JP2016179648A - Heat-shrinkable laminated film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat-shrinkable laminated film which can suppress concentration of stress of heat shrinkage stress, and is excellent in barrier properties.SOLUTION: A heat-shrinkable laminated film has at least three layers of a base material layer (A), a gas barrier layer (B) and a heat seal layer (C). In the film, the base material layer (A) contains at least a thermoplastic resin having a melting point of 130°C or higher, the gas barrier layer (B) contains at least a saponification product of an ethylene-vinyl alcohol copolymer, and the heat seal layer (C) contains at least a polyethylene-based resin, and satisfies the following conditions 1) to 3): 1) saponification product of ethylene-vinyl alcohol copolymer having melting point of 160°C or lower and ethylene content of 40 mol% or less; 2) thermal shrinkage in a length direction at 80°C of 5% or more; and 3) oxygen permeability at 23°C and 65% RH of 60 cc/mday atm or less.SELECTED DRAWING: None

Description

  The present invention relates to a heat-shrinkable laminated film suitable for packaging by a packaging machine and suitable for use in the field of food packaging that mainly requires gas barrier properties.

  Examples of the packaging method for covering food products include household wrap packaging, overlap packaging, twist packaging, bag packaging, skin packaging, pillow shrink packaging, stretch packaging, and top seal packaging. In particular, pillow shrink packaging and top seal packaging continuous packaging machines are widely distributed because they can package at high speed and have a good finish.

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

  For example, Patent Document 1 discloses that one surface layer is a polypropylene copolymer resin, the other surface layer is an ethylene-α-olefin copolymer resin, and an ethylene-vinyl alcohol copolymer saponified product as a gas barrier intermediate layer. A film comprising at least five layers in which adhesive resin layers are disposed on both sides thereof, having both gas barrier properties and heat shrinkage properties, and having excellent antifogging properties is disclosed.

JP 2007-152570 A

  However, in Patent Document 1, the saponified ethylene-vinyl alcohol copolymer tends to have a large thermal shrinkage stress due to strong interaction between molecules, and the container is easily deformed during gas pack packaging due to stress concentration due to relaxation of molecular orientation. Is an issue.

  The problem to be solved by the present invention is to provide a heat-shrinkable laminated film that suppresses stress concentration during heat shrinkage and has excellent barrier properties.

  As a result of intensive studies to solve the above problems, the present inventors have completed the present invention. That is, the present invention is as follows.

[1]
The gas barrier layer comprises at least three layers of a base material layer (A), a gas barrier layer (B), and a heat seal layer (C), and the base material layer (A) contains at least a thermoplastic resin having a melting point of 130 ° C. or higher. (B) includes at least a saponified ethylene-vinyl alcohol copolymer, the heat seal layer (C) includes at least a polyethylene resin, and further satisfies the following conditions 1) to 3): Laminated film.
1) The melting point of the saponified ethylene-vinyl alcohol copolymer is 160 ° C. or lower, and the ethylene content is 40 mol% or lower.
2) The thermal shrinkage in the width direction at 80 ° C. is 5% or more. 3) The oxygen permeability is 60 cc / m ² · day · atm or less at 23 ° C. and 65% RH.
[2]
The heat-shrinkable laminated film according to [1], wherein the difference in supercooling temperature, which is the difference between the melting point of the gas barrier layer and the temperature-falling crystallization temperature, is 25 ° C or higher.
[3]
The heat shrinkable laminated film according to [1] or [2], wherein the heat shrinkage stress in the width direction at 80 ° C. has no peak.
[4]
The heat-shrinkable laminated film according to any one of [1] to [3], wherein the total layer thickness is 30 μm or less.
[5]
The heat shrinkability according to any one of [1] to [4], including an adhesive layer (D) between the gas barrier layer (B) and the heat seal layer (C), and comprising at least four layers. Laminated film.
[6]
An adhesive layer (E) is included between the base material layer (A) and the gas barrier layer (B), and is composed of at least five layers. Further, the base material layer (A) / the adhesive layer (E) / the gas barrier. The heat-shrinkable laminated film according to [5], which is laminated in the order of layer (B) / adhesive layer (D) / heat seal layer (C).
[7]
The heat-shrinkable laminated film according to any one of [1] to [6], wherein at least one of the base material layer, the gas barrier layer, and the heat seal layer contains a thermoplastic elastomer.
[8]
The heat-shrinkable laminated film according to [7], wherein the ratio of the thickness of the layer containing the thermoplastic elastomer is 30% or more based on the total layer.
[9]
The heat-shrinkable laminated film according to any one of [1] to [8], wherein the base material layer (A) contains a polypropylene resin.
[10]
The heat-shrinkable laminated film according to any one of [1] to [9], wherein the heat shrinkage rate in the length direction at 120 ° C is 30% or more.

  According to the present invention, the saponified ethylene-vinyl alcohol copolymer uses a gas barrier layer (B) having a melting point of 160 ° C. or less and an ethylene content of 40 mol% or less, thereby suppressing stress concentration during heat shrinkage. Therefore, beautiful gas pack packaging with little container deformation is possible. Furthermore, since the present invention has a gas barrier layer containing a saponified ethylene-vinyl alcohol copolymer, it is suitable for packaging foods with strong odors and gas pack packaging.

  Hereinafter, embodiments of the present invention will be described in detail. In addition, this invention is not limited to the following embodiment, It can implement by changing variously within the range of the summary. The heat-shrinkable laminated film of this embodiment comprises at least three layers of a base material layer (A), a gas barrier layer (B), and a heat seal layer (C), and the base material layer (A) has a melting point of 130 ° C. or higher. The gas barrier layer (B) includes at least an saponified ethylene-vinyl alcohol copolymer, and the heat seal layer (C) is a polyethylene resin, preferably an ethylene-α-olefin copolymer. At least. In the heat-shrinkable laminated film, the base material layer (A) and the heat seal (C) are preferably located in the outermost layers. Moreover, in addition to the base material layer, the gas barrier layer, and the heat seal layer, an adhesive layer described later can be further included.

Examples of the layer structure of the heat-shrinkable laminated film include the following examples. According to these layer structures, the effect of the present invention is more remarkably exhibited.
-Base material layer / gas barrier layer / heat seal layer- 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 aspects of the layers of each layer constituting the heat-shrinkable laminated film will be described in detail.

[Base material layer (A)]
The base material layer of this embodiment is a layer that imparts heat resistance to the heat-shrinkable laminated film, and is preferably located in the outermost layer of the heat-shrinkable laminated film. Further, the base material layer can also serve as a stretched support layer when the heat-shrinkable laminated film is produced.

  From the viewpoint of imparting heat resistance, the base material layer of this embodiment preferably contains a thermoplastic resin having a melting point of 130 ° C. or higher. For example, polymethylene terephthalate, polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate. Polyesters such as phthalate and polylactic acid; aliphatic polyamide polymers such as nylon 6, nylon 12, and nylon 66; aliphatic polyamide copolymers such as nylon 6/66 and nylon 6/12; MXD6 (polymetaxylene adipa It is preferable to contain an aromatic polyamide polymer such as (mid) and the like, polymethylpentene, polypropylene resin, etc., and at least one of them is preferably selected. Further, from the viewpoint of imparting heat shrinkability, it is preferable to include a thermoplastic resin having a melting point of 160 ° C. or less, and it is more preferable to include a polypropylene resin. Of the base material layer, a polypropylene resin is preferably contained in a proportion of 50% by mass or more, more preferably in a proportion of 60% by mass or more, and further preferably in a proportion of 70% by mass or more.

  As the polypropylene resin, a propylene homopolymer and / or a propylene copolymer can be preferably used. For example, polypropylene, propylene-α-olefin copolymer, ternary copolymer of propylene, ethylene, and α-olefin. A polymer etc. can be used conveniently.

  The propylene homopolymer is a polymer obtained by polymerizing only propylene. As the polypropylene copolymer, a copolymer of propylene and at least one selected from ethylene and an α-olefin having 4 to 20 carbon atoms can be suitably 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.

  Examples of the α-olefin include ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-decene and 1-dodecene. 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicocene 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, butene comonomer, hexene comonomer and octene comonomer is generally easily available and is preferably used. it can.

  The polypropylene-based resin may be polymerized using a known catalyst such as a single-site catalyst or a multi-site catalyst. From the viewpoint of more excellent transparency, the polypropylene-based resin was polymerized using a single-site catalyst. It is preferable.

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

  As the polypropylene resin, a polypropylene resin in which the crystal / amorphous structure (morphology) is controlled in nano order can be used.

  Polypropylene resins can be used alone or in admixture. Mixing polypropylene and a propylene-α-olefin copolymer is preferable because the crystallinity of the base material layer tends to decrease and the heat shrinkability tends to improve. .

  The base material layer may contain components other than the thermoplastic resin. For example, optional additions such as thermoplastic resins, various surfactants, antiblocking agents, antistatic agents, lubricants, plasticizers, antioxidants, ultraviolet absorbers, colorants, inorganic fillers, etc., within the range that does not impair their properties An agent may be included.

  In order to impart antifogging properties to the heat-shrinkable laminated film of this embodiment, a glycerin fatty acid ester can be added as a surfactant to the base material layer. When adding glycerin fatty acid ester, it is preferable that the content is 0.1 mass% or more and 5.0 mass% or less on the basis of the said base material layer.

  Examples of glycerin fatty acid esters include mono-fatty acid esters of glycerin, di-fatty acid esters, tri-fatty acid esters, poly fatty acid esters, etc., and mono-glycerin esters, diglycerin esters of saturated or unsaturated fatty acids having 8 to 18 carbon atoms, A triglycerin ester, a tetraglycerin ester, etc. are mentioned. Among them, diglycerin oleate, diglycerin laurate, glyceryl stearate, glycerin monooleate, or a mixture thereof is preferred because it hardly inhibits the slipperiness and optical properties of the film. Furthermore, good anti-fogging properties can be imparted by adding an ethylene oxide adduct to lower the surface tension of water droplets. Examples of the ethylene oxide adduct include polyoxyethylene alkyl ether.

[Gas barrier layer (B)]
The gas barrier layer of this embodiment is a layer containing a saponified ethylene-vinyl alcohol copolymer and plays a role of improving the gas barrier properties of the heat-shrinkable laminated film. The melting peak temperature (hereinafter referred to as melting point) of the saponified ethylene-vinyl alcohol copolymer measured according to JIS-K-7210 is preferably 160 ° C. or less, and more preferably less than 160 ° C.

  Since the saponified ethylene-vinyl alcohol copolymer has a melting point of 160 ° C. or less, relaxation of molecular orientation is promoted during the heat shrinking process at the time of packaging. be able to.

  The melting point is the temperature at the peak of the endothermic reaction peak that appears in the melting curve obtained by differential scanning calorimetry (DSC). When there are a plurality of melting peaks, it is sufficient that the melting peak temperature on the highest temperature side is within the above numerical range (that is, in the present specification, the melting peak temperature on the highest temperature side is regarded as the melting point).

  Further, the saponified ethylene-vinyl alcohol copolymer tends to have good stretchability because the crystallinity and melting point decrease as the ethylene content increases. Generally, the melting point when the ethylene content is 32 mol% is 183 ° C., 38 mol. The melting point in the case of% is 173 ° C., and the melting point in the case of 44 mol% is 163 ° C. The ethylene content suitable for this embodiment 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 excellent in stretchability and gas barrier properties can be obtained.

  In general, the gas barrier performance tends to be better as the interaction between the molecular chains is larger. In particular, the saponified ethylene-vinyl alcohol copolymer is known to have large interaction between molecules and high gas barrier performance. . On the other hand, since the interaction between molecular chains is large, the heat shrinkage stress is large, and when used as a heat shrinkable film, the container of the package tends to be deformed.

  The saponified ethylene-vinyl alcohol copolymer in this embodiment can achieve both a melting point of 160 ° C. or less and an ethylene content of 40 mol% or less by controlling the crystal structure. Furthermore, in this embodiment, the difference in the supercooling temperature, which is the difference between the melting point and the cooling crystallization temperature, is larger than that of a general saponified ethylene-vinyl alcohol copolymer. In the case of such a gas barrier layer, since the heat shrinkage stress does not have a peak, the stress concentration is reduced, and the container deformation at the time of gas pack packaging can be suppressed. The subcooling temperature difference suitable for this embodiment is 25 ° C. or more, more preferably 27 ° C. or more, and further preferably 29 ° C. or more.

  The reason for the above effect is not necessarily clear, but is considered as follows. That is, the heat shrink property of the heat-shrinkable laminated film appears as the amorphous part stretched by the molecular orientation of the constituent resin relaxes and returns to the non-orientated state, and the crystalline part is amorphous to the melting temperature. It plays a role in stopping the shrinkage. In general, saponified ethylene-vinyl alcohol copolymers tend to dominate the heat shrinkage stress of the entire laminated film because of strong intermolecular interaction and large heat shrinkage stress. It is considered that a heat shrinkable laminated film excellent in barrier properties can be provided by suppressing stress concentration due to orientation relaxation of the amorphous part and the crystal part.

As for the gas barrier property of the heat-shrinkable laminated film, the oxygen transmission rate is measured at an oxygen condition of 65% RH and a measurement temperature of 23 ° C. From the viewpoint of being able to suppress oxygen permeation and suitable for gas pack packaging, the oxygen permeability after 3 hours from the start of measurement is 60 cc / m ² · day · atm or less, and 50 cc / m ² · day. It is preferably atm or less, more preferably 40 cc / m ² · day · atm or less. Such a heat-shrinkable laminated film having gas barrier properties can sufficiently suppress the permeation of oxygen.

[Heat seal layer (C)]
The heat seal layer of this embodiment is a layer that imparts heat sealability to the heat-shrinkable laminated film, and is preferably located in the outermost layer of the heat-shrinkable laminated film. The heat seal layer can also serve as a stretched support layer when producing a heat-shrinkable laminated film.

  Examples of the polyethylene resin constituting the heat seal layer of this embodiment include polyethylene and ethylene-α-olefin copolymers.

  Examples of polyethylene include high density polyethylene, medium density polyethylene, low density polyethylene (LDPE), and ultra low density polyethylene. Examples of the ultra-low density polyethylene include linear ultra-low density polyethylene (referred to as “VLDPE” or “ULDPE”).

Here, polyethylene can be classified by density based on JIS K 6922. Specifically, the density is referred to as high density polyethylene those 0.942 g / cm ³ or more and a density called medium density polyethylenes of less than 0.930 g / cm ³ or more and 0.942 g / cm ^3, the density Having a density of 0.910 g / cm ³ or more and less than 0.930 g / cm ³ is referred to as a low density polyethylene, and a density of less than 0.910 g / cm ³ is referred to as an ultra low density polyethylene.

  The ethylene-α-olefin copolymer refers to a copolymer of ethylene and at least one selected from the aforementioned α-olefins.

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

  In addition, as the ethylene-α-olefin copolymer, a copolymer of ethylene and at least one comonomer selected from propylene comonomer, butene comonomer, hexene comonomer, and octene comonomer is generally easily available. It can be suitably used.

  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 more excellent transparency, it may be polymerized using a single-site catalyst. Is preferred.

Polyethylene resin, from the viewpoint of heat sealability at low temperatures becomes better, the density is 0.860 g / cm ² or more and 0.925 g / cm ² or less preferably, 0.870 g / cm ² or more and 0 more preferable to be .920g / cm ² or less, further preferable to be 0.880 g / cm ² or more and 0.915 g / cm ² or less. As the density of the polyethylene resin is lower, the heat sealability at a low temperature tends to be improved. When the density is 0.925 g / cm ² or less, the heat sealability tends to be improved.

  As the polyethylene resin, a polypropylene resin having a crystal / amorphous structure (morphology) controlled in nano order can be used.

  Polyethylene resins can be used alone or in combination, and it is preferable to mix polyethylene and an ethylene-α-olefin copolymer because the crystallinity of the base material layer tends to decrease and the heat shrinkability tends to improve. .

  The heat seal layer may contain components other than the polyethylene-based resin. For example, optional additions such as thermoplastic resins, various surfactants, antiblocking agents, antistatic agents, lubricants, plasticizers, antioxidants, ultraviolet absorbers, colorants, inorganic fillers, etc., within the range that does not impair their properties An agent may be included.

  In order to impart antifogging properties to the heat-shrinkable laminated film of the present embodiment, the aforementioned glycerin fatty acid ester can be added as a surfactant to the heat seal layer.

[Adhesive layer (D), (E)]
The adhesive layer of this embodiment (hereinafter simply referred to as “adhesive layer”) can be formed from a resin composition containing a known adhesive resin.

  As the adhesive resin, a modified polyolefin resin obtained by graft polymerization of a polyolefin resin and at least one selected from α, β-unsaturated carboxylic acids and derivatives thereof can be suitably used.

  As the modified polyolefin-based resin, a modified propylene-based resin and / or a modified polyethylene-based resin is preferable from the viewpoint of excellent adhesiveness and heat resistance. Examples of modified propylene resins include polypropylene resins such as polypropylene, propylene-α-olefin copolymers, terpolymers of propylene, ethylene and α-olefin, and unsaturated acids such as maleic acid and fumaric acid. A modified polymer obtained by graft copolymerization of a carboxylic acid or an acid anhydride thereof is suitable. Polypropylene, propylene-α-olefin copolymer, terpolymer of propylene, ethylene and α-olefin, etc. A modified polymer obtained by graft copolymerization with maleic acid is more preferable. Examples of modified polyethylene resins include polyethylene resins such as polyethylene homopolymers, ethylene-propylene copolymers, ethylene-α-olefin copolymers, unsaturated carboxylic acids such as maleic acid and fumaric acid, or acid anhydrides thereof. A modified polymer obtained by graft copolymerization is preferably used, and a modified polymer obtained by graft copolymerizing maleic anhydride to an ethylene homopolymer, an ethylene-propylene copolymer, or an ethylene-α-olefin copolymer. More preferred.

  In the present embodiment, the adhesive layer may be a single layer, or may have two or more adhesive layers. For example, a first adhesive layer (D) provided between the heat seal layer and the gas barrier layer and a second adhesive layer (E) provided between the gas barrier layer and the base material layer may be included. .

  The adhesive layer can be used alone or in combination with a modified polyolefin resin. Moreover, in order to reduce crystallinity and to improve heat shrinkability, a modified polyolefin resin and other thermoplastic resins can be mixed and used. As another thermoplastic resin, for example, the above-mentioned polypropylene resin and / or polyethylene resin can be mixed and used.

  The heat-shrinkable laminated film of the present embodiment preferably has no peak at the measurement temperature of 80 ° C. in the length direction for the heat-shrinkage stress measured according to the measurement method ASTM-D2838 in order to suppress stress concentration. More preferably, the maximum value of the heat shrinkage stress immediately after the immersion is not more than the maximum value of the heat shrinkage stress after 3 minutes, and the maximum value of the heat shrinkage stress immediately after the immersion is more than the maximum value of the heat shrinkage stress after 3 minutes. A small value is preferable because it has an effect of further reducing stress concentration. Further, the maximum value of the heat shrinkage stress is preferably 3.0 MPa or less, and more preferably 2.5 MPa or less.

  In packaging that tightly wraps an object to be wrapped such as pillow shrink packaging, it is often used by packing meat, seafood, etc. in a plastic foam tray or molded tray, etc. Since the tray is easily deformed by the heat shrinkage stress, a package with a poor appearance is likely to occur.

  The heat-shrinkable laminated film of the present embodiment is more tight and suppresses tray deformation when packaging foods using an automatic packaging machine, unless the heat shrinkage stress in the width direction at 80 ° C. has a peak. A beautiful package can be obtained.

  The reason for the above effect is not necessarily clear, but when the heat shrinkage stress has a peak, the tray tends to be deformed because the stress is locally concentrated on a part of the tray. When the heat shrinkage stress does not have a peak, it is considered that the deformation of the container can be suppressed because the entire tray is easily stressed uniformly.

  In addition, food packaging trays used in automatic packaging machines are generally rectangular trays that are longer in the machine direction, that is, the length direction is wider than the width direction. The container is weak against deformation and easily deformed. For this reason, it is preferable that the width direction of the film does not have a peak of heat shrinkage stress because the deformation of the container is suppressed, and it is preferable that both the length direction and the width direction have no peak of heat shrinkage stress. It is more preferable because container deformation can also be suppressed.

  In the case of packaging with an automatic packaging machine, the film tunnel temperature tends to be lower by about 10 ° C. to 20 ° C. with respect to the hot air set temperature of the tunnel because the shrink tunnel passage time of the package is about several seconds. Therefore, in the heat-shrinkable laminated film of the present embodiment, the measurement of the heat-shrinkage stress, which is an indicator of container deformation, is immersed in an oil bath at 80 ° C. and evaluated for the assumption that the hot air set temperature is 100 ° C.

  The heat shrinkage stress is measured according to ASTM-D2838. When the film is sampled into a strip shape of 90 mm in the length direction / width direction (measurement length 50 mm + chuck grip 40 mm) and 10 mm in the width direction / length direction, and immersed in an oil bath at a temperature of 80 ° C. The maximum heat shrinkage stress is measured immediately after immersion and after immersion for 3 minutes.

  In order to obtain the heat shrinkage stress in the above range, it is preferable that at least one of the layers constituting the heat shrinkable laminated film contains a thermoplastic elastomer. The thermoplastic elastomer is a copolymer composed of ethylene and an α-olefin, or a copolymer composed of propylene and an α-olefin, and may be a so-called rubber-like or thermoplastic one. , A random copolymer composed of ethylene and 1-butene or propylene and 1-butene. The thermoplastic elastomer is preferably amorphous, but may be partially crystalline. The melting point is preferably 100 ° C. or lower. In the case of such a thermoplastic elastomer, the molecular orientation of the film is suppressed and the stress concentration can be reduced by the softening of the thermoplastic elastomer during film stretching in the production process. In order to further reduce the stress concentration, the ratio of the thickness of the layer containing the thermoplastic elastomer is preferably 30% or more, more preferably 40% or more with respect to the total layer.

  Further, in the heat-shrinkable laminated film of this embodiment, the heat shrinkage rate measured in accordance with the measurement method ASTM-D2732 is preferably 5% or more at 80 ° C. in the length direction, and is 10% or more. More preferably, it is more preferably 15% or more. Moreover, it is preferable that it is 30% or more at 120 degreeC, It is more preferable that it is 40% or more, It is further more preferable that both the length direction and the width direction are 40% or more. In general, in order to obtain a package with a tight finish in the pillow shrink packaging and the top seal packaging used in the present embodiment, a package with a tight and clean finish should be obtained if the heat shrinkage rate is 30% or more. Can do.

  In order to obtain a heat shrinkage rate in the above range, the melting point of the resin constituting the heat shrinkable laminated film is preferably 165 ° C or lower, more preferably 160 ° C or lower, and lower than 160 ° C. Further preferred. If the melting point of the resin constituting the heat-shrinkable laminated film is 165 ° C. or lower, relaxation of molecular orientation is promoted, and thus good heat-shrinkability suitable for shrinkage can be expressed.

  Further, the heat shrinkable laminated film has a heat shrinkage rate in the length direction of preferably 5% or less at 60 ° C., and more preferably 5% or less in either the length direction or the width direction. . Such a heat-shrinkable laminated film is preferable because it can suppress a dimensional change of the film during transportation and / or storage.

  The thickness of the heat-shrinkable laminated film is preferably 5 μm or more and 30 μm or less, more preferably 6 μm or more and 28 μm or less, and further preferably 7 μm or more and 26 μm or less. If the thickness of the heat-shrinkable laminated film is 5 μm or more, it is preferable in terms of improving pinhole resistance during transportation. If the thickness is 30 μm or less, the heat-shrinking force is reduced and a package with a good finish is realized. It is preferable in that it can be performed.

  The thickness of the gas barrier layer is preferably 2% or more and 15% or less, more preferably 3% or more and 10% or less, and more preferably 4% or more and 8% or less of the total thickness of the heat-shrinkable laminated film. More preferably. If the thickness of the gas barrier layer is reduced from 2% of the total thickness, there is a tendency that sufficient gas barrier performance does not appear, and if it exceeds 15%, stretching during production tends to become unstable. It is preferable that it is in the range from the viewpoint that both the stretching stability during production and the gas barrier property of the package can be achieved.

  Although the manufacturing method in particular of a heat-shrinkable laminated film is not restrict | limited, For example, the following method is mentioned.

[Method for producing heat-shrinkable film]
The method for producing a heat-shrinkable laminated film according to this embodiment is a process of laminating a laminate having at least three resin layers (hereinafter sometimes referred to as “unstretched original fabric”) by coextrusion and heating and stretching. Is provided. The coextrusion method will be described below.

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

  As the refrigerant used for the rapid cooling, water of 60 ° C. or less is usually suitably used. The refrigerant can be brought into direct contact with the molten resin or indirectly used as an internal refrigerant for the metal roll. When used as an internal refrigerant, oil or other known materials 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 original fabric is heated, for example, to a temperature equal to or higher than the softening temperature of the resin constituting the unstretched original fabric, for example, 1.5 (machine direction: longitudinal direction) in the MD. The film is stretched 3 times or more in the TD (Transverse Direction: transverse direction (width direction)). According to such a stretching process, a heat-shrinkable laminated film having the above-described predetermined heat shrinkage rate can be easily obtained.

  The draw ratio is appropriately selected according to the purpose, and if necessary, heat treatment (thermal relaxation treatment) can be performed after the drawing. According to the heat relaxation treatment, the molecular orientation of the heat-shrinkable laminated film is relaxed, so that dimensional changes during transportation and / or storage are further suppressed.

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

  The manufacturing method of this embodiment may include a crosslinking step of crosslinking the resin before or after stretching.

  When performing the crosslinking treatment, it is preferable to perform the crosslinking treatment by irradiation with energy rays before heating and stretching the resin. Thereby, the melt tension of the laminate in the heat stretching increases, and the stretching can be further stabilized. The stretched laminate may be irradiated with energy rays to crosslink the resin. Examples of energy rays to be used include ionizing radiation such as ultraviolet rays, electron beams, X-rays, and γ rays. Among these, an electron beam is preferable.

  In addition, surface treatment such as corona treatment, plasma treatment, ozone treatment, flame treatment, etc. can be performed on the surface of the laminate including the base material layer that has been heat-stretched by the above-described stretching step. Printability can be imparted to the film.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited only to these Examples. The melting point of the constituting resin and the interlayer strength, heat shrinkage rate, oxygen barrier property, warpage, and antifogging property of the laminated films of Examples and Comparative Examples were measured and evaluated by the following methods.

[Melting point of resin, temperature crystallization temperature]
In accordance with JIS-K-7210, 100 mg of resin was weighed, and the temperature was raised from 0 ° C. to 300 ° C. at a temperature rising rate of 10 ° C./min in order to cancel the thermal history of the resin, and the temperature falling rate was 10 ° C./min. The exothermic peak when the temperature was lowered from 300 ° C. to 0 ° C. was measured as the temperature-falling crystallization temperature, and the endothermic peak when the temperature was raised again from 0 ° C. to 300 ° C. at a temperature raising rate of 10 ° C./min. Was measured as the melting point.

[Heat shrinkage stress]
The measurement was performed according to ASTM-D2838. Immersion when the film is sampled into a strip of 90 mm in the length / width direction (measured length 50 mm + chuck grip 40 mm) and 10 mm in the width direction / length direction and immersed in an oil bath at a temperature of 80 ° C. Immediately after and after the immersion for 3 minutes, the maximum heat shrinkage stress was measured.

<Evaluation criteria>
A: The heat shrinkage stress in the width direction at 80 ° C. does not have a peak, and the maximum value of the heat shrinkage stress immediately after immersion is smaller than the maximum value of the heat shrinkage stress after 3 minutes, and the stress concentration can be suppressed. The heat shrinkage stress in the width direction at 0 ° C. has no peak, and the maximum value of the heat shrinkage stress immediately after the immersion is less than the maximum value of the heat shrinkage stress after 3 minutes, so that the stress concentration can be reduced. D: Heat shrinkage stress Has a peak, and stress concentration occurs during heat shrinkage.

[Heat shrinkage]
In accordance with ASTM-D2732, the laminated film was shrunk for 1 minute at temperatures of 80 ° C. and 120 ° C., and the thermal shrinkage rate of the laminated film was measured. It measured about the length direction and the width direction, respectively.

[Heat sealability]
The obtained laminated film was slit to a predetermined width, and a packaging speed of 30 using a TL-3000S manufactured by Ibaraki Seiki Co., Ltd. and an elliptical tray container for polypropylene top seal with 200 g of clay inside. Packaging was performed under the conditions of pack / min and heat seal pressure 0.4 MPa. The TD direction (width direction) of the laminated film was aligned with the minor axis direction of the tray container for packaging. The heat sealability was evaluated based on the following criteria by visually evaluating the surface roughness of the seal portion and the presence or absence of pinholes.

<Evaluation criteria>
A: The heat seal temperature range in which the surface of the seal part is not roughened and no pinholes are generated is 10 ° C. or higher, and the heat sealability is good.
D: The heat seal temperature range in which the surface of the seal part is not roughened and no pinholes are generated is less than 10 ° C., and the heat sealability is poor.

[Barrier properties]
Using an oxygen permeation analyzer manufactured by MOCON (OX-TRAN (registered trademark 2 / 21SH)), the oxygen transmission rate was measured at an oxygen condition of 65% RH and a measurement temperature of 23 ° C., and the measurement started for 3 hours. The oxygen barrier property was evaluated based on the value of oxygen permeability afterwards. The unit of measurement of oxygen permeability is “cc / m ² · day · atm”.

<Evaluation criteria>
A: The oxygen permeability is 50 cc / m ² · day · atm or less, and the gas barrier property is particularly good.
B: The oxygen permeability is 60 cc / m ² · day · atm or less, and the gas barrier property is good.
D: The oxygen permeability is larger than 60 cc / m ² · day · atm, and the gas barrier property is insufficient.

[Anti-fogging property]
The obtained laminated film was slit to a predetermined width, and packaging was performed using a polypropylene tray container into which 200 g of water at 20 ° C. was put. The antifogging property was evaluated by visually observing the appearance after 2 hours by placing the package in a refrigerator set at 5 ° C. and allowing it to stand.

<Evaluation criteria>
A: Water drops are not seen on the laminated film, and the appearance is good.
D: Since water droplets adhered to the laminated film, the inside of the film could not be confirmed, and the appearance was poor.

[Packaging finish]
The obtained laminated film was slit to a predetermined width, and packaged at a packaging speed of 40 packs / minute using a polystyrene tray container containing 200 g of clay inside using DW2002GP manufactured by Omori Machine Industry Co., Ltd. . Note that packaging was performed with the width direction of the laminated film aligned with the minor axis direction of the tray container. FB-800 manufactured by K & U System Co., Ltd. was used as the hot air tunnel, and the hot air temperature was set to 100 ° C. The finish of the package was visually evaluated by evaluating the appearance of the tray container according to the following criteria.

<Evaluation criteria>
A: The tray container is not deformed and has a beautiful finish.
B: Although a slight deformation | transformation is recognized by a tray container, it is a favorable finish.
D: Deformation is recognized in the tray container and the finish is poor.

Resins used in Examples and Comparative Examples are as follows.
PP1: Propylene copolymer (Sun Allomer Co., Ltd. PS522M, melting point 143 ° C.)
PP2: Propylene copolymer (Sun Allomer Co., Ltd. PL500A, melting point 161 ° C.)
PET1: Polyethylene terephthalate (Teijin Limited TRN-8580FC, melting point 250 ° C.)
Ny1: aliphatic polyamide (Ube Industries, Ltd. 5033B, melting point 220 ° C.)
Ny2: aromatic polyamide (Mitsubishi Gas Chemical Co., Ltd. S6007, melting point 235 ° C.)
PE1: Linear ultra-low density polyethylene (Dow Chemical Japan Co., Ltd. affinity 1880G, melting point 100 ° C.)
PE2: linear low-density polyethylene (Ube Maruzen Polyethylene Corporation Umerit 1540F, melting point 114 ° C.),
EVOH1: Saponified ethylene-vinyl alcohol copolymer (Nippon Synthetic Chemical Industry Co., Ltd. GH3804B, melting point 159 ° C., temperature drop crystallization temperature 129 ° C., ethylene content 38 mol%)
EVOH2: Saponified ethylene-vinyl alcohol copolymer (Kuraray H171, melting point 172 ° C., temperature drop crystallization temperature 148 ° C., ethylene content 38 mol%)
EVOH3: Saponified ethylene-vinyl alcohol copolymer (Kuraray Co., Ltd. E171B, melting point 162 ° C., temperature drop crystallization temperature 140 ° C., ethylene content 44 mol%)
GL1: Modified polyolefin resin (Mitsubishi Chemical Corporation Modic P565, melting point 143 ° C.)
GL2: Modified polypropylene resin (Mitsui Chemicals, Inc. Admer QF500, melting point 161 ° C.)
GL3: Modified polyethylene resin (Mitsui Chemicals, Inc. Admer NF587, melting point 120 ° C.)
EL1: Thermoplastic elastomer (Mitsui Chemicals, Inc. Toughmer XM7070, melting point 75 ° C.)
EL2: Thermoplastic elastomer (Mitsui Chemicals, Inc. Toughmer A0550S, melting point 50 ° C.)
AF1: Surfactant (RIKEN Vitamin Co., Ltd. L71D),

[Example 1]
Using a mixture of 97 mass% PP1 and 3 mass% AF1 as the base material layer, using EVOH1 as the gas barrier layer, using a mixture of 97 mass% PE1 and 3 mass% AF1 as the heat seal layer, GL2 is used as the adhesive layer (D), GL1 is used as the adhesive layer (E), and the layer arrangement is base material layer / adhesive layer / gas barrier layer / adhesive layer / heat seal layer. Was coextruded using an annular die so as to be 23/22/5/20/30, and then rapidly cooled and solidified with cold water to obtain a tube-shaped unstretched original fabric with uniform thickness accuracy in each layer. Specific layer structures are shown in Table 1.

  While heating this unstretched raw fabric in a stretching machine, it passes between two pairs of differential nip rolls, and air is injected to stretch 4 times in MD (length direction) and 4 times in TD (width direction) (area stretching ratio). 16 times) and heat treatment were performed to obtain a laminate film in which each layer was laminated. The evaluation results of the obtained heat-shrinkable laminated film are shown in Table 2.

[Examples 2 to 15]
A heat-shrinkable laminated film was obtained in the same manner as in Example 1 except that the composition of each layer was changed as shown in Table 1. The evaluation results of the obtained heat-shrinkable laminated film are shown in Table 2.

[Comparative Example 1]
Using a mixture of 97 mass% PP1 and 3 mass% AF1 as the base material layer, using EVOH2 as the gas barrier layer, using a mixture of 97 mass% PE1 and 3 mass% AF1 as the heat seal layer, GL2 is used as the adhesive layer (D), GL1 is used as the adhesive layer (E), and the layer arrangement is base material layer / adhesive layer / gas barrier layer / adhesive layer / heat seal layer. Was coextruded using an annular die so as to be 23/22/5/20/30, and then rapidly cooled and solidified with cold water to obtain a tube-shaped unstretched original fabric with uniform thickness accuracy in each layer. Specific layer structures are shown in Table 1.

  While heating this unstretched raw fabric in a stretching machine, it passes between two pairs of differential nip rolls, and air is injected to stretch 4 times in MD (length direction) and 4 times in TD (width direction) (area stretching ratio). 16 times) and heat treatment were performed to obtain a laminate film in which each layer was laminated. The evaluation results of the obtained heat-shrinkable laminated film are shown in Table 2.

[Comparative Example 2]
A heat-shrinkable laminated film was obtained in the same manner as in Example 1 except that the composition of each layer was changed as shown in Table 1. The evaluation results of the obtained heat-shrinkable laminated film are shown in Table 2.

  From the above results, it can be seen that the heat-shrinkable laminated films obtained in Examples 1 to 15 can suppress the stress concentration of heat-shrinkage stress and have a good packaging finish. Furthermore, it can be seen that it has excellent barrier properties, heat seal properties, and antifogging properties.

  On the other hand, from the above results, it can be seen that the heat-shrinkable laminated film obtained in Comparative Example 1 is not suitable for packaging because stress concentration of heat-shrinkage stress occurs. In the heat-shrinkable laminated film obtained in Comparative Example 2, it can be seen that the stress concentration of heat-shrinkage stress occurs and is not suitable for packaging as in Comparative Example 1.

  The heat-shrinkable laminated film of the present invention can suppress the stress concentration of heat-shrinkage stress and is excellent in barrier properties, and therefore is suitable for gas pack packaging for the purpose of long-term storage such as food and room temperature storage.

Claims (10)

The gas barrier layer comprises at least three layers of a base material layer (A), a gas barrier layer (B), and a heat seal layer (C), and the base material layer (A) contains at least a thermoplastic resin having a melting point of 130 ° C. or higher. (B) includes at least a saponified ethylene-vinyl alcohol copolymer, the heat seal layer (C) includes at least a polyethylene resin, and further satisfies the following conditions 1) to 3): Laminated film.
1) The melting point of the saponified ethylene-vinyl alcohol copolymer is 160 ° C. or lower, and the ethylene content is 40 mol% or lower.
2) The thermal shrinkage in the width direction at 80 ° C. is 5% or more. 3) The oxygen permeability is 60 cc / m ² · day · atm or less at 23 ° C. and 65% RH.   The heat-shrinkable laminated film according to claim 1, wherein a difference in supercooling temperature, which is a difference between a melting point of the gas barrier layer and a temperature-falling crystallization temperature, is 25 ° C or higher.   The heat shrinkable laminated film according to claim 1 or 2, wherein the heat shrinkage stress in the width direction at 80 ° C has no peak.   The heat-shrinkable laminated film according to any one of claims 1 to 3, wherein the total layer thickness is 30 µm or less.   The heat-shrinkable laminated film according to any one of claims 1 to 4, comprising an adhesive layer (D) between the gas barrier layer (B) and the heat seal layer (C), and comprising at least four layers. .   An adhesive layer (E) is included between the base material layer (A) and the gas barrier layer (B), and is composed of at least five layers. Further, the base material layer (A) / the adhesive layer (E) / the gas barrier. The heat-shrinkable laminated film according to claim 5, wherein the heat-shrinkable laminated film is laminated in the order of layer (B) / adhesive layer (D) / heat seal layer (C).   The heat-shrinkable laminated film according to any one of claims 1 to 6, wherein at least one of the base material layer, the gas barrier layer, and the heat seal layer contains a thermoplastic elastomer.   The heat-shrinkable laminated film according to claim 7, wherein the ratio of the thickness of the layer containing the thermoplastic elastomer is 30% or more with respect to the total layer.   The heat-shrinkable laminated film according to any one of claims 1 to 8, wherein the base material layer (A) contains a polypropylene resin.   The heat-shrinkable laminated film according to any one of claims 1 to 9, wherein a heat shrinkage rate in the length direction at 120 ° C is 30% or more.