Multilayer film, packaging material and packaging body

Abstract

To provide a multilayer film that can well adsorb a sulfur odor coming from contents and offers high visibility for the contents.SOLUTION: A multilayer film has: a first outer layer as a heat seal layer containing a propylene homopolymer (A) and a propylene-ethylene random copolymer (B), an inner layer containing a propylene-ethylene block copolymer (C) and an ethylene-propylene copolymer elastomer (D), and a second outer layer containing a propylene homopolymer (A) and a propylene-ethylene random copolymer (B), in the stated order. At least one of the inner layer and the second outer layer further contains zinc oxide particles, a content of the zinc oxide particles being 0.030-0.25 g / m2 per unit area of the multilayer film.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 polypropylene-based multilayer film that can be suitably used as a sealant film for packaging bags, even in severe treatments such as boiling water treatment and retort treatment, and to a packaging material and a package obtained using the polypropylene-based multilayer film. [Background technology]

[0002] Polypropylene-based films are excellent in rigidity and heat resistance, and are inexpensive, so they are sometimes used as sealant films in various packaging materials such as food packaging.One of their main uses is as packaging materials for retort foods, which are pasteurized and sterilized by high-temperature pressure treatment.

[0003] In packaged foods such as retort pouch foods that are pasteurized or sterilized at high temperatures, the contents can deteriorate or denature due to heat sterilization during manufacturing or long-term storage, resulting in the development of a denatured odor.The sources of this denatured odor are carbohydrates, fats and oils, proteins, etc., and among these, the denatured odor of proteins contained in meat, fish, soybeans, eggs, etc., and in particular the sulfurous odor derived from sulfur compounds, are often problematic.

[0004] Patent Document 1 proposes a packaging body characterized in that a coating agent consisting of a zinc compound and a solvent or dispersion medium is applied to the surface of an oxygen barrier material, which is a film consisting of a resin layer containing a polycarboxylic acid polymer formed on a base film. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-018551 Summary of the Invention [Problem to be solved by the invention]

[0006] Although the packaging material described in Patent Document 1 exhibits an odor adsorption function against sulfur odors, there is room for improvement in terms of visibility of the contents.

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a multilayer film that has excellent odor adsorption properties for sulfur odors emitted from contents and excellent visibility of contents. Another object of the present invention is to provide a packaging material and a package obtained using the multilayer film. [Means for solving the problem]

[0008] As a result of intensive research to solve the above problems, the inventors discovered that it is important to incorporate a predetermined amount of a mixture of different propylene-based polymers into the outer layers of a polypropylene-based multilayer film and to incorporate zinc oxide particles into at least one of the multiple layers, which led to the completion of the present invention.

[0009] A multilayer film according to one aspect of the present invention comprises a first outer layer which is a heat-sealable layer containing a propylene homopolymer (A) and a propylene-ethylene random copolymer (B), 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), in this order, wherein at least one of the inner layer and the second outer layer further contains zinc oxide particles, and the content of the zinc oxide particles is 0.030 to 0.25 g / m per unit area of ​​the multilayer film. 2 is.

[0010] In the above multilayer film, by blending zinc oxide particles into the polypropylene film, the amount of zinc oxide particles to be blended can be reduced. This makes it possible to prevent a decrease in the transparency of the film while ensuring odor adsorption properties for sulfur odors generated from the contents. Such a film can further improve the visibility of the contents compared to films using a coating agent containing zinc oxide particles (for example, Patent Document 1 above). This effect is particularly suitable for food retort treatment applications, where a sulfur odor is generated during retort treatment.

[0011] In one embodiment, the zinc oxide particles may have an average spherical equivalent diameter of 100 nm or less. This increases the surface area of ​​the zinc oxide, making it easier to achieve odor adsorption properties for sulfur odors. Furthermore, since the average spherical equivalent diameter of the zinc oxide is 100 nm or less and is smaller than the wavelength of visible light, light dispersion can be suppressed, making it easier to achieve better transparency.

[0012] In one embodiment, the first outer layer and the second outer layer contain 70 to 30 parts by mass of a propylene homopolymer (A) and 30 to 70 parts by mass of a propylene-ethylene random copolymer (B) having an ethylene content of 5% by mass or less, and the second outer layer may further contain zinc oxide particles. This makes it easier to suppress surface irregularities, which are a factor in reducing the transparency of the film. This makes it possible to achieve both better heat resistance and transparency.

[0013] In one embodiment, the inner layer contains 90 to 50 parts by mass of a propylene-ethylene block copolymer (C) and 10 to 50 parts by mass of an ethylene-propylene copolymer elastomer (D), and may further contain zinc oxide particles, which helps maintain the flexibility of the film and provide excellent cold impact resistance.

[0014] In one embodiment, the total thickness of the first outer layer and the second outer layer may be 25 to 42% of the thickness of the multilayer film, which makes it easier to achieve both transparency and heat sealability.

[0015] In one embodiment, the thickness of the inner layer may be 30 μm or more, which makes it easier to maintain the flexibility of the film and to obtain excellent cold impact resistance.

[0016] A packaging material according to one aspect of the present invention includes the multilayer film described above and a substrate.

[0017] A package according to one aspect of the present invention is made from the above-described packaging material. [Effects of the Invention]

[0018] According to the present invention, a multilayer film having excellent odor adsorption properties for sulfur odors emanating from contents and excellent visibility of contents can be provided. The present invention also provides a packaging material and a package obtained using the multilayer film. [Brief explanation of the drawings]

[0019] [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 packaging material according to one embodiment of the present invention. [Figure 3] FIG. 3 is a graph showing 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. [Figure 4] FIG. 4 is a distribution diagram of the equivalent sphere diameters of zinc oxide particles in the film produced in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0020] <Multilayer film> Figure 1 is a cross-sectional view of a multilayer film according to one embodiment of the present invention. The multilayer film 10 comprises 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 unstretched sealant film.

[0021] [First outer layer and second outer layer] 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 may be formed from the propylene homopolymer (A) and the propylene-ethylene random copolymer (B). The first outer layer and the second outer layer may be collectively referred to simply as outer layers. The first outer layer and the second outer layer may have the same composition or different compositions. When used as a packaging material, the first outer layer serves as a heat-seal layer and is positioned so as to come into contact with the contents.

[0022] (Propylene homopolymer (A)) The propylene homopolymer (A) can be produced by, for example, homopolymerizing propylene using a Ziegler-Natta catalyst, a metallocene catalyst, or a half-metallocene catalyst, without any particular limitation. By including the propylene homopolymer (A) in the outer layer, excellent heat resistance can be imparted to the outer layer.

[0023] The propylene homopolymer (A) may have a melting onset temperature of 150° C. or higher and a peak melting temperature of 155° C. or higher as measured by differential scanning calorimetry (JIS K 7121). A polymer having both a melting onset temperature and a peak melting temperature within these ranges has excellent heat resistance, and is less likely to fuse on the inner surface of a packaging bag after, for example, a retort treatment at a high temperature.

[0024] 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. The melt flow rate is a parameter that indicates the fluidity of a polymeric material when melted, and also a parameter that indicates the molecular weight. Therefore, if the melt flow rate is too high, the impact resistance of the polymeric material is likely to decrease, while if it is too low, the load on the extruder during molding processing increases, the processing speed decreases, and productivity is likely to decrease. From these perspectives, the melt flow rate can be 2.0 to 7.0 g / 10 min, and may be 2.0 to 5.0 g / 10 min.

[0025] (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 incorporating the propylene-ethylene random copolymer (B) in the outer layer, a multilayer film with excellent transparency can be obtained.

[0026] The propylene-ethylene random copolymer (B) can be one that has a melting onset temperature of 140°C or higher and a peak melting temperature of 145°C or higher when measured by differential scanning calorimetry (JIS K 7121). A copolymer with both a melting onset temperature and a peak melting temperature within this range has excellent heat resistance, and is less likely to fuse to the inner surface of a packaging bag after, for example, a severe retort treatment at 135°C for 40 minutes.

[0027] For propylene-ethylene random copolymer (B), the heat of fusion ΔH on the higher side of the measurement temperature 135°C when differential scanning calorimetry (JIS K 7121) was performed. h and the heat of fusion on the low temperature side ΔH l Ratio ΔH h / ΔH l A film having a ratio in the range of 1.5 to 2.5 can be used. When the ratio is equal to or less than the upper limit, the flexibility of the film is maintained, edge tearing of the heat-sealed portion after retort treatment can be suppressed, and the heat-seal strength is less likely to decrease. The lower limit of the ratio can be set to 1.5, from the viewpoint of preventing fusion on the inner surface of the packaging bag after retort treatment.

[0028] The ethylene content of the propylene-ethylene random copolymer (B) can be 5% by mass or less. By keeping the ethylene content at or below the upper limit, transparency is maintained without excessively decreasing heat resistance, and fusion on the inner surface of the packaging bag after retort treatment is easily suppressed. From this perspective, the ethylene content may be 4.5% by mass or less, or may be 4% by mass or less. The lower limit of the ethylene content is not particularly limited, but can be 2% by mass from the viewpoints of maintaining the flexibility of the film, suppressing edge tearing at the heat-sealed portion after retort treatment, and preventing a decrease in heat-seal strength.

[0029] The ethylene content of the propylene-ethylene random copolymer (B) can be measured according to the ethylene content determination method (IR method) described on pages 412-413 of the Polymer Analysis Handbook (May 10, 2013, 3rd printing), edited by the Polymer Analysis Discussion Group of the Japan Analytical Society.

[0030] The outer layer may contain 70 to 30 parts by mass of a propylene homopolymer (A) and 30 to 70 parts by mass of a propylene-ethylene random copolymer (B) having an ethylene content of 5% by mass or less. When the content of the propylene homopolymer (A) is 30 parts by mass or more, excellent heat resistance is easily maintained. Furthermore, when the content of the propylene homopolymer (A) is 70 parts by mass or less, i.e., when the content of the propylene-ethylene random copolymer (B) having an ethylene content of 5% by mass or less is at least 30 parts by mass, excellent transparency and heat sealability are easily achieved. From these viewpoints, the outer layer may contain 60 to 40 parts by mass of the propylene homopolymer (A) and 40 to 60 parts by mass of the propylene-ethylene random copolymer (B).

[0031] Inner Layer The inner layer contains a propylene-ethylene block copolymer (C) and an ethylene-propylene copolymer elastomer (D). The inner layer may be formed from the propylene-ethylene block copolymer (C) and the ethylene-propylene copolymer elastomer (D).

[0032] (Propylene-ethylene block copolymer (C)) Propylene-ethylene block copolymer (C) is a copolymer that can be obtained by producing a propylene polymer (C1) in the first step, followed by an ethylene-propylene copolymer (C2) by gas-phase polymerization in the second step. Propylene-ethylene block copolymer (C) 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 propylene-ethylene block copolymer (C) in the inner layer maintains the flexibility of the film, suppresses edge tearing at the heat-sealed area after retort processing, and facilitates excellent heat-sealability.

[0033] 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. If the melt flow rate is too high, the impact resistance of the film tends to decrease; if it is too low, the load on the extruder during molding processing increases, the processing speed decreases, and productivity tends to decrease. From these perspectives, the melt flow rate can be set to 0.5 to 2.5 g / 10 min, and may be 1.0 to 2.0 g / 10 min.

[0034] The propylene-ethylene block copolymer (C) may contain 90 to 60% by mass of the propylene polymer (C1) and 10 to 40% by mass of the ethylene-propylene copolymer (C2). When the amounts of each component are within these ranges, excellent heat-sealability is easily obtained.

[0035] The ethylene content of the ethylene-propylene copolymer (C2) contained in the propylene-ethylene block copolymer (C) is not particularly limited, but can be in the range of 20 to 40% by mass. By keeping the ethylene content below the upper limit, the tackiness of the product can be suppressed, making it less likely for contamination due to tackiness of the product to occur during production and making it easier to maintain excellent productivity. By keeping the ethylene content above the lower limit, the flexibility of the film can be maintained, and edge tearing of the heat-sealed portion after retort processing can be suppressed, making it easier to achieve excellent heat-sealability.

[0036] (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 reaction stage, followed by copolymerization of propylene with α-olefins in the second reaction stage. The inclusion of ethylene-propylene copolymer elastomer (D) in the inner layer contributes to the film's flexibility, reduces edge tearing at heat-sealed sections, and facilitates the attainment of excellent heat-sealability and cold-impact resistance.

[0037] 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 easier to maintain high productivity without slowing down the processing speed. 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 less likely that transparency will decrease.

[0038] The ethylene-propylene copolymer elastomer (D) can be one in which the ratio of propylene content to ethylene content (propylene content / ethylene content) is in the range of 1.5 to 4. When this ratio is above the lower limit, the flexibility of the film is maintained, edge tearing of the heat-sealed portion after retort processing can be suppressed, and excellent heat-sealability can be easily obtained. When this ratio is below the upper limit, the compatibility between the propylene-ethylene block copolymer (C) and the ethylene-propylene copolymer elastomer (D) is good, and transparency is less likely to decrease.

[0039] The inner layer may contain 90 to 50 parts by mass of a propylene-ethylene block copolymer (C) and 10 to 50 parts by mass of an ethylene-propylene copolymer elastomer (D). A propylene-ethylene block copolymer (C) content of 50 parts by mass or more facilitates maintaining excellent heat-sealability. Furthermore, a propylene-ethylene block copolymer (C) content of 90 parts by mass or less, i.e., a content of ethylene-propylene copolymer elastomer (D) of at least 10 parts by mass, allows for even better heat-sealability and cold impact resistance. From these perspectives, the inner layer may contain 80 to 60 parts by mass of the propylene-ethylene block copolymer (C) and 20 to 40 parts by mass of the ethylene-propylene copolymer elastomer (D).

[0040] [Zinc oxide particles] At least one of the inner layer and the second outer layer further contains zinc oxide particles. The content of the zinc oxide particles per unit area of ​​the multilayer film is 0.030 to 0.25 g / m 2 The thickness can be set to 0.045 to 0.18 g / m 2 and may be 0.09 to 0.15 g / m 2The zinc oxide particle content may be equal to or greater than the lower limit, thereby achieving excellent odor adsorption, while the zinc oxide particle content equal to or less than the upper limit, thereby achieving excellent transparency. The unit area of ​​the multilayer film can be referred to as the unit area of ​​the inner layer when zinc oxide particles are contained only in the inner layer, or the unit area of ​​the second outer layer when zinc oxide particles are contained only in the second outer layer. The zinc oxide particle content in each layer can be adjusted by changing the amount of zinc oxide particles added or the layer thickness.

[0041] The average spherical equivalent diameter of the zinc oxide particles can be 100 nm or less, and may be 90 nm or less. This increases the surface area of ​​the zinc oxide particles, thereby exhibiting excellent odor adsorption properties, and suppressing light scattering, thereby exhibiting excellent transparency. There is no particular lower limit for the average spherical equivalent diameter, but it can be 20 nm or more from the viewpoint of suppressing re-aggregation of the zinc oxide particles.

[0042] [Method for calculating the equivalent spherical diameter of zinc oxide] After embedding the multilayer film containing zinc oxide particles in epoxy resin, it was trimmed and surfaced using an ultramicrotome equipped with a diamond knife to prepare ultrathin sections. The cross-section of the ultrathin section (the layer containing zinc oxide particles) was then observed at a magnification of 50,000x using a scanning transmission electron microscope. A 3D reconstruction image of the observed image was then created using the 3D reconstruction software "Composer." Image analysis software (FEI, model number Avizo2019.2) was then used to calculate the volume of each zinc oxide particle observed within a 3281nm x 3281nm x 625nm area, and the diameter of a sphere equivalent to that volume was calculated. The average value was used as the average spherical equivalent diameter.

[0043] 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 thickness of the multilayer film can be 100 μm or less, and may be 50 to 70 μm.

[0044] The thickness of the outer layer (i.e., the total thickness of the first outer layer and the second outer layer) may be 25 to 42% of the thickness of the multilayer film. When the ratio of the outer layer thickness is equal to or greater than the lower limit, excellent transparency can be easily obtained, and when it is equal to or less than the upper limit, deterioration of the heat sealability of the film can be suppressed, making it easier to achieve practical use.

[0045] The thickness of the outer layer (i.e., the total thickness of the first outer layer and the second outer layer) may be 10 μm or more, or 15 μm or more. This makes it easy to ensure the transparency of the film and makes it difficult for the heat seal strength to decrease. There is no particular upper limit on the thickness of the outer layer, but it can be 40 μm or less, or 30 μm or less, or 20 μm or less, so as to make it easy to ensure cold impact resistance.

[0046] The thickness of the inner layer may be 30 μm or more, or 35 μm or more. This maintains the flexibility of the film, makes the film less likely to break after retort treatment, and reduces the heat seal strength. The upper limit of the thickness of the inner layer is not particularly limited, but may be 80 μm or less, or may be 70 μm or less, or may be 50 μm or less, for example, from the viewpoint of cost.

[0047] <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.

[0048] 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.

[0049] 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.

[0050] <Packaging material> The multilayer film may be used as a single film or may be laminated with a substrate, and there is no particular limitation on the method of use as a packaging material.

[0051] When a multilayer film is laminated with a substrate, the packaging material can include the multilayer film and the substrate. Specifically, such packaging materials can be obtained by laminating at least one substrate layer, such as biaxially oriented polyamide film (ONy), biaxially oriented polyester film (PET), printed paper, metal foil (AL foil), or transparent vapor-deposited film, onto the multilayer film 10 to form a laminate. FIG. 2 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 includes, in this order, a multilayer film 10, an adhesive layer 3, a substrate film 4, an adhesive layer 5, and a transparent vapor-deposited film 6. The laminate can be 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 the substrate can also be used.

[0052] 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.

[0053] <Package> The packaging body may be made into a bag from the above-mentioned packaging material, and there is no particular limitation on the bag-making style. For example, the above-mentioned packaging material (laminate) can be used for a flat bag, a three-sided bag, a two-sided bag, a gusseted bag, a standing pouch, a pouch with a spout, a pouch with a beak, etc., using a multilayer film as a sealing material. [Example]

[0054] The present invention will now be described in detail with reference to the following examples. (However, Examples 6 and 7 are reference examples.) The present invention will be described in detail using the following examples, but the present invention is not limited to the following examples.

[0055] <Preparing various materials> The following propylene homopolymer (A), propylene-ethylene random copolymer (B), propylene-ethylene block copolymer (C), ethylene-propylene copolymer elastomer (D), and zinc oxide masterbatches (E) and (F) were prepared.

[0056] (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).

[0057] (Propylene-ethylene random copolymer (B)) When differential scanning calorimetry (JIS K 7121) was performed, the melting onset temperature was 142°C, the melting peak temperature was 147°C, and ΔH h / ΔH l A propylene-ethylene random copolymer having a tensile strength of 1.84 and an ethylene content of 3.4% by mass.

[0058] 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. ΔH h / ΔH l is the heat of fusion ΔH at a temperature higher than 135°C when differential scanning calorimetry (JIS K 7121) is performed. h and the heat of fusion on the low temperature side ΔH l Figure 3 shows the total heat of fusion of propylene-ethylene random copolymer (B) and the results of dividing the heat of fusion at 135°C.

[0059] (Propylene-ethylene block copolymer (C)) A propylene-ethylene block copolymer having a melt flow rate (MFR: ISO 1133) of 2.0 g / 10 min (temperature 230°C, load 2.16 kg), containing 77.1 mass% propylene polymer and 22.9 mass% ethylene-propylene copolymer, with the ethylene content of the ethylene-propylene copolymer being 28.7 mass%.

[0060] (Ethylene-propylene copolymer elastomer (D)) An ethylene-propylene copolymer elastomer with 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 ratio of 2.7.

[0061] (Zinc oxide masterbatch (E)) A zinc oxide masterbatch prepared by melt-mixing 20% ​​by mass of zinc oxide particles with a primary particle size of 35 nm, the surface of which is coated with a high-density silica layer and a polysiloxane layer in that order, with 80% by mass of polypropylene resin.

[0062] (Zinc oxide masterbatch (F)) A zinc oxide masterbatch prepared by melt-mixing 20% ​​by mass of zinc oxide particles with a primary particle size of 35 nm and no coating treatment on the particle surface with 80% by mass of polypropylene resin.

[0063] <Preparation of laminated film> Example 1 For the outer layer, a resin mixture was used in which 50 parts by mass of propylene homopolymer (A) and 50 parts by mass of propylene-ethylene random copolymer (B) were mixed in the form of pellets. For the inner layer, 67.8 parts by mass of propylene-ethylene block copolymer (C) and 32.2 parts by mass of ethylene-propylene copolymer elastomer (D) were mixed in the form of pellets, and 0.63 parts by mass of zinc oxide masterbatch (E) was further mixed with 100 parts by mass of propylene-ethylene block copolymer (C) and ethylene-propylene copolymer elastomer (D). After layer formation, the zinc oxide content in the inner layer was 0.045 g / m. 2 The respective raw materials were fed to an extruder whose temperature was adjusted to 250°C, kneaded in a molten state, and laminated in a T-die extruder equipped with a feed block so that the first outer layer and second outer layer had a thickness of 10 μm, and the inner layer had a thickness of 40 μm, thereby producing the film of Example 1.

[0064] Example 2 A film of Example 2 was produced in the same manner as in Example 1, except that the blending ratio of the zinc oxide masterbatch (E) was changed as shown in Table 1.

[0065] Example 3 A film of Example 3 was produced in the same manner as in Example 2, except that the zinc oxide masterbatch (E) was changed to the zinc oxide masterbatch (F).

[0066] Example 4 The film of Example 4 was produced in the same manner as in Example 3, except that the blending ratio of the zinc oxide masterbatch (F) was changed as shown in Table 1.

[0067] Example 5 The film of Example 5 was produced in the same manner as in Example 1, except that the blending ratio of the zinc oxide masterbatch (E) was changed as shown in Table 1.

[0068] Example 6 The film of Example 6 was produced in the same manner as in Example 1, except that the layer containing the zinc oxide masterbatch (E) was changed to the second outer layer, and a resin mixture was used in which 5.21 parts by mass of the zinc oxide masterbatch (E) was mixed with 100 parts by mass of the propylene homopolymer (A) and the propylene-ethylene random copolymer (B).

[0069] Example 7 The film of Example 7 was produced in the same manner as in Example 6, except that the blending ratio of the zinc oxide masterbatch (E) was changed as shown in Table 1.

[0070] (Comparative Example 1) A film of Comparative Example 1 was produced in the same manner as in Example 1, except that the blending ratio of the zinc oxide masterbatch (E) was changed as shown in Table 1.

[0071] (Comparative Example 2) A film of Comparative Example 2 was produced in the same manner as in Example 3, except that the blending ratio of the zinc oxide masterbatch (F) was changed as shown in Table 1.

[0072] (Comparative Example 3) A film of Comparative Example 3 was produced in the same manner as in Example 6, except that the blending ratio of the zinc oxide masterbatch (E) was changed as shown in Table 1.

[0073] Comparative Example 4 A film of Comparative Example 4 was produced in the same manner as in Example 3, except that the blending ratio of the zinc oxide masterbatch (F) was changed as shown in Table 1.

[0074] (Comparative Example 5) A film of Comparative Example 5 was produced in the same manner as in Example 1, except that the blending ratio of the zinc oxide masterbatch (E) was changed as shown in Table 1.

[0075] <Various evaluations> The films obtained in each example were evaluated as follows, and the results are shown in Table 1.

[0076] [Zinc oxide mean spherical equivalent diameter] The films obtained in each example were embedded in epoxy resin, then trimmed and surfaced using an ultramicrotome equipped with a diamond knife to prepare ultrathin sections. The cross-sections of the ultrathin sections (layers containing zinc oxide particles) were then observed at 50,000x magnification using a scanning transmission electron microscope, and a 3D reconstruction image of the observed image was created using the 3D reconstruction software "Composer." Image analysis software (FEI, model number Avizo2019.2) was then used to calculate the volume of each zinc oxide particle observed within a 3281 nm × 3281 nm × 625 nm area, and the diameter of a sphere equivalent to that volume was calculated. The average value was used as the average spherical diameter. Figure 4 shows the spherical diameter distribution of zinc oxide particles in the film prepared in Example 1.

[0077] [Haze measurement after retort] The first outer layers of the films (polypropylene multilayer films) obtained in each example were placed facing each other and heat-sealed using a heat sealer manufactured by Tester Sangyo Co., Ltd. under the following conditions: sealing pressure 0.2 MPa, sealing time 1 second, sealing width 5 mm, and sealing temperature 200°C. Water was then filled and retort-treated at 135°C for 40 minutes. The retort-treated films were evaluated using a haze meter (model HM-150) manufactured by Murakami Color Research Laboratory in accordance with the haze measurement method specified in JIS K7136.

[0078] [Hydrogen sulfide reduction rate] A 12 μm thick biaxially oriented polyester film (PET), a 15 μm thick biaxially oriented polyamide film (ONy), a 7 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 with the following configuration. Laminated structure: PET / adhesive / ONy / adhesive / AL foil / adhesive / polypropylene film The polypropylene films of this laminate were placed facing each other and heat-sealed using a heat sealer manufactured by Tester Sangyo Co., Ltd. under conditions of a sealing pressure of 0.2 MPa, a sealing time of 1 second, a sealing width of 5 mm, and a sealing temperature of 200°C to produce packaging bags (three-sided bags). The packaging bags were then filled with an aqueous cysteine ​​solution containing 0.03% by weight of L-cysteine ​​and retorted at 135°C for 40 minutes. After retorting, the solution in the packaging bag was sampled and the hydrogen sulfide reduction rate was measured using a Pack Test (model WAK-S) manufactured by Kyoritsu Chemical Research Institute Co., Ltd. The hydrogen sulfide reduction rate was calculated by reacting the sampled solution with Pack Test reagent, measuring the absorbance at a wavelength of 668 nm using a spectrophotometer, and calculating the reduction rate of absorbance evaluated using the film obtained in each example relative to the absorbance measured using a packaging bag without zinc oxide.

[0079] [Heat sealability evaluation] Packaging bags (three-sided bags) were prepared in the same manner as above, then filled with water and retorted for 40 minutes at 135°C. The retorted film was cut into 15 mm wide x 80 mm pieces and subjected to T-peel at a tensile speed of 300 mm / min using a tensile tester manufactured by Shimadzu Corporation to measure the heat seal strength.

[0080] [Cold impact resistance evaluation] Using a film impact tester manufactured by Toyo Seiki Co., Ltd., the cold impact resistance of the films obtained in each example was evaluated under the conditions of a temperature of -5°C, a weight of 1.5 J, and a bullet size of 1.5 inches.

[0081] [Table 1] [Industrial Applicability]

[0082] The polypropylene-based multilayer film of the present invention has excellent odor adsorption properties for the sulfur odor emitted from retort foods, and also has high transparency necessary for visually checking the contents, making it suitable for use as a sealant film for retort packaging. [Explanation of symbols]

[0083] 10...multilayer film, 100...packaging material, 1a...first outer layer, 1b...second outer layer, 2...inner layer, 3...adhesive layer, 4...base film, 5...adhesive layer, 6...transparent vapor deposition film.

Claims

1. an outer layer which is a heat seal layer containing a propylene homopolymer (A) and a propylene-ethylene random copolymer (B); an inner layer containing a propylene-ethylene block copolymer (C) and an ethylene-propylene copolymer elastomer (D), The inner layer further contains zinc oxide particles, and the content of the zinc oxide particles per unit area of ​​the multilayer film is 0.030 to 0.25 g / m ２ It is a multilayer film.

2. 2. The multilayer film according to claim 1, wherein the zinc oxide particles have an average equivalent spherical diameter of 100 nm or less.

3. 3. The multilayer film according to claim 1, wherein the outer layer comprises 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) having an ethylene content of 5% by mass or less.

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

5. The multilayer film according to any one of claims 1 to 4, wherein the inner layer has a thickness of 30 µm or more.

6. A packaging material comprising the multilayer film according to any one of claims 1 to 5 and a substrate on the inner layer side of the multilayer film.

7. The packaging material described in claim 6, wherein the substrate is a biaxially oriented polyamide film, a biaxially oriented polyester film, or a transparent vapor deposition film.

8. A package produced from the packaging material according to claim 6 or 7.

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