JP3239247B2 - Ethylene-based heat-shrinkable film with small amount of eluted material by n-hexane extraction - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sanitary effluent from n-hexane extraction which is sanitary even when used for heat shrink wrapping of foods, pharmaceuticals, and the like in which an object to be wrapped comes into direct contact with a packaging film. More particularly, the present invention relates to an ethylene-based heat-shrinkable film suitably used for heat-shrinkable packaging of fresh foods and the like.

[0002]

2. Description of the Related Art Conventionally, an ethylene-based heat-shrinkable film has high heat-sealing strength and excellent low-temperature heat-shrinkability, and has been used as a heat-shrinkable packaging film for foods and the like.
In addition, the film is less sanitary than a polyvinyl chloride-based heat-shrinkable film and is hygienic, and thus is suitably used as a heat-shrinkable packaging film for foods and the like.

However, recently, an ethylene-based heat-shrinkable film having excellent low-temperature heat-shrinkability has been demanded, and a film meeting the demand has been developed. For example, Japanese Patent Publication No. 5-30855 describes a method for producing a heat-shrinkable film as described below. That is, the publication states that the density at 25 ° C. is 0.90 to 0.93 g.
/ Cm ³ , melt index 0.2-3.0 g / 1
0 minute ethylene-α-olefin copolymer (A ′) 90
And a density at 25 ° C of 0.87 to 0.
91 g / cm ³ and 0.014 g from the density of (A ')
/ Cm ³ or more, melt index 0.2 ~
A mixture of 5.0 g / 10 minutes of the ethylene-α-olefin copolymer (B ′) and 10 to 50% by weight is melt-extruded to form a substantially unstretched film at least in a uniaxial direction in a temperature range in which the film can be oriented. A method for producing a polyethylene-based heat-shrinkable film excellent in low-temperature heat-shrinkability, characterized by being stretched by 200% or more, is described.

However, the polyethylene heat-shrinkable film has a density at 25 ° C. of 0.870 to 0.91.
0 g / cm ³ and 0.014 g / cm ³ from the density of (A ′).
cm ³ or more, and the melt index is 0.2-5.
0 g / 10 min ethylene-α-olefin copolymer (B ′) ”, which has excellent low-temperature heat shrinkability, but has a wide molecular weight distribution and a low molecular weight substance. When the copolymer (B ') is used as a heat-shrinkable packaging film, the amount of eluted material by n-hexane extraction is large, especially when the copolymer (B') is used as a heat-shrinkable packaging film. In the heat shrink wrapping which comes into direct contact with the article to be packaged, there is a problem in hygiene. The US F
The DA standard specifies the amount of n-hexane extracted for packaging films used in contact with food from a hygienic point of view.

[0005]

SUMMARY OF THE INVENTION The present invention has a density of 0.
In an ethylene-based heat-shrinkable film containing an ethylene-α-olefin copolymer of 87 to 0.91 g / cm ³ , the amount of the eluate by n-hexane extraction is not reduced without lowering the low-temperature heat-shrinkability. It is an object of the present invention to provide an ethylene-based heat-shrinkable film that is reduced in contamination of a packaged object such as food.

[0006]

According to the present invention, the following means have been taken in order to solve the above-mentioned problems. That is,
The core layer is based on 100 parts by weight of the ethylene-α-olefin copolymer (A) having a density of 0.900 to 0.930 g / cm ³ .
And the density is lower than the density of the copolymer (A);
870~0.910g / cm becomes ³ ethylene -α- olefin copolymer (B) from 5 to 60 parts by weight of mixture, both outer layers is a density 0.915~0.935g / cm
^3. An ethylene-based heat-shrinkable film having a small amount of eluted product by n-hexane extraction comprising the ethylene-α-olefin copolymer (C) is provided, and preferably, each of the outer layers has a thickness of 2 to 2. There is provided an ethylene-based heat-shrinkable film having a small amount of eluate by the n-hexane extraction, characterized in that the film is 30 μm.

Hereinafter, the present invention will be described in more detail. Density 0.900 to 0.930 g / cm ³ used for the core layer
As the ethylene-α-olefin copolymer (A),
Ethylene and an α-olefin having 4 to 12 carbon atoms in 1 to 25
%, Preferably 1 to 15% by weight. The copolymer is generally called a linear low-density polyethylene. It is known that the copolymer has a good stretch processability and a film excellent in heat shrinkability can be obtained. It is also known that a film having excellent transparency and impact strength can be obtained.

[0008] Ethylene-α-olefin copolymer (A)
If the density is less than 0.900 g / cm ³ , stretching orientation is unlikely to occur, and the resulting film has a low heat shrinkage. Further, the density of the ethylene-α-olefin copolymer (A) is 0.930 g / cm ³
Exceeding the temperature is not preferable because the stretching process cannot be performed unless the temperature is high, and the low-temperature heat shrinkability of the obtained film decreases.

[0009] The density of the ethylene-
smaller than the density of the α-olefin copolymer (A),
0.870 to 0.910 g / cm ³ of the ethylene-α-olefin copolymer (B) includes ethylene and carbon number 4
A copolymer with α-olefins of No. 8 to No. 8 is used. And, as the α-olefin having 4 to 8 carbon atoms, butene-1, pentene-1, hexene-1, octene-1, 4
-Methylpentene-1 and the like, and those obtained by copolymerizing 5 to 20 mol% of these α-olefins are used. These resins are generally commercially available as modifiers for polyolefin resins.

[0010] Ethylene-α-olefin copolymer (B)
Is higher than the density of the ethylene-α-olefin copolymer (A), the effect of improving the low-temperature heat shrinkability is lost. The density is 0.910 g /
If it exceeds cm ³ , the effect of improving the low-temperature heat shrinkability will be lost. Further, if it is less than 0.870 g / cm ³ , the compatibility with the ethylene-α-olefin copolymer (A) becomes poor, and the film-forming property and the stretching processability become poor. In such a region, the heat shrinkage rate is lowered, and the film is unsuitable as a heat shrinkable packaging film.

[0011] Ethylene-α-olefin copolymer (A)
Of ethylene and ethylene-α-olefin copolymer (B)
When the ethylene-α-olefin copolymer (A) 100
Ethylene-α-olefin copolymer (B) based on parts by weight
Is 5 to 60 parts by weight . When the amount of the ethylene-α-olefin copolymer (B) is less than 5 parts by weight, there is no effect of improving the low-temperature heat shrinkage. This is not preferred as a packaging film, and the elution amount of the n-hexane extract is increased.

The density used for both outer layers is 0.915 to 0.9
As the ethylene-α-olefin copolymer (C) of 35 g / cm ³ , as with the ethylene-α-olefin copolymer (A), ethylene and an α-olefin having 4 to 12 carbon atoms are 1 to 25% by weight. %, Preferably 1 to 15% by weight
Is used. And, the density of the ethylene-α-olefin copolymer (C) is 0.915
If it is less than g / cm ³ , elution of the n-hexane extract cannot be suppressed. In addition, the density is 0.935 g
If it exceeds / cm ³ , the heat shrinkability at low temperature is lowered, and thus it is not suitable as a heat shrinkable packaging film.

The thickness of each of the ethylene-α-olefin copolymer (C) layers of the outer layers is 2 to 30 μm,
Is preferable. More preferably, the range is 5 to 25 μm. When the thickness of each of the outer layers is less than 2 μm,
If the amount of eluate from the n-hexane extraction increases, and if the thickness of both outer layers exceeds 30 μm, the low-temperature heat shrinkage decreases, which is both undesirable.

The method for producing the ethylene-based heat-shrinkable film of the present invention is not particularly limited, but it can be produced by the following method. That is, using two extruders and two types of three-layer dies, a laminated unstretched raw material having a core layer and both outer layers made of a predetermined resin composition is formed. Then, the heat-shrinkable film is obtained by uniaxially or biaxially stretching the raw unstretched laminate. Although there are various methods for stretching, in the case of biaxial stretching, an inflation biaxial stretching method is desirable in order to make the heat shrinkability balance in the longitudinal direction and the transverse direction uniform.

[0015]

In the ethylene-based heat-shrinkable film of the present invention, the ethylene-α-olefin copolymer (B) constituting the core layer has a wide molecular weight distribution and contains a large amount of low molecular weight substances. Since the molecular weight substance elutes, ethylene-α-olefin copolymer (A) or ethylene-α-olefin
It is generally known that there are more n-hexane extracts than the olefin copolymer (C). Therefore, a large amount of the n-hexane extract elutes from the layer containing the ethylene-α-olefin copolymer (B). Therefore, as in the present invention, the ethylene-α-olefin copolymer (B) -containing layer is provided on both sides of the layer containing ethylene-α-olefin copolymer (B),
By providing a layer made of the α-olefin copolymer (C), elution of the n-hexane extract from the ethylene-α-olefin copolymer (B) is blocked.

Further, the ethylene-α-olefin copolymer (C) layers of both outer layers have good adhesiveness to the core layer, can be laminated and stretched with the core layer, and have an extremely high stretching temperature. Therefore, the obtained laminated stretched film has good low-temperature heat shrinkage without impairing the low-temperature heat shrinkability, which is the maximum characteristic of the core layer.

[0017]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. It should be noted that the present invention is not limited to only the matters described in the embodiments. The amount of the extract with n-hexane was measured by the following method. First, a bag having an inner surface of 200 × 200 mm is made of a sample film, and 200 cc of n-hexane is sealed in the bag. Then, the bag was immersed in a water bath at 25 ° C. for 2 hours, and then the n-hexane was taken out and distilled to obtain a residue. Further, after the residue was dried, its weight was measured, and the amount of eluted product by n-hexane extraction was determined in units of g / m ² . The low-temperature heat shrinkability was evaluated by the heat shrinkage in hot water at 80 ° C.

Example 1 An ethylene-hexene copolymer (hexene content: 17 wt%) (A) having a density of 0.912 g / cm ^{3 was} added to a core layer in an amount of 10%.
0 parts by weight and a resin composition obtained by mixing 40 parts by weight of a density of 0.880 g / cm ³ ethylene-butene copolymer (butene content: 12 mol%) (B) were used, and 0.925 was used for both outer layers.
g / cm ^{3 of} an ethylene-hexene copolymer (hexene content: 13 wt%) (C) was used to obtain a laminated unstretched raw material by a co-extrusion method. Stretching was performed by the method to obtain an ethylene-based heat-shrinkable film. The thickness of each layer was set to 8 μm, 14 μm, and 8 μm from one outer layer. As a result of measuring the amount of eluate of the obtained ethylene-based heat-shrinkable film by n-hexane extraction, the result was as low as 0.38 g / m ² . The heat shrinkage in hot water at 80 ° C. was 44% and 44% in the vertical and horizontal directions, respectively, indicating that the heat shrinkage was excellent at low temperatures.

[0019] it was used in the core layer of Comparative Example 1 Example 1, and density 0.912 g / cm ³ of ethylene -α- olefin copolymer (A) 100 parts by weight of a density 0.880 g / cm ³ ethylene -α -After obtaining an unstretched raw material consisting solely of a resin composition mixed with 40 parts by weight of an olefin copolymer (B), the unstretched raw material is stretched by an inflation biaxial stretching method, and then heat-shrinkable. A film was obtained. The thickness of the film was 30 μm. The amount of eluate from the obtained heat-shrinkable film by n-hexane extraction was as large as 0.56 g / m ² . In addition, 1
The heat shrinkage in hot water at 00 ° C. was 41% and 52% in the vertical and horizontal directions, respectively, indicating excellent low-temperature heat shrinkability.

Comparative Example 2 An unstretched raw material consisting of only the ethylene-α-olefin copolymer (C) having a density of 0.925 g / cm ³ and used for the outer layer of Example 1 was obtained. On the contrary, stretching was performed by an inflation biaxial stretching method to obtain a heat-shrinkable film. The thickness of the film was 30 μm. The amount of eluate from the obtained heat-shrinkable film by n-hexane extraction was as small as 0.32 g / m ² . But 80 ° C
Heat shrinkage in hot water is 22
% And 21% were inferior in low-temperature heat shrinkability.

Comparative Example 3 A heat-shrinkable film was obtained in the same manner as in Example 1 except that polypropylene was used for both outer layers. In addition, the thickness of the obtained film and the thickness configuration of each layer were the same as those of the film of Example 1. However, although the amount of eluate by the n-hexane extraction was small, the heat shrinkage in hot water at 100 ° C. was 24% and 26% in the vertical and horizontal directions, respectively, and the low-temperature heat shrinkability was poor. .

Comparative Example 4 A heat-shrinkable film was obtained in the same manner as in Example 1 except that an ethylene-vinyl acetate copolymer (containing 10% by weight of vinyl acetate) was used for both outer layers. In addition, the thickness of the obtained film and the thickness configuration of each layer were the same as those of the film of Example 1. The amount of eluate from the obtained heat-shrinkable film by n-hexane extraction was as large as 0.61 g / m ² .
The low-temperature heat shrinkability was good.

Comparative Example 5 Density 0.912 g / c used for the core layer of Example 1 for both outer layers
m ³ of ethylene - except that hexene copolymer (A), by the same method as in Example 1 to give a heat-shrinkable film. In addition, the thickness of the obtained film and the thickness configuration of each layer were the same as those of the film of Example 1. The amount of the eluate obtained by extracting the heat-shrinkable film by n-hexane was 0.1.
It was as high as 49 g / m ² . The low-temperature heat shrinkability was good.

[0024]

The ethylene-based heat-shrinkable film of the present invention has a small amount of n-hexane extract eluted. It is a target. Moreover, since it has excellent low-temperature heat shrinkability, it is most suitable for heat shrink wrapping of fresh foods and the like that cannot be heated to high temperatures during heat shrink wrapping.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-22548 (JP, A) JP-A-3-215034 (JP, A) JP-A-63-10639 (JP, A) 237145 (JP, A) JP-A-59-149941 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B32B 1/00-35/00

Claims (2)

(57) [Claims] 1. The core layer has a density of 0.900 to 0.930 g.
/ Cm ³ ethylene-α-olefin copolymer (A) 1
The ethylene-α-olefin copolymer (B) of 0.870 to 0.910 g / cm ³ having a density lower than that of the copolymer (A) is added in an amount of 5 to 60 parts by weight with respect to 00 parts by weight.
And the outer layers had a density of 0.915-0.
An ethylene-based heat-shrinkable film comprising 935 g / cm ^{3 of} an ethylene-α-olefin copolymer (C) and having a small amount of eluted material by n-hexane extraction. 2. The heat-shrinkable ethylene-based film according to claim 1, wherein the thickness of each of the outer layers is 2 to 30 μm.