JPH02258526A - Overlap shrink wrapping method with laminated polyolefin heat shrinkable film - Google Patents

Abstract

PURPOSE:To perform overlap-shrink-wrapping which is cheap and easy to unseal by a method wherein laminated polyolefin heat shrinkable film of a specified material is used while front and back parts are fuse-sealed, a lengthwise direction is roughly wrapped and then the overlapped parts are heat-shrunk. CONSTITUTION:A laminated film wherein an intermediate layer comprises polypropylene resin, the coefficient of static friction on the surface of both outer layers is in the range of 0.2 to 0.8 while lateral shrinkage factor of polyethylene resin constituting the outer layers when it is heated to the softening point is 10% or less and the shrinkage factor when it is heated to the maximum heat shrinkability attaining temperature is 40% or higher is used to cover an object 3 to be wrapped in an approximately cylindrical shape. A lengthwise side is roughly wrapped in a state wherein the films are overlapped, its front and back parts are fuse-sealed by a fuse seal device 6, then the package is passed through a shrinking tunnel 7 to be heated from the surroundings to be shrunk and at the same time due to frictional resistance of the overlapped films the overlapped portions of the film are adhered to each other prior to start of film shrinking thereby obtaining an overlap shrink package 8.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to an overlap shrink wrapping method using a laminated polyolefin heat-shrinkable film, and more specifically, it relates to a method for wrapping an item to be packaged in a cylinder using a laminated polyolefin heat-shrinkable film. The present invention relates to an overlap shrink wrapping method in which the film is wrapped in a shape, the front and back are fixed by heat sealing, etc., and the longitudinal direction is heat-adhered in a state where the films are simply overlapped.

(Prior art) Shrink wrapping involves roughly wrapping an item in a heat-shrinkable plastic film, which is heated and shrunk using a heating device, and is tightly wrapped by closely following the shape of the item. It is characterized by a tight finish and good appearance.

It is also convenient for packaging multiple items at once, so-called integrated packaging, and has many other features, such as reducing packaging costs. For this reason, shrink wrapping is now widely used, including individual shrink wrapping for boxes and containers for alcoholic beverages, cosmetic boxes for cosmetics, medicine, etc., as well as shrink wrapping for packaging multiple items such as boxes, bottles, cans, etc. Generally f is used.

On the other hand, while shrink wrapping has the advantage of producing a tight finish, it also has the disadvantage that it is difficult to open because the edges of the film are more securely attached than with fusion knitting.

In order to improve this defect, currently the packaged item is covered in a cylindrical shape with a polyvinyl chloride film, the front and back are fixed with fusing knots, etc., and the film is heated and shrink-wrapped in the longitudinal direction with the film twisted together. The packaging is being done.

According to this method, since the overlapped parts are not completely adhered, this part can be opened more easily. Moreover, the overlap shrink wrapping machine of this method does not require a vertical sealing device because of overlapping, and has the feature that it is a simple but compact packaging machine.

However, although polyvinyl chloride film has good heat shrinkability, it has environmental problems such as corrosion caused by chlorine gas generated during heat rolls or waste incineration.
There are drawbacks such as hygienic problems due to the plasticizer used to plasticize the vinyl chloride resin.

Further, stretched films of crystalline polypropylene have the advantage of being excellent in optical properties such as transparency and gloss, mechanical properties such as tensile strength and impact strength, and non-toxic and odorless properties. However, when overlapping shrink wrapping is performed using a crystalline stretched polypropylene film as a polyvinyl chloride film, there is a drawback that the overlapping portions of the films do not come into close contact during shrink wrapping, making shrink wrapping impossible.

(Problem to be solved by the present invention) The purpose of the present invention is to
Alternatively, for hygiene reasons, we provide an overlamp shrink wrapping method that uses a laminated polyolefin heat shrinkable film that does not generate harmful substances to package items using an inexpensive and simple shrink wrapping machine, and that is easy to open. It's about doing.

(Second means for solving the problem) In order to achieve the above-mentioned problem, the inventors of the present application have conducted intensive studies,
Focusing on the relationship between the coefficient of static friction of the film, the heat shrinkage rate in the overlapping direction, that is, the transverse direction of the film, and the softening point temperature of the film used, various tests were conducted.
As a result, we have finally arrived at each invention of the present application. That is, the first invention of the present application is such that both the foreign guests are made of polyethylene resin, the intermediate layer is made of at least one polypropylene resin, and the static friction coefficient of both surfaces is in the range of 0.2 to 0.8. What is the lateral shrinkage rate of the polyethylene resin that makes up both outer parts 1j1 when heated to the softening point temperature? 6 or less, and further heated to the temperature at which the maximum thermal shrinkage rate is achieved, the shrinkage rate when f is 4
Using a laminated polyolefin heat-shrinkable film with a polyolefin content of 0% or more, the item to be packaged is covered in a cylindrical shape, and the front and back are fixed using fusing knots, etc., and the film is roughly wrapped in the longitudinal direction with just the overlapping films. The invention also includes an overlap shrink wrapping method in which the overlapping portions are then heated and shrunk using a heating device, and at the same time the overlapped portions are shrunk by the heating. In the invention, resin or maf selected from at least one of polyethylene resin, low thread polyethylene, ethylene-vinyl acetate copolymer, and ethylene-α-olefin copolymer is used.
This invention is characterized in that two or more of these resins are mixed to form a single resin, and furthermore, the third invention of the same claim is that in the first invention, polypropylene resin or polypropylene resin, The composition is made from at least one of ethylene-propylene copolymer and ethylene-propylene-butene copolymer.

Next, in order to explain each invention of the present application specifically and in detail, it will be explained based on one embodiment, but it goes without saying that the inventions of the present application are not limited to this.

Figure 1 is a schematic process diagram for overlapping shrink wrapping a rectangular box using a laminated heat-shrinkable film according to the present invention, and Figure 2 is a rectangular box wrapped in a cylindrical shape with a film and the front and back are fused. Fig. 3 is a perspective view of a shrink-wrapped package 5 in which the films are overlapped in the center of the packaged object, and the shrink wrap is roughly overlapped. 4 shows a sectional view taken along line AA of the package 8 shown in FIG. 3 after being shrink-wrapped.

Next, first of all, the outline of the packaging method steps shown in FIG. 1 will be explained. In FIG. 1, the laminated layer is unwound from the film roll IO, and the amphoteric layer is made of polyethylene + M fingers, and the middle layer is made of at least one layer of polypropylene resin. The heat-shrinkable film 1 has needle-like protrusions provided at appropriate locations, and suitable small holes for air venting are made using a guide roll 2, and then the laminated heat-shrinkable film with the small holes made. After the weight is supplied to the bag forming former 4, it covers the packaged object 3 in a substantially cylindrical shape. As shown in FIG. 2, the object 3 to be packaged is roughly wrapped in the vertical direction with just overlapping films (roughly wrapped package 5), and then the front and back are cut and rolled by a cutting and rolling device 6. and continue,
The belt 9 for transporting the package is placed with the overlapping film side down so as to form the shrink package shown in FIGS. 3 and 4.
The film is passed through the shrinkage tunnel 7 and heated from the surrounding area to shrink it. At the same time, the frictional resistance of the overlapped film brings the overlapped film into close contact with each other before the film starts to move due to shrinkage, resulting in overlap shrinkage. A package 8 is obtained. In this case, the size of the overlapping portion of the film can be appropriately selected depending on the shape of the packaged object and the properties of the film surface layer. That is, if the size of the overlapped portion of the film is too large, it will increase the packaging cost and cause defects in the appearance of the package.
A width of 80 mm is appropriate.

It is optional whether the package (Fig. 2, reference numeral 5) in which the object to be packaged is roughly wrapped with a film is placed on the transfer conveyor 9 in the posture shown, but it is preferable to place it as described above. Place the overlapped film side down on the transport conveyor! ! When placed, the weight of the packaged object is added to the frictional force between the films at the film claws, so the width or area of the film can be reduced (+11 points).

The frictional resistance force of the overlapping portion of the film in the present invention is:
It is expressed by the coefficient of static friction of the film measured by the ASTM D1894 method. If the film is too sagging, the frictional resistance of the overlapping portion of the film becomes small, and when the film starts shrinking due to heating, the film moves and close contact becomes impossible.

In addition, the heat shrinkage rate of the film used in the present invention is JIS
Based on Z 1709 measurement method, vertical, Vi
A 10 cm x I 0 cm square film was heated for 20 seconds in a predetermined glycerin bath, then cooled in water, and the shrinkage rate of the film was measured. The length of the film before shrinkage is Ωo1 The length of the film after shrinkage is σ
Then, the shrinkage rate becomes as follows.

Shrinkage rate - ((no -Q) / (1o)X 100
(%) Furthermore, the Vicat softening point temperature in the present invention is AS
The f value is measured by the TM D 1525 method, and the temperature at which the maximum thermal shrinkage rate is achieved is the JIS Z170
This is the temperature at which the laminated heat-shrinkable film exhibits the highest shrinkage rate, as measured by the 9 measuring method.

Generally, when a stretched film is heated, it begins to shrink and eventually melts when it becomes softer than the Vicat softening point temperature, but if the films are stacked above the Vicat softening point temperature, the films begin to stick together. The present inventors have discovered the present invention as a result of various studies on the relationship between the static friction coefficient of the film, the heat shrinkage rate, and the Vicat softening point temperature that enables the film to adhere closely. That is, if the coefficient of friction on both surfaces of the film is less than 0.2, the film will slip too much, and even if the shrinkage rate in the transverse direction when heated to the Vicat softening point temperature is less than 105, it will not reach the Vicat softening point temperature. The film will move and the film will not be able to adhere properly.

The coefficient of static friction is in the range of 0.2 to 0.8, and the shrinkage rate when heated to the Vicat softening point temperature of the polyethylene resin constituting both outer layers of the film is 10% or less, preferably 5% lower. Because the shrinkage stress caused by heating is weaker than the frictional resistance of the overlapping parts of the film, the film does not move and the overlapping parts of the films begin to stick together. The overlapping portion can maintain a close contact state. When the film that wraps the packaged item begins to adhere tightly at the softening point temperature, it will tightly wrap the packaged item by further heating. If it is less than 40%, the finish of the shrink wrap after heat shrinkage will be insufficient and the appearance of the package will be poor. If the shrinkage rate of the film in the transverse direction when heated to the Vicat softening point temperature exceeds 10%, the shrinking force of the film will be greater than the frictional resistance force of the overlapping part of the film, and heating the film will cause the film to overlap. The parts will separate before they come together, and the film will not be able to stick properly. On the other hand, the shrinkage rate of the film in the longitudinal direction can be appropriately selected depending on the shape of the object to be packaged. In addition, if the coefficient of static friction on both surfaces of the film exceeds 0.8, the film will not slip, resulting in disadvantages such as the film getting stuck in the homeer of the packaging machine, and wrinkles easily occurring during film formation. occurs. The range of the coefficient of static friction on both surfaces of the film is 0.
It is essential that it is 2 to 0.8, preferably 03 to
It is in the range of 0.6. The coefficient of static friction on both surfaces of the film of the present invention depends on the type of polyolefin resin used.
In addition, slipping agents such as ordinary higher fatty acid amide type, higher fatty acid ester type, wax type metal soap, silica, calcium carbonate, magnesium silicate, calcium phosphate, etc. can be used as long as other necessary physical properties such as transparency and gloss are not impaired. It can be obtained by mixing and adjusting appropriate amounts of anti-blocking agents. Furthermore, tackifiers, antistatic agents,
There is no problem in adding antifogging agents and other additives.

Further, the method for producing the laminated heat-shrinkable film of the present invention is not particularly limited, but it is preferably produced by the following method. That is, first, the laminated unstretched raw sheets are coextruded from a laminated die using a plurality of extruders. After the laminated unstretched raw sheet is cooled and solidified, it is reheated to a temperature at which it can be stretched, and expanded and stretched into two wheels using pressurized gas, or laterally stretched using a tenter stretching machine, or It is obtained by introducing the film between pairs of pinch rolls having different speeds and stretching in the longitudinal direction, and then stretching in the transverse direction using a tenter stretching machine. Although the stretching ratio in the present invention is not particularly limited, an area ratio of 4 to 40 times, preferably 6 to 30 times is appropriate.

Further, the thickness of the film used in the present invention is not particularly limited, but a total thickness of 8 μ to 200 μ is appropriate;
The thickness can be selected as appropriate depending on the packaged item, and if the protection of the contents is particularly required, the thickness can be increased; generally, the thickness is 1.
0μ to 100μ is used. Also, the thickness structure of each layer is not particularly limited, and the required cohesive strength, shrinkability,
It may be selected appropriately depending on the impact force, etc., and as the thickness of both outer layers becomes thinner, the adhesive force of the film in the overlapped portion becomes weaker. The preferred thickness of both outer layers is 2.5 microns or more.

Furthermore, although it is preferable that the polyethylene side resin used for both outer layers of the present invention be the same, it is not limited to this, and it goes without saying that it is also possible to use different resins for both outer layers. .

Examples of the polyethylene resin used in the present invention include low-density polyethylene with good heat sealability, ethylene-
Examples include vinyl acetate copolymers, ethylene-α-olefin copolymers, and mixtures thereof. The low-density polyethylene used in the present invention is a conventionally widely used ordinary low-density polyethylene having irregular long chain branches produced by radical polymerization reaction under high pressure, and having a density of 0.919 to 0.930 g/cm3 and a melt index of 0.1 to 8.0 are preferred. In addition, the ethylene-α-olefin copolymer used in the present invention is ethylene, propylene, butene-1, pentene-11hexene-1, octene-1,4-methyl-
Refers to an ethylene copolymer produced by copolymerizing a small amount of α-olefin having 3 to 8 carbon atoms such as Henten-1, and has a density of 0.880 to 0.955 g/cm' and a melt index of 1,1 to 8. Further, the ethylene-vinyl acetate copolymer used in the present invention is produced by a known radical polymerization method, and the vinyl acetate content is preferably 20% by weight or less, more preferably 15% by weight or less. %
It is as follows.

Further, the polypropylene resin used in the present invention is selected from at least one of ethylene-propylene copolymer and ethylene-propylene-butene copolymer, and the melting point of these polypropylene resins is The ethylene-propylene copolymer is preferably one in which propylene is copolymerized with about 2-5% by weight of ethylene, and the ethylene-propylene-butene copolymer is preferably in the range of 135 to 150°C. Preferably, propylene is copolymerized with about 3 to 8% by weight of ethylene and butene.

Furthermore, it is also possible to mix modifiers, slip agents, antiblock agents, tackifiers, antistatic agents, antifogging agents, and other additives/processing agents into these polypropylene resins.

(Effects of the present invention) As in the above-described present invention, the static friction coefficient of both surfaces of the film measured by ASTM-1894 method is in the range of 0.2 to 0.8, and the Vicat softening point temperature of the polyethylene resin of both outer layers is The film heat shrinkage rate in the lateral direction is 10%.
A laminated polyolefin heat-shrinkable film which has a shrinkage rate of 40% or more when heated to the temperature at which the maximum heat shrinkage rate is achieved can be used by covering the packaged item with the film in a cylindrical shape, If the film is fixed by heat sealing and heat-shrink wrapped with only overlapping films in the longitudinal direction, there will be no odor during heat-fixing, and there will be no shift in the overlap area, resulting in a shrink-wrapped product with a good packaging finish. Therefore, shrink wrapping can be performed using an inexpensive and simple shrink wrapping machine, and furthermore, the package can be easily opened from the overlapped portion.

(Examples) Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto.

Example 1 Ethylene-propylene resin (Sumitomo Chemical Co., Ltd., Noblen 5131.Mll, 2, density 0139 g/cm
3. Vicat softening point temperature 119°C) was used as the intermediate layer, and ethylene/vinyl acetate copolymer resin (Sumitomo Chemical Co., Ltd., Evatate D2021.EVA content 10%, M
I 1.5, density 0.92 g/cn+', Vicat softening point temperature 73°C) 100 parts by weight and 3 parts by weight slipping agent (S
Q 3, Mitsui Petrochemicals Co., Ltd., oleic acid amide) and 2 parts by weight of an anti-blocking agent (ABlo, Mitsui Petrochemicals Co., Ltd., silica) on both surfaces of a tubular coextruded laminated unstretched product. The raw fabric sort was obtained using a screw diameter 65φ extruder (for the middle layer), two screw diameter 40φ extruders (for the surface layer), and a three-layer coextrusion 11Oφ annular die. Next, one end of the laminated unstretched raw sheet was cut, and the intermediate layer thickness was 120 μm.
A film with a thickness of 15 μm on both surfaces and a width of 300 mm was produced.

This film was heated to 100°C using a tenter stretching machine and stretched 6 times in the transverse direction to a thickness of 25μ and a width of 1300mm.
A stretched film was obtained. The coefficient of static friction on both surfaces of the obtained film was 0.3, and the shrinkage rate in the lateral direction at 73°C, which is the Vicat softening point temperature of the resin constituting both outer layers, was 3%.
, 2% in the longitudinal direction, 120°C, which is the temperature at which the maximum thermal shrinkage rate is achieved.
The shrinkage rate in the transverse direction was 58%, and the shrinkage rate in the longitudinal direction was 23%.

This film was further cut into two rolls with a width of 620 mm, passed through an automatic packaging machine, and wrapped around a box with a width of 250 mm, a length of 300 nm + m, and a height of 30 mm, with the edges of the film overlapped by 20 mm. west,
In the length direction, fusing sealing was carried out with a margin of 25 μm from the box end at both ends.

Next, the box whose surroundings were covered with a film as described above was placed on a transfer conveyor with the overlapping part of the film facing down, and introduced into the shrink tunnel for heating, and the surroundings were heated with hot air at 170°C for 8 seconds. The film was further heated to shrink and shrink wrapped.

In the shrink-wrapped box, the overlapping portions of the film were also in close contact, and the package appearance was in good condition. In this case, there was no odor during heat sealing, and the package could be easily opened from the overlapped portion of the film.

Example 2 Ethylene-propylene resin (Sumitomo Chemical Co., Ltd., Noblen S 131. MIl, 2, density 0.89 g/
cm3, Vicat softening point temperature 119°C) as the intermediate layer, and linear low density polyethylene (Ultozex 2021,
L, Mitsui Petrochemical Industries, Ltd., MI2. I, density 0.
920g/Cm3, Vicat softening point temperature 100°C) 1
00 parts by weight, 3 parts by weight of a slipping agent (S Q 3, Mitsui Petrochemical Industries, Ltd., oleic acid amide) and 2 parts by weight of an anti-blocking agent (ABIO, Mitsui Petrochemicals, Ltd., Nrika). A tube-shaped coextruded laminated unstretched raw sheet, which will serve as the surface layer, is
5φ extruder (for middle layer) and 2 screws diameter 40
The product was produced using a 110φ annular die attached to a φ extruder (for surface layer) and used for co-extrusion of three layers. Next, one end of the laminated unstretched raw sheet was cut, and the intermediate layer Y7 was cut to 360 mm.
A film was obtained with a thickness of 45 μm on both surface layers and a medium diameter of 370 mm.

This film was first stretched 3 times in the machine direction by heating it to 90°C using two sets of rolls with different speeds, and then heated to 120°C using a tenter stretching machine. Stretched 6 times in the transverse direction, thickness 25μ, width 1.300mm
A stretched film was obtained. The coefficient of static friction on both surfaces of the obtained film was 05, and the shrinkage rate in the transverse direction at 100°C, which is the Vicat softening point temperature of the resin constituting both outer layers, was 9.
%, longitudinal direction is 7%, maximum heat shrinkage achieved in greenhouse 130
Shrinkage in transverse direction at °C is 60% and longitudinal shrinkage is 38%
Met. This film was further cut into two sets with a width of 620 mm.
Finished into a roll of 250 mm, passed through an automatic packaging machine, and
The periphery of a box measuring mm x length 300 mm x height 30 mm was covered with a film, the edges 2On+m of the film were overlapped, and a fusing-cutting rule was carried out with a margin of 25 mm from the box edges at both ends in the length direction.

Next, the box whose periphery was covered with a film as described above was placed on a transfer conveyor with the overlapping part of the film facing down, and introduced into the shrink tunnel for heating.
The film was heated from the surroundings with hot air at 0° C. for 8 seconds to shrink the film, and shrink-wrapped it.

In the shrink-wrapped box, the overlapping portions of the film were also in close contact, and the packaging appearance was good.

Furthermore, there was no odor when the sole was fused, and the package could be easily opened from the overlapped portion of the films.

Example 3 Ethylene-propylene resin (Sumitomo Chemical Co., Ltd., Noblen S l 31. Mll, 2, density 0.89 g
/cI113, Vicat softening point temperature 119°C) as the intermediate layer, linear low density polyethylene (Urtozex 202
1L, Mitsui Petrochemical Industries, Ltd.: vl12. I, density 0.920g/cm3, temperature 100° to Vicat softening
C) 100 parts by weight and 2 parts by weight of slipping agent (S Q 3 ,
A tubular coextruded product with both surface layers composed of a oleic acid amide (Mitsui Petrochemical Co., Ltd.) support antiblock agent (ABI 0 Mitsui Ishiura Chemical Co., Ltd., Nlica) Stretched original paper notebook,
It was obtained using a screw diameter 65φ extruder (for the middle layer), two screw diameter 40φ extruders (for the surface layer), and a 110φ annular die for co-extrusion of three layers. The thickness of each layer of this laminated unstretched Kyoto tan sort was 160 μm for the middle layer, 80 μm for both surface layers, and the tube width was 180 mm.

This laminated unstretched raw sheet was stretched by the conventional inflation method at a stretching temperature of 110°C for both lengthwise and crosswise directions.
The laminated stretched film obtained was stretched twice and heat-set while giving relaxation, and then both ends of the tube were cut to obtain a stretched film with an overall thickness of about 23 μm and a width of 660 mm. obtained f
The coefficient of static friction of this film is 0.6, which is the softening point temperature of the resin constituting both outer layers, and the shrinkage rate in the transverse direction at 100°C is 10% and 8% in the longitudinal direction, which is the temperature at which the maximum thermal shrinkage rate is achieved. The lateral shrinkage rate at 130°C is 55%,
In the vertical direction, it was 53%. This film is further cut,
Finished in a roll with a width of 620 mm, passed through an automatic packaging machine,
A box with a width of 250 mm, a length of 300 mm, and a height of 30 m+n was covered with a film, and the ends of the film were overlapped with each other by 20 mrrl, and fusing sealing was carried out with a margin of 25 mm from the box ends at both ends in the length direction.

Next, the box whose surroundings were covered with a film as described above was placed on a transfer conveyor with the overlapping part facing downward, and introduced into the shrink tunnel for heating, and heated with hot air at 170°C for 8 hours.
The film was heated from the surroundings for a second to shrink and shrink-wrapped.

In the shrink-wrapped box, the overlapping portions of the film were also in close contact, and the packaging appearance was good.

Further, there was no odor during fusing and sealing, and the shrink wrap could be easily opened from the overlapped portion of the films.

Comparative Example 1 In Example 1, a scouring agent (S
Q3) was added in an amount of 4 parts by weight, and the anti-blocking agent was added in an amount of 1 part by weight.
The middle layer thickness was 1 in the same manner except that the parts by weight were changed.
Width: 300m with a three-layer structure of 20μ and both surface layers each 15μ thick.
m raw fabric was produced.

This film was stretched at 100°C using a tenter stretching machine.
Heated and stretched 6 times in the transverse direction to a thickness of 25μ, medium 1300+
A stretched film of nanometer length was obtained. The coefficient of static friction on both surfaces of the obtained film is 0.1, the Vicat softening point temperature of the resin constituting both outer layers, the shrinkage rate of this film in the transverse direction at 73 ° C. is 3%, in the longitudinal direction 2%, At the temperature at which the maximum thermal shrinkage rate is achieved, the shrinkage rate in the horizontal direction is 58% and the shrinkage rate in the longitudinal direction is 23%.
Met.

This film was further cut in the same manner as in Example 1, and 2
After cutting to 620 mm inside the set, pass it through an automatic packaging machine and
Cover the periphery of a box of 0+nm x length 300mm x height 30mm with a film so that the edges of the film overlap by 20mm, and the length direction is 25mm from both ends and the box edge.
The film was melt-cut and sealed with a margin of 100 ml, and then heated in a heating shrink tunnel with the overlapping portion of the film facing downward to shrink the film and shrink-wrapped.

However, the appearance of the shrink-wrapped box packaging was poor because the overlapped portions of the films were shifted, and it was not possible to obtain a suitable shrink-wrapped product.

Comparative Example 2 In Example 2, the amount of scouring agent mixed was 2.5 parts by weight,
The width of the three-layer structure was 370 mm using the same method except that the thickness of the intermediate layer was 420 μm, and the thickness of both surface layers was 525 μm each.
mmo Kyoto fabric was produced. Next, this film
First, using two sets of rolls with different speeds, the temperature was 90°C.
Then, using a tenter stretching machine, the film was heated to 120° C. and stretched 7 times in the transverse direction to obtain a stretched film having a thickness of 25 μm and a width of 1300 mm.

The coefficient of static friction on both surfaces of the resulting film is 0.1, the Vicat softening point of the resin constituting both outer layers, the shrinkage rate in the transverse direction at 100°C is 14%, and the maximum thermal shrinkage rate in the longitudinal direction is 7%. At the achieved temperature of 130°C, the shrinkage rate in the horizontal direction is 65% and in the longitudinal direction is 38%.

This film was further cut in the same manner as in Example 2.
After cutting the set to a width of 620mm, pass it through an automatic packaging machine and
Cover the periphery of a box of 0 mm x length 300 mm + x height 30 mm with a film so that the ends of the film overlap by 20 mm, and in the length direction, cut the ends with a margin of 25 mm from the box ends, continue to bow, and cut the film. The film was heated in a heating shrink tunnel so that the overlapped portion was on the lower side to shrink the film and perform shrink wrapping.

However, the external appearance of the shrink-wrapped box packaging was poor because the overlapped portions of the films were shifted, and a sufficient shrink-wrapped product could not be obtained.

Comparative Example 3 A raw fabric with a three-layer tube width of 180 mm was produced in exactly the same manner as in Example 3, except that the thickness of the intermediate layer was 90 μm, and the thickness of both surface layers was 45 μm each.

This laminated unstretched raw sheet was stretched by the conventional inflation method at a stretching temperature of 110°C for 3 times in both the longitudinal and transverse directions.
The resulting laminated stretched film is heat-set without any relaxation, and the total thickness is about 23 μm, and the tube has a thickness of 4.
A stretched film of 80 mm was obtained. The coefficient of static friction on both surfaces of the obtained film is 0.3, the Vicat softening point temperature of the resin constituting both outer layers, the shrinkage rate in the transverse direction at 100°C is 3%, the longitudinal shrinkage is 3%, and the maximum thermal shrinkage is The shrinkage rate in the transverse direction at 130°C, which is the temperature at which the shrinkage rate was achieved, was 38% and the shrinkage rate in the machine direction was 35%. Cut one end of this dupe shape, open it into a tube, cut it into a film of 620 mm, and pass it through an automatic packaging machine to a size of 250 mm in diameter x 300 mm in length x 30 m in height.
Cover the periphery of a box of size m, and overlap the ends of the film by 20 mm, and the length direction is 25 mm from the box end on both ends.
After fusing and sealing the film with a margin of mm, the overlapping part of the film was placed on the lower side and heated in a heating shrink tunnel to shrink the film and perform shrink wrapping. However, the external appearance of the shrink-wrapped box was that although the overlapping parts of the films adhered well, there were many wrinkles throughout, and especially large corners remained, making it unattractive and making it difficult to obtain a sufficient shrink-wrapped product. I could not do it.

[Brief explanation of drawings]

Fig. 1 is a schematic process diagram showing an example of the overlap shrink wrapping method of the present invention, and Fig. 2 shows a rectangular box covered with a film in an almost cylindrical shape, the front and back sides of which are melt-sealed, and the center of the packaged item. FIG. 3 is a perspective view of the package before shrink wrapping, in which the films are overlapped and roughly overlap wrapped;
The figure is a perspective view showing the overlap-wrapped package after shrink wrapping, and FIG. 4 is a cross-sectional view taken along line AA of the wrapper after shrink wrapping in FIG. 3. ■・・・Laminated heat-shrinkable film 1′・・・Laminated heat-shrinkable film with small holes 2・
...Device 3 for making holes for air venting...Product to be packaged 4...Bag forming former 5...Roughly wrapped package 6...Heat sealing device 7 ... Shrinkage tunnel 8 ... Packaging body 9 after overlapping shrinkage ...
・Belt for transporting packages

Claims (1)

[Scope of Claims] 1. Both outer layers are made of polyethylene resin, the intermediate layer is made of at least one layer of polypropylene resin, and the static friction coefficient of both surfaces is in the range of 0.2 to 0.8, and both outer layers are made of A laminated polyolefin heat-shrinkable material that has a lateral shrinkage rate of 10% or less when heated to the softening point temperature of the polyethylene resin, and a shrinkage rate of 40% or more when heated to the temperature at which the maximum heat shrinkage rate is achieved. The object to be packaged is covered in a cylindrical shape using a plastic film, the front and back are fixed by heat sealing, etc., and the film is roughly wrapped in the longitudinal direction with just the overlapping films, and then heated and shrunk using a heating device. An overlap shrink wrapping method characterized in that the overlapping portions are also brought into close contact by the heating. 2. Polyethylene resin selected from at least one of low-density polyethylene, ethylene-vinyl acetate copolymer, and ethylene-α-olefin copolymer, or a mixture of two or more of these resins The overlap shrink wrapping method according to claim 1, characterized in that: 3. The overwrap shrink wrapping according to claim 1, wherein the polypropylene resin is selected from at least one of an ethylene-propylene copolymer and an ethylene-propylene-butene copolymer. Method.