AU737531B2 - Multi-layer plastics packaging for bales - Google Patents

Description

P/00/011 Regulation 3.2

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT *4

S.

Name of Applicant: Address of Applicant: Actual Inventor: Address for Service: AMCOR PACKAGING (AUSTRALIA) PTY LTD 15 Valentine Street Kewdale, Western Australia 6105

AUSTRALIA

Robert RUSSELL Hem DEEPLAUL Griffith Hack, Patent and Trade Mark Attorneys, 6th Floor, 256 Adelaide Terrace, Perth, Western Australia, 6000.

Standard Complete Specification for the invention entitled: MULTI-LAYER PLASTICS PACKAGING FOR BALES Details of Associated Provisional Applications: PP 0169 filed 31 October 1997 by AMCOR PACKAGING (AUSTRALIA) PTY LTD Details of Parent Application for Divisional Applications: The following is a full description of this invention, including the best method of performing it known to me:y rt -2- MULTI-LAYER PLASTICS PACKAGING FOR BALES FIELD OF THE INVENTION The present invention relates to a multi-layer plastics packaging for bales of compressible material and relates particularly, though not exclusively, to a multilayer coextruded plastic bag for wool bales.

BACKGROUND TO THE INVENTION Untreated sheep's wool, so called "greasy wool", is transported and stored in a compressed form as square wool bales with typical dimensions of 900 x 675 x 675 mm. Most wool bales are currently packaged in blended polypropylene 10 woven bags. Over 90% of Australian and New Zealand wool is exported, S"mostly in its untreated greasy form; and wool continues to be a major earner of export income in these countries. In the past, major buyers of Australian wool were Japan, the USSR, Italy, France, West Germany (now Germany) and Czechoslovakia (now the Czech Republic and the Slovak Republic). In 15 environment-conscious Germany, legislation was recently introduced making it mandatory to use only recyclable materials in packaging. Unfortunately, the woven polypropylene bags used for wool bales are not recyclable after use, as °wool fibres tend to get caught in the weave of the bags and it is not economical to try to separate the wool and polypropylene fibres for recycling. Also, the 20 woven polypropylene sometimes has a nylon thread component added to o:o improve the strength of the woven bag and stop stretching. It is impossible to separate the nylon from the polypropylene when attempting to recycle. Woven stretched High Density Polyethylene (HDPE) is also sometimes used for wool bales and is subject to the same disadvantages as the woven polypropylene bags.

A further disadvantage of the woven bags is that the wool bale not infrequently gets contaminated with polypropylene, HDPE or nylon threads. This may happen, for example, when the bale is speared to obtain a core sample for testing and analysis. The spear may cut and drag several fibres of the polypropyene, HDPE and/ or nylon thread into the wool bale as it pierces thE woven bag. Wool buyers have complained about such contamination as it is -3virtually impossible to detect and only becomes evident in the finished garment or cloth.

The Australian Wool Corporation (AWC) tried to address these problems by producing a mono-film bag of plastics material for wool bales. However, these bags were not successful as they were not sufficiently strong to withstand the rigours to which wool bags are subjected during transport and storage. For example, prior to export, all wool bales are further compressed in a special press called a "tri-packer" which compresses three bales of wool down to the size of a single wool bale. The AWC plastic bags were unable to withstand the high oo:: 10 temperatures and stresses and strains experienced in the tri-packer during compression of the three wool bales. A further problem with these prior art bags was that they tended to lose their shape over time and the sides would •bulge out due to creep, so that instead of a square bale, one ended up with a round bale.

S:.o 15 Commonly-owned Australian Patent No. 681888 discloses a plastics packaging for bales of compressible material such as wool. The packaging is made using a three layer coextruded film of plastics material, including a first layer of high stiffness plastics material and a second layer of easily weldable plastics material.

Whilst the packaging of 681888 was found to give satisfactory performance, 20 extensive testing has revealed some shortcomings in the mechanical properties e of the film in particular circumstances. For example, the tear resistance of the three layer film of 681888 was found to be too low to serve the industry successfully.

SUMMARY OF THE INVENTION The present invention was developed with a view to providing an improved plastics packaging for bales of compressible material, such as wool, which is less susceptible to at least some of the disadvantages of the prior art bags.

According to one aspect of the present invention there is provided a multi-layer plastics packaging for bales of compressible material, the packaging comprising: 4,I -4a multi-layer coextruded film of plastics material configured to contain the compressible material, said film comprising a first layer of high stiffness plastics material and a second layer of high strength plastics material, wherein said multi-layer film has a modulus of elasticity in the range 200 600 MPa, a tear resistance of at least 2200 gm and a tensile yield point in the range 10 to 20 MPa whereby, in use, said film is capable of retaining the compressible material substantially in the shape of a bale.

Preferably the thickness of said first layer is more than 25% and less than of the total thickness of the coextruded film.

10 Preferably said packaging is in the form of a bag, sealed at one end to form a substantially square bottom for the bale, and typically said compressible material S•is sheep's wool.

Preferably said high stiffness plastics material includes a high density polyethylene (HDPE) and said high strength plastics material includes a low density polyethylene (LDPE). More preferably, said high stiffness plastics o material is a blend of HDPE and ultra linear low density polyethylene (ULLDPE), and said high strength plastics material is a blend of LDPE and linear low density polyethylene (LLDPE).

-n o Typically said high density plastics material has a density in the range 0.935 to 0.965 gm/cm 3 and said low density plastics material has a density in the range 0.915 to 0.940 gm/cm 3 In one preferred form of the invention the multi-layer coextruded film consists of three layers of coextruded plastics material, wherein said first layer forms an intermediate or core layer and said second layer is one of two layers forming an outer and an inner layer respectively of the multi-layer film. Typically the thickness of all three layers is substantially the same and equal to approximately one third of the total thickness of the multi-layer film.

Preferably the bag is formed with four flaps at both ends, at least one of the flaps having an adhesive provided thereon to allow the bag to be closed when it is full of said compressible material. Typically three of the four flaps are provided with a double-sided pressure-sensitive, shear resistant adhesive tape for sealing the bag at both ends.

According to another aspect of the present invention there is provided a wool bale contained in a multi-layer plastics packaging as hereinbefore defined.

BRIEF DESCRIPTION OF THE DRAWINGS In order to facilitate a better understanding of the nature of the invention a 10 preferred embodiment of the multi-layer plastics packaging will now be S"described in detail, by way of example only, with reference to the accompanying S"drawings in which: Figure 1 illustrates the configuration of a preferred embodiment of the multilayer plastics packaging in the form of a bag for a wool bale; Figure 2 illustrates schematically the structure of a preferred embodiment of a multi-layer coextruded film used to manufacture the bag of Figure 1; and, Figure 3 illustrates schematically an alternative embodiment of a multi-layer °coextruded film.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The preferred embodiment of the multi-layer plastics packaging according to the invention illustrated in Figure 1 is in the form of a bag 10 for packaging bales of wool, the bag 10 being sealed at one end 12 to form a substantially square bottom for the bale. The walls 14 of the bag are formed using a conventional thermoplastic film forming technique, such as the tubular extrusion process in which an entrapped air column is employed to expand the extruded film tube in a vertical direction. In order to obtain the desired physical properties of the coextruded film a multi-layer film of plastics material is coextruded to form a composite laminar structure having a total thickness ranging from approximately -6- 250 pm up to 350 pm. The nature and physical properties of the coextruded film will be described in greater detail below.

To manufacture the bag 10 the extruded tube is folded and cut with four flaps at each end. Three of the four flaps at each end are provided with a specialised double-sided pressure sensitive, shear resistant adhesive tape. Each strip of adhesive tape is approximately 700 mm in length and 96 mm in width. As can be seen in Figure 1, flaps B and C at each end are provided with a single strip of adhesive tape, whereas flap D is provided with two strips of adhesive tape.

Furthermore, at the bottom end of the bag flap D is provided with an additional :i 10 two side strips of adhesive tape approximately 35 mmin width. The bottom S'end of the bag is pre-assembled to form a square bottom by firstly folding flap A over and then folding flap C so as to adhere to flap A. Then flap B is folded •over and adhered to the outside of flap C, and finally flap D is folded over to adhere to the outside of flap B.

15 The bag thus formed has four sides of approximately equal width corresponding substantially to the internal dimensions of a standard wool press of the kind S. used in thousands of wool sheds all over Australia and New Zealand. In an empty condition the bag 10 has side walls with a width dimension of 710 mm and a height of approximately 1000 mm. The full length of the bag 10, including 20 the flaps 18, in its unassembled condition is approximately 2200 mm, and the flaps 18 are each approximately 600 mm long.

Typically, when the wool bag 10 located in a wool press is full, the bag is closed by folding down each of the flaps A, B, C and D in a similar fashion to that described above for the bottom of the bag.

The structure of the multi-layer coextruded film employed to manufacture the wool bag 10 was carefully designed to obtain the necessary physical properties required of the wool bag in order to withstand the rough handling of wool bales during transportation and storage. The wool bag 10 must be capable of withstanding repeated puncturing by grappling hooks during handling and when speared for obtaining core samples, and if destined for export must also -7be capable of withstanding the extreme forces generated during compression in the tri-packer. The physical characteristics of the multi-layer film which have been found to be particularly significant for the preferred wool bag are: Stiffness, as measured by the modulus of elasticity; Puncture resistance and tear strength; Surface hardness or impact strength; Tensile toughness as measured by the tensile yield point; Ability to withstand higher temperatures; and, Low slip characteristic for safe transport.

These properties are obtained in the multi-layer coextruded plastics film Semployed to manufacture the wool bags 10 by a careful selection of the plastics materials used to form the extrusion. In particular, the coextruded film employed in the wool bag 10 comprises a first layer of high stiffness plastics material and a second layer of high strength plastics material. In a more 15 preferred form of the invention the multi-layer film comprises a third layer of high strength plastics material, and the first layer of high stiffness plastics material forms a core or intermediate layer of the multi-layer film. In a most 0:0 preferred form of the invention the desired physical characteristics or mechanical properties of the multi-layer film are achieved using a blend of various density polyethylene (PE) plastics materials in each of the first, second and third layers.

o:ooo The intermediate layer of high stiffness plastics material is designed to give the composite film improved stiffness as indicated by a higher modulus of elasticity.

This helps to resist creep and ensures the bag retains its original shape. The inner and outer layers of high strength plastics material gives the coextruded composite structure improved puncture and tear resistance.

Figure 2 illustrates schematically a three-layer coextruded film 22 used to manufacture the wool bag 10 of Figure 1. The three-layer film 22 comprises an outer layer 24 containing a blend of low density polyethylene (LDPE) and linear low density polyethylene (LLDPE), a core layer 26 containing a blend of high density polyethylene (HDPE) and ultra linear low density polyethylene -8- (ULLDPE), and an inner layer 28 also containing a blend of LDPE and LLDPE.

The preferred HDPEs have a density in the range 0.935 to 0.965 gm/cm 3 The LDPEs employed in the outer layer 24 and inner skin 28 of the coextruded film 22 are preferably blended with linear LDPEs. The preferred LDPEs have a density in the range 0.915 to 0.940 gm/cm 3 Each layer in the coextruded film 22 is approximately of equal thickness, and the total thickness of the film is typically in the range 250 to 350 mn.

The coextruded film with this structure has individual layers made of particular •plastic resins selected so that each individual layer contributes specific physical 10 properties to the composite structure. However, the precise mechanical or physical properties of the composite multi-layer structure cannot be readily oO*. predicted from a knowledge of the particular resins employed. The properties S"of one layer may interact in a counter-productive manner with the properties of an adjacent layer and therefore it has been found that the selection of the resins for each layer for their mechanical properties has to be carefully balanced, largely through trial and error, with the mechanical properties of adjacent layers to achieve the overall desired mechanical properties of the multi-layer film.

The HDPE layer 26 gives greater stiffness to the coextruded film. Importantly, S•the high density core layer 26 also has a higher tensile yield point, typically in the range 10 20 MPa, which inhibits creep and enables the wool bag to hold its square shape over time. Furthermore, the high density intermediate core layer 26 also gives the bags improved resistance to puncture. The typical puncture force of the multi-layer film 22 exceeds 165 N.

The outer layer 24 and inner layer 28, both consist of substantially identical blend of LDPE which imparts the desired tear and puncture resistance as well as the desired toughness of the coextruded film required for this application.

The LDPE layers help to ensure that punctures formed in the walls of the wool bag during transport and storage do not propagate. The tear resistance of the multi-layer film in the machine direction typically exceeds 2800 gm and in the transverse direction typically exceeds 3200 gm -9- Table 1 gives the typical physical properties of a variety of multi-layer coextruded films trialled in the manufacture of the packaging for wool bales using various resins and wall thicknesses. In Table 1 MD designates the machine direction and TD designates the transverse direction. Not all the films of Table 1 were considered satisfactory for the wool bales.

Other additives may be included in the plastic coextrusion, such as polybutene, antioxidant, slip process aids, in conventional manner.

resin materials prior to and antiblock and other Trial No. 7142A 7142B 7142E 7142G Thickness (pm) 255 315 260 258 Tear Resistance MD >3200 >3200 >3200 832 (Elmendorf) (gm) TD >3200 >3200 >3200 1088 Tensile Yield MD 13.1(50) 13.5(64) 11.5(45) 15.5(60) MPa TD 14.4(55) 14.4(68) 12.8(50) 16.8(65) Tensile Strength MD 32.6(125) 34(160) 37.2(145) 27.1(105) MPa TD 31.3(120) 35(165) 41(160) 64.4(250) Elongation at break MD 1300% 1340% 1360% 1000% TD 1265% 1390% 1400% 1250% Puncture Force in N 175 160 165 215 Puncture Elongation 23 23 25 (mm) Modulus of Elasticity 250(9.5) 285(14) 200(7.8) 594(23) MD 290(11.0) 320(15) 230(9) 491(19) MPa (N)

TD

Table 1 10 *5

S

S A Trials 7142A, 7142B, 7142E, 7142G With the exception of trial 7142G, the multi-layer films of Table 1 all employed an intermediate layer of LLDPE and inner and outer layers of LDPE/LLDPE blend.

Trial 7142G employed a blend of LLDPE/PP in all three layers.

Table 2 gives the typical physical properties of the most preferred multi-layer coextruded films which were trialled. The chemical composition of each of these films is described below.

Trials 7142C, 7142D, W.Bale and 7100D In its most preferred form the wool bag is manufactured from a three layer 10 coextruded film having an overall thickness of approximately 250pm to 310 pm, and an intermediate layer of ULLDPE/HDPE blend with inner layer and outer layers of LDPE/LLDPE blend. It is thought that the addition of the LLDPE to the inner and outer layers and the addition of the ULLDPE to the intermediate layer gives improved tear resistance and puncture resistance to the multi-layer film.

15 Trial No. 7142C 7142D W.Bale 7100D Thickness (pm) 253 310 292 310 Tear Resistance MD 2240 2880 2930 2960 (Elmendorf) (gm) TD >3200 >3200 >3200 >3200 Tensile Yield MD 14.5(55) 15.5(73) 13.6(60) 15.0(71) MPa TD 15.3(58) 16.2(76) 14.8(65) 17.0(77) Tensile Strength MD 34(128) 36(170) 34.1(150) 33.0(148) MPa TD 34.2(130) 38.3(180) 33(145) 36.0(165) Elongation at break MD 1265% 1350% 1400% 1265% TD 1350% 1400% 1425% 1400% Puncture Force in N 160 215 170 210 Puncture Elongation (mm) 25 23 25 Modulus of Elasticity MD 265(10) 280(13) 275(12) 444(20.0) MPa TD 330(12.5) 405(19) 295(13) 465(21.0)

S

5.55 S S S. S 5.55..

S S Table 2 11 It is not essential that the multi-layer coextruded film consists of three layers, as two, four or more layers can be employed if desired. Figure 3 illustrates a twolayer coextruded film 30 having a first layer 32 of high stiffness plastics material and a second layer 34 of high strength density plastics material. In order to obtain the required physical properties of the coextruded film it has been found that the layer of high stiffness plastics material should preferably comprise between 20 to of the total thickness of the film. If the first layer is made too thin then the tensile strength of the film is compromised and the wool bags start to lose their shape due to creep. On the other hand, if the second layer(s) of high strength plastics material is made too thin then the puncture resistance and tear strength of the coextruded film is compromised. In the embodiment of Figure 3, the first layer oo 32 is approximately 40% of the total thickness of the film Wool bales packaged with the multi-layer coextruded plastics film of the invention were found to be capable of withstanding the frictional heat and extreme pressures to which the bags are subjected during compression in the tri-packer, in preparation for export.

oo° Now that a preferred embodiment of the coextruded plastics packaging according to the invention has been described in detail, it will be evident to persons skilled in the packaging arts that numerous variations and modifications can be made, in addition to those already described, without departing from the basic inventive concepts. For example, whilst the preferred embodiment is in the form of a bag in order to conform as closely as possible to the wool industry standard for wool bales, the coextruded plastics packaging may take other forms, for example, sheet packaging. Furthermore, whilst the most preferred plastics material employed in the multi-layer coextruded film is polyethylene other plastics materials with the appropriate physical properties can also be employed. For example, chemically modified polypropylene or nylon with the appropriate stiffness could be employed in the first layer, whilst other plastic materials with the desired toughness can be used for the other layers. HDPE and linear LDPE are currently the most preferred plastics materials and are particularly advantageous as they enable the used bags 12 to be readily recycled without the need for separating the various components.

However, if recyclability is a less important feature, then other dissimilar plastics materials can be used. All such variations and modifications are to be considered within the scope of the present invention, the nature of which is to be determined from the foregoing description and the appended claims.

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Claims (14)

1. A multi-layer plastics packaging for bales of compressible material, the packaging comprising: a multi-layer coextruded film of plastics material configured to contain the compressible material, said film comprising a first layer of high stiffness plastics material and a second layer of high strength plastics material, wherein said multi- layer film has a modulus of elasticity in the range 200 600 MPa, a tear resistance of at least 2200 gm and a tensile yield point in the range 10 to 20 MPa whereby, in use, said film is capable of retaining the compressible material substantially in V0 10 the shape of a bale.

2. A multi-layer plastics packaging as defined in claim 1, wherein the thickness of said first layer is more than 25% and less than 50% of the total thickness of the S"coextruded film.

3. A multi-layer plastics packaging as defined in claim 2, wherein the multi-layer coextruded film consists of three layers of coextruded plastics material, wherein said first layer forms an intermediate or core layer and said second layer is one of o two layers forming an outer and an inner layer respectively of the multi-layer film.

4. A multi-layer plastics packaging as defined in claim 3, wherein the thickness of all three layers is substantially the same and equal to approximately one third of the total thickness of the multi-layer film.

A multi-layer plastics packaging as defined in claim 4, wherein said high stiffness plastics material includes a high density polyethylene (HDPE) and said high strength plastics material includes a low density polyethylene (LDPE). P -14-

6. A multi-layer plastics packaging as defined in claim 5, wherein said high stiffness plastics material is a blend of HDPE and ultra linear low density polyethylene (ULLDPE), and said high strength plastics material is a blend of LDPE and linear low density polyethylene (LLDPE).

7. A multi-layer plastics packaging as defined in claim 6, wherein the total thickness of the multi-layer film is in the range 250 to 350 pm.

8. A multi-layer plastics packaging as defined in claim 7, wherein the multi-layer film has a tear resistance in the machine direction in excess of 2800 gm and the transverse direction in excess of 3200 gin. o°•

9. A multi-layer plastics packaging as defined in claim 8, wherein the multi-layer film has a tensile yield point in the range 13 to 17 MPa. 1

10. A multi-layer plastics packaging as defined in claim 8, wherein the multi-layer film has modulus of elasticity in the range 265 to 465 MPa. oo0 i

11. A multi-layer plastics packaging as defined in any one of the preceding claims, wherein said packaging is in the form of a bag, sealed at one end to form ogoo• a substantially square bottom for the bale, and typically said compressible material is sheep's wool.

12. A multi-layer plastics packaging as defined in claim 11, wherein the bag is formed with four flaps at both ends, at least one of the flaps having an adhesive provided thereon to allow the bag to be closed when it is full of said compressible material.

13. A multi-layer plastics packaging s defined in claim 11, wherein three of the four flaps are provided with a double-sided pressure-sensitive, shear resistant adhesive tape for sealing the bag at both ends. S

14. A wool bale contained in a multi-layer plastics packaging as hereinbefore defined in any one of the preceding claims. Dated this 19th day of October 1998 AMCOR PACKAGING (AUSTRALIA) PTY LTD By Its Patent Attorneys GRIFFITH HACK Fellows Institute of Patent Attorneys of Australia. o* 9 S0