JP7073638B2 - Multilayer film manufacturing method - Google Patents

Description

The present invention relates to multilayer films and packages.

Retort foods that can be stored for a long time at room temperature are required from the viewpoint of improving the quality of life in an aging society and securing a lifeline in the event of a disaster. Retort foods are foods that have been sterilized by retort (pressurization and heating). Since the retort-sterilized product can be made sterile, it can be distributed at room temperature.

For example, in Patent Documents 1 and 2, as a film for retort food packaging, a multilayer polyamide layer including two or more polyamide layers via an adhesive layer, an oxygen barrier layer, an adhesive layer, and a sealant layer are described. , And a composite film in which these are laminated in this order has been proposed.

Further, Patent Document 3 describes high-density polyethylene of 30% by mass or more and 50% by mass or less, linear low-density polyethylene of 40% by mass or more and 50% by mass or less, and high-pressure method low of 10% by mass or more and 20% by mass or less. A film for retort food packaging having a sealant layer made of a resin mainly composed of a polyethylene resin composition made of high-density polyethylene has been proposed.

It is important that the packaging material used for packaging retort-packed foods and the like has transparency in order to confirm the appearance of the food.

Special Fairness 05-075586 Gazette Special Fair 05-075587 Gazette JP-A-2015-229301

However, in the composite films disclosed in Patent Documents 1 to 3, if the resin constituting the film is left for a while, components such as nylon absorb moisture and are contained in the film when the film is formed at a high temperature. There was a problem that the water that had been used evaporates and the film foams.

Further, in order to remove the water contained in the film, when a micron-sized hygroscopic agent is added, the film becomes turbid, and there is a problem that the transparency of the film cannot be ensured.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a multilayer film and a package in which the film does not foam during film molding at a high temperature and the transparency of the film is ensured. ..

As a result of diligent studies on the above problems, the present inventors have obtained a multilayer film and a package in which a moisture absorbing layer containing a metal oxide, a pinhole resistant layer, and an outer layer are laminated in this order. We have found that the water contained in the film is absorbed by the metal oxide, the film does not foam when the film is formed at a high temperature, and the transparency of the film can be ensured, and the present invention has been completed. ..
That is, the present invention is as follows.

[1] Step (A): A step of adding a metal oxide to a polyolefin resin and kneading the resin to disperse the metal oxide in the polyolefin resin to obtain a resin for forming a moisture absorbing layer. (B): Production of a multilayer film including a step of co-extruding the outer layer forming resin, the pinhole resistant layer forming resin, and the moisture absorbing layer forming resin in this order at 150 ° C. to 320 ° C. According to the method, in the multilayer film, a moisture absorbing layer containing the metal oxide, a pinhole resistant layer, and an outer layer are laminated in this order, and the polyolefin resin is a polyethylene resin, a polypropylene resin, or a polypropylene resin. A method for producing a multilayer film which is a modified polyethylene resin and has a content of the metal oxide in the moisture absorbing layer of 0.15 to 10% by mass.
[2] The method for producing a multilayer film according to [1], wherein the metal oxide has an average particle size of 25 to 500 nm.
[3] The metal oxide is at least one selected from the group consisting of calcium oxide, magnesium oxide, barium oxide, lithium oxide, cobalt oxide, sodium oxide, potassium oxide, and titanium oxide. The method for producing a multilayer film according to [1] or [2], which is a seed.
[4] The method for producing a multilayer film according to any one of [1] to [3], wherein the ratio of the thickness of the moisture absorbing layer to the total thickness of the multilayer film is 3 to 80%.

Since the multilayer film of the present invention contains a moisture absorbing layer containing a metal oxide, the moisture contained in the film is absorbed by the metal oxide, the film does not foam during film molding at a high temperature, and the film is transparent. Sex can also be ensured.

It is sectional drawing of the multilayer film which is one Embodiment to which this invention is applied.

Hereinafter, a multilayer film and a package to which the present invention is applied will be described in detail. In addition, in the drawings used in the following explanation, in order to make the features easy to understand, the featured parts may be enlarged for convenience, and the dimensional ratios of each component may not be the same as the actual ones. do not have.

<Multilayer film>
In the multilayer film of the present embodiment, a moisture absorbing layer containing a metal oxide, a pinhole resistant layer, and an outer layer are laminated in this order.

First, a configuration of a multilayer film according to an embodiment to which the present invention is applied will be described. FIG. 1 is a schematic cross-sectional view of a multilayer film 1 according to an embodiment to which the present invention is applied. As shown in FIG. 1, the multilayer film 1 of the present embodiment has an outer layer 2, an adhesive resin layer 3, a pinhole resistant layer 4, an oxygen barrier layer 5, a pinhole resistant layer 6, and an adhesive layer 7. A moisture absorbing layer 8 and a sealant layer 9 are provided, and these are laminated in this order to form a schematic structure.
The multilayer film 1 of the present embodiment can be used as a film for food packaging, particularly for retort food packaging.

The outer layer 2 is the outermost layer on one side of the multilayer film 1.
The resin contained in the outer layer 2 is not particularly limited, and examples thereof include a polyamide resin and the like. The outer layer 2 may contain one type of polyamide resin, or may contain two or more types in combination with other resins. Since the outer layer 2 contains the polyamide resin, the pinhole resistance of the multilayer film 1 can be improved. In addition, by producing a package using this multilayer film 1, it is possible to suppress a decrease in strength that occurs during retort treatment. Further, a resin other than the polyamide resin may be used as the resin contained in the outer layer 2. For example, polypropylene, polyethylene or the like may be used from the viewpoint of suppressing curling after the retort treatment. Further, polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polybutylene succinate, and polyethylene-2,6-naphthalate may be used.

The content of the polyamide resin in the outer layer 2 is preferably 3 to 50% by mass, more preferably 5 to 40% by mass.

In the present embodiment, the "retort treatment" means a treatment of heating the food at a temperature of 100 to 121 ° C. for 1 to 60 minutes in order to store the food for a long period of time.

Specific examples of the polyamide resin contained in the outer layer 2 include a polyamide resin obtained by polymerizing or copolymerizing a nylon salt composed of a three-membered ring or more of lactam, an amino acid, or a diamine and a dicarboxylic acid. Can be mentioned.

Specific examples of the three-membered ring or more lactam include, for example, ε-caprolactam, ω-enantractam, 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, 12-aminododecanoic acid and the like.

Specific examples of the diamine constituting the nylon salt include aliphatic amines, alicyclic diamines, and aromatic diamines. Examples of the aliphatic amine include tetramethylenediamine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, undecamethylenediamine, dodecamethylenediamine, 2,2,4-trimethylhexamethylenediamine, and the like. And 2,4,4-trimethylhexamethylenediamine and the like. Alicyclic diamines include 1,3-bis (aminomethyl) cyclohexane, 1,4-bis (aminomethyl) cyclohexane, isophoronediamine, piperazine, bis (4-aminocyclohexyl) methane, and 2,2-bis-. (4-Aminocyclohexyl) propane and the like can be mentioned. Examples of the aromatic diamine include metaxylylenediamine and paraxylylenediamine.

Specific examples of the dicarboxylic acid constituting the nylon salt include aliphatic dicarboxylic acid, alicyclic carboxylic acid, and aromatic dicarboxylic acid. Examples of the aliphatic dicarboxylic acid include glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sepatic acid, undecandionic acid, dodecandionic acid and the like. Examples of the alicyclic carboxylic acid include hexahydroterephthalic acid and hexahydroisophthalic acid. Examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, and naphthalenedicarboxylic acid (1,2-body, 1,3-body, 1,4-body, 1,5-body, 1,6-body, 1,7). -Body, 1,8-body, 2,3-body, 2,6-body, or 2,7-body) and the like.

Specific examples of the polyamide resin include 4-nylon, 6-nylon, 7-nylon, 11-nylon, 12-nylon, 46-nylon, 66-nylon, 69-nylon, 610-nylon, 611-. Nylon, 612-nylon, 6T-nylon, 6I nylon, 6-nylon and 66-nylon copolymer (nylon 6/66), 6-nylon and 610-nylon copolymer, 6-nylon and 611-nylon copolymer, 6 -Nylon and 12-nylon copolymer (nylon 6/12), 6-nylon and 612 nylon copolymer, 6-nylon and 6T-nylon copolymer, 6-nylon and 6I-nylon copolymer, 6-nylon and 66- Nylon and 610-nylon copolymer, 6-nylon and 66-nylon and 12-nylon copolymer (nylon 6/66/12), 6-nylon and 66-nylon and 612-nylon copolymer, 66-nylon and 6T- Examples include nylon copolymers, 66-nylon and 6I-nylon copolymers, 6T-nylon and 6I-nylon copolymers, and 66-nylon and 6T-nylon and 6I-nylon copolymers. Among them, 6-nylon, 12-nylon, 66-nylon, nylon 6/66, nylon 6/12, nylon 6/66/12 and the like are preferable from the viewpoint of heat resistance, mechanical strength, and availability. ..

Since the component such as nylon that may be contained in the outer layer 2 easily absorbs water, the water contained in the film evaporates when the film is formed at a high temperature, which may cause the film to foam. However, since the multilayer film 1 of the present embodiment contains the metal oxide described later in the moisture absorbing layer, the water contained in the film can be absorbed by the metal oxide, and the film foams when the film is formed at a high temperature. Can be prevented.

Further, the outer layer 2 may contain an antioxidant.
Specific examples of the antioxidant contained in the outer layer 2 include hydroxyphenylpropionic acid esters, phenol-based antioxidants, phosphorus-based antioxidants, sulfur-based antioxidants, and the like.

Examples of the hydroxyphenylpropionic acid ester include hydroxyphenylpropionic acid esters represented by the following formula (I).

In the formula (I), R ¹ represents an alkyl group having 1 to 3 carbon atoms, and a methyl group is preferable from the viewpoint of thermal stability. As the hydroxyphenylpropionic acid ester, 3,9-bis [2- [3- (3-t-butyl-4-hydroxy-5-methylphenyl) propionyloxy] -1,1-dimethylethyl] -2,4 8,10-Tetraoxaspiro [5.5] undecane, 3,9-bis [2- [3- (3-t-butyl-4-hydroxy-5-ethylphenyl) propionyloxy] -1,1-dimethylethyl ] -2,4,8,10-Tetraoxaspiro [5.5] undecane, and 3,9-bis [2- [3- (3-t-butyl-4-hydroxy-5-isopropylphenyl) propionyl) Oxy] -1,1-dimethylethyl] -2,4,8,10-tetraoxaspiro [5.5] undecane and the like can be mentioned.

The hydroxyphenylpropionic acid ester represented by the formula (I) is a reaction derivative such as 3- (3-alkyl-5-t-butyl-4-hydroxyphenyl) propionic acid or an acid chloride or an acid anhydride thereof. , 3,9-Bis (1,1-dimethyl-2-hydroxyethyl) 2,4,8,10-tetraoxaspiro [5.5] Undecane can be produced by reacting with a known method. can.

As the phenol-based antioxidant, the phosphorus-based antioxidant, and the sulfur-based antioxidant, known ones can be used. Examples of the phosphorus-based antioxidant include tris (2,4-di-t-butylphenyl) phosphite, tetrakis (2,4-di-t-butylphenyl) -4,4'-biphenylene phosphite and the like. Be done.

The content of the polyamide resin and the antioxidant in the outer layer 2 is not particularly limited, but the polyamide resin 100 is excellent in that it can reduce the decrease in strength of the multilayer film after the retort treatment and has excellent pinhole resistance. It preferably contains 0.01 to 1.0 parts by mass of the antioxidant, more preferably 0.01 to 0.5 parts by mass, and 0.05 to 0.25 parts by mass with respect to parts by mass. Is particularly preferable.

Specifically, the ratio of the thickness of the outer layer 2 is preferably in the range of 5 to 20%, more preferably 7 to 15% of the total thickness of the multilayer film 1, for example. .. When the ratio of the thickness of the outer layer 2 is within the above range, it is possible to suppress the occurrence of poor appearance in the film forming process and to secure the flexibility of the film.

The adhesive resin layer 3 is laminated between the outer layer 2 and the pinhole-resistant layer 4 so as to be adjacent to the outer layer 2 and the pinhole-resistant layer 4. The adhesive resin layer 3 enhances the adhesive force between the outer layer 2 and the pinhole-resistant layer 4, and can prevent peeling between the layers.

The adhesive resin layer 3 is a resin layer containing an adhesive resin. The adhesive resin contained in the adhesive resin layer 3 is not particularly limited, and examples thereof include acid-modified polyolefin-based resins, isocyanate compounds, polyester-based compounds, and polyurethane compounds. Specific examples of the polyolefin-based resin include polyethylene-based resin, polypropylene-based resin, and cyclic olefin-based resin. The adhesive resin layer may contain one type of adhesive resin or may contain two or more types of adhesive resin.

Specifically, the ratio of the thickness of the adhesive resin layer 3 is preferably, for example, 5 to 40%, more preferably 10 to 20% of the total thickness of the multilayer film 1. When the ratio is 5% or more, the water vapor barrier property is improved, and water absorption of the oxygen barrier layer 5 during heat treatment can be suppressed. On the other hand, when the ratio is 40% or less, the water absorbed by the oxygen barrier layer 5 can easily escape when the temperature is returned to room temperature after the heat treatment, so that the oxygen barrier layer 5 can easily recover from whitening.

The pinhole-resistant layer 4 is laminated between the adhesive resin layer 3 and the oxygen barrier layer 5 so as to be adjacent to the adhesive resin layer 3 and the oxygen barrier layer 5. The pinhole-resistant layer 4 can improve the pinhole resistance of the multilayer film 1. In addition, by producing a package using this multilayer film 1, it is possible to suppress a decrease in strength that occurs during retort treatment.

The pinhole resistant layer 4 preferably contains a polyamide resin. As the polyamide resin contained in the pinhole-resistant layer 4, specifically, for example, the same polyamide resin contained in the outer layer 2 can be used.

The content of the polyamide resin in the pinhole-resistant layer 4 is preferably 3 to 50% by mass, and more preferably 5 to 40% by mass.

Since components such as nylon that may be contained in the pinhole-resistant layer 4 easily absorb water, the water contained in the film evaporates when the film is formed at a high temperature, which causes the film to foam. obtain. However, since the multilayer film 1 of the present embodiment contains the metal oxide described later in the moisture absorbing layer, the water contained in the film can be absorbed by the metal oxide, and the film foams when the film is formed at a high temperature. Can be prevented.

Specifically, the ratio of the thickness of the pinhole-resistant layer 4 is preferably in the range of 3 to 20% of the total thickness of the multilayer film 1, and more preferably in the range of 5 to 15%. preferable. Here, when the ratio of the thickness of the pinhole-resistant layer 4 is within the above range, it is possible to improve the strength of the film and suppress the decrease in flexibility.

The oxygen barrier layer 5 is laminated between the pinhole-resistant layer 4 and the pinhole-resistant layer 6 so as to be adjacent to the pinhole-resistant layer 4 and the pinhole-resistant layer 6. The oxygen barrier layer 5 imparts excellent oxygen barrier properties to the multilayer film 1. Therefore, when the package is formed by using the multilayer film 1, oxygen can be suppressed from entering the inside of the package from the outer layer 2 side. The resin contained in the oxygen barrier layer 5 is not particularly limited as long as it has an oxygen barrier property, but for example, an ethylene-vinyl alcohol copolymer resin (hereinafter, may be simply referred to as “EVOH”). And so on.

The content of EVOH in the oxygen barrier layer 5 is preferably 3 to 30% by mass, more preferably 5 to 20% by mass.

EVOH can be produced by copolymerizing ethylene and vinyl acetate and then hydrolyzing a structural unit derived from vinyl acetate to generate a hydroxyl group. The oxygen barrier layer 5 of the present embodiment is described as EVOH (hereinafter referred to as "heat-resistant EVOH") to which heat resistance, water resistance, etc. are imparted by adding nylon or a cross-linking accelerator during the above-mentioned copolymerization. There is) can be included. When the oxygen barrier layer 5 contains heat-resistant EVOH, the heat resistance and water resistance of the oxygen barrier layer 5 are improved.

Further, as the EVOH contained in the oxygen barrier layer 5, in addition to the above heat-resistant EVOH, EVOH produced without adding nylon or a cross-linking accelerator during copolymerization (hereinafter, referred to as "ordinary EVOH" may be described. Yes) may also be included. By containing ordinary EVOH in addition to the heat-resistant EVOH, the film-forming property of the oxygen barrier layer 5 can be improved.

Here, when the oxygen barrier layer 5 contains normal EVOH and heat-resistant EVOH, the normal EVOH is preferably contained in an amount of 1 to 50% by mass, preferably 20 to 40% by mass, based on the total mass of the oxygen barrier layer 5. It is more preferable that it is contained. By containing 1% by mass or more of ordinary EVOH, the film forming property of the oxygen barrier layer 5 can be improved. On the other hand, when normal EVOH is contained in an amount of 50% by mass or less, sufficient oxygen barrier properties can be obtained. On the other hand, if the oxygen barrier layer 5 contains more than 50% by mass of normal EVOH, the retort resistance performance deteriorates (whitening after retorting, EVOH elutes and derami occurs, etc.), which is preferable. do not have.

The content of the structural unit derived from ethylene in EVOH is 20 to 60 because sufficient oxygen barrier property can be obtained in the oxygen barrier layer 5 and deterioration of appearance such as whitening after retort treatment can be suppressed. It is preferably mol%, more preferably 25-50 mol%. Further, the saponification degree in EVOH is preferably 90% or more, preferably 95%, from the viewpoint that sufficient oxygen barrier property can be obtained in the gas barrier layer and appearance deterioration such as whitening after retort treatment can be suppressed. The above is more preferable.

（式（ＩＩ）中、ｎは２以上の整数である。）

（式（ＩＩＩ）中、ｎは２以上の整数であり、Ｘ、Ｙは、置換基である。） Further, as the oxygen barrier layer 5, a known resin having a gas barrier property and low hygroscopicity, for example, an aromatic polyamide resin having an aromatic ring in the main chain may be used. Examples of the aromatic polyamide resin include those represented by the general formulas (II) and (III).

(In equation (II), n is an integer of 2 or more.)

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

Specifically, the ratio of the thickness of the oxygen barrier layer 5 is preferably in the range of 1 to 20% of the total thickness of the multilayer film 1, and is preferably in the range of 5 to 15%. More preferred. When the ratio of the thickness of the oxygen barrier layer 5 is within the above range, the performance of the oxygen transmittance required for the multilayer film 1 can be obtained, and the productivity (particularly cost) can be improved.

The pinhole-resistant layer 6 is laminated between the oxygen barrier layer 5 and the adhesive layer 7 so as to be adjacent to the oxygen barrier layer 5 and the adhesive layer 7. The pinhole-resistant layer 6 can improve the pinhole resistance of the multilayer film 1. In addition, by producing a package using this multilayer film 1, it is possible to suppress a decrease in strength that occurs during retort treatment.

The pinhole resistant layer 6 preferably contains a polyamide resin. As the polyamide resin contained in the pinhole-resistant layer 6, specifically, for example, the same polyamide resin contained in the outer layer 2 can be used.

The content of the polyamide resin in the pinhole-resistant layer 6 is preferably 3 to 50% by mass, and more preferably 5 to 40% by mass.

Since components such as nylon that may be contained in the pinhole-resistant layer 6 easily absorb water, the water contained in the film evaporates when the film is formed at a high temperature, which causes the film to foam. obtain. However, since the multilayer film 1 of the present embodiment contains the metal oxide described later in the moisture absorbing layer, the water contained in the film can be absorbed by the metal oxide, and the film foams when the film is formed at a high temperature. Can be prevented.

Specifically, the ratio of the thickness of the pinhole-resistant layer 6 is preferably in the range of 3 to 20% of the total thickness of the multilayer film 1, and more preferably in the range of 5 to 15%. preferable. When the ratio of the thickness of the pinhole-resistant layer 6 is within the above range, it is possible to achieve both the strength improvement and the flexibility of the film.

The adhesive layer 7 is laminated between the pinhole-resistant layer 6 and the core layer 8 so as to be adjacent to the pinhole-resistant layer 6 and the core layer 8. The adhesive layer 7 enhances the adhesive force between the pinhole-resistant layer 6 and the core layer 8, and can prevent peeling between the layers.

The adhesive layer 7 contains an adhesive resin. Specifically, as the adhesive resin contained in the adhesive layer 7, the same adhesive resin as the adhesive resin layer 3 can be used.

Specifically, the ratio of the thickness of the adhesive layer 7 is preferably in the range of 3 to 20% of the total thickness of the multilayer film 1, and more preferably in the range of 5 to 15%. preferable. When the ratio of the thickness of the adhesive layer 7 is within the above range, sufficient adhesive force can be obtained.

The moisture absorbing layer 8 is laminated between the adhesive layer 7 and the sealant layer 9 so as to be adjacent to the adhesive layer 7 and the sealant layer 9.
The resin contained in the moisture absorbing layer 8 is not particularly limited, and examples thereof include polyethylene resin, polypropylene resin, and modified polyethylene resin.

The content of the resin in the moisture absorbing layer 8 is preferably 3 to 60% by mass, more preferably 5 to 50% by mass.

The moisture absorbing layer 8 contains a metal oxide. The metal oxide can absorb the water contained in the film and prevent the film from foaming when the film is formed at a high temperature.

From the viewpoint of ensuring the transparency of the film, the metal oxide is preferably nano-sized. Specifically, the average particle size of the metal oxide is preferably 25 to 500 nm, more preferably 30 to 480 nm, and even more preferably 35 to 460 nm. When the average particle size of the metal oxide is 25 nm or more, the hygroscopicity of the film is further improved, and the foaming prevention property of the film is further improved. On the other hand, when the average particle size of the metal oxide is 500 nm or less, sufficient transparency of the film can be ensured.

The content of the metal oxide in the moisture absorbing layer 8 is preferably 0.05 to 20% by mass, more preferably 0.1 to 15% by mass, and preferably 0.15 to 10% by mass. Even more preferable. When the content of the metal oxide in the moisture absorbing layer 8 is 0.05% by mass or more, the hygroscopicity of the film is further improved, and the foaming prevention property of the film is further improved. On the other hand, when the content of the metal oxide in the moisture absorbing layer 8 is 20% by mass or less, sufficient transparency of the film can be ensured.

Metal oxides include calcium oxide (calcium oxide), magnesium oxide (magnesium oxide), barium oxide (barium oxide), lithium oxide (lithium oxide), cobalt oxide (cobalt oxide), and sodium oxide (oxidation). It is preferably at least one selected from the group consisting of sodium), potassium oxide (potassium oxide), and titanium oxide (titanium oxide), preferably calcium oxide (calcium oxide) and magnesium oxide (magnesium oxide). , Barium oxide (barium oxide), and at least one selected from the group consisting of lithium oxides are even more preferable.

Since the metal oxide is a relatively stable compound, it is difficult to decompose at high temperatures during film molding. Therefore, by using the metal oxide, it is possible to avoid the release of water due to the decomposition of the metal oxide.

The ratio of the thickness of the moisture absorbing layer 8 to the total thickness is preferably 3 to 80%, more preferably 4 to 70%, and even more preferably 5 to 60%. When the ratio of the thickness of the moisture absorbing layer 8 is within the above range, the hygroscopicity of the film is further improved, and the foaming prevention property of the film is further improved.

The sealant layer 9 is the outermost layer on the opposite side of the outer layer 2 of the multilayer film 1. The sealant layer 9 can bond the sealant layers 9 to each other or to other members. The bonding method is not particularly limited, and specific examples thereof include heat sealing, ultrasonic sealing, high frequency sealing, and impulse sealing. In this way, the package can be formed by adhering the multilayer films 1 provided with the sealant layer 9 to each other.

The sealant layer 9 preferably contains one or more types of polyolefin-based resin. Specific examples of the polyolefin resin contained in the sealant layer 9 include polypropylene, polyethylene, ethylene / vinyl acetate copolymer, ethylene / acrylic acid copolymer, ethylene / methacrylic acid copolymer, and ethylene / acrylic. Examples thereof include a methyl acid copolymer, an ethylene / methyl methacrylate copolymer, and an ethylene / ethyl acrylate copolymer. More specifically, for example, high-density polyethylene and polypropylene can be mentioned. The sealant layer 9 may be made of the above resin, may contain one kind of the above resin, or may contain two or more kinds of the above resin.

The sealant layer 9 can have an easy peel function, that is, a function excellent in peelability. Having an easy peel function means, for example, that the heat seal strength of the heat-sealed portion is 1N / 15 mm or more and less than 10N / 15 mm when measured according to JIS Z 0238.

Specifically, the ratio of the thickness of the sealant layer 9 is preferably, for example, 5% or more and 70% or less of the total thickness of the multilayer film 1, and more preferably 5% or more and 20% or less. It is preferable, and even more preferably, it is in the range of 5% or more and 10% or less. When the ratio of the thickness of the sealant layer 9 is within the above range, the sealing performance can be sufficiently exhibited, and even if the sealant layer 9 has an easy peel function, peeling failure does not occur.

<Manufacturing method of multilayer film>
Next, an example of the above-mentioned manufacturing method of the multilayer film 1 will be described.
The method for producing the resin composition in which the metal oxide is dispersed used for forming the moisture absorbing layer is not particularly limited, and a method of adding the metal oxide to the resin contained in the moisture absorbing layer 8 and kneading the resin can be mentioned. Be done. From the viewpoint of improving the dispersion efficiency, a dispersant, a coupling agent, or the like may be added at the time of kneading.

The method for producing the multilayer film 1 described above is not particularly limited, but is a coextrusion T-die method such as a feed block method or a multi-manifold method in which a resin or the like as a raw material is melt-extruded by several extruders. Examples thereof include an air-cooled or water-cooled coextrusion inflation method and a laminating method. Among them, the method of forming a film by the coextrusion T-die method is particularly preferable because it is excellent in controlling the thickness of each layer.

Subsequent steps include a dry laminating method, an extrusion laminating method, a hot melt laminating method, a wet laminating method, a thermal (heat) laminating method, etc., in which a single-layer sheet or film forming each layer is bonded together using an appropriate adhesive. And those methods are used in combination. Further, it may be laminated by a coating method.

The temperature at the time of film molding is preferably 150 ° C. to 320 ° C., more preferably 180 ° C. to 290 ° C.

<Packaging>
Next, an example of the configuration of the package, which is an embodiment to which the present invention is applied, will be described. The package of the present embodiment is a package formed by softening the above-mentioned multilayer film 1 and vacuum forming or compressed air forming the same. Specific examples of the package of the present embodiment include a skin pack package and a deeply squeezed package.

In deep-drawing packaging, one of the pair of films used for the packaging container is dented and molded into a shape suitable for the product at the container forming part of the deep-drawing packaging machine to make a bottom material, and the product is contained in the molded bottom material. After accommodating the film, the other film serving as a lid material is applied to deaerate the film, and the abutting portion of the pair of the films is heat-sealed.

Next, an example of the above-mentioned method for manufacturing a package will be described.
The method for manufacturing the package described above is not particularly limited, but specifically, first, the packaged object is placed on the mount. Next, the multilayer film 1 described above is softened and used to coat the object to be packaged so that the sealant layer 9 faces the mount. Next, the multilayer film 1 is stretched along the outer shape of the packaged object by suction, and then the mount and the multilayer film 1 are adhered to each other. The package of the present embodiment can be manufactured by the above manufacturing method. The above-mentioned structure of the package is an example, and the present invention is not limited to this. Specifically, for example, a package having a storage portion formed by deep drawing may be used.

<How to use the package>
Next, the method of using the above-mentioned package will be described.
The method of using the above-mentioned package is not particularly limited, but specifically, first, the food is enclosed in the package. Next, heat treatment is performed at 100 to 121 ° C. for 1 to 60 minutes (retort treatment). After that, by returning to room temperature, a retort food that can be stored for a long time is completed.

As described above, according to the multilayer film 1 of the present embodiment, since the moisture absorbing layer containing the metal oxide is contained, the water contained in the film is absorbed by the metal oxide, and the film is formed at a high temperature. The film does not foam, and the transparency of the film can be ensured.

Although the embodiments of the present invention have been described in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs and the like within a range that does not deviate from the gist of the present invention. For example, in the multilayer film 1 described above, the outer layer 2, the adhesive resin layer 3, the pinhole resistant layer 4, the oxygen barrier layer 5, the pinhole resistant layer 6, the adhesive layer 7, and the moisture absorbing layer 8 are included. Although the example of being provided with the sealant layer 9 has been described, a layer having another function may be newly provided between the layers or the outermost layer. Further, any layer other than the outer layer, the pinhole resistant layer, the moisture absorbing layer, and the sealant layer may be removed.

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

<Manufacturing of multilayer film>
As shown below, multilayer films of Examples 1 to 3 and Comparative Example 1 were prepared.

(Example 1)
As the multilayer film of Example 1, a multilayer film having the structure shown in FIG. 1 described above was produced.
As the resin contained in the outer layer, the first pinhole-resistant layer, and the second pinhole-resistant layer, a polyamide resin (manufactured by Ube Kosan Co., Ltd., product number: Ube Nylon 1022B) was prepared.
Further, as the adhesive resin layer and the resin contained in the adhesive layer, a polyolefin resin (manufactured by Mitsui Chemicals, Inc., product number: Admar NF536) was prepared.
Further, as the resin contained in the oxygen barrier layer, heat-resistant EVOH (manufactured by Kuraray Co., Ltd., product number: FR101B) and ordinary EVOH (manufactured by Kuraray Co., Ltd., product number: J171B) were prepared.
Further, as a resin contained in the moisture absorbing layer, a low density polyethylene resin (made of Ube-Maruzen polyethylene, product number: F222NH, density: 0.92 g / cm ³ ) was prepared.
Further, as a resin contained in the sealant layer, a high-density polyethylene resin (HDPE; manufactured by Prime Polymer Co., Ltd., product number: Hi-Zex 2100J) was prepared.

Calcium oxide (average particle size 250 nm) was added to the resin contained in the moisture-absorbing layer and kneaded for 10 minutes to disperse the metal oxide in the moisture-absorbing layer. At that time, the content of the metal oxide in the moisture absorbing layer was adjusted to be 0.60% by mass.

Next, the outer layer, the adhesive resin layer, the first pinhole resistant layer, the oxygen barrier layer, the second pinhole resistant layer, the adhesive layer, the moisture absorbing layer, and the sealant layer are formed in this order. A multilayer film was produced by coextrusion molding at 260 ° C. At that time, it was adjusted so that 70% by mass of heat-resistant EVOH was contained and 30% by mass of normal EVOH was contained with respect to the total mass of the oxygen barrier layer.

The total thickness of the multilayer film was 120 μm. The ratio of the thickness of each layer to the total thickness of the multilayer film is 20% for the outer layer, 10% for the adhesive resin layer, 15% for the first pinhole resistant layer, 10% for the oxygen barrier layer, and the second pinhole resistant. The layer was 15%, the adhesive layer was 10%, the moisture absorbing layer was 10%, and the sealant layer was 10%. Table 1 below shows the structure of the multilayer film.

(Example 2)
A multilayer film was produced in the same manner as in Example 1 except that magnesium oxide (average particle size 550 nm) was used instead of calcium oxide. Table 1 below shows the structure of the multilayer film.

(Example 3)
A multilayer film was produced in the same manner as in Example 1 except that the content of the metal oxide in the moisture absorbing layer was 25% by mass. Table 1 below shows the structure of the multilayer film.

(Example 4)
A multilayer film was produced in the same manner as in Example 1 except that the average particle size of the metal oxide was 20 nm. Table 1 below shows the structure of the multilayer film.

(Comparative Example 1)
A multilayer film was produced in the same manner as in Example 1 except that the metal oxide was not dispersed in the moisture absorbing layer. Table 1 below shows the structure of the multilayer film.

<Evaluation of film characteristics>
The multilayer films of Examples 1 to 3 and Comparative Example 1 were evaluated for foamability and transparency according to the following evaluation criteria, respectively.

(Effervescent)
The foamability was evaluated by visually confirming the presence or absence of foaming in the film-formed film as follows.
◯: No foaming has occurred.
Δ: Less foaming occurs.
X: Frequent foaming occurs.

(transparency)
The transparency was evaluated by measuring the cloudiness of the film-formed film (Nippon Denshoku Haze Meter NDH2000) and visually judging the visibility as follows.
◯: The degree of cloudiness is less than 10%, and it is not cloudy.
Δ: The degree of cloudiness is 10% or more and less than 15%, and it is slightly cloudy.
X: The degree of cloudiness is 15% or more, and it is cloudy.

*吸湿層以外の各層の数値は、総厚における各層の厚さの比率[%]を表す。 The results are shown in Table 1 below.

* The numerical value of each layer other than the moisture absorbing layer represents the ratio [%] of the thickness of each layer to the total thickness.

As shown in Table 1, in a multilayer film in which a moisture absorbing layer containing a metal oxide, a pinhole resistant layer, and an outer layer are laminated in this order, the film does not foam during film molding at a high temperature, and the film is further formed. It was confirmed that the transparency of the film was also ensured.
Further, in Examples 1 to 3, no abnormality of the multilayer film suggesting whitening or elution of the oxygen barrier layer was observed.

The multilayer film of the present invention can be used as a material for a package, particularly a package for retort foods. In addition, the package of the present invention may be used as a packaging bag, a packaging container, or the like for packaging foods, particularly retort-packed foods.

1 ... Multilayer film 2 ... Outer layer 3 ... Adhesive resin layer 4 ... Pinhole resistant layer 5 ... Oxygen barrier layer 6 ... Pinhole resistant layer 7 ... Adhesive layer 8 ... Moisture absorbing layer 9 ... Sealant layer

Claims (4)

Step (A): A step of adding a metal oxide to a polyolefin-based resin and kneading the mixture to disperse the metal oxide in the polyolefin-based resin to obtain a resin for forming a moisture-absorbing layer.
Step (B): A step of coextruding the outer layer forming resin, the pinhole resistant layer forming resin, and the moisture absorbing layer forming resin in this order at 150 ° C. to 320 ° C.
Is a method for manufacturing a multilayer film containing
The multilayer film has a hygroscopic layer containing the metal oxide and
With a pinhole resistant layer,
With the outer layer,
Are stacked in this order,
The polyolefin resin is a polyethylene resin, a polypropylene resin, or a modified polyethylene resin.
A method for producing a multilayer film in which the content of the metal oxide in the moisture absorbing layer is 0.15 to 10% by mass. The method for producing a multilayer film according to claim 1, wherein the metal oxide has an average particle size of 25 to 500 nm. The metal oxide is at least one selected from the group consisting of calcium oxide, magnesium oxide, barium oxide, lithium oxide, cobalt oxide, sodium oxide, potassium oxide, and titanium oxide. , The method for producing a multilayer film according to claim 1 or 2. The method for producing a multilayer film according to any one of claims 1 to 3, wherein the ratio of the thickness of the moisture absorbing layer to the total thickness of the multilayer film is 3 to 80%.

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