Biaxially oriented polypropylene film, package for food, and food package

Abstract

To provide a biaxially oriented polypropylene film with improved thermal dimensional stability.SOLUTION: A biaxially oriented polypropylene film 100 comprises a biaxially oriented film layer 101 comprising propylene polymer. When heated at 120°C for 15 minutes in accordance with JIS C2151: 2019, the biaxially oriented polypropylene film expands in a TD direction and shrinks in an MD direction.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a biaxially oriented polypropylene film, a food package, 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 property, transparency, mechanical strength, and rigidity, and is used, for example, 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 comprising a biaxially oriented film made of a propylene polymer composition containing 75 to 90 mass% of a propylene homopolymer (A) and 25 to 10 mass% of a tackifier (D), the biaxially oriented film having a layer made of a propylene-α-olefin random copolymer (C) having a melting point in the range of 125 to 145°C via a layer made of a propylene polymer (B) having a melting point of 155°C or higher on one side thereof, and a layer made of a propylene polymer (E) on the other side thereof. Patent Document 1 describes that the biaxially oriented multilayer polypropylene film 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 multilayer 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 mass of a highly crystallizable resin and 6 to 15% by mass 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 the above multilayer resin film 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] In recent years, from the viewpoint of environmental issues, there has been a demand for mono-material packaging materials. However, conventional biaxially oriented polypropylene films have sometimes been insufficient in thermal dimensional stability from the viewpoint of suppressing thermal wrinkles at the sealed portion during bag making and suppressing thermal expansion during vapor deposition and coating processing. That is, further improvement in thermal dimensional stability is required for biaxially oriented polypropylene films from the viewpoint of suppressing thermal wrinkles at the sealed portion during bag making and suppressing thermal expansion during vapor deposition and coating processing.

[0008] The present invention has been made in view of the above circumstances, and provides a biaxially oriented polypropylene film, a food packaging material, and a food packaging material, all of which have improved thermal dimensional stability. [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 biaxially oriented polypropylene film, which has the property of expanding in the TD direction and shrinking in the MD direction when heated at 120°C for 15 minutes, can improve thermal dimensional stability, thereby completing the present invention.

[0010] That is, according to the present invention, there are provided a biaxially oriented polypropylene film, a food packaging material, and a food packaging material as shown below.

[0011] [1] A biaxially stretched film layer containing a propylene-based polymer is provided, A biaxially oriented polypropylene film that expands in the TD direction and shrinks in the MD direction when heat-treated at 120℃ for 15 minutes in accordance with JIS C2151:2019. [2] The biaxially oriented polypropylene film according to [1] above, having a thermal expansion coefficient in the TD direction of 0.1% or more and 2.0% or less when heat-treated at 120 ° C. for 15 minutes in accordance with JIS C2151:2019. [3] The biaxially oriented polypropylene film according to [1] or [2] above, having a heat shrinkage rate in the MD direction of 5.0% or less when heat-treated at 120 ° C for 15 minutes in accordance with JIS C2151:2019. [4] The biaxially oriented polypropylene film according to any one of [1] to [3] above, having a thermal shrinkage rate in the TD direction of 8.5% or less when heat-treated at 150° C. for 15 minutes in accordance with JIS C2151:2019. [5] The biaxially oriented polypropylene film according to any one of [1] to [4] above, having a heat shrinkage rate in the MD direction of 8.0% or less when heat-treated at 150°C for 15 minutes in accordance with JIS C2151:2019. [6] According to JIS C2151:2019, the thermal shrinkage in the TD direction and the thermal shrinkage in the MD direction when heated at 150℃ for 15 minutes are measured. TD [%] and X MD When set to [%], X TD+X MD The biaxially oriented polypropylene film according to any one of the above [1] to [5], wherein the modulus of elasticity is less than 16.0%. [7] The biaxially oriented polypropylene film according to any one of [1] to [6] above, wherein the amount of structural units derived from α-olefins other than propylene contained in the biaxially oriented polypropylene film is 0.05 mol % or more, when the total amount of structural units derived from monomers contained in the biaxially oriented polypropylene film is taken as 100 mol %. [8] The biaxially oriented polypropylene film according to any one of the above [1] to [7], further comprising a surface resin layer on at least one surface of the biaxially oriented film layer. [9] The biaxially oriented polypropylene film according to [8], wherein the surface resin layer contains homopolypropylene (A).

[10] The content of the homopolypropylene (A) in the surface resin layer is 75% by mass or more and 100% by mass or less, when the entire surface resin layer is 100% by mass. The biaxially oriented polypropylene film according to [9].

[11] The biaxially oriented polypropylene film according to any one of the above [8] to

[10] , wherein the thickness of the surface resin layer is from 0.1 μm to 10.0 μm.

[12] The biaxially oriented polypropylene film according to any one of [1] to

[11] above, wherein the biaxially oriented film layer has a thickness of 5 μm or more and 100 μm or less.

[13] The biaxially oriented polypropylene film according to any one of the above [1] to

[12] , wherein the sum (T1+T2) of the tensile modulus of elasticity in the MD direction T1 and the tensile modulus of elasticity in the TD direction T2 of the biaxially oriented polypropylene film, 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 tensile speed of 5 mm / min, is 3000 MPa or more and 10000 MPa or less.

[14] The biaxially oriented polypropylene film according to any one of the above [1] to

[13] , which is a food packaging film.

[15] A food packaging material using the biaxially oriented polypropylene film according to any one of [1] to

[14] above.

[16] The food packaging body according to

[15] above, and a food product within the food package. Effect of the Invention

[0012] According to the present invention, it is possible to provide a biaxially oriented polypropylene film, a food packaging material, and a food packaging material having improved thermal dimensional stability. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a cross-sectional view showing a schematic example of the structure of a biaxially oriented polypropylene film according to the present embodiment. [Diagram 2] FIG. 1 is a cross-sectional view showing a schematic example of the structure of a biaxially oriented polypropylene film according to the present embodiment. [Diagram 3] FIG. 1 is a cross-sectional view showing a schematic example of the structure of a biaxially oriented polypropylene film according to the present embodiment. 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] <Biaxially oriented polypropylene film> 1 to 3 are cross-sectional views that diagrammatically show an example of the structure of a biaxially oriented polypropylene film 100 according to the present embodiment. The biaxially oriented polypropylene film 100 of this embodiment has a biaxially oriented film layer 101 containing a propylene-based polymer, and has the property of expanding in the TD direction and shrinking in the MD direction when heat-treated at 120°C for 15 minutes in accordance with JIS C2151:2019.

[0016] As described above, further improvement in the thermal dimensional stability of biaxially oriented polypropylene films is required from the viewpoint of suppressing thermal wrinkles in the sealed portions during bag making and from the viewpoint of suppressing thermal elongation during vapor deposition and coating processes. Here, the inventors have found through their research that the thermal dimensional stability of the biaxially oriented polypropylene film 100 can be improved by having the property of expanding in the TD direction and shrinking in the MD direction when heated at 120°C for 15 minutes, which has led to the present invention. Generally, a roll of biaxially oriented polypropylene film is unwound in the MD direction, and bag making, coating, vapor deposition, etc. are performed while tension is applied. In other words, since there is no tension in the TD direction, the biaxially oriented polypropylene film is susceptible to heat shrinkage when heated, and heat wrinkles are likely to occur in the sealed area. In addition, since there is tension in the MD direction, if the film has low heat resistance, it is likely to thermally elongate in the MD when heated. On the other hand, the biaxially oriented polypropylene film 100 of this embodiment has the property of expanding in the TD direction and shrinking in the MD direction when heated at 120° C. for 15 minutes, and therefore is unlikely to undergo thermal shrinkage in the TD direction or thermal elongation in the MD direction even when the biaxially oriented polypropylene film 100 is heated. Therefore, it is presumed that the biaxially oriented polypropylene film 100 of this embodiment has improved thermal dimensional stability, which makes it possible to further suppress thermal wrinkles in the sealed portion. That is, the biaxially oriented polypropylene film 100 of the present embodiment can improve the thermal dimensional stability. In addition, since the biaxially oriented polypropylene film 100 of this embodiment has improved thermal dimensional stability, it is possible to suppress thermal wrinkles in the sealed portions during bag production, thereby improving bag production properties.

[0017] The thermal expansion coefficient in the TD direction of the biaxially oriented polypropylene film 100 when heat-treated at 120°C for 15 minutes is, from the viewpoint of further improving the performance balance between thermal dimensional stability and bag formability, and from the viewpoint of further suppressing thermal wrinkles in the sealed parts and obtaining bag products with good thermal wrinkles in the sealed parts, preferably 0.1% or more, more preferably 0.2% or more, even more preferably 0.3% or more, even more preferably 0.4% or more, and even more preferably 0.5% or more, and from the viewpoint of further improving the performance balance between thermal dimensional stability and bag formability, it is preferably 2.0% or less, more preferably 1.5% or less, even more preferably 1.2% or less, even more preferably 1.0% or less, and even more preferably 0.8% or less. Generally, a roll of biaxially oriented polypropylene film is unwound in the MD direction, and bag making, coating, deposition, etc. are performed while tension is applied. That is, since no tension is applied in the TD direction, the biaxially oriented polypropylene film is easily affected by heat shrinkage when heated, and heat wrinkles are easily generated in the sealed portion. On the other hand, if the thermal expansion coefficient in the TD direction when heated at 120°C for 15 minutes is within the above range, heat shrinkage is unlikely to occur in the TD direction even when the biaxially oriented polypropylene film 100 is heated, and heat wrinkles in the sealed portion can be further suppressed. The thermal expansion coefficient in the TD direction of the biaxially oriented polypropylene film 100 when it is heat-treated at 120° C. for 15 minutes is calculated by the following method. First, a 10 cm x 10 cm test piece is cut out from the biaxially oriented polypropylene film 100, and this test piece is heat-treated for 15 minutes at 120° C. Next, when the length of the test piece in the TD direction after the heat treatment is TD1 [cm], the thermal expansion coefficient in the TD direction [%] is calculated by 100 x (TD1-10) / 10.

[0018] Furthermore, the heat shrinkage rate in the MD direction of the biaxially oriented polypropylene film 100 when heated at 120°C for 15 minutes is, from the viewpoint of further improving the performance balance between thermal dimensional stability and bag formability, and from the viewpoint of further suppressing thermal elongation of the film during processing, preferably 5.0% or less, more preferably 4.0% or less, even more preferably 3.0% or less, even more preferably 2.5% or less, even more preferably 2.2% or less, and even more preferably 2.0% or less, and may be 0.1% or more, 0.3% or more, or 0.5% or more. Generally, a roll of biaxially oriented polypropylene film is unwound in the MD direction, and bag making, coating, deposition, etc. are performed while tension is applied. In other words, since tension is applied in the MD direction, if the heat resistance of the film is low, the film is likely to thermally elongate in the MD direction when heated. On the other hand, if the heat shrinkage rate in the MD direction when heated at 120°C for 15 minutes is within the above range, it is possible to further suppress the thermal elongation in the MD direction when the biaxially oriented polypropylene film 100 is heated. The heat shrinkage rate in the MD direction of the biaxially oriented polypropylene film 100 when it is heat-treated at 120° C. for 15 minutes is calculated by the following method. First, a 10 cm x 10 cm test piece is cut out from the biaxially oriented polypropylene film 100, and this test piece is heat-treated at 120° C. for 15 minutes. Next, when the length of the test piece in the MD direction after the heat treatment is MD1 [cm], the heat shrinkage rate in the MD direction [%] is calculated by 100 x (10-MD1) / 10.

[0019] In addition, the thermal shrinkage rate X in the TD direction of the biaxially oriented polypropylene film 100 when heat-treated at 150° C. for 15 minutes TD From the viewpoint of further improving the performance balance between thermal dimensional stability and bag formability, is preferably 8.5% or less, more preferably 7.0% or less, even more preferably 5.0% or less, even more preferably 3.0% or less, even more preferably 2.0% or less, even more preferably 1.0% or less, even more preferably 0.8% or less, and may be 0.0% or more, 0.1% or more, or 0.2% or more.

[0020] In addition, the thermal shrinkage rate X in the MD direction of the biaxially oriented polypropylene film 100 when it is heat-treated at 150° C. for 15 minutes is MD From the viewpoint of further improving the performance balance between thermal dimensional stability and bag formability, is preferably 8.0% or less, more preferably 7.0% or less, even more preferably 6.0% or less, even more preferably 5.5% or less, even more preferably 5.0% or less, and even more preferably 4.8% or less, and may be 0.1% or more, 0.5% or more, 1.0% or more, 1.5% or more, 2.0% or more, or 2.5% or more.

[0021] The heat shrinkage rate in the TD direction and the heat shrinkage rate in the MD direction when the biaxially oriented polypropylene film 100 is heated at 150°C for 15 minutes are respectively X TD [%] and X MD When set to [%], X TD +X MD From the viewpoint of further improving the performance balance of the thermal dimensional stability and bag formability of the biaxially oriented polypropylene film 100, is preferably less than 16.0%, more preferably less than 10.0%, even more preferably less than 7.0%, even more preferably less than 6.0%, and even more preferably less than 5.0%. Also, biaxially oriented polypropylene film 100 x TD [%] and X MD [%] is calculated as follows: First, a 10 cm x 10 cm test piece is cut out from the biaxially oriented polypropylene film 100, and this test piece is heat-treated at 150 ° C for 15 minutes. Next, when the length in the TD direction of the test piece after the heat treatment is TD1 [cm] and the length in the MD direction of the test piece after the heat treatment is MD1 [cm], X TD [%] is calculated by 100×(10-TD1) / 10, where X MD [%] is calculated by 100×(10-MD1) / 10.

[0022] The thermal expansion coefficient and thermal shrinkage coefficient of the biaxially oriented polypropylene film 100 can be adjusted, for example, by adjusting the type and content ratio of the propylene-based polymer contained in the biaxially oriented film layer 101, the thickness and stretching ratio of the biaxially oriented film layer 101, the constituent material and thickness of the surface resin layer 103, etc. In addition, the thermal expansion coefficient and thermal shrinkage coefficient of the biaxially oriented polypropylene film 100 can be measured in accordance with JIS C2151:2019.

[0023] The sum (T1+T2) of the tensile modulus T1 in the MD direction and the tensile modulus T2 in the TD direction of the biaxially oriented polypropylene film 100, measured in accordance with JIS K7127 (1999) using a tensile tester at a measurement temperature of 23±2°C, 50±5% RH, and a tensile speed of 5 mm / min, is preferably 3000 MPa or more, more preferably 3500 MPa or more, even more preferably 4000 MPa or more, and is preferably 10000 MPa or less, more preferably 8000 MPa or less, and even more preferably 7500 MPa or less. When the sum (T1+T2) of the tensile modulus T1 in the MD direction and the tensile modulus T2 in the TD direction is equal to or greater than the lower limit, the biaxially oriented polypropylene film 100 can have a better balance of performance such as thermal dimensional stability, formability, water vapor barrier properties, mechanical properties, transparency, bag formability, and handleability. Furthermore, the stiffness of the biaxially oriented polypropylene film 100 can be improved, which in turn can prevent the film from shifting position during heat sealing, thereby preventing the occurrence of defective sealing. In other words, when the sum (T1+T2) of the tensile modulus in the MD direction T1 and the tensile modulus in the TD direction T2 is equal to or greater than the above-mentioned lower limit, the biaxially oriented polypropylene film 100 can have a better balance of thermal dimensional stability, formability, water vapor barrier properties, mechanical properties, transparency, bag formability, handleability, and packaging suitability. Furthermore, when the sum of the tensile modulus T1 in the MD direction and the tensile modulus T2 in the TD direction (T1+T2) is equal to or less than the upper limit value, problems such as breakage are less likely to occur during molding of the biaxially oriented polypropylene film 100, continuous stretch molding of the film becomes easier, and industrial continuous productivity can be further improved. Such a tensile modulus is a substitute value for quantitatively measuring the stiffness of a film, and can be adjusted, for example, by adjusting the type and content ratio of the propylene-based polymer contained in the biaxially oriented film layer 101, the thickness and stretching ratio of the biaxially oriented film layer 101, the constituent material and thickness of the surface resin layer 103, etc.

[0024] In addition, the tensile modulus T1 in the MD direction of the biaxially oriented polypropylene film 100 is preferably 1000 MPa or more, more preferably 1200 MPa or more, even more preferably 1300 MPa or more, even more preferably 1400 MPa or more, and even more preferably 1500 MPa or more, from the viewpoint of further improving the performance balance of the biaxially oriented polypropylene film 100, including thermal dimensional stability, formability, water vapor barrier properties, mechanical properties, transparency, bag formability, handleability, and packaging suitability, and is preferably 4000 MPa or less, more preferably 3500 MPa or less, even more preferably 3000 MPa or less, even more preferably 2800 MPa or less, and even more preferably 2600 MPa or less, from the viewpoint of further improving the performance balance of the biaxially oriented polypropylene film 100, including thermal dimensional stability, antistatic properties, bag formability, and packaging suitability.

[0025] In a package produced using the biaxially oriented polypropylene film 100, from the viewpoint of further improving the balance of the performance of the film's adhesion prevention to the seal bar during bag making and the seal appearance, the heat fusion strength (TD tensile direction) of the part heat fused under the conditions of 200°C, pressure 2.0 kgf, and sealing time 1.0 seconds is preferably 4.0N / 15mm or less, more preferably 3.5N / 15mm or less, even more preferably 3.0N / 15mm or less, even more preferably 2.5N / 15mm or less, even more preferably 2.0N / 15mm or less, and even more preferably 1.5N / 15mm or less. The lower limit of the heat fusion strength of the biaxially oriented polypropylene film 100 at 200°C is not particularly limited, but may be 0.01N / 15mm or more, 0.05N / 15mm or more, or 0.1N / 15mm or more. In this specification, the heat fusion strength is used as an index of the heat fusion resistance of the biaxially oriented polypropylene film surface. It can be determined that the lower the heat fusion strength, the better the heat fusion resistance of the biaxially oriented polypropylene film surface. Here, the heat fusion strength can be measured by the following method. First, two biaxially oriented polypropylene films 100 are heat fused under the conditions of 200°C, pressure of 2.0 kgf, and sealing time of 1.0 second to obtain a laminated film. Next, the two biaxially oriented polypropylene films 100 are peeled under the conditions of 15 mm width, 90 degree peel, peel speed of 300 mm / min, and tension in the TD direction, and the peel strength at that time is taken as the heat fusion strength. Such heat fusion strength can be adjusted, for example, by adjusting the type and content ratio of the homopolypropylene (A) and polymer (B) contained in the biaxially oriented film layer 101, the thickness and stretching ratio of the biaxially oriented film layer 101, the constituent material and thickness of the surface resin layer 103, etc.

[0026] The haze of the biaxially oriented polypropylene film 100, measured using a haze meter in accordance with JIS K7136:2000, is preferably 5.0% or less, more preferably 3.0% or less, even more preferably 2.5% or less, even more preferably 2.0% or less, even more preferably 1.5% or less, and even more preferably 1.0% or less, from the viewpoint of further improving the transparency of the biaxially oriented polypropylene film 100. Such haze can be adjusted, for example, by adjusting the type and content of the propylene-based polymer contained in the biaxially oriented film layer 101, the thickness and stretching ratio of the biaxially oriented film layer 101, the constituent material and thickness of the surface resin layer 103, etc.

[0027] Here, the food packaging produced using the biaxially oriented polypropylene film 100 exhibits sufficient performance in terms of water vapor barrier properties, and therefore the biaxially oriented polypropylene film 100 can be particularly suitably used as a food packaging film for packaging foods that require water vapor barrier properties.

[0028] From the viewpoint of stably obtaining food packaging with improved water vapor barrier properties, the water vapor permeability of the biaxially oriented polypropylene film 100, measured by the following method, is preferably 20.0 g / (m 2 ·24h) or less, more preferably 15.0g / (m 2 ·24h) or less, more preferably 12.0g / (m 2 ·24h) or less, more preferably 10.0g / (m 2 ·24h) or less, more preferably 8.0g / (m 2 24h or less. (Measurement method) The biaxially oriented polypropylene film 100 is folded and two sides are heat sealed to form a bag. Then, calcium chloride is placed in the bag 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 mass of calcium chloride is measured before and after storage, and the difference is used to determine the water vapor permeability (g / (m 2Calculate the time (24h). Such water vapor permeability can be adjusted, for example, by adjusting the type and content ratio of the propylene-based polymer contained in the biaxially oriented film layer 101, the thickness and stretching ratio of the biaxially oriented film layer 101, the constituent material and thickness of the surface resin layer 103, etc.

[0029] The amount of structural units derived from α-olefins other than propylene contained in the biaxially oriented polypropylene film 100, when the total amount of structural units derived from monomers contained in the biaxially oriented polypropylene film 100 is taken as 100 mol %, is preferably 0.05 mol % or more, more preferably 0.1 mol % or more, even more preferably 0.3 mol % or more, even more preferably 0.5 mol % or more, even more preferably 1.0 mol % or more, even more preferably 3.0 mol % or more, and even more preferably 4.0 mol % or more, from the viewpoint of further improving the performance balance of the moldability, thermal dimensional stability, and bag formability of the biaxially oriented polypropylene film 100. It is preferably 5.0 mol% or more, more preferably 8.0 mol% or more, and even more preferably 10.0 mol% or more, and from the viewpoint of further improving the performance balance of the thermal dimensional stability, water vapor barrier property, bag formability and transparency of the biaxially oriented polypropylene film 100, it is preferably 50.0 mol% or less, more preferably 30.0 mol% or less, even more preferably 25.0 mol% or less, even more preferably 20.0 mol% or less, even more preferably 15.0 mol% or less, even more preferably 12.0 mol% or less, even more preferably 10.0 mol% or less, and even more preferably 8.0 mol% or less. When the amount of structural units derived from α-olefins other than propylene contained in the biaxially oriented polypropylene film 100 is within the above range, the softening effect of the structural units derived from α-olefins suppresses the yield point stress at the start of stretching during the stretching process, improving ease of formability. In addition, the low melting point effect of the structural units derived from α-olefins more efficiently relieves residual stress in the heat setting process during film molding, improving formability and suppressing thickness unevenness. As a result, the thermal dimensional stability of the biaxially oriented polypropylene film 100 can be further improved. The amount of structural units derived from α-olefins other than propylene in the biaxially oriented polypropylene film 100 can be measured by the method described in the Examples.

[0030] The thickness of the biaxially oriented polypropylene film 100 is, from the viewpoint of further improving the balance of performance such as thermal dimensional stability, formability, water vapor barrier properties, cost, mechanical properties, transparency, bag formability, handleability, appearance, and light weight, preferably 5 μm or more, more preferably 10 μm or more, even more preferably 12 μm or more, and even more preferably 15 μm or more, and is preferably 100 μm or less, more preferably 50 μm or less, even more preferably 40 μm or less, even more preferably 30 μm or less, and even more preferably 25 μm or less.

[0031] Each layer constituting the biaxially oriented polypropylene film 100 will be described below.

[0032] [Biaxially oriented film layer] The biaxially oriented film layer 101 (also called a biaxially oriented polypropylene-based film layer) contains a propylene-based polymer. The biaxially stretched film layer 101 is formed, for example, by biaxially stretching a film made of a propylene-based polymer composition containing a propylene-based polymer.

[0033] The biaxially stretched film layer 101 may be a single layer or may have a structure in which a plurality of layers made of a propylene-based polymer composition are laminated, but it is necessary that it is biaxially stretched.

[0034] The thickness of the biaxially oriented film layer 101 is preferably 5 μm or more, more preferably 10 μm or more, even more preferably 12 μm or more, and even more preferably 15 μm or more, from the viewpoint of further improving the performance balance of the biaxially oriented polypropylene film 100, such as thermal dimensional stability, formability, water vapor barrier property, cost, mechanical properties, transparency, bag formability, handleability, appearance, and light weight, and is preferably 100 μm or less, more preferably 50 μm or less, even more preferably 40 μm or less, even more preferably 30 μm or less, and even more preferably 20 μm or less.

[0035] In the biaxially oriented polypropylene film 100, the ratio of the thickness of the biaxially oriented film layer 101 to the total thickness of the biaxially oriented polypropylene film 100 is preferably 50% or more, more preferably 60% or more, even more preferably 70% or more, even more preferably 75% or more, and preferably 100% or less, more preferably 99% or less, even more preferably 95% or less, even more preferably 90% or less.

[0036] (Propylene-Based Polymer Composition) The propylene-based polymer composition of the present embodiment contains a propylene-based polymer. The content of the propylene-based polymer in the propylene-based polymer composition of the present embodiment, i.e., the biaxially stretched film layer 101, is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, and for example, 100% by mass or less, when the entire propylene-based polymer composition is taken as 100% by mass, from the viewpoint of further improving the balance of performance such as thermal dimensional stability, environmental compatibility, heat resistance, water vapor barrier property, transparency, cost, mechanical properties, rigidity, bag formability, fluidity, moldability, handleability, appearance, and lightness of the biaxially stretched polypropylene film 100.

[0037] (Propylene polymer) The propylene-based polymer of the present embodiment is a polymer containing a structural unit derived from propylene, and examples thereof include homopolypropylene (A); at least one polymer (B) selected from the group consisting of random polypropylene (B1) and α-olefin copolymer (B2); and the like.

[0038] (Homopolypropylene (A)) Examples of the homopolypropylene (A) include propylene homopolymers and propylene copolymers having a content of structural units derived from α-olefins other than propylene of 2.0 mol % or less. When the total content of the structural units constituting the homopolypropylene (A) is taken as 100 mol %, the content of structural units derived from propylene is 98.0 mol % or more, preferably 98.5 mol % or more, more preferably 98.7 mol % or more, even more preferably 99.0 mol % or more, even more preferably 99.5 mol % or more, even more preferably 99.8 mol % or more, and is, for example, 100.0 mol % or less.

[0039] The α-olefin other than propylene includes, for example, one or more selected from the group consisting of ethylene and α-olefins having 4 to 20 carbon atoms, preferably one or more selected from the group consisting of ethylene and α-olefins having 4 to 6 carbon atoms, more preferably at least one selected from the group consisting of ethylene and 1-butene, and even more preferably ethylene. The content of structural units derived from α-olefins other than propylene, when the entire homopolypropylene (A) is taken as 100 mol %, is preferably 2.0 mol % or less, more preferably 1.5 mol % or less, even more preferably 1.3 mol % or less, even more preferably 1.0 mol % or less, even more preferably 0.5 mol % or less, and even more preferably 0.2 mol % or less. The homopolypropylene (A) in the biaxially oriented film layer 101 may be used alone or in combination of two or more kinds.

[0040] The isotactic mesopentad fraction (mmmm) of the homopolypropylene (A) is preferably 96.0% or more, more preferably 96.5% or more, even more preferably 97.0% or more, even more preferably 97.3% or more, even more preferably 97.5% or more, even more preferably 97.8% or more, and even more preferably 98.0% or more, from the viewpoint of further improving the balance of performance such as thermal dimensional stability, heat resistance, water vapor barrier property, mechanical properties, rigidity, and bag formability of the biaxially stretched polypropylene film 100. The upper limit of the isotactic mesopentad fraction (mmmm) of the homopolypropylene (A) 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 an index of stereoregularity, 13 It can be determined from C-nuclear magnetic resonance (NMR) spectrum by a known method. When two or more types of homopolypropylenes are used as the homopolypropylene (A), the isotactic mesopentad fraction of the homopolypropylene (A) can be the isotactic mesopentad fraction of a mixture obtained by melt blending two or more types of homopolypropylene (A) by a known method.

[0041] The melt flow rate (MFR) of the homopolypropylene (A), 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 1.0 g / 10 min or more, and even more preferably 2.0 g / 10 min or more, from the viewpoint of further improving the balance of performance between fluidity and moldability, and is preferably 20.0 g / 10 min or less, more preferably 10.0 g / 10 min or less, and even more preferably 7.0 g / 10 min or less, from the viewpoint of further stabilizing moldability. When two or more types of homopolypropylenes are used as the homopolypropylene (A), the MFR of the homopolypropylene (A) can be the MFR of a mixture obtained by melt blending two or more types of homopolypropylene (A) by a known method.

[0042] The melting point of the homopolypropylene (A) is preferably 150°C or higher, more preferably 155°C or higher, even more preferably 160°C or higher, and even more preferably 163°C or higher, from the viewpoint of further improving the performance balance of the biaxially oriented polypropylene film 100, such as thermal dimensional stability, heat resistance, water vapor barrier properties, mechanical properties, rigidity, bag formability, fluidity, and moldability, and is preferably 180°C or lower, more preferably 175°C or lower, even more preferably 170°C or lower, and even more preferably 168°C or lower. When two or more kinds of homopolypropylenes are used as the homopolypropylene (A), the melting point of the homopolypropylene (A) is the peak temperature of the maximum melting peak.

[0043] The homopolypropylene (A) can be produced by various methods, for example, by using a known catalyst such as a Ziegler-Natta catalyst or a metallocene catalyst.

[0044] (Polymer (B)) The polymer (B) includes at least one selected from the group consisting of random polypropylene (B1) and an α-olefin copolymer (B2).

[0045] The melt flow rate (MFR) of the polymer (B), measured in accordance with ASTM D1238 under conditions of 230°C and a load of 2.16 kg, is preferably 0.01 g / 10 min or more, more preferably 0.1 g / 10 min or more, even more preferably 0.5 g / 10 min or more, even more preferably 1.0 g / 10 min or more, even more preferably 2.0 g / 10 min or more, from the viewpoint of further improving the performance balance of the moldability and thermal dimensional stability of the biaxially oriented polypropylene film 100, and is preferably 30.0 g / 10 min or less, more preferably 20.0 g / 10 min or less, even more preferably 15.0 g / 10 min or less, even more preferably 12.0 g / 10 min or less, and even more preferably 10.0 g / 10 min or less. When two or more types of polymers are used as the polymer (B), the MFR of a mixture obtained by melt blending two or more types of the polymer (B) by a known method can be adopted.

[0046] From the viewpoint of further improving the balance of performance of the biaxially oriented polypropylene film 100, such as thermal dimensional stability, heat resistance, water vapor barrier properties, mechanical properties, rigidity, bag formability, fluidity, and moldability, the melting point of the polymer (B) is preferably 50°C or higher, more preferably 60°C or higher, even more preferably 70°C or higher, even more preferably 80°C or higher, and even more preferably 90°C or higher, and is preferably 155°C or lower, more preferably 150°C or lower, even more preferably 148°C or lower, and even more preferably 145°C or lower. When two or more kinds of polymers are used as polymer (B), the melting point of polymer (B) is the peak temperature of the maximum melting peak.

[0047] The weight average molecular weight (Mw) of the polymer (B) is preferably 100,000 or more, more preferably 150,000 or more, even more preferably 200,000 or more, and even more preferably 220,000 or more, from the viewpoint of further improving the performance balance of the formability, thermal dimensional stability, blocking resistance, and sheet payout property of the biaxially oriented polypropylene film 100, and is preferably 1,000,000 or less, more preferably 800,000 or less, more preferably 600,000 or less, even more preferably 500,000 or less, and even more preferably 450,000 or less, from the viewpoint of further improving the thermal dimensional stability.

[0048] The weight average molecular weight (Mw) / number average molecular weight (Mn) of the polymer (B) is preferably 1.5 or more, more preferably 1.8 or more, from the viewpoint of further improving the performance balance of the formability, thermal dimensional stability, blocking resistance, and sheet payout ability of the biaxially oriented polypropylene film 100, and is preferably 8.0 or less, more preferably 7.5 or less, even more preferably 7.0 or less, and even more preferably 6.8 or less, from the viewpoint of further improving the performance balance of the formability, thermal dimensional stability, blocking resistance, and sheet payout ability of the biaxially oriented polypropylene film 100. When two or more kinds of polymers are used as the polymer (B), the weight average molecular weight (Mw) and number average molecular weight (Mn) of the polymer (B) can be the weight average molecular weight (Mw) and number average molecular weight (Mn) of a mixture obtained by melt blending two or more kinds of the polymer (B) by a known method. The weight average molecular weight (Mw) and number average molecular weight (Mn) of the polymer (B) can be measured by the method described in the Examples.

[0049] From the viewpoint of further improving the performance balance of the formability and thermal dimensional stability of the biaxially oriented polypropylene film 100, the content of polymer (B) is preferably 1 mass% or more, more preferably 2 mass% or more, and even more preferably 3 mass% or more, when the entire biaxially oriented film layer 101 is taken as 100 mass%, and from the viewpoint of further improving the performance balance of the biaxially oriented polypropylene film 100, such as thermal dimensional stability, water vapor barrier property, transparency, mechanical properties, rigidity, bag formability, fluidity, and formability, the content of polymer (B) is preferably 50 mass% or less, more preferably 40 mass% or less, even more preferably 30 mass% or less, even more preferably 25 mass% or less, even more preferably 22 mass% or less, and even more preferably 20 mass% or less.

[0050] (Random polypropylene (B1)) The random polypropylene (B1) includes a random copolymer of propylene and an α-olefin other than propylene, in which the content of structural units derived from an α-olefin other than propylene is more than 2.0 mol % and not more than 15.0 mol %. The α-olefin other than propylene includes, for example, one or more selected from the group consisting of ethylene and α-olefins having 4 to 20 carbon atoms, preferably one or more selected from the group consisting of ethylene and α-olefins having 4 to 6 carbon atoms, more preferably at least one selected from ethylene and 1-butene, and even more preferably ethylene.

[0051] The content of structural units derived from α-olefins other than propylene in the random polypropylene (B1), when the entire random polypropylene (B1) is taken as 100 mol%, is preferably more than 2.0 mol%, more preferably 2.5 mol% or more, even more preferably 3.0 mol% or more, even more preferably 3.5 mol% or more, and even more preferably 4.0 mol% or more, from the viewpoint of further improving the performance balance of the moldability, thermal dimensional stability, and bag formability of the biaxially oriented polypropylene film 100, and is preferably 15.0 mol% or less, more preferably 12.0 mol% or less, even more preferably 10.0 mol% or less, even more preferably 8.0 mol% or less, and even more preferably 6.5 mol% or less, from the viewpoint of further improving the performance balance of the thermal dimensional stability, water vapor barrier property, bag formability, and transparency of the biaxially oriented polypropylene film 100. The amount of constituent units derived from an α-olefin other than propylene can be measured by the method described in the Examples.

[0052] The random polypropylene (B1) preferably contains one or more selected from the group consisting of a propylene-ethylene random copolymer, a propylene-ethylene-1-butene random copolymer, and a propylene-1-butene random copolymer, more preferably contains one or more selected from the group consisting of a propylene-ethylene random copolymer, and a propylene-1-butene random copolymer, and even more preferably contains a propylene-ethylene random copolymer. The random polypropylene (B1) in the biaxially oriented film layer 101 may be used alone or in combination of two or more kinds.

[0053] (α-Olefin copolymer (B2)) The α-olefin copolymer (B2) is a copolymer of two or more kinds of α-olefins, and includes, for example, an α-olefin copolymer in which the content of structural units derived from an α-olefin other than propylene exceeds 15.0 mol %. The α-olefin copolymer (B2) includes a random copolymer of propylene and an α-olefin other than propylene, in which the content of structural units derived from an α-olefin other than propylene exceeds 15.0 mol %. The α-olefin other than propylene includes, for example, one or more selected from the group consisting of ethylene and α-olefins having 4 to 10 carbon atoms, preferably one or more selected from the group consisting of α-olefins having 4 to 8 carbon atoms, more preferably at least one selected from 1-butene and 1-octene, and even more preferably 1-butene.

[0054] The content of structural units derived from α-olefins other than propylene in the α-olefin copolymer (B2), when the entire α-olefin copolymer (B2) is taken as 100 mol%, is preferably more than 15.0 mol%, more preferably 20.0 mol% or more, even more preferably 30.0 mol% or more, even more preferably 50.0 mol% or more, even more preferably 70.0 mol% or more, even more preferably 80.0 mol% or more, from the viewpoint of further improving the performance balance of the moldability, thermal dimensional stability and bag formability of the biaxially oriented polypropylene film 100, and is preferably 99.0 mol% or less, more preferably 98.0 mol% or less, even more preferably 95.0 mol% or less, even more preferably 92.0 mol% or less, even more preferably 90.0 mol% or less, from the viewpoint of further improving the performance balance of the thermal dimensional stability, water vapor barrier property, bag formability and transparency of the biaxially oriented polypropylene film 100. The amount of constituent units derived from an α-olefin other than propylene in the α-olefin copolymer (B2) can be measured by the method described in the Examples.

[0055] The α-olefin copolymer (B2) preferably comprises a random copolymer of propylene and one or more α-olefins selected from the group consisting of ethylene and α-olefins having 4 to 10 carbon atoms, more preferably a random copolymer of propylene and one or two α-olefins selected from the group consisting of 1-butene and 1-octene, and even more preferably a random copolymer of propylene and 1-butene. The α-olefin copolymer (B2) in the biaxially stretched film layer 101 may be used alone or in combination of two or more kinds.

[0056] The polymer (B) can be produced by various methods, for example, by using a known catalyst such as a Ziegler-Natta catalyst or a metallocene catalyst.

[0057] (Other Ingredients) To the propylene polymer composition of the present embodiment, various additives such as a tackifier, 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.

[0058] (Method for preparing propylene polymer composition) The propylene polymer composition of 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.

[0059] [Surface resin layer] It is preferable that the biaxially oriented polypropylene film 100 further comprises a surface resin layer 103 on at least one side of the biaxially oriented film layer 101 in order to impart functions such as heat resistance, heat sealability, antistatic properties, blocking resistance, printability, and slip properties to the film surface depending on the purpose. The surface resin layer 103 may be provided on both sides of the biaxially stretched film layer 101. By providing the surface resin layer 103 on both sides of the biaxially stretched film layer 101, different functions can be imparted to each surface of the film. In addition, the surface resin layer 103 is preferably provided on the outermost layer of the biaxially oriented polypropylene film 100 in order to further improve the functions of the biaxially oriented polypropylene film 100, such as heat resistance, heat sealability, antistatic properties, blocking resistance, printability, slip properties, etc., depending on the purpose.

[0060] The surface resin layer 103 is preferably provided so as to be in direct contact with the surface of the biaxially oriented film layer 101. This allows the manufacturing process of the biaxially oriented polypropylene film 100 to be simplified.

[0061] In the biaxially oriented polypropylene film 100, the thickness of the surface resin layer 103 is preferably 0.1 μm or more, more preferably 0.2 μm or more, even more preferably 0.5 μm or more, even more preferably 1.0 μm or more, and even more preferably 1.5 μm or more, from the viewpoint of further improving the functions of the biaxially oriented polypropylene film 100 such as heat resistance, antistatic properties, blocking resistance, printability, and slip properties, and is preferably 10.0 μm or less, more preferably 8.0 μm or less, even more preferably 6.0 μm or less, even more preferably 5.0 μm or less, and even more preferably 3.0 μm or less, from the viewpoint of further improving the performance balance of the biaxially oriented polypropylene film 100 such as heat resistance, thermal dimensional stability, formability, cost, mechanical properties, transparency, environmental compatibility, and light weight. Here, the thickness of the surface resin layer 103 refers to the thickness of the surface resin layer 103 provided on one side of the biaxially stretched film layer 101. That is, in this embodiment, when the surface resin layer 103 is provided on both sides of the biaxially stretched film layer 101, the above-mentioned thickness of the surface resin layer 103 indicates the thickness of the surface resin layer 103 provided on one side of the biaxially stretched film layer 101.

[0062] In the biaxially oriented polypropylene film 100, the surface resin layer 103 is preferably a single layer. This makes it possible to further simplify the manufacturing process of the biaxially oriented polypropylene film 100.

[0063] The surface resin 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 biaxially stretched polypropylene film 100 to be produced by a molding method such as coextrusion molding, i.e., by using a laminated film produced in a single molding, thereby further simplifying the manufacturing process of the biaxially stretched polypropylene film 100. Therefore, the surface resin layer 103 is preferably biaxially stretched.

[0064] The surface resin layer 103 may be subjected to a surface treatment in order to further improve the balance between the printability and blocking resistance of the biaxially oriented polypropylene film 100. Specifically, the surface may be subjected to a surface activation treatment such as a corona treatment, a flame treatment, a plasma treatment, a primer coat treatment, or an ozone treatment.

[0065] The surface resin layer 103 is composed of, for example, a polyolefin-based resin composition (A) containing a polyolefin. The polyolefin constituting the surface resin layer 103 includes, for example, one or more selected from the group consisting of homopolymers or copolymers of α-olefins such as ethylene, propylene, 1-butene, hexene-1, 4-methyl-pentene-1, 1-octene, etc.; high-pressure low-density polyethylene; linear low-density polyethylene (LLDPE); high-density polyethylene; homopolypropylene; random copolymers of propylene and α-olefins having 2 to 10 carbon atoms; ethylene-vinyl acetate copolymers (EVA); and ionomer resins. Among these, homopolypropylene is preferred as the polyolefin constituting the surface resin layer 103 from the viewpoint of further improving the balance of performance such as heat fusion resistance, thermal dimensional stability, heat resistance, water vapor barrier property, transparency, mechanical properties, rigidity, bag formability, fluidity, and moldability of the biaxially oriented polypropylene film 100. Here, the preferred embodiment of the homopolypropylene constituting the surface resin layer 103 is the same as the homopolypropylene (A) described above. That is, the homopolypropylene constituting the surface resin layer 103 preferably contains the homopolypropylene (A) described above.

[0066] The content of polyolefin in the polyolefin resin composition (A), i.e., the surface resin layer 103, is preferably 75% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, even more preferably 99% by mass or more, and preferably 100% by mass or less, when the entire polyolefin resin composition (A), i.e., the entire surface resin layer 103, is taken as 100% by mass, from the viewpoint of further improving the performance balance of the biaxially oriented polypropylene film 100, such as heat resistance, thermal dimensional stability, heat resistance, water vapor barrier property, transparency, mechanical properties, rigidity, bag formability, fluidity and moldability. The content of homopolypropylene (A) in the polyolefin resin composition (A), i.e., the surface resin layer 103, is preferably 75% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, even more preferably 99% by mass or more, and preferably 100% by mass or less, when the entire polyolefin resin composition (A), i.e., the entire surface resin layer 103, is taken as 100% by mass, from the viewpoint of further improving the performance balance of the biaxially oriented polypropylene film 100, such as heat resistance, thermal dimensional stability, heat resistance, water vapor barrier property, transparency, mechanical properties, rigidity, bag formability, fluidity and moldability.

[0067] (Other Ingredients) If necessary, various additives such as tackifiers, heat stabilizers, weather stabilizers, antioxidants, UV absorbers, lubricants, slip agents, nucleating agents, antiblocking agents, antistatic agents, antifogging agents, pigments, dyes, and inorganic or organic fillers may be added to the polyolefin resin composition (A) constituting the surface resin layer 103, within the scope that does not impair the purpose of this embodiment.

[0068] (Method for preparing polyolefin resin composition (A)) The polyolefin resin composition (A) can be prepared, for example, 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 heated roll, or the like.

[0069] <Method of manufacturing biaxially oriented polypropylene film> The biaxially oriented polypropylene film 100 can be obtained, for example, by co-extrusion molding a propylene-based polymer composition for forming the biaxially oriented film layer 101 and, if necessary, a polyolefin-based resin composition (A) for forming the surface resin layer 103 into a film, and then biaxially stretching the film obtained by the co-extrusion molding using a known biaxially oriented film production method such as a simultaneous biaxial stretching method, a sequential biaxial stretching method, or an inflation biaxial stretching method. The molding device and molding conditions are not particularly limited, and conventionally known molding devices and molding conditions can be adopted. As the molding device, a T-die extruder, a multi-layer T-die extruder, an inflation molding machine, a multi-layer inflation molding machine, etc. can be used. As the biaxial stretching conditions, for example, known OPP film manufacturing conditions can be adopted. More specifically, in the sequential biaxial stretching method, for example, the MD stretching temperature may be 100°C to 145°C, the MD stretching ratio may be in the range of 4.5 to 6 times, the TD stretching temperature may be 130°C to 190°C, and the TD stretching ratio may be in the range of 9 to 11 times. The biaxially oriented polypropylene film 100 can also be obtained by separately molding the biaxially oriented film layer 101 and, if necessary, the surface resin layer 103, laminating them together and molding them under heat.

[0070] <Applications of biaxially oriented polypropylene film> The biaxially oriented polypropylene film 100 can also be suitably used as a food packaging film that constitutes a food package.

[0071] The food package of this embodiment is a package using the biaxially oriented polypropylene film 100, for example a packaging bag used for containing food. Furthermore, the food package of this embodiment may use the biaxially oriented polypropylene film 100 in a part thereof or may use the biaxially oriented polypropylene film 100 in the entire food package depending on the application.

[0072] The food package of the present embodiment includes the food package of the present embodiment and food contained in the food package. That is, the food package of the present embodiment is the food package of the present embodiment that contains food.

[0073] 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. The biaxially oriented polypropylene film 100 may further include one or more layers selected from the group consisting of a sealant layer and a coating layer. The biaxially oriented polypropylene film 100 can also be used as a raw material for coating. EXAMPLES

[0074] The present embodiment will be described in detail below with reference to examples and comparative examples, but the present embodiment is not limited to the descriptions of these examples.

[0075] 1. Raw materials The raw materials used in the examples and comparative examples are shown below. (1) Homopolypropylene (A) h-PP1: homopolypropylene (MFR: 3.0 g / 10 min, melting point: 165°C, isotactic mesopentad fraction (mmmm): 98.0%, Mw: 370,000, Mn: 68,000, Mw / Mn: 5.4, content of propylene-derived structural units: 100 mol%) h-PP2: homopolypropylene (MFR: 3.0 g / 10 min, melting point: 159°C, isotactic mesopentad fraction (mmmm): 97.5%, Mw: 469,000, Mn: 56,300, Mw / Mn: 8.3, content of ethylene-derived structural units: 1.2 mol%, content of propylene-derived structural units: 98.8 mol%) (2) Polymer (B) r-PP1: Random polypropylene (MFR: 7.0 g / 10 min, melting point: 139°C, Mw: 322,000, Mn: 50,700, Mw / Mn: 6.4, content of ethylene-derived structural units: 3.2 mol%, content of 1-butene-derived structural units: 2.9 mol%, content of propylene-derived structural units: 93.9 mol%) r-PP2: Random polypropylene (MFR: 2.4 g / 10 min, melting point: 143°C, Mw: 436,000, Mn: 66,000, Mw / Mn: 6.6, content of ethylene-derived structural units: 4.4 mol%, content of propylene-derived structural units: 95.6 mol%) BPR1: 1-butene-propylene copolymer (MFR: 9.0 g / 10 min, melting point: 100°C, Mw: 227,000, Mn: 114,000, Mw / Mn: 2.0, content of 1-butene-derived structural units: 88.9 mol%, content of propylene-derived structural units: 11.1 mol%)

[0076] 2. Measurement and evaluation methods (1) Isotactic mesopentad fraction (mmmm) of homopolypropylene (A) The isotactic mesopentad fraction (mesopentad fraction, (mmmm)) was measured using a nuclear magnetic resonance spectrometer (AVANCE III cryo-500, manufactured by Bruker Biospin). 13 The measurement was performed by C-NMR. The sample was dissolved in the measurement solvent described below, and the measurement was performed, and the evaluation was performed based on the integrated intensity of each signal. [Measurement conditions] Measurement nuclei: 13 C(125MHz) Measurement mode: Single pulse proton broadband decoupling Pulse width: 45° Number of points: 64k Repeat time: 5.5 seconds Measurement solvent: orthodichlorobenzene / heavy benzene (4:1) Sample concentration: 50mg / 0.6mL Measurement temperature: 120℃ Window function: exponential (BF: 0.5Hz) Chemical shift standard: mmmm(CH3): 21.59ppm

[0077] (2) MFR of homopolypropylene (A) and polymer (B) Measured in accordance with ASTM D1238 at 230°C and a load of 2.16 kg.

[0078] (3) Melting points of homopolypropylene (A) and polymer (B) For the homopolypropylene (A) and the polymer (B), a differential scanning calorimeter (product name: Q200DSC manufactured by TA Instruments) was used to carry out a first differential scanning calorimeter measurement (1st run) consisting of a process of increasing the temperature from -30°C to 250°C at a rate of 10°C / min and a process of decreasing the temperature from 250°C to -30°C at a rate of 10°C / min under a nitrogen stream, and a second differential scanning calorimeter measurement (2nd run) consisting of a process of increasing the temperature from -30°C to 250°C at a rate of 10°C / min. The peak temperature of the maximum melting peak in the DSC curve in the second run was taken as the melting point.

[0079] (4) Weight average molecular weight (Mw) and number average molecular weight (Mn) of homopolypropylene (A) and polymer (B) The weight average molecular weight (Mw) and number average molecular weight (Mn) of the homopolypropylene (A) and the polymer (B) were measured by gel permeation chromatography (GPC). The GPC method was performed using a gel permeation chromatograph (Tosoh Corporation, HLC-8321 GPC / HT type) as follows. The separation columns were two TSKgel GNH6-HT and two TSKgel GNH6-HTL, each with a diameter of 7.5 mm and a length of 300 mm, the column temperature was 145°C, the mobile phase was o-dichlorobenzene and 0.025 mass% BHT as an antioxidant, and the flow rate was 1.0 mL / min, the sample concentration was 0.1% (w / v), the sample injection amount was 400 μL, and a differential refractometer was used as the detector. The molecular weight was calculated as polypropylene equivalent molecular weight using monodisperse polystyrene as the standard.

[0080] (5) Measurement of the content of structural units derived from α-olefins other than propylene in homopolypropylene (A) and polymer (B), and the content of structural units derived from α-olefins other than propylene in biaxially oriented polypropylene film The content of structural units derived from α-olefins other than propylene in the homopolypropylene (A) and polymer (B), as well as the content of structural units derived from α-olefins other than propylene in the biaxially oriented polypropylene film, were measured using a nuclear magnetic resonance apparatus (AVANCE III cryo-500, manufactured by Bruker Biospin). 13 The measurements were performed by C-NMR. The samples were dissolved in the following measurement solvent and the measurements were performed, and the evaluation was performed based on the integrated intensity of each signal. 13Signals were assigned using C-NMR spectra with reference to Macromolecules (1982) Ethylene-1-Butene Copolymers. 1. Monomer Sequence Distribution and Macromolecules (1977) Carbon-13 Nuclear Magnetic Resonance Determination of Monomer Composition and Sequence Distributions in Ethylene-Propylene Copolymers Prepared with a Stereoregular Catalyst System, and the contents (mol%) of ethylene-derived structural units, propylene-derived structural units, and 1-butene-derived structural units were quantified in each polymer. [Measurement conditions] Measurement nuclei: 13 C(125MHz) Measurement mode: Single pulse proton broadband decoupling Pulse width: 45° Number of points: 64k Repeat time: 5.5 seconds Measurement solvent: orthodichlorobenzene / heavy benzene (4:1) Sample concentration: 50mg / 0.6mL Measurement temperature: 120℃ Window function: exponential (BF: 0.5Hz) In addition, the content of structural units derived from α-olefins other than propylene contained in the biaxially oriented polypropylene film was measured using the biaxially oriented polypropylene film as a sample.

[0081] (6) Tensile modulus A test piece of 15 mm x 15 cm was cut out from the biaxially stretched polypropylene film. The tensile modulus of elasticity in the MD direction (T1) and the tensile modulus of elasticity in the TD direction (T2) of the test piece were measured using a tensile tester manufactured by Orientec Co., Ltd., 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.

[0082] (7) Water vapor permeability The biaxially oriented polypropylene film was folded back so that the surface resin layer 1 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 mass of calcium chloride was measured before and after storage, and the difference was used to determine the water vapor permeability (g / (m 2 -24h) were calculated respectively.

[0083] (8) Thermal expansion and shrinkage of biaxially oriented polypropylene film at 120℃ The thermal expansion coefficient and thermal shrinkage coefficient of the biaxially oriented polypropylene film at 120°C were measured in accordance with JIS C2151:2019. First, a 10 cm x 10 cm test piece was cut out from the biaxially oriented polypropylene film. The test piece was then heat-treated at 120°C for 15 minutes. At this time, the test piece was heated in a hot air circulation type thermostatic chamber (manufactured by ADVANTEC, product name: DRM620DE) while hanging without applying force. The test piece was then cooled to room temperature, and the length of the test piece was measured. The length of the test piece in the TD direction after the heat treatment was then taken as TD1 [cm], and the thermal expansion coefficient in the TD direction [%] was calculated by 100 x (TD1-10) / 10. The length of the test piece in the MD direction after the heat treatment was taken as MD1 [cm], and the thermal shrinkage coefficient in the MD direction [%] was calculated by 100 x (10-MD1) / 10. The above measurement was performed three times, and the average values ​​of the obtained measurements were adopted as the thermal expansion coefficient and thermal shrinkage coefficient of the biaxially oriented polypropylene film at 120°C, respectively.

[0084] (9) Heat shrinkage of biaxially oriented polypropylene film at 150℃ The heat shrinkage of the biaxially oriented polypropylene film at 150°C was measured in accordance with JIS C2151:2019. First, a 10 cm x 10 cm test piece was cut out from a biaxially oriented polypropylene film. The test piece was then heat-treated at 150°C for 15 minutes. At this time, the test piece was heated in a hot air circulation type thermostatic chamber (manufactured by ADVANTEC, product name: DRM620DE) while hanging without applying force. Next, the test piece was cooled to room temperature, and the length of the test piece was measured. Next, when the length of the test piece in the TD direction after the heat treatment is TD1 [cm] and the length of the test piece in the MD direction after the heat treatment is MD1 [cm], X TD [%] is calculated by 100×(10-TD1) / 10, X MD [%] was calculated by 100 × (10-MD1) / 10. The above measurement was carried out three times, and the average value of the obtained measurements was used as the heat shrinkage rate of the biaxially oriented polypropylene film at 150°C.

[0085] (10) Haze The haze of the biaxially stretched polypropylene film was measured using a haze meter (NDH5000, manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K7136:2000.

[0086] (11) Heat fusion strength at 200℃ Two biaxially oriented polypropylene films cut to a width of 15 mm were heat-sealed together at 200°C with a pressure of 2.0 kgf and a sealing time of 1.0 sec to obtain a laminated film. The two biaxially oriented polypropylene films were then peeled off at a width of 15 mm at 90° peeling, at a peeling speed of 300 mm / min, and pulled in the TD direction, and the peel strength at this time was determined as the heat-sealing strength.

[0087] (12) Bag making properties (wrinkles when heat sealed at 180°C) Two pieces of biaxially oriented polypropylene film cut to a width of 15 mm were heat-sealed together at 180°C under a pressure of 2.0 kgf for a sealing time of 1.0 seconds to obtain a laminated film. The presence or absence of heat wrinkles in the sealed area was then visually observed.

[0088] (13) Thermal dimensional stability The thermal dimensional stability of the biaxially oriented polypropylene film was evaluated according to the following criteria. AA (very good): Heat shrinkage rate at 150℃ (X MD +X TD ) is less than 5.0% A (fairly good): Heat shrinkage rate at 150°C (X MD +X TD ) is 5.0% or more and less than 7.0% B (Good): Heat shrinkage rate at 150℃ (X MD +X TD ) is 7.0% or more but less than 16.0% C (bad): Heat shrinkage rate at 150℃ (X MD +X TD ) is 16.0% or more

[0089] [Examples 1 to 7 and Comparative Example 1] Polypropylene films having the compositions shown in Table 1 were extruded and then biaxially stretched to produce biaxially stretched polypropylene films, which were then evaluated. The extrusion conditions and biaxial stretching conditions were as follows. In addition, the surface on the surface resin layer 2 side in Table 1 was subjected to corona treatment. Extrusion molding machine: 60mmφ multi-layer T-die extrusion molding machine (screw: L / D=27, manufactured by Screw Seiki Co., Ltd.) Extrusion temperature setting: 230-250℃, Processing speed: 20m / min (winding speed) Stretching temperature in MD direction [℃]: See Table 1 Stretching ratio in MD direction [times]: See Table 1 Stretching temperature in TD direction [℃]: See Table 1 Stretching ratio in TD direction [times]: See Table 1 Relaxation rate [%]: See Table 1 The relaxation rate herein means the maximum stretching width in the device settings divided by the tenter outlet width. In addition, the notation "A / B / C" for the stretching temperature in Table 1 means "preheating temperature (temperature at which the film roll before stretching is heated) / stretching temperature (temperature at which the film is stretched) / heat setting temperature (temperature at which the film is heat set (annealed) after stretching)."

[0090] [Table 1]

[0091] The biaxially oriented polypropylene film of the Example had improved thermal dimensional stability compared to the biaxially oriented polypropylene film of the Comparative Example. [Explanation of symbols]

[0092] 100 Biaxially oriented polypropylene film 101 Biaxially oriented film layer 103 Surface resin layer

Claims

1. a biaxially stretched film layer containing a propylene-based polymer; A biaxially oriented polypropylene film that expands in the TD direction and shrinks in the MD direction when heat-treated at 120°C for 15 minutes in accordance with JIS C2151:2019.

2. The biaxially oriented polypropylene film according to claim 1, having a thermal expansion coefficient in the TD direction of 0.1% or more and 2.0% or less when heat-treated at 120 ° C. for 15 minutes in accordance with JIS C2151:2019.

3. The biaxially oriented polypropylene film according to claim 1 or 2, having a heat shrinkage rate in the MD direction of 5.0% or less when heat-treated at 120 ° C. for 15 minutes in accordance with JIS C2151:2019.

4. The biaxially oriented polypropylene film according to claim 1 or 2, having a heat shrinkage rate in the TD direction of 8.5% or less when heat-treated at 150 ° C. for 15 minutes in accordance with JIS C2151:2019.

5. The biaxially oriented polypropylene film according to claim 1 or 2, having a heat shrinkage rate in the MD direction of 8.0% or less when heat-treated at 150 ° C. for 15 minutes in accordance with JIS C2151:2019.

6. According to JIS C2151:2019, the heat shrinkage rate in the TD direction and the heat shrinkage rate in the MD direction when heated at 150°C for 15 minutes were measured as X ＴＤ [%] and X ＭＤ When [%] is used, X ＴＤ +X ＭＤ 3. The biaxially oriented polypropylene film according to claim 1, wherein the elongation is less than 16.0%.

7. 3. The biaxially oriented polypropylene film according to claim 1, wherein the amount of structural units derived from α-olefins other than propylene contained in the biaxially oriented polypropylene film is 0.05 mol% or more when the total amount of structural units derived from monomers contained in the biaxially oriented polypropylene film is 100 mol%.

8. The biaxially oriented polypropylene film according to claim 1 or 2, further comprising a surface resin layer on at least one side of the biaxially oriented film layer.

9. The biaxially oriented polypropylene film according to claim 8, wherein the surface resin layer contains homopolypropylene (A).

10. 10. The biaxially oriented polypropylene film according to claim 9, wherein the content of the homopolypropylene (A) in the surface resin layer is 75% by mass or more and 100% by mass or less, when the entire surface resin layer is 100% by mass.

11. The biaxially oriented polypropylene film according to claim 8, wherein the thickness of the surface resin layer is 0.1 μm or more and 10.0 μm or less.

12. 3. The biaxially oriented polypropylene film according to claim 1, wherein the thickness of the biaxially oriented film layer is 5 μm or more and 100 μm or less.

13. The tensile modulus T of the biaxially oriented polypropylene film in the MD direction is measured using a tensile tester 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. １ and the tensile modulus in the TD direction T ２ The sum of (T １ +T ２ 3. The biaxially oriented polypropylene film according to claim 1, wherein the elongation stress (E) is 3,000 MPa or more and 10,000 MPa or less.

14. 3. The biaxially oriented polypropylene film according to claim 1, which is a food packaging film.

15. A food packaging product using the biaxially oriented polypropylene film according to claim 1 or 2.

16. The food packaging body according to claim 15; and a food product within the food package.

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