JP2024049162A - Packaging films, packaging materials and food packaging bodies - Google Patents

Abstract

[Problem] To provide a packaging film, packaging material, and food package that have an improved performance balance between thermal dimensional stability and bag tear resistance of the packaging material after high retort treatment. [Solution] The packaging film includes a biaxially oriented film layer 101 containing a propylene-based polymer and a surface layer (A) 103 provided on at least one side of the biaxially oriented film layer 101, and the difference in haze before and after application of an adhesive is 1.0% or more and 80.0% or less. [Selected Figure] Figure 1

Description

The present invention relates to packaging films, packaging materials, and food packages.

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

An example of a technology related to packaging films using such OPP films is described in Patent Document 1 (JP Patent Publication No. 2015-044406).

Patent Document 1 describes a matte-finished polypropylene laminated stretched film in which a polypropylene resin matte layer (B) having a three-dimensional average surface 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 describes that the laminated stretched polypropylene film can have a low shrinkage rate and high rigidity comparable to those of PET at 150° C., and can therefore be made thinner.

JP 2015-044406 A

In recent years, from the perspective of environmental issues, there has been a demand for packaging materials to be made of mono-materials.
However, in the case of conventional mono-material packaging materials using typical biaxially oriented polypropylene films, the thermal dimensional stability and bag rupture resistance of the packaging materials after high retort treatment (e.g., 135°C, 30 minutes) were sometimes insufficient.

The present invention was made in consideration of the above circumstances, and provides a packaging film, packaging material, and food package that have an improved performance balance between the thermal dimensional stability and bag tear resistance of the packaging material after high retort processing.

The present inventors have conducted extensive research to solve the above problems. As a result, they have discovered that a packaging film comprising a biaxially oriented film layer containing a propylene-based polymer and a surface layer (A) provided on at least one side of the biaxially oriented film layer, in which the difference in haze before and after adhesive application is 1.0% or more and 80.0% or less, improves the performance balance of the thermal dimensional stability and bag rupture resistance of the packaging material after high retort treatment, and have arrived at the present invention.

That is, the present invention provides the following packaging films, packaging materials, and food packages.

[1]
A biaxially stretched film layer containing a propylene-based polymer;
A packaging film comprising a surface layer (A) provided on at least one surface of the biaxially stretched film layer,
A packaging film having a difference in haze between before and after application of an adhesive, calculated by the following method 1, of 1.0% or more and 80.0% or less.
[Method 1]
A two-component curing polyurethane adhesive (a mixture of a urethane resin as a main agent, 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) so that the dry coating amount is 2.7 g/ ^m2 , and then the ethyl acetate solvent is dried to prepare an adhesive-coated sample. The difference in haze before and after adhesive coating is calculated by the formula "difference in haze before and after adhesive coating = total haze of the packaging film measured in accordance with JIS K7136 (2000) - total haze of the adhesive-coated sample measured in accordance with JIS K7136 (2000)".
[2]
The packaging film according to [1] above, wherein the adhesive-coated sample produced by the method 1 has an overall haze of 5.0% or less as measured in accordance with JIS K7136 (2000).
[3]
The packaging film according to [1] or [2] above, having an external haze of 2.0% or more as measured in accordance with JIS K7136 (2000).
[4]
The packaging film according to any one of [1] to [3] above, having an internal haze of 5.0% or less as measured in accordance with JIS K7136 (2000).
[5]
The packaging film according to any one of [1] to [4], wherein the surface layer (A) has an arithmetic mean roughness (Ra) of 40 nm or more as measured by a three-dimensional surface measuring machine in accordance with JIS B0601 (1994).
[6]
The packaging film according to any one of [1] to [5], wherein the surface layer (A) has a ten-point average roughness (Rz) of 600 nm or more as measured by a three-dimensional surface measuring machine in accordance with JIS B0601 (1994).
[7]
The packaging film according to any one of [1] to [6], wherein the content of structural units derived from α-olefins having 2 to 10 carbon atoms (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 %.
[8]
The packaging film according to any one of [1] to [7], wherein the propylene-based polymer includes homopolypropylene.
[9]
The packaging film according to any one of [1] to [8], wherein the biaxially oriented film layer further contains an α-olefin copolymer.
[10]
The packaging film according to [9], wherein the content of the α-olefin 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.
[11]
The packaging film according to [9] or [10] above, wherein the content of structural units derived from an α-olefin having a carbon number of 2 to 10 (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 α-olefin copolymer is taken as 100 mol %.
[12]
The packaging film according to any one of [9] to [11] above, wherein the α-olefin copolymer has an MFR of 0.01 g/10 min or more and 30.0 g/10 min or less, as measured in accordance with ASTM D1238 under conditions of 230° C. and a load of 2.16 kg.
[13]
The packaging film according to any one of [9] to [12] above, wherein the melting point of the α-olefin copolymer as measured by DSC is 60° C. or higher and 170° C. or lower.
[14]
The packaging film according to [8], wherein the isotactic mesopentad fraction (mmmm) of the homopolypropylene is 96.0% or more.
[15]
The packaging film according to any one of the above [1] to [14], wherein the surface layer (A) contains at least one selected from the group consisting of a propylene block copolymer, a propylene and ethylene copolymer, and an ethylene and butene copolymer.
[16]
The packaging film according to any one of [1] to [15], which expands in the TD direction when heat-treated at 120 ° C. for 15 minutes in accordance with JIS C2151 (2019).
[17]
The packaging film according to any one of [1] to [16] above, which is used as a food packaging material.
[18]
The packaging film according to [17] above, which is used as a packaging material for retort food.
[19]
A packaging material using the packaging film according to any one of [1] to [18] above.
[20]
The packaging material according to [19] above,
and a food product within the packaging material.

The present invention provides a packaging film, packaging material, and food package that have an improved performance balance between thermal dimensional stability and bag tear resistance of the packaging material after high retort processing.

FIG. 2 is a cross-sectional view showing a schematic example of the structure of the packaging film of the present embodiment. FIG. 2 is a cross-sectional view showing a schematic example of the structure of the packaging film of the present embodiment.

Below, an embodiment 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 ratio. Note that "~" between numbers in the text indicates "above" to "below" unless otherwise specified.

<Packaging film>
1 and 2 are cross-sectional views that diagrammatically show an example of the structure of a packaging film 100 according to the present embodiment.
The packaging film 100 of this embodiment is a packaging film comprising a biaxially oriented film layer 101 containing a propylene-based polymer and a surface layer (A) 103 provided on at least one side of the biaxially oriented film layer 101, and the difference in haze before and after application of the adhesive is 1.0% or more and 80.0% or less.

As described above, packaging films containing biaxially oriented polypropylene films are required to have an improved performance balance between thermal dimensional stability and bag rupture resistance of the packaging material after high retort treatment.
Here, according to the inventors' investigations, it was found that a packaging film in which the difference in haze before and after adhesive application is 1.0% or more and 80.0% or less can improve the performance balance of the thermal dimensional stability and bag rupture resistance of the packaging material after high retort treatment, which led to the present invention.
That is, according to a packaging material using the packaging film 100 of this embodiment, the performance balance of the thermal dimensional stability and bag rupture resistance of the packaging material after high retort treatment can be improved.
Furthermore, a packaging material using the packaging film 100 of this embodiment can improve the performance balance of the thermal dimensional stability, lamination strength, heat seal strength, and bag tear resistance of the packaging material after high retort processing.
In addition, according to the packaging film 100 of this embodiment, by applying an adhesive to the surface of the packaging film 100 and laminating other layers on the adhesive to produce a packaging material, it is possible to improve the transparency of the packaging material while improving the performance balance of the thermal dimensional stability, lamination strength, heat seal strength, and bag rupture resistance of the packaging material after high retort treatment.

In the packaging film 100 of this embodiment, the difference in haze before and after the application of the adhesive is 1.0% or more and 80.0% or less. In order to further improve the performance balance of the thermal dimensional stability and bag rupture resistance of the packaging material after high retort treatment, the difference in haze before and after the application of the adhesive of the packaging film 100 of this embodiment is 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, and in order to further improve the transparency of the packaging material, the difference is preferably 70.0% or less, more preferably 65.0% or less.
Here, the difference in haze before and after application of the adhesive is calculated by the following method 1.
[Method 1]
A two-component curing polyurethane adhesive (a mixture of a urethane resin as the main agent, 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) so that the dry coating amount is 2.7 g/ ^m2 , and then the ethyl acetate solvent is dried to prepare an adhesive-coated sample. The difference in haze before and after adhesive coating is calculated by the formula "difference in haze before and after adhesive coating = total haze of the packaging film measured in accordance with JIS K7136 (2000) - total haze of the adhesive-coated sample measured in accordance with JIS K7136 (2000)".
Here, 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 difference in haze of the packaging film 100 before and after application of adhesive 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, etc.

In the packaging film 100 of this embodiment, from the viewpoint of further improving the transparency of the packaging material, 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. 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 by the method 1 described above.
The overall haze of the adhesive-coated sample is measured using a haze meter in accordance with JIS K7136 (2000).

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 of the thermal dimensional stability and bag rupture resistance of the packaging material after high retort treatment, and preferably 80.0% or less, more preferably 70.0% or less, and even more preferably 65.0% or less, from the viewpoint of further improving the transparency of the packaging material.
The overall haze is an evaluation index for the unevenness of the surface of the packaging film. Large unevenness of the surface of the packaging film improves the adhesive strength when the packaging film is bonded to a non-oriented polypropylene film, and improves the performance balance of the thermal dimensional stability and bag rupture resistance of the packaging material.
The overall haze is measured by a haze meter in accordance with JIS K7136 (2000).

From the viewpoint of further improving the transparency of the packaging material, the packaging film 100 of this embodiment has an internal haze of 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. The lower limit of the internal haze is not particularly limited, and may be, for example, 0.1% or more, or 0.3% or more.
The internal haze is measured by a haze meter in accordance with JIS K7136 (2000).

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 of the thermal dimensional stability and bag rupture resistance of the packaging material after high retort treatment, and preferably 80.0% or less, more preferably 70.0% or less, and even more preferably 65.0% or less, from the viewpoint of further improving the transparency of the packaging material.
External haze is an evaluation index for the unevenness of the surface of a packaging film. Large unevenness on the surface of the packaging film improves the adhesive strength when the packaging film is bonded to a non-oriented polypropylene film, and improves the performance balance between the dimensional stability and the bag rupture resistance of the packaging material.
The external haze is calculated by the formula "external haze of the packaging film 100=total haze of the packaging film 100-internal haze of the packaging film 100".

The overall haze, internal haze, and external haze of the packaging film 100 can be adjusted, for example, by adjusting the constituent material, thickness, and stretch ratio of the biaxially stretched film layer 101, and the constituent material and thickness of the surface layer (A) 103, etc.

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 (wherein α-olefins exclude propylene) having a carbon number of 2 to 10 is preferably 1.5 mol% or more, 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 into a mono-material, it is preferably 20.0 mol% or less, more preferably 15.0 mol% or less, even 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 structural units derived from α-olefins (excluding propylene) having a carbon number of 2 or more and 10 or less 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 structural units derived from α-olefins having 2 to 10 carbon atoms (α-olefins excluding propylene) in the packaging film 100 can be measured by the method described in the Examples.

In the present embodiment, 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 processing, it is preferable that the packaging film 100 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 in the TD direction of the packaging film 100 when heated at 120°C for 15 minutes is, 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 suppressing the occurrence of wrinkles when the packaging film 100 is thermally processed, 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 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, 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 when the film is 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 out from the packaging film 100. The test piece is then heat-treated for 15 minutes at 120° C. The length of the test piece in the TD direction after the heat treatment is defined as TD ₁ [cm], and the thermal expansion coefficient in the TD direction [%] is calculated by 100 x (TD ₁ - 10)/10.

In addition, the heat shrinkage rate in the MD direction of the packaging film 100 when heated at 120°C for 15 minutes is, 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 reducing the elongation when the packaging film 100 is thermally processed, 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.
The thermal shrinkage rate of the packaging film 100 in the MD direction when the packaging film 100 is 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 out from the packaging film 100. The test piece is then heat-treated at 120° C. for 15 minutes. The length of the test piece in the MD direction after heat treatment is taken as MD ₁ [cm], and the heat shrinkage rate [%] in the MD direction is calculated by 100 x (10 - MD ₁ )/10.

In the packaging film 100, when 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 are X _TD [%] and X _MD [%], respectively, X _TD +X _MD 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, 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.
Moreover, X _TD [%] and X _MD [%] of the packaging film 100 are calculated by the following method.
A test piece of 10 cm x 10 cm is cut out from the packaging film 100. The test piece is then heat-treated at 150°C for 15 minutes. When the length of the test piece in the TD direction after the heat treatment is TD ₁ [cm] and the length of the test piece in the MD direction after the heat treatment is MD ₁ [cm], X _TD [%] is calculated by 100 x (10 - TD ₁ )/10, and X _MD [%] is calculated by 100 x (10 - MD ₁ )/10.

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.
In addition, the thermal expansion coefficient and thermal shrinkage coefficient of the packaging film 100 can be measured in accordance with JIS C2151 (2019).

From the viewpoint of further improving heat resistance, it is preferable that the thermal expansion coefficient in the TD direction of the packaging film 100 after the high retort treatment is such that the packaging film 100 expands in the TD direction.
More specifically, the thermal expansion coefficient in the TD direction of the packaging film 100 after high retort processing is preferably 0.1% or more, more preferably 0.2% or more, from the viewpoint of further improving heat resistance performance, and 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, from the viewpoint of further improving heat resistance performance.
The thermal expansion coefficient in the TD direction of the packaging film 100 after the high retort treatment is calculated by the method described in the Examples. That is, the thermal expansion coefficient in the TD direction of the packaging film 100 after the high retort treatment refers to the thermal expansion coefficient in the TD direction of the packaging film obtained by subjecting a laminate of the packaging film 100 and a sealant film to high retort treatment.

In addition, the thermal shrinkage rate in the MD direction of the packaging film 100 after high retort processing 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 performance of the packaging material, and may be 0.1% or more, 0.3% or more, or 0.5% or more, from the viewpoint of further improving the heat resistance performance of the packaging material.
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 subjecting a laminate obtained by laminating the packaging film 100 and a sealant film to high retort treatment.

From the viewpoint of further improving the strength of the packaging material, the lamination 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 subjecting the laminate, which is a laminate of the packaging film 100 and a sealant film, to high retort treatment.

From the viewpoint of further improving the strength of the packaging material, the heat seal strength of the packaging film 100 after the 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 the high retort treatment is measured by the method described in the Examples. That is, the heat seal strength of the packaging film 100 after the high retort treatment refers to the heat seal strength of the packaging film obtained by subjecting a laminate obtained by laminating the packaging film 100 and a sealant film to high retort treatment.

The number of times that the packaging film 100 is dropped 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 bag drops of the packaging film 100 after the high retort treatment is measured by the method described in the Examples. That is, the number of bag drops of the packaging film 100 after the high retort treatment refers to the number of bag drops of the packaging film obtained by subjecting the laminate of the packaging film 100 and a sealant film to the high retort treatment.

From the viewpoint of improving the balance of thermal dimensional stability, formability, water vapor barrier properties, cost, mechanical properties, transparency, bag formability, ease of handling, appearance, and light weight, 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.

The layers that make up the packaging film 100 are described below.

[Biaxially oriented film layer]
The biaxially stretched film layer 101 contains a propylene-based polymer.
The propylene-based polymer includes, for example, at least one selected from the group consisting of a propylene homopolymer, a propylene random copolymer, a propylene block copolymer, and the like.
The biaxially stretched film layer 101 is formed, for example, by biaxially stretching a film made of a propylene-based polymer composition containing homopolypropylene.

The biaxially stretched film layer 101 may be a single layer or may be a laminate of multiple layers made of a propylene-based polymer composition, but it is necessary that it is biaxially stretched.

From the viewpoint of further improving the balance of the thermal dimensional stability, formability, water vapor barrier properties, cost, mechanical properties, transparency, bag formability, handling properties, appearance, and light weight of the packaging film 100, 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, 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.

In the packaging film 100, the ratio of the thickness of the biaxially stretched 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.

The propylene-based polymer composition constituting the biaxially stretched film layer 101 of the present embodiment preferably 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 structural units derived from propylene 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, still more preferably 99.8 mol% or more, and is, for example, 100.0 mol% or less.

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 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, when the entire homopolypropylene is taken as 100 mol %.
The homopolypropylene in the biaxially oriented film layer 101 may be used alone or in combination of two or more kinds.

The content of homopolypropylene contained in the biaxially oriented film layer 101 of this embodiment is preferably 80% by mass or more, 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.

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 thermal dimensional stability, heat resistance, water vapor barrier properties, mechanical properties, rigidity, bag formability, and the like 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 and can be determined by a known method from ¹³ C-nuclear magnetic resonance (NMR) spectrum.
When two or more kinds of homopolypropylenes are used as the homopolypropylene, the isotactic mesopentad fraction of the homopolypropylene can be determined by melt blending the homopolypropylenes by a known method and subjecting the resulting mixture to ¹³ C-nuclear magnetic resonance (NMR) measurement.

From the viewpoint of further improving the balance of the thermal dimensional stability, heat resistance, water vapor barrier properties, mechanical properties, rigidity, bag formability, fluidity, moldability, etc. of the packaging film 100, 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, 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, the melting point of the homopolypropylene is the peak temperature of the maximum melting peak.

Homopolypropylene can be produced by various methods. For example, it can be produced using known catalysts such as Ziegler-Natta catalysts and metallocene catalysts.

The biaxially stretched film layer 101 of this embodiment preferably further contains an α-olefin copolymer.
Examples of the α-olefin copolymer include random copolymers of ethylene, propylene, 1-butene, and the like, and block copolymers of ethylene, propylene, 1-butene, and the like.
The α-olefin copolymer preferably comprises at least one selected from the group consisting of a random copolymer of propylene and an α-olefin (however, the α-olefin excludes propylene) and a block copolymer of propylene and an α-olefin (however, the α-olefin excludes propylene), more preferably comprises at least one selected from the group consisting of a random copolymer of propylene and an α-olefin having 2 to 10 carbon atoms (however, the α-olefin excludes propylene) and a block copolymer of propylene and an α-olefin having 2 to 10 carbon atoms (however, the α-olefin excludes propylene), and even more preferably comprises a random copolymer of propylene and an α-olefin having 2 to 10 carbon atoms (however, the α-olefin excludes propylene).
In the random copolymer of propylene and an α-olefin having from 2 to 10 carbon atoms (provided that the α-olefin excludes propylene), and in the block copolymer of propylene and an α-olefin having from 2 to 10 carbon atoms (provided that the α-olefin excludes propylene), the α-olefin having from 2 to 10 carbon atoms (provided that the α-olefin excludes propylene) preferably includes at least one selected from the group consisting of ethylene and α-olefins having from 4 to 6 carbon atoms, and more preferably includes at least one selected from the group consisting of ethylene and 1-butene.

The content of structural units derived from α-olefins having a carbon number of 2 to 10 (however, α-olefins exclude propylene) in the α-olefin copolymer 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 α-olefin copolymer is taken as 100 mol%, and 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, it is preferably 2.0 mol% or more, more preferably 3.0 mol% or more, and even more preferably 4.0 mol% or more, and from the viewpoint of making the packaging material into a mono-material, it 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.

The content of the α-olefin copolymer contained in the biaxially stretched film layer 101, when the total amount of all components contained in the biaxially stretched film layer 101 is taken as 100% by mass, is preferably 5% by mass or more, more preferably 8% by mass or more, and even more preferably 10% by mass 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 processing 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.

The MFR of the α-olefin copolymer 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, 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, 0.01 g/10 min or more, preferably 0.1 g/10 min or more, more preferably 0.5 g/10 min or more, even more preferably 1.0 g/10 min or more, and even more preferably 2.0 g/10 min or more, and 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, 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 α-olefin copolymers are used as the α-olefin copolymer, the MFR of the α-olefin copolymer can be the MFR of a mixture obtained by melt blending two or more types of α-olefin copolymers by a known method.

The melting point of the α-olefin copolymer contained in the biaxially stretched film layer 101 as measured by DSC is preferably 60° C. or higher, more preferably 80° C. or higher, even more preferably 100° C. or higher, even more preferably 110° C. or higher, even more preferably 125° C. or higher, even more preferably 130° C. or higher, and even more preferably 135° C. or higher, 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 170° C. or lower, more preferably 160° C. or lower, even more preferably 155° C. or lower, even more preferably 150° C. or lower, even more preferably 148° C. or lower, and even more preferably 145° C. or lower, 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.
When two or more kinds of α-olefin copolymers are used as the α-olefin copolymer, the melting point of the α-olefin copolymer is the peak temperature of the maximum melting peak.

The weight average molecular weight (Mw) of the α-olefin copolymer contained in the biaxially stretched film layer 101 is preferably 100,000 or more, more preferably 150,000 or more, even more preferably 200,000 or more, even more preferably 250,000 or more, and even more preferably 300,000 or more, from the viewpoint of further improving the performance balance of the thermal dimensional stability and 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 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 performance balance of the thermal dimensional stability and 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 α-olefin copolymer 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 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 ability, 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 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 ability.
When two or more types of α-olefin copolymers are used as the α-olefin copolymer, the weight average molecular weight (Mw) and number average molecular weight (Mn) of the α-olefin 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 α-olefin copolymers by a known method.

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.

α-Olefin copolymers can be produced by various methods. For example, they can be produced using known catalysts such as Ziegler-Natta catalysts and metallocene catalysts.

The propylene-based polymer composition constituting the biaxially stretched film layer 101 may contain 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, as necessary, to the extent that the purpose of this embodiment is not impaired.

The propylene-based polymer composition constituting the biaxially stretched film layer 101 can be prepared by mixing or melting and kneading each component 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.

[Surface layer (A)]
The packaging film 100 of this embodiment has a surface layer (A) 103 on at least one surface of a biaxially oriented film layer 101 .
The surface layer (A) 103 is preferably provided on the outermost layer of the packaging film 100 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.

It is preferable that the surface layer (A) 103 is provided so as to be in direct contact with the surface of the biaxially stretched film layer 101. This simplifies the manufacturing process of the packaging film 100.

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.

In the packaging film 100, it is preferable that the surface layer (A) 103 is a single layer. This can further simplify the manufacturing process of the packaging film 100.

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

The surface layer (A) 103 may be subjected to a surface treatment. Specifically, a surface activation treatment such as corona treatment, flame treatment, plasma treatment, primer coat treatment, ozone treatment, etc. is possible. It is preferable that the surface layer (A) 103 is subjected to a corona treatment from the viewpoint of further improving the performance balance of the laminate strength, heat seal strength, and bag tear resistance of the packaging material after high retort treatment.

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 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 of the thermal dimensional stability and bag rupture resistance of the packaging material after high retort treatment, more preferably contains at least one selected from the group consisting of a block copolymer of propylene and an α-olefin having 2 to 10 carbon atoms (however, the α-olefin excludes propylene), a copolymer of propylene and ethylene, and a copolymer of ethylene and butene, and even more preferably contains at least one selected from the group consisting of a block copolymer of propylene and an α-olefin having 2 to 6 carbon atoms (however, the α-olefin excludes propylene), a copolymer of propylene and ethylene, and a copolymer of ethylene and 1-butene.

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 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, 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, and is 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, from the viewpoint of making the packaging material into a mono-material.

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, and is preferably 100% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass 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 the high retort treatment.

The melting point of the polyolefin 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 60°C or higher, more preferably 65°C or higher, even more preferably 80°C or higher, even more preferably 100°C or higher, even more preferably 110°C or higher, even more preferably 125°C or higher, even more preferably 130°C or higher, and even more preferably 135°C or higher, from the viewpoint of further improving the balance of thermal dimensional stability and bag rupture resistance of the packaging material after high retort treatment. It is preferably 170°C or lower, more preferably 160°C or lower, even more preferably 155°C or lower, even more preferably 150°C or lower, even more preferably 149°C or lower, and even more preferably 148°C or lower.
When two or more types of polyolefins are used as the polyolefin selected from the group consisting of propylene block copolymers, propylene and ethylene copolymers, and ethylene and butene copolymers, the melting point of the polyolefin is the peak temperature of the maximum melting peak.

The polyolefin resin composition constituting the surface layer (A) 103 may contain various additives such as tackifiers, heat stabilizers, weather stabilizers, antioxidants, UV absorbers, lubricants, slipping agents, nucleating agents, antiblocking agents, antistatic agents, antifogging agents, pigments, dyes, and inorganic or organic fillers, as necessary, to the extent that the purpose of this embodiment is not impaired.

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

The arithmetic mean roughness (Ra) 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.

The ten-point average roughness (Rz) 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.

[Surface layer (B)]
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, it is preferable that the packaging film 100 further comprises a surface layer (B) 105 on the side opposite to the surface layer (A) 103 of the biaxially oriented film layer 101.
In addition, the surface layer (B) 105 is preferably provided as the outermost layer of the packaging film 100 in order to further improve the functions of the packaging film 100, such as heat resistance, heat sealability, antistatic properties, blocking resistance, printability, slip properties, etc., depending on the purpose.

It is preferable that the surface layer (B) 105 is provided so as to be in direct contact with the surface of the biaxially stretched film layer 101. This simplifies the manufacturing process of the packaging film 100.

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 sealability, antistatic properties, blocking resistance, printability, and slippage, 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 balance of the heat fusion resistance, thermal dimensional stability, formability, cost, mechanical properties, transparency, environmental compatibility, and light weight of the packaging film 100.

In the packaging film 100, it is preferable that the surface layer (B) 105 is a single layer. This makes it possible to further simplify the manufacturing process of the packaging film 100.

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

The surface layer (B) 105 may be subjected to a surface treatment. Specifically, a surface activation treatment such as corona treatment, flame treatment, plasma treatment, primer coating treatment, or ozone treatment may be performed.

The surface layer (B) 105 is made 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 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 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. 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.

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, when the total amount of all components contained in the surface layer (B) 105 is taken as 100% by mass.

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 (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 the handling properties during production of the packaging film 100 .

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

<Method of manufacturing packaging film 100>
The packaging 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 a polyolefin-based resin composition for forming the surface layer (A) 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, or the like 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 stretching temperature in the MD direction may be set to 100°C to 145°C, the stretching ratio in the MD direction may be set to a range of 4.5 to 6 times, the stretching temperature in the TD direction may be set to 130°C to 190°C, and the stretching ratio in the TD direction may be set to a range of 9 to 11 times.
The packaging film 100 can also be obtained by separately forming the biaxially oriented film layer 101 and the surface layer (A) 103, laminating them together, and subjecting them to heat forming.

<Applications 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.

<Packaging materials>
The packaging material of this embodiment is a packaging material using the packaging film 100 of this embodiment, and is, for example, a packaging material used for the purpose of containing food. Furthermore, the packaging material according to this embodiment may use the packaging film 100 in a part thereof or the packaging film 100 may be used in the entire packaging material depending on the application.

The packaging material of this embodiment is preferably retorted (e.g., at 127°C to 132°C for 20 minutes to 40 minutes), and more preferably high-retort (e.g., at 133°C to 138°C for 20 minutes to 40 minutes).

The package of this embodiment preferably includes a laminate including a packaging film 100, an adhesive layer, and a sealant layer in this order, and more preferably includes a laminate including a packaging film 100, an adhesive layer, and a sealant layer in this order, with the adhesive layer being provided on the surface of the surface layer (A) 103 opposite the biaxially stretched film layer 101.

The adhesive layer of the present embodiment may contain a known adhesive. Examples of the adhesive include laminate adhesives composed of organic titanium resin, polyethyleneimine resin, urethane resin, epoxy resin, acrylic resin, polyester resin, oxazoline group-containing resin, modified silicone resin, alkyl titanate, polyester polybutadiene, etc., or one-liquid or two-liquid polyol and polyisocyanate, water-based urethane, ionomer, etc. Alternatively, an aqueous adhesive whose main raw material is acrylic resin, vinyl acetate resin, urethane resin, polyester resin, etc. may be used.
From the viewpoint of further improving the heat resistance and water resistance of the packaging material, the adhesive layer of the present embodiment preferably contains an adhesive for dry lamination, typified by a polyurethane adhesive, and more preferably contains a solvent-based two-component curing type polyurethane adhesive.

The thickness of the adhesive layer in this embodiment is preferably 0.7 μm or more, more preferably 1.0 μm or more, even more preferably 2.0 μm or more, and even more preferably 2.5 μm or more, from the viewpoint of further improving the transparency of the packaging material, and is preferably 5.0 μm or less, more preferably 4.0 μm or less, and even more preferably 3.5 μm or less, from the viewpoint of making the packaging material into a mono-material.

The sealant layer of the present embodiment may be, for example, a layer formed of a resin composition containing one or more polyolefins selected from homopolymers or copolymers of α-olefins such as ethylene, propylene, butene-1, hexene-1, 4-methyl-1-pentene, octene-1, etc., polyethylenes such as high density polyethylene, medium density polyethylene, linear low density polyethylene, low density polyethylene, homopolypropylene, random copolymers of propylene with ethylene and α-olefins having 4 to 10 carbon atoms, low crystalline or amorphous ethylene-propylene random copolymers, etc., a layer formed of a resin composition containing ethylene-vinyl acetate copolymer (EVA), a layer formed of a resin composition containing EVA and polyolefin, etc. Among these, from the viewpoint of heat sealability, it is preferable to include one or more thermoplastic resins selected from low density polyethylene, linear low density polyethylene, homopolypropylene, and random copolymers of propylene with ethylene and α-olefins having 4 to 10 carbon atoms.

From the viewpoint of subjecting the packaging material of this embodiment to high retort processing, it is preferable that the sealant layer of this embodiment, which contains a thermoplastic resin, is unstretched.

The sealant layer of this embodiment may contain components other than the thermoplastic resin. For example, it may contain additives such as anti-fogging agents and anti-blocking agents, and adhesive resins such as urethane-based resins, urea-based resins, melamine-based resins, epoxy-based resins, and alkyd-based resins.

The thickness of the sealant layer in this embodiment is preferably 20 μm or more, more preferably 40 μm or more, and even more preferably 60 μm or more, from the viewpoint of further improving the performance balance of heat sealability, strength of the packaging material, and handling properties. The upper limit is not particularly limited, but may be, for example, 150 μm or less, 120 μm or less, or 100 μm or less.

The packaging material of this embodiment is manufactured, for example, by processing the laminate described above into a bag or the like.

<Food packaging>
The food package of the present embodiment includes the packaging material of the present embodiment and food contained in the packaging material. That is, the food package of the present embodiment is the food package of the present embodiment that contains food.

The above describes the embodiments of the present invention with reference to the drawings, but these are merely examples of the present invention, and various configurations other than those described above can also be adopted.

The present embodiment will be described in detail below with reference to examples and comparative examples. Note that the present embodiment is not limited in any way to the descriptions of these examples.

1. Raw Materials Raw materials used in the Examples and Comparative Examples are shown below.
(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%)

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 copolymers The content of structural units derived from α-olefins having 2 to 10 carbon atoms (α-olefins excluding propylene) in copolymers was measured by 13 C-NMR using a nuclear magnetic resonance apparatus (AVANCE III cryo-500 model, manufactured by Bruker Biospin). 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. The obtained ¹³ C-NMR spectrum was confirmed to be consistent with the results of 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 Distributions in Ethylene-Propylene Copolymers Prepared with a Stereoregular Catalyst. Signals were assigned with reference to the FT-IR System and the like, and the content (mol %) of ethylene-derived structural units, the content (mol %) of propylene-derived structural units, and the content (mol %) of 1-butene-derived structural units in the copolymer were each quantified.
[Measurement condition]
Measurement nucleus: ^13C (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: 50 mg/0.6 mL
Measurement temperature: 120°C
Window function: exponential (BF: 0.5 Hz)

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

(3) MFR of homopolypropylene and copolymer
The measurement was performed in accordance with ASTM D1238 at 230° C. and under a load of 2.16 kg.

(4) Melting point of homopolypropylene and copolymer Using a differential scanning calorimeter (product name: Q200DSC manufactured by TA Instruments), homopolypropylene and copolymer were subjected to a first differential scanning calorimeter measurement (1st Run) consisting of a process of increasing the temperature from -30°C to 250°C at a temperature increase rate of 10°C/min and a process of decreasing the temperature from 250°C to -30°C at a temperature decrease rate of 10°C/min under a nitrogen gas flow, 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 temperature increase 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.

(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 the 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 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 a detector. The molecular weight was calculated as polypropylene equivalent molecular weight using monodisperse polystyrene as a standard.

(6) Isotactic mesopentad fraction of homopropylene (mmmm)
The isotactic mesopentad fraction (mmmm) was measured by ¹³ C-NMR using a nuclear magnetic resonance apparatus (AVANCE III cryo-500 model, manufactured by Bruker Biospin). The sample was dissolved in the following measurement solvent and the measurement was performed, and the isotactic mesopentad fraction (mmmm) was evaluated from the integrated intensity of each signal.
[Measurement condition]
Measurement nucleus: ^13C (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: 50 mg/0.6 mL
Measurement temperature: 120°C
Window function: exponential (BF: 0.5 Hz)
Chemical shift reference: mmmm (CH ₃ ): 21.59 ppm

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

(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 according to the formula "external haze of packaging film = overall haze of packaging film - internal haze of packaging film".
[Haze of adhesive-coated samples]
A two-component curing polyurethane adhesive was applied to the surface of the surface layer (A) 103 with a Mayer bar so that the dry coating amount was 2.7 g/ ^m2 , and then the solvent, ethyl acetate, was dried to obtain an adhesive-coated sample. 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 in accordance with JIS K7136 (2000) using a haze meter (NDH5000, manufactured by Nippon Denshoku Industries Co., Ltd.) 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".

(9) Thermal expansion coefficient and thermal shrinkage coefficient of packaging film at 120 ° C. The thermal expansion coefficient and thermal shrinkage coefficient of the packaging film at 120 ° C. were measured in accordance with JIS C2151 (2019).
First, a test piece of 10 cm x 10 cm was cut out from the packaging 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.
Next, the length in the TD direction of the test piece after the heat treatment was taken as TD ₁ [cm], and the thermal expansion coefficient [%] in the TD direction was calculated by 100 × (TD ₁ - 10) / 10. The length in the MD direction of the test piece after the heat treatment was taken as MD ₁ [cm], and the thermal shrinkage coefficient [%] in the MD direction was calculated by 100 × (10 - MD ₁ ) / 10. The above measurement was carried out three times, and the average values of the measured values were used as the thermal expansion coefficient and the thermal shrinkage coefficient of the packaging film at 120 ° C., respectively.

(10) Heat shrinkage rate of packaging film at 150 ° C. The heat shrinkage rate of the packaging film at 150 ° C. was measured in accordance with JIS C2151 (2019).
First, a test piece of 10 cm x 10 cm was cut out from the packaging 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. The test piece was then cooled to room temperature, and the length of the test piece was measured.
Next, when the length in the TD direction of the test piece after the heat treatment was taken as TD ₁ [cm] and the length in the MD direction of the test piece after the heat treatment was taken as MD ₁ [cm], X _TD [%] was calculated by 100 × (10 - TD ₁ ) / 10, and X _MD [%] was calculated by 100 × (10 - MD ₁ ) / 10. The above measurement was carried out three times, and the average of the obtained measured values was adopted as the heat shrinkage rate of the packaging film at 150 ° C.

(11) Surface Roughness of Surface Layer (A) 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 in accordance with JIS B0601 (1994) using a three-dimensional surface measuring device (manufactured by Kosaka Laboratory Co., Ltd., three-dimensional surface roughness measuring device SE-3000) under the following measurement conditions.
Measurement length: MD direction: 400 μm, TD direction: 1000 μm
Number of lines measured: TD direction Number of lines: 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 using least squares method Stylus tip curvature radius: 2.0 μm/60° C.
Analysis software: Built-in "3D surface roughness analysis program"

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

(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.

(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 the lamination treatment obtained in (12). Then, a high retort treatment was performed by the method described in (13). Next, the length in the TD direction of the test piece after the high retort treatment was taken as TD ₁ [cm], and the thermal expansion coefficient in the TD direction [%] was calculated by 100 x (TD ₁ -10)/10. In addition, the length in the MD direction of the test piece after the high retort treatment was taken as MD ₁ [cm], and the thermal shrinkage coefficient in the MD direction [%] was calculated by 100 x (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-temperature retort processing]
The packaging film after the high retort treatment obtained in (13) was visually observed and evaluated as follows.
A (good): The packaging film is free of wrinkles and distortion.
B (bad): The packaging film had wrinkles or other imperfections, and distortion was observed.

(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 the laminate strength was equivalent to that of packaging films using polyethylene terephthalate (PET).

(16) Heat seal strength of packaging film after high retort treatment The unstretched polypropylene of the two packaging films obtained in (12) after the lamination treatment was stacked so that the MD/TD were aligned, and a laminated film was obtained by heat fusing under conditions of 170°C, pressure of 2.0 kgf, and sealing time of 1.0 seconds. Next, high retort treatment was performed by the method described in (13). Next, the test piece after the high retort treatment was cut into a width of 15 mm, and the two packaging films were peeled under conditions of 90° peeling, peeling speed of 300 mm/min, and tension in the TD direction, and the peel strength at that time was determined as the heat seal strength.
The samples with a heat seal strength of 25 N/15 mm or more were rated as good. The heat seal strength of the samples with a heat seal strength of 25 N/15 mm or more is equivalent to the heat seal strength of packaging films using polyethylene terephthalate (PET).

(17) Number of times the packaging film after high retort treatment was dropped The packaging film after high retort treatment obtained in (13) was stacked with the non-oriented polypropylene film side on the inside so that the MD/TD were aligned, and processed into a three-sided sealed bag with a length (MD direction) of 175 mm x width (TD direction) of 125 mm and 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 a surface part to which a 1 kg weight of the same size as the bag size was attached, so that the horizontal direction was the drop direction. The bag was repeatedly dropped until it broke, and the number of times it broke was counted. The above measurement was repeated five times, and the average value was taken as the number of times the bag was dropped.
Samples with six or more dropped bags were rated as good.

[Examples 1 to 5 and Comparative Examples 1 to 2]
Polypropylene films having the compositions shown in Table 1 were extruded and then biaxially stretched to produce packaging films, which were then evaluated. The extrusion conditions and biaxial stretching conditions were as follows. The surface of the surface layer (A) opposite to the biaxially stretched film layer was subjected to corona treatment.
Extrusion molding machine: 60 mmφ multi-layer T-die extrusion molding machine (screw: L/D=27, manufactured by Screw Seiki Co., Ltd.)
Extrusion temperature setting: 230 to 250°C, processing speed: 20 m/min (winding speed)
Stretching temperature in MD direction [°C]: See Table 1. Stretching ratio in MD direction [times]: See Table 1. Stretching temperature in TD direction [°C]: See Table 1. Stretching ratio in TD direction [times]: See Table 1. Relaxation rate [%]: See Table 1. Here, the relaxation rate refers to the maximum stretching 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 for heating the original film before stretching)/stretching temperature (temperature during stretching)/heat setting temperature (temperature during heat setting (annealing) after stretching)".

From Table 1, it can be seen that the packaging film of the example was evaluated as being good in both the thermal dimensional stability and the number of bag drops of the sample after high retort treatment. Furthermore, the packaging film of the example was also evaluated as being good in the lamination strength and heat seal strength. In other words, it can be seen that the packaging material using the packaging film of this embodiment improves the performance balance of the thermal dimensional stability and bag tear resistance of the packaging material after high retort treatment.

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

Claims (20)

A biaxially stretched film layer containing a propylene-based polymer;
A packaging film comprising a surface layer (A) provided on at least one surface of the biaxially stretched film layer,
A packaging film having a difference in haze between before and after application of an adhesive, calculated by the following method 1, of 1.0% or more and 80.0% or less.
[Method 1]
A two-component curing polyurethane adhesive (a mixture of a urethane resin as a main agent, 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) so that the dry coating amount is 2.7 g/ ^m2 , and then the ethyl acetate solvent is dried to prepare an adhesive-coated sample. The difference in haze before and after adhesive coating is calculated by the formula "difference in haze before and after adhesive coating = overall haze of the packaging film measured in accordance with JIS K7136 (2000) - overall haze of the adhesive-coated sample measured in accordance with JIS K7136 (2000)". The packaging film according to claim 1, wherein the overall haze of the adhesive-coated sample produced by method 1, as measured in accordance with JIS K7136 (2000), is 5.0% or less. The packaging film according to claim 1 or 2, which has an external haze of 2.0% or more as measured in accordance with JIS K7136 (2000). The packaging film according to any one of claims 1 to 3, which has an internal haze of 5.0% or less, measured in accordance with JIS K7136 (2000). The packaging film according to any one of claims 1 to 4, wherein the arithmetic mean roughness (Ra) 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). The packaging film according to any one of claims 1 to 5, wherein the ten-point average roughness (Rz) 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). The packaging film according to any one of claims 1 to 6, 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 %. The packaging film according to any one of claims 1 to 7, wherein the propylene-based polymer includes homopolypropylene. The packaging film according to any one of claims 1 to 8, wherein the biaxially oriented film layer further contains an α-olefin copolymer. The packaging film according to claim 9, wherein the content of the α-olefin 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. The packaging film according to claim 9 or 10, in which the content of structural units derived from α-olefins having a carbon number of 2 to 10 (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 α-olefin copolymer is taken as 100 mol %. The packaging film according to any one of claims 9 to 11, wherein the MFR of the α-olefin copolymer, measured in accordance with ASTM D1238 at 230°C and a load of 2.16 kg, is 0.01 g/10 min or more and 30.0 g/10 min or less. The packaging film according to any one of claims 9 to 12, wherein the melting point of the α-olefin copolymer measured by DSC is 60°C or higher and 170°C or lower. The packaging film according to claim 8, wherein the isotactic mesopentad fraction (mmmm) of the homopolypropylene is 96.0% or more. The packaging film according to any one of claims 1 to 14, 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. The packaging film according to any one of claims 1 to 15, which expands in the TD direction when heat-treated at 120°C for 15 minutes in accordance with JIS C2151 (2019). The packaging film according to any one of claims 1 to 16, which is used as a food packaging material. The packaging film according to claim 17, which is used as a packaging material for retort food. A packaging material using the packaging film according to any one of claims 1 to 18. A packaging material according to claim 19;
and a food product within the packaging material.

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