AU747177B2 - An improved multilayered material for forming a bag, and bags formed therefrom - Google Patents

Description

Y

p P00011 Regulation 3.2 Revised 2/98

AUSTRALIA

Patents Act, 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT TO BE COMPLETED BY THE APPLICANT NAME OF APPLICANT: ACTUAL INVENTOR: ADDRESS FOR SERVICE: PATRICK JOHN PRIMMER PATRICK JOHN PRIMMER Peter Maxwell Associates Level 6 Pitt Street SYDNEY NSW 2000 INVENTION TITLE: DETAILS OF ASSOCIATED

APPLICATION(S):

AN IMPROVED MULTILAYERED MATERIAL FOR FORMING A BAG, AND BAGS FORMED THEREFROM Divisional of Australian Petty Patent No. 719,589 (65,574/99) filed on 23 December 1999 The following statement is a full description of this invention including the best method of performing it known to me:- 2 The present invention relates to an improved multilayered material for forming a bag, and bags formed therefrom, particularly wool bags, but not excluding other bags.

Wool is conventionally carried in containers known as wool bags, and the filled wool bags are referred to as bales. Importantly, the wool bales should contain the wool in a compact and reasonably regular box like shape, which allows the bales to be stacked for economical and safe transport and storage.

They should have a static surface friction with each other that is sufficient to *prevent slippage of the stacks and to resist slipping from trucks during 10 transport. They should also have a dynamic surface friction against polished steel, which is low enough to prevent excessive heat build up during dumping, a process which is to be described in detail later.

Wool bags were traditionally made from material which was woven from jute yarns, but they are currently made from material which is woven from 15 either polyethylene split tape fibre yarns or nylon continuous multifilament yarns.

Woven wool bags have a substantial disadvantage, in that, whenever the bags are torn or cut or punctured, some fibres from the bag material can contaminate the wool.

The wool bags are punctured, sometimes accidentally, but often deliberately in the course of handling the bag or to test or to process the contents.

Some examples of deliberate punctures are as follows: a) To sample the wool, as is required for sale, some bags are cut and some wool fibres are removed from the bales.

b) To insert rods to hold down the wool in the baling press while the flaps of the bag are fastened.

c) By manual handling of bales with bale hooks.

d) To open the bales for removal of the wool for further processing.

Once the wool is contaminated with any fibre, particularly fibres with similar dimensions to the wool fibre, it is difficult and often impossible to separate the contaminating fibres from the wool fibres. This contamination often results in considerable devaluation to the final wool fabric.

If cut, torn or punctured, polyethylene split tape fibre has a strong tendency to fibrillate further, causing individual polyethylene fibres to contaminate the wool.

10 Polyethylene is non- substantive. This means that it does not attract, adsorb, nor retain dyes from solution. Therefore, when the wool is dyed, the polyethylene remains it original colour, which mostly contrasts with the dyed causing a conspicuous mark.

If cut, torn or punctured, nylon continuous multifilament tends to be 15 retained in the woven material of the bag, thereby minimising contamination of the wool.

~Nylon is substantive. This means that it does attract, adsorb and retain .some dyes from solution. Furthermore, it is substantive to a considerable number of dyes used to dye wool, and can be dyed with these dyes under similar conditions to those that are typically used to dye wool.

Although nylon is substantive, when dyed in the same dye bath as wool different colours usually occur, as the nylon initially adsorbs the dye more readily than the wool, and in light shades dyes to a deeper shade than the wool, but the nylon quickly saturates with the dyestuff, whereby the wool continues to adsorb dyestuff and builds to deeper shades than the nylon. The colour differences that result from nylon fibre contamination of the wool are tone in tone, and mostly, relatively inconspicuous.

Although a woven nylon bag is less likely to contaminate the wool, and as such contamination, when it occurs, is less likely to decrease the value of the wool, the woven nylon bags are about four to six times more expensive than the woven polyethylene bags. The use of woven nylon bags in place of woven polyethylene bags results in added expense to the wool producer.

When wool is baled at or near the shearing shed, it is compressed into the bags with a small press. Usually, the press has a capacity of a few tonnes force. This allows the wool to be economically handled and transported to larger centralised stores.

S 10 Once in these centralised stores, in order to reduce the space required for storage and shipping, the bales are further compressed to reduce their volume. This is done by a process known as dumping. The dump, usually, but not necessarily, compresses the bales in a three to one ratio.

The dump usually has over seven hundred tonnes of clamping force, so 15 that this high compression ratio can be obtained quickly. It is constructed so that at least three bales can be placed end to end in a cavity, so that all four sides of all bales and the outside ends of the end bales are constrained by the dump. The ends of the dump are then pushed together and steel straps are wrapped around the dumped bales and fastened so that the compression is retained on ejection from the dump.

The surface of the wool bag closest to the moving platen of the dump can move up to three metres in about one second. This results in considerable build up of air pressure in the bags, causing the bags to rub on the sides of the dump with considerable pressure. This pressure combined with the speed of the bag over the surface of the dump can, and often does, generate enough heat to melt the surface of the polyethylene bags.

The actual temperature generated at any point varies greatly, depending on the air pressure differences between the inside and outside surfaces of the bag during the dumping stroke, the surface speed of the bag relative to the contact points with the dump, the inherent coefficient of friction between the surface of the dump and the bag, the outward force exerted on the inside surfaces of the bag by the wool in the bags, the friction of the wool on the inside surfaces of the bag, and the initial and ambient temperatures of the bag, the dump and the air.

Attempts have been made to make wool bags from polyethylene film.

10 This film was made from a similar grade of polyethylene to that used to make the woven polyethylene bags. Both woven polyethylene and polyethylene film bags have a melting point of about 1300C.

In the dumping process, the polyethylene film bags often melt and explode, whereas the woven polyethylene bags, although showing some minor 15 surface melting, do not fail. The failure of polyethylene film bags is attributable generally to extra heat being generated and/or extra forces being applied to the bag and/or lower strength of the bag.

In particular, the failure may be due to: r r r a) b) c) d) e) f) g) between the The heat generated in dumping being excessive.

The temperature resistance of the bag material being inadequate.

The tear propagation of the bag material being inadequate.

The puncture resistance of the bag material being inadequate.

Minor surface melting resulting in destruction of the bag.

Effective ventilation of the bag being inadequate.

The surface contact area of the sticky molten polyethylene bag and the dump being much greater in the case of the smooth surface of the film than in the case of the textured surface of the woven fabric, consequently, greater frictional forces are generated.

In order to achieve sufficient reliability and speed during the dumping process, it is important that the temperature resistance of the bag be greater than the heat generated when dumping at economical speed and compression.

It is an object of the present invention to provide a wool bag which is cheaper to make than a woven nylon bag, does not degrade the wool with contamination, withstands the dump, and has suitable puncture and tear propagation resistance. Preferably, the wool bag should retain a good shape 10 for stacking, have suitable surface friction to prevent slipping when stacked or transported, be recyclable, be transparent, and be able to be durably marked by marking pens.

In order to withstand the dump, both for wool bags and for other bags, it is essential that the air must escape from the bag quickly, easily and uniformly, 15 so that the pressure difference between the inside and outside surface of the bag does not press the surface of the bag against the walls of the dump with sufficient force to generate enough temperature to cause failure of the bag.

It is also important that the surface of the bag be such that localised melting at contact points, if it occurs, will not cause a failure of the bag.

According to the present invention, there is provided a multilayered material for forming a bag, including: a) a first film adapted to be the outside surface film of the bag, said first film including: i) an outer first layer of a polymer having a melting point above about 1600C, and ii) an inner second layer of a polymer having a melting point which is lower than that of the outer first layer, b) a second film adapted to be the inside surface film of the bag, said second film including: i) an inner third layer of a polymer having a melting point which is lower than that of the outer first layer, ii) an outer fourth layer of a polymer having a melting point below the melting point of the outer first layer of the first film, but above the melting points of the inner second and third layers of the first and second films respectively, and Sc) a reinforcing means laminated between the first and second films, with the inner layers of each of the first and second films bonded to respective B opposed sides of the reinforcing means and to each other through the reinforcing means.

The outer layer of the first film has a melting point above about 16 0 0C so as to resist the frictional heat generated in the dump. Preferably, the outer 15 layer of the first film is also of a nature that it can be easily and durably written on with standard felt tip marking pens such as TEXTA(TM) pens.

The inner layer of the first film has a melting point which is lower than that of the outer first layer in order to assist in lamination of the two films and the reinforcing means. This melting point should ideally, but not necessarily, be the same as that of the inner layer of the second film. The inner layers of the first and second films should be preferably easily fusible or weldable to each other as well as being preferably able to bond to the reinforcing means at temperatures and pressures that will not harm the outer layers of either film, nor harm the reinforcing means.

The outer layer of the second film has a melting point below that of the outer layer of the first film, but above the melting point of the inner layers of the first and second films so that the outer layer of the second film can be easily 8 fusible or weldable to itself at a temperature and pressure that will not harm the outer layer of the first film, nor harm the reinforcing means.

The inner layer of the second film has a melting point which is lower than that of the outer layer of the first film in order to assist in lamination of the two films and the reinforcing means. This melting point should ideally, but not necessarily, be the same as that of the inner layer of the first film.

The reinforcing means is preferably a reinforcing mesh, net or fabric and should preferably be strong enough to prevent tears from propagating under the range of conditions typically encountered when handling wool bales.

When reinforcing mesh is used, the mesh typically has intersecting strands or yarns referred to as "warp" and "weft" yarns. Where warp and weft yarns cross, large bumps or "nodes" are formed by fusion of the crossing material. These modes should be large enough to leave raised bumps on the outside surface of the first film after laminating.

Optionally, a fourth component with nodes could be added between the .reinforcing means and the first film if the reinforcing means is so smooth so as not to give the desired bumpy surface to the outside of the first film.

Preferably, but not necessarily, all layers of both films and the reinforcing means should be compatible with each other in their molten state, possibly with the aid of compatiblisers, so that the bags can be easily recycled.

This lamination should preferably be done by the application of heat and pressure, controlled so that none of the outer layers, nor the reinforcing means, is harmed, but so that both films and the reinforcing means are firmly and permanently bonded together.

This resultant final material should preferably be perforated to allow the passage of air from inside the bags to outside the bags so as to minimise the 9 pressure difference between the inside and outside surface of the bags during the dumping process.

According to another aspect of the present invention, there is provided a bag constructed from the multilayered material as aforementioned, and preferably a wool bag constructed therefrom.

A sample structure of a preferred wool bag of the present invention is as follows: a) The outer layer of the first film, being the outside surface of the **bag, comprises a polymer having a melting point above the maximum expected 10 dumping temperature, and is preferably nylon, and may be either nylon 6, nylon 6.6 or nylon 666 or a blend of these. The melting point of these polymers is typically over about 1800C.

If nylon is used, it need only be thick enough to provide a constant or continuous surface, but may be thicker if necessary to aid economical 15 production or improve tear strength. Even if the thickness of the nylon is o° increased to aid economical production, it will still be relatively thin, and will only be a small fraction to the nylon otherwise required for woven nylon bags.

As nylon is an expensive polymer, this results in substantial cost savings.

b) An optional middle layer of the first film is of a cheaper material than the other layers, possibly of recycled material. This middle layer might be used to add cheap bulk or strength, to help balance out curl of the film, to help hold up the other layers when making the film or to help in bonding the various essential or functional layers together.

c) The inner layer of the first film comprises a polymer having a lower melting point than that of the outer layers of the first and second films.

The melting point of this layer is typically about 900C. This polymer might be single site metalocene low density polyethylene, or Surlyn T M or Primacore TM single site metalocene low density polyethylene, or Surlyn

M

or Primacore or other polymer that will bond to itself and to the reinforcing means, without damaging the reinforcing means or outer layers of the first or second films.

d) The reinforcing means may be a Netion T M type mesh made from polypropylene. This type of mesh is typically used for making bags for fruit, such as oranges or the like. Such a mesh is typically formed by extruding a number of monofilaments of a thermoplastic polymer simultaneously from each of two concentric round dies. These dies are rotated in opposite directions, so that the filaments from each die cross each other whilst still molten and therefore fuse or weld together. On cooling, the resultant mesh is then re- 10 heated and stretched in both longitudinal and lateral directions. This stretching is to line up the molecules of the filaments and consequently improve their strength. A further consequence of this stretching process is that the filaments are drawn down to about one third of their original cross sectional area, but the material at the cross over points does not draw down nearly as much, thereby 15 leaving a pronounced bump or node at that point. The mesh of this type is typically made from polypropylene, but could be made from polyethylene or nylon. The melting point of the reinforcing means should be over about 1300C.

When reinforcing mesh is used, it is multifunctional in a perforated wool bag material. It serves to: i) Prevent tears or punctures from propagating, particularly punctures created while using bale hooks.

ii) Create nodes on the outside surface of the bag. These nodes, in turn, assist the air to flow through the perforations then to escape between the outside surface of the bag and the typically polished steel walls of the dump. These nodes also serve to enhance the surface friction characteristics, in that they act as studs when applied to a soft surface, digging into that surface to improve grip. This helps 11 stabilise stacks of bales. The nodes also act as slides when applied to a polished hard surface by assisting the bags to slide in the dump without causing a failure of the bag.

A knotted net could be used in place of the Netlon T M as could a woven fabric, but to date, only Netlon T M type products provide reinforcement, dimensional stability, gaps or windows for bonding the first and second films together, and nodes, all in the one product.

e) The inner layer of the second film comprises a polymer having a **lower melting point than that of the outer layers of the first and second films.

10 The melting point of this layer is typically about 900C. This polymer might be TM TM Ssingle site metalocene low density polyethylene, or Surlyn T M or Primacore

TM

or other polymer that will bond to itself and to the reinforcing means, without S.damaging the reinforcing means or outer layers of the first or second films.

f) An optional middle layer of the second film is of a cheaper material than the other layers, possibly of recycled material. This middle layer might be used to add cheap bulk or strength, to help balance out curl of the film, to help hold up the other layers when making the film or to help in bonding ***the various essential or functional layers together.

g) The outer layer of the second film, being the inside surface of the bag, comprises a polymer having a melting point below that of the outer layer of the first film and that of the reinforcing mesh, but above that of the inner layers of the first and second films. The melting point of this layer is typically about 110"C. This polymer is preferably linear low density polyethylene.

h) The above structures may be firmly bonded together using tie or adhesive layers as required.

The above structure may be made by three possible methods, these being: a) Taking the first and second films described above, both films being co-extruded blown film, and placing the reinforcing mesh layer between them, so that the inner layers of each film face each other through the reinforcing mesh, then applying heat and pressure, typically via soft rubber coated and heated rollers, so that the three layers are firmly bonded together with the reinforcing mesh securely encapsulated between the first and second films.

10 b) Introducing the reinforcing mesh directly into a film casting line, so that the various layers of film are cast directly onto each other and directly onto the reinforcing mesh as required.

;22 c) Taking the first and second films described above, both films being co-extruded cast film, and placing the reinforcing mesh layer between 15 them, so that the inner layers of each film face each other through the °reinforcing mesh, then applying heat and pressure, typically via soft rubber coated and heated rollers, so that the three layers are firmly bonded together with the reinforcing mesh securely encapsulated between the first and second films.

The use of two multilayer films bonded together and encapsulating a preferred reinforcing mesh provides a material for forming a bag which is surprisingly strong and tear resistant.

An additional advantage of the preferred multilayered material of the present invention is that it may provide a transparent bag, so that it is possible to have some view of the contents without opening the bag. This assists the buyers of wool bales in readily assessing the quality of the contents of the bag.

13 The preferred studded surface texture, which results from the film encapsulation of the reinforcing mesh, has the added advantage that it increases the surface friction when placed on a soft, textured or rough surface where the studs or nodes can grip, but it reduces the surface friction when placed on hard smooth surfaces, such as the sides of the dump.

In order that the invention will be readily understood and put into practical effect, reference will now be made to the accompanying drawings, in which: Fig 1 is a schematic representation of a portion of a multilayered S 10 material for forming a wool bag according to a preferred embodiment of the present invention, Fig 2 is a sectional side view through X-X of Figure 1 cross-sectionally showing the nodes formed at the cross over points of the warp and weft yarns of the reinforcing mesh, and the film layers; 15 Fig 3 is a sectional side view through Y-Y of Figure 1 cross-sectionally showing the warp or weft yarns, and the film layers, and Fig 4 is a side view of a portion of the multilayered material of Figs 1 to 3 forming a wool bag and pressed against a plate of a dump during the dumping process.

The multilayered material 10 of Figs 1, 2 and 3 for forming a wool bag has a reinforcing mesh 12 which is encapsulated or sandwiched between two multilayer films 14, 16. The mesh 12 is formed from Netlon T M and comprises a grid of warp and weft yarns or strands 18, 20 intersecting at right angles.

Enlarged nodes 21 are formed where the strands 18, 20 intersect and are fused together at fused regions 23.

The first multilayer film 14 comprises an outer layer 22 of nylon and an inner layer 24 of single site metalocene low density polyethylene and an intermediate tie layer 26 formed from a material that can be bonded to both the nylon layer 22 and the single site metalocene low density polyethylene layer 24. The outer layer 22 of nylon is adapted to serve as the outside surface film of the bag.

The second multilayer film 16 comprises an outer layer 28 of linear low density polyethylene and an inner layer 30 of single site metalocene low **density polyethylene and an intermediate tie layer 32 formed from a material 10 that can be bonded to both the linear low density polyethylene layer 28 and the single site metalocene low density polyethylene layer The layers 24 and 30 of single site metalocene low density polyethylene can be heat activated to seal or fuse together at about 850C and they are bonded together through the windows 33 or between the squares of the mesh 12 taking care to minimise or preferably eliminate all gaps or channels between the first film 14, second film 16 and the mesh 12. Because the presence of the mesh 12 tends to keep the films 14 and 16 apart, particularly near the nodes 21 and alongside the strands 18,20, pressure should be applied by a soft surface that will yield and force the films 14 and 16 to bond fully with no gaps, so as to ensure that there is complete surface contact of the films 14, 16 along the full length and breadth of the strands 18, With reference to Figure 4, the material 10 has numerous apertures or holes 13 pierced therethrough so that air can pass between the inside and outside of the bag 40, particularly when the bag 40 contains wool 41 and serves as a wool bale.

For the purposes of compression, usually three bales, although the number may vary, are compressed into one bale. All sides of the end to end arranged bales are constrained by strong steel plates 42 of a dump, and the end plates are closed together to compress the wool bales.

During this process, the material of the wool bag of the present invention is not pressed flush against its adjacent plate 42 because the nodes 21 hold parts of the surface of the bag 40 away from the steel plates 42 of the dump creating potential air flow space 44. Some of the air contained within the wool bale can escape through the holes 13 of the material and then flow in the space 44 between the steel plates 42 and the outside surface of the bag.

o:oo As this situation is dynamic, not all air will escape instantly, causing 10 some varying pressure inside the bag, and some varying pressure in the space 44. However, the air pressure momentarily built up in the space 44 will act in part against the air pressure inside the bag 40, as both air pressures build up, S. then dissipate. This will have the effect of reducing the pressure that the surface of the material 10 of the bag 40 exerts on the steel plate 42, thereby 15 reducing heat generation from friction and also preventing explosion of the bag Various modifications may be made in details of design and construction without departing from the scope or ambit of the invention. without departing from the scope or ambit of the invention.

Claims (3)

1. A multilayered material for forming a bag, including: a) a first film adapted to be the outside surface film of the bag, said first film including: i) an outer first layer of a polymer having a melting point above about 160'C, and ii) an inner second layer of a polymer having a melting 609 0.. o point which is lower than that of the outer first layer, 0060 s sb) a second film adapted to be the inside surface film of the bag, csaid second film including: i) an inner third layer of a polymer having a melting point which is lower than that of the outer first layer, Sii) an outer fourth layer of a polymer having a melting point below the melting point of the outer first layer of the first film, but above the melting points of the inner second and third layers of the first and second films respectively, and 9*00 c) a reinforcing means laminated between the first and second films, with the inner layers of each of the first and second films bonded to respective opposed sides of the reinforcing means and to each other through the reinforcing means.

2. The multilayered material of claim 1 wherein the reinforcing means is mesh, the mesh comprising intersecting strands that are fused together at their cross over locations to form nodes that present raised bumps on the outside surface of the first film. 17

3. The multilayered material of claim 1 or claim 2 wherein the material is perforated to allow the passage of air between the inside and outside of the bag formed by the multilayered material. Dated this 8th day of August 2000 PATRICK JOHN PRIMMER Patent Attorneys for the Applicant 0006 PETER MAXWELL ASSOCIATES 0* 0 0 0 *0. 0 0 0 S