METHOD AND MACHINE FOR SHAPING FLEXIBLE BAGS WITH A SPECIAL BASE

Description

FIELD OF THE INVENTION

[0001] The invention relates to a method for forming flexible bags of the type comprising two walls connected by gussets and closed at one end by a bottom. It also relates to a machine implementing such a method. PRIOR ART

[0002] Industrial processes for manufacturing bags from flexible materials such as paper or synthetic materials have long been known. For example, document FR 1 270 400 describes a machine and a process in which a strip is unrolled and then formed into a casing. The casing is flattened so that it has a first and a second wall, then the casing is cut into sections so that at each end of the section there remains a tab which extends the first or second wall. In a folding step, the tab is folded and glued by being folded down onto the wall other than the one from which the tab originates. Bags can thus be manufactured at a high speed with a wide variety of materials and formats. Document FR 786 579 shows several examples of this technique. It shows in particular on the figures 4 to 6a manufacturing process in which the paper web is provided at regular intervals with transverse perforation lines, with one line in the center and two lines, axially offset from the center line on each length of the web.

[0003] The casing is formed by folding each edge over the central portion and gluing the two edges together along a central junction so that the perforations form two offset transverse lines on either side of the casing, respectively. The casing thus formed passes between a pair of drive rollers which drive the casing at a constant speed. The front portion of the casing is gripped by the folding device which comprises a counter-rotating drum and folding roller. The drum and folding roller rotate with a peripheral speed greater than that of the pair of drive rollers. The folding roller comprises a bar adapted to pinch the front of the casing against the drum, so that the front portion of the casing is pulled and torn apart along the perforations to form a section.At separation, due to the offsets between the perforation lines, a rear tab is thus formed on the section, as well as a front tab at the end of the casing. This front tab will be found on the next section. The front tab is folded by the folding device over a glued area to close the front part of the section. For this, the roller also has a folding blade, placed just behind the bar, which pushes the casing into a clamp carried by the drum so as to fold the casing.

[0004] In one variant, the casing is formed with gussets that connect the first and second walls. WO 2016 097310 A1 shows an example of such bags.

[0005] A method is also known for manufacturing square-bottomed bags which have the advantage of being able to be erected on the bottom and remain open and upright more easily. Document EP 2 864 114 B1 describes an example of a machine implementing such a method. In this example, a blank is first formed and has two skins connected together along two opposite edges by two gussets. The blank is placed flat on a table, one of the so-called lower skins being against the table, the other skin being on top and the gussets being folded down between the two skins. The blank is driven in translation on the table in a direction parallel to the gussets towards a drum around the periphery of which different stations are distributed.

[0006] First upsetting means produce a first fold line at the gussets, and a second fold line at a predetermined distance from the first line, in a direction perpendicular to the gussets. The upsetting means comprise a rotating blade holder and complementary grooves carried by a counter-rotating drum. As it advances, the front of the blank is caught between the drum and a roller. The drum comprises front pinching means for driving the blank by pinching the front edge of the lower skin. To facilitate the separation of the two skins, the opening roller comprises suction means which hold the upper skin against the roller after it has passed between it and the drum. Set back from the front pinching means, first lateral pinching means pinch the lateral edge of the blank at the junction between the gusset and the lower skin.Symmetrically, second pinching means pinch the lateral edge of the blank at the junction between the bellows and the upper skin. As the blank continues its passage between the roller and the drum, the lateral pinching means move apart from each other, open the blank and form a fold on the bellows in a radial plane of the drum and the roller. The second pinching means release the blank while, as the drum continues to move, spatulas fold the open part towards the centre. The upper skin folds backward at the second fold line. In the subsequent operations, second upsetting means mark two transverse lines, on either side of the second fold line. One of these lines coincides with the first fold line.Then the two flaps delimited by these fold lines are glued and folded over each other to close the flat bottom and thus form the bag.

[0007] The manufacturing operations for such a bag are much more complex than those for a flat bag, so production rates are much more limited.

[0008] Documents FR 2 351 021 A1 and FR 2 207 456 A5 show methods for converting flat bags into square-bottomed bags. However, these methods require a complex mechanism to move the top wall relative to the bottom wall. OBJECTIVES OF THE INVENTION

[0009] To solve these problems, the invention aims to propose a method and a machine for manufacturing bags which have the advantage of square-bottom bags but with production rates close to the manufacture of flat bags. DESCRIPTION OF THE INVENTION

[0010] With these objectives in view, the invention relates to a method of forming a flexible bag, the bag comprising a first wall and a second wall superimposed on the first wall, the walls being connected to each other along longitudinal edges by two gussets, according to which, successively: ▷ the bag is closed to form a closed end of the bag opposite an open end, ▷ the first wall is gripped at a predetermined distance from the closed end of the bag by lower clamps mounted on a lower support and the second wall by upper clamps mounted on an upper support and the walls are spread apart using the clamps, ▷ the second wall is released by the upper clamps and the closed end is folded down with a flapper onto the second wall, forming a first fold extending out onto the first wall between the lower clamps, a second fold extending out onto the second wall between the ends of the ribs, and a third fold returning onto the second wall symmetrically at the end of the bag relative to the second fold, thus creating a delimited bottom between the first and second folds, ▷ the method being characterized in that when the clamps are spread apart, a rib is formed on the gussets extending from one wall to the other.

[0011] Thus, the production of flat bags is followed by a special bottom forming step. The ribbing creates stiff sections that keep the walls apart before folding and then during use of the bag. Naturally, the gussets are folded diagonally, firstly from the closed end to the ends of the ribs and secondly from an internal fold line of the gussets to the ends of the ribs. Thanks to this process, bags with a rectangular bottom are formed from flat bags. This allows for production rates close to those of flat bag production with a similar function to square-bottom bags. The wall spreading step is similar to that in the square-bottom bag production process, but is applied to a bag that is already closed.The flap is held in place, for example, by gluing with a hotmelt glue or a solvent-based glue, or by welding when the material lends itself to it, for example if it is or includes a thermoplastic material.

[0012] According to an improvement, the second wall is pressed with support means after the upper clamps have been released. This facilitates the formation of the third fold by initiating the folding of the second wall on itself.

[0013] According to an improvement, a gap is maintained between the second wall and the first wall over at least part of the width of the bag and over its entire length in order to create an air supply channel from the open end to the closed end. Thus, when the first wall is moved away from the second wall, and thus a cavity is created at the closed end of the bag, air can fill the cavity via the supply channel. This avoids limiting the rate due to the excessively long filling time if the walls remained superimposed.

[0014] According to one embodiment, the bags are initially formed with the flap closed, stacked, and then unstacked to form the bottom. The flat bags can be produced at the optimum speed of the machine that produces them. Stacks of bags are then taken up by the number of machines necessary to form the special bottoms according to the invention.

[0015] According to another embodiment, the formation of the bottom is carried out in line with the formation of the bag. This avoids the intermediate storage and unstacking means necessary in the previous embodiment.

[0016] According to a geometric characteristic, the predetermined distance between the closed end and the first fold, respectively the second fold is substantially equal to the depth of the gussets. Thus, when opened, the bag has sides formed by the gussets which have the same width as the bottom.

[0017] The invention also relates to a machine for manufacturing flexible bags, the bag comprising a first wall and a second wall superimposed on the first wall, the walls being connected together along longitudinal edges by two gussets, one end of the bag being closed, the machine comprising receiving means for receiving in series bags moving in a main direction parallel to the longitudinal edges, the closed end being in front, a lower support for supporting two lower grippers, the lower grippers being arranged to grip the first wall at a predetermined distance from the closed end of the bag, an upper support for supporting upper grippers, the upper grippers being arranged to grip the second wall at a predetermined distance from the closed end of the bag,the upper support and the lower support being arranged to separate the lower clamps from the upper clamps to form a rib on the gussets extending from one wall to the other, a flapper for folding the bottom onto the second wall by forming a first fold exiting on the first wall between the lower clamps, a second fold exiting on the second wall between the ends of the ribs, and a third fold entering on the second wall symmetrically at the end of the bag relative to the second fold.,

[0018] According to a constructive arrangement, the lower and upper supports are counter-rotating cylinders, respectively lower and upper. Once the grippers have passed the neck between the cylinders, the grippers move away from each other due to the rotation of the cylinders. After a complete rotation, the grippers return to a position to take charge of the next bag.

[0019] According to an improvement, the machine comprises support means for pressing on the second wall after the upper clamps have been released and which comprise a rule extending in the direction of a generator of the upper cylinder, and actuating means for extracting the rule from the upper cylinder during the folding phase and then retracting it. The exit of the rule can be controlled for example by a cam system or by an electrically or pneumatically motorized control.

[0020] According to one constructive arrangement, the flapper is achieved by a flapping cylinder configured to clamp the bag against the lower support. The flapper first guides the closed end of the bag to a neck between it and the first support and then clamps the bag at this neck in order to properly form the folds, so that the bag is flattened for storage and transport.

[0021] According to an improvement, the lower support and / or the upper support comprises suction means for sucking up the first and / or the second wall respectively so as to separate them before being gripped by the clamps. This ensures that the clamps only grip the nearby wall in order to properly separate the walls.

[0022] According to an improvement, the suction means extend upstream of the upper support over a length sufficient to create at least one air supply channel from the open end of the bag to the closed end. These means allow the bag to be filled with air when the walls at the closed end are separated.

[0023] According to a constructive arrangement, the suction means comprise an air-permeable strip mounted in a loop and against which the second wall of the bag is sucked, the strip being driven to move at the same speed as the bag. The strip accompanies the movement of the second wall to avoid friction with it. The strip constitutes one of the walls of a box placed under vacuum, which makes it possible to create suction through the strip. To create permeability, the strip can be perforated at regular intervals.

[0024] According to an improvement, the machine comprises a stamping station for marking the walls of the bag according to a first marking at a predetermined distance from the closed end and according to a second marking at the same predetermined distance from the first marking. The first marking will then correspond to the first and second fold lines. The second marking will correspond to the third fold line. By marking the fold lines in advance, the formation of said folds is facilitated. The position of said fold lines is also ensured.

[0025] According to a constructive arrangement, the upsetting station comprises an upsetting cylinder and a counter-cylinder mounted counter-rotating parallel to each other, the upsetting cylinder comprising two blades extending along two generatrices and projecting from the surface of the cylinder and the counter-cylinder comprising a flexible surface. DESCRIPTION OF FIGURES

[0026] Other characteristics and advantages of the invention will emerge clearly from the description given below, for information purposes only and in no way limiting, with reference to the appended drawings, among which: ▷ the figure 1 is a schematic side view of a machine according to a first embodiment of the invention; ▷ the figure 2 is a perspective view of a flat bag before transformation according to the method of the invention; ▷ the figure 3 is a view similar to the figure 2 of the bag having undergone a stage of rib formation; ▷ the figure 4 is a view similar to the figure 2 of the bag during a folding phase; ▷ the Figure 5 is a side view of the bag of the figure 2 at the end of the drawdown phase; ▷ the figure 6 is a perspective view of the open bag standing upright ready to be filled ▷ the figure 7 is a view similar to the figure 1 according to a second embodiment ▷ the figure 8is a view similar to the figure 2 after carrying out the refoulement according to the second embodiment. DETAILED DESCRIPTION

[0027] A flexible bag manufacturing machine, according to a first embodiment and as shown schematically in the figure 1 , includes a classic bottom forming station 1, the detailed description of which is not repeated here. At the exit of the bottom forming station 1, a flat bag 2 is provided, the bag 2 comprising, as shown in the figure 2, a first wall 21 and a second wall 22 superimposed on the first wall 21. The walls 21, 22 are connected to each other along longitudinal edges 23 by two gussets 24. One end 20 of the bag 2 is closed by a flap 25 coming from the first wall 21 and glued to the second wall 22. The bag 2 is shown with a tab 26 which extends the first wall 21 beyond the end of the second wall 22 opposite the closed end. However, the invention also applies to the case where the tab 26 extends the second wall 22, or, more generally, whatever the shape of this end.

[0028] The machine further comprises receiving means 3, a lower support 4, an upper support 5, and a reel 6.

[0029] The receiving means 3 are provided to receive in series the bags 2 moving in a main direction parallel to the longitudinal edges coming from the bottom forming station 1, the closed end 20 in front. The receiving means 3 make it possible to pass the bags 2 one by one, at regular intervals until the next step.

[0030] The lower support has the shape of a rotatably mounted lower cylinder 4. The lower cylinder 4 supports two lower grippers 41, the lower grippers 41 being arranged to grip the first wall 21 of the bag 2 presented by the receiving means 3 at a predetermined distance from the closed end 20 of the bag 2. The lower grippers 41 are aligned on the same generatrix of the lower cylinder 4. The upper support has the shape of an upper cylinder 5 rotatably mounted in the opposite direction to that of the lower cylinder 4. The upper cylinder 5 supports upper grippers 51 which are arranged to grip the second wall 22 at the predetermined distance from the closed end 20 of the bag 2. For this, the lower 41 and upper 51 grippers are opposite each other without angular offset. The upper grippers 51 are aligned on the same generatrix of the upper cylinder 5.The gripping of the walls is carried out when the clamps are at the level of the neck between the lower and upper cylinders 4, 5.

[0031] To facilitate gripping by the grippers 41, 51, the upper and lower cylinders 4, 5 comprise suction means 8, for respectively sucking the first and second walls 21, 22 so as to separate them before gripping by the grippers 41, 51. These suction means 8 comprise two lower boxes 81 and two upper boxes 82 facing each other upstream of the upper support 5 and, for each box 81, 82, an air-permeable strip 83, 84 mounted in a loop. The permeable strip 83, 84 is placed against the box 81, 82 in front of an opening thereof and is driven to travel at the same speed as the bag. The strip 83, 84 is for example pierced with a row of holes in its middle. The box 81, 82 is placed under vacuum by means not shown so that the second wall 22 of the bag is sucked against the strip 84 of the upper box 82 and the first wall 21 of the bag is sucked against the strip 83 of the lower box 81.The length of the boxes 81, 82 is sufficient so that, when the grippers grip the upper and lower walls 21, 22, an air supply channel is created from the open end 21 of the bag to the closed end 20 by the separation of the walls due to the suction against the strips 83, 84. Preferably, the boxes 81, 82 are positioned to suction the edges of the walls 21, 22 at the gussets 24.

[0032] The upper support 5 and the lower support 4 are arranged to separate the lower clamps 41 from the upper clamps 51. The separation is obtained by continuing the rotation of the lower and upper cylinders 4, 5 so that the distance between the clamps 41, 51 increases. A rib 27 is thus formed on each of the bellows 24 extending from one wall to the other.

[0033] The machine further comprises support means 7 for pressing on the second wall 22 after the upper clamps 51 have been released. The support means 7 comprise a rule 71 extending in the direction of a generatrix of the upper cylinder 5, and actuating means for extracting the rule 71 from the upper cylinder 5 during the folding phase and then retracting it.

[0034] The flapper 6 is provided for folding the bottom onto the second wall 22. The flapper 6 is produced by a folding cylinder 6 configured to clamp the bag 2 against the lower cylinder 4 by rotating in the opposite direction to the lower cylinder 4.

[0035] The machine implements a special bottom forming process on 2-flat bags.

[0036] After one of the ends of the bag 2 has been closed in the bottom forming station 1 by a flap 25 coming from one of the walls 21 and glued to the other wall 22, in a manner known per se, the bag 2 is transported in a transport direction by the receiving means 3, the longitudinal edges 53 of the bag 2 being parallel to the transport direction F1, towards the neck between the upper and lower cylinders 4, 5, which are counter-rotating. The closed end 20 of the bag 2 protrudes beyond the neck and the suction means tend to separate the first 21 from the second wall 22. In addition, a channel is created inside the bag along each edge to put the bottom in communication with the opening of the bag. The lower 41 and upper 51 clamps are actuated to grip the first and second walls 21, 22 respectively at a predetermined distance from the closed end 20 of the bag 2. Thus the clamps 41, 51 are introduced into the space delimited by the bellows 24.They hold the first wall 21, respectively the second 22, on the lower cylinder 4, respectively the upper cylinder 5.

[0037] As the lower and upper cylinders 4, 5 continue to rotate, the walls are spread apart using the grippers 41, 51 to form a rib 27 on the bellows 24 extending from one wall to the other 21, 22, as shown in the figure 3 . The cavity thus created fills with air from the open end through the air supply channels. The upper clamps 51 are then controlled to release the second wall 22. The rule 71 of the support means 7 is deployed to press on the second wall 22 after the release of the upper clamps 51, as shown in figure 4 .

[0038] The bag 2 continues its trajectory towards the folding cylinder 6 to fold the closed end 20 of the bag 2 onto the second wall 22, forming a first fold 281 exiting onto the first wall 21 between the lower clamps 41, a second fold 282 exiting onto the second wall 22 between the ends of the ribs 27, and a third fold 283 returning onto the second wall 22 symmetrically at the end of the bag 2 relative to the second fold 282, thus creating a bottom 29 delimited between the first and second folds 281, 282. The distance between the closed end 20 and the first fold 281, respectively the second fold 282 is substantially equal to the depth of the gussets 24.

[0039] When using the bag 2, it can be opened from the open end by spreading the first and second walls 21, 22 apart, to obtain a shape as in the figure 6. Depending on the nature of the material of the bag 2, it can stand upright on the bottom 29 created according to the method. The material can be paper, plastic film or a thermoplastic woven material.

[0040] In a variant not shown, the bags are initially formed closed by the flap 25, they are stacked, then they are unstacked to produce the base 29. Unstacking means replace the base forming station 1 and feed the receiving means 3 with the bags one by one.

[0041] The action of the support means 7 is not essential, depending on the behavior of the material forming the bags. The third fold 283 can be formed naturally by the folding action.

[0042] According to a second embodiment of the invention, shown in the figure 7, the machine differs from that of the first embodiment in that it comprises a discharging station 9 for marking the walls of the bag and facilitating the shaping thereof. The discharging station 9 is placed upstream of the suction means 8 and comprises a discharging cylinder 91 and a counter-cylinder 91. The two cylinders 91, 92 are mounted to rotate parallel to each other and are counter-rotating. The discharging cylinder 91 comprises two blades 911, 912 extending along two generatrices and projecting from the surface of the cylinder 91. The counter-cylinder 92 comprises a flexible surface, produced for example by a rubber coating, at least opposite the blades 911, 912.

[0043] In operation, the peripheral speed of the cylinders 91, 92 is that of the bag movement. The blades 911, 912 successively pinch the bag 2 against the counter-cylinder 92 and thus produce two markings on each bag. Preferably, the first marking corresponds to the first fold 281 and to the second fold 282, while the second marking anticipates the third fold 283, as shown in the figure 8 . The preferred distance between the first marking and the edge of the closed end is equal to the depth of the bellows. The preferred distance between the second marking and the edge of the closed end is equal to twice the depth of the bellows. The rest of the operation is similar to that described previously.

Claims

1. Process for forming flexible bags (2), the bag (2) comprising a first wall (21) and a second wall (22) superposed over the first wall (21), the walls (21, 22) being connected to each other along their longitudinal edges (53) by two gussets (24), whereby successively: > the bag (2) is closed to form a closed end (20) of the bag (2) opposite to the open end, > at a predetermined distance from the closed end (20) of the bag (2) the first wall (21) is gripped by the lower grippers (41) mounted on a lower support (4) and the second wall (22) by the upper grippers (51) mounted on an upper support (5) and the walls are separated by means of the grippers (41, 51), > the second wall (22) is released by the upper grippers (51) and the closed end (20) is folded (25) by the folding device (6) on to the second wall (22) forming a first crease (281) extending on to the first wall (21) between the lower grippers (41), a second crease (282) extending on to the second wall (22), and a third crease (283) entering into the second wall (22) symmetrically with the end of the bag (2) with respect to the second crease (282), thus making the bottom (29) delimited between the first and second creases (281, 282), > the process being characterised by the fact that when the grippers (41, 51) are separated, a side (27) is formed on the gussets (24) extending from one wall to the other (21, 22) between the ends of the first crease (281) and the ends of the second crease (282).

2. Process as per claim 1 whereby a pressing system (7) presses on to the second wall (22) after the upper grippers (51) are released.

3. Process as per one of the above claims whereby a separation is maintained between the second wall (22) and the first wall (21) over at least part of the width of the bag (2) and over its entire length in order to create a channel to supply air from the open end to the closed end (20).

4. Process as per one of the above claims whereby bags closed by the flap (25) are formed initially, and stacked and then unstacked to make the bottom (29).

5. Process as per one of the claims 1 to 3 whereby the formation of the bottom (29) is accomplished in line with the formation of the bag (2).

6. Process as per one of the above claims whereby the predetermined distance between the closed end (20) and the first crease (281), respectively the second crease (282) is more or less equal to the depth of the gussets (24).

7. Machine for manufacturing flexible bags, the bag (2) comprising a first wall (21) and a second wall (22) superposed over the first wall (21), the walls (21, 22) being connected to each other along their longitudinal edges (53) by two gussets (24), one end (20) of the bag (2) being closed, the machine being characterised by the fact that it comprises a reception system (3) for receiving a series of bags (2) moving in a main direction (F1) parallel to the longitudinal edges (53), with the closed end (20) leading, a lower support (4) for supporting two lower grippers (41), the lower grippers (41) being arranged to grip the first wall (21) at a predetermined distance from the closed end (20) of the bag (2), an upper support (5) for supporting upper grippers (51), the upper grippers (51) being arranged to grip the second wall (22) at a predetermined distance from the closed end (20) of the bag (2), the upper support (5) and the lower support (4) being arranged to separate the lower grippers (41) from the upper grippers (51) to form a side (27) on the gussets (24) extending from one wall to the other (21, 22), a folding device (6) to fold the bottom (29) on to the second wall (22) by forming a first crease (281) extending on to the first wall (21) between the lower grippers (41), a second crease (282) extending on to the second wall (22) between the ends of the sides (27), and a third crease (283) entering on to the second wall (22) symmetrically at the end of the bag (2) with respect to the second crease (282).

8. Machine as per claim 7, in which the lower and upper supports are respectively lower and upper contrarotating cylinders (4, 5).

9. Machine as per claim 8, characterised by the fact it comprises a pressing system (7) for pressing on the second wall (22) after the upper grippers (51) are released and which comprises a ruler (71) extending in the direction of a generatrix of the upper cylinder (5), and an actuating system for extracting the ruler (71) from the upper cylinder (5) during the folding phase and then retracting it.

10. Machine as per one of claims 7 to 9 in which the folding device is made by a folding cylinder (6) configured to squeeze the bag (2) against the lower support (4).

11. Machine as per one of the claims 7 to 10 in which the lower support (4) and / or the upper support (5) comprise(s) a suction system (8) to suck respectively the first and / or second wall (21, 22) so as to separate them before being gripped by the grippers (41, 51).

12. Machine as per claim 11 in which the suction system (8) extends upstream of the upper support over a sufficient length to create at least one channel to feed air from the open end of the bag to the closed end (20).

13. Machine as per claim 12 in which the suction system (8) comprises a strip (83, 84) permeable to air mounted in a loop and against which the second wall (22) of the bag is sucked, the strip (83, 84) being driven to advance at the same speed as the bag (2).

14. Machine as per one of the claims 7 to 13, characterised by the fact it comprises a creasing station (9) to mark the walls of the bag as per a first marking at a predetermined distance from the closed end (20) and as per a second marking at the same predetermined distance from the first marking.

15. Machine as per claim 14 in which the creasing station (9) comprises a creasing cylinder (91) and a counter-cylinder (92) mounted contrarotating in parallel with each other, the creasing cylinder (91) comprises two blades (911, 912) extending along two generatrixes and protruding from the surface of the cylinder (91), the counter-cylinder (92) comprising a soft surface.