JP2021187098A - Gas barrier shrink film - Google Patents

Abstract

To provide a film which is excellent in gas barrier property even under a high humidity condition, prevents a container from being deformed upon gas pack packaging, and is excellent in mechanical characteristics.SOLUTION: A gas barrier shrink film includes at least four layers such as a base material layer (A), an adhesive layer (D), a gas barrier layer (B), and a heat seal layer (C), in which the adhesive layer (D) contains a thermoplastic resin and has a sea-island structure.SELECTED DRAWING: None

Description

The present invention relates to a gas barrier shrink film. In particular, the present invention relates to a gas barrier shrink film suitable for packaging by a packaging machine and mainly used in the food packaging field requiring gas barrier properties.

Examples of the packaging method for covering foodstuffs include household wrapping, overlap wrapping, twist wrapping, bagging wrapping, skin wrapping, pillow shrink wrapping, stretch wrapping, and top seal wrapping. In particular, continuous wrapping machines for pillow shrink wrapping and top seal wrapping are widely distributed because they can be packed at high speed and have a good finish.

Furthermore, in recent years, due to consideration for the environment, awareness of reducing the amount of unsold foods and the like at supermarkets and convenience stores has increased, and gas pack packaging for long-term storage and normal temperature storage of foods has been attracting attention. Gas pack packaging is a tool that suppresses the growth of bacteria and realizes long-term storage by enclosing the inside of the container with nitrogen gas or carbon dioxide gas, and the packaging film used is a gas barrier film with low oxygen permeability. Is suitable. As the gas barrier film, a film obtained by laminating a barrier resin and a polyolefin resin having a low temperature sealing property is known.

Gas pack packaging is used for meat and fish, but these are placed in supermarkets, convenience stores, etc. under low temperature and high humidity conditions. Therefore, the gas barrier property at a certain temperature and humidity is important. It is also important that the container does not deform during gas pack packaging.

For example, Patent Document 1 presents a multilayer film composed of a polyolefin-based resin, a modified polyolefin-based adhesive resin layer, a polyamide resin layer, and an ethylene-vinyl acetate copolymer saponified layer.
Further, Patent Document 2 includes a base material layer, a gas barrier layer, and a heat seal layer, the base material layer contains a thermoplastic resin having a melting point of 130 ° C. or higher, and the gas barrier layer is a polyethylene-vinyl alcohol copolymer saponified product. A multilayer film containing a polyethylene-based resin layer as a heat-sealing layer is presented.

Japanese Patent No. 3418204 Japanese Unexamined Patent Publication No. 2016-179648

However, since the polyamide resin layer is used in Patent Document 1, the gas barrier property at a certain temperature and humidity is inferior, and the container may be deformed during gas pack packaging.
Further, in Patent Document 2, a higher level of mechanical properties has not been achieved.

An object to be solved by the present invention is to provide a film having excellent gas barrier properties even under high humidity conditions, the container does not deform during gas pack packaging, and the mechanical properties are excellent.

As a result of diligent studies to solve the above problems, the present inventors have completed the present invention. That is, the present invention is as follows.
[1]
At least four layers of a base material layer (A), an adhesive layer (D), a gas barrier layer (B), and a heat seal layer (C) are provided.
A gas barrier shrink film characterized in that the adhesive layer (D) contains a thermoplastic resin and has a sea-island structure.
[2]
The adhesive layer (D) contains two types of thermoplastic resins (X) and (Y), and the density dx of the thermoplastic resin (X) and the density dy of the thermoplastic resin (Y) are dy−. The gas barrier shrink film according to [1], wherein dx> 30 kg / m ^3.
[3]
The gas barrier shrink film according to [2], wherein the thermoplastic resin (X) is a modified LLDPE.
[4]
The gas barrier shrink film according to [2] or [3], wherein the thermoplastic resin (Y) is HDPE.
[5]
The gas barrier shrink film according to any one of [2] to [4], wherein the mass ratio of the thermoplastic resin (X) to the thermoplastic resin (Y) is 10:90 to 90:10.
[6]
The gas barrier shrink film according to any one of [1] to [5], wherein the base material layer (A) contains at least a thermoplastic resin having a melting point of 130 ° C. or higher.
[7]
The gas barrier shrink film according to any one of [1] to [6], wherein the heat seal layer (C) contains at least a polyethylene resin.
[8]
The gas barrier shrink film according to any one of [1] to [7], wherein the heat shrinkage in the length direction at 100 ° C. is 30% or more.

Since the gas barrier shrink film of the present invention has the above-mentioned structure, it has excellent gas barrier properties even under high humidity conditions, and the container does not deform during gas pack packaging and has excellent mechanical properties.

Hereinafter, embodiments for carrying out the present invention (hereinafter, simply referred to as “the present embodiment”) will be described in detail. The following embodiments are examples for explaining the present invention, and are not intended to limit the present invention to the following contents. The present invention can be appropriately modified and carried out within the scope of the gist thereof.

[Gas barrier shrink film]
The gas barrier shrink film of the present embodiment includes at least four layers of a base material layer (A), an adhesive layer (D), a gas barrier layer (B), and a heat seal layer (C), and the adhesive layer (D) is , Contains thermoplastic resin and has a sea-island structure. The gas barrier shrink film preferably includes one base layer (A), one gas barrier layer (B), and one heat seal layer (C), and preferably includes one or more adhesive layers (D). The adhesive layer may be only an adhesive layer that satisfies the requirements of the adhesive layer (D) described later, or may include another adhesive layer.

As for the layer structure of the gas barrier shrink film, for example, the base material layer (A) and the heat seal layer (C) are the outermost layers (surface layers), and the adhesive layer (D) and the gas barrier layer (B) are inside. A layered structure having the above can be mentioned, and more specifically, the following examples can be given. According to these layered structures, the effect of the present invention is more remarkable.
-Base material layer / gas barrier layer / adhesive layer / heat seal layer-base material layer / adhesive layer / gas barrier layer / heat seal layer-base material layer / adhesive layer / gas barrier layer / adhesive layer / heat seal layer

Hereinafter, preferred embodiments of the layers of each layer constituting the gas barrier shrink film will be described in detail.

(Base material layer (A))
The base material layer (A) is a layer that imparts heat resistance to the gas barrier shrink film, and is preferably located at the outermost layer of the gas barrier shrink film. Further, the base material layer (A) can also serve as a stretch support layer during the production of the gas barrier shrink film.

From the viewpoint of imparting heat resistance, the base material layer (A) preferably contains a thermoplastic resin having a melting point of 130 ° C. or higher.
Examples of the thermoplastic resin having a melting point of 130 ° C. or higher include polymers such as polymethylene terephthalate, polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and polylactic acid; and fats such as nylon 6, nylon 12, and nylon 66. Group polyamide polymer; aliphatic polyamide copolymer such as nylon 6/66, nylon 6/12; aromatic polyamide polymer such as MXD6 (polymethoxylen adipamide); polymethylpentene; polypropylene resin; etc. Preferably, an aliphatic polyamide polymer, an aliphatic polyamide copolymer, and a polypropylene-based resin are more preferable, and a polypropylene-based resin is further preferable. One of these may be used alone, or a plurality of them may be used in combination.
The melting point of the thermoplastic resin is preferably 130 ° C. or higher and 230 ° C. or lower, more preferably 130 ° C. or higher and 160 ° C. or lower, from the viewpoint of imparting heat shrinkage.
The mass ratio of the thermoplastic resin having a melting point of 130 ° C. or higher in the base material layer (A) is preferably 50% by mass or more, more preferably 50% by mass with respect to 100% by mass of the base material layer (A). It is 60% by mass or more, more preferably 70% by mass or more. Above all, it is preferable that the base material layer (A) contains a polypropylene resin having a melting point of 130 ° C. or higher (preferably 130 ° C. or higher and 230 ° C. or lower) in an amount of 50% by mass or more, more preferably 60% by mass or more, still more preferable. Is 70% by mass or more.

As the polypropylene-based resin, a propylene homopolymer and a propylene-based copolymer can be preferably used. For example, polypropylene, a propylene-α-olefin copolymer, or a ternary copolymer of propylene, ethylene and α-olefin can be used. Etc. can be preferably used.
The propylene homopolymer is a polymer obtained by polymerizing only propylene.
As the propylene-based copolymer, a copolymer of propylene and at least one selected from ethylene and an α-olefin having 4 to 20 carbon atoms can be preferably used. More preferably, it is a copolymer of propylene and at least one selected from ethylene and an α-olefin having 4 to 8 carbon atoms, and a copolymer of propylene and ethylene is even more preferable.

Examples of the α-olefin include 1-butene, 1-pentene, 1-hexene, 1-octene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-decene, 1-dodecene, 1-. Examples thereof include tetradecene, 1-hexadecene, 1-octadecene, 1-eicosene and the like. These can be used alone or in combination of two or more.

As the propylene-α-olefin copolymer, a copolymer of propylene and at least one comonomer selected from ethylene comonomer, butenko monomer, hexenkomonomer and octenecomonomer is generally easily available and is preferably used. can.

The polypropylene-based resin may be polymerized using a known catalyst such as a single-site catalyst or a multi-site catalyst, and is polymerized using a single-site catalyst from the viewpoint of further excellent transparency. It is preferable that it is a thing.

The polypropylene-based resin may be a resin polymerized with a catalyst such as a Ziegler-Natta catalyst, or a resin polymerized with a metallocene-based catalyst or the like. That is, as the polypropylene-based resin, for example, syndiotactic polypropylene, isotactic polypropylene and the like can also be used.

As the polypropylene-based resin, a polypropylene-based resin having a crystalline / amorphous structure (morphology) controlled on the nano-order can also be used.
The polypropylene-based resin can be used alone or in combination, and when polypropylene and a propylene-α-olefin copolymer are mixed, the crystallinity of the base material layer tends to decrease and the heat shrinkage tends to improve, which is preferable. ..

The base material layer (A) is at least one selected from the group consisting of the polypropylene-based resin, the aliphatic polyamide polymer, and the aliphatic polyamide copolymer from the viewpoint of further excellent heat resistance and strength. It is preferably contained, and more preferably composed of only one selected from the group consisting of the polypropylene-based resin, the aliphatic polyamide polymer, and the aliphatic polyamide copolymer.
The base material layer (A) may be a layer composed of only a propylene homopolymer and a propylene-based copolymer from the viewpoint of further excellent heat resistance, and propylene alone is used with respect to 100% by mass of the base material layer. The polymer may contain 30% by mass or more and less than 50% by mass, and the propylene-based copolymer may contain more than 50% by mass and 70% by mass or less.

The base material layer (A) may contain components other than the above-mentioned thermoplastic resin. For example, any addition of thermoplastic resin, various surfactants, anti-blocking agents, antistatic agents, lubricants, plasticizers, antioxidants, ultraviolet absorbers, colorants, inorganic fillers, etc., as long as the characteristics are not impaired. It may contain an agent.

In order to impart anti-fog property to the gas barrier shrink film of the present embodiment, a glycerin-based fatty acid ester can be added to the base material layer (A) as a surfactant. When a glycerin-based fatty acid ester is added, the content thereof is preferably 0.1% by mass or more and 5.0% by mass or less based on the base material layer.

Examples of the glycerin-based fatty acid ester include monofatty acid ester of glycerin, difatty acid ester, trifatty acid ester, polyfatty acid ester, and monoglycerin ester and diglycerin ester of saturated or unsaturated fatty acid having 8 to 18 carbon atoms. Examples thereof include triglycerin ester and tetraglycerin ester. Among them, those containing diglycerin oleate, diglycerin laurate, glycerin stearate, glycerin monooleate, or a mixture thereof as main components are preferable because they do not easily impair the slipperiness and optical properties of the film. Further, by adding an ethylene oxide adduct to reduce the surface tension of the water droplet, good anti-fog property can be imparted. Examples of the ethylene oxide adduct include polyoxyethylene alkyl ether and the like.

(Gas barrier layer (B))
The gas barrier layer (B) is a layer containing an ethylene-vinyl alcohol copolymer saponified product (EVOH), and plays a role of improving the gas barrier property of the gas barrier property shrink film.

The melting peak temperature (hereinafter referred to as melting point) of the ethylene-vinyl alcohol copolymer saken product is preferably 180 ° C. or lower, more preferably 140 to 170 ° C., and even more preferably 150 to 160 ° C. When the melting point is 180 ° C. or lower (preferably 160 ° C. or lower), relaxation of molecular orientation is promoted during the heat shrinkage step during packaging, so that good heat shrinkage suitable for shrinkage applications can be exhibited.
In the present specification, the melting point is the temperature at the apex of the peak of the endothermic reaction appearing in the melting curve obtained by differential scanning calorimetry (DSC). When there are a plurality of melting peaks, the melting peak temperature on the hottest side may be within the above numerical range (that is, in the present specification, the melting peak temperature on the hottest side is regarded as the melting point).

The above ethylene-vinyl alcohol copolymer saken has higher crystallinity and melting point as the content of structural units derived from ethylene (which may be referred to as ethylene content in the present specification) increases, so that the stretchability becomes higher. Generally, the melting point is 183 ° C. when the ethylene content is 32 mol%, the melting point is 173 ° C. when the ethylene content is 38 mol%, and the melting point is 163 ° C. when the ethylene content is 44 mol%. The suitable ethylene content is 30 mol% or more and 40 mol% or less, more preferably 31 mol% or more and 39 mol% or less, and further preferably 32 mol% or more and 38 mol% or less. When the ethylene content is in the above range, a film having excellent stretchability and gas barrier property can be obtained.

In general, the gas barrier performance tends to be better as the interaction between molecular chains is larger, and it is known that the ethylene-vinyl alcohol copolymer saken product has a larger interaction between molecules and a higher gas barrier performance. .. On the other hand, since the interaction between the molecular chains is large, the heat shrinkage stress is large, and when used as a shrink (heat shrinkable) film, the container of the package is likely to be deformed.

By controlling the crystal structure of the ethylene-vinyl alcohol copolymer saken product, it is possible to achieve both a melting point of 180 ° C. or lower (preferably 160 ° C. or lower) and an ethylene content of 40 mol% or less. Furthermore, by using an ethylene-vinyl alcohol copolymer saponified product in which the supercooling temperature difference, which is the difference between the melting point and the temperature-decreasing crystallization temperature, is larger than that of the general ethylene-vinyl alcohol copolymer saponified product, the lamella can be used. In the case of a gas barrier layer containing such an ethylene-vinyl alcohol copolymer saponified product, the thickness is small and the crystals are easily homogenized, stress concentration is reduced, and container deformation during gas pack packaging can be suppressed. The supercooling temperature difference is preferably 25 ° C. or higher, more preferably 27 ° C. or higher, and even more preferably 29 ° C. or higher.

The reason why the above effect is achieved is not always clear, but it is considered as follows. That is, the heat shrinkage property of the gas barrier shrink film is expressed in an attempt to relax the amorphous part stretched by the molecular orientation of the constituent resin and return to the non-oriented state, and the crystalline part is expressed to the vicinity of the melting temperature. It plays a role in stopping the contraction of. In general, ethylene-vinyl alcohol copolymer kendies tend to control the heat shrinkage stress of the entire laminated film because the interaction between molecules is strong and the heat shrinkage stress is large, whereas the crystal structure is controlled. Therefore, it is considered that it is possible to provide a gas barrier shrink film having excellent barrier property while suppressing stress concentration due to relaxation of the orientation of the amorphous portion and the crystalline portion.

(Heat seal layer (C))
The heat-sealing layer (C) is a layer that imparts heat-sealing properties to the gas-barrier shrink film, and is preferably located at the outermost layer of the gas-barrier shrink film. In addition, the heat seal layer can also serve as a stretch support layer during the production of the gas barrier shrink film.

The heat-sealed layer (C) preferably contains a polyethylene-based resin containing a structural unit derived from ethylene, and more preferably composed of only an ethylene-based resin. Examples of the polyethylene-based resin include ethylene homopolymers and ethylene-α-olefin copolymers.
Examples of the polyethylene-based resin include high-density polyethylene, medium-density polyethylene, low-density polyethylene (LDPE) (preferably linear low-density polyethylene (LLDPE)), and ultra-low-density polyethylene. Examples of the ultra-low density polyethylene include linear ultra-low density polyethylene (referred to as “VLDPE” and “ULDPE”).

Here, the polyethylene-based resin can be classified by density based on JIS K6922. Specifically, the density is referred to as high density polyethylene those 942kg / ^{m 3} or more, density called medium density polyethylenes of less than 930 kg / ^{m 3} or more 942kg / ^{m 3,} density of 910 kg / ^{m 3} or more 930 kg Those with a density of less than / m ³ are called low-density polyethylene, and those with a density of ^{less than 910 kg / m 3} are called ultra-low density polyethylene.

The ethylene-α-olefin copolymer means a copolymer of ethylene and α-olefin. Examples of the α-olefin include propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-decene and 1-dodecene. Examples thereof include 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eikosen and the like.
As the ethylene-α-olefin copolymer, a copolymer of ethylene and at least one kind of comonomer selected from a propylene comonomer, a butencomonomer, a hexenkomonomer and an octenecomonomer is generally easily available and is suitable. Can be used.

The ethylene-α-olefin copolymer is a soft copolymer in which the ratio of α-olefin in all the monomers constituting the copolymer (based on the charged monomer) is 5% by mass or more and 30% by mass or less. Is preferable.

The polyethylene-based resin may be polymerized using a known catalyst such as a single-site catalyst or a multi-site catalyst, and from the viewpoint of further excellent transparency, the polyethylene-based resin may be polymerized using a single-site catalyst. Is preferable.

More polyethylene resin, from the viewpoint of heat sealability at low temperatures becomes better, the density is 860 kg / ^{m 3} or more 925 kg / ^{m 3} or less preferably, if it is 870 kg / ^{m 3} or more 920 kg / ^{m 3} or less It is preferable that it is 880 kg / m ³ or more and 915 kg / m ³ or less. The heat-sealing property at low temperatures as the density of the polyethylene resin is low tends to increase, if the density is 925 kg / m ³ or less, there is a tendency that heat-sealing property is improved.

As the polyethylene-based resin, a polyethylene-based resin having a crystalline / amorphous structure (morphology) controlled in the nano-order can also be used.

The polyethylene resin can be used alone or in combination, and when the ethylene homopolymer and the ethylene-α-olefin copolymer are mixed, the crystallinity of the heat seal layer is lowered, and the heat shrinkage and heat at low temperature are reduced. It is preferable because the sealing property tends to be improved.

The heat seal layer may contain a component other than the polyethylene resin. For example, any addition of thermoplastic resin, various surfactants, anti-blocking agents, antistatic agents, lubricants, plasticizers, antioxidants, ultraviolet absorbers, colorants, inorganic fillers, etc., as long as the characteristics are not impaired. It may contain an agent.

In order to impart anti-fog properties to the gas barrier shrink film of the present embodiment, the above-mentioned glycerin-based fatty acid ester can be added to the heat-sealed layer as a surfactant.

(Adhesive layer (D))
The gas barrier shrink film of the present embodiment contains a thermoplastic resin and has at least one adhesive layer (D) having a sea-island structure. For example, when there are a plurality of adhesive layers, one layer may be the adhesive layer (D) and the other layer may be another adhesive layer. Above all, from the viewpoint of achieving both excellent mechanical properties and flexibility, it is preferable that one adhesive layer is the adhesive layer (D).
The gas barrier shrink film of the present embodiment has a base material layer (A) as one surface layer and an internal layer (for example, a gas barrier layer (B)) from the viewpoint of achieving both excellent mechanical properties and stretchability. The adhesive layer of is preferably the adhesive layer (D).

The sea-island structure is preferably formed of two or more types of thermoplastic resins. For example, it can be configured to have a sea-island structure consisting of a continuous layer composed of a portion in which the thermoplastic resin (X) and the thermoplastic resin (Y) are compatible with each other and a dispersed layer composed of the thermoplastic resin (X). However, it is not limited to such a configuration.

Here, the sea-island structure refers to a structure in which one of a plurality of components is dispersed in an island-like manner in a continuous phase, and the island portion, which is usually a dispersed phase, is discontinuous. The islands are preferably evenly distributed throughout the adhesive layer (D). It is preferable that there are two or more islands.
It is preferably 15 to 45% of the area ratio of the island. The area ratio of the island can be measured by the method described in Examples described later.

In the two types of thermoplastic resins (X) and (Y) forming the sea-island structure, the density dx of the thermoplastic resin (X) and the density dy of the thermoplastic resin (Y) are dx <dy, and dy-. It is preferable that dx> 30 kg / m ^3. With this combination, a sea-island structure is easily formed by a continuous layer composed of a portion in which the thermoplastic resin (X) and the thermoplastic resin (Y) are compatible with each other and a dispersed layer composed of the thermoplastic resin (X). ..
^{The density difference dy-dx is more preferably 40 kg / m 3} or more, more preferably 40 kg / m 3 or more, from the viewpoint that a continuous phase in which the thermoplastic resin is dissolved is easily formed in the entire adhesive layer and the mechanical strength and flexibility are further excellent. Is 45 kg / m ³ or more. Further, it is preferably 60 kg / m ^{3 or less.}
For example, when the adhesive layer contains three or more kinds of thermoplastic resins, the thermoplastic resin having the highest density may be the thermoplastic resin (Y), and the thermoplastic resin having the lowest density may be the thermoplastic resin (X).

The mass ratio of the thermoplastic resin (X) to the thermoplastic resin (Y) is preferably 10:90 to 90:10, more preferably 20:80 to 80:20, and even more preferably 30:70 to 70. : 30. Within this range, the sea-island structure is easily formed, and the mechanical strength and flexibility are further improved.

Examples of the thermoplastic resin (X) include olefin resins having a polar group, and modified LLDPE is preferable. Since the modified LLDPE is difficult to crystallize, it easily forms an island structure having a sea-island structure. Examples of the modified LLDPE include a polyethylene resin such as an ethylene homopolymer, an ethylene-propylene copolymer, and an ethylene-α-olefin copolymer, and an unsaturated carboxylic acid such as maleic acid and fumaric acid or an acid anhydride thereof. A modified polymer graft-copolymerized with the above is preferable, and a modified polymer graft-copolymerized with maleic anhydride is more preferable. This makes it possible to sufficiently develop the adhesiveness. Further, by using a thermoplastic resin having a polar group, the adhesive layer has appropriate flexibility and can be easily drawn.

The modified LLDPE preferably has a density of 910 kg / m ³ or less.

The thermoplastic resin (Y) is preferably HDPE.
HDPE is high-density polyethylene, and the density is preferably 942 kg / m ³ or more.

When the thermoplastic resin (X) is a modified LLDPE and the thermoplastic resin (Y) is HDPE, the modified LLDPE is difficult to crystallize and the HDPE is easy to crystallize, so that they are not completely and uniformly compatible with each other. A part of the modified LLDPE and HDPE take a partially compatible state to form a eutectic structure. This eutectic structure portion becomes the sea component of the sea-island structure, and the remaining uncrystallized modified LLDPE becomes the island component. With this structure, both mechanical strength and flexibility can be achieved. Usually, when two or more kinds of thermoplastic resins having different densities are mixed in the adhesive layer, the adhesiveness is lowered. However, the present inventors have provided a sea-island structure in the adhesive layer (particularly, using two or more types of thermoplastic resins that are difficult to be compatible with each other due to the large density difference, and partially incompatible with the sea structure. It was found that the mechanical properties and flexibility are improved by providing a sea-island structure that is partly made into an island structure without being compatible with each other).
Further, although the polyamide-based resin has excellent mechanical strength, it easily absorbs moisture, which may reduce the gas barrier property. By providing a sea-island structure in the adhesive layer using a thermoplastic resin other than the polyamide resin (for example, a combination of an olefin resin having a polar group such as the above-mentioned modified LLDPE and high-density polyethylene), the adhesive layer is under high humidity. However, the gas barrier property can be maintained for a long period of time.
This crystal structure is particularly suitable for an adhesive layer of a shrink film that requires barrier properties.

Generally, when HDPE is used as a component of a film, it is difficult to use it as a gas barrier shrink film because the film becomes hard and difficult to stretch due to its crystallinity. However, it is presumed that it was possible to stretch due to the influence of some island components of the modified LLDPE, even though HDPE was used to form the sea-island structure.
Further, it is considered that sufficient mechanical strength of the entire film can be obtained due to the high mechanical strength of HDPE.

As described above, by containing the thermoplastic resin and having a sea-island structure, both strength and elongation can be achieved.

The gas barrier shrink film of the present embodiment may have an adhesive layer as a single layer, or may have two or more adhesive layers. For example, a first adhesive layer provided between the heat seal layer (C) and the gas barrier layer (B) and a second adhesive layer provided between the gas barrier layer (B) and the base material layer (A). And may be included.
The first adhesive layer and the second adhesive layer may be made of the same resin or may be different resins. Further, the thickness may be the same or different.
Further, in the present embodiment, at least one adhesive layer may contain a thermoplastic resin and have a sea-island structure, and the first adhesive layer may contain a thermoplastic resin and have a sea-island structure. However, the second adhesive layer may contain a thermoplastic resin and have a sea-island structure.

The adhesive layer other than the adhesive layer (D) is not particularly limited and may be a known adhesive layer.

Hereinafter, the characteristics of the gas barrier shrink film of the present embodiment will be described.
(Maximum heat shrinkage stress)
In order to suppress stress concentration, the gas barrier shrink film of the present embodiment preferably has a maximum heat shrinkage stress of 3.0 MPa or less, more preferably 2.5 MPa or less, at a measurement temperature of 100 ° C. for up to 3 minutes. ..
In packaging such as pillow shrink wrapping, in which the object to be packaged is tightly wrapped by the shrink method, meat, seafood, etc. are often packed in plastic foam trays or molded trays, and when the film shrinks due to heat. Since the tray is easily deformed by the heat shrinkage stress of the above, a package having a poor appearance is likely to occur.
When the gas barrier shrink film of the present embodiment has a maximum heat shrinkage stress in the length direction at 100 ° C. of 3.0 MPa or less, tray deformation is further suppressed when food or the like is packaged using an automatic packaging machine. You can get a tight and beautiful package.
Further, since the food packaging tray used in the automatic packaging machine is generally a rectangular tray whose length direction is longer than the width direction in the machine direction, the width direction is particularly resistant to deformation due to heat shrinkage stress. Weak and easy to deform the container. Therefore, it is preferable that the maximum heat shrinkage stress in the width direction of the film is 2.5 MPa or less because it is easy to suppress the deformation of the container, and the maximum heat shrinkage stress in both the length direction and the width direction is 3.0 MPa or less. However, it is more preferable because it can suppress the deformation of the container of the square tray.
In the case of packaging with an automatic packaging machine, the passage time of the package through the shrink tunnel is about several seconds, so the film surface temperature tends to be about 10 ° C to 20 ° C lower than the hot air set temperature of the tunnel. Therefore, in the gas barrier shrink film of the present embodiment, the measurement of the heat shrinkage stress, which is an index of container deformation, is performed by immersing it in an oil bath at 100 ° C. with respect to the assumption that the hot air set temperature is 120 ° C. Maximum thermal shrinkage stress is measured according to ASTM-D2838.

(Heat shrinkage rate)
The gas barrier shrink film of the present embodiment preferably has a heat shrinkage rate at 100 ° C. of 30% or more in the length direction and 25% or more in the width direction, which is measured according to the measurement method ASTM-D2732. It is more preferable that it is 30% or more in both the length direction and the width direction. In order to obtain a tight-finished package in the pillow shrink package and the top-seal package in which the gas barrier shrink film of the present embodiment is used, if the heat shrinkage rate is 25% or more, the package has a tight and clean finish. Can be obtained.

In order to obtain a heat shrinkage in the above range, the melting point of the resin constituting the gas barrier shrink film is preferably 165 ° C. or lower, more preferably 160 ° C. or lower, and further preferably less than 160 ° C. preferable. When the melting point of the resin constituting the gas barrier shrink film is 165 ° C. or lower, relaxation of molecular orientation is promoted, so that good heat shrinkage suitable for shrinkage applications can be exhibited.

Further, the gas barrier shrink film preferably has a heat shrinkage rate of 10% or less in the length direction at 60 ° C., and more preferably 10% or less in either the length direction or the width direction. Such a gas barrier shrink film is preferable because it can suppress a dimensional change of the film during transportation and storage.

Gas barrier property For the gas barrier property of the shrink film against oxygen, the oxygen permeability is measured with the oxygen condition of 65% RH and the measurement temperature of 23 ° C. It is possible to suppress the permeation of oxygen, in view of being suitable for gas pack packaging, the oxygen permeability is preferably not more than ^{17.0cm 3 · 20μm / m 2 ·} 24h · atm, more preferably 16. 0cm is less than or equal to ^{3 · 20μm / m 2 · 24h} · atm. A gas barrier shrink film having such a gas barrier property can sufficiently suppress the permeation of oxygen.

The tensile breaking stress in the MD direction of the gas barrier shrink film of the present embodiment is preferably 85 MPa or more, more preferably 90 MPa or more from the viewpoint of mechanical properties. The tensile breaking stress in the TD direction of the gas barrier shrink film of the present embodiment is preferably 65 MPa or more, more preferably 70 to MPa or more, from the viewpoint of mechanical properties.
The tensile breaking stress can be measured by the method described in Examples described later.

The tensile elongation at break in the MD direction of the gas barrier shrink film of the present embodiment is preferably 145% or more, more preferably 150% or more, from the viewpoint of resistance to blurring and flexibility. The tensile elongation at break in the TD direction of the gas barrier shrink film of the present embodiment is preferably 160% or more, more preferably 180% or more, from the viewpoint of resistance to blurring and flexibility.
The tensile elongation at break can be measured by the method described in Examples described later.

The heat shrinkage rate of the gas barrier shrink film of the present embodiment at 100 ° C. in the MD direction is preferably 30% or more, more preferably 30 to 45%, still more preferably, in order to improve the finish of the package. It is 35 to 45%. The heat shrinkage rate of the gas barrier shrink film of the present embodiment at 100 ° C. in the TD direction is preferably 25% or more, more preferably 25 to 40%, still more preferably 25%, in order to improve the finish of the package. It is 30-40%.
The heat shrinkage rate can be measured by the method described in Examples described later.

The maximum heat shrinkage stress of the gas barrier shrink film of the present embodiment at 100 ° C. in the MD direction is preferably 3.0 MPa or less, more preferably 1.0 to 2.5 MPa in order to suppress tray deformation of the package. Is. The maximum heat shrinkage stress of the gas barrier shrink film of the present embodiment at 100 ° C. in the TD direction is preferably 2.5 MPa or less, more preferably 1.0 to 2.0 MPa, in order to suppress tray deformation of the package. Is.
The thermal shrinkage stress can be measured by the method described in Examples described later.

Nitrogen gas permeability at 23 ° C. 65% RH of the gas barrier shrink film of this embodiment, from the viewpoint of gas barrier properties, preferably 1.6cm ³ · 20μm ^/ m is 2 · 24h · atm or less, more preferably 1.5cm is ^{3 · 20μm / m 2 · 24h} · atm or less. Nitrogen gas permeability at 5 ° C. 90% RH of the gas barrier shrink film of this embodiment, from the viewpoint of gas barrier properties, preferably 0.2cm ³ · 20μm ^/ m is 2 · 24h · atm or less, more preferably 0.1cm is ^{3 · 20μm / m 2 · 24h} · atm or less.
The nitrogen gas permeability can be measured by the method described in Examples described later.

Carbon dioxide permeability at 23 ° C. 65% RH of the gas barrier shrink film of this embodiment, from the viewpoint of gas barrier properties, preferably 52.0cm ³ · 20μm ^/ m is 2 · 24h · atm or less, more preferably 51.0cm is less than or equal to ^{3 · 20μm / m 2 · 24h} · atm. Carbon dioxide permeability at 5 ° C. 60% RH of the gas barrier shrink film of this embodiment, from the viewpoint of gas barrier properties, preferably 10.0cm ³ · 20μm ^/ m is 2 · 24h · atm or less, more preferably 9.0cm is less than or equal to ^{3 · 20μm / m 2 · 24h} · atm.
The carbon dioxide gas permeability can be measured by the method described in Examples described later.

Oxygen gas transmission rate at 23 ° C. 65% RH of the gas barrier shrink film of this embodiment, from the viewpoint of gas barrier properties, preferably 17.0cm ³ · 20μm ^/ m is 2 · 24h · atm or less, more preferably 16.0cm is less than or equal to ^{3 · 20μm / m 2 · 24h} · atm. Oxygen gas transmission rate at 5 ° C. 90% RH of the gas barrier shrink film of this embodiment, from the viewpoint of gas barrier properties, is preferably ^{7.5cm 3 · 20μm / m 2 ·} 24h · atm or less, more preferably 6.5cm is less than or equal to ^{3 · 20μm / m 2 · 24h} · atm.
The oxygen gas permeability can be measured by the method described in Examples described later.

The gas barrier shrink film of the present embodiment can be used for food packaging, and can be suitably used for food packaging particularly when stored at a low temperature (for example, more than 0 ° C. and 10 ° C. or lower).

[Manufacturing method of heat-shrinkable film]
The method for producing the heat-shrinkable laminated film is not particularly limited, and examples thereof include the following methods.
The method for producing a gas barrier shrink film according to the present embodiment is a step of laminating a laminate having at least four resin layers (hereinafter, sometimes referred to as "unstretched raw fabric") by a coextrusion method and heating and stretching. It is preferable to prepare. The coextrusion method will be described below.

In the coextrusion method, unstretched raw fabric can be obtained by melt-extruding each from a single extruder, laminating in a multilayer die, melt-coextruding, and quenching. Here, the method of melt coextrusion is not particularly limited, and examples thereof include a method using a multi-layer T die and a multi-layer circular die (annular die). Above all, a method using a multi-layered circular die is preferable. The use of a multi-layered circular die is advantageous in terms of space required for equipment and investment amount, is suitable for high-mix low-volume production, and makes it easier to obtain a desired heat shrinkage rate.

As the refrigerant used for quenching, water having a temperature of 60 ° C. or lower is usually preferably used. The refrigerant can be brought into direct contact with the molten resin or indirectly used as an internal refrigerant for a metal roll. When used as an internal refrigerant, oil or other known substances can be used in addition to water, and in some cases, it can be used in combination with blowing cold air.

In the stretching step, the obtained unstretched raw fabric is heated to, for example, a softening temperature or higher of the resin constituting the unstretched raw fabric, for example, 1.5 in the MD (Machine Direction: longitudinal direction (length direction)). It is stretched more than twice, and more than three times in the TD (Transverse Direction: lateral direction (width direction)). According to such a stretching step, a gas barrier shrink film having the above-mentioned predetermined heat shrinkage rate can be easily obtained.

The stretching ratio is appropriately selected according to the purpose, and if necessary, heat treatment (heat relaxation treatment) can be performed after stretching. According to the heat relaxation treatment, the molecular orientation of the gas barrier shrink film is relaxed, so that the dimensional change during transportation and / or storage is further suppressed.

The stretching step can also be performed by a direct inflation method in which air or nitrogen is blown into the tube immediately after melt extrusion to perform stretching. Also by this method, a gas barrier shrink film having a predetermined heat shrinkage rate can be easily obtained. However, in order to more reliably develop an appropriate heat shrinkage rate, a biaxial stretching method is preferable, and a tubular method (double bubble) in which the unstretched raw fabric obtained by the above-mentioned circular die is heated and biaxially stretched. Also called the method) is more preferable. That is, the gas barrier shrink film of the present embodiment is preferably a biaxially stretched multilayer film produced by a biaxially stretched tubular method.

The above-mentioned production method may include a cross-linking step of cross-linking the resin before or after stretching.

When the cross-linking treatment is performed, it is preferable to carry out the cross-linking treatment by irradiation with energy rays before heating and stretching the resin. As a result, the melt tension of the laminated body in heat stretching is increased, and the stretching can be further stabilized. The resin may be crosslinked by irradiating the stretched laminate with energy rays. Examples of the energy beam used include ionizing radiation such as ultraviolet rays, electron beams, X-rays, and γ-rays. Of these, electron beams are preferable.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to these Examples.

[evaluation]
The melting point of the constituent resin, and the tensile breaking stress, tensile breaking elongation, heat shrinkage rate, heat shrinkage stress, nitrogen gas permeability, carbon dioxide gas permeability, and oxygen gas permeability of the laminated films of Examples and Comparative Examples are as follows. It was measured and evaluated by the method. In addition, the adhesive layer was observed by the following method.

(Melting point)
The melting point is measured using differential scanning calorimetry (DSC). Weigh 5 mg of resin, raise the temperature from 0 ° C to 300 ° C under the condition of a temperature rise rate of 10 ° C / min, and from 300 ° C to 0 ° C under the condition of a temperature decrease rate of 10 ° C / min to cancel the thermal history of the resin. The temperature was lowered. Then, the endothermic peak when the temperature was raised from 0 ° C. to 300 ° C. again under the condition of a temperature rising rate of 10 ° C./min was measured as the melting point.

(Tension fracture stress / tensile elongation at break)
The tensile breaking stress is measured according to ASTM-D882. Using a tensile tester, the sample is pulled at a speed of 200 mm / min, and the stress (value obtained by dividing the tensile load value by the cross-sectional area of the test piece) and the elongation (elongation) when the sample is cut (broken) are determined. The tensile elongation is calculated by the following formula.
Tensile elongation (%) = 100 × (L−L ₀ ) / L ₀
L ₀ : Sample length before test L: Sample length at break

(Heat shrinkage at 100 ° C)
A film cut into a square of 100 mm in both vertical and horizontal directions is allowed to stand in a constant temperature bath set at an atmospheric temperature of 100 ° C. for 30 minutes, and calculated by the following formula.
Heat shrinkage rate (%) = 100 × (100-W) / 100
W: Dimensions of the film after being taken out of the constant temperature bath

(Maximum heat shrinkage stress at 100 ° C)
Maximum thermal shrinkage stress is measured according to ASTM-D2838. When the film is sampled in strips of 90 mm in the length direction / or width direction (measurement length 50 mm + chuck grip 40 mm) and 10 mm in the width direction / or length direction and immersed in an oil bath at a temperature of 100 ° C. The maximum heat shrinkage stress after immersion for 3 minutes is measured.

(Nitrogen gas permeability)
Nitrogen gas permeability was measured according to JIS K7126-1 (differential pressure method).
The measuring device is a differential pressure type gas / vapor permeability measuring device [GTR-30XAD2, G2700T / F], [GTR-30XAD, G6800T / F (S)] (manufactured by GTR Tech Co., Ltd., Yanaco Technical Science Co., Ltd.). It was used. A gas chromatograph [thermal conductivity detector (TCD)] was used as the detector. The test conditions are such that the partial pressure is 74.6 cmHg for the gas and 1.4 cmHg for the gas at a temperature of 23 ° C. and a humidity of 65% RH, and the partial pressure is 75.4 cmHg for the gas at a temperature of 5 ° C. and a humidity of 90% RH. The water vapor was set to 0.6 cmHg. The permeation direction was permeated from the food contact surface side. Transmission area is set to 15.2 × ¹⁰ -4 ^{m 2} (transmitting portion diameter φ4.4 × ^{10 -2} m), the number of tests was set to n = 1.
<Evaluation criteria for nitrogen gas permeability under conditions of 23 ° C and 65% RH>
〇 ^{(good): 1.5cm 3 · 20μm / m} 2 · 24h · atm or less △ (slightly ^{poor): 1.5cm 3 · 20μm / m} 2 · 24h · atm ultra ^{1.6cm 3 · 20μm / m 2 ·} 24h · atm × (poor) ^{hereinafter: 1.6cm 3 · 20μm / m 2} · 24h · atm than <5 ° C. evaluation criteria for the nitrogen gas permeability under conditions of 90% RH>
〇 ^{(good): 0.1cm 3 · 20μm / m} 2 · 24h · atm or less △ (slightly ^{poor): 0.1cm 3 · 20μm / m} 2 · 24h · atm ultra ^{0.2cm 3 · 20μm / m 2 ·} 24h · atm × (poor) ^{hereinafter: 0.2cm 3 · 20μm / m 2} · 24h · atm than

(Carbon dioxide permeability)
The carbon dioxide gas permeability was measured according to JIS K7126-1 (differential pressure method).
The measuring device is a differential pressure type gas / vapor permeability measuring device [GTR-30XAD2, G2700T / F], [GTR-30XAD, G6800T / F (S)] (manufactured by GTR Tech Co., Ltd., Yanaco Technical Science Co., Ltd.). It was used. A gas chromatograph [thermal conductivity detector (TCD)] was used as the detector. The test conditions are such that the partial pressure is 74.6 cmHg for a gas and 1.4 cmHg for a gas at a temperature of 23 ° C and a humidity of 65% RH, and the partial pressure is 75.6 cmHg for a gas at a temperature of 5 ° C and a humidity of 60% RH. The water vapor was adjusted to 0.4 cmHg. The permeation direction was permeated from the food contact surface side. Transmission area is set to 15.2 × ¹⁰ -4 ^{m 2} (transmitting portion diameter φ4.4 × ^{10 -2} m), the number of tests was set to n = 1.
<Evaluation criteria for carbon dioxide permeability under conditions of 23 ° C and 65% RH>
〇 ^{(good): 51.0cm 3 · 20μm / m} 2 · 24h · atm or less △ (slightly ^{poor): 51.0cm 3 · 20μm / m} 2 · 24h · atm ultra ^{52.0cm 3 · 20μm / m 2 ·} 24h · atm × (poor) ^{hereinafter: 52.0cm 3 · 20μm / m 2} · 24h · atm than <5 ° C. evaluation criteria for carbon dioxide permeability under conditions of 60% RH>
〇 ^{(good): 9.0cm 3 · 20μm / m} 2 · 24h · atm or less △ (slightly ^{poor): 9.0cm 3 · 20μm / m} 2 · 24h · atm ultra ^{10.0cm 3 · 20μm / m 2 ·} 24h · atm or less × ^{(poor): 10.0cm 3 · 20μm / m} 2 · 24h · atm than

(Oxygen gas permeability) The oxygen gas permeability was measured according to JIS K7126-1 (differential pressure method).
The measuring device is a differential pressure type gas / vapor permeability measuring device [GTR-30XAD2, G2700T / F], [GTR-30XAD, G6800T / F (S)] (manufactured by GTR Tech Co., Ltd., Yanaco Technical Science Co., Ltd.). It was used. A gas chromatograph [thermal conductivity detector (TCD)] was used as the detector. The test conditions are such that the partial pressure is 74.6 cmHg for the gas and 1.4 cmHg for the gas at a temperature of 23 ° C. and a humidity of 65% RH, and the partial pressure is 75.4 cmHg for the gas at a temperature of 5 ° C. and a humidity of 90% RH. The water vapor was set to 0.6 cmHg. The permeation direction was permeated from the food contact surface side. Transmission area is set to 15.2 × ¹⁰ -4 ^{m 2} (transmitting portion diameter φ4.4 × ^{10 -2} m), the number of tests was set to n = 1.
<Evaluation criteria for oxygen gas permeability under conditions of 23 ° C and 65% RH>
〇 ^{(good): 16.0cm 3 · 20μm / m} 2 · 24h · atm or less △ (slightly ^{poor): 16.0cm 3 · 20μm / m} 2 · 24h · atm ultra ^{17.0cm 3 · 20μm / m 2 ·} 24h · atm or less × ^{(poor): 17.0cm 3 · 20μm / m} 2 · 24h · atm than <5 ° C. evaluation criteria of the oxygen gas permeability under conditions of 90% RH>
〇 ^{(good): 6.5cm 3 · 20μm / m} 2 · 24h · atm or less △ (slightly ^{poor): 6.5cm 3 · 20μm / m} 2 · 24h · atm ultra ^{7.5cm 3 · 20μm / m 2 ·} 24h · atm × (poor) ^{hereinafter: 7.5cm 3 · 20μm / m 2} · 24h · atm than

(Cross section observation)
The cross sections of the heat-shrinkable laminated films obtained in Examples and Comparative Examples were observed by the following methods.
Measuring device: JEM-2100F (FE-TEM manufactured by JEOL Ltd.)
Measurement conditions: Acceleration voltage 200kV
Pretreatment conditions: A sample was embedded using a room temperature curable epoxy resin to prepare a cutting block. After RuO4 staining was applied to the cutting block, an ultrathin section having a thickness of 100 nm was prepared by Wet cutting using an ultramicrotome (using a diamond knife).
Observation conditions Ultra-thin sections were observed by TEM, and magnified photographs were taken (photographing magnification 20,000 to 40,000 times).
By observing two cross-sectional points of the adhesive layer (D), a phase-separated structure was confirmed, and a plurality of island structures spread uniformly throughout the continuous phase, and the sum of the areas of each island structure with respect to the total area. When the ratio (area ratio of the island) is 15 to 45%, the sea island structure is "yes", and when it is more than 0% and less than 15%, the sea island structure is "less". Similarly, two cross-sectional points of the adhesive layer (D) were observed, and the case where the phase separation structure was not confirmed and no island structure was observed was evaluated as “none” of the sea-island structure.
The area ratio of the island was calculated by the following method.
An image having a viewing angle of 1350 nm × 900 nm was equally divided vertically and horizontally at intervals of 50 nm, and the number of cells occupied by the island structure was counted from the total number of cells of 50 nm × 50 nm formed. The area ratio of the island with one cross section was calculated by dividing the number of squares occupied by the island structure by the total number of squares. Then, the average value of the area ratio of the islands having two cross sections was taken as the area ratio of the islands.

[Resin used]
The resins used in Examples and Comparative Examples are as follows.
-Ethylene-vinyl alcohol copolymer EVOH1: Ethylene-vinyl alcohol copolymer saken product (product name "Soanol AT4403B", manufactured by Mitsubishi Chemical Corporation, MFR 3.5 g / 10 minutes, ethylene content 44 mol%)
EVOH2: Ethylene-vinyl alcohol copolymer saken product (product name "G Soanol GH3804B", manufactured by Mitsubishi Chemical Corporation, MFR 4.0 g / 10 minutes, ethylene content 38 mol%)
Ethylene-α-olefin copolymer LLDPE1: Ethylene-α-olefin copolymer (product name "Umerit 0520F", manufactured by Ube Kosan Co., Ltd., density 904 kg / m ³ , MFR 2.0 g / 10 minutes, melting point 118 ° C)
LLDPE2: Ethylene-α-olefin copolymer (product name "Sumikasen E FV203", manufactured by Sumitomo Chemical Co., Ltd., density 913 kg / m ³ , MFR 2.0 g / 10 minutes, melting point 115 ° C)
LLDPE3: Ethylene-α-olefin copolymer (product name "SLH218", manufactured by Braskem, density 916 kg / m ³ , MFR 2.3 g / 10 minutes, melting point 125 ° C.)
Polypropylene PP1: propylene homopolymer (product name "SunAllomer PL500A", manufactured by SunAllomer Ltd., density 900 kg / m ³ , MFR 3.5 g / 10 minutes, melting point 160 ° C)
PP2: Ethylene-propylene copolymer (product name "SunAllomer PC540R", manufactured by SunAllomer Ltd., density 900 kg / m ³ , MFR 5.3 g / 10 minutes, melting point 132 ° C)
Polyolefin Elastomer POP1: Ethylene-1 octene copolymer (product name "Affinity PT1450G1", manufactured by Dow Chemical Japan Co., Ltd., density 902 kg / m ³ , MFR 7.5 g / 10 minutes, melting point 97 ° C)
POP2: Ethylene-propylene copolymer (product name "Versify 3200", manufactured by Dow Chemical Japan Co., Ltd., density 876 kg / m ³ , MFR 8.0 g / 10 minutes, melting point 81 ° C)
-Adhesive resin PEGL1: Modified ethylene-α-olefin copolymer (Product name "Admer NF587", manufactured by Mitsui Chemicals, Inc., density 907 kg / m ³ , MFR 2.3 g / 10 minutes, melting point 120 ° C)
PEGL2: Modified ethylene-α-olefin copolymer (product name "Admer NF307", manufactured by Mitsui Chemicals, Inc., density 922 kg / m ³ , MFR 1.3 g / 10 minutes, melting point 120 ° C.)
PEGL3: Modified ethylene-α-olefin copolymer (product name "Admer NF550", manufactured by Mitsui Chemicals, Inc., density 910 kg / m ³ , MFR 6.2 g / 10 minutes, melting point 120 ° C.)
PPGL1: Modified polypropylene polymer (product name "Admer QF580", manufactured by Mitsui Chemicals, Inc., density 896 kg / m ³ , MFR 7.7 g / 10 minutes, melting point 140 ° C.)
PPGL2: Modified polypropylene polymer (product name "Admer QF500", manufactured by Mitsui Chemicals, Inc., density 901 kg / m ³ , MFR 3.0 g / 10 minutes, melting point 165 ° C)
Polyamide NY1: Polyamide 6 (product name "UBE NYLON 1022B", manufactured by Ube Industries, Ltd., density 1140 kg / m ³ , melting point 225 ° C)
NY2: Polyamide 6/66 copolymer (product name "UBE NYLON 5034B", manufactured by Ube Industries, Ltd., density 1140 kg / m ³ , melting point 192 ° C)
NY3: Hexamethylenediamine / phthalic acid copolymerized nylon (amorphous nylon) (Product name "Sealer PA3426", manufactured by Mitsui Dow Polychemical Co., Ltd., density 1190 kg / m ³ )
High-density polyethylene HDPE1: High-density polyethylene (product name "HIZEX 5000SF", manufactured by Prime Polymer Co., Ltd., density 956 kg / m ³ , MFR 0.66 g / 10 minutes, melting point 133 ° C)
HDPE2: High-density polyethylene (product name "HIZEX 3300F", manufactured by Prime Polymer Co., Ltd., density 950 kg / m ³ , MFR 1.1 g / 10 minutes, melting point 132 ° C)
HDPE3: High-density polyethylene (product name "Suntech HD S362", manufactured by Asahi Kasei Corporation, density 952 kg / m ³ , MFR 0.8 g / 10 minutes, melting point 132 ° C)
HDPE4: High-density polyethylene (product name "Suntech HD B161", manufactured by Asahi Kasei Corporation, density 963 kg / m ³ , MFR 1.35 g / 10 minutes, melting point 134 ° C)
HDPE5: High-density polyethylene (product name "SGF4950", manufactured by Asahi Kasei Corporation, density 956 kg / m ³ , MFR 0.34 g / 10 minutes, melting point 133 ° C)
The MFR refers to a value measured in accordance with JIS K7210 or ASTM D1238. The melting point is a value measured by differential scanning calorimetry (DSC).

[Examples 1 to 11 and Comparative Examples 1 to 3]
Using the resins shown in Table 1, a 5-layer film was formed by the double bubble inflation method. Then, biaxial stretching was performed in the MD direction and the TD direction at the stretching ratios shown in Table 1 to obtain a stretched laminated film. The thickness of each layer is as shown in Table 1.
The stretching ratio in the MD direction was adjusted by the speed ratio of pinch rolls between bubbles, and the stretching ratio in the TD direction was adjusted by the volume of air enclosed in the bubbles. The MD direction referred to here is a long direction (flow direction) when the laminated film is extruded. On the other hand, the TD direction refers to the width direction (horizontal direction) when the laminated film is extruded.

In the gas barrier shrink film of Examples 1 to 12, the adhesive layer between the base material layer (A) and the gas barrier layer (B) was confirmed to have a sea-island structure, and was the adhesive layer (D), but the gas barrier layer ( No sea-island structure was confirmed in the adhesive layer between the layers of B) and the heat seal layer (C), and the adhesive layer was another adhesive layer.
Further, in the heat-shrinkable laminated film of Example 13, the adhesive layer between the gas barrier layer (B) and the heat-sealed layer (C) was confirmed to have a sea-island structure, and was the adhesive layer (D). The adhesive layer between the layer (A) and the gas barrier layer (B) had no sea-island structure and was another adhesive layer.
In Comparative Examples 1 to 4, no sea-island structure was observed in any of the adhesive layers.

Claims (8)

At least four layers of a base material layer (A), an adhesive layer (D), a gas barrier layer (B), and a heat seal layer (C) are provided.
A gas barrier shrink film characterized in that the adhesive layer (D) contains a thermoplastic resin and has a sea-island structure. The adhesive layer (D) contains two types of thermoplastic resins (X) and (Y), and the density dx of the thermoplastic resin (X) and the density dy of the thermoplastic resin (Y) are dy−. The gas barrier shrink film according to claim 1, wherein dx> 30 kg / m ^3. The gas barrier shrink film according to claim 2, wherein the thermoplastic resin (X) is a modified LLDPE. The gas barrier shrink film according to claim 2 or 3, wherein the thermoplastic resin (Y) is HDPE. The gas barrier shrink film according to any one of claims 2 to 4, wherein the mass ratio of the thermoplastic resin (X) to the thermoplastic resin (Y) is 10:90 to 90:10. The gas barrier shrink film according to any one of claims 1 to 5, wherein the base material layer (A) contains at least a thermoplastic resin having a melting point of 130 ° C. or higher. The gas barrier shrink film according to any one of claims 1 to 6, wherein the heat seal layer (C) contains at least a polyethylene resin. The gas barrier shrink film according to any one of claims 1 to 7, wherein the heat shrinkage in the length direction at 100 ° C. is 30% or more.