JP5453129B2 - Heat-shrinkable stretched laminated film, method for producing the same, and top seal package - Google Patents

Description

  The present invention relates to a heat-shrinkable stretched laminated film suitable for packaging by a packaging machine, and mainly suitable for use in the food packaging field where gas barrier properties and odor barrier properties are required, a method for producing the same, and a top seal package. .

  Various types of plastic packaging containers have been developed and proposed for packaging foods and drinks, pharmaceuticals, cosmetics, and the like. Furthermore, in recent years, due to environmental considerations, awareness of reducing the disposal of unsold foods at supermarkets and convenience stores has increased, and gas pack packaging for the purpose of long-term storage of foods and storage at room temperature has attracted attention.

Conventionally, a film in which a polyamide-based resin that is a barrier resin and a polyolefin-based resin having a low-temperature sealing property are laminated is known as a packaging film to be used.
For example, Patent Document 1 discloses a stretched film obtained by laminating both surface layers as a polypropylene resin and the intermediate layer as a layer containing an aromatic polyamide resin.
In Patent Document 2, at least one outer layer is a layer made of a polypropylene resin, and an intermediate layer is laminated as a layer made of a polyamide resin composition containing an aromatic diamine copolymer and an aromatic diamine polymer. A biaxially stretched film is disclosed.
In Patent Document 3, a modified polyolefin resin layer, a polyamide resin layer, an ethylene-vinyl alcohol copolymer resin layer, a modified polyolefin resin layer, and an ethylene-α-olefin copolymer resin layer are laminated in this order. Thus, a stretched film that has been crosslinked to impart heat resistance is disclosed.

JP 09-29908 A JP 2000-79669 A JP 2007-185910 A

However, as described in Patent Documents 1 to 3, when a film having a good barrier property, particularly a film having a nylon resin layer, is stretched, it is packaged when the packaged item is a soft item or a container with a strong strong heat shrinkage stress. Things may be deformed.
Furthermore, in Patent Documents 1 and 2, the resin of both outer layers is substantially the same, and if the surface that the heat seal bar contacts does not have heat resistance, the film is fused to the seal bar at the time of sealing, or The problem is that defects such as rough surfaces tend to occur.
In Patent Document 3, heat resistance is imparted to the outer layer, which is a non-sealing surface, by applying electron beam crosslinking treatment, but there are cases where cost and maintenance work are required.

  In addition, as a consideration for the environment, there is a growing awareness of reducing the amount of film discarded for food packaging. Pillow shrink packaging, which is a conventional general-purpose packaging method, is excellent in that the package has an excellent appearance and can be applied to any container, but has a drawback in that the film uses a large area. Therefore, there is a need for a film for top seal packaging that serves as a lid for a tray container by directly heat-sealing the top surface of the tray container to be packaged.

  The problem to be solved by the present invention is that heat-shrinkable stretching that can be used as a cover material of a top-seal packaging body while being capable of being top-sealed with good heat-sealing properties while suppressing deformation of the container in the heat-shrinking step. It is providing a laminated film, its manufacturing method, and a top seal package provided with the said film.

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 surface layer (A) containing a propylene-based copolymer having a melting point of 140 ° C. or lower;
An adhesive layer (B);
A core layer (C) containing an aromatic polyamide copolymer;
An adhesive layer (D);
A surface layer (E) containing 45 to 80% by weight of a propylene homopolymer having a melting point of 155 ° C. or higher, and 55 to 20% by weight of a propylene copolymer having a melting point of 140 ° C. or lower;
Is a heat shrinkable stretched laminated film comprising
The heat shrinkage rate measured according to the measurement method ASTM-D2732 is 5 to 20% at 100 ° C.,
A heat-shrinkable stretched laminated film having a maximum heat shrinkage stress in the TD direction measured in accordance with a measuring method ASTM-D2838 of 0.4 N / cm or less at 100 ° C.
2. 1. The tensile elastic modulus of the core layer (C) is 3000 MPa or more, and the thickness of the core layer (C) is 1 to 5 μm. The heat shrinkable stretched laminated film described in 1.
3. 1. Tensile elastic modulus is 700 to 1600 MPa and thickness is 10 to 25 μm. Or 2. The heat shrinkable stretched laminated film described in 1.
4). 1. ~ 3. A method for producing a heat-shrinkable stretched laminated film according to any one of
A laminate in which the surface layer (A), the adhesive layer (B), the core layer (C), the adhesive layer (D), and the surface layer (E) are laminated by a coextrusion method is used in an MD direction and a TD direction. A production method in which biaxial stretching is performed at a stretching ratio of 5.0 to 8.0.
5. 1. ~ 3. A top seal package comprising the heat-shrinkable stretched laminated film according to any one of the above.

  According to the present invention, when the heat-shrinkable stretched laminated film has the above-described configuration, one surface layer (heat-resistant layer) containing a resin having a relatively high melting point is used as a film surface with which a heat seal bar contacts in top-sealed packaging. In addition, it is possible to increase the difference in melting point between the heat-resistant layer and the other surface layer (sealing layer) containing a resin having a relatively low melting point. It can be enlarged, and sealing troubles in the automatic packaging machine can be reduced. Furthermore, since the heat-shrinkable stretched laminated film has a low shrinkage stress, it can be top-sealed while suppressing deformation of the tray container in the heat-shrinking process, and has an appropriate rigidity. It can be used as a lid for a package. In addition, the present invention has a tight and beautiful finish, is excellent in hermetic sealing properties, pinhole resistance, alcohol resistance and antifogging properties, and is low cost and environmentally friendly. Furthermore, since this invention is excellent in barrier property, it is suitable for packaging of food with strong smell 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 stretched laminated film of this embodiment includes a surface layer (A), an adhesive layer (B), a core layer (C), an adhesive layer (D), and a surface layer (E) in this order.

  The surface layer (A) is composed of a propylene copolymer having a melting point of 140 ° C. or lower. The surface layer (A) functions as a seal layer when heat-sealing. The propylene-based copolymer is an inexpensive resin having an appropriate rigidity, and is suitable as a sealant resin for a film for use as a lid material for top seal packaging. When the melting point of the propylene-based copolymer exceeds 140 ° C., the heat seal temperature is set high, and small wrinkles and pinholes are likely to occur, and the power consumption is likely to increase.

  Specific examples of the propylene-based copolymer of the surface layer (A) include a copolymer of propylene and ethylene, a copolymer of propylene and an α-olefin having 4 to 8 carbon atoms, and propylene, ethylene and 4 to 4 carbon atoms. 8 is a copolymer with an α-olefin, and may be a random copolymer or a block copolymer.

  Specific examples of the α-olefin having 4 to 8 carbon atoms include 1-butene, 4-methyl-pentene, 1-pentene, 1-hexene and 1-octene, but are not particularly limited thereto. These copolymerization components may be used alone or in combination of two or more. Among these, a propylene-ethylene copolymer and a propylene-ethylene-1-butene copolymer are preferable because they are relatively inexpensive and easy to produce a film of good quality with little thickness variation.

The propylene-based copolymer of the surface layer (A) has an melt flow rate value (hereinafter also referred to as MFR _{230 ° C.} ) measured according to JIS-K-7210 (temperature 230 ° C., load 2.16 kgf). It is preferable that it is 0.5-8.0 at the point which is excellent in the property, the stability of extending | stretching, and the kneadability of an antifogging agent. A polypropylene resin modifier may be added to the surface layer (A). Examples of the polypropylene-based resin modifier include 1-butene, ethylene-based elastomer, propylene-based elastomer, and the like, and those having a melting point of 140 ° C. or less are preferable in order to maintain heat sealability. By adding the modifier, when the film is formed by biaxial stretching, the stretching orientation degree of the surface layer (A) can be suppressed, and heat shrinkage stress can be suppressed.

  Propylene copolymers having a melting point of 140 ° C. or lower may be used alone or in combination of two or more. The content of the propylene copolymer having a melting point of 140 ° C. or lower is preferably 50 to 100% by weight, more preferably 60 to 100% by weight, and further 70 to 100% by weight based on the entire surface layer (A). preferable.

In order to impart antifogging properties to the heat-shrinkable stretched laminated film of the present embodiment, a glycerin fatty acid ester can be added to the surface layer (A). When the glycerin fatty acid ester is added, the content is preferably 0.1 to 5.0% by weight based on the entire surface layer (A).
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 preferable because it is difficult to inhibit the slipperiness and optical properties of the film and is easy to use.

  Furthermore, you may add liquid additives, such as antioxidant, an antistatic agent, petroleum resin, and mineral oil, to the surface layer (A) to such an extent that antifogging property is not impaired.

The adhesive layer (B) is a layer having a function of adhering the surface layer (A) and the core layer (C). As the adhesive resin used for the adhesive layer (B), a known resin that can bond a polypropylene resin and a polyamide resin can be used.
Examples of the adhesive resin include a modified polypropylene resin obtained by grafting at least one monomer selected from a polyolefin resin, an α, β-unsaturated carboxylic acid and a derivative thereof.

  The core layer (C) is composed of an aromatic polyamide copolymer. The aromatic polyamide copolymer used for the core layer (C) may be used alone or in combination of two or more. The aromatic polyamide copolymer means crystalline nylon (polyamide) having an aromatic ring in the main chain. Specific examples thereof include, for example, metaxylylene adipamide (MXD6Ny), metaxylene Examples include polycondensates of range amine, adipic acid and isophthalic acid. Aromatic polyamide-based copolymers have better gas barrier properties and odor barrier properties than aliphatic nylons such as nylon 6 and nylon 6/66, and have strength such as pinhole resistance, stretchability, and moldability. It is good, suppresses changes in color tone and deterioration of the object to be packaged by light, and further has high rigidity, and is therefore suitable as a material constituting the core layer (C). The content of the aromatic polyamide-based copolymer is preferably 90 to 100% by weight based on the entire core layer (C).

  The tensile modulus of the core layer (C) composed of the aromatic polyamide copolymer is preferably 3000 MPa or more. In this case, even if the core layer (C) is thinned, the rigidity as a lid for the tray container can be maintained. Moreover, since there exists a tendency which becomes weak with respect to an impact when a tensile elasticity modulus is too large, it is preferable that the tensile elasticity modulus of a core layer (C) is 5000 Mpa or less. In addition, a tensile elasticity modulus can be measured based on ASTM-D882.

  The thickness of the core layer (C) is preferably 1 to 5 μm. In general, a barrier resin such as a polyamide resin is more expensive than a polyolefin resin, so that the production cost can be reduced by setting the thickness to 5 μm or less. Moreover, it is easy to have oxygen barrier performance required for rigidity and gas pack packaging by setting it as 1 micrometer or more.

  The adhesive layer (D) is a layer having a function of adhering the core layer (C) and the surface layer (E). In order to adhere the propylene-based resin and the polyamide-based resin in the same manner as the adhesive layer (B) described above. These known adhesive resins are used. Note that it is not always necessary to use the same type of adhesive layer (B) and adhesive layer (D) at the same time.

  The surface layer (E) is composed of 45 to 80% by weight of a propylene homopolymer having a melting point of 155 ° C. or higher and 55 to 20% by weight of a propylene copolymer having a melting point of 140 ° C. or lower, based on the entire surface layer (E). It is a heat-resistant layer containing.

  Here, the propylene copolymer used for the surface layer (E) is the same as the propylene copolymer used for the surface layer (A), but it is not always necessary to use the same type for both layers. The surface layer (E) is preferably a layer having a melting point different from that of the surface layer (A). The larger the difference between the melting points of the surface layer (A) and the surface layer (E) (preferably 10 ° C. or higher, more preferably 20 ° C. or higher). ) It is possible to suppress packaging troubles such as surface roughness of the surface layer (E) contacting the seal bar, or heat seal of the seal bar and the surface layer (E). In addition, melting | fusing point of surface layer (A) and surface layer (E) can be measured with a differential scanning calorimeter (DSC), respectively.

  When the content of the propylene homopolymer having a melting point of 155 ° C. or higher is less than 45% by weight, the heat resistance of the surface layer (E) is lowered, and troubles such as pinhole generation and fusion to a seal bar are likely to occur. . On the other hand, if the content of the propylene homopolymer having a melting point of 155 ° C. or higher exceeds 80% by weight, the stretching stability at the time of film formation is lowered, and the curling of the film is likely to occur.

  Also, if a propylene homopolymer having a melting point of 155 ° C. or higher is not mixed with a propylene copolymer having a melting point of 140 ° C. or lower by 20% by weight or more, the film-forming stability is deteriorated, and the productivity and quality are lowered. It becomes easy. Furthermore, since the thermal contraction stress of the obtained film becomes large, when packaging is performed using the obtained film, the container of the package may be deformed. Further, when the propylene copolymer having a melting point of 140 ° C. or less is mixed in an amount exceeding 55% by weight, the heat sealability tends to be lowered.

The MFR _{230 ° C.} of the surface layer (E) is a propylene-based copolymer and a propylene homopolymer, each having a sufficient heat shrinkage ratio and excellent film productivity (extrusion moldability and stretching stability). It is preferably 5 to 8.0. In addition, a polypropylene resin modifier may be added to the surface layer (E). Examples of the polypropylene-based resin modifier include 1-butene, ethylene-based elastomer, propylene-based elastomer, and the like, but those having a melting point of 155 ° C. or higher are preferable in order to maintain heat resistance. By adding the modifier, when the film is formed by biaxial stretching, the stretching orientation degree of the surface layer (E) can be suppressed, and heat shrinkage stress can be suppressed. The addition amount of the polypropylene resin modifier is preferably 0 to 30% by weight based on the entire surface layer (E).

  Each of the layers (A) to (E) described above may contain various additives such as a plasticizer, an antioxidant, a colorant, an ultraviolet absorber, a lubricant, an inorganic filler, and a crystal nucleating agent.

  In order to obtain a package with a suitable finish when packaged using the heat-shrinkable stretched laminated film of the present embodiment, the heat shrinkage rate measured according to the measurement method ASTM-D2732 in the film is 100 ° C. It is necessary that the maximum heat shrinkage stress in the TD direction (lateral direction) measured in accordance with the measurement method ASTM-D2838 is 0.4 N / cm or less at 100 ° C. The reason why the temperature is set to 100 ° C. is that in the top seal packaging field, the temperature of the shrink tunnel that causes film shrinkage is around 100 ° C. The “TD direction” refers to the direction perpendicular to the film flow direction, that is, the width direction of the original roll, and the “MD direction” described later refers to the film flow direction, ie, the original roll. Point the winding direction.

  The heat-shrinkable stretched laminated film of the present embodiment requires that the heat shrinkage rate be 5% or more in order to obtain a tightly finished package in top seal packaging, and the heat shrinkage rate exceeds 20%. The tray container is deformed and the finish of the package tends to be lowered. The heat shrinkage rate is preferably 5 to 15%.

  In addition, the maximum heat shrinkage stress in the TD direction of the heat shrinkable stretched laminated film of the present embodiment is 0.4 N / at 100 ° C. in order to suppress the deformation of the tray container that occurs at the time of heat shrinking to a level that causes no practical problem. It must be cm or less, and 0.35 N / cm or less is preferable.

  Here, when top-sealing the tray container, the TD direction of the film is usually aligned with the lateral direction of the tray container (the short side direction in the rectangular container, the short axis direction in the elliptical container). In this case, the tray container tends to be largely deformed in the lateral direction due to the structure of the tray container at the time of heat shrinking. In the heat-shrinkable stretched laminated film of this embodiment, the maximum heat-shrinkage stress in the TD direction is 0.4 N / cm or less at 100 ° C. It can be suppressed to a level where there is no problem.

  The thickness of the heat-shrinkable stretched laminated film of this embodiment is preferably 10 to 25 μm. Since the heat shrinkage stress is almost proportional to the thickness, the thicker the film, the more the heat shrinkage stress increases and the tray container is easily deformed at the time of heat shrinking. Therefore, the film thickness is preferably 25 μm or less, more preferably 20 μm or less. . Moreover, if the thickness of a film is 10 micrometers or more, it will become moderate rigidity and is excellent in the touch feeling after packaging.

  The tensile elastic modulus (rigidity) of the heat-shrinkable stretched laminated film of this embodiment is preferably 700 to 1600 MPa. When the tensile modulus is 1600 MPa or less, resistance due to rigidity is small during thermal shrinkage, and sufficient shrinkage is easily obtained. When the tensile modulus is 700 MPa or more, it is easy to obtain an appropriate rigidity as a cover material for the top seal packaging. The tensile elastic modulus is more preferably 1000 to 1600 MPa. In addition, a tensile elasticity modulus can be measured based on ASTM-D882.

  The method for forming the heat-shrinkable stretched laminated film of the present embodiment is first extruded from a die by a known co-extrusion method such as a T-die type co-extrusion method or a circular die type co-extrusion method (A) to ( After laminating each layer of E), it is rapidly cooled to extract an unstretched original fabric (laminate).

  Next, the raw material on which the layers (A) to (E) are laminated as described above is heated and biaxially stretched under a temperature condition suitable for imparting orientation to form a multilayer film. Since it is easy to obtain a multilayer film having a maximum heat shrinkage stress at 100 ° C. of 0.4 N / cm or less, the stretching temperature is preferably 110 to 130 ° C., more preferably 115 to 130 ° C., and the stretching ratio is MD direction and TD direction. Each is preferably set to 5.0 to 8.0 times.

Moreover, it is preferable to perform heat processing, such as a hot air blowing type, a hot roller type, or an indirect heating type such as an infrared heater after stretching, alone or in combination. The above heat treatment tends to suppress the occurrence of curling of the film, which is unusable when used in a continuous packaging machine.
Furthermore, in order to improve printing suitability, surface treatment such as corona treatment or plasma treatment may be performed after stretching.

  Next, an example of a process for obtaining a top seal package using the heat-shrinkable stretched laminated film of the present embodiment as a packaging film will be described. First, the top surface of a plastic container (tray container) filled with an article to be packaged is directly covered with a packaging film, heat sealed with a heat seal bar, and simultaneously cut with a cutter blade to obtain individual packages. Next, a tightly finished package is obtained by heat-shrinking the film with a hot-air shrink tunnel whose temperature is adjusted to around 100 ° C. in advance. When the object to be packaged is in contact with the film, the contacted part is not shrunk with hot air, so steam or hot water may be used in combination.

  In the manufacturing method of the package of this embodiment, immediately before top-sealed packaging with a heat-shrinkable stretched laminated film, nitrogen, carbon dioxide, or a mixed gas thereof is sprayed toward the package, and the package is immediately packaged and sealed. By doing so, it can be packed in a gas pack. Gas pack packaging can prevent oxidative deterioration of the packaged item and has the effect of extending the shelf life of food.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited only to these Examples. The tensile elastic modulus, heat shrinkage rate, maximum heat shrinkage stress, oxygen barrier property, heat sealability, and finish of the package body of the laminated films of Examples and Comparative Examples were measured and evaluated by the following methods.

[Tensile modulus]
The entire laminated film and the tensile elastic modulus of the core layer (C) were measured according to ASTM-D882. The tensile elastic modulus of the core layer (C) was measured by obtaining a single layer film of the core layer (C) by sampling the laminated film with a tape or the like. It measured about MD direction (longitudinal direction) and TD direction (transverse direction), respectively, and the average value was used as a tensile elasticity modulus.

[Heat shrinkage]
Based on ASTM-D2732, the laminated film was shrunk for 10 minutes at a temperature of 100 ° C., and the thermal shrinkage rate of the laminated film was measured. It measured about MD direction and TD direction, respectively, and the average value was used as a heat contraction rate.

[Maximum heat shrinkage stress]
Based on ASTM-D2838, the heat shrink stress at 100 ° C. in the TD direction of the laminated film was measured. The measurement was continuously performed for 5 minutes, and the maximum value was used as the maximum heat shrinkage stress.

[Oxygen 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 / MPa / day”.

[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 done at packs / minute. The laminated film was packaged by aligning the TD direction with the minor axis direction of the tray container. 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>
◯: At the lower limit heat seal setting temperature at which the seal strength is 2 N / 15 mm width or more, the surface of the seal portion is not rough and no pinhole is generated.
X: At the lower heat seal setting temperature at which the seal strength is 2 N / 15 mm width or more, the surface of the seal portion is roughened or pinholes are generated.

[Package finish]
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 done at packs / minute. The laminated film was packaged by aligning the TD direction with the minor axis direction of the tray container. The hot air tunnel used BBT-600S manufactured by K & U System Co., Ltd., the hot air temperature was set to 100 ° C., the appearance was visually evaluated, and the finish of the package was evaluated according to the following criteria.
<Evaluation criteria>
○: No deformation (distortion or warping) is observed in the tray container, and there is little corner residue.
X: Deformation (distortion or warping) is recognized in the tray container, or there are many corners remaining due to insufficient shrinkage.

  Table 1 shows the abbreviations of the synthetic resins used in Examples and Comparative Examples.

[Example 1]
First, it melt-coextruded using the cyclic | annular 5-layer die with the layer structure shown in Table 2, Then, it solidified with the cold water of about 15 degreeC, and produced the tube-shaped unstretched original fabric of about 700 micrometers in total thickness. Next, the unstretched original fabric was biaxially stretched at a stretch ratio shown in Table 2 by an inflation method, and then heat-treated with a 90 ° C. heating roll and a 100 ° C. infrared heater to obtain a final thickness of about 20 μm. A coextrusion stretched laminated film was obtained.
The evaluation results of the obtained laminated film are shown in Table 2. The obtained laminated film was excellent in rigidity, had a low maximum thermal shrinkage stress in the TD direction, and had a good finish after packaging.

[Examples 2 to 4]
The resin shown in Table 2 was used in the same manner as in Example 1 except for the resin composition ratio and the draw ratio to obtain a 20 μm coextruded stretched laminated film.
The evaluation results of the obtained laminated film are shown in Table 2. The obtained laminated film was excellent in rigidity, had a low maximum thermal shrinkage stress in the TD direction, and had a good finish after packaging.

[Example 5]
The resin shown in Table 2 was used in the same manner as in Example 1 except for the resin composition ratio and the draw ratio to obtain a 17 μm coextruded stretched laminated film.
The evaluation results of the obtained laminated film are shown in Table 2. The obtained laminated film was excellent in rigidity, had a low maximum thermal shrinkage stress in the TD direction, and had a good finish after packaging.

[Comparative Example 1]
The resin shown in Table 3 was used in the same manner as in Example 2 except for the draw ratio to obtain a 20 μm coextruded stretched laminated film.
Table 3 shows the evaluation results of the obtained laminated film. In the stretching process, the film was easily punctured so that bubbles were broken, and the obtained laminated film had a high heat shrinkage rate. When the top seal package was formed, the container was deformed and was unsuitable as a packaging film.

[Comparative Example 2]
The resin shown in Table 3 was used in the same manner as in Example 1 except for the resin composition ratio and the draw ratio to obtain a 20 μm coextruded stretched laminated film.
Table 3 shows the evaluation results of the obtained laminated film. Since sufficient seal strength could not be obtained at the same heat seal temperature as in Examples 1 to 5, when the set temperature was increased, the surface of the seal portion was rough and inferior in beauty.

[Comparative Example 3]
With the resins shown in Table 3, a 20 μm coextruded stretched laminated film was produced in the same manner as in Example 1 except for the resin composition ratio and stretch ratio. And since it decreased compared with Comparative Examples 1, 2, 4 to 6, the film forming stability was inferior, for example, the thickness accuracy and transparency were inferior, and the inflation bubbles were easily punctured.
Table 3 shows the evaluation results of the obtained laminated film. Since the obtained laminated film had a high maximum thermal shrinkage stress in the TD direction, container deformation occurred when it was formed into a package, which was inappropriate as a packaging film.

[Comparative Example 4]
The resin shown in Table 3 was used in the same manner as in Example 1 except for the resin composition ratio and the draw ratio to obtain a 20 μm coextruded stretched laminated film.
Table 3 shows the evaluation results of the obtained laminated film. When the obtained laminated film is heat-sealed at the same temperature as in Examples 1 to 5, the surface of the seal portion is rough and inferior in beauty, and a pinhole is partially generated, which is impractical as a gas pack packaging film. It was the target.

[Comparative Example 5]
The resin shown in Table 3 was used in the same manner as in Example 3 except for the draw ratio to obtain a 20 μm coextruded stretched laminated film.
Table 3 shows the evaluation results of the obtained laminated film. Since the heat shrinkage rate of the laminated film was small, there was a looseness or slackness of the film of the package, and the beauty of the finished product was lowered.

[Comparative Example 6]
A 20 μm coextruded stretched laminated film was obtained in the same manner as in Example 2 except for the resin of the core layer (C).
Table 3 shows the evaluation results of the obtained laminated film. The obtained laminated film has a low tensile elastic modulus, so that sufficient rigidity as a cover material for a top seal package cannot be obtained. Further, since the oxygen permeability is high, it is not suitable as a gas pack packaging film.

  As shown in Table 2, all of the laminated films of Examples 1 to 5 are heat-shrinkable stretched laminated films in which the package when top-sealed is packaged does not cause container deformation and realizes a tight packaging finish. . The laminated films of Examples 1 to 5 are heat-shrinkable stretched laminated films having both stable heat sealability, rigidity, and oxygen barrier properties necessary for gas pack packaging.

On the other hand, it can be seen from the results of Comparative Example 1 that if the draw ratio is too high, the bubble is easily broken so that the bubble is broken, and the productivity is inferior. Moreover, although the obtained laminated film has a maximum heat shrinkage stress in the TD direction of 0.4 N / cm or less, the heat shrinkage rate is too high, and thus container deformation occurs in the heat shrink process of the top seal packaging. I understand.
From the result of Comparative Example 2, if the melting point of the propylene-based copolymer resin of the surface layer (A) that is the sealant layer is too high, the heat seal temperature must be increased, and the surface layer (E) is welded to the seal bar. It can be seen that the surface is rough and pinholes are generated, which is impractical.
From the results of Comparative Example 3, it can be seen that if the surface layer (E) is made of a polypropylene resin having a melting point of 155 ° C. or more, the film-forming stability is poor and the productivity and quality are lowered. Furthermore, since the maximum heat shrinkage stress of the obtained laminated film also becomes large, it turns out that the container deformation | transformation of a package body will arise like the comparative example 1. FIG.
From the result of Comparative Example 4, when the content of the propylene copolymer having a melting point of 140 ° C. or lower in the surface layer (E) is too large, the heat resistance of the surface layer (E) is lowered, so that the surface layer (E) is formed on the seal bar. It can be seen that it is impractical because of welding, rough surfaces, and pinholes.
From the results of Comparative Example 5, it can be seen that, when the film stretch ratio is lowered, the shrinkage rate is too low, so that the shrinkage in the heat shrink process is insufficient, and the package is loosened or loosened, resulting in poor finishing.
From the results of Comparative Example 6, it can be seen that when aliphatic polyamide is used as the polyamide resin of the core layer (C), the feel as a lid material is inferior due to low rigidity. Furthermore, since oxygen barrier property is low compared with aromatic polyamide, it turns out that it is not suitable for gas pack packaging.

  The present invention is suitable for packaging with an automatic packaging machine, and is suitable for use in top-sealing packaging of food and drink, pharmaceuticals, cosmetics, and the like.

Claims (5)

A surface layer (A) containing a propylene-based copolymer having a melting point of 140 ° C. or lower;
An adhesive layer (B);
A core layer (C) containing an aromatic polyamide copolymer;
An adhesive layer (D);
A surface layer (E) containing 45 to 80% by weight of a propylene homopolymer having a melting point of 155 ° C. or higher, and 55 to 20% by weight of a propylene copolymer having a melting point of 140 ° C. or lower;
Is a heat shrinkable stretched laminated film comprising
The heat shrinkage rate measured according to the measurement method ASTM-D2732 is 5 to 20% at 100 ° C.,
A heat-shrinkable stretched laminated film having a maximum heat shrinkage stress in the TD direction measured in accordance with a measuring method ASTM-D2838 of 0.4 N / cm or less at 100 ° C.   2. The heat-shrinkable stretched laminated film according to claim 1, wherein the core layer (C) has a tensile modulus of 3000 MPa or more and the core layer (C) has a thickness of 1 to 5 μm.   The heat-shrinkable stretched laminated film according to claim 1 or 2, wherein the tensile elastic modulus is 700 to 1600 MPa and the thickness is 10 to 25 µm. A method for producing the heat-shrinkable stretched laminated film according to any one of claims 1 to 3,
A laminate in which the surface layer (A), the adhesive layer (B), the core layer (C), the adhesive layer (D), and the surface layer (E) are laminated by a coextrusion method is used in an MD direction and a TD direction. A production method in which biaxial stretching is performed at a stretching ratio of 5.0 to 8.0.   A top seal package comprising the heat-shrinkable stretched laminated film according to any one of claims 1 to 3.