JP7112835B2 - 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 workability, 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 Document 2 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

Although the OPP film has water vapor barrier properties, it is inferior in heat sealing properties. Therefore, when the OPP film is used for a food package such as a food packaging bag, it is necessary to laminate an unstretched polypropylene film (hereinafter also referred to as a CPP film) having excellent heat sealability on the OPP film. By further laminating the CPP film on the OPP film, the heat seal strength of the obtained food package is increased, and the intrusion of moisture and oxygen at the sealed part is suppressed, and the water vapor barrier property and oxygen barrier property of the food package are improved. can be
Here, since the OPP film and the CPP film have poor adhesiveness, it was necessary to laminate the CPP film to the OPP film using an adhesive. Therefore, the food packaging film using the OPP film used for the food packaging includes a process of further laminating the CPP film using an adhesive, so there are many manufacturing processes, which simplifies the manufacturing process and reduces the cost. There was room for improvement in terms of

The present invention has been made in view of the above circumstances, and a food packaging film that can realize a food package that has appropriate film stiffness and sufficient water vapor barrier properties, and is excellent in cost and productivity. It provides

The present inventors have made intensive studies to solve the above problems. As a result, as the OPP film, a biaxially stretched film composed of a propylene polymer composition containing a highly stereoregular propylene polymer is adopted to improve the stiffness and water vapor barrier properties of the OPP film itself, and further biaxially stretched. By directly providing only a thin heat seal layer on one surface of the film layer, it was found that a food package having sufficient water vapor barrier properties can be obtained without using a CPP film having excellent heat seal properties. I came up with the invention.

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

[1]
A film for packaging food,
a biaxially stretched film layer composed of a propylene polymer composition containing a highly stereoregular propylene polymer;
a heat seal layer provided so as to be in direct contact with at least one surface of the biaxially stretched film layer;
with
The content of the highly stereoregular propylene polymer is 70% by mass or more and 100% by mass or less when the entire propylene polymer composition is taken as 100% by mass,
The isotactic mesopentad fraction (mmmm) of the highly stereoregular propylene polymer is 96% or more,
The heat seal layer is the outermost layer, and the thickness of the heat seal layer is 0.1 μm or more and 10 μm or less ,
A food packaging film , wherein the heat seal layer comprises a propylene homopolymer .
[2]
In the food packaging film according to [1],
A food packaging film, wherein the heat seal layer is a single layer.
[3]
In the food packaging film according to [1] or [2],
A food packaging film, wherein the heat seal layer is biaxially oriented.
[4]
In the food packaging film according to any one of [1] to [3],
A packaging film for food, wherein said food comprises dry food.
[5]
In the food packaging film according to [4],
The food packaging film, wherein the dried food has a water activity of 0.05 or more and 0.3 or less.
[6]
In the food packaging film according to any one of [1] to [5],
A food package having a heat seal strength of 1.5 N/15 mm or more in a portion where the heat seal layers of the food packaging film are heat-sealed under the conditions of 110° C., pressure of 1.0 kgf, and sealing time of 0.5 seconds. the film.
[7]
In the food packaging film according to any one of [1] to [6],
The thickness of the biaxially stretched film is 2.5 μm or more and 99.8 μm or less,
A food packaging film having a water vapor permeability of 4.5 g/(m ² ·24 h) or less and a thickness of 5 μm or more and 100 μm 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 with 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.
[8]
In the food packaging film according to any one of [1] to [7],
Food packaging film used for outer packaging bags.
[9 ]
In the food packaging film according to any one of [ 1] to [ 8 ],
The food packaging film, wherein the heat seal layer comprises an olefinic elastomer.
[10]
A food package using the food packaging film according to any one of [1] to [ 9 ].

According to the present invention, it is possible to realize a food packaging body having appropriate film stiffness and sufficient water vapor barrier properties, and to provide a food packaging film excellent in terms of cost, productivity, and the like.

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>
FIG. 1 is a cross-sectional view 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 is composed of a biaxially stretched film layer 101 made of a propylene polymer composition containing a highly stereoregular propylene polymer; and a heat seal layer 103 provided so as to be in direct contact with at least one surface of the axially stretched film layer 101, the heat seal layer 103 being the outermost layer and having a thickness of 0.1 μm or more. 10 μm or less.
Here, in the present embodiment, when the heat seal layer 103 is provided on both sides of the biaxially stretched film layer 101, the 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.

As described above, the OPP film has water vapor barrier properties but is inferior in heat sealability. Therefore, when the OPP film is used for a food package such as a food packaging bag, it has been necessary to laminate a CPP film or the like, which has excellent heat-sealing properties, on the OPP film. By further laminating the CPP film on the OPP film, the heat seal strength of the obtained food package is increased, and the intrusion of moisture and oxygen at the sealed part is suppressed, and the water vapor barrier property and oxygen barrier property of the food package are improved. can be
Here, since the OPP film and the CPP film have poor adhesiveness, it was necessary to laminate the CPP film to the OPP film using an adhesive. Therefore, the food packaging film using the OPP film used for the food packaging includes a process of further laminating the CPP film using an adhesive, so there are many manufacturing processes, which simplifies the manufacturing process and reduces the cost. There was room for improvement in terms of

The present inventors have made intensive studies to solve the above problems. First, the use of a film provided with a relatively thin heat-seal layer having a thickness of 0.1 μm or more and 10 μm or less so as to be in direct contact with at least one surface of a conventional OPP film was examined as a packaging film.
However, the food package produced using such a film has poor sealing performance, and the water vapor barrier property is sufficiently satisfactory compared to the food package produced using the laminated film of the OPP film and the CPP film. It was nothing.
Therefore, the inventors of the present invention conducted further studies on the basis of the above findings. As a result, as the OPP film, a biaxially stretched film composed of a propylene polymer composition containing a highly stereoregular propylene polymer is adopted to improve the stiffness and water vapor barrier properties of the OPP film itself. The present inventors have found that even if the package itself has poor sealing performance, it is possible to realize a food package having appropriate film stiffness and sufficient water vapor barrier properties. In addition, the present inventors have found that the bag-manufacturing properties are good because of the appropriate film stiffness.
That is, according to the food packaging film 100 according to the present embodiment, it is possible to realize a food package having appropriate film stiffness and sufficient water vapor barrier properties.
In addition, since the food packaging film 100 according to the present embodiment can directly form the heat seal layer 103 on the biaxially stretched film layer 101, an adhesive is not used like a laminated film of an OPP film and a CPP film. There is no need to perform a step of further laminating the CPP film using the CPP film, so that the manufacturing process can be simplified, and as a result, the productivity can be improved. In addition, since there is no need to use a CPP film, costs can be reduced. In addition, since the film has an appropriate stiffness, it is possible to reduce defects due to bending, wrinkling, etc. during processing.
As described above, according to the present embodiment, it is possible to realize a food package having appropriate film stiffness and sufficient water vapor barrier properties, and to provide a food packaging film 100 that is excellent in cost and productivity. can.

Here, the food package produced using the food packaging film 100 according to the present embodiment has loop stiffness and heat sealability compared to the food package produced using the laminated film of the OPP film and the CPP film. Since the properties are simultaneously excellent, a film having excellent productivity and heat seal strength can be obtained. Since the heat seal strength is low and the sealing property is poor, the oxygen barrier property is inferior, but surprisingly, the water vapor barrier property shows sufficient performance even if the sealing property is poor. 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, the water vapor transmission rate measured by the following method is 4.5 g/(m ² ·24 h) or less from the viewpoint of stably obtaining a food package having excellent water vapor barrier properties. is preferred, and 4.0 g/(m ² ·24 h) or less is more preferred.
(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 with 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 a water vapor transmission rate can be achieved, for example, by adjusting the content ratio of the propylene polymer and the tackifier contained in the biaxially stretched film layer 101, the constituent materials and thickness of the heat seal layer 103, and the like.

The food packaging film 100 according to this embodiment has excellent heat sealability. In the food package produced using the food packaging film 100, from the viewpoint of further improving the sealing strength, the heat seal layers 103 of the food packaging film 100 were heated to 110°C, a pressure of 1.0 kgf, and a sealing time of 0.5. The heat seal strength of the portion heat-sealed under the condition of seconds is preferably 1.5 N/15 mm or more, more preferably 2.0 N/15 mm or more, and still more preferably 3.0 N/15 mm or more.
Here, the heat seal strength can be measured by the following method. First, the heat seal layers 103 of two food packaging films 100 are heat-sealed under conditions of 110° C., pressure of 1.0 kgf, and sealing time of 0.5 seconds to obtain a laminated film. Next, the two food packaging films 100 are peeled off under the conditions of 15 mm width, 90 degree peeling, and peeling speed of 300 mm/min, and the peel strength at that time is defined as the heat seal strength.
Such a heat-sealing strength can be achieved, for example, by adjusting the content ratio of the propylene polymer and the tackifier contained in the biaxially stretched film layer 101, the constituent materials and thickness of the heat-sealing layer 103, and the like.

In the food packaging film 100 according to the present embodiment, the sum of the loop stiffness value in the MD direction and the loop stiffness value in the TD direction measured under the conditions of 23 ° C., 50% RH, 15 mm width, 50 mm circumference, and 20 mm pushing distance is preferably 15.0 N/15 mm or more and 30 N/15 mm or less, more preferably 20.0 N/15 mm or more and 30.0 N/15 mm or less.
When the sum of the loop stiffness value in the MD direction and the loop stiffness value in the TD direction satisfies the above range, the food packaging film 100 according to the present embodiment maintains the water vapor barrier property and further improves the stiffness. As a result, misalignment of the film during heat sealing can be suppressed, and the occurrence of sealing defects can be suppressed. That is, when the sum of the loop stiffness value in the MD direction and the loop stiffness value in the TD direction satisfies the above range, the food packaging film 100 according to the present embodiment has a better balance between the water vapor barrier property and the packaging suitability. be able to.
Such a loop stiffness value is a substitute value for quantitatively measuring the stiffness of the film. , can be achieved by adjusting the constituent material and thickness of the heat seal 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. , usually 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, moldability, light weight, 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-based film layer) according to the present embodiment is, for example, a film composed of a propylene polymer composition containing a highly stereoregular propylene polymer, which is biaxially stretched. It was 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 polymer composition are laminated, but it is necessary to be biaxially stretched. is.

In addition, in the food packaging film 100, the ratio of the thickness of the biaxially stretched film layer 101 to the overall thickness of the food packaging film 100 is preferably 0.50 or more and 0.998 or less, more preferably 0.60. 0.99 or less, more preferably 0.70 or more and 0.97 or less, and still more preferably 0.75 or more and 0.95 or less.

(Propylene polymer composition)
The propylene polymer composition according to this embodiment contains a highly stereoregular propylene polymer.
Here, by including the highly stereoregular propylene polymer in the biaxially stretched film layer 101, the water vapor barrier properties of the biaxially stretched film layer 101 can be improved. Although the reason for this is not clear, it is believed that the highly stereoregular propylene polymer has excellent crystallinity.

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

(High stereoregularity propylene polymer)
In the present embodiment, the highly stereoregular propylene polymer refers to a propylene polymer having an isotactic mesopentad fraction (mmmm), which is an index of stereoregularity, of 96% or more.
The isotactic mesopentad fraction (mmmm) of the highly stereoregular propylene 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 polymer is not particularly limited, but from the viewpoint of ease of production, it is 99.5% or less, more preferably 99.3%. % 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 highly stereoregular propylene polymer according to this embodiment can be produced by various methods. For example, it can be produced using known catalysts such as Ziegler-Natta catalysts and metallocene catalysts.

The melt flow rate (MFR) of the highly stereoregular propylene polymer according to the present embodiment, which is measured under conditions of 230° C. and a load of 2.16 kg according to 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.

(other ingredients)
The propylene polymer composition according to the present embodiment may optionally contain a heat stabilizer, a weather stabilizer, an antioxidant, an ultraviolet absorber, a lubricant, a slip agent, a nucleating agent, an antiblocking agent, an antistatic agent, Various additives such as anti-fogging agents, pigments, dyes, inorganic or organic fillers may be added as long as the purpose of the present embodiment is not impaired.

(Method for preparing propylene polymer composition)
The propylene 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 has a heat seal layer 103 as the outermost layer 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 .

In the food packaging film 100, the heat seal layer 103 has a thickness of 0.1 μm or more and 10 μm or less, preferably 0.2 μm or more and 9 μm or less, 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 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 improved.
In addition, since the thickness of the heat seal layer 103 is equal to or less than the above upper limit value, the adhesiveness to the biaxially stretched film layer 101 is improved, and it can be laminated on the biaxially stretched film layer 101 without using an adhesive. It becomes possible. That is, since the heat seal layer 103 can be provided 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 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 made of, for example, a polyolefin-based resin composition 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; linear low density polyethylene (LLDPE); high density polyethylene; polypropylene; propylene/α-olefin random copolymer; ethylene/vinyl acetate copolymer (EVA);
Among these, as the polyolefin constituting the heat seal layer 103, a propylene/α-olefin random copolymer and propylene alone are used because they have an excellent balance of adhesion to the biaxially stretched film layer 101 and heat sealability. At least one selected from polymers is preferred.
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 (excluding the olefin-based elastomer) constituting the heat seal layer 103 according to the present embodiment is preferably 90° C. or higher and 175° C. or lower, more preferably 95° C. or higher and 170° C. or lower, and still more preferably 100° C. or higher. It is in the range of 167°C or less. 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 property 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, an α-olefin polymer having 2 to 20 carbon atoms or ethylene, which has a melting point of preferably 110° C. or lower, more preferably 100° C. or lower, and still more preferably 80° C. or lower, or 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 according to the present embodiment, that is, the heat seal layer 103, is preferably 50% by mass or more and 100% by mass or less, when the entire polyolefin resin composition is 100% by mass. It is preferably 70% by mass or more and 100% by mass or less, 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. As a result, the adhesiveness to the biaxially stretched film layer 101 and the heat-sealing property can be well balanced.
In addition, the content of the olefin elastomer in the polyolefin resin composition according to the present embodiment, that is, the heat seal layer 103, is preferably 10% by mass or more and 50% by mass or less, more preferably 15% by mass, based on the polyolefin content. 45 mass % or less, more preferably 20 mass % or more and 40 mass % or less (however, the total content of the olefinic elastomer content and the polyolefin content is 100 mass %).

(other ingredients)
The polyolefin resin composition constituting the heat seal layer 103 according to the present embodiment may optionally contain a heat stabilizer, a weather stabilizer, an antioxidant, an ultraviolet absorber, a lubricant, a slip agent, a nucleating agent, and a blocking agent. Various additives such as antistatic agents, antistatic agents, antifogging agents, pigments, dyes, inorganic or organic fillers may be added to the extent that the purpose of the present embodiment is not impaired.

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; ), 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)
The propylene 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

<Method for producing food packaging film>
The food packaging film 100 according to the present embodiment includes, for example, the propylene polymer composition for forming the biaxially stretched film layer 101, the polyolefin resin composition for forming the heat seal layer 103, can be obtained by biaxially stretching a laminated film obtained by coextrusion molding into a film using a known biaxially stretched film manufacturing method such as a simultaneous biaxial stretching method or a sequential biaxial stretching method.
The molding apparatus and molding conditions are not particularly limited, and conventionally known molding apparatuses and molding conditions can be employed. A multi-layer T-die extruder, a multi-layer inflation molding machine, or the like can be used as a molding device. 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.
The food packaging film 100 according to the present embodiment can also be obtained by forming the biaxially stretched film layer 101 and the heat seal layer 103 separately, laminating them, and thermoforming.

<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. .

A food package using the food packaging film 100 according to the present embodiment can exhibit sufficient water vapor barrier properties even for dry foods that particularly require water vapor barrier properties. The film 100 can be used particularly suitably as a packaging film for packaging foods including dry foods.
Here, the dry food according to the present embodiment refers to food in a dry or semi-dry state (including pet food). Here, the food in a dry state refers to a food with a moisture content of 15% by mass or less, and the food in a semi-dry state refers to a food with a moisture content of more than 15% by mass and less than 50% by mass. food. Dry foods include, for example, nuts foods, snack foods, cereal foods, luxury goods, dried noodles/pastas, grains/flours, dried vegetables, confectionery, rice confectionery, dairy products, seasonings, etc. can be mentioned.
Among these, from the viewpoint that the effects of the present embodiment can be obtained more effectively, it is preferable that the dry food includes rice crackers, and dried rice crackers coated with soy sauce and dried beans, or coated with soy sauce on the surface. It is more preferred to include uncoated rice crackers.
Moreover, from the viewpoint of obtaining the effects of the present embodiment more effectively, the water activity of the dried food is preferably 0.05 or more and 0.3 or less.

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 be employed.
Examples of embodiments will be added below.
1. A film for packaging food,
a biaxially stretched film layer composed of a propylene polymer composition containing a highly stereoregular propylene polymer;
a heat seal layer provided so as to be in direct contact with at least one surface of the biaxially stretched film layer;
with
The food packaging film, wherein the heat seal layer is the outermost layer and the heat seal layer has a thickness of 0.1 μm or more and 10 μm or less.
2. 1. In the food packaging film described in
A food packaging film, wherein the heat seal layer is a single layer.
3. 1. or 2. In the food packaging film described in
A food packaging film, wherein the heat seal layer is biaxially oriented.
4. 1. to 3. In the food packaging film according to any one of
A packaging film for food, wherein said food comprises dry food.
5. 4. In the food packaging film described in
The food packaging film, wherein the dry food has a water activity of 0.05 or more and 0.3 or less.
6. 1. to 5. In the food packaging film according to any one of
Food packaging, wherein the heat seal layers of the food packaging film are heat-sealed under the conditions of 110° C., pressure of 1.0 kgf, and sealing time of 0.5 seconds, and the heat seal strength of the portion is 1.5 N/15 mm or more. the film.
7. 1. to 6. In the food packaging film according to any one of
A food packaging film having a water vapor transmission rate of 4.5 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 with 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.
8. 1. to 7. In the food packaging film according to any one of
Food packaging film used for outer packaging bags.
9. 1. to 8. In the food packaging film according to any one of
A food packaging film, wherein the isotactic mesopentad fraction (mmmm) of the highly stereoregular propylene polymer is 96% or more.
10. 1. to 9. In the food packaging film according to any one of
A food packaging film in which the heat seal layer contains at least one selected from propylene/α-olefin random copolymers and propylene homopolymers.
11. 1. to 10. In the food packaging film according to any one of
The food packaging film, wherein the heat seal layer comprises an olefinic elastomer.
12. 1. 11. In the food packaging film according to any one of
A food packaging film, wherein the ratio of the thickness of the biaxially stretched film layer to the overall thickness of the food packaging film is 0.50 or more and 0.998 or less.
13. 1. 12. A food package using the food packaging film according to any one of.

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 polymer PP1: Highly stereoregular propylene homopolymer (MFR: 3 g/10 minutes, melting point: 164°C, isotactic mesopentad fraction (mmmm): 98.5%, manufactured by Prime Polymer Co., Ltd. )
PP2: Propylene homopolymer (MFR: 3 g/10 minutes, melting point: 161°C, isotactic mesopentad fraction (mmmm): 95%, manufactured by Prime Polymer Co., Ltd.)
PP3: propylene/ethylene random copolymer (MFR: 5 g/10 minutes, melting point: 126°C, manufactured by Japan Polypropylene Corporation)
PP4: Olefin-based elastomer (propylene-butene copolymer) (MFR: 7 g/10 min, melting point: 75°C, manufactured by Mitsui Chemicals, Inc.)

2. Measurement and evaluation method (1) Isotactic mesopentad fraction (mmmm) of propylene 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) Melting point of propylene polymer The temperature of the maximum melting peak of the DSC curve of the propylene polymer obtained using a DSC (differential scanning calorimeter) was defined as the melting point.

(4) Loop stiffness value Using a loop stiffness tester manufactured by Toyo Seiki Co., Ltd., the loop stiffness value in the MD direction and the loop stiffness in the TD direction under the conditions of 23 ° C., 50% RH, width 15 mm, circumferential length 50 mm, and pushing distance 20 mm values were measured respectively.

(5) Water vapor barrier property The food packaging film was folded so that the heat seal layer 2 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.
Next, the water vapor barrier property of the food packaging film was evaluated according to the following criteria.
◎: Water vapor transmission rate is 4.0 g / (m ² · 24 h) or less ○: Water vapor transmission rate exceeds 4.0 g / (m ² · 24 h) 4.5 g / (m ² · 24 h) or less ×: Water vapor transmission rate exceeds 4.5g/( ^m2・24h)

(6) Heat-sealing strength A laminated film was obtained by heat-sealing the heat-sealing layers 2 of two food packaging films cut to a width of 15 mm under the conditions of 110°C, pressure of 1.0 kgf, and sealing time of 0.5 seconds. got Then, the two food packaging films were peeled under the conditions of 15 mm width, 90 degree peeling, and peeling speed of 300 mm/min, and the peel strength at that time was taken as the heat seal strength.

[Example 1 and Comparative Example 1]
Each layer was co-extruded with the layer structure shown in Table 1, and then biaxially stretched to prepare a food packaging film, and each evaluation was performed. Co-extrusion molding conditions and biaxial stretching conditions are as follows.
Multi-layer extruder: 60 mmφ multi-layer T-die extruder (L/D = 27, manufactured by Screw Seiki Co., Ltd.)
Extrusion setting temperature: 200-250°C, processing speed: 13.5m/min
Longitudinal stretching temperature: 110-120°C
Longitudinal draw ratio: 5.0 times Lateral draw temperature: 140-170°C
Lateral draw ratio: 10.0 times

When the food packaging film of the example was used, a food package having moderate loop stiffness and sufficient water vapor barrier properties could be obtained.

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

Claims (8)

A film for packaging food,
a biaxially stretched film layer composed of a propylene polymer composition containing a highly stereoregular propylene polymer;
a heat seal layer provided so as to be in direct contact with at least one surface of the biaxially stretched film layer;
with
The content of the highly stereoregular propylene polymer is 70% by mass or more and 100% by mass or less when the entire propylene polymer composition is taken as 100% by mass,
The isotactic mesopentad fraction (mmmm) of the highly stereoregular propylene polymer is 96% or more,
The heat seal layer is the outermost layer, and the thickness of the heat seal layer is 0.1 μm or more and 10 μm or less,
The heat seal layer comprises a propylene homopolymer,
The heat seal layer contains an olefinic elastomer,
A food packaging film , wherein the heat seal layer is biaxially oriented . In the food packaging film according to claim 1,
A food packaging film, wherein the heat seal layer is a single layer. In the food packaging film according to claim 1 or 2 ,
A packaging film for food, wherein said food comprises dry food. In the food packaging film according to claim 3 ,
The food packaging film, wherein the dry food has a water activity of 0.05 or more and 0.3 or less. In the food packaging film according to any one of claims 1 to 4 ,
A food package having a heat seal strength of 1.5 N/15 mm or more in a portion where the heat seal layers of the food packaging film are heat-sealed under the conditions of 110° C., pressure of 1.0 kgf, and sealing time of 0.5 seconds. the film. In the food packaging film according to any one of claims 1 to 5 ,
The thickness of the biaxially stretched film is 2.5 μm or more and 99.8 μm or less,
A food packaging film having a water vapor permeability measured by the following method of 4.5 g/(m ² ·24 h) or less and a thickness of 5 μm or more and 100 μm or less.
(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 with 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 6 ,
Food packaging film used for outer packaging bags. A food package using the food packaging film according to any one of claims 1 to 7 .

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