WO2013121874A1

WO2013121874A1 - Heat-shrinkable multilayer film

Info

Publication number: WO2013121874A1
Application number: PCT/JP2013/051849
Authority: WO
Inventors: 隆久上山; 忠良伊藤; 伊藤　大輔; 裕太関谷
Original assignee: 株式会社クレハ
Priority date: 2012-02-16
Filing date: 2013-01-29
Publication date: 2013-08-22
Also published as: JPWO2013121874A1; JP6054364B2

Abstract

The purpose of the present invention is to provide a heat-shrinkable multilayer film which ensures excellent multiple sealing and excellent self-welding and which combines heat shrinkability, gas barrier properties and heat sealability. This heat-shrinkable multilayer film is provided with a multilayer structure which comprises a surface layer, an intermediate layer (T1), a gas barrier layer and a sealing layer and in which the surface layer is arranged on one surface with the sealing layer on the other surface, wherein: the surface layer comprises a propylene-ethylene copolymer; the gas barrier layer is a polyvinylidene chloride-based resin; and the melting point difference between the surface layer and the sealing layer is 35 to 60°C.

Description

Heat shrinkable multilayer film

The present invention relates to a heat-shrinkable multilayer film that enables efficient packaging of raw meat, processed meat, and the like.

Since raw meat, processed meat, etc. are irregular in shape, they are usually shrink-wrapped from the viewpoint of appearance and freshness. A film used for shrink wrapping is formed of a multilayer having at least a surface layer forming an outer surface, a gas barrier layer having gas barrier properties, and a seal layer forming an inner surface, and has a good appearance and freshness depending on the properties of each layer. As a characteristic for realizing the retention, heat shrinkability, transparency, gas barrier property, or heat sealability is imparted. Examples of the shrink film having gas barrier properties include polypropylene or a polypropylene-based copolymer as a surface layer, ethylene vinyl alcohol copolymer (EVOH) or nylon 6,12 copolymer or nylon 6,66 copolymer as a gas barrier layer, and ethylene as a sealing layer. A film in which an α-olefin copolymer is laminated is disclosed (see, for example, Patent Documents 1 to 3).

Furthermore, a film used for shrink wrapping is required to have a lap seal for the purpose of improving workability. Overlap sealability means that when a packaging bag is formed with a multilayer film with the sealing layer facing inward, and the packaging bags are stacked and heat sealed, the sealing layers of each packaging bag are heat-sealed, and the surface It refers to the property that the layers are not heat-sealed or heat-sealed only to such an extent that they can be peeled off. By having this overlap sealability, heat sealing can be performed in a state where a part of the packaging bag is overlapped. Therefore, the number of packaging bags that can be heat sealed at a time can be increased, and the operation becomes efficient. Moreover, it becomes unnecessary to arrange so that packaging bags may not overlap, and workability | operativity of an operator can be improved.

As a heat-shrinkable multilayer film having a lap seal property, a film having a lap seal property is disclosed by crosslinking a surface layer forming an outer surface and uncrosslinking a seal layer forming an inner surface. (For example, refer to Patent Document 4). In addition, the outer surface is made of a resin having a relatively high melting temperature such as a polyamide resin or a polyester resin, and the inner surface is formed of a resin having a relatively low melting temperature such as a polyolefin resin. Disclosed is a film provided with an overlap seal by providing a temperature difference (see, for example, Patent Documents 5 to 8).

Furthermore, when packaging irregular shaped foods such as raw meat and processed meat with a heat-shrinkable multilayer film, consumers may prefer that the excess portion of the film after shrinkage of the bag or pouch (hereinafter referred to as the “ear part”) is poor in appearance. I can't go wrong. The fact that the sealing layers of the bag or pouch ears are fused by heat treatment (hereinafter referred to as self-weld) does not stand out the gravy (hereinafter referred to as drip) generated from raw or processed meat after packaging. That is why it is preferred by consumers. When the self-weld property is inferior, that is, when there is no fusion of the ears after heat treatment, or when there is almost no fusion, the drip accumulates in the ears during storage after packaging, and the appearance becomes poor. . The heat treatment here refers to heat treatment such as heat shrinkage, heat sterilization, and cooking at a specific temperature. A packaging laminate having self-weld properties is disclosed (see, for example, Patent Document 9).

JP 2007-152570 A Japanese Patent Laid-Open No. 10-80984 JP-A-10-29283 Japanese Patent Laid-Open No. 9-39179 International Publication No. 2008/099799 European Patent No. 1131205 European Patent Application Publication No. 1985443 European Patent Application Publication No. 2147783 International Publication No. 2000/47406

In the film described in Patent Document 4, the temperature range in which the inner surfaces can be heat-sealed without heat-sealing the outer surfaces is narrow, and the overlap sealability is insufficient. Although the films described in Patent Documents 5 to 8 have excellent lap sealing properties, resins having a high melting temperature such as polyamide resin and polyester resin must naturally have a high extrusion temperature. However, when polyvinylidene chloride resin (PVDC) is used for the intermediate layer for the purpose of imparting gas barrier properties, the processing temperature cannot be increased considering the decomposition of PVDC. For this reason, the die temperature cannot be increased, and a resin having a high melting temperature such as a polyamide resin or a polyester resin cannot be stably extruded. Therefore, the smoothness of the film surface may be deteriorated and appearance defects may occur.

An object of the present invention is to provide a heat-shrinkable multilayer film which is excellent in lap sealability and self-weld property and has heat shrinkability, gas barrier properties and heat sealability.

The heat-shrinkable multilayer film according to the present invention has a multilayer structure having a surface layer, an intermediate layer T1, a gas barrier layer, and a seal layer, and the multilayer structure has the surface layer disposed on one surface, And in the heat-shrinkable multilayer film formed by arranging the seal layer on the other surface, the surface layer contains a propylene-ethylene copolymer, and the gas barrier layer contains a polyvinylidene chloride resin. The difference in melting temperature between the surface layer and the sealing layer is 35 to 60 ° C.

In the heat-shrinkable multilayer film according to the present invention, the multilayer structure preferably further includes an intermediate layer T2 between the gas barrier layer and the seal layer. It works as a reinforcing layer of the seal layer and can improve the seal strength. Moreover, stretchability can be improved.

In the heat-shrinkable multilayer film according to the present invention, it is preferable that the seal layer contains at least one of an ionomer and an ethylene-vinyl acetate copolymer. It can be set as the film excellent in extending | stretching property and low temperature sealing property.

The heat-shrinkable multilayer film according to the present invention preferably has a self-weld property by heat treatment. Appearance after vacuum packaging can be improved.

The present invention can provide a heat-shrinkable multilayer film that is excellent in lap sealability and self-weld property and has heat shrinkability, gas barrier properties, and heat sealability.

Next, the present invention will be described in detail with reference to embodiments, but the present invention is not construed as being limited to these descriptions. As long as the effect of the present invention is exhibited, the embodiment may be variously modified.

The heat-shrinkable multilayer film according to this embodiment includes a multilayer structure having a surface layer, an intermediate layer T1, a gas barrier layer, and a seal layer, and the multilayer structure has the surface layer disposed on one surface. And in the heat-shrinkable multilayer film formed by disposing the seal layer on the other surface, the surface layer contains a propylene-ethylene copolymer, and the gas barrier layer is a polyvinylidene chloride resin. The difference in melting temperature between the surface layer and the sealing layer is 35 to 60 ° C.

(Surface layer)
The surface layer is a layer that is disposed on one surface of the multilayer structure and becomes the outer surface of the bag, and has a role of imparting heat resistance and gloss. In the heat-shrinkable multilayer film according to the present embodiment, the surface layer contains a propylene-ethylene copolymer. Examples of the propylene-ethylene copolymer include a propylene-ethylene random copolymer, a propylene-ethylene block copolymer, and a propylene-ethylene-butene terpolymer. These may be used alone or in combination of two or more. Among these, a propylene-ethylene random copolymer is particularly preferable from the viewpoints of stretchability and transparency.

The propylene-ethylene copolymer is preferably a copolymer of 60 to 99.9% by mass of propylene and 0.1 to 40% by mass of another monomer (comonomer). More preferably, the proportion of propylene in the propylene-ethylene copolymer is 75 to 99.5% by mass.

The density of the resin used for the surface layer is preferably 0.880 g / cm ³ or more and 0.940 g / cm ³ or less. More preferably, it is 0.890 g / cm ³ or more and 0.925 g / cm ³ or less.

The melt flow rate (MFR) (230 ° C., 2.16 kg) of the resin used for the surface layer is preferably 1.0 g / 10 min or more and 25 g / 10 min or less. More preferably, it is 2.0 g / 10 min or more and 20 g / 10 min.

The melting temperature of the resin used for the surface layer is preferably 130 ° C. or higher and 170 ° C. or lower. More preferably, it is 135 degreeC or more and 160 degrees C or less. Especially preferably, it is 140 degreeC or more and 155 degrees C or less. If it is less than 130 ° C., the heat resistance is insufficient, and the surface layer may melt during thermal processing such as sealing. If it exceeds 170 ° C., the extrusion processing temperature becomes high, so that the PVDC in the gas barrier layer may be decomposed. Moreover, the smoothness of the surface may be inferior or the stretchability may be hindered.

The surface layer may contain various additives such as a crystal nucleating agent, a lubricant, an antistatic agent, a softening agent, a heat stabilizer, a plasticizer, and an antioxidant. Crystal nucleating agents improve transparency, heat resistance, moldability, and the like. For example, sorbitol compounds such as dibenzylidene sorbitol; organophosphate compounds; rosinate compounds; Aliphatic dicarboxylic acid or metal salt thereof; aromatic carboxylic acid or metal salt thereof. The lubricant reduces the boundary friction between the film and the machine surface of the bag making machine or the packaging machine. For example, hydrocarbon lubricants such as liquid paraffin and polyethylene wax; aliphatic systems such as stearic acid and lauric acid Lubricants; aliphatic amide-based lubricants such as stearamide and erucamide; ester-based lubricants such as ethylene glycol monostearate and monoglyceride stearate; metal soaps such as zinc stearate and calcium stearate. Of these lubricants, fatty acid amide lubricants and metal soaps are preferably used from the viewpoint of excellent compatibility with polyolefin resins. Antistatic agents cause static electricity damage, such as the product sticking to rolls due to static electricity, reducing the mechanical suitability of bags, etc., and the product sticking to each other, reducing the workability when taking out one product at a time. For example, an anionic surfactant, a cationic surfactant, a nonionic surfactant, an amphoteric surfactant, or a mixture thereof. The softening agent suppresses the bending phenomenon of the film at the time of shrinkage. For example, polyolefin elastomer such as ethylene-α olefin copolymer and propylene-α olefin copolymer; ethylene-vinyl acetate copolymer, etc. Polyethylene, polyisobutylene, polybutene, polybutadiene, butadiene-styrene copolymer, neoprene, natural rubber.

The thickness of the surface layer is preferably 0.5 μm or more and 40 μm or less. More preferably, they are 1 micrometer or more and 10 micrometers or less.

¡Powder can be applied to the surface of the surface layer. The powder has a role of expanding the temperature range in which the layers can be sealed. The powder is, for example, starch. The average particle size of the powder is preferably 5 to 50 μm. Further, a plurality of kinds of powders having different particle sizes may be blended to have a distribution in the average particle size.

(Intermediate layer T1)
The mid layer T1 preferably contains a polyolefin resin. Examples of the polyolefin resin include low density polyethylene (LDPE); medium density polyethylene (MDPE); polypropylene (PP); a copolymer of propylene and an α-olefin having 2 or 4 to 8 carbon atoms; an ethylene-α-olefin copolymer. Polymer: ethylene-vinyl acetate copolymer (EVA), ethylene-alkyl acrylate having 1 to 4 carbon atoms, ethylene-methacrylic acid copolymer, ethylene-methacrylic acid-unsaturated carboxylic acid copolymer, etc. Polar comonomer copolymer; ionomer. The ethylene-α olefin copolymer includes a copolymer obtained using a Ziegler-Natta catalyst and a copolymer obtained using a metallocene catalyst. The α-olefin as a comonomer used for the polymerization of the ethylene-α-olefin copolymer is, for example, butene-1, having 4 carbon atoms, pentene-1, 5 carbon atoms, 4-methylpentene-1 having 6 carbon atoms, or Hexene-1 or octene-1 having 8 carbon atoms. Specific examples of the ethylene -α-olefin copolymer, the density is ^{0.900g / cm 3 ~ 0.909g / cm} 3 very low density polyethylene (VLDPE), density of 0.910g ^/ cm 3 ~ 0.925g It is a linear low density polyethylene (LLDPE) that is / cm ³ . Among them, EVA, ethylene-alkyl acrylate having 1 to 4 carbon atoms, ethylene-methacrylic acid copolymer, ethylene-methacrylic acid-unsaturated carboxylic acid in terms of stretchability, adhesion to the surface layer and transparency. Particularly preferred are ethylene-polar comonomer copolymers such as acid copolymers; ionomers. The resins used for the intermediate layer T1 may be used alone or in combination of two or more. In addition to the polyolefin-based resin, the intermediate layer T1 may contain various additives such as a lubricant, an antistatic agent, a heat stabilizer, a plasticizer, an antioxidant, and a softening agent. In this, it is more preferable to contain a softening agent at the point which can suppress the bending phenomenon of the film at the time of shrinkage | contraction. Examples of the softener include polyolefin elastomers such as ethylene-α olefin copolymers and propylene-α olefin copolymers; ethylene copolymers such as ethylene-vinyl acetate copolymers; polyisobutylenes; polybutenes; polybutadienes; Butadiene-styrene copolymer; neoprene; natural rubber.

The melting temperature of the resin used for the intermediate layer T1 is not particularly limited, but is preferably 70 ° C. or higher and 120 ° C. or lower. More preferably, it is 80 degreeC or more and 100 degrees C or less.

Density of the resin used for the intermediate layer T1 is preferably less 0.880 g / cm ³ or more 0.960 g / cm ^3. More preferably, the 0.900 g / cm ³ or more 0.940 g / cm ³ or less.

The MFR (190 ° C., 2.16 kg) of the resin used for the intermediate layer T1 is preferably 0.5 g / 10 min or more and 20 g / 10 min or less. More preferably, it is 1.0 g / 10 min or more and 15 g / 10 min or less.

The thickness of the intermediate layer T1 is preferably 5 μm or more and 50 μm or less. More preferably, they are 10 micrometers or more and 40 micrometers or less. The intermediate layer T1 may be formed of one layer or two or more layers. When the intermediate layer T1 is formed of two or more layers, the layers may have the same composition, or the layers may have different compositions.

(Adhesive layer S1)
An adhesive layer S1 may be further provided between the intermediate layer T1 and the gas barrier layer. The adhesive layer S1 is a layer adjacent to the gas barrier layer, and has a role of improving adhesion to the gas barrier layer. The adhesive layer S1 preferably contains an adhesive resin such as an ethylene-polar comonomer copolymer or an acid-modified polyolefin. Examples of ethylene-polar comonomer copolymers include ethylene-vinyl acetate copolymers, ethylene-alkyl acrylates having 1 to 4 carbon atoms, ethylene-methacrylic acid copolymers, and ethylene-methacrylic acid-unsaturated carboxylic acid copolymers. , An ethylene-acrylic acid copolymer. The acid-modified polyolefin is, for example, a reaction product of an olefin homo- or copolymer and an unsaturated carboxylic acid such as maleic acid or fumaric acid, an acid anhydride, an ester, or a metal salt. The resins used for the adhesive layer S1 may be used alone or in combination of two or more. In addition, adhesive layer S1 may contain various additives, such as a heat stabilizer, a plasticizer, and antioxidant other than adhesive resin.

The melting temperature of the resin used for the adhesive layer S1 is not particularly limited, but is preferably 70 ° C or higher and 130 ° C or lower. More preferably, it is 80 degreeC or more and 120 degrees C or less.

Density of the resin used in the adhesive layer S1 is preferably not more than 0.880 g / cm ³ or more 0.960 g / cm ^3. More preferably, the 0.900 g / cm ³ or more 0.940 g / cm ³ or less.

The MFR (190 ° C., 2.16 kg) of the resin used for the adhesive layer S1 is preferably 0.5 g / 10 min or more and 20 g / 10 min or less. More preferably, it is 1.0 g / 10 min or more and 15 g / 10 min or less.

The thickness of the adhesive layer S1 is preferably 0.5 μm or more and 10 μm or less. More preferably, they are 1 micrometer or more and 5 micrometers or less.

(Gas barrier layer)
The gas barrier layer has a role of preventing deterioration of contents by suppressing permeation of oxygen, water vapor and the like. The gas barrier layer contains a polyvinylidene chloride (PVDC) resin as a gas barrier resin.

The polyvinylidene chloride resin is, for example, a copolymer of 2 to 40% by mass of another monomer (comonomer) copolymerizable with 60 to 98% by mass of vinylidene chloride (VDC).

Examples of the comonomer include vinyl chloride; alkyl acrylate esters such as methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, stearyl acrylate (alkyl group having 1 to 18 carbon atoms). Alkyl methacrylates such as methyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, stearyl methacrylate (alkyl group having 1 to 18 carbon atoms); vinyl cyanide such as acrylonitrile and methacrylonitrile; Aromatic vinyl such as styrene; vinyl ester of aliphatic carboxylic acid having 1 to 18 carbon atoms such as vinyl acetate; alkyl vinyl ether having 1 to 18 carbon atoms; acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, etc. Vinyl polymerizable unsaturated carboxylic acids; alkyl esters of vinyl polymerizable unsaturated carboxylic acids such as maleic acid, fumaric acid and itaconic acid (including partial esters, having 1 to 18 carbon atoms in the alkyl group); Body, functional group-containing monomer, polyfunctional monomer and the like.

These comonomers can be used alone or in combination of two or more. Among these comonomers, vinyl chloride, methyl acrylate or lauryl acrylate is preferable. When the copolymerization ratio of the comonomer is too small, the internal plasticization becomes insufficient and the melt processability is lowered. When the copolymerization ratio of the comonomer is too large, the gas barrier property is lowered. The copolymerization ratio of the comonomer is preferably 3 to 35% by mass, more preferably 10 to 25% by mass.

The reduced viscosity (ηsp / C) of the polyvinylidene chloride-based resin is preferably 0.035 to 0.070, more preferably from the viewpoint of processability when molded into a film, suitability for packaging machinery, cold resistance, and the like. It is 0.040 to 0.065, and particularly preferably 0.045 to 0.063. If the reduced viscosity of the polyvinylidene chloride-based resin is too low, the processability is deteriorated, and if it is too high, a tendency toward coloring is exhibited, so neither is preferred. Two or more types of polyvinylidene chloride resins having different reduced viscosities can be used in combination, thereby improving workability. When two or more kinds of polyvinylidene chloride resins are used in combination, the reduced viscosity of the mixed resin is preferably within the above range.

The polyvinylidene chloride resin can be blended with other resins as desired. Other resins include, for example, ethylene-vinyl acetate copolymer, (meth) acrylic acid ester, preferably (co) polymer of alkyl group (meth) acrylic acid alkyl ester having 1 to 18 carbon atoms [for example, (Methyl (meth) acrylate- (meth) butyl acrylate copolymer), methyl methacrylate-butadiene-styrene copolymer, and the like. These other resins can be blended when preparing the polyvinylidene chloride resin composition, or can be contained in the coloring resin composition blended with the polyvinylidene chloride resin. The other resin is usually used at a ratio of 20 parts by mass or less with respect to 100 parts by mass of the polyvinylidene chloride resin.

The gas barrier resins may be used alone or in combination of two or more. The gas barrier resin and the polyolefin-based resin can obtain good adhesiveness by interposing the adhesive layer S1 and the adhesive layer S2 described later. The gas barrier layer may contain various additives such as a heat stabilizer, a plasticizer, and an antioxidant in addition to the gas barrier resin.

The thickness of the gas barrier layer is preferably 1 μm or more and 40 μm or less. More preferably, they are 3 micrometers or more and 30 micrometers or less, Especially preferably, they are 4 micrometers or more and 10 micrometers or less. The gas barrier layer may be formed of one layer or two or more layers. When two or more gas barrier layers are formed, each layer may have the same composition, or each layer may have a different composition.

(Seal layer)
The sealing layer is disposed on the surface opposite to the surface layer, becomes the inner surface of the bag, and has a role of sealing the bag by heat sealing. The sealing layer preferably contains a polyolefin resin. Examples of polyolefin resins include low-density polyethylene (LDPE); ethylene-α olefin copolymer; ethylene-vinyl acetate copolymer (EVA), ethylene-alkyl acrylate having 1 to 4 carbon atoms, and ethylene-methacrylic acid copolymer. Polymers, ethylene-polar comonomer copolymers such as ethylene-methacrylic acid-unsaturated carboxylic acid copolymers; ionomers. The ethylene-α olefin copolymer includes a copolymer obtained using a Ziegler-Natta catalyst and a copolymer obtained using a metallocene catalyst. The α-olefin as a comonomer used for the polymerization of the ethylene-α-olefin copolymer is, for example, butene-1, having 4 carbon atoms, pentene-1, 5 carbon atoms, 4-methylpentene-1 having 6 carbon atoms, or Hexene-1 or octene-1 having 8 carbon atoms. Specific examples of the ethylene -α-olefin copolymer, the density is 0.900 g / cm ³ or more 0.909 g / cm ³ or less very low density polyethylene (VLDPE), density of 0.910 g / cm ³ or more zero. It is a linear low density polyethylene (LLDPE) that is 925 g / cm ³ or less. For example, an ionomer uses, as a base polymer, an ethylene-unsaturated carboxylic acid copolymer or an ethylene-ethylenically unsaturated carboxylic acid-ethylenically unsaturated carboxylic acid ester terpolymer, and carboxyls in these copolymers. A resin in which the group is neutralized with a cation can be mentioned. The unsaturated carboxylic acid is preferably, for example, methacrylic acid or acrylic acid. The copolymerization ratio of unsaturated carboxylic acid is preferably 3 to 20% by mass. More preferably, it is 5 to 15% by mass, and particularly preferably 7 to 13% by mass. When the copolymerization ratio of the unsaturated carboxylic acid is too large, the sealing strength tends to decrease. The unsaturated carboxylic acid ester is preferably an alkyl ester of (meth) acrylic acid having 1 to 6 carbon atoms. The copolymerization ratio of the unsaturated carboxylic acid ester is preferably 3 to 30% by mass. More preferably, it is 4 to 15% by mass, and particularly preferably 5 to 10% by mass. If the copolymerization ratio of the unsaturated carboxylic acid ester is too large, the bag-making property tends to deteriorate due to excessive flexibility and stickiness, and the sealing strength tends to decrease. Examples of the cation used for neutralization include Na ⁺ , K ⁺ , Li ⁺ , Cs ⁺ , Ag ⁺ , Hg ⁺ , Cu ⁺ , Mg ²⁺ , Zn ²⁺ , Be ²⁺ , Ca ²⁺ , Ba ²⁺ and Cu ^2+. , Cd ²⁺ , Hg ²⁺ , Sn ²⁺ , Pb ²⁺ , Fe ²⁺ , Co ²⁺ , Ni ²⁺ , Al ³⁺ , Sc ³⁺ , Fe ³⁺ , Y ³⁺ , and organic amines. Among these, Na ⁺ , K ⁺ , Ca ²⁺ , Zn ^{2+ and the} like are preferably used. The ratio of the metal or organic amine content in the resin to the acid content in the resin (degree of neutralization) is preferably 1 to 15%. More preferably, it is 3 to 15%. If it exceeds 15%, there may be a case where a practically required level of sealing strength cannot be obtained. An ionomer having a neutralization degree of 15% or less may be prepared by blending two or more ionomers having different ionization degrees. The ionomer can be used by blending with, for example, an ethylene-methacrylic acid copolymer, an ethylene-methacrylic acid-acrylic acid ester terpolymer, etc. The blend ratio of the ionomer is 50% by mass or more. Preferably there is. Of these resins used for the seal layer, EVA and ionomer are particularly preferable in terms of stretchability, low temperature sealability and self-weldability. The vinyl acetate content of EVA is preferably 5 to 30% by mass. More preferably, it is 10 to 25% by mass, and particularly preferably 12 to 18% by mass. The resins used for the seal layer may be used alone or in combination of two or more. The seal layer may contain various additives such as a heat stabilizer, a plasticizer, and an antioxidant in addition to the polyolefin resin.

The density of the resin used for the seal layer is preferably 0.880 g / cm ³ or more and 0.940 g / cm ³ or less. More preferably, the 0.900 g / cm ³ or more 0.925 g / cm ³ or less.

The MFR (190 ° C., 2.16 kg) of the resin used for the seal layer is preferably 0.5 g / 10 min or more and 20 g / 10 min or less. More preferably, it is 1.0 g / 10 min or more and 15 g / 10 min or less.

The melting temperature of the resin used for the seal layer is preferably 80 ° C. or higher and 130 ° C. or lower. More preferably, it is 85 degreeC or more and 100 degrees C or less, Most preferably, it is 85 degreeC or more and 95 degrees C or less. If it is less than 80 degreeC, blocking generate | occur | produces at the time of extending | stretching, and extending | stretching film forming property may be inferior. If the temperature exceeds 130 ° C., the temperature at which the inner surface of the seal starts is shifted to the high temperature side, and therefore the temperature range in which the double seal can be performed may be narrowed. Moreover, in order to express self-weld property, it is preferable that the melting temperature of resin used for a sealing layer is 80 degreeC or more and 100 degrees C or less. More preferably, it is 80 degreeC or more and 95 degrees C or less, Most preferably, it is 85 degreeC or more and 95 degrees C or less.

The melting temperature of the seal layer is lower than the melting temperature of the surface layer, and the difference in melting temperature is 35 ° C. or more and 60 ° C. or less. More preferably, it is 40 degreeC or more and 60 degrees C or less, Most preferably, it is 45 degreeC or more and 60 degrees C or less. When the difference in melting temperature between the surface layer and the sealing layer is less than 35 ° C., the temperature range in which the overlapping sealing property is exhibited is narrow, and the practicality is lacking. When the difference in melting temperature between the surface layer and the seal layer exceeds 60 ° C., the difference in processing temperature increases, and when the melting temperature of the seal layer is relatively high, the melting temperature of the surface layer becomes relatively high. In this case, since the extrusion temperature becomes high, as a result, the PVDC of the gas barrier layer may be decomposed or the smoothness of the surface may be inferior. Moreover, when the melting temperature of the surface layer is relatively low, the melting temperature of the seal layer is relatively low. In this case, blocking of the seal layer may occur.

The thickness of the seal layer is preferably 3 μm or more and 50 μm or less. More preferably, they are 5 micrometers or more and 30 micrometers or less, Especially preferably, they are 8 micrometers or more and 20 micrometers or less.

(Intermediate layer T2)
An intermediate layer T2 may be further provided between the gas barrier layer and the seal layer. The intermediate layer T2 functions as a reinforcing layer of the seal layer and has a role of improving the seal strength. Also, it has a role of improving stretchability and shrinkage. The mid layer T2 preferably contains a polyolefin resin. As the polyolefin-based resin, those exemplified in the intermediate layer T1 can be used, and EVA, ethylene-alkyl acrylate having 1 to 4 carbon atoms, ethylene-methacrylic acid in terms of stretchability, adhesion to the seal layer and transparency. Copolymers, ethylene-polar comonomer copolymers such as ethylene-methacrylic acid-unsaturated carboxylic acid copolymers; ionomers are particularly preferred. The resins used for the intermediate layer T2 may be used alone or in combination of two or more. The intermediate layer T2 may contain various additives such as a heat stabilizer, a plasticizer, and an antioxidant in addition to the polyolefin resin.

The melting temperature of the resin used for the intermediate layer T2 is not particularly limited, but is preferably 70 ° C or higher and 120 ° C or lower. More preferably, it is 80 degreeC or more and 100 degrees C or less.

Density of the resin used for the intermediate layer T2 is preferably less 0.880 g / cm ³ or more 0.960 g / cm ^3. More preferably, the 0.900 g / cm ³ or more 0.940 g / cm ³ or less.

The MFR (190 ° C., 2.16 kg) of the resin used for the intermediate layer T2 is preferably 0.5 g / 10 min or more and 20 g / 10 min or less. More preferably, it is 1.0 g / 10 min or more and 15 g / 10 min or less.

The thickness of the intermediate layer T2 is preferably 3 μm or more and 50 μm or less. More preferably, they are 5 micrometers or more and 30 micrometers or less, Especially preferably, they are 8 micrometers or more and 20 micrometers or less. The intermediate layer T2 may be formed of one layer or two or more layers. When the intermediate layer T2 is formed of two or more layers, the layers may have the same composition, or the layers may have different compositions.

(Adhesive layer S2)
An adhesive layer S2 may be further provided between the gas barrier layer and the intermediate layer T2. The adhesive layer S2 is a layer adjacent to the gas barrier layer, and has a role of improving the adhesion to the gas barrier layer. As the adhesive layer S2, the adhesive resin exemplified in the adhesive layer S1 can be used, and each of them can be used alone or in combination of two or more. The adhesive layer S2 may contain various additives such as a heat stabilizer, a plasticizer, and an antioxidant in addition to the adhesive resin.

The melting temperature of the resin used for the adhesive layer S2 is not particularly limited, but is preferably 70 ° C or higher and 130 ° C or lower. More preferably, it is 80 degreeC or more and 120 degrees C or less.

Density of the resin used in the adhesive layer S2 is preferably not more than 0.880 g / cm ³ or more 0.960 g / cm ^3. More preferably, the 0.900 g / cm ³ or more 0.940 g / cm ³ or less.

The MFR (190 ° C., 2.16 kg) of the resin used for the adhesive layer S2 is preferably 0.5 g / 10 min or more and 20 g / 10 min or less. More preferably, it is 1.0 g / 10 min or more and 15 g / 10 min or less.

The thickness of the adhesive layer S2 is preferably 0.5 μm or more and 10 μm or less. More preferably, they are 1 micrometer or more and 5 micrometers or less.

(Heat-shrinkable multilayer film)
The heat-shrinkable multilayer film according to the present embodiment has a multilayer structure having at least a surface layer, an intermediate layer T1, a gas barrier layer, and a seal layer. The multilayer structure may be formed in various forms depending on the use as long as a surface layer is disposed on one surface and a seal layer is disposed on the other surface. Examples of the multilayer structure include a four-layer structure in which a surface layer, an intermediate layer T1, a gas barrier layer, and a seal layer are sequentially stacked, and five layers in which a surface layer, an intermediate layer T1, a gas barrier layer, an intermediate layer T2, and a seal layer are sequentially stacked. Structure, surface layer, intermediate layer T1, adhesive layer S1, gas barrier layer, intermediate layer T2, and 6-layer structure in which a seal layer is sequentially laminated, surface layer, intermediate layer T1, adhesive layer S1, gas barrier layer, adhesive layer S2, intermediate layer It has a seven-layer structure in which T2 and a seal layer are sequentially laminated. However, these are merely examples, and the present invention is not limited to these.

The thickness of the heat-shrinkable multilayer film according to this embodiment is preferably 20 μm or more and 150 μm or less. More preferably, they are 30 micrometers or more and 120 micrometers or less, Most preferably, they are 40 micrometers or more and 80 micrometers or less. If it is less than 20 μm, the mechanical strength may be insufficient. If it exceeds 150 μm, the time required for heat sealing becomes long, and the packaging suitability may be inferior. Further, the stretch processability may be inferior.

The heat-shrinkable multilayer film according to this embodiment preferably has a self-weld property. The self-weld property refers to the property that the sealing layers are fused together by heat at the ear portion after shrinkage of the bag or pouch when heat treatment such as heat shrinkage, heat sterilization, cooking, etc. is performed at a specific temperature. For example, in the case of raw meat packaging, heat shrinkage may be performed at 85 ° C., and in the case of processed meat, heat sterilization may be performed at 95 ° C. At this time, it is preferable that the integral average fusion | bonding force of the sealing layers in the bag or the ear | edge part after shrinkage | contraction is 1 N / 15mm or more. More preferably, it is 3N / 15mm or more, Most preferably, it is 5N / 15mm or more. If it is less than 1 N / 15 mm, it does not have a substantial self-weld property, and drip accumulates in the ear during storage after packaging, which may deteriorate the appearance.

The heat-shrinkable multilayer film according to this embodiment has a hot-water shrinkage rate of at least 30% at 80 ° C. in at least one of the machine direction of the film (MD direction) or the direction perpendicular to the machine direction of the film (TD direction). It is preferable that it is 60% or less. More preferably, it is 35% or more and 55% or less. Particularly preferably, it is 45% or more and 55% or less. When the hot water shrinkage rate is less than 30%, the shrinkage amount is insufficient and the appearance of the package may deteriorate. If the hot water shrinkage rate exceeds 60%, the contents may be deformed by excessive shrinkage. Here, the hot water shrinkage ratio is obtained by immersing the difference between the length in the MD direction or the TD direction of the film before being immersed in hot water (80 ° C.) and the length of the film after being immersed in hot water in hot water. It is expressed as a percentage divided by the length in the MD direction or TD direction of the previous film.

The heat-shrinkable multilayer film according to this embodiment has a lap seal. Here, the lap sealing property is a multilayer film with a sealing layer facing inward to form a packaging bag, and when the packaging bags are stacked and heat sealed, the sealing layers of each packaging bag are heat-sealed, And the surface layer does not heat-seal or refers to the property of heat-sealable to such an extent that it can be peeled off. At this time, the fusion strength between the seal layers (also referred to as seal strength) is preferably 10 N / 15 mm or more. More preferably, it is 15 N / 15 mm or more. When the fusion strength between the sealing layers of each packaging bag is less than 10 N / 15 mm, the sealing performance is insufficient, and air may enter the bag during the packaging process or during transportation. On the other hand, the fusion strength between the surface layers is preferably 1.5 N / 15 mm or less, and more preferably 1.0 N / 15 mm or less. When the fusion strength between the surface layers exceeds 1.5 N / 15 mm, it is difficult to say that when the packaging bags are separated from each other, the resistance is large and the layer has a practical overlap seal. Moreover, the measuring method of seal strength is as having described in the Example.

Next, a method for manufacturing the heat-shrinkable multilayer film according to this embodiment will be described.

The method for producing a heat-shrinkable multilayer film according to this embodiment comprises at least a resin composition for forming a surface layer, a resin composition for forming an intermediate layer T1, a resin composition for forming a gas barrier layer, and a resin composition for forming a seal layer. Each has a lamination step of forming a laminate having a multilayer structure and a stretching step of stretching the laminate.

In the heat-shrinkable multilayer film according to this embodiment, the method for forming a multilayer structure is not particularly limited, but is preferably a melt extrusion method. The melt extrusion method is, for example, an inflation method or a T-die method. Among these, the inflation method is more preferable. Next, a description will be given by taking as an example a method of manufacturing by an inflation method.

(Lamination process)
In the lamination step, an unstretched laminate having a multilayer structure is formed. First, at least a resin composition for forming a surface layer, a resin composition for forming an intermediate layer T1, a resin composition for forming a gas barrier layer, and a resin composition for forming a seal layer, and if necessary, an intermediate layer T2 forming resin composition The resin composition for forming each layer of the resin composition for forming the adhesive layer S1 and the resin composition for forming the adhesive layer S2 is put into an extruder and melted. Next, with a circular die, a surface layer is disposed on one surface and a seal layer is disposed on the other surface, and then melt-bonded and coextruded into a tubular shape. At this time, it is more preferable to arrange the surface layer on the outside of the tube and arrange the seal layer on the inside. This is cooled with cooling water to obtain a flat tubular unstretched laminate.

(Stretching process)
In the stretching step, the obtained flat tubular unstretched laminate is stretched to form a stretched film. First, a flat tubular unstretched laminate is heated by, for example, passing through a hot water bath, and then air is blown into the tubular to form a bubble-shaped tubular film, which is cooled with a cold air ring. However, simultaneous biaxial stretching is performed in the MD direction and the TD direction. In the stretching step, the temperature for heat-treating the unstretched laminate is preferably 70 to 95 ° C, more preferably 75 to 90 ° C. The temperature of the cold air ring is preferably 5 to 25 ° C. The stretching ratio is preferably 2 to 4 times in each of the MD direction and the TD direction. The draw ratio in the MD direction and the draw ratio in the TD direction may be the same or different.

In this embodiment, it is preferable to perform a thermal relaxation treatment after stretching in terms of dimensional stability.

(Radiation irradiation process)
The method for producing a heat-shrinkable multilayer film according to this embodiment preferably further includes a radiation irradiation step. In the case of irradiation with radiation, stretch film-forming properties, mechanical strength, and the like are improved by the appropriate crosslinking effect. In particular, by irradiating the surface layer with radiation, it is possible to further widen the temperature range that can be overlaid. The radiation is, for example, α rays, β rays, electron beams (EB), γ rays, and X rays. Among these, an electron beam and a γ-ray are preferable from the viewpoint of a crosslinking effect before and after irradiation, and an electron beam is particularly preferable from the viewpoints of workability in manufacturing a molded product or high production capacity.

The above-mentioned radiation irradiation conditions may be appropriately set according to the intended use. For example, the electron beam irradiation conditions are preferably an acceleration voltage in the range of 150 to 500 kV and an absorbed dose of 50 to 250 kGy (kilogrey), and more preferably 80 to 200 kGy.

The radiation irradiation process may be performed between the lamination process and the stretching process, or may be performed after the stretching process. Further, the irradiation of radiation may be in-line performed after the laminating process or after the stretching process and without the winding process, or may be performed offline after the laminating process or after the stretching process and after the winding process.

Next, examples of the present invention will be described. However, the present invention is not limited to these examples.

Table 1 shows the types of resin used. Hereinafter, the abbreviated names shown in Table 1 are used. Table 2 shows the layer configurations of the examples and comparative examples, and Table 3 shows the difference in melting temperature between the surface layer and the seal layer.

In addition, the measuring method of the melting temperature of resin, a surface layer, and a sealing layer is as follows. The melting temperature of each layer was prepared by peeling or scraping each layer. Moreover, when it was thought that there was no influence on the melting temperature of each layer even if it measured in the state laminated | stacked with the other layer, the melting temperature of each layer was calculated | required in the state laminated | stacked with the other layer.

<Melting temperature (Tm)>
Using a differential scanning calorimeter (DSC8500, manufactured by PerkinElmer), the melting temperature (Tm) was measured with the following temperature program. Tm was the endothermic peak of (second temperature increase) in (5) of the temperature program shown below. In addition, when it had a some peak, let the maximum melting peak temperature be Tm.
Temperature program;
(1) Temperature rise at -30 to 200 ° C at 20 ° C / min (2) Hold at 200 ° C for 1 minute (3) Temperature drop from 200 to -30 ° C at 20 ° C / min (4) Hold at -30 ° C for 1 minute (5 ) -30 ~ 200 ℃ Heating at 20 ℃ / min

(Example 1)
PP-Et-1 as surface layer, EVA-1 as intermediate layer T1, EMA as adhesive layer S1, PVDC as gas barrier layer, EMA as adhesive layer S2, EVA-2 as intermediate layer T2, and Ionomer as seal layer Each was extruded with a machine and the molten resin was introduced into an annular die. Here, from the outside to the inside, melt-bonding was performed in order of PP-Et-1 / EVA-1 / EMA / PVDC / EMA / EVA-2 / Ionomer, and coextrusion was performed. The molten tubular body flowing out from the die outlet was cooled by a cold water shower ring at 10 to 20 ° C. to obtain a tubular body having a flat width of 113 mm. The flat tubular body was irradiated with an electron beam in-line in an electron beam irradiation apparatus having an acceleration voltage of 275 kV to give an irradiation dose of 100 kGy. Next, after passing the flat tubular body through a hot water bath at 82 ° C., it is converted into a bubble-shaped tubular body film, and is cooled in a longitudinal direction (MD) by an inflation method while cooling with a cold air ring of 5 to 20 ° C. Simultaneous biaxial stretching was performed at a stretching ratio of 3.4 times in the transverse direction (TD) 4 times. Next, the biaxially stretched film was thermally relaxed to produce a biaxially stretched film (heat-shrinkable multilayer film). The flat width of the obtained heat-shrinkable multilayer film was 340 mm. The layer composition ratio (the value in parentheses is the thickness of each layer) is PP-Et-1 (2.0 μm) / EVA-1 (22 μm) / EMA (1.5 μm) / PVDC (7 μm) / EMA (1. 5 μm) / EVA-2 (10 μm) / Ionomer (10 μm). The total thickness of the film was 54 μm.

(Example 2)
PP-Et-1 as surface layer, EVA-1 as intermediate layer T1, EMA as adhesive layer S1, PVDC as gas barrier layer, EMA as adhesive layer S2, EVA-2 as intermediate layer T2, and Ionomer as seal layer Each was extruded with a machine and the molten resin was introduced into an annular die. Here, from the outside to the inside, melt-bonding was performed in order of PP-Et-1 / EVA-1 / EMA / PVDC / EMA / EVA-2 / Ionomer, and coextrusion was performed. The molten tubular body flowing out from the die outlet was cooled by a cold water shower ring at 10 to 20 ° C. to obtain a tubular body having a flat width of 120 mm. The flat tubular body was irradiated with an electron beam in-line in an electron beam irradiation apparatus having an acceleration voltage of 275 kV to give an irradiation dose of 120 kGy. Next, after passing the flat tubular body through a hot water bath at 82 ° C., it is converted into a bubble-shaped tubular body film, and is cooled in a longitudinal direction (MD) by an inflation method while cooling with a cold air ring of 5 to 20 ° C. Simultaneous biaxial stretching was performed at a draw ratio of 3.2 times in the transverse direction (TD) 7 times. Next, the biaxially stretched film was thermally relaxed to produce a biaxially stretched film (heat-shrinkable multilayer film). The flat width of the obtained heat-shrinkable multilayer film was 380 mm. The layer composition ratio (the value in parentheses is the thickness of each layer) is PP-Et-1 (4.2 μm) / EVA-1 (35 μm) / EMA (2.1 μm) / PVDC (5.6 μm) / EMA ( 2.1 μm) / EVA-2 (14 μm) / Ionomer (14 μm). The total thickness of the film was 77 μm.

(Example 3)
Layer composition ratio (numbers in parentheses are the thickness of each layer) PP-Et-1 (2.0 μm) / Ionomer (22 μm) / EMA (1.5 μm) / PVDC (7 μm) / EMA (in order from the outside to the inside) A heat-shrinkable multilayer film was produced in the same manner as in Example 1 except that the temperature was 1.5 μm) / EVA-3 (10 μm) / EVA-2 (10 μm) and the temperature of the hot water bath was 83 ° C.

(Example 4)
Layer composition ratio (numbers in parentheses are the thickness of each layer) PP-Et-1 (2.0 μm) / Ionomer (22 μm) / EMA (1.5 μm) / PVDC (7 μm) / EMA (in order from the outside to the inside) 1.5 μm) / EVA-3 (10 μm) / EVA-4 (10 μm) A heat-shrinkable multilayer film was produced in the same manner as in Example 1 except that the temperature of the hot water bath was 83 ° C.

(Example 5)
A heat-shrinkable multilayer film was produced in the same manner as in Example 1 except that the surface layer was changed to PP-Et-2.

(Example 6)
A heat-shrinkable multilayer film was produced in the same manner as in Example 1 except that the surface layer was changed to PP-Et-3.

(Example 7)
A heat-shrinkable multilayer film was produced in the same manner as in Example 1 except that the surface layer was changed to a blend of PP-Et-2 and PP-Et-3 and the blend ratios were 50 wt% and 50 wt%, respectively. did.

(Example 8)
A heat-shrinkable multilayer film was produced in the same manner as in Example 1 except that the surface layer was changed to a blend of PP-Et-4 and PP-Et-5, and the blend ratios were 75 wt% and 25 wt%, respectively. did.

(Comparative Example 1)
Layer composition ratios (numerical values in parentheses are the thickness of each layer) VLDPE (2.0 μm) / EVA-1 (22 μm) / EMA (1.5 μm) / PVDC (7 μm) / EMA (1. A heat-shrinkable multilayer film was produced in the same manner as in Example 1 except that 5 μm) / EVA-2 (10 μm) / Ionomer (10 μm).

(Comparative Example 2)
The layer composition ratio (the values in parentheses are the thickness of each layer) in order from the outside to the inside, LLDPE (2.0 μm) / EVA-1 (22 μm) / EMA (1.5 μm) / PVDC (7 μm) / EMA (1. A heat-shrinkable multilayer film was produced in the same manner as in Example 1 except that 5 μm) / EVA-2 (10 μm) / Ionomer (10 μm).

(Comparative Example 3)
Layer composition ratio (numbers in parentheses are the thickness of each layer) VLDPE (2 μm) / Ionomer (22 μm) / EMA (1.5 μm) / PVDC (7.0 μm) / EMA (1.5 μm) in order from the outside to the inside A heat-shrinkable multilayer film was produced in the same manner as in Example 1 except that / EVA-2 (15 μm) / VLDPE (5 μm) was used and the temperature of the hot water bath was 85 ° C.

The following evaluation was performed on the heat-shrinkable multilayer films of the obtained Examples and Comparative Examples. The evaluation results are shown in Table 4.

<Hot water shrinkage>
In accordance with ASTM D-2732, a film sample marked with a distance of 10 cm in each of the machine direction (longitudinal direction, MD direction) and the direction perpendicular to the machine direction (lateral direction, TD direction) is 80 After being immersed in hot water adjusted to ° C. for 10 seconds, it was taken out and immediately cooled with water at room temperature. Thereafter, the marked distance was measured, and the decrease value from 10 cm was displayed as a percentage as the ratio to the original length of 10 cm. The test was performed 5 times, and the average value in the MD direction and the TD direction was taken as the hot water shrinkage rate.

<Overlap sealability>
Two sets of the obtained cylindrical films are stacked and fixed to a vacuum timer 3.0 using a vacuum packaging machine (AGW, manufactured by Multivac), and the seal bar temperature is changed to 145 ° C, 155 ° C and 165 ° C. The TD direction and the seal line were sealed in parallel at each temperature. The measurement of the seal bar temperature was performed by attaching a thermolabel (5E, manufactured by NOF Corporation) to the seal bar. While the two sets of films were superposed, the overlapping portion was cut to a width of 15 mm to obtain a sample piece. Hereinafter, for convenience, the seal between the seal layers in the film on the side in contact with the seal bar is referred to as an inner surface (upper), and the seal between the seal layers in the film on the side not in contact with the seal bar is referred to as an inner surface (lower). Moreover, the seal | sticker of the surface layers of the overlapping part of two sets of films is called an outer surface. The seal strength of each part was measured using a universal tensile tester (Tensilon RTM-100, manufactured by Orientec Corp.). At this time, the distance between chucks was 20 mm, and the test speed was 300 mm / min. Table 4 shows the seal strength of the inner surface (upper), inner surface (lower), and outer surface at each temperature as the seal strength. Further, the overlap sealability was judged from the seal strengths of the inner surface (upper), inner surface (lower), and outer surface as follows.
○: The seal strength of the inner surface (upper) and the inner surface (lower) is 10 N / 15 mm or more, and the strength of the outer surface is 1.5 N / 15 mm or less, indicating a lap seal property (practical level).
X: The seal strength of the outer surface exceeds 1.5 N / 15 mm, and does not show the overlap sealability (practical level).

<Overall evaluation of overlap sealability>
In the overlap sealability evaluation, comprehensive evaluation was performed as follows.
++++: Three circles were evaluated in the overlap sealability evaluation (practical level).
++: The evaluation of the overlap sealability was 2 (practical level).
+: One in the evaluation of overlap sealability was 1 (practical lower limit level).
-: The evaluation of the overlap sealability was 0 (no practical level).

<Self-weld property evaluation> (inner self-weld property)
The obtained cylindrical film was processed into a bag shape, the inside was evacuated, the opening was sealed, and the ear part when packaging the contents was simulated. The obtained sample was immersed in hot water at 85 ° C. or 95 ° C. for 1 second to shrink, then taken out and immediately cooled in normal temperature water. The contracted sample is left in a constant temperature and humidity chamber at 23 ° C. and 50% relative humidity for 24 hours or more, and then the portion where the inner surfaces of the seal layers are fused is cut to a width of 15 mm, and the length of the fused portion is 30 mm. A sample piece was obtained. The integral average fusing force of the obtained sample pieces was measured for self-weld property at 85 ° C. and self-weld property at 95 ° C. using a universal tensile tester (Tensilon RTM-100, manufactured by Orientec Corp.). At this time, the distance between chucks was 20 mm, and the test speed was 200 mm / min. If the integrated average fusing force is 1 N / 15 mm or more, the self-weldability is at a practical level.

As shown in Table 4, all of the heat-shrinkable multilayer films of the examples were excellent in hot water shrinkage and had practical lap sealing properties and self-weld properties.

On the other hand, since Comparative Examples 1, 2, and 3 did not have a propylene-ethylene copolymer in the surface layer, they did not have lap sealing properties.

Claims

A multilayer structure having a surface layer, an intermediate layer T1, a gas barrier layer, and a seal layer is provided. The multilayer structure has the surface layer disposed on one surface and the seal layer disposed on the other surface. In the heat shrinkable multilayer film formed,
The surface layer contains a propylene-ethylene copolymer,
The gas barrier layer contains a polyvinylidene chloride resin,
A heat-shrinkable multilayer film, wherein a difference in melting temperature between the surface layer and the sealing layer is 35 to 60 ° C.
The heat-shrinkable multilayer film according to claim 1, wherein the multilayer structure further includes an intermediate layer T2 between the gas barrier layer and the seal layer.
The heat-shrinkable multilayer film according to claim 1 or 2, wherein the seal layer contains at least one of an ionomer and an ethylene-vinyl acetate copolymer.
The heat-shrinkable multilayer film according to any one of claims 1 to 3, wherein the heat-shrinkable multilayer film has self-weld property by heat treatment.