JPH01253445A - Multilayer heat shrinkable film - Google Patents

Abstract

PURPOSE:To obtain a multilayer heat shrinkable film having excellent heat shrinkability at low temperatures, excellent heat shrinking package adaptability temperature range, preferable slipperiness, optical properties, and excellent melt sealability by providing a shielding layer between an outermost layer and a core layer. CONSTITUTION:There is obtained a tubular coextruded multilayer unoriented original sheet having both outermost layers made of crystalline polypropylene resin having 135-150 deg.C of melting point, a core layer made of normal chain low density polyethylene resin having 0.890-0.910g/cm<3> of density and 60-80 deg.C of Vicat softening point, a shielding layer made of a resin composition in which the crystalline polypropylene resin used for both the outermost layers and the polyethylene resin used as the core layer are mixed by weight in a range of 2:1-3:1, and a structure of the outermost layer, the shielding layer, the core layer, the shielding layer and the outermost layer. The thickness of the shielding layer ranges from 1-30% of the whole thickness, and the melt flow index (MI) of the crystalline polypropylene resin is higher than that of the low density polypropylene resin. Lubricant and antiblocking agent are added to the outermost layers and the same lubricant as that of both the outermost layers is added to the core layer and the shielding layer.

Description

[Detailed Description of the Invention] (Industrial Application Field) The multilayer heat-shrinkable film of the present invention can be used to roughly wrap a product and heat-shrink it using a heating device (shrink tunnel) to achieve tight packaging. This method is used for heat shrink packaging. It is used for heat shrink packaging of cup foods, lactic acid bacteria beverages, paper packaged beverages, frozen/refrigerated foods, pharmaceuticals, aerosol cans, and daily necessities such as stationery and toys. It is especially suitable for stacking packaging and tamper-proof packaging. It exhibits excellent effects.

<Prior art> As heat-shrinkable films conventionally used in the field of heat-shrinkable packaging, there are various films made of polyethylene resin, polypropylene resin, polyvinyl chloride resin, etc. It is commercially available. Even inside,
Heat-shrinkable films made of polypropylene resin are widely used due to their inherent excellent properties such as transparency, gloss, moisture resistance, and non-polluting properties. However, compared to heat-shrinkable films made of polyvinyl chloride resin, etc., heat-shrinkable films made of polypropylene resin cannot be made to shrink unless heated to considerably higher temperatures, and the heat-shrinkable packaging temperature The range is narrow and suitability for heat shrink packaging is not necessarily good.

As a method to solve these drawbacks, the present inventors have developed a method in which both outer layers are made of a polypropylene resin and the core layer is made of a special linear low-density polyethylene resin. etc. were found. (Tokugansho (i2-4
8444) However, in the above method, when the amount of anti-blocking agent or lubricant added is the normal amount, there is a problem that slipperiness is insufficient and sensitivity during packaging is reduced. Therefore, if a large amount of lubricant is added to the outermost layer in an attempt to obtain good lubricity, the interlayer adhesion will decrease.
The fusing seal strength and physical strength have become weaker. Moreover, when a large amount of anti-blocking agent was added to the outermost layer, not only the transparency deteriorated, but also the hot tack property deteriorated and the melt sealability deteriorated.

(Problems to be Solved by the Invention) The present invention provides an excellent multilayer heat-shrinkable film using polypropylene resin, which has excellent heat-shrinkability at low temperatures and a wide temperature range suitable for heat-shrink packaging. In addition to obtaining slipperiness, the objective is to improve optical properties and melt-cut sealing properties.

In other words, even if the lubricant and anti-blocking agent are added in the usual amount, so as not to interfere with the inherent transparency and gloss of polypropylene resin, as well as the fusing and sealing properties that are important for heat-shrinkable packaging. The purpose of this invention is to provide a film structure that provides good slipperiness.

(Means for Solving the Problem) First, the inventors of the present invention have previously discovered a film made of a polypropylene-based resin for both outer layers and a special linear low-density polyethylene resin for the core layer. Various studies were conducted to find out why good lubricity could not be obtained with the addition of a normal amount of lubricant in a laminated heat-shrinkable film made of . As a result, it was found that the lubricant added to the polypropylene resin in the outermost layer migrated to the special linear low-density polyethylene resin in the core layer, making it difficult to bleed onto the surface.

Therefore, in the present invention, the problem was solved by providing a shield N between the outermost layer and the core layer so that the lubricant added to the outermost layer does not easily migrate to the core layer.

That is, it has good heat shrinkability at low temperatures and a suitable temperature range for heat shrink packaging, and also has good slip properties and optical properties.
In order to obtain a multilayer heat-shrinkable film that also has excellent melt sealability, the following film structure is used. First, both outer layers are made of crystalline polypropylene resin with a melting point of 135 to 150°C, and the core layer has a density of 0.890 to 0.
．． 910 g/c++? So, Vikaft softening point is 60~8
It is made of a resin composition mainly composed of a linear low-density polyethylene resin at 0°C, and at least one of the outer layers and the core layer contains the above-mentioned crystalline polypropylene resin and the above-mentioned linear low-density polyethylene resin. Resins selected from density polyethylene resins are mixed in a weight ratio of 2:3 to 3:1,
Moreover, a barrier layer made of a resin composition in which the melt flow index (hereinafter referred to as Pvi I) of the crystalline polypropylene resin is higher than that of the linear low density polyethylene resin is inserted, and furthermore, at least A lubricant is added not only to one of the outermost layers but also to the barrier layer and the core layer. More preferably, the crystalline polypropylene resin of the barrier layer is the same as the crystalline polypropylene resin used in both outer layers, and the linear low dust polyethylene resin of the barrier layer. The same resin as the linear low density polyethylene resin used for the core layer is used. Furthermore, each thickness of the barrier layer is preferably 7 to 30% of the total thickness.

Hereinafter, the configuration of the present invention will be explained in detail. First, the basic film structure of the multilayer heat-shrinkable film of the present invention is as follows:
Outermost layer/blocking N/core N/blocking N/outermost layer, or; yo, outermost layer/blocking N/core layer/outermost layer.

And, non-class N: The crystalline polypropylene resin to be used has a melting point in the range of 135 to 150°C. Copolymerization of about t% of ethylene and butene to propylene, 3 to 8-.
Copolymerization of approximately t% is preferably used.

Next, the linear low-density polyethylene resin used for the intermediate layer is a resin in which ethylene and α-olefin are copolymerized to introduce short chain branches into the linear main chain. In addition, the number of short chain branches of this resin is greater than the number of branches of conventional general linear low density polyethylene,
Therefore, the density should be set at 0.890 to 0.910 g/
cm' and low softening point of 60 to 8.
The temperature is kept as low as 0℃. Note that a resin composition mainly composed of a linear low-density polyethylene resin refers to not only the linear low-density polyethylene resin itself, but also the linear low-density polyethylene resin containing up to about 30 wt% of polyethylene resin or polypropylene resin. , or a resin composition containing one or more polyolefin resins such as ethylene-vinyl acetate copolymer.

Furthermore, as the crystalline polypropylene resin used for the barrier layer inserted between at least one of the outer layer and the core layer, a resin selected from among the crystalline polypropylene resins that can be used for the outer layer of both grades is used. It will be done. However, the crystalline polypropylene resin must have a higher MI than the linear low density polyethylene resin described below. Note that it is preferable to use the same crystalline polypropylene resin used for both outer layers as the crystalline polypropylene resin in terms of heat shrinkability and productivity.

As the linear low-density polyethylene resin used for the barrier layer, a resin selected from linear low-density polyethylene resins that can be used for the core layer is used. However, as mentioned above, the linear low density polyethylene resin must have a lower Ml than the Ml of the crystalline polypropylene resin. In addition, it is preferable to use the same resin as the linear low-density polyethylene resin used for the core layer as the linear low-density polyethylene resin in terms of heat shrinkability and productivity.

Incidentally, MI in the present invention is JIS for both crystalline polypropylene resin and linear low density polyethylene resin.
K-72! Temperature 230°C according to Method A of O.

This is a value measured under the same conditions with a load of 2160 g.

To explain in more detail the relationship between each of these resins and the present invention, firstly, if the melting point of the crystalline polypropylene resin used for both class outer layers exceeds 150°C, it will be difficult to stretch at low temperatures. As the material is processed, its heat-shrinkability at low temperatures not only decreases, but also its heat-shrinkability at high temperatures deteriorates, reducing its suitability for heat-shrinkable packaging. On the other hand, if the melting point is less than 135°C, the heat resistance will be poor and melt whitening will easily occur in the shrink tunnel, resulting in a decrease in suitability for heat shrink packaging.

Next, when the density of the linear low-density polyethylene resin used for the core layer exceeds 0.910 g/(-I11', the stretchability decreases, and in particular, stretching at low temperatures becomes impossible. As a result, the heat shrinkability at low temperatures is poor, and the suitable temperature range for heat shrink packaging becomes narrow.Also, the above density is 0.8
If it is less than 90 g/cm', it will be difficult to perform heat treatment to eliminate natural shrinkage of the resulting multilayer heat-shrinkable film, resulting in deformation of the film or deterioration of its smoothness. Furthermore, if the Vicat softening point of linear low-density polyethylene exceeds 80°C, it will become difficult to stretch at low temperatures, and it will be necessary to stretch at high temperatures, so the heat shrinkability at low temperatures will not improve. , it is not possible to widen the suitable temperature range for heat shrink packaging.

In addition, if the Vicat softening point is less than 60°C, the temperature will be too high in the optimum temperature range in which the crystalline polypropylene resin of both class outer layers is stretched, and the Nobeoki effect will not be fully exhibited, resulting in heat shrink packaging. It does not lead to improvement in aptitude.

In addition, when other polyolefin resins mentioned above are mixed into these straight-chain low-density polyethylene resins in an amount exceeding 3kt9≦, the ease of stretching process that the straight-chain low-density polyethylene resins have, It becomes impossible to provide excellent heat shrinkage properties as a heat shrinkable film.

Furthermore, the crystalline polypropylene resin and linear low-density polyethylene resin used in the barrier layer that prevents the transfer of lubricant between the outermost layer and the core layer, which are important features of the present invention, will be explained. First of all, these resins cannot exhibit the heat shrinkability that is a feature of the present invention unless they can be used for the outer rain layer and the core layer. The MI of the crystalline polypropylene resin is the M of the linear low density polyethylene resin.
If it is lower than 1, the compatibility will be poor, the formation during melt extrusion will be poor, and the transparency of the resulting multilayer heat-shrinkable film will be poor. Generally, when polypropylene resin and polyethylene resin are mixed, if a small amount of one of the resins is used, the formation will not deteriorate so much and the transparency will not be reduced. If not, the compatibility will be insufficient, resulting in poor formation and reduced transparency.

Furthermore, if the composition ratio of crystalline polypropylene resin and linear low density polyethylene resin is outside the range of 2:3 to 3:1, the lubricant will not function as a shielding layer and the features of the present invention will be lost. Put it away. The reason is not clear, but
It is believed that if the composition ratio of the crystalline polypropylene resin exceeds the above conditions, the lubricant in the barrier layer tends to migrate to the core layer, reducing the barrier effect. In this case, the lubricant in the outermost layer is considered to be easily transferred to the barrier layer since it is mostly a crystalline polypropylene resin component of the barrier layer.

Furthermore, if the linear low-density polyethylene resin exceeds the above conditions, the lubricant in the outermost layer tends to migrate to the barrier layer, and the barrier effect is likely to be lost. In this case as well, the lubricant in the barrier layer is likely to transfer easily because the core layer contains a large amount of linear low-density polyethylene resin. If most of the resin used is the same resin, it is thought that the lubricant will easily transfer between the eyebrows. Moreover, if the ratio of crystalline polypropylene resin in the barrier layer becomes too large, the lubricant that has migrated to the barrier layer will be easily attracted to the core layer, and the ratio of linear low-density polyethylene resin in the barrier layer will increase. If it is too long, it is thought that the lubricant added to the outermost crystalline polypropylene resin layer is likely to be attracted to the barrier layer.

In addition, such a barrier layer may be provided only between the outermost layer and the core layer if good slipperiness is required for only one outermost layer, but generally, the barrier layer is provided between the outermost layer and the core layer. It is preferable to provide it between both. Furthermore, providing such a barrier layer between the outer rain layer and the core layer further increases the interlayer adhesive strength, which also leads to improvements in the fusing seal strength and physical strength.

As the lubricant to be added to the barrier layer and the core layer, amide-based lubricants that are commonly used in the past can be used. The barrier layer contains about 1,000 to 3,000 ppm, and the core layer contains about 20 ppm.
It is preferable to add about 00 to 4000 ppm. still,
If the amount added is too large, the interlayer adhesive strength will decrease, which is not preferable. In addition, one layer of the same lubricant used for the barrier layer and core layer is added only to the outermost layer that requires slipperiness.
It may be added in an amount of about 000 to 2000 ppm, but it is generally added to the outer layer of rainfall. In addition, for the outermost layer that requires slipperiness, a general silica-based anti-blocking agent can also be used.
It is preferable to add about 2000 ppm.

The overall thickness of the multilayer heat-shrinkable film of the present invention is preferably within the range of 10 to 30 μm in view of its intended use. As for the thickness of the barrier layer, it is preferable from the viewpoint of barrier effect and heat shrinkage properties that the thickness ratio of the layer is within the range of 7 to 30% of the total thickness as described above. Furthermore, it is preferable that the thickness of the core layer be within the range of 25 to 70% of the total thickness, in view of the suitable temperature range for heat shrink packaging.

It should be noted that, within the scope of not changing the gist of the present invention, there is no hindrance to mixing resin or various additives into each layer or providing a new layer.

Next, the method for producing the multilayer heat-shrinkable film of the present invention is not particularly limited, but it is preferably produced by the following method. That is, a plurality of stretched raw sheets are coextruded from a multilayer die using a plurality of extruders. After the multilayer unstretched raw sheet is cooled and solidified, it is reheated to a temperature at which it can be stretched, and stretched by at least 3.0 times in both the longitudinal and transverse directions. As for the stretching method, both the tenter type and the inflation method are possible, but since it is easy to closely approximate the heat shrinkage characteristics in the longitudinal and transverse directions, it is preferable to use the inflation method. is preferred. For this purpose, it is necessary to use a multilayer circular die to obtain the multilayer unstretched raw sheet as a multilayer tubular sheet.

If the obtained multilayer biaxially stretched film is left to naturally shrink, deformation and surface condition will deteriorate due to the natural shrinkage of the film itself, so in order to prevent this, the heat shrinkage characteristics are not reduced too much. It is more preferable to perform heat treatment to reduce the amount of natural shrinkage.

As a heat-shrink packaging method using the multilayer heat-shrinkable film of the present invention, a heat-shrink packaging line used for conventional heat-shrinkable films made of polypropylene resin can be used as is. In addition, the multilayer heat-shrinkable film of the present invention has excellent slip properties, so it has good mechanical suitability during packaging, and not only can it be easily packaged, but the temperature inside the shrink tunnel does not have to be set severely. It is also possible to easily obtain a good heat-shrinkable package.

(Effects of the Invention) Next, the present invention will be explained in detail. First, the multilayer heat-shrinkable film of the present invention has excellent low-temperature heat-shrinkability because the linear low-density polyethylene resin of the core layer has excellent low-temperature heat-shrinkability. Heat shrinkage can be initiated.

Moreover, since the crystalline polypropylene resin of the outer layer of bacterial flora has heat resistance, a good heat-shrinkable package can be obtained without melting and whitening even at high temperatures. That is,
By adopting such a film configuration, the suitable temperature range for heat shrink packaging can be widened. Moreover, the resin used for the outer layer of bacterial flora not only has excellent stretchability, but also
Since the resin used for the core layer also has good stretchability at low temperatures, it can be easily stretched at low temperatures and the low-temperature shrinkability can be improved. Furthermore, by providing a barrier layer between the outermost layer and the core layer to prevent the transfer of lubricant, the outermost
Since the lubricant does not migrate to the core layer and bleeds to the surface, good lubricity can be obtained even with a small amount of lubricant added. Furthermore, since the resins used in the barrier layer have excellent compatibility with each other, transparency is also good, and a heat-shrinkable package with excellent display effects can be obtained. In addition, by reducing the amount of lubricant added and providing a barrier layer with good adhesion to both the outermost layer and the core layer, interlayer adhesion is further increased, improving fusion seal strength and physical strength. do. In addition, since the amount of anti-blocking agent added is small, not only transparency is improved, but also hot tack properties are improved, eliminating sealing defects during fusing sealing.

(Example) The present invention will be specifically explained by showing Examples and Comparative Examples below.

Example 1 A crystalline polypropylene resin with a melting point of 138°C was used as the bacterial flora outer layer, and the density was 0.900 g/CM? A linear low-density polyethylene resin with a Vicat softening point of 70°C was used as the core 1, and a weight ratio of the crystalline polypropylene resin used for the bacterial flora outer layer and the linear low-density polyethylene resin used for the core layer was added. 1:l: A tubular coextruded multilayer unstretched raw sheet having a structure of outermost layer/blocking N/core layer/blocking N/outermost layer with the mixed resin composition as a blocking layer is extruded using three extruders. and three types of 5N were obtained using a circular die for coextrusion. During extrusion molding, the coextrusion was immediately followed by rapid cooling using a water cooling method. Note that the N flux of the crystalline polypropylene resin and the linear low density polyethylene resin used in Example 1 was 3.2 g/min and 1.8 g/min, respectively. Then, to the bacterial flora outer layer: 1500 ppm of a lubricant and 1500 ppm of an anti-blocking agent were added here, and the same lubricant as the bacterial flora outer layer was added to the core layer and barrier layer at 3000 ppm and 2000 ppm, respectively.

In addition, the total thickness of the obtained multilayer unstretched raw sheet was 240
μ, and the thickness ratio of each layer is from one outermost layer to 〇.

It was 5:2:0.5:1.

This multilayer unstretched raw sheet was stretched 4.2 times in both the longitudinal and transverse directions using a conventional inflation method. A stretched film could be obtained. Then, this biaxially stretched film was heat-set while being relaxed to obtain a multilayer heat-shrinkable film having a total thickness of about 15 μm.

Using the obtained multilayer heat-shrinkable film, two notebooks were integrated into heat-shrinkable packaging. As a result, it can be easily placed on the packaging machine without any trouble, and the shrink tunnel temperature set at 160℃ can be raised or lowered by 15 degrees.
Even if the material is changed by ゛C, a good finish can be obtained without poor tightness or wrinkles in some corners, and also without melting and whitening. Ta. In addition, there is no poor hot tack property when sealing by fusing: there is no occurrence of a defective seal, and the strength of the fusing seal of the resulting heat-shrinkable package is strong, and even if the package is folded, it will not break from the fusing seal. There was no need to bag it.

(Comparative Examples 1 to 2) The outer layer of rainfall was made of a crystalline polypropylene resin with a melting point of 154°C in Comparative Example 1 and 132°C with a melting point in Comparative Example 2, and the same resin as in Example 1 was used for the core layer and barrier layer. In addition, a multilayer unstretched raw sheet was prepared in the same manner as in Example 1, and the thickness structure and overall thickness of each layer, as well as the type and amount of additives in each layer, were the same as in Example 1. Coextruded by method.

The obtained multilayer unstretched raw sheet was biaxially stretched in the same manner as in Example 1 using the conventional inflation method. As a result, Comparative Example 1 could not be stretched at a higher temperature than Example 1. However, in Comparative Example 2, stretching was possible even at low temperatures.

Then, these biaxially stretched films were heat-set in the same manner as in Example 1 to obtain a multilayer heat-shrinkable film.

Using the obtained multilayer heat-shrinkable film, a box with 11 windows (commonly known as a wind box) was heat-shrink wrapped. As a result, in Comparative Example 1, the heat shrinkability was poor not only when the shrink tunnel temperature was low, but also at high temperatures, and wrinkles were formed in some corners, so that a good heat shrink package could not be obtained. In addition, in Comparative Example 2, the heat shrinkability at low temperatures was good, but the heat resistance was poor, and if the shrink tunnel temperature rose even a little, melting and whitening occurred at the window part of the wind box, and the temperature suitable for heat shrink packaging was lowered. The range was narrow, and it was difficult to obtain a good heat-shrinkable package.

(Comparative Example 3) The outer rain layer was made of the same crystalline polypropylene resin as in Example 1, and the core layer was made of a general linear low-density polyethylene resin with a density of 0.919 g/cm' and a Vicat softening point of 90°C. The same resin composition as in Example 1 was used for the barrier layer, and the thickness structure and overall thickness of each layer, as well as the type and amount of additives in each layer, were the same as in Example 1. The stretched raw sheet was coextruded in the same manner as in Example 1.

As in Example 1, the obtained multilayer unstretched raw sheet was subjected to biaxial stretching using the conventional inflation method.

However, stretching cannot be performed unless the temperature at the starting point of stretching is raised to a temperature close to the melting point of the linear low-density polyethylene resin of the core layer, and the stretching stability is poor.

(Comparative Examples 4 to 5) The same resin as in Example 1 was used for both the rain layer, the core layer, and the barrier layer, and only the mixing ratio of the crystalline polypropylene resin and the linear low-density polyethylene resin of the barrier layer was used. The weight ratio was 1:2 in Comparative Example 4 and 4:1 in Comparative Example 5, and the thickness structure of each layer, the overall thickness, and the type and amount of additives in each layer were determined. The same multilayer unstretched raw sheet as in Example 1 was coextruded by the same method as in Example 1.

As in Example 1, the obtained multilayer unstretched original sheets could be easily biaxially stretched and heat-set, and a multilayer heat-shrinkable film could be obtained. However, the resulting multilayer heat-shrinkable films had poor slip properties and were difficult to hang on packaging machines.

Comparative Example 6 The same resin as in Example 1 was used for both outermost layers and the core layer, and the barrier layer was made of a crystalline polypropylene resin with a melting point of 137°C and a M of 11.2 g/min, and a density of 0.900 E. /
cm', Hikat softening point of 67°C, M14.2 g/m group linear low density polyethylene resin mixed in a weight ratio of 1:1, and the thickness structure of each layer, overall thickness, and A multilayer unstretched raw sheet was coextruded in the same manner as in Example 1, with the same types and amounts of additives in each layer as in Example 1.

The obtained multilayer unstretched original sheet could be easily biaxially stretched and heat-set as in Example 1, and a multilayer heat-shrinkable film could be obtained. However, the resulting multilayer heat-shrinkable film had poor texture and poor transparency, and its display effect was poor when used for heat-shrink packaging.

(Comparative Example 7) A multilayer heat-shrinkable film was prepared in the same manner as in Example 1 except for the amount of lubricant and anti-blocking agent added to each layer.
obtained by the same method. That is, 50% of lubricant was added to both outermost layers.
00 ppm, an anti-blocking agent was added at 1500 ppm, and no lubricant was added to the core layer and the barrier layer.

However, despite the addition of a large amount of lubricant to the outermost layer of the obtained multilayer heat-shrinkable film, its surface had poor slipperiness and was difficult to hang onto packaging machines.

(Comparative Example 8) The same resin as in Example 1 was used for both outermost layers and the core layer, and a 2-type, 3-layer multilayer heat-shrinkable film with no barrier layer was prepared by changing the number of extruders and the multilayer circular die. It was obtained in the same manner as in Example 1 except for changing the type of. The thickness ratio of each layer was 1:3:1, and the film thickness was 15 μm, which is the same as in Example 1. Then, apply 3000 lubricant to both outermost layers.
3,000 ppm of an anti-blocking agent was added, and 5,000 ppm of a lubricant was added to the core layer.

However, despite the addition of a large amount of lubricant to each layer, the obtained multilayer heat-shrinkable film did not have much improved slipperiness, and in iv), the interlayer adhesive strength decreased, The strength of the fused seal was weakened. Furthermore, since a large amount of anti-blocking agent was added, hot tack properties were reduced, and sealing failures were likely to occur during fusing sealing.

Claims (1)

[Scope of Claims] 1) Both outermost layers are made of crystalline polypropylene resin with a melting point of 135 to 150°C, and the core layer has a density of 0.890 to 0.9.
10g/cm^3, the resin composition is made of a resin composition mainly composed of a linear low density polyethylene resin with a Vicat softening point of 60 to 80°C, and the above-mentioned crystals are included in at least one of the outermost layers and the core layer. A polypropylene resin and each resin selected from the above linear low density polyethylene resin are mixed in a weight ratio of 2:3 to 3:1, and
A barrier layer made of a resin composition in which the melt flow index of the crystalline polypropylene resin is higher than the melt flow index of the linear low density polyethylene resin is inserted, and at least one of the outermost layers as well as the barrier layer A multilayer heat-shrinkable film in which a lubricant is also added to the core layer. 2) The crystalline polypropylene resin of the layer inserted into at least one of the outermost layers and the core layer according to claim 1 is the same as the resin used for both outermost layers. Multilayer heat shrinkable film. 3) The linear low-density polyethylene resin of the layer inserted into at least one of the outermost layers and the core layer according to claim 1 is the same as the resin used for the core layer. , multilayer heat-shrinkable film. 4) A multilayer heat-shrinkable film, wherein the thickness of each layer inserted between at least one of the outermost layers and the core layer according to claim 1 is 7 to 30% of the total thickness.