JP2005329978A - Packaging cloth - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a packaging material which has a superior low-temperature shrinkability, low-temperature sealability, and impact resistance. <P>SOLUTION: The packaging material is a woven or knitted packaging cloth which at least includes, as part of its warps and wefts, a string-like stretch material that is made of a polyolefin compound containing a linear low-density polyethylene of 10 to 90 mass% produced by using a metallocene catalyst, which polyethylene has a density of 0.905 to 0.945 g/cm<SP>3</SP>and shows a melt flow rate of 0.1 to 3 g/10 min, and a random polypropylene of 90 to 10 mass% which contains an ethylene of 2 to 12 mass% and shows a melt flow rate of 10 g/10 min or less. The packaging cloth is particularly suitable for packaging a heavy material or a circular material. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a packaging cloth. In particular, the present invention relates to a material suitable for packaging of annular materials.

Conventionally, heat shrinkable films using polyvinyl chloride, long-chain branched polyethylene, or the like are often used for shrink wrapping. However, these heat-shrinkable films have disadvantages inferior in mechanical strength such as tear strength, tensile strength, and wear resistance. Moreover, since it has notch propagation property, there exists a fault that the film for packaging breaks at the corner | angular edge part and protrusion part of a to-be-packaged object, and various troubles are caused during storage or transportation. For this reason, the conventional heat-shrinkable film is hardly used in the heavy wrapping field, and is used exclusively in the light wrapping field with relatively little mechanical damage. And in the conventional heat-shrinkable film, since the temperature which can perform a shrink pack is high, the content of the packaged object may be limited.
Furthermore, the direction and amount of shrinkage are limited by the film forming machine. For example, the direction and amount of free shrinkage according to the shape of the package, such as the vertical direction, high shrinkage, low shrinkage, vertical shrinkage, high shrinkage, and conversely, the vertical direction, low shrinkage, horizontal direction, high shrinkage, etc. Selection is not possible. In other words, the contraction behavior is changed only at a part of the total width in the vertical and horizontal directions. Accordingly, shrink packaging of a packaged object having a simple shape is possible, but the current shrinkage packaging cannot be performed if the shape of the packaged object becomes even a little complicated. In addition, the conventional heat-shrinkable film is the maximum width that can be manufactured with a width of 1000 to 1500 mm at the current technical level due to limitations in film forming technology. It was not used in the packaging field.
Therefore, the present applicant has found a thin stretched product exhibiting excellent heat shrinkability in order to solve the problems of the heat shrinkable film used in the shrink wrapping (see, for example, Patent Document 1). ).
Japanese Patent No. 2859762

  However, there is a need for a packaging material that can shrink at lower temperatures in order to protect the package and reduce the type constraints. Moreover, the packaging material which can fully heat seal at low temperature from the point of speeding up of a packaging process etc. is calculated | required. Furthermore, higher impact resistance is also desired.

  The present invention has been made to solve the above-mentioned problems, and aims at a packaging material excellent in low-temperature shrinkage, low-temperature sealability, and impact resistance.

The packaging cloth of the present invention has a density of 0.905 to 0.945 g / cm ³ and a melt flow rate of 0.1 to ³ g / 10 minutes of a linear low density polyethylene 10 to 90% by mass of a metallocene catalyst, A thin stretched product made of a polyolefin composition containing an ethylene content of 2 to 12% by mass and a random polypropylene of 90 to 10% by mass with a melt flow rate of 10 g / 10 min or less is used for at least part of the warp and the weft. And woven or knitted.

  The packaging cloth of the present invention exhibits extremely excellent low-temperature shrinkage, low-temperature sealing properties, and impact resistance, and is particularly suitable for packaging heavy items and annular items.

The linear low density polyethylene based on the metallocene catalyst used in the present invention is a known metallocene catalyst and is composed of ethylene and propylene; butene-1; 4-methylpentene-1; hexene-1; octene-1, etc. -It can obtain by copolymerizing an olefin and there is no limitation in those polymerization methods. For example, it can be produced using any method such as a gas phase method, a slurry method, and a solution method.
The density of the linear low density polyethylene is 0.905 to 0.945 g / cm ³ . Preferably it is less than 0.935 g / cm ³ . When the density of the linear low-density polyethylene is greater than 0.945 g / cm ³ , there is no problem with the strength of the cloth, but the heat shrinkability is reduced. For this reason, the shrinkage binding force is reduced, and as a result, the shrink wrapping property is extremely deteriorated. On the other hand, if the density of the linear low-density polyethylene is 0.945 g / cm ³ or less, the heat shrinkage rate and other problems are solved, and if it is less than 0.935 g / cm ^3, it is greatly improved. . However, when the density is less than 0.905 g / cm ³ , a problem occurs in the stretchability of the film, which tends to occur. The linear low density polyethylene having a density in the above-described range needs to have a short branch. There is no particular limitation on the length of the branched chain, but it is desirable that the number of carbon atoms is 10 or less, and if the branch is a long chain as in the high-pressure polyethylene, the stretchability is poor and the thermal shrinkage tends to be insufficient. This is not preferable.
Furthermore, the melt flow rate of linear low density polyethylene (190 ° C., 2.16 kg, hereinafter referred to as “MFR”) has an MFR of 3.0 g / 10 min or less from the viewpoint of strength and heat shrinkability. From the viewpoint of moldability and stretchability, the MFR is preferably 0.1 g / 10 min or more.
Such linear low-density polyethylene is commercially available, and examples thereof include “NF444A” manufactured by Nippon Polyethylene Co., Ltd.

On the other hand, the random polypropylene in the present invention is obtained by an ordinary method using ethylene and propylene as comonomers, but it is important that the ethylene content is 2 to 12% by mass. That is, when the ethylene content is less than 2% by mass, the heat shrinkability is lowered, so that the shrinkage binding force is reduced and the shrink wrapping property becomes very poor. On the other hand, when the ethylene content is 2% by mass or more, the heat shrinkability is greatly increased and the shrink wrapping property is improved. However, when the ethylene content exceeds 12% by mass, there is a problem that stretchability is significantly lowered and the strength becomes insufficient. The composition of propylene copolymer and propylene homopolymer can also be applied to the present invention when the ethylene content is 2 to 12% by mass.
Furthermore, the MFR of the random polypropylene used in the present invention needs to be 10 g / 10 min or less. That is, when the MFR exceeds 10 g / 10 min, the heat shrinkability is greatly lowered, and the shrink wrapping property is extremely deteriorated. There is no particular problem if the MFR is 10 g / 10 min or less. However, the MFR is preferably 0.5 g / 10 min or more from the viewpoint of film moldability and stretchability, and the MFR is preferably 8 g / 10 min or less from the viewpoint of film moldability, strength, and heat shrinkability.
Such random polypropylene is commercially available, and examples thereof include “PB222A” manufactured by Sun Allomer Co., Ltd.

  In the present invention, the composition ratio by mixing a linear low density polyethylene having a short chain branch and a random polypropylene is important. That is, it is characterized by having 10 to 90% by mass of linear low-density polyethylene having short chain branches and 90 to 10% by mass of random polypropylene. If the linear low density polyethylene having a short chain branch exceeds 90 parts by mass and the random polypropylene is less than 10 parts by mass, the stretchability and strength are insufficient. On the other hand, when the composition of the linear low density polyethylene having a short chain branch is less than 10 parts by mass and the random polypropylene is 90 parts by mass or more, the shrinkage rate decreases. Furthermore, there arises a problem that the heat sealability is deteriorated.

  There are various methods for producing a thin stretched product composed of a composition mainly composed of a linear low density polyethylene having a short chain branch having such a blending ratio and a random polypropylene. For example, first, Molded into a film by melt extrusion and cooled. Then, after cooling, slitting is appropriately performed with a slitter, followed by heating and stretching to obtain a thin stretched product. This melt-extrusion molding can be performed using a method generally used conventionally, for example, an inflation extruder. That is, in melt extrusion molding, a composition mainly composed of linear low-density polyethylene having short chain branches and random polypropylene is extruded into a film in a molten state from a slit of a die and cooled. After cooling, slitting is performed with a slitter, and a thin stretched product can be obtained by stretching at a high magnification, preferably 2 to 9 times, preferably in a temperature range of 60 to 120 ° C. Can be used as In this stretching process, when the heating temperature exceeds 120 ° C., not only the stretchability is deteriorated but also slippage occurs between the molecular chains. For this reason, the stretching operation does not contribute to the alignment effectively, and a predetermined strength and heat shrinkage rate cannot be obtained. In the stretching, there is no particular problem as long as the stretching temperature is less than 120 ° C. However, when the temperature is less than 60 ° C., whitening tends to occur, various physical properties are decreased, or stretchability is decreased. Therefore, it is preferable to perform stretching in a temperature range of 60 to 120 ° C. In particular, the preferred stretching temperature is 70 to 110 ° C., and in this temperature range, the stretchability is excellent, and the physical properties with the most balanced strength, heat shrinkage rate, and shrinkage temperature are obtained. Furthermore, although the draw ratio at the time of extending | stretching depends on desired intensity | strength, Preferably it is 4-8 times. If the draw ratio is less than 4, there may be a problem in the strength of the obtained fine stretched product. Further, if the draw ratio exceeds 8 times, there may be a problem in stretchability. Then, in order to reduce the natural shrinkage after the stretching process or to prevent the paper tube of the winder from being crushed, heat treatment may be performed in a fixed state immediately after the stretching process. Alternatively, it may be desirable to perform such heat treatment. At the time of melt extrusion molding, a monofilament can be obtained by using a nozzle for the die slit, and a filamentous product having a plurality of monofilaments can be obtained as a thin stretched product.

The thread-like product, monofilament and tape-like product (hereinafter referred to as “thread-like product”), which are the finely stretched product of the present invention having high shrinkage and high strength obtained in this way, are part or all of the warp, The shrink-wrapping cloth of the present invention can be obtained by weaving or knitting part or all or part or all of both warp and weft. Weaving and knitting may be carried out by a conventional loom or knitting machine technique. The specifications of the used filamentous material may be selected and determined as appropriate depending on the shape of the package. For example, if a shrink cloth that shrinks only in the warp direction (does not shrink in the horizontal direction) is required, the filamentous material according to the present invention is used for the warp, and the filamentous material having a low thermal shrinkage rate is used for the weft. Good. On the other hand, when a shrink cloth is required that shrinks only in the horizontal direction and does not shrink in the vertical direction, a weaving spec that reverses the warp and weft may be used. Furthermore, when a shrink cloth that shrinks in both the vertical and horizontal directions is necessary, the filamentous material according to the present invention may be used for both the warp and the weft. In addition, for example, when shrink-wrapping a different type of packaged object such as an automobile foil disc, the yarns according to the present invention, which have different thermal shrinkage rates, are used as warp yarns according to the respective molds. A filamentous material having a certain heat shrinkage rate may be used. The heat shrinkage rate is adjusted by appropriately changing the density of the linear low density polyethylene having short chain branches and the ethylene content of the random polypropylene, the melt flow rate, the composition ratio, the stretching temperature, the stretching ratio, etc. can do.
As the die slit used in the practice of the present invention, those conventionally used in general, such as a T-shaped die, a circular die, a filament-like nozzle, and a band-like rectangular nozzle, can be used. And cooling after extrusion molding can use any of water cooling, air cooling, contact with a chill roll, etc., for example. Furthermore, the drawing process may use any drawing method such as open drawing, roll drawing, wet drawing, hot plate drawing, etc., but since the difference between the melting point and the optimum drawing temperature is large, it is relatively inexpensive and heat control is possible. It is preferable to use hot plate stretching, which is easy to perform.
In addition, you may mix | blend an antioxidant, an ultraviolet-ray deterioration inhibitor, a lubricant, a pigment, and also different resin with the polyolefin composition used in this invention as needed. Further, depending on the intended use, a thermoplastic resin may be laminated on the packaging cloth of the present invention in accordance with a conventional method. Furthermore, in order to improve mechanical properties such as abrasion resistance, the packaging cloth of the present invention may be laminated by a method such as sandwich lamination in which an intermediate layer is sandwiched between two or more sheets. . When two or more sheets are laminated, the abrasion resistance against vibration is greatly improved and more effective than the number of sheets.

  If it is the packaging cloth mentioned above, it will become the thing which cold shrinkage property, low temperature sealing property, and impact resistance improved more.

Although the present invention can be used for various shrink wrappings, it is particularly suitable for packaging of annular objects such as tires and wound products of electric wires, and heavy objects.
As the annular packaging, the packaging cloth described above is used, and after the outer periphery of the annular package is surrounded so that the shrinking direction thereof coincides with the outer circumferential direction of the annular package, the overlapping portion of the packaging material is formed. Then, the packaging cloth is contracted by heating to form an intermediate package in which sleeve ends smaller than the inner diameter of the annular material are formed on both end surfaces of the annular material. A method is preferred in which both the sleeve forming portions are pressed from the outside along the inner diameter of the annular material, joined in a ring shape on the inner peripheral surface, and further, the portion inside is cut and removed. That is, a first step of covering the packaging cloth along the outer circumferential direction of the annular object, a second step of sleeve-wrapping in the heating furnace, and a heat sealing and heat cutting of the inner circumference of the annular object. A method having three steps is preferred.

Specific examples will be described in detail with reference to the drawings.
First, as a first step, as shown in FIG. 1A, the packaging cloth 1 is pulled out from the two rolls 3 and 3, and each is positioned at a position near the middle between the two rolls 3 and 3. By performing heat sealing, a flat packaging surface 4 made of the packaging cloth 1 is formed. An annular object 2 such as a tire is locked to a movable body (not shown) so that its axis is parallel to the two rolls 3 and 3, and the outer peripheral surface of the annular object 2 is installed so as to face the packaging surface 4. The The rolls 3 and 3 around which the packaging cloth 1 is wound are arranged at a larger interval in the vertical direction of the drawing than the outer diameter of the annular material. In this state, the annular object 2 locked to the moving body (not shown) is moved in the direction of the packaging surface 4 formed of the packaging cloth 1. By this movement, about half of the outer peripheral surface of the annular object 2 is covered with the packaging surface 4. This state is shown in FIG. Further, the annular material 2 is moved, and immediately after the annular material 2 has completely passed between the two rolls 3, 3, the heating plates 5, 5 approach each other in the vertical direction of the drawing, whereby the packaging cloth 1 is formed in a cylindrical shape along the outer periphery of the annular object 2, and then heat sealing and heat cutting are performed by pressing the hot plates 5 and 5. This state is shown in FIG. In this way, the cylindrical packaging cloth 1 that encloses the annular material 2 is formed at the center.
Next, as a second step, the cylindrical packaging cloth 1 containing the annular material 2 is thermally shrunk by passing through a heating furnace, thereby performing a sleeve packaging step. An annular package (hereinafter abbreviated as an intermediate package) 6 formed from the packaging cloth 1 by this sleeve packaging process is shown in FIG. The intermediate wrapping body 6 is formed on the inner side of the outer wrapping portion 7 wrapping the outer periphery of the annular product 2, the end surface wrapping portions 8 and 8 for wrapping both end surfaces of the annular product 2, and the end surface wrapping portions 8 and 8. The sleeve mouth forming portions 10 and 10 having the sleeve mouth 9 at the center thereof. The diameter of the sleeve port 9 is adjusted in advance according to the width of the packaging cloth, the shrinkage rate, etc. so as to be smaller than the inner diameter of the annular object 2. Here, the relationship between the width of the packaging cloth 1 and the waist width of the annular object 2 depends on the shrinkage ratio of the packaging cloth 1, but the width of the packaging cloth 1 is about the width of the waist of the annular object 2. A range of 1.1 to 1.3 times is preferable.
Finally, as a third step, as shown in FIG. 3A, the sleeve mouth forming portions 10, 10 are formed using a ring sealer 13 including a heating portion 11 and a receiving plate 12 having the same outer diameter as the heating portion 11. By pressing and joining along the inner diameter of the annular object 2 from the outside, the sleeve port forming portions 10 and 10 are joined on the inner peripheral surface of the annular object 2. This state is shown in FIG. Here, this joining is preferably performed immediately after passing through the heating furnace in order to facilitate deepening. Thereafter, the unnecessary sleeve opening forming portions 10 and 10 inside the heat seal portion 14 formed by the above-described process are heat-cut, whereby the annular material shown in FIG. 3C is packaged.

The heat seal by the ring sealer 13 and the heat cut of the unnecessary sleeve opening forming portion 10 inside the heat seal portion 14 will be described in detail with reference to FIG. The ring sealer 13 is used in a process of heat sealing and heat cutting in a ring shape, and has a mechanism capable of simultaneously performing heat sealing and heat cutting. The ring sealer 13 includes a heating unit 11 and a receiving plate 12. The heating unit 11 and the receiving plate 12 are movably attached so as to be close to and away from a support (not shown). The heating unit 11 is connected to the substrate 16 provided with the pressing unit 15. , Handle 17, heat seal part 18, and movable part 20 provided with heat knife 19. The holding portion 15 is a cylindrical shape provided at the end of a plurality of columnar connecting portions 21... Projecting toward the receiving plate 12 provided along the outer periphery in the vicinity of the outer periphery of the end surface on the receiving plate 12 side of the substrate 16. belongs to. An air pipe 22 for cooling is provided inside the vicinity of the end of the pressing portion 15 on the receiving plate 12 side. The movable portion 20 is a disc-shaped member formed on the inner side of the connecting portions 21..., And the U-shaped handle 17 formed on the end surface opposite to the receiving plate 12 projects the substrate 16 toward the receiving plate. It is movably attached so that it can approach and separate. On the end surface of the movable portion 20 on the receiving plate 12 side, a plurality of columnar connecting portions 23... Projecting toward the receiving plate 12 are provided in the vicinity of the outer periphery along the outer periphery of the movable portion 20. Is wound with a coil spring 24. A cylindrical heat seal portion 18 is attached to the end of the connecting portion 23 on the receiving plate 12 side so as to be movable toward and away from the receiving plate direction, and the coil spring 24 is connected to the heat sealing portion 18. Is urged in the direction of the receiving plate. A heater 25 is provided inside the end of the heat seal portion 18 on the receiving plate side. Further, the movable portion 20 is provided with a plurality of columnar connecting portions 26... Projecting toward the receiving plate 12 inside the connecting portions 23... As well as the connecting portion 23. It is provided similarly.
A cylindrical heat knife 19 having a blade portion 28 formed at the end of the receiving plate 12 can approach and separate in the direction of the receiving plate at the end of the connecting portion 26 on the receiving plate 12 side. The coil spring 27 urges the heat knife 19 in the direction of the receiving plate. In the heat knife 19, a heater 29 is provided in the vicinity of the root of the blade portion 28 as in the heat seal portion 18. These are formed of a commonly used metal material, but as a material for forming the pressing portion 15, a heat insulating material such as elastic plastic is preferably used.
When this ring sealer 13 is used for an annular package, the ring sealer 13 and the intermediate package 6 are first arranged at the position shown in FIG. Next, the receiving plate 12 and the pressing portion 15 are joined so as to sandwich the packaging cloth 1. Furthermore, the movable part 20 is pressed to the receiving plate 12 side by pushing the handle 17 to the receiving plate 12 side. Thereby, the heat seal part 18 and the heat knife 19 can press-contact with the packaging cloth 1, and the packaging cloth 1 can be heat sealed and cut in a circle. Here, since the coil springs 24 and 27 respectively press the heat seal portion 18 and the heat knife 19 against the receiving plate 12 with a constant pressure, the heat sealing and heat cutting of the packaging cloth 1 can be performed satisfactorily.
In the above-described example, the packaging cloth 1 is formed from a long product wound around the two rolls 3 and 3. However, in the present invention, the present invention is not limited to this. Even if a sheet-like packaging cloth is used, the shrink wrapping body can be formed by the same method.

In this method, since the annular material is packaged by shrinking the packaging cloth, heat sealing, heat cutting, or the like, the automation of the packaging becomes easy. Further, unlike the packaging form in which strip-shaped paper or film is stacked, the contents are not exposed because it is hermetically packaged.
In addition, the obtained annular package body has a packaging cloth in close contact with the surface of the annular product.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but it goes without saying that the scope of the present invention is not limited thereto.
60% by mass of a linear low density polyethylene (“NF444A” manufactured by Nippon Polyethylene Co., Ltd.) with a metallocene catalyst having a density of 0.912 g / cm ³ and a melt flow rate of 2.0 g / 10 min, and an ethylene content of 7 A mixture containing 40% by mass of random polypropylene (“PB222A” manufactured by Sun Allomer Co., Ltd.) having a melt flow rate of 0.8 g / 10 min by mass was prepared.
Using this mixture, a film having a thickness of 50 μm was produced by an inflation method. After slitting with a slitter, the film was stretched 7.0 times at 80 ° C. to obtain a 1000 denier tape. Their tensile strength and thermal shrinkage were measured. The results are as shown in Table 1.

  In addition, the drawability 5 indicates that there was no breakage in operation even when the drawing treatment was continuously applied for 1.5 hours in the tape manufacturing process, and there was no problem in operation.

  Using this tape as the warp, the tape (stretching temperature: 130 ° C, 7.0 times) manufactured using high-density polyethylene (MFR: 0.8 g / 10 min) is used as the weft. Then, the cloth was woven into a plain weave with a 2700 mm width through machine.

As a comparative example, 60% by mass of linear low density polyethylene (“UF320” manufactured by Nippon Polyethylene Co., Ltd.) using a Ziegler catalyst with a density of 0.922 g / cm ³ and a melt flow rate of 0.9 g / 10 min. A mixture of 40% by mass of random polypropylene (“PB222A” manufactured by Sun Allomer Co., Ltd.) having an ethylene content of 7% by mass and a melt flow rate of 0.8 g / 10 min was prepared.
Using this mixture, a film having a thickness of 50 μm was produced by an inflation method. After slitting with a slitter, the film was stretched 7.0 times at 80 ° C. to obtain a 1000 denier tape. Their tensile strength and thermal shrinkage were measured. The results are as shown in Table 1.
Using this tape as the warp, the tape (stretching temperature: 130 ° C, 7.0 times) manufactured using high density polyethylene (MFR: 0.8 g / 10 min) is used as the weft. Then, the cloth was woven into a plain weave with a 2700 mm width through machine.

  Table 2 shows the results of measurement of various physical properties of the cloths of the above Examples and Comparative Examples.

* 1 After immersion for 1 minute in a glycerin bath.
* 2 Dirt: 38mm diameter hemisphere, 1m height.
* 3 Wrapped with a 5% margin in length for automobile tires (outer diameter 625mm, inner diameter 355mm), heat sealed at the end, and the cross would block in the shrink tunnel in 20 seconds. The lowest temperature at which the sleeve mouth can shrink to below the inner diameter of the tire without any problems.
* 4 The minimum transit time that can be heat-sealed as in the previous section and tightly packed inside the shrink tunnel at 185 ° C.
* 5 ◎ ... very good, ○ ... good, × ... bad.
* 6 Number of times perforation was recognized.

  From Table 2, it can be seen that the cloth according to this example is superior in various strengths, heat shrinkage and shrink wrapping properties as compared with the cloth of the comparative example.

  Although the present invention can be used for various shrink wrappings, it is particularly applicable to wrapping of annular products such as tires and wound products of electric wires and heavy products, and is highly useful.

It is a perspective view which shows the process for forming the intermediate | middle package of a cyclic | annular package. It is a perspective view of an intermediate package. It is a perspective view which shows the process which shows manufacture of a cyclic | annular package. It is a perspective view which shows a ring sealer.

Explanation of symbols

1 Packaging Film 2 Ring 6 Intermediate Package

Claims (2)

10 to 90% by mass of linear low density polyethylene by metallocene catalyst with a density of 0.905 to 0.945g / cm ³ and a melt flow rate of 0.1 to 3g / 10min, and an ethylene content of 2 to 12% %, A thin stretched product made of a polyolefin composition containing 90 to 10% by mass of random polypropylene having a melt flow rate of 10 g / 10 min or less is woven or knitted using at least a part of warp and weft. A packaging cloth characterized by that. The packaging cloth according to claim 1, wherein the packaging cloth is used for packaging an annular material.

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