Sealant film, packaging material and packaging bag

Abstract

To provide a sealant film which enables material recycling of a recycled material containing two or more kinds of resins, while sufficiently having heat sealabilty and mechanical characteristics, a packaging material and a packaging bag.SOLUTION: A sealant film 1a includes a recycled material-containing layer 2 containing a recycled material containing two or more kinds of resins, and a sealant layer 3 laminated on one main surface of the recycled material-containing layer, wherein the sealant film 1a is subjected to electron beam irradiation treatment, the recycled material-containing layer 2 contains a domain having transmission brightness, when transmission observation is carried out from a plan-view direction of the sealant film, smaller than that of its periphery, and the domain has a maximum area of 1,000 μm2 or less and a maximum aspect ratio of 10 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a sealant film, a packaging material, and a packaging bag. [Background technology]

[0002] In general, plastic films have properties such as light weight, chemical stability, ease of processing, flexibility and strength, and the ability to be mass-produced, and are therefore used in a wide variety of applications. Their applications are diverse, including packaging materials for food products, pharmaceuticals, etc., intravenous drip packs, shopping bags, posters, tapes, optical films used in LCD televisions, etc., protective films, window films attached to windows, greenhouses, building materials, etc. Specific materials include thermoplastic resins such as polyethylene, polypropylene, polystyrene, polymethyl methacrylate, polycarbonate, polyamide, polyethylene terephthalate, and polybutylene terephthalate, and thermosetting resins such as epoxy resin, polyurethane, and polyimide.

[0003] Appropriate plastic materials are selected depending on the application, and multiple types are sometimes layered to form laminates. Mixing multiple plastic materials into a single layer can also be used to compensate for the shortcomings of a single material. Other examples include laminates with aluminum foil to provide light blocking properties, printed layers with ink designs to enhance product design, and adhesive layers to bond incompatible plastic materials.

[0004] Recycling of plastic products is expected to be a key approach to addressing recent environmental issues, and various recycling methods are being considered. For example, technologies have been established for material recycling of PET bottles, in which collected products are washed, crushed, and reused as raw materials, as well as chemical recycling, in which the products are converted into monomers. Furthermore, Patent Document 1 listed below discloses technology related to a sealant film containing recycled polyethylene resin, and describes that recycled polyethylene can be recovered from used polyethylene molded bodies or waste materials from their production, and can be obtained through various processes such as crushing, washing, filtration, and extraction.

[0005] In contrast, plastic film is made up of a variety of materials, so it is difficult to reuse it as a raw material simply by washing and crushing it. Specifically, because it is a mixture of an unspecified number of resins, it is difficult to obtain uniform melt properties (fluidity) and to mold it, and even if it could be molded, it would lack mechanical strength.

[0006] Due to these restrictions, most plastic films are sent for thermal recycling, but due to the large amount of plastic film in circulation, there is a strong demand for plastic film to be recycled as raw materials for film products such as packaging materials.

[0007] Methods for recycling plastic films have been studied to date. For example, Patent Document 2 below proposes a method for efficiently extracting EVOH (ethylene-vinyl alcohol copolymer) from a multilayer resin molded product containing an EVOH layer that functions as a gas barrier film. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication No. 2022 / 124229 [Patent Document 2] International Publication No. 2022 / 158287 Summary of the Invention [Problem to be solved by the invention]

[0009] However, the above method involves dissolving EVOH in an EVOH extractant and then recovering the EVOH by precipitation, which increases the labor and cost and makes it difficult to use.

[0010] Patent Document 1 proposes a sealant film in which an intermediate layer containing recycled polyethylene is placed between two virgin polyethylene layers made from virgin material that has never been processed, and the film is evaluated for its deodorizing and concealing properties, but does not disclose the specific structure or evaluation of a sealant film that uses plastic film made from various materials as recycled material.

[0011] Therefore, the inventors of the present invention investigated recycling plastic films as raw materials for sealant films and found that when different types of resins are mixed, resin components other than the resin with the highest content ratio form aggregates, which affect the smoothness and physical properties of the film. If this effect significantly impairs the heat-sealing properties and mechanical properties of the film, it becomes difficult to increase the recycled plastic content in packaging materials.

[0012] The present invention has been made in consideration of the above circumstances, and aims to provide a sealant film, a packaging material, and a packaging bag that have sufficient heat sealability and mechanical properties and enable material recycling of recycled materials containing two or more types of resins. [Means for solving the problem]

[0013] The present invention relates to the following [1] to [8].

[0014] [1] A sealant film comprising a recycled material-containing layer containing recycled materials containing two or more resins, and a sealant layer laminated on one main surface of the recycled material-containing layer, wherein the sealant film has been subjected to electron beam irradiation treatment, and the recycled material-containing layer includes domains whose transmission brightness is smaller than that of the surrounding area when the sealant film is observed in a planar view, and the domains have a maximum area of ​​1000 μm 2 and a maximum aspect ratio of 10 or less. [2] The sealant film according to [1], wherein the recycled material-containing layer has an average brightness value of 200 or more in HSV color space data and a standard deviation of brightness of 10 or less. [3] The sealant film according to [1] or [2], wherein the sealant layer contains the same type of resin as the resin with the highest content in the recycled material-containing layer. [4] A sealant film according to any one of [1] to [3], further comprising an auxiliary layer laminated on the other main surface of the recycled material-containing layer, wherein the auxiliary layer contains the same type of resin as the resin with the highest content in the recycled material-containing layer. [5] A sealant film according to any one of [1] to [4], wherein the resin with the highest content ratio among the two or more resins contained in the recycled material is a polyethylene-based resin or a polypropylene-based resin. [6] A packaging material comprising the sealant film according to any one of [1] to [5]. [7] The packaging material described in [6], wherein the content of plastic material contained in the recycled material is 10% by mass or more based on the total amount of plastic material in the packaging material. [8] A packaging bag made from the packaging material described in [6] or [7]. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a sealant film, a packaging material, and a packaging bag that have sufficient heat sealability and mechanical properties and enable material recycling of recycled materials containing two or more types of resins. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic cross-sectional view showing one embodiment of a sealant film according to the present invention. [Figure 2] 10A and 10B are schematic diagrams for explaining the aspect ratio of a low-transmittance lightness region. [Figure 3] FIG. 2 is a schematic cross-sectional view showing another embodiment of the sealant film according to the present invention. [Figure 4] 1 is a schematic cross-sectional view showing one embodiment of a laminate according to the present invention. [Figure 5] 1 is a schematic cross-sectional view showing one embodiment of a packaging material according to the present invention. [Figure 6] FIG. 2 is a schematic cross-sectional view showing another embodiment of a packaging material according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the present invention will be described in detail. Note that Figures 1 to 6 are schematic diagrams, and the size and shape of each part are appropriately exaggerated for ease of understanding. Furthermore, the embodiments shown below are merely examples of configurations for embodying the technical idea of ​​the present invention, and the technical idea of ​​the present invention is not limited to the materials, shapes, structures, etc. of the components described below. The technical idea of ​​the present invention can be modified in various ways within the technical scope defined by the claims.

[0018] <Sealant film> The sealant film of this embodiment comprises a recycled material-containing layer containing recycled material containing two or more types of resin, and a sealant layer laminated on one main surface of the recycled material-containing layer, and has been subjected to electron beam (EB) irradiation treatment.

[0019] Fig. 1 is a schematic cross-sectional view showing one embodiment of a sealant film. The sealant film 1a shown in Fig. 1 includes a recycled material-containing layer 2 and a sealant layer 3 laminated on one main surface of the recycled material-containing layer 2.

[0020] (Recycled material containing layer) Examples of recycled materials contained in the recycled material-containing layer include post-consumer recycled (PCR) materials such as bottles and packaging bags for beverages, detergents, and seasonings that have been collected from the market, food containers for lunch boxes and instant noodles, packaging bags for food and garbage bags, and plastic products such as hangers, stationery, daily necessities, home appliances, and toys; and post-industry recycled (PIR) materials such as defective products that do not become products discharged from factories, scraps generated during the manufacturing process, and plastic products used for transportation and packaging.

[0021] In the sealant film of this embodiment, from the viewpoint of material recycling of plastic films, a laminate (packaging material) made by bonding together multiple types of resin sheets, a packaging bag made from such a laminate, a laminate (packaging material) made by bonding together the same types of resin sheets, or a packaging bag made from such a laminate, or a mixture of these, may be used. Examples of packaging bags include refill pouches for toiletries.

[0022] The recycled material contained in the recycled material-containing layer includes two or more resins. Examples of the two or more resins include thermoplastic resins, thermosetting resins, and cured products thereof (including crosslinked products). The two or more resins also include, for example, resin components (such as thermosetting resins) that constitute adhesives and their cured products.

[0023] Examples of thermoplastic resins include polyolefin resins, acrylic resins, polycarbonate resins, polyester resins, polyamide resins, etc. Examples of thermosetting resins include epoxy resins, polyurethane resins, polyimide resins, etc.

[0024] Examples of polyolefin resins include polyethylene-based resins such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), medium-density polyethylene (MDPE), high-density polyethylene (HDPE), and ethylene-α-olefin copolymers, as well as polypropylene-based resins such as homopolypropylene (PP), block polypropylene, random polypropylene, and propylene-α-olefin copolymers.

[0025] Examples of polyester resins include polyethylene terephthalate, polybutylene terephthalate, and polylactic acid.

[0026] An example of the polyamide resin is nylon 6.

[0027] The two or more resins may include a first resin that is contained in the recycled material at the highest ratio and a second resin that is incompatible with the first resin or that may form aggregates in the first resin. The type of resin contained in the recycled material-containing layer can be confirmed using a microscopic infrared spectrophotometer or the like.

[0028] The first resin and the second resin may be the following combinations: (a) Thermoplastic resins, thermosetting resins and their hardened products (b) Hydrocarbon-based resins and heteroatom-containing resins (c) A resin that dissolves in a predetermined solvent and a resin that does not dissolve in the predetermined solvent

[0029] Examples of the hydrocarbon resin in (b) include polyolefin resins and polystyrene resins, and examples of the heteroatom-containing resin include acrylic resins, polyester resins, and polyamide resins.

[0030] The predetermined solvent in (c) includes aromatic hydrocarbons, chlorinated hydrocarbons, etc. The resin insoluble in the predetermined solvent includes crosslinked resins, cured thermosetting resins, etc.

[0031] The first resin having the highest content in the recycled material may be a polyethylene resin or a polypropylene resin from the viewpoint of recycling packaging bags for pouch products, etc. In this case, the second resin may be, for example, at least one of polyester resin, polyamide resin, and a resin component constituting an adhesive and its cured product.

[0032] The content of the first resin in the recycled material-containing layer may be 75 to 98 mass %, 75 to 95 mass %, or 80 to 90 mass % based on the total mass of the recycled material-containing layer.

[0033] The content of the second resin in the recycled material-containing layer may be 2 to 33 parts by mass, 5 to 33 parts by mass, or 11 to 25 parts by mass relative to 100 parts by mass of the first resin.

[0034] The content of recycled material in the recycled material-containing layer may be 13% by mass or more, 33% by mass or more, 50% by mass or more, or 100% by mass, based on the total mass of the recycled material-containing layer.

[0035] The resin having the highest content in the recycled material-containing layer may be the same as the resin having the highest content in the recycled material, for example, at least one polyethylene resin selected from the group consisting of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), medium-density polyethylene (MDPE), and high-density polyethylene (HDPE).

[0036] The recycled material-containing layer may contain virgin material such as virgin resin. The virgin material may be blended so that the resin with the highest content in the recycled material is the same as the resin with the highest content in the recycled material-containing layer. The virgin material may be, for example, the same as the polyolefin resin described above, and may be at least one polyethylene resin selected from the group consisting of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), medium-density polyethylene (MDPE), and high-density polyethylene (HDPE).

[0037] The virgin resin may be a petroleum-derived resin or a biomass-derived resin. The biomass-derived resin may be a biomass-derived polyethylene-based resin. Examples of the biomass-derived polyethylene-based resin include a homopolymer of plant-derived ethylene derived from bioethanol obtained from plant raw materials, and a copolymer of the plant-derived ethylene with other monomers.

[0038] The recycled material-containing layer includes a domain (hereinafter also referred to as a "low transmission brightness region") whose transmission brightness is lower than the surrounding area when the sealant film is observed through transmission from a direction in which the sealant film is viewed in plan view, and the domain has a maximum area of ​​1000 μm 2 and the maximum aspect ratio is 10 or less.

[0039] The maximum area and maximum aspect ratio of the low-transmittance lightness region are calculated by the following procedure. (i) Using a stereomicroscope system SZX16 (product name, manufactured by Olympus Corporation), observation images (image size: 243 μm × 851 μm) of the sealant film in the planar direction are obtained at 10 random locations. (ii) The 10 images obtained are analyzed using WinROOF2021 (product name, manufactured by Mitani Corporation). In the image analysis, the low-transmittance brightness region and the surrounding high-transmittance brightness region are binarized to calculate the area, minimum diameter, and maximum diameter of each low-transmittance brightness region. Note that, when binarizing, the visual shape of the low-transmittance brightness region can be matched with the colored range by appropriately combining the following operations. (a) Adjusting brightness and contrast to emphasize low-transparency areas (b) Adjust the threshold to match the visible low-transmittance brightness area with the colored range. (c) If there are areas where adjacent low-transmittance brightness areas are recognized as one area, or areas where perforated low-transmittance brightness areas are recognized as multiple areas, perform division or integration processing as necessary.

[0040] 2 is a schematic diagram illustrating the aspect ratio of a low-transmission brightness region. The low-transmission brightness region 20 and the surrounding high-transmission brightness region 30 are shown in FIG. 2. The aspect ratio of the low-transmission brightness region 20 is expressed as the maximum diameter (long axis) D L and the minimum diameter (minor axis) D S Relative to D L / D S It should be noted that the minimum value of the aspect ratio is 1, and the shape of the low transmittance lightness area is not limited to the elliptical shape shown in FIG.

[0041] The maximum area of ​​the low transmittance brightness region identified by the above method is 1000 μm 2 exceeding 1000 μm 2 If low-transmittance brightness regions exceeding this value exist, localized swelling due to the agglomerates will occur on the film surface, resulting in reduced heat-sealing properties and mechanical properties. Furthermore, if the maximum aspect ratio of the low-transmittance brightness regions exceeds 10, i.e., if low-transmittance brightness regions with an aspect ratio of more than 10 exist, they will combine with adjacent low-transmittance brightness regions to form pseudo-large agglomerates, with an area of ​​1000 μm or more. 2 This brings about the same disadvantage as when there is a low transmittance area exceeding 100%.

[0042] In order to adapt to general manufacturing equipment and increase the recycled content of the sealant film, the maximum area of ​​the low transmittance brightness region is 50 μm 2 It may be more than 200 μm 2 It may be more than 400 μm 2 The maximum aspect ratio of the low-transmittance lightness region may be 6 or more.

[0043] When a film in the form of a product such as a pouch is used as a raw material for recycled materials, it may be contaminated with coloring components such as ink. In this case, if the colored portion is localized in the recycled material-containing layer, the appearance becomes significantly poor due to color unevenness. Therefore, when the film is used as a product, it is necessary to add a white printed layer or a white layer containing a white pigment. In contrast, with the sealant film according to this embodiment, even if the recycled material contains a coloring component such as ink, the maximum area and maximum aspect ratio of the low-transmittance lightness region satisfy the above-mentioned conditions, thereby suppressing the appearance defect. This avoids the disadvantage of the increased environmental impact due to the need for materials and processes to provide the above-mentioned additional layers compared to when a sealant film is produced from virgin material alone.

[0044] From the same viewpoint as above, it is preferable that the low transmittance lightness region is dispersed over the entire surface of the recycled material-containing layer rather than being localized, resulting in high uniformity of color.

[0045] From the same viewpoint as above, the recycled material-containing layer may have an average brightness value of 200 or more and a standard deviation of brightness of 10 or less in HSV color space data.

[0046] The average value and standard deviation of the brightness in the HSV color space data of the recycled material-containing layer are calculated by the following procedure. (i) The sealant film is cut into a size of ±200 mm width from the center in the width direction (400 mm width) and 250 mm in the machine direction. (ii) The cut-out sample is scanned using a digital full-color multifunction printer MP C6503 (manufactured by Ricoh Co., Ltd., product name) under the following reading conditions to obtain an image. [Reading conditions] Type: Full color, text and photos, Resolution: 600, Size: A3 (iii) The obtained image is analyzed using the image analysis software ImageJ to calculate the average brightness value and standard deviation for the entire image. The image analysis involves converting the image saved in TIF format to an HSB stack, and obtaining the average value and standard deviation calculated from the V value (brightness) histogram from the histogram analysis results for the HSV color space data. The V value ranges from 0 to 255.

[0047] From the viewpoint of adjusting the color when the sealant film is used as a transparent packaging material, the recycled material-containing layer may have an average brightness of 210 to 240 and a standard deviation of brightness of 6 or less.

[0048] The recycled material-containing layer may have a thickness of 20 to 80 μm.

[0049] In order to reduce the maximum area and maximum aspect ratio of the low transmittance brightness region in the recycled material-containing layer, for example, the following adjustment means can be mentioned. (a) Reducing the proportion of recycled material in the recycled material-containing layer (b) Increasing the content of the first resin in the recycled material. (c) When extruding a recycled material-containing layer, increase the screw rotation speed. (d) When extruding the recycled material-containing layer, the narrowing of the flow path is avoided as much as possible, and a mechanism is created in which elongation stress is not easily applied. (e) Recycled materials are used by mixing them with pelletized or virgin resin using a twin-screw extruder to form a masterbatch.

[0050] In order to increase the average brightness in the recycled material-containing layer, for example, the maximum area of ​​the low-transmittance brightness region can be reduced by the above-mentioned adjusting means, and in order to reduce the standard deviation of brightness in the recycled material-containing layer, for example, the resin to be mixed with the recycled material can be selected to increase the fluidity so that the domains forming the low-transmittance brightness region are not localized.

[0051] (sealant layer) Examples of resins that form the sealant layer include polyethylene, polypropylene, polystyrene, polymethyl methacrylate, ethylene vinyl acetate, polyvinyl alcohol, ethylene-vinyl alcohol copolymer, polyvinylidene chloride, polyacrylonitrile, polylactic acid, cyclic polyolefin, polycarbonate, polyamide, polyethylene terephthalate, polybutylene terephthalate, and derivatives thereof. These may be used alone or in combination of two or more.

[0052] From the viewpoint of heat sealing property, the sealant layer may contain the same type of resin as the resin with the highest content in the recycled material-containing layer, and virgin resin may be blended to achieve this. For example, if the resin with the highest content in the recycled material-containing layer is a polyethylene-based resin, the sealant layer may contain a polyethylene-based resin, or the polyethylene-based resin may be the main component (e.g., the content in the sealant layer is 95% by mass or more). Also, if the resin with the highest content in the recycled material-containing layer is a polypropylene-based resin, the sealant layer may contain a polypropylene-based resin, or the polypropylene-based resin may be the main component (e.g., the content in the sealant layer is 95% by mass or more).

[0053] From the viewpoint of film processability, the MFR of the polyethylene resin may be 0.05 to 15 g / 10 min, or 0.1 to 8 g / 10 min. The MFR here refers to a value measured in accordance with JIS K7210 (190°C, load 2.16 kg).

[0054] From the viewpoint of film processability, the MFR of the polypropylene resin may be 0.05 to 20 g / 10 min, or 0.1 to 10 g / 10 min. The MFR here refers to a value measured in accordance with JIS K7210 (230°C, load 2.16 kg).

[0055] From the viewpoint of heat sealing property and rigidity, the crystallinity of the polypropylene resin as measured by the heat of fusion using a differential scanning calorimeter (DSC) may be 25% or more and 60% or less, or 30% or more and 55% or less.

[0056] In this specification, the crystallinity of a polypropylene-based resin is calculated from the ratio of the heat of fusion ΔHm obtained by integrating the endothermic peak during melting of the sample to the heat of fusion ΔH100 of a completely crystalline body having a crystallinity of 100% obtained by theoretical calculation, according to the following formula: Crystallinity [%]=(ΔHm / ΔH100)×100 The heat of fusion ΔH100 of a completely crystalline substance can be the value described in the following document. For example, the ΔH100 of polypropylene can be 207 J / g. Reference: Japan Society of Plastics Processing: Plastic Materials in Molding Processing, 335 (2011), Morikita Publishing Co., Ltd.

[0057] The thickness of the sealant layer may be 20 μm or more, 40 μm or more, or 80 μm or more from the viewpoint of heat sealing properties, and may be 150 μm or less, 120 μm or less, or 100 μm or less from the viewpoint of reducing the total thickness when used as a packaging material. The thickness of the sealant layer may be 5 μm or more and 60 μm or less, 5 μm or more and 55 μm or less, 5 μm or more and 50 μm or less, 5 μm or more and 40 μm or less, 5 μm or more and 30 μm or less, 5 μm or more and 20 μm or less, 10 μm or more and 65 μm or less, 10 μm or more and 60 μm or less, 10 μm or more and 55 μm or less, 10 μm or more and 50 μm or less, 10 μm or more and 40 μm or less, 10 μm or more and 30 μm or less, 15 μm or more and 60 μm or less, or 20 μm or more and 60 μm or less.

[0058] The recycled material-containing layer and the sealant layer may contain additives such as compatibilizers, nucleating agents, reinforcing fillers, antioxidants, heat stabilizers, weathering agents, light stabilizers, plasticizers, UV absorbers, antistatic agents, flame retardants, flame retardant aids, slip agents, antiblocking agents, antifogging agents, lubricants, pigments, dyes, dispersants, copper inhibitors, neutralizing agents, bubble inhibitors, weld strength improvers, natural oils, synthetic oils, waxes, etc. The additives may be used alone or in combination of two or more.

[0059] Examples of nucleating agents and reinforcing fillers include talc, silica, clay, montmorillonite, calcium carbonate, lithium alumina carbonate, titanium oxide, metals such as aluminum, iron, silver, and copper, hydroxides such as aluminum hydroxide and magnesium hydroxide, celluloses such as cellulose microfibrils and cellulose acetate, fibrous fillers such as glass fibers, polyethylene terephthalate fibers, nylon fibers, polyethylene naphthalate fibers, aramid fibers, vinylon fibers, and polyacrylate fibers, carbons such as carbon nanotubes, and elastomers such as ethylene propylene rubber (EPR).

[0060] Examples of the antioxidant include phenolic compounds, organic phosphite compounds, and thioether compounds.

[0061] Examples of the heat stabilizer and light stabilizer include hindered amine compounds.

[0062] Examples of the ultraviolet absorber include benzophenone compounds, benzotriazole compounds, and benzoate compounds.

[0063] Examples of the antistatic agent include nonionic compounds, cationic compounds, and anionic compounds.

[0064] Examples of the flame retardant include halogen-based compounds, phosphorus-based compounds, nitrogen-based compounds, inorganic compounds, boron-based compounds, silicone-based compounds, sulfur-based compounds, and red phosphorus-based compounds.

[0065] Examples of the flame retardant aid include antimony compounds, zinc compounds, bismuth compounds, magnesium hydroxide, and clay silicates.

[0066] The sealant film of the present embodiment is subjected to electron beam irradiation treatment, which increases the crosslink density of the resin contained in the sealant film by electron beam irradiation, thereby further improving the mechanical strength of the sealant film.

[0067] The electron beam irradiation treatment may be carried out from the side opposite to the side of the sealant film where the sealant layer is provided (in the case of a packaging material provided with a sealant film, the side opposite to the surface that comes into contact with the contents or filled material).

[0068] The sealant film of this embodiment may be subjected to electron beam irradiation treatment during or after the formation of the laminate or packaging material described below. For example, an ink layer or an overcoat layer that is cured by electron beam irradiation may be provided on the sealant film, and the electron beam irradiation conditions may be set so that the sealant film is irradiated with a predetermined dose of electron beams when these layers are cured. In particular, in the case of multi-color printing, further strength improvement can be expected by accumulating the EB irradiation of each color. Furthermore, in the case of a packaging material in which a sealant film is laminated with a gas barrier layer, a base film, or the like, the electron beam irradiation conditions may be set so that the sealant film is irradiated with a predetermined dose of electron beams during EB sterilization performed after pouching or filling with contents. From the viewpoint of improving puncture strength, etc., the acceleration voltage and irradiation energy of the electron beam may be adjusted so that the electron beam dose on the sealant film is preferably 10 KGy or more and 2000 KGy or less, or 20 KGy or more and 500 KGy or less. From the same viewpoint, the dose of the electron beam, the acceleration voltage of the electron beam, and the irradiation energy may be adjusted so that the gel fraction of the sealant film falls within the range described below.

[0069] The sealant film of this embodiment may have a gel fraction of 0.5% or more and 85% or less, or 20% or more and 80% or less, as calculated by the following method. The gel fraction can be used as an indicator of crosslink density, and when the gel fraction is in the above range, it is easy to achieve both an improvement in the mechanical strength of the sealant film by increasing the crosslink density of the recycled material-containing layer and ensuring heat sealability by preventing excessive crosslinking of the sealant layer. (Calculation method of gel fraction) The gel fraction is calculated by utilizing the insolubility of the crosslinked portion in a solvent, and can be calculated by immersing the sealant film in an organic solvent such as xylene, drying the remaining insoluble film, measuring its mass, and then calculating the gel fraction from the mass of the sealant film before dissolution and the mass of the insoluble film after drying. Specifically, the gel fraction can be calculated by the following procedure. (i) First, Xg of sealant film was wrapped in Yg of stainless steel mesh and heated and immersed in a solvent. The heating temperature and immersion time were 120°C and 8 hours, respectively. (ii) Next, the sealant film wrapped in the stainless steel mesh is removed from the solvent and vacuum dried at 60°C for 3 hours. (iii) The mass (Zg) of the sealant film wrapped in the stainless steel mesh after drying is measured, and the gel fraction is calculated using the following formula (1). Gel fraction (mass%) = [(ZY) / X] × 100 ... (1)

[0070] Even with a low EB irradiation dose, physical strength may be improved by EB irradiation, and even a slight increase in gel fraction is considered to be crosslinking. In such cases, a shift in melting peak intensity to lower temperatures and a decrease in melting enthalpy are observed in DSC (differential scanning calorimetry) analysis.

[0071] Fig. 3 is a schematic cross-sectional view showing another embodiment of a sealant film. The sealant film 1b shown in Fig. 3 comprises a recycled material-containing layer 2, a sealant layer 3 laminated on one main surface of the recycled material-containing layer 2, and an auxiliary layer 4 laminated on the other main surface of the recycled material-containing layer 2, and has been subjected to electron beam irradiation treatment. As such, the sealant film of this embodiment may further comprise an auxiliary layer laminated on the main surface of the recycled material-containing layer opposite to the side on which the sealant layer is laminated.

[0072] When auxiliary layer 4 is intended to function as a laminating layer, it may have the same configuration as the above-described sealant layer 3. Furthermore, auxiliary layer 4 may contain the same type of resin as the resin with the highest content in recycled material-containing layer 2. In this case, higher laminating strength makes it easier to improve adhesion with other layers.

[0073] The auxiliary layer 4 may contain one or more of the above-mentioned additives, if necessary.

[0074] The thickness of the auxiliary layer 4 may be 20 μm or more, 40 μm or more, or 80 μm or more from the viewpoint of the mechanical properties and adhesion of the sealant film, and may be 150 μm or less, 120 μm or less, or 100 μm or less from the viewpoint of reducing the total thickness when used as a packaging material.

[0075] The electron beam irradiation treatment may be performed on the sealant film 1b from the side opposite to the side where the sealant layer is provided (the auxiliary layer side) (in a packaging material including a sealant film, the side opposite to the surface that comes into contact with the contents or filled material). The sealant film 1b may have the above-mentioned gel fraction.

[0076] Incidentally, packaging bags such as pouches are usually produced by forming a packaging material including a sealant film. However, if pinholes occur in the packaging material constituting the packaging bag due to friction during transportation, outside air or components of the base material layer may enter the packaging bag, potentially affecting the hygiene of the contents. Furthermore, when filling the packaging bag with contents having sharp corners, pinholes may occur from the inside to the outside of the packaging bag. Therefore, it is desirable that the sealant film used as the packaging material has excellent puncture strength. The sealant film of this embodiment has excellent puncture strength due to the fact that it has been subjected to electron beam irradiation treatment.

[0077] <Method of manufacturing sealant film> The sealant film of the present embodiment can be produced by a conventionally known method, for example, a method of extrusion laminating a recycled material-containing film formed from a resin composition constituting the recycled material-containing layer with a resin composition constituting the sealant layer, or a method of forming the recycled material-containing layer and the sealant layer by coextrusion molding can be used.

[0078] In the former method, the recycled material-containing film can be produced by melting the resin composition constituting the recycled material-containing layer in an injection molding machine or extrusion molding machine (e.g., a twin-screw extruder) and then forming the film in a T-die through a feed block or multi-manifold, or by an inflation method. The recycled material can be produced by collecting, cleaning, and pulverizing various types of plastic waste, melt-molding them in an extruder, and pelletizing them. For extrusion lamination, an extrusion laminating machine or the like can be used.

[0079] In the latter method, for example, a sealant film can be produced by melt-kneading and co-extruding the resin composition constituting the recycled material-containing layer and the resin composition constituting the sealant layer using a multi-layer extrusion molding machine.

[0080] The resin composition constituting the recycled material-containing layer may contain only recycled material, or may further contain virgin resin or additives to impart various desired properties such as viscosity adjustment, mechanical property reinforcement, etc. Furthermore, when the recycled material and virgin resin are mixed, they may be dry-blended in which the virgin resin and the recycled material are simultaneously charged into a hopper and melt-kneaded to form a film, or they may be melt-blended in which the virgin resin and the recycled material are separately melt-kneaded in a twin-screw extruder to form a masterbatch.

[0081] In order to reduce the maximum area and maximum aspect ratio of the low transmittance brightness region in the recycled material-containing layer, the layer may be pelletized using a twin-screw extruder, molded under high shear conditions, or an acid-modified polyolefin resin or the like may be blended as a compatibilizer.

[0082] The film can be cooled in a manner consistent with the molding machine used, and for example, in the T-die method, air cooling methods such as an air chamber, vacuum chamber, or air knife, or water cooling methods such as dipping a cooling roll in a cold water pan can be used. When imparting a surface texture by shaping, a method in which a molten resin is poured into the contact area between a nip roll made of silicone rubber, NBR rubber, fluororesin, or the like and a cooling roll made of machined metal, with a pressure of 0.1 MPa or more applied, and then cooled.

[0083] In this embodiment, the sealant film produced as described above can be subjected to electron beam irradiation treatment. Electron beam irradiation increases the crosslink density of the resin contained in the sealant film, improving the mechanical strength of the sealant film. The electron beam irradiation treatment is preferably performed from the side opposite to the side of the sealant film on which the sealant layer is provided (in the case of a packaging material equipped with a sealant film, the side opposite to the surface that comes into contact with the contents or filled material).

[0084] Furthermore, the sealant film produced as described above has a low-transmittance brightness region in the recycled material-containing layer whose maximum area and maximum aspect ratio satisfy the above-mentioned conditions, and thus the mechanical strength can be easily improved by electron beam irradiation treatment. 2 exceeding 1000 μm 2 If there are low-transmission brightness regions exceeding this value, it becomes difficult to increase the crosslink density by electron beam irradiation, and it becomes difficult to improve the mechanical strength. Furthermore, if the maximum aspect ratio of the low-transmission brightness regions specified by the above-mentioned method exceeds 10, that is, if there are low-transmission brightness regions with an aspect ratio exceeding 10, adjacent low-transmission brightness regions will combine to form pseudo-large-sized aggregates, and the area will become 1000 μm or more. 2 The same disadvantages as those in the case where there is a low transmittance brightness area exceeding 100% are likely to occur.

[0085] As an apparatus that can be used to irradiate a sealant film with an electron beam, a conventionally known low-energy type is preferably used, such as a curtain-type electron beam irradiation apparatus (LB1023, manufactured by i-Electron Beam Inc.), a line-type low-energy electron beam irradiation apparatus (EB-ENGINE, manufactured by Hamamatsu Photonics K.K.), and a drum-roll type electron beam irradiation apparatus (EZ-CURE, manufactured by i-Electron Beam Inc.).

[0086] The dose of the electron beam irradiated to the sealant film and the acceleration voltage of the electron beam can be set as appropriate, and may be adjusted as appropriate within a range in which the electron beam does not reach the sealant layer when irradiated to the main surface of the sealant film opposite the sealant layer side. In this case, the crosslink density of the sealant layer is improved by the electron beam, and a decrease in the heat sealability of the sealant layer can be suppressed. In addition, the dose of the electron beam, the acceleration voltage of the electron beam, and the irradiation energy may be adjusted so that the gel fraction of the sealant film falls within the above-mentioned range.

[0087] The dose of the electron beam may be 10 kGy or more and 2000 kGy or less, or 20 kGy or more and 500 kGy or less.

[0088] The acceleration voltage of the electron beam may be 30 kV or more and 300 kV or less, 50 kV or more and 300 kV or less, or 50 kV or more and 250 kV or less.

[0089] The irradiation energy of the electron beam may be 20 keV or more and 750 keV or less, 25 keV or more and 500 keV or less, 30 keV or more and 400 keV or less, or 20 keV or more and 200 keV or less.

[0090] The oxygen concentration in the electron beam irradiation apparatus may be 500 ppm or less, or may be 100 ppm or less. By performing electron beam irradiation under such conditions, it is possible to suppress the generation of ozone and also to prevent the radicals generated by electron beam irradiation from being deactivated by oxygen in the atmosphere. Such conditions can be achieved, for example, by creating an inert gas (nitrogen, argon, etc.) atmosphere inside the apparatus.

[0091] The sealant film may be subjected to a surface modification treatment to improve suitability for subsequent processes. For example, the surface to be laminated may be subjected to a surface modification treatment to improve printability and lamination suitability when laminating with other layers or substrate films. Examples of surface modification treatments include methods for oxidizing the film surface to express functional groups, such as corona discharge treatment, plasma treatment, and flame treatment, and wet process modifications such as coating with an easy-adhesion layer.

[0092] The method for producing the sealant film is not limited to the above-mentioned method, and the sealant film produced by the molding machine may be subjected to in-line or off-line stretching treatment. There are no limitations on the addition of other necessary steps or additives as appropriate.

[0093] <Laminate> The laminate of this embodiment includes the sealant film of this embodiment described above. FIG. 4 is a schematic cross-sectional view showing one embodiment of the laminate of this embodiment. The laminate 10a shown in FIG. 4 further includes a gas barrier layer 12 on the side of the auxiliary layer 4 opposite to the recycled material-containing layer 2 side in the sealant film 1b shown in FIG. 3. The laminate 10a can have improved gas barrier properties (for example, oxygen barrier properties and water vapor barrier properties). The gas barrier layer may have a single-layer structure or a multilayer structure.

[0094] Examples of the gas barrier layer 12 include a vapor-deposited layer (vapor-deposited film) made of a metal or inorganic oxide, a metal foil such as aluminum foil, and a film of an ethylene-vinyl alcohol copolymer, a polyamide resin, a polyvinylidene chloride resin, a polyacrylonitrile resin, or the like.

[0095] The vapor-deposited layer may have a single layer structure or a multilayer structure. Examples of the vapor-deposited layer include a vapor-deposited layer composed of a metal such as aluminum, and an inorganic oxide such as aluminum oxide, silicon oxide, magnesium oxide, calcium oxide, zirconium oxide, titanium oxide, boron oxide, hafnium oxide, and barium oxide.

[0096] The deposition layer can be formed by a conventionally known method, for example, physical vapor deposition (PVD) methods such as vacuum deposition, sputtering, and ion plating, and chemical vapor deposition (CVD) methods such as plasma chemical vapor deposition, thermal chemical vapor deposition, and photochemical vapor deposition, and can be appropriately selected depending on the deposition material, etc.

[0097] When the vapor-deposited layer is an aluminum vapor-deposited film, the OD value thereof may be from 2 to 3.5 in terms of productivity, oxygen barrier property, and water vapor barrier property of the laminate. Note that, in this specification, the OD value refers to the value measured in accordance with JIS-K-7361.

[0098] When the vapor-deposited layer is an inorganic oxide layer using silicon oxide, the O / Si ratio of the inorganic oxide layer may be 1.5 or more from the viewpoint of transparency. Furthermore, the O / Si ratio may be 2.0 or less from the viewpoint of barrier properties. To obtain the above-mentioned effects more fully, the O / Si ratio of the inorganic oxide layer may be 1.5 or more and 2.0 or less, or 1.6 or more and 1.8 or less.

[0099] The O / Si ratio of the inorganic oxide layer can be determined by X-ray photoelectron spectroscopy (XPS). For example, an X-ray photoelectron spectrometer (manufactured by JEOL Ltd., trade name: JPS-90MXV) is used as the measurement device, and measurements can be performed using a non-monochromated MgKα (1253.6 eV) X-ray source at an X-ray output of 100 W (10 kV-10 mA). For quantitative analysis to determine the O / Si ratio, relative sensitivity factors of 2.28 for O1s and 0.9 for Si2p can be used.

[0100] The thickness of the vapor-deposited layer may be 1 nm or more and 150 nm or less, 5 nm or more and 60 nm or less, or 5 nm or more and 40 nm or less. When the thickness of the vapor-deposited layer is 1 nm or more, oxygen barrier property and water vapor barrier property are easily obtained. When the thickness of the vapor-deposited layer is 150 nm or less, cracks in the vapor-deposited layer are easily prevented, and the recyclability of the sealant film is easily maintained.

[0101] The auxiliary layer 4 provided with the gas barrier layer may have the same structure as the above-described sealant layer 3. When the auxiliary layer 4 contains a polyolefin resin, the polyolefin resin preferably has high crystallinity from the viewpoints of printability, vapor deposition suitability, strength, and heat resistance. The polyolefin resin may be a virgin resin and / or a chemically recycled resin.

[0102] When the polyolefin resin is polyethylene, high-density polyethylene (HDPE) and medium-density polyethylene (MDPE) are preferred from the viewpoints of printability, strength, and heat resistance, and medium-density polyethylene is more preferred from the viewpoint of suitability for stretching. When the polyolefin resin is polypropylene, the crystallinity determined by the heat of fusion using a differential scanning calorimeter (DSC) may be 40% or more or 45% or more from the viewpoints of printability, strength, and heat resistance, and may be 60% or less or 55% or less from the viewpoint of impact resistance.

[0103] The content of non-material recycled resin (virgin resin such as petroleum-derived resin or biomass-derived resin) in auxiliary layer 4, on which the gas barrier layer is provided, can be made higher than the content of non-material recycled resin in the recycled-material-containing layer. In this case, it is possible to smooth out partial swelling caused by aggregates on the surface of the recycled-material-containing layer and improve the mechanical properties and gas barrier properties of the laminate.

[0104] The thickness of the auxiliary layer 4 on which the gas barrier layer is provided may be 20 μm or more, 40 μm or more, or 80 μm or more from the viewpoint of gas barrier properties and adhesion, and may be 150 μm or less, 120 μm or less, or 100 μm or less from the viewpoint of reducing the total thickness when used as a packaging material.

[0105] <Packaging material> The packaging material of this embodiment includes the sealant film of this embodiment described above. Fig. 5 is a schematic cross-sectional view showing one embodiment of the packaging material. The packaging material 100 shown in Fig. 5 includes a sealant film 1b including an auxiliary layer 4, and a base film 6 laminated onto the auxiliary layer 4 via an adhesive layer 5.

[0106] The base film 6 is not particularly limited as long as it has mechanical strength and dimensional stability, and examples of the base film 6 that can be used include plastic film, paper, nonwoven fabric, etc. Examples of materials that can be used for the plastic film include polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate, polyolefins such as polyethylene and polypropylene, polystyrene, polyamides such as 6-nylon, polycarbonate, polyacrylonitrile, and polyimide.

[0107] The base film 6 is preferably a stretched film from the viewpoint of mechanical strength and dimensional stability.

[0108] By containing the same type of resin (also referred to as "the same resin") as the resin with the highest content in the sealant film, the entire packaging material can be made into a mono-material, improving the recyclability of the packaging material. In this case, all layers constituting the sealant film (for example, the sealant layer, or the sealant layer and auxiliary layer) may contain the same type of resin as the resin with the highest content in the recycled material-containing layer.

[0109] The content of the same resin in the packaging material may be 90% by mass or more, based on the total amount of the packaging material. In this case, the packaging material can be said to be a monomaterial packaging material made of a single material. From the perspective of further improving recyclability, the content of the same resin in the packaging material may be 92.5% by mass or more, or 95% by mass or more, based on the total amount of the packaging material.

[0110] From the viewpoint of transparency, the haze value of the base film 6 may be 30% or less, or may be 20% or less. In this specification, the haze value of the film refers to the value measured in accordance with JIS K 7105.

[0111] The substrate film 6 may be subjected to a surface treatment, which can improve adhesion to adjacent layers. The method of surface treatment is not particularly limited, and examples include physical treatments such as corona discharge treatment, ozone treatment, low-temperature plasma treatment using oxygen gas and / or nitrogen gas, and glow discharge treatment, as well as chemical treatments such as oxidation treatment using chemicals.

[0112] An anchor coating layer may be provided on the surface of the base film 6 using a conventionally known anchor coating agent.

[0113] The thickness of the base film 6 may be 10 μm or more and 50 μm or less, or 12 μm or more and 30 μm or less. When the thickness of the base film is 10 μm or more, it is easy to improve the strength of the laminate. Furthermore, when the thickness of the base film is 50 μm or less, it is easy to maintain the processability of the laminate.

[0114] The adhesive layer 5 is a layer that bonds the base film 6 and the sealant film. In the packaging material 100, the auxiliary layer 4 of the sealant film and the base film 6 are bonded via the adhesive layer 5.

[0115] The adhesive constituting the adhesive layer is not particularly limited, but may be a dry laminating adhesive, such as a two-component curing urethane adhesive, a polyester urethane adhesive, a polyether urethane adhesive, an acrylic adhesive, a polyester adhesive, a polyamide adhesive, or an epoxy adhesive.

[0116] When the packaging material is used for a packaging bag for retort use, a two-component curing urethane adhesive that is retort resistant can be used.

[0117] From the viewpoint of hygiene, the adhesive layer 5 may not contain 3-glycidyloxypropyltrimethoxysilane (GPTMS).

[0118] From the viewpoint of environmental consideration, the adhesive layer 5 may contain a biomass material.

[0119] The adhesive layer 5 may not contain a solvent from the viewpoint of environmental consideration.

[0120] The adhesive layer 5 may be chlorine-free from the viewpoint of suppressing discoloration of recycled resins and the like after recycling and the generation of odors due to heat treatment.

[0121] The thickness of the adhesive layer 5 may be 0.3 μm or more and 5.0 μm or less. From the viewpoint of adhesive strength, the thickness of the adhesive layer may be 0.3 μm or more, 0.5 μm or more, or 1 μm or more, and from the viewpoint of recyclability, the thickness may be 5.0 μm or less, 3.5 μm or less, or 2.5 μm or less. When the thickness of the adhesive layer is equal to or less than the above upper limit, the proportion of monomaterials in the packaging material can be increased.

[0122] The packaging material of the present embodiment may further include a functional layer such as a print layer and a gas barrier layer. These functional layers may be provided on the above-mentioned base film.

[0123] The printed layer may be formed on the surface of the base film on which the sealant film is provided, in which case the printed layer can be prevented from coming into contact with the outside air and from deteriorating over time.

[0124] The print layer may represent letters, patterns, symbols, or a combination thereof.

[0125] From the viewpoint of producing a packaging material with less environmental impact, the printed layer may be formed using ink derived from biomass.

[0126] The method for forming the printed layer is not particularly limited, and any conventionally known printing method such as gravure printing, offset printing, flexographic printing, etc. Among these, flexographic printing may be used from the viewpoint of environmental load.

[0127] The gas barrier layer can be provided on the substrate film and may have the same structure as the gas barrier layer 12 described above.

[0128] The gas barrier layer may also be formed by laminating a laminate film of a metal foil and a plastic film, or a plastic film with a vapor-deposited layer (vapor-deposited film) made of the above-mentioned metal or inorganic oxide, etc. Examples of plastic films include polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate, polyolefins such as polyethylene and polypropylene, polystyrene, polyamides such as 6-nylon, polycarbonate, polyacrylonitrile, and polyimide.

[0129] Fig. 6 is a schematic cross-sectional view showing another embodiment of a packaging material. The packaging material 102 shown in Fig. 6 includes a laminate 10a in which a sealant film 1b having a laminated structure of a sealant layer 3, a recycled material-containing layer 2, and an auxiliary layer 4, and a gas barrier layer 12 are laminated in this order, and a base film 6 having a printed layer 7 bonded to the gas barrier layer 12 side of the laminate via an adhesive layer 5. In the packaging material 102, as described above, the printed layer 7 is formed on the surface of the base film 6 on the side where the sealant film is provided.

[0130] The packaging material of this embodiment can be modified in various ways in addition to the configuration described above, and may have the following configuration. (a) Sealant film of this embodiment / adhesive layer / gas barrier film / adhesive layer / substrate film (b) Sealant film / adhesive layer / gas barrier film of this embodiment (c) Sealant film of this embodiment / gas barrier layer (e.g., vapor deposition layer) / adhesive layer / substrate film The gas barrier film may be a substrate film provided with a gas barrier layer, a laminated film of a metal foil and a plastic film, or a vapor-deposited film, as described above, or may be a metal foil such as aluminum foil, or a film such as an ethylene-vinyl alcohol copolymer, a polyamide resin, a polyvinylidene chloride resin, or a polyacrylonitrile resin.

[0131] From the viewpoint of material recycling, the content of plastic material contained in the packaging material of this embodiment may be 10% by mass or more, or 25% by mass or more, based on the total amount of plastic material in the packaging material. When the packaging material of this embodiment is a laminate packaging material, materials other than plastic (for example, adhesives, printing inks, aluminum foil, etc.) may be excluded from the weight calculation.

[0132] Examples of plastic materials contained in recycled materials (so-called recycled plastics) include resins contained in the recycled materials contained in the recycled material-containing layer according to the present embodiment. Pre-consumer materials among recycled plastics may be calculated by multiplying the weight by 1 / 2.

[0133] The packaging material of this embodiment can be used for stand-up pouches, three-sided bags, two-sided bags, gusseted bags, pouches with spouts, pouches with beaks, and the like.

[0134] <Packaging bag> The packaging bag of this embodiment is made from the packaging material of this embodiment described above. The manufacturing style of the packaging bag is not particularly limited, but the packaging bag may be a stand-up pouch, a three-sided bag, a two-sided bag, a gusset bag, a pouch with a spout, a pouch with a beak, or the like. [Example]

[0135] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0136] <Preparing recycled materials> (Recycled material 1) Recycled material 1 was obtained by compressing, cutting, and granulating a film consisting of an LLDPE film (Mitsui Chemicals Tocello, product name "TUX FC-S," 100 μm thick), an adhesive layer, a PET film (Toray Advanced Film, product name "VM-PET 1310," 12 μm thick, aluminum vapor deposition), an adhesive layer, a printing layer, and an Ny film (Toyobo, product name "Harden Film N1100," 15 μm thick). The adhesive layer was formed by dry lamination using an adhesive mixture of DiC Dry LX-500 (DIC Graphics, product name) as the base agent, KW75 (DIC Graphics, product name) as the curing agent, and NC401 (Toyo Ink, product name) as the solvent.

[0137] (Recycled material 2) Recycled material 2 was obtained by compressing, cutting, and granulating a film consisting of a PP film (manufactured by Toray Advanced Film Co., Ltd., product name "Torayfan NO ZK207," film thickness 100 μm), an adhesive layer, a PET film (manufactured by Toray Advanced Film Co., Ltd., "VM-PET 1310," film thickness 12 μm, aluminum vapor deposition), an adhesive layer, a printed layer, and an Ny film (manufactured by Toyobo Co., Ltd., product name "Harden Film N1100," film thickness 15 μm) laminated in this order. The adhesive layer was formed in the same manner as Recycled material 1.

[0138] (Recycled material 3) Recycled material 3 was obtained by compressing, cutting, and granulating a film consisting of an LLDPE film (manufactured by Mitsui Chemicals Tocello, product name "TUX FC-S," film thickness 100 μm), an adhesive layer, an HDPE film (manufactured by Tamapoly, product name "HF31," film thickness 35 μm), an adhesive layer, a printed layer, and an HDPE film (manufactured by Tamapoly, product name "HF31," film thickness 35 μm) laminated in that order. The adhesive layer was formed in the same manner as for recycled material 1.

[0139] <Preparation of sealant film> Example 1 The recycled material 1 and LLDPE (Prime Polymer, product name "Evolue SP2040") were charged in a weight ratio of 1:1 into the hopper extruding the recycled material-containing layer, and LLDPE (Prime Polymer, product name "Evolue SP2040") was charged into the hopper extruding the sealant layer. A single-screw multi-layer extruder was used to co-extrude an 80 μm-thick recycled material-containing layer and a 20 μm-thick sealant layer to produce a sealant film. The screw rotation speed when extruding the recycled material-containing layer was 16 rpm, and narrowing of the flow path before the T-die was minimized, creating a mechanism that was less susceptible to elongational stress.

[0140] The surface of the sealant film obtained above opposite to the sealant layer side was irradiated with electron beams using an electron beam irradiation device (line irradiation type low energy electron beam irradiation device EES-L-DP01, manufactured by Hamamatsu Photonics K.K.) under the following conditions. (Irradiation conditions) Voltage: 120kV Irradiation dose: 100kGy Oxygen concentration inside the device: 100 ppm or less Line speed: 25m / min

[0141] Example 2 A sealant film was produced and irradiated with electron beams in the same manner as in Example 1, except that only recycled material 1 was placed in the hopper for extruding the recycled material-containing layer.

[0142] Example 3 A sealant film was produced and irradiated with electron beams in the same manner as in Example 2, except that recycled material 2 was placed in the hopper extruding the recycled material-containing layer instead of recycled material 1, and homopolypropylene resin (hPP) (manufactured by Prime Polymer Co., Ltd., product name "Prime Polypro F-300SP") was used in the hopper extruding the sealant layer.

[0143] Example 4 A sealant film was produced in the same manner as in Example 2, except that recycled material 2 was charged into the hopper for extruding the recycled material-containing layer instead of recycled material 1, and the sealant film was irradiated with electron beams.

[0144] Example 5 A sealant film was produced in the same manner as in Example 1, except that recycled material 3 and LLDPE (manufactured by Prime Polymer Co., Ltd., product name "Evolue SP2040") were added to the hopper for extruding the recycled material-containing layer in a weight ratio of 1:1, and the sealant film was irradiated with electron beams.

[0145] Example 6 A sealant film was produced in the same manner as in Example 2, except that recycled material 3 was charged into the hopper for extruding the recycled material-containing layer instead of recycled material 1, and the sealant film was irradiated with electron beams.

[0146] Example 7 Only recycled material 1 was placed in the hopper extruding the recycled material-containing layer, LLDPE (Prime Polymer, product name "Evolue SP2040") was placed in the hopper extruding the sealant layer, and LLDPE (Prime Polymer, product name "Evolue SP2040") was placed in the hopper extruding the auxiliary layer. A 20 μm-thick auxiliary layer, an 80 μm-thick recycled material-containing layer, and a 20 μm-thick sealant layer were formed in this order by coextrusion molding using a single-screw multi-layer extruder to produce a sealant film. The screw rotation speed when extruding the recycled material-containing layer was 16 rpm, and narrowing of the flow path before the T-die was minimized, creating a mechanism that was less susceptible to elongational stress.

[0147] The sealant film obtained above was irradiated with electron beams in the same manner as in Example 1.

[0148] (Reference example 1) A commercially available PE sealant film (manufactured by Tamapoly Co., Ltd., product name "MZ434") was prepared.

[0149] (Comparative Example 1) A sealant film was produced in the same manner as in Example 1, except that an orifice was inserted before the T-die to apply elongation stress when extruding the recycled material-containing layer, and the sealant film was irradiated with electron beams.

[0150] (Comparative Example 2) A sealant film was produced in the same manner as in Example 2, except that the screw rotation speed was reduced to 10 rpm when extruding the recycled material-containing layer, and then irradiated with electron beams.

[0151] (Comparative Example 3) A sealant film was produced and irradiated with electron beams in the same manner as in Example 3, except that when extruding the recycled material-containing layer, the screw rotation speed was reduced to 10 rpm and an orifice was inserted before the T-die to apply elongational stress.

[0152] Comparative Example 4 A sealant film was produced and irradiated with electron beams in the same manner as in Example 4, except that when extruding the recycled material-containing layer, the screw rotation speed was reduced to 10 rpm and an orifice was inserted before the T-die to apply elongational stress.

[0153] (Comparative Example 5) A sealant film was produced in the same manner as in Example 5, except that the screw rotation speed was reduced to 10 rpm when extruding the recycled material-containing layer, and then irradiated with electron beams.

[0154] (Comparative Example 6) A sealant film was produced in the same manner as in Example 6, except that an orifice was inserted before the T-die to apply elongation stress when extruding the recycled material-containing layer, and the film was irradiated with electron beams.

[0155] <Analysis of layers containing recycled materials> (Maximum area and aspect ratio of low transmittance area) The maximum area and maximum aspect ratio of the low transmittance brightness region in the recycled material-containing layer were calculated by the following procedure. (i) Using a stereo microscope system SZX16 (product name, manufactured by Olympus Corporation), observation images (image size: 243 μm × 851 μm) were taken at 10 random locations in the planar direction of the sealant film. (ii) The 10 images obtained were analyzed using WinROOF2021 (product name, manufactured by Mitani Corporation). In the image analysis, the low-transmittance brightness region and the surrounding high-transmittance brightness region were binarized, and the following operations were appropriately performed during the binarization to match the visual shape of the low-transmittance brightness region with the colored range. (a) Adjusting brightness and contrast to emphasize low-transparency areas (b) Adjust the threshold to match the visible low-transmittance brightness area with the colored range. (c) If there are areas where adjacent low-transmittance brightness areas are recognized as one area, or areas where perforated low-transmittance brightness areas are recognized as multiple areas, perform division or integration processing as necessary.

[0156] (Average and standard deviation of brightness) The average value and standard deviation of the brightness in the HSV color space data of the recycled material-containing layer were calculated by the following procedure. (i) The sealant film was cut into a size of ±200 mm width from the center in the width direction (400 mm width) and 250 mm in the machine direction. (ii) The cut-out sample was scanned using a digital full-color multifunction printer MP C6503 (manufactured by Ricoh Co., Ltd., product name) under the following reading conditions to obtain an image. [Reading conditions] Type: Full color, text and photos, Resolution: 600, Size: A3 (iii) The obtained images were analyzed using the image analysis software ImageJ, and the average brightness value and standard deviation for the entire image were calculated. For image analysis, the images saved in TIF format were converted to an HSB stack, and the average value and standard deviation were calculated from the histogram of the V value (brightness) from the histogram analysis results of the HSV color space data. The V value range was 0 to 255.

[0157] <Evaluation of sealant film> (gel fraction) The gel fraction of the sealant film was calculated by the following method. [Calculation method of gel fraction] (i) First, Xg of sealant film was cut into a 3.2cm x 3.2cm piece, wrapped in Yg of stainless steel mesh (9cm x 6cm), and heated and immersed in 350ml of xylene. The heating temperature and immersion time were 120°C and 8 hours, respectively. (ii) Next, the sealant film wrapped in the stainless steel mesh is removed from the solvent and vacuum dried at 60°C for 3 hours. (iii) The mass (Zg) of the sealant film wrapped in the stainless steel mesh after drying is measured, and the gel fraction is calculated using the following formula (1). Gel fraction (mass%) = [(ZY) / X] × 100 ... (1) The gel fraction of the film not irradiated with electron beams, such as that in Reference Example 1, was 0.0% by mass.

[0158] (Heat seal strength) Two sealant films were stacked with the sealant film layer side facing each other, heat-sealed over a 20 mm width, leaving a 10 mm edge, and then cut off 5 mm from each long edge to prepare 10 mm-wide test specimens. The heat-sealing temperature was varied in 10°C increments from 120 to 180°C. Each test specimen was stretched at 100 mm / min using a Tensilon universal testing machine RTG-1310 (manufactured by A&D Co., Ltd.). Regardless of the heat-sealing temperature, a test specimen was evaluated as "Excellent" if it exhibited strength equal to or greater than that of a commercially available sealant film (Reference Example 1). A test specimen that fractured, even if its strength was less than that of the commercially available sealant film, was evaluated as "Good." A test specimen that exhibited interfacial delamination or cohesive failure was evaluated as "Poor."

[0159] (breaking elongation) Test pieces measuring 15 mm x 25 mm were cut from the sealant film, with the long side aligned in the film production direction. The test pieces were placed in a Tensilon universal testing machine RTG-1310 (manufactured by A&D Co., Ltd.) with a chuck distance of 20 mm and pulled at 100 mm / sec. Test pieces that showed elongation equal to or greater than that of a commercially available sealant film (Reference Example 1) were evaluated as "Good," while those that did not match the elongation of the commercially available sealant film were evaluated as "Poor."

[0160] (Puncture strength) A test piece measuring 50 mm x 50 mm was cut from the sealant film. Using a Tenshiro AD-7703 (product name, manufactured by A&D Co., Ltd.) and a dedicated semicircular needle with a diameter of 1.0 mm and a tip radius of 0.5 mm, the maximum force (N) until the needle penetrated was measured under the conditions of a test speed of 50 mm / min, a load cell of 100 N, and a load range of 10 N (10%), and this was evaluated as the puncture strength. A test piece that showed a strength 1 to 1.5 times that of a commercially available sealant film (Reference Example 1) was evaluated as "Good," and a test piece that was inferior to the commercially available sealant film was evaluated as "Poor."

[0161] (Appearance 1) A laminate was obtained by providing a laminate structure of an adhesive layer, a PET film (manufactured by Toyobo Co., Ltd., E5202, film thickness 12 μm), an adhesive layer, a printed layer, and an Ny film (manufactured by Toyobo, product name "Harden Film N1100", film thickness 15 μm) on the surface opposite the sealant layer of the sealant film. On the other hand, a comparative laminate was obtained by providing the same laminate structure as above on a commercially available sealant film (Reference Example 1). If the laminate had the same appearance (color) as the comparative laminate, it was evaluated as "Good", and if the appearance (color) appeared to be different from the comparative laminate, it was evaluated as "Poor".

[0162] (Appearance 2) A laminate was obtained by providing a laminate structure consisting of an adhesive layer, a PET film (manufactured by Toray Advanced Film Co., Ltd., "VM-PET 1310", film thickness 12 μm, aluminum vapor deposition), an adhesive layer, a printed layer, and an Ny film (manufactured by Toyobo, product name "Harden Film N1100", film thickness 15 μm) on the surface opposite the sealant layer of the sealant film. On the other hand, a comparative laminate was obtained by providing a similar laminate structure to the above on a commercially available sealant film (Reference Example 1). If the laminate had the same appearance (surface smoothness (lack of unevenness)) as the comparative laminate, it was rated as "◎"; if the appearance (surface smoothness (lack of unevenness)) was inferior to the comparative laminate but there was no practical problem, it was rated as "◯"; and if there was a practical problem, it was rated as "×".

[0163] [Table 1]

[0164] [Table 2]

[0165] As shown in Table 1, the sealant films of Examples 1 to 7 had heat seal strength and breaking elongation equal to or greater than those of commercially available sealant films, and it was confirmed that they had sufficient heat sealability and mechanical properties despite containing recycled materials.

[0166] Furthermore, with the sealant films of Examples 1 to 7, even though the recycled material contains a printed layer, it is possible to obtain laminates having appearances equal to or better than those produced using commercially available sealant films, thereby eliminating the need for materials and processes for providing an additional layer to conceal appearance defects. This confirms that the present invention makes it possible to realize packaging materials that utilize recycled materials while reducing costs and environmental impact. [Explanation of symbols]

[0167] 1a, 1b... sealant film, 2... recycled material-containing layer, 3... sealant layer, 4... auxiliary layer, 5... adhesive layer, 6... base film, 7... printing layer, 10a... laminate, 12... gas barrier layer, 20... low transmittance brightness region (aggregate), 30... high transmittance brightness region, 100, 102... packaging material.

Claims

1. A sealant film comprising: a recycled material-containing layer containing a recycled material containing two or more types of resin; and a sealant layer laminated on one main surface of the recycled material-containing layer, The sealant film is subjected to electron beam irradiation treatment, the recycled material-containing layer includes a domain having a lower transmission brightness than the surrounding area when the sealant film is observed in a plane view; The domain has a maximum area of ​​1000 μm ２ and a maximum aspect ratio of 10 or less.

2. 2. The sealant film according to claim 1, wherein the recycled material-containing layer has an average brightness value of 200 or more and a standard deviation of brightness of 10 or less in HSV color space data.

3. The sealant film according to claim 1 , wherein the sealant layer contains the same type of resin as the resin having the highest content in the recycled material-containing layer.

4. Further provided is an auxiliary layer laminated on the other main surface of the recycled material-containing layer, The sealant film according to claim 1 , wherein the auxiliary layer contains the same type of resin as the resin with the highest content in the recycled material-containing layer.

5. The sealant film according to claim 1, wherein the resin having the largest content ratio among the two or more types of resin contained in the recycled material is a polyethylene-based resin or a polypropylene-based resin.

6. A packaging material comprising the sealant film according to any one of claims 1 to 5.

7. 7. The packaging material according to claim 6, wherein the content of plastic material contained in the recycled material is 10% by mass or more based on the total amount of plastic material in the packaging material.

8. A packaging bag made from the packaging material according to claim 6.

9. A packaging bag made from the packaging material according to claim 7.

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