JPH08112885A - Heat-shrinkable film - Google Patents

Abstract

PURPOSE: To provide heat-shrinkable film, which has high thermal shrinkage stress and tearing strength and out of which heat-shrink packaging body having enough nerve, strong tying force and bag breaking strength and, in addition, excellent opening properties is obtained. CONSTITUTION: The film consists of both the outer layers made of straight-chain low-density polyethylene resin or preferably made of ethylene-α-olefin copolymer having the density of 0.860-0.925g/cm<3> and core layer made of the mixture of straight-chain low-density polyethylene resin or preferably made of ethylene-α- olefin copolymer having the density of 0.860-0.925g/cm<3> and polypropylene-based resin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for heat-shrink packaging, and is excellent in bag breaking strength and cohesion and requires heat-shrink packaging, and heat resistance and fusing heat sealing of film. The present invention relates to a heat-shrinkable film suitable for use in heat-shrinkable packaging that requires heat resistance of a part.

[0002]

2. Description of the Related Art In heat shrink wrapping, a heat shrinkable film which is passed through a heat shrink tunnel to shrink the heat shrinkable film covering the package is packaged in a tight state. In recent years, as a film used for such heat shrink packaging,
A heat-shrinkable film made of polyethylene resin or polypropylene resin is used in consideration of price, incineration after use, and the like.

However, from these heat-shrinkable films, the stiffness of the film is weak and it is difficult to open, or the tear strength is weak and the bag is easily broken during handling, or the heat-shrink stress is weak and the binding force is weak. It has the drawback of being poor, and a heat-shrinkable package which has solved all these drawbacks has not yet been obtained. Further, in the heat shrink wrapping, the temperature inside the heat shrink tunnel is usually set as high as possible in order to increase the amount of heat shrinkage and give the package more tightness. However, if the temperature inside the heat shrink tunnel is set to a high temperature, there is a problem in that the heat shrink film becomes white or melts and holes are formed. Further, when passing through the heat shrinking tunnel, bag breakage frequently occurred from the fusing heat seal portion.

[0004]

DISCLOSURE OF THE INVENTION The present invention provides a heat-shrinkable film which is difficult to be broken during handling, has a strong binding force, and can provide a heat-shrinkable package having excellent openability. The purpose is to do. Further, the present invention, even if the temperature in the heat shrink tunnel is set to a high value so as to generate a sufficient amount of heat shrinkage and to impart tightness to the package, the heat shrinkable film is whitened or melted. It is an object of the present invention to provide a good heat-shrinkable film in which holes are not opened and a bag does not break from the heat-cutting heat heel portion.

[0005]

According to the present invention, both outer layers are made of a linear low-density polyethylene resin, and the core layer is made of a mixture of a linear low-density polyethylene resin and a polypropylene resin. A heat-shrinkable film having a density of 0.860 to 0.8 is provided, and preferably both outer layers are a copolymer of ethylene and α-olefin.
It consists 0.925 g / cm ³ of linear low density polyethylene resin, the core layer is a copolymer of ethylene and α- olefin, linear density 0.860~0.925g / cm ³ Low Provided is a heat-shrinkable film comprising a mixture of a density polyethylene resin and a polypropylene resin, wherein both outer layers are ethylene and α having 6 or more carbon atoms.
A copolymer with an olefin and having a density of 0.860-0.
It is made of a linear low-density polyethylene resin of 925 g / cm ³ , and the core layer is a copolymer of ethylene and an α-olefin having 4 or more carbon atoms and has a density of 0.860 to 0.925 g /
There is provided a heat-shrinkable film comprising a mixture of a linear low-density polyethylene resin having a cm ³ and a polypropylene resin, and both outer layers are made of ethylene and an α-olefin having 6 or more carbon atoms. Copolymer with a density of 0.9
It is made of linear low-density polyethylene resin of 10 to 0.925 g / cm ³ , and the core layer is ethylene and α having 4 or more carbon atoms.
A copolymer with an olefin and having a density of 0.860-0.
A heat-shrinkable film comprising a mixture of a linear low-density polyethylene resin of 925 g / cm ³ and a polypropylene resin is provided, and both outer layers are ethylene and an α-olefin having 6 or more carbon atoms. And a linear low-density polyethylene resin having a density of 0.910 to 0.925 g / cm ³ , and the core layer is a copolymer of ethylene and an α-olefin having 6 or more carbon atoms. , Density 0.9
Provided is a heat-shrinkable film comprising a mixture of a linear low-density polyethylene resin of 10 to 0.925 g / cm ³ and a polypropylene resin, and a linear low-density polyethylene resin of a core layer. The above heat-shrinkable films are provided in which the mixing ratio of the mixture of propylene and a polypropylene resin is 20:80 to 80:20 (weight ratio), and further, a crosslinking treatment is performed. Each of the heat-shrinkable films is provided.

The present invention will be described in more detail below. The heat-shrinkable film of the present invention uses linear low-density polyethylene resin for both outer layers. Among the polyethylene-based resins, the linear low-density polyethylene resin is preferable because it has good stretchability and a film excellent in heat shrinkability. As such a linear low-density polyethylene resin, a resin having a density of 0.860 to 0.925 g / cm ³ is preferable, and a density of 0.910 to 0.
It is a linear low-density polyethylene resin of 925 g / cm ³ .

A density of less than 0.910 g / cm ³ , especially
When a linear low-density polyethylene resin having a density of less than 0.860 g / cm ³ is used, the stiffness of the film and the shrinkage stress may be slightly reduced, so that the resulting package is inferior in opening property and binding force. There are times Also, the density is 0.925g /
If a linear low-density polyethylene resin having a viscosity of more than ³ cm ³ is used, the tear strength of the heat-shrinkable film may be somewhat reduced, so that the resulting package may be easily broken during handling. Furthermore, the stretch processability for imparting heat shrinkability deteriorates.

As the α-olefin copolymerized with ethylene, those having carbons of 4 or more and 8 or less are usually used. Preferably, one having 6 or more carbon atoms is used. When a linear low-density polyethylene resin obtained by copolymerizing the α-olefin having a carbon number of less than 6 is used, the tear strength of the heat-shrinkable film may be somewhat reduced.
The resulting package may be easily broken during handling.

Next, the heat-shrinkable film of the present invention uses a mixture of a linear low-density polyethylene resin and a polypropylene resin for the core layer. As described above, the linear low-density polyethylene resin is preferable among the polyethylene-based resins because it has a good stretchability and a heat-shrinkable film. A polypropylene resin is particularly preferable because it has a particularly good drawability and a film having excellent heat shrinkability can be obtained. Moreover, the linear low-density polyethylene resin gives a film excellent in tear strength, and the polypropylene resin gives a film excellent in shrinkage stress and elasticity.

Further, the linear low density polyethylene resin preferably has a density of 0.860 to 0.925 g / cm ³ , and more preferably a density of 0.910 to 0.
It is 925 g / cm ³ .

A density of less than 0.910 g / cm ³ , especially
When a linear low-density polyethylene resin having a density of less than 0.860 g / cm ³ is used, the stiffness and shrinkage stress of the heat-shrinkable film may be slightly reduced, and the opening property and the cohesive force of the resulting package may be reduced. Is sometimes inferior. Also, the density is 0.925
When a linear low-density polyethylene resin having a g / cm ^{3 or more} is used, the tear strength of the heat-shrinkable film may be somewhat lowered, so that the obtained package may be easily broken during handling.

As the α-olefin to be copolymerized with ethylene, one having a carbon number of 4 or more and 8 or less is usually used. Preferably, one having 6 or more carbon atoms is used. When the linear low-density polyethylene resin having a carbon number of less than 6 is used, the tear strength of the heat-shrinkable film may be reduced to some extent, so that the obtained package may be easily broken during handling.

As the polypropylene resin, not only polypropylene homopolymer but also copolymers such as ethylene-propylene copolymer and ethylene-propylene-butene copolymer, or a mixture thereof can be used. . In particular, ethylene-propylene copolymers and ethylene-propylene-butene copolymers are preferable from the viewpoint of improving low-temperature heat-shrinking characteristics so that the heat-shrinkable packaging finish is good.

The mixing ratio (polymerization ratio) of the linear low-density polyethylene resin and the polypropylene resin is preferably in the range of 20:80 to 80:20. More preferably, it is in the range of 30:70 to 70:30. If the mixing ratio of the linear low-density polyethylene resin is less than 20% by weight, that is, if the mixing ratio of the polypropylene resin exceeds 80% by weight, the tear strength of the heat-shrinkable film may decrease.
Further, when the mixing ratio of the linear low-density polyethylene resin exceeds 80% by weight, that is, when the mixing ratio of the polypropylene resin is less than 20% by weight, the stiffness of the heat-shrinkable film and the heat shrinkage stress are lowered. There is a case.

The total thickness of the heat-shrinkable film of the present invention is not particularly limited, but is 10 to 40 μm because the film of the present invention is used for heat-shrink packaging.
Is preferably within the range.

As for the thickness of each layer, the thickness of the core layer is preferably 20 to 70% of the total thickness, that is, the total thickness of both outer layers is preferably 80 to 30% of the total thickness. When the thickness of the core layer is less than 20% of the total thickness (that is, the total thickness of both outer layers exceeds 80% of the total thickness), the strength and heat shrinkage stress of the heat-shrinkable film are reduced. Sometimes,
The resulting package may be inferior in opening property and binding force. Further, the thickness of the core layer exceeds 70% of the total thickness (that is, the total thickness of both outer layers is less than 30% of the total thickness).
If so, the tear strength of the heat-shrinkable film may be reduced, and the resulting package may be easily broken during handling. The thickness of both outer layers does not necessarily have to be the same, but in terms of the curl property of the heat-shrinkable film,
It is preferable that they have the same thickness.

The heat-shrinkable film of the present invention may be provided with an adhesive resin layer or an oxygen-blocking resin layer as an intermediate layer between both outer layers and the core layer, or the heat-shrinkable film of the present invention. Regenerated and reduced products such as unsuitable products produced during production can be inserted between both outer layers and the core layer or the core layer can be separated into two layers and inserted between them. Further, a lubricant, an anti-blocking agent, an antioxidant or the like can be added to each layer, if necessary.

The method for producing the heat-shrinkable film of the present invention is not particularly limited, but it is generally produced by the following method. That is, both outer layers are linear low-density polyethylene resin, and the core layer is a layered unstretched raw material of a mixture of linear low-density polyethylene resin and polypropylene resin coextruded by a plurality of extruders and a multilayer die. . Then, the obtained laminated unstretched raw fabric is reheated to a temperature at which it can be stretched and stretched by a tenter system or an inflation system to obtain a heat-shrinkable film.

Further, in the present invention, in order to improve the heat resistance of the heat-shrinkable film and the heat-resistant strength of the fusion-sealed portion, the laminated unstretched raw fabric is subjected to a crosslinking treatment and subjected to a stretching process, or The heat-shrinkable film of the present invention can also be obtained by subjecting to stretching treatment and then crosslinking treatment. The cross-linking treatment is performed by irradiation with electron beams or γ-rays, or by adding a cross-linking agent. In particular, the method of irradiating with an electron beam or γ-ray is preferable because it is simple and easy to crosslink.

The irradiation dose of the electron beam or γ-ray is not particularly limited, but may be appropriately selected depending on the heat resistance of the heat-shrinkable film, the fusion heat seal strength, the film constitution, the raw materials used, and the like. . For example, in the case of irradiating an unstretched raw fabric with an electron beam or γ-ray, the range of 1 to 20 Mrad is preferable. When the dose of electron beam or γ-ray is less than 1 Mrad, the heat resistance of the heat-shrinkable film and the heat resistant strength of the fusing heat-sealed portion are not sufficiently improved, and further, the stretching processability cannot be expected. Further, when the irradiation dose of the electron beam or γ-ray exceeds 20 Mrad, the heat shrinkability of the heat-shrinkable film is good and the drawability is good, but the cut property at the time of fusing and heat sealing is deteriorated.

When the stretched film that has been stretched is irradiated with an electron beam or γ-ray, the range of 1 to 10 Mrad is preferable. The irradiation dose of electron rays and γ rays is 1 Mrad
If it does not satisfy the above condition, the heat resistance of the heat-shrinkable film and the heat-resistant strength of the fusing heat-sealed portion are not sufficiently improved. Also, when the dose of electron beam or γ-ray exceeds 10 Mrad,
The heat-shrinkable film has good heat resistance, but the cut property at the time of fusing and heat-sealing deteriorates. Further, if the irradiation dose of the electron beam or γ-ray exceeds 10 Mrad, heat shrinkage occurs during processing, which is not preferable.

As the electron beam used in the present invention, Cockcrot-Walton type, Van de Graft type,
50 emitted from various electron beam accelerators such as transformer rectification type
Energy in the range of ~ 300 KeV, preferably 100-300 KeV is preferred. Further, the atmosphere for irradiating the electron beam or γ-ray is preferably a nitrogen gas atmosphere or the like, and the oxygen concentration is preferably 100 PPM or less.

[0023]

In the heat-shrinkable film of the present invention, the linear low density polyethylene resin having excellent tear strength is laminated on both surface layers, and the linear shrinkable film having excellent tear strength is also provided on the core layer. Due to the use of the mixture containing the low density polyethylene resin, the film has excellent tear strength. Therefore, when using the heat-shrinkable film of the present invention,
A heat-shrinkable package that is difficult to break during handling is obtained. Furthermore, the heat-shrinkable film of the present invention has a high heat-shrinkage stress because the mixture of the core layer contains a polypropylene resin that easily causes high heat-shrinkage stress. Therefore, when the heat-shrinkable film of the present invention is used, a heat-shrinkable package having excellent binding force can be obtained. In addition, since the mixture of the core layer contains the polypropylene-based resin that can be obtained in a strong film,
The heat-shrinkable film of the present invention is strong. Therefore, when the heat-shrinkable film of the present invention is used, a heat-shrinkable package having excellent openability can be obtained.

Further, the linear low density polyethylene resin is
When the electron beam or γ-ray irradiation treatment is applied, a crosslinking reaction occurs and heat resistance is improved. On the other hand, when the polypropylene-based resin is irradiated with an electron beam or a γ-ray, a decomposition reaction occurs and the heat resistance is lowered. However, when the polypropylene resin is mixed with the linear low-density polyethylene resin, the decomposed polypropylene resin becomes surrounded by the linear low-density polyethylene resin in which a part of its molecular chain is cross-linked. It seems to be. Therefore, when a mixture of a linear low-density polyethylene resin and a polypropylene resin is subjected to irradiation treatment with an electron beam or γ-ray, the heat resistance is improved, though not as much as the cross-linked linear low-density polyethylene resin. Also, the heat resistance of the fusing heat-sealed portion is improved. Furthermore, the mixture of the linear low-density polyethylene resin and the polypropylene resin is far superior to the polypropylene resin alone in melt adhesion to the linear low-density polyethylene resin.

From the above, the heat-shrinkable film of the present invention comprises the linear low-density polyethylene resin for both outer layers, and
When a mixture of linear low-density polyethylene resin and polypropylene resin in the core layer is cross-linked by irradiation with electron beam or γ-ray, whitening or perforation due to melting is unlikely to occur when passing through a heat shrink tunnel. Become. In addition, the heat resistance of the fusing heat-sealed portion is also improved, and when passing through the heat-shrinking tunnel, bag breakage from the sealed portion is less likely to occur. still,
The heat resistance of the laminated film is generally said to be greatly affected by the heat resistance of the resin of the surface layer.

Further, the mixture of the linear low-density polyethylene resin and the polypropylene resin in the core layer has a good melt adhesion with the linear low-density polyethylene resin in the surface layer, and therefore, when it is fused by heat-sealing. In addition, both resins are easily melted to obtain a good fusing heat seal. In addition, when the resins of both outer layers and the core layer are crosslinked, the heat resistance of the fusing heat seal portion is also excellent.

[0027]

EXAMPLES Hereinafter, the contents of the present invention will be described more specifically by showing Examples and Comparative Examples. The present invention is not limited to the matters described in the examples. Further, the film properties, heat shrink wrapping suitability, and the like in the present invention were measured by the following methods.

[Heat Shrinkability (Heat Shrinkage)] One Side is 100 m
The sample cut into squares of m was immersed in a glycerin bath set at each temperature, and the heat shrinkage amount at each temperature at each side was calculated as 100% (heat shrinkage rate) of the length of the original side. Indicated. [Shrinkage stress] A strip-shaped test piece having a film width of 15 mm
There is no slack between chucks with a spacing of 30 mm, and moreover,
After keeping it in a tight state, it was immersed in a glycerin bath at 110 ° C., and the stress generated between the chucks at that time was measured with a strain gauge. [Tear strength] The tear load was measured by an Elemendorff according to ASTM D1922. [Tensile Elastic Modulus (Young's Modulus)] According to ASTM D882, film width 10 mm, chuck distance 50 mm, tensile speed 5 mm / min, chart speed 250 mm / min,
A tensile test was performed under the conditions, and a stress-strain curve was drawn. Then, the load when 1% strain was generated was read, and the Young's modulus was calculated by converting the load. [Bag strength] Three video cases were heat-shrink-wrapped to about 1.
What is dropped from the height of 5 m to the floor of cement and does not break even if dropped 20 times or more is "○", but it does not break even if dropped 5 times or more, but it does not break by 20 times. What was done was shown by "△", and what was broken by 5 times was shown by "x". [Bundling power] Three video cases are heat-shrink-wrapped. Good binding power and excellent tightness are indicated by "○", binding power is a little weak and tightness is inferior, but it is a problem as a commercial product. Those that did not exist were marked with a “Δ”, and those that were weak in cohesiveness and poor in tenacity and that were not practically usable products were shown with a “x”. [Opening] Lightly rubbing the film in a half-folded roll and twisting it with your fingertips 2-3 times to open it with "○", twisting it more than "△", and with your fingertips Those that cannot be opened are indicated by "x". [Heat resistance of film] A sample cut into a circle with a diameter of 200 mm was held in a holder in a tight state without causing slack, and was passed through a heat-shrinking tunnel set to each temperature for 5 seconds to obtain a film. Showed the maximum temperature at which the surface of the steel did not whiten or melted and no holes were formed. [Heat resistance of fusing heat-sealing part] A circular sample having a fusing heat-sealing part in the central portion and having a diameter of 200 mm is held in a holder in a tight state without causing slack as in the heat resistance measurement of the film, Pass through a heat-shrink tunnel set at 150 ° C for 5 seconds and open the fusing heat-sealing part with "○", and up to 2 out of 10 "△", out of 10 Those having three or more holes are indicated by "x".

Example 1 An ethylene-octene copolymer (linear low-density polyethylene resin, density: 0.920 g / cm ³ ) was used for both outer layers, and an ethylene-hexene copolymer (linear low-density polyethylene was used for the core layer. Resin, density: 0.912 g / cm ³ ) and ethylene-
A tubular laminated unstretched raw fabric made of a mixture in which the propylene copolymer was mixed at a weight ratio of 30:70 was molded with two extruders and a two-kind three-layer multilayer circular die. The thickness of the unstretched raw fabric was 240 μm, and the thickness constitution of each layer was 1: 2: 1. The obtained unstretched raw fabric,
Biaxial stretching processing was performed by a conventional general inflation method to obtain a heat-shrinkable film having a thickness of 19 μm.
Table 1 shows the properties of the obtained heat-shrinkable film and suitability for heat-shrinkable packaging. As is clear from Table 1, the heat-shrinkable film of Example 1 had good elasticity and excellent tear strength and heat-shrinkage stress. The package using the heat-shrinkable film of Example 1 was not easily broken during handling, and was excellent in binding force and openability.

Examples 2 to 4 Ethylene-butene copolymer (linear low-density polyethylene resin, density: 0.919 g / cm ³ ) for both outer layers (Example 2), ethylene-octene copolymer (linear chain) Low density polyethylene resin, density: 0.902 g / cm ³ ) (Example 3), ethylene-octene copolymer (linear low density polyethylene resin, density: 0.930 g / cm ³ ) (Example 4) As in Example 1, each core layer was an ethylene-hexene copolymer (linear low-density polyethylene resin, density: 0.9
12 g / cm ³ ) and an ethylene-propylene copolymer were mixed in a weight ratio of 30:70 to form a tubular unstretched raw material, which was the same as in Example 1 except that two extruders and two types 3 were used. The layers were formed by a multi-layer circular die.
The thickness of the unstretched raw fabric and the thickness configuration of each layer were the same as in Example 1. Further, the obtained unstretched raw fabric,
Similar to Example 1, biaxial stretching was performed by a conventional general inflation method to obtain each heat-shrinkable film having a thickness of 19 μm. Table 1 also shows the characteristics of each of the obtained heat-shrinkable films and the heat-shrinkable packaging suitability.

As is clear from Table 1, the heat-shrinkable film of Example 2 had good heat-shrinkage stress and stiffness of the waist, but the tear strength was higher than that of the heat-shrinkable film of Example 1. Was a little inferior. The package using the heat-shrinkable film was excellent in binding force and opening property, but compared with the package using the heat-shrinkable film of Example 1, it was easier to break the bag during handling. It was However, there was no problem in practical use. Further, the heat-shrinkable film of Example 3 was excellent in tear strength, but was slightly inferior to the heat-shrinkable film of Example 1 in heat shrinkage stress and stiffness. The package using the heat-shrinkable film was difficult to be broken during handling, but was slightly inferior in binding force and opening property to the package using the heat-shrinkable film of Example 1. Was there. However, there was no problem in practical use. Further, the heat-shrinkable film of Example 4 had good heat-shrinkage stress and stiffness of the waist like the heat-shrinkable film of Example 2, but compared with the heat-shrinkable film of Example 1. The tear strength was slightly inferior. The package using the heat-shrinkable film was excellent in binding force and opening property, but it was easier to break the bag during handling, as compared with the package using the heat-shrinkable film of Example 1. . But,
There was no problem in practice.

Examples 5 to 7 Each outer layer was an ethylene-octene copolymer (linear low density polyethylene resin, density: 0.920 g / cm ³ ), and the core layer was an ethylene-butene copolymer (linear chain). Low density polyethylene resin, density: 0.915 g / cm ³ ) (Example 5), ethylene-hexene copolymer (linear low density polyethylene resin, density: 0.905 g / cm ³ ) (Example 6) , Ethylene-hexene copolymer (linear low-density polyethylene resin, density: 0.928 g / cm ³ ) (Example 7) and ethylene-propylene copolymer in a weight ratio of 3
A tube-shaped laminated unstretched raw fabric made of a mixture mixed at 0:70 was molded by two extruders and a two-layer, three-layer multilayer circular die as in Example 1. The thickness of the unstretched raw fabric and the thickness configuration of each layer were the same as in Example 1. Further, the obtained unstretched raw fabric was biaxially stretched by a conventional general inflation method as in Example 1 to obtain each heat-shrinkable film having a thickness of 19 μm. Table 1 also shows the characteristics of each of the obtained heat-shrinkable films and the heat-shrinkable packaging suitability.

As is clear from Table 1, the heat-shrinkable film of Example 5 had good heat-shrinkage stress and stiffness, but the tear strength was higher than that of the heat-shrinkable film of Example 1. Was a little inferior. The package using the heat-shrinkable film was excellent in binding force and opening property, but compared with the package using the heat-shrinkable film of Example 1, it was easier to break the bag during handling. It was However, there was no problem in practical use. The heat-shrinkable film of Example 6 was excellent in tear strength, but was slightly inferior to the heat-shrinkable film of Example 1 in heat shrinkage stress and stiffness. The package using the heat-shrinkable film was difficult to be broken during handling, but was slightly inferior in binding force and opening property to the package using the heat-shrinkable film of Example 1. Was there. However, there was no problem in practical use. Further, the heat-shrinkable film of Example 7 had good heat-shrinkage stress and stiffness of the waist like the heat-shrinkable film of Example 5, but compared with the heat-shrinkable film of Example 1. The tear strength was slightly inferior. The package using the heat-shrinkable film was excellent in binding force and opening property, but it was easier to break the bag during handling, as compared with the package using the heat-shrinkable film of Example 1. . But,
There was no problem in practice.

Comparative Example 1 The ethylene-octene copolymer (linear low density polyethylene resin, density: 0.902 g / cm ³ ) used in both outer layers of Example 3 was used in both outer layers and the core layer. A heat-shrinkable film was obtained in the same manner as in Example 1 except that the simple substance was used. The properties of the obtained heat-shrinkable film and suitability for heat-shrinkable packaging are also shown in Table 1. As is clear from Table 1,
The heat-shrinkable film of Comparative Example 1 was excellent in tear strength, but was inferior in heat-shrinkage stress and film stiffness. The package using the heat-shrinkable film has a poor binding force and is inferior in opening property, and is unsuitable for practical packaging.

Comparative Example 2 The same as Example 1 except that the core layer was replaced by the mixture of the linear low-density polyethylene resin and the polypropylene resin, and only the polypropylene resin used in the core layer of Example 1 was used. A heat shrinkable film was obtained by various methods. The properties of the obtained heat-shrinkable film and suitability for heat-shrinkable packaging are also shown in Table 1. As is clear from Table 1, the heat-shrinkable film of Comparative Example 2 was excellent in heat-shrinkage stress and stiffness of the film, but was inferior in tear strength. The package using the heat-shrinkable film is apt to be broken during handling and is not suitable for practical packaging.

Example 8 As in Example 1, both outer layers had an ethylene-octene copolymer (linear low density polyethylene resin, density: 0.920 g).
/ Cm ³ ), the core layer is an ethylene-hexene copolymer (linear low-density polyethylene resin, density: 0.912 g / cm 3
³ ) and ethylene-propylene copolymer in a weight ratio of 3
A tubular laminated unstretched raw fabric made of a mixture mixed at 0:70 was molded. The thickness of the unstretched original fabric is 240
The thickness composition of each layer in μm was 1: 2: 1. After irradiating this unstretched raw fabric with an electron beam of 5 Mrad, biaxial stretching is performed by a conventional general inflation method,
A heat-shrinkable film having a thickness of 19 μm was obtained. Table 2 shows the physical properties and the like of the obtained heat-shrinkable film. The heat-shrinkable film of Example 8 was excellent in tear resistance, heat-shrinkage stress, and film stiffness in practical use, as well as in heat resistance and heat-resistant strength of the fusing heat-sealing portion. It was

Example 9 The heat-shrinkable film of Example 1, that is, the unstretched raw film of Example 8 was subjected to biaxial stretching by the inflation method in the same manner as in Example 8 without irradiating the electron beam. To obtain a stretched film. Further, this stretched film was irradiated with an electron beam of 5 Mrad to obtain a heat-shrinkable film. The physical properties and the like of the obtained heat-shrinkable film are also shown in Table 2. As with the heat-shrinkable film of Example 8, the heat-shrinkable film of Example 9 did not cause any practical problems in tear strength, heat-shrinkage stress, and stiffness of the film.
It was excellent in heat resistance and heat resistance of the fusion heat seal part.

Comparative Example 3 Similar to the heat-shrinkable film of Comparative Example 1, the ethylene-octene copolymer (linear low-density polyethylene resin, linear low-density polyethylene resin, used in both outer layers and core layer of Example 3) was used. Density: 0.9
02 g / cm ³ ), a tubular unstretched original fabric was molded. Then, as in Example 8, the obtained unstretched raw fabric was irradiated with an electron beam of 5 Mrad, and then biaxially stretched by a conventional general inflation method,
A heat-shrinkable film having a thickness of 19 μm was obtained. The properties and the like of the obtained heat-shrinkable film are also shown in Table 2. Like the heat-shrinkable film of Comparative Example 1, the heat-shrinkable film of Comparative Example 3 was excellent in tear strength, but was inferior in heat-shrinkage stress and film stiffness. The heat-shrinkable film was excellent in heat resistance and heat resistance of the fusing heat-sealed portion.

Comparative Example 4 Similar to the heat-shrinkable film of Comparative Example 2, the polypropylene resin used in the core layer of Example 1 was used instead of the mixture of the linear low-density polyethylene resin and the polypropylene resin in the core layer. A tube-shaped unstretched original fabric was molded using only the above. Then, similarly to Example 8, the obtained unstretched raw fabric was irradiated with an electron beam of 5 Mrad and then biaxially stretched by a conventional general inflation method to obtain a heat-shrinkable film having a thickness of 19 μm. . The properties and the like of the obtained heat-shrinkable film are also shown in Table 2. Like the heat-shrinkable film of Comparative Example 2, the heat-shrinkable film of Comparative Example 4 was excellent in heat-shrinkage stress and stiffness of the film, but was inferior in tear strength. In addition, the heat resistance and heat resistance of the fusing heat seal part were also poor.

[0040]

[Table 1]

[0041]

[Table 2]

[0042]

The heat-shrinkable film of the present invention has tear strength because both outer layers are linear low-density polyethylene resin and the core layer is formed of a mixture of chain low-density polyethylene resin and propylene resin. The resulting heat-shrinkable package is difficult to tear during handling, and the film is elastic, so the resulting heat-shrinkable package can be easily opened, and since the heat-shrinkable stress is strong, it can be obtained. The heat-shrinkable package has excellent binding force. Further, the heat-shrinkable film of the present invention can be further crosslinked to improve heat resistance and heat-resistant strength of the fusion-cut seal portion. From these facts, the heat-shrinkable film of the present invention can be suitably used for heat-shrink wrapping of products such as food products and daily sundries.
Further, since the heat-shrinkable film of the present invention has excellent heat resistance, it is possible to set the heat-shrink tunnel temperature at a high value, so that it is possible to obtain a heat-shrink package having a good packaging finish at a high speed. When passing through the heat shrink tunnel, the film does not whiten or have holes, or the fusing heat seal does not cause bag breakage.
Trouble with heat shrinkage disappears.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Eiki Uehara 1515 Nakatsu-cho, Marugame-shi, Kagawa Okura Industrial Co., Ltd.

Claims (7)

[Claims] 1. A heat-shrinkable film, wherein both outer layers are made of a linear low-density polyethylene resin, and the core layer is made of a mixture of a linear low-density polyethylene resin and a polypropylene resin. 2. Both outer layers are a copolymer of ethylene and α-olefin and have a density of 0.860 to 0.925 g / cm 2.
Made of linear low-density polyethylene resin of ³ , the core layer is
It is a copolymer of ethylene and α-olefin and has a density of 0.
A heat-shrinkable film comprising a mixture of 860 to 0.925 g / cm ³ of a linear low-density polyethylene resin and a polypropylene resin. 3. Both outer layers are composed of ethylene and α having 6 or more carbon atoms.
A copolymer with an olefin and having a density of 0.860-0.
It is made of a linear low-density polyethylene resin of 925 g / cm ³ , and the core layer is a copolymer of ethylene and an α-olefin having 4 or more carbon atoms and has a density of 0.860 to 0.925 g /
A heat-shrinkable film comprising a mixture of a linear low-density polyethylene resin having a cm ³ and a polypropylene resin. 4. Both outer layers are made of ethylene and α having 6 or more carbon atoms.
A copolymer with an olefin and having a density of 0.910-0.
It is made of a linear low-density polyethylene resin of 925 g / cm ³ , and the core layer is a copolymer of ethylene and an α-olefin having 4 or more carbon atoms and has a density of 0.860 to 0.925 g /
A heat-shrinkable film comprising a mixture of a linear low-density polyethylene resin having a cm ³ and a polypropylene resin. 5. Both outer layers are made of ethylene and α having 6 or more carbon atoms.
A copolymer with an olefin and having a density of 0.910-0.
It is made of a linear low-density polyethylene resin of 925 g / cm ³ , and the core layer is a copolymer of ethylene and an α-olefin having 6 or more carbon atoms and has a density of 0.910 to 0.925 g /
A heat-shrinkable film comprising a mixture of a linear low-density polyethylene resin having a cm ³ and a polypropylene resin. 6. The mixing ratio of the mixture of the linear low-density polyethylene resin and the polypropylene resin in the core layer is 20:
It is 80-80: 20 (weight ratio), The heat-shrinkable film in any one of Claim 1 thru | or 5 characterized by the above-mentioned. 7. The heat-shrinkable film according to claim 1, which has been subjected to a crosslinking treatment.