JPH0516231A - Heat-shrinkable film - Google Patents

Abstract

PURPOSE:To provide a heat-shrinkable film improved in the finish of the end surface in the lateral direction thereof at the time of the packing of a sleeve. CONSTITUTION:First and third layers composed of an ethylene/propylene random copolymer with ethylene content of 5.8wt.% and a second layer composed of a mixture of a 40/30/30 wt. ratio of an ethylene/propylene random copolymer with ethylene content of 5.8wt.%, polybutene-1 with an m.p. of 78 deg.C and low density polyethylene with density of 0,9 are subjected to co-extrusion molding to obtain a two-kind three-layered laminate which is, in turn, uniaxially stretched to produce a heat-shrinkable film.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to heat-shrinkable films.

[0002]

As a heat-shrinkable film, ethylene-
It is known that a propylene copolymer film is uniaxially stretched.

[0003]

However, the above-mentioned heat-shrinkable film has insufficient lateral elongation,
For example, in the case of sleeve packaging, there is a drawback in that the end face in the lateral direction is poorly finished.

[0004]

Means for Solving the Problems The inventors of the present invention have made extensive studies in view of the above situation, and found that a heat-shrinkable film in which an olefin polymer mixture containing a butene polymer as an essential component is uniaxially stretched, The inventors have found that the above problems can be solved and completed the present invention.

That is, the present invention provides a multilayer laminate having a heat-shrinkable film in which a mixture of a butene polymer and an olefin polymer other than that is uniaxially stretched, and a mixture layer of at least one butene polymer and another olefin polymer. The present invention provides a heat-shrinkable film in which the whole body is uniaxially stretched.

In the present invention, it is particularly important that the polymer component of butene is mixed, and the butene may be a polymer of itself, or as a copolymer with an olefin other than butene. It may be mixed.

The form of the mixture in the present invention includes, for example, a mixture of an ethylene polymer, a propylene polymer and a butene polymer, a mixture of an ethylene-propylene copolymer and a butene polymer, an ethylene polymer and a propylene-butene copolymer. Examples include a mixture of coalescence. As the mixture, a mixture of an ethylene-propylene copolymer and a butene polymer is preferable in terms of good compatibility.

As the butene polymer in the present invention, any olefin polymer having 4 carbon atoms can be used. Examples of the butene polymer include those having a melting point of 100 ° C. or lower, such as polybutene-1 and polybutene-2, and polybutene-1 is preferable.

As the olefin polymer other than the butene polymer in the present invention, any known and conventional one can be used, and examples thereof include an ethylene polymer and a propylene polymer. As the olefin polymer, an ethylene homopolymer is preferable when the film is fused at a low temperature, and a propylene homopolymer is preferable when the film needs a high tensile modulus, transparency and gloss. As the olefin polymer, for example, an ethylene-propylene copolymer can of course be used. As the ethylene-propylene copolymer, those having an ethylene content of 3 to 7% by weight are preferable among 1 to 10% by weight from the viewpoint of good low temperature shrinkability.

Next, the film of the present invention will be described by taking, for example, a uniaxially stretched film of a mixture of an ethylene-propylene copolymer and a butene polymer which is most preferable as the above mixture.

The mixing ratio of the ethylene-propylene copolymer and the butene polymer is not particularly limited, but usually 10 to 80 parts by weight of butene polymer per 100 parts by weight of ethylene-propylene copolymer, preferably the lateral direction. 20 to 40 parts by weight in terms of good heat shrinkability and good film formation. A film obtained by uniaxially stretching such a mixture of an ethylene-propylene copolymer and a butene polymer has excellent shrinkability in the transverse direction.

The mixture according to the present invention and other forms will be described. As the ethylene polymer in the mixture of the ethylene polymer and the propylene-butene copolymer, those having a density of 0.92 or less and having a low-temperature shrinkability as much as possible can be used, but among them, a linear low-density ethylene polymer is preferable. . Further, the mixing ratio of these is ethylene-propylene, when the total of ethylene, propylene and butene is 100.
The ratio is preferably the same as the mixing ratio of the propylene copolymer and the butene polymer. As the propylene-butene copolymer, those copolymerized at such a ratio may be used. Finally, a mixture of an ethylene polymer, a propylene polymer and a butene polymer will be described. The mixing ratio of the ethylene polymer, the propylene polymer and the butene polymer is 100% when the total of ethylene, propylene and butene is 100. The ratio is preferably the same as the mixing ratio of the propylene copolymer and the butene polymer.

If desired, the mixture may contain other polymers. For example, a film obtained by uniaxially stretching a mixture containing an ethylene-propylene copolymer and a butene polymer and further containing a low-density ethylene polymer is excellent not only in the transverse shrinkage but also in the longitudinal low temperature shrinkage. It has excellent properties and strain.

Examples of the low-density ethylene polymer that can be used at this time include linear and branched ones, but linear ones are preferable. Ethylene
The mixing ratio of the propylene copolymer, the butene polymer and the low density ethylene polymer is not particularly limited, but the mixing ratio of the ethylene-propylene copolymer and the butene polymer is such that the butene polymer is 100 parts by weight of the ethylene-propylene copolymer. 20 to 100 parts by weight of the polymer, and the mixing ratio of the ethylene-propylene copolymer and the low density ethylene polymer is 20 to 100 parts by weight of the low density ethylene polymer per 100 parts by weight of the ethylene propylene copolymer. preferable. The uniaxially stretched film having such a structure gradually shrinks from a low temperature during heat shrinkage, and therefore, for example, when the sleeve is packaged, the finish of the sleeve end surface is good.

The heat-shrinkable film of the present invention in which a mixture of a butene polymer and other olefin polymers is uniaxially stretched can be used as it is, but usually a mixture layer of butene polymer and other olefin polymers is used. At least 1
It is used by uniaxially stretching after laminating other resin on the surface. The lamination may be on one side or both sides, and the number of layers is not limited.

For example, a three-layer film in which a mixture layer of butene polymer and other olefin polymer is used as a central layer and other resin layers on both outer layers are laminated, and butene polymer is formed on both outer layers of the three-layer film. A multilayer film can be obtained by uniaxially stretching a mixture layer of other olefin polymers and further uniaxially stretching a 7-layer film or the like in which other resin layers are laminated on both outer layers.

The resin to be laminated is not particularly limited, but examples thereof include ethylene polymers and propylene polymers. When the surface of the heat-shrinkable film is required to have smoothness and sufficient tensile elasticity, it is preferable to use a propylene polymer. Of course, ethylene-propylene polymer can also be used.

For example, a three-blend of ethylene-propylene copolymer, butene polymer and low-density ethylene polymer is the core layer, and the outer two layers are, for example, ethylene-propylene copolymer having a relatively high melting point. The heat-shrinkable film in which the entire laminate is uniaxially stretched has no fear of breakage of the seal portion, a tight package can be obtained, and no worry of forced cooling. In addition, the appearance (haze, gloss) is improved, and the product display effect can be enhanced.

The thickness constitution of each layer of the above-mentioned two-kind three-layer uniaxially stretched film is not particularly limited, but the layer constitution ratio of the ethylene-propylene copolymer including both surface layers is 20 to 40% of the whole. In that case, cracking does not occur between the core layer and the surface layer during heat shrinkage of the film, there is no fear of whitening of the film, and the shrinkage ratio in the longitudinal direction as well as the shrinkage ratio in the lateral direction is extremely excellent. Becomes

Ethylene-based on the total thickness of 100%
In the case of a uniaxially stretched film having three blended layers of a propylene copolymer, a butene polymer, and a low-density ethylene polymer, for example, a uniaxially stretched film having four ethylene-propylene copolymer layers, the total of the three blended layers is The thickness is preferably 60% or more.

Further, the lower the melting point of the ethylene-propylene copolymer as the surface layer, the easier the end surface of the package will be fused when the film is heat-shrinked. The surface layer and the core layer have very good adhesiveness, and it is not necessary to provide an adhesive layer between both layers, but if necessary, use various adhesives such as acrylic, polyester, urethane and isocyanate adhesives together. You can

In the heat-shrinkable film of the present invention, if necessary, a water repellent, an oil repellent, an internal lubricant, an antifogging agent, a flame retardant, an aromatic, a colorant, a slip agent, an antiblocking agent, It is also possible to add various additives such as antistatic agents, release agents, fillers and metal powders in the required amounts.

For recycling, single-layered uniaxially stretched film can collect the film ears and unconforming products at the time of film formation, and two-kind three-layer uniaxially stretched film can have ears of film and unconforming products. Can be recovered in the second layer.

The conditions for forming the heat-shrinkable film of the present invention are not particularly limited, but the film is usually formed by a T-die, and in the case of a multilayer film, a multi-manifold,
A film can be formed by a co-extrusion method for both feed blocks. Regarding the stretching step, it is preferable to stretch the film in the stretching direction at a stretching ratio of 2 to 6 times, preferably 2.5 to 3.5 times. However, even if the draw ratio exceeds 3 times, there is not much difference in the shrinkage rate of each film formed. Further, for the longitudinal stretching of the film, an ordinary roll-shaped stretching machine can be used,
When the film is stretched after heating with a heating roll at 70 to 100 ° C., the low-temperature shrinkability of the film is not impaired, stretching unevenness is less likely to occur, and there is almost no load on the stretching roll, which is preferable. When using a heating roll having a temperature higher than 100 ° C., the stretching roll and the next cooling roll during cooling are
It is preferable that the temperature is set to 0 ° C., and the tension between the drawing roll and the cooling roll is not applied and cooling is performed while freely contracting.

[0025]

EXAMPLES Next, the present invention will be specifically described by way of examples. Hereinafter, unless otherwise specified,% means “% by weight” and part means “part by weight”.

Example 1 40 parts of ethylene-propylene random copolymer (ethylene content 5.8%), 30 parts of linear low-density polyethylene (density 0.912) and polybutene-1 (melting point 78 ° C.) 3
With 0 part of the mixture as the center, and both outsides thereof being the same ethylene-propylene copolymer as described above, extrusion was performed with a T-die at a total layer constitution ratio of 30% to obtain a laminated film of 45 μm. This laminated unstretched raw film was stretched 3.0 times in the machine direction at a roll temperature of 90 ° C. by a stretching roll to obtain a 15 μm laminated longitudinally stretchable heat-shrinkable film. A shrink tunnel test was conducted on an integrated package (2 × 5 pieces) of a snack box using the polypropylene-based longitudinally uniaxially stretched heat-shrinkable film. When the sample was passed through a shrink tunnel set at a temperature of 170 ℃ in the tunnel and a heating time of 15 seconds, wrinkles on the end face,
A package having a very good finish was obtained without fusion. Further, although the set temperature in the tunnel was changed by 10 ° C. up and down, there was no change in the finish of the package, and a rough temperature setting was sufficient. Also, the seal part did not break during the passage through the tunnel and immediately after the passage through the tunnel. Regarding the appearance, both gloss and transparency were the same as those of the polypropylene film.

Example 2 40 parts of ethylene-propylene random copolymer (ethylene content 5.8%), 30 parts of linear low-density polyethylene (density 0.912) and polybutene-1 (melting point 78 ° C.) 3
The mixture of 0 part was extruded through a T-die to obtain a laminated film having a thickness of 45 μm. This single-layer unstretched raw film was stretched 3.0 times in the machine direction at a roll temperature of 90 ° C. by a stretching roll to obtain a 15 μm single-layer lengthwise stretchable heat-shrinkable film. A shrink tunnel test was conducted on an integrated package (2 × 5 pieces) of a snack box using the polypropylene-based longitudinally uniaxially stretched heat-shrinkable film. When the sample was passed through a shrink tunnel with a preset temperature of 160 ° C in the tunnel and a heating time of 15 seconds, wrinkles on the end face
There was almost no fusion, and a good package having tension on the end face was obtained. Further, although the preset temperature in the tunnel was changed by 10 ° C. up and down, there was no change in the finish of the package and no breakage of the seal portion of the film during heating did not occur.

Comparative Example 1 Only the ethylene-propylene random copolymer used in Example 1 was extruded with a T die to obtain a film of 45 μm.
This laminated unstretched raw film was stretched 3.0 times in the machine direction at a roll temperature of 90 ° C. by a stretching roll to obtain a 15 μm single-layer longitudinally stretched shrink film. Using the obtained polypropylene-based longitudinally uniaxially stretched shrink film, a shrink tunnel test was performed on an integrated package (2 × 5 pieces) of snacks (box). When the sample was passed through a shrink tunnel set at a temperature set in the tunnel of 170 ° C. and a tunnel heating time of 15 seconds, wrinkles were generated on the end faces due to insufficient shrinkage in both the longitudinal and lateral directions of the package. Further, although the set temperature in the tunnel was changed up and down by 10 ° C., the wrinkles of the film did not disappear. In addition, fusion of the end surface of the package of the film did not occur.

The physical properties of the heat-shrinkable films of Examples 1 and 2 and Comparative Example 1 are shown in Table 1.

[0030]

[Table 1]

It can be seen from Table 1 that the heat-shrinkable film of the present invention is remarkably excellent in terms of lateral shrinkage.

[0032]

Since the heat-shrinkable film of the present invention contains a butene polymer, it has a remarkable effect that the shrinkage in the lateral direction during heat shrinkage is larger than that of the conventional film.

Since the film of claim 4 further contains a low density polyethylene component, the low temperature shrinkability is better. In the film of claim 7, since the ethylene-propylene copolymer having a high melting point is further used for both surface layers, there is no end face fusion during heat shrinkage of the film, and the appearance of the package is very good.

The conventional heat-shrinkable polyethylene film has a low rigidity and requires a thickness, but the film of the present invention can have a higher rigidity and a smaller thickness.

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Claims (8)

[Claims] 1. A heat-shrinkable film in which a mixture of a butene polymer and another olefin polymer is uniaxially stretched. 2. A mixture of an ethylene polymer, a butene polymer and a propylene polymer, a mixture of an ethylene-propylene copolymer and a polybutene, an ethylene polymer and a propylene polymer.
A heat-shrinkable film in which at least one mixture selected from the group consisting of a mixture with a butene copolymer is uniaxially stretched. 3. A heat-shrinkable film in which a mixture of an ethylene-propylene copolymer (A) and a butene polymer (B) is uniaxially stretched. 4. The mixing ratio of the copolymer (A) and the polymer (B) is such that the polymer (B) per 100 parts by weight of the copolymer (A).
The film according to claim 3, which is 10 to 80 parts by weight. 5. A heat-shrinkable film obtained by uniaxially stretching a mixture of an ethylene-propylene copolymer (A), a butene copolymer (B) and a low density ethylene polymer (C). 6. The mixture ratio of the copolymer (A) and the polymer (B) is 20 to 100 parts by weight of the polymer (B) per 100 parts by weight of the copolymer (A), and the copolymer ( The film according to claim 5, wherein the mixing ratio of A) and the polymer (C) is 20 to 100 parts by weight of the polymer (C) per 100 parts by weight of the copolymer (A). 7. A heat-shrinkable film in which the entire multilayer laminate having a mixture layer of at least one butene polymer and another olefin polymer is uniaxially stretched. 8. A first layer comprising an ethylene-propylene copolymer (A) and an ethylene-propylene copolymer (A).
And a butene polymer (B) and a low density polyethylene polymer (C), and a third layer consisting of an ethylene-propylene copolymer (A) are laminated in this order, and the whole thereof. Is a uniaxially stretched heat-shrinkable film.