Sealant film and method for producing the same, packaging material, and package

Abstract

To provide a sealant film which is excellent in odor adsorptivity to sulfur odor generated from a content, and is excellent in impact resistance and heat resistance.SOLUTION: A sealant film contains (A) a resin component, and (B) zinc oxide particles, wherein (A) the resin component contains (a1) a propylene-ethylene block copolymer, and (a2) an ethylene-based polymer having an ethylene content of 80 mass% or more, the content of (a1) the propylene-ethylene block copolymer is 70-97 mass% based on the total amount of (A) the resin component, the content of (a2) the ethylene-based polymer is 3-30 mass% based on the total amount of (A) the resin component, and the content of (B) the zinc oxide particles is 0.05-4.5 mass% based on the total amount of the sealant film.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a sealant film, a manufacturing method thereof, a packaging material, and a package. More specifically, the present invention relates to a polypropylene sealant film that can be suitably used as a sealant film for packaging bags even in harsh treatments such as boiling water treatment and retort treatment, a manufacturing method thereof, and a packaging material and a package obtained using the polypropylene sealant 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 package characterized by applying a coating agent consisting of a zinc compound and a solvent or dispersion medium 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.

[0005] Patent Document 2 proposes a package comprising a substrate film having a barrier layer, an adhesive layer, and a sealant layer, the adhesive layer containing an adhesive component and zinc oxide particles. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-18551 [Patent Document 2] Japanese Patent Application Publication No. 2017-94533 Summary of the Invention [Problem to be solved by the invention]

[0007] When a polypropylene-based film is used as a sealant film, it is required to have impact resistance so that the packaging bag will not break even if dropped, and heat resistance so that the inner surface of the packaging bag will not fuse during high-temperature heat sterilization. In addition, in recent years, odor adsorption ability against the sulfur odor generated from the contents has become a requirement. However, with conventional polypropylene-based sealant films, it is currently difficult to achieve a good balance between excellent impact resistance and heat resistance and odor adsorption ability against the sulfur odor.

[0008] The present invention has been made in view of the above circumstances, and aims to provide a sealant film that has excellent odor adsorption properties for sulfur odors emitted from contents, as well as excellent impact resistance and heat resistance, and a method for producing the same. Another aim of the present invention is to provide a packaging material and a package obtained using the sealant film. [Means for solving the problem]

[0009] As a result of extensive research aimed at solving the above problems, the inventors discovered that it is important to mix a propylene-ethylene block copolymer and an ethylene-based polymer in predetermined amounts and further blend zinc oxide particles, which led to the completion of the present invention.

[0010] That is, the present invention provides the following sealant film, its manufacturing method, packaging material, and package. [1] A sealant film containing (A) a resin component and (B) zinc oxide particles, wherein the (A) resin component contains (a1) a propylene-ethylene block copolymer and (a2) an ethylene-based polymer having an ethylene content of 80% by mass or more, the content of the (a1) propylene-ethylene block copolymer being 70 to 97% by mass based on the total amount of the (A) resin component, the content of the (a2) ethylene-based polymer being 3 to 30% by mass based on the total amount of the (A) resin component, and the content of the (B) zinc oxide particles being 0.05 to 4.5% by mass based on the total amount of the sealant film. [2] The sealant film according to [1] above, wherein the ethylene content of the (a1) propylene-ethylene block copolymer is less than 20% by mass. [3] The sealant film according to either [1] or [2] above, wherein the total content of the (a1) propylene-ethylene block copolymer and the (a2) ethylene-based polymer is 80 mass% or more based on the total amount of the (A) resin component. [4] The density of the (a2) ethylene polymer is 0.870 to 0.920 g / cm 3 The sealant film according to any one of the above [1] to [3], [5] The sealant film according to any one of the above [1] to [4], which has a thickness of 50 μm or more. [6] A method for producing a sealant film, comprising the step of forming a sealant film using a sealant resin composition containing (A) a resin component and (B) zinc oxide particles, wherein the (A) resin component contains (a1) a propylene-ethylene block copolymer and (a2) an ethylene-based polymer having an ethylene content of 80% by mass or more, the content of the (a1) propylene-ethylene block copolymer in the sealant film is 70 to 97% by mass based on the total amount of the (A) resin components in the sealant film, the content of the (a2) ethylene-based polymer in the sealant film is 3 to 30% by mass based on the total amount of the (A) resin components in the sealant film, and the content of the (B) zinc oxide particles in the sealant film is 0.05 to 4.5% by mass based on the total amount of the sealant film. [7] The method for producing a sealant film according to [6] above, wherein the ethylene content of the (a1) propylene-ethylene block copolymer is less than 20% by mass. [8] The method for producing a sealant film according to either [6] or [7] above, wherein the total content of the (a1) propylene-ethylene block copolymer and the (a2) ethylene-based polymer in the sealant film is 80 mass% or more based on the total amount of the (A) resin component in the sealant film. [9] The density of the (a2) ethylene polymer is 0.870 to 0.920 g / cm 3 The method for producing a sealant film according to any one of the above [6] to [8], wherein

[10] The method for producing a sealant film according to any one of the above [6] to [9], wherein the thickness of the sealant film is 50 μm or more.

[11] A packaging material comprising the sealant film according to any one of the above [1] to [5] and a substrate.

[12] A package made from the packaging material described in

[11] above.

[0011] The sealant film described in [1] above contains (a1) a propylene-ethylene block copolymer and (a2) an ethylene-based polymer in a specific ratio. By blending (B) zinc oxide particles in a specific ratio, the sealant film can maintain excellent heat resistance and cold impact resistance while also imparting odor adsorption properties to the sulfur odor emanating from the contents. This film can impart superior impact resistance to packaging bags compared to films using coating agents containing zinc oxide particles (e.g., Patent Document 1) or films incorporating zinc oxide particles into adhesive components (e.g., Patent Document 2). This effect is particularly suitable for food retort applications, where a sulfur odor is generated during retort processing.

[0012] In the above sealant film, by incorporating zinc oxide particles (B) into a sealant film containing (a1) a propylene-ethylene block copolymer and (a2) an ethylene-based polymer, the amount of zinc oxide particles (B) incorporated can be reduced. This prevents the aggregation of the zinc oxide particles (B), thereby maintaining excellent odor adsorption properties and suppressing a decrease in impact resistance. Such a film is more likely to achieve excellent odor adsorption and impact resistance than films using a coating agent containing zinc oxide particles (e.g., Patent Document 1) or films containing zinc oxide particles in an adhesive component (e.g., Patent Document 2).

[0013] The sealant film contains 70 to 97 parts by mass of (a1) a propylene-ethylene block copolymer and 3 to 30 parts by mass of (a2) an ethylene polymer, which facilitates obtaining excellent impact resistance and heat resistance. Furthermore, the ethylene content of (a2) the ethylene polymer is 80% by mass or more, which facilitates obtaining excellent impact resistance.

[0014] In the sealant film described in [4] above, the density of the ethylene polymer (a2) is 0.870 to 0.920 g / cm 3 This makes it easy to obtain excellent impact resistance.

[0015] The sealant film described in [5] above has a thickness of 50 μm or more, which makes it easy to obtain excellent impact resistance. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide a sealant film that has excellent odor adsorption properties for sulfur odors emitted from contents, as well as excellent impact resistance and heat resistance, and a method for producing the same. The present invention also provides packaging materials and packages obtained using the sealant film. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a cross-sectional view of a sealant film according to one embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view of a sealant film according to one embodiment of the present invention. [Figure 3] FIG. 3 is a cross-sectional view of a sealant film according to one embodiment of the present invention. [Figure 4] FIG. 4 is a cross-sectional view of a packaging material according to one embodiment of the present invention. [Figure 5] FIG. 5 is a cross-sectional view of a packaging material according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings where necessary, but the present invention is not limited to the following embodiments.

[0019] <Sealant film> FIG. 1 is a cross-sectional view of a sealant film according to one embodiment of the present invention. The sealant film 10 contains (A) a resin component (hereinafter sometimes referred to as "component (A)") and (B) zinc oxide particles (hereinafter sometimes referred to as "component (B)"). The component (A) contains (a1) a propylene-ethylene block copolymer (hereinafter sometimes referred to as "component (a1)") and (a2) an ethylene-based polymer having an ethylene content of 80% by mass or more (hereinafter sometimes referred to as "(a2) ethylene-based polymer" or "component (a2)"). In the sealant film 10, the content of the component (a1) is 70 to 97% by mass based on the total amount of the component (A), the content of the component (a2) is 3 to 30% by mass based on the total amount of the component (A), and the content of the component (B) is 0.05 to 4.5% by mass based on the total amount of the sealant film. The sealant film 10 can be used as a polypropylene-based unstretched sealant film.

[0020] ((A) Resin component) Component (A) contains 70 to 97 mass% of component (a1) and 3 to 30 mass% of component (a2), based on the total mass of component (A). Component (A) may contain other resin components in addition to components (a1) and (a2). Details of the resin components are described below.

[0021] [(a1) Propylene-ethylene block copolymer] (a1) Propylene-ethylene block copolymer is a copolymer that can be obtained by producing propylene homopolymer (i) in the first step, and then producing ethylene-propylene copolymer (ii) by gas phase polymerization in the second step. (a1) Propylene-ethylene block copolymer is not a block copolymer in which the end of propylene homopolymer (i) is bonded to the end of ethylene-propylene copolymer (ii), but rather a type of blend copolymer. By containing (a1) propylene-ethylene block copolymer, the sealant film can be made impact resistant while maintaining its heat resistance.

[0022] The (a1) propylene-ethylene block copolymer 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 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.

[0023] The (a1) propylene-ethylene block copolymer may contain 90 to 60 mass % of the propylene homopolymer (i) and 10 to 40 mass % of the ethylene-propylene copolymer (ii). When the amounts of each component are within these ranges, excellent impact resistance is easily obtained.

[0024] The ethylene content of the propylene homopolymer (i) contained in the (a1) propylene-ethylene block copolymer may be 4% by mass or less. By ensuring that the ethylene content is equal to or less than the upper limit, heat resistance can be imparted to the film, making it easier to prevent fusion on the inner surface of the packaging bag after retort treatment.

[0025] The ethylene content of the ethylene-propylene copolymer (ii) contained in the propylene-ethylene block copolymer (a1) is not particularly limited, but can be in the range of 20 to 40 mass%. When the ethylene content is equal to or less than the upper limit, the tackiness of the product (propylene-ethylene block copolymer (a1)) can be suppressed, and contamination due to tackiness of the product during production is less likely to occur, making it easier to maintain excellent productivity. When the ethylene content is equal to or greater than the lower limit, it is easier to obtain excellent impact resistance.

[0026] The ethylene content of the (a1) propylene-ethylene block copolymer as a whole may be less than 20% by mass, may be 7.0 to 15.0% by mass, or may be 7.5 to 12.0% by mass. When the ethylene content is equal to or less than the upper limit, excellent impact resistance is easily obtained while maintaining excellent heat resistance. When the ethylene content is equal to or more than the lower limit, excellent impact resistance is easily obtained.

[0027] As described above, the (a1) propylene-ethylene block copolymer contains a propylene homopolymer component (i) and an ethylene-propylene copolymer component (ii) as constituent components. In the (a1) propylene-ethylene block copolymer, the ratio Mw(EPR) / Mw(PP) of the weight-average molecular weight Mw(EPR) of the ethylene-propylene copolymer (ii) to the weight-average molecular weight Mw(PP) of the propylene homopolymer (i) may be 1.5 or less. This facilitates imparting excellent impact resistance while maintaining heat resistance. From this perspective, the ratio may be 1.3 or less, or may be 1.2 or less. The lower limit of the ratio is not particularly limited, but may be, for example, 1.1 or more.

[0028] The weight-average molecular weight ratio Mw(EPR) / Mw(PP) can be measured as follows. First, 200 ml of n-decane is added to 5 g of (a1) propylene-ethylene block copolymer and completely dissolved at 145°C. After cooling to room temperature, the precipitate is filtered and separated. The filtered product is designated as propylene homopolymer component (i), and the remaining solution is completely solvent-free in a dryer to obtain ethylene-propylene copolymer component (ii). 20 ml of mobile phase for GPC measurement is added to each of the resulting components, and after dissolving at 145°C, the mixture is hot-filtered through a sintered filter with a pore size of 1.0 μm. The filtrate is used as the measurement solution. The molecular weight is measured using a Tosoh HLC-8321GPC / HT high-temperature gel permeation chromatograph, with a column size of 7.5 mm inner diameter, 300 mm length, a temperature of 140 °C, o-dichlorobenzene (stabilizer: 0.025% BHT) as the mobile phase, and a flow rate of 1.0 ml, using a simple PS conversion method. The ratio of the weight average molecular weight Mw(PP) of the propylene homopolymer component (i) to the weight average molecular weight Mw(EPR) of the ethylene-propylene copolymer component (ii) is defined as the weight average molecular weight ratio Mw(EPR) / Mw(PP).

[0029] [(a2) Ethylene-based polymer having an ethylene content of 80% by mass or more] As the (a2) ethylene-based polymer, linear low-density polyethylene, ethylene-α-olefin copolymer elastomer, ethylene-propylene copolymer elastomer, etc. By including the (a2) ethylene-based polymer, the sealant film can be imparted with even better impact resistance.

[0030] (a2) As an ethylene polymer, a polymer having a density of 0.870 to 0.920 g / cm 3 This makes it easy to obtain excellent impact resistance.

[0031] (a2) The ethylene polymer to be used has an ethylene content of 80% by mass or more, which makes it easier to obtain excellent impact resistance.

[0032] [Other resin components] The resin component (A) may contain other resin components that do not fall under the category of (a1) propylene-ethylene block copolymer and (a2) ethylene-based polymer. Examples of other resin components include homopolypropylene, copolymers of propylene and other monomers, and ethylene-based polymers with an ethylene content of less than 80% by mass. Examples of other monomers used in the polymer include α-olefins such as ethylene, 1-butene, and 1-hexene. The copolymer may be a random copolymer, a block copolymer, or a graft copolymer.

[0033] The content of the (a1) propylene-ethylene block copolymer in the (A) resin component is 70 to 97 mass% based on the total amount of the (A) resin component. When the content of the (a1) propylene-ethylene block copolymer is 70 mass% or more, the sealant film is likely to maintain excellent heat resistance. When the content of the (a1) propylene-ethylene block copolymer is 97 mass% or less, the sealant film is able to be imparted with excellent impact resistance. From the above viewpoints, the content of the (a1) propylene-ethylene block copolymer is preferably 75 to 85 mass%, more preferably 78 to 82 mass%.

[0034] The content of the (a2) ethylene polymer in the (A) resin component is 3 to 30% by mass based on the total amount of the (A) resin component. When the content of the (a2) ethylene polymer is 3% by mass or more, the sealant film can be imparted with excellent impact resistance. When the content of the (a2) ethylene polymer is 30% by mass or less, the sealant film can easily maintain excellent heat resistance. From the above viewpoints, the content of the (a2) ethylene polymer is preferably 10 to 25% by mass, and more preferably 15 to 20% by mass.

[0035] From the viewpoint of obtaining a sealant film having superior heat resistance and impact resistance, the total content of the (a1) propylene-ethylene block copolymer and the (a2) ethylene polymer in the (A) resin component is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, based on the total amount of the (A) resin component, and this content may be 100% by mass.

[0036] ((B) Zinc oxide particles) The sealant film further contains (B) zinc oxide particles in addition to (A) resin component. The content of (B) zinc oxide particles is 0.05 to 4.5 mass% based on the total amount of the sealant film. By setting the content of (B) zinc oxide particles to the above lower limit or more, excellent odor adsorption properties can be obtained. Furthermore, by setting the content of (B) zinc oxide particles to the above upper limit or less, impact resistance is less likely to decrease. From the above viewpoints, the content of (B) zinc oxide particles is preferably 0.05 to 4.0 mass%, more preferably 0.1 to 2.0 mass%.

[0037] The (B) zinc oxide particles may be blended into all layers of the sealant film, or the sealant film may be made up of multiple layers, with some layers containing the (B) zinc oxide particles and others not containing the (B) zinc oxide particles.

[0038] The average spherical equivalent diameter of the (B) zinc oxide particles can be 100 nm or less, and may be 90 nm or less. This increases the surface area of ​​the (B) 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 (B) zinc oxide particles.

[0039] [(B) Method for calculating the equivalent spherical diameter of zinc oxide particles] (B) The sealant film containing zinc oxide particles was embedded in epoxy resin, then trimmed and surfaced using an ultramicrotome equipped with a diamond knife to prepare ultrathin sections. The cross-section of the ultrathin section ((B) zinc oxide particle-containing layer) was then observed at 50,000x magnification 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 the 3281 nm x 3281 nm x 625 nm area, and the diameter of a sphere equivalent to that volume was calculated. The average value was used as the mean spherical equivalent diameter.

[0040] (Layer structure of sealant film) Although the sealant film 10 shown in Fig. 1 is a single-layer film, the sealant film may be a multi-layer film. Figs. 2 and 3 are cross-sectional views of sealant films according to one embodiment of the present invention. The sealant film 20 shown in Fig. 2 comprises a first layer 1 and a second layer 2. The sealant film 30 shown in Fig. 3 comprises a first layer 1, a second layer 2, and a third layer 3. The sealant film may also comprise four or more layers.

[0041] In the sealant film 20, the composition of the first layer 1 and the composition of the second layer 2 may be the same or different, as long as the sealant film 20 as a whole satisfies the above-mentioned conditions of the sealant film of the present invention. The (B) zinc oxide particles may be contained in only one of the first layer 1 and the second layer 2, or in both. From a hygienic standpoint, it is preferable that the (B) zinc oxide particles are not contained in the layer that comes into contact with the contents when the sealant film 20 is made into a packaging bag. Therefore, in the sealant film 20, when the first layer 1 is on the content side, it is preferable that the first layer 1 does not contain the (B) zinc oxide particles, and the second layer 2 contains the (B) zinc oxide particles.

[0042] In the sealant film 30, the compositions of the first layer 1, the second layer 2, and the third layer 3 may be the same or different, as long as the sealant film 30 as a whole satisfies the above-described requirements for the sealant film of the present invention. The (B) zinc oxide particles may be contained in any one, two, or all of the first layer 1, second layer 2, and third layer 3. From a hygienic standpoint, it is preferable that the (B) zinc oxide particles are not contained in the layer that comes into contact with the contents when the sealant film 30 is made into a packaging bag. Therefore, in the sealant film 30, when the first layer 1 faces the contents, it is preferable that the first layer 1 does not contain (B) zinc oxide particles, and one or both of the second layer 2 and the third layer 3 contain (B) zinc oxide particles.

[0043] The thickness of the sealant film (total thickness in the case of a multilayer film) can be 50 μm or more to maintain excellent impact resistance. There is no particular upper limit, but if the film is too thick, it will be cost-intensive. For this reason, the thickness of the sealant film can be 100 μm or less, and may be 50 to 80 μm.

[0044] When the sealant film is a multilayer film, the thickness of each layer is not particularly limited, but when the multilayer film has layers containing (B) zinc oxide particles and layers not containing (B) zinc oxide particles, the total thickness of the layers containing (B) zinc oxide particles may be 10 μm or more, 15 to 50 μm, or 20 to 40 μm, and the total thickness of the layers not containing (B) zinc oxide particles may be 5 μm or more, 7 to 40 μm, or 10 to 30 μm.

[0045] <Method of manufacturing sealant film> The method for producing a sealant film according to the present embodiment includes forming a sealant film using a sealant resin composition containing (A) a resin component and (B) zinc oxide particles, wherein the (A) resin component contains (a1) a propylene-ethylene block copolymer and (a2) an ethylene-based polymer having an ethylene content of 80% by mass or more, the content of the (a1) propylene-ethylene block copolymer in the sealant film being 70 to 97% by mass based on the total amount of the (A) resin components in the sealant film, the content of the (a2) ethylene-based polymer in the sealant film being 3 to 30% by mass based on the total amount of the (A) resin components in the sealant film, and the content of the (B) zinc oxide particles in the sealant film being 0.05 to 4.5% by mass based on the total amount of the sealant film.

[0046] In the manufacturing method of this embodiment, when the sealant film is a multilayer film, at least one of the multiple layers may be formed using the above-mentioned resin composition. For example, at least one of the multiple layers constituting the multilayer film may be formed using a resin composition containing (A) the resin component and (B) zinc oxide particles, and the remaining layers may be formed using a composition that does not contain (B) the zinc oxide particles. Note that all of the multiple layers constituting the multilayer film may be formed using a resin composition containing (A) the resin component and (B) the zinc oxide particles. The composition forming each layer may be adjusted so that the final sealant film satisfies the above-mentioned conditions.

[0047] When the sealant film is a monolayer film, the sealant film can be formed using a resin composition containing (A) a resin component and (B) zinc oxide particles, wherein the (A) resin component contains (a1) a propylene-ethylene block copolymer and (a2) an ethylene-based polymer having an ethylene content of 80% by mass or more, the content of the (a1) propylene-ethylene block copolymer in the resin composition being 70 to 97% by mass based on the total amount of the (A) resin components in the resin composition, the content of the (a2) ethylene-based polymer in the resin composition being 3 to 30% by mass based on the total amount of the (A) resin components in the resin composition, and the content of the (B) zinc oxide particles in the resin composition being 0.05 to 4.5% by mass based on the resin composition.

[0048] The method for producing the sealant 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.

[0049] 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.

[0050] ((B) Manufacturing method of masterbatch containing zinc oxide particles) The zinc oxide particles (B) to be incorporated into the sealant film can be prepared by kneading them with propylene-ethylene block copolymer (a1) in a twin-screw kneader to prepare a masterbatch. This prevents secondary aggregation of the zinc oxide particles (B), making it easier to achieve excellent odor adsorption properties. Twin-screw kneaders can include co-rotating twin-screw extruders and counter-rotating twin-screw extruders, and the screw configuration can be any type, including full-flighted screws and kneading disk types.

[0051] The content of (B) zinc oxide particles in the masterbatch containing the (B) zinc oxide particles is not particularly limited, but can be 10 to 30 mass% based on the total amount of the masterbatch. When the content of (B) zinc oxide particles in the masterbatch is equal to or less than the upper limit, secondary aggregation of the (B) zinc oxide particles in the masterbatch can be suppressed, making it easier to achieve excellent odor adsorption. When the content of (B) zinc oxide particles in the masterbatch is equal to or greater than the lower limit, it is possible to prevent the masterbatch from becoming too concentrated when diluting the masterbatch during film formation, making it easier to distribute the zinc oxide particles throughout the film during film formation, making it easier to achieve excellent odor adsorption.

[0052] The obtained sealant film may be subjected to a surface modification treatment to improve suitability for subsequent processes as needed. For example, to improve printability when used as a single film or lamination suitability when used as a laminate, 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.

[0053] <Packaging material> The sealant film may be used as a single film or may be laminated with a substrate to form a laminate, and there are no particular restrictions on how it may be used as a packaging material.

[0054] When the sealant film is laminated with a substrate, the packaging material can include the above-mentioned sealant film and substrate. Specifically, such packaging material can be obtained by laminating at least one layer of a substrate such as a biaxially oriented polyamide film (ONy), a biaxially oriented polyester film (PET), printing paper, or a metal foil (AL foil) onto the above-mentioned sealant film 10, 20, or 30 to form a laminate.

[0055] 4 and 5 are cross-sectional views of a packaging material according to one embodiment of the present invention. The packaging material 100 shown in FIG. 4 comprises, in this order, a sealant film 10, an adhesive layer 11, a base film 12, an adhesive layer 11, and a base film 13. The packaging material 200 shown in FIG. 5 comprises, in this order, a sealant film 10, an adhesive layer 11, a base film 12, an adhesive layer 11, an AL foil 14, an adhesive layer 11, and a base film 13. In FIGS. 4 and 5, the sealant film 10 may be replaced with a multilayer sealant film 20 or 30. In this case, the sealant film 20 or 30 is laminated so that the surface that contacts the contents (e.g., the surface on the first layer 1 side) is the surface opposite the adhesive layer 11. A typical dry lamination method in which the films that constitute the laminate are bonded together using an adhesive can be suitably used to produce the laminate. However, if necessary, a method in which the multilayer film is directly extrusion laminated onto the base can also be used.

[0056] 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.

[0057] <Package> The packaging body may be made into a bag from the above packaging material, and there is no particular limitation on the bag-making style. For example, the above 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 sealant film as a sealing material. [Example]

[0058] The present invention will be described in detail below using examples, but the present invention is not limited to the following examples.

[0059] <Preparing various materials> The following propylene-ethylene block copolymer (a1-1), ethylene polymers (a2-1) and (a2-2), propylene-ethylene-α-olefin copolymer (a3-1), and propylene-1-butene copolymer (a3-2) were prepared as the (A) resin component. The following zinc oxide masterbatch (B-1) was also prepared as the (B) zinc oxide particles.

[0060] (Propylene-ethylene block copolymer (a1-1)) A propylene-ethylene block copolymer (ethylene content: 7.9% by mass) has a melt flow rate (MFR: ISO 1133) of 1.8 g / 10 min (temperature 230°C, load 2.16 kg), contains 81.5% by mass of propylene homopolymer and 18.5% by mass of ethylene-propylene copolymer, the ethylene content of the propylene homopolymer is 3.2% by mass, the ethylene content of the ethylene-propylene copolymer is 28.7% by mass, and the ratio of the weight average molecular weight of the ethylene-propylene copolymer, Mw(EPR), to the weight average molecular weight of the propylene homopolymer, Mw(PP), is 1.16.

[0061] (Ethylene polymer (a2-1)) As the ethylene polymer (a2-1), SP1510 (trade name, ethylene content: 90% by mass or more), a linear low-density polyethylene manufactured by Prime Polymer Co., Ltd., was prepared.

[0062] (Ethylene polymer (a2-2)) As the ethylene polymer (a2-2), an ethylene-α-olefin copolymer elastomer A-1085S (trade name, ethylene content: 80% by mass or more) manufactured by Mitsui Chemicals, Inc. was prepared.

[0063] (Propylene-ethylene-α-olefin copolymer (a3-1)) As the propylene-ethylene-α-olefin copolymer (a3-1), PN-3560 (trade name, ethylene content: 5% by mass), a propylene-ethylene-α-olefin copolymer elastomer manufactured by Mitsui Chemicals, Inc., was prepared.

[0064] (Propylene-1-butene copolymer (a3-2)) As the propylene-1-butene copolymer (a3-2), XM-7090 (trade name, ethylene-free), a propylene-α-olefin copolymer elastomer manufactured by Mitsui Chemicals, Inc., was prepared.

[0065] (Zinc oxide masterbatch (B-1)) The zinc oxide masterbatch (B-1) was prepared by melt-mixing 20% ​​by mass of zinc oxide particles with a primary particle size of 35 nm and no surface coating treatment with 80% by mass of propylene-ethylene block copolymer (a1-1) using a co-rotating twin-screw extruder, extruding the mixture into strands, and pelletizing it.

[0066] <Preparation of sealant film> Example 1 A resin mixture was prepared by mixing 90 parts by mass of a propylene-ethylene block copolymer (a1-1) and 10 parts by mass of an ethylene polymer (a2-1) in the form of pellets, and further mixing 1.01 parts by mass of a zinc oxide masterbatch (B-1) per 100 parts by mass of the propylene-ethylene block copolymer (a1-1) and the ethylene polymer (a2-1). The resin mixture was kneaded in a molten state using an extruder controlled at 250°C, and the thickness was adjusted to 60 μm using a T-die extruder equipped with a feed block, producing the sealant film of Example 1.

[0067] (Examples 2 and 3) Sealant films of Examples 2 and 3 were produced in the same manner as in Example 1, except that the blending ratio of the ethylene polymer (a2-1) was changed as shown in Table 1.

[0068] (Examples 4 and 5) Sealant films of Examples 4 and 5 were produced in the same manner as in Example 1, except that the blending ratio of the zinc oxide masterbatch (B-1) was changed as shown in Table 1.

[0069] Example 6 A sealant film of Example 6 was produced in the same manner as in Example 2, except that the ethylene polymer (a2-2) was used as the ethylene polymer.

[0070] Example 7 A sealant film of Example 7 was produced in the same manner as in Example 3, except that the ethylene polymer (a2-2) was used as the ethylene polymer.

[0071] Example 8 A resin mixture was prepared by mixing 90 parts by mass of propylene-ethylene block copolymer (a1-1) and 10 parts by mass of ethylene polymer (a2-1) in pellet form as a first resin mixture for forming the first layer. A resin mixture was prepared by mixing 90 parts by mass of propylene-ethylene block copolymer (a1-1) and 10 parts by mass of ethylene polymer (a2-1) in pellet form as a second and third resin mixture for forming the second and third layers. A resin mixture was prepared by further mixing 0.30 parts by mass of zinc oxide masterbatch (B-1) with 100 parts by mass of the propylene-ethylene block copolymer (a1-1) and ethylene polymer (a2-1) in total.

[0072] Using three extruders controlled at a temperature of 250°C, the first resin mixture was extruded from one extruder and the second and third resin mixtures were extruded from the other two extruders, and each was kneaded in a molten state.Then, using a T-die extruder with a feed block, the first layer was 10 μm thick, and the second and third layers were each 25 μm thick, for a total thickness of 60 μm, to produce the sealant film of Example 8, which had a three-layer structure of first layer / second layer / third layer.

[0073] Examples 9 to 10 The sealant films of Examples 9 and 10 were produced in the same manner as in Example 8, except that the blending ratio of the zinc oxide masterbatch (B-1) in the second layer and the third layer was changed as shown in Table 2, and the first layer was laminated to a thickness of 40 μm, the second layer and the third layer were laminated to a thickness of 10 μm each, for a total thickness of 60 μm.

[0074] (Comparative Example 1) A sealant film of Comparative Example 1 was produced in the same manner as in Example 1, except that the zinc oxide masterbatch (B-1) was not mixed into the resin mixture.

[0075] (Comparative Example 2) A sealant film of Comparative Example 2 was produced in the same manner as in Example 1, except that no ethylene polymer was mixed into the resin mixture.

[0076] (Comparative Example 3) A sealant film of Comparative Example 3 was produced in the same manner as in Example 1, except that the ethylene polymer (a2-1) was replaced with a propylene-ethylene-α-olefin copolymer (a3-1).

[0077] Comparative Example 4 A sealant film of Comparative Example 4 was produced in the same manner as in Example 1, except that the ethylene polymer (a2-1) was replaced with a propylene-1-butene copolymer (a3-2).

[0078] (Comparative Examples 5 to 6) The sealant films of Comparative Examples 5 and 6 were prepared in the same manner as in Example 1, except that the blending ratio of the propylene-ethylene block copolymer (a1-1) and the ethylene polymer (a2-1) was changed as shown in Table 3.

[0079] (Comparative Example 7) A sealant film of Comparative Example 7 was produced in the same manner as in Example 1, except that the blending ratio of the zinc oxide masterbatch (B-1) was changed as shown in Table 3.

[0080] (Comparative Example 8) A sealant film of Comparative Example 8 was produced in the same manner as in Example 9, except that the blending ratio of the zinc oxide masterbatch (B-1) in the second layer and the third layer was changed as shown in Table 4.

[0081] <Various evaluations> The sealant films obtained in each example were evaluated as follows, and the results are shown in Tables 1 to 4.

[0082] (Preparation of laminate) 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 sealant film (polypropylene film) obtained in each example were bonded together using a urethane adhesive by dry lamination to produce a laminate with the following configuration: When the sealant film had a three-layer structure, the third layer was bonded on the AL foil side (the first layer was on the content side when the packaging bag was formed). Laminated structure: PET / adhesive / ONy / adhesive / AL foil / adhesive / polypropylene film

[0083] (Hydrogen sulfide reduction rate) Two sheets of the above laminate were prepared, with the sealant films facing each other. Using a heat sealer manufactured by Tester Sangyo Co., Ltd., three sides were heat-sealed under the following conditions: sealing pressure 0.2 MPa, sealing time 1 second, sealing width 5 mm, and sealing temperature 200°C. This produced a packaging bag with an opening (three-sided bag: inner dimensions 80 mm x 110 mm). The packaging bag was then filled with 30 mL of a cysteine ​​solution containing 0.03% by weight of L-cysteine. The opening was heat-sealed under the same conditions as above, and the bag was then 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, Inc. The hydrogen sulfide reduction rate was calculated by reacting the collected solution with the 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 sealant film obtained in each example relative to the absorbance measured using a packaging bag that did not contain zinc oxide (a packaging bag using the sealant film of Comparative Example 1).

[0084] (Impact resistance evaluation) Two sheets of the sealant film obtained in each example were prepared, placed opposite each other, and heat-sealed on three sides to produce a bag size (inner dimensions) of 90 mm x 160 mm 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. This resulted in a packaging bag (three-sided bag) with an opening. When the sealant film had a three-layer structure, the first layers of the two sealant films were placed opposite each other for heat sealing. This packaging bag was filled with 150 ml of 0.1% by weight saline solution, and the opening was heat-sealed under the same conditions as above. The retort-treated bag was then stored in a 0°C refrigerator for 3 days. The sample was then removed from the 0°C refrigerator and immediately dropped vertically from a height of 0.7 m. Ten samples were used, and the percentage of packaging bags that remained intact after 10 drops (survival rate) was determined. Regarding impact resistance (cold impact resistance), a survival rate of 40% or more was judged to be good.

[0085] (Heat resistance evaluation) The films obtained in each example were heat-sealed together using a heat sealer manufactured by Tester Sangyo Co., Ltd. under the following conditions: sealing pressure 0.03 MPa, sealing time 30 seconds, sealing width 10 mm, and sealing temperature 135°C. The heat-sealed films were then 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 fusion strength of the heat-sealed portions. Regarding heat resistance, a fusion strength of 2 N / 15 mm or less was considered good.

[0086] [Table 1]

[0087] [Table 2]

[0088] [Table 3]

[0089] [Table 4] [Industrial Applicability]

[0090] The sealant film of the present invention has excellent odor adsorption properties for the sulfur odor emitted from retort foods, as well as excellent impact resistance that prevents the packaging bag from breaking when dropped, and heat resistance that prevents the inner surface from fusing even during high-temperature heat sterilization, making it suitable for use as a sealant film for retort packaging. [Explanation of symbols]

[0091] 1...first layer, 2...second layer, 3...third layer, 10, 20, 30...sealant film, 11...adhesive layer, 12, 13...base film, 14...AL foil, 100, 200...packaging material.

Claims

1. A sealant film containing (A) a resin component and (B) zinc oxide particles, the (A) resin component contains (a1) a propylene-ethylene block copolymer and (a2) an ethylene-based polymer having an ethylene content of 80% by mass or more, the content of the (a1) propylene-ethylene block copolymer is 70 to 97 mass% based on the total amount of the (A) resin component, the content of the (a2) ethylene polymer is 3 to 30 mass% based on the total amount of the (A) resin component, A sealant film, wherein the content of the (B) zinc oxide particles is 0.05 to 4.5 mass% based on the total amount of the sealant film.

2. The sealant film according to claim 1, wherein the ethylene content of the propylene-ethylene block copolymer (a1) is less than 20% by mass.

3. 2. The sealant film according to claim 1, wherein the total content of the propylene-ethylene block copolymer (a1) and the ethylene-based polymer (a2) is 80 mass% or more based on the total amount of the resin component (A).

4. The density of the (a2) ethylene polymer is 0.870 to 0.920 g / cm ３ The sealant film according to claim 1, wherein

5. The sealant film according to claim 1, having a thickness of 50 μm or more.

6. A method for producing a sealant film, comprising a step of forming a sealant film using a sealant resin composition containing (A) a resin component and (B) zinc oxide particles, the (A) resin component contains (a1) a propylene-ethylene block copolymer and (a2) an ethylene-based polymer having an ethylene content of 80% by mass or more, the content of the propylene-ethylene block copolymer (a1) in the sealant film is 70 to 97 mass% based on the total amount of the resin component (A) in the sealant film; the content of the (a2) ethylene-based polymer in the sealant film is 3 to 30 mass% based on the total amount of the (A) resin component in the sealant film, The method for producing a sealant film, wherein the content of the zinc oxide particles (B) in the sealant film is 0.05 to 4.5 mass% based on the total amount of the sealant film.

7. The method for producing a sealant film according to claim 6, wherein the ethylene content of the propylene-ethylene block copolymer (a1) is less than 20% by mass.

8. 7. The method for producing a sealant film according to claim 6, wherein the total content of the propylene-ethylene block copolymer (a1) and the ethylene-based polymer (a2) in the sealant film is 80 mass% or more based on the total amount of the resin component (A) in the sealant film.

9. The density of the (a2) ethylene polymer is 0.870 to 0.920 g / cm ３ The method for producing a sealant film according to claim 6,

10. The method for producing a sealant film according to claim 6, wherein the sealant film has a thickness of 50 μm or more.

11. A packaging material comprising the sealant film according to any one of claims 1 to 5 and a substrate.

12. A package produced from the packaging material according to claim 11.

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