Multi-layer film, packaging material, and package

Abstract

To provide a multilayer film that has an excellent odor absorptivity for sulfur odor resulting from content, excellent visibility for the content, and an excellent ultraviolet cut property cutting ultraviolet light that alters the content, changes the color of the content and deteriorates the content.SOLUTION: A multilayer film comprises a first outer layer that is a heat seal later 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. The multilayer film further contains zinc oxide particles in an amount of 3.0 to 5.0 mass%.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a multilayer film, a packaging material, and a package. Specifically, the present invention relates to a polypropylene-based multilayer film that can be suitably used as a sealant film for a packaging bag even in severe treatments such as boiling water treatment and retort treatment, and a packaging material and a package obtained using the polypropylene-based multilayer film.

Background Art

[0002] Polypropylene-based films are excellent in rigidity and heat resistance and are inexpensive, so they may be used as sealant films in various packaging materials such as food packaging. The main applications include packaging materials for retort foods that are subjected to pressurization treatment at high temperatures for sterilization and disinfection.

[0003] In packaged foods that are subjected to high-temperature sterilization and disinfection treatments such as retort foods, the contents may deteriorate and denature during manufacturing heat sterilization or long-term storage, resulting in the generation of a denatured odor. The sources of this denatured odor are carbohydrates, fats and oils, proteins, etc. Among them, the denatured odor of proteins contained in meat, fish, soybeans, eggs, etc., especially the sulfur odor derived from sulfur compounds, often becomes a problem.

[0004] Patent Document 1 proposes a package characterized in that a coating agent composed of a zinc compound and a solvent or a dispersion medium is applied to the surface of an oxygen barrier material which is a film composed of a resin layer containing a polycarboxylic acid-based polymer formed on a base film.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Although the package described in Patent Document 1 exhibits an odor adsorption function against sulfur odor, there is room for improvement in terms of the visibility of the contents and the ultraviolet ray cutting property of cutting ultraviolet light that causes the contents to deteriorate, discolor, or degrade.

[0007] The present invention has been made in view of the above circumstances, and an object thereof is to provide a multilayer film excellent in odor adsorption properties against sulfur odor generated from the contents, visibility of the contents, and ultraviolet ray cutting property of cutting ultraviolet light. Another object of the present invention is to provide a packaging material and a package obtained by using the multilayer film.

Means for Solving the Problems

[0008] As a result of intensive studies to solve the above problems, the inventors have found that it is important to mix and contain different propylene-based polymers in a predetermined amount in the outer layer of the polypropylene-based multilayer film and to incorporate zinc oxide particles in a predetermined amount into the polypropylene-based multilayer film, and thus the present invention has been completed.

[0009] The multilayer film according to one aspect of the present invention includes a first outer layer that is a heat-sealing 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 this order. The inner layer is Further contains zinc oxide particles, The average sphere-equivalent diameter of the zinc oxide particles is 100 nm or less, The zinc oxide particles are in the multilayer film Only the inner layer in 0.97 ~ 1.37 is contained in a mass% ratio.

[0010] In the above multilayer film, by blending zinc oxide particles in the polypropylene film at the above blending ratio, the amount of zinc oxide particles to be blended can be reduced. Thereby, while ensuring the odor adsorption property and the ultraviolet cut property against the sulfur odor generated from the contents, it is possible to suppress the decrease in the transparency of the film. Such a film can impart ultraviolet cut property while further improving the visibility of the contents as compared with the case where a coating agent containing zinc oxide particles is used (for example, the above Patent Document 1). The said effect is suitable especially in the food retort treatment use where sulfur odor generates at the time of retort treatment.

[0011] In one aspect, when the total of the propylene-ethylene block copolymer (C) and the ethylene-propylene copolymer elastomer (D) is 100 parts by mass, the inner layer contains 50 to 90 parts by mass of the propylene-ethylene block copolymer (C) and 10 to 50 parts by mass of the ethylene-propylene copolymer elastomer (D). Thus Good. Thereby, the flexibility of the film is maintained, and excellent cold impact resistance is easily obtained.

[0012] In one aspect, when the total of the propylene homopolymer (A) and the propylene-ethylene random copolymer (B) is 100 parts by mass, the first outer layer and the second outer layer contain 30 to 70 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. Thus Good. Thereby, it becomes easy to suppress the surface irregularities which are a factor in lowering the transparency of the film. Thereby, it becomes possible to achieve both more excellent heat resistance and transparency.

[0013] In one aspect, the total thickness of the first outer layer and the second outer layer may be 25 to 42% based on the thickness of the multilayer film. Thereby, it becomes easy to achieve both transparency and heat sealability.

[0014] In one aspect, the thickness of the inner layer may be 30 μm or more. Thereby, it becomes easy to maintain the flexibility of the film, and excellent cold impact resistance is easily obtained.

[0015] The packaging material according to one aspect of the present invention includes the above multilayer film and a base material.

[0016] The package according to one aspect of the present invention is formed into a bag from the above packaging material.

Advantages of the Invention

[0017] According to the present invention, it is possible to provide a multilayer film excellent in odor adsorption properties against sulfur odor generated from the contents, visibility of the contents, and ultraviolet ray blocking properties. The present invention can also provide a packaging material and a package obtained by using the multilayer film.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0019] <Multilayer Film> FIG. 1 is a cross-sectional view of a multilayer film according to an 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 non-stretched polypropylene-based sealant film.

[0020] [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 the outer layer. 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-sealing layer and is arranged to contact the contents.

[0021] (Propylene homopolymer (A)) The production method of the propylene homopolymer (A) is not particularly limited. For example, it can be obtained by a method of homopolymerizing propylene using a Ziegler-Natta catalyst, a metallocene catalyst, or a half-metallocene catalyst. By containing the propylene homopolymer (A) in the outer layer, excellent heat resistance can be imparted to the outer layer.

[0022] As the propylene homopolymer (A), those having a melting start temperature of 150 °C or higher and a melting peak temperature of 155 °C or higher when measured by differential scanning calorimetry (JIS K 7121) can be used. Those having both the melting start temperature and the melting point peak temperature within this range have excellent heat resistance. For example, after performing a retort treatment at a high temperature, fusion hardly occurs on the inner surface of the packaging bag.

[0023] As the propylene homopolymer (A), those 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 min can be used. The melt flow rate is a parameter indicating the fluidity of a polymer material during melting and is also a parameter indicating the molecular weight. Therefore, if the melt flow rate is too high, the impact resistance of the polymer material is likely to decrease. If it is too low, the extruder load during molding processing increases, the processing speed decreases, and the productivity is likely to decrease. From these viewpoints, 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.

[0024] (Propylene-ethylene random copolymer (B)) The production method of the propylene-ethylene random copolymer (B) is not particularly limited. For example, it can be obtained by copolymerizing ethylene as a comonomer in a main monomer composed of propylene using a Ziegler-Natta type catalyst, a metallocene catalyst, or a half-metallocene catalyst. By containing the propylene-ethylene random copolymer (B) in the outer layer, a multilayer film having excellent transparency and flexibility can be obtained.

[0025] As the propylene-ethylene random copolymer (B), those having a melting start temperature of 140 °C or higher and a melting point peak temperature of 145 °C or higher when differential scanning calorimetry (JIS K 7121) is performed can be used. Those having both the melting start temperature and the melting point peak temperature within this range have excellent heat resistance. For example, after performing a severe retort treatment at 135 °C for 40 minutes, fusion hardly occurs on the inner surface of the packaging bag.

[0026] As the propylene-ethylene random copolymer (B), the heat of fusion ΔH on the high-temperature side of the measurement temperature of 135 °C when differential scanning calorimetry (JIS K 7121) is performed h and the heat of fusion ΔH on the low-temperature side l The ratio ΔH h / ΔH l in the range of 1.5 to 2.5 can be used. When the above ratio is below the upper limit value, the flexibility of the film is maintained, the edge breakage of the heat-sealed part can be suppressed after the retort treatment, and the heat-sealing strength is difficult to decrease. The lower limit value of the above ratio can be set to 1.5 from the viewpoint that fusion hardly occurs on the inner surface of the packaging bag after the retort treatment.

[0027] The ethylene content of the propylene-ethylene random copolymer (B) can be 5% by mass or less. By the ethylene content being below the upper limit value, while maintaining transparency, the heat resistance does not excessively decrease, and it becomes easier to suppress fusion on the inner surface of the packaging bag after retort processing. From this perspective, the ethylene content may be 4.5% by mass or less, and may be 4% by mass or less. The lower limit of the ethylene content is not particularly limited, but from the perspective that the flexibility of the film is maintained, edge breakage can be suppressed at the heat seal part after retort processing, and the heat seal strength is difficult to decrease, it can be 2% by mass.

[0028] The ethylene content of the propylene-ethylene random copolymer (B) can be measured according to the quantitative method (IR method) of ethylene content described on pages 412 - 413 of the Polymer Analysis Handbook edited by the Polymer Analysis Discussion Group of the Japan Society for Analytical Chemistry (May 10, 2013, 3rd printing).

[0029] When the total of the propylene homopolymer (A) and the propylene-ethylene random copolymer (B) is 100 parts by mass, the outer layer may contain 30 - 70 parts by mass of the propylene homopolymer (A) and 30 - 70 parts by mass of the propylene-ethylene random copolymer (B) with an ethylene content of 5% by mass or less. By the content ratio of the propylene homopolymer (A) being 30 parts by mass or more, it is easy to maintain excellent heat resistance. Also, by the content ratio of the propylene homopolymer (A) being 70 parts by mass or less, that is, by the content of the propylene-ethylene random copolymer (B) with an ethylene content of 5% by mass or less being at least 30 parts by mass or more, it is easy to exhibit excellent transparency and heat sealability. From these perspectives, when the total of the propylene homopolymer (A) and the propylene-ethylene random copolymer (B) is 100 parts by mass, the outer layer may contain 40 - 60 parts by mass of the propylene homopolymer (A) and 40 - 60 parts by mass of the propylene-ethylene random copolymer (B).

[0030] [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).

[0031] (Propylene-ethylene block copolymer (C)) The propylene-ethylene block copolymer (C) is a copolymer that can be obtained by producing a propylene polymer (C1) in the first step and then producing an ethylene-propylene copolymer (C2) by gas-phase polymerization in the second step. The propylene-ethylene block copolymer (C) is not a block copolymer in which the propylene polymer terminal and the ethylene-propylene copolymer terminal are bonded, but a kind of blend-type copolymer. By containing the propylene-ethylene block copolymer (C) in the inner layer, the flexibility of the film is maintained, the edge breakage of the heat-sealed part can be suppressed after retort treatment, excellent heat-sealability can be easily obtained, and excellent cold impact resistance can be easily obtained.

[0032] As the propylene-ethylene block copolymer (C), those having 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 minutes can be used. If the melt flow rate becomes too high, the impact resistance of the film is likely to decrease. If it is too low, the extruder load during molding processing increases, the processing speed decreases, and the productivity is likely to decrease. From these viewpoints, the melt flow rate can be 0.5 to 2.5 g / 10 minutes, and may be 1.0 to 2.0 g / 10 minutes.

[0033] The propylene-ethylene block copolymer (C) may contain 90 to 60% by mass of the above propylene polymer (C1) and 10 to 40% by mass of the ethylene-propylene copolymer (C2). When each component is within this range, excellent heat-sealability can be easily obtained.

[0034] 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 the ethylene content being below the upper limit value, the tackiness of the product can be suppressed, and it is difficult for contamination due to the tack of the product to occur during production, and it is easy to maintain excellent productivity. By the ethylene content being above the lower limit value, the flexibility of the film is maintained, edge breakage of the heat-sealed part can be suppressed after retort treatment, it is easy to obtain excellent heat-sealing properties, and excellent cold impact resistance is also easily obtained.

[0035] (Ethylene-propylene copolymer elastomer (D)) The ethylene-propylene copolymer elastomer (D) can be obtained, for example, by a slurry polymerization method carried out in the presence of an inert hydrocarbon such as hexane, heptane, kerosene, or a liquefied α-olefin solvent such as propylene, or a gas phase polymerization method without a solvent. Specifically, the ethylene-propylene copolymer elastomer (D) is obtained using a known multi-stage polymerization method. That is, it is a polymerized high rubber-containing polypropylene-based resin that can be obtained by polymerizing propylene and / or a propylene-α-olefin polymer in the first-stage reaction and then copolymerizing propylene and an α-olefin in the second-stage reaction. By the inner layer containing the ethylene-propylene copolymer elastomer (D), it is easy to impart flexibility to the film, edge breakage of the heat-sealed part can be suppressed, it is easy to obtain excellent heat-sealing properties, and excellent cold impact resistance is also easily obtained.

[0036] As the ethylene-propylene copolymer elastomer (D), those having 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 can be used. By the melt flow rate being above the lower limit value, the load on the extruder during molding processing becomes small, it is difficult for the processing speed to decrease, and it is easy to maintain excellent productivity. By the melt flow rate being below the upper limit value, the compatibility between the propylene-ethylene block copolymer (C) and the ethylene-propylene copolymer elastomer (D) becomes good, and it is difficult for the transparency to decrease.

[0037] As the ethylene-propylene copolymer elastomer (D), those 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 at least the lower limit, the flexibility of the film is maintained, the edge breakage of the heat-sealed portion can be suppressed after retort treatment, and excellent heat-sealing property can be easily obtained. When the above ratio is at most 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 hardly lowered.

[0038] The inner layer may contain 50 to 90 parts by mass of the propylene-ethylene block copolymer (C) and 10 to 50 parts by mass of the ethylene-propylene copolymer elastomer (D) when the total of the propylene-ethylene block copolymer (C) and the ethylene-propylene copolymer elastomer (D) is 100 parts by mass. When the content ratio of the propylene-ethylene block copolymer (C) is 50 parts by mass or more, it is easy to maintain excellent heat-sealing property. Further, when the content ratio of the propylene-ethylene block copolymer (C) is 90 parts by mass or less, that is, when the content of the ethylene-propylene copolymer elastomer (D) is at least 10 parts by mass or more, further excellent heat-sealing property and excellent cold impact resistance can be exhibited. From these viewpoints, the inner layer may contain 60 to 80 parts by mass of the propylene-ethylene block copolymer (C) and 20 to 40 parts by mass of the ethylene-propylene copolymer elastomer (D) when the total of the propylene-ethylene block copolymer (C) and the ethylene-propylene copolymer elastomer (D) is 100 parts by mass.

[0039] [Zinc Oxide Particles] The polypropylene-based multilayer film further contains zinc oxide particles. The zinc oxide particles may be contained in one or both of the outer layers, may be contained in the inner layer, or may be contained in one or both of the outer layers and the inner layer. The content of the zinc oxide particles is in the multilayer film The inner layer of in 0.97 ~ 1.37 mass% by It can be. By having the content of the zinc oxide particles be at least the lower limit, excellent odor adsorption properties can be obtained, and excellent ultraviolet ray cut-off properties can also be obtained. By having the content of the zinc oxide particles be at most the upper limit, excellent transparency can be exhibited.

[0040] The average sphere-equivalent diameter of the zinc oxide particles can be 100 nm or less, and may be 90 nm or less. Thereby, the surface area of the zinc oxide particles increases, and it is easy to exhibit excellent odor adsorption properties. Also, by being 100 nm or less, while suppressing visible light dispersion, ultraviolet ray cut-off properties can be imparted by scattering ultraviolet light, which has a short wavelength, while exhibiting excellent transparency. The lower limit of the average sphere-equivalent diameter is not particularly limited, but from the viewpoint of suppressing re-aggregation of the zinc oxide particles, it can be 20 nm or more.

[0041] [Method for calculating the sphere-equivalent diameter of zinc oxide] After embedding a multilayer film containing zinc oxide particles with an epoxy resin, trimming, face exposure, and producing an ultra-thin section are performed with an ultramicrotome equipped with a diamond knife. Then, using a scanning transmission electron microscope, the cross-section of the ultra-thin section (the layer containing zinc oxide particles) is observed at an observation magnification of 50,000 times. A three-dimensional reconstructed image of the observation image is created using 3D reconstruction software "Composer". Then, using image analysis software (model number Avizo2019.2 manufactured by FEI), the volume of each zinc oxide particle observed in the range of 3281 nm × 3281 nm × 625 nm is calculated, the diameter of a sphere equal to that volume is calculated, and the average value thereof is taken as the average sphere-equivalent diameter.

[0042] The thickness of the multilayer film is not particularly limited as long as it is within a range that can be used as a film for packaging materials, for example, but if the film is too thick, it will result in a cost disadvantage. For this reason, the thickness of the multilayer film can be 100 μm or less, and may be 50 - 70 μm.

[0043] 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% based on the thickness of the multilayer film. When the ratio of the thickness of the outer layer is at least the lower limit value, it is easy to obtain excellent transparency, and when it is at most the upper limit value, it is possible to suppress a decrease in the heat sealability of the film, and practicality can be easily obtained.

[0044] 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, and may be 15 μm or more. Thereby, it is easy to ensure the transparency of the film, and the heat seal strength is less likely to decrease. The upper limit of the thickness of the outer layer is not particularly limited, but in order to easily ensure cold resistance impact resistance, it can be 40 μm or less, may be 30 μm or less, and may be 20 μm or less.

[0045] The thickness of the inner layer may be 30 μm or more, and may be 35 μm or more. Thereby, the flexibility of the film is maintained, the film is less likely to break after retort processing, and the heat seal strength is less likely to decrease. The upper limit of the thickness of the inner layer is not particularly limited, but for example, from the viewpoint of cost, it can be 80 μm or less, may be 70 μm or less, and may be 50 μm or less.

[0046] <Method for manufacturing a multilayer film> The method for manufacturing the multilayer film is not particularly limited, and known methods can be used. For example, as the thermoforming method, there are a melt kneading method using a general kneader such as a single-screw extruder, a twin-screw extruder, or a multi-screw extruder, a method of heating and removing the solvent after dissolving or dispersing and mixing each component, and the like. Considering workability, a single-screw extruder or a twin-screw extruder can be used. When using a single-screw extruder, examples of the screw include a full-flight screw, a screw with a mixing element, a barrier flight screw, a fluted screw, etc., and these can be used without particular limitation. As the twin-kneading device, a co-rotating twin-screw extruder, a counter-rotating twin-screw extruder, etc. can be used, and as the screw shape, a full-flight screw, a kneading disk type, etc. can be used without particular limitation.

[0047] In the above method, after melting the multilayer film by a single-screw extruder or a twin-screw extruder, etc., it is possible to use a method of forming a film with a T-die through a feed block or a multi-manifold.

[0048] The obtained multilayer film may be appropriately subjected to a surface modification treatment to improve the post-process suitability as needed. For example, in order to improve the printing suitability when using a single film or the lamination suitability when using in a laminate, a surface modification treatment may be performed on the printing surface or the surface in contact with the base material. Examples of the surface modification treatment include a treatment that generates functional groups by oxidizing the film surface such as corona discharge treatment, plasma treatment, and flame treatment, and a modification treatment by a wet process that forms an easy-adhesion layer by coating.

[0049] <Packaging material> The multilayer film may be used as a single film or may be used by laminating with a base material, and the method of using it as the packaging material is not particularly limited.

[0050] When used by laminating a multilayer film on a base material, the packaging material can include the above-described multilayer film and the base material. Specifically, such a packaging material can be obtained by laminating at least one layer of a base material such as a biaxially stretched polyamide film (ONy), a biaxially stretched polyester film (PET), printed paper, a metal foil (AL foil), a transparent vapor-deposited film, etc. on the above-described multilayer film 10 to form a laminate. FIG. 2 is a cross-sectional view of a packaging material according to an embodiment of the present invention. The packaging material 100 shown in the figure includes a multilayer film 10, an adhesive layer 3, a base material film 4, an adhesive layer 5, and a transparent vapor-deposited film 6 in this order. As a method for manufacturing the laminate, a normal dry lamination method of bonding the films constituting the laminate with an adhesive can be preferably employed, but a method of directly extrusion laminating the multilayer film on the base material can also be employed as necessary.

[0051] The lamination structure of the laminate can be appropriately adjusted according to the required characteristics of the package, for example, the barrier property that satisfies the quality retention period of the food to be packaged, the size and impact resistance that can withstand the weight of the contents, the visibility of the contents, etc.

[0052] <Package> The package may be formed into a bag from the above-described packaging material, and there is no particular limitation on the bag-making style. For example, the above-described packaging material (laminate) can be used for flat bags, three-side bags, clasp bags, gusset bags, standing pouches, pouches with spouts, pouches with beaks, etc. that use the multilayer film as a sealing material.

Examples

[0053] Hereinafter, the present invention will be described in detail using examples, but the present invention is not limited only to the following examples.

[0054] <Preparation of Various Materials> The following propylene homopolymer (A), propylene-ethylene random copolymer (B), propylene-ethylene block copolymer (C), ethylene-propylene copolymer elastomer (D), and zinc oxide masterbatch (E) were prepared.

[0055] (Propylene homopolymer (A)) A propylene homopolymer having a melting start temperature of 153 °C and a melting peak temperature of 159 °C when measured by differential scanning calorimetry (JIS K 7121), and a melt flow rate (MFR: ISO 1133) (temperature 230 °C, load 2.16 kg) of 3.0 g / 10 min.

[0056] (Propylene-ethylene random copolymer (B)) A propylene-ethylene random copolymer having a melting start temperature of 142 °C, a melting peak temperature of 147 °C, ΔH h / ΔH l of 1.84, and an ethylene content of 3.4 mass%.

[0057] The measurement of the ethylene content was carried out in accordance with the quantitative method (IR method) of ethylene content described on pages 412 - 413 of the Polymer Analysis Handbook edited by the Polymer Analysis Discussion Group of the Japan Society for Analytical Chemistry (May 10, 2013, 3rd edition).

[0058] ΔH h / ΔH l is the ratio of the heat of fusion ΔH h on the higher temperature side to the heat of fusion ΔH l on the lower temperature side when measured by differential scanning calorimetry (JIS K 7121). Figure 3 is a diagram 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.

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

[0060] (Ethylene-propylene copolymer elastomer (D)) An ethylene-propylene copolymer elastomer having a melt flow rate (MFR: ISO 1133) of 0.6 g / 10 min at a temperature of 230°C and a load of 2.16 kg, and a propylene content / ethylene content of 2.7.

[0061] (Zinc oxide masterbatch (E)) A zinc oxide masterbatch obtained by melt-mixing 20% by mass of zinc oxide particles having a primary particle size of 35 nm and not subjected to a coating treatment on the particle surface and 80% by mass of a polypropylene-based resin.

[0062] <Preparation of laminated film> (Example 1) For forming the outer layer, a resin mixture obtained by mixing 50 parts by mass of a propylene homopolymer (A) and 50 parts by mass of a propylene-ethylene random copolymer (B) in a pellet state was used. Also, for forming the inner layer, 67.8 parts by mass of a propylene-ethylene block copolymer (C) and 32.2 parts by mass of an ethylene-propylene copolymer elastomer (D) were mixed in a pellet state, and further, zinc oxide masterbatch (E) was mixed in an amount of 5.07 parts by mass with respect to 100 parts by mass of the propylene-ethylene block copolymer (C) and the ethylene-propylene copolymer elastomer (D). The zinc oxide content in the polypropylene film after layer formation Inner layer was adjusted to 0.97 mass% using a resin mixture thus adjusted. Each raw material was supplied to an extruder heated to 250°C, kneaded in a molten state, and laminated using a T-die extruder having a feed block so that the thicknesses of the first outer layer and the second outer layer were each 10 μm and the thickness of the inner layer was 40 μm, thereby producing the film of Example 1.

[0063] (Example 2) The 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.

[0064] (Example 3) A film of Example 3 was produced in the same manner as in Example 1, except that the blending ratio of zinc oxide masterbatch (E) was changed as shown in Table 1.

[0065] (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 zinc oxide masterbatch (E) was changed as shown in Table 1.

[0066] (Comparative Example 2) A film of Comparative Example 2 was produced in the same manner as in Example 1, except that the blending ratio of zinc oxide masterbatch (E) was changed as shown in Table 1.

[0067] <Various Evaluations> The following evaluations were performed on the films obtained in each example. The results are shown in Table 1.

[0068] [Haze Measurement after Retort] The first outer layers of the films (polypropylene multilayer films) obtained in each example were opposed to each other, and heat-sealed using a heat sealer manufactured by Tester Sangyo Co., Ltd. under the conditions of a seal pressure of 0.2 MPa, a seal time of 1 second, a seal width of 5 mm, and a seal temperature of 200 °C to produce a packaging bag (three-side bag). Then, it was filled with water and subjected to a retort treatment at 135 °C for 40 minutes. In accordance with the haze measurement method described in JIS K7136, the transparency of the film subjected to the retort treatment was evaluated using a spectroscopic color and haze meter (model number COH7700) manufactured by Nippon Denshoku Industries Co., Ltd. In this measurement, if the haze after retort was 30% or less, it was evaluated as good.

[0069] [Hydrogen Sulfide Reduction Rate] A biaxially oriented polyester film (PET) with a thickness of 12 μm, an AL foil with a thickness of 7 μm, a biaxially oriented polyamide film (ONy) with a thickness of 15 μm, and the film (polypropylene-based film) obtained in each example were laminated using a urethane-based adhesive by a normal dry lamination method to form a laminate having the following configuration. Laminate structure: PET / adhesive / AL foil / adhesive / ONy / adhesive / polypropylene-based film

[0070] The polypropylene-based films of this laminate were opposed to each other, and heat-sealed using a heat sealer manufactured by Tester Sangyo Co., Ltd. under the conditions of a seal pressure of 0.2 MPa, a seal time of 1 second, a seal width of 5 mm, and a seal temperature of 200 °C to produce a packaging bag (three-sided bag). Then, a cysteine aqueous solution containing 0.03% by mass of L-cysteine was filled into the packaging bag, and retort treatment was performed at 135 °C for 40 minutes. After the retort treatment, the solution in the packaging bag was collected, and the hydrogen sulfide reduction rate was measured using a Pack Test (model number WAK-S) manufactured by Kyoritsu Chemical-Check Laboratories Co., Ltd. The calculation of the hydrogen sulfide reduction rate was performed by reacting the collected solution with the Pack Test reagent, measuring the absorbance at a wavelength of 668 nm with a spectrophotometer, and calculating from the reduction rate of the absorbance evaluated using the films obtained in each example with respect to the absorbance measured with a packaging bag not containing zinc oxide. In this measurement, if the hydrogen sulfide reduction rate was 90% or more, it was evaluated as good.

[0071] [UV transmittance after retort] The first outer layers of the obtained films (polypropylene multilayer films) were opposed to each other, and heat-sealed using a heat sealer manufactured by Tester Sangyo Co., Ltd. under the conditions of a seal pressure of 0.2 MPa, a seal time of 1 second, a seal width of 5 mm, and a seal temperature of 200 °C to produce a packaging bag (three-sided bag). After that, water was filled, and retort treatment was performed at 135 °C for 40 minutes. For the films subjected to the retort treatment, transmittance measurements were performed at each wavelength in the measurement wavelength range of 800 nm to 200 nm using an ultraviolet-visible spectrophotometer (model number UV-2600) manufactured by Shimadzu Corporation. From the obtained results, the average value of the transmittance was determined for the wavelengths in the region of 380 nm to 300 nm, and the average UV transmittance after retort was calculated. In this measurement, if the UV transmittance after retort was 15% or less, it was evaluated as good.

[0072]

Table 1

[0073] The polypropylene multilayer films according to Examples 1 to 3 showed good results in haze after retort, hydrogen sulfide reduction rate, and average ultraviolet transmittance after retort, and had both odor adsorption properties against sulfur odor, transparency after retort treatment (visibility of the contents), and ultraviolet cut-off properties.

[0074] On the other hand, the polypropylene multilayer film according to Comparative Example 1 had a high average ultraviolet transmittance after retort and insufficient ultraviolet cut-off properties.

[0075] In addition, the polypropylene multilayer film according to Comparative Example 2 had a high haze after retort and insufficient transparency after retort treatment.

Industrial Applicability

[0076] The polypropylene-based multilayer film of the present invention has excellent odor adsorption properties against sulfur odor generated from retort foods, high transparency necessary for visual recognition of the contents, and ultraviolet cut-off properties for cutting ultraviolet light that causes the contents to deteriorate, discolor, and degrade, and can be suitably used as a sealant film for retort packaging.

Explanation of Signs

[0077] 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. A multilayer film comprising: a first outer layer which is a heat-sealing 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); a second outer layer containing a propylene homopolymer (A) and a propylene-ethylene random copolymer (B), provided in this order; wherein the inner layer further contains zinc oxide particles; wherein the average spherical equivalent diameter of the zinc oxide particles is 100 nm or less; and wherein the zinc oxide particles are contained in the inner layer only of the multilayer film at a ratio of 0.97 to 1.37% by mass. A multilayer film.

2. When the total of the propylene-ethylene block copolymer (C) and the ethylene-propylene copolymer elastomer (D) is 100 parts by mass, the inner layer contains 50 to 90 parts by mass of the propylene-ethylene block copolymer (C) and 10 to 50 parts by mass of the ethylene-propylene copolymer elastomer (D). The multilayer film according to Claim 1.

3. When the total of the propylene homopolymer (A) and the propylene-ethylene random copolymer (B) is 100 parts by mass, the first outer layer and the second outer layer contain 30 to 70 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. The multilayer film according to Claim 1.

4. 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. The multilayer film according to any one of Claims 1 to 3.

5. The thickness of the inner layer is 30 μm or more. The multilayer film according to any one of Claims 1 to 4.

6. A packaging material comprising the multilayer film according to any one of Claims 1 to 5 and a base material.

7. A package formed by making a bag from the packaging material according to Claim 6.

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