JP7404631B2 - Multilayer film and packaging - Google Patents

Description

The present invention relates to multilayer films and packaging.

From the standpoint of improving the quality of life in an aging society and securing lifelines in the event of a disaster, there is a need for retort food that can be stored at room temperature for a long period of time. Retort food refers to food that has been sterilized by retort (pressurized heating).Products that have been sterilized by retort can be made commercially sterile, allowing them to be distributed at room temperature.

A film for retort food packaging includes, for example, a multilayer polyamide layer including two or more polyamide layers via an adhesive layer, a gas barrier layer, an adhesive layer, and a sealant layer, which are arranged in this order. Various films such as laminated composite films (for example, Patent Documents 1 and 2) have been proposed.

Packaging materials used for packaging retort foods and the like are required to have oxygen barrier properties that prevent oxygen from permeating in order to maintain quality such as taste and freshness of the food.

Japanese Patent Application Publication No. 3-136851 Patent No. 3-138149

However, conventional films have a problem in that the oxygen barrier properties of the gas barrier layer deteriorate during retort processing. Further, there was also a problem that the moldability of the entire film was poor.

The present disclosure has been made in view of the above circumstances, and aims to provide a multilayer film that can suppress deterioration of oxygen barrier properties during retort processing and has improved formability, and a package using the same. Take it as a challenge.

In order to solve the above problems, the present invention employs the following configuration.
[1]. A multilayer film in which an outer layer containing a polyolefin resin and a hydrogenated styrene-butadiene copolymer, an oxygen barrier layer containing a polyamide resin having an aromatic ring, and a sealant layer containing a polyolefin resin are laminated in this order. .
[2]. The multilayer film according to [1], wherein the multilayer film is for packaging retort food.
[3]. The multilayer film according to [1] or [2], wherein the content of the polyamide resin having an aromatic ring in the oxygen barrier layer is 40 to 60% by mass based on the total mass of the multilayer film.
[4]. Any one of [1] to [3], wherein the sealant layer is formed by laminating a layer containing a polyolefin resin of a homopolymer or a block copolymer and a layer containing a polyolefin resin of a random copolymer. The multilayer film described.
[5]. The multilayer film according to [4], wherein the layer containing the homopolymer or block copolymer polyolefin resin contains a hydrogenated product of a styrene-butadiene copolymer.
[6]. A package comprising the multilayer film according to any one of [1] to [5].

The multilayer film of the present invention includes an outer layer containing a polyolefin resin and a hydrogenated styrene-butadiene copolymer, an oxygen barrier layer containing a polyamide resin having an aromatic ring, and a sealant layer containing a polyolefin resin. Since it has a structure in which the layers are laminated in order, it is possible to suppress a decrease in oxygen barrier properties during retort treatment, and the moldability is excellent.

Moreover, since the package of the present invention includes the multilayer film described above, it is possible to suppress a decrease in oxygen barrier properties during retort processing and has excellent moldability.

FIG. 1 is a schematic cross-sectional view of a multilayer film of this embodiment.

Hereinafter, a multilayer film and a package that are one embodiment of the present invention will be described in detail. Note that the drawings used in the following explanations may show characteristic parts enlarged for convenience in order to make the characteristics easier to understand, and the dimensional ratio of each component may not be the same as the actual one. do not have.

<Multilayer film>
The structure of the multilayer film of this embodiment will be explained. FIG. 1 is a schematic cross-sectional view of the multilayer film 1 of this embodiment. As shown in FIG. 1, the multilayer film 1 of this embodiment includes an outer layer 2, a first adhesive layer 3, an oxygen barrier layer 4, a second adhesive layer 5, and a sealant layer 6. It has a schematic structure in which the components are laminated in order.

The multilayer film 1 can be used for packaging that undergoes pressure and heat sterilization treatment such as retort treatment. The multilayer film 1 can be used to package foods such as meat, raw noodles, processed foods, and pickles, and can particularly be used for packaging retort foods.

In this embodiment, "retort processing" refers to, for example, pressurizing at a pressure of 1.3 to 3.0 (kgf/cm ² ) and a temperature of 100 to 130°C for 3 to 60 minutes in order to preserve food for a long period of time. It means heating.

The multilayer film 1 preferably has an oxygen permeability of 0.5 to 5.0 ml/m 2 , more preferably 0.5 to 3.0 ml/m ² , and more preferably 0.5 to 3.0 ml/m ² before retort treatment. More preferably, it is 1.0 ml/m ² .
The multilayer film 1 preferably has an oxygen permeability of 0.5 to 10.0 ml/m ² after retort treatment, more preferably 0.5 to 6.0 ml/m 2 , and more preferably 0.5 to 6.0 ml/m ² . More preferably, it is 2.0 ml/m ² .
In the multilayer film 1, the decrease in oxygen permeability before and after retort treatment is preferably 1 ml/m ² or less, more preferably 0.5 ml/m ² or less, and 0.3 ml/m ² or less. It is even more preferable.
Note that the oxygen permeability of the multilayer film 1 before and after the retort treatment can be measured by the JIS K7126B method (isobaric method).

Regarding the formability of the multilayer film 1, when a deep drawing package is formed using the multilayer film 1, it is preferable that it can be formed to a drawing depth of 10 mm, and more preferably that it can be formed to a drawing depth of 50 mm.
If the moldability of the multilayer film 1 is within the above range, the multilayer film 1 will have excellent moldability.

The haze of the multilayer film 1 is preferably 3 to 30%, more preferably 3 to 20%, even more preferably 3 to 10%.
If the haze of the multilayer film 1 is within the above range, the multilayer film 1 will have excellent transparency.

The thickness of the multilayer film 1 is preferably 50 to 300 μm, more preferably 80 to 250 μm, and even more preferably 100 to 200 μm.
The strength of the multilayer film 1 can be improved because the thickness of the multilayer film 1 is greater than or equal to the lower limit. On the other hand, since the thickness of the multilayer film 1 is equal to or less than the upper limit value, the multilayer film 1 is prevented from becoming excessively thick.

[Outer layer]
The outer layer 2 is the outermost layer on one side of the multilayer film 1. Outer layer 2 contains polyolefin resin.
By including the polyolefin resin in the outer layer 2, the coefficient of thermal expansion is the same as that of the polyolefin resin contained in the sealant layer 6, which is the outermost layer on the other side of the multilayer film 1, so that curling after retort processing can be suppressed.
The outer layer 2 may contain one type of polyolefin resin, or may contain two or more types of polyolefin resin.

Specifically, the polyolefin resin contained in the outer layer 2 includes, for example, polypropylene (PP), polyethylene (PE), ethylene/vinyl acetate copolymer (EVA), ethylene/acrylic acid copolymer (EAA), and ethylene. /methacrylic acid copolymer (EMAA), ethylene/methyl acrylate copolymer (EMA), ethylene/methyl methacrylate copolymer (EMMA), ethylene/ethyl acrylate copolymer (EEA), ionomer resin, etc. can be mentioned. Examples of polyethylene (PE) include low density polyethylene (LDPE) and linear low density polyethylene (LLDPE).

Among polyolefin resins, polypropylene is preferred. Since polypropylene is a general-purpose resin among polyolefin resins, cost reduction is possible.

The content of the polyolefin resin in the outer layer 2 is preferably 70 to 99% by mass, more preferably 80 to 97% by mass, and 85 to 95% by mass, based on the total mass of the outer layer 2. It is even more preferable.
If the content of the polyolefin resin in the outer layer 2 is within the above range, curling after retort treatment can be suppressed.

The outer layer 2 contains a hydrogenated styrene-butadiene copolymer.
By including the hydrogenated styrene-butadiene copolymer in the outer layer 2, high impact resistance can be imparted to the multilayer film 1. Since the hydrogenated styrene-butadiene copolymer has high impact resistance, it can complement the hard and brittle properties of the aromatic ring-containing polyamide resin contained in the oxygen barrier layer 4 in the multilayer film 1.

The content of the hydrogenated styrene-butadiene copolymer in the outer layer 2 is preferably 1 to 30% by mass, more preferably 3 to 20% by mass, based on the total mass of the outer layer 2. , more preferably 5 to 15% by mass.
If the content of the hydrogenated styrene-butadiene copolymer in the outer layer 2 is within the above range, high impact resistance can be imparted to the multilayer film 1.

The thickness of the outer layer 2 is preferably 5 to 90 μm, more preferably 8 to 60 μm, and even more preferably 10 to 40 μm.

The thickness of the outer layer 2 is preferably 5% or more and 30% or less of the total thickness of the multilayer film 1, more preferably 8% or more and 25% or less, and even more preferably 10% or more and 20% or less. preferable.

When the thickness of the outer layer 2 or the ratio thereof is equal to or greater than the above lower limit, it is possible to suppress occurrence of poor appearance during the film forming process.

[First adhesive layer]
The first adhesive layer 3 is laminated between and adjacent to the outer layer 2 and the oxygen barrier layer 4.
The first adhesive layer 3 increases the interlayer adhesive force between the outer layer 2 and the oxygen barrier layer 4, and can prevent separation between the layers.

The first adhesive layer 3 is a resin layer containing adhesive resin. The adhesive resin contained in the first adhesive layer 3 includes, but is not particularly limited to, acid-modified polyolefin resins, isocyanate compounds, polyester compounds, polyurethane compounds, and the like. Further, specific examples of the polyolefin resin include polyethylene resin, polypropylene resin, and cyclic olefin resin.
The first adhesive layer 3 may contain one type of adhesive resin, or may contain two or more types of adhesive resin.

The thickness of the first adhesive layer 3 is preferably 1 to 60 μm, more preferably 2 to 40 μm, and even more preferably 3 to 20 μm.

The thickness ratio of the first adhesive layer 3 is preferably 1% or more and 20% or less of the total thickness of the multilayer film 1, more preferably 2% or more and 15% or less, and 3% or more and 10% or less. It is more preferable that

When the thickness of the first adhesive layer 3 or the ratio thereof is equal to or greater than the above lower limit, the adhesive strength between the layers is improved, and interlayer peeling during molding can be suppressed.

[Oxygen barrier layer]
The oxygen barrier layer 4 is laminated between and adjacent to the first adhesive layer 3 and the second adhesive layer 5.
The oxygen barrier layer 4 provides the multilayer film 1 with excellent oxygen barrier properties. Therefore, when a package is formed using the multilayer film 1, it is possible to suppress oxygen from entering the package from the outer layer 2 side.

The oxygen barrier layer 4 contains a polyamide resin having an aromatic ring.
By including the polyamide resin having an aromatic ring in the oxygen barrier layer 4, the multilayer film 1 can be provided with excellent oxygen barrier properties, moldability, and transparency.
The oxygen barrier layer 4 may contain one type of polyamide resin having an aromatic ring, or may contain two or more types.

The polyamide resin having an aromatic ring included in the oxygen barrier layer 4 may have the aromatic ring only in the main chain, only in the side chain, or may have the aromatic ring only in the main chain and in the side chain. It may be present in both side chains. Among these, it is preferable that the polyamide resin has an aromatic ring at least in the main chain.
In addition, in this specification, "main chain" means a chain structure formed by polymerization of monomers (monomers). There are long ones.

Specifically, as the polyamide resin having an aromatic ring contained in the oxygen barrier layer 4, for example, a lactam having three or more membered rings, an amino acid, or a nylon salt consisting of a diamine and a dicarboxylic acid can be homopolymerized or copolymerized. Examples include polyamide resins having an aromatic ring obtained by

Specific examples of the lactam having three or more membered rings include ε-caprolactam, ω-enantholactam, ω-laurolactam, α-pyrrolidone, and α-piperidone.

Specific examples of the amino acid include 6-aminocaproic acid, 7-aminoheptanoic acid, 9-aminononanoic acid, 11-aminoundecanoic acid, and 12-aminododecanoic acid.

Specific examples of the diamine constituting the nylon salt include aliphatic amines, alicyclic diamines, and aromatic diamines. Examples of aliphatic amines include tetramethylene diamine, hexamethylene diamine, heptamethylene diamine, octamethylene diamine, nonamethylene diamine, decamethylene diamine, undecamethylene diamine, dodecamethylene diamine, 2,2,4-trimethylhexamethylene diamine, and 2,4,4-trimethylhexamethylene diamine. Examples of alicyclic diamines include 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, isophoronediamine, piperazine, bis(4-aminocyclohexyl)methane, and 2,2-bis- Examples include (4-aminocyclohexyl)propane. Examples of the aromatic diamine include metaxylylene diamine and para-xylylene diamine.

Specific examples of the dicarboxylic acid constituting the nylon salt include aliphatic dicarboxylic acids, alicyclic carboxylic acids, and aromatic dicarboxylic acids. Examples of aliphatic dicarboxylic acids include glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, cepatic acid, undecanedioic acid, and dodecanedioic acid. Examples of alicyclic carboxylic acids include hexahydroterephthalic acid and hexahydroisophthalic acid. Aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, naphthalene dicarboxylic acids (1,2-, 1,3-, 1,4-, 1,5-, 1,6-, 1,7- -, 1,8-, 2,3-, 2,6-, or 2,7-, and the like.

（式（I）中、ｎは２以上の整数である。）

（式（II）中、ｎは２以上の整数であり、Ｘ、Ｙは、置換基である。） Specifically, the polyamide resin having an aromatic ring contained in the oxygen barrier layer 4 is, for example, a compound represented by the general formula (I) (hereinafter, this compound may be referred to as metaxylylene adipamide). ), compounds represented by general formula (II), and the like.

(In formula (I), n is an integer of 2 or more.)

(In formula (II), n is an integer of 2 or more, and X and Y are substituents.)

Among the polyamide resins having an aromatic ring, the above metaxylylene adipamide is preferred. Metaxylylene adipamide can be produced by copolymerizing metaxylylene diamine and adipic acid.

The content of the polyamide resin having an aromatic ring in the oxygen barrier layer 4 is preferably 40 to 60% by mass, more preferably 42 to 58% by mass, based on the total mass of the multilayer film 1. , more preferably 45 to 55% by mass.
If the content of the polyamide resin having an aromatic ring in the oxygen barrier layer 4 is within the above range, the multilayer film 1 can be provided with excellent oxygen barrier properties, moldability, and transparency.

The oxygen barrier layer 4 may contain a known resin having oxygen barrier properties, such as ethylene-vinyl alcohol copolymer resin (EVOH).

The oxygen barrier layer 4 may contain a transparency improver. As the transparency improver contained in the oxygen barrier layer 4, known ones can be used.
By including the transparency improver in the oxygen barrier layer 4, whitening after retort treatment can be prevented.

The thickness of the oxygen barrier layer 4 is preferably 20 to 130 μm, more preferably 30 to 120 μm, and even more preferably 40 to 110 μm.

When the thickness of the oxygen barrier layer 4 or the ratio thereof is equal to or greater than the above lower limit, the oxygen permeability performance required of the multilayer film 1 can be obtained. On the other hand, when the thickness of the oxygen barrier layer 4 or the ratio thereof is equal to or less than the above upper limit, productivity (particularly cost) can be improved.

[Second adhesive layer]
The second adhesive layer 5 is laminated between and adjacent to the oxygen barrier layer 4 and the sealant layer 6. The second adhesive layer 5 increases the interlayer adhesive force between the oxygen barrier layer 4 and the sealant layer 6, and can prevent separation between the layers.

The second adhesive layer 5 is a resin layer containing adhesive resin. Specifically, as the adhesive resin contained in the second adhesive layer 5, for example, the same adhesive resin as the first adhesive layer 3 can be used.

The thickness or ratio thereof of the second adhesive layer 5 can be the same as that of the first adhesive layer 3.

[Sealant layer]
Sealant layer 6 is the outermost layer of multilayer film 1 opposite outer layer 2 . The sealant layers 6 can be bonded to each other or to other members. The bonding method is not particularly limited, but specific examples include heat sealing, ultrasonic sealing, high frequency sealing, impulse sealing, and the like. In this way, a package can be formed by adhering the multilayer films 1 provided with the sealant layer 6 to each other or to other members.

Sealant layer 6 contains polyolefin resin.
By containing the polyolefin resin, the sealant layers 6 can be easily bonded to each other or to other members.
The sealant layer 6 may contain one type of polyolefin resin, or may contain two or more types of polyolefin resin.

The polyolefin resin contained in the sealant layer 6 may be either a homopolymer or a copolymer, and the copolymer may be either a block copolymer or a random copolymer.

Specifically, the polyolefin resin contained in the sealant layer 6 includes, for example, polypropylene (PP), polyethylene (PE), ethylene/vinyl acetate copolymer (EVA), ethylene/acrylic acid copolymer (EAA), Ethylene/methacrylic acid copolymer (EMAA), ethylene/methyl acrylate copolymer (EMA), ethylene/methyl methacrylate copolymer (EMMA), ethylene/ethyl acrylate copolymer (EEA), and ionomer resin etc. Examples of polyethylene (PE) include low density polyethylene (LDPE) and linear low density polyethylene (LLDPE).

Among polyolefin resins, polypropylene is preferred. Since polypropylene is a general-purpose resin among polyolefin resins, cost reduction is possible.

The content of the polyolefin resin in the sealant layer 6 is preferably 70 to 99% by mass, more preferably 80 to 97% by mass, and 85 to 95% by mass, based on the total mass of the sealant layer 6. It is more preferable that
If the content of the polyolefin resin in the sealant layer 6 is within the above range, the sealant layers 6 can be easily bonded to each other or to other members.

The sealant layer 6 can have an easy peel function, that is, a function with excellent peelability when opening the package. Having an easy peel function means, for example, that when the heat seal strength of the heat sealed portion is measured according to JIS Z 0238, it is 1 N/15 mm or more and less than 10 N/15 mm.

The sealant layer 6 may contain a hydrogenated styrene-butadiene copolymer.
By containing the hydrogenated styrene-butadiene copolymer in the sealant layer 6, high impact resistance can be imparted to the multilayer film 1. Since the hydrogenated styrene-butadiene copolymer has high impact resistance, it can complement the hard and brittle properties of the aromatic ring-containing polyamide resin contained in the oxygen barrier layer 4 in the multilayer film 1.

The content of the hydrogenated styrene-butadiene copolymer in the sealant layer 6 is preferably 1 to 30% by mass, and preferably 3 to 20% by mass, based on the total mass of the sealant layer 6. The amount is more preferably 5 to 15% by mass.
If the content of the hydrogenated styrene-butadiene copolymer in the sealant layer 6 is within the above range, high impact resistance can be imparted to the multilayer film 1.

The thickness of the sealant layer 6 is preferably 5 to 100 μm, more preferably 10 to 80 μm, and even more preferably 15 to 50 μm.

The thickness of the sealant layer 6 is preferably 10% or more and 35% or less, more preferably 13% or more and 30% or less, and 15% or more and 25% or less of the total thickness of the multilayer film 1. More preferred.

If the thickness or the ratio thereof of the sealant layer 6 is within the above range, the sealing performance can be sufficiently exhibited, and even if the sealant layer 6 has an easy peel function, peeling defects will not occur.

The sealant layer 6 may be one layer or may have a multilayer structure of two or more layers. When the sealant layer 6 has a multilayer structure of two or more layers, the sealant layer 6 includes a layer containing a homopolymer or block copolymer polyolefin resin and a layer containing a random copolymer polyolefin resin. Good too.
By providing a layer containing a random copolymer polyolefin resin as the sealant layer 6, the sealing performance of the multilayer film 1 can be further improved.

In the sealant layer 6, a layer containing a random copolymer polyolefin resin and a layer containing a homopolymer or block copolymer polyolefin resin are laminated in this order from the sealant layer 6 side to the outer layer 2 side. Alternatively, they may be laminated in this order from the outer layer 2 side to the sealant layer 6 side, but preferably they are laminated in this order from the sealant layer 6 side to the outer layer 2 side.

In the sealant layer 6, a layer containing a random copolymer polyolefin resin and a layer containing a homopolymer or block copolymer polyolefin resin are laminated in this order from the sealant layer 6 side to the outer layer 2 side. Since the layer containing the random copolymer polyolefin resin is located on the sealant layer 6 side, the sealing performance of the multilayer film 1 can be further improved, and at the same time, the layer containing the homopolymer or block copolymer resin on the outer layer 2 side can be further improved. High impact resistance can be imparted to the multilayer film 1 by the layer containing the polyolefin resin.

In the sealant layer 6, the layer containing a homopolymer or block copolymer polyolefin resin and the layer containing a random copolymer polyolefin resin may be two layers in total, or may be alternately repeated one or more times. It may also be a structure in which two layers are laminated.

The thickness of the layer containing the homopolymer or block copolymer polyolefin resin is preferably 55% or more and 85% or less, more preferably 60% or more and 80% or less of the total thickness of the sealant layer 6. More preferably, it is 65% or more and 75% or less.
The thickness of the layer containing the random copolymer polyolefin resin is preferably 15% or more and 45% or less, more preferably 20% or more and 40% or less, and 25% or more of the total thickness of the sealant layer 6. More preferably, it is 35% or less.

The layer containing a homopolymer or block copolymer polyolefin resin may contain a hydrogenated product of a styrene-butadiene copolymer.
When the layer containing the homopolymer or block copolymer polyolefin resin contains the hydrogenated styrene-butadiene copolymer, high impact resistance can be imparted to the multilayer film 1. Since the hydrogenated styrene-butadiene copolymer has high impact resistance, it can complement the hard and brittle properties of the aromatic ring-containing polyamide resin contained in the oxygen barrier layer 4 in the multilayer film 1.

The content of the hydrogenated styrene-butadiene copolymer in the layer containing the homopolymer or block copolymer polyolefin resin is based on the total mass of the layer containing the homopolymer or block copolymer polyolefin resin. It is preferably 1 to 30% by weight, more preferably 3 to 20% by weight, and even more preferably 5 to 15% by weight.
If the content of the hydrogenated styrene-butadiene copolymer in the layer containing the homopolymer or block copolymer polyolefin resin is within the above range, high impact resistance can be imparted to the multilayer film 1. I can do it.

<Method for manufacturing multilayer film>
Next, an example of a method for manufacturing the multilayer film 1 described above will be described.
The method for manufacturing the multilayer film 1 described above is not particularly limited, but may include a coextrusion T-die method such as a feed block method or a multi-manifold method, in which raw material resin, etc. is melt-extruded using several extruders; Examples include an air-cooled or water-cooled coextrusion inflation method, and a lamination method. Among these, a method of forming a film using a coextrusion T-die method is particularly preferred since it is excellent in controlling the thickness of each layer.

Subsequent processes include a dry lamination method, extrusion lamination method, hot melt lamination method, wet lamination method, thermal (thermal) lamination method, etc. in which the single-layer sheets or films forming each layer are bonded together using an appropriate adhesive. and combinations of these methods. Alternatively, they may be laminated by coating.

<Package>
Next, an example of the configuration of a package that is an embodiment of the present invention will be described. The package of this embodiment is a package formed by softening the multilayer film 1 described above and vacuum forming or pressure forming the same. Specifically, the package of this embodiment includes a deep drawing package.

Deep-draw packaging is a bottom material in which one of a pair of films used for packaging containers is indented into a shape suitable for the product in the container forming section of a deep-draw packaging machine, and the product is placed inside the formed bottom material. After accommodating the container, the other film serving as the lid material is applied to degas the container, and the abutting portions of the pair of films are heat-sealed.

<How to use the package>
Next, a method of using the above-mentioned package will be explained. Although the method of using the above-mentioned package is not particularly limited, specifically, first, food is enclosed in the package. Next, heat treatment is performed at 95 to 121° C. for 1 to 60 minutes (retort treatment). After that, by returning it to room temperature, a retort food that can be stored for a long period of time is completed.

Although the embodiments of the present invention have been described above in detail with reference to the drawings, the specific configuration is not limited to these embodiments, and includes designs within the scope of the gist of the present invention. For example, in the multilayer film 1 described above, an example has been described in which the outer layer 2, the first adhesive layer 3, the oxygen barrier layer 4, the second adhesive layer 5, and the sealant layer 6 are configured. A new layer having another function may be provided between the layers or on the outermost layer.

Hereinafter, the effects of the present invention will be explained in detail using Examples and Comparative Examples, but the present invention is not limited to the following Examples.

<Preparation of multilayer film>
Multilayer films of Example 1 and Comparative Examples 1 and 2 were produced as shown below.

(Example 1)
As the multilayer film of Example 1, a multilayer film having the configuration shown in FIG. 1 described above was produced.
As resins included in the outer layer, polypropylene resin (manufactured by Sumitomo Chemical Co., Ltd., product number: FS2011DG3) and hydrogenated styrene-butadiene rubber (manufactured by JSR Corporation, product number: 2324P) were prepared.
In the outer layer, the mixing ratio was adjusted so that the polypropylene resin was 92% by mass and the hydrogenated styrene-butadiene rubber was 8% by mass.

A polyolefin resin (manufactured by Mitsui Chemicals, Inc., product number: QB550) was prepared as the resin contained in the first adhesive layer.
A polyolefin resin (manufactured by Mitsui Chemicals, Inc., product number: QB550) was prepared as the resin contained in the second adhesive layer.

Meta-xylylene adipamide (manufactured by Mitsubishi Gas Chemical Co., Ltd., product number: S6121) was prepared as a resin included in the oxygen barrier layer.

As resins included in the first sealant layer, polypropylene resin (manufactured by Sumitomo Chemical Co., Ltd., product number: FS2011DG3) and hydrogenated styrene-butadiene rubber (manufactured by JSR Corporation, product number: 2324P) were prepared.
In the first sealant layer, the mixing ratio was adjusted so that the polypropylene resin was 92% by mass and the hydrogenated styrene-butadiene rubber was 8% by mass.
A polypropylene resin (manufactured by Sumitomo Chemical Co., Ltd., product number: S131) was prepared as the resin contained in the second sealant layer.

Next, the outer layer, the first adhesive layer, the oxygen barrier layer, the second adhesive layer, the first sealant layer, and the second sealant layer were coextruded in this order to produce a multilayer film. In coextrusion molding, the temperature of the roll for solidifying the molten resin was 40°C.

Note that the total thickness of the multilayer film was 150 μm. The ratio of the thickness of each layer to the total thickness of the multilayer film is 15% for the outer layer, 5% for the first adhesive layer, 50% for the oxygen barrier layer, 5% for the second adhesive layer, and 18% for the first sealant layer. , the second sealant layer was 7%. Table 1 below shows the structure of the multilayer film.
Further, the content of metaxylylene adipamide in the oxygen barrier layer was 57% by mass based on the total mass of the multilayer film.

(Comparative example 1)
A multilayer film was produced in the same manner as in Example 1, except that the ratio of each layer was changed in the coextrusion molding. Table 1 below shows the structure of the multilayer film.

(Comparative example 2)
A multilayer film was produced in the same manner as in Example 1, except that no hydrogenated styrene-butadiene rubber was added (no mixing) in the coextrusion molding. Table 1 below shows the structure of the multilayer film.

<Retort processing>
The retort treatment was carried out using a pressurized hot water cooking sterilizer manufactured by Kusunoki Boiler Co., Ltd. TOC-1) at 120°C for 30 minutes. The results are shown in Table 1.

<Evaluation of oxygen barrier property>
The multilayer films produced in Example 1 and Comparative Examples 1 and 2 were evaluated for oxygen barrier properties before and after retort treatment. The oxygen barrier property was evaluated by measuring the amount of oxygen permeation in an atmosphere of 25° C. and 60% RH.
The oxygen permeation amount was measured using an oxygen permeability measuring device (for example, "OX-TRAN MODEL 2/21" manufactured by MOCON Co., Ltd.) in accordance with the method described in JIS K 7126B method. The results are shown in Table 1.

<Evaluation of moldability>
Evaluation of moldability was performed using a continuous deep drawing packaging machine (MULTIVAC R535). Specifically, when a deep-drawn package is formed using the multilayer films of Example 1 and Comparative Examples 1 and 2, the moldability is good if the drawing depth is 10 mm, and the formability is good if the drawing depth is 50 mm. It was rated as good. The results are shown in Table 1 below.

<Evaluation of cloudiness>
Cloudiness was evaluated based on JISK7136. Specifically, the multilayer films of Example 1 and Comparative Examples 1 and 2 were measured using a haze meter (NDH2000) manufactured by Nippon Denshoku Industries, Ltd. The results are shown in Table 1 below.

<Evaluation of impact resistance>
Impact resistance was evaluated by a falling weight test. The multilayer films of Example 1 and Comparative Examples 1 and 2 were fixed on a horizontal surface, and a weight (tip R5, weight 800 g) was dropped from a height of 30 cm onto the top surface of the multilayer film to give an impact to prevent cracks. Impact resistance was evaluated by observing whether or not the impact occurred. The results are shown in Table 1 below.

*各層の数値は、総厚における各層の厚さの比率を表す。

*The value for each layer represents the ratio of the thickness of each layer to the total thickness.

As shown in Table 1, it was confirmed that the multilayer films of Example 1 and Comparative Examples 1 and 2 all had good moldability.
On the other hand, it was confirmed that the multilayer film of Example 1 was more suppressed in deterioration of oxygen barrier properties during retort treatment than the multilayer film of Comparative Example 1.
Furthermore, it was confirmed that the multilayer film of Example 1 had improved transparency compared to the multilayer film of Comparative Example 2.
Furthermore, it was confirmed that the multilayer film of Example 1 had improved impact resistance than the multilayer film of Comparative Example 2.

The multilayer film of the present invention can be used as a material for packaging, especially food packaging that requires heat sterilization. Furthermore, the packaging body of the present invention can be used as packaging bags, packaging containers, etc. for packaging foods, particularly foods that require heat sterilization.

1...Multilayer film 2...Outer layer 3...First adhesive layer 4...Oxygen barrier layer 5...Second adhesive layer 6...Sealant layer

Claims (4)

an outer layer containing a polyolefin resin and a hydrogenated styrene-butadiene copolymer;
an oxygen barrier layer containing a polyamide resin having an aromatic ring;
a sealant layer containing a polyolefin resin;
A multilayer film for packaging retort food, in which are laminated in this order,
The content of the polyamide resin having an aromatic ring in the oxygen barrier layer is 45 to 60% by mass based on the total mass of the multilayer film ,
The multilayer film has a decrease in oxygen permeability of 1 ml/m ² or less before and after retort treatment. The multilayer film according to claim 1 , wherein the sealant layer is formed by laminating a layer containing a polyolefin resin of a homopolymer or a block copolymer and a layer containing a polyolefin resin of a random copolymer. The multilayer film according to claim 2 , wherein the layer containing the homopolymer or block copolymer polyolefin resin contains a hydrogenated product of a styrene-butadiene copolymer. A package comprising the multilayer film according to any one of claims 1 to 3 .

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