JP7190141B2 - Heat-shrinkable gas barrier film - Google Patents

Description

The present invention relates to a heat-shrinkable gas barrier film.

In recent years, the food industry has become more aware of the need to reduce food waste and loss due to concerns about reducing the environmental burden, and there has been a growing movement to extend the expiration date of food products. As one of means for extending the expiration date of the food, gas exchange packaging has been known for a long time.

As the form of the gas replacement packaging, food is placed in a plastic container (tray, etc.) having gas barrier properties, the inside of the container is replaced with gas, and then the container is top-sealed with a lid material having gas barrier properties. A generally known method is to wrap food with a heat-shrinkable film having gas barrier properties in a pillow packaging machine while replacing the gas. The former has a high gas replacement rate, but since gas barrier properties are required for all food packaging materials, the cost of packaging materials remains an issue. The latter makes it possible to use non-barrier containers (general-purpose trays, etc.) and enables high-speed continuous packaging. A packaging form using a packaging machine is preferably adopted.

By the way, as a heat-shrinkable gas barrier film used in the above overlapping method, a film obtained by laminating a resin layer having a high gas barrier property and an olefin resin layer is known. Examples of such a film include: Both outer layers are made of a resin composition obtained by mixing 100 parts by weight of a specific ethylene-α-olefin copolymer [A] with 10 to 50 parts by weight of a specific ethylene-α-olefin copolymer [B], A multi-layer film for heat-shrinkable packaging has been proposed, characterized in that the core layer is composed of a saponified ethylene-vinyl acetate copolymer, and the intermediate layer between both outer layers and the core layer is composed of a polyolefin-based adhesive resin ( Patent document 1).

However, in the multi-layer film for heat-shrinkable packaging proposed in Patent Document 1, the saponified ethylene-vinyl acetate copolymer used as the core layer has strong intermolecular interaction, so the heat-shrinkage stress of the film tends to increase. Therefore, there was a concern that the container (tray, etc.) would be deformed during packaging.

Therefore, in order to solve the above problem, a heat-shrinkable laminated film specified by the heat shrinkage rate at a specific temperature and the heat shrinkage stress at a specific temperature, specifically,
[1] A substrate layer (A) containing at least a thermoplastic resin having a melting point of 130° C. or higher, a gas barrier layer (B) containing at least an ethylene-vinyl alcohol copolymer saponified product, and a heat seal layer containing at least a polyethylene resin A heat-shrinkable laminated film comprising at least three layers of (C) and further satisfying the following conditions 1) to 3).
1) The saponified ethylene-vinyl alcohol copolymer has a melting point of 160° C. or less and an ethylene content of 40 mol % or less.
² ) The heat shrinkage rate in the width direction at 80°C is 5% or more.
[2] A base layer comprising a layer (A) and a layer (B) laminated via an interface having an interlayer strength of 0.5 N/15 mm or less, wherein the layer (A) contains a polypropylene resin. A heat-shrinkable laminated film, wherein the layer (B) comprises at least a seal layer containing a polyethylene-based resin, and further satisfies the following conditions (1) and (2).
(1) The difference between the thermal contraction rate of the layer (A) and the thermal contraction rate of the layer (B) in either the length direction (MD) or the width direction (TD) when peeled at the interface is , 10% or less at 100°C.
(2) having a gas barrier layer containing a saponified ethylene-vinyl alcohol copolymer, and having an oxygen barrier of 60 cc/m ² ·day·atm or less at 23°C and 65% RH (Patent Document 3); The surface layer of is made of polypropylene copolymer resin, the other surface layer is made of ethylene-α-olefin copolymer resin, the gas barrier intermediate layer is made of ethylene-vinyl alcohol copolymer resin, and both sides are made of adhesive resin A heat-shrinkable laminated film comprising at least five layers arranged and characterized by the following (1) to (6).
(1) The thermal shrinkage of the film at 140°C is 40-80%.
(2) The maximum thermal shrinkage stress of the film at 140°C is 0.5 to 3.0 MPa. (3) The polypropylene-based copolymer resin constituting one surface layer has a maximum melting peak temperature (Tm) of 130 to 155° C. measured with a differential scanning calorimeter (DSC) in accordance with JIS-K7121. thing.
(4) The ethylene-α-olefin copolymer resin constituting the other surface layer has a maximum melting peak temperature (Tm) of 85 to 85 as measured with a differential scanning calorimeter (DSC) in accordance with JIS-K7121. It should be 125°C.
(5) A modified polypropylene-based adhesive resin layer is arranged as an adhesive resin layer between the gas barrier layer and one surface layer made of a polypropylene-based copolymer resin.
(6) A modified polyethylene adhesive resin layer is arranged as an adhesive resin layer between the gas barrier layer and the other surface layer made of an ethylene-α-olefin copolymer resin (Patent Document 4)
is proposed.

[4] In a multilayer film comprising at least four layers having a surface layer (A) made of an ethylene α-olefin copolymer or the like on both sides of a gas barrier resin layer (B) made of a polyamide or the like, Between the surface layer (A) and the gas barrier resin layer (B), a mixed resin layer (C) made of a mixed resin of a polybutene-1 resin, a polypropylene resin, and a modified polyolefin resin adhesive resin is arranged. ,
The thermal shrinkage rate at 80 ° C. is 15% or more in at least one of the vertical and horizontal directions, and the difference between the average thermal shrinkage rate in the vertical and horizontal directions at 80 ° C. and the same average thermal shrinkage rate at 100 ° C. 20% or less, the average vertical and horizontal heat shrinkage stress at 80 ° C. is 70 g / mm ² or more, and the heat shrinkage force at the same temperature is 110 g / 15 mm width or less. multi-layer film (Patent Document 5) and [5] The surface layer is made of a mixed resin composition of ethylene / α-olefin copolymer and branched low density polyethylene, and among the inner layers, at least one layer (a) is , a layer containing 50% or more of a specific ethylene-vinyl acetate copolymer saponified product, at least four or more layers in which an adhesive layer is arranged on one side or both sides of the inner layer, and between the surface layer and the inner layer A heat-shrinkable gas barrier film characterized by having an adhesive layer disposed thereon and having the following physical properties.
(1) Gel fraction is 5 to 40 wt%
(2) The thermal shrinkage rate at 140°C is 55% or more in the vertical direction and the horizontal direction (3) The thermal shrinkage stress at 100°C is less than 230 g/mm ² in the vertical direction and the horizontal direction (4) The area was shrunk by 30% Post-film haze less than 4.5% (Patent Document 6)
is proposed.

JP-A-10-024530 JP 2016-179648 A JP 2015-221507 A JP 2007-152570 A JP-A-7-266513 Japanese Patent Application Laid-Open No. 2004-202876

The films proposed in Patent Documents 2 to 6 are used in the bag-making process of a packaging machine that performs overlap heat-shrink packaging after or while gas replacement (hereinafter also referred to as "gas replacement overlap packaging machine"). , there was a concern that the container (tray, etc.) would be deformed if the stress in the width direction (TD) in which the film tried to return to its original shape during bag making was large. In the bag-making process of No. 1, no mention is made of the stress of the film that occurs when the bag is made tight while being stretched in the width direction (TD).
In addition, the films proposed in Patent Documents 2 to 6 are made tight while being stretched in the width direction (TD) in the bag making process of the gas-exchanged overlap packaging machine, whereas the film is made tight in the longitudinal direction (TD). MD) is thermally shrunk with a slight margin in the front and back so that continuous sealing and cutting can be performed. If the ratio is close to 1:1, the shrinkage in the longitudinal direction (MD) is insufficient, and wrinkles remain on the top surface of the package containing food, etc., and the four corners of the package become sharp. I was afraid it would get worse.

Therefore, in the present invention, when fresh foods and processed foods that do not last long in an oxygen atmosphere are packaged, especially with a gas replacement overlap packaging machine, while maintaining the known required properties such as gas barrier properties and shrinkage finish properties. To provide a heat-shrinkable gas barrier film capable of suppressing deformation of containers (trays, etc.) after packaging to such an extent that even easily deformable thin containers (trays, etc.) do not impair aesthetic appearance. .

As a result of intensive studies by the present inventors to solve such problems, a specific modulus value, a specific heat shrinkage rate in the longitudinal direction (MD) and the width direction (TD), and a specific heat shrinkage rate ratio (MD /TD), the heat-shrinkable gas barrier film has little deformation in the width direction (TD) of the container (tray, etc.) in the bag making process of the gas replacement overlap packaging machine, and also has excellent shrink finish. This is what completed the present invention.

That is, the present invention is as follows.
[1] A heat laminated stretched film comprising at least a heat seal layer (A), an adhesive layer (B), a gas barrier layer (C), an adhesive layer (B) and a heat seal layer (A) in this order,
The heat seal layer (A) is a layer containing an ethylene-based resin as a main component,
The adhesive layer (B) is a layer containing an olefin-based adhesive resin as a main component,
The gas barrier layer (C) is a layer mainly composed of saponified ethylene-vinyl acetate copolymer,
A heat-shrinkable gas barrier film, which satisfies the following conditions (1) to (3).
(1) The 30% modulus value in the width direction (TD) is 5.0 N/cm or less.
(2) The thermal contraction rate at 120 ° C. in the longitudinal direction (MD) and the width direction (TD) is 40% or more, and the thermal shrinkage rate at 120 ° C. in the longitudinal direction (MD) and 120 in the width direction (TD) The ratio (MD/TD) to the heat shrinkage rate at °C is 1.10 or more.
(3) The oxygen permeability is 20 cc/m ² ·day·atm or less at 23°C and 65% RH.
[2] The heat-shrinkable gas barrier film of [1], wherein the (MD/TD) is 1.15 or more.
[3] The heat-shrinkable gas barrier film according to [1] or [2], which is used for gas exchange overlap packaging.

The heat-shrinkable gas barrier film of the present invention has the effect of having excellent shrink finish and being able to suppress deformation of the container.

The present invention will be described in detail below.
It should be noted that the present invention is not limited to the following embodiments, and various modifications can be made within the scope of the present invention.
The heat-shrinkable gas barrier film of the present invention comprises at least a heat seal layer (A), an adhesive layer (B), a gas barrier layer (C), an adhesive layer (B) and a heat seal layer (A) in this order, that is, A heat-sealing layer (A), an adhesive layer (B), a gas barrier layer (C), an adhesive layer (B) and a heat-sealing layer (A) are laminated and stretched by heating in at least this order, and comprise at least five layers. It is.

<Heat seal layer (A)>
In the present invention, the heat-sealable layer (A) is a layer that allows the heat-shrinkable gas barrier film to exhibit heat-sealable effects, and is preferably arranged as the outermost layer.
In the present invention, the heat-seal layer (A) is a layer containing an ethylene-based resin as a main component, and the ethylene-based resin functions to impart excellent features such as shrink finish and fusion-cut sealability in automatic packaging machines. .
Examples of ethylene-based resins include homopolymers of ethylene and/or copolymers of ethylene and a small amount of other monomers.
In addition, in this invention, ethylene resin can be used individually by 1 type or in combination of 2 or more types.

Examples of homopolymers of ethylene include low density polyethylene (LDPE), linear low density polyethylene (LLDPE), medium density polyethylene (MDPE) and high density polyethylene (HDPE).

In copolymers of ethylene and a small amount of other monomers, the other monomers are not particularly limited, and carbon atoms such as propylene, butene-1, hexene-1, octene-1 and 4-methyl-pentene-1 Examples include α-olefins of numbers 3 to 8, vinyl acetate, (meth)acrylic acid alkyl esters, (meth)acrylic acid, and metal ion neutralized products of (meth)acrylic acid.
In this specification, (meth)acrylic acid is a generic term for acrylic acid and methacrylic acid, and refers to either one or both of them.

In the present invention, the heat-seal layer (A) is mainly composed of an ethylene-based resin, and the content of the ethylene-based resin is, for example, 70% in 100% by mass of the components constituting the heat-seal layer (A). % by mass, preferably 80% by mass, more preferably 90% by mass, still more preferably 95% by mass, and even more preferably 97% by mass.

When food is packaged using the heat-shrinkable gas barrier film of the present invention, the surface of the film is hydrophobic. Therefore, depending on the food, moisture adhering to the film surface becomes water droplets due to evaporation of water in the food. fogging, which may reduce the identifiability of the packaged item. In such a case, the heat-shrinkable gas barrier film of the present invention contains an antifogging agent (glycerin fatty acid ester, etc.)
By using the anti-fogging agent on the film surface to make the film surface hydrophilic, it is possible to make it a water film instead of water droplets, so it is possible to suppress the occurrence of fogging and package the package. Appearance suitable as a multilayer film can be obtained.
The content of the antifogging agent is, for example, 0% by mass to 4% by mass in 100% by mass of the components constituting the heat seal layer (A).

In the present invention, thermoplastic resins, lubricants, surfactants, antiblocking agents, antistatic agents, antioxidants, etc., may be added to the heat seal layer (A) as long as they do not impair the effects of the present invention. can be used as appropriate for the purpose of exhibiting their effective performance.

<Adhesive layer (B)>
In the present invention, the adhesive layer (B) is a layer that exerts an effect of increasing the adhesive strength between layers in the heat shrinkable gas barrier film, and is preferably arranged between the heat seal layer (A) and the gas barrier layer (C). be done.
In the present invention, the adhesive layer (B) is a layer containing an olefinic adhesive resin as a main component. The olefin-based adhesive resin has a functional group introduced into the main chain of the olefin resin by a graft reaction, so it has the property of adhering to a layer composed of an olefin resin, a gas barrier layer, a metal film, etc. by thermal reaction. Therefore, by disposing the adhesive layer (B) between the heat seal layer (A) and the gas barrier layer (C), the heat seal layer (A) and the gas barrier layer (C), which are originally difficult to bond between layers, are bonded together. can. In addition, the adhesive layer (B) containing an olefin-based adhesive resin as a main component has excellent molding processability similar to that of an olefin-based resin, so that it can also exhibit an effect as a stretching support layer.

As the olefin-based adhesive resin, modified propylene-based adhesive resin is preferable from the viewpoint of excellent heat resistance. A modified polymer obtained by graft-copolymerizing an unsaturated carboxylic acid such as maleic acid or fumaric acid or an acid anhydride thereof to a propylene-based resin such as the original copolymer is suitable.
In addition, in the present invention, the olefinic adhesive resin can be used alone or in combination of two or more.

In the present invention, the adhesive layer (B) is composed mainly of an olefin-based adhesive resin, and from the viewpoint of achieving both interlayer adhesion and stretching stability between the heat seal layer (A) and the gas barrier layer (C), , The content of the olefin-based adhesive resin is, for example, 50% by mass, preferably 80% by mass, more preferably 90% by mass in 100% by mass of the components constituting the adhesive layer (B). , more preferably 95% by mass, and still more preferably 100% by mass.
If the content of the olefin-based adhesive resin is less than 50% by mass, the interlayer adhesion between the heat seal layer (A) and the gas barrier layer (C) is reduced, and the heat seal layer ( A) There is a risk that the stretch followability during stretching between the layers A), the adhesive layer (B), and the gas barrier layer (C) may be reduced, and this may cause delamination, making it impossible to obtain the desired film. There is In order to further improve the stretching stability of the adhesive layer (B) to the extent that the adhesive layer (B) does not cause delamination during stretching of the unstretched film, the adhesive layer (B) contains an olefin-based adhesive having excellent stretchability. The resin may be contained in an amount of 0% by mass to 50% by mass based on 100% by mass of the components constituting the adhesive layer (B).

<Gas barrier layer (C)>
In the present invention, the gas barrier layer (C) is a layer that allows the heat-shrinkable gas barrier film to exhibit gas barrier properties, and is preferably arranged between two adhesive layers (B).
In the present invention, the gas barrier layer (C) is a layer containing a saponified ethylene-vinyl acetate copolymer as a main component. Since the saponified ethylene-vinyl acetate copolymer has an abundance of hydroxy groups, hydrogen bonding between the hydroxy groups significantly narrows the inter-molecular gaps. The heat-shrinkable gas barrier film of the invention inhibits gas permeation, that is, has excellent gas barrier properties.
On the other hand, when the saponified ethylene-vinyl acetate copolymer contains water, the hydrogen bond between molecules weakens, resulting in a decrease in gas barrier properties. Therefore, it is known to form a multilayer structure in which a saponified ethylene-vinyl acetate copolymer layer is sandwiched between layers composed of a thermoplastic resin such as a polyolefin resin or a polystyrene resin.

Saponified ethylene-vinyl acetate copolymer changes the gas barrier property and stretchability of the film based on the composition ratio of ethylene and vinyl alcohol. tends to decline.
The saponified ethylene-vinyl acetate copolymer preferably has an ethylene content of 25 mol % to 48 mol % and a saponification degree of 95% or more from the viewpoint of gas barrier properties and stretching processability.
In addition to the ethylene content, there is also a grade of modified ethylene-vinyl acetate copolymer saponified material that has greatly improved moldability by controlling the crystallinity and melting point of the ethylene-vinyl acetate copolymer saponified material. do.

In the present invention, the gas barrier layer (C) is mainly composed of a saponified ethylene-vinyl acetate copolymer, and the content of the saponified ethylene-vinyl acetate copolymer constitutes the gas barrier layer (C). In 100% by mass of the component to be .

The layer structure of the heat-shrinkable gas barrier film of the present invention is a layer structure of at least five layers. A 5-layer structure consisting of the sealing layer (A) can be mentioned. Layers other than the heat seal layer (A), adhesive layer (B) and gas barrier layer (C) are not particularly limited as long as they do not interfere with the object of the present invention.

The thickness composition ratio of each layer of the heat-shrinkable gas barrier film of the present invention is not particularly limited as long as the object of the present invention can be achieved. Although the total thickness of the film is not particularly limited, it is preferably 10 μm to 35 μm for use as a heat-shrinkable packaging material.

Regarding the physical properties of the heat-shrinkable gas barrier film of the present invention, (1) the 30% modulus value in the width direction (TD) is 5.0 N/cm or less, (2) the longitudinal direction (MD) and the width direction (TD) ) are each 40% or more, and the ratio of the heat shrinkage rate at 120 ° C. in the longitudinal direction (MD) and the heat shrinkage rate at 120 ° C. in the width direction (TD) (MD / TD) is 1.10 or more, and (3) the oxygen permeability is 20 cc/m ² ·day·atm or less at 23° C. and 65% RH.

The 30% modulus value in the width direction (TD) is 5.0 N/cm or less, preferably 4.7 N/cm or less. If the 30% modulus value in the TD exceeds 5.0 N/cm, the film tends to return to the TD when the TD is stretched to form a tight bag in the bag-making process of the gas-exchanged overlap packaging machine. There is a concern that the force applied will increase and the container (tray, etc.) will be deformed.
On the other hand, the 30% modulus value in TD is preferably 1.0 N/cm or more.
If it is less than 1.0 N/cm, the film tends to stretch in the TD in the bag making process of the gas replacement overlap packaging machine, and the margin of the TD of the bag product is difficult to stabilize. Large corners and overall wrinkles are conspicuous in the film, and there is a concern that the appearance will be spoiled.

If the heat shrinkage at 120°C in the MD and TD is less than 40%, the heat shrinkability of the film may be insufficient, resulting in large corners and overall wrinkles in the film after heat shrink packaging. stand out and may spoil the appearance.
In addition, the ratio (MD/TD) of the heat shrinkage rate at 120°C in the longitudinal direction (MD) and the heat shrinkage rate at 120°C in the width direction (TD) is 1.10 or more, and is 1.15 or more. is preferred, and 1.20 or more is more preferred. Regarding the margin of the packaging bag by the gas displacement overlap packaging machine, the width direction (TD) is tight, but the longitudinal direction (MD) is large, so the above heat shrinkage ratio (MD / TD) is 1.10. If it is less than that, the heat shrinkability of the MD of the film may be insufficient, so there is a concern that sharp corners may remain and the appearance may be impaired.

In addition, the oxygen permeability at 23° C. and 65% RH is 20 cc/m ² ·day·atm or less, preferably 15 cc/m ² ·day·atm or less, from the viewpoint of keeping food fresh. If it exceeds 20 cc/m ² ·day·atm, there is a concern that the effect of preserving the freshness of the food that is the content will be reduced.

Regarding the form of food packaging using the heat-shrinkable gas barrier film of the present invention, meat, processed meat, seafood, etc., whose freshness is difficult to maintain, are packed in containers such as foam trays and molded trays, and are wrapped in containers such as foam trays and molded trays. A mode in which food is wrapped and heat-shrink-wrapped by a wrap packaging machine is preferable from the viewpoint of food waste loss suppression, since it is possible to suppress deterioration in the freshness retention of the food.

For example, the heat-shrinkable gas barrier film of the present invention can be used in a packaging machine such as FW3451GB manufactured by Fuji Machinery Co., Ltd., so that containers such as meat trays can be overlapped and heat-shrink wrapped while gas is replaced. . As a result, instead of manually overwrapping in the backyard of the store, the heat-shrinkable gas barrier film of the present invention is used to automatically package the products at a pack center or the like, and then deliver them to each store. Since it can be delivered, it also has the effect of contributing to the elimination of labor shortages.

[Method for producing heat-shrinkable gas barrier film]
Next, the manufacturing method of the film of the present invention is exemplified. A multilayer film produced using the components constituting each layer described above is stretched by a known simultaneous biaxial stretching method. The draw ratio is preferably 3 to 5 times in both the vertical and horizontal directions. If it is less than 3 times, the heat shrinkage of the resulting film may be low, and a satisfactory shrink finish may not be obtained.

Hereinafter, the case of five-layer lamination annular film forming and stretching will be taken as an example and explained in detail.
First, heat seal layers formed from a resin composition containing an ethylene-based resin and an anti-fogging agent are provided on both surface layers, adhesive layers mainly composed of an olefin-based adhesive resin are provided on both intermediate layers, and ethylene-vinyl acetate Melt kneading is carried out using 3 or 5 extruders so that the gas barrier layer mainly composed of a saponified polymer becomes the core layer, and the mixture is circularly co-extruded from a 5-layer circular die attached to the tip of the extruder. , to prepare a tubular unstretched multilayer film by rapidly cooling and solidifying without stretching. Next, the obtained tubular unstretched multilayer film is supplied to a tubular stretching device, reheated to a temperature range capable of high orientation, and expanded and stretched by applying gas pressure to the inside of the tube to stretch the film at a longitudinal and lateral stretch ratio. Simultaneous biaxial orientation occurs at 3 to 5 times. The multilayer film taken out from the stretching apparatus can be optionally heat-treated or annealed, thereby reducing the residual stress of the film at room temperature and suppressing natural shrinkage during storage.
Also, in the heat treatment, by setting the product of the speed ratio from the heat treatment inlet to the outlet (hereinafter referred to as total draw), the specific modulus value in the present invention and the longitudinal direction (MD) thermal shrinkage at 120 ° C. A film that satisfies a specific ratio (MD/TD) to the heat shrinkage in the width direction (TD) at 120° C. can be obtained more easily.

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these Examples.

The methods of measurement and evaluation in Examples and Comparative Examples were carried out as shown below.
1. Film thickness: Measured according to JIS Z 1709.
2. Thickness ratio: Measured by observing the cross section of the film with a microscope.
3. 30% modulus value: According to JIS K 7127, the MD and TD of the film were measured with a gripping distance of 50 mm, and the value at an elongation of 30% was calculated.
4. Thermal shrinkage: Measured at 120°C according to ASTM-D 2732 . At that time, the ratio of the measured values of MD and TD (MD/TD) was calculated.
5. Oxygen permeability: Measured under conditions of 23°C and 65% RH according to JIS K 7126 (isobaric method).
6. Packaging evaluation: Using an automatic packaging machine (model: FW3451GB) manufactured by Fuji Machinery Co., Ltd., non-barrier trays containing dummy contents are overlap-wrapped while being filled with gas under appropriate bag-making margin conditions, and heated to 123 ° C. After staying in the set shrink tunnel for 2 to 3 seconds, 10 packaging samples after passing through the tunnel were subjected to tray container deformation evaluation and shrink finish evaluation.
<Tray container deformation evaluation>
◯: Almost no deformation of the lateral portion of the tray of the packaged sample for all 10 packaged samples. x: For all 10 packaged samples, the lateral portion of the tray of the packaged sample is conspicuously deformed and the appearance is spoiled.
<Evaluation of shrink finish>
○: For all 10 packaging samples, the shrink film and the object to be packaged have a sufficiently tight feeling, and the four corners of the packaging sample are almost free from corners.
x: For all 10 packaging samples, the feeling of tightness between the shrink film and the object to be packaged is insufficient, or the four corners of the packaging sample are sharply angled, impairing the appearance.

Example 1
As shown in Table 1, from 97 parts by mass of a linear low-density polyethylene (A1) having a density of 0.913 g/cm ³ and an MI of 2.4 g/10, and 3 parts by mass of an antifogging agent (D1) of a glycerin fatty acid ester component, A resin composition consisting of 100 parts by mass of modified polypropylene (B1) having a density of 0.896 g / cm ³ and an MI of 7.7 g / 10 minutes is used as both adhesive layers, and a density of 1.160 g / cm ³ , MI 4.0 g/10 min, ethylene content 38 mol %, resin composition composed of 100 parts by mass of saponified ethylene-vinyl acetate copolymer (C1) was used as a gas barrier layer, and was melt-kneaded by three extruders. After that, the extrusion rate of each extruder was set so that the thickness ratio was 3/2/1/2/3, and co-extrusion was carried out downward through a five-layer annular die. The five-layered tube thus formed was allowed to slide on the outer surface of a cylindrical cooling mandrel in which cooling water was circulating, while the outer side was passed through a water tank to cool the tube, and the unstretched film was obtained. This tubular unstretched film is guided to a tubular biaxial stretching device, air is supplied to the inside of the tubular unstretched film, and at the same time the pressure is reduced to below the melting point of all the resins constituting the tubular unstretched film. The film was stretched 4 times in both length and width while being heated at a temperature, and then heat-treated in a heat treatment section while taking a total draw of 1.02 times to obtain a heat-shrinkable gas barrier film with a film thickness of 15 μm.
The resulting film was good in all of the oxygen barrier property, tray container deformation evaluation, and shrink finish evaluation.

Example 2
As shown in Table 1, a heat-shrinkable gas barrier film with a film thickness of 15 µm was obtained in the same manner as in Example 1, except that the thickness ratio was changed to 2/2/1/2/2.
The resulting film was good in all of the oxygen barrier property, tray container deformation evaluation, and shrink finish evaluation.

Example 3
As shown in Table 1, the same method as in Example 1 was performed except that the draw ratio (MD × TD) was 5 × 4 times and the total draw in the heat treatment section was 1.10. A shrinkable gas barrier film was obtained.
The resulting film was good in all of the oxygen barrier property, tray container deformation evaluation, and shrink finish evaluation.

Example 4
As shown in Table 1, the same method as in Example 1 was performed except that the thickness ratio was set to 1/4/1/4/1 and the total draw in the heat treatment section was set to 1.00 to obtain a film having a thickness of 15 μm. A shrinkable gas barrier film was obtained.
The resulting film was good in all of the oxygen barrier property, tray container deformation evaluation, and shrink finish evaluation.

Example 5
As shown in Table 1, the film thickness was 15 μm in the same manner as in Example 1 except that the thickness ratio was 1/2/1/2/1 and the draw ratio (MD×TD) was 4×3. A heat-shrinkable gas barrier film was obtained.
The resulting film was good in all of the oxygen barrier property, tray container deformation evaluation, and shrink finish evaluation.

Comparative example 1
As shown in Table 2, the same method as in Example 1 was performed except that the thickness ratio was set to 2/2/1/2/2 and the total draw in the heat treatment section was set to 1.00 to obtain a film having a thickness of 15 μm. A shrinkable gas barrier film was obtained.
The resulting film was good in oxygen barrier property and tray container deformation evaluation, but was insufficient in shrink finish evaluation.

Comparative example 2
As shown in Table 2, except that the draw ratio (MD × TD) was 4 × 3 times, the thickness ratio was 1/2/1/2/1, and the total draw in the heat treatment section was 0.98, A heat-shrinkable gas barrier film having a film thickness of 15 μm was obtained in the same manner as in Example 1.
The resulting film had good oxygen barrier properties, but was insufficient in both tray container deformation evaluation and shrink finish evaluation.

Comparative example 3
As shown in Table 2, the same method as in Example 1 was performed except that the thickness ratio was 1/4/1/4/1 and the total draw in the heat treatment section was 1.03. A shrinkable gas barrier film was obtained.
The obtained film was good in terms of oxygen barrier property and shrinkage finishing property, but the evaluation of tray container deformation was insufficient.

Comparative example 4
As shown in Table 2, a heat-shrinkable gas barrier film having a film thickness of 15 μm was obtained in the same manner as in Example 1, except that the total draw in the heat treatment section was 1.04.
The obtained film was good in terms of oxygen barrier property and shrinkage finishing property, but the evaluation of tray container deformation was insufficient.

The heat-shrinkable gas barrier film of the present invention can extend the freshness retention period of foodstuffs, etc., in the form of heat-shrinkable overlap packaging of containers such as trays containing foodstuffs by means of a gas replacement packaging machine. In addition, the heat-shrinkable gas barrier film of the present invention is suitable as a heat-shrinkable packaging material that is excellent in shrinkage finishing properties in a gas replacement packaging machine, can suppress deformation of containers (trays, etc.), and does not impair the aesthetic appearance of packages. can be used.

Claims (3)

A heat laminated stretched film comprising at least a heat seal layer (A), an adhesive layer (B), a gas barrier layer (C), an adhesive layer (B) and a heat seal layer (A) in this order,
The heat seal layer (A) is a layer containing an ethylene-based resin as a main component,
The adhesive layer (B) is a layer containing an olefin-based adhesive resin as a main component,
The gas barrier layer (C) is a layer mainly composed of saponified ethylene-vinyl acetate copolymer,
A heat-shrinkable gas barrier film, which satisfies the following conditions (1) to (3).
(1) The 30% modulus value in the width direction (TD) is 5.0 N/cm or less.
(2) The thermal contraction rate at 120 ° C. in the longitudinal direction (MD) and the width direction (TD) is 40% or more, and the thermal shrinkage rate at 120 ° C. in the longitudinal direction (MD) and 120 in the width direction (TD) The ratio (MD/TD) to the heat shrinkage rate at °C is 1.10 or more.
(3) The oxygen permeability is 20 cc/m ² ·day·atm or less at 23°C and 65% RH. 2. The heat-shrinkable gas barrier film according to claim 1, wherein the (MD/TD) is 1.15 or more. 3. The heat-shrinkable gas barrier film according to claim 1, which is used for gas exchange overwrap packaging.