JP2019059122A - Multilayer film and package - Google Patents

Abstract

To provide a multilayer film in which width shrinkage after film production is suppressed, and a package.SOLUTION: A multilayer film has a sealant layer containing a polyolefin resin and an outer layer containing a polyamide resin, where a phase difference average value (Rth) in a film thickness direction is 100 nm or more.SELECTED DRAWING: Figure 1

Description

  The present invention relates to multilayer films and packages.

  From the point of the improvement of the quality of life in the aging society and the securing of the lifeline at the time of disaster, the retort food which can be stored for a long time at normal temperature is required. Retort food refers to retort (pressure heating) sterilized food. The retort-sterilized product can be distributed at normal temperature because it can be made sterile.

  For example, Patent Documents 1 and 2 disclose, 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. A composite film is proposed in which these are laminated in this order.

  In addition, in Patent Document 3, high density polyethylene of 30% by mass to 50% by mass, linear low density polyethylene of 40% by mass to 50% by mass, and high pressure method low of 10% by mass to 20% by mass A film for retort food packaging has been proposed which is provided with a sealant layer consisting mainly of a polyethylene resin composition consisting mainly of density polyethylene.

Japanese Patent Publication No. 05-075586 Japanese Patent Publication No. 05-755587 JP, 2015-229301, A

  However, the composite films disclosed in Patent Documents 1 to 3 have a problem that width contraction occurs after film formation. This invention is made in view of the said situation, Comprising: It makes it a subject to provide the multilayer film and package by which width | variety shrinkage | contraction after film forming was suppressed.

  As a result of intensive studies on the above problems, the present inventors have found that width contraction after film formation can be suppressed by using a multilayer film having a specific retardation average value (Rth) in the film thickness direction. We came to complete the invention. That is, the present invention is as follows.

[1] A multilayer film comprising a sealant layer containing a polyolefin resin and an outer layer containing a polyamide resin, and having a retardation average value (Rth) in the film thickness direction of 100 nm or more.
[2] The multilayer film according to [1], further comprising an intermediate layer between the sealant layer and the outer layer.
[3] The multilayer according to [1] or [2], wherein the polyolefin resin is high density polyethylene, linear low density polyethylene, low density polyethylene, ethylene copolymer, polypropylene, or polypropylene copolymer the film.
[4] The multilayer film according to any one of [1] to [3], wherein the polyamide resin is 6-nylon, 12-nylon, 66-nylon, copolymer nylon, or amorphous nylon.
[5] The multilayer film according to any one of [1] to [4], wherein the intermediate layer comprises a barrier layer.
[6] A package comprising the multilayer film according to any one of [1] to [5].

  Since the multilayer film and the package of the present invention have a specific retardation average value (Rth) in the film thickness direction, width contraction after film formation can be suppressed.

It is a cross-sectional schematic diagram of the multilayer film of this embodiment. It is a retardation-change amount plot of a multilayer film.

  Hereinafter, the multilayer film and package which are one Embodiment to which this invention is applied are demonstrated in detail. In the drawings used in the following description, in order to make the features easy to understand, the features that are the features may be enlarged for the sake of convenience, and the dimensional ratio of each component may be limited to the same as the actual Absent.

<Multilayer film>
The structure of the multilayer film of the present embodiment will be described. FIG. 1 is a schematic cross-sectional view of a multilayer film 1 of the present embodiment. As shown in FIG. 1, the multilayer film 1 of the present embodiment includes 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 core layer 8 and a sealant layer 9, which are laminated in this order and roughly configured.
The multilayer film 1 of the present embodiment can be used as a film for food packaging, in particular for retort food packaging.

  The multilayer film 1 of the present embodiment includes a sealant layer 9 containing a polyolefin resin and an outer layer 2 containing a polyamide resin, and the retardation average value (Rth) in the film thickness direction is 100 nm or more.

The multilayer film 1 of the present embodiment is, as an intermediate layer, between the sealant layer 9 and the outer layer 2, the adhesive resin layer 3, the pinhole resistant layer 4, the oxygen barrier layer 5, and the pinhole resistant layer 6. , An adhesive layer 7 and a core layer 8. These intermediate layers are optional layers in the multilayer film 1, and the multilayer film 1 may not have these one or two or more layers, but is superior to the multilayer film 1 by being provided. Characteristics can be given.
However, the multilayer film 1 preferably includes a barrier layer as an intermediate layer. Thus, the multilayer film 1 provided with the barrier layer can suppress the content deterioration when the film is used as a package.

  The outer layer 2 is the outermost layer on one side of the multilayer film 1. The outer layer 2 contains a polyamide resin. When the outer layer 2 contains a polyamide-based resin, the pinhole resistance of the multilayer film 1 can be improved. Moreover, by producing a package using this multilayer film 1, it is possible to suppress the reduction in strength that occurs when retort processing is performed. Further, the outer layer 2 may contain other resins in addition to the polyamide resin. Examples of other resins include polypropylene and polyethylene from the viewpoint of suppressing curling after retort treatment.

  In addition, in this embodiment, in order to make a foodstuff preserve | save a long-term, the process heated at the temperature of 100-121 degreeC for 1 to 60 minutes is meant.

  Specifically, as the polyamide-based resin contained in the outer layer 2, for example, a polyamide obtained by homopolymerization or copolymerization of a lactam having 3 or more rings, an amino acid, or a nylon salt composed of diamine and dicarboxylic acid. Examples include resin-based resins.

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

  Specific examples of the amino acids 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. As aliphatic amines, tetramethylenediamine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, undecamethylenediamine, dodecamethylenediamine, 2,2,4-trimethylhexamethylenediamine, And 2,4,4-trimethylhexamethylene diamine and the like. Examples of alicyclic diamines include 1,3-bis (aminomethyl) cyclohexane, 1,4-bis (aminomethyl) cyclohexane, isophorone diamine, piperazine, bis (4-aminocyclohexyl) methane, and 2,2-bis- (4-aminocyclohexyl) propane and the like. Examples of the aromatic diamine include metaxylylene diamine and paraxylylene 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. As aromatic dicarboxylic acid, terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid (1,2-body, 1,3-body, 1,4-body, 1,5-body, 1,6-body, 1,7) -, 1, 8-body, 2,3-body, 2, 6-body or 2, 7-body) and the like.

Specifically as a polyamide-type resin, 4-nylon, 6-nylon, 7-nylon, 11-nylon, 12-nylon, 46-nylon, 66-nylon, 69-nylon, 610-nylon, 611, for example. -Nylon, 612-nylon, 6T-nylon, 6I nylon, copolymer nylon, amorphous nylon, etc., and among them, 6-nylon, 12-from the viewpoint of heat resistance, mechanical strength and availability. Preferred are nylon, 66-nylon, copolymer nylon, and amorphous nylon. Specifically as copolymer nylon, for example, copolymer of 6-nylon and 66-nylon (nylon 6/66), copolymer of 6-nylon and 610-nylon, copolymer of 6-nylon and 611-nylon, 6 -Copolymer of nylon and 12-nylon (nylon 6/12), copolymer of 6-nylon and 612 nylon, copolymer of 6-nylon and 6T-nylon, copolymer of 6-nylon and 6I-nylon, 6-nylon and 66- Copolymer of nylon and 610-nylon, copolymer of 6-nylon and 66-nylon and 12-nylon (nylon 6/66/12), copolymer of 6-nylon and 66-nylon and 612-nylon, 66-nylon and 6T- Copolymers of nylon, 66-nylon and 6I-nylon Mer, 6t-copolymers of nylon and 6I- nylon, and 66-copolymers such as nylon and 6t-nylon and 6I- nylon.
The outer layer 2 may contain one type of the above-mentioned resin, or may contain two or more types.

  The outer layer 2 may also contain an antioxidant. Specific examples of the antioxidant contained in the outer layer 2 include hydroxyphenyl propionate, phenol-based antioxidant, phosphorus-based antioxidant, and sulfur-based antioxidant.

  Examples of the hydroxyphenyl propionate include hydroxyphenyl propionate represented by the following formula (I).

In Formula (I), R ¹ represents an alkyl group having 1 to 3 carbon atoms, and in particular, a methyl group is preferable in terms of heat stability. As hydroxyphenyl propionate, 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 etc. are mentioned.

  The hydroxyphenyl propionate represented by the formula (I) can be used with 3- (3-alkyl-5-t-butyl-4-hydroxyphenyl) propionic acid or a reactive derivative thereof such as acid chloride or acid anhydride. , 3,9-bis (1,1-dimethyl-2-hydroxyethyl) 2,4,8,10-tetraoxaspiro [5,5] undecanes by a known method. it can.

  Well-known thing can be used for a phenolic antioxidant, phosphorus type antioxidant, and sulfur type antioxidant. Examples of phosphorus antioxidants include tris (2,4-di-t-butylphenyl) phosphite, and tetrakis (2,4-di-t-butylphenyl) -4,4′-biphenylene phosphite and the like. Be

  The content of the polyamide-based resin and the antioxidant in the outer layer 2 is not particularly limited. However, the polyamide-based resin can reduce the reduction in strength of the multilayer film after retort treatment and is excellent in pinhole resistance. It is preferable to contain 0.01-1.0 mass part of antioxidant with respect to 100 mass parts of resin, it is more preferable to contain 0.01-0.5 mass part, and 0.05-0.25 mass part It is particularly preferred to include.

  Specifically, the thickness ratio of the outer layer 2 is preferably, for example, in the range of 3 to 30% of the total thickness of the multilayer film 1, and more preferably in the range of 5 to 25%. . While being able to suppress generation | occurrence | production of an appearance defect in the film forming process as the ratio of the thickness of the outer layer 2 is in the said range, the softness | flexibility of a film can be ensured.

  The adhesive resin layer 3 is laminated between the outer layer 2 and the pinhole resistant layer 4 so as to be adjacent thereto. The adhesion between the outer layer 2 and the pinhole resistant layer 4 is enhanced by the adhesive resin layer 3, and peeling between the layers can be prevented.

  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 an acid-modified polyolefin resin, an isocyanate compound, a polyester compound, and a polyurethane compound. Moreover, specifically as a polyolefin resin, a polyethylene-type resin, a polypropylene resin, cyclic olefin resin etc. are mentioned, for example. The adhesive resin layer may contain one type of adhesive resin, or may contain two or more types.

  Specifically, the thickness ratio of the adhesive resin layer 3 is, for example, preferably 5 to 40% of the total thickness of the multilayer film 1, and more preferably 10 to 20%. When the ratio is 5% or more, the water vapor barrier property is improved, and it is possible to suppress the water absorption of the oxygen barrier layer 5 when the heat treatment is performed. On the other hand, when the ratio is 40% or less, when the temperature is returned to normal temperature after the heat treatment, the water absorbed by the oxygen barrier layer 5 is easily removed, and the oxygen barrier layer 5 is easily recovered from the 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 thereto. The pinhole resistance of the multilayer film 1 can be improved by the pinhole resistance layer 4. Moreover, by producing a package using this multilayer film 1, it is possible to suppress the reduction in strength that occurs when retort processing is performed.

  The pinhole resistant layer 4 preferably contains a polyamide resin. Specifically, as the polyamide resin contained in the pinhole resistant layer 4, for example, the same one as the polyamide resin contained in the outer layer 2 can be used.

  Specifically, the ratio of the thickness of the pinhole resistant layer 4 is preferably, for example, 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 suppress the decrease in flexibility while improving the strength of the film.

  Specifically as a barrier layer, an oxygen barrier layer, a water vapor barrier layer, etc. are mentioned, for example. Among these, the barrier layer is preferably an oxygen barrier layer.

  The oxygen barrier layer 5 is laminated between the pinhole resistant layer 4 and the pinhole resistant layer 6 so as to be adjacent thereto. The oxygen barrier layer 5 provides the multilayer film 1 with excellent oxygen barrier properties. Therefore, when the package is formed using the multilayer film 1, it is possible to suppress the entry of oxygen into the interior 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 oxygen barrier properties, but, for example, ethylene-vinyl alcohol copolymer resin (hereinafter, may be simply referred to as "EVOH") Can be mentioned. When the oxygen barrier layer 5 contains EVOH, the film forming property of the oxygen barrier layer 5 can be improved.

  EVOH can be produced by copolymerizing ethylene and vinyl acetate and then hydrolyzing a vinyl acetate component to form a vinyl alcohol group. The oxygen barrier layer 5 may additionally include EVOH produced by adding nylon or a crosslinking accelerator at the time of copolymerization (hereinafter, may be simply referred to as “EVOH having heat resistance”). Thereby, the heat resistance and the water resistance of the oxygen barrier layer 5 are improved.

  When the oxygen barrier layer 5 contains EVOH, normal EVOH and EVOH having heat resistance may be mixed. At that time, it is preferable that 50% by mass or more of the total mass of the oxygen barrier layer 5 is included in the heat resistant EVOH. By containing 50% by mass or more of EVOH having heat resistance, it is possible to improve retort resistance performance (whitening suppression after retort, EVOH elution and prevention of delamination occurrence, etc.).

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

（式（１）中、ｎは２以上の整数である。）

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

(In the formula (1), n is an integer of 2 or more.)

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

  Specifically, the thickness ratio of the oxygen barrier layer 5 is, for example, preferably in the range of 1 to 20% of the total thickness of the multilayer film 1, and more preferably in the range of 5 to 15%. . When the ratio of the thickness of the oxygen barrier layer 5 is within the above range, the performance of the oxygen permeability 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 thereto. The pinhole resistance of the multilayer film 1 can be improved by the pinhole resistance layer 6. Moreover, by producing a package using this multilayer film 1, it is possible to suppress the reduction in strength that occurs when retort processing is performed.

  The pinhole resistant layer 6 preferably contains a polyamide resin. Specifically, as the polyamide resin contained in the pinhole resistant layer 6, for example, the same one as the polyamide resin contained in the outer layer 2 can be used.

  Specifically, the thickness ratio of the pinhole resistant layer 6 is preferably, for example, 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, both the strength improvement and the flexibility of the film can be achieved.

  The adhesive layer 7 is laminated between the pinhole resistant layer 6 and the core layer 8 so as to be adjacent to them. The adhesion between the pinhole resistant layer 6 and the core layer 8 is enhanced by the adhesive layer 7, and peeling between the layers can be prevented.

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

  Specifically, the thickness ratio of the adhesive layer 7 is, for example, 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. If the thickness ratio of the adhesive layer 7 is within the above range, sufficient adhesion can be obtained.

  The core layer 8 is laminated between the adhesive layer 7 and the sealant layer 9 so as to be adjacent thereto. The core layer 8 provides the multilayer film 1 with excellent flexibility, impact resistance and water vapor barrier properties.

The core layer 8 preferably contains a polyolefin resin having a density of less than 0.95 g / cm ³ . Specific examples of the polyolefin resin having a density of less than 0.95 g / cm ³ include polyethylene resins and polypropylene resins, more specifically, medium density polyethylene, linear low density polyethylene, and low. Density polyethylene is mentioned.

  Specifically, the thickness ratio of the core layer 8 is preferably, for example, in the range of 20 to 60% of the total thickness of the multilayer film 1. Here, if the ratio of the core layer 8 is within the above range, productivity can be improved and the ratio of other functional layers can be maintained.

  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 adhere to the sealant layers 9 or to other members. The bonding method is not particularly limited, and specific examples include a heat seal, an ultrasonic seal, a high frequency seal, an impulse seal and the like. Thus, a package can be formed by adhering the multilayer films 1 provided with the sealant layer 9 to each other.

  The sealant layer 9 contains a polyolefin resin. Specific examples of the polyolefin resin contained in the sealant layer 9 include high density polyethylene, linear low density polyethylene, low density polyethylene, ethylene copolymer, polypropylene, and polypropylene copolymer. When the sealant layer 9 contains the above-mentioned resin, the sealant layers 9 can be easily adhered to each other or to other members. The sealant layer 9 may contain one kind of the above-mentioned resin, or may contain two or more kinds.

  The sealant layer 9 can have an easy peel function, that is, a function excellent in peelability at the time of opening. Having an easy peel function means, for example, 3N / 15 mm or more and less than 10 N / 15 mm when the heat seal strength of the heat-sealed portion is measured according to JIS Z 0238.

  Specifically, the thickness ratio of the sealant layer 9 is preferably, for example, 3% or more and 60% or less of the total thickness of the multilayer film 1, and more preferably in the range of 4% or more and 20% or less. preferable. If the ratio of the thickness of the sealant layer 9 is within the above range, the sealing performance can be sufficiently exhibited, and the peeling failure does not occur even if it has the easy peel function.

The retardation δ in the film thickness direction of the multilayer film is defined by the following equation.
Retardation δ = photoelastic coefficient β × thickness d × stress σ
The phase shift (phase difference) when light emitted from the light source passes through the multilayer film is measured by a polarization image sensor and output. Then, the in-plane average of the phase difference at each point in the plane is taken as the phase difference average value (Rth).

  When a plot was carried out between the retardation average value (Rth) in the film thickness direction of the multilayer film 1 and the amount of change after film formation, it was found that there is a high negative correlation between them (see FIG. 2) ). In addition, it was found that the tendency of the ceiling was not seen even at high phase difference. That is, the inventors of the present invention found that the width shrinkage after film formation of the multilayer film can be suppressed by increasing the phase difference in the film thickness direction. In FIG. 2, for example, a variation of 3.0 mm means that a contraction of 3.0 mm has occurred.

  When the retardation average value (Rth) in the film thickness direction of the multilayer film is increased, the polyolefin resin contained in the sealant layer is crystallized, and the polyamide resin contained in the outer layer is ordered (stabilized). It is presumed that width contraction during film formation of the film is suppressed. In addition, ordering (stabilization) refers to movement of molecules so as to be in a more stable state although they do not reach crystals.

Specifically, the multilayer film 1 has a retardation average value (Rth) in the film thickness direction of 100 nm or more, preferably 150 nm or more. When the retardation average value (Rth) in the film thickness direction is within the above range, width contraction at the time of film formation of the multilayer film can be suppressed. Specifically, when the film thickness of the multilayer film is 30 mm, when the retardation average value (Rth) in the film thickness direction is 100 nm or more, the shrinkage amount in the film thickness direction can be 4.0 mm or less When the retardation average value (Rth) in the film thickness direction is 150 nm or more, the shrinkage amount in the film thickness direction can be 3.0 mm or less.
The higher the retardation average value (Rth) in the film thickness direction, the more preferable it is because width contraction during film formation of the multilayer film is suppressed.

<Method of manufacturing multilayer film>
Next, an example of the manufacturing method of the multilayer film 1 mentioned above is demonstrated.
The method for producing the multilayer film 1 described above is not particularly limited, but a co-extrusion T-die method such as a feed block method or a multi-manifold method in which a resin as a raw material is melt-extruded by several extruders. Among them, a method of forming a film by a co-extrusion T-die method is particularly preferable in that the thickness control of each layer is excellent, including an air cooling type or a water cooling type co-extrusion inflation method and a laminating method.

  As a subsequent step, a dry lamination method, an extrusion lamination method, a hot melt lamination method, a wet lamination method, a thermal (thermal) lamination method, etc., in which a single layer sheet or film forming each layer is laminated using a suitable adhesive And those methods are used in combination. Moreover, you may laminate | stack by the method by coating.

<Packaging body>
Next, an example of the configuration of a package according to an embodiment of the present invention will be described. The package of the present embodiment is a package formed by softening the multilayer film 1 described above and vacuum-molding or pressure-molding the same. Specifically, the package of the present embodiment includes, for example, a skin pack package, a deep-draw package, and the like.

  Deep draw packaging refers to forming one of the pair of films used for the packaging container into a shape suitable for the product in the container forming part of the deep draw packaging machine to form a bottom material, and the product in the formed bottom material And the other film to be a lid material is deaerated and degassing, and the contact portion of the pair of films is heat sealed.

  Next, an example of the manufacturing method of the package mentioned above is demonstrated. Although the manufacturing method of the package body mentioned above is not specifically limited, Specifically, a to-be-packaged thing is first mounted on a mount. Next, the multilayer film 1 described above is softened and used to coat the package so that the sealant layer 9 faces the backing. Next, the multilayer film 1 is stretched along the outer shape of the package by suction, and then the mount and the multilayer film 1 are adhered. The package of the present embodiment can be manufactured by the above manufacturing method. In addition, the structure of the package body mentioned above is an example, It is not limited to this. Specifically, for example, a package in which the storage portion is formed by deep drawing may be used.

<How to use the package>
Next, a method of using the above-described package will be described. Although it does not specifically limit as a method of using the package body mentioned above, Specifically, a food is first enclosed in a package body. Next, it heat-processes on the conditions of 95-121 degreeC and 1 to 60 minutes (retort process). After that, by returning to normal temperature, a retortable 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 it has a specific retardation average value in the film thickness direction, width shrinkage after film formation can be suppressed.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes design and the like within the scope 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 core layer 8 Although an example configured to include the sealant layer 9 has been described, a layer having another function may be newly provided between each layer and the outermost layer.

  Hereinafter, the effects of the present invention will be described in detail using examples and comparative examples, but the present invention is not limited to the following examples.

<Production of multilayer film>
As shown below, multilayer films of Examples 1 to 5 and Comparative Example 1 were produced.

Example 1
As the multilayer film of Example 1, the multilayer film of the configuration shown in FIG. 1 described above was produced.
As a resin contained in the outer layer, the first pinhole resistant layer, and the second pinhole resistant layer, a polyamide resin (manufactured by Ube Industries, Ltd., product number: Ube nylon 1022 B) was prepared.
As a resin contained in the adhesive resin layer and the adhesive layer, a polyolefin resin (manufactured by Mitsui Chemicals, Inc., product number: Admar NF 536) was prepared.
As a resin contained in the oxygen barrier layer, EVOH (manufactured by Kuraray, product number: J171B) was prepared.
As a resin contained in the core layer, a polyolefin resin (manufactured by Prime Polymer Co., product number: Neozex 2540R, density: 0.923 g / cm ³ ) was prepared.
As a resin contained in the sealant layer, a linear low density polyethylene resin (LLDPE; manufactured by Ube Maruzen Polyethylene, product number: advantage 1540 F, density: 0.913 g / cm ³ ) was prepared.

  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 core layer, and the sealant layer in this order. It extruded and produced the multilayer film. At that time, it was adjusted so that 30% by mass of EVOH was contained with respect to the total mass of the oxygen barrier layer. In co-extrusion, the temperature of the roll for solidifying the molten resin was 90.degree.

  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 13% for the outer layer, 13% for the adhesive resin layer, 8% for the first pinhole resistant layer, 8% for the oxygen barrier layer, and second pinhole resistant The layer was 8%, the adhesive layer was 13%, the core layer was 24%, and the sealant layer was 13%. 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 the temperature of the roll for solidifying the molten resin was 80 ° C. in co-extrusion molding. 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 temperature of the roll for solidifying the molten resin was 70 ° C. in co-extrusion molding. Table 1 below shows the structure of the multilayer film.

(Example 4)
In co-extrusion molding, a multilayer film was produced in the same manner as in Example 1 except that the temperature of the roll for solidifying the molten resin was 70 ° C. and the total thickness of the multilayer film was 150 mm. Table 1 below shows the structure of the multilayer film.

(Example 5)
In co-extrusion molding, a multilayer film was produced in the same manner as in Example 1 except that the temperature of the roll for solidifying the molten resin was 70 ° C. and the total thickness of the multilayer film was 210 mm. 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 temperature of the roll for solidifying the molten resin was 30 ° C. in co-extrusion molding. Table 1 below shows the structure of the multilayer film.

<Evaluation of film characteristics>
The characteristics of the multilayer films of Examples 1 to 5 and Comparative Example 1 were evaluated by the following method.

(Phase difference)
The phase difference measurement used a birefringence evaluation apparatus (WPA-100-L manufactured by Photonic Lattice, Inc.). The multilayer films of Examples 1 to 5 and Comparative Example 1 are placed on the measurement stage of the above-described apparatus, and a film is measured by measuring the phase difference generated when light emitted from the light source passes through the film with a polarization image sensor. The retardation average value (Rth) in the thickness direction was measured (birefringent pixel number: 384 × 288 pixels, measurement field size: 340 × 250 mm).

(Width contraction)
The measurement of the width contraction was performed by a measuring microscope (manufactured by Nikon Corporation). Both ends of the film were marked in advance, and the distance between two points was measured by a measuring microscope. The film was stored in an oven set at 60 ° C., the change with time of the distance between two points was measured, and the amount of change from the initial value at the end of the change was taken as the amount of contraction. The results are shown in Table 1 below.
Moreover, what carried out the plot between the phase difference average value (Rth) of the film thickness direction of these Examples and a comparative example and change amount is shown in FIG. For example, a variation of 3.0 mm means that it has shrunk by 3.0 mm.

*各層の数値は、総厚における各層の厚さの比率を表す。

* The numerical value of each layer represents the ratio of the thickness of each layer in the total thickness.

As shown in Table 1, in the multilayer films of Examples 1 to 5 in which the retardation average value (Rth) in the film thickness direction is 100 nm or more, the comparison in which the retardation average value (Rth) in the film thickness direction is less than 100 nm It was confirmed that the width shrinkage was suppressed more than the multilayer film of Example 1.
Moreover, in Examples 1-5, abnormality of the multilayer film which suggests whitening and elution of an oxygen barrier layer was not recognized.

  The multilayer film of the present invention can be used as a packaging material, particularly a packaging material for food which requires heat sterilization. In addition, the package of the present invention is applicable to packaging bags, packaging containers, and the like for packaging food, particularly foods that require heat sterilization.

DESCRIPTION OF SYMBOLS 1 ... Multilayer film 2 ... Outer layer 3 ... Adhesive resin layer 4 ... Pin-hole resistance layer 5 ... Oxygen barrier layer 6 ... Pin-hole layer 7

Claims (6)

A sealant layer containing a polyolefin resin,
And an outer layer containing a polyamide-based resin,
A multilayer film characterized in that the retardation average value (Rth) in the film thickness direction is 100 nm or more.   The multilayer film according to claim 1, further comprising an intermediate layer between the sealant layer and the outer layer.   The multilayer film according to claim 1 or 2, wherein the polyolefin resin is high density polyethylene, linear low density polyethylene, low density polyethylene, ethylene copolymer, polypropylene, or polypropylene copolymer.   The multilayer film according to any one of claims 1 to 3, wherein the polyamide resin is 6-nylon, 12-nylon, 66-nylon, copolymerized nylon, or amorphous nylon.   The multilayer film according to any one of claims 1 to 4, wherein the intermediate layer comprises a barrier layer.   A package comprising the multilayer film according to any one of claims 1 to 5.

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