WO2014199340A1

WO2014199340A1 - Packing machine and method for producing a sealed package of cigarettes in a modified atmosphere

Info

Publication number: WO2014199340A1
Application number: PCT/IB2014/062184
Authority: WO
Inventors: Fulvio Boldrini
Original assignee: G.D Societa' Per Azioni
Priority date: 2013-06-12
Filing date: 2014-06-12
Publication date: 2014-12-18
Also published as: ITBO20130294A1

Abstract

A packing machine (18) and method for producing a sealed package (3) of cigarettes in a modified atmosphere, and whereby: a group (4) of cigarettes is formed at a group- forming station (21); a stiffener (12) is applied to the group (4) of cigarettes at an application station (22); at a wrapping station (47), a sheet (7) of packing material is wrapped longitudinally into a tube about the group (4) of cigarettes enclosed in the stiffener (12), to form a tubular wrapping; a longitudinal sealing device (48) forms a longitudinal seal (9) on the tubular wrapping; and a transverse sealing device (49) cyclically forms on the tubular wrapping a succession of transverse seals (10), each located between two consecutive groups (4) of cigarettes. A closed main chamber (58) is provided, which houses at least the wrapping station (47); and a feed device (62) is provided to feed a packing gas at higher than atmospheric pressure into the main chamber (58).

Description

PACKING MACHINE AND METHOD FOR PRODUCING A SEALED PACKAGE OF CIGARETTES IN A MODIFIED ATMOSPHERE

TECHNICAL FIELD

The present invention relates to a packing machine and method for producing a sealed package of cigarettes in a modified atmosphere.

The present invention may be applied to advantage to a sealed package of cigarettes with a reclosable extraction opening, to which the following description refers purely by way of example.

BACKGROUND ART

A rigid hinged-lid packet of cigarettes normally comprises an inner package enclosing a group of cigarettes; and a rigid outer container housing the inner package.

To better preserve the organoleptic characteristics of the cigarette tobacco, a sealed inner package has recently been proposed, which is formed by folding and heat-sealing a sheet of impermeable packing material. To withdraw the cigarettes, the sealed inner package has an extraction opening normally covered with an adhesive Open and close' flap. More specifically, the adhesive flap is coated with non-dry, re-stick adhesive which allows it to be stuck repeatedly in the closed positioned closing the cigarette extraction opening. Patent Application DE102010019867A1, for example, describes a flow-pack packing machine for producing a sealed package of cigarettes, and which comprises a group-forming station, where a group of cigarettes is formed in a group-forming pocket of a group-forming conveyor; a wrapping station where a sheet of packing material, with a cigarette extraction opening and a reclosable adhesive flap, is wrapped longitudinally into a tube about the group of cigarettes to form a tubular wrapping; a longitudinal sealing device for forming a longitudinal seal on, and so stabilizing the shape of, the tubular wrapping; and a transverse sealing device located downstream from the longitudinal sealing device to cyclically form on the tubular wrapping a succession of transverse seals, each located between two consecutive groups of cigarettes.

To better preserve the cigarettes inside the sealed inner package, it has been proposed to form the sealed inner package in a modified atmosphere (e.g. an atmosphere composed of inert gases, normally such as nitrogen) . Attempts made so far, however, to adapt existing cigarette packing machines to the production of sealed inner packages in a modified atmosphere have proved disappointing, i.e. the resulting cigarette packing machines are both ineffective (i.e. produce poor-quality packets) and inefficient (i.e. very slow- operating) .

DESCRIPTION OF THE INVENTION

It is an object of the present invention to provide a packing machine and method for producing a sealed package of cigarettes in a modified atmosphere, which packing machine and method are designed to eliminate the above drawbacks while at the same time being cheap and easy to implement.

According to the present invention, there are provided a packing machine and method for producing a sealed package of cigarettes in a modified atmosphere, as claimed in the accompanying Claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A non-limiting embodiment of the present invention will be described by way of example with reference to the attached drawings, in which:

Figure 1 shows a front view in perspective, in a closed configuration, of a packet of cigarettes comprising a sealed package in accordance with the present invention;

Figure 2 shows a front view in perspective of the Figure 1 packet of cigarettes in a partly open configuration;

Figure 3 shows a rear view in perspective of the Figure 1 packet of cigarettes in a closed configuration;

Figure 4 shows a front view in perspective of a sealed package of the Figure 1 packet;

Figure 5 shows a rear view in perspective of the Figure 4 sealed package;

Figure 6 shows a front view in perspective of a group of cigarettes contained inside the Figure 4 sealed package ;

Figure 7 shows a front view in perspective of the Figure 4 sealed package prior to finally folding two lateral fin seals;

Figure 8 shows a plan view of a sheet of heat-seal packing material from which to form the Figure 4 sealed package ;

Figure 9 shows a front view in perspective of a stiffener which is inserted inside the Figure 4 sealed package ;

Figure 10 shows a rear view in perspective of the Figure 9 stiffener;

Figure 11 shows a front view in perspective of the Figure 9 stiffener prior to finally folding a centre stabilizing tab;

Figure 12 shows a blank from which to form the Figure 9 stiffener;

Figure 13 shows a schematic plan view of an initial packing unit of a packing machine for producing the Figure 1 packet of cigarettes;

Figure 14 shows a schematic side view of the Figure 13 initial packing unit;

Figure 15 shows a schematic view in perspective of part of the Figure 13 initial packing unit;

Figure 16 shows a schematic view in perspective of an application station of the Figure 13 initial packing unit ;

Figure 17 shows a schematic front view of a folding wheel of the Figure 13 initial packing unit;

Figure 18 shows a schematic front view of the Figure 13 initial packing unit;

Figure 19 shows a larger-scale detail of Figure 18. PREFERRED EMBODIMENTS OF THE INVENTION

Number 1 in Figures 1, 2 and 3 indicates as a whole a rigid packet of cigarettes. Packet 1 of cigarettes comprises a cup-shaped cardboard outer container 2; and a sealed package 3 (shown more clearly in Figures 4 and 5) housed inside container 2.

Outer container 2 has an open top end; and a cup- shaped lid hinged to outer container 2 along a hinge (Figure 3) to rotate, with respect to outer container 2, between an open position (Figure 2) and a closed position (Figures 1 and 3) opening and closing the open top end respectively. When the lid is in the closed position, outer container 2 is in the form of a rectangular parallelepiped having a top wall and an opposite parallel bottom wall; a front wall and an opposite parallel rear wall (n which the hinge is formed); and two opposite parallel lateral walls. Four longitudinal edges are defined between the lateral walls and the front and rear walls; and eight transverse edges are defined between the top and bottom walls and the front, rear, and lateral walls.

As shown in Figures 4 and 5, sealed package 3 houses a parallelepiped-shaped group 4 of cigarettes

(Figure 6), and has a cigarette extraction opening 5

(shown by the dash line in Figure 4) at the top and front. Cigarette extraction opening 5 is located centrally, is closed by an Open & close' adhesive flap 6, and extends over part of a front wall of sealed package 3, and part of a top wall of sealed package 3. Adhesive flap 6 normally adheres to the part of sealed package 3 surrounding extraction opening 5, to close

(seal) extraction opening 5, and can be lifted up temporarily to open, and withdraw a cigarette through, extraction opening 5.

Sealed package 3 is formed by folding a rectangular sheet 7 of impermeable, heat-seal packing material

(Figure 8) having a U-shaped incision defining extraction opening 5. Adhesive flap 6 is glued to sheet 7 of packing material, is rectangular, and completely covers the incision (i.e. extraction opening 5) . Non- dry, re-stick adhesive is applied between adhesive flap 6 and sheet 7 of packing material, i.e. adhesive that remains tacky and, even over a long period of time, allows adhesive flap 6 to be detached from and stuck back onto sheet 7 of packing material numerous times. In a preferred embodiment, the non-dry, re-stick adhesive is applied beforehand to an inner face of adhesive flap 6, prior to applying adhesive flap 6 to sheet 7 of packing material.

The non-dry, re-stick adhesive between adhesive flap 6 and sheet 7 of packing material glues the portion of sheet 7 of packing material surrounded by the incision (i.e. at extraction opening 5) permanently (i.e. non-detachably, even in use) to adhesive flap 6, so that, when adhesive flap 6 is lifted off sheet 7 of packing material, the portion of sheet 7 of packing material surrounded by the incision (i.e. at extraction opening 5) lifts up together with adhesive flap 6 to open extraction opening 5. Conversely, the non-dry, re- stick adhesive between adhesive flap 6 and sheet 7 of packing material glues the portion of sheet 7 of packing material surrounding the incision (i.e. surrounding extraction opening 5) temporarily (i.e. detachably in use) to adhesive flap 6, so adhesive flap 6 is normally maintained contacting sheet 7 of packing material to close (seal) extraction opening 5.

Adhesive flap 6 has a grip tab 8, which has no non- dry, re-stick adhesive on the side (i.e. surface) facing sheet 7 of packing material, and is located close to and beneath extraction opening 5. Grip tab 8 serves to make adhesive flap 6 easier to grip and lift up. In other words, to lift up adhesive flap 6, the user simply grips grip tab 8, which is in no way fixed to sheet 7 of packing material, unlike the rest of adhesive flap 6.

As shown in Figures 4 and 5, sealed package 3 is stabilized, i.e. kept in the folded configuration, by a central (or longitudinal) fin seal 9 on the front wall and lateral walls of sealed package 3, and by two lateral (or transverse) fin seals 10 on the lateral walls of sealed package 3. The central fin seal 9 forms a tubular wrapping with two open ends at the lateral walls of sealed package 3, is at first perpendicular to the front wall of sealed package 3, and, once it is formed, is folded 90° onto the front wall of sealed package 3 (as shown in Figures 4 and 7) . The two lateral fin seals 10 close the tubular wrapping laterally, are at first perpendicular to the corresponding lateral walls of sealed package 3 (as shown in Figure 7), and, once they are formed, are folded 90° onto the corresponding lateral walls of sealed package 3 (as shown in Figures 4 and 5) .

As shown in Figure 7, the formation of each lateral fin seal 10 produces two triangular end flaps 11 projecting from opposite ends of the corresponding lateral wall of sealed package 3; and, after each lateral fin seal 10 is folded 90° onto the corresponding lateral wall of sealed package 3, the two triangular end flaps 11 are folded 180° onto the corresponding lateral wall of sealed package 3, and over the previously folded lateral fin seal 10. In one embodiment, each triangular end flap 11 is heat sealed to the corresponding lateral wall of sealed package 3 to fix it in the desired position shown in Figures 4 and 5. Alternatively, each triangular end flap 11 may be fixed in the desired position shown in Figures 4 and 5 simply by outer container 2 surrounding sealed package 3.

As shown in Figures 9 and 10, sealed package 3 comprises a U-shaped stiffener 12 made of cardboard (identical to that of outer container 2) and inserted inside sealed package 3, contacting group 4 of cigarettes .

Stiffener 12 comprises a rectangular front wall 13 positioned contacting the front wall of group 4 of cigarettes; two lateral walls 14 connected to opposite edges of front wall 13 and positioned contacting the lateral walls of group 4 of cigarettes; and a bottom wall 15 positioned contacting the bottom wall of group 4 of cigarettes. Front wall 13 has a U-shaped top window for facilitating withdrawal of the cigarettes from group 4, by exposing a top area of the front wall of group 4 of cigarettes at extraction opening 5. Stiffener 12 also comprises two lateral stabilizing tabs 16 connected to lateral walls 14, and which are folded 90° onto the outer surface of bottom wall 15 (i.e. on the opposite side to group 4 of cigarettes) ; and a centre stabilizing tab 17 connected to bottom wall 15, and which is folded 180° onto the outer surface of bottom wall 15 (i.e. on the opposite side to group 4 of cigarettes) and over the two previously folded lateral stabilizing tabs 16. To show more clearly the way in which stabilizing tabs 16 and 17 are folded, Figure 11 shows stiffener 12 prior to finally folding central stabilizing tab 17, i.e. before centre stabilizing tab 17 is folded onto the outer surface of bottom wall 15 (i.e. on the opposite side to group 4 of cigarettes) and over the two previously folded lateral stabilizing tabs 16.

As shown more clearly in Figure 12, the two lateral stabilizing tabs 16 are connected to corresponding lateral walls 14 of stiffener 12 along two transverse fold lines, and centre stabilizing tab 17 is connected to bottom wall 15 of stiffener 12 along a further transverse fold line which at first is parallel to the other two transverse fold lines.

When manipulating group 4 of cigarettes and stiffener 12 combined, stiffener 12 can be stabilized (i.e. kept in the folded configuration) by simply pushing on bottom wall 15 (or, rather, on stabilizing tabs 16 and 17 externally covering bottom wall 15) from the outside (i.e. on the opposite side to group 4 of cigarettes) by means of a pad (described in detail below) . Pushing on bottom wall 15 using a pad from the outside (i.e. on the opposite side to group 4 of cigarettes), in fact, keeps stabilizing tabs 16 and 17 in the correct position on bottom wall 15. In other words, pushing on bottom wall 15 from the outside (i.e. on the opposite side to group 4 of cigarettes) grips stabilizing tabs 16 and 17 between the pad and bottom wall 15 to 'freeze' stiffener 12 in the folded configuration .

Once sealed package 3 is completed, i.e. formed, stiffener 12 serves to reinforce and maintain the shape of sealed package 3, so as to prevent sealed package 3 from collapsing, after some of the cigarettes are extracted from it, thus making it difficult to extract the remaining cigarettes and, in particular, making it extremely difficult to open and close adhesive flap 6. When forming sealed package 3, stiffener 12 serves to protect the cigarettes mechanically and to simplify/improve handling of group 4 of cigarettes (i.e. prevent group 4 of cigarettes from falling apart) .

Number 18 in Figure 13 indicates as a whole a packing machine for producing packet 1 of cigarettes described above.

Packing machine 18 comprises an initial packing unit 19 for producing sealed package 3 by forming group 4 of cigarettes and folding and sealing sheet 7 of packing material about group 4 of cigarettes; and a known final packing unit 20 (shown highly schematically) for producing outer container 2 by folding a collar and a blank successively about sealed package 3.

Initial packing unit 19 comprises a group-forming station 21 for forming group 4 of cigarettes; an application station 22 where stiffener 12 is applied to group 4 of cigarettes; and a packing station 23 where sheet 7 of packing material is wrapped about group 4 of cigarettes to form sealed package 3.

As shown in Figure 15, group-forming station 21 comprises a vertical hopper 24 with a number of bottom outlets; and a group-forming belt conveyor 25, which supports a number of group-forming pockets 26 and travels continuously to feed group-forming pockets 26 along a group-forming path PI (Figure 16) extending past the outlets of hopper 24. As shown in Figure 16, group- forming conveyor 25 comprises an endless belt looped about two powered end pulleys. Consequently, group- forming path PI is U-shaped, and comprises a straight horizontal bottom branch extending in front of the outlets of hopper 24; and a straight top branch, which extends through application station 22 and terminates at a transfer device 36, which transfers each group 4 of cigarettes inside a group-forming pocket 26 to a packing seat 27 on a continuously-moving packing conveyor 28, which moves parallel to and is synchronized with group- forming conveyor 25 to feed packing seats 27 along a straight horizontal packing path P2.

In a preferred embodiment, the two powered end pulleys about which the belt of group-forming conveyor 25 is looped are movable linearly back and forth, parallel to the straight branches of group-forming path PI; and, at the same time, the rotation speed of the two powered end pulleys is variable in time with their linear back and forth movement. The linear back and forth movement of the pulleys, combined with the variation in their rotation speed, enables the group- forming pockets 26 in front of the outlets of hopper 24 (i.e. the group-forming pockets 26 along the straight bottom branch of group-forming path PI) to be stopped temporarily to transfer groups 4 of cigarettes from the outlets of hopper 24 to group-forming pockets 26. At the same time, the linear back and forth movement of the pulleys, combined with the variation in their rotation speed, provides for keeping the group-forming pockets 26 along the straight top branch of group-forming path PI at a constant travelling speed and synchronized at all times with packing seats 27 (travelling continuously along packing path P2) of packing conveyor 28.

Application station 22 comprises an application belt conveyor 29 located alongside group-forming conveyor 25 to feed stiffener 12 parallel to the straight top branch of group-forming path PI. In a preferred embodiment, application conveyor 29 has suction, and retains stiffener 12 by suction on the underside surface of the conveyor belt. In other words, application conveyor 29 is located higher than group- forming conveyor 25, and stiffener 12 is suspended by suction underneath application conveyor 29.

As stated, a transfer device 36 (shown schematically in Figure 16) between group-forming path PI and packing path P2 extracts stiffener 12 and group 4 of cigarettes together and simultaneously from group- forming pocket 26 on group-forming conveyor 25, and inserts stiffener 12 and group 4 of cigarettes into a corresponding packing seat 27 on packing conveyor 28 moving parallel to and in time with group-forming conveyor 25. Transfer device 36 is located at the end of group-forming path PI, and transfers stiffener 12 and group 4 of cigarettes from the group-forming pocket 26 on group-forming conveyor 25 to the corresponding packing seat 27 on packing conveyor 28. As shown in Figure 15, a flow-pack type wrapping station 47 (shown schematically in Figure 15) is located along packing path P2, and which wraps sheet 7 of packing material longitudinally into a tube about group 4 of cigarettes to form a tubular wrapping. Sheets 7 of packing material are initially joined in the form of a continuous strip of packing material, which is unwound off a reel and continuously wound longitudinally into a tube about the succession of groups 4 of cigarettes. At wrapping station 47, a known longitudinal sealing device 48 forms longitudinal seal 9 on the tubular wrapping to stabilize the shape of the tubular wrapping; and a known folding device (not shown) connected to longitudinal sealing device 48 folds the fin-shaped longitudinal seal 9, as soon as it is formed, 90° onto the corresponding wall of group 4 of cigarettes (with the front wall 13 of stiffener in between) .

A transverse sealing device 49 downstream from longitudinal sealing device 48 cyclically forms on the tubular wrapping a succession of transverse seals 10, each located between two consecutive groups 4 of cigarettes, and also cuts along the centreline of each transverse seal 10 to separate the two consecutive sealed packages 3 sharing the same transverse seal 10.

As shown in Figure 17, downstream from transverse sealing device 49, a folding wheel 50 is mounted to rotate about a horizontal axis of rotation 51, and has a number of folding pockets 52, each for receiving a corresponding sealed package 3. Folding wheel 50 has a folding device 53 which preferably has fixed folding screws (i.e. fixed folding devices) and initially folds each fin-shaped transverse seal 10 ninety degrees onto the corresponding lateral wall of group 4 of cigarettes (with a lateral wall 14 of stiffener 12 in between) . Next, i.e. after folding each lateral fin seal 10 ninety degrees onto the corresponding lateral wall of sealed package 3, folding device 53 folds triangular end tabs 11 onto the corresponding lateral wall of sealed package 3, and over the folded lateral fin seal 10 (as shown in Figures 4 and 5) . Folding wheel 50 also has a sealing device 54 for heat sealing each triangular end tab 11 to the corresponding lateral wall of sealed package 3, to secure it in the desired position shown in Figures 4 and 5. In a different embodiment, each triangular end tab 11 may be kept in the desired position shown in Figures 4 and 5 simply by outer container 2 enclosing sealed package 3; in which case, sealing device 54 is dispensed with. It is important to note that the seals made by sealing device 54 fix both each triangular end tab 11 and each lateral fin seal 10 to the corresponding lateral wall of sealed package 3, so as to secure end tabs 11 and transverse fin seals 10 in their folded configurations .

As shown in Figure 17, a continuously-moving belt conveyor 55 is interposed between transverse sealing device 49 and folding wheel 50 to transfer sealed packages 3 successively from transverse sealing device 49 to folding wheel 50. Folding wheel 50 is mounted to rotate intermittently, i.e. in steps, about axis of rotation 51, and therefore comprises an input pusher 56 for inserting sealed package 3 inside a corresponding folding pocket 52; and an output pusher 57 for expelling sealed package 3 from corresponding folding pocket 52.

As shown in Figures 18 and 19, packing machine 18 comprises a closed main chamber 58 housing wrapping station 47 and longitudinal sealing device 48. More specifically, main chamber 58 only houses wrapping station 47 and longitudinal sealing device 48 (application station 22 and transverse sealing device 49 being located outside main chamber 58) . In a different embodiment not shown, longitudinal sealing device 48 is located outside main chamber 58, which only houses wrapping station 47. Main chamber 58 has an inlet opening 59 for sheets 7 of packing material (which are initially joined in the form of a continuous strip of packing material unwound off a reel) ; an inlet opening 60 for group 4 of cigarettes enclosed in stiffener 12; and an outlet opening 61 for the tubular wrapping. Outlet opening 61 of closed main chamber 58 is located between longitudinal sealing device 48 and transverse sealing device 49; and inlet opening 59 of main chamber 58 is located between application station 22 and wrapping station 47.

Main chamber 58 is connected to a feed device 62 for feeding packing gas at higher than atmospheric pressure into main chamber 58, to keep main chamber 58 at higher than atmospheric pressure. By way of example, the packing gas substantially comprises an inert gas (typically nitrogen), to which sterilizing and/or aromatic compounds may be added.

In one possible embodiment, shown in the attached drawings, a closed secondary chamber 63 is located adjacent to main chamber 58 (i.e. shares a wall with main chamber 58), and is located directly upstream from main chamber 58, at inlet opening 59. Secondary chamber 63 is connected to an aspirator 64, which aspirates continually from secondary chamber 63 to keep it at below atmospheric pressure. Secondary chamber 63 has an inlet opening 65 aligned with inlet opening 59 of main chamber 58; and an inlet opening 66 aligned with inlet opening 60 of main chamber 58; and because, as stated, secondary chamber 63 shares a wall with main chamber 58, an outlet opening of secondary chamber 63 coincides with inlet opening 60 of main chamber 58. In one possible embodiment, shown in the attached drawings, a closed secondary chamber 67 is located adjacent to main chamber 58 (i.e. shares a wall with main chamber 58), and is located directly downstream from main chamber 58, at outlet opening 61. Secondary chamber 67 is connected to an aspirator 68, which aspirates continually from secondary chamber 67 to keep it at below atmospheric pressure. Because, as stated, secondary chamber 67 shares a wall with main chamber 58, an inlet opening of secondary chamber 67 coincides with outlet opening 61 of main chamber 58; and secondary chamber 67 also has an outlet opening 69 aligned with outlet opening 61 of main chamber 58.

In one possible embodiment, each aspirator 64, 68 is connected to a separator 70 for separating and recovering the packing gas . The packing gas recovered by separator 70 may be fed to feed device 62 for immediate recycling .

Secondary chambers 63 and 67 serve to recover the packing gas and prevent it from leaking into the atmosphere (undesirable but inevitable) through openings 59, 60, 61 in main chamber 58. Secondary chambers 63 and 67 are therefore only used when the packing gas contains compounds (e.g. sterilizers) not to be dispersed into the atmosphere, and/or to reduce packing gas consumption by recycling it through separator 70. When preventing the packing gas from being dispersed into the atmosphere is unnecessary (inconvenient), secondary chambers 63, 67 may therefore even be dispensed with.

Packing machine 18 described has numerous advantages .

Firstly, packing machine 18 described provides for producing sealed packages 3 in a modified atmosphere both effectively (i.e. sealed packages 3 of excellent quality) and efficiently (i.e. at high output rates of as many as 500-700 sealed packages 3 a minute) .

Secondly, packing machine 18 described is cheap and easy to produce.

And finally, given the small overall volume of main chamber 58, unwanted packing gas dispersion on packing machine 18 described is reduced to a minimum.

Claims

1) A packing machine (18) for producing a sealed package (3) of cigarettes in a modified atmosphere; the packing machine (18) comprising:

a group-forming station (21) where a group (4) of cigarettes is formed in a group-forming pocket (26) of a group-forming conveyor (25) which feeds the group- forming pocket (26) along a group-forming path (PI) extending past an outlet of a hopper (24) ;

a wrapping station (47) where a sheet (7) of packing material, having a cigarette extraction opening (5) and a reclosable adhesive flap (6), is wrapped longitudinally into a tube about the group (4) of cigarettes to form a tubular wrapping;

a longitudinal sealing device (48) for forming a longitudinal seal (9) on the tubular wrapping to stabilize the shape of the tubular wrapping; and

a transverse sealing device (49) located downstream from the longitudinal sealing device (48), and which cyclically forms on the tubular wrapping a succession of transverse seals (10), each located between two consecutive groups (4) of cigarettes;

the packing machine (18) being characterized by comprising :

a closed main chamber (58) housing at least the wrapping station (47) and having a first inlet opening (59) for the sheet (7) of packing material; a second inlet opening (60) for the group (4) of cigarettes; and an outlet opening (61) for the tubular wrapping; and

a feed device (62) for feeding a packing gas at higher than atmospheric pressure into the main chamber (58) to keep the main chamber (58) at higher than atmospheric pressure.

2) A packing machine (18) as claimed in Claim 1, wherein the main chamber (58) also houses the longitudinal sealing device (48) .

3) A packing machine (18) as claimed in Claim 2, wherein the outlet opening (61) of the closed main chamber (58) is located between the longitudinal sealing device (48) and the transverse sealing device (49) .

4) A packing machine (18) as claimed in Claim 1, 2 or 3, and comprising an application station (22) for applying to the group (4) of cigarettes a stiffener (12) made of rigid material and comprising a front wall (13), and two lateral walls (14) connected to opposite edges of the front wall (13) .

5) A packing machine (18) as claimed in Claim 4, wherein the first inlet opening (59) of the main chamber (58) is located between the application station (22) and the wrapping station (47) .

6) A packing machine (18) as claimed in one of Claims 1 to 5, and comprising:

a closed first secondary chamber (63) adjacent to the main chamber (58) and located directly upstream from the main chamber (58) , at the first inlet opening (59) ; and

a first aspirator (64) connected to the first secondary chamber (63), and which aspirates continually from the first secondary chamber (63) to keep the first secondary chamber (63) at below atmospheric pressure.

7) A packing machine (18) as claimed in one of Claims 1 to 6, and comprising:

a closed second secondary chamber (67) adjacent to the main chamber (58) and located directly downstream from the main chamber (58) , at the outlet opening (61) ; and

a second aspirator (68) connected to the second secondary chamber (67), and which aspirates continually from the second secondary chamber (67) to keep the second secondary chamber (67) at below atmospheric pressure .

8) A packing machine (18) as claimed in Claim 6 or 7, wherein each aspirator (64, 68) is connected to a separator (70) for separating and recovering the packing gas .

9) A packing method for producing a sealed package (3) of cigarettes in a modified atmosphere; the packing method comprising the steps of:

forming a group (4) of cigarettes in a group- forming pocket (26) of a group-forming conveyor (25) which feeds the group-forming pocket (26) along a group- forming path (PI) extending past an outlet of a hopper (24) ;

wrapping a sheet (7) of packing material, having a cigarette extraction opening (5) and a reclosable adhesive flap (6), longitudinally into a tube about the group (4) of cigarettes enclosed in a stiffener (12), to form a tubular wrapping;

longitudinally sealing the tubular wrapping by means of a longitudinal sealing device (48) to stabilize the shape of the tubular wrapping; and

transversely sealing the tubular wrapping by means of a transverse sealing device (49) located downstream from the longitudinal sealing device (48), to cyclically form a succession of transverse seals (10), each located between two consecutive groups (4) of cigarettes;

the packing method being characterized in that:

the step of wrapping the sheet (7) of packing material longitudinally into a tube about the group (4) of cigarettes is performed in a closed main chamber (58) having a first inlet opening (59) for the sheet (7) of packing material, a second inlet opening (60) for the group (4) of cigarettes enclosed in the stiffener (12), and an outlet opening (61) for the tubular wrapping; and a feed device (62) is provided to feed a packing gas at higher than atmospheric pressure into the main chamber (58) to keep the main chamber (58) at higher than atmospheric pressure.

10) A packing method as claimed in Claim 9, and comprising the further step of applying to the group (4) of cigarettes a stiffener (12) made of rigid material and comprising a front wall (13), and two lateral walls (14) connected to opposite edges of the front wall (13) .

11) A packing method as claimed in Claim 9 or 10, wherein :

a closed first secondary chamber (63) is located adjacent to the main chamber (58) and directly upstream from the main chamber (58), at the first inlet opening (59) ; and

a first aspirator (64) is connected to the first secondary chamber (63), and aspirates continually from the first secondary chamber (63) to keep the first secondary chamber (63) at below atmospheric pressure.

12) A packing method as claimed in Claim 9, 10 or 11, wherein:

a closed second secondary chamber (67) is located adjacent to the main chamber (58) and directly downstream from the main chamber (58), at the outlet opening (61) ; and a second aspirator (68) is connected to the second secondary chamber (67), and aspirates continually from the second secondary chamber (67) to keep the second secondary chamber (67) at below atmospheric pressure.

13) A packing method as claimed in Claim 11 or 12, wherein each aspirator (64, 68) is connected to a separator (70) for separating and recovering the packing gas .