JP2570359B2 - Multi-layer shrink film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a multilayer film which is soft and has excellent low-temperature shrinkage properties, transparency, gloss, blocking resistance, and preferably tear resistance. The present invention relates to a film for shrink packaging.

<Prior art> Currently, polypropylene, polyvinyl chloride, polyethylene, etc. are known as materials for shrink wrapping films, but each has advantages and disadvantages, and can be obtained in all aspects. Not.

Polyvinyl chloride has excellent transparency and excellent low-temperature shrinkage, but has poor low-temperature resistance and tear resistance, and has problems such as generation of corrosive gas during fusing and sealing.

Recently, as a polyethylene, a film which has been subjected to an axial stretching treatment using a linear low-density polyethylene as a material has been released.However, although the film has excellent low-temperature resistance and seal strength, it has poor transparency or low-temperature shrinkage. There is a problem that is not good.

As the polypropylene, a propylene-ethylene random copolymer obtained by copolymerizing about 3 to 5% by weight of ethylene,
There is a biaxially stretched film of propylene-ethylene-butene-1 ternary random copolymer obtained by copolymerizing ethylene in an amount of about 1 to 3 wt% and butene-1 in an amount of about 3 to 10 wt%. However, it has the drawback that the low-temperature shrinkage is not so good and the tear resistance is poor.
Among the same propylene-based polymers, there is a film made of a propylene-butene-1 copolymer obtained by copolymerizing a relatively large amount of butene-1 (JP-A-53-113692). Although it is possible to obtain a film exhibiting low-temperature shrinkage comparable to a vinyl film, the film has drawbacks such as poor blocking resistance and poor tear resistance.

In addition to the above-described single-layer film, a multilayer shrink film having a linear polyethylene resin as a core layer and a propylene-ethylene copolymer as both skin layers is known (Japanese Patent Application Laid-Open No. 58-166049). No.). However, according to the findings of the present inventors, it is true that both the advantages of the linear polyethylene resin and the propylene-ethylene copolymer are combined, the transparency and gloss are excellent, and the tear resistance is also improved to some extent. However, there is a problem that the low-temperature shrinkability is not so good.

<Problems to be solved by the invention> In view of the above situation, the present invention has
An object of the present invention is to provide a film for shrink packaging having excellent properties such as blocking resistance, low-temperature resistance, and strength of a seal portion, preferably excellent tear resistance, and extremely excellent low-temperature shrinkage.

<Means for Solving the Problems> The present inventors have proposed a specific propylene-based soft resin having a low Vicat softening point in the intermediate layer, a linear ultra-low density polyethylene,
Alternatively, they have found that a shrink wrapping film having all of the above properties can be obtained by using them as a plurality of layers and using a specific polypropylene resin as both outermost layers, and completed the present invention.

That is, the present invention provides an intermediate layer having a Vicat softening point of 115.
℃ ° C or lower, consisting essentially of a polypropylene resin having a Vicat softening point equal to or higher than the Vicat softening point of the intermediate layer soft resin and between 80 ° C and 150 ° C. After film formation, it is essentially composed of a multilayer shrink film that has been stretched and a linear ultra-low density polyethylene as an intermediate layer, and a polypropylene resin having a Vicat softening point of 80 ° C to 150 ° C as both outermost layers. The present invention relates to a multilayer shrink film which is formed and then stretched.

The features of the multilayer shrink film of the present invention are that, despite exhibiting a low-temperature shrinkage comparable to that of a polyvinyl chloride shrink film, it has excellent blocking resistance, transparency, gloss, low-temperature resistance, seal portion strength, and the like. Are excellent in the above characteristics, preferably excellent in tear resistance, in addition, the finish is beautiful with little generation of wrinkles at the corners during shrink wrapping, and no generation of corrosive gas during fusing seal.

 Hereinafter, the present invention will be described in detail.

The polypropylene-based resin used as both outermost layers of the multilayer shrink film of the present invention is a known resin, and includes propylene-ethylene random copolymer, propylene-ethylene-butene-1 ternary random copolymer, and propylene-butene-1 copolymer. It is a propylene-based copolymer such as a polymer, of which the latter two have good low-temperature stretching properties, and have a Vicat softening point of 80 ° C to 150 ° C, preferably 85 ° C to 140 ° C. And more preferably 85
C to 130C. If the Vicat softening point exceeds the upper limit, stretching at low temperatures becomes impossible or the film is devitrified, which is not preferable.If the Vicat softening point is lower than the lower limit, the blocking resistance and the slipperiness of the film are poor. It is not preferable. In addition, in the propylene-based copolymer, the polypropylene-based resin containing the specific propylene-α-olefin copolymer in an amount of 20% by weight or more is stretched at a low temperature.
It is preferable because devitrification hardly occurs during stretching and the stretching processability is good.

The specific propylene-α-olefin copolymer,
The catalyst system is a known catalyst for the stereoregular polymerization of α-olefins, a so-called Ziegler-Natta catalyst, that is, an organic compound of a group IV-VIII transition metal compound and a group I-III typical metal of the periodic table. Using a compound comprising a compound and a third component such as an electron donating compound, it can be produced by a solvent polymerization method of polymerizing in a solvent or a gas phase polymerization method of polymerizing in a gas phase. For example, it can be obtained by a method of polymerizing the copolymer (B) described in Japanese Patent Application No. 61-164505, but any method can be used as long as it satisfies the conditions specified below.

The propylene-α-olefin copolymer is a copolymer of propylene and an α-olefin having 4 or more carbon atoms or propylene, an α-olefin having 4 or more carbon atoms and ethylene, and having 4 or more carbon atoms of the copolymer. α-olefin content is 8 to 35 mol% The ethylene content of the copolymer is 5 mol% or less The copolymer satisfies the condition that the cold xylene-soluble portion of the copolymer is 15 to 70 wt%.

The propylene-α-olefin copolymer is used in combination with a small amount of α-olefin having 4 or more carbon atoms or ethylene as a comonomer. Examples of the α-olefin having 4 or more carbon atoms include butene-1, pentene-1, and hexene-.
A single or combined use of 1,4-methyl-pentene-1 and the like can be mentioned. For example, when gas phase polymerization is carried out, butene-1 which can take a high partial pressure because it is difficult to liquefy is mainly used. preferable.

The propylene-α-olefin copolymer has an α-olefin content of 4 or more carbon atoms of 8 to 35 mol%,
~ 30 mol% is preferred. If the content of the α-olefin having 4 or more carbon atoms is below the lower limit, the film is devitrified or stretched at a low temperature when stretched at a low temperature. Slip and blocking resistance deteriorate, which is not preferable.

The ethylene content of the propylene-α-olefin copolymer is at most 5 mol%, preferably at most 3 mol%.
If the ethylene content exceeds the upper limit, the transparency of the film deteriorates with time and the blocking resistance deteriorates, which is not preferable.

The cold xylene-soluble portion (CXS) of the propylene-α-olefin copolymer is 15 to 70 wt%, and more preferably 16 to 60 wt%. If the CXS is below the lower limit, devitrification at the time of stretching at a low temperature or breaking is not preferred, and if the CXS exceeds the upper limit, the slip and blocking resistance of the stretched film are deteriorated, which is preferable. Absent.

In a preferred embodiment of the polypropylene resin used for both outermost layers in the present invention, the blending ratio of the propylene-α-olefin copolymer contained therein is 20% by weight or more, preferably 30% by weight or more. The propylene-α-
When the blending ratio of the olefin copolymer falls below the lower limit,
It is not preferable because of devitrification or breaking at the time of stretching at a low temperature.

In the present invention, the melt index (MI: measured at 230 ° C.) of the polypropylene resin used for both outermost layers is 0.5 to 20 g / 1.
It's 0 minutes. This resin has a Vicat softening point of 150 ° C
The above propylene copolymer (for example, polypropylene homopolymer) can be added. In this case, the Vicat softening point of the composition preferably falls within the range specified above. Further, a small amount of another polymer compound may be added to the resin.

The propylene-based soft resin used as the intermediate layer of the multilayer shrink film of the present invention is, in the polypropylene resin for the outermost layer, a Vicat softening point of 115 ° C or lower and a Vicat softening point of 110 ° C or lower. And more preferably 105 ° C. or lower.

If the Vicat softening point exceeds the upper limit, it is not preferable because stretching at a low temperature cannot be performed or the film is devitrified.

The Vicat softening point of the propylene-based soft resin used as the intermediate layer must be equal to or lower than the Vicat softening point of the polypropylene resin for the outermost layer.

This is because the advantage of a multilayer film structure is lost.

That is, the polypropylene resin for the outermost layer is required to have a higher Vicat softening point than the resin for the intermediate layer in order to impart properties such as heat resistance, blocking resistance, and scratch resistance of the film.

As a preferred embodiment of the propylene-based soft resin used as the intermediate layer, the propylene-α-olefin copolymer defined in the section of the propylene-based resin for the outermost layer is 20% by weight.
Those containing the above are preferred. This is because low-temperature stretching becomes easier and devitrification during stretching hardly occurs.

A preferred embodiment of the propylene-based soft resin used as the intermediate layer is a resin composition obtained by blending a propylene-based polymer with a hydrocarbon resin such as a petroleum resin (JP-A-49-9964).
No. 5, JP-A-49-99646, and Japanese Patent Application No. 61-260982).

The linear ultra-low-density polyethylene used as the intermediate layer of the multilayer shrink film of the present invention is a copolymer of ethylene and an α-olefin having substantially no long-chain branching, and has a density of 0.850 to 0.907 g / cm ³ , preferably 0.850 to 0.905 g / cm ³ .

If the density exceeds the upper limit, stretching at low temperatures becomes impossible, and the low-temperature shrinkability deteriorates, and the effect of improving the tear resistance and low-temperature resistance of the film is not so good. Copolymers having a density below the lower limit are not preferred because they are substantially difficult to obtain.

As the α-olefin, propylene, butene-1,
Hexene-1,4-methylpentene-1, octene-
1, decene-1 and the like can be exemplified, but they can be used alone or in combination. As the polymerization method, using a transition metal catalyst, solution polymerization under medium and low pressure, a method of gas polymerization, or polymerization using a transition metal catalyst under high pressure and high temperature similar to obtaining high pressure polyethylene (For example, Japanese Patent Application Laid-Open No. 59-230011, Japanese Patent Application No.
Reference examples 5 and 6 of 63048 publication.

Conventionally known linear low-density polyethylene, film stretching in a single layer is possible, but when it becomes linear ultra-low density polyethylene, film stretching in a single layer reduces the density to its limit. Although it seems that it was impossible, it was thought that it would not be possible to use it for the stretching process necessary to obtain a shrink film, but by making it an intermediate layer of a multilayer film, Surprisingly, stretching was possible, and an excellent shrink film was obtained.

The linear ultra-low-density polyethylene has crystallinity corresponding to its density, but may be a rubber-like copolymer having almost no crystallinity. The melt index (MI: measured at 190 ° C.) is 0.1 to 20 g / 10 minutes.

A linear low-density polyethylene can be blended with the linear ultra-low-density polyethylene, but the density of the blend preferably falls within the range specified above.
Further, within a range not significantly impairing the effects of the present invention, a high-pressure process polyethylene, ethylene-vinyl acetate copolymer, ionomer, ethylene-methyl methacrylate, ethylene-ethyl acrylate, ethylene-acrylate, etc. Is also good.

The resin used in the intermediate layer of the present invention has a melt index of 0.1 to 30 g / 10 minutes.

(However, 230 ° C for propylene resin and 1 for ethylene resin
Measured at 90 ° C. ).

In a preferred embodiment of the multilayer shrink film of the present invention, a plurality of intermediate layers are provided, each of which uses a propylene-based soft resin and a linear ultra-low density polyethylene as defined above.

This film can improve the inferior tear resistance of the multilayer shrink film when using a propylene-based soft resin as the intermediate layer, and also has a problem when high-speed packaging, when using a linear ultra-low density polyethylene as the intermediate layer. This has the advantage that the slow shrinkage rate can be improved.

In the multilayer shrink film of the present invention, the thickness ratio of the intermediate layer and the outermost layers is preferably 0.05 to 0.35 for the outermost layer and 0.30 to 0.90 for the intermediate layer.

The multilayer shrink film of the present invention may be provided with other layers in addition to the intermediate layer and both outermost layers as essential components.
(For example, a repro layer etc.) In the present invention, the resin composition constituting each layer includes an antistatic agent, an antiblocking agent, a lubricant, an antifogging agent, a stabilizer,
And an additive such as a nucleating agent can be added.

As a processing method for obtaining the multilayer shrink film of the present invention, first, a known sheet processing method such as a T-die casting method using a multilayer die or a water-cooled inflation method can be employed. Next, as a stretching method, a known uniaxial stretching method such as roll stretching or roll rolling, and a known biaxial stretching method such as tenter biaxial stretching or tubular biaxial stretching can be adopted.

The stretching temperature is preferably as low as possible from the viewpoint of improving the low-temperature shrinkability of the obtained film.However, if the Vicat softening points of the polypropylene resins of both outermost layers are high, stretching at low temperatures becomes difficult. . Suitable stretching temperatures range from room temperature to 150 ° C.

The stretching ratio is preferably 2 to 10 times. In this case, the stretching ratio of MD and TD does not necessarily need to be balanced, and can be arbitrarily selected according to each use. Further, heat setting may be performed.

The data and evaluation in Examples and Comparative Examples were performed according to the following methods.

(1) Haze value According to ASTM-D1003.

(2) Young's modulus According to ASTM-D882.

However, film test piece shape: 20 × 120 strip type. Distance between chucks: 50 mm. Peeling speed: 5 mm / min. (3) Tear strength (Elmendorf) According to ASTM-D1922.

(4) Heat shrinkage A film sample of 5 cm square was placed in a glycerin bath at a predetermined temperature.
Measure the shrinkage when immersed for 2 seconds.

(5) Vicat softening point According to ASTM-D1525. (However, the load is 1 kg.) (6) Density Conforms to ASTM-D1505.

However, the sample preparation conforms to JIS K 6760.

(7) Cold xylene soluble part (CXS) After dissolving 5 g of polymer in 500 ml of xylene, it is gradually cooled to room temperature. Then, after leaving in a bath at 20 ° C. for 4 hours, filtration was performed.
The filtrate is concentrated, dried, dried and weighed.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the examples unless it exceeds the gist.

<Example> Example 1 (Reference Example) As the resin for the outermost layer, Sumitomo Noblen was used. FS6623 (Mel
Index 5.9 g / 10 minutes, propylene-ethylene-butyl
Ten-1 ternary random copolymer (ethylene content 2.1wt
%, Butene-1 content 5.1 wt%), Vicat softening point 125 ° C)
And a resin for the intermediate layer, manufactured by Sumitomo Chemical Co., Ltd.
Density polyethylene (Excellen −VL, CN2002, Echile
-Butene-1 copolymer, density 0.899 g / cm^Three, Melt-in
Dex 2.2 g / 10 min).

By a pressing method, a multilayer sheet having a total thickness of 500μ was prepared, in which the thickness of the intermediate layer was 300μ and the thickness of both outermost layers was 100μ, respectively. Then, a 90 square sheet was collected to obtain a biaxially stretched film under the following conditions.

Stretching machine: Toyo Seiki desktop biaxial stretching machine Temperature: 90 ° C Preheating time: 3 minutes Stretching magnification: 5 × 5 times (simultaneous biaxial stretching) Stretching speed: 5m / min Note that the stretching temperature is less than 90 ° C Then, stretching was impossible.

Table 1 shows the physical properties of the thus obtained film having a thickness of about 20 μm. This film was a good film which was soft, excellent in transparency and tear strength, and excellent in low-temperature shrinkage and without stickiness.

Example 2 As a resin for the outermost layer, a propylene-butene-1 copolymer (butene-1 content: 19.0 mol%, CXS: 23.1 wt%, melt index: 4.5 g / 10 min, Vicat softening point: 99 ° C.) As the resin for the intermediate layer, the same resin as the resin for the intermediate layer used in Example 1 was used. Example 1 by pressing method
A multilayer sheet having a thickness of 500 μ was obtained in the same manner as described above. A biaxially stretched film was obtained from the multilayer sheet under the same conditions as in Example 1 except that the stretching temperature was changed to 70 ° C. Note that stretching was impossible at a temperature of less than 70 ° C. as the stretching temperature.

Table 1 shows the physical properties of the thus obtained film having a thickness of about 20 μm. This film was soft, excellent in transparency and tear strength, and extremely excellent in low-temperature shrinkability, and was a good film without stickiness.

Example 3 The resin for the outermost layer used in Example 2 as the resin for the outermost layer
The same resin as in Example 1 was used as the resin for the intermediate layer.
75% by weight of linear ultra-low density polyethylene used and linear low
Density polyethylene (Sumikasen -L, FA201-0,
Index 1.8 g / 10 min, density 0.921 g / cm^Three) 25 weight
% Resin composition (melt index 2.1 g / 10
Min, density 0.905g / cm^Three)It was used. Implemented by the press method
A multilayer sheet having a thickness of 500 μ was obtained in the same manner as in Example 1. this
Stretching temperature of 70 ° C from the multilayer sheet under the stretching conditions of Example 1
A 26-axis stretched film was obtained under the same conditions except that the film was changed to.
As for the stretching temperature, at a temperature lower than 70 ° C.,
It was impossible. About 20μ thick film obtained above
The properties are shown in Table 1. This film was the same as the film of Example 2.
The film was as good as the film.

Example 4 As the resin for the outermost layer, the tree for the outermost layer used in Example 2 was used.
Use the same material as fat, and use Toughmer A
-4085 (Mitsui Petrochemical's ethylene-butene-1 copolymer
Body, melt index 3.6g / 10min, density 0.88g / cm^Three)
used. In the pressing method, a thickness of 50
A 0μ multilayer sheet was obtained. From this multilayer sheet,
Except that the stretching temperature was changed to 70 ° C under the stretching conditions of 1, the same
Under the conditions, a biaxially stretched film was obtained. In addition, as the stretching temperature
Cannot be stretched at a temperature of less than 70 ° C. the above
Table 1 shows the physical properties of the film having a thickness of about 20 .mu.
This film has the same good film quality as the film of Example 2.
It was Lum.

Example 5 As the resin for the outermost layer, Sumitomo Noblen was used. WF816 (Pro
Pyrene-ethylene random copolymer ethylene content 4.8wt
%, Melt index 9.0g / 10min) 70 parts by weight
The same propylene used as the resin for the outermost layer in Example 2
Resin composition comprising 30 parts by weight of butene-1 copolymer
(Melt index 7.5g / 10 minutes, Vicat softening point 112
° C) and used in Example 1 as a resin for the intermediate layer.
The same resin as the resin for the intermediate layer was used. Press method
In the same manner as in Example 1, a multilayer sheet having a thickness of 500 μ was obtained. This
From the multilayer sheet of Example 1, the stretching temperature was set to 80 under the stretching conditions of Example 1.
The biaxially stretched film was obtained under the same conditions except that the temperature was changed to ° C.
Was. The stretching temperature is less than 80 ° C.
Was impossible. About 20μ thick film obtained above
The physical properties are shown in Table 1. This film is soft and transparent
Excellent in heat resistance and tear strength, and also excellent in low temperature shrinkability
In addition, it was a good film without stickiness.

Example 6 As the resin for the outermost layer, the same resin as the resin for the outermost layer used in Example 5 was used, and as the resin for the intermediate layer, a propylene-butene-1 copolymer (butene-1 content 21.1 mol%, CXS 26.2 wt%, melt index 3.5 g / 10 min, Vicat softening point 90 ° C) were used. By a pressing method, a multilayer sheet having a thickness of 500 μ was obtained in the same manner as in Example 1. From this multilayer sheet, the stretching temperature was 80 ° C. under the stretching conditions of Example 1.
A biaxially stretched film was obtained under the same conditions except that the film was changed to.
Note that stretching was not possible at a stretching temperature of less than 80 ° C. Table 1 shows the physical properties of the thus obtained film having a thickness of about 20 μm.

This film was moderately soft, excellent in transparency and low-temperature shrinkage, and was not sticky and had good blocking resistance.

Example 7 As the resin for the outermost layer, the tree for the outermost layer used in Example 2 was used.
Use the same resin as
Petroleum resin (Arakawa Chemical Alcon)
P-115) to which 15 parts by weight was added was used. Pre
In the same manner as in Example 1, a multilayer
I got it. From this multilayer sheet, the stretching conditions of Example 1 were used.
Then, biaxial rolling was performed under the same conditions except that the stretching temperature was changed to 70 ° C.
A drawn film was obtained. The stretching temperature is less than 70 ° C
Stretching was not possible at the temperature. About 20μ thickness obtained above
The film physical properties are shown in Table 1.

This film was moderately soft, had excellent transparency and low-temperature shrinkage, and was not sticky and had good blocking resistance.

Example 8 As the resin for the outermost layer, the same resin as the resin for the outermost layer used in Example 5 was used. As the first resin for the intermediate layer,
The second resin was the same as the resin for the intermediate layer used in Example 7, and the second resin was the same as the resin for the intermediate layer used in Example 1.

By pressing, the thickness of each of the two intermediate layers is 15
0μ sheet and both outermost layers have a thickness of 100
were laminated to form a multilayer sheet having a total thickness of 500μ. A biaxially stretched film was obtained from this multilayer sheet under the same conditions as in Example 1 except that the stretching temperature was changed to 80 ° C. Note that stretching was not possible at a stretching temperature of less than 80 ° C. Table 1 shows the physical properties of the thus obtained film having a thickness of about 20 μm.

This film was soft, excellent in transparency, low-temperature shrinkage, and tear resistance, was not sticky, and was a good film having a high shrinkage rate when measuring heat shrinkage.

Comparative Example 1 Tree for outermost layer used in Example 1 as resin for outermost layer
Use the same resin as
N -L (linear low density polyethylene FA201-0, mel
Toe index 1.8g / 10min, density 0.921g / cm^ThreeUse
Was. In the same manner as in Example 1, press the
A multilayer sheet was obtained. From this multilayer sheet, the
Under the same conditions except that the stretching temperature was changed to 110 ° C under the stretching conditions
A biaxially stretched film was obtained. The stretching temperature was 11
Stretching was not possible at temperatures below 0 ° C. Got above
The physical properties of the film having a thickness of about 20 μm are shown in Table 2. This file
The film had poor cold shrinkage.

Comparative Example 2 As the resin for the outermost layer, the same resin as the resin for the outermost layer used in Example 2 was used.
The same resin as used for the intermediate layer was used. By a pressing method, a multilayer sheet having a thickness of 500 μ was obtained in the same manner as in Example 1. A biaxially stretched film was obtained from this multilayer sheet under the same conditions as in Example 1 except that the stretching temperature was changed to 90 ° C. In addition, stretching was impossible at a temperature lower than 90 ° C. as the stretching temperature. Table 2 shows the physical properties of the thus obtained film having a thickness of about 20 μm. This film did not have very good low temperature shrinkage.

Comparative Example 3 The same resin as the outermost layer resin used in Example 1 was used in a single layer. A sheet having a thickness of 500 μ was obtained by a pressing method.
From this sheet, the stretching temperature was set to 120 under the stretching conditions of Example 1.
A biaxially stretched film was obtained under the same conditions except that the temperature was changed to ° C. Note that stretching was impossible at a temperature of less than 120 ° C. as the stretching temperature. Table 2 shows the physical properties of the thus obtained film having a thickness of about 20 μm. This film did not have good low-temperature shrinkability.

Comparative Example 4 The same resin as the outermost layer resin used in Example 2 was used in a single layer. A sheet having a thickness of 500 μ was obtained by a pressing method.
From this sheet, the stretching temperature was 90 ° C. under the stretching conditions of Example 1.
A biaxially stretched film was obtained under the same conditions except that the film was changed to.
In addition, stretching was impossible at a temperature lower than 90 ° C. as the stretching temperature. Table 2 shows the physical properties of the thus obtained film having a thickness of about 20 μm. This film did not have very good low temperature shrinkage.

Comparative Example 5 The same resin as the intermediate layer resin used in Comparative Example 1 was used in a single layer. A sheet having a thickness of 500 μ was obtained by a pressing method.
From this sheet, the stretching temperature was set to 110 under the stretching conditions of Example 1.
A biaxially stretched film was obtained under the same conditions except that the temperature was changed to ° C. Note that stretching was impossible at a temperature of less than 110 ° C. as the stretching temperature. Table 2 shows the physical properties of the thus obtained film having a thickness of about 20 μm. This film had good tear strength, but poor low-temperature shrinkability.

Comparative Example 6 The same resin as the resin for the intermediate layer used in Example 1 was used in a single layer. A sheet having a thickness of 500 μ was obtained by a pressing method.
From this sheet, biaxial stretching was attempted under the same conditions as in Example 1 except that the stretching temperature was changed over a wide range. However, no satisfactory film was obtained under any of the conditions.

Comparative Example 7 The same resin as the intermediate layer resin used in Example 7 was used in a single layer. A sheet having a thickness of 500 μ was obtained by a pressing method.
From this sheet, a biaxially stretched film was obtained under the same conditions as in Example 1 except that the stretching temperature was changed to 70 ° C. However, this film was remarkably tacky and had poor blocking resistance.

<Effects of the Invention> The multilayer shrink film of the present invention has good low-temperature shrinkability, and is excellent in transparency and blocking resistance. Also, when shrink-wrapped, wrinkles at the corners were less generated and the finish was beautiful.

Further, since the film is soft, there is no problem that the packaged object is warped. In addition, there is no generation of corrosive gas at the time of fusing and sealing, and it has an extremely large practical value that it can be manufactured at low cost.

Claims (4)

(57) [Claims] 1. An intermediate layer essentially consisting of a propylene-based soft resin having a Vicat softening point of 115 ° C. or lower, and both outermost layers having a Vicat softening point not lower than the Vicat softening point of the intermediate layer soft resin, and at 80 ° C. A multilayer shrink film consisting essentially of the following polypropylene resin having a temperature of up to 150 ° C., and after being formed into a film, subjected to a stretching treatment. Polypropylene resin containing at least 20% by weight or more of a copolymer of propylene and an α-olefin having 4 or more carbon atoms or a copolymer of propylene and an α-olefin having 4 or more carbon atoms and ethylene, wherein the copolymer satisfies the following conditions: . When the content of α-olefin having 4 or more carbon atoms in the copolymer is 8
The ethylene content of the copolymer is 5 mol% or less. The cold xylene soluble part of the copolymer is 15 to 70 wt%. 2. The multilayer shrink film according to claim 1, wherein the intermediate layer is a resin composition obtained by blending a propylene copolymer with a hydrocarbon resin. 3. An intermediate layer consisting essentially of linear ultra-low density polyethylene, and both outermost layers having a Vicat softening point of 80.
A multilayer shrink film consisting essentially of the following polypropylene-based resin having a temperature of from 150 ° C to 150 ° C, and after being formed into a film, stretched. Polypropylene resin containing at least 20% by weight or more of a copolymer of propylene and an α-olefin having 4 or more carbon atoms or a copolymer of propylene and an α-olefin having 4 or more carbon atoms and ethylene, wherein the copolymer satisfies the following conditions: . When the content of α-olefin having 4 or more carbon atoms in the copolymer is 8
The ethylene content of the copolymer is 5 mol% or less. The cold xylene soluble part of the copolymer is 15 to 70 wt%. 4. At least one of the plurality of intermediate layers consists essentially of a propylene-based soft resin having a Vicat softening point of 115 ° C. or less, and at least one layer consists essentially of linear ultra-low density polyethylene. As both outermost layers, the Vicat softening point is essentially equal to or higher than the Vicat softening point of the propylene-based soft resin for the intermediate layer, and is essentially composed of the following polypropylene-based resin having a temperature of 80 ° C to 150 ° C. Multi-layer shrink film made. Polypropylene resin containing at least 20% by weight or more of a copolymer of propylene and α-olefin having 4 or more carbon atoms or α-olefin having 4 or more carbon atoms and ethylene and satisfying the following conditions (1) to (4): . When the content of α-olefin having 4 or more carbon atoms in the copolymer is 8
The ethylene content of the copolymer is 5 mol% or less. The cold xylene soluble part of the copolymer is 15 to 70 wt%.