JPH085171B2 - Heat shrinkable packaging method and polypropylene resin laminated heat shrinkable film used in the method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The invention of the present application is such that an article is roughly wrapped with a heat-shrinkable plastic film and heat-shrinked by a heating device (shrinkage tunnel or the like) so as to conform to the shape of the article. Heat shrink wrapping method (1st
Invention) and a polypropylene resin laminated heat-shrinkable film (second invention) used in the heat-shrinkable packaging method of the first invention.

(Prior Art) Conventionally, as a heat-shrinkable film used for heat-shrinkable packaging, there are various films made of polypropylene resin, polyethylene resin, polyvinyl chloride resin, etc., and many are commercially available. . Among them, the heat-shrinkable film made of polypropylene resin is widely used due to its excellent properties such as transparency, gloss, moisture resistance, and no pollution. However, the heat-shrinkable film made of polypropylene resin cannot cause heat shrinkage unless it is heated to a considerably high temperature.
The temperature range suitable for heat shrink wrapping is narrow, and even a slight change in shrink temperature causes a large change in shrinkage rate. Therefore, in the conventional heat-shrinkable film made of polypropylene resin, if the temperature in the shrinking tunnel is too low, the shrinkage is insufficient and the resulting heat-shrinkable package is wrinkled.
However, even if such wrinkles occur, if the temperature inside the shrinking tunnel is raised a little too high, the heat-shrinkable film is melted this time, resulting in puncturing, such as puncturing. Causes whitening and fusion between the packages. Such a phenomenon occurs especially when the temperature distribution in the shrinking tunnel is non-uniform, or when the packaging speed is set to a high speed and the time for passing through the shrinking tunnel is greatly shortened, and the temperature is instantaneously raised to a high temperature. Cheap.

Thus, when heat-shrink packaging is performed using a heat-shrinkable film made of polypropylene resin, the temperature inside the shrink tunnel must be finely adjusted according to these conditions. As a method for improving such a defect, various measures have been conventionally made. For example, by mixing polyethylene or polybutene, or ethylene-vinyl acetate copolymer with polypropylene resin, or by using polypropylene-based resin obtained by copolymerizing propylene with ethylene or butene, shrinkage can be caused even at low temperature. In the same way
We are trying to solve these drawbacks. However, it cannot be said that these problems have been sufficiently solved in the heat-shrinkable film made of polypropylene resin improved by the above method. For example, when the shape of the packaged object is complicated and there are projections, and when the heat-shrinkable film shrinks, a part that cannot adhere to the packaged object may occur, and the thermal conductivity of the packaged object is In the case of a large size, when heated in the shrinking tunnel, there is a large difference in temperature between the part where the heat-shrinkable film is in close contact with the object to be packaged and the part where it is not. Therefore, when the temperature in the shrinking tunnel is increased in order to sufficiently heat-shrink the heat-shrinkable film that is in close contact with the packaged object, the heat-shrinkable film in the part that is not in close contact with the packaged object melts, Perforation, whitening, fusion of the packages, or rubbing may cause bag breakage. This tendency is particularly remarkable when the temperature distribution in the shrinking tunnel is nonuniform and when high-speed packaging is performed. This is because the conventional method uses a polypropylene resin component having a low melting point in an attempt to improve only the shrinkability at a low temperature, and thus the heat resistance is lowered.

(Problems to be Solved by the Invention) The invention of the present application allows the heat-shrinkable film made of polypropylene resin to retain its characteristics as compared with conventional ones,
Moreover, the present invention provides a heat-resistant polypropylene resin laminated heat-shrinkable film and a heat-shrinkable packaging method using the laminated heat-shrinkable film.

According to the present invention, when the temperature distribution in the shrinking tunnel is somewhat non-uniform, or when the product is heated at a high temperature in a high-speed packaging for a short time, the packaged product has a complicated shape and has protrusions. Even in this case, by setting the temperature in the shrinking tunnel to a high temperature, there can be obtained a heat-shrinkable package which has no shrinkage defect, does not cause flutter-like shrinkage unevenness, and has a good finish. Moreover, in the shrinking tunnel, the laminated heat-shrinkable film melts a portion that is not in close contact with the packaged object, and the bag is broken by perforation, whitening, fusion between the packaged objects, or rubbing due to vibration. There is nothing that will happen.

(Means for Solving Problems) In the present invention, a heat-shrinkable film made of a polypropylene resin is laminated with two or more layers of different polypropylene resin compositions in order to have heat resistance. When used for heat shrink wrapping, the layer that comes to the outside of the package is limited. Then, the polypropylene resin composition used for each layer has specific conditions to solve the above problems. More specifically, in a biaxially stretched polypropylene resin laminated heat-shrinkable film having two or more layers, one of the (first
The outermost layer and the intermediate layer or the other (second) outermost layer are represented by the following formula (1). Where W: weight ratio (%) of each resin component of the first outermost layer T; melting point (° C) of each resin component of the first outermost layer n; number of each resin component of the first outermost layer w; intermediate Weight ratio (%) of each resin component of the layer or the second outermost layer t; Melting point (° C) m of each resin component of the intermediate layer or the second outermost layer; Each resin component of the intermediate layer or the second outermost layer Number of X; ◎ If the laminated heat-shrinkable film has a two-layer structure, the second
X = 800 in the outermost layer of ◎ When the laminated shrinkable film has three or more layers,
When at least one of the intermediate layers satisfies the formula (1) with X = 800, X = 0 in the second outermost layer, and when both the intermediate layers do not satisfy the formula (1) with X = 800. The second outermost layer satisfies X = 800, and the first outermost layer represented by the formula (1) is heat-shrink wrapped so that the outermost layer is on the outside of the package. Is.

In a polypropylene resin laminated heat-shrinkable film in which each layer satisfies the above formula (1), a heat-shrinkable package having a good finish when heat-shrink-wrapped so that the first outermost layer is on the outside. Is obtained. Moreover, even if the temperature inside the shrinking tunnel is increased to sufficiently perform the heat shrinkage, the laminated heat shrinkable film melts and is perforated or whitened, or the packages are rubbed against each other or rubbed by vibration. There is no such thing as a bag breaking due to a match. Further, a good finish can be obtained even when the laminated heat-shrinkable film having a protrusion portion is heat-shrink-wrapped at a high speed, and the laminated heat-shrinkable film does not adhere to the object to be wrapped. Melts in
It does not cause various troubles.

However, when the polypropylene-based resin laminated heat-shrinkable film of the present invention has a two-layer structure, or when the second outermost layer has a structure of three or more layers and X = 800 and satisfies the formula (1), When the first outermost layer is heat-shrinked so as to be the inner side during heat-shrink wrapping, when the temperature in the shrink tunnel is normal, it does not melt and cause perforation, but the packages are Fusing may occur, or vibration may cause the packages to rub against each other to break the bag. This tendency is particularly strong when overheated at a high temperature for a short time so as to cause thermal contraction at a high speed.

As described above, a novel point of the present invention is that in a biaxially stretched laminated heat-shrinkable film having two or more layers, the heat resistance of each layer composed of various polypropylene-based resin components is compared with that of each polypropylene-based resin component. It is defined as the sum of the products of the melting point and the weight ratio. Moreover, in the present invention, the reason why the excellent effect is exhibited is that the polypropylene resin laminated heat-shrinkable film is
(2) The outermost layer (the layer that comes to the outside during heat shrink packaging) is provided with a layer having a specific heat resistance. When heat-shrink packaging is performed, the heat resistance is excellent and the outermost layer is on the outside.

In the present invention, the melting point of each polypropylene resin component was measured by the differential scanning calorimetry method.

Examples of the polypropylene resin that can be used in the present invention include crystalline polypropylene resin, or propylene and α
-Copolymers with olefins, or a mixture of a crystalline polypropylene resin and a polyolefin resin other than the crystalline polypropylene resin, and a mixture of two or more of these polypropylene resins. The copolymer of propylene and α-olefin, ethylene-propylene copolymer and butene-propylene copolymer, or,
An ethylene-butene-propylene copolymer is preferably used. As the polyolefin resin mixed with the crystalline polypropylene resin, polyethylene resin, polybutene resin, ethylene-vinyl acetate copolymer, ethylene-butene copolymer and the like are used.

The number of polypropylene resin components used in each layer is not particularly limited,
One type of polypropylene resin may be used, or two or more types of polypropylene resin components may be used.

In the present invention, even copolymers or mixtures of the same kind are different if the proportions of the constituent components are different.

Specific examples of the constitution of the polypropylene resin laminated heat-shrinkable film of the present invention include the following constitutions. First, as a two-layer structure, a crystalline polyethylene resin / ethylene-propylene copolymer, or an ethylene-propylene copolymer / ethylene-butene-propylene copolymer, or a crystalline polypropylene resin / crystalline polypropylene resin And a mixture of ethylene-vinyl acetate copolymer and the like. Also, as a three-layer structure, a crystalline polypropylene resin / ethylene-propylene copolymer / crystalline polypropylene resin, or a crystalline polypropylene resin / ethylene-butene-propylene copolymer / crystalline polypropylene resin, or Crystalline polypropylene resin / ethylene-propylene copolymer / mixture of crystalline polypropylene resin and ethylene-propylene copolymer, or crystalline polypropylene resin / ethylene-propylene copolymer and ethylene-butene-propylene copolymer blend/
Ethylene-propylene copolymer or a mixture of crystalline polypropylene resin and ethylene-propylene copolymer /
Ethylene-butene-propylene copolymer / ethylene-propylene copolymer and the like. Furthermore, the four-layer structure is a crystalline polypropylene resin / ethylene-propylene copolymer / ethylene-butene-propylene copolymer / crystalline polypropylene resin.

In each of the above-mentioned constitutions, the first described layer (which is the first outermost layer in the claims) is used so as to be the outer side at the time of heat shrink packaging.

Further, among the above-mentioned constitutions, a three-layer constitution is desirable as a constitution which can sufficiently exert the effects of the present invention and has good productivity. Moreover, the above three-layer structure includes the first and second
In that both outermost layers of the same resin composition have the same heat resistance as described above, or from the viewpoint of general physical properties such that the resulting laminated film is difficult to curl, and further in terms of productivity. Are particularly preferred.

The thickness of the polypropylene resin laminated heat-shrinkable film of the present invention is preferably in the range of 10 μ to 40 μ. Regarding the thickness structure of each layer, it is preferable that one (first) outermost layer (the layer that comes to the outside during heat shrink packaging) is at least 3 μm or more. Moreover, 2
In the case of a layer structure, the thickness of the other (second) outermost layer (the layer that comes inside during heat shrink wrapping), and in the case of a three-layer structure, X = 800 in each intermediate layer, satisfying formula (1) It is preferable that the sum of the thicknesses of the layers to be formed, or the thickness of the second outermost layer when each intermediate layer is X = 800 and does not satisfy the formula (1) is 50% or more of the total thickness.

The heat shrinkage rate of the polypropylene resin laminated heat shrinkable film of the present invention is not particularly limited, but generally 18% or more in 110 ° C. glycerin is preferably used.

The method for producing the polypropylene resin laminated heat-shrinkable film of the present invention is not particularly limited, but it is preferably produced by the following method. That is, the laminated sheet is co-extruded from the lamination die using a plurality of extruders. Then, after the laminated sheet is cooled and solidified, it is reheated to a temperature at which it can be stretched, stretched at least 2.0 times in both the longitudinal and transverse directions, and then cooled.
The stretching method may be either a tenter method or an inflation method, but it is preferable to manufacture by the inflation method because it is easy to make the heat shrinkage amounts in the longitudinal direction and the transverse direction the same. For that purpose, it is necessary to use a multilayer circular die as the laminated sheet to obtain a multilayer tubular sheet. The resulting polypropylene-based resin laminated heat-shrinkable film does not deteriorate in heat shrinkage in order to prevent it because the natural shrinkage of the film itself causes the deformation and surface condition to deteriorate when left to stand naturally. It is more preferable to reduce the amount of natural shrinkage by heat treatment.

The heat shrink wrapping method using the polypropylene resin laminated heat shrinkable film of the present invention is other than using the first outermost layer described in the formula (1) at the outer side at the time of heat shrink wrapping. Can use the heat shrink packaging line that has been used conventionally. However, since the polypropylene-based resin laminated heat-shrinkable film of the present invention has excellent heat resistance in the shrink tunnel, the laminated heat-shrinkable film melts even if the temperature in the shrink tunnel is set high. It is possible to cause sufficient heat shrinkage without such a thing. Moreover, at the time of high-speed packaging, the temperature in the shrinking tunnel can be raised to shorten the transit time of the package.

(Effects of the Invention) When heat-shrink packaging is performed using the polypropylene resin laminated heat-shrinkable film of the present invention, a heat-shrinkable package having a good finish is obtained without causing fluffy shrinkage unevenness. To be A good heat-shrinkable package can be obtained without causing any trouble even if the temperature distribution in the shrinking tunnel is somewhat uneven or the packaging speed is high. In particular, even when the object to be packaged has a complicated shape with a protrusion, the laminated heat-shrinkable film is melted at a portion not adhered to the object to be packaged by heating in the shrinking tunnel. , There is no such thing as perforation or whitening. In addition, there is no possibility that the fusion of such laminated heat-shrinkable film will cause the fusion of the packaging bodies in the shrinking tunnel, or the vibration will cause the packaging bodies to rub against each other to break the bag. .

The polypropylene-based resin laminated heat-shrinkable film of the present invention naturally has excellent properties such as transparency, luster, moisture resistance, and pollution-free properties which polypropylene resins originally have. Is.

(Examples) Examples and comparative examples are shown below to more specifically describe the heat-shrinkable packaging method of the present invention and the heat-shrinkable film used in the method.

Examples 1 to 3 and Comparative Examples 1 to 8 Various polypropylene resin compositions are used, and the diameter is 50 mmφ.
Using two extruders and a circular die for two-layer coextrusion, a tube-shaped extruded laminated powder stretched raw film was obtained. Then, in this co-extrusion molding, immediately after the co-extrusion molding, it was rapidly cooled by a conventional water cooling method. In the comparative example, a laminated end-stretched original fabric film made of the same polypropylene resin composition was also produced. In addition, the obtained laminated stretched original fabric film has one (first)
The outermost layer (outer layer during heat shrink packaging) is 53μ, and the other (second) outermost layer (inner layer during heat shrink packaging)
It was 105μ and the folding diameter was 150mm.

These laminated end-stretched original fabric films were biaxially stretched 3.5 times in both the longitudinal and transverse directions by a conventional inflation method to obtain laminated biaxially stretched films. Then, the laminated biaxially stretched film is heat-fixed while being relaxed,
A polypropylene resin laminated heat-shrinkable film having a total thickness of about 15 μm and a folding diameter of about 480 mm was obtained.

Each constitution of the obtained laminated heat-shrinkable films, the heat resistance of each layer, and the heat-shrink packaging of the aerosol can having the protrusion with the first outermost layer on the outer side. The situation is shown in Table 1.

The heat shrinkage was performed by passing through a shrink tunnel having a length of about 2 m for about 3 seconds. Further, the heat shrinkage ratios of these polypropylene resin laminated heat shrinkable films shown in Table 1 were both in the range of 23% to 28% and showed good heat shrinkage ratio.

As is clear from the examples shown in Table 1, the polypropylene resin laminated heat-shrinkable film satisfying the formula (1) is used, and the heat shrink-wrapped package according to the method of the present invention has a good finish. Was there. Moreover, the conventional polypropylene resin heat-shrinkable film can be sufficiently heat-shrinked without causing any trouble even at a high temperature such that it melts in the shrinking tunnel and causes various troubles. done.

On the other hand, in the polypropylene resin laminated heat-shrinkable film of the comparative example which does not satisfy the formula (1), the temperature in the shrinking tunnel is very narrow so that a good heat-shrinkable package can be obtained, or Caused problems such as uneven shrinkage. Moreover, the laminated heat-shrinkable film is easily melted at a portion which is not in close contact with the object to be packaged, and perforation, whitening, and the like are likely to occur, and the packages are fused with each other or the packages are rubbed against each other due to vibration. It was easy to break the bag.

Examples 4 to 8 and Comparative Examples 9 to 10 Using various polypropylene-based resin compositions, a diameter of 50 mmφ
Except for using three extruders and a circular die for three-layer co-extrusion, a three-layer tubular co-extruded laminated end-stretched raw film is prepared in the same manner as in Examples 1-3 and Comparative Examples 1-8. Obtained.

These laminated end-stretched raw fabric films were biaxially stretched and heat-set in the same manner as in Examples 1 to 3 and Comparative Rows 1 to 8, and one (first) outermost layer (the outer side during heat shrink wrapping) was used. Layer is about 4μ, the middle layer is about 12μ, and the other (second) outermost layer (the layer that is inside when heat shrink wrapping) is about 4μ.
Thus, a polypropylene resin laminated shrinkable film having a folding diameter of about 480 mm was obtained.

Each of the obtained laminated heat-shrinkable films, and the heat resistance of each layer thereof, as in Examples 1 to 3 and Comparative Examples 1 to 8, the first outermost layer is on the outer side. Then, Table 2 shows the situation when the heat-shrink packaging of the aerosol can having the protrusions is performed.

The contraction tunnel used and the passage time were the same as those in Examples 1 to 3 and Comparative Examples 1 to 8. Further, the heat shrinkage rates of these polypropylene resin laminated heat shrinkable films shown in Table 2 were both in the range of 22% to 25%, and showed good heat shrinkage rates.

From the polypropylene-based resin laminated heat-shrinkable films of Examples 4 to 8 satisfying the formula (1), heat-shrinkable packages having good finish were obtained by the method of the present invention.
Moreover, the laminated heat-shrinkable film of these Examples causes no trouble even by passing through the shrinkage tunnel having a temperature higher than the shrinkage tunnel temperature usually used in the conventional polypropylene resin laminated heat-shrinkable film. There was no heat shrinkage.

However, with the polypropylene-based resin laminated heat-shrinkable films of Comparative Examples 9 to 10 which do not satisfy the formula (1), good heat-shrinkable packages could not be obtained. Moreover, as in Examples 4 to 8, various troubles occurred when the shrinking tunnel temperature was increased in order to sufficiently perform the thermal shrinkage.

Comparative Example 11 Using the polypropylene-based resin laminated heat-shrinkable films of Example 1 and Example 8, Example 1 and Example 8 were used.
In the same manner as above, a heat-shrinkable package of an aerosol can having a protrusion was prepared. However, in both cases, the first outermost layer (Example 1,
Alternatively, in Example 8, heat shrink wrapping was carried out with the layer that was placed outside during heat shrink wrapping) being on the inside. The contraction tunnel used and the passage time were the same as in Example 1 and Example 8.

As a result, the laminated heat-shrinkable film was not melted to cause perforation at each shrinking tunnel temperature at which a good finish was obtained in Example 1 or Example 8. However, in the shrinking tunnel, the packages were fused with each other, or the packages were rubbed against each other due to the vibration and the bag was broken. Moreover, when the shrinking tunnel temperature was lowered, the heat shrinkability became insufficient this time, and due to the uneven heat shrinkage, flapping wrinkles were formed.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location B29K 105: 02 B29L 9:00

Claims (10)

[Claims] 1. A crystalline polypropylene resin, a copolymer of propylene and α-olefin, a mixture of a crystalline polypropylene resin and a polyolefin resin other than the crystalline polypropylene resin, or a mixture thereof. A biaxially stretched laminated heat-shrinkable film comprising two or more layers, wherein the first outermost layer and the intermediate layer or the second outermost layer are represented by the following formula (1). Where W: weight ratio (%) of each resin component of the first outermost layer T; melting point (° C) of each resin component of the first outermost layer n; number of each resin component of the first outermost layer w; intermediate Weight ratio (%) of each resin component of the layer or the second outermost layer t; Melting point (° C) m of each resin component of the intermediate layer or the second outermost layer; Each resin component of the intermediate layer or the second outermost layer Number of X; ◎ If the laminated heat-shrinkable film has a two-layer structure, the second
In the outermost layer of, X = 800 ◎ When the laminated heat-shrinkable film has three or more layers,
When at least one layer of the respective intermediate layers satisfies the formula (1) with X = 800, X = 0 in the second outermost layer, and when both the intermediate layers do not satisfy the formula (1) with X = 800, A polypropylene-based resin laminated heat-shrinkable film satisfying X = 800 is used for the second outermost layer, and heat-shrinkable packaging is performed so that the first outermost layer of the film is on the outside of the package. And heat shrink packaging method. 2. A copolymer of propylene and α-olefin is an ethylene-propylene copolymer, a butene-propylene copolymer, or an ethylene-butene-propylene copolymer. The heat shrink wrapping method according to item 1. 3. A polyolefin resin other than the crystalline polypropylene resin is a polyethylene resin, a polybutene resin, an ethylene-vinyl acetate copolymer or an ethylene-butene copolymer. The heat shrink wrapping method according to item 1. 4. The heat shrink packaging method according to claim 1, wherein the polypropylene resin laminated heat shrink film has a three-layer structure. 5. The heat shrink packaging method according to claim 4, wherein both outermost layers of the three-layer structure have the same resin composition. 6. A crystalline polypropylene resin, a copolymer of propylene and α-olefin, or a mixture of a crystalline polypropylene resin and a polyolefin resin other than the crystalline polypropylene resin, or a mixture thereof. A biaxially stretched laminated heat-shrinkable film of two or more layers, which is an outer layer of a package during heat-shrinkable packaging.
The outermost layer and the intermediate layer or the second outermost layer are represented by the following formula (1) However, W: Polymerization ratio (%) of each resin component of the first outermost layer T; Melting point (° C) of each resin component of the first outermost layer n; Number of each resin component of the first outermost layer w; Intermediate Weight ratio (%) of each resin component of the layer or the second outermost layer t; Melting point (° C) m of each resin component of the intermediate layer or the second outermost layer; Each resin component of the intermediate layer or the second outermost layer Number of X; ◎ If the laminated heat-shrinkable film has a two-layer structure, the second
In the outermost layer of, X = 800 ◎ When the laminated heat-shrinkable film has three or more layers,
When at least one of the intermediate layers satisfies the formula (1) with X = 800, X = 0 in the second outermost layer, and when both the intermediate layers do not satisfy the formula (1) with X = 800. The second outermost layer is a polypropylene resin laminated heat-shrinkable film for heat-shrinkable packaging, which satisfies X = 800. 7. A copolymer of propylene and α-olefin, wherein the ethylene-propylene copolymer region is a butene-propylene copolymer or an ethylene-butene-propylene copolymer. A polypropylene-based resin laminated heat-shrinkable film according to item 6. 8. A polyolefin resin other than the crystalline polypropylene resin is a polyethylene resin, a polybutene resin, an ethylene-vinyl acetate copolymer or an ethylene-butene copolymer. The polypropylene-based resin laminated heat-shrinkable film according to item 6. 9. The polypropylene resin laminated heat-shrinkable film according to claim 6, wherein the laminated heat-shrinkable film has a three-layer structure. 10. The polypropylene resin laminated heat-shrinkable film according to claim 9, wherein both outermost layers of the three-layer structure have the same resin composition.