Food packaging film and food packaging body

Abstract

To provide a food packaging film with small thickness variations and improved water vapor barrier properties. [Solution] A film for packaging food, comprising a biaxially stretched film layer containing a propylene-based polymer, wherein, when measured in accordance with JIS K7127 (1999) using a tensile tester under conditions of a measurement temperature of 23±2°C, 50±5% RH, and a pulling speed of 5 mm / min, the sum of the tensile modulus of elasticity T1 in the MD direction and the tensile modulus of elasticity T2 in the TD direction of the food packaging film is defined as T3, and the T3 is 6600 MPa or more and 7500 MPa or less.

Description

[Technical Field]

[0001] This invention relates to food packaging films and food packaging bodies. [Background technology]

[0002] Biaxially oriented polypropylene film (hereinafter also referred to as OPP film) has an excellent balance of properties 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 (Japanese Patent Publication No. 2008-73926) and Patent Document 2 (Japanese Patent Publication No. 2004-82499).

[0004] Patent Document 1 describes a biaxially oriented multilayer polypropylene film characterized in that one side of the biaxially oriented film is 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), has a layer made of a propylene-α-olefin random copolymer (C) with a melting point in the range of 125 to 145°C, via a layer made of a propylene-based polymer (B) with a melting point of 155°C or higher, and the other side of the biaxially oriented film has a layer made of a propylene-based polymer (E). Patent Document 1 states that a biaxially oriented multilayer polypropylene film having the above-described structure can suppress the seepage of petroleum resin and other substances onto the film surface, and exhibits excellent lamination strength and moisture resistance.

[0005] Patent Document 2 describes a multilayer resin film comprising a polyvinyl alcohol-based resin layer further having an adhesive layer on at least one surface of a biaxially oriented polypropylene-based resin layer containing 10 to 40% by weight of a highly crystallized resin and 6 to 15% by weight of a petroleum resin, wherein the oxygen permeability at a relative humidity of 85% RH and a temperature of 23°C is 600 mL / m². 2The pressure is less than or equal to day·MPa, and the water vapor transmission rate at a relative humidity of 90%RH and a temperature of 40°C is 3.5g / m³. 2 A multilayer resin film characterized by having a thickness of 20 μm or less is described. Patent Document 2 states 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 Publication No. 2008-73926 [Patent Document 2] Japanese Patent Publication No. 2004-82499 [Overview of the project] [Problems that the invention aims to solve]

[0007] From the perspective of reducing environmental impact, there is a need for further improvement in the water vapor barrier properties of OPP film. Improved water vapor barrier properties would allow for thinner OPP film, thereby reducing the amount of propylene polymer used and thus lowering the environmental burden. Our investigations have shown that using a highly crystalline propylene polymer as the propylene polymer constituting the OPP film can improve the water vapor barrier properties of the OPP film. However, it has become clear that using such a highly crystalline propylene polymer can easily lead to uneven stretching, and that the thickness of the OPP film obtained after the biaxial stretching process may become uneven. Thus, the inventors have found that there is a trade-off relationship between water vapor barrier properties and thickness uniformity in OPP films. In other words, the inventors have found that there is room for improvement in OPP films in terms of balancing both improved water vapor barrier properties and suppression of thickness uniformity.

[0008] This invention has been made in view of the above circumstances, and provides a food packaging film with less thickness variation and improved water vapor barrier properties. [Means for solving the problem]

[0009] The inventors diligently studied to solve the above problems. As a result, they found that the tensile modulus of elasticity of food packaging films is an effective design guideline for improving the balance between improving water vapor barrier properties and suppressing thickness unevenness. Based on the above findings, the inventors conducted further intensive studies and discovered that by controlling the sum of the tensile modulus in the MD direction and the tensile modulus in the TD direction to a specific range, a food packaging film with reduced thickness variation and improved water vapor barrier properties can be obtained, leading to the present invention.

[0010] In other words, the present invention provides the following food packaging film and food packaging body.

[0011] [1] A film for packaging food, The film comprises a biaxially oriented film layer containing a propylene polymer, When T3 is defined as the sum of the tensile modulus T1 in the MD direction and the tensile modulus T2 in the TD direction of the above food packaging film, measured using a tensile testing machine in accordance with JIS K7127 (1999) under the conditions of a measurement temperature of 23±2℃, 50±5%RH, and a tensile speed of 5mm / min, Food packaging film with the above T3 being between 6600 MPa and 7500 MPa. [2] In the food packaging film described in [1] above, A differential scanning calorimeter was used to analyze the above biaxially oriented film layer. The first differential scanning calorimetry (1st Run) consists of a process of raising the temperature from -50°C to 250°C at a heating rate of 10°C / min, an isothermal process of maintaining the temperature at 250°C for 10 minutes, and a process of cooling from 250°C to -50°C at a cooling rate of 10°C / min. The second differential scanning calorimetry measurement (2nd Run) consisting of a process of heating from -50°C to 250°C at a heating rate of 10°C / min, and when continued, in the DSC curve 2 obtained by the second differential scanning calorimetry measurement, an endothermic peak A is observed in the range of 150°C or more and 180°C or less, when the heat quantity of the endothermic peak A is Q, a food packaging film in which T3 / Q is 50 or more and 80 or less. [3] In the food packaging film according to the above [1] or [2], a food packaging film in which the difference (T2 - T1) between the tensile modulus T2 in the TD direction and the tensile modulus T1 in the MD direction of the food packaging film is 2000 Mpa or more and 4000 MPa or less. [4] In the food packaging film according to any one of the above [1] to [3], a food packaging film in which the tensile modulus T1 in the MD direction of the food packaging film is 1500 MPa or more and 3000 MPa or less. [5] In the food packaging film according to any one of the above [1] to [4], a food packaging film further comprising a heat-seal layer on at least one surface of the biaxially stretched film layer. [6] In the food packaging film according to the above [5], a food packaging film in which the heat-seal layer is provided so as to directly contact the one surface of the biaxially stretched film layer. [7] In the food packaging film according to the above [5] or [6], a food packaging film in which the heat-seal layer contains one or more selected from homopolypropylene and a random copolymer of propylene and an α-olefin having 2 to 10 carbon atoms. [8] In the food packaging film according to any one of the above [1] to [7], A food packaging film further comprising a surface layer on one side of the above-mentioned biaxially oriented film layer. [9] In the food packaging film described in [8] above, The above surface layer is a food packaging film containing an antiblocking agent.

[10] In the food packaging film described in [8] or [9] above, The above surface layer is a food packaging film comprising one or more selected from homopolypropylene and a random copolymer of propylene and an α-olefin having 2 to 10 carbon atoms.

[11] In a food packaging film described in any one of the above [1] to

[10] , A food packaging film in which the tackifier content in the biaxially oriented film layer is 10% by mass or less when the total mass of the biaxially oriented film layer is taken as 100% by mass.

[12] In a food packaging film described in any one of the above [1] to

[11] , The water vapor transmission rate measured by the following method is 6.0 g / (m³). 2 Food packaging film with a shelf life of 24 hours or less. (Measurement method) The food packaging film described above is folded so that the heat-seal layer faces inward, and two sides are heat-sealed to form a bag. Then, calcium chloride is added as the contents. Next, the other side is heat-sealed to create a bag with a surface area of ​​0.01 m². 2 A bag is prepared to achieve the following conditions. Next, the resulting bag is stored for 72 hours at 40°C and 90% RH. The weight of calcium chloride is measured before and after storage, and the water vapor transmission rate (g / m³) is calculated from the difference. 2 Calculate (24 hours).

[13] In a food packaging film described in any one of the above [1] to

[12] , Food packaging film used for outer packaging bags.

[14] A food packaging body using any one of the food packaging films described in [1] to

[13] above. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a food packaging film with less thickness variation and improved water vapor barrier properties. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic cross-sectional view showing an example of the structure of a food packaging film according to an embodiment of the present invention. [Figure 2] This is a schematic cross-sectional view showing an example of the structure of a food packaging film according to an embodiment of the present invention. [Modes for carrying out the invention]

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

[0015] <Food packaging film> Figures 1 and 2 are schematic cross-sectional views illustrating an example of the structure of a food packaging film 100 according to an embodiment of the present invention. The food packaging film 100 according to this embodiment is a film for packaging food, comprising a biaxially oriented film layer 101 containing a propylene polymer, and when the sum of the tensile modulus T1 in the MD direction and the tensile modulus T2 in the TD direction of the food packaging film is taken as T3, measured using a tensile testing machine in accordance with JIS K7127 (1999) under the conditions of a measurement temperature of 23±2℃, 50±5%RH, and a tensile speed of 5 mm / min, the sum of T3 is 6600 MPa or more, more preferably 7000 MPa or more, even more preferably 7100 MPa or more, and 7500 MPa or less. This makes it possible to realize a food packaging film with less thickness variation and improved water vapor barrier properties.

[0016] As mentioned above, from the perspective of reducing environmental impact, there is a need for further improvement in the water vapor barrier properties of OPP film. Improved water vapor barrier properties would allow for thinner OPP film, thereby reducing the amount of propylene polymer used and thus reducing the environmental impact. Our investigations have shown that using a highly crystalline propylene polymer as the propylene polymer constituting the OPP film can improve the water vapor barrier properties of the OPP film. However, it has become clear that using such a highly crystalline propylene polymer can easily lead to uneven stretching, and that the thickness of the OPP film obtained after the biaxial stretching process may become uneven. Thus, the inventors have found that there is a trade-off relationship between water vapor barrier properties and thickness uniformity in OPP films. In other words, the inventors have found that there is room for improvement in OPP films in terms of balancing both improved water vapor barrier properties and suppression of thickness uniformity.

[0017] The inventors diligently studied to solve the above problems. As a result, they found that the tensile modulus of elasticity of food packaging films is an effective design guideline for improving the balance between improving water vapor barrier properties and suppressing thickness unevenness. Based on the above findings, the inventors conducted further intensive studies and found that by controlling the sum of the tensile modulus T1 in the MD direction and the tensile modulus T2 in the TD direction, T3, a food packaging film can be obtained with reduced thickness variation and improved water vapor barrier properties. In other words, the food packaging film 100 according to this embodiment makes it possible to realize a food packaging body with less thickness variation and improved water vapor barrier properties. Furthermore, the food packaging film 100 according to this embodiment can improve water vapor barrier properties, so sufficient water vapor barrier properties can be obtained even if the thickness of the biaxially oriented film layer 101 is reduced. Therefore, the food packaging film 100 according to this embodiment can reduce the amount of propylene polymer used in food packaging films and packaging bodies, thereby reducing the environmental burden. Based on the above, according to this embodiment, it is possible to realize an environmentally friendly food packaging material with sufficient water vapor barrier properties, and to provide a food packaging film 100 with minimal thickness variations and excellent appearance, packaging suitability, and bag-making properties.

[0018] The food packaging film 100 according to this embodiment is controlled so that the T3 is between 6600 MPa and 7500 MPa. This allows for a balanced improvement in both water vapor barrier properties and the suppression of thickness unevenness. The reason for this is not clear, but the following reasons are possible. First, it is believed that by setting T3 to be equal to or greater than the lower limit, the crystallinity of the biaxially oriented film layer 101 can be increased, and as a result, the water vapor barrier properties of the food packaging film 100 according to this embodiment can be improved. Furthermore, it is believed that by setting T3 to be equal to or less than the upper limit, uneven stretching due to crystallization of the biaxially oriented film layer 101 can be reduced, and as a result, thickness variations that occur during stretching of the biaxially oriented film layer 101 can be reduced. Furthermore, if the above T3 is below the above upper limit, problems such as cutting will be less likely to occur during film forming, continuous stretching and forming of the film will be easier, and industrial continuous productivity can be improved. Here, the sum of the tensile modulus T1 in the MD direction and the tensile modulus T2 in the TD direction, T3, can be achieved, for example, by adjusting the content ratio of the propylene polymer in the biaxially oriented film layer 101 and the conditions during the stretching process. More specifically, the tensile modulus of the food packaging film 100 can be adjusted by using two or more propylene polymers with different melting points and heat of fusion as the propylene polymers constituting the biaxially oriented film layer 101, or by appropriately adjusting the stretching ratio during the stretching process, the temperature during stretching, and the temperature and time of the heat treatment.

[0019] In the food packaging film 100 according to this embodiment, when a differential scanning calorimeter is used to perform a first differential scanning calorimeter measurement (1st Run) on a biaxially oriented film layer 101, consisting of a process of raising the temperature from -50°C to 250°C at a heating rate of 10°C / min, an isothermal process of maintaining the temperature at 250°C for 10 minutes, and a process of lowering the temperature from 250°C to -50°C at a cooling rate of 10°C / min, and a second differential scanning calorimeter measurement (2nd Run) consisting of a process of raising the temperature from -50°C to 250°C at a heating rate of 10°C / min, an endothermic peak A is observed in the range of 150°C to 180°C in the DSC curve 2 obtained from the second differential scanning calorimeter measurement, and when the amount of heat of the endothermic peak A is Q, it is preferable that T3 / Q is 50 to 80, more preferably 55 to 75, and even more preferably 57 to 72. This allows for a more balanced improvement in both water vapor barrier properties and the suppression of thickness variations. The lower limit of the heat quantity Q of the endothermic peak A is preferably 95 J / g or more, more preferably 100 J / g or more, even more preferably 105 J / g or more, and particularly preferably 110 J / g or more, from the viewpoint of further improving the water vapor barrier properties of the food packaging film 100. From the viewpoint of further suppressing thickness unevenness, the upper limit of the heat quantity Q of the endothermic peak A is preferably 120 J / g or less, more preferably 118 J / g or less, and even more preferably 115 J / g or less. Here, the amount of heat at the endothermic peak A is calculated by determining the area enclosed by the melting endothermic curve containing endothermic peak A and the baseline. The baseline is defined as the line drawn by differentiating the heat flow with respect to time before and after endothermic peak A to display the deriv. heat flow, and connecting the point where the change in deriv. heat flow begins (i.e., the point where the flat region of deriv. heat flow ends) and the point where the change in deriv. heat flow ends (i.e., the point where the deriv. heat flow enters the flat region). Furthermore, if multiple endothermic peaks are observed in the range of 150°C to 180°C, the largest peak will be designated as endothermic peak A. Here, the heat quantity Q of the endothermic peak A of the biaxially oriented film layer 101 can be achieved, for example, by adjusting the content ratio of the propylene polymer contained in the biaxially oriented film layer 101 and the various conditions during the stretching process. More specifically, it is possible to adjust the heat quantity Q of the endothermic peak A of the biaxially oriented film layer 101 by using two or more propylene polymers with different melting points, crystallinity, stereoregularity, etc., in combination and adjusting their ratio, or by appropriately adjusting the stretching ratio during the stretching process, the temperature during stretching, the temperature and time of the heat treatment, etc.

[0020] Furthermore, in the food packaging film 100 according to this embodiment, the difference between the tensile modulus T2 in the TD direction and the tensile modulus T1 in the MD direction (T2-T1) is preferably 4000 MPa or less, more preferably 3500 MPa or less, and even more preferably 3150 MPa or less. If the difference between the tensile modulus T2 in the TD direction and the tensile modulus T1 in the MD direction (T2-T1) is less than or equal to the above upper limit, shrinkage of the food packaging film 100 can be suppressed. As a result, misalignment of the seal portion inside the food packaging, the occurrence of wrinkles inside the food packaging, and damage to the food packaging itself can be more effectively suppressed. In the food packaging film 100 according to this embodiment, the lower limit of the difference (T2-T1) between the tensile modulus T2 in the TD direction and the tensile modulus T1 in the MD direction is not particularly limited, but is, for example, 2000 MPa or more, preferably 2500 MPa or more.

[0021] Furthermore, in the food packaging film 100 according to this embodiment, the lower limit of the tensile modulus T1 in the MD direction is preferably 1500 MPa or higher, more preferably 1800 MPa or higher, and even more preferably 2050 MPa or higher. If the tensile modulus T1 in the MD direction is greater than or equal to the lower limit value, the balance between heat sealability, water vapor barrier properties, and transparency of the food packaging film 100 according to this embodiment can be further improved. Furthermore, the stiffness of the food packaging film 100 according to this embodiment can be further improved, and as a result, misalignment of the film during heat sealing can be suppressed, and sealing defects can be further suppressed. In other words, if the tensile modulus T1 in the MD direction is greater than or equal to the above lower limit, the balance of heat sealability, water vapor barrier properties, transparency, and packaging suitability of the food packaging film 100 according to this embodiment can be further improved. Furthermore, in the food packaging film 100 according to this embodiment, the upper limit of the tensile modulus T1 in the MD direction is preferably 3000 MPa or less, more preferably 2500 MPa or less, and even more preferably 2200 MPa or less. If the tensile modulus T1 in the MD direction is below the above upper limit, the unevenness in stretching due to crystallization of the biaxially oriented film layer 101 can be further reduced, and as a result, the thickness unevenness that occurs when stretching the biaxially oriented film layer 101 can be further reduced.

[0022] Here, the food packaging body produced using the food packaging film 100 according to the present embodiment exhibits sufficient water vapor barrier performance. Therefore, it can be particularly preferably used as a film constituting a food packaging body for packaging foods (for example, dried foods) that require water vapor barrier performance but do not require much oxygen barrier performance.

[0023] The food packaging body produced using the food packaging film 100 according to the present embodiment has sufficient water vapor barrier performance. In the food packaging film 100, from the viewpoint of stably obtaining a food packaging body with excellent water vapor barrier performance, the water vapor permeability measured by the following method is preferably 6.0 g / (m 2 ·24 h) or less, more preferably 5.5 g / (m 2 ·24 h) or less, and even more preferably 5.0 g / (m 2 ·24 h) or less. (Measurement method) Fold the food packaging film 100 so that the heat seal layer 103 is on the inner surface, and heat seal both sides to form a bag shape. Then, put calcium chloride as the content. Next, heat seal the other side to make a bag with a surface area of 0.01 m 2 . Then, store the obtained bag under the conditions of 40 °C and 90% RH for 72 hours. Measure the weight of calcium chloride before and after storage, and calculate the water vapor permeability (g / (m 2 ·24 h)) from the difference. Such water vapor permeability can be achieved, for example, by adjusting the DSC characteristics of the biaxially stretched film layer 101 such as the endothermic peak characteristics and exothermic peak characteristics described above, the content ratio of the propylene-based polymer contained in the biaxially stretched film layer 101, the constituent material and thickness of the heat seal layer 103, etc.

[0024] The thickness of the food packaging film 100 according to this embodiment is not particularly limited, but can be arbitrarily set according to desired purposes such as water vapor barrier properties, cost, mechanical strength, and transparency, and is not particularly limited, but for example it is 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 food packaging film 100 is within the above range, a better balance of bag-making properties, mechanical properties, handling properties, appearance, transparency, moldability, and lightness is achieved.

[0025] The following describes each layer that makes up the food packaging film 100.

[0026] [Biaxially oriented film layer] The biaxially oriented film layer 101 (also referred to as a biaxially oriented polypropylene film layer) according to this embodiment is formed by biaxially oriented a film composed of a propylene polymer composition containing a propylene polymer, for example.

[0027] The biaxially oriented film layer 101 according to this embodiment may be a single layer or a configuration in which multiple layers made of a propylene polymer composition are laminated, but it is necessary that it be biaxially oriented.

[0028] Furthermore, 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 50% or more and 100%, more preferably 60% or more and 99%, even more preferably 70% or more and 97%, and particularly preferably 75% or more and 95%.

[0029] (Propylene-based polymer composition) The propylene polymer composition according to this embodiment contains a propylene polymer. The propylene polymer content in the propylene polymer composition according to this embodiment, i.e., the biaxially oriented film layer 101, is preferably 50% to 100% by mass, more preferably 70% to 100% by mass, even more preferably 90% to 100% by mass, and particularly preferably 95% to 100% by mass, when the total propylene polymer composition is considered as 100% by mass. This allows for a better balance of the film's stiffness, water vapor barrier properties, mechanical properties, handling properties, appearance, and moldability.

[0030] (Propylene polymer) Examples of propylene-based polymers according to this embodiment include propylene homopolymers and copolymers of propylene with ethylene or α-olefins having 4 to 20 carbon atoms. Examples of 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 with propylene or block copolymers. The content of constituent 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 total amount of the propylene-based polymer is considered to be 100 mol%. The propylene polymer in the biaxially oriented film layer 101 may be used alone or in combination of two or more types. Among these, propylene homopolymer is preferred as the propylene polymer from the viewpoint of obtaining a biaxially oriented film layer 101 with an even better balance of performance such as heat resistance, water vapor barrier properties, mechanical properties, and rigidity.

[0031] Here, in order to set the sum of the tensile modulus T1 in the MD direction and the tensile modulus T2 in the TD direction, T3, and the heat quantity Q of the endothermic peak A of the biaxially oriented film layer 101 within the above range, it is important to select an appropriate propylene polymer. More specifically, the biaxially oriented film layer 101 according to this embodiment can be adjusted by using two or more propylene polymers with different melting points, crystallinity, stereoregularity, etc., and by adjusting their ratios, thereby adjusting the heat quantity Q of T3 and the endothermic peak A mentioned above.

[0032] For example, the propylene polymer contained in the biaxially oriented film layer 101 according to this embodiment may include a first propylene polymer having a melting point in the range of 130°C to 162°C as determined by DSC measurement, and a second propylene polymer having a melting point in the range of 162°C to 180°C as determined by DSC measurement. In this case, when the total amount of the first propylene polymer and the second propylene polymer contained in the biaxially oriented film layer 101 is taken as 100% by mass, the content of the second propylene polymer is preferably 1% by mass or more, more preferably 10% by mass or more, even more preferably 25% by mass or more, even more preferably 35% by mass or more, and particularly preferably 50% by mass or more, from the viewpoint of improving the water vapor barrier properties of the food packaging film 100. Furthermore, when the total amount of the first propylene polymer and the second propylene polymer contained in the biaxially oriented film layer 101 is taken as 100% by mass, the content of the second propylene polymer is preferably 85% by mass or less, more preferably 75% by mass or less, and even more preferably 70% by mass or less, from the viewpoint of further suppressing thickness unevenness of the food packaging film 100.

[0033] Furthermore, in this embodiment, the second propylene polymer is preferably a highly stereoregular propylene polymer. Here, a highly stereoregular propylene polymer refers to a propylene polymer having an isotactic mesopentad fraction (mmmm), which is an indicator of stereoregularity, of 96.0% or more. The isotactic mesopentad fraction (mmmm) of the highly stereoregular propylene polymer according to this embodiment is preferably 96.5% or more, and 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 manufacture, 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 the 13C nuclear magnetic resonance (NMR) spectrum using known methods.

[0034] The propylene polymer according to this embodiment can be produced by various methods. For example, it can be produced using known catalysts such as Ziegler-Natta catalysts or metallocene catalysts.

[0035] According to ASTM D1238, the melt flow rate (MFR) of the propylene polymer according to this embodiment, measured under conditions of 230°C and a 2.16 kg load, 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 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.

[0036] (Other ingredients) The propylene polymer composition according to this embodiment may optionally contain various additives such as tackifiers, heat stabilizers, weather stabilizers, antioxidants, ultraviolet absorbers, lubricants, slip agents, nucleating agents, antiblocking agents, antistatic agents, antifogging agents, pigments, dyes, and inorganic or organic fillers, to the extent that they do not impair the purpose of this embodiment.

[0037] As the tackifier in this embodiment, a resinous substance having tackiness-imparting properties that is generally manufactured and sold as a tackifier can be used. Examples of such tackifiers include chroman resins such as chroman-indene resin; phenolic resins such as phenol-formaldehyde resin and xylene-formaldehyde resin; terpene resins such as terpene-phenol resin, terpene resin (α,β-pinene resin), aromatically modified terpene resin, and hydrogenated terpene resin; petroleum hydrocarbon resins such as synthetic polyterpene resin, aromatic hydrocarbon resin, aliphatic hydrocarbon resin, aliphatic cyclic hydrocarbon resin, aliphatic-alicyclic petroleum resin, aliphatic-aromatic petroleum resin, unsaturated hydrocarbon polymer, and hydrocarbon tackifier resin; hydrogenated petroleum hydrocarbon resins (also called hydrogenated petroleum hydrocarbon resins); rosin resins such as rosin pentaerythritol ester, rosin glycerin ester, hydrogenated rosin, hydrogenated rosin ester, special rosin ester, and rosin-based tackifiers. Among these, at least one selected from petroleum hydrocarbon resins and hydrogenated petroleum hydrocarbon resins is preferred, with hydrogenated petroleum hydrocarbon resins being more preferred, from the viewpoint of having good compatibility with propylene polymers and being able to 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 it is preferably 90% or more, more preferably 95% or more, and even more preferably 99% or more, due to its superior compatibility with propylene polymers.

[0038] Here, the content of the tackifier in the propylene polymer composition, i.e., the biaxially oriented film layer 101, according to this embodiment, is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 3% by mass or less, and particularly preferably 1% by mass or less, when the total biaxially oriented film layer 101 is considered to be 100% by mass, from the viewpoint of the recyclability and cost reduction of the food packaging film 100, as well as from the viewpoint of suppressing a decrease in the flexural elasticity of the food packaging film 100, and improving processability, dimensional stability, and transparency.

[0039] (Method for preparing a propylene polymer composition) The propylene polymer composition according to this embodiment can be prepared by mixing or melting / kneading each component using a dry blender, tumbler mixer, Banbury mixer, single-screw extruder, twin-screw extruder, high-speed twin-screw extruder, hot roll, etc.

[0040] [Heat seal layer] In this embodiment, the food packaging film 100 preferably includes a heat seal layer 103 on at least one surface of the biaxially oriented film layer 101 in order to provide heat sealability. The heat seal layer 103 may be provided on both sides of the biaxially oriented film layer 101. Furthermore, from the viewpoint of improving the heat-seal properties of the food packaging film 100, it is preferable that the heat-seal layer 103 be provided on the outermost layer of the food packaging film 100 according to this embodiment.

[0041] Furthermore, it is preferable that the heat seal layer 103 is provided in direct contact with the surface of the biaxially oriented film layer 101. This simplifies the manufacturing process of the food packaging film 100.

[0042] In the food packaging film 100, the thickness of the heat seal layer 103 is preferably 0.1 μm or more and 10 μm or less, more preferably 0.2 μm or more and 9 μm or less, even 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 oriented film layer 101. By ensuring that the thickness of the heat-seal layer 103 is equal to or greater than the above lower limit, the heat-seal properties of the food packaging film 100 can be further improved. Furthermore, by keeping the thickness of the heat-seal layer 103 below the above upper limit, the blocking and slip properties required for food packaging films can be further improved. In other words, by providing a heat-seal layer 103 in direct contact with the surface of the biaxially oriented film layer 101, the manufacturing process of the food packaging film 100 can be simplified. In this embodiment, when heat seal layers 103 are provided on both sides of the biaxially oriented film layer 101, the above thickness of the heat seal layer 103 refers to the thickness of the heat seal layer 103 provided on one side of the biaxially oriented film layer 101.

[0043] In the food packaging film 100, the heat-seal layer 103 provided on one side is preferably a single layer. This further simplifies the manufacturing process of the food packaging film 100.

[0044] Furthermore, it is preferable that the heat seal layer 103 is formed by biaxial stretching simultaneously with the film layer 101, which is in its pre-biaxial stretching state. This allows the food packaging film 100 to be manufactured using a molding method such as co-extrusion, i.e., a laminated film produced in a single molding process, thereby further simplifying the manufacturing process of the food packaging film 100. Therefore, it is preferable that the heat seal layer 103 is biaxially stretched.

[0045] (Polyolefin) The heat seal layer 103 according to this embodiment is composed of, for example, a polyolefin-based resin composition (A) containing a polyolefin. Examples of polyolefins constituting the heat seal layer 103 include homopolymers or copolymers of α-olefins such as ethylene, propylene, butene-1, hexene-1, 4-methylpentene-1, and octene-1; high-pressure low-density polyethylene; linear low-density polyethylene (LLDPE); high-density polyethylene; polypropylene; random copolymers of propylene and α-olefins having 2 to 10 carbon atoms; ethylene vinyl acetate copolymer (EVA); ionomer resins, etc. Among these, as the polyolefin constituting the heat seal layer 103, at least one selected from homopolypropylene and a random copolymer of propylene and an α-olefin having 2 to 10 carbon atoms is preferred, due to its excellent balance of adhesion to the biaxially oriented film layer 101 and heat sealability. Furthermore, from the viewpoint of heat sealability and heat seal strength stability, it is preferable that the heat seal layer 103 includes an olefin-based elastomer among the polyolefins mentioned above.

[0046] The propylene-α-olefin random copolymer according to this embodiment is a random copolymer of propylene and α-olefin (where α-olefin is excluding propylene), and examples of α-olefins include ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, etc. These copolymers may be used individually or as a mixture of two or more. Among propylene-α-olefin random copolymers, propylene-ethylene random copolymer, propylene-ethylene-1-butene random copolymer, and propylene-1-butene random copolymer are preferred.

[0047] The melting point of the polyolefin constituting the heat seal layer 103 according to this embodiment is preferably in the range of 60°C to 175°C, more preferably 65°C to 170°C, and even more preferably 70°C to 167°C. When the melting point of the polyolefin is above the lower limit of the above value, stickiness on the surface of the heat seal layer 103 can be suppressed, and the blocking resistance of the food packaging film 100 can be improved. Furthermore, if the melting point of the polyolefin is below the above upper limit, the heat-sealability of the food packaging film 100 can be improved.

[0048] Examples of the olefin-based elastomers mentioned above include α-olefin polymers having 2 to 20 carbon atoms with a melting point preferably 110°C or lower, more preferably 100°C or lower, even more preferably 80°C or lower, or no melting point observed, or copolymers of ethylene and α-olefins; copolymers of ethylene and unsaturated carboxylic acids or unsaturated carboxylic acid esters; and the like. Specifically, examples include ethylene-propylene copolymer, ethylene-1-butene copolymer, ethylene-1-hexene copolymer, ethylene-4-methylpentene-1 copolymer, ethylene-1-octene copolymer, propylene homopolymer, propylene-ethylene copolymer, propylene-ethylene-1-butene copolymer, 1-butene homopolymer, 1-butene-ethylene copolymer, 1-butene-propylene copolymer, 4-methylpentene-1 homopolymer, 4-methylpentene-1-propylene copolymer, 4-methylpentene-1-1-butene copolymer, 4-methylpentene-1-propylene-1-butene copolymer, propylene-1-butene copolymer, ethylene-vinyl acetate copolymer, ethylene-methacrylic acid copolymer, ethylene-methyl methacrylate copolymer, and the like. From the viewpoint of heat sealability and heat seal strength stability, propylene-1-butene copolymer is particularly preferred.

[0049] According to ASTM D1238, the melt flow rate (MFR) of the polyolefin constituting the heat seal layer 103 according to this embodiment, measured under conditions of 230°C and a 2.16 kg load, 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 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.

[0050] The polyolefin content in the polyolefin resin composition (A) in this embodiment, i.e., the heat seal layer 103, is preferably 50% to 100% by mass, more preferably 70% to 100% by mass, even more preferably 90% to 100% by mass, and particularly preferably 95% to 100% by mass, when the total polyolefin resin composition (A) is considered as 100% by mass. This makes it possible to achieve a better balance of adhesion to the biaxially oriented film layer 101 and heat sealability. Furthermore, the content of the olefin-based elastomer in the polyolefin-based resin composition (A) according to this embodiment, i.e., in the heat seal layer 103, is preferably 10% by mass or more and 50% by mass or less, more preferably 15% by mass or more and 45% by mass or less, and even more preferably 20% by mass or more and 40% by mass or less, when the polyolefin content in the biaxially oriented film layer 101 is taken as 100% by mass.

[0051] (Other ingredients) The polyolefin resin composition (A) constituting the heat seal layer 103 according to this embodiment may optionally contain various additives such as tackifiers, heat stabilizers, weather stabilizers, antioxidants, ultraviolet absorbers, lubricants, slip agents, nucleating agents, antiblocking agents, antistatic agents, antifogging agents, pigments, dyes, and inorganic or organic fillers, to the extent that they do not impair the purpose of this embodiment. In particular, the heat seal layer 103 according to this embodiment preferably contains an antiblocking agent from the viewpoint of improving the blocking resistance of the food packaging film 100 according to this embodiment. Examples of antiblocking agents include talc, silica, clay, calcium carbonate, synthetic zeolite, starch, aluminum oxide, acrylic resin, methacrylic resin, silicone resin, and polytetrafluoroethylene resin.

[0052] Furthermore, from the viewpoint of improving the heat sealability of the heat seal layer 103, it is preferable that the heat seal layer 103 contains substantially no tackifier. More specifically, the tackifier content 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. Here, a tackifier is generally a resinous substance that has the property of imparting tackiness and is manufactured and sold as such. Examples of such tackifiers include chroman resins such as chroman-indene resin; phenolic resins such as phenol-formaldehyde resin and xylene-formaldehyde resin; terpene resins such as terpene-phenol resin, terpene resin (α,β-pinene resin), aromatically modified terpene resin, and hydrogenated terpene resin; petroleum hydrocarbon resins such as synthetic polyterpene resin, aromatic hydrocarbon resin, aliphatic hydrocarbon resin, aliphatic cyclic hydrocarbon resin, aliphatic-alicyclic petroleum resin, aliphatic-aromatic petroleum resin, unsaturated hydrocarbon polymer, and hydrocarbon tackifier resin; hydrogenated petroleum hydrocarbon resins (also called hydrogenated petroleum hydrocarbon resins); rosin resins such as rosin pentaerythritol ester, rosin glycerin ester, hydrogenated rosin, hydrogenated rosin ester, special rosin ester, and rosin-based tackifiers.

[0053] (Method for preparing polyolefin resin composition (A)) The polyolefin resin composition (A) according to this embodiment can be prepared, for example, by mixing or melting / kneading each component using a dry blender, tumbler mixer, Banbury mixer, single-screw extruder, twin-screw extruder, high-speed twin-screw extruder, hot roll, etc.

[0054] [Surface layer] In order to improve the printability of the surface, the food packaging film 100 according to this embodiment preferably further includes a surface layer 105 on the side of the biaxially oriented film layer 101 opposite to the side on which the heat seal layer 103 is provided, as shown in Figure 2. Furthermore, from the viewpoint of improving the printability of the food packaging film 100, it is preferable that the surface layer 105 be provided as the outermost layer of the food packaging film 100 according to this embodiment.

[0055] Furthermore, it is preferable that the surface layer 105 is provided in direct contact with the surface of the biaxially oriented film layer 101. This simplifies the manufacturing process of the food packaging film 100.

[0056] In the food packaging film 100, the thickness of the surface layer 105 is preferably 0.1 μm or more and 10 μm or less, more preferably 0.2 μm or more and 9 μm or less, even 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 surface layer 105 refers to the thickness of the surface layer 105 provided on one side of the biaxially oriented film layer 101. By ensuring that the thickness of the surface layer 105 is equal to or greater than the above lower limit, the printability of the food packaging film 100 can be further improved. Furthermore, by keeping the thickness of the surface layer 105 below the above upper limit, the blocking and slip properties required during printing can be further improved. In other words, by providing a surface layer 105 in direct contact with the surface of the biaxially oriented film layer 101, the manufacturing process of the food packaging film 100 can be simplified.

[0057] In the food packaging film 100, the surface layer 105 is preferably a single layer. This further simplifies the manufacturing process of the food packaging film 100.

[0058] Furthermore, it is preferable that the surface layer 105 is formed by biaxial stretching simultaneously with the film in the pre-biaxial stretching state of the biaxially stretched film layer 101. This allows the food packaging film 100 to be manufactured using a molding method such as co-extrusion, i.e., a laminated film produced in a single molding process, thereby further simplifying the manufacturing process of the food packaging film 100. Therefore, it is preferable that the surface layer 105 is biaxially stretched.

[0059] Furthermore, the surface layer 105 may be subjected to surface treatment from the viewpoint of improving the printability of the food packaging film 100. Specifically, surface activation treatments such as corona treatment, flame treatment, plasma treatment, primer coating treatment, and ozone treatment may be performed.

[0060] (Polyolefin) The surface layer 105 according to this embodiment is composed of, for example, a polyolefin-based resin composition (B) containing a polyolefin. Examples of polyolefins constituting the surface layer 105 include homopolymers or copolymers of α-olefins such as ethylene, propylene, butene-1, hexene-1, 4-methylpentene-1, and octene-1; high-pressure low-density polyethylene; linear low-density polyethylene (LLDPE); high-density polyethylene; polypropylene; random copolymers of propylene and α-olefins having 2 to 10 carbon atoms; ethylene-vinyl acetate copolymer (EVA); ionomer resins, etc. Among these, as the polyolefin constituting the surface layer 105, at least one selected from homopolypropylene and a random copolymer of propylene and an α-olefin having 2 to 10 carbon atoms is preferred, due to its excellent balance of adhesion to the biaxially oriented film layer 101 and printability.

[0061] The propylene-α-olefin random copolymer according to this embodiment is a random copolymer of propylene and α-olefin (where α-olefin is excluding propylene), and examples of α-olefins include ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, etc. These copolymers may be used individually or as a mixture of two or more. Among propylene-α-olefin random copolymers, propylene-ethylene random copolymer, propylene-ethylene-1-butene random copolymer, and propylene-1-butene random copolymer are preferred.

[0062] The melting point of the polyolefin constituting the surface layer 105 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 above the lower limit of the above value, stickiness of the surface of the surface layer 105 can be suppressed, and the blocking resistance of the food packaging film 100 can be improved.

[0063] According to ASTM D1238, the melt flow rate (MFR) of the polyolefin constituting the surface layer 105 of this embodiment, measured under conditions of 230°C and a 2.16 kg load, 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 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.

[0064] The polyolefin content in the polyolefin resin composition (B) according to this embodiment, i.e., the polyolefin content in the surface layer 105, is preferably 50% to 100% by mass, more preferably 70% to 100% by mass, even more preferably 90% to 100% by mass, and particularly preferably 95% to 100% by mass, when the total polyolefin resin composition (B) is considered as 100% by mass. This makes it possible to achieve a better balance of adhesion to the biaxially oriented film layer 101 and printability.

[0065] (Other ingredients) The polyolefin resin composition (B) constituting the surface layer 105 according to this embodiment may optionally contain various additives such as tackifiers, heat stabilizers, weather stabilizers, antioxidants, ultraviolet absorbers, lubricants, slip agents, nucleating agents, antiblocking agents, antistatic agents, antifogging agents, pigments, dyes, and inorganic or organic fillers, to the extent that they do not impair the purpose of this embodiment. In particular, the surface layer 105 according to this embodiment preferably contains an antiblocking agent from the viewpoint of improving the blocking resistance of the food packaging film 100 according to this embodiment. Examples of antiblocking agents include those similar to the antiblocking agent used in the heat seal layer 103 mentioned above.

[0066] (Method for preparing polyolefin resin composition (B)) The polyolefin resin composition (B) according to this embodiment can be prepared, for example, by mixing or melting / kneading each component using a dry blender, tumbler mixer, Banbury mixer, single-screw extruder, twin-screw extruder, high-speed twin-screw extruder, hot roll, etc.

[0067] <Method for manufacturing food packaging film> The food packaging film 100 according to this embodiment can be obtained, for example, by co-extruding a resin composition (P) for forming a biaxially oriented film layer 101, a polyolefin-based resin composition (A) for optionally forming a heat-seal layer 103, and a polyolefin-based resin composition (B) for forming a surface layer 105 into a film, and then biaxially stretching the resulting film using a known biaxially oriented 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 include T-die extruders, multi-layer T-die extruders, inflation molding machines, or multi-layer inflation molding machines. For biaxial stretching conditions, for example, known manufacturing conditions for OPP film can be adopted. More specifically, in the sequential biaxial stretching method, for example, the longitudinal stretching temperature should be in the range of 100°C to 145°C, the longitudinal stretching ratio in the range of 4.5 to 6 times, the transverse stretching temperature in the range of 130°C to 190°C, and the transverse stretching ratio in the range of 9 to 11 times. Furthermore, the food packaging film 100 according to this embodiment can also be obtained by separately molding a biaxially oriented film layer 101 and, if necessary, a heat-seal layer 103 and a surface layer 105, and then laminating and heat-molding these layers.

[0068] <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 packaging body. The food packaging body according to this embodiment is, for example, a packaging bag itself used for the purpose of containing food, or food contained in such a bag. Furthermore, the food packaging body according to this embodiment may use the food packaging film 100 in part, or the food packaging film 100 may be used throughout the entire food packaging body, depending on the application.

[0069] The food packaging film 100 according to this embodiment is preferably used in outer packaging bags where water vapor barrier properties are required. Furthermore, when the food packaging film 100 according to this embodiment is used in an integrated packaging body composed of food, individual packaging bags for individually packaging food, and an outer packaging bag for packaging multiple individual packaging bags, it is preferable to use the food packaging film 100 in the outer packaging bag in the integrated packaging body where water vapor barrier properties are required. This makes it possible to obtain an integrated packaging body with sufficient water vapor barrier properties.

[0070] The embodiments of the present invention have been described above with reference to the drawings, but these are merely examples of the present invention, and various other configurations can also be adopted. [Examples]

[0071] This embodiment will be described in detail below with reference to examples and comparative examples. However, this embodiment is not limited in any way to the descriptions of these examples.

[0072] 1.Raw materials The raw materials used in the examples and comparative examples are shown below. (1) Propylene polymer PP1: Highly stereoregularized propylene homopolymer (MFR: 3g / 10min, melting point: 167℃, isotactic mesopentad fraction (mmmm): 98.5%) PP2: Propylene homopolymer (MFR: 3g / 10min, melting point: 161℃, isotactic mesopentad fraction (mmmm): 92%) PP3: Propylene-α-olefin random copolymer (MFR: 7g / 10min, melting point: 137℃)

[0073] 2. Measurement and Evaluation Methods (1) Isotactic mesopentad fraction of propylene polymers (mmmm) The measurement of isotactic mesopentade fraction (mesopentade fraction, (mmmm)) is performed. 13 The analysis was performed using 1C-NMR. The isotactic mesopentad fraction was calculated according to the method described by Zambelli et al. in Macromolecules, Vol. 6, p. 925 (1973), and the isotactic meso-average chain length was calculated according to the method described by JCRandall in Chapter 2 of "Polymer Sequence Distribution" (1977) (Academic Press, New York).

[0074] (2) MFR of propylene polymers Measurements were taken in accordance with ASTM D1238, under conditions of 230°C and a 2.16 kg load.

[0075] (3) Differential scanning calorimetry Approximately 5.0 mg of test material was cut from the food packaging film obtained in the examples and comparative examples. Next, the sample was subjected to a differential scanning calorimeter (product name: Q200DSC, manufactured by TA Instruments Corporation) for the first differential scanning calorimeter measurement (1st Run), which consisted of heating the sample from -50°C to 250°C at a heating rate of 10°C / min under a nitrogen atmosphere, an isothermal process of maintaining the temperature at 250°C for 10 minutes, and cooling the sample from 250°C to -50°C at a cooling rate of 10°C / min. The second differential scanning calorimeter measurement (2nd Run) consisted of heating the sample from -50°C to 250°C at a heating rate of 10°C / min. From the obtained DSC curve of the 2nd Run, the heat quantity Q (J / g) of the endothermic peak A was determined.

[0076] (4) Tensile modulus Test specimens measuring 15 mm × 15 cm were cut from the food packaging films obtained in the examples and comparative examples. Then, using a tensile testing machine manufactured by Orientec Co., Ltd., the tensile modulus T1 in the MD direction and the tensile modulus T2 in the TD direction of the test specimens were measured in accordance with JIS K7127 (1999) under the conditions of a measurement temperature of 23 ± 2 °C, 50 ± 5% RH, and a tensile speed of 5 mm / min.

[0077] (5) Evaluation of thickness variations Using a sequential biaxial stretching machine, a biaxially oriented polypropylene film approximately 1 m wide in the direction perpendicular to the flow direction was prepared using the method described below. Ten sheets of film were stacked and divided into nine equal parts in the 1 m width direction, and the thickness was measured at eight points excluding both ends. The measured values ​​were applied to the following formula to calculate X. A smaller X indicates better thickness uniformity. X = (Maximum thickness - Minimum thickness) / (Maximum thickness + Minimum thickness) Next, the thickness variations of food packaging films were evaluated according to the following criteria. ◎: X is less than 2% ○: X is between 2% and less than 4% △: X is between 4% and 6% ×: The value of X is 6% or greater.

[0078] (6) Evaluation of unevenness in extension The stretched film's appearance was inspected visually to determine if any noticeably thicker sections remained in the film, excluding the 150mm at both ends. If thicker sections remained, it indicated uneven stretching and unstable film properties. ◎: No unevenness in extension ×: Uneven stretching

[0079] (7) Water vapor barrier properties A food packaging film was folded over so that the heat-seal layer was on the inside, and two sides were heat-sealed to form a bag. Then, calcium chloride was added as the contents. Next, the other side was heat-sealed to create a bag with a surface area of ​​0.01 m². 2A bag was fabricated to achieve the following conditions. Next, the resulting bag was stored for 72 hours at 40°C and 90% RH. The weight of calcium chloride was measured before and after storage, and the water vapor transmission rate (g / m³) was calculated from the difference. 2 The values ​​for each 24 hours were calculated. Here, a heat-seal layer was formed on one side of the biaxially oriented polypropylene film obtained in the examples and comparative examples. Next, the water vapor barrier properties of food packaging films were evaluated according to the following criteria. ◎◎: Water vapor transmission rate is 5.0 g / (m 2 ·24h) or less ◎: Water vapor transmission rate is 5.0 g / (m³) 2 ·24h) Exceeded 5.5g / (m 2 ·24h) or less ○: Water vapor transmission rate is 5.5 g / (m³) 2 ·24h) Excess 6.0g / (m 2 ·24h) or less ×: Water vapor transmission rate is 6.0 g / (m 2 ·24h) exceeded

[0080] [Examples 1-11 and Comparative Examples 1-3] Biaxially oriented polypropylene films were extruded using the compositions shown in Tables 1 and 2, and then subjected to biaxial stretching to produce food packaging films. Each film was then evaluated. The extrusion molding conditions and biaxial stretching conditions are as follows. Extrusion molding machine: 60mmφ multilayer T-die extrusion molding machine (screw: L / D=27, manufactured by Screw Seiki Co., Ltd.) Extrusion setting temperature: 230~250℃, Processing speed: 20m / min (winding speed) Longitudinal stretching temperature: 115~130℃ Vertical stretching ratio: 5x Lateral stretching temperature: 140~175℃ Lateral stretching ratio: 10x

[0081] [Table 1]

[0082] [Table 2]

[0083] The food packaging films in the examples had less variation in thickness than the food packaging films in the comparative examples. Furthermore, using the food packaging films in the examples resulted in food packaging with improved water vapor barrier properties compared to using the food packaging films in the comparative examples. [Explanation of Symbols]

[0084] 100 Food packaging film 101 Biaxially oriented film layer 103 Heat seal layer 105 Surface layer

Claims

1. Food packaging film for packaging food, The film comprises a biaxially oriented film layer containing a propylene polymer, The tensile modulus T in the MD direction of the food packaging film is measured in accordance with JIS K7127 (1999) using a tensile testing machine under the conditions of a measurement temperature of 23±2°C, 50±5%RH, and a tensile speed of 5 mm / min. １ and the tensile modulus T in the TD direction ２ and the total value T ３ In that case, Said T ３ The pressure is between 6600 MPa and 7500 MPa. Tensile modulus T in the MD direction １ This is a food packaging film with a pressure of 1500 MPa or more and 2200 MPa or less. The water vapor transmission rate measured by the following method is 6.0 g / (m³). ２ - 24 hours or less, The biaxially oriented film layer further comprises a heat seal layer on at least one surface, The biaxially oriented film layer is composed of a propylene polymer composition, and the content of the propylene polymer in the propylene polymer composition is 90% by mass or more and 100% by mass or less, when the total amount of the propylene polymer composition is considered to be 100% by mass. The propylene polymer contained in the biaxially oriented film layer includes a first propylene polymer having a melting point in the range of 130°C to 162°C as determined by DSC measurement, and a second propylene polymer having a melting point in the range of 162°C to 180°C as determined by DSC measurement. The isotactic mesopentad fraction (mmmm) of the second propylene polymer is 96.0% or higher. A food packaging film in which, when the total amount of the first propylene polymer and the second propylene polymer contained in the biaxially oriented film layer is taken as 100% by mass, the content of the second propylene polymer in the biaxially oriented film layer is 1% by mass or more and 85% by mass or less. (Measurement method) The food packaging film is folded so that the heat-seal layer faces inward, and two sides are heat-sealed to form a bag. Then, calcium chloride is placed inside as the contents. Next, the other side is heat-sealed to create a bag with a surface area of ​​0.01 m². ２ A bag is prepared to achieve the following conditions. Next, the resulting bag is stored for 72 hours at 40°C and 90% RH. The weight of calcium chloride is measured before and after storage, and the water vapor transmission rate (g / m³) is calculated from the difference. ２ Calculate 24 hours.

2. In the food packaging film according to claim 1, A differential scanning calorimeter is used to analyze the biaxially oriented film layer. The first differential scanning calorimetry (1st Run) consists of a process of raising the temperature from -50°C to 250°C at a heating rate of 10°C / min, an isothermal process of maintaining the temperature at 250°C for 10 minutes, and a process of cooling from 250°C to -50°C at a cooling rate of 10°C / min. The second differential scanning calorimetry (2nd Run) consists of a process of raising the temperature from -50°C to 250°C at a heating rate of 10°C / min, When you continue doing that, In the DSC curve 2 obtained from the second differential scanning calorimetry, an endothermic peak A was observed in the range of 150°C to 180°C. When the amount of heat at the aforementioned endothermic peak A is Q, T ３ A food packaging film with a T / Q of 50 or more and 80 or less.

3. In the food packaging film according to claim 1 or 2, The tensile modulus T in the TD direction of the aforementioned food packaging film ２ and the tensile modulus T in the MD direction １ The difference (T ２ -T １ Food packaging film having a pressure of 2500 MPa or more and 4000 MPa or less.

4. In a food packaging film according to any one of claims 1 to 3, The heat-seal layer is provided so as to be in direct contact with one of the surfaces of the biaxially oriented film layer in a food packaging film.

5. In a food packaging film according to any one of claims 1 to 4, A food packaging film comprising one or more materials selected from homopolypropylene and a random copolymer of propylene and an α-olefin having 2 to 10 carbon atoms.

6. In a food packaging film according to any one of claims 1 to 5, A food packaging film further comprising a surface layer on one surface of the biaxially oriented film layer.

7. In the food packaging film according to claim 6, The aforementioned surface layer is a food packaging film containing an antiblocking agent.

8. In the food packaging film according to claim 6 or 7, The aforementioned surface layer is a food packaging film comprising one or more selected from homopolypropylene and a random copolymer of propylene and an α-olefin having 2 to 10 carbon atoms.

9. In a food packaging film according to any one of claims 1 to 8, A food packaging film in which the content of the tackifier contained in the biaxially oriented film layer is 10% by mass or less when the total mass of the biaxially oriented film layer is taken as 100% by mass.

10. In a food packaging film according to any one of claims 1 to 9, Food packaging film used for outer packaging bags.

11. A food packaging body using the food packaging film described in any one of claims 1 to 10.

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