JPH0939179A - Thermally shrinking cylindrical multilayer film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to thermally seal or vacuum-seal bags stacked by setting the difference in the melting points of both layers one layer consisting of a copolymer of methylene and olefin with the density and the melting point of an outer surface resin layer falling within a specified range, and the other consisting of a copolymer of ethylene and olefin with the density and the melting point of a thermally sealable resin layer falling within a specified range, to a specified value or higher. SOLUTION: This thermally shrinking cylindrical multilayer film consists of an outer surface resin layer S1 with the gel fraction x of the outermost surface part of 35-70wt.% and an adhesive and thermally shrinking resin layer T1 with the innermost gel fraction y of an adhesive and thermally shrinking resin layer 71 of 10-40wt.%, the gel fraction gradient of 0.6 or less expressed by y/x, the junction part modified by an electron beam between T1 and a vinylidene chloride resin layer C, and a thermally sealable resin layer S which is substantially noncrosslinked. In addition, the thermally shrinking cylindrical multilayer film is composed of an ethylene-α-olefin copolymer with (1) the SI density of 0.900-0.915g/cm<3> and the melting point of 115-125 deg.C and an ethylene.α-olefin copolymer with (2) the S2 density of 0.895-0.915g/cm<3> , and the melting point of 94-108 deg.C, and with the difference of the melting point between S1 and S2 of 10 deg.C or higher.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-shrinkable tubular product used for the purpose of heat-shrink-wrapping a food containing fat-irregular foods such as raw meat and processed meat as a content. The present invention relates to a technique for improving a multilayer film.

[0002]

2. Description of the Related Art Conventionally, for example, in Japanese Examined Patent Publication No. 4-4149, an outer surface resin layer (S1
Layer), adhesive heat-shrinkable resin layer (T1 layer), vinylidene chloride resin layer (C layer), adhesive heat-shrinkable resin layer (T2)
Layer) and a heat-sealable resin layer (S2 layer) are laminated in this order, and the gel fraction (X) of the outermost part of the S1 layer (the side away from the C layer) is X. 25
˜70 wt%, the gel fraction (Y) of the innermost portion of the T1 layer (C layer side) is 5% or more and 40 wt% or less, and the gel fraction gradient represented by (Y / X) is 0.6 or less. And the above T
Disclosed is a heat-shrinkable tubular multi-layer film in which the joint between the first layer and the C layer is a joint in the state of being modified with an electron beam, and the heat-sealing resin layer (S2 layer) is substantially uncrosslinked. Is known.

According to the description of this publication, the above-mentioned method for producing a laminated film is simply to form a tubular laminate by a coextrusion method, then irradiate an electron beam from the outer surface of the tubular article, and thereafter, This is a cross-linking / stretching method that stretches and utilizes the cross-linking and stretching effect. The characteristic is that the irradiated electron beam cross-links (gel fraction) gradient to the layers (S1, T1 layers) on the cylinder surface side. To give sufficient cross-linkage to the S1 and T1 layers,
Further, electron beam modification is also applied to the joint interface between the T1 layer and the C layer, but the irradiation dose to the C layer is reduced due to the attenuation, and the heat-sealing resin layer (S2 layer) is further reduced. It has the characteristic that it is not substantially crosslinked.

As the outer surface resin layer (S1), what is called an ethylene vinyl acetate copolymer resin, a linear low density polyethylene resin or an ultra low density polyethylene resin is used, and its role is to roughly change the contents. It provides abuse resistance when handled. As the heat-sealable resin layer (S2 layer), those called linear low-density polyethylene resin, ultra-low-density polyethylene resin, and ethylene-vinyl acetate copolymer resin are used, and their role is to provide heat-adhesiveness. Is. As the adhesive heat-shrinkable resin layer (T1, T2),
What is called ethylene vinyl acetate copolymer resin, ethylene-ethyl acrylate copolymer resin (EEA), ethylene-acrylic acid copolymer resin (EAA), etc. is used, and the core layer (C layer), outer surface It serves to enhance the adhesive force between the resin layer (S1) and the heat-sealing resin layer (S2 layer). As the vinylidene chloride-based resin used for the core layer (C layer), a copolymer resin of vinylidene chloride and vinyl chloride, methyl acrylate or butyl acrylate is used, which imparts oxygen barrier properties to the laminated film, Has the role of preventing corruption.

The first feature of the film produced by the above method is the effect of improving the sealing performance exhibited by the combination of the surface crosslinked resin layer and the substantially uncrosslinked sealing resin layer. Specifically, it is an effect that the time required until the completion of sealing can be shortened, that the demand for improvement in packaging capacity can be met, and that the temperature range suitable for sealing can be expanded to significantly reduce the occurrence rate of defective sealing during practical use.

On the other hand, recently, as new polyolefin resins, ethylene and butene-1, hexene-1,4-methylpentene-1, octene-obtained by so-called single-site catalysts (also called metallocene catalysts and Kaminsky catalysts) have been obtained. A linear copolymer of ethylene-α-olefin having a very low density such as 1 and a narrow molecular weight distribution is introduced to the market (for example, Modern Plastics I).
international-al, October, 199
3, p. 99), it is considered to be used in a multilayer film having a gas barrier resin as a core layer (JP-A-6-32).
0685, EP0597502-A2, EP06
34433-A2).

JP-A-6-320685 discloses an ultra-low density obtained by a metallocene catalyst in at least the innermost layer in a multilayer film including a core layer (C layer) made of a gas barrier resin and a layer made of an olefin resin. The use of a linear copolymer of ethylene-α / olefin having a narrow molecular weight distribution improves the odor of the film. Further, in EP0597502-A2, a linear copolymer of ethylene-α-olefin having a very low density and a narrow molecular weight distribution, which is polymerized by using a single-site catalyst in a multilayer film including a core layer made of a gas barrier resin, is heated. A laminated film configured to be used as a sealing inner layer or another layer is disclosed, and it is said that the impact resistance of the laminated film is enhanced. In addition, EP0634433-
A2 is a heat-sealable inner layer of a linear copolymer of ethylene-α-olefin having a narrow molecular weight distribution and a low melting point obtained by polymerizing using a single-site catalyst in a multilayer film including a core layer made of a gas barrier resin. Alternatively, a laminated film having a configuration used for another layer is disclosed, and it is stated that the heat shrinkability of the laminated film is improved and the impact resistance is also improved.

On the other hand, the main use of the packaging material according to the present invention is that a meat processor (called a meat packer) divides beef, horses and pigs into respective parts, and divides the divided chunks of meat into a tubular shape. It is used when placed in a bag, tightly packed and distributed to final retail stores such as supermarkets. The actual usage conditions of meat processors are described below.

First, in a meat processing company, slaughtered and refrigerated cattle, horses, and pigs are divided into respective parts, and the lumps of meat are put in a cylindrical bag, and a heat seal at the opening is put in a decompression chamber in a bag. The inside of the chamber is also depressurized, and then the decompression chamber is returned to normal pressure. Next, by spraying hot water of about 70 ° C. to 90 ° C. onto the vacuum-packed meat block or dipping the vacuum-packed meat block into hot water of about 70 ° C. to 90 ° C., a film is formed. Heat shrinks to give a tight packing feeling, and prevents the exudation of blood, gravy, etc. to give an anti-rot effect. The hot water temperature at this time is preferably about 80 ° C because the discoloration called "burning" occurs on the surface of the meat under high temperature conditions, and therefore the film that highly shrinks at about 80 ° C is preferred. . The heat treated bag is then dipped in cold water at about 5 ° C. to cool.

In recent years, in the final retail stores such as supermarkets, there is a strong demand for labor saving and labor cost reduction, and it is requested that meat processors subdivide chilled raw meat into smaller pieces and deliver them. are doing. Therefore, in the meat processor, when dividing slaughtered and refrigerated cattle, horses, and pigs into individual parts, they are divided into smaller sizes than before, and many meat chunks are tightly packed in many sachets. ,
Shipping is needed. A problem at that time is a step of closing the opening in the decompression chamber in the above-mentioned raw meat packaging process. That is, the bag is set in a vacuum packaging machine, the decompression chamber is hermetically closed, and the vacuum pump sufficiently depressurizes the film until it comes into close contact with the meat block. This is a troublesome process of returning to atmospheric pressure, opening the decompression chamber, and taking out the bag. Therefore, if it is possible to set and process a large number of bags at a time when vacuum packaging, there is a portion where the bags overlap each other,
It became possible to carry out efficient vacuum packaging, and the appearance of such a laminated film was expected.

[0011]

However, as described in Japanese Patent Publication No. 4-4149, the vinylidene chloride resin layer (C layer) is used as a gas barrier core layer and its surface layer (S1 layer, T1 layer). ) Is a specific gel fraction range,
And with a specific gel fraction gradient, and in the multilayer film in which the sealing layer resin is substantially uncrosslinked, it is effective in reducing the time required for heat-sealing and reducing the defective sealing rate, but different bags If they overlap each other, good sealing cannot be performed. In other words, if you try to make a good seal, the overlapping parts of the bag will not be peeled by heat fusion, and if you try to peel it forcibly, the bag will break and it will not make sense of vacuum packaging, and the heat between the bags If heat fusion conditions are adjusted to prevent fusion and heat sealing is attempted at a low temperature, the inner surface will be poorly sealed, and appropriate sealing conditions cannot be selected.

Further, JP-A-6-320685, E
P0597502-A2 and EP0634433-A2 have the idea that even if a large number of bags are vacuum-packed or heat-sealed at the same time, thermal fusion of different overlapping bags can be prevented and the inner layer can be heat-sealed completely. There is nothing in the first place. That is, the laminated film of the example described in the above publication, while also having the basic characteristics of the conventional heat-shrinkable tubular multilayer film, prevents heat fusion between different bags, and complete heat seal of the inner layer. It is impossible to do.

The object of the present invention is to combine heat-shrinkability and vacuum-packing treatment in a state in which bags are overlapped with each other while having basic characteristics such as low-temperature heat-shrinkability and oil resistance on the inner surface of a conventional heat-shrinkable tubular multilayer film. To provide a heat-shrinkable tubular multilayer film.

[0014]

That is, according to the present invention, an outer surface resin layer (S1 layer) is provided from the outside of the cylinder toward the inside of the cylinder.
At least an adhesive heat-shrinkable resin layer (T1 layer), a vinylidene chloride resin layer (C layer), an adhesive heat-shrinkable resin layer (T2 layer), and a heat-sealable resin layer (S2 layer) are laminated in this order. It consists of 5 layers, and the gel fraction (X) of the outermost surface of the S1 layer
Is 35% by weight to 70% by weight, and the gel fraction (Y) of the innermost portion of the T1 layer (a portion adjacent to the C layer) is 10% by weight to 40% by weight.
% By weight, the gel fraction gradient represented by (Y / X) is 0.6 or less, the junction between the T1 layer and the C layer is electron beam modified, and the S2 layer is substantially In the non-crosslinked heat-shrinkable tubular multilayer film, (1) the outer surface resin layer (S1 layer) has a density of 0.900 g / cm ^{3 to} 0.915.
g / cm ³ and and made of a copolymer of ethylene-.alpha. · olefin a melting point of 115 ° C. to 125 ° C.,
(2) The heat-sealable resin layer (S2 layer) has a density of 0.8.
Was ^{95g / cm 3 ~0.915g / cm 3} , and a melting point is a copolymer of ethylene-.alpha. · olefin is 94 ℃ ~108 ℃, (3) the outer surface resin layer (S1
Layer) and the heat-sealing resin layer (S2 layer) have a melting point difference of 10 ° C. or more, which is a heat-shrinkable tubular multilayer film.

The details of the present invention will be described below. First, the difference between the laminated film of the present invention and the laminated film of the prior art is that (a) the gel fraction (X) of the outermost surface portion of the outer surface resin layer (S1 layer) is 35% by weight to 70% by weight, Density is 0.9
00 g / cm ^{3 to} 0.915 g / cm ³ , melting point 115
° C. a copolymer of to 125 ° C. ethylene-.alpha. · olefin, the heat-sealable resin layer (S2 layer) in a state of substantially uncrosslinked, its density 0.895g / cm ³ ~0.915
g / cm ³ , ethylene having a melting point of 94 ° C to 108 ° C-
It is a copolymer of α-olefin, and is summarized in that (b) the difference in melting point between the outer surface resin layer (S1 layer) and the heat-sealing resin layer (S2 layer) is 10 ° C or more.

The roles of (a) and (b) above will be described with reference to FIG. FIG. 1 is an experimental view showing a temperature range in which bags according to the present invention can be heat-sealed by overlapping them. The horizontal axis of the figure indicates the temperature, and the temperature is the temperature of the seal bar measured by the thermo label. The vertical axis shows the temperature range in which the inner surface can be sealed, the temperature range in which the overlap can be sealed, and the temperature range in which the overlap cannot be sealed, in the order of the following three types of films.

(A) Film of the present invention (corresponding to film No. 1 of Example 1) The gel fraction (X) of the outermost surface of the S1 layer is 52% by weight. The density of the S1 layer is 0.905 g / cm ^3. , Ethylene-α-olefin copolymer having a melting point of 123 ° C. The S2 layer is substantially uncrosslinked and has a density of 0.895 g.
/ Cm ³ and a melting point of 94 ° C. ethylene-α · olefin copolymer (B) Conventional film (corresponding to Film No. 2 of Comparative Example 1) Gel fraction (X ) Is an ethylene-α-olefin copolymer having a density of 0.895 g / cm ³ and a melting point of 94 ° C. (C) Conventional film (Comparative Example 2 film No. 3) Correspondence) The gel fraction (X) of the outermost surface portion of the S1 layer is 52% by weight. Both the S1 layer and the S2 layer have a density of 0.905 g / cm ³ and a melting point of 123 ° C. An ethylene-α-olefin copolymer diagram. According to 1, the film (A) of the present invention can be heat-sealed on the inner surface from about 90 ° C., and the temperature at which the outer surfaces of the bag are heat-sealed is from about 150 ° C. The reason is that the S1 layer has a gel fraction (X) of 52 at the outermost surface.
% By weight, difficult to flow when melted,
The S2 layer is in a substantially uncrosslinked state and is in a state of being easily heat-bonded when the outer surfaces are compared with each other.
The difference in the melting points of the layers is 29 ° C., which is due to their combined effect.

The temperature range in which the bag can be overlapped and sealed is about 90 ° C. to 150 ° C., and its width (hereinafter, the temperature range in which the overlap and seal can be made) is about 60 ° C. According to the experimental analysis by the present inventors, the above-mentioned temperature range capable of overlapping and sealing is required to be 40 ° C. or more in order to enable heat sealing in a state where different bags overlap each other. This is because the long and narrow seal bar of the vacuum packaging machine has uneven temperature depending on the location, and the overlapping portion of the bag has a delay in heat transfer, so that the temperature range that can be overlap-sealed is 40 ° C. If it is less than the above range, the inner surface will be incompletely sealed, or conversely, the rate of occurrence of defects in which the bags are heat-sealed and cannot be separated becomes extremely high, which is not suitable for practical use.

On the other hand, in the case of the conventional film (B), the outer surfaces of the bag are heat-sealed to each other (temperature range in which overlapping and sealing is impossible).
However, the temperature range in which the bag can be overlap-sealed is about 90 ° C to 110 ° C. The reason is that the S1 layer has the same melting point of 94 ° C as ethylene-α as the S2 layer.
・ Because it is a copolymer of olefins. Therefore, the temperature range in which superposition sealing is possible is as narrow as about 20 ° C., and superposition sealing of bags is practically impossible.

The conventional film (C) is capable of heat-sealing the inner surface of the bag (inner surface sealable temperature range) from about 130 ° C., and the overlapping sealable temperature range of the bag is about 130 ° C. To 150 ° C. The reason is that the S2 layer is ethylene-
This is because it is a copolymer of α-olefin. Therefore,
The temperature range that can be overlap-sealed is as narrow as about 20 ° C, and it is practically impossible to overlap-seal the bag.

That is, the film of the present invention has a gel fraction (X) of 35% to 70% by weight at the outermost surface of the S1 layer, and since the S2 layer is substantially uncrosslinked, the film is When heat-sealed, the outer surface (S1 layer) is less likely to flow, and the bags are less likely to be heat-sealed.
The heat-sealing layers (S2 layers) that are substantially uncrosslinked are in a state in which they are more easily heat-sealed than the outer surfaces (S1 layers), and the S1 layers are linear with a low density and a relatively high melting point. It is a low density polyethylene resin, and the S2 layer is a linear ultra-low density polyethylene resin having a low density and a relatively low melting point,
The melting point difference between the S1 layer and the S2 layer is 10 ° C. or more,
Furthermore, the density of the S2 layer is 0.895 g / cm ^{3 to} 0.9.
The ethylene-α-olefin copolymer having a melting point of 15 g / cm ³ and a melting point of 94 ° C. to 108 ° C. has a characteristic that the heat-sealing start temperature is lower than the actual melting point, and the combination effect thereof. By
The heat-shrinkable tubular multi-layered film can be heat-sealed and vacuum-wrapped in a state where the bags are overlapped with each other while having the basic characteristics of the conventional heat-shrinkable tubular multi-layered film.

Here, the gel fraction (X) of the outermost surface of the S1 layer must be in the range of 35% by weight to 70% by weight. When the gel fraction (X) is less than 35% by weight, the effect of preventing heat fusion between the outer surfaces becomes insufficient, and when the gel fraction (X) exceeds 70% by weight, the stretched film-forming property of the laminated film is improved. Is inferior and the low temperature heat shrinkability becomes insufficient.

The density of the S1 layer is 0.900 g / cm ³ or more.
It is necessary to be 0.915 g / cm ³ . If the density is less than 0.900 g / cm ³ , the film will be blocked in a wound state, resulting in handling problems, and if the density exceeds 0.915 g / cm ³ , the low temperature heat shrinkability of the bag will be poor. This is because The melting point range needs to be 115 ° C to 125 ° C. If the melting point is less than 115 ° C, the heat-sealing start temperature of the outer surface becomes too low, the difference in melting point from the S2 layer becomes small, the temperature range in which superposition sealing is possible becomes narrow, and the melting point is 125 ° C.
If it exceeds, the low temperature heat shrinkability of the bag will be inferior.

The resin of the S2 layer has a density range of 0.
It is necessary to be 895 g / cm ^{3 to} 0.915 g / cm ³ . When the density is less than 0.895 g / cm ³ ,
This is because the opening property of the bag becomes poor and the bag cannot be easily opened by hand, and when the density exceeds 0.915 g / cm ³ , the low temperature heat shrinkability of the bag is inferior.

The melting point range needs to be 94 ° C to 108 ° C. If the melting point is less than 94 ° C, the oil resistance of the inner surface of the bag becomes poor, and if the melting point exceeds 108 ° C,
This is because the sealing start temperature of the inner surface becomes high and the temperature range in which superposition sealing is possible becomes narrow. The melting point of the S1 layer is 115 ° C.
Selected from resins of ~ 125 ° C, S2 layer has a melting point of 94 ° C
It is selected from resins having a temperature of ˜108 ° C., but it is necessary that the combination is such that the difference in melting point between the S1 layer and the S2 layer is 10 ° C. or more. The difference in melting point between the S1 and S2 layers is 10 ° C.
If it is less than 40 ° C., the temperature range in which superposition sealing is possible is less than 40 ° C., and the superposition sealing property becomes poor. The upper limit of the melting point difference between the S1 layer and the S2 layer is 31 ° C. This is because a combination having a melting point difference of more than 31 ° C. will have to sacrifice low-temperature heat shrinkability, oil resistance on the inner surface, and other properties that the bag should have.

Used as the S1 layer, having a density of 0.900 g
/ Cm ^{3 to} 0.915 g / cm ³ and a melting point of 1
Specific examples of the ethylene-α-olefin copolymer having a temperature of 10 ° C to 125 ° C include ethylene, butene-1, pentene-1, 4-methylpentene-1, and hexene-1,
A copolymer resin with an α-olefin having 4 to 12 carbon atoms represented by octene-1 and the like can be given. A linear low-density polyethylene resin or a linear ultra-low-density polyethylene resin obtained by using a conventional Ziegler-Natta catalyst as a polymerization catalyst can be appropriately selected and used.

The density used as the S2 layer is 0.895 g /
cm ^{3 to} 0.915 g / cm ³ and a melting point of 94
Specific examples of the ethylene-α-olefin copolymer having a temperature of ℃ to 108 ℃ are represented by ethylene and butene-1, pentene-1, 4-methylpentene-1, hexene-1, octene-1 and the like. A linear ultra-low density polyethylene resin obtained by using a so-called single-site catalyst as a polymerization catalyst, which is a copolymer resin with an α-olefin having 4 to 12 carbon atoms.

Further, the adhesive heat-shrinkable resin layer (T1, T
2) include ethylene vinyl acetate copolymer resin (EV
A), ethylene-ethyl acrylate copolymer resin (E
EA), ethylene-acrylic acid copolymer resin (EAA)
Examples of known resins such as Core layer (C layer)
Examples of the vinylidene chloride-based resin used in the above include copolymer resins of vinylidene chloride and vinyl chloride, methyl acrylate, butyl acrylate, and the like.

In the laminated film of the present invention, the thickness of all layers of the film is in the range of 30 to 100 μm, preferably 40.
˜80 μm. If the thickness is less than 30 μm, the mechanical strength of the film will be insufficient, and if it exceeds 100 μm, the time required for heat sealing of the film will be undesirably long. The thickness of the core layer (C layer) in the laminated film is preferably in the range of 3 to 20 μm. If the thickness of the C layer is less than 3 μm, the gas barrier property of the laminated film is insufficient, and
When it exceeds m, the abuse resistance of the laminated film is deteriorated, which is not preferable.

The outer surface resin layer (S1 layer) has a thickness of 2
To 50 μm, preferably 5 to 40 μm. When the thickness is less than 2 μm, the effect of hindering heat fusion between the outer surfaces of the bag is insufficient, which is not preferable.
When it exceeds μm, the laminated film is warped, which is not preferable. The thickness of the heat sealable resin layer (S2 layer) is 5 to 40.
It is in the range of μm, preferably in the range of 5 to 30 μm. When the thickness is less than 5 μm, the oil resistance and mechanical strength of the seal portion are insufficient, which is not preferable, and when the thickness exceeds 40 μm, the laminated film is warped, which is not preferable.

Next, a preferable production method for obtaining the film of the present invention will be described. The method for producing a laminated film according to the present invention uses an annular multi-layer die, a vinylidene chloride resin as a core layer (C layer), adjacent to both surfaces of the C layer, and an adhesive heat-shrinkable resin layer (T1, A tubular laminate having an outer surface resin layer (S1 layer) and a heat-sealable resin layer (S2 layer) disposed via a T2 layer) is formed by a coextrusion method, and an electron beam is irradiated from the outer surface of the tubular object. After that, the tubular laminate is stretched to utilize the cross-linking / stretching effect.
It can be manufactured in the same manner as disclosed in Japanese Patent No. 4149. The formed tubular film is heat-sealed at one end and cut along the heat-sealed line to be used as a tubular bag for packaging raw meat or the like.

Further, blocking and the outer surface of the laminated film, or coating of about 0.1mg / m ² ~5mg / m ² starch powder on the inner and outer surfaces of the laminate film in order to improve the opening of the bag, S1 layer, A slip agent such as erucic acid amide can be added to the S2 layer.

[0033]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail below with reference to Examples and Comparative Examples. First, the method for measuring and evaluating the physical properties in the present invention will be described. <Gel Fraction> Obtained by the following operation based on ASTM D2765.

About 50 mg of a sample sampled from a predetermined place (outermost surface portion in the case of S1 layer, innermost case in the case of T1) by 0.01 m
Weigh with a balance having an accuracy of g (W ₀ g). The pouch of a 150-mesh SUS screen in which oil has been removed by previously immersing it in acetone for 24 hours and the sample are combined and weighed by the above balance (W ₁ g).

Wrap the sample in a pouch. The pouch-wrapped sample is kept in boiling paraxylene for 12 hours using a separable flask and a condenser. The sample wrapped in the pouch is dried by a vacuum dryer until the weight becomes constant. The sample wrapped in the pouch is weighed with the same balance (W ₂ g).

Gel fraction (% by weight) = {1- (W ₁ −
W ₂ ) / W ₀ } × 100 The gel fraction is calculated by the above formula. As a precaution when adjusting the sample for the above gel fraction measurement, • When using a specific layer of the laminate as a sample, attach it slowly with ethanol and use it as the sample.

When the surface layer portion of the specific layer of the parison is used as a sample, it is 10 mm × more than the portion of the peeled layer having good flatness.
A 20 mm section is taken, and the surface layer portion is sliced with a thickness of 20 μm using a microtome of an optical microscope to obtain a sample. In addition, after peeling off the specific layer of the stretched film, it is possible to slice the one which is heat-shrinked and returned to the parison state.

<Melting point> According to JIS-K7121, a measuring device used was DSC-7 manufactured by Perkin Elmer.
The melting point is indicated by the temperature of the highest peak among the melting peaks. <Density> According to the D method of JIS-K7112, a density gradient tube method specific gravity measuring device manufactured by Shibayama Scientific Instruments Co., Ltd. was used. An isopropyl alcohol / water system was used as the specific gravity liquid.

<MI (melt index)> ASTM
It measured according to D1238. <Overlap sealable temperature range> Beef loin (width approx. 250 mm, length approx. 300 mm, thickness approx. 150 m) is put into two tubular bags each having a folding width of 400 mm and a length of 650 mm.
m) is put in, and about 10 cm of each bag end is overlapped, and two bags are simultaneously set in a vacuum packaging machine.
Then, the decompression chamber is hermetically closed, and after vacuuming, heat sealing is performed under a predetermined temperature condition to vacuum-pack the meat chunk. Then, take out two bags from the vacuum packaging machine at the same time, dip them in hot water at 75 ° C for about 4 seconds to perform heat shrinkage treatment, and then at 5 ° C.
Soak in cold water to cool. Heat seal temperature condition 70
Raise the temperature from ℃ to 20 ℃ in increments, and check the seal on the inner surface of the bag with a seal checker (Ageless R seal checker (manufactured by Mitsubishi Gas Chemical Co., Inc.)) for the presence of pinholes. Let T ₁ be the temperature at which the part is completely sealed. Further, the temperature at which the two bags do not separate due to heat fusion when immersed in cold water is T ₂ . The (T ₂ -T ₁₎ was superimposed sealing temperature range.

For vacuum packaging, an impulse-sealing type FVM-WM machine manufactured by Furukawa Seisakusho Co., Ltd. was used for sealing for 2 seconds.
The cooling time was 2 seconds, and the sealing temperature was changed by changing the voltage. The seal temperature was measured by sticking a thermo label (a sticker for temperature measurement, manufactured by IP Giken Co., Ltd.) on the seal bar. Symbol Level value and evaluation ⊚: The temperature range in which the overlap sealing is possible is 60 ° C or more, and the superposition sealing property is extremely excellent.

◯: A temperature range in which superposition sealing is possible is 40 ° C. or more and less than 60 ° C., and the superposition sealing property is excellent. Δ: The temperature range in which the overlap sealing is possible is 20 ° C. or more and less than 40 ° C., and the overlay sealing property is poor. ×: The temperature range that can be overlap-sealed is less than 20 ° C, and the overlap-sealing is impossible.

<Low-Temperature Heat Shrinkability> A film cut into squares of 10 cm in length and width is immersed in hot water at 75 ° C. for 5 seconds to shrink in a relaxed state, and the shrinkage ratio with respect to the original length in the length and width directions. The shrinkage rate is averaged. In addition, the measurement is 1 after the film formation.
It carried out using the film stored at 5 degreeC for 1 week.

Symbol Level value and evaluation ⊚: Shrinkage rate is 33% or more, and low temperature heat shrinkability is very excellent. ◯: Shrinkage rate is 28% or more and less than 33%, and low temperature heat shrinkability is excellent. Δ: Shrinkage is 23% or more and less than 28%, and low-temperature heat shrinkability is poor. X: Shrinkage rate is less than 23%, and low temperature heat shrinkability is very poor.

<Inner surface oil resistance> One end of the film-formed seamless tubular film was heat-sealed under the condition that the maximum strength was obtained and cut along the heat-sealing line to manufacture a bag. After applying beef tallow to the bottom seal portion of the bag, the beef raw meat was pushed in until it hit the bottom seal portion, and vacuum packaging was performed. Twenty of these packages were passed through a hot water shower at 90 ° C. for the time specified below, and the presence or absence of breakage of the bottom seal portion was examined to evaluate the oil resistance on the inner surface. If the number of fractured pieces is 1 or less, it is considered good.

Symbol Level value and evaluation ⊚: Good after 12 seconds, very good oil resistance on the inner surface. ◯: Good after 8 seconds, excellent oil resistance on the inner surface. Δ: Good after 4 seconds, inferior internal oil resistance. X: Poor even after 4 seconds and very poor oil resistance on the inner surface.

<Outer surface blocking property> A laminated film having a width of 400 mm was wound around a 3-inch vinyl chloride bobbin for 500 m with a winding tension of 1.0 kg. After the wound film was stored at 40 ° C. for 1 week, the film was unwound and evaluated by its feeling. Symbol Level value and evaluation ◎: Easy to feed, excellent in external blocking property.

A: There is some resistance, but there is no problem in practical use, and the outer surface blocking property is excellent. (Triangle | delta): It is easy to block and pay out, and there is a problem in practical use, and the outer surface is inferior in blocking property. X: Blocked and unable to be drawn out, very poor in external surface blocking property.

<Bag opening property> A laminated film having a width of 400 mm was wound around a 3-inch vinyl chloride bobbin for 500 m with a winding tension of 1.0 kg. After the wound film was stored at 28 ° C. for 1 week, one end of a seamless tubular film was heat-sealed and cut along a heat-sealing line to manufacture a bag having a length of 800 mm. The unsealed mouth of the manufactured bag was opened by hand, and the feeling was evaluated.

Symbol Level Value and Evaluation ◎: Can be easily opened by hand. Very good bag opening. A: Excellent resistance to bag opening, with some resistance but no problem in practical use. Δ: Those that could not be opened easily and had a practical problem. Poor bag opening. X: It is very difficult to open. Very poor bag openability.

<Comprehensive Evaluation> Symbol Level Value and Evaluation ⊚: Excellent as a heat-shrinkable tubular film that maintains the conventional basic characteristics and can be overlaid and sealed between bags. ◯: Excellent as a heat-shrinkable tubular film that retains the conventional basic properties and can be overlaid and sealed between bags.

Δ: It is inferior as a heat-shrinkable tubular film that maintains the conventional basic properties and can be overlaid and sealed between bags. X: It is very inferior as a heat-shrinkable tubular film that maintains the conventional basic properties and can be overlap-sealed between bags. Next, the polymers used in this example and comparative examples are shown. VL1: ethylene-octene-1 copolymer (density 0.
905 g / cm ³ , melting point 123 ° C., MI = 0.8 g / 1
0 minutes, equivalent to Dow Chemical's Athein 4203) VL2: ethylene-octene-1 copolymer (density: 0.
912 g / cm ³ , melting point 125 ° C., MI = 3.3 g / 1
0 minutes, equivalent to Dow Chemical's Athein 4202) VL3: ethylene-butene-1 copolymer (density 0.8)
90 g / cm ³ , melting point 113 ° C., MI = 0.8 g / 10
Min, Sumitomo Chemical's Excellen EUL130 equivalent product) VL4: ethylene-butene-1 copolymer (density 0.9)
00 g / cm ³ , melting point 115 ° C., MI = 2.0 g / 10
Min, Sumitomo Chemical Exelen VL200 equivalent product) LL1: ethylene-4-methylpentene-1 copolymer (density 0.915 g / cm ³ , melting point 116 ° C., MI =
2.3 g / 10 minutes, Mitsui Petrochemical, Ultzex 1
520L equivalent product) LL2: ethylene-hexene-1 copolymer (density: 0.
912 g / cm ³ , melting point 118 ° C., Sumikasen α-FZ102 equivalent manufactured by Sumitomo Chemical Co., Ltd. ・ LL3: ethylene-hexene-1 copolymer (density: 0.
918 g / cm ³ , melting point 120 ° C., Sumikasen FZ104 equivalent product made by Sumitomo Chemical Co., Ltd. ・ LL4: ethylene-octene-1 copolymer (density: 0.
923 g / cm ³ , melting point 122 ° C., MI = 4.0, Dow Rex 5004 equivalent product manufactured by Dow Chemical Co.) SC1: Ethylene-octene-1 copolymer (density: 0.
895 g / cm ³ , melting point 94 ° C., MI = 1.6 g / 10
Min., Affinity PF1140 equivalent product manufactured by Dow Chemical Co., Ltd.)-SC2: ethylene-octene-1 copolymer (density: 0.
902 g / cm ³ , melting point 100 ° C., MI = 1.0 g / 1
0 minutes, Dow Chemical Co. Affinity PL1880 or equivalent) SC3: Ethylene-octene-1 copolymer (density: 0.
910 g / cm ³ , melting point 103 ° C., MI = 1.0 g / 1
0 minutes, Affinity PL1845 equivalent product manufactured by Dow Chemical Co., Ltd.) SC4: Ethylene-octene-1 copolymer (density: 0.
915 g / cm ³ , melting point 108 ° C., MI = 1.0 g / 1
0 minutes, Affinity FM1570 equivalent product manufactured by Dow Chemical Co.) SC5: ethylene-butene-1 copolymer (density 0.9)
00 g / cm ³ , melting point 86 ° C., MI = 3.5 g / 10
Min, Exxon EXACT3027 equivalent product) SC6: ethylene-butene-1 copolymer (density 0.8
85 g / cm ³ , melting point 66 ° C., MI = 2.2 g / 10
Min., EXACT4021 equivalent manufactured by Exxon) -EVA1: ethylene-vinyl acetate copolymer (density 0.
927 g / cm ³ , vinyl acetate content 10% by weight, melting point 9
7 ° C., MI = 3.0 g / 10 min, Tosoh Corporation Ultrasen UE540 equivalent product) EVA2: ethylene-vinyl acetate copolymer (density: 0.
936 g / cm ³ , vinyl acetate content 15% by weight, melting point 9
1 ° C., MI = 1.5 g / 10 minutes, Tosoh Corp. Ultrasen UE630 equivalent product) EVA3: ethylene-vinyl acetate copolymer (density 0.
941 g / cm ³ , vinyl acetate content 20% by weight, melting point 8
6 ° C., MI = 1.5 g / 10 min, Tosoh Corporation Ultrasen UE631 equivalent product) PVD1: Vinylidene chloride-vinyl chloride copolymer (vinyl chloride content 17% by weight, molecular weight 90,000, manufactured by Asahi Kasei Kogyo Co., Ltd.) -PVD2: vinylidene chloride-vinyl chloride copolymer (vinyl chloride content 20% by weight, molecular weight 110,000, manufactured by Asahi Chemical Industry Co., Ltd.)-PVD3: vinylidene chloride-methyl acrylate copolymer (methyl acrylate content 8% by weight, molecular weight 9) Ten thousand
Asahi Kasei Kogyo Co., Ltd.)

[0052]

Example 1 VL1 was applied to the S1 layer using four extruders.
Each layer is composed of S1 / T1 / C / T2 / S2 by using a layer made of, a T1 layer and a T2 layer made of EVA2, a C layer made of PVD1 and an S2 layer made of SC1.
(= 10% / 20% / 10% / 40% / 20%) to form a five-layer structure, extruded from a circular multilayer die, and extruding the extruded laminate by rapidly cooling it with cold water at 20 ° C., folding width 1
A parison with a thickness of 00 mm and a thickness of 660 μm was obtained. In this parison, ENERGYSCIENCE INC. Electron beam irradiation was performed under the conditions of an accelerating voltage of 175 KV and an irradiation dose of 12 megarads using a manufactured electro curtain <registered trademark> (non-scanning type). Air is injected into the cross-linked parison and heated to about 80 ° C, and inflation is biaxially stretched about 3 times in the longitudinal direction and about 4 times in the lateral direction to obtain a folding width of 400 mm and an average thickness of 55
A 500 μm tubular film of 500 μm was wound around a 3-inch vinyl chloride bobbin to obtain a total of 3 500 m-rolled films.

Further, one end of the obtained tubular film was heat-sealed under the condition that the maximum strength was obtained and cut along the heat-sealing line to produce a bag having a folding width of 400 mm and a length of 650 mm (Film No. 1).

[0054]

Comparative Example 1 The same procedure as in Example 1 was repeated except that the layer made of SC1 was used as the S1 layer in Example 1, and a total of 3 cylindrical films 500m each having a folding width of 400 mm and an average thickness of 55 μm were prepared. I got a roll. Also, folding width 400m
A bag having a length of m and a length of 650 mm was manufactured (Film N
o. 2).

[0055]

[Comparative Example 2] The same procedure as in Example 1 was repeated except that a layer made of VL1 was used as the S2 layer in Example 1, and a total of 3 cylindrical films 500m each having a folding width of 400 mm and an average thickness of 55 μm were prepared. I got a roll. In addition, one end of the obtained tubular film is heat-sealed under the condition that the maximum strength is obtained, cut along the heat-sealing line, and the folding width is 400 m.
A bag having a length of m and a length of 650 mm was manufactured (Film N
o. 3).

The evaluation results of Example 1 and Comparative Examples 1 and 2 described above are summarized in Table 1. In addition, in Table 1, the structure of the film, the physical properties of the ethylene-α / olefin linear copolymer used in the S1 layer and the S2 layer, and the gel fraction measurement results of the S1 layer and the T1 layer are also shown. . The gel fraction was 20% for the entire S1 layer and T1 layer, and 20% for the outermost portion of the S1 layer (the surface layer portion on the side remote from the C layer was measured using a microtome).
gel fraction (X) of the portion (thickness of μm was used as a sample), and the innermost portion of the T1 layer (the surface layer portion on the C layer side was sliced with a microtome to a thickness of 20 μm to obtain a sample)
The gel fraction (Y) of the portion (1) was measured, and the gel fraction gradient (Y / X) was calculated from (X) and (Y).

Film No. in Table 1 1 to No. FIG. 1 shows the result of the temperature range in which the film of Example 3 can be overlapped and sealed, and illustrates the difference between the film of the present invention and the film of the prior art. The temperature range that can be overlaid and sealed is about 60 for the film of the present invention (film No. 1)
In contrast to the conventional film (No. 2,
No. In 3), the temperature range in which superposition sealing is possible is 20 ° C. It was found that the bag made of the film of the present invention can be efficiently processed by setting a large number of bags at a time in a vacuum packaging machine in such a tight state that there are overlapping portions. . On the other hand, the film of the prior art has a narrow temperature range capable of being overlapped and sealed at 20 ° C.
Since temperature unevenness due to the location of the long and narrow seal bar of the vacuum packaging machine and the overlapping parts of the bag may cause delay in heat transfer, if you try to vacuum-pack many bags at once, The overlapped part is heat-sealed and cannot be separated, or if the heat-sealing is to be prevented, the inner surface will be incompletely sealed, and the defective rate is high and it is not suitable for efficient vacuum packaging processing. It can be seen that it is.

[0058]

[Table 1]

[0059]

[Embodiment 2] In Embodiment 1, an EV is applied to the T1 layer and the T2 layer.
Using a layer made of A1 and a layer made of PVD2 for the C layer,
The electron beam irradiation conditions are as shown in Table 2, 7 megarads, 1
Cylindrical film 50 having a folding width of 400 mm and an average thickness of 55 μm by repeating the same procedure as in Example 1 except that 0 megarad, 12 megarad, and 15 megarad were changed.
Three rolls of 0 m each were obtained. However, the stretching temperature was adjusted so that the folding width of each film was 400 mm and the average thickness was 55 μm.

Further, one end of the obtained tubular film was heat-sealed under the condition that the maximum strength was obtained and cut along the heat-sealing line to produce a bag having a folding width of 400 mm and a length of 650 mm (Film No. 4 to No. 7).

[0061]

Comparative Example 3 A tubular film having a folding width of 400 mm and an average thickness of 55 μm was repeated by repeating the same procedure as in Example 2 except that the electron beam irradiation amount was changed to 3 megarads and 17 megarads. Three rolls of 500 m each were obtained. However, the stretching temperature was adjusted so that the folding width of each film was 400 mm and the average thickness was 55 μm.

Further, one end of the obtained tubular film was heat-sealed under the condition that the maximum strength was obtained and cut along the heat-sealing line to produce a bag having a folding width of 400 mm and a length of 650 mm (Film No. 8, No. 9). The evaluation results of Example 2 and Comparative Example 3 described above are summarized in Table 2. In Table 2, electron beam irradiation conditions, S1 layer, T1
The gel fraction measurement results of the layers are also shown.

Film No. 4 to No. The measured values of the gel fraction of the S2 layer of the film No. 9 were all less than 0.5% by weight, and were substantially uncrosslinked. The results in Table 2 show that the gel fraction (X) of the outermost surface of the S1 layer is preferably 35% by weight to 70% by weight. The gel fraction (X) of the outermost surface of the S1 layer is 35% by weight
It can be seen that if it is smaller, the temperature range in which superposition sealing is possible becomes narrower, which makes it unsuitable for efficient vacuum packaging processing (Film No. 8).

Under the condition that the gel fraction (X) of the outermost surface of the S1 layer exceeds 70%, the low temperature heat shrinkage is inferior, and food such as chilled raw meat is used as a content and heat shrinked. It can be seen that it becomes unsatisfactory as a packaging material for tight packaging. The reason for this is that the gel fraction becomes too high in some areas, resulting in poor stretch film formability,
Unless the stretching temperature is set higher, a film having a predetermined stretching ratio cannot be obtained, so that the low temperature heat shrinkage ratio is considered to have a low value (Film No. 9).

Therefore, in the film of the present invention, the range of the gel fraction is the gel fraction (X) of the outermost surface of the S1 layer.
Must be 35% to 70% by weight, and T
The range of the gel fraction (Y) of the innermost part (C layer side) of one layer is 10
% To 40% by weight and the gradient of gel fraction (Y /
It can be seen that X) is 0.6 or less. Also, S1
The gel fraction of the entire layer, T1 layer, is from 20% by weight to 6%.
It can be seen that the range is 5% by weight (Film N
o. 4 to No. 7).

[0066]

[Table 2]

[0067]

Example 3 S1 layer, T1 using 4 extruders
Each resin layer shown in Table 3 is used for the layer, the C layer, the T2 layer, and the S2 layer, and each layer is S1 / T1 / C / T2 / S2 (= 6.7% /
(33.3% / 13.3% / 26.7% / 20%) having a five-layer structure, extruded from a circular multi-layer die, and extruding the laminated body by rapidly cooling it with cold water at 20 ° C., folding width 1
A parison with a thickness of 00 mm and a thickness of 720 μm was obtained. In this parison, ENERGYSCIENCE INC. Electron beam irradiation was performed under the conditions of an accelerating voltage of 200 KV and an irradiation dose of 10 megarads using a manufactured Electro Curtain <registered trademark> (non-scanning type). Air is injected into the cross-linked parison and heated to about 80 ° C, and inflation is biaxially stretched about 3 times in the longitudinal direction and about 4 times in the lateral direction to obtain a folding width of 400 mm and an average thickness of 60
A 500 μm tubular film of 500 μm was wound around a 3-inch vinyl chloride bobbin to obtain a total of 3 500 m-rolled films. However, the stretching temperature of each film was finely adjusted so that the folding width was 400 mm and the thickness was 60 μm.

Further, one end of the obtained tubular film was heat-sealed under the condition that the maximum strength was obtained and cut along the heat-sealing line to produce a bag having a folding width of 400 mm and a length of 650 mm (Film No. 10-13).

[0069]

COMPARATIVE EXAMPLE 4 The same procedure as in Example 3 was repeated except that the resin layers shown in Table 3 were used for the S1, T1, C, T2 and S2 layers. Thickness 60
Three rolls each of 500 m roll of a μm tubular film were obtained.
In addition, one end of the obtained tubular film was heat-sealed under the condition that the maximum strength was obtained and cut along the heat-sealing line to manufacture a bag having a folding width of 400 mm and a length of 650 mm (Film Nos. 14 to 16). ).

Incidentally, S1 and T of Example 3 and Comparative Example 4
In order to investigate the distribution of gel fraction in the thickness direction in one layer, a 10 μm film of VL4 and EVA3 was prepared,
FIG. 2 shows the results of measurement and analysis of the gel fraction of each film after closely overlapping and irradiating under the same conditions so as to have a predetermined thickness. Under this irradiation condition, the outermost gel fraction (X) of the S1 layer is about 50% by weight, and the innermost (C layer side) gel fraction (Y) of the T1 layer is 20% by weight.
Further, it can be seen that the gel fraction gradient (Y / X) is 0.6 or less. VL1, VL2, VL instead of VL4
The same procedure as above was repeated using 3, 10 μm films of LL1, LL3, and SC4, and the gel fraction of each film was measured and analyzed. The results of the gel fraction of the film of 20 μm from the outermost outermost layer of the S1 layer are shown below.

VL1: (X) = 48% by weight, (Y / X) = 0.42 VL2: (X) = 46% by weight, (Y / X) = 0.43 VL3: (X) = 49% by weight , (Y / X) = 0.41 LL1: (X) = 45% by weight, (Y / X) = 0.44 LL3: (X) = 43% by weight, (Y / X) = 0.47 SC4: (X) = 45% by weight, (Y / X) = 0.44. 10 to film No. The gel fractions of the S2 layers of the films of No. 23 were all 0.5% by weight or less and were substantially uncrosslinked.

Table 3 collectively shows the evaluation results of Example 3 and Comparative Example 4 described above. According to Table 3, first, the S1 layer of the present invention has a density of 0.900 g / cm ^{3 to} 0.915 g / cm ^3.
The reason why it is necessary to be an ethylene-α-olefin copolymer having a melting point of 115 ° C to 125 ° C will be explained. That is, since the outermost surface of the S1 layer has a specific gel fraction, it is difficult for the outermost layer of the film to be heat-sealed, the difference in melting point between the resins of the S1 layer and the S2 layer, and the ethylene content of the S2 layer.
The synergistic effect is maximized and the excellent (bag-to-bag) superposition sealing property is achieved by the fact that the α-olefin copolymer has the property of being easily heat-sealed at a lower temperature than the decrease in the melting point. It is expressed.
Further, when an ethylene-α-olefin copolymer having a high melting point is used for the S1 layer and the melting point difference from the S2 layer is widened, the temperature range capable of being overlap-sealed tends to be widened (film Nos. 11 and 12). (Comparison with film Nos. 10 and 13). When the melting point of the S1 layer becomes higher, the density also tends to increase at that time, resulting in a slight decrease in the low temperature shrinkability of the bag (Film Nos. 12 and 13 and Film No. 13).
(Comparison of 10 and 11). Therefore, the resin of the S1 layer to be selected can be changed depending on whether the priority is given to the efficiency at the time of vacuum packaging or the case where the low temperature heat shrinkability is emphasized. If the resin density of the S1 layer exceeds 0.915 g / cm ³ , the low-temperature heat shrinkability of the bag will not reach 30%, and as a packaging material for packaging foods such as chilled raw meat, heat shrinking and tightly packaging. Is inconvenient (Film No. 1
4). Further, if the density of the S1 layer is less than 0.900 g / cm ³ , blocking of the outer surface of the film occurs in the state of being wound into a roll, which is inconvenient (Film No. 1).
5).

When an ethylene-α-olefin copolymer having a density of 0.915 g / cm ³ and a melting point of 108 ° C. is used for the S1 layer, even if the melting point difference from the S2 layer is 14 ° C.,
The temperature range in which overlap sealing was possible was narrow (Film No. 16). In this case, both the S1 layer and the S2 layer are
Is the density ^{0.895g / cm 3 ~0.915g / cm 3} , and to the melting point is a copolymer of 94 ° C. -108 ° C. ethylene -α- olefin, melting point difference even 14 ° C., overlaid The temperature range that can be fitted and sealed is small. This means that the density used as the S1 layer in the present invention is 0.900 g / cm ^{3 to} 0.915 g /
cm ³ and the melting point of the ethylene-α-olefin copolymer having a melting point of 115 ° C. to 125 ° C., and the density used as the S2 layer in the present invention is 0.8.
95 g / cm ³ was ~0.915g / cm ^3, and a melting point indicates the importance of utilizing the difference in the heat sealing characteristics of the copolymer of ethylene -α- olefin is 94 ° C. -108 ° C. There is.

[0074]

[Table 3]

[0075]

Example 4 The same procedure as in Example 3 was repeated except that the resin layers shown in Table 4 were used for the S1, T1, C, T2 and S2 layers, and the folding width was 400 mm and the average thickness was 400 mm. 60
A 500 μm tubular film of 500 μm was wound around a 3-inch vinyl chloride bobbin to obtain a total of 3 500 m-rolled films. However, the stretching temperature of each film was finely adjusted so that the folding width was 400 mm and the thickness was 60 μm.

Further, one end of the obtained tubular film was heat-sealed under the condition that the maximum strength was obtained and cut along the heat-sealing line to produce a bag having a folding width of 400 mm and a length of 650 mm (Film No. 17-19).

[0077]

Comparative Example 5 Example 3 was repeated except that the resin layers shown in Table 4 were used for the S1, T1, C, T2 and S2 layers.
By repeating the same procedure as above, three rolls of 500 m each each having a folding width of 400 mm and an average thickness of 60 μm were obtained. Further, one end of the obtained tubular film was heat-sealed under the condition that the maximum strength was obtained, and cut along the heat-sealing line to produce a bag having a folding width of 400 mm and a length of 650 mm (Film Nos. 20 to 24). ).

Film No. In order to investigate the distribution of the gel fraction in the S1 and T1 layers of 24 in the thickness direction, LL4
Of 10 μm, and after closely superimposing them to a predetermined thickness and irradiating them under the same conditions, the gel fraction of the film of 20 μm from the outermost outermost S1 layer was measured. Is shown below. LL2: (X) = 44% by weight, (Y / X) = 0.45 LL4: (X) = 42% by weight, (Y / X) = 0.48 Evaluation results of Example 4 and Comparative Example 5 above Are summarized in Table 4. From Table 4, the S2 layer of the present invention has a density of 0.895.
g / cm ³ was ~0.915g / cm ^3, and a melting point of 9
The reason why the ethylene-α-olefin copolymer at 4 ° C to 108 ° C is required and the difference in melting point between the S1 layer and the S2 layer is required to be 10 ° C or more will be described.

That is, the density of the S2 layer is 0.895 g /
cm ^{3 to} 0.915 g / cm ³ and a melting point of 94 ° C.
It is an ethylene-α-olefin copolymer having a temperature of up to 108 ° C, and when the difference in melting point between the S1 layer and the S2 layer is a value of 10 ° C or more, the film overlap sealing temperature range is wide and low temperature heat shrinkage occurs. It is understood that the evaluation results are satisfactory for all of the properties, the oil resistance on the inner surface, the blocking property on the outer surface, and the bag openability (Film Nos. 17 to 19). When a relatively high density, high melting point ethylene-α-olefin copolymer is used for the S2 layer, the bag has excellent openability, and therefore, when the efficiency during vacuum packaging is prioritized and when the bag is used, Depending on the case where importance is attached to the opening property of No. 2, it is possible to change the resin of the S2 layer to be selected (comparison between film No. 17 and No. 19).

It is also understood that when the melting point of the S2 layer is less than 94 ° C., the oil resistance on the inner surface of the bag is unsatisfactory (film No. 20 to No. 21). Further, when the density is less than 0.895 g / cm ³ , it is found that the oil resistance on the inner surface of the bag is unsatisfactory and the opening property of the bag is insufficient (Film No. 2).
1).

When the difference between the melting points of the S1 layer and the S2 layer is less than 10 ° C., the temperature range in which superposition sealing is possible is less than 40 ° C., which is unsatisfactory (Film No.
22, no. 23). Also, if an attempt is made to increase the melting point difference between the S1 layer and the S2 layer and a S2 layer having a low melting point is selected, the oil resistance of the inner surface of the bag becomes insufficient (film No. 20, No. 21), and the inner surface of the bag It can be seen that if a resin having a high melting point is selected for the S1 layer in order to widen the difference in melting point while maintaining the oil resistance of the above, the low temperature heat shrinkability becomes poor and the film becomes unsatisfactory (Film N
o. 23). At this time, if VL4 is used for the S1 layer and EVA2 is used for the S2 layer in an attempt to widen the difference in melting points while maintaining the low temperature heat shrinkability, the inner oil resistance is also inferior, which is unsatisfactory. (Film N
o. 24).

[0082]

[Table 4]

[0083]

As described above, by satisfying the constitution of the present invention, it has the conventional basic characteristics such as low temperature heat shrinkability and oil resistance on the inner surface, and heat sealing and vacuum packaging in a state where bags are overlapped. A heat-shrinkable tubular laminated film capable of being obtained is obtained.

[Brief description of drawings]

FIG. 1 is an experimental diagram showing an inner surface sealable temperature range, an overlap sealable temperature range, and an overlap seal impossible temperature range of a laminated film of the present invention and the prior art.

FIG. 2 is an experimental analysis diagram showing gel fractions in the thickness direction of the S1 layer and T1 layer before stretching in Example 3.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location // B65D 71/08 B65D 71/08 A 85/50 85/50 B B29K 23:00 27:00 105: 02 B29L 9:00 23:00

Claims (1)

[Claims] 1. An outer surface resin layer (S1 layer), an adhesive heat-shrinkable resin layer (T1 layer), a vinylidene chloride resin layer (C layer), and an adhesive heat shrinkage from the outside of the cylinder to the inside of the cylinder. Resin layer (T2 layer) and heat-sealing resin layer (S2 layer) laminated in this order at least 5 layers, and the gel fraction (X) of the outermost surface of the S1 layer is 35% by weight to 70%. % By weight, the gel fraction (Y) of the innermost portion of the T1 layer (the portion adjacent to the C layer) is 10% by weight to 40% by weight, and the gel fraction gradient represented by (Y / X) is 0.6. In the heat-shrinkable tubular multilayer film, wherein the joint between the T1 layer and the C layer is electron beam modified, and the S2 layer is substantially uncrosslinked: (1) The outer surface The density of the resin layer (S1 layer) is 0.900.
g / cm ³ was ~0.915g / cm ^3, and a melting point is a copolymer of ethylene-.alpha. · olefin is 115 ° C. to 125 ° C., (2) the heat sealable resin layer (S2 layer) Density 0.8
Was ^{95g / cm 3 ~0.915g / cm 3} , and a melting point is a copolymer of ethylene-.alpha. · olefin is 94 ° C. -108 ° C., and (3) the outer surface resin layer (S1 layer) above A heat-shrinkable tubular multilayer film having a melting point difference of 10 ° C. or more from the heat-sealing resin layer (S2 layer).