Packaging film, packaging material, and food package

Abstract

This packaging film (100) comprises: a biaxially stretched film layer (101) containing homopolypropylene; and a surface layer (A) (103) provided on at least one surface of the biaxially stretched film layer (101), wherein, when the total molar number of all monomer-derived constitutional units contained in the packaging film (100) is 100 mol%, the content of constitutional units derived from C2-C10 α-olefins (where the α-olefins exclude propylene) is 1.5-20.0 mol%.

Description

Packaging films, packaging materials, and food packaging

[0001] The present invention relates to a packaging film, a packaging material, and a food package.

[0002] Biaxially oriented polypropylene films (hereinafter also referred to as OPP films) have an excellent balance of performance such as processability, water vapor barrier properties, transparency, mechanical strength, and rigidity, and are used, for example, as packaging films for packaging food.

[0003] An example of a technology relating to packaging films using such OPP films is described in Patent Document 1 (JP 2015-044406 A).

[0004] Patent Document 1 describes a matte-finished polypropylene laminated stretched film in which a polypropylene resin matte layer (B) having a three-dimensional surface average roughness of 0.15 μm or more is laminated on at least one surface of a polypropylene resin layer (A), the polypropylene laminated stretched film being characterized by having a heat shrinkage rate of 9% or less in the MD and TD directions at 150° C., an impact strength of 0.6 J or more, and a haze of 40% or more. Patent Document 1 also describes that the polypropylene laminated stretched film can have a low shrinkage rate and high rigidity comparable to those of PET at 150° C., and therefore can be made thinner.

[0005] JP 2015-044406 A

[0006] In recent years, from the viewpoint of environmental issues, there has been a demand for mono-material packaging materials. However, conventional mono-material packaging materials using general biaxially oriented polypropylene film sometimes have insufficient thermal dimensional stability and tear resistance after high-temperature retort treatment (e.g., 135°C, 30 minutes).

[0007] The present invention has been made in consideration of the above circumstances, and provides a packaging film, packaging material, and food package having an improved performance balance between thermal dimensional stability and bag tear resistance of the packaging material after high-temperature retort treatment.

[0008] The present inventors conducted extensive research to solve the above-mentioned problems, and as a result, they discovered that a packaging film comprising a biaxially oriented film layer containing homopolypropylene and a surface layer (A) provided on at least one side of the biaxially oriented film layer, in which the content of structural units derived from α-olefins having 2 to 10 carbon atoms (α-olefins excluding propylene) is 1.5 mol % to 20.0 mol % when the total number of moles of structural units derived from all monomers contained in the packaging film is taken as 100 mol %, provides an improved balance of thermal dimensional stability and bag rupture resistance of the packaging material after high-speed retort treatment, thereby completing the present invention.

[0009] That is, according to the present invention, there are provided the following packaging films, packaging materials, and food packages.

[0010] [1] A packaging film comprising a biaxially oriented film layer containing homopolypropylene and a surface layer (A) provided on at least one side of the biaxially oriented film layer, wherein the content of structural units derived from α-olefins having 2 to 10 carbon atoms (α-olefins excluding propylene) is 1.5 mol% to 20.0 mol% when the total number of moles of structural units derived from all monomers contained in the packaging film is 100 mol%. [2] The packaging film according to [1], wherein the biaxially oriented film layer further contains a random copolymer of propylene and an α-olefin having 2 to 10 carbon atoms (α-olefins excluding propylene). [3] The packaging film according to [2], wherein the content of the random copolymer in the biaxially oriented film layer is 5 mass% to 20 mass% when the total amount of all components contained in the biaxially oriented film layer is 100 mass%. [4] The packaging film according to [2] or [3], wherein the content of structural units derived from α-olefins having 2 to 10 carbon atoms (α-olefins excluding propylene) is 2.0 mol% to 10.0 mol%, when the total moles of structural units derived from all monomers contained in the random copolymer is taken as 100 mol%. [5] The packaging film according to any of [2] to [4], wherein the MFR of the random copolymer measured in accordance with ASTM D1238 at 230°C and a load of 2.16 kg is 0.01 g / 10 min to 30.0 g / 10 min. [6] The packaging film according to any of [2] to [5], wherein the melting point of the random copolymer measured by DSC is 125°C to 150°C. [7] The packaging film according to any of [1] to [6], wherein the isotactic mesopentad fraction (mmmm) of the homopolypropylene is 96.0% or more. [8] The packaging film according to any one of [1] to [7], wherein the surface layer (A) contains at least one selected from the group consisting of a propylene block copolymer, a propylene-ethylene copolymer, and an ethylene-butene copolymer.[9] The packaging film according to any one of [1] to [8], wherein the arithmetic mean roughness (Ra) of at least one surface of the surface layer (A) is 40 nm or more, as measured by a three-dimensional surface measuring machine in accordance with JIS B0601 (1994).

[10] The packaging film according to any one of [1] to [9], wherein the ten-point mean roughness (Rz) of at least one surface of the surface layer (A) is 600 nm or more, as measured by a three-dimensional surface measuring machine in accordance with JIS B0601 (1994).

[11] The packaging film according to any one of [1] to

[10] , wherein the external haze of the packaging film is 2.0% or more, as measured by a three-dimensional surface measuring machine in accordance with JIS K7136 (2000).

[12] The packaging film according to any one of [1] to

[11] , wherein the internal haze of the packaging film is 5.0% or less, as measured by a three-dimensional surface measuring machine in accordance with JIS K7136 (2000).

[13] The packaging film according to any one of [1] to

[12] , which expands in the TD direction when heat-treated at 120°C for 15 minutes in accordance with JIS C2151 (2019).

[14] The packaging film according to any one of [1] to

[13] , which is used as a packaging material for food.

[15] The packaging film according to

[14] , which is used as a packaging material for retort food.

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

[15] .

[17] A food package comprising the packaging material according to

[16] , and food contained in the packaging material.

[0011] According to the present invention, it is possible to provide a packaging film, a packaging material, and a food package that have an improved performance balance between the thermal dimensional stability and the bag tear resistance of the packaging material after high-temperature retort treatment.

[0012] 1 is a cross-sectional view schematically showing an example of the structure of a packaging film of the present embodiment. 2 is a cross-sectional view schematically showing an example of the structure of a packaging film of the present embodiment.

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the drawings are simplified and do not correspond to the actual dimensional ratios. Note that "~" between numbers in the text indicates "above" to "below" unless otherwise specified.

[0014] 1 and 2 are cross-sectional views schematically showing an example of the structure of a packaging film 100 of this embodiment. The packaging film 100 of this embodiment includes a biaxially oriented film layer 101 containing homopolypropylene and a surface layer (A) 103 provided on at least one surface of the biaxially oriented film layer 101, and when the total number of moles of structural units derived from all monomers contained in the packaging film 100 is taken as 100 mol %, the content of structural units derived from α-olefins having 2 to 10 carbon atoms (α-olefins excluding propylene) is 1.5 mol % to 20.0 mol %.

[0015] As described above, packaging films containing biaxially oriented polypropylene film are required to have an improved performance balance between the thermal dimensional stability and bag rupture resistance of the packaging material after high-temperature retort processing. Here, the inventors' studies have revealed that a packaging film containing 1.5 mol% to 20.0 mol% of structural units derived from α-olefins having 2 to 10 carbon atoms (excluding propylene) when the total moles of structural units derived from all monomers contained in the packaging film are taken as 100 mol%, and this finding led to the present invention. That is, a packaging material using the packaging film 100 of this embodiment can improve the performance balance between the thermal dimensional stability and bag rupture resistance of the packaging material after high-temperature retort processing. Furthermore, a packaging material using the packaging film 100 of this embodiment can improve the performance balance between the thermal dimensional stability, lamination strength, heat seal strength, and bag rupture resistance of the packaging material after high-temperature retort processing.

[0016] In the packaging film 100 of this embodiment, when the total number of moles of structural units derived from all monomers contained in the packaging film 100 is taken as 100 mol %, the content of structural units derived from α-olefins having 2 to 10 carbon atoms (however, α-olefins exclude propylene) is 1.5 mol % or more and 20.0 mol % or less. In the packaging film 100 of this embodiment, when the total number of moles of structural units derived from all monomers contained in the packaging film is taken as 100 mol%, the content of structural units derived from α-olefins having 2 to 10 carbon atoms (however, α-olefins exclude propylene) is preferably 1.6 mol% or more, more preferably 1.8 mol% or more, even more preferably 2.0 mol% or more, even 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 5.0 mol% or more from the viewpoint of further improving the performance balance of the thermal dimensional stability and bag rupture resistance of the packaging material after high retort treatment, and from the viewpoint of making the packaging material mono-material, it is preferably 15.0 mol% or less, more preferably 10.0 mol% or less, even more preferably 8.0 mol% or less, even more preferably 7.0 mol% or less, even more preferably 6.0 mol% or less, and even more preferably 5.5 mol% or less. Furthermore, when the content of the structural unit derived from an α-olefin having from 2 to 10 carbon atoms (α-olefins excluding propylene) in the packaging film 100 of this embodiment is within the above range, the formability of the packaging film 100 is further improved and thickness unevenness is further reduced. The content of the structural unit derived from an α-olefin having from 2 to 10 carbon atoms (α-olefins excluding propylene) in the packaging film 100 can be measured by the method described in the examples.

[0017] The packaging film 100 of this embodiment has an overall haze of preferably 2.0% or more, more preferably 3.0% or more, even more preferably 5.0% or more, even more preferably 10.0% or more, even more preferably 20.0% or more, even more preferably 30.0% or more, even more preferably 40.0% or more, and even more preferably 50.0% or more, from the viewpoint of further improving the performance balance between the thermal dimensional stability and bag rupture resistance of the packaging material after high retort treatment. Furthermore, from the viewpoint of further improving the transparency of the packaging material, the overall haze is preferably 80.0% or less, more preferably 70.0% or less, and even more preferably 65.0% or less. The overall haze is an index for evaluating the unevenness of the surface of the packaging film. Large unevenness on the surface of the packaging film improves the adhesion strength when the packaging film is bonded to an unstretched polypropylene film, improving the performance balance between the dimensional stability and bag rupture resistance of the packaging material. The overall haze is measured using a haze meter in accordance with JIS K7136 (2000).

[0018] From the viewpoint of further improving the transparency of the packaging material, the packaging film 100 of this embodiment preferably has an internal haze of 5.0% or less, more preferably 3.0% or less, even more preferably 2.0% or less, even more preferably 1.5% or less, and even more preferably 1.0% or less. The lower limit of the internal haze is not particularly limited, but may be, for example, 0.1% or more, or 0.3% or more. The internal haze is measured using a haze meter in accordance with JIS K7136 (2000).

[0019] The packaging film 100 of this embodiment has an external haze of preferably 2.0% or more, more preferably 3.0% or more, even more preferably 5.0% or more, even more preferably 10.0% or more, even more preferably 20.0% or more, even more preferably 30.0% or more, even more preferably 40.0% or more, and even more preferably 50.0% or more, from the viewpoint of further improving the performance balance between the thermal dimensional stability and bag rupture resistance of the packaging material after high retort treatment. Furthermore, from the viewpoint of further improving the transparency of the packaging material, the external haze is preferably 80.0% or less, more preferably 70.0% or less, and even more preferably 65.0% or less. The external haze is an index for evaluating the unevenness of the surface of the packaging film. Large unevenness on the surface of the packaging film improves the adhesive strength when the packaging film is bonded to an unstretched polypropylene film, improving the performance balance between the dimensional stability and bag rupture resistance of the packaging material. The external haze is calculated using the formula "external haze of packaging film 100 = overall haze of packaging film 100 - internal haze of packaging film 100."

[0020] The overall haze, internal haze, and external haze of the packaging film can be adjusted, for example, by adjusting the constituent material, thickness, and stretching ratio of the biaxially stretched film layer 101, and the constituent material and thickness of the surface layer (A) 103.

[0021] In the packaging film 100 of this embodiment, the overall haze of the adhesive-coated sample is preferably 5.0% or less, more preferably 3.0% 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 packaging material. The lower limit of the overall haze of the adhesive-coated sample is not particularly limited, but may be, for example, 0.1% or more, or 0.3% or more. Here, the adhesive-coated sample is prepared as follows. A two-component curing polyurethane adhesive (a blend of a urethane resin as the main component, an isocyanate curing agent, and an ethyl acetate solvent in a ratio of 9.0:1.0:7.5 (mass ratio)) is applied to the surface of the surface layer (A) in a dry coating amount of 2.7 g / m. ２The adhesive is applied so that the ethyl acetate solvent is then dried to prepare an adhesive-coated sample. As the two-component curing polyurethane adhesive in this specification, for example, the two-component curing polyurethane adhesive described in the Examples can be used. The overall haze of the adhesive-coated sample is measured using a haze meter in accordance with JIS K7136 (2000).

[0022] In the packaging film 100 of this embodiment, the difference in haze before and after adhesive application is preferably 1.0% or more, preferably 2.0% or more, more preferably 3.0% or more, even more preferably 4.0% or more, even more preferably 5.0% or more, even more preferably 10.0% or more, even more preferably 20.0% or more, even more preferably 30.0% or more, even more preferably 40.0% or more, even more preferably 50.0% or more, from the viewpoint of further improving the performance balance of the thermal dimensional stability and bag rupture resistance of the packaging material after high retort treatment, and is preferably 80.0% or less, more preferably 70.0% or less, even more preferably 65.0% or less, from the viewpoint of further improving the transparency of the packaging material. The difference in haze before and after adhesive application is calculated using the formula "difference in haze before and after adhesive application = overall haze of packaging film - overall haze of adhesive-coated sample".

[0023] In order to further improve the performance balance between the thermal dimensional stability and bag rupture resistance of the packaging material after high-speed retort processing, it is preferable that the packaging film 100 of this embodiment expands in the TD direction when heat-treated at 120°C for 15 minutes in accordance with JIS C2151 (2019). More specifically, the thermal expansion coefficient of the packaging film 100 in the TD direction when heat-treated at 120°C for 15 minutes is 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, from the viewpoints of further improving the performance balance of the thermal dimensional stability and bag-rupture resistance of the packaging material after high retort treatment and further suppressing the occurrence of wrinkles when the packaging film 100 is thermally processed. Furthermore, from the viewpoints of further improving the performance balance of the thermal dimensional stability and bag-rupture resistance of the packaging material after high retort treatment and further suppressing the occurrence of wrinkles when the packaging film 100 is thermally processed, the thermal expansion coefficient is preferably 2.0% or less, more preferably 1.5% or less, even more preferably 1.2% or less, and even more preferably 1.0% or less. The thermal expansion coefficient of the packaging film 100 in the TD direction when heat-treated at 120°C for 15 minutes is calculated by the following method. A 10 cm x 10 cm test piece is cut out from the packaging film 100. Next, the test piece is heat-treated at 120° C. for 15 minutes. Then, the length of the test piece in the TD direction after the heat treatment is measured. １ [cm], and the thermal expansion coefficient in the TD direction [%] is 100 × (TD １ -10) / 10.

[0024] Furthermore, the heat shrinkage rate in the MD direction of the packaging film 100 when heat-treated at 120°C for 15 minutes is 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, from the viewpoint of further improving the performance balance between the thermal dimensional stability and bag rupture resistance of the packaging material after high retort treatment and further reducing the elongation when the packaging film 100 is thermally processed, and may be 0.1% or more, 0.3% or more, or 0.5% or more. The heat shrinkage rate in the MD direction of the packaging film 100 when heat-treated at 120°C for 15 minutes is calculated by the following method. A test piece of 10 cm x 10 cm is cut from the packaging film 100. Next, the test piece is heat-treated at 120°C for 15 minutes. Next, the length in the MD direction of the test piece after heat treatment is measured. １ [cm], and the heat shrinkage rate [%] in the MD direction is calculated as 100 × (10 - MD １ ) / 10.

[0025] The heat shrinkage rate in the TD direction and the heat shrinkage rate in the MD direction when the packaging film 100 was heated at 150° C. for 15 minutes were respectively X ＴＤ [%] and X ＭＤ When [%] is used, X ＴＤ +X ＭＤ From the viewpoint of further improving the performance balance between the thermal dimensional stability and the bag tear resistance of the packaging material after high retort treatment, the X of the packaging film 100 is preferably 7.0% or less, more preferably 6.5% or less, even more preferably 6.0% or less, and even more preferably 5.5% or less. The lower limit is not particularly limited, but may be, for example, 0.2% or more, or 0.5% or more. ＴＤ [%] and X ＭＤ [%] is calculated by the following method: A test piece of 10 cm x 10 cm is cut out from the packaging film 100. Then, the test piece is heat-treated at 150°C for 15 minutes. Then, the length in the TD direction of the test piece after the heat treatment is １ The length of the test piece in the MD direction after heat treatment is defined as MD [cm]. １ When [cm], X ＴＤ[%] is 100 × (10-TD １ ) / 10, and X ＭＤ [%] is 100 x (10-MD １ ) / 10.

[0026] The thermal expansion coefficient and thermal shrinkage coefficient of the packaging film 100 can be adjusted, for example, by adjusting the constituent material, thickness, and stretching ratio of the biaxially stretched film layer 101, and the constituent material and thickness of the surface layer (A) 103. The thermal expansion coefficient and thermal shrinkage coefficient of the packaging film 100 can be measured in accordance with JIS C2151 (2019).

[0027] The thermal expansion coefficient of the packaging film 100 in the TD direction after high retort treatment preferably expands in the TD direction from the viewpoint of further improving heat resistance. More specifically, the thermal expansion coefficient of the packaging film 100 in the TD direction after high retort treatment is preferably 0.1% or more, more preferably 0.2% or more, from the viewpoint of further improving heat resistance. Also, from the viewpoint of further improving heat resistance, it is preferably 2.0% or less, more preferably 1.5% or less, even more preferably 1.2% or less, and even more preferably 1.0% or less. The thermal expansion coefficient of the packaging film 100 in the TD direction after high retort treatment is calculated by the method described in the Examples. That is, the thermal expansion coefficient of the packaging film 100 in the TD direction after high retort treatment refers to the thermal expansion coefficient in the TD direction of a packaging film obtained by high retort treating a laminate obtained by laminating the packaging film 100 and a sealant film.

[0028] Furthermore, from the viewpoint of further improving the heat resistance of the packaging material, the heat shrinkage rate in the MD direction of the packaging film 100 after the high retort treatment is preferably 5.0% or less, more preferably 4.0% or less, and even more preferably 3.0% or less. From the viewpoint of further improving the heat resistance of the packaging material, it may be 0.1% or more, 0.3% or more, or 0.5% or more. The heat shrinkage rate in the MD direction of the packaging film 100 after the high retort treatment is calculated by the method described in the Examples. That is, the heat shrinkage rate in the MD direction of the packaging film 100 after the high retort treatment refers to the heat shrinkage rate in the MD direction of the packaging film obtained by high retort treating a laminate obtained by laminating the packaging film 100 and a sealant film.

[0029] From the viewpoint of further improving the strength of the packaging material, the laminate strength of the packaging film 100 after the high retort treatment is preferably 2.5 N / 15 mm or more, more preferably 3.0 N / 15 mm or more, and even more preferably 4.0 N / 15 mm or more. The upper limit is not particularly limited, but may be, for example, 10.0 N / 15 mm or less, or 8.0 N / 15 mm or less. The laminate strength of the packaging film 100 after the high retort treatment is measured by the method described in the Examples. That is, the laminate strength of the packaging film 100 after the high retort treatment refers to the laminate strength of the packaging film obtained by high retort treating a laminate obtained by laminating the packaging film 100 and a sealant film.

[0030] From the viewpoint of further improving the strength of the packaging material, the heat seal strength of the packaging film 100 after high retort treatment is preferably 25 N / 15 mm or more, more preferably 26 N / 15 mm or more, and even more preferably 27 N / 15 mm or more. The upper limit is not particularly limited, but may be, for example, 40 N / 15 mm or less, or 35 N / 15 mm or less. The heat seal strength of the packaging film 100 after high retort treatment is measured by the method described in the Examples. That is, the heat seal strength of the packaging film 100 after high retort treatment refers to the heat seal strength of the packaging film obtained by high retort treating a laminate obtained by laminating the packaging film 100 and a sealant film.

[0031] The number of times that the packaging film 100 falls after the high retort treatment is preferably 6 or more from the viewpoint of further improving the strength of the packaging material. The number of times that the packaging film 100 falls after the high retort treatment is measured by the method described in the Examples. That is, the number of times that the packaging film 100 falls after the high retort treatment refers to the number of times that a laminate obtained by laminating the packaging film 100 and a sealant film falls after the high retort treatment.

[0032] From the viewpoint of further improving the balance of thermal dimensional stability, formability, water vapor barrier properties, cost, mechanical properties, transparency, bag-making properties, handleability, appearance, and lightness, the thickness of the packaging film 100 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, 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.

[0033] Each layer constituting the packaging film 100 will be described below.

[0034] [Biaxially Stretched Film Layer] The biaxially oriented film layer 101 contains homopolypropylene. The biaxially oriented film layer 101 is formed, for example, by biaxially stretching a film made of a propylene-based polymer composition containing homopolypropylene.

[0035] 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.

[0036] The thickness of the biaxially stretched 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 balance of the thermal dimensional stability, formability, water vapor barrier property, cost, mechanical properties, transparency, bag-making properties, handleability, appearance, and lightness of the packaging film 100, 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.

[0037] In the packaging film 100, the ratio of the thickness of the biaxially oriented film layer 101 to the total thickness of the packaging 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.

[0038] The propylene-based polymer composition constituting the biaxially stretched film layer 101 of this embodiment contains homopolypropylene. Examples of homopolypropylene include propylene homopolymers and propylene-based copolymers having a content of structural units derived from α-olefins other than propylene of 1.5 mol% or less. When the total number of moles of structural units derived from all monomers contained in the homopolypropylene is taken as 100 mol%, the content of propylene-derived structural units in the homopolypropylene is 98.5 mol% or more, preferably 98.7 mol% or more, more preferably 99.0 mol% or more, even more preferably 99.5 mol% or more, and still 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 is taken as 100 mol%, is preferably 1.5 mol% or less, 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 in the biaxially stretched film layer 101 may be used alone or in combination of two or more types.

[0040] The content of homopolypropylene contained in the biaxially oriented film layer 101 of this embodiment is preferably 80% by mass or more, more preferably 82% by mass or more, even more preferably 85% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more, when the total amount of all components contained in the biaxially oriented film layer 101 is taken as 100% by mass, from the viewpoint of further improving the performance balance of the thermal dimensional stability and bag rupture resistance of the packaging material after high retort treatment, and may be 100% by mass or less, or may be 98% by mass or less.

[0041] The isotactic mesopentad fraction (mmmm) of the homopolypropylene 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 the thermal dimensional stability, heat resistance, water vapor barrier property, mechanical properties, rigidity, bag formability, etc. of the packaging film 100. The upper limit of the isotactic mesopentad fraction (mmmm) of the homopolypropylene 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 by a known method from a C-nuclear magnetic resonance (NMR) spectrum. When two or more types of homopolypropylene are used as the homopolypropylene, the isotactic mesopentad fraction of the homopolypropylene can be the isotactic mesopentad fraction of a mixture obtained by melt blending two or more types of homopolypropylene by a known method.

[0042] The melting point of the homopolypropylene 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 balance of the thermal dimensional stability, heat resistance, water vapor barrier properties, mechanical properties, rigidity, bag formability, flowability, moldability, etc. of the packaging film 100, 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 types of homopolypropylene are used as the homopolypropylene, the melting point of the homopolypropylene is the peak temperature of the maximum melting peak.

[0043] Homopolypropylene can be produced by various methods, for example, by using known catalysts such as Ziegler-Natta catalysts and metallocene catalysts.

[0044] The propylene-based polymer composition constituting the biaxially stretched film layer 101 of the present embodiment preferably further contains a random copolymer of propylene and an α-olefin having from 2 to 10 carbon atoms (provided that α-olefins exclude propylene). The α-olefin having from 2 to 10 carbon atoms (provided that α-olefins exclude propylene) preferably contains at least one selected from the group consisting of ethylene and α-olefins having from 4 to 6 carbon atoms, and more preferably contains at least one selected from the group consisting of ethylene and 1-butene.

[0045] The content of structural units derived from α-olefins having from 2 to 10 carbon atoms (α-olefins excluding propylene) in the random copolymer of propylene and α-olefins having from 2 to 10 carbon atoms (α-olefins excluding propylene) contained in the biaxially stretched film layer 101 is more than 1.5 mol%, when the total number of moles of structural units derived from all monomers contained in the random copolymer is taken as 100 mol%. From the viewpoint of further improving the performance balance between the thermal dimensional stability and bag rupture resistance of the packaging material after high retort treatment and further improving the formability of the packaging film 100, the content is preferably 2.0 mol% or more, more preferably 3.0 mol% or more, and even more preferably 4.0 mol% or more. From the viewpoint of making the packaging material a mono-material, the content is preferably 10.0 mol% or less, more preferably 9.0 mol% or less, even more preferably 8.0 mol% or less, and even more preferably 7.0 mol% or less.

[0046] The content of the random copolymer of propylene and an α-olefin having 2 to 10 carbon atoms (α-olefins excluding propylene) contained in the biaxially oriented film layer 101 is preferably 5% by mass or more, more preferably 8% by mass or more, and even more preferably 10% by mass or more, when the total amount of all components contained in the biaxially oriented film layer 101 is taken as 100% by mass, from the viewpoint of further improving the performance balance of the thermal dimensional stability and bag rupture resistance of the packaging material after high retort treatment and further improving the formability of the packaging film 100, and is preferably 20% by mass or less, more preferably 18% by mass or less, and even more preferably 17% by mass or less, from the viewpoint of making the packaging material a mono-material.

[0047] The MFR of the random copolymer of propylene and an α-olefin having 2 to 10 carbon atoms (however, α-olefins exclude propylene) contained in the biaxially stretched film layer 101, measured in accordance with ASTM D1238 under conditions of 230°C and a load of 2.16 kg, is 0.01 g / 10 min or more, preferably 0.1 g / 10 min or more, from the viewpoint of further improving the performance balance of the thermal dimensional stability and bag rupture resistance of the packaging material after high retort treatment and further improving the formability of the packaging film 100. From the viewpoint of further improving the performance balance between the thermal dimensional stability and bag rupture resistance of the packaging material after high retort treatment, the MFR is 30.0 g / 10 min or less, preferably 20.0 g / 10 min or less, 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 random copolymers are used as the random copolymer, the MFR of the random copolymer can be the MFR of a mixture obtained by melt-blending two or more types of random copolymers by a known method.

[0048] The melting point of the random copolymer of propylene and an α-olefin having from 2 to 10 carbon atoms (α-olefins excluding propylene) contained in the biaxially oriented film layer 101, as measured by DSC, is preferably 125°C or higher, more preferably 130°C or higher, and even more preferably 135°C or higher, from the viewpoint of further improving the performance balance between the thermal dimensional stability and bag rupture resistance of the packaging material after high retort treatment, and is preferably 150°C or lower, more preferably 148°C or lower, and even more preferably 145°C or lower, from the viewpoint of further improving the performance balance between the thermal dimensional stability and bag rupture resistance of the packaging material after high retort treatment. When two or more types of random copolymers are used as the random copolymer, the melting point of the random copolymer is the peak temperature of the maximum melting peak.

[0049] The weight average molecular weight (Mw) of the random copolymer of propylene and an α-olefin having 2 to 10 carbon atoms (however, α-olefins exclude propylene) contained in the biaxially stretched film layer 101 is preferably 100,000 or more, more preferably 150,000 or more, and even more preferably 200,000 or more, from the viewpoints of further improving the performance balance of the thermal dimensional stability and bag rupture resistance of the packaging material after high retort treatment, further improving the formability of the packaging film 100, and further improving the sheet payout property. The molecular weight 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 more, and even more preferably 450,000 or less, from the viewpoint of further improving the performance balance of the thermal dimensional stability and bag rupture resistance of the packaging material after high retort treatment, further improving the formability of the packaging film 100, and further improving the payout properties of the sheet.

[0050] The weight average molecular weight (Mw) / number average molecular weight (Mn) of the random copolymer of propylene and an α-olefin having from 2 to 10 carbon atoms (however, α-olefins exclude propylene) contained in the biaxially stretched film layer 101 is preferably 1.5 or more, more preferably 1.8 or more, from the viewpoints of further improving the performance balance between the thermal dimensional stability and bag rupture resistance of the packaging material after high retort treatment, further improving the formability of the packaging film 100, and further improving the sheet payout ability; and from the viewpoints of further improving the performance balance between the thermal dimensional stability and bag rupture resistance of the packaging material after high retort treatment, further improving the formability of the packaging film 100, and further improving the sheet payout ability, the weight average molecular weight (Mw) / number average molecular weight (Mn) of the random copolymer of propylene and an α-olefin having from 2 to 10 carbon atoms (however, α-olefins exclude propylene) contained in the biaxially stretched film layer 101 is preferably 8.0 or less, more preferably 7.5 or less, even more preferably 7.0 or less, even more preferably 6.8 or less. When two or more types of random copolymers are used as the random copolymer, the weight average molecular weight (Mw) and number average molecular weight (Mn) of the random copolymer can be the weight average molecular weight (Mw) and number average molecular weight (Mn) of a mixture obtained by melt blending two or more types of random copolymers by a known method.

[0051] In this specification, the weight average molecular weight (Mw) and number average molecular weight (Mn) are values ​​measured by the method described in the examples.

[0052] A random copolymer of propylene and an α-olefin having from 2 to 10 carbon atoms (α-olefins excluding propylene) can be produced by various methods, for example, by using a known catalyst such as a Ziegler-Natta catalyst or a metallocene catalyst.

[0053] If necessary, 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 to the propylene polymer composition constituting the biaxially stretched film layer 101 within a range that does not impair the object of this embodiment.

[0054] The propylene-based polymer composition constituting the biaxially stretched film layer 101 can be prepared by mixing or melting and 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.

[0055] [Surface layer (A)] The packaging film 100 of this embodiment has a surface layer (A) 103 on at least one surface of the biaxially stretched film layer 101. The surface layer (A) 103 is preferably provided as the outermost layer of the packaging film 100, from the viewpoint of further improving the performance balance between the thermal dimensional stability and the bag rupture resistance of the packaging material after high retort treatment.

[0056] The surface layer (A) 103 is preferably provided so as to be in direct contact with the surface of the biaxially stretched film layer 101. This allows the manufacturing process of the packaging film 100 to be simplified.

[0057] In the packaging film 100, the thickness of the surface layer (A) 103 is preferably 0.1 μm or more, more preferably 0.2 μm or more, even more preferably 0.5 μm or more, and even more preferably 0.8 μm or more, from the viewpoint of further improving the performance balance of the thermal dimensional stability and bag rupture resistance of the packaging material after high retort treatment, 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 4.0 μm or less, from the viewpoint of further improving the performance balance of the thermal dimensional stability and bag rupture resistance of the packaging material after high retort treatment.

[0058] In the packaging film 100, the surface layer (A) 103 is preferably a single layer, which can further simplify the manufacturing process of the packaging film 100.

[0059] The surface layer (A) 103 is preferably formed by biaxially stretching simultaneously with the biaxially stretched film layer 101 in a state before biaxial stretching. This allows the packaging film 100 to be produced by a molding method such as co-extrusion molding, i.e., using a laminated film produced in a single molding operation, thereby further simplifying the manufacturing process of the packaging film 100. Therefore, the surface layer (A) 103 is preferably biaxially stretched.

[0060] The surface layer (A) 103 may be subjected to a surface treatment. Specifically, it may be subjected to a surface activation treatment such as a corona treatment, a flame treatment, a plasma treatment, a primer coating treatment, an ozone treatment, etc. From the viewpoint of further improving the performance balance of the lamination strength, the heat seal strength, and the bag rupture resistance of the packaging material after high retort treatment, it is preferable that the surface layer (A) 103 be subjected to a corona treatment.

[0061] The surface layer (A) 103 is made of a polyolefin-based resin composition containing a polyolefin. The polyolefin constituting the surface layer (A) 103 includes at least one selected from the group consisting of homopolymers or copolymers of α-olefins such as ethylene, propylene, 1-butene, hexene-1,4-methyl-pentene-1, and 1-octene; high-pressure low-density polyethylene; linear low-density polyethylene (LLDPE); high-density polyethylene; homopolypropylene; random copolymers of propylene and α-olefins having from 2 to 10 carbon atoms; ethylene-vinyl acetate copolymers (EVA); and ionomer resins. Among these, the polyolefin constituting the surface layer (A) 103 preferably contains at least one selected from the group consisting of a block copolymer of propylene, a copolymer of propylene and ethylene, and a copolymer of ethylene and butene, from the viewpoint of further improving the performance balance between the thermal dimensional stability and the bag rupture resistance of the packaging material after high retort treatment, more preferably at least one selected from the group consisting of a block copolymer of propylene and an α-olefin having from 2 to 10 carbon atoms (provided that the α-olefin does not include propylene), a copolymer of propylene and ethylene, and a copolymer of ethylene and butene, and even more preferably at least one selected from the group consisting of a block copolymer of propylene and an α-olefin having from 2 to 6 carbon atoms (provided that the α-olefin does not include propylene), a copolymer of propylene and ethylene, and a copolymer of ethylene and 1-butene.

[0062] The content of structural units derived from α-olefins having 2 to 10 carbon atoms (α-olefins excluding propylene) contained in the surface layer (A) 103 is, when the total number of moles of structural units derived from all monomers contained in the surface layer (A) 103 is taken as 100 mol%, from the viewpoint of further improving the performance balance of the thermal dimensional stability and bag rupture resistance of the packaging material after high retort treatment, preferably 1.0 mol% or more, more preferably 2.0 mol% or more, even more preferably 3.0 mol% or more, even more preferably 5.0 mol% or more, even more preferably 10.0 mol% or more, even more preferably 15.0 mol% or more, and even more preferably 20.0 mol% or more; and from the viewpoint of mono-materialization of the packaging material, preferably 50.0 mol% or less, more preferably 40.0 mol% or less, even more preferably 35.0 mol% or less, even more preferably 32.0 mol% or less, and even more preferably 30.0 mol% or less.

[0063] The total content of polyolefins selected from the group consisting of propylene block copolymers, propylene and ethylene copolymers, and ethylene and butene copolymers in the surface layer (A) 103 is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, when the total amount of all components contained in the surface layer (A) 103 is taken as 100% by mass, from the viewpoint of further improving the performance balance of the thermal dimensional stability and bag rupture resistance of the packaging material after the high retort treatment.Furthermore, from the viewpoint of further improving the performance balance of the thermal dimensional stability and bag rupture resistance of the packaging material after the high retort treatment, the total content is preferably 100% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less.

[0064] If necessary, 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 to the polyolefin resin composition constituting the surface layer (A) 103, within a range that does not impair the object of this embodiment.

[0065] The polyolefin resin composition constituting the surface layer (A) 103 can be prepared, for example, by mixing or melting and 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.

[0066] The arithmetic mean roughness (Ra) of at least one surface of the surface layer (A) 103, measured by a three-dimensional surface measuring machine in accordance with JIS B0601 (1994), is preferably 40 nm or more, more preferably 45 nm or more, and even more preferably 50 nm or more, from the viewpoint of further improving the performance balance of the thermal dimensional stability and bag rupture resistance of the packaging material after high retort treatment, and is preferably 750 nm or less, more preferably 700 nm or less, and even more preferably 650 nm or less, from the viewpoint of further improving the transparency of the packaging material.

[0067] The ten-point average roughness (Rz) of at least one surface of the surface layer (A) 103, measured by a three-dimensional surface measuring machine in accordance with JIS B0601 (1994), is preferably 600 nm or more, more preferably 650 nm or more, and even more preferably 680 nm or more, from the viewpoint of further improving the performance balance of the thermal dimensional stability and bag rupture resistance of the packaging material after high retort treatment, and is preferably 5500 nm or less, more preferably 5300 nm or less, and even more preferably 5100 nm or less, from the viewpoint of further improving the transparency of the packaging material.

[0068] [Surface layer (B)] From the viewpoint of imparting functions such as heat fusion resistance, heat sealing properties, antistatic properties, blocking resistance, printability, slip properties, etc. to the film surface depending on the purpose, the packaging film 100 preferably further comprises a surface layer (B) 105 on the surface of the biaxially stretched film layer 101 opposite to the surface layer (A) 103. Furthermore, from the viewpoint of further improving the functions of the packaging film 100 depending on the purpose, such as heat fusion resistance, heat sealing properties, antistatic properties, blocking resistance, printability, slip properties, etc., the surface layer (B) 105 is preferably provided as the outermost layer of the packaging film 100.

[0069] The surface layer (B) 105 is preferably provided so as to be in direct contact with the surface of the biaxially stretched film layer 101. This allows the manufacturing process of the packaging film 100 to be simplified.

[0070] In the packaging film 100, the thickness of the surface layer (B) 105 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 packaging film 100, such as heat fusion resistance, heat sealing property, antistatic property, blocking resistance, printability, and slip property; and from the viewpoint of further improving the balance of the heat fusion resistance, thermal dimensional stability, formability, cost, mechanical properties, transparency, environmental compatibility, and light weight of the packaging film 100, the thickness 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.

[0071] In the packaging film 100, the surface layer (B) 105 is preferably a single layer, which can further simplify the manufacturing process of the packaging film 100.

[0072] The surface layer (B) 105 is preferably formed by biaxially stretching simultaneously with the biaxially stretched film layer 101 in a state before biaxial stretching. This allows the packaging film 100 to be produced by a molding method such as co-extrusion molding, i.e., using a laminated film produced in a single molding operation, thereby further simplifying the manufacturing process of the packaging film 100. Therefore, the surface layer (B) 105 is preferably biaxially stretched.

[0073] The surface layer (B) 105 may be subjected to a surface treatment, specifically, a surface activation treatment such as a corona treatment, a flame treatment, a plasma treatment, a primer coating treatment, or an ozone treatment.

[0074] The surface layer (B) 105 is composed of a polyolefin-based resin composition containing a polyolefin. The polyolefin constituting the surface layer (B) 105 includes at least one selected from the group consisting of homopolymers or copolymers of α-olefins such as ethylene, propylene, 1-butene, hexene-1,4-methyl-pentene-1, and 1-octene; high-pressure low-density polyethylene; linear low-density polyethylene (LLDPE); high-density polyethylene; homopolypropylene; random copolymers of propylene and α-olefins having from 2 to 10 carbon atoms; ethylene-vinyl acetate copolymers (EVA); and ionomer resins. Among these, homopolypropylene is preferred as the polyolefin constituting the surface layer (B) 105 from the viewpoint of further improving the balance of the heat-sealing resistance, thermal dimensional stability, heat resistance, water vapor barrier properties, transparency, mechanical properties, rigidity, bag-formability, flowability, and moldability of the packaging film 100. Here, the preferred embodiment of the homopolypropylene constituting the surface layer (B) 105 is the same as the homopolypropylene contained in the biaxially oriented film layer 101 described above.

[0075] When the total amount of all components contained in the surface layer (B) 105 is taken as 100% by mass, the content of homopolypropylene in the surface layer (B) 105 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, from the viewpoint of further improving the balance of the heat fusion resistance, thermal dimensional stability, heat resistance, water vapor barrier property, transparency, mechanical properties, rigidity, bag formability, fluidity, moldability, etc. of the packaging film 100.

[0076] 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, inorganic or organic fillers, etc. may be added to the polyolefin resin composition constituting the surface layer (B) 105, within a range that does not impair the object of this embodiment. The polyolefin resin composition constituting the surface layer (B) 105 preferably contains an antiblocking agent, from the viewpoint of further improving handleability when producing the packaging film 100.

[0077] The polyolefin resin composition constituting the surface layer (B) 105 can be prepared, for example, by mixing or melting and 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.

[0078] [Other Layers] The packaging film 100 may further include a sealant layer. For example, a sealant layer may be provided on the surface of the surface layer (B) 105 .

[0079] <Method for Manufacturing Packaging Film 100> The packaging film 100 can be obtained by, for example, co-extrusion molding a propylene-based polymer composition for forming the biaxially stretched film layer 101 and a polyolefin-based resin composition for forming the surface layer (A) 103 into a film, and then biaxially stretching the resulting film using a known biaxially stretched film manufacturing method such as simultaneous biaxial stretching, sequential biaxial stretching, or inflation biaxial stretching. The molding apparatus and molding conditions are not particularly limited, and conventionally known molding apparatuses and molding conditions can be used. Examples of molding apparatuses that can be used include a T-die extruder, a multilayer T-die extruder, an inflation molding machine, and a multilayer inflation molding machine. The biaxial stretching conditions can be, for example, those used for manufacturing OPP films. More specifically, in the sequential biaxial stretching method, for example, the stretching temperature in the MD direction may be 100° C. to 145° C., the stretching ratio in the MD direction may be in the range of 4.5 to 6 times, the stretching temperature in the TD direction may be 130° C. to 190° C., and the stretching ratio in the TD direction may be in the range of 9 to 11 times. The packaging film 100 can also be obtained by separately molding the biaxially stretched film layer 101 and the surface layer (A) 103, laminating them together, and heat-molding them.

[0080] <Uses of Packaging Film> The packaging film 100 can be suitably used as a packaging film constituting a packaging material for food, and is more preferably used as a packaging film constituting a packaging material for retort food.

[0081] <Packaging Material> The packaging material of this embodiment is a packaging material that uses the packaging film 100 of this embodiment, and is a packaging material used for the purpose of containing food, for example. Furthermore, the packaging material of this embodiment may use the packaging film 100 in part thereof, or the packaging film 100 may be used for the entire packaging material, depending on the application.

[0082] The packaging material of this embodiment is preferably subjected to retort treatment (e.g., 127°C or higher and 132°C or lower, for 20 minutes or longer and 40 minutes or shorter), and more preferably subjected to high retort treatment (e.g., 133°C or higher and 138°C or lower, for 20 minutes or longer and 40 minutes or shorter).

[0083] The packaging material of this embodiment is produced, for example, by bonding the packaging film 100 of this embodiment and a sealant film for lamination or the like together and processing them into a bag shape. When the packaging film 100 has a sealant layer, the packaging material of this embodiment can also be produced by bonding the ends of the sealant layer together to form a bag shape.

[0084] <Food Package> The food package of this embodiment includes the packaging material of this embodiment and food inside the packaging material. That is, the food package of this embodiment is the food packaging material of this embodiment that contains food.

[0085] Although the embodiments of the present invention have been described above with reference to the drawings, these are merely examples of the present invention, and various other configurations can also be adopted.

[0086] 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.

[0087] 1. Raw Materials The raw materials used in the Examples and Comparative Examples are as follows: (1) Homopolypropylene 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) Copolymer 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%) b-PP1: block polypropylene (MFR: 5.0 g / 10 min, melting point: 148°C, content of ethylene-derived structural units: 30.4 mol%, content of propylene-derived structural units: 69.6 mol%) EBR1: ethylene-1-butene copolymer (MFR: 6.7 g / 10 min, melting point: 66°C, content of ethylene-derived structural units: 88.3 mol%, content of 1-butene-derived structural units: 11.7 mol%)

[0088] 2. Measurement and Evaluation Methods (1) Content of structural units derived from α-olefins having 2 to 10 carbon atoms (α-olefins excluding propylene) in homopolypropylene and copolymers The content of structural units derived from α-olefins having 2 to 10 carbon atoms (α-olefins excluding propylene) in homopolypropylene and copolymers was measured using a nuclear magnetic resonance apparatus (AVANCE III cryo-500 model, manufactured by Bruker Biospin). １３ Measurement was performed by C-NMR. The sample was dissolved in the following measurement solvent and the measurement was performed, and evaluation was performed based on the integrated intensity of each signal. １３ The C-NMR spectrum was confirmed in accordance with the literature: Macromolecules (1982) Ethylene-1-Butene Copolymers. 1. Commoner Sequence Distribution and Macromolecules (1977) Carbon-13 Nuclear Magnetic Resonance Determination of Monomer Composition and Sequence Distribution in Ethylene-Propylene Copolymers Prepared with a Stereoregular Catalyst. Signals were assigned with reference to the FTIR System and the like, and the contents (mol %) of ethylene-derived structural units, propylene-derived structural units, and 1-butene-derived structural units in the homopolypropylene and copolymer were quantified. [Measurement conditions] Measurement nucleus: １３ C (125 MHz) Measurement mode: Single pulse proton broadband decoupling Pulse width: 45° Number of points: 64k Repetition time: 5.5 seconds Measurement solvent: orthodichlorobenzene / heavy benzene (4:1) Sample concentration: 50 mg / 0.6 mL Measurement temperature: 120°C Window function: exponential (BF: 0.5 Hz)

[0089] (2) Content of structural units derived from α-olefins having 2 to 10 carbon atoms (α-olefins excluding propylene) in a packaging film. The packaging film was dissolved in a measurement solvent under the same measurement conditions as in the above method (1), １３ Measurement was performed by C-NMR.

[0090] (3) MFR of homopolypropylene and copolymer: Measured in accordance with ASTM D1238 at 230°C under a load of 2.16 kg.

[0091] (4) Melting Point of Homopolypropylene and Copolymer Using a differential scanning calorimeter (product name: Q200DSC manufactured by TA Instruments), the homopolypropylene and copolymer were subjected to a first differential scanning calorimeter (1st Run) consisting of a process of increasing the temperature from -30°C to 250°C at a heating rate of 10°C / min and a process of decreasing the temperature from 250°C to -30°C at a heating rate of 10°C / min under a nitrogen stream, and a second differential scanning calorimeter (2nd Run) consisting of a process of increasing the temperature from -30°C to 250°C at a heating rate of 10°C / min. The peak temperature of the maximum melting peak in the DSC curve in the 2nd Run was taken as the melting point.

[0092] (5) Weight-average molecular weight (Mw) and number-average molecular weight (Mn) of homopolypropylene and copolymer The weight-average molecular weight (Mw) and number-average molecular weight (Mn) of homopolypropylene and copolymer 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 contained o-dichlorobenzene and 0.025% by mass of BHT as an antioxidant, and was moved at a rate of 1.0 mL / min. The sample concentration was 0.1% (w / v), the sample injection volume was 400 μL, and a differential refractometer was used as the detector. The molecular weight was calculated as polypropylene equivalent using monodisperse polystyrene as the standard.

[0093] (6) Isotactic mesopentad fraction (mmmm) of homopropylene The isotactic mesopentad fraction (mmmm) was measured using a nuclear magnetic resonance apparatus (AVANCE III cryo-500 model, manufactured by Bruker Biospin). １３ Measurement was performed by C-NMR. The sample was dissolved in the following measurement solvent and the measurement was performed, and the evaluation was performed based on the integrated intensity of each signal. [Measurement conditions] Measurement nucleus: １３ C (125 MHz) Measurement mode: Single pulse proton broadband decoupling Pulse width: 45° Number of points: 64 k Repetition time: 5.5 seconds Measurement solvent: orthodichlorobenzene / heavy benzene (4:1) Sample concentration: 50 mg / 0.6 mL Measurement temperature: 120 °C Window function: exponential (BF: 0.5 Hz) Chemical shift reference: mmmm (CH ３ ): 21.59ppm

[0094] (7) Actual Thickness of Packaging Film The thickness of the packaging film was measured using a micrometer (manufactured by Hybrid Manufacturing Co., Ltd., trade name: Automatic Micrometer). The thickness was measured at five points within the packaging film, and the average value was taken as the actual thickness of the packaging film.

[0095] (8) Haze [Haze of packaging film] According to JIS K7136 (2000), the overall haze and internal haze of the packaging film were measured using a haze meter (NDH5000, manufactured by Nippon Denshoku Industries Co., Ltd.). The external haze of the packaging film was calculated using the formula "external haze of packaging film = overall haze of packaging film - internal haze of packaging film". [Haze of adhesive-coated sample] A two-component curing polyurethane adhesive was applied to the surface of the surface layer (A) 103 in a dry coating amount of 2.7 g / m. ２The adhesive was applied using a Mayer bar so that the ethyl acetate solvent was dried, and an adhesive-coated sample was obtained. The two-component curing polyurethane adhesive used was a mixture of 9.0 parts by mass of a urethane resin (manufactured by Mitsui Chemicals, Inc., product name: Takelac A525S), 1.0 part by mass of an isocyanate curing agent (manufactured by Mitsui Chemicals, Inc., product name: Takenate A50), and 7.5 parts by mass of ethyl acetate. The overall haze of the adhesive-coated sample was measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., NDH5000) in accordance with JIS K7136 (2000). The difference in haze before and after adhesive application was calculated using the formula "difference in haze before and after adhesive application = overall haze of packaging film - overall haze of adhesive-coated sample".

[0096] (9) Thermal expansion coefficient and thermal shrinkage coefficient of packaging film at 120°C The thermal expansion coefficient and thermal shrinkage coefficient of packaging 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 packaging film. Then, the test piece was heat-treated at 120°C for 15 minutes. At this time, the test piece was heated by hanging it without applying force in a hot air circulation type thermostatic oven (manufactured by ADVANTEC, product name: DRM620DE). Next, after cooling the test piece to room temperature, the length of the test piece was measured. Next, the length in the TD direction of the test piece after heat treatment was measured. １ [cm], and the thermal expansion coefficient in the TD direction [%] is 100 × (TD １ The length of the test piece in the MD direction after the heat treatment was calculated as follows: MD １ [cm], and the heat shrinkage rate [%] in the MD direction is calculated as 100 × (10 - MD １ The above measurement was carried out three times, and the average value was calculated as the measured value.

[0097] (10) Heat shrinkage of packaging film at 150°C The heat shrinkage of the packaging 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 the packaging film. Then, the test piece was heat-treated at 150°C for 15 minutes. At this time, the test piece was heated in a hot air circulation type thermostatic oven (manufactured by ADVANTEC, product name: DRM620DE) while hanging without applying force. Next, after cooling the test piece to room temperature, the length of the test piece was measured. Next, the length in the TD direction of the test piece after heat treatment was measured. １ The length of the test piece in the MD direction after heat treatment is defined as MD [cm]. １ When [cm], X ＴＤ [%] is 100 × (10-TD １ ) / 10, and X ＭＤ [%] is 100 x (10-MD １ The above measurement was carried out three times, and the average value was calculated as the measured value.

[0098] (11) Surface Roughness of Surface Layer (A) In accordance with JIS B0601 (1994), the arithmetic mean roughness (Ra) and ten-point mean roughness (Rz) of the surface of the surface layer (A) 103 opposite to the biaxially stretched film layer 101 side were measured using a three-dimensional surface measuring machine (manufactured by Kosaka Laboratory Co., Ltd., three-dimensional surface roughness measuring machine SE-3000) under the following measurement conditions. Measurement length: MD direction; 400 μm, TD direction; 1000 μm Number of measurements: Number of lines in TD direction; 201 Measurement pitch: MD direction; 0.5 μm, TD direction; 2 μm Z measurement magnification: 5000 Leveling: least squares method Z origin: zero point alignment by least squares method Stylus tip curvature radius: 2.0 μm / 60° C. Analysis software: "three-dimensional surface roughness analysis program" built into the device

[0099] (12) Lamination Treatment The corona-treated surface of a 60 μm-thick unstretched polypropylene film (manufactured by Mitsui Chemicals Tohcello, Inc., product name: RXC-22) was bonded to the adhesive-coated surface layer (A) of the packaging film so that the MD / TD of the surface layer was aligned, to produce a laminated packaging film. The adhesive used was a two-component curing polyurethane adhesive (a blend of 9.0 parts by mass of a urethane resin (manufactured by Mitsui Chemicals, Inc., product name: Takelac A525S), 1.0 part by mass of an isocyanate curing agent (manufactured by Mitsui Chemicals, Inc., product name: Takenate A50), and 7.5 parts by mass of ethyl acetate).

[0100] (13) High-Retort Treatment The packaging film after the lamination treatment obtained in (12) was subjected to high-retort treatment in a high-temperature, high-pressure retort sterilizer at 135°C for 30 minutes to obtain a packaging film after high-retort treatment.

[0101] (14) Thermal dimensional stability of packaging film after high retort treatment [Thermal expansion coefficient and thermal shrinkage coefficient of packaging film after high retort treatment] A test piece of 10 cm x 10 cm was cut out from the packaging film after lamination treatment obtained in (12). Then, high retort treatment was carried out by the method described in (13). Next, the length in the TD direction of the test piece after high retort treatment was measured. １ [cm], and the thermal expansion coefficient in the TD direction [%] is 100 × (TD １ The length of the test piece in the MD direction after high retort treatment was calculated as follows: MD １ [cm], and the heat shrinkage rate [%] in the MD direction is calculated as 100 × (10 - MD １ ) / 10. Samples with a thermal expansion coefficient [%] in the TD direction of 0.0% or more were rated as good. [Distortion of packaging film after high retort treatment] The packaging film after the high retort treatment obtained in (13) was visually observed and rated as follows: A (good): There were no wrinkles or the like in the packaging film, and no distortion was observed. B (poor): There were wrinkles or the like in the packaging film, and distortion was observed.

[0102] (15) Lamination strength of packaging film after high retort treatment For the packaging film after high retort treatment obtained in (13), the surface layer (A) of the packaging film and the unstretched polypropylene film were peeled off under the conditions of 15 mm width, 90-degree peel, and peel strength of 300 mm / min, and the peel strength at this time was taken as the laminate strength. Samples with a laminate strength of 2.5 N / 15 mm or more were rated as good. Samples with a laminate strength of 4.0 N / 15 mm or more were rated as very good because their laminate strength was equivalent to that of packaging films using polyethylene terephthalate (PET).

[0103] (16) Heat Seal Strength of Packaging Film After High Retort Treatment Two unstretched polypropylene packaging films obtained in (12) were stacked together with the MD / TD aligned, and heat-sealed under conditions of 170°C, 2.0 kgf pressure, and 1.0 second sealing time to obtain a laminated film. High retort treatment was then performed using the method described in (13). The test pieces after high retort treatment were then cut into 15 mm widths, and the two packaging films were peeled at a 90° peel angle, at a peel rate of 300 mm / min, and pulled in the TD direction. The peel strength measured at this time was taken as the heat seal strength. Samples with a heat seal strength of 25 N / 15 mm or more were rated as good. Samples with a heat seal strength of 25 N / 15 mm or more were equivalent to the heat seal strength of packaging films using polyethylene terephthalate (PET).

[0104] (17) Number of Bag Drops of Packaging Film After High Retort Treatment The packaging film after high retort treatment obtained in (13) was stacked with the unstretched polypropylene film side facing inward so that the MD / TD were aligned, and processed into a three-sided sealed bag measuring 175 mm in length (MD direction) x 125 mm in width (TD direction) with a seal width of 10 mm. This three-sided sealed bag was filled with 200 mL of water, sealed, and left to stand in a 5°C atmosphere for 24 hours or more. In the same atmosphere, the bag was dropped from a height of 30 cm from the side with a 1 kg weight of the same size as the bag attached, so that the horizontal direction was the drop direction. The bag was repeatedly dropped until it broke, and the number of bag breaks was counted. The above measurement was repeated five times, and the average value was taken as the number of bag drops. Samples with a number of bag drops of 6 or more were rated as good.

[0105] Examples 1 to 5 and Comparative Examples 1 and 2 Polypropylene films were extruded with the compositions shown in Table 1, and then biaxially stretched to produce packaging films. Evaluations were then performed. The results of each evaluation are shown in Table 1. The extrusion molding conditions and biaxial stretching conditions were as follows. Corona treatment was also performed on the surface of the surface layer (A) opposite the biaxially stretched film layer. Extruder: 60 mmφ multilayer T-die extruder (screw: L / D = 27, manufactured by Screw Seiki Co., Ltd.) Extrusion temperature setting: 230 to 250°C, Processing speed: 20 m / min (take-up speed). MD stretching temperature [°C]: shown in Table 1. MD stretch ratio [times]: shown in Table 1. TD stretching temperature [°C]: shown in Table 1. TD stretch ratio [times]: shown in Table 1. Relaxation rate [%]: shown in Table 1. Here, the relaxation rate refers to the maximum stretch ratio width in the device settings divided by the tenter exit width. In addition, the notation "A / B / C" for the stretching temperature in Table 1 means "preheating temperature (temperature at which the raw film is heated before stretching) / stretching temperature (temperature at which stretching is performed) / heat setting temperature (temperature at which heat setting (annealing) is performed after stretching)."

[0106]

[0107] From Table 1, it can be seen that the packaging films of the Examples were evaluated as being good in both the thermal dimensional stability and the number of bag drops of the samples after high retort treatment. Furthermore, the packaging films of the Examples were also evaluated as being good in lamination strength and heat seal strength. In other words, it can be seen that the packaging material using the packaging film of this embodiment has an improved performance balance between the thermal dimensional stability and bag tear resistance of the packaging material after high retort treatment.

[0108] This application claims priority based on Japanese Patent Application No. 2022-155454, filed on September 28, 2022, the disclosure of which is incorporated herein by reference in its entirety.

[0109] 100 Packaging film 101 Biaxially stretched film layer 103 Surface layer (A) 105 Surface layer (B)

Claims

1. A biaxially oriented film layer containing homopolypropylene; A packaging film comprising a surface layer (A) provided on at least one surface of the biaxially stretched film layer, A packaging film in which the content of structural units derived from α-olefins having a carbon number of 2 to 10 (α-olefins excluding propylene) is 1.5 mol % or more and 20.0 mol % or less, when the total number of moles of structural units derived from all monomers contained in the packaging film is 100 mol %.

2. The packaging film according to claim 1 , wherein the biaxially oriented film layer further comprises a random copolymer of propylene and an α-olefin having 2 to 10 carbon atoms (provided that the α-olefin does not include propylene).

3. The packaging film according to claim 2, wherein the content of the random copolymer in the biaxially oriented film layer is 5% by mass or more and 20% by mass or less when the total amount of all components contained in the biaxially oriented film layer is 100% by mass.

4. The packaging film according to claim 2 or 3, wherein the content of structural units derived from an α-olefin having 2 to 10 carbon atoms (α-olefins excluding propylene) is 2.0 mol % or more and 10.0 mol % or less when the total number of moles of structural units derived from all monomers contained in the random copolymer is taken as 100 mol %.

5. 4. The packaging film according to claim 2, wherein the MFR of the random copolymer, measured in accordance with ASTM D1238 at 230° C. under a load of 2.16 kg, is 0.01 g / 10 min or more and 30.0 g / 10 min or less.

6. The packaging film according to claim 2 or 3, wherein the melting point of the random copolymer as measured by DSC is 125° C. or higher and 150° C. or lower.

7. The packaging film according to any one of claims 1 to 3, wherein the homopolypropylene has an isotactic mesopentad fraction (mmmm) of 96.0% or more.

8. The packaging film according to any one of claims 1 to 3, wherein the surface layer (A) comprises at least one selected from the group consisting of a propylene block copolymer, a propylene-ethylene copolymer, and an ethylene-butene copolymer.

9. The packaging film according to any one of claims 1 to 3, wherein the arithmetic mean roughness (Ra) of at least one surface of the surface layer (A) is 40 nm or more, as measured by a three-dimensional surface measuring device in accordance with JIS B0601 (1994).

10. The packaging film according to any one of claims 1 to 3, wherein the ten-point average roughness (Rz) of at least one surface of the surface layer (A) is 600 nm or more, as measured by a three-dimensional surface measuring device in accordance with JIS B0601 (1994).

11. The packaging film according to any one of claims 1 to 3, wherein the packaging film has an external haze of 2.0% or more, measured in accordance with JIS K7136 (2000).

12. The packaging film according to any one of claims 1 to 3, wherein the internal haze of the packaging film, measured in accordance with JIS K7136 (2000), is 5.0% or less.

13. The packaging film according to any one of claims 1 to 3, which expands in the TD direction when heat-treated at 120 ° C. for 15 minutes in accordance with JIS C2151 (2019).

14. The packaging film according to any one of claims 1 to 3, which is used as a food packaging material.

15. The packaging film according to claim 14, which is used as a packaging material for retort food.

16. A packaging material using the packaging film according to any one of claims 1 to 3.

17. A packaging material according to claim 16; and a food product within the packaging material.