ISO 1133) (temperature 230°C, load 2.16 kg) of 0.5–3.5 g / 10 min can be used. When the melt flow rate is above the lower limit, the extruder load during molding is reduced, the processing speed is difficult to decrease, and excellent productivity is easily maintained. When the melt flow rate is below the upper limit, the compatibility between the propylene-ethylene block copolymer (C) and the ethylene-propylene copolymer elastomer (D) becomes good, and transparency is difficult to reduce.

[0055] As the ethylene-propylene copolymer elastomer (D), a mass ratio of propylene content to ethylene content (propylene content / ethylene content) of 1.5 to 4.0 can be used. When the ratio is above the lower limit, the film's flexibility can be maintained, edge cracking of the heat-sealed portion can be suppressed after high-temperature cooking, and excellent heat-sealing properties can be easily obtained. When the ratio is below the upper limit, the compatibility between the propylene-ethylene block copolymer (C) and the ethylene-propylene copolymer elastomer (D) becomes good, and the transparency is less likely to decrease.

[0056] The inner layer may contain 90 to 50 parts by mass of propylene-ethylene block copolymer (C) and 10 to 50 parts by mass of ethylene-propylene copolymer elastomer (D). By containing 50 parts by mass or more of propylene-ethylene block copolymer (C), excellent heat-sealing properties are easily maintained. Furthermore, by containing 90 parts by mass or less of propylene-ethylene block copolymer (C), i.e., at least 10 parts by mass of ethylene-propylene copolymer elastomer (D), even better heat-sealing properties and excellent cold-impact resistance can be exhibited. From these perspectives, the inner layer may contain 80 to 60 parts by mass of propylene-ethylene block copolymer (C) and 20 to 40 parts by mass of ethylene-propylene copolymer elastomer (D).

[0057] [Polyphenolic compounds]

[0058] At least one of the first outer layer, the inner layer, and the second outer layer further contains a polyphenolic compound. When the inner layer further contains a polyphenolic compound in addition to the propylene-ethylene block copolymer (C) and the ethylene-propylene copolymer elastomer (D), it can impart deodorization function to the membrane while maintaining the membrane's transparency. When the outer layer further contains a polyphenolic compound in addition to the propylene homopolymer (A) and the propylene-ethylene random copolymer (B), it can impart deodorization function to the membrane.

[0059] The content of polyphenolic compounds, based on the total amount of the multilayer film, can be 1.5–8.0% by mass, 1.5–5.0% by mass, 2.0–4.5% by mass, or 3.0–4.0% by mass. By setting the polyphenolic compound content above the lower limit, excellent deodorization effects against sulfur odors originating from sulfur compounds can be easily obtained; by setting it below the upper limit, excellent transparency is easily achieved.

[0060] Examples of polyphenolic compounds include tannins, tannic acid, gallic acid, and condensed tannins, which are high-molecular-weight polyphenols. Condensed tannins are found in persimmon fruit (astringent persimmon), unripe bananas, grape skins, and seeds, and can be obtained as concentrates by pressing or solvent extraction. These polyphenolic compounds can be used alone or in combination of two or more.

[0061] From the perspective of ensuring excellent deodorization, persimmon tannin is particularly suitable as a condensed tannin. Astringent persimmon is known to contain a large amount of persimmon tannin, which is a type of condensed tannin. Persimmon tannin is a high-molecular-weight proanthocyanidin polymer composed of epicatechin, catechin-3-gallate, epigallocatechin, and gallocatechin-3-gallate. Persimmon tannin has multiple highly reactive hydroxyl groups. Therefore, it is believed that it can exert a deodorizing effect by binding to and encapsulating odor components. Furthermore, compared to other organic or inorganic deodorants or antibacterial agents that are not naturally derived, persimmon tannin has fewer environmental or human health impacts and is particularly suitable for packaging materials for high-temperature cooked foods.

[0062] When persimmon tannins are included in multilayer films, refined persimmon tannins can be used, or astringent persimmons themselves, which contain persimmon tannins, can be used. When using astringent persimmons, the tannin content can be adjusted using thermoplastic resins. By using astringent persimmons, the process of refining persimmon tannins can be omitted, which is more economical.

[0063] There are no particular restrictions on the thickness of multilayer films, as long as they can be used as packaging materials; however, excessively thick films have a cost disadvantage. Therefore, the thickness of multilayer films can be less than 100 μm, or even 50–70 μm.

[0064] The thickness of the outer layer (i.e., the total thickness of the first and second outer layers) can be 25% to 42% based on the thickness of the multilayer film. When the outer layer thickness ratio is above the lower limit, excellent transparency can be easily obtained, while when it is below the upper limit, the reduction in the heat-sealing performance of the film can be suppressed, and practicality can be easily obtained.

[0065] The thickness of the outer layer (i.e., the total thickness of the first and second outer layers) can be 10 μm or more, or even 15 μm or more. This makes it easy to ensure the transparency of the film and makes it difficult to reduce the heat-sealing strength. There is no particular upper limit to the thickness of the outer layer; to easily ensure cold-impact resistance, it can be less than 40 μm, less than 30 μm, or even less than 20 μm.

[0066] The thickness of the inner layer can be 30 μm or more, or even 35 μm or more. This maintains the membrane's flexibility, makes it difficult to break after high-temperature cooking, and minimizes the reduction in heat-sealing strength. There is no particular upper limit to the thickness of the inner layer; for example, from a cost perspective, it can be less than 80 μm, less than 70 μm, or even less than 50 μm.

[0067] <Manufacturing Methods of Multilayer Films>

[0068] There are no particular restrictions on the method for manufacturing multilayer films, and well-known methods can be used. For example, as a thermoforming process, methods such as melt mixing using general mixers like single-screw extruders, twin-screw extruders, and multi-screw extruders can be used; methods such as dissolving or dispersing the components and then removing the solvent by heating can also be used. Considering operability, single-screw extruders or twin-screw extruders can be used. When using a single-screw extruder, examples of screws include fully threaded screws, screws with mixing elements, split screws, and grooved screws, and these can be used without particular restrictions. As a twin-screw extruder, co-rotating twin-screw extruders and anti-rotating twin-screw extruders can be used, and as for the screw shape, fully threaded screws and kneading disc screws can be used without particular restrictions.

[0069] The above methods can be used to melt the multilayer film using a single-shaft extruder or a twin-shaft extruder, and then form the film using a T-die through an oil supply sleeve or manifold.

[0070] As needed, the resulting multilayer film can also undergo surface modification treatments to improve its adaptability to subsequent processes. For example, to improve the printability of the monomer film or the lamination adaptability when used in a stack, the surface in contact with the printing surface or the substrate can be modified. Examples of surface modification treatments include corona discharge treatment, plasma treatment, flame treatment, etc., which generate functional groups by oxidizing the film surface; or modification treatments using wet processes that form an easy-to-adhere layer through coating.

[0071] Packaging Materials

[0072] Multilayer films can be used as single-layer films or laminated with substrates; there are no particular restrictions on how they are used as packaging materials.

[0073] When a multilayer film is laminated with a substrate, the packaging material can have the aforementioned multilayer film and substrate. Specifically, such a packaging material can be obtained by laminating at least one layer of a substrate such as biaxially stretched polyamide film (ONy), biaxially stretched polyester film (PET), printed paper, metal foil (Al foil), or transparent vapor-deposited film onto the aforementioned multilayer film to form a laminate. Figure 2 This is a cross-sectional view of a packaging material according to one embodiment of the present disclosure. The packaging material 100 shown in the figure sequentially comprises a multilayer film 10, an adhesive layer 3, a substrate film 4, an adhesive layer 5, and a transparent vapor-deposited film 6. As a method for manufacturing the laminate, in addition to the conventional dry lamination method of using an adhesive to bond the substrate film or the like onto the multilayer film, a method of directly extruding and laminating the multilayer film onto the substrate film or the like as needed can also be cited.

[0074] The stacked structure of the package can be appropriately adjusted according to the required characteristics of the package, such as the barrier properties required to maintain the quality of the packaged food, the size / impact resistance corresponding to the weight of the contents, and the visibility of the contents.

[0075] <Packaging>

[0076] The packaging body (bag) can be made from the above-mentioned packaging materials, and there are no particular restrictions on its bag style. For example, the above-mentioned packaging materials (layered bodies) can be used in flat-bottom bags, three-side seal bags, gusseted bags, accordion bags, stand-up pouches, spout bags, and bags with spouts, etc., using multi-layer films as sealing materials.

[0077] Example

[0078] The present disclosure is illustrated in detail by the following examples, but the present disclosure is not limited to the following examples.

[0079] <Preparation of various materials>

[0080] Prepare the following: propylene homopolymer (A), propylene-ethylene random copolymer (B), propylene-ethylene block copolymer (C), ethylene-propylene copolymer elastomer (D), and deodorant masterbatch (E).

[0081] (propylene homopolymer (A))

[0082] The propylene homopolymer with a melting start 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) was measured.

[0083] (Propylene-ethylene random copolymer (B))

[0084] The melting onset temperature and melting peak temperature during differential scanning calorimetry (JIS K 7121) were 142℃, 147℃, and ΔH. h / ΔH l A random copolymer of propylene and ethylene with a content of 1.84% by mass and an ethylene content of 3.4% by mass.

[0085] The ethylene content was determined according to the quantitative method (IR method) for ethylene content described on pages 412-413 of the Handbook of Polymer Analysis (3rd printing, May 10, 2013) compiled by the Polymer Analysis Conference of the Japan Society for Analytical Sciences.

[0086] ΔH h / ΔH l It is 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 heat of fusion ΔH at a lower temperature l The proportion. Figure 3 A graph showing the total heat of fusion of the propylene-ethylene random copolymer (B) and the results of dividing the heat of fusion at 135°C.

[0087] (Propylene-ethylene block copolymer (C))

[0088] The melt flow rate (MFR: ISO 1133) (temperature 230°C, load 2.16 kg) is 2.0 g / 10 min, and it contains 77.1% by mass of propylene polymer and 22.9% by mass of ethylene-propylene copolymer, with the ethylene-propylene copolymer containing 28.7% by mass of ethylene.

[0089] (Ethylene-propylene copolymer elastomer (D))

[0090] An ethylene-propylene copolymer elastomer with a melt flow rate (MFR: ISO 1133) of 0.6 g / 10 min (temperature 230 °C, load 2.16 kg) and a propylene content / ethylene content (mass ratio) of 2.7.

[0091] (Deodorant Masterbatch (E))

[0092] As the deodorant masterbatch (E), MB-FPW-PE manufactured by Rilis Scientific Industries Co., Ltd. is used.

[0093] Fabrication of Multilayer Films (Polypropylene Multilayer Films)

[0094] (Example 1)

[0095] In the outer layer formation, a resin mixture is prepared in granular form, comprising 50 parts by mass of propylene homopolymer (A) and 50 parts by mass of propylene-ethylene random copolymer (B).

[0096] In the inner layer formation, a resin mixture is prepared in granular form, comprising 67.8 parts by mass of propylene-ethylene block copolymer (C) and 32.2 parts by mass of ethylene-propylene copolymer elastomer (D), and further comprising 3.09 parts by mass of deodorant masterbatch (E) mixed relative to a total of 100 parts by mass of propylene-ethylene block copolymer (C) and ethylene-propylene copolymer elastomer (D) (adjusted to achieve a persimmon tannin content of 2.0% by mass in the multilayer film).

[0097] Each resin mixture was fed into an extruder with the temperature set to 250°C and mixed in a molten state. The mixture was then laminated using a T-die extruder with an oil supply sleeve, with the first outer layer and the second outer layer having a thickness of 10 μm and the inner layer having a thickness of 40 μm, to produce the film of Example 1.

[0098] (Example 2)

[0099] Except for changing the proportion of the deodorant masterbatch (E) as shown in Table 1, the membrane of Example 2 was made in the same manner as in Example 1.

[0100] (Example 3)

[0101] Except for changing the proportion of the deodorant masterbatch (E) as shown in Table 1, the membrane of Example 3 was prepared in the same manner as in Example 1.

[0102] (Example 4)

[0103] Except for changing the proportion of the deodorant masterbatch (E) as shown in Table 1, the membrane of Example 4 was prepared in the same manner as in Example 1.

[0104] (Comparative Example 1)

[0105] Except that the deodorant masterbatch (E) was not used, the membrane of Comparative Example 1 was prepared in the same manner as in Example 1.

[0106] <Various Reviews>

[0107] The membranes obtained in each case were evaluated as follows. The results are shown in Table 1.

[0108] [Haze Measurement After High-Temperature Cooking]

[0109] The first outer layers of the multilayer films obtained in each example were placed face to face and heat-sealed using a heat-sealing machine manufactured by Tester Industrial Co., Ltd., under conditions of sealing pressure of 0.2 MPa, sealing time of 1 second, sealing width of 5 mm, and sealing temperature of 200°C to create a packaging body (three-side sealed bag). Then, water was filled into the packaging body, and a high-temperature boiling treatment was performed at 135°C for 40 minutes. The films subjected to the high-temperature boiling treatment were evaluated using a spectrophotometer / haze meter (model COH7700) manufactured by Nippon Denshoku Industrial Co., Ltd., according to the haze measurement method described in JIS K7136.

[0110] [Hydrogen sulfide reduction rate]

[0111] Using a urethane-based adhesive, a 12 μm thick biaxially stretched polyester film (PET), a 7 μm thick Al foil, a 15 μm thick biaxially stretched polyamide film (ONy), and the multilayer film obtained in each example are bonded together using a conventional dry lamination method to form a laminate with the following configuration.

[0112] The laminate consists of: PET / adhesive / Al foil / adhesive / ONy / adhesive / multilayer film.

[0113] The multilayer films (first outer layer) of the laminated body were placed face to face and heat-sealed using a heat-sealing machine manufactured by Tester Industrial Co., Ltd., under conditions of sealing pressure of 0.2 MPa, sealing time of 1 second, sealing width of 5 mm, and sealing temperature of 200°C, to produce a packaging body (three-side sealed bag). Then, the packaging body was filled with an aqueous solution of cysteine ​​containing 0.03% by mass of L-cysteine, and subjected to a high-temperature boiling treatment at 135°C for 40 minutes. After the high-temperature boiling treatment, the solution in the packaging body was collected, and the hydrogen sulfide reduction rate was determined using a PACKTEST (model WAK-S) manufactured by Kyoritsu Chemical Research Institute Co., Ltd. The hydrogen sulfide reduction rate was calculated by reacting the collected solution with the PACKTEST reagent and measuring the absorbance at a wavelength of 668 nm using a spectrophotometer, and by the reduction rate of the absorbance measured using the multilayer film obtained in each example relative to the absorbance measured using the multilayer film without deodorant (Comparative Example 1).

[0114] Table 1

[0115]

[0116] *The amount of deodorant masterbatch is relative to 100 parts by mass of components (C) and (D).

[0117] Industrial availability

[0118] The polypropylene-based multilayer film disclosed herein can be preferably used in high-temperature retort packaging sealant films that have excellent deodorizing effects against sulfurous odors produced by high-temperature cooking of food, while also providing excellent transparency for viewing the contents.

[0119] Symbol Explanation

[0120] 10+ layers of film, 100 packaging materials, 1a first outer layer, 1b second outer layer, 2 inner layer, 3 adhesive layer, 4 substrate film, 5 adhesive layer, 6 transparent vapor-deposited film.

Claims

1. A multilayer film, comprising, in sequence: The first outer layer, containing propylene homopolymer (A) and propylene-ethylene random copolymer (B), is used as the heat-sealing layer; An inner layer containing a propylene-ethylene block copolymer (C) and an ethylene-propylene copolymer elastomer (D); and A second outer layer containing propylene homopolymer (A) and propylene-ethylene random copolymer (B), wherein At least one of the first outer layer, the inner layer, and the second outer layer further contains a polyphenol compound.

2. The multilayer film of claim 1, wherein, The content of the polyphenolic compound is 1.5 to 8.0% by mass, based on the total amount of the multilayer film.

3. The multilayer film of claim 1 or 2, wherein, The inner layer contains 90-50 parts by weight of the propylene-ethylene block copolymer (C) and 10-50 parts by weight of the ethylene-propylene copolymer elastomer (D), and further contains the polyphenol compound.

4. The multilayer film of claim 1 or 2, wherein, The first outer layer and the second outer layer contain 70 to 30 parts by mass of the propylene homopolymer (A) and 30 to 70 parts by mass of the propylene-ethylene random copolymer (B), and further contain the polyphenol compound.

5. The multilayer film of claim 1 or 2, wherein, The polyphenolic compound is a condensed tannin.

6. The multilayer film of claim 1 or 2, wherein, The total thickness of the first outer layer and the second outer layer is 25% to 42% based on the thickness of the multilayer film.

7. The multilayer film of claim 1 or 2, wherein, The thickness of the inner layer is 30 μm or more.

8. A packaging material comprising a multilayer film and a substrate as described in any one of claims 1 to 7.

9. A packaging body made of the packaging material of claim 8.

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