JP2014533612A - Heat-shrinkable multilayer film and method for producing the same - Google Patents

Abstract

An object of the present invention is to provide a heat-shrinkable multilayer film excellent in transparency and lap sealing properties, and having heat-shrinkability, gas barrier properties and heat-sealability, and a method for producing the same. The heat-shrinkable multilayer film according to the present invention comprises a multilayer structure having a surface layer including a surface layer, a gas barrier layer, and an inner layer including a seal layer, the multilayer structure has a surface layer disposed on one surface, and In the heat-shrinkable multilayer film having a seal layer disposed on the other surface, the surface layer contains silicone and the surface layer is crosslinked.

Description

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

  Since raw meat, processed meat, and the like are irregular in shape, shrink wrapping is usually performed from the viewpoint of appearance and freshness maintenance. 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.

  Furthermore, the 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 1). In addition, the outer surface is formed of a resin having a relatively high melting point such as polyamide resin or polyester resin, and the inner surface is formed of a resin having a relatively low melting point such as polyolefin resin. By providing, the film | membrane which provided the overlap sealing property is disclosed (for example, refer patent documents 2-5).

JP-A-9-39179 International Publication No. 2008/099799 European Patent No. 1131205 European Patent Application Publication No. 1985443 European Patent Application Publication No. 2147783

  The film described in Patent Document 1 has a narrow temperature range in which the inner surfaces can be heat-sealed without heat-sealing the outer surfaces, and the overlap sealability is insufficient. Although the films described in Patent Documents 2 to 5 have excellent lap sealing properties, the polyamide resin or the polyester resin is inferior in heat shrinkability compared to the polyolefin resin. Inability to follow, a wave is generated on the outer surface, and optical properties such as glossiness and transparency are deteriorated. Moreover, it is necessary to naturally raise the temperature of extrusion processing for resins having a high melting point such as polyamide resin and polyester resin. 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 point such as a polyamide resin or a polyester resin cannot be stably extruded. Therefore, the smoothness of the film surface may be deteriorated and an appearance defect may occur.

  An object of the present invention is to provide a heat-shrinkable multilayer film excellent in transparency and lap sealing properties, and having heat-shrinkability, gas barrier properties and heat-sealability, and a method for producing the same.

  The heat-shrinkable multilayer film according to the present invention has a multilayer structure having a surface layer including a surface layer, a gas barrier layer, and an inner layer including a seal layer, and the multilayer structure has the surface layer disposed on one surface. And the heat-shrinkable multilayer film formed by disposing the seal layer on the other surface is characterized in that the surface layer contains silicone and the surface layer is crosslinked.

  In the heat-shrinkable multilayer film according to the present invention, the gel fraction of the surface layer is preferably in the range of 20% to 80%. The temperature range that can be stacked and sealed can be made wider.

  In the heat-shrinkable multilayer film according to the present invention, the surface layer preferably contains a polyolefin resin. Heat resistance and glossiness can be improved.

  In the heat-shrinkable multilayer film according to the present invention, the surface layer preferably contains 0.05% to 5% by mass of the silicone. The temperature range that can be stacked and sealed can be made wider. Moreover, transparency can be made favorable.

  In the heat-shrinkable multilayer film according to the present invention, the surface layer preferably contains 1% by mass to 10% by mass of the silicone. The temperature range that can be stacked and sealed can be made wider. Moreover, transparency can be made favorable.

  The method for producing a heat-shrinkable multilayer film according to the present invention comprises a multilayer structure having a surface layer including a surface layer, a gas barrier layer, and an inner layer including a seal layer, and the multilayer structure has the surface layer on one surface. And a method for producing a heat-shrinkable multilayer film comprising the sealing layer on the other surface, at least a surface layer-forming resin composition containing a silicone, a gas barrier layer-forming resin composition, and Extruding the resin composition for forming a seal layer to form a laminate having the multilayer structure, Step B for stretching the laminate, and irradiating the surface layer with an electron beam to form the surface layer Cross-linking step C, and after step A, the step B and the step C are sequentially performed, or after the step A, the step C and the step B are sequentially performed. Process to advance Re and performs II.

  In the method for producing a heat-shrinkable multilayer film according to the present invention, the step C is preferably a step of crosslinking until the gel fraction of the surface layer is in the range of 20% to 80%. The temperature range that can be stacked and sealed can be made wider.

  INDUSTRIAL APPLICABILITY The present invention can provide a heat shrinkable multilayer film excellent in transparency and lap sealability, and having heat shrinkability, gas barrier properties and heat sealability, and a method for producing the same.

  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 including a surface layer, a gas barrier layer, and an inner layer including a seal layer, and the multilayer structure has a surface layer disposed on one surface, And in the heat-shrinkable multilayer film formed by disposing a seal layer on the other surface, the surface layer contains silicone and the surface layer is crosslinked.

(Surface)
The surface layer includes at least a 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 this embodiment, the surface layer preferably contains a polyolefin resin from the viewpoint of heat resistance and gloss. 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, and ethylene-α olefin. Ethylene such as copolymers, ethylene-vinyl acetate copolymer (EVA), ethylene-alkyl acrylates having 1 to 4 carbon atoms, ethylene-methacrylic acid copolymers, ethylene-methacrylic acid-unsaturated carboxylic acid copolymers -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 . These may be used alone or in combination of two or more. Among these, VLDPE and LLDPE are particularly preferable from the viewpoint of stretchability. Moreover, PP is particularly preferable from the viewpoint of heat resistance.

The density of the resin used for the surface layer is preferably 0.880 g / m ³ or more and 0.940 g / m ³ or less. More preferably, the 0.900 g / ^{m 3} or more 0.925 g / ^{m 3} or less.

  The melting point of the resin used for the surface layer is preferably 90 ° C. or higher and 160 ° C. or lower. More preferably, it is 110 degreeC or more and 150 degrees C or less. If it is less than 90 degreeC, heat resistance may be insufficient. If the temperature exceeds 160 ° C., the extrusion processing temperature becomes high, so that the smoothness of the surface may be inferior or the stretchability may be hindered. Further, when PVDC is used for the gas barrier layer, decomposition of PVDC may occur.

  The surface layer contains silicone. In the heat-shrinkable multilayer film according to this embodiment, the surface layer preferably contains 1% by mass to 10% by mass of silicone. More preferably, it is 1 mass% or more and 5 mass% or less, Most preferably, it is 1.25 mass% or more and 2.5 mass% or less. If it is less than 1% by mass, the temperature range in which the overlap sealability is exhibited may be narrowed. When it exceeds 10 mass%, transparency may be inferior. The surface layer may contain various additives such as a heat stabilizer, a plasticizer, an antioxidant, and a softener in addition to the polyolefin resin and silicone. 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, polyisobutylene, polybutene, polybutadiene, Butadiene-styrene copolymer, neoprene, natural rubber.

  Silicone is a compound having a main skeleton based on siloxane bonds, such as polydimethylsiloxane, polymethylphenylsiloxane, and polymethylvinylsiloxane. These may be used alone or in combination of two or more. Of these, polydimethylsiloxane is more preferred.

The kinematic viscosity of silicone has a correlation with the molecular weight of silicone. That is, the higher the kinematic viscosity of silicone, the greater the molecular weight of the silicone. In the heat-shrinkable multilayer film according to this embodiment, the kinematic viscosity at 25 ° C. of the silicone is preferably 100 mm ² / sec (cSt) or more and 1.5 million mm ² / sec (cSt) or less. More preferably, it is not 500 mm ² / sec 1,000,000 mm ² / sec or more, and particularly preferably 1000 mm ² / sec 100,000 mm ² / sec or more. If it is less than 100 mm < ² > / sec, in melt extrusion, the frictional force with a barrel or a screw may fall, and stable extrusion may not be performed. If it exceeds 1,500,000 mm ² / sec, mixing with the resin may become difficult or mixing may be liable to occur.

  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.

  The surface layer preferably further includes an intermediate layer T1 between the surface layer and the gas barrier layer. The intermediate layer T1 has a role of improving transparency and stretchability. The mid layer T1 preferably contains a polyolefin resin. As the polyolefin-based resin, those exemplified in the surface layer can be used. EVA, ethylene-alkyl acrylate having 1 to 4 carbon atoms, and ethylene-methacrylic acid copolymer are used in terms of stretchability, adhesion to the surface layer, and transparency. Particularly preferred are polymers, ethylene-polar comonomer copolymers such as ethylene-methacrylic acid-unsaturated carboxylic acid copolymers, and 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 resin, the intermediate layer T1 may contain various additives such as 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, polyisobutylene, polybutene, polybutadiene, Butadiene-styrene copolymer, neoprene, natural rubber.

  The melting point 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.

  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 30 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.

  The surface layer preferably further includes an adhesive layer S1 as a layer adjacent to the gas barrier layer. The adhesive layer S1 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 the ethylene-polar comonomer copolymer include ethylene-vinyl acetate copolymer, ethylene-alkyl acrylate having 1 to 4 carbon atoms, ethylene-methacrylic acid copolymer, and ethylene-methacrylic acid-unsaturated carboxylic acid copolymer. , 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 point 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.

  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.

The surface layer is cross-linked. The degree of crosslinking can generally be expressed as a gel fraction. The gel fraction can be determined as follows. When the surface layer separated from the heat-shrinkable multilayer film is immersed in a solvent such as 1,2,4-trichlorobenzene, the crosslinked portion remains as an undissolved substance (gel). The gel fraction refers to the ratio of the dry mass W2 of the undissolved material remaining undissolved and the mass W1 of the surface layer before being dissolved with a solvent, expressed as a percentage. That is, the gel fraction can be obtained by Equation 1.
(Equation 1) Gel fraction [%] = (W2 / W1) × 100

  In the heat-shrinkable multilayer film according to the present embodiment, the gel fraction of the surface layer is preferably in the range of 20% to 80%. The gel fraction is more preferably 25% or more and 75% or less, and particularly preferably 30% or more and 70% or less. If the gel fraction is less than 20%, the temperature range that expresses the overlap sealability may become narrow. The inventors have found that as the degree of cross-linking increases (the gel fraction increases), the temperature range over which the double seal can be performed tends to increase. If the gel fraction exceeds 80%, there may be a problem in stretch processability. In addition, this invention is not restrict | limited to a crosslinking reaction and a crosslinked structure.

  In the present embodiment, layers other than the surface layer constituting the surface layer (for example, the intermediate layer T1 or the adhesive layer S1) may contain silicone within a range that does not impair the effects of the present invention. In the form in which the surface layer and the layer other than the surface layer contain silicone, or the form in which only the surface layer contains silicone, the surface layer preferably contains 0.05% by mass or more and 5% by mass or less of silicone. More preferably, it is 0.1 mass% or more and 2.5 mass% or less, Most preferably, it is 0.3 mass% or more and 2.2 mass% or less. If it is less than 0.05 mass%, the temperature range in which the overlap sealability is exhibited may be narrowed. When it exceeds 5 mass%, transparency may be inferior. For example, when the surface layer and the intermediate layer T1 contain silicone, not only the surface layer but also the intermediate layer T1 is crosslinked.

(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, for example, polyvinylidene chloride (PVDC) resin or ethylene-vinyl alcohol copolymer (EVOH) as a gas barrier resin.

  The polyvinylidene chloride resin is, for example, a copolymer of 60 to 98% by mass of vinylidene chloride (VDC) and 2 to 40% by mass of another monomer (comonomer) that can be copolymerized.

  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, and the like. To 18); methyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, stearyl methacrylate and other alkyl methacrylates (alkyl group having 1 to 18 carbon atoms); 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, itacon Acid Polymerizable unsaturated carboxylic acids; alkyl esters of vinyl polymerizable unsaturated carboxylic acids such as maleic acid, fumaric acid, itaconic acid (including partial esters, having 1 to 18 carbon atoms in the alkyl group); Body, functional group-containing monomer, and polyfunctional monomer.

  These comonomers may 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 viewpoints of processability in molding into a film, suitability for packaging machinery, cold resistance, and the like. It is 0.040-0.065, Most preferably, it is 0.045-0.063. 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 copolymers, (meth) acrylic acid esters, preferably (co) polymers of alkyl group (meth) acrylic acid alkyl esters having 1 to 18 carbon atoms [for example, (Meth) methyl acrylate- (meth) butyl acrylate copolymer], methyl methacrylate-butadiene-styrene copolymer. 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.

  An example of the ethylene-vinyl alcohol copolymer is a saponified ethylene-vinyl acetate copolymer. The saponified ethylene-vinyl acetate copolymer preferably has an ethylene content of 25 to 48 mol% and a saponification degree of 98% or more. When the ethylene content of the saponified ethylene-vinyl acetate copolymer is less than 25 mol%, insoluble matter tends to be generated. When the ethylene content exceeds 48 mol%, the oxygen gas barrier property tends to deteriorate. Further, when the saponification degree of the saponified ethylene-vinyl acetate copolymer is less than 98%, the oxygen gas barrier property tends to deteriorate.

  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.

(Inner layer)
The inner layer includes at least a 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), medium density polyethylene (MDPE), ethylene-α olefin copolymer, ethylene-vinyl acetate copolymer (EVA), and ethylene-alkyl having 1 to 4 carbon atoms. An acrylate, an ethylene-methacrylic acid copolymer, an ethylene-polar comonomer copolymer such as an ethylene-methacrylic acid-unsaturated carboxylic acid copolymer, and an 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 0.900 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. These may be used alone or in combination of two or more. Among these, EVA and ionomer are particularly preferable in terms of stretchability and low temperature sealability. 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 / m ³ or more and 0.940 g / m ³ or less. More preferably, the 0.900 g / ^{m 3} or more 0.925 g / ^{m 3} or less.

  The melting point of the resin used for the seal layer is preferably 80 ° C. or higher and 110 ° C. or lower. More preferably, it is 85 degreeC or more and 100 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. When the temperature exceeds 110 ° C., the temperature range in which multiple seals can be performed may be narrowed.

  The melting point of the sealing layer is lower than the melting point of the surface layer, and the difference in melting point is preferably 10 ° C. or higher and 60 ° C. or lower. More preferably, it is 15 degreeC or more and 55 degrees C or less, Most preferably, they are 20 degreeC or more and 50 degrees C or less. When the difference in melting point between the surface layer and the seal layer is less than 10 ° C., the temperature range that expresses the overlap sealability may be narrowed. When the difference in melting point between the surface layer and the seal layer exceeds 60 ° C., the processing temperature difference increases, and when the melting point of the seal layer is relatively high, the melting point of the surface layer becomes relatively high. If it does so, since extrusion processing temperature becomes high, as a result, the smoothness of a surface may be inferior, or ductility may be inhibited. Further, when the melting point of the surface layer is relatively low, the melting point of the sealing layer is relatively low. Then, 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.

  The inner layer preferably further includes an intermediate layer T2 between the gas barrier layer and the seal layer. The intermediate layer T2 has a role of improving transparency and stretchability. The mid layer T2 preferably contains a polyolefin resin. As the polyolefin-based resin, those exemplified in the surface layer can be used, and EVA, ethylene-alkyl acrylate having 1 to 4 carbon atoms, ethylene-methacrylic acid copolymer are used in terms of stretchability, adhesion to the surface layer, and transparency. Particularly preferred are polymers, ethylene-polar comonomer copolymers such as ethylene-methacrylic acid-unsaturated carboxylic acid copolymers, and ionomers. 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 point 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.

  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.

  The inner layer preferably further includes an adhesive layer S2 as a layer adjacent to the gas barrier layer. The adhesive layer S2 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 point 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.

  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, a gas barrier layer, and an inner 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 three-layer structure in which a surface layer, a gas barrier layer, and a seal layer are sequentially stacked, a five-layer structure in which a surface layer, an adhesive layer S1, a gas barrier layer, an adhesive layer S2, and a seal layer are sequentially stacked, and a surface layer , Intermediate layer T1, adhesive layer S1, gas barrier layer, adhesive layer S2, and 6-layer structure in which an adhesive layer S2 and a seal layer are sequentially laminated, surface layer, intermediate layer T1, adhesive layer S1, gas barrier layer, adhesive layer S2, intermediate layer T2, and seal layer Is a seven-layer structure in which 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. 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.

  In the heat-shrinkable multilayer film according to the present embodiment, the haze measured according to JIS K 7136: 2000 “How to determine haze of plastic-transparent material” is preferably 25% or less. More preferably, it is 20% or less.

  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. 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 seal strength between the seal layers (also referred to as fusion strength or adhesion strength) is preferably 5 N / 15 mm or more. More preferably, it is 10N / 15mm or more, Most preferably, it is 15N / 15mm or more. If the fusion strength between the sealing layers of each packaging bag is less than 5 N / 15 mm, the sealing property 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, the manufacturing method of the heat-shrinkable multilayer film which concerns on this embodiment is demonstrated.

  The method for producing a heat-shrinkable multilayer film according to this embodiment includes a multilayer structure having a surface layer including a surface layer, a gas barrier layer, and an inner layer including a seal layer, and the multilayer structure has a surface layer on one surface. In the method for producing a heat-shrinkable multilayer film, which is disposed and a seal layer is disposed on the other surface, at least a silicone-containing surface layer-forming resin composition, a gas barrier layer-forming resin composition, and a seal layer Each of the forming resin compositions is extruded to form a laminate A having a multilayer structure, Step B for stretching the laminate, and Step C for irradiating the surface layer with an electron beam to crosslink the surface layer. And after the process A, the process flow I that sequentially proceeds the process B and the process C is performed, or after the process A, the process flow II that sequentially proceeds the process C and the process B is performed. Next, the process flow I will be described as an example.

  In the method for producing a 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 of an example of a method of manufacturing by an inflation method.

(Process A)
In step A, an unstretched laminate having a multilayer structure is formed. First, at least a silicone-containing resin composition for forming a surface layer, a resin composition for forming a gas barrier layer, and a resin composition for forming a seal layer, and, if necessary, a resin composition for forming an intermediate layer T1, an intermediate layer T2. A resin composition for forming each of the resin composition for forming, 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. In the subsequent process C, the surface layer can be efficiently irradiated with an electron beam to crosslink the surface layer more efficiently. This is cooled with cooling water to obtain a flat tubular unstretched laminate.

  In step A, the silicone may be blended in a form contained in a master batch. In the silicone master batch, the base resin is not particularly limited as long as it does not impair the effect of the present invention, and examples thereof include LDPE, VLDPE, LLDPE, and EVA.

(Process B)
In Step B, 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 step B, the temperature at which the unstretched laminate is heat-treated is preferably 70 to 95 ° C, and more preferably 75 to 90 ° C. Moreover, it is preferable that the temperature of a cold wind air ring is 5-25 degreeC. The draw ratio is preferably 2 to 4 times in the MD direction and the TD direction, respectively. 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.

(Process C)
In step C, the surface layer is irradiated with an electron beam (EB, electron beam) to crosslink the surface layer. In the method for producing a heat-shrinkable multilayer film according to the present embodiment, the step C has a range in which the gel fraction of the surface layer is 20% or more and 80% or less in that the temperature range that can be overlap-sealed can be made wider. It is preferable that it is the process of bridge | crosslinking until it becomes. The gel fraction is more preferably 25% or more and 75% or less, and particularly preferably 30% or more and 70% or less. The degree of crosslinking can be controlled, for example, by adjusting various conditions such as absorbed dose and acceleration voltage.

  In Step C, the electron beam irradiation conditions may be appropriately set according to the target degree of crosslinking, and as an example, the acceleration voltage is in the range of 150 to 500 kV, and the absorbed dose is 50 to 250 kGy (kilo gray). It is preferable that it is 80 to 200 kGy. In the present embodiment, the electron beam irradiation may be in-line performed after the stretched film is formed and without the winding process, or may be off-line performed after the stretched film is formed and after the winding process. .

  So far, after the process A, the process flow I in which the process B and the process C are sequentially performed has been described. However, after the process A, the process flow II in which the process C and the process B are sequentially performed may be performed. Further, after the step A, before the stretching in the step B, a step D for irradiating the unstretched laminate with an electron beam may be further provided. By performing the process D, for example, the cross-linking reaction can proceed between the resin contained in the surface layer and the resin contained in the intermediate layer, and the stretchability and heat resistance can be further increased.

  Next, although an example of the present invention is given and explained, the present invention is not limited to these examples.

<Example 1>
(Process A)
As the resin composition for forming the surface layer in the first layer, ultra-low density polyethylene (Moertech V0398CN, manufactured by Prime Polymer Co., Ltd., density 0.907 g / cm ³ , melting point (Tm) 117 ° C., hereinafter referred to as VLDPE-1). A silicone master batch (hexasilicone ML-950, manufactured by Hexa Chemical Co., Ltd., base resin: LDPE, silicone concentration: 50% by mass, hereinafter referred to as MB-1) is blended in an amount of 5% by mass (hereinafter VLDPE-1 + 5 wt%). MB-1) and an ethylene / vinyl acetate copolymer (Evaflex V430RC, manufactured by Mitsui DuPont Polychemical Co., Ltd., vinyl acetate content 19 mol%, density 0) as the resin composition for forming the intermediate layer T1 in the second layer. .94g / cm ^3, melting point 84 ° C., hereinafter referred to EVA-1.) was blended MB-1 5% by weight (Hereinafter referred to as EVA-1 + 5 wt% MB-1), an ethylene / methyl acrylate copolymer (Elvalloy 1218AC, manufactured by Mitsui / Dupont Polychemical Co., Ltd., density 0) as the resin composition for forming the adhesive layer S1 in the third layer. .94 g / cm ³ , melting point 94 ° C., hereinafter referred to as EMA-1) and vinylidene chloride / vinyl chloride copolymer (made by Kureha, density 1.71 g / as a resin composition for forming a gas barrier layer in the fourth layer) cm ³ , melting point 145 ° C., hereinafter referred to as PVDC-1), EMA-1 as the resin composition for forming the adhesive layer S2 in the fifth layer, and ionomer (High Milan) as the resin composition for forming the seal layer in the sixth layer. 1601, Du Pont-Mitsui Polychemicals Co., Ltd., density 0.94 g / cm ^3, melting point 97 ° C., since, its in that Ionomer-1.) and a plurality of extruders Each extruded and melted resin is introduced into an annular die and melted in order from the outside to the inside so that it has a 6-layer structure of surface layer, intermediate layer T1, adhesive layer S1, gas barrier layer, adhesive layer S2 and seal layer. Bonded and coextruded. 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 160 mm.

(Process B)
After passing the flat tubular body obtained in step A through a hot water bath at 86 ° C., it is converted into a bubble-shaped tubular body film by the inflation method while cooling with a cold air ring at 15 to 20 ° C. by the inflation method (MD Direction) and biaxial stretching at a stretching ratio of 2.8 times in the transverse direction (TD direction). Next, the biaxially stretched film was heated at 40 ° C. for 1 second to be thermally relaxed to produce a biaxially stretched film (heat-shrinkable multilayer film). The flat width of the obtained heat-shrinkable multilayer film is 400 mm, and the thickness of each layer is 3 μm for the surface layer, 10 μm for the intermediate layer T1, 1.5 μm for the adhesive layer S1, 4 μm for the gas barrier layer, and 1 for the adhesive layer S2. 0.5 μm and the seal layer was 30 μm, and the total thickness of the film was 50 μm.

(Process C)
The biaxially stretched film obtained in Step B was irradiated with an electron beam in an electron beam irradiation apparatus with an acceleration voltage of 275 kV offline. As electron beam irradiation conditions, irradiation was performed with an absorbed dose of 100 kGy.

<Example 2>
In Example 1, MB-1 blended with the resin composition for forming the surface layer and the resin composition for forming the intermediate layer T1 was a silicone masterbatch (silicone concentrate BY27-002, manufactured by Toray Dow Corning, Base Resin: LDPE). A heat-shrinkable multilayer film was produced in the same manner as in Example 1 except that the silicone concentration was changed to 50% by mass and hereinafter referred to as MB-2.

<Example 3>
In Example 1, a heat-shrinkable multilayer film was produced in the same manner as in Example 1 except that MB-1 was not blended in the resin composition for forming the intermediate layer T1 and the acceleration voltage for electron beam irradiation was changed to 250 kV. did.

<Example 4>
In Example 3, a heat-shrinkable multilayer film was produced in the same manner as in Example 3 except that the thickness of the surface layer was 1.5 μm and the thickness of the intermediate layer T1 was 11.5 μm.

<Example 5>
In Example 3, instead of VLDPE-1 + 5 wt% MB-1 as a resin composition for forming a surface layer, VLDPE-1 was blended with 10% by mass of MB-1 (hereinafter referred to as VLDPE-1 + 10 wt% MB-1. And a heat-shrinkable multilayer film was produced in the same manner as in Example 3 except that the acceleration voltage of electron beam irradiation was changed to 275 kV.

<Example 6>
In Example 3, instead of VLDPE-1 + 5 wt% MB-1 as the resin composition for forming the surface layer, VLDPE-1 was blended with 2.5 mass% of MB-1 (hereinafter, VLDPE-1 + 2.5 wt% MB -1), and a heat-shrinkable multilayer film was produced in the same manner as in Example 3 except that the acceleration voltage of electron beam irradiation was changed to 275 kV.

<Example 7>
In Example 3, a heat-shrinkable multilayer film was produced in the same manner as in Example 3 except that the irradiation dose during electron beam irradiation was changed to 80 kGy.

<Example 8>
In Example 3, a heat-shrinkable multilayer film was produced in the same manner as in Example 3 except that the irradiation dose during electron beam irradiation was changed to 150 kGy.

<Example 9>
In Example 1, as the resin composition for forming the adhesive layer S1 and the resin composition for forming the adhesive layer S2, in place of EMA-1, adhesive polyethylene (Admer SF730, manufactured by Mitsui Chemicals, density 0.92 g / cm ³⁾ , Melting point 119 ° C., hereinafter referred to as mod-VL), instead of PVDC-1 as the gas barrier layer forming resin composition, saponified ethylene / vinyl acetate copolymer (Eval EPG156B, manufactured by Kuraray Co., Ltd., ethylene content 48) A heat-shrinkable multilayer film was produced in the same manner as in Example 1 except for changing to mol%, density 1.11 g / cm ³ , melting point 160 ° C., hereinafter referred to as EVOH-1.

<Example 10>
In Example 3, a heat-shrinkable multilayer film was produced in the same manner as in Example 3 except that VLDPE-1 was used instead of EVA-1 as the resin composition for forming the intermediate layer T1. In the obtained heat-shrinkable multilayer film, the boundary between the surface layer and the intermediate layer T1 becomes unclear, and the surface layer, the adhesive layer S1, the gas barrier layer, the adhesive layer S2, and the sealing layer are sequentially simulated from the outside to the inside. It became the laminated | stacked 5 layer structure.

<Example 11>
In Example 3, instead of VLDPE-1 + 5 wt% MB-1 as the resin composition for forming the surface layer, linear low density polyethylene (MORETECH 0238CN, manufactured by Prime Polymer Co., Ltd., density 0.916 g / cm ³ , melting point 119 ° C. , Hereinafter referred to as LLDPE-1), and heat-shrinkable multilayer film in the same manner as in Example 3 except that 5% by mass of MB-1 was blended (hereinafter referred to as LLDPE-1 + 5 wt% MB-1). Manufactured.

<Example 12>
In Example 4, instead of VLDPE-1 + 5 wt% MB-1 as the surface layer forming resin composition, VLDPE-1 was replaced with a silicone master batch (prototype, silicone: polydimethylsiloxane (Shin-Etsu Silicone KF-96H-1 million cs). , Manufactured by Shin-Etsu Chemical Co., Ltd.), silicone concentration: 9% by mass, kinematic viscosity of silicone: 1,000,000 mm ² / sec, base resin: VLDPE-1, hereinafter referred to as MB-3). A heat-shrinkable multilayer film was produced in the same manner as in Example 4 except that the film was made of VLDPE-1 + 28 wt% MB-3.

<Example 13>
In Example 4, instead of VLDPE-1 + 5 wt% MB-1 as the surface layer forming resin composition, VLDPE-1 was replaced with a silicone master batch (prototype, silicone: polydimethylsiloxane (Shin-Etsu Silicone KF-96H-100,000 cs). (Shin-Etsu Chemical Co., Ltd.), silicone concentration: 10% by mass, silicone kinematic viscosity: 100,000 mm ² / sec, base resin: VLDPE-1, hereinafter referred to as MB-4) Hereinafter, a heat-shrinkable multilayer film was produced in the same manner as in Example 4 except that VLDPE-1 + 25 wt% MB-4 was used.

<Example 14>
In Example 4, instead of VLDPE-1 + 5 wt% MB-1 as the surface layer forming resin composition, VLDPE-1 was replaced with a silicone masterbatch (prototype, silicone: polydimethylsiloxane (Shin-Etsu Silicone KF-96H-10,000 cs). (Shin-Etsu Chemical Co., Ltd.), silicone concentration: 10% by mass, silicone kinematic viscosity: 10,000 mm ² / sec, base resin: VLDPE-1, hereinafter referred to as MB-5) Hereinafter, a heat-shrinkable multilayer film was produced in the same manner as in Example 4 except that VLDPE-1 + 25 wt% MB-5 was used.

<Example 15>
In Example 4, instead of VLDPE-1 + 5 wt% MB-1 as the surface layer forming resin composition, VLDPE-1 was replaced with a silicone master batch (prototype, silicone: polydimethylsiloxane (Shin-Etsu Silicone KF-96-1,000cs). , Manufactured by Shin-Etsu Chemical Co., Ltd.), silicone concentration: 10 mass%, kinematic viscosity of silicone: 1,000 mm ² / sec, base resin: VLDPE-1, hereinafter referred to as MB-6)) was blended in an amount of 12.5 mass%. A heat-shrinkable multilayer film was produced in the same manner as in Example 4 except that the film was made of VLDPE-1 + 12.5 wt% MB-6.

<Example 16>
(Process A)
VLDPE-1 + 10 wt% MB-1 as the resin composition for forming the surface layer in the first layer, and ethylene / vinyl acetate copolymer (Evaflex V5715, Mitsui / Dupont Poly as the resin composition for forming the intermediate layer T1 in the second layer. Chemical Company, vinyl acetate content 19 mol%, density 0.94 g / cm ³ , melting point 89 ° C., hereinafter referred to as EVA-2), and EMA-1 as a resin composition for forming the adhesive layer S1 in the third layer. The fourth layer is PVDC-1 as the gas barrier layer forming resin composition, the fifth layer is EMA-1 as the adhesive layer S2 forming resin composition, and the sixth layer is ethylene as the intermediate layer T2 forming resin composition. - vinyl acetate copolymer (Evaflex V5714C, Du Pont-Mitsui Polychemicals Co., Ltd., vinyl acetate content of 15 mol%, density 0.94 g / cm ^3, melting point 89 ° C., after, EV -3 called. A), ionomer seventh layer as a sealing layer forming resin composition (Himilan AM79301, DuPont-Mitsui Polychemicals Co., Ltd., density 0.94 g / cm ^3, melting point 91 ° C., hereinafter referred Ionomer-2 .) Are respectively extruded by a plurality of extruders, the molten resin is introduced into an annular die, and the surface layer, intermediate layer T1, adhesive layer S1, gas barrier layer, adhesive layer S2, intermediate layer T2 are sequentially introduced from the outside to the inside. And it melt-bonded so that it might become 7-layer structure of a sealing layer, and coextruded. 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.

(Process D)
The flat tubular body obtained in step A was irradiated with an electron beam in-line in an electron beam irradiation apparatus having an acceleration voltage of 275 kV. As electron beam irradiation conditions, irradiation was performed with an absorbed dose of 100 kGy.

(Process B)
After the step D, the flat tubular body is passed through a hot water bath at 81.5 ° C., then formed into a bubble-shaped tubular body film, and is cooled by a cold air ring at 5 to 20 ° C. in the longitudinal direction ( Simultaneous biaxial stretching was performed at a draw ratio of 3.5 times in the MD direction and 3.4 times in the transverse direction (TD direction). Next, the biaxially stretched film was heated at 42 ° C. for 0.5 seconds to be thermally relaxed to produce a biaxially stretched film (heat-shrinkable multilayer film). The flattened width of the obtained heat-shrinkable multilayer film is 380 mm, and the thickness of each layer is as follows: surface layer is 1.5 μm, intermediate layer T1 is 22 μm, adhesive layer S1 is 1.5 μm, gas barrier layer is 7 μm, adhesive layer S2 was 1.5 μm, the intermediate layer T2 was 10 μm, the seal layer was 10 μm, and the total thickness of the film was 53.5 μm.

(Process C)
The biaxially stretched film obtained in Step B was irradiated with an electron beam in an electron beam irradiation apparatus with an acceleration voltage of 250 kV offline. As electron beam irradiation conditions, irradiation was performed with an absorbed dose of 100 kGy.

<Example 17>
In Example 16, instead of VLDPE-1 + 10 wt% MB-1 as the surface layer forming resin composition, VLDPE-1 was blended with 25% by mass of MB-4 (hereinafter referred to as VLDPE-1 + 25 wt% MB-4). Except for the above, a heat-shrinkable multilayer film was produced in the same manner as in Example 16.

<Example 18>
In Example 16, instead of VLDPE-1 + 10 wt% MB-1 as the resin composition for forming the surface layer, VLDPE-1 containing 25% by mass of MB-5 (hereinafter referred to as VLDPE-1 + 25 wt% MB-5). Except for the above, a heat-shrinkable multilayer film was produced in the same manner as in Example 16.

<Example 19>
In Example 18, except that EVA-1 was used instead of EVA-3 as the resin composition for forming the intermediate layer T2, and EVA-3 was used instead of Iomer-2 as the resin composition for forming the seal layer. A hot water shrinkable multilayer film was produced in the same manner as in Example 18.

<Example 20>
(Process A)
A VLDPE-1 blended with 56% by mass of MB-3 (hereinafter referred to as VLDPE-1 + 56 wt% MB-3) as a resin composition for forming a surface layer in the first layer, and an intermediate layer T1 formed in the second layer. Adhesive to EVA-1 as a resin composition, EMA-1 as a resin composition for forming an adhesive layer S1 as a third layer, PVDC-1 as a resin composition for forming a gas barrier layer as a fourth layer, and a fifth layer EMA-1 as the resin composition for forming the layer S2, and Ionomer-1 as the resin composition for forming the seal layer in the sixth layer were respectively extruded by a plurality of extruders, and the molten resin was introduced into the annular die, In order from the inside to the inside, the layers were melt-bonded and co-extruded so as to have a six-layer structure of a surface layer, an intermediate layer T1, an adhesive layer S1, a gas barrier layer, an adhesive layer S2, and a seal layer. 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 160 mm.

(Process C)
The flat tubular body obtained in step A was irradiated with an electron beam at an acceleration voltage of 250 kV and an absorbed dose of 100 kGy offline.

(Process B)
After passing the flat tubular body obtained in Step C through a hot water bath at 86 ° C., it is converted into a bubble-shaped tubular body film by the inflation method while cooling with a cold air ring at 15 to 20 ° C. by the inflation method. Direction) and biaxial stretching at a stretching ratio of 2.8 times in the transverse direction (TD direction). Next, the biaxially stretched film was heated at 40 ° C. for 1 second to be thermally relaxed to produce a biaxially stretched film (heat-shrinkable multilayer film). The flattened width of the obtained heat-shrinkable multilayer film is 400 mm, and the thickness of each layer is 1.5 μm for the surface layer, 11.5 μm for the intermediate layer T1, 1.5 μm for the adhesive layer S1, 4 μm for the gas barrier layer, and bonded. Layer S2 was 1.5 μm and seal layer was 30 μm, and the total thickness of the film was 50 μm.

<Example 21>
In Example 20, instead of VLDPE-1 + 56 wt% MB-3 as a resin composition for forming a surface layer, VLDPE-1 was blended with 25 mass% of MB-5 (hereinafter referred to as VLDPE-1 + 25 wt% MB-5). Except for the above, a heat-shrinkable multilayer film was produced in the same manner as in Example 20.

<Comparative Example 1>
In Example 1, a heat-shrinkable multilayer film was produced in the same manner as in Example 1 except that MB-1 was not added to the resin composition for forming the surface layer and the resin composition for forming the intermediate layer T1.

<Comparative example 2>
A heat-shrinkable multilayer film was produced in the same manner as in Example 1 except that Step C was not performed in Example 1.

<Comparative Example 3>
In Example 16, a heat-shrinkable multilayer film was produced in the same manner as in Example 16 except that MB-1 was not blended in the resin composition for forming a surface layer and Step C was not performed.

<Comparative example 4>
In Example 20, a heat-shrinkable multilayer film was produced in the same manner as in Example 20, except that MB-3 was not added to the resin composition for forming the surface layer and the resin composition for forming the intermediate layer T1.

  About the heat-shrinkable multilayer film of the obtained Example and the comparative example, the kind of used resin was put together in Table 1, the kind of silicone was put together in Table 2, and the kind of masterbatch was put together in Table 3. Table 4 shows the layer configurations of Examples and Comparative Examples, and Table 5 shows stretching conditions and electron beam irradiation conditions.

  The following evaluation was performed about the heat-shrinkable multilayer film of the obtained Example and the comparative example. The evaluation results are shown in Table 6.

<Hot water shrinkage>
In accordance with ASTM D-2732, a film sample marked at a distance of 10 cm in the machine direction (longitudinal direction, MD direction) and the direction perpendicular to the machine direction (lateral direction, TD direction) is 80 cm. 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.

<Transparency> (Haze)
Based on JIS K7136: 2000, the haze (Haze [%]) of the film was measured using the haze meter (NDH2000, Nippon Denshoku Industries Co., Ltd.). The haze value means that the smaller the value, the better the transparency, and the larger the value, the worse the transparency.

<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 155 ° C, 160 ° 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 the upper seal inner surface, and the seal between the seal layers in the film on the side not in contact with the seal bar is referred to as the lower seal inner surface. Moreover, the seal | sticker of the surface layers of the overlapping part of two sets of films is called a seal | sticker 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. The overlap sealability was judged from the seal strengths of the upper seal inner surface, the lower seal inner surface and the seal outer surface as follows.
◯: The seal strength of the inner surface of the upper seal and the inner surface of the lower seal is 5 N / 15 mm or more, and the strength of the outer surface of the seal is 1 N / 15 mm or less, indicating a lap seal property (practical level).
X: The seal strength of the outer surface of the seal is 1 N / 15 mm or more, 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).
-: 0 in the evaluation of the overlap sealability (practical level).

<Inner seal strength>
In the overlap sealability evaluation, the seal strength of the upper seal inner surface and the lower seal inner surface at a seal temperature of 155 ° C. was evaluated as the inner surface seal strength. The seal strength of the upper seal inner surface and the lower seal inner surface was 5 N / 15 mm or more as a practical level, and the seal strength of the upper seal inner surface and the lower seal inner surface was less than 5 N / 15 mm as an unusable level.

<Gel fraction>
The surface layers (first, second, and third layers) were peeled from the substrate to obtain a sample, and the mass of the sample was set to W1 [g]. Next, the sample was immersed in 10 ml of 1,2,4-trichlorobenzene and kept at 120 ° C. for 2 hours, and then the undissolved material was collected and dried overnight. The dry mass of this undissolved material was set to W2 [g], and the gel fraction was calculated from Equation 1.
(Equation 1) Gel fraction [%] = (W2 / W1) × 100

  As shown in Table 6, all the heat-shrinkable multilayer films of the examples were excellent in transparency and hot-water shrinkage, and had practical lap sealing properties. It was confirmed that any of the production methods of the process flow I and the process flow II can obtain a heat-shrinkable multilayer film having good transparency, hot-water shrinkability, and lap sealability. Of these, the process flow I was particularly good.

  On the other hand, since the surface layer did not contain silicone, the comparative example 1 did not have an overlap seal property even when irradiated with an electron beam. In Comparative Example 2, the surface layer contained silicone, but it was not irradiated with an electron beam, and it was not cross-linked, so it did not have overlap sealability. Since the surface layer did not contain silicone, the comparative example 3 did not have overlap sealability. In Comparative Example 4, since the surface layer did not contain silicone, even when irradiated with an electron beam, it did not have overlap sealability.

Claims (7)

A multilayer structure having a surface layer including a surface layer, a gas barrier layer, and an inner layer including a seal layer, wherein 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 silicone;
The heat-shrinkable multilayer film, wherein the surface layer is crosslinked.   2. The heat-shrinkable multilayer film according to claim 1, wherein the surface layer has a gel fraction in the range of 20% to 80%.   The heat-shrinkable multilayer film according to claim 1 or 2, wherein the surface layer contains a polyolefin resin.   The heat-shrinkable multilayer film according to any one of claims 1 to 3, wherein the surface layer contains 0.05 mass% or more and 5 mass% or less of the silicone.   The heat-shrinkable multilayer film according to any one of claims 1 to 4, wherein the surface layer contains the silicone in an amount of 1% by mass to 10% by mass. A multilayer structure having a surface layer including a surface layer, a gas barrier layer, and an inner layer including a seal layer, wherein the multilayer structure has the surface layer disposed on one surface and the seal layer disposed on the other surface; In the method for producing a heat-shrinkable multilayer film,
Step A for forming a laminate having the multilayer structure by extruding at least a resin composition for forming a surface layer containing a silicone, a resin composition for forming a gas barrier layer, and a resin composition for forming a seal layer, and
Step B of stretching the laminate;
And irradiating the surface layer with an electron beam to crosslink the surface layer, and
After the step A, the process flow I for sequentially proceeding with the process B and the process C is performed, or after the step A, the process flow II for sequentially proceeding with the process C and the process B is performed. A method for producing a heat-shrinkable multilayer film.   The method for producing a heat-shrinkable multilayer film according to claim 6, wherein the step C is a step of crosslinking until the gel fraction of the surface layer is in a range of 20% to 80%.