GB2205812A - Making sacks - Google Patents

Abstract

A multi-ply sack is formed from superimposed blanks 1,2, fig 2 having stepped (3,4,11,12) end edges provided with tabs 9,10,16 and side folds SF,CF. The blanks are pasted at 29,30,31 and folded at SF,CF, fig 3, so that tabs 9,10 adhere together and the piles form tubes. Paste (32, fig 5) is applied to the projecting ends of the blanks between the steps and to tab 10, and the blanks are folded at EF, fig 4, to close the end. The end may be opened by pulling tabs 16,10 and breaking adhesive bond 29. The sack may be single ply. <IMAGE>

Description

"IMPROVED PACKAGING" The present invention relates to packaging, and is particularly concerned with paper sacks such as are used for powder or granular materials. The sacks of the present invention may be used for example to contain flour in bakery quantities, cement, agricultural chemicals such as fertilisers, or granular plastics materials.

Currently, flour millers pack bulk flour in multi-wall paper sacks which are supplied to them with one closed end and an open end. The open end is closed by sewing with jute and cotton threads after filling the sack. The stitching is usually arranged so that by pulling a single strand, the stitching may be unlaced and the sack opened. Such sacks have the disadvantage that fibres from the threads can contaminate the contents of the bag during opening.

An object of the present invention is to provide a single or multi-wall paper sack which may be easily opened without the risk of contaminating the contents of the sack, the sack being opened not at the end closed after filling but at the end closed by glueing during manufacture of the sack.

According to one aspect of the present invention, a blank for a paper sack has an end edge and a fold line disposed generally perpendicularly thereto, a step being formed in the end edge at its intersection with the fold line so that a first region of the blank, situated to one side of the fold line extends in the direction of the fold line beyond the remainder of the blank, the blank being further formed with two tabs extending from the end edge and situated symmetrically about the fold line.

Preferably the tab situated on the first region of the blank projects beyond the other tab.

Most preferably the blank includes two parallel fold lines, the end edge of the blank between the fold lines being displaced in relation to the remainder of the end edge of the blank by the formation of steps where the fold lines intersect the end edge. The tabs are positioned symmetrically about one of the fold lines, and may be equidistant from both fold lines in the folded configuration of the blank.

As an alternative to single folds at the longitudinal edges of the sacks, the blanks may be folded several times to form gussetted sides in a manner known in the art.

According to a second aspect of the invention, a multi-wall sack may be formed from two or more blanks. In such arrangements, the set of blanks will include at least one inner ply blank and an outer ply blank of equal lengths, the inner ply blank having an end edge and a fold line perpendicular thereto, the end edge having a step at its intersection with the fold line to form raised and lowered end regions to respective sides of the fold line and the end edge being formed with first and second tabs extending from the raised and lowered end regions respectively and disposed symmetrically about the fold line, and the outer ply blank having an end edge and a fold line generally perpendicular thereto, a step being formed in the end edge at its intersection with the fold line to form raised and lowered end portions to respective sides of the fold line, the step in the end edge of the outer ply blank being of greater height than the step in the inner ply blank end edge, and the outer ply blank being formed with a third tab positioned on the raised end portion of the end edge at a location spaced from the fold line by a distance equal to the spacing of the tabs of the inner ply blank from its fold line.

Preferably the first and third tabs are coterminous, and the second tab terminates level with the edge of the raised edge portion of the outer ply blank.

Most preferably, the inner and outer ply blanks have a further fold line parallel to the first, with steps formed in the end edges of the blanks to provide a raised portion between the fold lines.

According to yet a further aspect of the invention, a method for producing paper sacks comprises the steps of: a) forming a blank having an end edge and a first fold line perpendicular thereto, the end edge being stepped at. its intersection with the fold line to provide relatively raised and lowered end regions to respective sides of the fold line and having first and second tabs extending from the raised end region and lowered end region respectively of the end edge at locations spaced symmetrically about the fold line; b) applying a controlled amount of paste across the width of at least one of the tabs; c) applying paste to a side edge region of the blank parallel to the fold line;; d) folding the blank along the fold line to bring the pasted face of the said one tab into contact with the other tab, and the pasted edge region into contact with its opposite edge region of the blank; e) applying paste across the width of the raised end region of the blank end edge on its side in contact with the second tab, and to the face of the second tab remote from the first tab; and f) folding the raised end region and the first and second tabs about a fold line perpendicular to the first fold line so as to overlie the remainder of the blank and be secured thereto by the paste.

In the preferred method, the blanks are formed as a continuous strip with their end edges defined by perforation lines.

Paste is applied to the tab or tabs and to the longitudinal edges of the blanks, and they are then folded using one or two longitudinal folds to form a tube. The blanks are then separated, and subsequently the pasting and folding steps e) and f) are performed.

The invention comprehends, as a further aspect, a method of forming multi-wall sacks wherein inner and outer ply blanks as described above are superimposed, paste is applied to one or both of the tabs of the inner ply and to the edge regions of the inner and outer plies parallel to their fold lines, the blanks are folded so as to bring the pasted face or faces of the tabs of the inner ply together and to join the pasted edge regions of the inner and outer plies to their respective opposite edges, paste is then applied to the exposed face of the second tab and to the raised end portion of the outer ply blank and a fold formed so that the second tab overlies and is secured to the exposed face of the lowered end portion of the outer ply blank, with the first tab overlying the second tab and the third tab and the raised end portion of the outer ply blank overlying the first and second tabs.

Clearly in single and multi-wall sacks, the side edges may be gussetted by forming three edge folds instead of one in a manner known in the art. The folded gussets may be pasted in position at their ends, or may simply be held by the folded raised end portion of the outer ply blank.

A multi-wall paper sack according to the present invention will now be described in detail, with reference to the accompanying drawings, in which: Figure 1 shows a view of an end of the blanks from which the inner and outer plies of the sack are formed; Figure 2 shows the two plies superimposed; Figure 3 shows the plies after folding to form a tube; Figure 4 shows the finished end of the sack; and Figures 5 and 6 are sectional views along lines V-V and VI-VI of Figure 4.

Referring now to the Figures, there is seen in Figure 1 a pair of blanks 1, 2 for forming a two-ply multi-wall sack. To form a single-wall sack, only blank 1 is required. The blank 1 is generally of strong kraft paper, and forms the inner ply of the multi-wall sack. Blank 2 is of a finer paper and forms the outer ply of the sack, this ply usually being printed to identify the contents of the sack.

The sacks are generally formed from continuous rolls of paper the length dimension L of the blanks being arranged longitudinally of the paper. Clearly the length L of both blanks will be the same.

Since the blanks are formed from continuous strip material, the two ends of the blank are complementary. Only the upper ends of the blanks, as seen in Figure 1, will be described: the lower ends of course correspond.

Blanks 1 and 2 have a length L, and a width equal to the width of the paper strip. Running along the blanks are two fold lines CF and SF, which will define the edges of the sack when the blanks are assembled.

Referring to blank 1, the upper edge 6 of the blank between the fold lines CF and SF is higher than the upper edge 7 of the blank to the right of fold CF, and upper edge 8 to the left of fold SF.

Steps 3 and 4 join the edges 6, 7 and 8.

Extending upwards from edge 6 is a tab 9, positioned centrally between the fold lines SF, CF. A second tab 10 extends from edge 7, at a position such that when the blank is folded about fold line CF, the two tabs 9 and 10 will be superimposed.

Blank 2, which will form the outer ply, has likewise two steps 11, 12 situated on the fold lines CF, SF, to divide the upper edge of the blank into three parts 13, 14, 15. Edge parts 13 and 15 are colinear, and edge part 14 is raised above them. Steps 11 and 12 are greater in height than steps 3 and 4, so that edge part 14 is spaced further from edge parts 13 and 15 than edge part 7 of blank 1 is from its neighbours 7 and 8.

Extending from edge part 14 of blank 2 is a tab 16, positioned to coincide with tab 9 of blank 1. The heights of tabs 9 and 16 are arranged so that when the two blanks are superimposed, tabs 9 and 16 are coterminous.

Figure 2 shows the two blanks superimposed prior to folding along lines CF, SF. The two blanks will be in contact, but are shown separated for clarity. Steps 3 and 4 of blank 1 coincide respectively with steps 12 and 11 of blank 2, and edge parts 13 and 15 of blank 2 are positioned beneath edges 8 and 7 of blank 1 respectively. Paste is then applied to the upper surface of blank 2. This surface ultimately forms the interior of the sack, and paste is applied sparingly across the width of at least one of tabs 9 and 10 either as a continuous bead or line 29, or as a series of dots or in some other pattern.

Paste is also applied on the upper surfaces of the blanks as seen in Figure 2, along longitudinal edge regions 30, 31 of blanks 1 and 2, for reasons which will be explained.

The two blanks are then folded first along line CF, and then along line SF. This brings them to the position shown in Figure 3.

In this position, tabs 9 and 10, are positioned above tab 16, and the longitudinal edges 30, 31 of the respective blanks will overlap their respective opposite edges.

In this posItion, the paste applied to tabs 9 and 10 will fasten these tabs together, and the paste applied to the longitudinal edge regions 30, 31 will form the folded plies into tubes. The edges of the plies are staggered in a known manner, so that each ply is fastened to itself.

Folding the blanks along fold line CF positions the pasted faces of the tabs 9 and 10 together, and thus secures them.

When the sack blanks have been formed into a tube by folds CF and SF, it will be clear that the areas of the blanks between the steps 3, 4, 11 and 12 project longitudinally beyond their overlying plies, as seen in Figure 3. To complete the sack end, paste 32 is first applied onto these longitudinally projecting portions (indicated by hatching), and to the upper surface of tab 10, keeping those parts of tabs 9 and 16 which project beyond tab 10 free of paste.

The blanks are then folded about line EF seen in Figure 3, to the final configuration shown in Figures 4 to 6.

As is clear from Figure 5, in the central region of the sack end tab 10 is secured by paste 32 to its adjacent outer ply. Paste line 29 secures tab 10 to tab 9. On either side of the tabs 9, 10, the longitudinally projecting portions of the blanks are folded over and secured by paste 32 to the outer ply, thus providing a neat appearance.

The reason for the sparing application of paste at 29 to the tab 9 will now be appreciated. The sack end formed as described is easily opened by grasping the free ends of tabs 16 and 10, and peeling them away from the sack. This will rupture the joint formed by paste 29, and will tear the material of the plies adjacent to tabs 10 and 16, to leave an opening at the end edge of the sack approximately the width of the tabs 10, 16. Preferably the adhesive of bead 29 is selected and applied so as to minimise fibre damage to the inner ply. This opening is easily enlarged to the full width of the sack by manual tearing.

To facilitate tearing of the tabs 10, 16, nicks or slits 34 may be formed in the outer ply or in both plies at the junctions of the tabs and the blank.

The sacks will preferably be formed continuously from strip material, the strips being first perforated to define the ends of the blanks, then cross-pasted to apply paste bead 29 to the tab 9 and/or 10. The strips are then edge pasted to apply paste to areas 30, 31, and the strips then pass to a tube-forming station where folds are made along lines CF and SF. The individual sack blanks are then separated from the strip, ready to be fed to a further pasting and folding station where paste 33 is applied to the longitudinally projecting areas, and these are folded over about fold line EF to form the sack end. The sack blanks may be fed continuously from the separating station to the final pasting and folding station, via a rotating station where each blank is turned through 900, or the blanks may be palletised after separation for subsequent finishing.

Claims (18)

1. A blank for a sack having a transverse end edge and a longitudinal side fold disposed generally perpendicularly thereto, a step being formed in the end edge at its intersection with the side fold so that a first region of the blank, situated to one side of the side fold, extends in the direction of the side fold beyond the remainder of the blank, the blank being further formed with two tabs extending from the end edge and situated symmetrically about the side fold.

2. A blank according to Claim 1, wherein the tab extending from the first region of the blank projects further, in the longitudinal direction, than the tab extending from the second region.

3. A blank according to Claim 1 or Claim 2, wherein a second side fold extends parallel to the said side fold to intersect the end edge, and the said first region of the blank is bounded by steps formed at the intersections of the side folds with the end edge.

4. A blank according to Claim 3, wherein at least one of the tabs is positioned equidistantly from the two side folds.

5. A blank according to any preceding Claim wherein the longitudinal side folds are formed by single crease lines.

6. A sack formed from a blank configured according to any preceding Claim.

7. A method of forming a sack, comprising the steps of: a) forming a blank having a transverse end edge and a longitudinal first side fold perpendicular thereto, the end edge being stepped at its intersection with the side fold to provide relatively raised and lowered end regions to respective sides of the side fold and having first and second tabs extending from the raised end region and lowered end region respectively of the end edge at locations spaced symmetrically about the side fold; b) applying a controlled amount of paste across the width of at least one of the tabs; c) applying paste to a side edge region of the blank parallel to the side fold; d) folding the blank along the side fold to bring the pasted face of the said one tab into contact with the other tab, and the pasted longitudinal edge region into contact with its opposite longitudinal edge region of the blank;; e) applying paste across the width of the raised end region of the transverse end edge of the blank on its side in contact with the second tab, and to the face of the second tab remote from the first tab; and f) folding the raised end region and the first and second tabs about a transverse fold line perpendicular to the first side fold so as to overlie the remainder of the blank and be secured thereto by the paste.

8. A method according to Claim 8, wherein the blank includes a second side fold parallel to the first, folding of the blank along its side folds bringing the pasted face of said one tab into contact with the other tab and bringing the pasted longitudinal edge region into contact with its opposite longitudinal edge region.

9. A method according to Claim 7 or Claim 8, wherein the blanks are formed as a continuous strip with their transverse end edges defined by perforation lines, the blanks being separated after step d) and prior to pasting and folding steps e) and f).

10. A set of blanks for forming a multi-wall sack, including at least one inner ply blank and an outer ply blank of equal longitudinal extent, the inner ply blank having a transverse end edge and a side fold perpendicular thereto, the end edge having a step at its intersection with the fold line to form raised and lowered end regions to respective sides of the side fold and the end edge being formed with first and second tabs extending from the raised and lowered end regions respectively and disposed symmetrically about the side fold, and the outer ply blank having a transverse end edge and a side fold generally perpendicular thereto, a step being formed in the end edge at its intersection with the side fold to form raised and lowered end portions to respective sides of the fold line, the step in the end edge of the outer ply blank being of greater height than the step in the inner ply blank end edge, and the outer ply blank being formed with a third tab positioned on the raised end portion of the end edge at a location spaced from the side fold by a distance equal to the spacing of the tabs of the inner ply blank from its side fold.

11. A set of blanks according to Claim 10, wherein the first and third tabs are coterminous, and the second tab terminates level with the edge of the raised edge portion of the outer ply blank.

12. A set of blanks according to Claim 10 or Claim 11, wherein the inner and outer ply blanks have a further side fold parallel to the first, with steps formed in the transverse end edges of the blanks to provide a respective raised portion between the side folds of each ply blank.

13. A method of producing a multi-wall sack wherein inner and outer ply blanks as described in Claims 10, 11, or 12 are superimposed, paste is applied to one or both of the tabs of the inner ply and to the edge regions of the inner and outer plies parallel to their side folds, the blanks are folded so as to bring the pasted face or faces of the tabs of the inner ply together and to join the pasted edge regions of the inner and outer plies to their respective opposite edges, paste is then applied to the exposed face of the second tab and to the raised end portion of the outer ply blank and a transverse fold formed so that the second tab overlies and is secured to the exposed face of the lowered end portion of the outer ply blank, with the first tab overlying the second tab and the third tab and the raised end portion of the outer ply blank overlying the first and second tabs.

14. A blank according to any of Claims 1 to 5 or 10 to 12, wherein the side folds are constituted by three parallel crease lines, the tabs being positioned symmetrically relative to the central crease line of a side fold.

15. A method according to Claim 13 or Claim 14, wherein the first and third tabs are coterminous, and the second tab terminates level with the edge of the raised edge portion of the outer ply blank.

16. An easy open sack substantially as herein described with reference to Figures 1 to 6 of the accompanying drawings.

17. A method for forming a sack substantially as herein described.

18. A blank for forming a sack substantially as herein described.