Food packaging film and food packaging body

Abstract

To provide a food packaging film which can achieve a food package having sufficient water vapor barrier property and is excellent in cost and productivity.SOLUTION: A food packaging film 100 is a film for packaging food, includes a biaxially oriented film layer 101 formed of a propylene polymer composition containing a propylene polymer and a tackifier, and a heat seal layer 103 provided on at least one surface of the biaxially oriented film layer 101 so as to be brought into direct contact with each other, where the heat seal layer 103 is an outermost layer and a thickness of the heat seal layer 103 is 0.1 μm or more and 10 μm or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a food packaging film and a food package. [Background technology]

[0002] Biaxially oriented polypropylene film (hereinafter referred to as OPP film) has an excellent balance of performance such as processability, water vapor barrier properties, transparency, mechanical strength, and rigidity, and is used as a packaging film for packaging food.

[0003] Examples of technologies relating to food packaging films using such OPP films include those described in Patent Document 1 (JP-A No. 2008-73926) and Patent Document 2 (JP-A No. 2004-82499).

[0004] Patent Document 1 describes a biaxially oriented multilayer polypropylene film characterized by having a layer of a propylene-α-olefin random copolymer (C) having a melting point in the range of 125 to 145°C on one side of a biaxially oriented film made of a propylene polymer composition containing 75 to 90% by weight of a propylene homopolymer (A) and 25 to 10% by weight of a tackifier (D), with a layer of a propylene-based polymer (B) having a melting point of 155°C or higher sandwiched therebetween, and a layer of a propylene-based polymer (E) on the other side of the biaxially oriented film. Patent Document 2 describes that a biaxially oriented multilayer polypropylene film having the above-described structure can inhibit the seepage of petroleum resins and the like onto the film surface, and has excellent lamination strength and moisture resistance.

[0005] Patent Document 2 describes a multilayer resin film that further comprises a polyvinyl alcohol resin layer via an adhesive layer on at least one surface of a biaxially oriented polypropylene resin layer containing 10 to 40% by weight of a highly crystalline resin and 6 to 15% by weight of a petroleum resin, and that has an oxygen permeability of 600 mL / m at a relative humidity of 85% RH and a temperature of 23°C. 2·day·MPa or less, and the water vapor permeability at a relative humidity of 90%RH and a temperature of 40°C is 3.5g / m 2 The multilayer resin film is characterized by a thickness of 20 μm or less. Patent Document 2 describes that a multilayer resin film having the above-described structure has excellent oxygen gas barrier properties and moisture resistance. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-73926 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-82499 Summary of the Invention [Problem to be solved by the invention]

[0007] Although OPP film has water vapor barrier properties, it has poor heat-sealing properties. Therefore, when using OPP film in food packaging such as food packaging bags, it has been necessary to laminate a film with excellent heat-sealing properties, such as a non-oriented polypropylene film (hereinafter also referred to as CPP film), to the OPP film. By further laminating a CPP film to the OPP film, the heat-sealing strength of the resulting food packaging is increased, the penetration of moisture and oxygen at the seal area is suppressed, and the water vapor barrier properties and oxygen barrier properties of the food packaging can be improved. However, because OPP film and CPP film have poor adhesion, the CPP film had to be laminated to the OPP film using an adhesive. As a result, food packaging films using OPP film used in food packages require a step of further laminating the CPP film using an adhesive, which requires many manufacturing steps, leaving room for improvement in terms of simplifying the manufacturing process and reducing costs.

[0008] The present invention has been made in view of the above circumstances, and aims to provide a food packaging film that can realize a food package having sufficient water vapor barrier properties and is also excellent in terms of cost and productivity. [Means for solving the problem]

[0009] The present inventors have conducted extensive research to solve the above problems, and as a result, have found that by using a biaxially stretched film made of a propylene polymer composition containing a propylene polymer and a tackifier as the OPP film to enhance the water vapor barrier properties of the OPP film itself, and further by providing only a thin heat seal layer directly on one side of the biaxially stretched film layer, it is possible to obtain a food package having sufficient water vapor barrier properties without using a CPP film with excellent heat seal properties, thereby completing the present invention.

[0010] That is, according to the present invention, there are provided the food packaging film and food package shown below.

[0011] [1] A film for packaging food, comprising: a biaxially stretched film layer composed of a propylene polymer composition containing a propylene polymer and a tackifier; 、 Hi a heat seal layer; Equipped with El A food packaging film, the above The propylene polymer is composed only of propylene homopolymer. the law of nature, With respect to the heat seal layer, (i) two heat seal layers are provided with a thickness of 0.1 μm or more and 10 μm or less so as to be in direct contact with both sides of the biaxially stretched film layer, respectively, or (ii) only one heat seal layer is provided with a thickness of 0.1 μm or more and 10 μm or less so as to be in direct contact with only one side of the biaxially stretched film layer, In the case of (ii) above, the food packaging film is made up of only two layers, the biaxially stretched film layer and the heat seal layer. Food packaging film. [2] In the food packaging film described in [1] above, The food packaging film has a single heat seal layer. [3] In the food packaging film according to the above [1] or [2], The food packaging film wherein the heat seal layer is biaxially stretched. [4] In the food packaging film according to any one of [1] to [3] above, The food packaging film, wherein the food comprises a dried food. [5] In the food packaging film described in [4] above, A food packaging film for the above dried food, in which the water activity is 0.05 or more and 0.3 or less. [6] In the food packaging film according to any one of [1] to [5] above, Food packaging film used for outer packaging bags. [7] In the food packaging film according to any one of [1] to [6] above, A food packaging film in which the softening temperature of the tackifier is 100°C or higher and 150°C or lower. [8] In the food packaging film according to any one of [1] to [7] above, The food packaging film, wherein the tackifier comprises at least one selected from petroleum hydrocarbon resins and hydrogenated petroleum hydrocarbon resins. [9] In the food packaging film described in [8] above, The food packaging film, wherein the tackifier comprises a hydrogenated petroleum hydrocarbon resin.

[10] In the food packaging film according to any one of [1] to [9] above, A food packaging film, wherein the content of the tackifier contained in the biaxially stretched film layer is 1% by mass or more and 50% by mass or less, when the entire biaxially stretched film layer is taken as 100% by mass.

[11] In the food packaging film according to any one of [1] to

[10] above, A food packaging film, wherein the propylene polymer contained in the biaxially stretched film layer comprises a propylene homopolymer.

[12] In the food packaging film according to any one of [1] to

[11] above, A food packaging film, wherein the propylene polymer contained in the biaxially oriented film layer comprises a highly stereoregular propylene polymer.

[13] In the food packaging film described in

[12] above, The food packaging film is one in which the highly stereoregular propylene polymer has an isotactic mesopentad fraction (mmmm) of 96% or more.

[14] In the food packaging film according to any one of [1] to

[13] above, The food packaging film, wherein the heat seal layer comprises at least one selected from a propylene-α-olefin random copolymer and a propylene homopolymer.

[15] In the food packaging film according to any one of [1] to

[14] above, A food packaging film in which the ratio of the thickness of the biaxially stretched film layer to the total thickness of the food packaging film is 0.50 or more and 0.998 or less.

[16] A food packaging product using the food packaging film according to any one of [1] to

[15] above. [Effects of the Invention]

[0012] According to the present invention, it is possible to realize a food packaging product having sufficient water vapor barrier properties, and to provide a food packaging film that is excellent in terms of cost and productivity. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a cross-sectional view schematically illustrating an example of the structure of a food packaging film according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the drawings are schematic diagrams and do not correspond to the actual dimensional ratios. Note that "~" between numbers in the text indicates "above" to "below" unless otherwise specified.

[0015] <Food packaging film> FIG. 1 is a cross-sectional view showing a schematic example of the structure of a food packaging film 100 according to an embodiment of the present invention. The food packaging film 100 of this embodiment is a film for packaging food, and comprises a biaxially oriented film layer 101 made of a propylene polymer composition containing a propylene polymer and a tackifier, and a heat seal layer 103 provided so as to be in direct contact with at least one surface of the biaxially oriented film layer 101, the heat seal layer 103 being the outermost layer, and the thickness of the heat seal layer 103 being 0.1 μm or more and 10 μm or less. Here, in this embodiment, when the heat seal layer 103 is provided on both sides of the biaxially stretched film layer 101, the above thickness of the heat seal layer 103 indicates the thickness of the heat seal layer 103 provided on one side of the biaxially stretched film layer 101.

[0016] As mentioned above, OPP film has water vapor barrier properties but poor heat sealing properties. Therefore, when using OPP film for food packaging such as food packaging bags, it is necessary to laminate a CPP film or other film with excellent heat sealing properties to the OPP film. By further laminating a CPP film on the OPP film, the heat sealing strength of the resulting food package is increased, the intrusion of moisture and oxygen at the seal area is suppressed, and the water vapor barrier properties and oxygen barrier properties of the food package can be improved. However, because OPP film and CPP film have poor adhesion, the CPP film had to be laminated to the OPP film using an adhesive. As a result, food packaging films using OPP film used in food packages require a step of further laminating the CPP film using an adhesive, which requires many manufacturing steps, leaving room for improvement in terms of simplifying the manufacturing process and reducing costs.

[0017] The present inventors have conducted extensive research to solve the above problems. First, they considered using a film as a packaging film in which a heat seal layer having a relatively thin thickness of 0.1 μm to 10 μm is provided so as to be in direct contact with at least one side of a conventional OPP film. However, food packaging made using such films had poor sealing properties and did not have fully satisfactory water vapor barrier properties compared to food packaging made using laminated films of OPP film and CPP film. Based on the above findings, the present inventors conducted further intensive research and found that by using a biaxially stretched film made of a propylene polymer composition containing a propylene polymer and a tackifier as the OPP film to enhance the water vapor barrier properties of the OPP film itself, it is possible to realize a food package having sufficient water vapor barrier properties even if the food package itself has poor sealing properties. That is, the food packaging film 100 according to this embodiment can provide a food package with sufficient water vapor barrier properties. Furthermore, in the food packaging film 100 according to this embodiment, the heat seal layer 103 can be formed directly on the biaxially oriented film layer 101, eliminating the need for a step of laminating a CPP film using an adhesive, as is required for a laminated film of an OPP film and a CPP film, thereby simplifying the manufacturing process and improving productivity. Furthermore, because there is no need to use a CPP film, costs can be reduced. As described above, according to this embodiment, it is possible to realize a food packaging body having sufficient water vapor barrier properties, and it is also possible to provide a food packaging film 100 that is excellent in terms of cost and productivity.

[0018] Here, food packages made using the food packaging film 100 according to this embodiment have lower heat seal strength and poorer airtightness than food packages made using a laminated film of an OPP film and a CPP film, and therefore have inferior oxygen barrier properties, but surprisingly, despite the poor airtightness, they exhibit sufficient water vapor barrier properties. Therefore, they are particularly suitable for use as films constituting food packages for packaging foods that require water vapor barrier properties but not so much oxygen barrier properties (e.g., dried foods).

[0019] Food packages produced using the food packaging film 100 according to this embodiment have sufficient water vapor barrier properties. From the viewpoint of stably obtaining food packages with excellent water vapor barrier properties, the food packaging film 100 is required to have a water vapor permeability of 4.5 g / (m 2 ) as measured by the following method. 2 24h) or less, and 4.0g / (m 2 24h) or less, and 3.5g / (m 2 It is more preferable that the time is 24 hours or less. (Measurement method) The food packaging film 100 is folded back so that the heat seal layer 103 faces inward, and the two sides are heat sealed to form a bag. Calcium chloride is then placed inside as the contents. The other side is then heat sealed to form a bag with a surface area of ​​0.01 m. 2 The resulting bag is then stored at 40°C and 90% RH for 72 hours. The weight of the calcium chloride is measured before and after storage, and the difference is used to determine the water vapor permeability (g / (m 2 Calculate the time (24h). Such a water vapor permeability can be achieved, for example, by adjusting the content ratio of the propylene polymer and tackifier contained in the biaxially stretched film layer 101, the constituent material and thickness of the heat seal layer 103, and the like.

[0020] The food packaging film 100 according to this embodiment has excellent heat sealability. To further improve the seal strength of a food package produced using the food packaging film 100, the heat seal strength of the portion where the heat seal layers 103 of the food packaging film 100 are heat-sealed together under conditions of 110°C, a pressure of 1.0 kgf, and a sealing time of 0.5 seconds is preferably 0.5 N / 15 mm or more, more preferably 1.0 N / 15 mm or more, even more preferably 1.5 N / 15 mm or more, still more preferably 2.0 N / 15 mm or more, and particularly preferably 3.0 N / 15 mm or more. The heat seal strength can be measured by the following method. First, the heat seal layers 103 of two food packaging films 100 are heat-sealed together at 110°C, a pressure of 1.0 kgf, and a sealing time of 0.5 seconds to obtain a laminated film. Next, the two food packaging films 100 are peeled together at a width of 15 mm, a 90-degree peel angle, and a peel speed of 300 mm / min, and the peel strength at this point is taken as the heat seal strength. Such heat seal strength can be achieved by adjusting the content ratio of the propylene polymer and tackifier contained in the biaxially stretched film layer 101, the constituent material and thickness of the heat seal layer 103, and the like.

[0021] In the food packaging film 100 according to this embodiment, the sum of the loop stiffness value in the MD direction and the loop stiffness value in the TD direction measured under conditions of 23°C, 50% RH, a width of 15 mm, a circumference of 50 mm, and a pushing distance of 20 mm is preferably 15.0 mN / 15 mm or more and 30 mN / 15 mm or less, and more preferably 20.0 mN / 15 mm or more and 30.0 mN / 15 mm or less. When the sum of the loop stiffness values ​​in the MD and TD directions satisfies the above range, the stiffness of the food packaging film 100 according to this embodiment can be further improved while maintaining the water vapor barrier property, thereby preventing film misalignment during heat sealing and preventing sealing defects. In other words, when the sum of the loop stiffness values ​​in the MD and TD directions satisfies the above range, the balance between the water vapor barrier property and packaging suitability of the food packaging film 100 according to this embodiment can be further improved. Such a loop stiffness value is a substitute value for quantitatively measuring the stiffness of the film, and can be achieved, for example, by adjusting the content ratio of the propylene polymer and tackifier contained in the biaxially stretched film layer 101, the stereoregularity of the propylene polymer, the constituent materials and thickness of the heat seal layer 103, etc.

[0022] The thickness of the food packaging film 100 according to this embodiment is not particularly limited, but can be set arbitrarily depending on the desired objectives such as water vapor barrier properties, cost, mechanical strength, transparency, etc., and is not particularly limited, but is usually 5 μm or more and 100 μm or less, preferably 10 μm or more and 50 μm or less, and more preferably 15 μm or more and 40 μm or less. When the thickness of the food packaging film 100 is within the above range, the balance of bag-making properties, mechanical properties, handling properties, appearance, moldability, light weight, and the like is better.

[0023] Each layer that constitutes the food packaging film 100 will be described below.

[0024] [Biaxially stretched film layer] The biaxially stretched film layer 101 (also referred to as a biaxially stretched polypropylene-based film layer) in this embodiment is formed, for example, by biaxially stretching a film composed of a propylene polymer composition containing a propylene polymer and a tackifier.

[0025] The biaxially stretched film layer 101 according to this embodiment may be a single layer or may be a laminate of multiple layers made of a propylene polymer composition, but it is necessary that it is biaxially stretched.

[0026] In addition, in the food packaging film 100, the ratio of the thickness of the biaxially oriented film layer 101 to the total thickness of the food packaging film 100 is preferably 0.50 or more and 0.998 or less, more preferably 0.60 or more and 0.99 or less, more preferably 0.70 or more and 0.97 or less, and even more preferably 0.75 or more and 0.95 or less.

[0027] (Propylene polymer composition) The propylene polymer composition according to this embodiment contains a propylene polymer and a tackifier. Here, by including a tackifier in the biaxially oriented film layer 101, it is possible to improve the water vapor barrier properties of the biaxially oriented film layer 101. Although the reason for this is not clear, it is thought that the tackifier penetrates into the amorphous portion of the propylene polymer, thereby suppressing the permeation of water vapor through the amorphous portion.

[0028] The lower limit of the content of the tackifier contained in the propylene polymer composition of this embodiment, i.e., the biaxially stretched film layer 101, is preferably 1% by mass or more, more preferably 3% by mass or more, even more preferably 5% by mass or more, and particularly preferably 10% by mass or more, when the entire propylene polymer composition is taken as 100% by mass, from the viewpoint of further improving the water vapor barrier property of the food packaging film 100. Furthermore, the lower limit of the content of the tackifier contained in the propylene polymer composition of this embodiment, i.e., the biaxially stretched film layer 101, is preferably 13% by mass or more, when the entire propylene polymer composition is taken as 100% by mass, from the viewpoint of further improving the heat seal strength of the food packaging film 100 at low temperatures (e.g., around 110°C). Furthermore, the upper limit of the content of the tackifier contained in the propylene polymer composition of this embodiment, i.e., the biaxially stretched film layer 101, is preferably 50% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less, when the entire propylene polymer composition is taken as 100% by mass, from the viewpoint of suppressing a decrease in the bending elasticity of the food packaging film 100 and improving processability, dimensional stability, transparency, etc.

[0029] The total content of the propylene polymer and tackifier contained in the propylene polymer composition according to this embodiment, i.e., the biaxially stretched film layer 101, is preferably 50% by mass or more and 100% by mass or less, more preferably 70% by mass or more and 100% by mass or less, even more preferably 90% by mass or more and 100% by mass or less, and particularly preferably 95% by mass or more and 100% by mass or less, when the entire propylene polymer composition is taken as 100% by mass. This makes it possible to achieve a better balance between water vapor barrier properties, mechanical properties, handleability, appearance, moldability, etc.

[0030] (propylene polymer) Examples of the propylene polymer according to this embodiment include propylene homopolymers and copolymers of propylene with ethylene or an α-olefin having 4 to 20 carbon atoms. Examples of the α-olefin having 4 to 20 carbon atoms include 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, and 1-eicosene. Among these, ethylene or an α-olefin having 4 to 10 carbon atoms is preferred, and ethylene is more preferred. These α-olefins may form random copolymers or block copolymers with propylene. The content of structural units derived from ethylene or an α-olefin having 4 to 20 carbon atoms is preferably 5 mol % or less, and more preferably 2 mol % or less, when the entire propylene polymer is taken as 100 mol %. The propylene polymer in the biaxially stretched film layer 101 may be used alone or in combination of two or more. Among these, propylene homopolymer is preferred as the propylene polymer from the viewpoint of obtaining a biaxially stretched film layer 101 having a better balance of properties such as heat resistance, water vapor barrier properties, mechanical properties, and rigidity.

[0031] Furthermore, from the viewpoint of improving the water vapor barrier properties of the food packaging film 100 while suppressing a decrease in bending elasticity caused by the tackifier, a highly stereoregular propylene polymer is preferred as the propylene polymer. Here, the inventors have found through their studies that blending a tackifier with a propylene polymer improves the water vapor barrier property of the resulting biaxially stretched film layer, but deteriorates its flexural modulus. Based on this finding, the inventors have conducted further intensive studies and have found for the first time that the use of a highly stereoregular propylene polymer as the propylene polymer used in the biaxially stretched film layer 101 can suppress the deterioration of flexural modulus caused by the tackifier. In other words, by using a highly stereoregular propylene polymer as the propylene polymer contained in the biaxially oriented film layer 101, the water vapor barrier properties of the food packaging film 100 can be improved while suppressing the decrease in bending elasticity caused by the tackifier.

[0032] In this embodiment, the highly stereoregular propylene polymer refers to a propylene polymer having an isotactic mesopentad fraction (mmmm), which is an index of stereoregularity, of 96% or more. The isotactic mesopentad fraction (mmmm) of the highly stereoregular propylene polymer according to this embodiment is preferably 96.5% or more, more preferably 97.0% or more. The upper limit of the isotactic mesopentad fraction (mmmm) of the highly stereoregular propylene polymer is not particularly limited, but from the viewpoint of ease of production, it is 99.5% or less, more preferably 99.3% or less, and even more preferably 99.0% or less. The isotactic mesopentad fraction (mmmm) is 13 It can be determined from a C-nuclear magnetic resonance (NMR) spectrum by a known method.

[0033] The propylene polymer according to the present embodiment can be produced by various methods, for example, by using a known catalyst such as a Ziegler-Natta catalyst or a metallocene catalyst.

[0034] The melt flow rate (MFR) of the propylene polymer according to the present embodiment, measured in accordance with ASTM D1238 under conditions of 230°C and a load of 2.16 kg, is preferably 0.5 g / 10 min or more, more preferably 1 g / 10 min or more, and even more preferably 2 g / 10 min or more, from the viewpoint of fluidity and moldability, and is preferably 20 g / 10 min or less, more preferably 10 g / 10 min or less, and even more preferably 7 g / 10 min or less, from the viewpoint of further stabilizing moldability.

[0035] (tackifier) As the tackifier according to this embodiment, a resinous substance having the property of imparting tackiness, which is generally manufactured and sold as a tackifier, can be used. Examples of such tackifiers include chroman-based resins such as chroman-indene resins; phenol-based resins such as phenol-formaldehyde resins and xylene-formaldehyde resins; terpene-based resins such as terpene-phenolic resins, terpene resins (α,β-pinene resins), aromatic-modified terpene resins, and hydrogenated terpene resins; petroleum-based hydrocarbon resins such as synthetic polyterpene resins, aromatic hydrocarbon resins, aliphatic hydrocarbon resins, aliphatic-cyclic hydrocarbon resins, aliphatic-alicyclic petroleum resins, aliphatic-aromatic petroleum resins, unsaturated hydrocarbon polymers, and hydrocarbon-based tackifying resins; hydrogenated products of the above petroleum-based hydrocarbon resins (also called hydrogenated petroleum hydrocarbon resins); and rosin-based resins such as pentaerythritol esters of rosin, glycerin esters of rosin, hydrogenated rosin, hydrogenated rosin esters, special rosin esters, and rosin-based tackifiers. Among these, at least one selected from petroleum-based hydrocarbon resins and hydrogenated petroleum-based hydrocarbon resins is preferred, with hydrogenated petroleum-based hydrocarbon resins being more preferred, as they are compatible with propylene polymers and can more effectively improve the water vapor barrier properties of the food packaging film 100. Here, the hydrogenation rate of the hydrogenated petroleum hydrocarbon resin is not particularly limited, but is preferably 90% or more, more preferably 95% or more, and even more preferably 99% or more, in terms of better compatibility with propylene polymers.

[0036] The lower limit of the softening temperature of the tackifier according to this embodiment, measured in accordance with JIS K2207, is not particularly limited, but is preferably 100°C or higher, more preferably 110°C or higher, even more preferably 125°C or higher, and particularly preferably 130°C or higher. When the softening temperature is at least the above lower limit, the generation of smoke and the like during molding of the biaxially stretched film layer 101 can be suppressed, and as a result, contamination of the molding machine can be suppressed. Furthermore, molecular motion of the tackifier in the biaxially stretched film layer 101 is further inhibited, thereby further improving the water vapor barrier property of the biaxially stretched film layer 101. The upper limit of the softening temperature is not particularly limited, but is preferably 150° C. or less, more preferably 145° C. or less, and even more preferably 140° C. or less. When the softening temperature is equal to or less than the upper limit, compatibility with the propylene polymer is improved, and the appearance of the biaxially stretched film layer 101 can be improved.

[0037] (Other ingredients) To the propylene polymer composition according to this embodiment, various additives such as a heat stabilizer, a weather stabilizer, an antioxidant, an ultraviolet absorber, a lubricant, a slipping agent, a nucleating agent, an antiblocking agent, an antistatic agent, an antifogging agent, a pigment, a dye, and an inorganic or organic filler may be added as needed, within the range that does not impair the object of this embodiment.

[0038] (Method for preparing propylene polymer composition) The propylene polymer composition according to the present embodiment can be prepared by mixing or melt-kneading the components using a dry blend, a tumbler mixer, a Banbury mixer, a single-screw extruder, a twin-screw extruder, a high-speed twin-screw extruder, a heat roll, or the like.

[0039] [Heat seal layer] In order to provide heat sealing properties, the food packaging film 100 according to this embodiment has a heat seal layer 103 as the outermost layer on at least one side of the biaxially oriented film layer 101. The heat seal layer 103 may be provided on both sides of the biaxially oriented film layer 101.

[0040] In the food packaging film 100, the thickness of the heat seal layer 103 is 0.1 μm or more and 10 μm or less, preferably 0.2 μm or more and 9 μm or less, more preferably 0.5 μm or more and 8 μm or less, and particularly preferably 1 μm or more and 8 μm or less. Here, the thickness of the heat seal layer 103 refers to the thickness of the heat seal layer 103 provided on one side of the biaxially stretched film layer 101. When the thickness of the heat seal layer 103 is equal to or greater than the above lower limit, the heat sealability of the food packaging film 100 can be improved. Furthermore, by having the thickness of the heat seal layer 103 be equal to or less than the above upper limit, the adhesion to the biaxially oriented film layer 101 is improved, and it becomes possible to laminate the heat seal layer 103 on the biaxially oriented film layer 101 without using an adhesive. In other words, it becomes possible to provide the heat seal layer 103 so that it is in direct contact with the surface of the biaxially oriented film layer 101, and therefore the manufacturing process of the food packaging film 100 can be simplified.

[0041] In the food packaging film 100, the heat seal layer 103 provided on one side is preferably a single layer, which can further simplify the manufacturing process of the food packaging film 100.

[0042] Furthermore, the heat seal layer 103 is preferably formed by biaxially stretching simultaneously with the biaxially stretched film layer 101 in a state before biaxial stretching. This allows the food packaging film 100 to be produced using a molding method such as co-extrusion, i.e., a laminated film produced in a single molding operation, thereby further simplifying the manufacturing process for the food packaging film 100. Therefore, the heat seal layer 103 is preferably biaxially stretched.

[0043] (Polyolefin) The heat seal layer 103 according to this embodiment is made of, for example, a polyolefin-based resin composition containing polyolefin. Examples of the polyolefin constituting the heat seal layer 103 include homopolymers or copolymers of α-olefins such as ethylene, propylene, butene-1, hexene-1, 4-methyl-pentene-1, and octene-1; high-pressure low-density polyethylene; linear low-density polyethylene (LLDPE); high-density polyethylene; polypropylene; propylene-α-olefin random copolymers; ethylene-vinyl acetate copolymers (EVA); and ionomer resins. Among these, at least one polyolefin selected from propylene-α-olefin random copolymers and propylene homopolymers is preferred as the polyolefin constituting the heat seal layer 103, as it has an excellent balance of adhesion to the biaxially oriented film layer 101, heat sealability, etc.

[0044] The propylene-α-olefin random copolymer according to the present embodiment is a random copolymer of propylene and an α-olefin (however, the α-olefin does not include propylene), and examples of the α-olefin include ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, etc. These copolymers may be used alone or in combination of two or more. Among the propylene-α-olefin random copolymers, propylene-ethylene random copolymers, propylene-ethylene-1-butene random copolymers, and propylene-1-butene random copolymers are preferred.

[0045] The melting point of the polyolefin constituting the heat seal layer 103 according to this embodiment is preferably in the range of 90° C. to 175° C., more preferably 95° C. to 170° C., and even more preferably 100° C. to 167° C. When the melting point of the polyolefin is equal to or higher than the lower limit, stickiness on the surface of the heat seal layer 103 can be suppressed, and the blocking properties of the food packaging film 100 can be improved. Furthermore, when the melting point of the polyolefin is equal to or lower than the upper limit, the heat sealability of the food packaging film 100 can be improved.

[0046] The melt flow rate (MFR) of the polyolefin constituting the heat seal layer 103 according to this embodiment, measured in accordance with ASTM D1238 at 230°C under a load of 2.16 kg, is preferably 0.5 g / 10 min or more, more preferably 1 g / 10 min or more, and even more preferably 2 g / 10 min or more, from the viewpoint of fluidity and moldability, and is preferably 20 g / 10 min or less, more preferably 10 g / 10 min or less, and even more preferably 7 g / 10 min or less, from the viewpoint of further stabilizing moldability.

[0047] The content of polyolefin in the polyolefin resin composition according to this embodiment, i.e., the heat seal layer 103, is preferably 50% by mass or more and 100% by mass or less, more preferably 70% by mass or more and 100% by mass or less, even more preferably 90% by mass or more and 100% by mass or less, and particularly preferably 95% by mass or more and 100% by mass or less, when the entire polyolefin resin composition is taken as 100% by mass. This allows for a better balance between adhesion to the biaxially stretched film layer 101, heat sealability, etc.

[0048] (Other ingredients) If necessary, various additives such as heat stabilizers, weather stabilizers, antioxidants, ultraviolet absorbers, lubricants, slipping agents, nucleating agents, antiblocking agents, antistatic agents, antifogging agents, pigments, dyes, and inorganic or organic fillers may be added to the polyolefin resin composition constituting the heat seal layer 103 according to this embodiment, within a range that does not impair the object of this embodiment.

[0049] Furthermore, from the viewpoint of improving the heat sealability of the heat seal layer 103, it is preferable that the tackifier according to this embodiment is substantially not contained in the heat seal layer 103. More specifically, the content of the tackifier in the heat seal layer 103 is preferably 0.5% by mass or less, more preferably 0.1% by mass or less, even more preferably 0.01% by mass or less, and particularly preferably 0% by mass.

[0050] (Method for preparing polyolefin resin composition) The propylene polymer composition according to the present embodiment can be prepared by mixing or melt-kneading the components using a dry blend, a tumbler mixer, a Banbury mixer, a single-screw extruder, a twin-screw extruder, a high-speed twin-screw extruder, a heat roll, or the like.

[0051] <Method of manufacturing food packaging film> The food packaging film 100 according to this embodiment can be obtained, for example, by co-extrusion molding the above-mentioned propylene polymer composition for forming the biaxially stretched film layer 101 and the above-mentioned polyolefin resin composition for forming the heat seal layer 103 into a film, and then biaxially stretching the resulting laminated film using a known biaxially stretched film manufacturing method such as simultaneous biaxial stretching or sequential biaxial stretching. The molding apparatus and molding conditions are not particularly limited, and conventionally known molding apparatus and molding conditions can be used. Examples of molding apparatus that can be used include a multilayer T-die extruder and a multilayer inflation molding machine. For biaxial stretching conditions, for example, known OPP film production conditions can be used. More specifically, in the sequential biaxial stretching method, the longitudinal stretching temperature may be 100°C to 145°C, the longitudinal stretching ratio may be 4.5 to 6 times, the transverse stretching temperature may be 130°C to 190°C, and the transverse stretching ratio may be 9 to 11 times. The food packaging film 100 according to this embodiment can also be obtained by separately molding the biaxially stretched film layer 101 and the heat seal layer 103, laminating them together, and then heat molding them.

[0052] <Applications of food packaging film> The food packaging film 100 according to this embodiment can also be suitably used as a film constituting a food package. The food package according to this embodiment is, for example, a packaging bag used for containing food, or a bag containing food. Furthermore, the food package according to this embodiment may use the food packaging film 100 in part, or the food packaging film 100 may be used for the entire food package, depending on the application.

[0053] Food packaging using the food packaging film 100 of this embodiment can exhibit sufficient water vapor barrier properties even for dried foods, which particularly require water vapor barrier properties, so the food packaging film 100 of this embodiment can be particularly suitably used as a packaging film for packaging foods, including dried foods. Here, the term "dried food" in this embodiment refers to food in a dry or semi-dried state (including pet food). Here, "dried food" refers to food with a moisture content of 15% by mass or less, and "semi-dried food" refers to food with a moisture content of more than 15% by mass and less than 50% by mass. Examples of dried foods include nuts, snack foods, cereals, luxury foods, dried noodles and pasta, grains and flours, dried vegetables, confectioneries, rice crackers, dairy products, and seasonings. Among these, from the viewpoint of more effectively obtaining the effects of this embodiment, it is preferable that the dried food include rice crackers, and it is more preferable that the dried food include dried rice crackers and dried beans coated with soy sauce, or rice crackers that are not coated with soy sauce on the surface. Furthermore, from the viewpoint of more effectively obtaining the effects of this embodiment, the water activity of the dried food is preferably 0.05 or more and 0.3 or less.

[0054] The food packaging film 100 according to this embodiment is preferably used for outer packaging bags that require water vapor barrier properties. Furthermore, when the food packaging film 100 according to this embodiment is used in an integrated package consisting of food, individual packaging bags for individually packaging the food, and an outer packaging bag for packaging the multiple individual packaging bags, the food packaging film 100 is preferably used in the outer packaging bag, which is required to have water vapor barrier properties in the integrated package, thereby making it possible to obtain an integrated package with sufficient water vapor barrier properties.

[0055] Although the embodiments of the present invention have been described above with reference to the drawings, these are merely examples of the present invention, and various other configurations can also be adopted. The following is a reference form. [1] A film for packaging food, comprising: a biaxially stretched film layer composed of a propylene polymer composition containing a propylene polymer and a tackifier; a heat seal layer provided so as to be in direct contact with at least one surface of the biaxially stretched film layer; Equipped with The food packaging film, wherein the heat seal layer is the outermost layer and has a thickness of 0.1 μm or more and 10 μm or less. [2] In the food packaging film described in [1] above, The food packaging film has a single heat seal layer. [3] In the food packaging film according to the above [1] or [2], The food packaging film wherein the heat seal layer is biaxially stretched. [4] In the food packaging film according to any one of [1] to [3] above, The food packaging film, wherein the food comprises a dried food. [5] In the food packaging film described in [4] above, A food packaging film for the above dried food, in which the water activity is 0.05 or more and 0.3 or less. [6] In the food packaging film according to any one of [1] to [5] above, Food packaging film used for outer packaging bags. [7] In the food packaging film according to any one of [1] to [6] above, A food packaging film in which the softening temperature of the tackifier is 100°C or higher and 150°C or lower. [8] In the food packaging film according to any one of [1] to [7] above, The food packaging film, wherein the tackifier comprises at least one selected from petroleum hydrocarbon resins and hydrogenated petroleum hydrocarbon resins. [9] In the food packaging film described in [8] above, The food packaging film, wherein the tackifier comprises a hydrogenated petroleum hydrocarbon resin.

[10] In the food packaging film according to any one of [1] to [9] above, A food packaging film, wherein the content of the tackifier contained in the biaxially stretched film layer is 1% by mass or more and 50% by mass or less, when the entire biaxially stretched film layer is taken as 100% by mass.

[11] In the food packaging film according to any one of [1] to

[10] above, A food packaging film, wherein the propylene polymer contained in the biaxially stretched film layer comprises a propylene homopolymer.

[12] In the food packaging film according to any one of [1] to

[11] above, A food packaging film, wherein the propylene polymer contained in the biaxially oriented film layer comprises a highly stereoregular propylene polymer.

[13] In the food packaging film described in

[12] above, The food packaging film is one in which the highly stereoregular propylene polymer has an isotactic mesopentad fraction (mmmm) of 96% or more.

[14] In the food packaging film according to any one of [1] to

[13] above, The food packaging film, wherein the heat seal layer comprises at least one selected from a propylene-α-olefin random copolymer and a propylene homopolymer.

[15] In the food packaging film according to any one of [1] to

[14] above, A food packaging film in which the ratio of the thickness of the biaxially stretched film layer to the total thickness of the food packaging film is 0.50 or more and 0.998 or less.

[16] A food packaging product using the food packaging film according to any one of [1] to

[15] above. [Example]

[0056] The present embodiment will be described in detail below with reference to examples and comparative examples, but the present embodiment is not limited to the descriptions of these examples.

[0057] 1.Raw materials The raw materials used in the examples and comparative examples are shown below. (1) Propylene polymer PP1: Propylene homopolymer (MFR: 3 g / 10 min, melting point: 157°C, isotactic mesopentad fraction (mmmm): 95%, manufactured by Prime Polymer Co., Ltd.) PP2: Highly stereoregular propylene homopolymer (MFR: 3 g / 10 min, melting point: 164°C, isotactic mesopentad fraction (mmmm): 98.5%, manufactured by Prime Polymer Co., Ltd.) PP3: Propylene-ethylene random copolymer (MFR: 6 g / 10 min, melting point: 109°C, manufactured by Prime Polymer Co., Ltd.) PP4: Propylene homopolymer (MFR: 3 g / 10 min, melting point: 161°C, manufactured by Prime Polymer Co., Ltd.) (2) Tackifier TF1: Hydrogenated petroleum hydrocarbon resin (softening point: 137°C)

[0058] 2. Measurement and evaluation methods (1) Isotactic mesopentad fraction of propylene polymer (mmmm) The isotactic mesopentad fraction (mesopentad fraction, (mmmm)) is measured by 13The isotactic mesopentad fraction was calculated according to the method described in Zambelli et al., Macromolecules, Vol. 6, p. 925 (1973), and the isotactic meso-average sequence length was calculated according to the method described in J.C.Randall, "Polymer Sequence Distribution," Chapter 2 (1977) (Academic Press, New York).

[0059] (2) MFR of propylene polymer Measured in accordance with ASTM D1238 at 230°C under a load of 2.16 kg.

[0060] (3) Melting point of propylene polymer The temperature of the maximum melting peak in the DSC curve of the propylene polymer obtained using a DSC (differential scanning calorimeter) was taken as the melting point.

[0061] (4) Loop stiffness value Using a loop stiffness tester manufactured by Toyo Seiki Co., Ltd., the loop stiffness values ​​in the MD and TD directions were measured under the conditions of 23°C, 50% RH, width 15 mm, circumference 50 mm, and indentation distance 20 mm.

[0062] (5) Water vapor barrier properties The food packaging film was folded over so that the heat seal layer 2 was on the inside, and the two sides were heat sealed to form a bag. Calcium chloride was then placed inside as the contents. The other side was then heat sealed to form a bag with a surface area of ​​0.01 m. 2 The bags were then stored at 40°C and 90% RH for 72 hours. The weight of the calcium chloride was measured before and after storage, and the difference in weight was used to determine the water vapor permeability (g / (m 2 ·24h)) were calculated respectively. Next, the water vapor barrier properties of the food packaging films were evaluated according to the following criteria. ◎◎: Water vapor permeability is 3.5g / (m 2 ·24h) or less ◎: Water vapor permeability is 3.5g / (m2 ·24h) Excess 4.0g / (m 2 ·24h) or less 〇: Water vapor permeability is 4.0g / (m 2 ·24h) Excess 4.5g / (m 2 ·24h) or less ×: Water vapor permeability is 4.5g / (m 2 ·24h) exceeded

[0063] (6) Heat seal strength The heat seal layers 2 of two food packaging films cut to a width of 15 mm were heat-sealed together at 110°C, a pressure of 1.0 kgf, and a sealing time of 0.5 seconds to obtain a laminated film. The two food packaging films were then peeled together at a width of 15 mm, a 90-degree peel angle, and a peel speed of 300 mm / min, and the peel strength measured at this point was recorded as the heat seal strength.

[0064] (7) Evaluation of the shelf life of dried foods Rice crackers (water activity: 0.09) were used as the dried food, polypropylene film (#20HC-OP) manufactured by Mitsui Chemicals Tocello was used as the packaging material for the individual packaging bags, and the food packaging films obtained in the Examples and Comparative Examples were used as the packaging material for the outer packaging bags, and an integrated package was fabricated using each of these. Here, the number of individual packaging bags was nine, and the total weight of the rice crackers in the entire integrated package was 90 g. Additionally, 10 g of desiccant was placed in the space between the outer packaging bag and the individual packaging bag.

[0065] Next, the obtained integrated package was stored in an environment of 40°C and 90% RH for 36 days, The weight change of the rice crackers was measured. Next, the storage stability of the dried food was evaluated according to the following criteria. ○: Weight change of rice crackers is 5g or less ×: The weight change of rice crackers exceeds 5g It was confirmed that the taste and texture of the dried foods rated as ◯ remained unchanged from before storage, while the texture of the foods rated as × changed from before storage.

[0066] [Examples 1 to 6 and Comparative Examples 1 and 2] Each layer was co-extruded and then biaxially stretched to produce food packaging films, each with the layer structure shown in Table 1, and each evaluation was performed. The co-extrusion conditions and biaxial stretching conditions were as follows: Multi-layer extrusion molding machine: 60 mmφ multi-layer T-die extrusion molding machine (L / D=27, manufactured by Screw Seiki Co., Ltd.) Extrusion temperature setting: 200-250℃, processing speed: 13.5m / min Longitudinal stretching temperature: 110-120℃ Longitudinal stretching ratio: 5.0 times Lateral stretching temperature: 140~170℃ Lateral stretching ratio: 10.0 times

[0067] [Table 1]

[0068] When the food packaging films of the examples were used, food packages having sufficient water vapor barrier properties were obtained. [Explanation of symbols]

[0069] 100 Food packaging film 101 Biaxially oriented film layer 103 Heat seal layer

Claims

1. A film for packaging food, comprising: a biaxially stretched film layer composed of a propylene polymer composition containing a propylene polymer and a tackifier; a heat seal layer; A food packaging film (excluding biaxially stretched film structures containing polyterpene resins) comprising: the food product comprises a dry food product; the propylene polymer consists solely of a propylene homopolymer, The content of the tackifier contained in the biaxially stretched film layer is 5% by mass or more and 30% by mass or less, when the entire biaxially stretched film layer is taken as 100% by mass, The food packaging film has two heat seal layers, each having a thickness of 0.1 μm or more and 10 μm or less, that are in direct contact with both sides of the biaxially stretched film layer.

2. The food packaging film according to claim 1, The food packaging film has a single heat seal layer.

3. The food packaging film according to claim 1 or 2, The food packaging film wherein the heat seal layer is biaxially stretched.

4. The food packaging film according to any one of claims 1 to 3, The food packaging film is for packaging dried foods having a water activity of 0.05 or more and 0.3 or less.

5. The food packaging film according to any one of claims 1 to 4, Food packaging film used for outer packaging bags.

6. The food packaging film according to any one of claims 1 to 5, The food packaging film, wherein the softening temperature of the tackifier is 100°C or higher and 150°C or lower.

7. The food packaging film according to any one of claims 1 to 6, The food packaging film, wherein the tackifier comprises at least one selected from petroleum-based hydrocarbon resins and hydrogenated petroleum-based hydrocarbon resins.

8. The food packaging film according to claim 7, A food packaging film, wherein the tackifier comprises a hydrogenated petroleum hydrocarbon resin.

9. The food packaging film according to any one of claims 1 to 8, A food packaging film, wherein the propylene homopolymer contained in the biaxially oriented film layer comprises a highly stereoregular propylene polymer.

10. The food packaging film according to claim 9, The food packaging film, wherein the highly stereoregular propylene polymer has an isotactic mesopentad fraction (mmmm) of 96% or more.

11. The food packaging film according to any one of claims 1 to 10, The heat seal layer of the food packaging film comprises at least one selected from a propylene-α-olefin random copolymer and a propylene homopolymer.

12. The food packaging film according to any one of claims 1 to 11, A food packaging film, wherein the ratio of the thickness of the biaxially stretched film layer to the total thickness of the food packaging film is 0.50 or more and 0.998 or less.

13. A food packaging product using the food packaging film according to any one of claims 1 to 12.

Images