JP6289261B2 - Heat shrinkable laminated film - Google Patents

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 a film having at least one layer made of a gas barrier resin composition, having both gas barrier properties and stretchability, and having excellent heat shrinkage characteristics.

JP 2000-117872 A

However, since the resin of both outer layers is substantially the same in Patent Document 1 and the surface with which the heat seal bar contacts does not have heat resistance, the film is fused to the seal bar during sealing, or the surface becomes rough. The problem is that heat seal defects such as these are likely to occur.
The problem to be solved by the present invention is to provide a heat-shrinkable laminated film that achieves stable heat-sealing properties, suppresses warping, 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) A substrate 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 comprising at least the layer (B) including at least a sealing layer containing a polyethylene resin and further satisfying the following conditions 1) and 2).
1) The difference between the thermal shrinkage rate of the layer (A) in either the length direction (MD) or the width direction (TD) and the thermal shrinkage rate of the layer (B) when peeled at the interface is 10% or less at 100 ° C.
2) It has a gas barrier layer containing an ethylene-vinyl alcohol copolymer resin , and the oxygen barrier 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 resin constituting the heat-shrinkable laminated film has a melting point of 170 ° C. or lower.
(3) The heat shrinkable laminate according to (1) or (2), wherein the difference between the maximum melting point of the resin constituting the base material layer and the maximum melting point of the resin constituting the seal layer is 30 ° C. or less. the film.
(4) The heat shrinkable laminated film according to any one of (1) to (3), wherein the heat shrinkage rate in the length direction of all layers is 30% or more at 100 ° C.
(5) The heat shrinkable laminated film according to any one of (1) to (4), wherein the heat shrinkage rate in the width direction of all layers is 5% or less at 60 ° C.
(6) The heat-shrinkable laminated film according to any one of (1) to (5), wherein the total layer thickness is 25 μm or less.
(7) The base material layer, a first adhesive layer containing a modified polyolefin resin, a gas barrier layer containing a saponified ethylene-vinyl alcohol copolymer, and a second adhesive containing a modified polyolefin resin And the sealing layer are laminated in this order, and the interface between the first adhesive layer and the gas barrier layer or the interface between the gas barrier layer and the second adhesive layer is 0.5 N / 15 mm. The heat-shrinkable laminated film according to any one of (1) to (6), which has the following interlayer strength.
(8) The heat-shrinkable laminated film according to (7) , wherein the melting point of the first adhesive layer is not more than the melting point of the second adhesive layer.
(9) The heat-shrinkable laminated film according to any one of (1) to (8), wherein a warp when left at 23 ° C. and 50% RH for 1 hour is 5 mm or less.

  According to the present invention, a layer containing a polypropylene resin is used as a base material layer with which a heat seal bar contacts, and a layer containing a polyethylene resin is used as a seal layer, so that the base material layer and the seal layer are The melting point difference can be increased, and the temperature range in which heat sealing can be stably performed can be expanded, so that sealing troubles in the automatic packaging machine can be reduced. Furthermore, the present invention comprises a layer (A) and a layer (B) laminated via an interface having an interlayer strength of 0.5 N / 15 mm or less, and the layer (A) when peeled at the interface Since the difference between the heat shrinkage ratio of the layer and the heat shrinkage ratio of the layer (B) is 10% or less at 100 ° C., it is possible to suppress warpage and improve the handling property of the packaging process. 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 the present embodiment has an interface having an interlayer strength of 0.5 N / 15 mm or less, and can be separated into a layer (A) and a layer (B) at the interface. The layer (A) includes at least a base material layer containing polypropylene, and the layer (B) includes at least a sealing layer containing polyethylene. In the heat-shrinkable laminated film, preferably, the base material layer and the seal are each located in the outermost layer. Further, in addition to the base material layer and the seal layer, a gas barrier layer, an adhesive layer, and the like, which will be described later, may 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. “//” represents an interface having an interlayer strength of 0.5 N / 15 mm or less, and at this interface, the layer (A) and the layer (B) can be separated.
Base material layer // gas barrier layer / sealing layer / base material layer / gas barrier layer // sealing layer / base material layer // adhesion layer / gas barrier layer / sealing layer / base material layer / adhesion layer / gas barrier layer // sealing layer -Base material layer / adhesive layer // gas barrier layer / adhesive layer / seal layer-Base material layer / adhesive layer / gas barrier layer // adhesive layer / seal layer Hereinafter, suitable layers of each layer constituting the heat-shrinkable laminated film An aspect is explained in full detail.

[Layer (A)]
The layer (A) includes at least a base material layer containing a polypropylene resin. Moreover, the said layer (A) can further contain the gas barrier layer containing the adhesive layer which expresses the adhesive strength between each layer, and / or saponified ethylene-vinyl alcohol copolymer, for example.
[Layer (B)]
The layer (B) includes at least a sealing layer containing a polyethylene resin. Moreover, the said layer (B) can further contain the gas barrier layer containing the adhesive layer which expresses the adhesive strength between each layer, and / or the saponified ethylene-vinyl alcohol copolymer, for example.
[Base material layer]
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.

The base material layer of this embodiment contains a polypropylene resin, preferably contains a polypropylene resin in a proportion of 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass. It contains in the ratio of% 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 propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-decene, 1-dodecene, -Tetradecene, 1-hexadecene, 1-octadecene, 1-eicosane 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 combination, and it is preferable to mix polypropylene and a propylene-α-olefin copolymer 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 polypropylene 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 the glycerin fatty acid ester is added, the content is preferably 0.1 to 5.0% by mass based on the 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.

[Seal layer]
The 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 seal layer can also serve as a stretched support layer when producing a heat-shrinkable laminated film.
Examples of the polyethylene resin constituting the 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, those having a density of 0.942 g / cm ³ or more are referred to as high-density polyethylene, and those having a density of 0.930 g / cm ³ or more and less than 0.942 g / cm ³ are referred to as medium-density polyethylene. Those having a density of 0.910 g / cm ³ or more and less than 0.930 g / cm ³ are referred to as low density polyethylene, and those having a density of less than 0.910 g / cm ³ are referred to as 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. Further, in the ethylene-α-olefin copolymer, the copolymer is constituted. The proportion of α-olefin in all monomers (based on the charged monomer) is preferably a soft copolymer of 5 to 30% by mass.
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.
The polyethylene resin preferably has a density of 0.860 to 0.925 g / cm ² and more preferably 0.870 to 0.920 g / cm ² from the viewpoint of further improving heat sealability at low temperatures. Preferably, it is 0.880 to 0.915 g / cm ² . 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 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 seal layer.

[Gas barrier layer]
The gas barrier layer of this embodiment (hereinafter simply referred to as “gas barrier layer”) 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 170 ° C. or less, more preferably 165 ° C., 160 More preferably, it is not higher than ° C.

Since the saponified ethylene-vinyl alcohol copolymer has a melting point of 170 ° 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 decreases as the ethylene content increases, and the ethylene content is preferably 30 to 50 mol%, more preferably 33 to 46 mol%. Preferably, 36-40 mol% is more preferable. When the ethylene content is in the above range, a film excellent in stretchability and gas barrier properties can be obtained.

As for the gas barrier property, the oxygen transmission rate is measured by setting the oxygen condition to 65% RH and the measurement temperature to 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 / atm / day or less, and is 50 cc / m ² / atm. / Day or less is preferable. Such a heat-shrinkable laminated film having gas barrier properties can sufficiently suppress the permeation of oxygen.

[Adhesive layer]
The adhesive layer of this embodiment (hereinafter, simply referred to as “adhesive layer”) is a layer that is disposed between two layers having low adhesive strength and adheres the two layers, and contains a known adhesive resin. It can be formed from a resin composition.
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, and ethylene-α olefin copolymers, and unsaturated boronic acids such as maleic acid and fumaric acid, or acid anhydrides thereof. A modified polymer obtained by graft copolymerization is preferable, and a modified polymer obtained by graft copolymerization of maleic anhydride to an ethylene homopolymer, an ethylene-propylene copolymer, or an ethylene-α-olefin copolymer is more preferable. Is 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 provided between the base material layer and the gas barrier layer and a second adhesive layer provided between the gas barrier layer and the seal layer may be included.
By adjusting the residual stress due to the molecular orientation of the adhesive layer, it can play a role of suppressing warpage, and can also play a role as a stretched support layer in the production of a heat-shrinkable laminated film.

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 the other thermoplastic resin, for example, the above-mentioned polypropylene resin and / or polyethylene resin can be mixed and used.
The warp of the heat-shrinkable laminated film is preferably 5 mm or less, more preferably 4 mm or less, and even more preferably 3 mm or less when left to stand at 23 ° C. and 50% RH for 1 hour. According to such a heat-shrinkable laminated film, good handling properties can be achieved in the packaging process.

  In order to achieve the warpage within the above range, the heat-shrinkable laminated film has a heat shrinkage ratio of the layer (A) and the layer (B) which are delaminated at the interface having an interlayer strength of 0.5 N / 15 mm or less. Warpage can be suppressed when the difference from the thermal shrinkage is 10% or less at 100 ° C. Preferably it is 7% or less, More preferably, it is 5% or less. In addition, the difference between the thermal shrinkage rate of the layer (A) and the thermal shrinkage rate of the layer (B) is that either the length direction (hereinafter also referred to as MD) or the width direction (hereinafter also referred to as TD). It is preferably 10% or less at 100 ° C., and more preferably 10% or less in either the length direction or the width direction.

In the case of a laminate such as a heat-shrinkable laminate film, residual stress may remain in the molded product because various forces are applied to the molten resin during the molding process. Residual stress includes strain caused by molecular orientation and strain caused by elastic deformation of molecules generated at the stage of solidification, and varies depending on the resin composition and molding conditions. Here, for example, since the conventional laminated film has various forming processes such as heat stretching and dry lamination, the residual stress of each layer is biased, and as a result, the entire laminated film may be warped.
On the other hand, the heat-shrinkable laminated film including the layer (A) and the layer (B) having a small difference in heat shrinkage rate reduces the bias of residual stress generated between the layers, and warps the entire heat-shrinkable laminated film. It can be sufficiently suppressed.

  In this embodiment, when the difference between the maximum melting point of the resin constituting the base material layer and the maximum melting point of the resin constituting the seal layer is 30 ° C. or less, the heat shrinkage of the layer (A) and the layer (B) The difference in rate can be reduced, and the difference in melting point is more preferably 25 ° C. or less, and further preferably 20 ° C. or less. In the case of such a laminated body, the unevenness of the residual stress generated between the layers can be reduced, and the warp of the entire heat-shrinkable laminated film can be sufficiently suppressed.

  The reason for the above effect is not necessarily clear, but is considered as follows. In other words, the heat-shrinkable properties of heat-shrinkable laminated films appear when the amorphous part stretched by the molecular orientation of the constituent resin shrinks to return to the non-oriented state, whereas the crystal part melts. It plays the role of keeping the shrinkage of the amorphous part close to the temperature. That is, by reducing the maximum melting point difference between the resins constituting the layer (A) and the layer (B), the difference in thermal shrinkage between the layer (A) and the layer (B) can be reduced. Conceivable.

  In the present embodiment, it is possible to further suppress warpage by laminating at least two layers of the layers constituting the heat-shrinkable laminated film by a coextrusion method. For example, layer (A) and layer (B) are formed by laminating five layers of base material layer / first adhesive layer / gas barrier layer / second adhesive layer / seal layer in the order described above by the coextrusion method. The difference in heat shrinkage ratio can be further reduced. When the layers are laminated by the coextrusion method in the order described above, for example, the layer (A) is a base layer, a first adhesive layer and a gas barrier layer, and the layer (B) is a second adhesive layer and a sealing layer. Can be peeled off.

  From the viewpoint of suppressing warpage, the melting point of the first adhesive layer is preferably equal to or lower than the melting point of the second adhesive layer. The first adhesive layer preferably contains a modified polyolefin resin having a melting point of 130 ° C. or lower, more preferably contains a modified polyolefin resin having a melting point of 125 ° C. or lower, and contains a modified polyethylene resin having a melting point of 125 ° C. or lower. More preferably. Further, the second adhesive layer preferably contains a modified polyolefin resin having a melting point of 170 ° C. or less, more preferably contains a modified polyolefin resin having a melting point of 165 ° C. or less, and a modified polyolefin resin having a melting point of 160 ° C. or less. It is more preferable to contain. Further, the melting point of the second adhesive layer is preferably 15 ° C. or higher, more preferably 20 ° C. or higher, and further preferably 25 ° C. or higher than the melting point of the first adhesive layer. When the adhesive layer is arranged as described above, it is possible to adjust the residual stress due to the molecular orientation of the adhesive layer, and thus it is possible to realize a heat-shrinkable stretched laminated film with good handling that suppresses warpage.

  Further, when the heat-shrinkable laminated film is laminated by a dry lamination method or the like, the interlayer strength tends to decrease the antifogging property due to the influence of the anchor coat layer. It is preferable to laminate the layer (A) and the layer (B) by a method. Furthermore, when laminating by the coextrusion method, from the viewpoint of antifogging properties, the interlayer strength at the interface between the layer (A) and the layer (B) is preferably 0.5 N / 15 mm or less, and 0.4 N / mm or less. It is more preferable that it is 0.3 N / 15 mm or less. In order to suppress delamination, the interlayer strength may be 0.1 N / 15 mm or more. The heat-shrinkable film laminated through the interface having such interlayer strength can achieve excellent antifogging properties and can be finished into a package having a good appearance.

  Moreover, it is preferable that the heat-shrinkable laminated film of this embodiment is 30% or more at 100 degreeC in the length direction, and the heat-shrink rate measured based on measuring method ASTM-D2732 is 35% or more. It is more preferable that both the length direction and the width direction are 35% or more at 100 ° C. 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. As a heat shrink condition that can achieve a heat shrinkage ratio of 30% or more, the heat shrink temperature is preferably 100 ° C. or lower, more preferably 95 ° C. or lower, and further preferably 90 ° C. or lower. When the heat shrink temperature that can achieve a heat shrinkage rate of 30% or higher is 100 ° C. or lower, it is possible to suppress the container deformation of the tray with a high expansion ratio that is easily deformed by heat in the shrinking process at the time of packaging. Finished packaging can be obtained.

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 170 ° C. or lower, more preferably 165 ° C., and further preferably 160 ° C. or lower. preferable. If the melting point of the resin constituting the heat-shrinkable laminated film is 170 ° C. or lower, relaxation of molecular orientation is promoted, so that good heat-shrinkability suitable for shrinkage can be expressed.
The heat shrinkable laminated film preferably has a heat shrinkage rate in the width direction of 5% or less at 60 ° C., and more preferably 5% or less in both the length direction and 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 to 25 μm, more preferably 6 to 23 μm, and further preferably 7 to 20 μm. 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 23 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 to 15% of the total thickness of the heat-shrinkable laminated film, more preferably 3 to 10%, and even more preferably 4 to 8%. If the thickness of the gas barrier layer is reduced from 2% of the total thickness, sufficient gas barrier performance tends not to be exhibited, 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 the present embodiment comprises a step of laminating a laminate having at least two resin layers (hereinafter sometimes referred to as “unstretched original fabric”) by a coextrusion method 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, and stretched to, for example, MD 1.5 times or more and TD 3 times or more. 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.
The obtained heat-shrinkable laminated film was peeled into layer (A) and layer (B) using an adhesive tape.

[Melting point of constituent resin]
100 mg of resin is weighed in accordance with JIS-K-7210, and the temperature is raised from 0 ° C. to 200 ° C. under the condition of a temperature rising rate of 10 ° C./min to cancel the heat history of the resin, and the temperature falling rate is 10 ° C./min. After the temperature was lowered from 200 ° C. to 0 ° C. under the conditions described above, the melting point when the temperature was raised from 0 ° C. to 200 ° C. again at the temperature raising rate of 10 ° C./min was measured and evaluated.

[Interlayer strength]
The interlayer strength between the layer (A) and the layer (B) of the obtained heat-shrinkable laminated film is 15 mm wide under an environment of 23 ° C. and 50% RH using an autograph manufactured by Shimadzu Corporation. Using the slit sample, a T-type peel test was performed under the conditions of a sample length of 50 mm, a chuck interval of 10 mm, and a tensile speed of 300 mm / min.
Furthermore, the thermal contraction rate at 100 ° C. was measured for each of the layer (A) and the layer (B) in the same manner as the following thermal contraction rate measurement method.

[Heat shrinkage]
In accordance with ASTM-D2732, the laminated film was shrunk at a temperature of 100 ° C. and 60 ° C. for 1 minute, and the thermal shrinkage rate of the laminated film was measured. Each of the length direction and the width direction was measured, and the average value was used as the heat shrinkage rate.

[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 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 where the surface of the seal part is not rough 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 rough and pinholes are not 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 / atm / day”.
<Evaluation criteria>
A: Oxygen permeability is 50 cc / m ² / atm / day or less and gas barrier property is better B: Oxygen permeability is 60 cc / m ² / atm / day or less and gas barrier property is better D: Oxygen permeability is Greater than 60cc / m ² / atm / day, insufficient gas barrier properties

[warp]
After heat-shrinkable laminated film cut to MD300mm and TD300mm for 1 hour in a 23 ° C 50% RH environment, MD250mm incisions were made at TD100mm intervals, and the height rising from the horizontal position of the incision part at MD125mm was measured. Then, the amount of warpage was obtained. The arithmetic average value of the measurement results at the two notches was calculated, and the measurement was performed using this arithmetic average value as a warp.
<Evaluation criteria>
A: The warp of the laminated film is 3 mm or less, and the handling is even better B: The warp of the laminated film is 4 mm or less, and the handling is better C: The warp of the laminated film is 5 mm or less, and the handling is good D: Lamination Film warpage is greater than 5mm, making handling difficult

[Anti-fogging property]
The obtained laminated film was slit to a predetermined width and packaged using a polypropylene tray container in which 200 g of water at 20 ° C. was put. The anti-fogging property was evaluated by putting the package into a refrigerator set at 5 ° C. and static, and visually evaluating the appearance after 2 hours according to the following criteria.
<Evaluation criteria>
A: Water droplets 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 115 ° 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: Deformation (distortion and warpage) is not recognized in the tray container, and there is little corner residue.
B: Deformation (distortion or warping) is not recognized in the tray container, but a corner residue is recognized.
D: Deformation (distortion or warping) is observed in the tray container, and there is a lot of corner residue due to insufficient shrinkage.

Resins used in Examples and Comparative Examples are as follows.
PP1: Propylene-based copolymer (Sun Allomer Co., Ltd. PS522M, melting point 145 ° C.)
PP2: Propylene copolymer (Sun Allomer Co., Ltd. PF621S, melting point 143 ° C.)
PP3: propylene copolymer (Sun Allomer Co., Ltd. 5C37F, melting point 142 ° C.),
PP4: Propylene copolymer (Sun Allomer Co., Ltd. PL500A, melting point 161 ° C.),
PE1: Linear ultra-low density polyethylene (Dow Chemical Japan Co., Ltd.) affinity 1880G, melting point 100 ° C.)
PE2: linear low-density polyethylene (Prime Polymer SP2020, melting point 116 ° C.),
PE3: linear low-density polyethylene (Ube Maruzen Polyethylene Co., Ltd. Umerit 1520F, melting point 118 ° C.),
PE4: High-pressure method low-density polyethylene (Asahi Kasei Chemicals Corporation M2102, melting point 112 ° C.),
EVOH1: Saponified ethylene-vinyl alcohol copolymer (Nippon Synthetic Chemical Industry Co., Ltd., EP-E105A, melting point 165 ° C., ethylene content 44 mol%),
EVOH2: Saponified ethylene-vinyl alcohol copolymer (Kuraray SP292, melting point 165 ° C, ethylene content 44 mol%),
EVOH3: Saponified ethylene-vinyl alcohol copolymer (Nippon Synthetic Chemical Industry Co., Ltd. GH 3804B, melting point 159 ° C., ethylene content 38 mol%)
EVOH4: Saponified ethylene-vinyl alcohol copolymer (Nippon Synthetic Chemical Industry Co., Ltd. AT4403, melting point 164 ° 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.)
GL4: Modified polypropylene resin (Mitsui Chemicals, Inc. Admer QF580, melting point 145 ° C.),
GL5: Anchor coat agent (Unitika Arrow Base SB1200)
AF1: Surfactant (RIKEN Vitamin Co., Ltd. L71D),
AF2: surfactant (RIKEN Vitamin Co., Ltd. B205),

[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 sealing layer, GL1 is used as one adhesive layer, GL2 is used as the second adhesive layer, and the layer arrangement is a base layer / first adhesive layer / gas barrier layer / second adhesive layer / sealing layer with respect to all layers of each layer After co-extrusion using a circular die so that the ratio (%) is 22.5 / 22.5 / 10.0 / 22.5 / 22.5, the layers are quenched and solidified with cold water, and each layer has a uniform thickness. A tube-shaped unstretched raw fabric with high accuracy was obtained. Specific layer structures are shown in Table 1.
While heating this unstretched raw fabric in a stretching machine, it is passed between two pairs of differential nip rolls, injected with air, stretched 4 times in MD, stretched 4 times in TD (16 times in area stretch ratio), and heat-treated, A laminate film in which each layer was laminated was obtained.
In the obtained heat-shrinkable laminated film, the layer (A) comprises a base material layer / first adhesive layer / gas barrier layer, the layer (B) comprises a second adhesive layer / sealing layer, and the interlayer strength is 0. 3 N / 15 mm. Table 4 shows the evaluation results of the obtained heat-shrinkable laminated film.

[Examples 2 to 11]
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 Tables 1 to 3. The evaluation result of the obtained heat-shrinkable laminated film is shown in Tables 4-6.

[Comparative Example 1]
As shown in Table 3, PE3 is used as the base material layer and the sealing layer, EVOH1 is used as the gas barrier layer, GL3 is used as the first adhesive layer, GL4 is used as the second adhesive layer, and the layer arrangement is based on The layer ratio (%) of each layer in the material layer / first adhesive layer / gas barrier layer / second adhesive layer / sealing layer is 22.5 / 22.5 / 10.0 / 22.5 / 22. Coextruded using an annular die so as to be 5, and then rapidly cooled and solidified with cold water to obtain a tube-shaped unstretched original fabric with uniform thickness accuracy in each layer.
While heating this unstretched raw fabric in a stretching machine, it is passed between two pairs of differential nip rolls, injected with air, stretched 4 times in MD, stretched 4 times in TD (16 times in area stretch ratio), and heat-treated, A laminate film in which each layer was laminated was obtained.
In the obtained heat-shrinkable laminated film, the layer (A) comprises a base material layer / first adhesive layer / gas barrier layer, the layer (B) comprises a second adhesive layer / sealing layer, and the interlayer strength is 0. It was 5 N / 15 mm. The evaluation results of the obtained heat-shrinkable laminated film are shown in Table 6.

[Comparative Example 2]
As a base material layer, a mixture of 97% by mass of PP4 and 3% by mass of AF1 is used, as a seal layer, a mixture of 97% by mass of PE4 and 3% by mass of AF1 is used, and EVOH1 is used as a gas barrier layer. Using GL2 as the adhesive layer and GL3 as the second adhesive layer, a tube-shaped unstretched original fabric having a uniform thickness accuracy was obtained for each layer.
While heating this unstretched raw fabric in a stretching machine, it is passed between two pairs of differential nip rolls, injected with air, stretched 4 times in MD, stretched 4 times in TD (16 times in area stretch ratio), and heat-treated, A laminate film was obtained.
The obtained heat-shrinkable laminated film was laminated in the order of base material layer / first adhesive layer / gas barrier layer / second adhesive layer / seal layer, and layer (A) was base material layer / first adhesive. The layer (B) was composed of a second adhesive layer / sealing layer, and the interlayer strength was 0.5 N / 15 mm. The evaluation results of the obtained heat-shrinkable laminated film are shown in Table 6.

[Comparative Example 3]
As a base material layer, a mixture of 95% by weight of PP4, 3% by weight of AF1, and 2% by weight of AF2 is used, and a seal layer is a mixture of 95% by weight of PE4, 3% by weight of AF1, and 2% by weight of AF2. Using EVOH1 as a gas barrier layer, a tube-shaped unstretched original fabric having a uniform thickness accuracy was obtained for each layer.
While heating this unstretched raw fabric in a stretching machine, it is passed between two pairs of differential nip rolls, injected with air, stretched 4 times in MD, stretched 4 times in TD (16 times in area stretch ratio), and heat-treated, Each layer was laminated by a dry laminating method using GL5 as an adhesive layer to obtain a laminate film.
The obtained heat-shrinkable laminated film is laminated in the order of the base material layer / first adhesive layer / gas barrier layer / second adhesive layer / seal layer, and peeling to the layer (A) and the layer (B) It was impossible. The evaluation results of the obtained heat-shrinkable laminated film are shown in Table 6.

From the above results, the heat-shrinkable laminated films obtained in Examples 1 to 11 have good sealing properties, warpage is suppressed, excellent antifogging properties, and the finish of the package is good. I understand.
On the other hand, it can be seen from the above results that the heat-shrinkable laminated film obtained in Comparative Example 1 is not suitable because a sealing failure is likely to occur during heat sealing. It can be seen that the heat-shrinkable laminated film obtained in Comparative Example 2 is unsuitable because the warp has occurred and handling during packaging is poor. It can be seen that the film obtained in Comparative Example 3 has a poor anti-fogging property because it is laminated by a laminating method and is not suitable for packaging.

  The heat-shrinkable laminated film of the present invention achieves stable heat-sealability, suppresses warping, and has excellent barrier properties, and is suitable for gas pack packaging for the purpose of long-term storage of foods, etc. Yes.

Claims (9)

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) comprises at least a base material layer containing a polypropylene resin, The layer (B) includes at least a seal layer containing a polyethylene resin, and further satisfies the following conditions (1) and (2).
(1) The difference between the thermal shrinkage rate of the layer (A) in either the length direction (MD) or the width direction (TD) and the thermal shrinkage rate of the layer (B) when peeled at the interface is 10% or less at 100 ° C.
(2) It has a gas barrier layer containing an ethylene-vinyl alcohol copolymer resin , and the oxygen barrier 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 the resin constituting the heat-shrinkable laminated film has a melting point of 170 ° C. or lower.   The heat-shrinkable laminated film according to claim 1 or 2, wherein the difference between the maximum melting point of the resin constituting the base layer and the maximum melting point of the resin constituting the seal layer is 30 ° C or less.   The heat-shrinkable laminated film according to any one of claims 1 to 3, wherein the heat shrinkage rate in the length direction of all layers is 30% or more at 100 ° C.   The heat-shrinkable laminated film according to any one of claims 1 to 4, wherein the heat shrinkage rate in the width direction of all layers is 5% or less at 60 ° C.   The heat-shrinkable laminated film according to any one of claims 1 to 5, wherein the total layer thickness is 25 µm or less.   The base layer, a first adhesive layer containing a modified polyolefin resin, a gas barrier layer containing an ethylene-vinyl alcohol copolymer saponified product, a second adhesive layer containing a modified polyolefin resin, The seal layers are laminated in this order, and the interface between the first adhesive layer and the gas barrier layer or the interface between the gas barrier layer and the second adhesive layer is 0.5 N / 15 mm or less. The heat-shrinkable laminated film according to any one of claims 1 to 6, which has strength. The heat-shrinkable laminated film according to claim 7 , wherein the melting point of the first adhesive layer is not more than the melting point of the second adhesive layer.   The heat-shrinkable laminated film according to any one of claims 1 to 8, wherein a warp when left at 23 ° C and 50% RH for 1 hour is 5 mm or less.