JPH0218983B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a stretch packaging film in which the film is stretched during packaging. In recent years, cans, beverages, paper cartons, bottled beverages, books bound with bands, miscellaneous goods, etc. that have been stacked on cardboard trays or without using trays have been wrapped in film. A method of wrapping the material while stretching it in two axial directions, and a method of wrapping it in a sleeve while stretching it in one axial direction and wrapping only the ear portions in a sleeve are becoming popular from the viewpoint of resource saving. Furthermore, stretch packaging, in which a film is stretched and wrapped around a palletized load, is now being widely adopted in industry as an energy-saving packaging method. Furthermore, in the field of pallet stretching, it is reasonable to wrap a film around an object to be packaged and then fix the film only by its self-adhesive force without heat-sealing the ends of the film. However, in the case of a single-layer film made of a single resin composition, when adhesiveness is imparted to the film,
Since the surface of the packaged item is sticky after packaging, handling properties are reduced due to blocking during various distribution processes (packaged items falling over, etc.). Further, in order to solve the above-mentioned problem, if slipperiness is imparted to the film, the film loses its adhesive strength, and the ends of the film must be treated by heat sealing. Therefore, it is necessary to overcome the above-mentioned tradeoffs. Furthermore, the so-called stretch packaging mentioned above is a method of tightly gathering and packaging various items to be packaged by utilizing the stress generated by stretching the film in uniaxial or biaxial directions, which is the most important feature of stretch packaging. However, there is a problem with materials that are hard and difficult to stretch, such as the low-density polyethylene films currently on the market, which do not function as expected. That is, the next three points are that. (1) The low-density polyethylene film currently on the market is hard and difficult to stretch, so if you try to stretch it forcibly, it will break, or even if you can stretch it a little, the stretch will be small. For this reason, the cohesive force necessary for packaging cannot be obtained, making it unsuitable. (2) Conventional low-density polyethylene films have a problem in that when the edges of the packaged object are sharp and protruding, the film being stretched tends to come into contact with the sharp protrusions and break. For this reason, the shape of the packaged object is limited to relatively round ones,
Countermeasures such as using cardboard trays to stack the items to be packaged and rounding the corners of the pallets are required. (3) Furthermore, after packaging, the film wrapped around the surface of the packaged item is in a taut state because the film maintains cohesiveness due to residual stress generated when the film is stretched during packaging. However, in the case of the above-mentioned low-density polyethylene film, if the film is cut by hitting a sharp protrusion or by being hit by a sharp protrusion from the outside, the tear in the film propagates and spreads from the cut, and as a result, When unpacked, the exterior functionality is often lost. For this reason, it cannot withstand physical distribution and is subject to various restrictions on physical distribution conditions compared to cardboard packaging. These problems are the reason why stretch packaging, although promising as energy-saving packaging, has not become widely popular. Of course, the cohesion required for packaging as described in problem (1) above can be achieved by, for example, selecting a film whose main component is ethylene-vinyl acetate copolymer, the vinyl acetate content of the resin composition, and the melt flow rate. It can be obtained by using it after the above-mentioned conditions, and the problems of the above-mentioned low-density polyethylene film can be solved. However, if the corners of the items to be packaged are sharp, or if the corners of the cardboard tray or pallet on which the items are stacked are sharp, if the film is stretched while wrapping, it may hit the sharp corners. A new problem arises in that the film is torn as if it were being torn. Furthermore, the problem that single-layer films made only of low-density polyethylene are hard, difficult to stretch, and break easily can be solved by using a laminated film made by laminating the aforementioned low-density polyethylene film with, for example, an ethylene-vinyl acetate copolymer film. However, there still remains the problem that if the stretched film during packaging hits the corners of the items to be packaged, or the corners of the cardboard tray or pallet on which the items are stacked, the film will tear. However, this problem of the film tearing during packaging can be solved by rounding the corners of the packaged items and the cardboard tray. However, when film-wrapped items are placed in the distribution process, the packaging film tends to tear due to residual tension and properties, so if small tears occur when it comes into contact with various objects,
The tear propagates and expands into a large tear, which causes the package to be unpacked, causing a fatal problem in which the packaging function is completely lost. The present invention was devised in view of these conventional problems, and its object is to provide a stretch packaging film that satisfies the following performance requirements for industrial use without any problems. (1) Appropriate elongation stress suitable for bundling while stretching, and final elongation stress at break and elongation rate are large. Appropriate elongation force for strings means that the elongation stress of the film is too strong (hard). The stress is such that it does not deform or damage the shape of the packaged object, and on the contrary, the elongation stress of the film is too weak to weaken the packaging binding force. At the same time, the stress is such that the film does not stretch with a slight force after packaging and the packaged items do not collapse. (2) When the film is stretched and wrapped over an object, it will not tear even if it comes into contact with sharp protrusions on the object, and the film should have high tear strength. (3) Even if a sharp protrusion comes into contact with the packaged film, which is under residual tension, it will not break, and even if it does break, the break will not spread and cause the packaged item to be unpacked. (4) The film's slipperiness and self-adhesiveness are appropriate for various types of items to be packaged, and the film has transparency to the extent that the items to be packaged can be seen.Furthermore, the film has a wide thermal fusion temperature range and has a high fusion strength. be strong. That is, the stretch packaging film of the present invention is
1 to 15% by weight, preferably 6 to 15% by weight of α-olefin selected from ethylene and butene-1, hexene-1, 4-methylpentene-1, and octene-1
10% by weight copolymerization, a melt flow rate (hereinafter abbreviated as MFR) of 0.1 to 3 g/10 minutes, preferably 0.5 to 2 g/10 minutes, and a ratio of weight average molecular weight to number average molecular weight (hereinafter referred to as (abbreviated as Q value) 2-6, preferably 2.5-5 ethylene-α
- A first layer consisting of a first resin composition containing an olefin copolymer as a main component, and a vinyl acetate content of 3.5 to 25
MFR0.3-5 by weight, preferably 11-18% by weight
g/10 min, preferably 0.4 to 2.5 g/10 min, and a second layer made of a second resin composition containing an ethylene-vinyl acetate copolymer as a main component. In the present invention, MFR is measured at 190°C in accordance with JISK6760. Here, the main component of the first resin composition is α-
Ethylene-α with an olefin concentration of 1 to 15% by weight
- Olefin copolymer, and this copolymer
The reason why we made the molecular weight distribution extremely narrow with a Q value of 2 to 6 at MFR of 0.1 to 3 g/10 minutes is to increase the tensile breaking strength of the film in the various stretch film packaging methods mentioned above, and to This is to increase the tear resistance against the corners so that it can withstand industrial use. In addition, after packaging, the film is kept under tension so that it will not tear even if it hits a sharp protrusion during the various logistics processes before reaching the final consumption site, and even if a small tear occurs, the film should not be torn. This is to prevent the tear from propagating and expanding due to the tear resistance of the film. Furthermore, in detail, the reason why the MFR of the ethylene-α-olefin copolymer was limited to 0.1 to 3 g/10 min is that even if the Q value is 6 or less, the MFR is
If the MFR is less than 0.1 g/10 minutes, the film will be hard and difficult to stretch, and if the MFR exceeds 3 g/10 minutes, the film will be weak and easily tear during packaging, so the Q value was limited to 2 to 6. The reason is that when the Q value exceeds 6, even if the MFR is between 0.1 and 3, the same phenomenon as the reason for limiting the MFR described above will occur. On the other hand, if the Q value is less than 2, extrusion during film forming is difficult. Ethylene, which is the main component of the second resin composition
The vinyl acetate content of vinyl acetate copolymer is 3.5~
The reason for limiting the vinyl acetate content to 25wt% is that if the vinyl acetate content is less than 3.5wt%, the film will be stiff and difficult to stretch, causing it to tear during packaging and deform or damage the packaged item. This is because, if the film exceeds this value, unless a large amount of lubricating inorganic filler is added to the film, the surface of the film will become excessively sticky, and the film will not be able to satisfy the required strength. That is, if a large amount of lubricant inorganic filler is added, not only will the surface of the film become cloudy and the transparency will deteriorate, but the film will also become too soft, and even if it can be wrapped, the film will stretch with a slight force after wrapping. This is because the cargo may tilt during transportation and cause the cargo to collapse. Also, MFR0.3~5g/
The reason for limiting the time to 10 minutes is that if the MFR exceeds 5g/10 minutes, the final breaking strength of the film is low, making it easy to tear the film during packaging.
This is because if the MFR is less than 0.3 g/10 minutes, the film will not stretch easily and will be easily torn during packaging. If it is necessary to adjust the slipperiness of the film surface and the self-adhesive force, the first resin composition and the second resin composition may be added in an amount of 0.01 to 5 parts by weight based on 100 parts by weight of the resin constituting these compositions. At least one of a lubricant, an inorganic filler, and an adhesive may be added. The lubricants include fatty acid amides such as olefinic acid amide, stearic acid amide, and erucic acid amide, fatty acid glycerin ester compounds such as stearic acid monoglyceride, stearic acid diclyceride, oleic acid monoglyceride, and oleic acid diglyceride, and polyethylene glycol adducts thereof. Can be mentioned. Inorganic fillers include inorganic substances such as light and heavy calcium carbonate, talc, and silica, and adhesives include castor oil derivatives, low-molecular viscous substances such as polybutene, sorbitan fatty acid esters, rosin and rosin derivatives, and petroleum resins. and their hydrogenated substances, such as tackifiers, rubbers, etc. The thickness of the first layer and the second layer to be laminated is usually within the range of 10 to 73 microns, preferably 10 to 60 microns for the first layer, and 7 to 60 microns, preferably 10 to 60 microns for the second layer. Used within the micron range. The layer thickness ratio of the laminated first layer and second layer is preferably 0.2 to 3, particularly 0.2 to 1, for the second layer to 1 for the first layer. If the second layer is less than 0.2, the film will be hard and difficult to stretch, and if it is stretched during packaging, it will partially stretch only near the gripping part or deform the packaged item.If it exceeds 3, the tear strength will decrease. This is because during packaging, the stretched film comes into contact with the packaged object and the corners of the cardboard tray or pallet and breaks. The reason for laminating the first layer and the second layer is that
A single-layer film made of a resin composition is hard and difficult to stretch, so if you try to stretch it forcibly, the film may tear, or even if it does not tear, it may deform or damage the packaged item. Even so, since the film is not stretched uniformly, thinned areas due to local stretching may tear during the distribution process after packaging. Furthermore, in the field of pallet stretching, it is reasonable to wrap a film around an object to be packaged and then fix the film only by its self-adhesive force without heat-sealing the ends of the film. On the other hand, in the case of a single-layer film made of resin compositions for the first and second layers, when the film is made sticky, the surface of the packaged item becomes sticky after packaging, which makes it difficult to handle various logistics processes. Blocking reduces cargo handling (packages falling over, etc.). On the other hand, in order to solve the above-mentioned problem, if slipperiness is imparted to the film, the adhesive force of the film is lost, and the end of the film must be treated with a heel seal. According to the present invention, the above-mentioned antinomian problem can be overcome by laminating the first layer and the second layer. In other words, by laminating the first layer with a composition in which a tackifier is added to the second layer of resin, and using the adhesive surface in contact with the surface of the packaged object during packaging, the end of the film is fixed only by the film's self-adhesion. Moreover, since the first layer becomes the outermost layer of the packaged item after packaging, it is possible to prevent troubles caused by blocking in various logistics processes. On the other hand, when using only a single layer film made of the second resin composition, the film stretches almost uniformly as described above.
It has a moderate elongation stress, but on the other hand, if the corners of the packaged items are sharp, or if the corners of the corrugated pole tray or pallet on which the packaged items are stacked are sharp, these corners may be This is because if you touch it, it will tear and tear. Therefore, the stretch packaging film of the present invention utilizes the tear resistance of the first layer resin composition and the excellent elongation stress and self-adhesive strength of the second layer resin composition to laminate both resins. In addition to a two-layer film in which both resins are laminated on each other, a three-layer film in which the first layer is the center layer and the outermost layer is the second layer can also be used. However, in the field of pallet stretch packaging, it is reasonable to wrap the film around the packaged item and then use the self-adhesive force of the film alone without heat-sealing the end of the film. In the case of film, the surface of the packaged item is sticky after being packaged, so that blocking during the distribution process may cause the package to fall over, resulting in poor handling. Therefore, a two-layer film in which the first layer is laminated with a composition in which a tackifier is added to the resin of the second layer is used so that the adhesive side is in contact with the surface of the packaged object during packaging, so that the end of the film is This is preferable because it can be fixed using only self-adhesion, and since the first layer becomes the outermost layer of the packaged item after packaging, troubles caused by blocking during the distribution process can be prevented. The first layer and the second layer are laminated by coextrusion inflation molding. This molding method will be explained below. Ethylene-α- which is the main component of the first resin composition
Olefin copolymers have a linear main chain and virtually no long chain branching from conventional high-pressure low-density polyethylene, and have different performance in terms of molecular structure, melting characteristics, and solid-state properties. There is specificity in rheology during melting. Therefore, conventional molding methods cannot be applied as is. That is, the above copolymer has the characteristics of high melt viscosity under shear stress, low melt viscosity when no shear stress is applied, and short stress relaxation time during elongation, so it can be used in die slips. The behavior of the film becomes unstable, and with the usual conventional forming method, there is a problem that wavy unevenness occurs in the film and it is not possible to form a film with a quality that can be used for practical purposes.
That is, due to the high melt viscosity under high shear stress at the exit of the die lip, melt fracture occurs when the film exits the die lip, causing wavy unevenness in the film and extremely poor transparency. On the other hand, in a state where no shear stress is applied, the melt viscosity is low, so stress due to its own weight concentrates on the soft parts from immediately after the melt of the first resin composition leaves the die lip until it is cooled and solidified. The tube becomes unstable and film formation becomes difficult. In order to avoid this, if the extrusion rate is lowered, there is a problem that productivity decreases. The coextrusion inflation molding method of the present invention was obtained by overcoming the above-mentioned problems, and the shear rate of the molten resin at the exit of the annular die slip is set to 20 to 100 sec ^-1 .
Preferably, the film is formed in the range of 20 to 65 sec ^-1 , and on the premise that the film is formed as described above, it is possible to use either of the above-mentioned packaging method in which the film is stretched only in one direction and the packaging method in which the film is stretched in two directions. In this case, the blow ratio during film molding is in the range of 3 to 6, preferably 3 to 4.5. The reason for limiting the blowing ratio to the range of 3 to 6 is that if the blowing ratio is less than 3, the tear resistance, tensile strength and elongation at break, which are important qualities for film packaging suitability, will be unbalanced in the longitudinal and transverse directions of the film. This is because the film may tear or tear when stretched during packaging. On the other hand, if the blow ratio exceeds 6, the quality of the film will be unbalanced in the longitudinal and lateral directions as described above, and the film will tear or tear during packaging. Note that the thickness of the film obtained by laminating is usually
It is about 20-80μ. Furthermore, the packaging film of the present invention is used with the first layer being the outermost layer and the second layer being the side facing the packaged item. Next, Examples of the present invention will be explained together with Comparative Examples to clarify that the desired effects of the present invention can be obtained. (1) Example 1 Ethylene-butene-1 copolymer (butene-1 content
8.0 wt%, MFR 1 g/10 min, Q value 3.4) A mixture of 100 parts by weight, 0.1 part of silica powder with an average particle size of 5 μ, and 0.3 part of stearic acid amide was mixed, and this was passed through an extruder with a screw diameter of 50φmmL/D24. Meanwhile, a mixture of 100 parts by weight of ethylene-vinyl acetate copolymer (MFR 2.5 g/10 minutes, vinyl acetate 15 wt%), 0.1 part of the above silica powder, and 0.1 part of stearamide was prepared. Screw this with a screw diameter of 65φmmL/
Knead at 170℃ using a D25 extruder, and mix both at 1
The stacking ratio of the first layer containing ethylene-butene as the main component to the second layer containing ethylene-vinyl acetate as the main component, at a die temperature of 200°C and at the die exit. Blow ratio 4 at 27sec ^-1
Double inflation molded. This film had a good appearance without any unevenness of the rippling liquid. Fujipack system uses this film to stretch the film in two axial directions for stretch wrapping.
When 30 youth cans were stacked and packaged on a cardboard tray using an A-120 packaging machine manufactured by Co., Ltd., a suitable amount of elongation was obtained, and the film could be packaged tightly without tearing at the corners of the cardboard tray. In addition, this package can be mixed into a cargo truck and transported over a distance of approximately
After being transported 100 km, the packaging film was checked to see if it was torn or not, and it was found to be in good condition. Table 1 shows the quality of this film. (2) Examples 2, 3, 4, 5, 6, 7 The quality of films obtained by molding in exactly the same manner as in Example 1 except that the resin of the ethylene-α-olefin copolymer was changed was measured using Comparator 1. , 2 are shown in Table 1. Furthermore, the quality of single-layer films obtained by molding the first and second layers used in Example 1 to a film thickness of 40 μm is shown in Table 1 as Comparative Examples 3 and 4. (3) Examples 8, 9, 10, 11 The quality of the film obtained in the same manner as in Example 1 except that the layer thickness ratio of the first layer and the second layer in Example 1 was changed was compared with that of Comparative Example. They are shown in Table 2 along with 5 and 6. (4) Examples 12, 13, 14 Table 3 shows the quality of films molded in exactly the same manner as in Example 1, except that the blow ratio during inflation molding was changed. (5) Example 15 Tokiwa Industries uses the film of Example 1 to uniaxially stretch the film and stretch wrap it.
When a cardboard box was packaged using Pewo Pack 400 SN packaging machine manufactured by Pewo Pack Co., Ltd., the film did not tear at the corners of the cardboard box, showing good workability, and the finished packaging was tight and good. (6) Example 16 Ethylene-butene-1 copolymer (butene-1 content 8.0 wt%, MFR 1 g/10 min Q value 3.4) was kneaded at 200°C using an extruder with a screw diameter of 50 φ mm L/D24. , ethylene-vinyl acetate copolymer (MFR2.5, vinyl acetate 15wt%) 98wt% and sorbitan oleate (Daiichi Kogyo Seiyaku Co., Ltd. Sorgen)
40A) Prepare a 2wt% mixture, knead it at 170℃ using an extruder with a screw size of 65φmmL/D25, feed both to one annular die, and mix the mixture with the first one consisting of ethylene-butene 1 copolymer. A second layer containing ethylene-vinyl acetate copolymer as a main component for layer 1
A film was molded to an inner thickness of 25 μm in the same manner as in Example 1 using the layer thickness ratio of Layer 1 at a die temperature of 200° C. Using Konan Denki Co., Ltd.'s Economaster packaging machine, which stretches the film uniaxially and wraps it in stretch packaging, it is placed in a cardboard box (size 47 cm) on a wooden pallet.
When 6 pieces (57cm x 55cm height) were loaded and wrapped at a film stretching rate of about 20%, there was no tearing at the corners of the wooden pallets or cardboard boxes, and the packaging workability was good. Furthermore, when the film was notched with a knife after packaging, the tear hole hardly propagated and expanded, and the film was in good condition. (7) Example 17 Instead of the ethylene-butene-1 copolymer used in Example 16, ethylene-hexene-1 copolymer (hexene-1 content 9.0 wt%, MFR 1 g/10 min Q value)
A film was formed in the same manner as in Example 16 except that 4.8) was used. This film was pallet stretch wrapped in the same manner as in Example 16 and was found to be good.

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Claims (1)

[Claims] 1 Ethylene and butene-1, hexene-1, 4-
Copolymerized with 1 to 15% by weight of α-olefin selected from methylpentene-1 and octene-1, with a melt flow rate of 0.1 to 3 g/10 minutes and a ratio of weight average molecular weight to number average molecular weight of 2 ~
A first layer consisting of a first resin composition mainly composed of the ethylene-α-olefin copolymer No. 6, a vinyl acetate content of 3.5 to 25% by weight, and a melt flow rate of 0.3.
A stretch packaging film comprising a second layer comprising a second resin composition containing an ethylene-vinyl acetate copolymer as a main component at a rate of ~5 g/10 min.