Food packaging film and food packaging body

Abstract

To provide a food packaging film that can realize a food package having sufficient water vapor barrier properties and is also excellent in cost and productivity. [Solution] The food packaging film 100 of the present invention 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 side of the biaxially oriented film layer 101, wherein the heat seal layer 103 is the outermost layer and the thickness of the heat seal layer 103 is 0.1 μm or more and 10 μm or less.

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, also 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-2008-73926) and Patent Document 2 (JP-A-2004-82499).

[0004] Patent Document 1 describes a biaxially oriented multilayer polypropylene film characterized in that it has 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), via a layer of a propylene-based polymer (B) having a melting point of 155°C or higher, and a layer of a propylene-based polymer (E) on the other side of the biaxially oriented film. Patent Document 2 describes that the biaxially oriented multilayer polypropylene film having the above-mentioned structure can suppress the seepage of petroleum resins and the like onto the film surface, and has excellent laminate strength and moisture resistance.

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

[0006] [Patent Document 1] JP 2008-73926 A [Patent Document 2] JP 2004-82499 A Summary of the Invention [Problem to be solved by the invention]

[0007] Although OPP film has water vapor barrier properties, it has poor heat sealability. Therefore, when using OPP film for food packaging such as food packaging bags, it is necessary to laminate a non-oriented polypropylene film (hereinafter also referred to as CPP film) that has excellent heat sealability to the OPP film. By further laminating a CPP film to the OPP film, the heat seal strength of the obtained food packaging is increased, the intrusion of moisture and oxygen into the sealed portion is suppressed, and the water vapor barrier property and oxygen barrier property of the food packaging can be improved. Here, since the OPP film and the CPP film have poor adhesion, it was necessary to laminate the CPP film onto the OPP film using an adhesive. Therefore, food packaging films using OPP film for food packaging products require many manufacturing steps because they include a step of further laminating the CPP film using an adhesive, and there was room for improvement in terms of simplifying the manufacturing process and reducing costs.

[0008] The present invention has been made in consideration of the above circumstances, and provides 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 a food package having sufficient water vapor barrier properties can be obtained without using a CPP film having excellent heat sealability 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 directly providing only a thin heat seal layer on one side of the biaxially stretched film layer, thereby completing the present invention.

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

[0011] [1] A film for packaging food, comprising: a biaxially oriented 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 the thickness of the heat seal layer is 0.1 μm or more and 10 μm or less. [2] In the food packaging film described in [1] above, The food packaging film, wherein the heat seal layer is a single 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 the above [1] to [3], The food packaging film, wherein the food comprises a dry food. [5] In the food packaging film described in [4] above, A food packaging film for the above dried foods, the water activity of which is between 0.05 and 0.3. [6] In the food packaging film according to any one of the above [1] to [5], Food packaging film used for outer packaging bags. [7] In the food packaging film according to any one of the above [1] to [6], A food packaging film, wherein 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 the above [1] to [7], The food packaging film, wherein the tackifier comprises at least one selected from petroleum-based hydrocarbon resins and hydrogenated petroleum-based hydrocarbon resins. [9] In the food packaging film described in [8] above, The food packaging film, wherein the tackifier comprises a hydrogenated petroleum-based hydrocarbon resin.

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

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

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

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

[11] , 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, wherein 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 the above [1] to

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

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

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

[16] A food package using the food packaging film described in any one of [1] to

[15] above. Effect of the Invention

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

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

[0014] Hereinafter, an embodiment 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 ratio. 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 composed 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. 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 described above, OPP film has water vapor barrier properties but poor heat sealability. Therefore, when OPP film is used for food packaging such as food packaging bags, it is necessary to laminate a CPP film or the like having excellent heat sealability on the OPP film. By further laminating a CPP film on the OPP film, the heat seal strength of the obtained food packaging is increased, the intrusion of moisture and oxygen into the sealed portion is suppressed, and the water vapor barrier properties and oxygen barrier properties of the food packaging can be improved. Here, since the OPP film and the CPP film have poor adhesion, it was necessary to laminate the CPP film onto the OPP film using an adhesive. Therefore, food packaging films using OPP film for food packaging products require many manufacturing steps because they include a step of further laminating the CPP film using an adhesive, and there was 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 having a relatively thin heat seal layer, having a thickness of 0.1 μm or more and 10 μm or less, in direct contact with at least one side of a conventional OPP film as a packaging film. However, food packaging made using such films had poor sealing properties and were not fully satisfactory in terms of water vapor barrier properties compared to food packaging made using laminated films of OPP film and CPP film. Therefore, the present inventors have further studied based on the above findings, and as a result, have found that by using a biaxially stretched film composed of a propylene polymer composition containing a propylene polymer and a tackifier as the OPP film and enhancing the water vapor barrier property of the OPP film itself, it is possible to realize a food package having sufficient water vapor barrier property even if the food package itself has poor sealing property. That is, the food packaging film 100 according to this embodiment can provide a food package having sufficient water vapor barrier properties. In addition, in the food packaging film 100 according to the present embodiment, since the heat seal layer 103 can be formed directly on the biaxially stretched film layer 101, there is no need to perform a step of further laminating the CPP film using an adhesive as in the case of a laminated film of an OPP film and a CPP film, and the manufacturing process can be simplified, thereby improving productivity. In addition, since there is no need to use a CPP film, costs can be reduced. As described above, according to this embodiment, a food packaging body having sufficient water vapor barrier properties can be realized, and a food packaging film 100 that is also excellent in terms of cost and productivity can be provided.

[0018] Here, food packages made using the food packaging film 100 according to this embodiment have poor oxygen barrier properties due to low heat seal strength and poor sealing properties compared to food packages made using a laminated film of an OPP film and a CPP film, but surprisingly, despite the poor sealing properties, they exhibit sufficient water vapor barrier properties. Therefore, they can be particularly suitably used as a film constituting a food package for packaging foods (e.g., dried foods) that require water vapor barrier properties but not so much oxygen barrier properties.

[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 has a water vapor permeability of 4.5 g / (m2) 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 even 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 is on the inside, and the two sides are heat sealed to form a bag. Then, calcium chloride is placed in as the content. Next, the other side is heat sealed to form a bag with a surface area of ​​0.01 m. 2 The bag is then stored for 72 hours at 40°C and 90% RH. 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. In order 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, even more preferably 2.0 N / 15 mm or more, and particularly preferably 3.0 N / 15 mm or more. Here, 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 to each other under conditions of 110°C, pressure of 1.0 kgf, and sealing time of 0.5 seconds to obtain a laminated film. Next, the two food packaging films 100 are peeled off under conditions of 15 mm width, 90 degree peeling, and peeling speed of 300 mm / min, and the peel strength at this time is taken as the heat seal strength. Such a heat seal strength can be achieved, for example, by adjusting the content ratio of the propylene polymer and tackifier contained in the biaxially oriented film layer 101, the constituent material and thickness of the heat seal layer 103, and the like.

[0021] In the food packaging film 100 of 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, width 15 mm, circumference 50 mm, and pushing distance 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 can be further improved while maintaining the water vapor barrier property of the food packaging film 100 according to this embodiment, and as a result, the film positional deviation during heat sealing can be suppressed, and the occurrence of sealing defects can be suppressed. 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 a film, and can be achieved, for example, by adjusting the content ratio of the propylene polymer and tackifier contained in the biaxially oriented film layer 101, the stereoregularity of the propylene polymer, and the constituent materials and thickness of the heat seal layer 103.

[0022] The thickness of the food packaging film 100 in 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 formability, mechanical properties, handleability, appearance, moldability, lightweight property, and the like is excellent.

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

[0024] [Biaxially oriented film layer] The biaxially oriented film layer 101 (also referred to as a biaxially oriented 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 overall 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 includes 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 property of the biaxially oriented film layer 101. Although the reason for this is not clear, it is believed that the tackifier penetrates into the amorphous portion of the propylene polymer, 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 mass% or more, more preferably 3 mass% or more, even more preferably 5 mass% or more, and particularly preferably 10 mass% or more, when the entire propylene polymer composition is taken as 100 mass%, from the viewpoint of further improving the water vapor barrier property of the food packaging film 100. In addition, the lower limit of the tackifier content 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). In addition, 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, still 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 of water vapor barrier properties, mechanical properties, handleability, appearance, moldability, etc.

[0030] (Propylene polymer) Examples of the propylene polymer according to the present embodiment include propylene homopolymers and copolymers of propylene and ethylene or α-olefins having 4 to 20 carbon atoms. Examples of the α-olefins 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 α-olefins having 4 to 10 carbon atoms are preferred, and ethylene is more preferred. These α-olefins may form random copolymers or block copolymers with propylene. The content of the structural units derived from ethylene or α-olefins 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 kinds. Among these, from the viewpoint of obtaining a biaxially stretched film layer 101 having a better balance of properties such as heat resistance, water vapor barrier property, mechanical properties, and rigidity, a propylene homopolymer is preferred as the propylene polymer.

[0031] Moreover, from the viewpoint of improving the water vapor barrier properties of the food packaging film 100 while suppressing the decrease in bending elasticity caused by the tackifier, the propylene polymer is preferably a highly stereoregular propylene polymer. Here, according to the study of the present inventors, it was found that when a propylene polymer is blended with a tackifier, the water vapor barrier property of the obtained biaxially stretched film layer is improved, but the bending elasticity is deteriorated. Based on the above findings, the present inventors further studied intensively and found for the first time that the decrease in bending elasticity caused by the tackifier can be suppressed by using a highly stereoregular propylene polymer as the propylene polymer used in the biaxially stretched film layer 101. 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 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 viewpoints 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 the present 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 resin; phenol-based resins such as phenol-formaldehyde resin and xylene-formaldehyde resin; terpene-based resins such as terpene-phenol resin, terpene resin (α,β-pinene resin), aromatic modified terpene resin, and hydrogenated terpene resin; petroleum-based hydrocarbon resins such as synthetic polyterpene resin, aromatic hydrocarbon resin, aliphatic hydrocarbon resin, aliphatic cyclic hydrocarbon resin, aliphatic and alicyclic petroleum resin, aliphatic and aromatic petroleum resin, unsaturated hydrocarbon polymer, and hydrocarbon tackifying resin; hydrogenated products of the above petroleum-based hydrocarbon resins (also called hydrogenated petroleum hydrocarbon resin); and rosin-based resins such as pentaerythritol ester of rosin, glycerin ester of rosin, hydrogenated rosin, hydrogenated rosin ester, special rosin ester, and rosin-based tackifier. Among these, from the viewpoint of compatibility with propylene polymers and more effectively improving the water vapor barrier properties of the food packaging film 100, at least one selected from petroleum-based hydrocarbon resins and hydrogenated petroleum-based hydrocarbon resins is preferred, and hydrogenated petroleum-based hydrocarbon resins are more preferred. Here, the hydrogenation rate of the hydrogenated petroleum-based 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 the propylene polymer.

[0036] The lower limit of the softening temperature of the tackifier according to the present 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 equal to or higher than the above lower limit, the generation of smoke or the like during molding of the biaxially stretched film layer 101 can be suppressed, and as a result, the dirt of the molding machine can be suppressed. Furthermore, molecular motion of the tackifier in the biaxially stretched film layer 101 is further inhibited, so that the water vapor barrier property of the biaxially stretched film layer 101 can be further improved. 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 becomes better, and the appearance of the biaxially stretched film layer 101 can be improved.

[0037] (Other Ingredients) To the propylene polymer composition according to the present 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 necessary within a range that does not impair the object of the present 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 impart heat sealability to the food packaging film 100 according to this embodiment, a heat seal layer 103 is provided as an outermost layer on at least one surface of a biaxially oriented film layer 101. The heat seal layer 103 may be provided on both surfaces 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 as to be 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 surface is preferably a single layer, which can further simplify the manufacturing process of the food packaging film 100.

[0042] In addition, 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 laminated film produced by a molding method such as coextrusion molding, i.e., by one molding operation, and therefore the manufacturing process of the food packaging film 100 can be further simplified. Therefore, the heat seal layer 103 is preferably biaxially stretched.

[0043] (Polyolefin) The heat seal layer 103 according to the present 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, the polyolefin constituting the heat seal layer 103 is preferably at least one selected from propylene-α-olefin random copolymers and propylene homopolymers, since this 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 is excluding 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, the stickiness of the surface of the heat seal layer 103 can be suppressed, and the blocking property of the food packaging film 100 can be improved. Furthermore, when the melting point of the polyolefin is equal to or lower than the above 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 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.

[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, still 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 makes it possible to achieve a better balance between adhesion to the biaxially stretched film layer 101, heat sealability, and the like.

[0048] (Other Ingredients) If necessary, various additives such as heat stabilizers, weather stabilizers, antioxidants, UV 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 in this embodiment, within a range that does not impair the object of this embodiment.

[0049] Moreover, from the viewpoint of improving the heat sealability of the heat seal layer 103, it is preferable that the tackifier according to the present embodiment is not substantially 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-based 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 oriented film layer 101 and the above-mentioned polyolefin resin composition for forming the heat seal layer 103 into a film-like laminate film, and then biaxially stretching the laminate film using a known biaxially oriented film manufacturing method such as a simultaneous biaxial stretching method or a sequential biaxial stretching method. The molding device and molding conditions are not particularly limited, and conventionally known molding devices and molding conditions can be used. As the molding device, a multi-layer T-die extruder or a multi-layer inflation molding machine can be used. As the biaxial stretching conditions, for example, known OPP film manufacturing conditions can be used. More specifically, in the sequential biaxial stretching method, for example, the longitudinal stretching temperature may be 100°C to 145°C, the longitudinal stretching ratio may be in the range of 4.5 to 6 times, the transverse stretching temperature may be 130°C to 190°C, and the transverse stretching ratio may be in the range of 9 to 11 times. The food packaging film 100 according to this embodiment can also be obtained by separately forming the biaxially oriented film layer 101 and the heat seal layer 103, laminating them together, and heat forming 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 itself used for the purpose of containing food, or the bag containing food. Furthermore, the food package according to this embodiment may use the food packaging film 100 in a part thereof, or the food packaging film 100 may be used in 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 dried food according to the present embodiment refers to food in a dry or semi-dried state (including pet food). Here, a dry food refers to a food with a moisture content of 15% by mass or less, and a semi-dried food refers to a 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, cereal foods, luxury foods, dried noodles and pastas, grains and flours, dried vegetables, confectioneries, rice crackers, dairy products, and seasonings. Among these, from the viewpoint of obtaining the effects of this embodiment more effectively, it is preferable for the dried food to include rice crackers, and it is more preferable for the dried food to include dried rice crackers and dried beans coated with soy sauce, or rice crackers that are not coated with soy sauce on the surface. In order to more effectively obtain 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 the present 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 a plurality of the individual packaging bags, it is preferable to use the food packaging film 100 in the outer packaging bag for which water vapor barrier properties are required in the integrated package, thereby making it possible to obtain an integrated package having 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 configurations other than those described above can also be adopted. EXAMPLES

[0056] Hereinafter, the present embodiment will be described in detail 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: 6g / 10min, melting point: 109℃, Prime Polymer) PP4: Propylene homopolymer (MFR: 3g / 10min, melting point: 161℃, manufactured by Prime Polymer Co., Ltd.) (2) Tackifier TF1: Hydrogenated petroleum-based 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 13 The isotactic meso pentad 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 JC Randal, "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 and 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 by using a differential scanning calorimeter (DSC) 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 direction and the TD direction 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 back so that the heat seal layer 2 was on the inside, and the two sides were heat sealed to form a bag. Then, calcium chloride was placed inside as the content. 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 for 72 hours at 40°C and 90% RH. 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 property of the food packaging film was evaluated according to the following criteria. ◎◎: Water vapor permeability is 3.5g / (m 2 ·24h) or less ◎: Water vapor permeability is 3.5g / (m 2 ·24h) Excess 4.0g / (m 2 ·24h) or less ○: 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 off 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 time was recorded as the heat seal strength.

[0064] (7) Evaluation of the preservation quality of dried foods Rice snacks (water activity: 0.09) were selected as the dried food, polypropylene film (#20HC-OP) manufactured by Mitsui Chemicals Tohcello was selected as the packaging material for forming the individual packaging bags, and the food packaging films obtained in the Examples and Comparative Examples were selected as the packaging material for forming the outer packaging bags, and integrated packages were produced. Here, the number of individual packaging bags was nine, and the total weight of the rice snacks in the entire integrated package was 90g. 10g 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 snacks was measured. Next, the storage stability of the dried foods was evaluated according to the following criteria. ○: Weight change of rice crackers is 5g or less ×: The weight change of rice crackers is more than 5g. In addition, it was confirmed that the taste and texture of the dried foods rated as ◯ remained unchanged from before storage, whereas the texture of the foods rated as × changed from before storage.

[0066] [Examples 1 to 6 and Comparative Examples 1 to 2] Each layer was co-extruded in the layer structure shown in Table 1, and then biaxially stretched to produce food packaging films, which were then evaluated. The co-extrusion conditions and biaxial stretching conditions were as follows: Multi-layer extrusion molding machine: 60mmφ 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 stretch 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 food packaging body using a food packaging film for packaging food (excluding a biaxially oriented film structure comprising an extruded and stretched mixture of (1) high crystallinity polypropylene (HCPP) having an intermolecular stereoregularity of more than 93% and (2) a polyterpene resin in an amount that improves moisture resistance), comprising: The food packaging film comprises a biaxially oriented film layer made of a propylene polymer composition containing a propylene polymer and a tackifier, and a heat seal layer provided so as to be in direct contact with at least one surface of the biaxially oriented film layer, the heat seal layer being an outermost layer, and the thickness of the heat seal layer being 0.1 μm or more and 10 μm or less, The food packaging film is arranged so that the heat seal layer faces the inner surface, and the heat seal layers are heat sealed together to form a bag shape, the heat seal layer comprises a propylene homopolymer; The food packaging film is a food packaging material having a total loop stiffness value in the MD direction and the TD direction of 15.0 mN / 15 mm or more and 30 mN / 15 mm or less, measured under conditions of 23° C., 50% RH, width 15 mm, circumference 50 mm, and indentation distance 20 mm (provided that the food packaging film is a food packaging material having a high stereoregularity polypropylene having a mesopentad fraction of 97 to 99.5%, and at least one resin selected from a petroleum resin substantially free of polar groups and a terpene resin substantially free of polar groups). and a metallized film formed by forming a metal layer on the B layer of a biaxially oriented polypropylene film for metallization, the B layer being characterized in that the B layer of the biaxially oriented polypropylene film for metallization has a longitudinal tensile modulus of elasticity of 3.5 GPa or more at room temperature, and the metallized film is characterized in that the metal layer is formed on the B layer of the biaxially oriented polypropylene film for metallization, the B layer being a resin layer (A layer) made of a mixture of one or more of the above polypropylene resins and a polypropylene resin having a crystal fusion heat of 20 to 90 J / g.

2. The food packaging according to claim 1, The food packaging material, wherein the heat seal layer is a single layer.

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

4. The food packaging material according to any one of claims 1 to 3, The food package wherein the food comprises a dry food.

5. The food packaging according to claim 4, The food packaging material contains a dried food having a water activity of 0.05 or more and 0.3 or less.

6. The food packaging material according to any one of claims 1 to 5, The food packaging body is an outer packaging bag.

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

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

9. The food packaging according to claim 8, The food packaging material, wherein the tackifier comprises a hydrogenated petroleum hydrocarbon resin.

10. The food packaging material according to any one of claims 1 to 9, A food packaging body, wherein the content of the tackifier contained in the biaxially oriented film layer is 1% by mass or more and 50% by mass or less, when the entire biaxially oriented film layer is taken as 100% by mass.

11. The food packaging according to any one of claims 1 to 10, The food packaging material, wherein the propylene polymer contained in the biaxially oriented film layer comprises a propylene homopolymer.

12. The food packaging according to any one of claims 1 to 11, The propylene polymer contained in the biaxially oriented film layer comprises a highly stereoregular propylene polymer.

13. The food packaging according to claim 12, The food packaging material, wherein the highly stereoregular propylene polymer has an isotactic mesopentad fraction (mmmm) of 96% or more.

14. The food packaging according to any one of claims 1 to 13, A food package, wherein the ratio of the thickness of the biaxially oriented film layer to the total thickness of the food packaging film is 0.50 or more and 0.998 or less.

15. A food packaging film that can be used for the food packaging body according to any one of claims 1 to 14, a biaxially oriented 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 an outermost layer, and the thickness of the heat seal layer is 0.1 μm or more and 10 μm or less.

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