Laminated film and packaging materials for food packaging

Abstract

To provide a laminated film for food packaging that allows both easy tying and easy untying, as well as a packaging material provided with the laminated film.SOLUTION: A laminated film for food packaging sequentially includes a first resin layer, a second resin layer, and a third resin layer, the laminated film having a tensile modulus in a TD direction of 250 MPa or more and 400 MPa or less, wherein the first resin layer comprises a polyethylene resin and calcium hydroxide particles, the second resin layer comprises a polyethylene resin, and the third resin layer comprises a polyethylene resin.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a laminated film for packaging food and a packaging material including the laminated film. [Background technology]

[0002] An example of a packaging material is a food packaging bag. Food packaging bags are generally used in the food sales section of supermarkets and the like. The film that makes up the food packaging bag is required to be self-supporting when displaying food and to be transparent so that the food can be seen, and the bag may be made of a laminated film including an OPP (biaxially oriented polypropylene) film.

[0003] Furthermore, laminated films constituting food packaging bags may contain antibacterial ingredients such as calcium hydroxide to maintain food freshness and prevent odors. For example, Patent Document 1, which relates to an application for an invention previously created by the present inventor, discloses a food packaging film comprising a first resin layer containing a first resin and calcium hydroxide particles, the first resin including an ethylene-propylene-butene terpolymer. Patent Document 1 also describes that this film may further comprise a second resin layer containing a second resin, the second resin including a polyolefin homopolymer, or the film may be biaxially stretched. Patent Document 1 explains that this film, in a food packaging bag manufactured so that the first resin layer forms the inner surface of the bag, can prevent calcium hydroxide particles from falling out of the first resin layer and can sufficiently maintain the freshness of fresh foods such as vegetables placed inside the bag.

[0004] For example, Patent Document 2, which relates to a patent application for another invention previously created by the present inventor, discloses an odor-proof bag having an inner layer that forms the inner surface of the bag, the inner layer containing a resin and calcium hydroxide particles, and either containing no surfactant or containing 1000 ppm or less of surfactant relative to the mass of the resin, and the surface roughness Ra of the inner surface of the inner layer being 2 μm or greater. This odor-proof bag may be configured with an odor barrier layer containing a material with high gas barrier properties (e.g., ethylene-vinyl alcohol copolymer (EVOH)) between outer and inner layers, each containing linear low-density polyethylene (PE-LLD). Patent Document 2 explains that this odor-proof bag exhibits the odor-proofing properties of the calcium hydroxide particles, while the inner surface having the above-mentioned surface roughness makes it relatively easy to open. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2020-196489 [Patent Document 2] Japanese Patent Application Publication No. 2020-55598 Summary of the Invention [Problem to be solved by the invention]

[0006] In supermarkets and other stores, when customers have food items packed after paying, they are sometimes provided with plastic bags made of a single layer of resin film. These plastic bags can be used by placing food inside the bag and then tying the bag in a knot to close the opening. However, because these plastic bags are made of a single layer of resin film, adding a large amount of calcium hydroxide particles with a particle size of a few micrometers to this single layer significantly reduces the bag's strength and makes it more susceptible to breakage. In contrast, food packaging bags made of laminated film can avoid a significant decrease in strength even if the first resin layer contains calcium hydroxide particles because they are supported by the second resin layer, etc.

[0007] However, with conventional food packaging bags made of laminated film, even if you try to tie a knot in the bag, the knot will naturally come undone immediately, making it difficult to tie and close the bag. For this reason, food packaging bags made of laminated film have traditionally been used by fusing the laminated film together to close the opening of the bag. While this method allows the bag to be closed in places where a heat sealing machine is available (e.g., relatively large stores such as supermarkets), it is difficult to close the bag in places where a heat sealing machine is not available (e.g., many convenience stores and many ordinary homes). Furthermore, the aforementioned Patent Documents 1 and 2 do not particularly discuss tying the laminated film or bag to make a knot or untying the knot.

[0008] Therefore, an object of the present invention is to provide a laminated film for food packaging that is easy to tie and untie, and a packaging material that includes the laminated film. [Means for solving the problem]

[0009] In order to solve the above problems, one embodiment of the laminate film is a laminate film for food packaging having, in order, a first resin layer, a second resin layer, and a third resin layer, and has a tensile modulus in the TD direction of 250 MPa or more and 400 MPa or less, the first resin layer comprising a polyethylene resin and calcium hydroxide particles, the second resin layer comprising a polyethylene resin, and the third resin layer comprising a polyethylene resin.

[0010] In the laminate film according to one embodiment, each of the first resin layer, the second resin layer, and the third resin layer contains a polyethylene resin, and therefore, compared to a laminate film containing, for example, a polypropylene resin film or an EVOH film, the laminate film is moderately soft and tends to have a tensile modulus in the TD direction of 250 MPa or more and 400 MPa or less. The laminate film according to one embodiment has a tensile modulus in the TD direction of 250 MPa or more and 400 MPa or less, which makes it easy to tie and untie a knot. Furthermore, in the laminate film according to one embodiment, the first resin layer contains calcium hydroxide particles, which helps to preserve the freshness of the packaged food and makes it easy to untie a knot.

[0011] The packaging material according to an embodiment may be a packaging material including the laminated film according to an embodiment. [Effects of the Invention]

[0012] As described above, the present invention can provide a laminate film for packaging food that is easy to tie and untie, and a packaging material including the laminate film. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a cross-sectional view showing the structure of a laminated film according to one embodiment. [Figure 2] Fig. 2(a) is a plan view showing the overall configuration of a packaging material (food packaging bag) according to one embodiment, and Fig. 2(b) is a view showing the configuration of the packaging material (food packaging bag) according to one embodiment as viewed from side A in Fig. 2(a). DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, a laminated film according to one embodiment and a packaging material including the laminated film will be described with reference to the drawings.

[0015] The laminate film 10 according to one embodiment shown in Fig. 1 is a laminate film for food packaging, which has a three-layer structure including, in order, a first resin layer 11, a second resin layer 12, and a third resin layer 13. Each of these resin layers (11, 12, and 13) contains polyethylene resin as a resin component. In other words, the laminate film 10 can also be said to be a polyethylene laminate film having three polyethylene resin layers.

[0016] From the viewpoint of having appropriate rigidity for easy binding and unbinding, the laminated film 10 has a tensile modulus in the TD direction of 250 MPa or more and 400 MPa or less, and preferably 300 MPa or more and 350 MPa or less. The value of "tensile modulus" in this specification is the arithmetic mean value of the tensile modulus measured in the TD direction of five (n=5) laminated film samples (test piece type 2: rectangular shape with a total length of 150 mm and a width of 15 mm) in accordance with JIS K 7127:1999 "Plastics - Test methods for tensile properties" and JIS K 7161-1:2014 "Plastics - Determination of tensile properties - Part 1: General rules" using an Instron universal testing machine (68FM-300 model) and a non-contact video extensometer (AVE2) under test conditions of 23±2°C and 50±10% RH, with an initial distance between chucks of 100 mm, a gauge length of 50 mm, and a test speed of 1 mm / min. The measured tensile modulus of each laminate film sample is calculated by calculating the slope of the stress / strain curve corresponding to two strain points, ε1 = 0.05% and ε2 = 0.25%, based on the specified strain values ​​at those two points (JIS K 7161-1:2014, 10.3.2). The TD direction is the transverse direction perpendicular to the machine direction (MD) of the laminate film 10 during production. If the tensile modulus in the TD direction is less than 250 MPa, the laminate film is too soft and prone to stretching and breaking when tied or untied, making it particularly difficult to untie the knot without breaking the laminate film. Furthermore, if the tensile strength in the MD direction is 400 MPa or greater, the laminate film is too hard and easily unravels, making it difficult to tie. As described below, the laminated film 10 has three layers (11, 12, and 13) all made of polyethylene resin, so it is moderately soft and is configured so that the tensile modulus in the TD direction tends to be 250 MPa or more and 400 MPa or less.

[0017] Polyethylene resin is a resin having a chemical structure formed by the polymerization of ethylene. Examples of polyethylene resin include one type of polyethylene selected from the group consisting of very low density polyethylene (hereinafter also referred to as "PE-VLD"), low density polyethylene (hereinafter also referred to as "PE-LD"), linear low density polyethylene (hereinafter also referred to as "PE-LLD"), medium density polyethylene (hereinafter also referred to as "PE-MD"), and high density polyethylene (hereinafter also referred to as "PE-HD"), or a mixture of two or more types of polyethylene.

[0018] PE-VLD is a copolymer of ethylene and α-olefin, and generally has a density of 0.88 g / cm 3 More than 0.910g / cm 3 PE-LD is polyethylene polymerized by a high-pressure method to form long-chain branches in the molecular structure, and has a density of 0.910 g / cm 3 More than 0.930g / cm 3 The molecular weight distribution of polymers produced by single-site catalysts is less than 100% (JIS K 6748:1995). PE-LLD, PE-MD, and PE-HD can be obtained by using multi-site catalysts such as Phillips catalysts (chromium / silica catalysts) and Ziegler-Natta catalysts (titanium chloride / organoaluminum catalysts), or single-site catalysts such as Kaminsky catalysts (metallocene catalysts). PE-LLD, PE-MD, and PE-HD can each be polymerized by a single-site catalyst, a multi-site catalyst, or a mixture containing both. Polymers produced by single-site catalysts have a narrow molecular weight distribution and are excellent in heat sealing properties. On the other hand, polymers produced by multi-site catalysts have a broad molecular weight distribution and are easy to process, such as extrusion. PE-LLD has a density of 0.910 g / cm. 3 More than 0.925g / cm 3 The following ethylene copolymer (JIS K 68990-1:2000) is obtained by copolymerization of ethylene and α-olefin. PE-MD has a density of 0.926 g / cm 3 More than 0.942g / cm 3 PE-HD is polyethylene with a density of 0.942 g / cm 3The polyethylene resin is the above-mentioned polyethylene (JIS K 6748:1995). The density of the polyethylene resin can be determined by a measurement method in accordance with Method D (density gradient tube method) of JIS K 7112:1999 "Plastics - Method for measuring density and specific gravity of non-foamed plastics." Examples of the α-olefins mentioned here include 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, and 1-octene.

[0019] The first resin layer 11 in the laminate film 10 contains, in addition to polyethylene resin, calcium hydroxide particles 19. When packaging food using the laminate film 10, it is preferable to arrange the first resin layer 11 on the side (inside) where the food will be contained, as this makes it easier for the calcium hydroxide particles 19 to exert their freshness-preserving and deodorizing effects on the food. In other words, the first resin layer 11 is preferably the innermost layer of the laminate film 10 arranged on the side where the food will be contained.

[0020] The polyethylene resin contained in the first resin layer 11 is not particularly limited as long as it does not contradict the object of the present invention, and may be, for example, one or more of the polyethylene resins described above. From the viewpoint of making the laminated film 10 easier to bind and harder to unravel while minimizing the falling off of the calcium hydroxide particles 19 by forming the first resin layer 11 having an appropriate softness, the polyethylene resin contained in the first resin layer 11 may be, for example, one or more polyethylenes selected from PE-LD and PE-LLD, preferably PE-LD, and more preferably a polyethylene having a density of 0.916 g / cm 3 More than 0.920g / cm 3 The following is PE-LLD.

[0021] The content of the polyethylene resin in the first resin layer 11 may be, for example, 80% by mass or more, preferably 90% by mass or more, and more preferably 92% by mass or more, from the viewpoint of easily imparting an appropriate strength to the first resin layer 11. Furthermore, the content of the polyethylene resin in the first resin layer 11 may be, for example, 99.5% by mass or less, preferably 99.0% by mass or less, and more preferably 95% by mass or less, from the viewpoint of leaving room for the first resin layer 11 to contain a sufficient amount of calcium hydroxide particles. Note that, in this specification, the term "content" refers to the total content of two or more components when a resin layer or a polyethylene resin composition from which the resin layer or the polyethylene resin composition contains two or more components. For example, when PE-LD and PE-LLD, which correspond to polyethylene resins, are contained in the first resin layer 11, the content of the polyethylene resin in the first resin layer 11 refers to the total content of PE-LD and PE-LLD.

[0022] From the viewpoint of maintaining freshness and preventing odors in food, the calcium hydroxide particles 19 may have a purity of, for example, 90% by mass or more, preferably 95% by mass or more, and more preferably 97% by mass or more.

[0023] If some calcium hydroxide particles protrude from the first resin layer 11, the first resin layers 11 are less likely to block each other when the laminate film 10 is untied and then untied, making it easier to unravel. From this perspective, the particle diameter of the calcium hydroxide particles 19 is preferably 1.0 μm or more, and more preferably 2.0 μm or more. On the other hand, if the particle diameter of the calcium hydroxide particles is too large, the calcium hydroxide particles are more likely to fall off from the first resin layer 11. From the perspective of minimizing this falling off and facilitating efficient production of the laminate film 10, the particle diameter of the calcium hydroxide particles 19 is preferably 10 μm or less, and more preferably 8.0 μm or less.

[0024] The "particle diameter" of the calcium hydroxide particles 19 in this specification is the particle diameter (D) at which the cumulative value in the volume-based cumulative particle size distribution reaches 50%, measured by a method in accordance with JIS Z 8825:2013 "Particle size analysis - laser diffraction and scattering method." 50 The median diameter is the average particle size (D ). The measurement sample may be calcium hydroxide particles before they are mixed with the polyethylene resin that is the raw material for the first resin layer 11 during the production of the laminate film 10, or calcium hydroxide particles collected from the first resin layer 11 after the production of the laminate film 10. A laser diffraction particle size distribution analyzer (Seishin Enterprise Co., Ltd., Model LMS-2000e) can be used as the measurement device. Specifically, a scattering measurement mode is employed, and a laser beam is irradiated onto a wet cell in which a dispersion liquid containing the measurement sample (calcium hydroxide particles) is circulated, to obtain a scattered light distribution from the measurement sample. The scattered light distribution is approximated by a log-normal distribution, and within the range of the particle size distribution (horizontal axis, σ) set to a minimum of 0.020 μm and a maximum of 2000 μm, a cumulative density of 50% (D ) on a volume basis is obtained. 50 ) is the particle size of the calcium hydroxide particles 19.

[0025] From the viewpoint of maintaining freshness and preventing odors in food, the content of calcium hydroxide particles 19 in the first resin layer 11 may be, for example, 0.5% by mass or more, preferably 1.0% by mass or more, and more preferably 2.0% by mass or more. Furthermore, from the viewpoint of minimizing the falling off of calcium hydroxide particles 19 from the first resin layer 11, the content of calcium hydroxide particles 19 in the first resin layer 11 may be, for example, 15% by mass or less, preferably 10% by mass or less, and more preferably 8.0% by mass or less.

[0026] From the viewpoint of preventing blocking and facilitating untangling of knots, the surface roughness Ra of the inner surface 17 of the laminate film 10 formed by the first resin layer 11 (i.e., the surface of the laminate film 10 on which the first resin layer 11 is exposed) is preferably 2.0 μm or more. In this specification, the surface roughness Ra is the arithmetic mean roughness defined in JIS B 0601:2013. The surface roughness Ra can be measured using, for example, a laser microscope (VK-100) manufactured by Keyence Corporation.

[0027] In addition to the polyethylene resin and calcium hydroxide particles 19, the first resin layer 11 may further contain a small amount of additives as needed. Examples of additives include an antiblocking agent, a colorant, or a fatty acid ester surfactant. The content of the fatty acid ester surfactant in the first resin layer 11 may be, for example, 1000 ppm or less, preferably 100 ppm or less, and more preferably 10 ppm or less. The fatty acid ester surfactant functions as an internal lubricant that disperses a large number of calcium hydroxide particles 19 evenly throughout the first resin layer 11.

[0028] The first resin layer 11 may contain, for example, 10 ppm or less of fatty acid amide-based ionic surfactant, preferably 5.0 ppm or less, and more preferably does not contain any fatty acid amide-based ionic surfactant. Absence of fatty acid amide-based ionic surfactant can be confirmed by a content below the detection limit of a typical measuring device, meaning, for example, that it is less than 1.0 ppm. Examples of fatty acid amide-based surfactants include stearic acid amide, oleic acid amide, erucic acid amide, methylene bisstearic acid amide, and ethylene bisstearic acid amide. While fatty acid amide-based surfactants bleed out to the surface of the resin layer and function as an external lubricant (slip agent), they may potentially promote the detachment of calcium hydroxide particles 19 from the first resin layer 11, especially for those particles that protrude from the first resin layer 11 at a relatively high rate. Therefore, from the viewpoint of allowing the calcium hydroxide particles 19 to exert an anti-blocking effect and making it easier to untie knots in the laminated film 10, it is even more preferable that the film does not contain a fatty acid amide-based ionic surfactant, as described above.

[0029] The first resin layer 11 may further contain, as a resin component, a copolymer of ethylene and a structural unit that does not fall under the category of an α-olefin, so long as the amount is small enough to achieve the object of the present invention. Examples of such copolymers include ethylene-vinyl acetate copolymer and tetrafluoroethylene-ethylene copolymer. The content of the ethylene copolymer in the first resin layer 11 may be, for example, 5% by mass or less, preferably 2% by mass or less, and more preferably zero.

[0030] The thickness of the first resin layer 11 may be, for example, 5 μm or more, preferably 7 μm or more, and more preferably 9 μm or more, from the viewpoint of providing a certain degree of rigidity so that the laminate film 10 is less likely to tear. The thickness of the first resin layer 11 may be, for example, 15 μm or less, preferably 13 μm or less, and more preferably 11 μm or less, from the viewpoint of making it easier to bind the laminate film 10. Note that, when calcium hydroxide particles 19 protrude from the first resin layer 11, the thickness of the first resin layer 11 includes the thickness of the protruding portions. The thickness of the resin layer in this specification can be measured using an electron microscope. Specifically, the thickness can be determined by observing the cross section of the laminate film 10 at a magnification of 500x, measuring the thickness at five randomly selected points on the first resin layer 11, and arithmetically averaging these measurements.

[0031] The second resin layer 12 in the laminate film 10 is an intermediate layer made of polyethylene resin and sandwiched between the first resin layer 11 and the third resin layer 13. Conventional laminate films for packaging food use a relatively hard resin such as polypropylene or ethylene-vinyl alcohol copolymer as the resin component of the intermediate layer, making them hard and difficult to tie. In contrast, the laminate film 10 uses a soft polyethylene resin as the resin component of the second resin layer 12 (intermediate layer), making it soft and easy to tie.

[0032] The polyethylene resin contained in the second resin layer 12 may be, for example, one or more of the above-mentioned polyethylenes. From the viewpoint of achieving both a certain degree of rigidity and ease of binding in the laminate film 10, the polyethylene resin contained in the second resin layer 12 is preferably a mixture of PE-HD and one or more polyethylenes selected from PE-LD and PE-LLD. From the same viewpoint, the polyethylene resin contained in the second resin layer 12 is preferably a polyethylene having a density of 0.916 g / m 3 More than 0.920g / cm 3 The following PE-LLD and density are 0.945g / cm 3 More than 0.955g / cm 3A mixture with the following PE-HD is more preferred.

[0033] From the viewpoint of providing the laminate film 10 with appropriate rigidity and ease of binding by the ethylene resin, the content of the polyethylene resin in the second resin layer 12 may be, for example, 95% by mass or more, preferably 98% by mass or more, and more preferably 99.5% by mass or more. From a similar viewpoint, when the polyethylene resin contained in the second resin layer 12 is a mixture of PE-HD and one or more polyethylenes selected from PE-LD and PE-LLD, the content of the one or more polyethylenes selected from PE-LD and PE-LLD in the second resin layer 12 is preferably 40% by mass or more and 60% by mass or less, and the content of PE-HD in the second resin layer 12 is preferably 40% by mass or more and 60% by mass or less. From a similar viewpoint, when the polyethylene resin contained in the second resin layer 12 is PE-LLD and PE-HD, the content of PE-LLD in the second resin layer 12 is preferably 40% by mass or more and 60% by mass or less, and the content of PE-HD in the second resin layer 12 is preferably 40% by mass or more and 60% by mass or less.

[0034] In addition to the polyethylene resin, the second resin layer 12 may further contain a small amount of additives as needed. The additives may be those described above in the description of the first resin layer 11, and it is preferable that the second resin layer 12 does not contain a fatty acid amide-based ionic surfactant. The second resin layer 12 may further contain, as a resin component, a copolymer of ethylene and a structural unit that does not fall under the category of α-olefin, as long as the amount is small enough to achieve the object of the present invention. Such a copolymer may be one described above in the description of the first resin layer 11, and the content of such a copolymer in the second resin layer 12 may be, for example, 5% by mass or less, preferably 2% by mass or less, and it is even more preferable that the second resin layer 12 does not contain such a copolymer.

[0035] The thickness of the second resin layer 12 may be, for example, 1 μm or more, and preferably 2 μm or more, from the viewpoint of imparting a certain degree of rigidity so that the laminate film 10 is less likely to tear. The thickness of the second resin layer 12 may be, for example, 5 μm or less, and preferably 3 μm or less, from the viewpoint of making it easier to bind the laminate film 10. The thickness of the second resin layer 12 is measured in the same manner as the thickness of the first resin layer 11.

[0036] The third resin layer 13 in the laminate film 10 is the outermost layer made of a polyethylene resin. The polyethylene resin contained in the third resin layer 13 may be, for example, one or more of the above-mentioned polyethylenes. From the viewpoint of achieving both a certain degree of strength and ease of binding in the laminate film 10, the polyethylene resin contained in the third resin layer 13 is preferably a mixture of PE-LD and PE-LLD, and more preferably a polyethylene resin having a density of 0.916 g / cm. 3 More than 0.920g / cm 3 The following PE-LLD and density are 0.920g / cm 3 More than 0.925g / cm 3 It is a mixture with the following PE-LD.

[0037] From the viewpoint of providing the laminate film 10 with an appropriate strength and ease of binding by the ethylene resin, the content of the polyethylene resin in the third resin layer 13 may be, for example, 95% by mass or more, preferably 98% by mass or more, and more preferably 99.5% by mass or more. From the same viewpoint, when the polyethylene resin contained in the third resin layer 13 is a mixture of PE-LD and PE-LLD, the content of PE-LD in the third resin layer 13 may be, for example, 10% by mass to 90% by mass or less, 20% by mass to 80% by mass or less, or 12% by mass to 20% by mass or less, and the content of PE-LLD in the third resin layer 13 may be, for example, 10% by mass to 90% by mass or less, 20% by mass to 80% by mass or less, or 80% by mass to 88% by mass.

[0038] In addition to the polyethylene resin, the third resin layer 13 may further contain a small amount of additives as needed. The additives may be those described above in the description of the first resin layer 11, and it is preferable that the third resin layer 13 does not contain a fatty acid amide-based ionic surfactant. The third resin layer 13 may further contain, as a resin component, a copolymer of ethylene and a structural unit that does not fall under the category of α-olefin, as long as the amount is small enough to achieve the object of the present invention. Such a copolymer may be one described above in the description of the first resin layer 11, and its content in the third resin layer 13 may be, for example, 5% by mass or less, preferably 2% by mass or less, and it is even more preferable that the third resin layer 13 does not contain any copolymer.

[0039] The thickness of the third resin layer 13 may be, for example, 5 μm or more, preferably 7 μm or more, and more preferably 9 μm or more, from the viewpoint of imparting a certain degree of rigidity so that the laminate film 10 is less likely to tear. The thickness of the third resin layer 13 may be, for example, 15 μm or less, preferably 13 μm or less, and more preferably 11 μm or less, from the viewpoint of making it easier to bind the laminate film 10. The thickness of the third resin layer 13 is measured in the same manner as the thickness of the first resin layer 11.

[0040] The thickness of the laminate film 10 may be, for example, 11 μm or more, preferably 16 μm or more, and more preferably 20 μm or more, from the viewpoint of providing a certain degree of rigidity so as to make it less likely to tear. The thickness of the laminate film 10 may be, for example, 32 μm or less, preferably 28 μm or less, and more preferably 23 μm or less, from the viewpoint of making it easier to tie. The thickness of the laminate film 10 is measured in the same manner as the thickness of the first resin layer 11.

[0041] The laminate film 10 can be produced, for example, by coextrusion, in which the raw materials for the first resin layer 11, the second resin layer 12, and the third resin layer 13 are extruded in this order, and is preferably produced by a coextrusion inflation method. In production by the coextrusion inflation method, coextrusion is usually carried out at a blow-up ratio of 1.2 to 10 times. In the coextrusion inflation method, it is preferable to use a water-cooled or air-cooled inflation molding machine.

[0042] A packaging material according to one embodiment is made of a laminate film 10, and is, for example, a food packaging bag 50 shown in Figures 2(a) and 2(b). From the viewpoint of preserving the freshness of food and preventing odors with calcium hydroxide particles 19, it is preferable that the food packaging bag 50 has an inner surface made of a first resin layer 11 (Figure 1) of the laminate film 10 and an outer surface (51 and 52) made of a third resin layer 13 (Figure 1) of the laminate film 10.

[0043] The food packaging bag 50 can be obtained, for example, by folding the laminate film 10 shown in Fig. 1 with the third resin layer 13 facing outward (with the first resin layer 11 facing inward) so that one surface 51 (Fig. 2(b)) of the third resin layer 13 of the folded laminate film 10 overlaps with the other surface 52 (Fig. 2(b)), and then bonding one end 54 of the folded laminate film to the other end 55 as shown in Figs. 2(a) and 2(b). Bonding may be by adhesive or by melt bonding using heat sealing.

[0044] The matters disclosed in this specification include the following. (1) A laminated film having a first resin layer, a second resin layer, and a third resin layer in this order, The tensile modulus in the TD direction is 250 MPa or more and 400 MPa or less, the first resin layer comprises a polyethylene resin and calcium hydroxide particles, the second resin layer comprises a polyethylene resin, the third resin layer comprises a polyethylene resin; Laminated film for food packaging. (2) The laminated film according to (1) above, wherein the content of the calcium hydroxide particles in the first resin layer is 1.0% by mass or more and 10% by mass or less, and the particle diameter of the calcium hydroxide particles is 1.0 μm or more and 10 μm or less. (3) The polyethylene resin in the first resin layer has a density of 0.916 g / cm 3 More than 0.920g / cm 3 Linear low-density polyethylene (PE-LLD) is: The polyethylene resin in the second resin layer is a polyethylene resin having a density of 0.945 g / cm 3 and a linear low-density polyethylene (PE-LLD). 3 More than 0.955g / cm 3 It is a mixture of high density polyethylene (PE-HD) The polyethylene resin in the third resin layer is a polyethylene resin having a density of 0.920 g / cm 3 and a linear low-density polyethylene (PE-LLD). 3 More than 0.925g / cm 3 The laminated film according to (1) or (2) above, which is a mixture with low-density polyethylene (PE-LD), which is: (4) the second resin layer has a linear low-density polyethylene (PE-LLD) content of 40% by mass or more and 60% by mass or less, and a high-density polyethylene (PE-HD) content of 40% by mass or more and 60% by mass or less, The laminated film described in (3) above, wherein the third resin layer has a linear low-density polyethylene (PE-LLD) content of 10% by mass or more and 90% by mass or less, and a low-density polyethylene (PE-LD) content of 10% by mass or more and 90% by mass or less. (5) A packaging material comprising the laminated film described in any one of (1) to (4) above.

[0045] The present invention is not limited to the above-described embodiments and can be embodied in various forms, including improvements, modifications, or variations based on the knowledge of those skilled in the art, without departing from the spirit of the present invention. The present invention may be embodied in a form in which any specific feature is replaced with another technique within the scope of producing the same function or effect. For example, a laminate film for food packaging may be a film in which a fourth polyethylene resin layer or a fifth polyethylene resin layer is laminated to the third resin layer 13 of the three-layer laminate film 10 illustrated in FIG. 1. Furthermore, compared to the three-layer laminate film 10 illustrated in FIG. 1, an adhesive layer may be provided between the first resin layer 11 and the second resin layer 12 and / or between the second resin layer 12 and the third resin layer 13. The packaging material is not limited to the food packaging bag 50 illustrated in FIG. 2, and may be any packaging material that can be easily tied by tying a knot with a laminate sheet. For example, a bag in which the laminate film 10 is gusseted may be used. [Example]

[0046] The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

[0047] Example 1 To prototype a three-layer laminated film consisting of a first resin layer (innermost layer), a second resin layer (middle layer), and a third resin layer (outermost layer), PE-LLD (density: 0.918 g / cm 3 ) and PE-LD (density: 0.923 g / cm 3 ) and PE-HD (density: 0.951 g / cm 3) and calcium hydroxide particles (particle diameter in the range of 1.0 μm to 10 μm). Using these preparations, a composition containing 92% by mass of PE-LLD and 8% by mass of calcium hydroxide particles was prepared as the raw material for the first resin layer. A composition containing 50% by mass of PE-LLD and 50% by mass of PE-HD was prepared as the raw material for the second resin layer. A composition containing 85% by mass of PE-LLD and 15% by mass of PE-LD was prepared as the raw material for the third resin layer. Each of these prepared compositions was then heated and melt-kneaded separately in an extrusion molding machine, and extruded into a tubular shape from a die by a co-extrusion inflation method to produce a three-layer laminate film. A portion of this tubular laminate film corresponding to the lower end (bottom) of the bag was heat-sealed, and a portion corresponding to the upper end (opening) of the bag was cut to produce a prototype food packaging bag according to Example 1.

[0048] In Example 1, the dimensions of the prototype bag were 400 mm length x 250 mm width x 60 μm thickness, and the thickness of the laminated film constituting this bag was 30 μm (0.030 mm). A type 2 test piece (a rectangular shape with a total length of 150 mm, a width of 15 mm, and a thickness of 0.030 mm) was cut out from this laminated film, and the tensile modulus in the TD direction was measured using the method described above, and was found to be 254 MPa.

[0049] <Comparative Example 2> As Comparative Example 2, a commercially available food packaging bag composed of a single-layer film consisting only of an OPP film layer was prepared. The dimensions of this bag were 500 mm long x 350 mm wide, and the thickness of the laminated film constituting this bag was 30 μm. Test specimen Type 2 was cut out from this single-layer film, and the tensile modulus in the TD direction was measured using the method described above, resulting in a value of 2,100 MPa.

[0050] <Comparative Example 3> As Comparative Example 3, a commercially available bag composed of a multilayer film containing multiple polyethylene resin layers was prepared. The dimensions of this bag were 500 mm long x 350 mm wide, and the thickness of the multilayer film constituting this bag was 30 μm. Test specimen Type 2 was cut out from this multilayer film, and the tensile modulus in the TD direction was measured using the method described above, resulting in a value of 426 MPa. The innermost layer of this multilayer film was observed with an optical microscope, but no particles (e.g., calcium hydroxide particles) were found to be embedded therein. Therefore, it is believed that the innermost layer of this multilayer film is essentially composed of polyethylene resin only.

[0051] <Comparative Example 4> As Comparative Example 4, a commercially available bag composed of a single-layer film consisting of only a PE-HD resin layer was prepared. The dimensions of this bag were 340 mm long x 230 mm wide, and the thickness of the film constituting this bag was 17 μm. Test specimens of type 2 were cut out from this film, and the tensile modulus in the TD direction was measured using the method described above, resulting in a value of 238 MPa.

[0052] <Evaluation test 1: Ease of tying a bag knot> Five panelists (A to E) were selected for the evaluation tests. In each of the following evaluation tests 1 and 2, each panelist was given no prior information and performed the evaluation without knowing the behavior or thoughts of the other panelists. In evaluation test 1, three bags each according to Example 1 and Comparative Examples 2 to 4 were placed side by side on a table in a room (n=3). Each panelist was asked to tie a knot in each bag in any order so as to close the top end (opening) of the bag, and to rate the ease of tying each bag on a five-point scale using the following criteria: 5 points: The knot is easy to tie and does not appear to come undone on its own. 3 points: It is possible to tie a knot, but the film of the bag will stretch enough to prevent a hole, or the knot will likely come undone. 1 point: The bag develops a hole when tying the knot, or the knot comes undone on its own.

[0053] The evaluation results of Evaluation Test 1 are shown in Table 1 below. [Table 1]

[0054] <Evaluation test 2: Evaluation of ease of untying the bag knot> Each bag knotted in the above-mentioned Evaluation Test 1 was left for 1 hour at room temperature of approximately 20°C. After that, each panelist (n=3) was asked to untie the knots they had tied on each bag in Evaluation Test 1 in any order. They were then asked to rate the ease of untying the knots on each bag on a five-point scale using the following criteria. Note that the bag of Comparative Example 2 was not evaluated in Evaluation Test 2 because the knot came undone quickly and naturally. 5 points: After the knot was untied, there was no sign of the film stretching in the bag. 3 points: After the knot on the bag was untied, the film was clearly stretched. Score 1: The bag cannot be untied, or the bag stretches and develops a hole when untied.

[0055] The evaluation results of Evaluation Test 2 are shown in Table 2 below. [Table 2]

[0056] <Evaluation test 3: Evaluation of the sealing ability of the bag knot> Fifteen bags (Samples 1 to 15) were prepared for each group of Example 1 and Comparative Examples 2 to 4. Each bag was inflated with as much air as possible and then tied with a knot near the top end to close the opening. The bag was tied with a constant pulling force of 20 N, 50 N, or 80 N using an Aiko Engineering RZE-10 digital force gauge. The tied bags were placed in a 60-liter glass water tank (Kotobuki Kogei Co., Ltd.) under atmospheric pressure and submerged. Air leakage from the bag was visually confirmed within 60 seconds of submersion. Results were evaluated as "Good" if no air leakage occurred, and "Poor" if air leakage occurred.

[0057] The evaluation results of Evaluation Test 3 are shown in Table 3 below. [Table 3]

[0058] As shown in Tables 1 to 3, the bag of Comparative Example 2 was made of a film with a tensile modulus in the TD direction that was too high, making it too stiff. Even if a knot was tied in the bag, the knot would unravel spontaneously, making it impossible to tie the bag and resulting in a watertight bag. The bag of Comparative Example 3 was made of a multilayer film with a slightly higher tensile modulus in the TD direction that was slightly stiff. Although it was possible to tie a knot in the bag, the knot could not be maintained (the tying force) without pulling the bag strongly, resulting in a problem that a portion of the film was stretched during the tying process and watertightness was difficult to achieve. The bag of Comparative Example 4 was made of a film with a tensile modulus in the TD direction that was slightly too low, making it too soft. Although it was possible to tie a knot in the bag, the film was stretched and holes were formed during the tying and untying processes, resulting in a problem that watertightness could not be achieved.

[0059] In contrast, the bag of Example 1 had a film with a moderate tensile modulus in the TD direction and moderate hardness, making it easy to tie a knot in the bag without stretching it, and similarly easy to untie the knot. Furthermore, the bag of Example 1 was shown to consistently achieve watertightness regardless of the strength of the pulling force (20 N, 50 N, or 80 N) used to tie the knot. From these experimental results, the inventors of the present application discovered that a laminated film with a tensile modulus in the TD direction of 250 MPa or more and 400 MPa or less can easily achieve both ease of tying and untieing a bag, leading to the completion of the present invention. [Explanation of symbols]

[0060] 10: laminated film, 11: first resin layer, 12: second resin layer, 13: third resin layer, 17: inner surface, 19: calcium hydroxide particles, 50: food packaging bag, 51: one side, 52: other side, 53: folded portion, 54: one end, 55: other end

Claims

1. A three-layer laminate film for food packaging having a first resin layer, a second resin layer, and a third resin layer in this order, The tensile modulus in the TD direction is 250 MPa or more and 400 MPa or less, and the thickness is 11 μm or more, the first resin layer is an innermost layer having a thickness of 5 μm or more and disposed on the food-packaged side, and comprises linear low-density polyethylene (PE-LLD) having a density of 0.916 g / cm 3 or more and 0.920 g / cm 3 or less and calcium hydroxide particles; the second resin layer is an intermediate layer having a thickness of 5 μm or less, comprising a mixture of the linear low-density polyethylene (PE-LLD) and a high-density polyethylene (PE-HD) having a density of 0.945 g / cm 3 or more and 0.955 g / cm 3 or less; the third resin layer is an outermost layer having a thickness of 5 μm or more and comprising a mixture of the linear low-density polyethylene (PE-LLD) and a low-density polyethylene (PE-LD) having a density of 0.920 g / cm 3 or more and 0.925 g / cm 3 or less; Laminated film.

2. 2. The laminated film according to claim 1, wherein the content of the calcium hydroxide particles in the first resin layer is 1.0 mass% or more and 10 mass% or less, and the particle diameter of the calcium hydroxide particles is 1.0 μm or more and 10 μm or less.

3. A laminated film as described in claim 1, having a thickness of 32 μm or less.

4. the second resin layer has a linear low-density polyethylene (PE-LLD) content of 40% by mass or more and 60% by mass or less, and a high-density polyethylene (PE-HD) content of 40% by mass or more and 60% by mass or less, 2. The laminated film according to claim 1, wherein the third resin layer has a content of the linear low-density polyethylene (PE-LLD) of 10% by mass or more and 90% by mass or less, and a content of the low-density polyethylene (PE-LD) of 10% by mass or more and 90% by mass or less.

5. A packaging material comprising the laminated film according to any one of claims 1 to 4.

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