Carton formed from a blank, corresponding blank and method of forming the carton

Abstract: The bottom of a paperboard carton has flat panels (9a,9b), with overlapping edge portions (9c,9d), in which respective corresponding flaps (17a,17b) are provided. Either one or other of the flaps (17a,17b) is folded down so that the other flap overlies the folded flap before the carton bottom is hermetically sealed. The advantage of the invention is that a common carton blank can be used to avoid problems of carton orientation, the folded flap avoiding problems due to cut edges of paperboard coming into contact with the carton contents.

Description: This invention relates to a carton blank, a carton formed from the blank and a method of making a carton. Cartons are usually made of paperboard coated on both sides with a thermoplastic film, such as polyethylene. A blank of this material is formed into a sleeve, for example of square cross-section, and panels, at respective ends of the sleeve, are then folded inwardly to form the carton top and bottom. Overlapping edge portions of these panels are heated and subjected to pressure in order to weld seams together to seal the carton top and bottom. Cartons typically contain liquid food products, such as milk, fruit juice, and soft drinks. Some foods are produced in a form intended to have a long shelf-life. The carton manufacturer is therefore required to provide cartons which are relatively free from microbial contamination, such as fungicidal spores and bacteria. These could otherwise initiate decomposition of the food, thereby shortening its potential shelf-life. Microbes may reside in paperboard and they become trapped between the thermoplastic films when the paperboard is coated. If the coated paperboard is then cut and folded so that a "raw edge" of the paperboard can come into direct contact with the contents of the carton, microbial contamination may occur. A further problem, which is faced by carton manufacturers and the food industry, is to make reliable hermetic seals so that cartons, filled with a product, do not leak as a result of subsequent handling. In a typical carton, top and bottom panels are creased and folded to form a gable top and a flat base. This is achieved by machines which are loaded with sleeves formed from blanks that are then conveyed, one at a time, between several work stations, where respective operations are performed. A work sequence may include, for example, (a) initial sleeve formation, then, in the machine (b) forming the carton bottom and and making an hermetic seal, (c) attaching a pouring spout to one of the panels which will form a gable top, (d) filling the carton, and (e) forming the carton top and making the final hermetic seal. Each step, in the sequence, must be performed repeatably and reliably to make hermetic seals. The food industry, for example, is highly competitive and there is hence a demand for machines which can operate at ever increasing speed so as to fill and seal a greater number of cartons within a given time. High speed machines are carefully designed and operated to ensure that hermetic seals are repeatably and accurately made. On occasion, however, wear and tear or some other factor may create conditions where folds and seams are not made entirely as they should and slight discrepancies may affect the integrity of the hermetic seals. Accordingly, any way of simplifying the design or handling of cartons is of extreme benefit to manufacturers. Machines are designed, to form, fill and seal cartons, but cartons are also designed to suit the characteristics of machines. Certain features of cartons, such as the size and position of creases, the way in which panels are folded, the position of fitments (such as pouring spouts) and the way information is printed on the carton, will vary in accordance with differences in automated forming and filling techniques. For example, a ridge sealing the carton top may run either parallel with, or perpendicularly to the seam which seals the carton bottom. A fitment may need to be attached to either one of the sloping side panels in a carton top. In either or both of these cases, it is important to consider the orientation of the carton as it proceeds from one work station to another, to ensure that the carton is correctly presented or offered up to a tool which performs a certain task. Moreover, the carton may be designed to avoid, as far as possible, the need for a device to rotate the carton into a different orientation before the operation, at a work station, can be performed. In the case of twin-track machines, which are used to double production speed, carton blanks need to be provided which are mirror-images of one another, so that "right-handed" cartons are supplied on one track, whilst "left-handed" cartons are supplied on the other track. (The abbreviations are RH and LH will be henceforth used to indicate such orientations.) However, there is then the disadvantage that both RH and LH cartons need to be manufactured. There is also the problem of mis-loading and/or loss of phase if RH and LH cartons do not alternate on a transport path. If an operator replenishes an LH track with RH cartons, this will stop and/or jam the machine. It must then be switched off and serviced to remove the damaged carton, thereby disrupting work and causing a loss of production. This will also occur if, for some reason, two LH or RH cartons are accidentally fed in sequence. The bottom of a typical paperboard carton comprises confronting flat panels and inwardly creased panels. The creased panels enable the flat panels to be folded towards each other so that an edge portion of one flat panel overlaps a corresponding edge portion of the other flat panel to form a flat bottom. Heat and pressure are applied to the overlapping portions to form a seam. In order to avoid the problem of a "raw edge" a so-called "J-fold" may be employed in a small flap in the edge portions of one of the flat panels as disclosed in EP-A-0112553 (this is explained in more detail below). However, at least in a twin track machine, for example, the J-fold must be orientated with respect to other features of the carton, and it is necessary to reverse the order in which the flat panels overlap each other in the twin-tracks, and both RH and LH cartons are then required. The invention seeks to avoid the above-mentioned problems, particularly when forming and sealing a carton bottom, and to provide a carton which can, at least on most occasions, be made from a common blank. According to one aspect of the invention, we provide a carton formed from a blank which is formed into a sleeve having respective panels which are formed into a carton top and a carton bottom, the carton bottom being formed by confronting flat panels and confronting inwardly creased panels, the creased panels enabling the flat panels to be folded towards one another, so that an edge portion of one flat panel overlaps the corresponding edge portion of the other flat panel, whereby portions of the panels, including said overlapping edge portions, can be welded together to seal the carton bottom hermetically, characterised in that slits are made in substantially corresponding positions in the edge portions of both of the confronting flat panels to define respective flaps; the flaps being positioned so that when the edge portions are made to overlap, either one of the flaps is folded down and the other flap overlies the folded flap; the flap to be folded down being selected with regard to the intended orientation of the carton prior to sealing the carton bottom and forming a folded edge on the inside of the carton extending between the creased panels. The invention also extends to a method of forming a carton, and to the carton blank, as mainly claimed in claims 4 and 8. Although the invention is not confined to the use of twin track machines, a particular advantage of these flaps is that a common design of carton blank can be used to provide sleeves to feed both RH and LH tracks of a twin track machine. Although the flat panels will be caused to overlap differently in the RH and LH tracks, either one of the flaps can be folded down to avoid a "raw edge" on the inside surface of the carton bottom (normally bridged by the apices of triangular portions formed by the inwardly creased and folded panels). As a common design of carton blank can be used, there will be no need to print two different orientations of design on the carton blanks for use in the RH and LH tracks. A further advantage occurs in the case where fitments, such as screw top pouring spouts, are applied to cartons. In a single track machine, it is possible to install a mechanism on either side of the track to apply a fitment. In twin track machines, space is a limiting factor between the tracks and fitments need to be applied on the outside of each track. This necessitates the use of both RH and LH cartons. However, the flaps of the invention avoid the need for such mirror-image cartons. Although a carton in one track will be rotated through 180° with respect to a carton in the other track, either one of the flaps can be folded down so that the other flap overlies it before the bottom panels are subjected to heat and pressure to make the seal. Preferably, one of the flaps is slightly smaller than the other, so that the opposite edges of the smaller flap are spaced inwardly from the corresponding side edges of the larger flap. This ensures that a better seal is made when the carton bottom is welded. There is no need to space the top edge of one flap inwardly from the top edge of the other flap, because the top edge of the folded flap will effectively draw back due to the fold, i.e. one flap is folded and the other is not in the sealed carton bottom. However, one top edge could be spaced inwardly from the other, if required. The invention can be applied to cartons of various designs, as long as the bottom is formed by confronting flat panels and confronting creased panels or their equivalent. The flaps provide a very simple solution but a surprisingly good result. It is not obvious to make slits in the edge portions of both confronting flat panels, because this would apparently increase the risk of leakage. In the "single-J" design of the prior art carton, the flap in the edge portion of one panel is tucked under and almost totally enveloped by the edge portion of the opposite panel. The single pair of slits is therefore totally covered by the marginal edge portion of 'top' panel. This total coverage is apparently lost by making pairs of slits in the edge portions of both of the confronting flap panels. In the invention, the slits are in substantially corresponding positions in the confronting flat panels and this would apparently increase the risk of leakage. Surprisingly, this has not been found to occur in practice and the integrity of the seal is good. The seal integrity is further improved by making one flap slightly smaller than the other because, with a carton made from plastics coated paperboard for example, the molten plastics can flow over the edge of the smaller flap and onto the marginal regions of the larger flap, not covered by the smaller flap, when the carton bottom is welded. Carton and machine manufacturers have made several attempts, in the past, to overcome the kind of orientation problems mentioned above but, despite the long-term existence of the well-known single "J fold" in the industry, no solution was advanced which depends on using a double contacting flap construction as taught by this invention. The above-mentioned problems will be better understood with regard to the following description of certain prior art cartons. This, and a description of a preferred embodiment of the invention, will be given with reference to the accompanying drawings, in which:- Fig. 1 is a perspective view of a typical prior art paperboard carton; Figs. 2 and 3 are perspective views of the bottom of the carton shown in Fig. 1 and respectively showing early and late closing stages; Figs. 4,5 and 6,7 are similar pairs of perspective views of a prior art carton bottom with a single J-fold and a carton bottom of an embodiment of the invention respectively; Figs. 8,9 and 10 are respectively a plan view looking down from the inside, a plan view from the underside and a section on line X-X of the prior art carton bottom shown in Figs. 1-3; Figs. 11,12 and 13 are similar view of the carton bottom shown in Figs. 4,5; Figs. 14,15 and 16 are also similar view of the carton bottom, embodying the invention, shown in Figs. 6,7; Fig. 17 being a section on line BB; flaps folded one way; Figs. 18,19 and 20 are again similar view of the carton bottom shown in Figs. 6,7; Fig. 21 being a section on line BB; flaps folded the other way; Fig. 22 shows the flaps superimposed to indicate their relative sizes; and Fig. 23 shows the underside of the carton with die stake marks. Referring to Figs. 1-3, a paperboard carton 1 is made from a blank formed into a sleeve 2 of square cross-section. The carton has a gable top made from confronting, sloping flat panels 3a,3b and confronting, inwardly creased panels 4a,4b (4b is not visible). Upper edge portions of these panels meet at a vertical ridge 5, which is welded, by the application of heat and pressure, to close the carton top after it has been filled. Fitments can be applied to cartons, such as tear-off flaps and screw-top pouring spouts. Carton 1 has a pouring spout 6, located in a hole in panel 3a. Spout 6, which is screw-threaded, has a flange welded to panel 3a, and a screw top 7 as a removable closure. The carton bottom 8 is flat and its basic method of construction is schematically illustrated in Figs. 2 and 3. Confronting flat panels 9a,9b can be folded towards one another due to the "concertina" action of confronting creased panels 10a,10b. Creases, shown in the drawing and well-known in the art, facilitate folding. Folding is effected by machinery (not shown nor described) also well-known in the art. Fig. 3 shows a stage at which folding is almost complete and where edge portions, 9c,9d of panels 9a,9b respectively, overlap one another so that they can then be welded together. A central part of this overlap covers triangular parts of the creased folds in panels 10a,10b. As the welding technique is generally well-known in the art, it will not be described in detail. However, it is noted that the creases, folds, shape and position of the panels is such that the paperboard is deformed and welded in such a way as to seal off cut edges of paperboard as far as possible (except as described with references to Figs 8-10) so that any liquid in the carton does not come into contact with such cut edges. Referring to Fig. 8, which is a plan view, in section, of the prior art carton bottom 8, the triangular portions 11 can be seen looking down inside the carton. One of the overlapping edges 12, i.e. of panel 9b, can also be seen and it is slightly displaced from an axis through each triangular apex. As the paperboard is coated on both of its major surfaces with a plastic film 13, the paperboard 14 is sandwiched between the films 13. Hence, when the sheet material is cut, a cut or "raw" edge of paperboard remains. Due to the way in which the carton bottom is formed, a raw edge 12 extends between the triangular portions 11, although other raw edges (hidden beneath triangular portions 11) can be sealed off due to their positions and the deformability of the paperboard when the carton bottom is sealed. As edge 12 of panel 9b is a raw edge, it can contaminate the contents of the carton (as also shown in section XX of Fig. 10). Fig. 9 is a plan view of the underside of the prior art carton bottom 8, showing the other raw edge 15, of panel 9a, but this is of no consequence because it is on the outside of the carton. Fig. 9 also shows a crimping pattern 16 (which varies from one design of carton to another), which assists in making an hermetic seal when the carton bottom is welded. In the section shown in Fig. 10, the panels are depicted prior to welding so as to illustrate more clearly how edge portions 9c,9d overlap. The "gaps" would be closed by welding. Figs. 4,5 and 11-13 are similar perspective, plan and sectional views of the bottom of another prior art carton having a so-called "J fold". This J fold is defined by a small flap 17 which is folded back after making parallel slits in edge portion 9d of panel 9b. The flap 17 is tucked under edge portion 9c of panel 9a in the closing stage, shown in Fig. 5. As the flap 17 forms a folded edge or J fold 17c, this folded edge, and not the raw edge 12 is visible in the interior sectioned plan view of Fig. 11. This "J" fold is made by folding back flap 17 as can be seen in section YY of Fig. 13. The folded edge 17c is nearer the apices of triangular portions 11 as shown in Fig. 11. The leading edge of flap 17 has been purposely shown projecting slightly beyond overlapping edge portion 9c in Fig. 12, to facilitate description. When the overlap is welded, a U-shaped bulge 18 tends to be formed in panel 9a, as shown in Fig. 12, due to the presence of the folded flap. A stake or crimping pattern (not shown) may also be used to improve the integrity of the seal. J-type folds have been known for many years in the carton industry, as a means for solving the "raw edge" problem. However, the industry has only applied the flap 17 to the underlying edge portion (9d) of the overlap, and this construction is prone to the "orientation" problem described above, which involves the need for RH and LH cartons because a common carton blank cannot be used to serve (e.g.) a twin track machine. Various prior attempts made to overcome this problem have not met with success. A carton bottom, according to the preferred embodiment of the invention, is illustrated in Fig. 6,7 and 14-22. As shown in Fig. 6, flaps 17a,17b are provided in both edge portions 9c,9d of panels 9a,9b. These flaps 17a,17b are formed by making substantially corresponding pairs of parallel slits in the edge portions 9c,9d. These flaps are illustrated as bent outwardly in Fig. 6, from respective creases 17c, running parallel to the edges of panels 9a,9b, for the purpose of explanation. The creases 17c facilitate the folding of one or other flap, as will be explained below. In the closing stage shown in Fig. 7, one of the flaps 17a is folded back and the other flap 17b overlies the folded flap 17a so that their inner surfaces are brought into contact with one another, when the edge portions 9c,9d are made to overlap. In the carton orientation shown in Fig. 7, the folded flap 17a is in the underlying edge portion of panel 9b. The unfolded flap 17b, in the edge portion of panel 9a, merely overlies the folded flap 17a. The carton bottom is then welded to provide an hermetic seal. Whilst the flaps 17 can have corresponding shape and dimensions, it is preferred to make one flap slightly smaller than the other to improve the seal around the raw edges of the flaps. In this case, one flap slightly overlaps the other so that when heat is applied the plastics coating melts and runs over the edges of the smaller flap and onto the overlapping margin of the larger flap. Fig. 22 shows the relative shapes of a larger flap 17a and a smaller flap 17b (behind the larger flap and represented by broken lines). The side edges of flap 17a are spaced by small margins 20 from the side edges of flap 17b; the length of the slits 21 in each marginal portion 9c,9d being the same. When one or other flap 17a,17b is folded, its top edge will draw back from the top edge of the unfolded flap. Fig. 23 shows die stake marks 25,26 on the underside of the carton to ensure that possible leak paths are blocked. These die stake marks are made by conventional machines known to those skilled in the art. Although one flap is preferably larger than the other, it is not large enough to prevent its passage through the smaller cut out of the smaller flap if it is folded over the small flap, rather than in the other direction. A typical "overlap" between larger and smaller flaps would leave a margin 20 of about 0.5-1.0 mm around each side edge. Rectangular flaps are preferred but they could be square or other shapes (e.g. trapezoidal). Figs. 14-17 show different views of a carton bottom with flaps 17a,17b folded in one direction (.e. to suit a carton having one form of LH or RH orientation. Figs. 18-21 show similar views of the same carton bottom with flaps 17a,17b folded in the opposite direction. Fig. 14 is a plan view, looking down inside the carton, showing the flap panels 9a,9b and triangular portions 11 formed by the inwardly creased panels 10a,10b. The fold 17c is above a median line bisecting the apices of the triangular portions 11. The edge portion 9c of panel 9a lies over the edge portion 9d of panel 9b (note also the position of the overlap 23 which is used in forming the blank into a sleeve), as shown in the underside view of Fig. 15. The sections on lines AA and BB respectively in Figs. 16 and 17 respectively show the relative positions of the flaps 17a,17b and the overlapping panels 9a,9b. The side portions of these flaps are sealed against the triangular portion 11 as will be apparent from Fig. 14. The leading edge portion 17d of the larger (upper) flap 17a also overlaps the raw edge 17e of the small (lower) flap 17b. This has been exaggerated for clarity. As the paperboard is deformable, the flaps 17a,17b (shown in Fig. 16) obscure the overlapping edge portions 9c,9d which can be seen in Fig. 17. Figs. 18-22 are similar to those in Figs. 14-17, except that the smaller flap 17b has been folded over the larger flap 17a, and the edge portion 9d of panel 9b overlies the edge portion 9c of flap 9a. Also the carton bottom is rotated through 180° (see position of the overlap 23). When the carton blank is fed through a machine to form the carton, at the stage when the carton bottom is formed, one or other flap 17a,17b is bent backwardly, to form a fold, whilst the other flap is then introduced over the folded flap prior to sealing. The way in which the flaps are folded may vary to suit different machines. A carton embodying the invention can be made from a common design of blank, because the carton bottom can arrive, at a work station, in either a forward, or reverse orientation and either of the flaps 17a,17b can be folded before the various portions are welded.

Claims: A carton (1) formed from a blank which is formed into a sleeve (2) having respective panels which are formed into a carton top and a carton bottom (8), the carton bottom (8) being formed by confronting flat panels (9a,9b) and confronting inwardly creased panels (11), the creased panels (11) enabling the flat panels (9a,9b) to be folded towards one another, so that an edge portion of one flat panel (9b) overlaps the corresponding edge portion of the other flat panel (9a), whereby portions of the panels, including said overlapping edge portions, can be welded together to seal the carton bottom hermetically, characterised in that slits (21) are made in substantially corresponding positions in the edge portions of both of the confronting flat panels (9a,9b) to define respective flaps (17a,17b); the flaps (17a,17b) being positioned so that when the edge portions (9c,9d) are made to overlap, either one of the flaps (17a,17b) is folded down and the other flap (17b or 17a) overlies the folded flap (17a or 17b); the flap to be folded down being selected with regard to the intended orientation of the carton prior to sealing the carton bottom (8) and forming a folded edge (17c) on the inside of the carton extending between the creased panels (11). A carton according to Claim 1 wherein the flaps (17a,17b) have identical shapes and dimensions. A carton according to Claim 1 wherein one of the flaps (17a,17b) is slightly smaller than the other, so that at least opposite side edge portions of the smaller flap is spaced inwardly from the side edge portions of the larger flap. A method of making a carton (1) including the steps of: (a) making a blank from sheet material, (b) forming the blank into a sleeve (2), (c) forming one end of the sleeve (2), having confronting flat panels (9a,9b) and confronting inwardly creased panels (11), into a carton bottom (8), the creased panels (11) enabling the flat panels (9a,9b) to be folded towards one another, so that an edge portion of one flat panel overlaps the corresponding edge portion of the other flat panel, (d) welding the overlapping edge portions together to seal the carton bottom (8) hermetically, characterised by making slits (21) in the edge portion of both of the flat panels (9b,9b) so as to define flaps (17a,17b), causing said edge portions to overlap, after folding either one or the other of said flaps (17a,17b) beneath the other flap (17b,17a) before said welding which seals the carton bottom (8) so that a folded edge (17c) extends on the inside of the carton between the creased panels (11). A method according to Claim 4 wherein either one of the flaps is folded through approximately 180° to underlie the other flap. A method according to Claim 4 wherein either one of the flaps forms a fold and the other flap is introduced over the folded flap before welding the carton bottom. A method according to any one of Claims 4-6, when used in a twin track machine for forming filling and sealing cartons and wherein the machine is loaded with carton sleeves which are of a common design, which are then formed into cartons according to claim 1. A carton blank formed of paperboard which is cut and creased for forming into a carton (1) according to claim 1, 2 or 3, the blank having panels for forming four side walls of the carton and an overlapping joining flap, a carton top and a carton bottom (8), with the carton bottom (8) being formed of two creased panels (11) and two flat panels (9a,9b) foldably connected to bottom edges of respective side wall panels, characterised in that each of the two flat panels (9a,9b) has spaced slits (21) formed in corresponding positions in edge portions thereof to define respective flaps (17a,17b) in the flat panels (9a,9b) which flaps (17a,17b) are further defined by fold lines (17c) connecting the flaps to their respective flat panel edge portions whereby, in the carton formed from the blank, either one of said flat panels (9a,9b) can form the inner panel of the carton bottom with its respective flap (17a or 17b) being folded back outwardly to define a folded edge (17c) extending on the inside of the carton between the creased panels, and the other flap (17b or 17a) will overlie the folded back flap (17a or 17b).

Inventors: HALL JAMES, JORDAN ERIC, HALL, JAMES, JORDAN, ERIC
Applicants: REXAM PKL LIMITED
Application year: 1995
Main classification: B65D5
IPC codes: B65D5