GB1592386A

GB1592386A - Multiwall bags

Info

Publication number: GB1592386A
Application number: GB3685177A
Authority: GB
Original assignee: ST Regis Paper Co
Current assignee: ST Regis Paper Co
Priority date: 1976-09-01
Filing date: 1977-09-02
Publication date: 1981-07-08

Description

(54) IMPROVEMENTS RELATING TO MULTIWALL BAGS (71) We, ST. REGIS PAPER COM- PANY, a Corporation organised and existing under the laws of the State of New York, United States of America, of 150 East 42nd Street, New York, New York 10017, United States of America do hereby declare the invention for which we pray that a Patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to multiwall bags, packages formed from such bags, and methods for producing such bags.

It is known in the art to provide so-called "breakaway pouch bags", such as those disclosed in S. Patents Nos. 3,807,626, 3,910,488 and 3,958,749.

The first two of the above mentioned Patents disclose open end, pinch bottom, multiwall bags having an inner ply of heat sealable plastics material, such as polyethylene, and one or more outer plies of a non-heat sealable material, such as paper or equivalent. The plastics inner ply is lightly bonded at both bag ends to the contiguous outer ply for manual detachment therefrom. The plastics ply is heat sealed to closure at the lower bag end and folded over with the outer plies and the latter adhered to the opposite bag wall in a pinch bottom end closure. At the upper, open bag end, after commodity filling, the plastics ply is also heat sealed to closure and folded over with the outer plies, and the latter sealed against the opposite bag wall also in a pinch type end closure, forming a bag having an inner pouch enclosed within an outer pouch.

Owing to the light bonding action between the plastics inner ply and the contiguous outer ply, the outer plies of the bag may be opened and the latter stripped from the inner ply, leaving intact-the inner ply that is heat sealed at both ends and that contains the so packaged commodity. Bags of such construction constitute effective breakaway inner pouch bags. However, stripping away the outer plies must be done carefully in order to prevent rupture of the inner pouch and this may be difficult, especially at the corners of gusseted bags. Further, the opening of such bags involves the destruction of the outer plies of material.

The bags of Patent No. 3,958,749 similarly emply an inner ply of heat sealable plastics material and one or more outer plies of non-heat sealable material, such as paper or equivalent, and have a bottom end closure similar to that above described for the first two Patents. At the open bag end, however, the plastics ply is peripherally perforated below the area of bonding of the plastics ply to the contiguous outer ply. The open bag end is closed after commodity filling by heat sealing the plastics ply below the line of perforations and by closing the outer plies above the line of perforations.

The filled bag is opened at the bottom closure in the outer plies, for example, by means of a tear cord, and the inner ply may be withdrawn intact with its sealed in packaged contents by tensional severance along said line of perforations. Bags of such construction similarly constitute effective breakaway pouch bags as aforesaid. The production of bags of this construction, however, involves the provision of perforating equipment on a bag tubing machine for the film and requires precise registration and regulation of depth of perforations. Also, during closing, the bag must be folded accurately at the open end after filling, as uneven sealing and folding can cause the bag to be sealed above the perforations and result in leakage of the packaged commodity out of the inner pouch.

It is also known in the art to insert in an open end multiwall bag, a plastics pouch which is then filled with a commodity to be packaged, such as powdered dry milk. The pouch is then closed, e.g. with a tie cord, and the open end of the bag is closed, for instance by sewing. However, this procedure involves expensive manual operations of inserting a pouch in each bag and closing the pouch and the bag after filling, etc.

The present invention seeks to provide a multiwall bag that at least partly overcomes the disadvantages of the above-discussed known bags and procedures.

Accordingly, one aspect of the present invention provides an open mouth, multiwall bag comprising an inner pouch and an outer pouch formed, respectively, from an inner tube of heat sealable material and an outer tube of non-heat sealable material, the tubes being such that the inner tube is capable of being heat sealed to closure by the application of heat and pressure to the outer tube with the resulting heat sealed region being capable of being severed by scoring pressure applied to the outer tube, said inner and outer tubes being bonded to each other in respective zones of attachment at both ends thereof, the tubes being otherwise detached from each other, a portion of the inner tube adjacent to one end thereof and spaced inwardly from the associated zone of attachment having been heat sealed to closure by the application of heat and pressure to the outer tube with the resulting heat sealed region having been severed by scoring pressure applied to the outer tube, thus separating the inner tube into an upper portion that constitutes the inner pouch with a portion of said heat sealed region constituting a closure at the lower end thereof and a lower portion bonded to said one end of the outer tube, and said outer tube having been separately sealed to closure at said one end to form the outer pouch having a separate closure disposed beyond the closure of said inner pouch.

A bag in accordance with the invention thus comprises inner and outer pouches that are separately sealed closed by respective closures at one end thereof, with the opposite ends being open and constituting a mouth of the bag. The inner and outer pouches are secured to each other in the zone of attachment at the ends thereof opposite their respective closures, i.e. at the mouth of the bag, but are otherwise detached from each other.

The open ends of the inner and outer pouches may be separately sealed closed to produce respective closures in a manner similar to that in which the closures were formed at said one ends thereof. Thus, after a bag in accordance with the invention has been filled via the mouth with a commodity to be packaged, the inner pouch into which the commodity is thus charged may be heat sealed to closure in a region adjacent to said mouth and spaced inwardly from the associated zone of attachment by the application of heat and pressure to the outer pouch, and the resulting heat sealed region severed by scoring pressure applied to the outer pouch, for example by passing the outer tube transversely between a pair of bevelled pressure wheels, to seal the inner pouch closed and to sever completely the inner pouch containing the commodity from the outer pouch which is thereupon closed, for example in a sewn or pinch end closure.

As thus packaged, the commodity is contained within a completely sealed, sift and leak proof inner pouch which is in turn housed within a competely sealed outer pouch, providing dual protection of the commodity against contamination, insect penetration, etc. The inner pouch is completely unattached to the outer pouch and may be withdrawn therefrom with its sealed-in packaged contents by merely opening the outer pouch at one end. For this purpose the outer pouch may be provided with an "easy to open" feature such as a rip cord of a sewn end bag or a tear cord of a pinch bottom bag.

Hence, a further aspect of the invention provides a package formed from a bag embodying the invention, the inner pouch of said bag containing a substance and having been heat sealed to closure in a region adjacent to the opposite end thereof and spaced inwardly from the associated zone of attachment by the application of heat and pressure to the outer pouch, the resulting heat sealed region having been severed by scoring pressure applied to said outer pouch, and said outer pouch having been sealed to closure beyond the region of severance of said inner tube, whereby the inner pouch containing the substance is sealed closed at both ends and is completely detached from and disposed within the closed outer pouch.

In order to discharge the packaged contents from such a package, the outer pouch of the bag is opened at one end, for example by an easy to open feature as aforesaid, and the bag inverted whereupon the inner pouch with its sealed-in contents may be gravity dumped from the outer pouch in a manner similar to dumping a pillow from a pillow case, leaving the inner pouch and its contents intact and also leaving the outer pouch intact except for the opening at one end.

The outer pouch may thus be reused for other purposes, for example by trimming the end, refilling and closing with a sewn end.

The present invention thus eliminates the need to destroy the outer pouch in order to remove the inner pouch, as was the case with the bags disclosed in U.S. Patents Nos.

3,807,626 and 3,910,488. The invention further does not require the provision of perforating equipment and does not require accurate folding of the bag during closure, as with the bags disclosed in U.S. Patent No.

3,958,749.

In yet a further aspect, the present invention provides a method of producing a bag embodying the invention, which method comprises superimposing one or more plies of a non-heat sealable material on a ply of heat sealable material in laterally offset rela tion to form a stepped stack, each ply having a first pair of edges that are laterally offset with respect to those of the or each adjacent ply, and a second pair of opposed edges; bonding each ply to the or each adjacent ply in the stack at the ends of the plies adjacent to said second pair of edges, with said plies unattached intermediate said ends; bonding each ply to itself along the laterally offset edges to form the ply of heat sealable material into an inner tube disposed within an outer tube formed by said ply or plies of non-heat sealable material; heat sealing the inner tube to closure over a zone adjacent one end of the tube by heat and pressure applied to the outer tube; severing said inner tube in said heat sealed zone while hot by applying scoring pressure to said outer tube, thus forming an inner pouch; and closing said outer tube at said end beyond the region of severance of said inner tube, thus forming an outer pouch, whereby said inner pouch is attached to said outer pouch only in a region adjacent to the ends of the tubes opposite the closed ends of the tubes.

The invention will now be described by way of example with reference to the accompanying drawings, in which: FIGURE 1 is a perspective view of a multiwall, gusseted, pinch bottom bag of a preferred construction according to the invention as factory produced and supplied to a commodity packer; FIGURE 2 is a horizontal cross section taken on the line 2-2 of Figure 1, on an enlarged scale; FIGURE 3 is a vertical cross section on the line 3-3 of Figure 1, on a reduced scale; FIGURE 4 is a vertical section on a reduced scale, of an open-ended bag blank as produced on a conventional stepped end tuber, for conversion to a bag according to Figures 1 to 3; FIGURE 5 is a view similar to Figure 4 illustrating heat sealing of the inner ply of the blank adjacent to the lower end of the blank by means of hot compression bars applied to the outer ply of the blank; FIGURE 6 is a view similar to Figures 4 and 5 illustrating severance of the inner ply in the heat sealed zone of Figure 5 by means of bevelled compression rolls creasing or scoring the outer bag plies against the inner ply; FIGURE 6a is a part-sectional elevation, on an enlarged scale, of one of the compression rolls shown in Figure 6; FIGURE 7 is an enlarged, fragmentary, longitudinal sectional view of the bag of Figure 1 with the inner ply filled with a commodity and heat sealed at the open end thereof; FIGURE 8 is a view similar to Figure 7 after severance of the inner ply at the open bag end; FIGURE 9 is a similar view illustrating heat reactivation of a hot melt adhesive applied to the outer plies at the open bag end; FIGURE 10 is a similar view illustrating sealing of the outer plies at the open bag end betweenpressure rolls; FIGURE 11 is a schematic view in elevation of apparatus for automatically accomplishing in progressive sequence the closing operations illustrated in Figures 7 to 10; FIGURE 12 is a perspective view on a reduced scale, of a filled bag closed at both ends, illustrating opening of the outer plies by means of a tear cord at the initially closed bag end; FIGURE 13 is a fragmentary perspective view on a slightly larger scale, of the bag opened in this manner; FIGURE 14 is a perspective view on a similar scale to Figure 12 illustrating the withdrawal from the opened bag of Figure 13 of the inner pouch with its sealed-in packaged contents; FIGURE 15 is part-sectional elevation of a flat, pinch bottom bag in accordance with the invention having stepped plies at the bag ends; FIGURE 16 is a similar view of a gusseted, sewn end bag; FIGURE 17 is a similar view of a flat, sewn end gusseted bag; and FIGURE 18 a partial longitudinal sectional view on an enlarged scale, of each of Figures 16 and 17.

Referring to the drawings, Figures 1 to 3 illustrate a bag 10 comprising an inner tube, or pouch, comprising a single ply 11 of a heat sealable plastics material, such as polyethylene, and an outer tube, or pouch, 12 comprising a plurality of contiguous plies 13 to 16 of a non-heat sealable material, such as paper.

The lower end of C of the bag 10 is factory closed to form a pinch bottom closure, and the upper end 0 is left open to permit filling of the bag. The bag 10 further comprises a front wall F and rear wall R, with a pair of oppositely disposed gussets G1 and G2 interposed between the walls. At the open bag end 0, each gusset G1 and G2 has a front gusset portion A and a rear gusset portion B which is stepped up and exposed above the front gusset portion A thereof.

The bag further includes a rear wall portion C' which is stepped up and exposed above the rear gusset portion B. Further, at the open end 0, the outer bag plies 13 to 16 are progressively stepped up from the outermost to the innermost ply in the front wall and rear gusset portions, and are stepped up in the reverse order from the innermost to the outermost ply in the rear wall, thus exposing portions of the outer plies in the same ascending order from the front wall via the rear gusset portions to the rear wall. As can be seen, the inner plastics ply 11 is flush cut with the contiguous paper ply 13 in the front and rear walls at the upper end 0.

To enable closure of the outer plies of the bag at the open end 0, a hot melt reactivatable adhesive in a dormant state is preapplied to at least parts of the exposed regions of portions B and Cl, and optionally also to some of front wall plies, as indicated by stippling S. A suitable adhesive is a thermoplastic resin adhesive which may be a composition of polyethylene, wax and a tackifier, such as a rosin ester.

The bag 10 is made from an open ended bag blank 17 (Figure 4) produced on a conventional stepped end tuber. The inner plastics ply 11 of the blank 17 is circumferentially bonded at its opposite ends 18 and 19 to the contiguous paper ply 13, leaving the plastics ply detached therefrom throughout its intermediate zone extending between regions 20 and 21. The paper plies 13 to 16 are in turn circumferentially bonded to each other at both ends of the blank 17 by means of spot pasting. For example, as shown in Figure 1, plies 14 and 15 are bonded together by means of paste spots 22, and plies 15 and 16 are bonded together by means of paste spots 23. As can be seen, the lower end C of the blank has a stepped construction similar to that of the upper end 0 of the bag 10 and of the blank 17.

Referring to Figure 5, the first step in converting the bag blank 17 into the bag 10 involves transversely heat sealing to closure the inner plastics ply 11 over a zone 24 adjacent the lower end of the unattached intermediate zone thereof. The heat sealing is effected by means of a pair of aligned heated bars 25 and 26 that are moved towards each other to compress oppositely disposed walls of the outermost ply 16 of the blank 17. The bars 25 and 26 are raised to a sufficient temperature to heat the plasitcs ply 11 to the temperature of plasticity and fusion bonding in the zone 24. When the plastics ply 11 is made of polyethylene film in accordance with a preferred embodiment of this invention, the ply 11 is compressively heated in this manner in zone 24 to a temperature of about 1900C. to 2040C. for about 25 seconds at the lower end C of the bag, and to temperature of about 200"C. to 250"C. for about 8 seconds on closure of the open bag end 0, as discussed below.

Referring to Figure 6, immediately following the heat sealing of the inner ply 11 in zone 24, and while the ply 11 is still heated to plasticity in zone 24, the blank 17 is caused to be laterally traversed by a pair of bevelled compression rolls 27 and 2 , suitable dimensions for which are shown in Figure 6a. The rolls 27 and 28 are caused to bear against the outermost ply 16 of the blank 17 so as to crease or score the outer bag plies 13 to 16 with a compressive force sufficient to sever completely the zone 24 of the inner ply 11 at region 29, dividing the zone 24 into an upper end closure 24a and a lower end closure 24b and hence dividing the ply 11 into separate upper and lower sections ila and llb, respectively. A suitable compressive force is about 30 psi. The upper section 1 la thus constitutes a sack or pouch which is sealed to closure at its lower end by closure 24a, the section 1 la being attached to the contiguous paper ply 13 only in the region adjacent to the upper end 18 of the blank. The region of severance 29 is so disposed in the heat sealed zone 24 that the upper end closure 24a is of greater length than the lower end closure 24b in order to impart maximum sealing strength to the bottom closure of the upper section, or pouch, 1 lea of the inner ply 11.

The bag blank as thus fabricated is now ready for closure of the outer plies at its lower end, to form a sift and leak proof pinch bottom closure. Closure is effected by applying a hot melt adhesive, for example the adhesive mentioned above, to parts of the exposed portions of the stepped lower and C of the blank 17, as indicated by stippling S in Figure 6. The lower end C is then folded about transverse fold line X-X and about an interposed tear cord 32 (Figure 3) and the outer plies sealed against the opposite bag wall in the region 33 of Figure 3, pressure being applied as necessary.

The upper end 0 of the bag 10 is closed, after filling with a commodity to be packaged, by a procedure similar to that above described with reference to the lower end C.

Thus, referring to Figure 7, after the bag has been filled with a commodity 35 to be packaged, the inner ply 11 is heat sealed to closure in a zone 36 below the bonded region at end 18 by means of a pair of aligned hot compression bars 37 and 38 being compressed against oppositely disposed walls of the outermost ply 16 and being heated to a suitable temperature. Referring to Figure 8, the heat sealed zone 36 of the inner ply 11 is then severed in the region 40 to produce upper end closure 40a of the pouch 1 la by means of bevelled compression rolls 41 and 42 that have a similar construction and operation to the compression rolls 27 and 28 discussed above. The outer plies of the upper end are then closed by reactivating the hot melt adhesive S preapplied to portions of the open bag end as above discussed, by means of a hot air blast 43 as shown in Figure 9, folding the outer plies over about the fold line Y-Y, and sealing the outer plies against an outer wall of the bag by means of pressure rolls 44 and 45 (Figure huts, after the open end of the filled bag 10 has been closed in this manner, the packaged contents 35 will be completely sealed within the plastics pouch 1 1a, the ends of which have been heat sealed at end closures 40a and 24a, with the pouch 1 la being wholly detached from the closed outer pouch 12. Hence, when the outer plies of the bag are opened by manipulation of the tear cord 32 at the lower end C of the bag in the manner shown in Figure 12, providing an opening bounded by edges 12a and 12b (Figure 13), the heat sealed pouch 1 1a containing the commodity 35 can be discharged intact from the outer pouch (Figure 14) without additional injury or damage to the outer pouch 12. The outer pouch 12 remains sealed closed at the bag end 0, and thus constitutes an outer ply bag which may be used for other purposes.

The stepped gusset, stepped ply, pinch bottom lower and upper end closure construction of the outer pouch 12 of the bag 10 provides a sift and leak proof enclosure for the inner commodity-containing heat sealed pouch 2a. Hence, even if the latter should inadvertently be broken, for example as a result of rough handling or being dropped from excessive heights, the commodity will still be retained in the sift and leak proof casing formed by the completely sealed outer pouch 12.

Figure 11 illustrates schematically a method and means for closing the open end of the bag 10 after filling. Filled bags 50 are successively loaded onto an endless conveyor belt 51, and are passed successively between a pair of opposite disposed hot compression bars 5z for heat sealing the inner bag ply at the open bag end at about 200-265"C. for about 8 seconds; between a pair of bevelled rolls 53 for severing the heat sealed inner ply while the heat seal is still hot and plastic; past a hot air blast 54 for reactivating at about 260"C for a few seconds the hot melt adhesive preapplied to the outer bag plies; through a folding device 55 for folding the outer bag plies over onto the outer bag wall; between pairs of squeeze rolls 56 for adhesively bonding the outer ply closure; and to a delivery station as at 57.

The invention may also be applied to bags other than gussetted pinch-bottom pouch bags. For example, Figure 15 illustrates the invention applied to a non-gussetted (or flat) stepped end pinch bottom bag 60, the inner plastics ply of which is heat sealed and severed at the factory closed bottom closure in region 61, and the outer plies folded to form a pinch bottom closure 62 with an interposed tear cord 63. After filling, the top closure is effected by heat sealing and severing the inner ply region 64, and the outer ply closure accomplished by reactivating preapplied hot melt adhesive 65, and folding over the outer plies and sealing against the outer bag wall.

The invention is also applicable to sewn end bags, both gussetted (or flat), as illustrated in Figures 16 and 17, respectively, and in Figure 18 in section. In each of the bags shown in these Figures, an inner ply 66 is heat sealed and severed adjacent both bag ends, before and after filling, respectively, in the regions 68 and 67, and the outer plies 69 are sewn closed at both bag ends with tape overlaps 70 and 71.

Multiwall bags according to the invention find special utility for the packaging and shipment, in about 25 to 100 pound lots, of powdered comestibles, such as powdered dry milk or eggs, flour, soya meal, cereals, and the like, and also chemicals, such as pharmaceuticals, and oderiferous materials, such as fertilizer.

Bags according to the invention may be produced by superimposing one or more plies of non-heat sealable material and a ply of heat sealable material in laterally offset relation to form a stepped stack, each ply having a first pair of edges that are laterally offset with respect to those of the or each adjacent ply, and a second pair of opposed edges; bonding each ply to the or each adjacent ply in the stack at the ends of the plies adjacent to the second pair of edges, with the plies unattached intermediate the ends; bonding each ply to itself along the laterally offset edges to form the ply of heat sealable material into an inner tube disposed within an outer tube formed by said ply or plies of non-heat sealable material; heat sealing opposed walls of the inner tube to closure over a zone adjacent one end of the tube by sufficient compressive heat applied to the outer tube to fuse said opposed inner tube walls together; severing the inner tube in the heat sealed zone while at fusion heat by applying scoring pressure to the outer tube, thus forming an inner pouch; and closing the outer tube at the end beyond the region of severance of the inner tube, for example in a sewn end or pinch bottom closure, thus forming an outer pouch, whereby the inner pouch is attached to the outer pouch only in a region adjacent to the ends of the tubes opposite the closed ends of the tubes. The tubing and bonding operations may be carried out on a conventional tuber, such as that disclosed in U.S. Patent No. 2,897,730, and by the method described therein.

The stepped pattern at the bag ends may be modified if desired. For example, referring to Figure 1, the pattern at the open bag end 0 may be modified to step the front gusset portions A up with respect to the front wall F, retaining the rear gusset portions B stepped up with respect to the front gusset portions, and the rear wall portions C stepped up with respect to the rear gusset portions. Also some or all of the plies may be successively stepped up in the front gusset portions in the order progressing from the innermost to the outermost ply. These modifications enhance the resistance to sifting, leakage and insect penetration of the outer pouch structure.

AT WE CLAIM IS: 1. An open mouth, multiwall bag comprising an inner pouch and an outer pouch formed, respectively, from an inner tube of heat sealable material and an outer tube of non-heat sealable material, the tubes being such that the inner tube is capable of being heat sealed to closure by the application of heat and pressure to the outer tube with the resulting heat sealed region being capable of being severed by scoring pressure applied to the outer tube, said inner and outer tubes being bonded to each other in respective zones of attachment at both ends thereof, the tubes being otherwise detached from each other, a portion of the inner tube adjacent to one end thereof and spaced inwardly from the associated zone of attachment having been heat sealed to closure by the application of heat and pressure to the outer tube with the resulting heat sealed region having been severed by scoring pressure applied to the outer tube, thus separating the inner tube into an upper portion that constitutes the inner pouch with a portion of said heat sealed region constituting a closure at the lower end thereof and a lower portion bonded to said one end of the outer tube, and said outer tube having been separately sealed to closure at said one end to form the outer pouch having a separate closure disposed beyond the closure of said inner pouch.

2. A bag according to claim 1, wherein said inner and outer tubes are of flexible sheet materials.

3. A bag according to claim 1 or 2, wherein said inner tube is of plastics material.

4. A bag according to claim 3, wherein said inner tube comprises polyethylene film.

5. A bag according to any one of the preceding claims, wherein said outer tube is of paper.

6. A bag according to any one of the preceding claims, including means integral with said outer tube at said closure of said outer pouch for opening said outer pouch.

7. A bag according to claim 6, wherein said means comprise a tear cord.

8. A bag according to any one of the preceding claims, wherein said inner tube comprises a single ply of heat sealable material.

9. A bag according to any one of the preceding claims, wherein said outer tube comprises a plurality of continguous plies of non-heat sealable material.

10. A bag according to claim 9, wherein said plurality of contiguous plies are bonded together at both ends of said outer tube.

11. A bag according to claim 10, having a pair of oppositely disposed walls with one wall extending beyond the other at each end of said inner and outer tubes to provide an overlap wall portion thereat and having at least some of said outer plies successively stepped one beyond another at each end of the outer tube in each said wall to provide exposed portions of stepped plies, the closure of said outer pouch being produced by folding over said overlap wall portion at said one end of said outer tube and adhesively bonding the folded over portion against one said bag wall.

12. A bag according to claim 11, wherein a heat reactivatable bonding agent in a dormant state is applied to at least said overlap wall at the opposite ends of said inner and outer tubes, said outer tube being closable at said opposite end by reactivating said bonding agent, folding over said overlap wall portion and sealing the folded over portion against the

Claims

**WARNING** start of CLMS field may overlap end of DESC **. be successively stepped up in the front gusset portions in the order progressing from the innermost to the outermost ply. These modifications enhance the resistance to sifting, leakage and insect penetration of the outer pouch structure. AT WE CLAIM IS:

1. An open mouth, multiwall bag comprising an inner pouch and an outer pouch formed, respectively, from an inner tube of heat sealable material and an outer tube of non-heat sealable material, the tubes being such that the inner tube is capable of being heat sealed to closure by the application of heat and pressure to the outer tube with the resulting heat sealed region being capable of being severed by scoring pressure applied to the outer tube, said inner and outer tubes being bonded to each other in respective zones of attachment at both ends thereof, the tubes being otherwise detached from each other, a portion of the inner tube adjacent to one end thereof and spaced inwardly from the associated zone of attachment having been heat sealed to closure by the application of heat and pressure to the outer tube with the resulting heat sealed region having been severed by scoring pressure applied to the outer tube, thus separating the inner tube into an upper portion that constitutes the inner pouch with a portion of said heat sealed region constituting a closure at the lower end thereof and a lower portion bonded to said one end of the outer tube, and said outer tube having been separately sealed to closure at said one end to form the outer pouch having a separate closure disposed beyond the closure of said inner pouch.

7. A bag according to claim 6, wherein said means comprise a tear cord.

12. A bag according to claim 11, wherein a heat reactivatable bonding agent in a dormant state is applied to at least said overlap wall at the opposite ends of said inner and outer tubes, said outer tube being closable at said opposite end by reactivating said bonding agent, folding over said overlap wall portion and sealing the folded over portion against the opposite wall of the bag.

13. A bag according to claim 11 or 12, including a pair of oppositely disposed gussets interposed between said walls, said gussets having terminal portions exposed within said overlap wall portion at each end of said inner and outer tubes, the closure of said outer pouch being produced by folding over said overlap wall portion and exposed gusset portions at said one end of said outer tube and adhesively bonding the folded over portion against one bag wall.

14. A bag according to claim 13 when dependent on claim 12, wherein said heat reactivatable bonding agent is applied to said exposed gusset portions at said opposite ends of said inner and outer tubes.

15. A bag according to claim 13 or 14, wherein at each end of said inner and outer tubes each said gusset has exposed within said overlap wall portion a front gusset portion and a rear gusset portion which is stepped above said front gusset portion.

16. An open mouth, multiwall bag substantially as herein described with reference to, and as shown in, Figures 1, 2 and 3 of the accompanying drawings.

17. A package formed from a bag in accordance with any one of the preceding claims, the inner pouch of said bag containing a substance and having been heat sealed to closure in a region adjacent to the opposite end thereof and spaced inwardly from the associated zone of attachment by the application of heat and pressure to the outer pouch, the resulting heat sealed region having been severed by scoring pressure applied to said outer pouch, and said outer pouch having been sealed to closure beyond the region of severance of said inner tube, whereby the inner pouch containing the

substance is sealed closed at both ends and is completely detached from and disposed within the closed outer pouch.

18. A package substantially as herein described with reference to, and as shown in, Figures 10 and 12 of the accompanying drawings.

19. A package substantially as herein described with reference to, and as shown in, Figure 1 5 of the accompanying drawings.

20. A package substantially as herein described with reference to, and as shown in, Figures 16 and 18 of the accompanying drawings.

21. A package substantially as herein described with reference to, and as shown in, Figures 17 and 18 of the accompanying drawings.

22. A method of producing a bag in accordance with claim 1, which method comprises superimposing one or more plies of a non-heat sealable material on a ply of a heat sealable material in laterally offset relation to form a stepped stack, each ply having a first pair of edges that are laterally offset with respect to those of the or each adjacent ply, and a second pair of opposed edges; bonding each ply to the or each adjacent ply in the stack at the ends of the plies adjacent to said second pair of edges; with said plies unattached intermediate said ends; bonding each ply to itself along the laterally offset edges to form the ply of heat sealable material into an inner tube disposed within an outer tube formed by said ply or plies of non-heat sealable material; heat sealing the inner tube to closure over a zone adjacent one end of the tube by heat and pressure applied to the outer tube; severing said inner tube in said heat sealed zone while hot by applying scoring pressure to said outer tube, thus forming an inner pouch; and closing said outer tube at said end beyond the region of severance of said inner tube thus forming an outer pouch, whereby said inner pouch is attached to said outer pouch only in a region adjacent to the ends of the tubes opposite the closed ends of the tubes.

23. A method of producing an open mouth, multiwall bag substantially as herein described with reference to Figures 3, 4, 5 and 6 of the accompanying drawings.

24. A bag produced by the method of claim 22 or 23.