AU681888B2 - Coextruded plastics packaging for bales - Google Patents

Description

P/O/0U Reglation 3.2

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name of Applicant: Address of Applicant: Actual Inventor: Address for Service: GROMARK PACKAGING PTY LTD 15 Valentine Street Kewdale WA 6105

AUSTRALIA

JEFFREY CHARLES BURCH ANDREW J HARGREAVES Griffith Hack, Patent and Trade Mark Attorneys, 6th Floor, 256 Adelaide Terrace, Perth, Western Australia, 6000.

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S S 5 Standard Complete Specification for the invention entitled: COEXTRUDED PLASTICS PACKAGING FOR BALES Details of Associated Provisional Applications: PM0439 filed on 6 August 1993 Details of Parent Application for Divisional Applications: ,ThbdLfoj ng Is a full description of this Invention, including the best method f p fi lring it known to me:- A :4r rw -2 COEXTRUDED PLASTICS PACKAGING FOR BALES The present invention relates to a coextruded plastics packaging for bales of compressible material and relates particularly, though not exclusively, to a coextruded plastic bag for wool bales.

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 woven bags. Over 90% of Australian and New Zealand wool is exported, mostly in its untreated greasy form, and wool continues to be a major earner of export 44060:income in these countries. in the past, major buyers of to Australian wool were Japan, the USSR, Italy, France, West 9 15 Germany (now Germany) and Czechoslovakia (now the Czech Republic and~ the Slovak Republic). In environmentconscious Germany, legislation was recently introduced making it mandatory to use only recyclable materials in Spackaging. 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 a 0 0 polypropylene fibres for recycling. Also, the woven polypropylene sometimes has a nylon thread component added to 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 (HOPE) 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 infrequantly 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 polypropylene, HOPE and/or nylon -3 thread into the wool bale as it pierces the woven bag.

Wool buyers have complained about such contamination as it is virtually impossible to detect and only becomes evident in the finished garment or cloth.

The Australian Wool Corporation (AWC) tried to address these problems by producin~g 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 "tni-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 temperatures and stresses and strains experienced in the tni-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 20 up with a round bale.

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 *0:00 25 prior art bags.

:11, According to one aspect of the present invention toothere is provided a coextruded plastics packaging for bales ,&Ito of compressible material, the packaging comprising: 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 easily weldable plastics material, wherein said high stiffness plastics material has a modulus of elasticity in the range 500 1500 MPa and a tensile yield point in the range 10 to l4Pa whereby, in use, said film is capable of retaining the compressible material substantially in the shape of a bale.

4 Preferably the thickness of said outer layer is more than 25% and less than 50% of the total thickness of the coextruded film.

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

Preferably said high stiffness plastics material is high density polyethylene (HDPE) and said easily weldable plastics material is low density polyethylene (LDPE). More preferably, said HDPE contains a butyl-rubber additive (for example, that sold under the trade mark KRAYTON) to improve the quality of the extrusion and increase the impact strength of the HDPE, and said LDPE is a linear LDPE, for example, that sold under the trade mark

DOWLEX.

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 20 to 0.940 gm/cm 3 lae In one preferred form of the invention the multilayer coextruded film consists of three layers of coextruded plastics material; an outer layer of HDPE, an foo*.. inner layer of linear LDPE and an intermediate layer or 1h 25 core of linear LDPE. Typically the thickness of all three layers is substantially the same and equa). to approximately one third of the total thickness of the coextruded film.

Preferably the bag is formed w;Lth four flap at its open end, 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 the bag is also provided with a plurality of air holes to allow air to escape from within the bag when the bale is compressed.

According to another aspect of the present invention there is provided a wool bale contained in a 4

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According to a still further aspect of the present invention there is provided a method of compressin~g a plurality of bales of compressible material contained in a coextruded plastics pack~aging as hereinbefore defined, the method comprising: applying a lubricant to the outer surfaces of the plastics packaging prior to compression whereby, in use, said lubricant helps to reduce the coefficient of friction of the outer surfaces and minimise heat generated during compression.

Typically the step of applying the lubricant comprises spraying the lubricant onto the outer surfaces as ~the bales are conveyed to a compression machine, Advantageo~usly said lubricant is a common liquid detergent of the kind used for domestic cleaning.

in order to facilitate a better understanding of the nature of the invention a preferred embodiment of the coextruded plastics packaging will now be described in detail, by way of example only, with reference to the accompanying drawings in which: Figure I illustrates the configuration of a a he preferred embodiment of the coextruded plastics packaging in the form of a bag for a wool bale; 25 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, F'igure 3 illustrates schematically an alternative embodiment of a multi-layer coextruded film.

The preferred embodiment of the coextruded 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 and guaseted 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 -6 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-lay'er film of plastics material is coextruded to form a composite laminar structure having a total thickness ranging from approximately 150 [IM up to 300 gim. 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 into a flat double layer configuration, and the gussets are formed by thermo-sealing the bottom of the bags along oblique lines 16 in a conventional manner. The bag thus formed has four sides of approximately equal width corresponding substantially to the internal dimensions of a 15 standard wool press of the kind used in thousands of wool sheds all over Australia and New Zealand. in its folu 1 ded, flattened condition the bag 10 has two side walls with a width dimension of 725 mm whilst the other two side walls have a width dimension of 715 mm. The w(',ol bag 10 is provided with four flaps 18 at its open end, at least one of the flaps having an adhesive provided thereon to allow the bag to be closed when it is full of compressed wool, The full length of the bag 10, including the f laps 18, in its flattened condition is approximately 2050 mm, and the flaps 18 are each approximately 600 mm long.

Typically, when the wool bag 10 located in a wool 4 press Is full, the bag is closed by first folding down two of the flaps 18 extending fromv opposite side walls 14 of the bag, one f lap being sealed to the other by removing ai cover strip to expose the adhesive. Then the other two flaps are folded down and the same process is- repeated.

The adhesive emnployed is typically a high-strength adhesive such as, for example, synthetic rubber resin.

The wool bag 10 is also provided with a plurality of holen 20 at 200 mm, intervals in the side walls thereof to allow air tc escape from within the bag both during precsing of the wool and during compression of the bale during handling

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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 ol bag 10 must be capable of standing up to repeated p=nc ring by grappling hooks during handling and when speared for obtaining core samples, and if destined for export must als~o be capable of withstanding the extreme forces generated during compression in the tni-packer. The physical characteristics of the coextruded film which have been found to be particularly significant for the wool bag are: 15 Puncture resistance and tear strength Stiffness, as measured by the modulus of elasticity, Surface hardness or impact strength Trensile toughness as measured by the 20 tensile yield point Ability to withstand higher temperatures.

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These properties are obtained in the multi-layer coextruded plastics film employed to manufacture the wool bags 10 by a careful selection of the plastics materials used to form the extrusion, tn particular, the coextruded film employed in the wool bag 10 comprises a first outer layer or skin of high stiffness plastics material and a second inner layer of easily weldable plastics material.

in a preferred form of the invention the coextruded film comprises a third inner layer or inner akin of easily weldable plastics material, and the second layer of high toughness plastics material forms a core or intermediate layer of the coextruded film.

The outer layer of high stiffness plastics 8 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 layer of easily weldable plastics material enables the bags to be thermally sealed and gusseted at the bottom end, The core layer of high toughness 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 coextruded film 22 comprises an outer skin 24 of high density polyethylene (HDPE), a core layer 26 of low density polyethylene (LDPE) and an inner skin 28 also I t" of low density polyethylene (LDPE). The preferred HDPE e 15 consists essentially of ethylene copolymerised with a prescribed quantity, typically 10%, of a butyl rubber compound such as that sold under the trade mark KRAYTON.

The KRAYTON additive is found to improve the quality of the extrusion by enhancing cross-linking of ethylene chains in the extrusion and thus increasing the impact strength. The preferred HDPEs have a density in the range 0.935 to 0.965 gm/cm

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The LDPES employed in the core layer 26 and inner skin 28 of the coextruded film 22 are preferably linear o*eo LDPES, for example, of the kind sold under the trade mark DOWLX. The preferred linear 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 150 to 300 m, The coextruded film with this structure has individual layers made of particular plastic resins selected so that each individual layer contributes unique physical properties to the composite structure.

The HDPE outer layer 24 gives greater stiffness to the coextruded film and tends to have a rougher surface than the LDPE inner skin 28. Hence the outer skin 24 9 enables the wool bags to slip during compression by reducing the coefficient of friction between the outer surface of the bag and adjacent bags or an adjacent pressure plate in a wool press or the tri-packer. On the other hand, the high density outer skin 24 is designed not to be too slippery so that the wool bales are still easily stackable. The high density outer skin 24 also has a higher melt temperature and therefore can withstand higher pressures without melting or tearing. importantly, the high density outer layer 24 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 outer layer 24 also gives the coextrusion improved surface hardness and 15 therefore gives the bags improved resistance to puncture.

54 The typical impact strength of the coextruded film 22, as measured by the standard technique of dropping a dart from 600 mm onto the film, exceeds 1300 gm.

The intermediate core layer 26 and inner skin layer 28, both consist of substantially identical linear LDPE which impart the desired tear and puncture resistance as well as the desired toughness of the coextruded film required for this application, The linear LDPE layers help to ensure that punctures formed in the walls of tho wool 25 bag during transport and storage do not propagate. The linear LDP9 inner skin 28 also enables 'he bottom end 12 of the wool bag 10 to be scaled and the gussets to be formed due to the lower melt temperature of the linear LDPE, in its most preferred form the wool bag is manufactured from a three layer coextruded film having an overall thickness of approximately 250 gm, and an outer skin of HDPE having a density of approximately .960 gm/cm 3 and an innor core and inner skin layer of linear LDPE having a density of approximately .920 gm/cm Table 1 gives the typical physical properties of a preferred form of a three layer coextruded film employed in the manufacture of thd packaging for wool bales. In Table 1 MD 10 designates the machine direction and TD designates the transverse direction.

Gauge Ave: 256pm Tensile Strength MD: 31.3 MPa Range: 47(230-277) at Break (ASTMD 882) TD: 32.3 MPa Dart Impact (Body): 1300gin Elongation at Break MD: 1205% (Toughness) (Edgefold): 600gin TD: 1390% Tear Resistance MD: 1152gm Punct. Porce Break 17.5N (Elmendorf) TD: 2976gm Punct. Elong. Break: 27mmn Tensile Yield MD: 16.8 MPa Modulus of Elasticity MD: 391 MPa TD: 16.0 MPa TD: 430 MPa Layer Composition: 33% 67% 0 @10000 0 00 00 I 0*00 @001 S S 0@ I

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*5e5 Table 1 Other additives may be included in the plastic resin materials prior to coextrusion, such as polybutene, antioxidant, slip and antiblock and other process aids, in conventional manner.

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 20 illustrates a two-layer coextruded film 30 having an outer skin 32 of high density plastics material and an inner skin 34 of low density plastics material. In order to obtain the required physical propertiones of the coextruded film it has been found that the outer layer of high stiffness plastics material should preferably comprise between 20 to of the total thickness of the film. If the outer 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 inner layer(s) of easily weldable and/or high toughness plastics material is made too thin then the puncture resistance and tear strength of the coextruded film in compromised. In the embodiment of Figure 3, the outer layer 32 is approximately 11 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.

Furthermore, it has been found that by spraying a lubricant onto the exterior surface of the wool bales prior to loading into the tri-packer, the bales can be more readily put into the tni-packer without snagging or getting caught on the walls. Furthermore, the lubricant also helps to reduce friction between adjacent bags and the walls of the packer during compression so that the exterior surfaces can slide without tearing or fusing as with the prior art bags, Liquid detergent of the kind used for domestic cleaning has been found to be suitable as a lubricant and can be easily sprayed onto the exterior surface of the bales as they move along the conveyor to the tni-packer. The presence of small quantities of detergent in the greasy wool does not present a problem as the wool is inevitably washed during subsequent processing.

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 anld modifications can be made, in addition to thozie already 5,55 described, without departing from the basic inventive concepts, For example, whilst the pref erred embodiment is in the form of a bag in order to conform as closely as poviible to the wool industry standard for wool bales, the coextruded plastics packaging may take other fo~rms, 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 he employed. F'or example, chemically modified polypropylene or nylon with the appropriate stiffness could be employed 12 in the outer layer, whilst other plastic materials with the desired toughness and weldability can be used for the inner layers. HDPE and linear LDPE are currently the most preferred plastics materials and are particularly advantageous as they enable the used bags 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 (10)

1. 2. A coextruded plastics packaging as defined in claim 1, wherein the thickness of said first layer is more is than 25% and less than 50% of the total thickness of the 0. coextruded film. a 0
2. 3. A coextruded plastics packaging as defined in claim 2, wherein said high stiffness plastics material is a high density plastics material having a density in the 20 range 0,935 to 0.965 gm/cm 3 and said easily weldable a" plastics material is a low density plastics material having a density in the range 0.915 to 0.940 gm/cm 3
3. 4. A coextruded plastics packaging as defined in
4. 9. ai claim 3, wherein said high stiffness plastics material is high density polyethylene (HDPE). A coextruded plastics packaging as defined in claim 4, wherein said easily weldable plastics material is a linear low density polyethylene (LDPE). 6. A coextruded plastics packaging as defined in claim 5, wherein the multi-layer coextruded film consists of three layers of coextruded plastics material, a first .t I 14 layer of HDPE, a second layer of linear LDPE and a third layer of linear LDPE. 7. A coextruded plastics packaging as defined in claim 6, wherein the thickness of all three layers is substantially the same and equal to approximately one third of the total thickness of the coextruded film and wherein the total thickness of the coextruded film is in the range 150 to 300 pm. 8. A coextruded plastics packaging as defined in claim 7, wherein the physical properties of the coextruded film are characterised by a modulus of elasticity with a minimum value of 380 MPa and a tensile yield point having a minimum value of 15 MPa. a 9. A coextruded plastics packaging as defined in any 15 one of the preceding claims, wherein said packaging is in the form of a bag, sealed at one end to form a C substantially square bottom for the bale, and typically C said compressible material is sheep's wool.
5. 10. A coextruded plastics packaging as defined in 20 claim 9, wherein the bag is formed with four flaps at its open end, 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.
6. 11. A coextruded plastics packaging as defined in claim 10, wherein the bag is also provided with a plurality of air holes to allow air to escape from within the bag when the bale is compressed.
7. 12. A method of compressing a plurality of bales of compressible material contained in a coextruded plastics packaging as defined in any one of the preceding claims, Xitv c the method comprising: 15 applying a lubricant to the outer surfaces of the plastics packaging prior to compression whereby, in use, said lubricant helps to reduce the coefficient of friction of the outer surfaces and minimise heat generated during compression.
8. 13. A method of compressing a plurality of bales of compressible material as defined in claim 12, wherein the step of applying the lubricant comprises spraying the lubricant onto the outer surfaces as the bales are conveyed to a compression machine.
9. 14. A method of compressing a plurality of bales of compressible material as defined in claim 13, wherein said lubricant is a common liquid detergent of the kind used for domestic cleaning. 15 15. A wool bale contained in a coextruded plastics *i S packaging as defined in any one of claims 1 to 11. S e
10. 16. A coextruded plastics packaging substantially as herein described with reference to and as illustrated in any one or more of the accompanying drawings. Dated this 6th day of February 1997 GROMARK PACKAGING PTY LTD By Its Patent Attorneys GRIFFITH HACK Fellows Institute of Patent Attorneys of Australia. I yll i-. I ABSTRACT A coextruded plastics packaging in the form of a bag for packaging bales of wool, the bag (10) being sealed and gusseted at one end (12) to form a substantially square bottom for the bale. The gussets are formed by thermo- sealing the bottom of the bag (10) along oblique lines The wool bag (10) is provided with four flaps (18) at its open end, at least one of the flaps having an adhesive provided thereon to allow the bag to be closed when it is full of compressed wool. The structure of the multi-layer coextruded film employed to manufacture the wool bag (10) is carefully designed to obtain the necessary #00. physical properties required in order to withstand the rough handling of wool bales during transportation and 15 storage. The coextruded film comprises a first outer layer of high stiffness plastics material, a second inner layer of high toughness plastics material forming a core or intermediate layer, and a third inner layer of easily weldable plastics material. A high density polyethylene 20 (HDPE) is employed for the outer skin of the coextruded film, whilst the core layer and inner skin are both linear low density polyethylene (LDPE). Holes (20) are provided in the sidewalls (14) of the bag to allow air to escape from within the bag both during pressing of the wool and during compression of the bale during handling and storage. 0