A bottom sealing station in a filling and sealing machine and a method of folding and closing a bottom of a container precursor

Abstract

The invention relates to a bottom sealing station (10) in a filling and sealing machine, the bottom sealing station (10) being configured to fold and seal a plurality of bottom closure panels (110, 112, 114, 118) of a container precursor (100) to form a closed bottom (B) of the container precursor (100), wherein one of the bottom closure panels (110, 112, 114, 116) comprises a bottom section (110a) and a central tab (110b), the central tab (110b) being foldably connected to the bottom section (110a) allowing the central tab (110b) to be folded over against an outer surface of the bottom section (110a), wherein the bottom sealing station (10) comprises a tab retainer (200) configured to temporarily retain the central tab (110b) while the bottom section (110a) is folded inwards, wherein the tab retainer (200) comprises a concave working surface (201) for engaging a free edge (109) of the tab (110b). The invention furthermore relates to a method of folding and closing a bottom (B) of a container precursor (100).

Description

[0001] A BOTTOM SEALING STATION IN A FILLING AND SEALING MACHINE AND A METHOD OF FOLDING AND CLOSING A BOTTOM OF A CONTAINER PRECURSOR

[0002] FIELD OF THE INVENTION

[0003] The present invention generally relates to a bottom sealing station in a filling and sealing machine, and more particularly to a bottom sealing station being configured to fold and seal a plurality of bottom closure panels of a container precursor to form a closed bottom of the container precursor, wherein one of the bottom closure panels comprises a bottom section and a central tab, and wherein the bottom sealing station comprises a tab retainer configured to temporarily retain the central tab while the bottom section is folded inwards. It further relates to a method of folding and closing a bottom of a container precursor.

[0004] BACKGROUND

[0005] Within the art of paperboard-based packaging, it is known to produce a blank which is folded and sealed to produce a container. The container may then be utilised to hold a pourable product, e.g. a liquid, such as dairy products like milk or yoghurt, or juices. The pourable product is typically filled into the container within a filling and sealing machine that also forms and seals the bottom and top of the container. Such machines may be referred to as a forming, filling, and sealing machine, or simply a filling and sealing machine.

[0006] In a filling and sealing machine, the containers are conveyed along various operation stations to form the container from a flat, tubular sleeve, to a closed and sealed container containing a liquid.

[0007] One of the operations is to fold, close and seal the container bottoms. An open-top container with side walls and a sealed bottom is thus formed, and this partially formed container is then transferred to subsequent stations of the machine e.g. filling of a liquid, top folding and sealing.

[0008] As the container is used to hold a liquid, it is important that the bottom and top of the container is properly sealed to avoid deficiencies such as leakage and potentially reduced shelf life. Furthermore, it is important to avoid raw edges of the paperboard carton coming into contact with the liquid within the container. For this reason, it is known to provide one of the bottom closure panels with a tab that is folded back over the panel from which it extends. An example of this is shown in US 3,412,922 which describes a blank comprising a bottom closure panel with a tab that can be folded back over the bottom closure panel to avoid wicking.

[0009] In order to pull back the tab during folding, a tab retainer is used to engage the tab and retain or pull it backwards out of the plane of the remaining part of the panel while the remaining part of the panel is folded inwards. Timing and precise operation of the various folding tools is crucial to obtain a correct, consistent, and stable folding. If the tools are not operating correctly, it may result in deficiencies such as that the tab is not folded, is only partly folded, is incorrectly folded, or is buckled, etc. This again can lead to leakages, weakening of the container structure, and contamination.

[0010] US5324250A discloses an apparatus and method for folding the bottom panels of a carton blank that includes side walls, first and third bottom panels extending from opposite side walls, second and fourth bottom panels extending from opposite side walls, and a bottom panel flap extending from the third bottom panel. The apparatus includes a frame, a rotatable supporting assembly, two rotatable folding fingers mounted on the frame for inwardly folding the second and fourth bottom panels, a tuck folder mounted on the rotatable mounting assembly for inwardly folding the third bottom panel, a guide mounted on the frame for contacting and inwardly folding the first bottom panel, and a bending member mounted on the rotatable supporting assembly for outwardly folding the bottom panel flap. One portion of the bending member is curved to define a concave surface that faces the tuck folder.

[0011] The bending member can also be provided with a convex surface positioned on each side of the concave surface.

[0012] Thus, there is a need for improving the precision and the reliability of the folding of the bottom of a container.

[0013] SUMMARY OF THE INVENTION

[0014] An object according to the present invention is to remedy at least one of the abovementioned disadvantages or problems.

[0015] Thus, an object according to the present invention is to provide a bottom sealing station with improved reliability and / or precision in folding the bottom of the container precursor.

[0016] Concave here means that the surface is rounded inwards, i.e. it provides a hollow shape. The term bottom closure panel as used herein refers to a bottom closure sub -panel of a blank.

[0017] The present invention is set forth and characterized in the independent claims, while the dependent claims describe other characteristics of the invention.

[0018] Accordingly, the present invention relates to a bottom sealing station in a filling and sealing machine, the bottom sealing station being configured to fold and seal a plurality of bottom closure panels of a container precursor to form a closed bottom of the container precursor, wherein one of the bottom closure panels comprises a bottom section and a central tab, the central tab being foldably connected to the bottom section allowing the central tab to be folded over against an outer surface of the bottom section. The bottom sealing station comprises a tab retainer configured to temporarily retain the central tab while the bottom section is folded inwards. The central tab is thus folded outwardly, i.e. out of the plane of the bottom section, against the outer surface of the bottom section to a folded position. The tab retainer comprises a concave working surface for engaging a free edge of the tab. The concave path provided by the concave working surface has shown to improve integrity of the folding by reducing inconsistencies in the folding of the central tab. Buckling is avoided and folding is more consistent.

[0019] In one aspect, the present invention relates to a bottom sealing station in a filling and sealing machine, the bottom sealing station being configured to fold and seal a plurality of bottom closure panels of a container precursor to form a closed bottom of the container precursor, wherein the bottom sealing station comprises bottom panel folders configured to fold inwards the bottom closure panels, wherein one of the bottom closure panels comprises a bottom section and a central tab, the central tab being foldably connected to the bottom section allowing the central tab to be folded over against an outer surface of the bottom section to a folded position, wherein the bottom sealing station comprises a tab retainer configured to temporarily retain the central tab while the bottom section is folded inwards so that the central tab is brought to the folded position, wherein the tab retainer comprises a concave working surface for engaging a free edge of the tab, and wherein the concave working surface provides a concave gliding path for the tab, and wherein the tab retainer is configured to be moved to a working position and to remain in the working position during contact between the tab retainer and the central tab.

[0020] In the closed bottom of the container, the central tab lies flat against the outer surface of the bottom section, covered by the opposite bottom panel.

[0021] When not in the working position, the tab retainer may be placed in a retracted position. The working position may be a stationary position, i.e. the tab retainer is not moved while in contact with the central tab. The retracted position may also be a stationary position.

[0022] The free edge may be parallel to the fold line of the central tab.

[0023] Folding inwards of the bottom section means that it is folded to form part of the bottom of the container.

[0024] The tab retainer comprises a first, inner edge and a second, outer edge defining the outer end and the inner end of the concave working surface, respectively. The tab retainer comprises a rear surface opposite the concave working surface, which rear surface may be planar. Because a point on a panel will move in a circular path during folding of said panel about a fold line, the concave working surface is highly advantageous. The tab is retained for as long as possible during folding of the bottom panels. Furthermore, the exact form of the concave surface, e.g.. radius and arc length, is also optimized to fold the central tab over as much as possible while it glides along the concave surface.

[0025] The concave working surface is configured to allow the free edge of the central tab to slide along the concave surface in a direction from the first, inner edge to the second, outer edge. The working surface should be smooth, i.e. it should be configured to allow continuous and unimpeded gliding of the free edge of the central tab without resistance or obstruction due to surface irregularities. The working surface may for example have a brushed or a polished surface. The working surface may be coated with a coating providing non-stick properties and / or reduced friction. The coating may for example be a PTFE or equivalent.

[0026] When the edge of the central tab reaches the second, outer edge of the tab retainer, the central tab slips off the tab retainer. By this time, the opposite bottom closure panel is folded against the bottom section with the overfolded central tab, so that the central tab remains folded backwards. Thus, the outer edge of the tab retainer may be a terminal edge allowing the central tab to be released from the tab retainer.

[0027] The tab retainer may be configured to retain the central tab by interaction only with one continuous concave surface.

[0028] The tab retainer comprises an arm and a finger, wherein the concave working surface is arranged on the finger. The arm connects the tab retainer to a tool holder of the bottom sealing station.

[0029] The concave working surface is arranged towards an inner surface of the central tab. The container precursor may be a tubular sleeve formed of paperboard material. The tubular sleeve may have a square or rectangular cross-section. The paperboard material may comprise a laminate or layered structure comprising e.g. thermally adhesive layers, barrier layers etc.

[0030] The tab retainer may be made of a metal, such as steel, e.g. stainless steel.

[0031] The bottom sealing station may comprise a leading bottom panel folder and a trailing bottom panel folder. It may also comprise a pair of breaker wings.

[0032] The concave working surface may be a right cylindrical concave surface. The concave surface may in other embodiments be elliptical or parabolic.

[0033] The concave working surface has a radius of curvature ranging from 65-115 mm, more preferably 70 - 100 mm, or more preferably 80-100 mm. This radius is optimized for both retaining the central tab for as long as possible and also folding the central tab over as much as possible. Generally, a smaller size container, e.g. a 0.5 1 container, will require a smaller radius of curvature of the concave working surface than a larger container, e.g. a 1 liter or 2 liter container. The tab retainer may thus be adapted for a specific size container.

[0034] The thickness at the end of the tab retainer may be between 2-7 mm, more preferably 2-6 mm, or more preferably 3-5 mm. The thickness of the tab retainer may decrease gradually going from the inner edge to the outer edge due to the concave working surface. The thickness is measured in a plane orthogonal to a longitudinal axis of the tab retainer from the concave working surface to the opposite, rear surface. The thickness at the end may be the thickness as measured at the outer edge of the concave working surface. The above thickness ranges ensure that the tab retainer can retain the central tab for as long as possible while the opposite bottom closure panel is folded inwards.

[0035] The tool end of the tab retainer may also be referred to as the tip of the tab retainer. The tool end may be adjacent the outer edge of the concave working surface.

[0036] The tool end of the tab retainer may comprise a substantially flat end surface being approximately perpendicular to the longitudinal axis of the tab retainer

[0037] The width of the working surface may be between 50 - 95 % of the width of the central tab, more preferably 60 - 80 %, or more preferably 80 - 100 %. The width means the distance from side to side of the finger across the working surface. The arc length of the concave working surface may be between 20 - 60 mm, more preferably 25- 50 mm, more preferably 30 - 50 mm. The arc length is measured along the concave working surface from the outer edge to the inner edge.

[0038] The tab retainer may comprise a guiding surface arranged adjacent an inner edge of the concave working surface, the guiding surface allowing the edge of the central tab to slide along the guiding surface and over to the concave working surface. The guiding surface may be a planar surface. The guiding surface provides a snag -free transition for the free edge of the central tab over to the concave working surface. Thus, if the free edge of the central tab contacts the tab retainer in the area of the guiding surface, the central tab will slide along the guiding surface and over to the concave working surface where it continues gliding towards the outer edge of the tab retainer.

[0039] The present invention also relates to a method of folding and closing a bottom of a container precursor comprising a plurality of bottom closure panels, wherein one of the bottom closure panels comprises a bottom section and a central tab, the central tab being foldably connected to the bottom section allowing the central tab to be folded over against an outer surface of the bottom section to a folded position. The method comprises the step of bringing the central tab to the folded position by interaction with a concave surface.

[0040] In one aspect, the present invention relates to a method of folding and closing a bottom of a container precursor in a bottom sealing station of a filling and sealing machine, wherein the container precursor comprises a plurality of bottom closure panels, wherein one of the bottom closure panels comprises a bottom section and a central tab, the central tab being foldably connected to the bottom section allowing the central tab to be folded over against an outer surface of the bottom section to a folded position, wherein the bottom sealing station comprises bottom panel folders and a tab retainer, the tab retainer comprising a concave working surface for engaging a free edge of the tab, wherein the method comprises:

[0041] - moving the tab retainer to a working position,

[0042] - folding inwards the bottom closure panels by the bottom panel folders,

[0043] - temporarily retaining the central tab by the tab retainer while the bottom closure panels are being folded inwards so that the central tab is brought to the folded position, wherein the central tab is brought to the folded position by sliding a free edge of the tab along the concave working surface of the tab retainer while the tab retainer remains in the working position. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The following drawings are appended to facilitate the understanding of the invention. The drawings show embodiments of the invention, which will now be described by way of example only, where:

[0045] Figure l is a top view of a blank.

[0046] Figure 2 is a top view showing the folding of a blank to prepare for bottom-sealing.

[0047] Figure 3 is a perspective view of the bottom of the container after having been folded.

[0048] Figure 4 is a perspective view of a container formed from a blank.

[0049] Figure 5 is a perspective view of a working side of a tab retainer.

[0050] Figure 6 is a side view of a tab retainer.

[0051] Figure 7a - 7d shows a tab retainer in use from it engages a central tab on a bottom closure panel until the central tab has slipped off the tab retainer.

[0052] Figure 8 shows a bottom closure panel comprising a bottom section and protruding central tab.

[0053] DETAILED DESCRIPTION OF THE INVENTION

[0054] Having generally described this invention, a further understanding can be obtained by reference to certain specific embodiments, which are provided herein for purposes of illustration only, and are not intended to limit the scope of the claims unless otherwise specified.

[0055] Firstly, an example of a blank for forming a container 1 will be described.

[0056] A prior art container precursor 100 in the form of a carton blank 100’ is disclosed in Fig. 1. The blank 100’ is disclosed with the surface configured to form the outside surface of the container 1 facing the viewer.

[0057] The blank 100’ is made from a multi-ply paper or paperboard sheet on which is laminated one or a plurality of barrier layers for holding content, e.g. a liquid, and / or prevent migration of air and flavour degrading substances through the sheet. At least portions of the blank may be coated with a layer of thermoplastic material allowing the container 1 formed from the blank to be sealed by plastic welding.

[0058] The blank 100’ is generally rectangular and comprises a first, bottom edge 101, a second, top edge 103 and parallel, third and second, side edges 105, 107. The side edges 105 and 107 are linear and parallel, whereas the top and bottom edges 101 and 103 have an irregular shape. The blank 100’ also comprises a plurality of crease lines defining folding lines along which the blank 100’ is configured to be folded when formed into the container.

[0059] The blank 100’ comprises five panels, P1-P5, separated by longitudinal crease lines 102, 104, 106 and 108 defining folding lines extending across the panel 100 from the bottom edge 101 to the top edge 103.

[0060] Each panel P1-P5 comprises a first sub-panel 110, 112, 114, 116, 118 forming a bottomclosure sub-panel, a second sub-panel 120, 122, 124, 126, 128 forming a wall section subpanel, and a third sub-panel 130, 132, 134, 136, 138 forming a top-closure sub-panel. The bottom closure sub-panels 110, 112, 114, 116 and 118 are configured to form a bottom closure of the container, and the top-closure sub-panels 130, 132, 134, 136, 138 a top closure of the container. The wall section sub-panel 120 of the first panel Pl is configured to form a rear wall of the container and the wall section sub-panel 124 of the third panel P3 a front wall. The wall sections 122 and 126 of the second and fourth panels P2, P4 are configured to form side walls of the container. The fifth panel P5 is configured to be attached to an inside surface of the first panel Pl adjacent the side edge 105 when the container is formed.

[0061] The blank 100’ displays positions TCI, TC2, TC3, TC4, BC1, BC2, BC3 andBC4 defining top and bottom corners of the container when formed. The top comer positions TCI, TC2, TC3 and TC4 are arranged along a line extending across the panels P1-P5 orthogonal to the side edges 105 and 107. Likewise, the comer positions BC1, BC2, BC3 and BC4 are arranged along a line extending across the panels P1-P5 orthogonal to the side edges 105 and 107 parallel to the line along which the top comer positions TCI, TC2, TC3 and TC4 is arranged.

[0062] The first panel Pl comprises a bottom crease line 140 extending from the position BC1 to a position on the side edge 105 level to BC1. In other words, the bottom crease line 140 extends transversely across the panel Pl in a direction which is orthogonal to the side edge 105 and to the longitudinal crease line 102. The bottom crease line 140 forms a border between the bottom-closure sub-panel 110 and the wall section sub-panel 120 of the panel. Further, the first panel Pl comprises a top crease line 150 extending from the position TCI to a position on the side edge 105 level to TCI. Consequently, the top crease line 150 also extends transversely across the panel Pl in a direction which is orthogonal to the side edge 105 and to the longitudinal crease line 102, i.e. parallel to the bottom crease line 140. The top crease line 150 forms a border between the wall section sub-panel 120 and the topclosure sub-panel 130.

[0063] The bottom-closure sub-panel 110 comprises a bottom section 110a and a central flap or tab 110b. The central tab 110b assists in securing a safe closure of the bottom of the container. The tab 110b is to be folded backwards over the remaining part of the sub-panel 110, i.e. the bottom section 110a, during forming of the bottom B, so that it lies between sub-panel 110 and 114 in the closed bottom B of the container 1 (as shown in Fig. 3), thereby preventing a raw edge of the carton, when filled with a liquid, from coming into contact with the liquid inside the container 10. Within the art of carton production, the function of such tabs is known as such and the function of the tab 110b will not be discussed further here.

[0064] The top-closure sub-panel 130 comprises a top-fin crease line 160 extending transversely across the panel Pl parallel to the top crease line 150, i.e. in a direction which is orthogonal to the side edge 105 and to the longitudinal crease line 102. The top-fin crease line 160 defines a folding line forming a border between a roof panel section 170 and a top-fin panel section 180 of the top-closure panel 130.

[0065] The second panel P2 comprises a bottom crease line 142 extending transversely across the panel P2 between positions BC1 and BC2. BC1 and BC2 are level, i.e. arranged along a line which is orthogonal to the longitudinal crease lines 102 and 104. Consequently, the bottom crease line 142 extends transversely across the panel P2 in a direction which is orthogonal to the longitudinal crease lines 102 and 104. The bottom crease line 142 forms a border between the bottom-closure sub-panel 112 and the wall section sub-panel 122. The second panel P2 further comprises a top crease line 152 extending across the panel P2 between positions TCI and TC2 and defining a folding line forming a border between the wall section sub-panel 122 and the top closure sub-section 132. TCI and TC2 are level, i.e. are arranged along a line which is orthogonal to the longitudinal crease lines 102 and 104.

[0066] The top-closure sub-panel 132 comprises a top-fin crease line 162 extending transversely across the panel Pl parallel to the top crease line 152, i.e. in a direction which is orthogonal to the longitudinal crease line 102 and to the longitudinal crease line 104. The top-fin crease line 162 defines a folding line forming a border between a gusset panel section 172 and a top-fin panel section 182 of the top-closure panel 132.

[0067] The gusset panel section 172 of the top-closure panel 132 comprises diagonal crease lines 173a, 173b and the top-fin panel section 182 comprises a vertical crease line 183, the crease lines 173a, 173b, 183 forming folding lines which are to assist folding of the top-closure sub-panel 132 when the bottom closure of the container is to be formed.

[0068] The bottom-closure sub-panel 112 comprises diagonal crease lines 113a, 113b forming folding lines which are to assist folding of the bottom-closure sub-panel 112 when the bottom closure of the container is to be formed.

[0069] The third panel P3 comprises a bottom crease line 144 extending transversely across the panel P3 between positions BC2 and BC3. BC2 and BC3 are level, i.e. arranged along a line which is orthogonal to the longitudinal crease lines 104 and 106. Consequently, the bottom crease line 144 extends transversely across the panel P4 in a direction which is orthogonal to the longitudinal crease lines 102 and 104. The bottom crease line 144 defines a folding line forming form a border between the bottom-closure sub-panel 114 and the wall section sub-panel 124 of the panel P3. Further, the third panel P3 comprises a top crease line 154 extending across the panel P3 between the top comer positions TC2 and TC3, which top crease line 154 defines a folding line forming a border between the wall section sub-panel 124 and the top-closure sub-panel 134.

[0070] The top-closure sub-panel 134 comprises a top-fin crease line 164 extending transversely across the panel P3 in a direction which is orthogonal to the longitudinal crease lines 104 and 106, i.e. parallel to the bottom crease line 144. The top-fin crease line 164 defines a folding line forming a border between a roof panel section 174 and a top-fin panel section 184 of the top-closure panel 134.

[0071] The fourth panel P4 comprises a bottom crease line 146 extending transversely across the panel P4 between positions BC3 and BC4. BC3 and BC4 are level, i.e. arranged along a line which is orthogonal to the longitudinal crease lines 106 and 108. Consequently, the bottom crease line 146 extends transversely across the panel P4 in a direction which is orthogonal to the longitudinal crease lines 106 and 108. The bottom crease line 146 defines a folding line forming a border between the bottom-closure sub-panel 116 and the wall section sub-panel 126. The fourth panel P4 further comprises a top crease line 156 extending across the panel P4 between positions TC3 and TC4 defining a folding line forming a border between the wall section sub-panel 126 and the top closure sub-section 136. TC3 and TC4 are level, i.e. are arranged along a line which is orthogonal to the longitudinal crease lines 106 and 108.

[0072] The top-closure sub-panel 136 comprises a top-fin crease line 166 extending transversely across the panel Pl parallel to the top crease line 156, i.e. in a direction which is orthogonal to the longitudinal crease line 106 and to the longitudinal crease line 108. The top-fin crease line 166 defines a folding line forming a border between a gusset panel section 176 and a top-fin panel section 186 of the top-closure panel 136.

[0073] The gusset panel section 176 of the top-closure panel 136 comprises diagonal crease lines 177a, 177b and the top-fin panel section 186 comprises a vertical crease line 187, the crease lines 177a, 177b, 187 forming folding lines which are to assist folding of the top-closure sub-panel 136 when the bottom closure of the container is to be formed.

[0074] The bottom-closure sub-panel 116 comprises diagonal crease lines 117a, 117b defining folding lines configured to assist folding of the bottom-closure sub-panel 116 when the bottom closure of the container is to be formed.

[0075] In the fifth panel P5, two co-linear bottom crease lines 148a, 148b define a folding line extending across the panel P5, which folding line is co-linear to the bottom crease lines 140, 142, 144, 146 in panels P1-P4 and forms a border between the bottom-closure subpanel 118 and the body sub-panel 128 of panel P5. Also, two co-linear top crease lines 158a, 158b define a folding line which is generally co-linear to the top crease line 150 of the first panel Pl, which folding line forms a border between the body sub-panel 128 and the top-closure sub-panel 138. Furthermore, two co-linear top-fin crease lines 168a, 168b define a folding line which is generally co-linear to the top-fin crease lines 160 and 164 of panels Pl and P3, which folding line forms a border between a roof panel section 178 and a top-fin panel section 188 of the top-closure sub-panel 138.

[0076] The container 1 may be provided with a circular through-going opening 200 for receiving a pour spout fitment, e.g. in the roof panel section 174, to facilitate opening of the container by the consumer.

[0077] In the following, a process of forming a bottom B of a container 1 from a tubular sleeve will be explained using a blank 100’ as illustrated in Fig. 1 as example.

[0078] As explained in the background section, in a filling and sealing machine the container precursors 100 are conveyed along various steps to form the container 1 from a tubular sleeve with open top and bottom, to a closed and sealed container 1 containing a liquid. In the following, only the process of forming the bottom B will be described.

[0079] The tubular sleeve is first fed to a loading station within the machine. At the loading station, the tubular sleeve is loaded onto a mandrel of a rotating turret, so that the tubular sleeve is in correct position on the mandrel for processing at the bottom sealing station 10. The tubular sleeve may e.g. be formed by a blank 100’ as shown in Figure 1, wherein the fifth panel P5 is attached to an inside surface of the first panel Pl adjacent the side edge 105. The tubular sleeve thus comprises an open top and an open bottom wherein the bottom closure sub -panels 110, 112, 114, 116 forms an extension at a bottom end of the panels 120, 122, 124, 126 and the top closure sub-panels 130, 132, 134, 136 forms an extension at the opposite top end of the panels 120, 122, 124, 126.

[0080] The mandrel is one out of several mandrels, e.g. four or six mandrels, arranged on a rotatable turret of the machine. The mandrels extend radially outwards from the turret in an equally spaced manner. The mandrel is elongate, comprises a square or rectangular cross section, substantially with the same shape as the interior of the tubular sleeve, and has a substantially flat end surface.

[0081] Fig. 2 illustrates how the bottom closure sub-panels of the blank 100’ are folded together to form the closed bottom B of the container 1. The bottom forming and closing process is performed in a bottom sealing station 10 comprising a bottom folding assembly. The bottom folding assembly comprises a pair of breaker wings, a leading bottom panel folder 230, a trailing bottom panel folder 220, and a tab retainer 200. At the bottom sealing station 10, the bottom closure sub-panels 110, 112, 114, 116 of the tubular sleeve are folded to form a closed bottom B, as shown in Figure 3. Before folding, the bottom closure sub-panels 110, 112, 114, 116 extend outwardly from the tubular sleeve, as an extension of the container precursor side wall panels 120, 122, 124, 126. The bottom closure sub-panels 110, 112, 114, 116 may also be referred to as bottom closure panels. In the tubular sleeve formed from the blank 100’, the bottom closure sub-panel 114 is opposite the bottom closure sub-panel 110 with the central tab 110b.

[0082] Firstly, a pair of opposing breaker wings press the triangular sections of the side panels 112, 116 inwards to form an inwards pre-fold, ensuring that when the bottom closure sub-panels 110, 114 are folded inwards, the triangular sections of the side panels 112, 116 will be folded inwards against the interior of the container 10.

[0083] Then, a tab retainer 200 is moved to its working position WOP before a pair of bottom panel folders 220, 230 are rotated inwardly and downwardly towards the longitudinal center axis C of the mandrel, ref. e.g. Fig. 7a. The tab retainer 200 remains stationary in this working position WOP during folding of the bottom panels 110, 112, 114, 116.

[0084] The bottom closure sub-panel 110 of panel Pl is folded inwards by the trailing bottom panel folder 220 and the bottom closure sub-panel 114 of panel P3 is folded inwards by the leading bottom panel folder 230. As the bottom closure sub-panels 110, 114 are pressed inwards by the bottom panel folders 220, 230, the bottom -closure subpanels 112, 116 will fold inwards at the diagonal crease lines 113a, 113b and 117a, 117b. The bottom closure sub-panel 110 of panel Pl, will then fold over the bottom closure sub-panels 112, 116, and the bottom closure sub-panel 114 of panel P3, will fold over the bottom closure sub-panel 110 of panel Pl. The tab retainer 200 is configured to engage and retain the tab 110b of the bottom closure sub-panel 110, essentially bending it backwards while the trailing bottom panel folder 220 presses the sub-panel 110 inwards. The tab 110b is thus folded back over the sub-panel 110 to lie between the outer sub -panel 114 and the sub -panel 110, thereby preventing a raw edge of the carton, when filled with a liquid, from coming into contact with the liquid inside the container 10. The bottom closure sub-panels may be heated prior to folding.

[0085] Figure 3 illustrates the closed bottom B of the container precursor 100 obtained after folding as explained above. The part 110a’ of the bottom-closure sub-panel 110 of panel Pl is exposed to the outside when the blank 100’ is folded to produce the container 1. Bottom-closure sub-panel 114 is folded over against bottom -closure subpanel 110, covering the part 110a” and the overfolded central tab 110b. The part 110a” of the bottom -closure sub-panel 110 of panel Pl is intended to be sealed to the bottom-closure sub-panel 114. There is no crease line between the parts 110a’ and 110a” of the first, bottom-closure sub -panel 110.

[0086] Figure 4 illustrates the container 10, formed following folding, bottom- and sidesealing, filling and top-sealing of a blank 100’. The container 1 of fig. 4 may for example be made from the blank 100’ illustrated in fig. 1.

[0087] The tab retainer 200 and it use will now be described more in detail. Figure 5 shows a tab retainer 200 in perspective view and Figure 6 shows the tab retainer in a side view. The tab retainer 200 comprises an arm 220 which connects the tab retainer 200 to a tool holder (not shown) of the bottom sealing station 10. At the end of the arm 220 is the working end of the tool, which may be referred to as the finger 230. The finger 230 comprises a concave working surface 201. The concave working surface 201 is a cylindrical concave surface having a radius of e.g. 65-115 mm. The concave working surface 201 comprises an outer edge 20 lo at the tip of the finger 210, and an inner edge 20 li closer to the arm 220. The concave working surface 201 provides a curved gliding path for the central tab 110b where the outer edge 20 lo and the inner edge 20 li defines the start and end of the curved path.

[0088] The width W of the tab retainer 200 is smaller than the width of the central tab 110b so that the tab retainer 200 does not interfere with the remaining part of the panel, i.e. the bottom section 110a of panel 110.

[0089] At the tip of the tab retainer 200 is a flat end surface 211, arranged perpendicularly to the longitudinal direction Z of the tab retainer 200. Opposite the concave working surface 201 is a flat rear surface 202 arranged in a plane parallel to the longitudinal direction Z. A guiding surface 203, best seen in Fig. 5, is provided adjacent the inner edge 20 li of the concave working surface 201.

[0090] Figures 7a - 7d shows the tab retainer 200 in use during the process of folding the bottom closure sub-panels 110 and 114, also referred to as bottom closure panels 110, 114, inwards by the bottom panel folders 220, 230. The tab retainer 200 is, before folding of the panels, placed in its working position WOP relative to the container precursor 100, i.e. the end of the tab retainer 200 is lowered to a position inside the interior space defined by the bottom closure sub-panels 110, 112, 114, 116 as they are before folding. The concave working surface 201 faces the inside of the bottom closure sub-panel 110 and is centered relative to the central tab 110b. When the tab retainer 200 is in its working position WOP, it is positioned so that when the bottom closure sub-panel 110 is folded inwards about the fold line 140, the free edge 109 of the central tab 110b comes into contact with the concave working surface 201 of the tab retainer 200. The point of initial contact should be closer to the inner edge 20 li than to the outer edge 20 lo and may even be at the guiding surface 203. The tab retainer 200 remains stationary in the working position WOP during contact with the central tab 110b and is not retraced until the central tab 110b has slipped off the tab retainer 200, see Figures 7a-7c. The bottom panel folders 220, 230 are depicted only in Fig. 7a, and only schematically to illustrate the working principle. The black arrows show the direction of movement of the bottom panel folders 220, 230 during the process shown in Figs. 7a-7d. The bottom panel folders 220, 230 have been omitted from the Figures 7b -7d, although they are indeed present and active during the process.

[0091] Fig. 7a shows when the bottom closure sub-panels 110, 114 are partly folded inwards so that the central tab 110b on the sub-panel 110 is in contact with an upper part of the concave working surface 201, near the inner edge 201i. The central tab 110b is thus bent backwards out of the plane of the bottom section 110a of the panel 110. Because of this, the central tab 110b is folded outwardly towards the outer surface of the bottom section 110a.

[0092] In Fig 7b, the bottom section 110a is folded further inwards while the free edge 109 of the central tab 110b has slid further down and along the concave working surface 201. The central tab 110b is thus bent further backwards relative to the bottom section 110a. At the same time the opposite bottom closure sub-panel 114 has also been further folded inwards.

[0093] In Fig. 7c, the bottom section 110a has been further folded so that its outer part including at least part of the central tab 110b is now below the opposite bottom closure sub-panel 114 and the free edge 109 of the central tab 110b has now slid all the way to the outer edge 201 o where it slips off the tab retainer 200. The tab retainer 200 can now be removed, e.g. by retracting upwards as seen by the black arrow in Fig. 7c. The tab retainer 200 may be moved to a retracted position RP, as illustrated by Figure 7d, where it may remain until again being moved to the working position WOP before folding of the next container precursor. Thus, the tab retainer 200 may be movable between a retracted position RP and a working position WOP, wherein the retracted position RP and the working position WOP may be stationary positions. In the retracted position RP, the tab retainer 200 is out of the way so that it does not disturb or interfere with other tools or with the container precursor 100. Because of the above-lying sub-panel 114, the central tab 110b is prevented from returning to its unfolded position and since both sub-panels 110 and 114 are continued to be folded by the bottom panel folders 220, 230, as shown in Fig. 7d, the central tab 110b remains folded by the pressure from the panel 114 until it lays flat against the outer surface of the bottom section 110a and covered by the panel 114, as in Fig. 3. The bottom of the container is now closed and the interior of the container bottom B is now absent of raw paperboard edges. Sealing of the bottom B may achieved by heating the panels, which comprise an adhesive, according to well known practice.

[0094] The invention is not limited to a blank 100’ as shown in Fig. 1, and may be used on other blanks having a different configuration that are also provided with a central tab 110b. For example, the bottom closure sub-panel 110 may comprise a bottom section 110a and central tab 110b protruding out from the bottom section 110a, as illustrated in Fig. 8. In the preceding description, various aspects of the independent claims have been described. For purposes of explanation, specific numbers, systems and configurations were set forth in order to provide a thorough understanding of the invention and its workings. However, this description is not intended to be construed in a limiting sense. Various modifications and variations of the illustrative embodiment, as well as other embodiments of the system, which are apparent to persons skilled in the art to which the disclosed subject matter pertains, are deemed to lie within the scope of the present invention as defined in the attached claims.

Claims

CLAIMS1. A bottom sealing station (10) in a filling and sealing machine, the bottom sealing station (10) being configured to fold and seal a plurality of bottom closure panels (110, 112, 114, 116) of a container precursor (100) to form a closed bottom (B) of the container precursor (100), wherein the bottom sealing station (10) comprises bottom panel folders (220, 230) configured to fold inwards the bottom closure panels (110, 112, 114, 116), wherein one of the bottom closure panels (110, 112,114, 116) comprises a bottom section (110a) and a central tab (110b), the central tab (110b) being foldably connected to the bottom section (110a) allowing the central tab (110b) to be folded over against an outer surface of the bottom section (110a) to a folded position, wherein the bottom sealing station (10) comprises a tab retainer (200) configured to temporarily retain the central tab (110b) while the bottom section (110a) is folded inwards so that the central tab (110b) is brought to the folded position, wherein the tab retainer (200) comprises a concave working surface (201) for engaging a free edge (109) of the tab (110b) , and wherein the concave working surface provides a concave gliding path for the tab (110b), characterized in that the tab retainer (200) is configured to be moved to a working position (WOP) and to remain in the working position (WOP) during contact between the tab retainer (200) and the central tab (110b).

2. The bottom sealing station (10) according to claim 1, wherein the concave working surface (201) is a right cylindrical concave surface.

3. The bottom sealing station (10) according to claim 2, wherein the concave working surface (201) has a radius of curvature ranging from 65-115 mm, more preferably 70 - 100 mm, or more preferably 80-100 mm.

4. The bottom sealing station (10) according to any of the preceding claims, wherein the thickness at an end (210) of the tab retainer (200) is between 2-7 mm, more preferably 2-6 mm, or more preferably 3-5 mm.

5. The bottom sealing station (10) according to any of the preceding claims, wherein the width (W) of the working surface (201) is between 50 - 95 % of the width of the central tab (110b), more preferably 60 - 80 %, or more preferably 80 - 100 %.

6. The bottom sealing station (10) according to any of the preceding claims, wherein the arc length of the concave working surface (201) is between 20 - 60 mm, more preferably 25- 50 mm, more preferably 30 - 50 mm.

7. The bottom sealing station (10) according to any of the preceding claims, wherein the tab retainer (200) comprises a guiding surface (203) arranged adjacent an inner edge (20 li) of the concave working surface (201), the guiding surface (203) allowing the edge (109) of the central tab (110b) to slide along the guiding surface (203) and over to the concave working surface (201).

8. Method of folding and closing a bottom (B) of a container precursor (100) in a bottom sealing station (10) of a filling and sealing machine, wherein the container precursor (100) comprises a plurality of bottom closure panels (110, 112, 114, 116), wherein one of the bottom closure panels (110, 112, 114, 116) comprises a bottom section (110a) and a central tab (110b), the central tab (110b) being foldably connected to the bottom section (110a) allowing the central tab (110b) to be folded over against an outer surface of the bottom section (110a) to a folded position, wherein the bottom sealing station (10) comprises bottom panel folders (220, 230) and a tab retainer (200), the tab retainer (200) comprising a concave working surface (201) for engaging a free edge (109) of the tab (110b), wherein the method comprises:- moving the tab retainer (200) to a working position (WOP),- folding inwards the bottom closure panels (110, 112, 114, 116) by the bottom panel folders (220, 230),- temporarily retaining the central tab (110b) by the tab retainer (200) while the bottom closure panels (110, 112, 114, 116) are being folded inwards so that the central tab (110b) is brought to the folded position, wherein the central tab (110b) is brought to the folded position by sliding a free edge (109) of the tab (110b) along the concave working surface (201) of the tab retainer (200) while the tab retainer (200) remains in the working position (WOP).

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