JP7321682B2 - Food packaging film and food package - Google Patents

Description

TECHNICAL FIELD The present invention relates to food packaging films 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 property, transparency, mechanical strength and rigidity, and is used as a packaging film for packaging food. It is

Technologies related to food packaging films using such OPP films include, for example, those described in Patent Document 1 (Japanese Patent Application Laid-Open No. 2008-73926) and Patent Document 2 (Japanese Patent Application Laid-Open No. 2004-82499). be done.

Patent Document 1 describes a biaxially stretched film made of a propylene polymer composition containing 75 to 90% by weight of a propylene homopolymer (A) and 25 to 10% by weight of a tackifier (D). A layer comprising a propylene/α-olefin random copolymer (C) having a melting point in the range of 125 to 145° C. is interposed between the layers comprising the above propylene-based polymer (B), and in addition to the above biaxially stretched film describes a biaxially oriented multilayer polypropylene film characterized by having a layer comprising a propylene-based polymer (E) on one side.
Patent Literature 1 describes that the biaxially oriented multilayer polypropylene film having the structure described above can suppress exudation of petroleum resin or the like onto the film surface and is excellent in lamination strength and moisture resistance.

In Patent Document 2, an adhesive layer is applied to at least one surface of a biaxially oriented polypropylene resin layer containing 10 to 40% by weight of a highly crystalline resin and 6 to 15% by weight of a petroleum resin. , a multilayer resin film further having a polyvinyl alcohol-based resin layer, wherein the oxygen permeability at a relative humidity of 85% RH and a temperature of 23 ° C. is 600 mL / m ² day MPa or less, and the relative humidity is 90% A multilayer resin film characterized by having a water vapor transmission rate of 3.5 g/m ² ·day·20 µm or less at RH and a temperature of 40°C is described.
Patent Document 2 describes that the multilayer resin film having the structure described above has excellent oxygen gas barrier properties and moisture resistance.

JP-A-2008-73926 JP-A-2004-82499

OPP films are required to have further improved water vapor barrier properties from the viewpoint of reducing environmental impact. When the water vapor barrier property is improved, the thickness of the OPP film can be reduced, so the amount of propylene-based polymer used can be reduced, and the environmental load can be reduced.
Here, according to the studies of the present inventors, it was found that the use of a highly crystalline propylene-based polymer as the propylene-based polymer constituting the OPP film can improve the water vapor barrier properties of the OPP film. . However, it has become clear that the use of such a highly crystalline propylene-based polymer tends to cause stretching unevenness, and the thickness unevenness of the OPP film obtained after the biaxial stretching step may increase.
Thus, the inventors have found that there is a trade-off relationship between the water vapor barrier property and the thickness unevenness in the OPP film. In other words, the present inventors have found that the OPP film has room for improvement in terms of improving both the improved water vapor barrier property and the suppression of thickness unevenness in a well-balanced manner.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides a food packaging film having reduced unevenness in thickness and improved water vapor barrier properties.

The present inventors have made intensive studies to solve the above problems. As a result, as the propylene-based polymer constituting the biaxially stretched film layer, a first propylene-based polymer having a melting point measured by DSC in the range of 130°C to 162°C and a melting point measured by DSC of 162°C to 180°C were found. The present inventors have found that a food packaging film with reduced thickness unevenness and improved water vapor barrier properties can be obtained by using a second propylene-based polymer within the following range in combination, leading to the present invention.

That is, according to the present invention, the following food packaging film and food package are provided.

[1]
A film for packaging food,
comprising a biaxially stretched film layer comprising a propylene-based polymer;
The propylene-based polymer includes a first propylene-based polymer having a melting point in the range of 130°C to 162°C as measured by DSC, and a second propylene-based polymer having a melting point in the range of 162°C to 180°C as measured by DSC. Food packaging films, including coalescing and.
[2]
In the food packaging film described in [1] above,
When the total amount of the first propylene polymer and the second propylene polymer contained in the biaxially stretched film layer is 100% by mass, the second propylene polymer in the biaxially stretched film layer A food packaging film having a content of 1% by mass or more and 85% by mass or less.
[3]
In the food packaging film according to [1] or [2] above,
A food packaging film, wherein the second propylene-based polymer has an isotactic mesopentad fraction (mmmm) of 96.0% or more.
[4]
In the food packaging film according to any one of [1] to [3] above,
According to JIS K7127 (1999), measured using a tensile tester under the conditions of a measurement temperature of 23 ± 2 ° C., 50 ± 5% RH, and a tensile speed of 300 mm / min, the MD direction tensile of the food packaging film A food packaging film having a total value (T ₁ +T ₂ ) of an elastic modulus T ₁ and a tensile elastic modulus T ₂ in the TD direction of 5,000 MPa or more and 10,000 MPa or less.
[5]
In the food packaging film according to any one of [1] to [4] above,
A food packaging film further comprising a heat seal layer on at least one side of said biaxially oriented film layer.
[6]
In the food packaging film according to [5] above,
The food packaging film, wherein the heat seal layer is provided so as to be in direct contact with the one surface of the biaxially stretched film layer.
[7]
In the food packaging film according to [5] or [6] above,
A food packaging film in which the heat seal layer contains one or more selected from homopolypropylene and random copolymers of propylene and α-olefins having 2 to 10 carbon atoms.
[8]
In the food packaging film according to any one of [1] to [7] above,
A food packaging film further comprising a surface layer on one side of said biaxially oriented film layer.
[9]
In the food packaging film according to [8] above,
The food packaging film, wherein the surface layer comprises an anti-blocking agent.
[10]
In the food packaging film according to [8] or [9] above,
The food packaging film, wherein the surface layer comprises one or more selected from homopolypropylene and random copolymers of propylene and α-olefins having 2 to 10 carbon atoms.
[11]
In the food packaging film according to any one of [1] to [10] above,
A food packaging film, wherein the content of the tackifier contained in the biaxially stretched film layer is 10% by mass or less when the entire biaxially stretched film layer is taken as 100% by mass.
[12]
In the food packaging film according to any one of [1] to [11] above,
A food packaging film having a water vapor transmission rate of 6.0 g/(m ² ·24 h) or less as measured by the following method.
(Measuring method)
The food packaging film is folded back so that the heat-seal layer faces the inside, and the two sides are heat-sealed to form a bag. After that, calcium chloride is added as the content. The other side is then heat-sealed to form a bag having a surface area of 0.01 m ² . The resulting bag is then stored for 72 hours under conditions of 40° C. and 90% RH. The weight of calcium chloride before and after storage is measured, and the water vapor permeability (g/(m ² ·24h)) is calculated from the difference.
[13]
In the food packaging film according to any one of [1] to [12] above,
Food packaging film used for outer packaging bags.
[14]
A food package using the food packaging film according to any one of [1] to [13] above.

According to the present invention, it is possible to provide a food packaging film with reduced unevenness in thickness and improved water vapor barrier properties.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which showed typically an example of the structure of the food packaging film of embodiment which concerns on this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which showed typically an example of the structure of the food packaging film of embodiment which concerns on this invention.

An embodiment of the present invention will be described below with reference to the drawings. It should be noted that the drawings are schematic diagrams and do not correspond to actual dimensional ratios. In addition, unless otherwise specified, "~" between numbers in the text represents the following from the above.

<Food packaging film>
1 and 2 are cross-sectional views schematically showing an example of the structure of a food packaging film 100 according to an embodiment of the present invention.
The food packaging film 100 according to the present embodiment is a film for packaging food, and includes a biaxially stretched film layer 101 containing a propylene-based polymer, and the propylene-based polymer has a melting point measured by DSC. A first propylene-based polymer having a melting point in the range of 130° C. or higher and 162° C. or lower and a second propylene-based polymer having a melting point measured by DSC in the range of higher than 162° C. and 180° C. or lower are included. As a result, it is possible to realize a food packaging film with reduced unevenness in thickness and improved water vapor barrier properties.

As described above, OPP films are required to have further improved water vapor barrier properties from the viewpoint of reducing environmental impact. When the water vapor barrier property is improved, the thickness of the OPP film can be reduced, so the amount of propylene-based polymer used can be reduced, and the environmental load can be reduced.
Here, according to the studies of the present inventors, it was found that the use of a highly crystalline propylene-based polymer as the propylene-based polymer constituting the OPP film can improve the water vapor barrier properties of the OPP film. . However, it has become clear that the use of such a highly crystalline propylene-based polymer tends to cause stretching unevenness, and the thickness unevenness of the OPP film obtained after the biaxial stretching step may increase.
Thus, the inventors have found that there is a trade-off relationship between the water vapor barrier property and the thickness unevenness in the OPP film. In other words, the present inventors have found that the OPP film has room for improvement in terms of improving both the improved water vapor barrier property and the suppression of thickness unevenness in a well-balanced manner.

The present inventors have made intensive studies to solve the above problems. As a result, as the propylene-based polymer constituting the biaxially stretched film layer, a first propylene-based polymer having a melting point measured by DSC in the range of 130°C to 162°C and a melting point measured by DSC of 162°C to 180°C were found. It has been found that a food packaging film with reduced thickness unevenness and improved water vapor barrier properties can be obtained by using a second propylene-based polymer within the following range in combination.
That is, according to the food packaging film 100 according to the present embodiment, it is possible to realize a food package with small unevenness in thickness and improved water vapor barrier properties.
Moreover, according to the food packaging film 100 according to the present embodiment, since the water vapor barrier property can be improved, sufficient water vapor barrier property can be obtained even if the thickness of the biaxially stretched film layer 101 is made thinner. Therefore, according to the food packaging film 100 according to the present embodiment, it is possible to reduce the amount of the propylene-based polymer used in the food packaging film and package, thereby reducing the environmental load.
As described above, according to the present embodiment, it is possible to realize an environment-friendly food package having sufficient water vapor barrier properties, and a food package with small thickness unevenness and excellent appearance, packaging aptitude, and bag-making properties. A film 100 can be provided.

The biaxially stretched film layer 101 containing a propylene-based polymer according to the present embodiment includes a first propylene-based polymer having a melting point in the range of 130° C. or higher and 162° C. or lower as measured by DSC, and and a second propylene-based polymer having a melting point in the range of more than 162° C. and 180° C. or less. As a result, both the improvement of the water vapor barrier property and the suppression of thickness unevenness can be improved in a well-balanced manner. Although the reason for this is not clear, the following reasons are conceivable.
First, since the biaxially stretched film layer 101 contains the first propylene-based polymer, it is possible to reduce stretching unevenness due to crystallization of the biaxially stretched film layer 101. As a result, the biaxially stretched film layer 101 is stretched. It is thought that the thickness unevenness that sometimes occurs can be reduced. In addition, since the biaxially stretched film layer 101 contains the second propylene-based polymer, the crystallinity of the biaxially stretched film layer 101 can be increased. It is considered that the barrier property can be improved.

The food packaging film 100 according to the present embodiment conforms to JIS K7127 (1999) and is measured using a tensile tester under conditions of a measurement temperature of 23 ± 2 ° C., 50 ± 5% RH, and a tensile speed of 5 mm / min. The total value (T ₁ + T ₂ ) of the tensile elastic modulus T ₁ in the MD direction and the tensile elastic modulus T ₂ in the TD direction is preferably 5000 MPa or more, more preferably 6000 MPa or more, and 7000 MPa or more is more preferably 7100 MPa or more, preferably 10000 MPa or less, more preferably 9000 MPa or less, even more preferably 8000 MPa or less, and particularly preferably 7500 MPa or less.
When the total value (T ₁ +T ₂ ) of the tensile elastic modulus T ₁ in the MD direction and the tensile elastic modulus T ₂ in the TD direction is equal to or greater than the above lower limit, the heat sealability of the food packaging film 100 according to the present embodiment , a good balance between water vapor barrier properties and transparency can be achieved. Furthermore, the food packaging film 100 according to the present embodiment can be made to have good stiffness, and as a result, it is possible to suppress positional deviation of the film during heat sealing, and it is possible to suppress the occurrence of sealing defects. .
That is, when the total value (T ₁ +T ₂ ) of the tensile elastic modulus T ₁ in the MD direction and the tensile elastic modulus T ₂ in the TD direction is equal to or greater than the above lower limit, the heat of the food packaging film 100 according to the present embodiment A good balance can be achieved between sealing properties, water vapor barrier properties, transparency and packaging suitability.
Further, when the total value (T ₁ +T ₂ ) of the tensile elastic modulus T ₁ in the MD direction and the tensile elastic modulus T ₂ in the TD direction is equal to or less than the above upper limit, troubles such as cutting during film forming are less likely to occur. As a result, the film can be easily stretched continuously, and industrial continuous productivity can be improved.
Such a tensile modulus is a substitute value for quantitatively measuring the stiffness of the film. It can be achieved by adjusting various conditions at the time of treatment. More specifically, the combination of the first propylene-based polymer and the second propylene-based polymer as the propylene-based polymer constituting the biaxially stretched film layer 101, the stretching ratio during stretching, and the stretching temperature The tensile modulus of the food packaging film 100 can be adjusted by appropriately adjusting the temperature, time, etc. of the heat treatment.

Here, the food package produced using the food packaging film 100 according to this embodiment exhibits sufficient performance in terms of water vapor barrier properties. Therefore, it can be particularly suitably used as a film constituting a food package for packaging foods (for example, dry foods) that require water vapor barrier properties but do not require much oxygen barrier properties.

A food package produced using the food packaging film 100 according to this embodiment has sufficient water vapor barrier properties. In the food packaging film 100, from the viewpoint of stably obtaining a food package having excellent water vapor barrier properties, the water vapor transmission rate measured by the following method should be 6.0 g/(m ² 24 h) or less. is preferably 5.5 g/(m ² ·24 h) or less, and more preferably 5.0 g/(m ² ·24 h) or less.
(Measuring method)
The food packaging film 100 is folded so that the heat-seal layer 103 faces inside, and the two sides are heat-sealed to form a bag. After that, calcium chloride is added as the content. The other side is then heat-sealed to form a bag having a surface area of 0.01 m ² . The resulting bag is then stored for 72 hours under conditions of 40° C. and 90% RH. The weight of calcium chloride before and after storage is measured, and the water vapor permeability (g/(m ² ·24h)) is calculated from the difference.
Such water vapor permeability is, for example, the DSC characteristics of the biaxially stretched film layer 101 such as the endothermic peak characteristics and exothermic peak characteristics described above, the content of the propylene-based polymer contained in the biaxially stretched film layer 101, the heat seal It can be achieved by adjusting the constituent material, thickness, etc. of the layer 103 .

Although the thickness of the food packaging film 100 according to the present embodiment is not particularly limited, it can be arbitrarily set according to desired purposes such as water vapor barrier properties, cost, mechanical strength, transparency, etc., and is not particularly limited. , for example, 5 μm or more and 100 μm or less, preferably 10 μm or more and 50 μm or less, more preferably 15 μm or more and 40 μm or less.
When the thickness of the food packaging film 100 is within the above range, the bag-making properties, mechanical properties, handleability, appearance, transparency, moldability, lightness, etc. are well balanced.

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

[Biaxially stretched film layer]
The biaxially stretched film layer 101 (also referred to as a biaxially stretched polypropylene film layer) according to the present embodiment is formed by, for example, biaxially stretching a film composed of a propylene-based polymer composition containing a propylene-based polymer. It is formed by

The biaxially stretched film layer 101 according to the present embodiment may be a single layer, or may be a structure in which a plurality of layers made of a propylene-based polymer composition are laminated, but it may be biaxially stretched. is necessary.

In addition, in the food packaging film 100, the ratio of the thickness of the biaxially stretched film layer 101 to the total thickness of the food packaging film 100 is preferably 50% or more and 100% or less, more preferably 60% or more and 99%. or less, more preferably 70% or more and 97% or less, and particularly preferably 75% or more and 95% or less.

(Propylene polymer composition)
The propylene-based polymer composition according to this embodiment contains a propylene-based polymer.
The content of the propylene-based polymer contained in the propylene-based polymer composition according to the present embodiment, that is, the biaxially stretched film layer 101, is preferably 50% by mass when the entire propylene-based polymer composition is taken as 100% by mass. % or more and 100 mass % or less, more preferably 70 mass % or more and 100 mass % or less, still more preferably 90 mass % or more and 100 mass % or less, and particularly preferably 95 mass % or more and 100 mass % or less. This makes it possible to improve the balance of film stiffness, water vapor barrier properties, mechanical properties, handleability, appearance, moldability, and the like.

(Propylene polymer)
Examples of the propylene-based polymer according to the present embodiment include propylene homopolymers, copolymers of propylene and ethylene or α-olefins having 4 to 20 carbon atoms, and the like. Examples of the α-olefins having 4 to 20 carbon atoms include 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicosene and the like. Among these, ethylene or an α-olefin having 4 to 10 carbon atoms is preferred, and ethylene is more preferred. These α-olefins may form random copolymers or block copolymers with propylene. The content of structural units derived from ethylene or an α-olefin having 4 to 20 carbon atoms is preferably 5 mol% or less, and 2 mol% or less when the entire propylene-based polymer is 100 mol%. is more preferable. The propylene-based polymer in the biaxially stretched film layer 101 may be used singly or in combination of two or more.
Among these, a propylene homopolymer is preferable as the propylene-based polymer from the viewpoint of obtaining a biaxially stretched film layer 101 having a more excellent performance balance such as heat resistance, water vapor barrier properties, mechanical properties and rigidity.

As described above, the propylene-based polymer contained in the biaxially stretched film layer 101 according to the present embodiment has a melting point measured by DSC of 130° C. or higher and 162° C. or lower, preferably 133° C. or higher and 162° C. or lower. 1 propylene-based polymer and a second propylene-based polymer having a melting point of more than 162° C. and 180° C. or less, preferably 163° C. or more and 175° C. or less, as measured by DSC.
When the total amount of the first propylene-based polymer and the second propylene-based polymer contained in the biaxially stretched film layer 101 is 100% by mass, the content of the second propylene-based polymer is From the viewpoint of improving water vapor barrier properties, the content is preferably 1% by mass or more, more preferably 10% by mass or more, even more preferably 25% by mass or more, and even more preferably 35% by mass or more. It is preferably 50% by mass or more, and particularly preferably 50% by mass or more.
Further, when the total amount of the first propylene-based polymer and the second propylene-based polymer contained in the biaxially stretched film layer 101 is 100% by mass, the content of the second propylene-based polymer is From the viewpoint of further suppressing thickness unevenness of 100, the content is preferably 85% by mass or less, more preferably 75% by mass or less, and even more preferably 70% by mass or less.

Moreover, in the present embodiment, the second propylene-based polymer is preferably a highly stereoregular propylene-based polymer. Here, the highly stereoregular propylene-based polymer refers to a propylene-based polymer having an isotactic mesopentad fraction (mmmm), which is an index of stereoregularity, of 96.0% or more.
The isotactic mesopentad fraction (mmmm) of the highly stereoregular propylene-based polymer according to the present embodiment is preferably 96.5% or more, more preferably 97.0% or more. The upper limit of the isotactic mesopentad fraction (mmmm) of the highly stereoregular propylene-based polymer is not particularly limited, but from the viewpoint of ease of production, it is 99.5% or less, more preferably 99.5%. It is 3% or less, more preferably 99.0% or less.
The isotactic mesopentad fraction (mmmm) can be determined from ¹³ C-nuclear magnetic resonance (NMR) spectrum by a known method.

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

The melt flow rate (MFR) of the propylene-based polymer according to the present embodiment measured under the conditions of 230° C. and a load of 2.16 kg according to ASTM D1238 is preferably 0.00 from the viewpoint of fluidity and moldability. 5 g/10 min or more, more preferably 1 g/10 min or more, still more preferably 2 g/10 min or more, and from the viewpoint of further stabilizing moldability, preferably 20 g/10 min or less, more preferably 10 g/10 min. minutes or less, more preferably 7 g/10 minutes or less.

(other ingredients)
The propylene-based polymer composition according to the present embodiment may optionally contain a tackifier, a heat stabilizer, a weather stabilizer, an antioxidant, an ultraviolet absorber, a lubricant, a slip agent, a nucleating agent, and an antiblocking agent. , antistatic agents, antifogging agents, pigments, dyes, inorganic or organic fillers, and the like may be added within a range that does not impair the purpose of the present embodiment.

As the tackifier according to the present embodiment, a resinous substance having a property of imparting tackiness, which is generally manufactured and sold as a tackifier, can be used.
Such tackifiers include, for example, chroman-based resins such as chroman-indene resins; phenol-based resins such as phenol-formaldehyde resins and xylene-formaldehyde resins; terpene-phenol resins, terpene resins (α, β-pinene resins ), aromatic modified terpene resins, terpene resins such as hydrogenated terpene resins; synthetic polyterpene resins, aromatic hydrocarbon resins, aliphatic hydrocarbon resins, aliphatic cyclic hydrocarbon resins, aliphatic/alicyclic petroleum-based hydrocarbon resins such as petroleum-based petroleum resins, aliphatic/aromatic petroleum resins, unsaturated hydrocarbon polymers, and hydrocarbon-based tackifying resins; rosin resins such as rosin pentaerythritol esters, rosin glycerin esters, hydrogenated rosin, hydrogenated rosin esters, special rosin esters, and rosin tackifiers. can.
Among these, petroleum-based hydrocarbon resins and hydrogenated petroleum-based hydrocarbon resins are selected from the viewpoint of being compatible with propylene-based polymers and capable of more effectively improving the water vapor barrier properties of the food packaging film 100. At least one selected is preferred, and a hydrogenated petroleum hydrocarbon resin is more preferred.
Here, the hydrogenation rate of the hydrogenated petroleum-based hydrocarbon resin is not particularly limited. % or more.

Here, the content of the tackifier contained in the propylene-based polymer composition according to the present embodiment, that is, the biaxially stretched film layer 101, is determined from the viewpoint of recyclability and cost reduction of the food packaging film 100, From the viewpoint of suppressing a decrease in flexural elasticity of the packaging film 100 and improving workability, dimensional stability, transparency, etc., when the entire biaxially stretched film layer 101 is 100% by mass, it is preferably 10%. % by mass or less, more preferably 5% by mass or less, still more preferably 3% by mass or less, and particularly preferably 1% by mass or less.

(Method for preparing propylene-based polymer composition)
The propylene-based polymer composition according to the present embodiment is prepared by mixing or melting/kneading each component by dry blending, tumbler mixer, Banbury mixer, single-screw extruder, twin-screw extruder, high-speed twin-screw extruder, hot roll, or the like. It can be prepared by

[Heat seal layer]
The food packaging film 100 according to this embodiment preferably has a heat seal layer 103 on at least one surface of the biaxially stretched film layer 101 in order to impart heat sealability. The heat seal layer 103 may be provided on both sides of the biaxially stretched film layer 101 .
Moreover, the heat seal layer 103 is preferably provided as the outermost layer of the food packaging film 100 according to the present embodiment from the viewpoint of improving the heat sealability of the food packaging film 100 .

Moreover, the heat seal layer 103 is preferably provided on the surface of the biaxially stretched film layer 101 so as to be in direct contact therewith. Thereby, the manufacturing process of the food packaging film 100 can be simplified.

In the food packaging film 100, the thickness of the heat seal layer 103 is preferably 0.1 μm or more and 10 μm or less, more preferably 0.2 μm or more and 9 μm or less, still more preferably 0.5 μm or more and 8 μm or less, and particularly preferably 1 μm or more and 8 μm. It is below. Here, the thickness of the heat seal layer 103 refers to the thickness of the heat seal layer 103 provided on one side of the biaxially stretched film layer 101 .
When the thickness of the heat seal layer 103 is equal to or greater than the above lower limit, the heat sealability of the food packaging film 100 can be further improved.
Further, when the thickness of the heat seal layer 103 is equal to or less than the above upper limit, the blocking property and slip property required for the food packaging film can be further improved.
That is, by providing the heat seal layer 103 so as to be in direct contact with the surface of the biaxially stretched film layer 101, the manufacturing process of the food packaging film 100 can be simplified.
Here, in the present embodiment, when the heat seal layer 103 is provided on both sides of the biaxially stretched film layer 101, the above thickness of the heat seal layer 103 is equal to the thickness of the heat seal layer 103 provided on one side of the biaxially stretched film layer 101. thickness.

In the food packaging film 100, the heat seal layer 103 provided on one side is preferably a single layer. Thereby, the manufacturing process of the food packaging film 100 can be further simplified.

Moreover, the heat seal layer 103 is preferably formed by biaxially stretching simultaneously with the film of the biaxially stretched film layer 101 before biaxial stretching. As a result, the food packaging film 100 can be produced using a molding method such as a co-extrusion molding method, that is, the laminated film produced by one-time molding, thereby further simplifying the manufacturing process of the food packaging film 100. can do. Therefore, the heat seal layer 103 is preferably biaxially stretched.

(polyolefin)
The heat seal layer 103 according to this embodiment is composed of, for example, a polyolefin-based resin composition (A) containing polyolefin. Examples of the polyolefin constituting the heat seal layer 103 include homopolymers or copolymers of α-olefins such as ethylene, propylene, butene-1, hexene-1, 4-methyl-pentene-1, and octene-1; High pressure low density polyethylene; linear low density polyethylene (LLDPE); high density polyethylene; polypropylene; random copolymer of propylene and α-olefin having 2 to 10 carbon atoms; ethylene/vinyl acetate copolymer (EVA ); and ionomer resins.
Among these, as the polyolefin constituting the heat seal layer 103, the number of carbon atoms is 2 or more and 10 or less with homopolypropylene and propylene from the viewpoint of excellent balance of adhesion with the biaxially stretched film layer 101 and heat sealability. is preferably at least one selected from random copolymers with α-olefins.
From the viewpoint of stability of heat sealability and heat seal strength, the heat seal layer 103 preferably contains an olefin elastomer among the above polyolefins.

The propylene/α-olefin random copolymer according to the present embodiment is a random copolymer of propylene and α-olefin (where α-olefin excludes propylene). , 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene and the like. These copolymers may be used alone or in combination of two or more.
Among the propylene/α-olefin random copolymers, propylene/ethylene random copolymers, propylene/ethylene/1-butene random copolymers, and propylene/1-butene random copolymers are preferred.

The melting point of the polyolefin constituting the heat seal layer 103 according to the present embodiment is preferably in the range of 60°C to 175°C, more preferably 65°C to 170°C, even more preferably 70°C to 167°C. When the melting point of the polyolefin is equal to or higher than the above lower limit, stickiness of the surface of the heat seal layer 103 can be suppressed, and the blocking resistance of the food packaging film 100 can be improved.
Further, when the melting point of the polyolefin is equal to or lower than the above upper limit, the heat sealability of the food packaging film 100 can be improved.

As the olefin elastomer, for example, the melting point is preferably 110° C. or less, more preferably 100° C. or less, still more preferably 80° C. or less, or an α-olefin polymer having 2 to 20 carbon atoms or ethylene, which has no observable melting point. and α-olefin; copolymers of ethylene and unsaturated carboxylic acid or unsaturated carboxylic acid ester; and the like.
Specifically, ethylene/propylene copolymer, ethylene/1-butene copolymer, ethylene/1-hexene copolymer, ethylene/4-methylpentene-1 copolymer, ethylene/1-octene copolymer , propylene homopolymer, propylene/ethylene copolymer, propylene/ethylene/1-butene copolymer, 1-butene homopolymer, 1-butene/ethylene copolymer, 1-butene/propylene copolymer, 4-methylpentene-1 homopolymer, 4-methylpentene-1/propylene copolymer, 4-methylpentene-1/1-butene copolymer, 4-methylpentene-1/propylene/1-butene copolymer propylene/1-butene copolymer, ethylene/vinyl acetate copolymer, ethylene/methacrylic acid copolymer, ethylene/methyl methacrylate copolymer, and the like.
A propylene/1-butene copolymer is particularly preferred from the viewpoint of heat sealability and heat seal strength stability.

The melt flow rate (MFR) of the polyolefin constituting the heat seal layer 103 according to the present embodiment, which is measured under the conditions of 230° C. and a load of 2.16 kg according to ASTM D1238, is, from the viewpoint of fluidity and moldability, It is preferably 0.5 g/10 min or more, more preferably 1 g/10 min or more, still more preferably 2 g/10 min or more, and from the viewpoint of further stabilizing moldability, preferably 20 g/10 min or less, more preferably is 10 g/10 minutes or less, more preferably 7 g/10 minutes or less.

The content of polyolefin in the polyolefin resin composition (A) according to the present embodiment, that is, the heat seal layer 103, is preferably 50% by mass or more when the entire polyolefin resin composition (A) is taken as 100% by mass. It is 100 mass % or less, more preferably 70 mass % or more and 100 mass % or less, still more preferably 90 mass % or more and 100 mass % or less, and particularly preferably 95 mass % or more and 100 mass % or less. As a result, the adhesiveness to the biaxially stretched film layer 101 and the heat-sealing property can be well balanced.
Further, the content of the olefin-based elastomer in the polyolefin-based resin composition (A) according to the present embodiment, that is, the heat seal layer 103, is when the content of the polyolefin contained in the biaxially stretched film layer 101 is taken as 100% by mass. , preferably 10% by mass or more and 50% by mass or less, more preferably 15% by mass or more and 45% by mass or less, and still more preferably 20% by mass or more and 40% by mass or less.

(other ingredients)
The polyolefin resin composition (A) constituting the heat seal layer 103 according to the present embodiment may optionally contain a tackifier, a heat stabilizer, a weather stabilizer, an antioxidant, an ultraviolet absorber, a lubricant, Various additives such as slip agents, nucleating agents, anti-blocking agents, antistatic agents, anti-fogging agents, pigments, dyes, inorganic or organic fillers may be added as long as they do not impair the purpose of the present embodiment. In particular, the heat seal layer 103 according to this embodiment preferably contains an antiblocking agent from the viewpoint of improving the blocking resistance of the food packaging film 100 according to this embodiment.
Antiblocking agents include, for example, talc, silica, clay, calcium carbonate, synthetic zeolite, starch, aluminum oxide, acrylic resins, methacrylic resins, silicon resins, polytetrafluoroethylene resins and the like.

Moreover, from the viewpoint of improving the heat-sealing property of the heat-sealing layer 103, it is preferable that the heat-sealing layer 103 does not substantially contain a tackifier. More specifically, the content of the tackifier in the heat seal layer 103 is preferably 0.5% by mass or less, more preferably 0.1% by mass or less, even more preferably 0.01% by mass or less, particularly Preferably it is 0% by mass.
Here, the tackifier is a resinous substance that is generally manufactured and sold as a tackifier and has the property of imparting tackiness.
Such tackifiers include, for example, chroman-based resins such as chroman-indene resins; phenol-based resins such as phenol-formaldehyde resins and xylene-formaldehyde resins; terpene-phenol resins, terpene resins (α, β-pinene resins ), aromatic modified terpene resins, terpene resins such as hydrogenated terpene resins; synthetic polyterpene resins, aromatic hydrocarbon resins, aliphatic hydrocarbon resins, aliphatic cyclic hydrocarbon resins, aliphatic/alicyclic petroleum-based hydrocarbon resins such as petroleum-based petroleum resins, aliphatic/aromatic petroleum resins, unsaturated hydrocarbon polymers, and hydrocarbon-based tackifying resins; rosin resins such as rosin pentaerythritol esters, rosin glycerin esters, hydrogenated rosin, hydrogenated rosin esters, special rosin esters, and rosin tackifiers. can.

(Method for preparing polyolefin resin composition (A))
The polyolefin-based resin composition (A) according to the present embodiment is prepared by, for example, dry blending each component, tumbler mixer, Banbury mixer, single-screw extruder, twin-screw extruder, high-speed twin-screw extruder, hot roll, etc. Alternatively, it can be prepared by melting and kneading.

[Surface layer]
In order to improve the printability of the surface of the food packaging film 100 according to this embodiment, as shown in FIG. It is preferable to further include a surface layer 105 on the surface.
Moreover, from the viewpoint of improving the printability of the food packaging film 100, the surface layer 105 is preferably provided as the outermost layer of the food packaging film 100 according to the present embodiment.

Moreover, the surface layer 105 is preferably provided so as to be in direct contact with the surface of the biaxially stretched film layer 101 . Thereby, the manufacturing process of the food packaging film 100 can be simplified.

In the food packaging film 100, the thickness of the surface layer 105 is preferably 0.1 μm or more and 10 μm or less, more preferably 0.2 μm or more and 9 μm or less, still more preferably 0.5 μm or more and 8 μm or less, and particularly preferably 1 μm or more and 8 μm or less. is. Here, the thickness of the surface layer 105 refers to the thickness of the surface layer 105 provided on one side of the biaxially stretched film layer 101 .
When the thickness of the surface layer 105 is at least the above lower limit, the printability of the food packaging film 100 can be further improved.
Further, when the thickness of the surface layer 105 is equal to or less than the above upper limit, the blocking property and slip property required during printing can be further improved.
That is, by providing the surface layer 105 so as to be in direct contact with the surface of the biaxially stretched film layer 101, the manufacturing process of the food packaging film 100 can be simplified.

In the food packaging film 100, the surface layer 105 is preferably a single layer. Thereby, the manufacturing process of the food packaging film 100 can be further simplified.

Moreover, the surface layer 105 is preferably formed by biaxially stretching simultaneously with the film of the biaxially stretched film layer 101 before biaxial stretching. As a result, the food packaging film 100 can be produced using a molding method such as a co-extrusion molding method, that is, the laminated film produced by one-time molding, thereby further simplifying the manufacturing process of the food packaging film 100. can do. Therefore, the surface layer 105 is preferably biaxially stretched.

Moreover, the surface layer 105 may be surface-treated from the viewpoint of improving the printability of the food packaging film 100 . Specifically, surface activation treatment such as corona treatment, flame treatment, plasma treatment, primer coating treatment, and ozone treatment may be performed.

(polyolefin)
The surface layer 105 according to this embodiment is composed of, for example, a polyolefin-based resin composition (B) containing polyolefin. Examples of the polyolefin constituting the surface layer 105 include homopolymers or copolymers of α-olefins such as ethylene, propylene, butene-1, hexene-1, 4-methyl-pentene-1, and octene-1; Law low density polyethylene; linear low density polyethylene (LLDPE); high density polyethylene; polypropylene; random copolymer of propylene and α-olefin having 2 to 10 carbon atoms; ethylene/vinyl acetate copolymer (EVA) ; and ionomer resins.
Among these, as the polyolefin constituting the surface layer 105, homopolypropylene and propylene and alpha having 2 or more and 10 or less carbon atoms are used because they have an excellent balance of adhesiveness with the biaxially stretched film layer 101 and printability. - At least one selected from random copolymers with olefins is preferred.

The propylene/α-olefin random copolymer according to the present embodiment is a random copolymer of propylene and α-olefin (where α-olefin excludes propylene). , 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene and the like. These copolymers may be used alone or in combination of two or more.
Among the propylene/α-olefin random copolymers, propylene/ethylene random copolymers, propylene/ethylene/1-butene random copolymers, and propylene/1-butene random copolymers are preferred.

The melting point of the polyolefin forming the surface layer 105 according to the present embodiment is preferably in the range of 90°C to 175°C, more preferably 95°C to 170°C, even more preferably 100°C to 167°C. When the melting point of the polyolefin is equal to or higher than the above lower limit, stickiness of the surface of the surface layer 105 can be suppressed, and the blocking resistance of the food packaging film 100 can be improved.

The melt flow rate (MFR) of the polyolefin constituting the surface layer 105 according to the present embodiment, which is measured under the conditions of 230° C. and a load of 2.16 kg in accordance with ASTM D1238, is preferable from the viewpoint of fluidity and moldability. is 0.5 g/10 min or more, more preferably 1 g/10 min or more, still more preferably 2 g/10 min or more, and from the viewpoint of further stabilizing moldability, preferably 20 g/10 min or less, more preferably It is 10 g/10 minutes or less, more preferably 7 g/10 minutes or less.

The content of polyolefin in the polyolefin resin composition (B) according to the present embodiment, that is, the surface layer 105, is preferably 50% by mass or more and 100% by mass when the entire polyolefin resin composition (B) is taken as 100% by mass. % by mass or less, more preferably 70% by mass or more and 100% by mass or less, still more preferably 90% by mass or more and 100% by mass or less, and particularly preferably 95% by mass or more and 100% by mass or less. This makes it possible to improve the balance between adhesion to the biaxially stretched film layer 101 and printability.

(other ingredients)
The polyolefin resin composition (B) constituting the surface layer 105 according to the present embodiment may optionally contain a tackifier, a heat stabilizer, a weather stabilizer, an antioxidant, an ultraviolet absorber, a lubricant, and a slip. Various additives such as agents, nucleating agents, anti-blocking agents, antistatic agents, anti-fogging agents, pigments, dyes, inorganic or organic fillers may be added to the extent that the purpose of the present embodiment is not impaired.
In particular, the surface layer 105 according to this embodiment preferably contains an antiblocking agent from the viewpoint of improving the blocking resistance of the food packaging film 100 according to this embodiment.
Examples of the anti-blocking agent include those similar to the anti-blocking agent used for the heat seal layer 103 described above.

(Method for preparing polyolefin resin composition (B))
The polyolefin-based resin composition (B) according to the present embodiment is prepared by, for example, dry blending each component using a tumbler mixer, a Banbury mixer, a single screw extruder, a twin screw extruder, a high speed twin screw extruder, a hot roll, or the like. Alternatively, it can be prepared by melting and kneading.

<Method for producing food packaging film>
The food packaging film 100 according to the present embodiment includes, for example, a resin composition (P) for forming the biaxially stretched film layer 101 and, if necessary, a polyolefin resin composition for forming the heat seal layer 103. The film obtained by co-extrusion molding the product (A) and the polyolefin resin composition (B) for forming the surface layer 105 into a film is subjected to a known simultaneous biaxial stretching method or sequential biaxial stretching. It can be obtained by biaxially stretching using a biaxially stretched film manufacturing method such as a method.
The molding apparatus and molding conditions are not particularly limited, and conventionally known molding apparatuses and molding conditions can be employed. As the molding apparatus, a T-die extruder, a multilayer T-die extruder, an inflation molding machine, a multilayer inflation molding machine, or the like can be used. For the biaxial stretching conditions, for example, known OPP film production conditions can be adopted. More specifically, in the sequential biaxial stretching method, for example, the longitudinal stretching temperature is 100° C. to 145° C., the longitudinal stretching ratio is 4.5 to 6 times, the lateral stretching temperature is 130° C. to 190° C., and the lateral stretching is Magnification may be in the range of 9 to 11 times.
In addition, the food packaging film 100 according to the present embodiment is formed by separately forming the biaxially stretched film layer 101 and, if necessary, the heat seal layer 103 and the surface layer 105, and then laminating and thermoforming these layers. can also be obtained by

<Uses of food packaging films>
The food packaging film 100 according to this embodiment can also be suitably used as a film constituting a food package. The food package according to the present embodiment is, for example, a packaging bag itself used for containing food or a food contained in the bag. In addition, the food packaging film 100 may be used for a part of the food package according to the present embodiment, or the food packaging film 100 may be used for the entire food package. .

The food packaging film 100 according to the present embodiment is preferably used for exterior packaging bags that require water vapor barrier properties.
Further, when the food packaging film 100 according to the present embodiment is used for an integrated package composed of a food, an individual packaging bag for individually packaging the food, and an exterior packaging bag for packaging a plurality of individual packaging bags, the food is The packaging film 100 for use is preferably used for exterior packaging bags that require water vapor barrier properties in integrated packages. This makes it possible to obtain an integrated package having sufficient water vapor barrier properties.

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

Hereinafter, the present embodiment will be described in detail with reference to examples and comparative examples. It should be noted that the present embodiment is not limited to the description of these examples.

1. Raw Materials Raw materials used in Examples and Comparative Examples are shown below.
(1) Propylene-based polymer PP1: highly stereoregular propylene homopolymer (MFR: 3 g/10 min, melting point: 167°C, isotactic mesopentad fraction (mmmm): 98.5%)
PP2: Propylene homopolymer (MFR: 3 g/10 minutes, melting point: 161°C, isotactic mesopentad fraction (mmmm): 92%)
PP3: propylene/α-olefin random copolymer (MFR: 7 g/10 min, melting point: 137°C)

2. Measurement and evaluation method (1) Isotactic mesopentad fraction (mmmm) of propylene-based polymer
The isotactic mesopentad fraction (mesopentad fraction, (mmmm)) was measured using ¹³ C-NMR. The isotactic mesopentad fraction was determined according to the method described in Zambelli et al., Macromolecules, Vol. C. Randall, Polymer Sequence Distribution, Chapter 2 (1977) (Academic Press, New York).

(2) MFR of propylene polymer
It was measured under conditions of 230° C. and a load of 2.16 kg according to ASTM D1238.

(3) Tensile modulus A test piece of 15 mm x 15 cm was cut out from the food packaging films obtained in Examples and Comparative Examples. Next, using a tensile tester manufactured by Orientec Co., Ltd., in accordance with JIS K7127 (1999), the MD direction of the test piece under the conditions of a measurement temperature of 23 ± 2 ° C., 50 ± 5% RH, and a tensile speed of 5 mm / min. The tensile modulus _T1 and the tensile modulus _T2 in the TD direction were measured respectively.

(4) Evaluation of thickness unevenness Using a sequential biaxial stretching machine, a biaxially stretched polypropylene film having a width of about 1 m in the direction perpendicular to the machine direction was produced by the method described below. 10 sheets of the film were piled up, divided into 9 equal parts in the direction of 1 m width, and the thickness was measured at 8 points excluding both ends. X was calculated by applying the measured value to the following formula. The smaller X is, the better the thickness unevenness is.
X = (maximum thickness - minimum thickness) / (maximum thickness + minimum thickness)
Then, thickness unevenness of the food packaging film was evaluated according to the following criteria.
◎: X is less than 2% ○: X is 2% or more and less than 4% △: X is 4% or more and less than 6% ×: X is 6% or more

(5) Evaluation of Stretching Unevenness The appearance of the stretch-molded film was checked, and it was visually confirmed whether or not there was a clearly thick portion remaining in the portion excluding 150 mm at both ends. If the thick portion remains, it means that the film is stretched unevenly, and the physical properties of the film are not stable.
◎: No stretching unevenness ×: Stretching unevenness

(6) Water Vapor Barrier Property A food packaging film was folded so that the heat-seal layer was on the inside, and the two sides were heat-sealed to form a bag. After that, calcium chloride was added as the content. Then, the other side was heat-sealed to prepare a bag having a surface area of 0.01 m ² . The resulting bag was then stored for 72 hours under conditions of 40° C. and 90% RH. The weight of calcium chloride before and after storage was measured, and the water vapor permeability (g/(m ² ·24h)) was calculated from the difference.
Here, a heat seal layer was formed on one surface of the biaxially oriented polypropylene films obtained in Examples and Comparative Examples.
Next, the water vapor barrier property of the food packaging film was evaluated according to the following criteria.
◎◎: Water vapor transmission rate is 5.0 g / (m ² · 24 h) or less ◎: Water vapor transmission rate exceeds 5.0 g / (m ² · 24 h) 5.5 g / (m ² · 24 h) or less ○: Water vapor transmission 5.5 g / (m ² · 24 h) more than 6.0 g / (m ² · 24 h) or less ×: Water vapor permeability exceeds 6.0 g / (m ² · 24 h)

[Examples 1-11 and Comparative Examples 1-2]
Biaxially oriented polypropylene films having the compositions shown in Tables 1 and 2 were extruded and then biaxially oriented to prepare food packaging films, which were evaluated. Extrusion molding conditions and biaxial stretching conditions are as follows.
Extruder: 60 mmφ multi-layer T-die extruder (screw: L/D = 27, manufactured by Screw Seiki Co., Ltd.)
Extrusion set temperature: 230-250°C, processing speed: 20m/min (winding speed)
Longitudinal stretching temperature: 115-130°C
Longitudinal draw ratio: 5 times Lateral draw temperature: 140-175°C
Horizontal stretch ratio: 10 times

The food packaging films of Examples had less thickness unevenness than the food packaging films of Comparative Examples. Moreover, when the food packaging film of the example was used, it was possible to obtain a food package having improved water vapor barrier properties as compared with the case of using the food packaging film of the comparative example.

100 food packaging film 101 biaxially stretched film layer 103 heat seal layer 105 surface layer

Claims (10)

A film for packaging food,
comprising a biaxially stretched film layer comprising a propylene-based polymer;
The propylene-based polymer includes a first propylene-based polymer (excluding the highly stereoregular propylene-based polymer) having a melting point in the range of 137° C. or higher and 162° C. or lower as measured by DSC, and a first propylene-based polymer having a melting point of 163° C. a second propylene-based polymer having a temperature in the range of ° C. to 180 ° C.,
When the total amount of the first propylene-based polymer and the second propylene-based polymer contained in the biaxially-stretched film layer is 100% by mass, the second propylene-based polymer in the biaxially-stretched film layer The content of is 1% by mass or more and 85% by mass or less,
A food packaging film having a melt flow rate (MFR) of 7 g/10 minutes or less measured under conditions of 230° C. and a load of 2.16 kg according to ASTM D1238 of the propylene-based polymer,
further comprising a heat seal layer on one side of the biaxially stretched film layer;
Further comprising a surface layer on the surface of the biaxially stretched film layer opposite to the surface on which the heat seal layer is provided ,
A food packaging film , wherein the second propylene-based polymer has an isotactic mesopentad fraction (mmmm) of 96.0% or more . In the food packaging film according to claim 1 ,
According to JIS K7127 (1999), measured using a tensile tester under the conditions of a measurement temperature of 23 ± 2 ° C., 50 ± 5% RH, and a tensile speed of 5 mm / min, the MD direction tensile of the food packaging film A food packaging film having a total value (T ₁ +T ₂ ) of an elastic modulus T ₁ and a tensile elastic modulus T ₂ in the TD direction of 5,000 MPa or more and 10,000 MPa or less. In the food packaging film according to claim 1 or 2 ,
The food packaging film, wherein the heat seal layer is provided so as to be in direct contact with the one surface of the biaxially stretched film layer. In the food packaging film according to any one of claims 1 to 3 ,
A food packaging film in which the heat seal layer contains one or more selected from homopolypropylene and random copolymers of propylene and α-olefins having 2 to 10 carbon atoms. In the food packaging film according to any one of claims 1 to 4 ,
The food packaging film, wherein the surface layer comprises an anti-blocking agent. In the food packaging film according to any one of claims 1 to 5 ,
The food packaging film, wherein the surface layer comprises one or more selected from homopolypropylene and random copolymers of propylene and α-olefins having 2 to 10 carbon atoms. In the food packaging film according to any one of claims 1 to 6 ,
A food packaging film, wherein the content of the tackifier contained in the biaxially stretched film layer is 10% by mass or less when the entire biaxially stretched film layer is taken as 100% by mass. In the food packaging film according to any one of claims 1 to 7 ,
A food packaging film having a water vapor transmission rate of 6.0 g/(m ² ·24 h) or less as measured by the following method.
(Measuring method)
The food packaging film is folded so that the heat-seal layer faces the inside, and the two sides are heat-sealed to form a bag. After that, calcium chloride is added as the content. The other side is then heat-sealed to form a bag having a surface area of 0.01 m ² . The resulting bag is then stored for 72 hours under conditions of 40° C. and 90% RH. The weight of calcium chloride before and after storage is measured, and the water vapor permeability (g/(m ² ·24h)) is calculated from the difference. In the food packaging film according to any one of claims 1 to 8 ,
Food packaging film used for outer packaging bags. A food package using the food packaging film according to any one of claims 1 to 9 .

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