AU2003200681B2

AU2003200681B2 - A multiwall sack

Info

Publication number: AU2003200681B2
Application number: AU2003200681A
Authority: AU
Inventors: Larry Challis
Original assignee: Opal Packaging Australia Pty Ltd
Current assignee: Opal Packaging Australia Pty Ltd
Priority date: 2002-03-04
Filing date: 2003-02-26
Publication date: 2006-11-02
Anticipated expiration: 2023-02-26
Also published as: AU2003200681A1

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Applicant(s): AMCOR LIMITED A.C.N. 000 017 372 Invention Title: A MULTIWALL SACK The following statement is a full description of this invention, including the best method of performing it known to me/us: 2 A MULTIWALL SACK The present invention relates to a multi-wall sack.

The multi-wall sack of the present invention has been developed to address the needs of the cement industry to have a cement sack that can be filled and distributed without generating as much dust as the current cement sack.

The term "multi-wall sack" is understood to mean herein that the wall of the sack is made up of a plurality of layers of material.

The conventional cement sack is constructed from two or more outer layers of kraft paper and one inner layer of polyethylene film. The kraft paper is permeable to water and air. The polyethylene film is impermeable to water and air and is used to provide a moisture barrier.

The conventional cement sack is filled with cement by a process that fluidises cement with air and then pumps the fluid mixture into the sack through a valve located in a corner of one end wall of the sack.

In order to enable air to escape from this fluidised mixture of cement and air the sack is manufactured with perforations in the polyethylene film and the kraft paper layers. Without these holes the sack will not fill quickly and will not fill to an accurate cement weight.

The current cement sack has been available for several decades and is deficient for several reasons. For example, the polyethylene moisture barrier is compromised by the perforations. In addition, the perforations in the IND- 3 polyethylene film and kraft paper layers allow cement dust to escape from the sack while filling the sack and this o can make the environment in the filling plant quite dusty.

An object of the present invention is to provide an improved cement sack.

00 C In broad terms the present invention provides a e multi-wall sack that includes side walls and end walls, a substantial part but not all of the area of the side walls being impermeable to water and air, and the area that is not water/air impermeable and is water/air permeable being at least substantially confined to a section or sections of the side walls that can form a bottom wall of the sack when the sack is filled with product, such as cement, and sealed and placed with other filled sacks in one row of a stack of sacks, whereby the top wall or walls of one or more filled sacks in an underlying row of sacks can form a water impermeable barrier for the bottom wall of the sack.

In more specific terms, according to the present invention there is provided a multi-wall sack that includes side walls and end walls, wherein the side walls include at least two layers and the layers include: a layer that is permeable to water and air; and a layer that includes an area that is impermeable to water and air, whereby the area that is water/air impermeable covers a substantial part but not all of the area of the side walls, whereby the remaining area of the side walls is at least substantially confined to a section or sections of the side walls that can form a bottom wall of the sack when the sack is filled with H,\angelal\keep\GRM4 Speci\Amcor\A MULTIWALL SACK Amendments.doc 12/10/06 IND- 4

O

product and sealed and placed with other filled sacks in one row of a stack of 0 sacks, and whereby the top wall or walls of one or more filled sacks in an underlying row of sacks can form a water impermeable barrier for the bottom wall of the sack.

00 C The above-described sack can allow air to escape p from the sack during and after the sack has been filled S 10 with material.

Consequently, the above-described sack fulfils the conflicting requirements of providing a sack that can allow air to escape from the sack during and after the sack has been filled with product, such as cement, and prevent moisture from entering the sack and damaging the product in the sack.

The sack is particularly suited for "dusty" materials such as cement and other powdered materials. In this context, whilst the sack is permeable to air while it is being filled with product and prior to the sack being placed in the above-described stack, the location of the impermeable and permeable areas of the sack makes it possible to minimise release of powdered product compared with the conventional cement sack.

The above-described sack does not require perforations in water/air impermeable material in order to allow air to escape from the sack after the sack has been filled with material as is required in the abovedescribed current cement sack.

Preferably the water/air permeable layer is made from water/air permeable material.

The water/air permeable material may be any Hs\ange~a1\keep\GRM Speci\A.Cer\A MULTIWALL SACK -Aendrentsdoc 12/10/06 5 suitable material for a multi-wall sack.

One, although not the only, suitable water/air permeable material is kraft paper.

Alternatively, the water/air permeable layer (a) may be made from water/air impermeable material that includes perforations.

The water/air impermeable material may be any suitable material for a multi-wall sack.

One, although not the only, suitable water/air permeable material is polyethylene.

Preferably the water/air impermeable area is selected so that the remaining area of the side walls is sufficient to allow air to escape from the sack while the sack is being filled with product or within a predetermined short period of time after the sack has been filled with material.

Layer may only comprise the water/air impermeable area, whereby the layer does not cover all of the side walls.

Alternatively, layer may cover all of the side walls and includes the water/air impermeable area and an area of water/air permeable material or water/air impermeable material that includes perforations.

The water/air impermeable area may be made from any suitable water/air impermeable material for a multiwall sack.

Alternatively, the water/air impermeable area may be made from any suitable water/air permeable material for 6 a multi-wall sack that is treated chemically to be water impermeable.

Preferably the end walls of the sacks are impermeable to water.

The end walls of the sack may include the abovedescribed layers and with the water/air impermeable area of layer covering the end walls.

In any given situation, the selection of the water/air permeable and impermeable materials will depend on cost and end-use application issues.

The sack may include more than two layers.

Preferably the sack is a cement sack.

According to the present invention there is also provided a stack of the above-described sack, the stack having a plurality of rows of the sacks and each row including a plurality of the sacks, with the top walls of the sacks in one row forming a water impermeable barrier for the bottom walls of the sacks in the next higher row of the stack.

The present invention is described further with reference to the accompanying drawings, of which: Figure 1 is a partially cut-away perspective view of a conventional cement sack; Figure 2 is a partially cut-away perspective view of one embodiment of a sack in accordance with the present invention; Figure 3 is a cross-section along the line 3-3 of 7 Figure 2; and Figure 4 is a side elevation of a stack of a plurality of the sack shown in Figures 2 and 3 on a pallet.

The following description is in the context of cement sacks.

The present invention is not limited to this enduse application and extends to sacks for any materials that require storage in water resistance sacks.

With reference to Figure 1, the conventional cement sack, generally identified by the numeral 3, is generally quadrilateral in two mutually perpendicular directions and has side walls 5 and end walls 7.

The sack 3 also includes a valve 21 for filling the sack located in a corner of one end wall 7 of the sack 3.

The sack is a multi-wall construction with the following layers of material starting with the outermost layer and moving inwardly to the innermost layer: kraft paper 9, kraft paper 11, polyethylene film 13, and kraft paper 17.

The kraft paper is a water/air permeable material and the polyethylene is a water/air impermeable material.

The sack 3 also includes pinholes, generally identified by the numeral 15, in the kraft paper layers 9, 11, and 17 and the polyethylene film layer 13 that form the side walls 5 of the sack 3. The pinholes 15 are provided to allow air to escape from the sack 3 during and after filling the sack 3 with a fluidised mixture of cement and air.

8 As discussed above, the pinholes 15 are essential to allow efficient filling of the sack 3 with cement to a required cement weight. However, the pinholes 15 are a disadvantage because they allow cement to escape via the holes into the cement filling plant and thereby create a dusty environment and compromise the water resistance barrier provided by the polyethylene film. In addition, the pinholes 15 make the sack 3 permeable to moisture, with the result that the quality of the cement in the sack may be adversely affected.

The embodiment of the sack in accordance with the present invention shown in Figures 2 and 3 is the same general shape as the conventional cement sack shown in Figure 1.

Specifically, the sack 3 shown in Figures 2 and 3 includes side walls 5 and end walls 7 and a valve 21 in a corner of one end wall 7.

The sack 3 is also a multi-wall construction for the side walls 5 and the end walls 7, save for the area of the side walls 5 that in use forms the bottom wall of the sack in the orientation shown in Figures 2 to 4.

Specifically, save for the area of the side walls that in use forms the bottom wall of the sack in the orientation shown in Figures 2 to 4, the side walls 5 and end walls 7 of the sack 3-include the following layers from the outermost layer to the innermost layer: kraft paper 23, kraft paper 25, polyethylene film 27, and kraft paper 29. As is indicated above, the kraft paper is a water/air permeable material and the polyethylene is a water/air impermeable material. Each of these layers of kraft paper and polyethylene film has no perforations.

Thus, this area of the side walls 5 is impermeable to 9 water and air.

The area of the side walls 5 that forms the bottom wall of the sack in the orientation shown in Figures 2 to 4 has the above-described layers of kraft paper but does not include the above-described layer of polyethylene film. Thus, this area of the side walls 5 is permeable to water and air. Thus, air can escape from the sack 3 via the bottom wall while the sack is being filled with a fluidised mixture of cement and air.

In addition, with the above-described sack 3, all round protection to water penetration is achieved by stacking filled sacks on top of each other as shown in Figure 4 whereby the polyethylene film layers of the top walls of the sacks 3 of one layer in effect form water barriers for the bottom walls of the sacks 3 placed on top of these sacks.

Many modifications may be made to the preferred embodiment of the present invention described above without departing from the spirit and scope of the present invention.

By way of example, in an alternative, although not the only of embodiment of the present invention, the sack is a multi-wall construction with a plurality of layers, each of which forms the side walls and end walls of the sack, with one of the layers being formed from a water impermeable material that has perforations in an area that in use forms the bottom wall of the sack in the orientation shown in Figures 2 to 4

Claims

2. The sack defined in claim 1 wherein the water/air permeable layer is made from water/air permeable material.
3. The sack defined in claim 2 wherein the water/air permeable material is kraft paper.
4. The sack defined in claim 1 wherein the water/air permeable layer is made from water/air impermeable material that includes perforations. The sack defined in claim 4 wherein the water/air H.\anea\keep\GR4 Speci\Amcor\A MULTIWALL SACK Anendmenta.doc 12/10/06 11 e< impermeable material is polyethylene. 0 6. The sack defined in any one of the preceding claims wherein water/air impermeable area of layer is selected so that the remaining area of the side walls is sufficient to allow air to escape from the sack while the 00 sack is being filled with product or within a short 0 predetermined time after the sack has been filled with (N material. C
7. The sack defined in any one of the preceding claims wherein layer only comprises the water/air impermeable area, whereby the layer does not cover all of the side walls.
8. The sack defined in any one claims 1 to 6 wherein layer covers all of the side walls and includes the water/air impermeable area and an area of water/air permeable material or water/air impermeable material that includes perforations.
9. The sack defined in any one of the preceding claims wherein the end walls of the sacks are impermeable to water. The sack defined in claim 9 wherein the end walls of the sack include the layers and with the water/air impermeable area of layer covering the end walls.
11. A multi-wall sack includes side walls and end walls, a substantial part but not all of the area of the side walls being impermeable to water and air, and the area that is not water/air impermeable and is water/air permeable being at least substantially confined to a section or sections of the side walls that can form a bottom wall of the sack when the sack is filled with H:\angelal\keep\GRM Speci\Amcor\A MULTIWALL SACK Amendments.doc 12/10/06 IN 12 eg product and sealed and placed with other filled sacks in Sone row of a stack of sacks, and whereby the top wall or 0 walls of one or more filled sacks in an underlying row of sacks can form a water impermeable barrier for the bottom wall of the sack. 00 12. A stack of a plurality of the sacks defined in C any one of the preceding claims, the stack having a plurality of rows of the sacks and each row including a plurality of the sacks, with the top walls of the sacks in Sone row forming a water impermeable barrier for the bottom walls of the sacks in the next higher row of the stack.
13. A multi-wall sack substantially as hereinbefore described with reference to the accompanying drawings.
14. A stack of a plurality of the sacks substantially as hereinbefore described with reference to the accompanying drawings. H,\angelal\keep\GRM Speci\Amcor\A MULTIWALL SACK Amendmente.doc 12/10/06