JP3097874B2 - Crosslinked heat shrinkable laminated film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat shrinking method in which a product is roughly wrapped, heat shrunk by a heating device such as a shrinking tunnel, and closely adhered to the shape of the product, thereby tightly wrapping the product. The present invention relates to a crosslinked heat-shrinkable laminated film used for packaging.

[0002]

2. Description of the Related Art Conventionally, a heat-shrinkable film composed of an ethylene-based polymer has been obtained by crosslinking a low-density ethylene homopolymer or an ethylene-vinyl acetate copolymer by irradiating it with ionizing radiation and then stretching the film. There is.
The crosslinked heat-shrinkable film made of such an ethylene-based polymer is excellent in tear strength, impact strength of a fusing seal portion, and cold resistance as compared with those made of a propylene-based polymer, and has a soft shrink wrapping finish. However, on the other hand, transparency and film strength were not sufficient. Therefore, when a linear low-density ethylene-α-olefin copolymer is commercially available, in order to solve these problems, instead of the low-density ethylene homopolymer or ethylene-vinyl acetate copolymer, the resin is used. Came to be used. A crosslinked heat-shrinkable film composed of a linear low-density ethylene-α-olefin copolymer has higher transparency and film than a crosslinked heat-shrinkable film formed from a low-density ethylene homopolymer or an ethylene-vinyl acetate copolymer. Strength was improved. However, because of the cross-linking, the poor heat sealability has not been improved yet, and the improvement has been desired.

Therefore, various studies have been made to improve the heat sealing property of the crosslinked heat-shrinkable film. For example, first, since the poor heat sealability is caused by crosslinking, it has been studied to suppress the degree of crosslinking as much as possible. However, when the degree of cross-linking is lowered, not only the stretching process during the production becomes difficult, but also excellent properties as a heat-shrinkable film imparted by cross-linking, such as a high heat shrinkage and heat shrinkage stress are impaired. There was a problem to say.

[0004] Further, the following studies have been made on the basis of improving the heat sealing property by selectively lowering the degree of crosslinking only in the surface layer portion of the film. That is, Japanese Patent Application Laid-Open No. 57-197161 discloses an olefin resin having a different degree of crosslinking characterized by laminating olefin resin layers having different ionizing radiation crosslinking properties and irradiating the laminate with ionizing radiation. A method for producing a laminated film having layers is disclosed. However, the laminated film obtained by this method has excellent properties as a crosslinked heat-shrinkable film provided by being formed from a linear low-density ethylene-α-olefin copolymer, that is, good transparency and strong film strength. However, there is an inconvenience that it is impaired when laminated with different types of resins such as a low-density ethylene homopolymer and an ethylene-vinyl acetate copolymer.

Further, a method of impregnating a surface layer portion of a film with a crosslinking inhibitor and then irradiating the film with ionizing radiation to cause cross-linking in a portion excluding the surface layer portion of the film, and then stretching the film is disclosed in Japanese Patent Application Laid-Open Publication No. Sho. Japanese Patent Application Laid-Open No. 50-72942 also discloses a method of irradiating a laminated film comprising a base layer and a surface layer containing a crosslinking inhibitor provided on at least one surface thereof with ionizing radiation to cause crosslinking and then stretching the film. It is disclosed in Japanese Unexamined Patent Publication No. 50-12167. Although these methods have an advantage that a crosslinked heat-shrinkable film can be formed only from a linear low-density ethylene-α-olefin copolymer, the crosslinking inhibitor added to the surface layer bleeds to the surface to lower the transparency. At the same time, there is a problem that heat sealability is deteriorated.

[0006]

DISCLOSURE OF THE INVENTION The present invention is based on the fact that the excellent properties of a crosslinked heat-shrinkable film provided by being formed from a linear low-density ethylene-α-olefin copolymer, To provide a crosslinked heat-shrinkable laminated film made of a linear low-density ethylene-α-olefin copolymer having good stretch processability during production and excellent heat sealability without being impaired by being laminated. With the goal.

[0007]

According to the present invention, a linear low-density ethylene-α forming the base layer is provided on both sides of a base layer formed from a linear low-density ethylene-α olefin copolymer.
Density of at least 0.01 g /
a laminated film having a surface layer formed of cm ³ or more larger linear low density ethylene -α-olefin copolymer,
A crosslinked heat-shrinkable laminated film obtained by irradiating with ionizing radiation for 5 to 30 Mrad and then stretching by heating is provided. In particular, the density of the linear low-density ethylene-α-olefin copolymer forming the surface layer is 0. The crosslinked heat-shrinkable laminated film having a weight of 910 g / cm ³ or more is provided.

The present inventors have conducted intensive studies to achieve the above object, and applied the same irradiation dose to a linear low-density ethylene-α-olefin copolymer having different densities in a specific dose range. Focusing on the fact that the degree of cross-linking of the two resins is remarkably different even at a small difference in density when irradiated, and as a result of various tests and examinations, as a result of adopting the constitution of the present invention, the linear low A crosslinked heat-shrinkable laminated film made of a high-density ethylene-α-olefin copolymer has been found to have good stretchability during production, and good heat-shrinkage properties, and has excellent heat-sealing properties, thus completing the present invention. Reached.

The linear low-density ethylene-α-olefin copolymer used in the present invention has a density of 0.93
A copolymer of ethylene and a small amount of α-olefin having a linear molecular structure of 0 g / cm ³ or less and having little or no branching or cross-linking along the polymer chain. In general, α-olefins copolymerized with ethylene include propylene, butene-1, pentene-1,4-methylpentene,
Heptene, hexene-1, octene-1 and the like are used alone or in combination. The density of the linear low-density ethylene-α-olefin copolymer is lower when the α-olefin copolymerized with ethylene has a larger carbon number and when the amount of the α-olefin copolymerized with ethylene is larger.

[0010] The crosslinked heat-shrinkable laminated film of the present invention comprises a linear low-density ethylene-based film having a base layer formed on both sides of the above-mentioned linear low-density ethylene-α-olefin copolymer base layer.
Density is at least 0.01 g more than α-olefin copolymer
/ Cm ³ or more, preferably 0.02 g / cm ³ or more, to the laminated film having a surface layer composed of a linear low-density ethylene-α-olefin copolymer, which is exposed to ionizing radiation for 5 to 30 times.
It is irradiated with Mrad, preferably 10 to 25 Mrad, and then heated and stretched. Linear low density ethylene-α
On both sides of a base layer made of an olefin copolymer, a linear low-density ethylene-α olefin copolymer having a density at least 0.01 g / cm ³ or more larger than the linear low-density ethylene-α olefin copolymer forming the base layer When a laminated film having a surface layer is appropriately irradiated with ionizing radiation in an irradiation dose range of 5 to 30 Mrad, only the base layer having a lower density than the surface layer is selectively highly crosslinked, and the surface layer is less crosslinked than the base layer. do not do. The laminated film in which only the base layer is selectively mainly crosslinked as described above has good stretchability at the time of production because the base layer is highly crosslinked, and has good heat shrinkage imparted by crosslinking. It has properties, that is, high heat shrinkage and heat shrinkage stress, and has excellent heat sealing properties because the surface layer is less crosslinked than the base layer.

When the irradiation amount is more than 30 Mrad, both the base layer and the surface layer undergo the same high degree of crosslinking, so that the stretchability at the time of production is good.
Although the heat shrinkage property is good, only a poor heat seal property can be obtained because the surface layer is highly crosslinked. When the irradiation amount is less than 5 Mrad, the degree of crosslinking is too low, so that the stretching process during the production becomes difficult.

The density of the linear low-density ethylene-α-olefin copolymer forming the surface layer is at least 0.01 g / cm ³ higher than the density of the linear low-density ethylene-α-olefin copolymer forming the base layer. It is preferably larger than that, more preferably larger than 0.02 g / cm ³ . When the difference in density is 0.01 g / cm ³ or more, preferably 0.02 / cm ³ or more, 5 to 30 Mra
d, preferably when the irradiation is appropriately selected within the irradiation range of 10 to 25 Mrad, the difference in the degree of crosslinking between the base layer and the surface layer can be further increased. That is, the base layer can be more sufficiently crosslinked, and the degree of crosslinking of the surface layer can be sufficiently suppressed, and the heat-shrinkable film and the heat-shrinkability of the heat-shrinkable film obtained after heat-stretching can be further improved.

The density of the linear low-density ethylene-α-olefin copolymer forming the surface layer is not particularly limited, but is preferably 0.910 g / cm ³ or more. Linear low density ethylene-α forming surface layer
When the density of the olefin copolymer is low, the melting point is low and the heat resistance is inferior, so when the heat shrink wrapping is performed, the temperature of the heat shrink tunnel is increased for the purpose of obtaining a good heat shrink finish,
On the surface of the film after the heat shrinkage, a whitening state occurs through a semi-molten state generally called "burn", and a clean finish cannot be obtained. In the case of a conventional crosslinked heat-shrinkable film, the surface portion also has a high degree of crosslinking, so that even if the density is low, such a problem hardly occurs. However, the crosslinked heat-shrinkable laminated film of the present invention is one in which the degree of crosslinking of the surface layer is suppressed in order to improve the heat sealability.
Therefore, in order to prevent such problems from occurring, it is preferable that the density of the linear low-density ethylene-α-olefin copolymer forming the surface layer is as large as possible, and the density is at least 0.910 g / cm ³ or more. It is preferable to have

In the crosslinked heat-shrinkable laminated film of the present invention, the thickness constitution of each layer is not particularly limited, but the ratio of the thickness of the base layer is preferably in the range of 30 to 80% with respect to the total thickness. If the ratio of the thickness of the base layer is too small, the stretching processability is poor, and even if the stretching can be performed, the obtained heat-shrinkable film is inferior in heat-shrinkability. On the other hand, if the ratio of the thickness of the base layer is too large, the ratio of the thickness of the surface layer is reduced, and the heat sealing strength is reduced. Although the overall thickness of the film is not particularly limited, it is 1 mm for heat shrink wrapping.
It is preferably from 0 to 40 μm.

[0015] In addition, other resins, lubricants, anti-blocking agents,
Mixing additives such as an antifogging agent and an antistatic agent or providing a new layer is not hindered at all.

As a method for producing the crosslinked heat-shrinkable laminated film of the present invention, there are the following methods. That is, first,
On both sides of a base layer made of a linear low-density ethylene-α-olefin copolymer, a linear low-density ethylene-α-olefin copolymer having a higher density than the linear low-density ethylene-α-olefin copolymer forming the base layer Make a laminated film with a surface layer. The method for producing the laminated film is not particularly limited, and may be performed by a conventionally known method. For example, a method of laminating three molded films, a method of extrusion lamination, and a method of coating may be used. In particular, an inflation molding method using a plurality of extruders and a multilayer die, a T-die molding method, or the like. Is most suitable.

Next, α-ray, β-ray, γ
The linear low-density ethylene-α-olefin copolymer constituting the laminated film is cross-linked by irradiating ionizing radiation such as a beam, a neutron beam and an accelerating electron beam. When an accelerating electron beam is used as the ionizing radiation to be irradiated, it is necessary to select irradiation equipment and irradiation conditions capable of performing irradiation as uniformly as possible in the thickness direction of the film before stretching.

The crosslinked heat-shrinkable laminated film of the present invention can be obtained by heating and stretching this crosslinked laminated film. As a means for stretching, a known tenter-type or tubular-type stretching apparatus is appropriately used depending on whether the laminated film is in a sheet shape or a tube shape. Also, the stretching ratio can be adjusted as needed.
It may be stretched about 2 to 5 times per axis. Subsequently, heat setting may be performed while giving relaxation. The crosslinked heat-shrinkable laminated film of the present invention, by forming the surface layer from a linear low-density ethylene-α-olefin copolymer having a higher density than the base layer, selectively selectively crosslinks only the resin forming the base layer to a high degree. The surface layer is less crosslinked than the base layer. For this reason, the crosslinked heat-shrinkable laminated film of the present invention is disadvantageous in that it retains the excellent properties of the conventional crosslinked heat-shrinkable film formed from a linear low-density ethylene-α-olefin copolymer, and has a disadvantage. Poor sealing performance can be improved.

[0019]

EXAMPLES The present invention will be described below more specifically with reference to examples, but the present invention is not limited to these examples.
In the present invention, various properties of the crosslinked heat-shrinkable laminated film were measured by the following methods. Thermal shrinkage (machine direction) the vertical length L ₀ film was 1 minute free shrink in glycerine bath for each temperature, measure the vertical length L after shrinkage was determined from the following equation. Shrinkage ratio (vertical direction) (%) = (L ₀ −L) / L ₀ × 100 Thermal shrinkage stress (vertical direction) A test piece having a width of 10 mm and a length of 50 mm is inserted into a gap between chucks of 30 mm.
mm and mounted in a glycerin bath at each temperature. At that time, the stress generated between the chucks was determined as a heat shrinkage stress in a unit of “kg / cm ² ”.・ Heat seal strength Two films are stacked in a state where the longitudinal direction of each film is aligned, and the film is sealed by fusing with a hot wire in a red hot state in the lateral direction. Next, a test specimen for a tensile test having a fusing seal portion having a width of 15 mm and a length of 70 mm positioned at the center is cut out from the sample. Then, this test piece was mounted on a tensile tester so that the distance between the chucks was 30 mm, and the tensile speed was 300 mm / mi.
Measured as the maximum strength required for breaking at n. This value is the heat seal strength in the unit of Kg / 15 mm. In general, when a heat-shrinkable film such as the heat-shrinkable film of the present invention is used to heat-shrink-wrap an article, at least 1.30 is required due to transportation and handling problems.
It is preferable to have a heat seal strength of Kg / 15 mm. Heat-resistant temperature A box made of corrugated cardboard, 20 cm long, 20 cm wide and 5 cm high, whose upper surface is cut into a square of 10 cm × 10 cm, is roughly hermetically sealed using a heat-shrinkable film, and pin holes for air release are provided as appropriate. Next, this is passed through a heat shrink tunnel set at a certain temperature and shrink-wrapped, and then the state of the film in the portion where the box is cut out is observed. This operation was repeated while increasing the temperature of the heat collection tunnel by 5 ° C. in increments of 5 ° C., and the maximum temperature at which a good shrink wrapping finish without “whitening” was obtained was determined as the “heat-resistant temperature”. This heat resistant temperature is the highest heat shrink tunnel temperature at which a good heat shrink wrap finish is obtained without "burn".

(Examples 1, 2, 3) A linear low-density ethylene-α-olefin copolymer (resin number 5) having a density of 0.930 g / cm ³ shown in Table 1 was used as both surface layers.
A tube-shaped co-extruded three-layer unstretched raw sheet having a base layer of a linear low-density ethylene-α-olefin copolymer of 890 g / cm ³ (resin No. 1) was subjected to three extruders and a circular for three-layer co-extrusion. Obtained by die. The total thickness of the obtained three-layer unstretched raw sheet was about 220 μ, and the thickness ratio of each layer was about 1: 3: 1 from one outermost layer. At the time of extrusion molding, immediately after the co-extrusion, rapid cooling was performed by a conventional water cooling method. Then, the three-layer unstretched raw sheet was irradiated with electron beams of 7, 15, and 25 Mrad in a nitrogen atmosphere through an electron beam accelerator manufactured by Nissin High Voltage. Next, these three-layer unstretched raw sheets were stretched 4.0 times in both the machine direction and the transverse direction by a conventional inflation method, but an easily stretched multilayer biaxially stretched film could be obtained. The multilayer biaxially stretched film was heat-set while being relaxed to obtain a heat-shrinkable laminated film having a total thickness of 15 μm. Table 2 shows the measured values of the resin composition and physical properties such as heat seal strength of the obtained film. Each film showed high heat shrinkage and heat shrinkage stress at each temperature, and also had good heat seal strength. In addition, the film strength and transparency were good.

Example 4 Density 0.921 shown in Table 1
g / cm ³ of a linear low-density ethylene-α-olefin copolymer (resin number 4) as both surface layers, and a density of 0.905 g / cm ³
A tubular co-extruded three-layer unstretched raw sheet having a base layer of a linear low-density ethylene-α-olefin copolymer (resin No. 2) of cm ³ was obtained in the same manner as in Examples 1, 2 and 3. . Then, using this tubular co-extruded three-layer unstretched raw sheet, an electron beam of 15 Mrad was irradiated in the same manner as in Examples 1, 2 and 3. Further, Example 1,
A 15 μm heat-shrinkable laminated film having a total thickness of 15 μm was produced in the same manner as in 2 and 3. As a result, stretching could be easily performed. In addition, the measured values of physical properties such as the resin composition and heat seal strength of the obtained film are shown in Table 2, and all the films show high heat shrinkage and heat shrinkage stress at each temperature, and have good heat seal strength. Met. In addition, the film strength and transparency were good.

Example 5 Density 0.912 shown in Table 1
g / cm ³ of a linear low-density ethylene-α-olefin copolymer (resin No. 3) as both surface layers, and a density of 0.890 g / cm ^3.
A tubular coextruded three-layer unstretched raw sheet having a linear low-density ethylene-α-olefin copolymer (resin number 1) of cm ³ as a base layer was obtained by the same method as in Examples 1, 2 and 3. Then, this tubular co-extruded three-layer unstretched raw sheet was prepared in the same manner as in Examples 1, 2 and 3 for 10 times.
An Mrad electron beam was applied. Further, a trial production of a heat-shrinkable laminated film having a total thickness of 15 μm was performed by using the tubular co-extruded three-layer unstretched raw sheet in the same manner as in Examples 1, 2 and 3. As a result, stretching could be easily performed. In addition, the measured values of physical properties such as the resin composition and the heat seal strength of the obtained film are shown in Table 2, and all the films show high heat shrinkage and heat shrinkage stress at each temperature, and also have good heat seal strength. Met.
In addition, the film strength and transparency were good.

Example 6 Density 0.905 shown in Table 1
g / cm ³ of a linear low-density ethylene-α-olefin copolymer (resin number 2) for both surface layers, and a density of 0.890 g / cm ³
A tubular coextruded three-layer unstretched raw sheet having a linear low-density ethylene-α-olefin copolymer (resin number 1) of cm ³ as a base layer was obtained by the same method as in Examples 1, 2 and 3. The tubular co-extruded three-layer unstretched raw sheet is then coated with the same method as in Examples 1, 2 and 3 for 10 times.
Irradiated with a Mard electron beam. Further, a trial production of a heat-shrinkable laminated film having a total thickness of 15 μm was performed using the tubular co-extruded three-layer unstretched raw sheet in the same manner as in Examples 1, 2 and 3. As a result, stretching could be easily performed. In addition, the measured values of physical properties such as the resin composition and the heat seal strength of the obtained film are shown in Table 2, and all the films show high heat shrinkage and heat shrinkage stress at each temperature, and also have good heat seal strength. Met.
In addition, the film strength and transparency were good. However, the heat resistance temperature was lower than those of other Examples and Comparative Examples, and the heat shrink wrapping suitability at high temperatures was poor.

(Comparative Examples 1 and 2) A tubular coextruded three-layer unstretched raw sheet obtained by the same resin composition and method as in Examples 1, 2 and 3 was applied in the same manner as in Examples 1, 2 and 3. 4 and 35 Mard electron beams. next,
Stretching was attempted in the same manner as in Examples 1, 2 and 3. As a result, the film irradiated with the 4 Mrad electron beam could not be stretched. In the case of irradiation with an electron beam of 35 Mrad, although the elongation was good, the obtained overall thickness was 15 mm.
The heat seal strength of the μ heat shrinkable laminated film was low as shown in Table 2.

(Comparative Examples 3 and 4) Density 0.9 shown in Table 1
A linear low-density ethylene-α-olefin copolymer (resin number 3) of 12 g / cm ³ was used as both surface layers, and had a density of 0.905.
A tubular coextruded three-layer unstretched raw sheet having a g / cm ³ linear low-density ethylene-α-olefin copolymer (resin No. 2) as a base layer was obtained by the same method as in Examples 1, 2, and 3. Was. Then, the tubular co-extruded three-layer unstretched raw sheet was treated with the same method as in Examples 1, 2 and 3 to obtain 1 sheet.
Irradiation with electron beams of 0 and 15 Mrad was performed. Further, a trial production of a heat-shrinkable laminated film having a total thickness of 15 μm was performed using the tubular co-extruded three-layer unstretched raw sheet in the same manner as in Examples 1, 2 and 3. As a result, 10M
Irradiated with rad electron beam could not be stretched. When irradiated with a 15 Mrad electron beam, although the film could be stretched favorably, the obtained overall thickness of the heat-shrinkable laminated film having a thickness of 15 μm was low as shown in Table 2.

Comparative Example 5 Density 0.921 shown in Table 1
A tubular coextruded single-layer unstretched raw sheet made of a linear low-density ethylene-α-olefin copolymer (resin No. 4) of g / cm ³ was obtained in the same manner as in Examples 1 and 2.
Then, the tubular co-extruded single-layer unstretched raw sheet was irradiated with an electron beam of 15 Mrad in the same manner as in Examples 1, 2 and 3. Then, stretching was attempted in the same manner as in Examples 1, 2 and 3, but could not be satisfactorily stretched.

(Comparative Example 6) Density 0.905 shown in Table 1.
A tubular coextruded single-layer unstretched raw sheet made of a linear low-density ethylene-α-olefin copolymer (resin No. 2) of g / cm ³ was obtained in the same manner as in Examples 1, 2 and 3. Then, 15 Mrad was applied to this tubular co-extruded single-layer unstretched raw sheet in the same manner as in Examples 1, 2 and 3.
Was irradiated. Further, a trial production of a heat-shrinkable laminated film having a total thickness of 15 μm was performed using the tubular co-extruded single-layer unstretched raw sheet in the same manner as in Examples 1, 2, and 3. As a result, stretching could be easily performed. However, the heat seal strength of the obtained film was insufficient as can be seen from Table 2. Further, the heat resistance temperature was lower than those of the other Examples and Comparative Examples, and the suitability for heat shrink wrapping at high temperatures was poor.

(Comparative Example 7) Density 0.930 shown in Table 1
g / cm ³ linear low-density ethylene-α-olefin copolymer (resin No. 5) was used as both surface layers, and the density was 0.940 g / cm ^3.
cm ³ of ethylene-vinyl acetate copolymer (resin number 6,
A tubular coextruded three-layer stretched raw sheet having a base layer (vinyl acetate content: 15% by weight) was obtained by the same method as in Examples 1, 2 and 3. Then, the tube-shaped co-extruded three-layer fully stretched raw sheet was irradiated with an electron beam of 10 Mrad in the same manner as in Examples 1, 2 and 3. Further, the three-layer unstretched raw sheet in the form of a tube was co-extruded in Examples 1 and 2.
A 15 μm heat-shrinkable laminated film having a total thickness of 15 μm was produced in the same manner as in Examples 3 and 3. As a result, stretching could be easily performed. However, the tensile strength and transparency (haze) of the obtained heat-shrinkable laminated film are shown in Table 2.
Was insufficient as shown in FIG.

Comparative Example 8 Density 0.930 shown in Table 1
g / cm ³ of a linear low-density ethylene-α-olefin copolymer (resin number 5) as both surface layers, and a density of 0.921 g / cm ^3.
A tubular coextruded three-layer unstretched raw sheet having a low-density ethylene homopolymer (resin number 7) of ³ cm3 as a base layer,
Obtained by the same method as in Examples 1, 2 and 3. Then, the tube-shaped co-extruded three-layer unstretched raw sheet was irradiated with an electron beam of 10 Mrad in the same manner as in Examples 1, 2 and 3. Further, a trial production of a heat-shrinkable laminated film having a total thickness of 15 μm was performed using the tubular co-extruded three-layer unstretched raw sheet in the same manner as in Examples 1, 2 and 3. As a result, stretching could be easily performed.
However, the tensile strength and transparency (haze) of the obtained heat-shrinkable laminated film were insufficient as shown in Table 2.

[0030]

[Table 1]

[0031]

[Table 2- (1)]

[Table 2- (2)]

[0032]

The cross-linked heat-shrinkable laminated film of the present invention comprises:
By forming the surface layer with a linear low-density ethylene-α-olefin copolymer having a higher density than the base layer, only the resin forming the base layer is selectively and highly crosslinked, and the surface layer is not crosslinked much as compared with the base layer. Things. Therefore, the laminated film of the present invention, like the conventional crosslinked heat-shrinkable laminated film, the excellent properties of the linear low-density ethylene-α-olefin copolymer are impaired by laminating different kinds of resins. Without the need to use additives such as a crosslinking inhibitor, the linear low-density ethylene-α-olefin copolymer original excellent properties, such as transparency, while maintaining the film strength, heat shrinkage and Excellent heat shrinkage stress and excellent heat sealability.

Continuation of front page (56) References JP-A-1-22548 (JP, A) JP-A-50-72942 (JP, A) JP-A-50-12167 (JP, A) JP-A-63-262242 (JP) , A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B32B 1/00-35/00 B29C 61/00-61/10

Claims (2)

(57) [Claims] 1. A base layer formed from a linear low-density ethylene-α-olefin copolymer, having a density of at least 0.01 g / cm on both sides of the base layer formed from the linear low-density ethylene-α-olefin copolymer. A laminated film having a surface layer formed from a linear low-density ethylene-α-olefin copolymer having a size of ³ or more is irradiated with ionizing radiation by 5 to 30 Mrad.
A crosslinked heat-shrinkable laminated film obtained by irradiating and then heat-stretching. 2. A linear low-density ethylene forming a surface layer.
2. The crosslinked heat-shrinkable laminated film according to claim 1, wherein the density of the α-olefin copolymer is 0.910 g / cm ³ or more.