Description

Technical Field

[0001] The present invention relates to the packaging machines for tissue paper products; more specifically, the object of the invention is a packaging machine for products, such as kitchen towel rolls and toilet rolls, wrapped in paper sheet.

State of the Art

[0002] In the paper industry, the paper products, particularly toilet rolls and kitchen towel rolls, are typically wrapped in sheets of thermoplastic film or, in the case of single rolls, in paper sheets. Packs containing a single roll are usually used for toilet rolls, while multi-roll packs, packaged with heat-sealable films, are used for both toilet rolls and kitchen towel rolls. Generally, the single-roll packs wrapped in paper film are not sealed, while larger packs, wrapped in thermoplastic film, are thermally sealed.

[0003] To make these packs, the packaging machines have conveyors that, in the case of multi-roll packs, feed rows of rolls, arranged coaxially with one another with horizontal axis, to a station for grouping the rolls and forming a group of rolls arranged side by side in one or more layers. The groups of rolls are then conveyed to a vertically moving elevator that lifts each group of rolls to a wrapping station. The wrapping station wraps the group of rolls in a wrapping film, completing the pack of rolls. An example of these packaging machines is disclosed in the patent documents W02009060490 and EP12289669B1. This type of packaging is called primary packaging and is that typically used for retail. The resulting packs are conveyed to the secondary packaging, where they are grouped and bagged in large plastic bags. Examples of these packaging machines are disclosed in EP1442984, EP1771335. Finally, the bags containing the packs are placed on pallets and sent to warehouses or shipped directly to distributors.

[0004] In general, the groups of rolls are packaged by wrapping a thermoplastic wrapping film, such as polyethylene or other synthetic polymers, around a group of rolls, wrapping it around the four sides and forming a kind of parallelepiped with rectangular faces open on two opposite side faces. Then, the side flaps of the sheet projecting from the two side faces are folded, thus completing the covering of the rolls. Finally, the folds of the thermoplastic film are stabilized through heat-sealing made by heated Teflon-coated belts, as shown for example in EP1381543B1. In the case of single rolls to be packaged with paper sheets, the heated Teflon-coated belts heat- activate an adhesive, with which the sheets are pretreated on the whole surface.

[0005] In the case of single rolls to be packaged, the sheets can also be stabilized without using glue. For example, in EP1518787B1, the stabilization of the sheet wrapped around the single roll is done by twisting the flaps projecting from the flat faces of the roll and pressing them into the core of the roll with a punch. In other cases, as described in EP2766266B1, the flaps projecting from the flat faces are partially folded in sequence and stabilized by pressing each partial fold into the core with a series of punches.

[0006] Closing the single rolls without using glue has many disadvantages. The paper, twisted or folded several times and pressed into the core of the roll core is prone to tearing and breaking. In addition, not using glues makes the sealing very precarious, often causing the reopening of the package. Therefore, not only the quality of these packages is very low, but also the appearance thereof is compromised. The number of discarded packages is also very high because, once the wrapping sheet has been torn, the package must be discarded.

[0007] One further major shortcoming of the prior art systems is the use of heated Teflon-coated belts, which are, as it is well-known, poorly energy-efficient. In addition, the Teflon-coated belts also have a very short useful life, as they shall be replaced very often. The very rapid wear of the Teflon-coated belts also results in high production variability because the efficiency of the belts drops dramatically in a short time, causing a lot of production waste. Moreover, in the case of packaging with paper sheet, the Teflon-coated belts are not efficient in transmitting heat to the glue that shall be reactivated; therefore, to achieve sufficiently acceptable sealing, the machine speed must be reduced, compromising productivity. As an alternative, it is necessary to heat the belts much more, thus shortening even more the useful life thereof and consuming more energy. A further disadvantage of the Teflon-coated belt is that it does not provide the roll with a uniform and sufficiently rigid contrast surface for sealing the folds of the wrapping sheet.

[0008] Despite the greater problems in using a paper sheet instead of a classic thermoplastic film, high environmental awareness is increasingly pushing the paper industry toward the use of natural and recyclable materials, such as paper, instead of materials of a fossil nature, such as plastic heat-sealable films or synthetic films in general.

Summary

[0009] The object of the invention is to provide an improved machine for packaging products made of tissue paper or non-woven fabric, such as kitchen towel rolls and toilet rolls, napkins, handkerchiefs, wipes, and interfolded products, which is capable to overcome the current limitations in the use of paper wrapping materials. More in particular, the object of the invention is to provide a packaging machine for packaging tissue paper products that is suitable to speed up the packaging step and to combine efficiency, flexibility and quality of the packages produced.

[0010] A further object of the invention is to provide a packaging machine for packaging rolls and/or other paper products, which uses greener and more environmentally friendly packaging materials, such as paper, overcoming all the disadvantages mentioned above.

[0011] These and other objects are achieved through a packaging machine for packaging tissue paper products, comprising: o a product feeding station for grouping and feeding, one by one in succession, groups of products comprised of at least one product, o a wrapping station for wrapping paper wrapping sheets around the groups of products, o downstream of the wrapping station, a sealing station for sealing the paper wrapping sheets wrapped around the groups of products. [0012] According to the invention, the sealing station comprises a channel for moving forward the groups of products and a pair of sealing members provided opposite each other on the two sides of said channel, and each sealing member has a uniform sealing surface composed of heating material, of the type in which eddy currents can be induced when the material is subjected to a change in the magnetic field.

[0013] For example, the material is a ferromagnetic material, such as steel, iron or alloys thereof, or even other materials, or a paramagnetic material, such as aluminum or alloys thereof, or other materials.

[0014] For example, the heating material has a relative magnetic permeability of 1 or more.

[0015] Preferably, the sealing members are driven between at least two return members. In some embodiments, one of the two return members is motorized. For example, each sealing member may comprise at least one flexible element driven between at least two return members.

[0016] The sealing surface of each sealing member is heated, and it is therefore preferably associated with an electromagnetic induction device or inductor adapted to induce eddy currents in the material, so that the material is adapted to heat up by joule effect and can heat-seal. In general, the electromagnetic inductor is associated with each sealing member.

[0017] In order optimally to seal the packages, the temperature of the heated sealing surfaces shall be between 100° C and 400° C, depending on the type and quality of the paper material or single sheet or web material and/or depending on the format of the package to be produced.

[0018] The same objects of the invention are achieved even if at least one of the two sealing members, or both the sealing members in preferred embodiments, comprises one or more plates of ferromagnetic or paramagnetic material, having uniform sealing surfaces and preferably moved by at least one flexible member. In this case, the flexible member can also be a belt, or more belts, or alternately chains or another suitable flexible member. [0019] For example, multiple adjacent plates are provided, which have contact zones for the thermal conduction between the same plates; these contact zones may be provide, for example, only along one or more section of the moving path realized by the flexible member, e.g., at least the section corresponding to the moment when the plates travel along the sealing section within the channel wherein the products move forward. The contact zones are preferably provided close to the sides of the plates and provide, for example, for side recesses and corresponding side projections, coupled together so that the adjacent plates overlap each other. Side recesses and side projections preferably have respective faces, parallel to the sealing surface of the plate, which face each other; while moving forward in the feeding channel, the side projections are in contact with the side recesses at these faces. Preferably, the area and the shape of the cross-section of a projection can approximately match the area and the shape of the cross-section of a recess.

[0020] The channel of the sealing station may comprise a conveyor to move the groups of products forward along the sealing station in a product sealing direction. When the sealing members are motorized, the forward movement of the products in the sealing station is achieved by means of the conveyors and the sealing members opposite each other on two sides of the groups of products. In alternative configurations, the groups of products are moved forward by the sealing members, and the conveyor is replaced by a slide surface.

[0021] To facilitate the forward movement of the groups of products exiting the wrapping station, the sealing station moves the groups of products forward at a higher speed than the speed of exit from the wrapping station.

[0022] Advantageously, the packaging machine comprises adjusting members for adjusting the sealing pressure.

[0023] In some embodiments, the packaging machine comprises a feeding station for feeding paper wrapping sheets. The paper wrapping sheets preferably have grammage between 10 g/m ² and 100 g/m ² and thickness between 10 pm and 500 pm. The paper wrapping sheets can be obtained by cutting, through a cutting unit, a continuous paper web material unwound from a reel. The sheet feeding station is provided upstream of the wrapping station relative to the sheet feeding direction. The paper wrapping sheets may include a sealant for sealing the wrapped sheet around the groups of products. The sealant can be applied to the paper wrapping sheets in the sheet feeding station. Alternatively, the wrapping sheets can be cut from a paper web material that has already been treated with sealant and wound on a reel so that no sealant has to be applied in the sheet feeding station. Thus, the paper wrapping sheet is defined by two parallel sides and two sides that are transverse to the sheet feeding direction towards the wrapping station. Preferably, the sides transverse to the sheet feeding direction are obtained by cutting through the cutting unit.

[0024] If the wrapping sheets, or the continuous paper web material cut into wrapping sheets, receive the sealant, the sheet feeding station comprises a dispensing device for applying the sealant to the wrapping sheets or the paper web material. In the case of wrapping sheets, the dispensing device is provided downstream of the cutting unit, whilst, in the case of paper web material, the dispensing device is provided upstream of the cutting unit in the sheet feeding direction towards the wrapping station.

[0025] Preferably, the dispensing device comprises at least one dispenser for applying a line of sealant along a parallel direction of one of the two sides parallel to the sheet feeding direction, and at least one dispenser for applying a line of sealant along a direction parallel to each of the two sides transverse to the sheet feeding direction.

[0026] Preferably, the lines are continuous or discontinuous, have length equal to or less than the length of the respective sides of the wrapping sheet, and are arranged at a distance from the respective side, or respective edge of the sheet, comprised between 0.5 mm and 50 mm, preferably between 1 mm and 25 mm.

[0027] Advantageously, the dispensers can be of the spreading type, but it is also possible to apply the sealant using other systems, such as rollers or sprays.

[0028] In some embodiments, the station for feeding the paper wrapping sheets comprises a detecting device for detecting the position of the paper wrapping sheets or the paper web material along the sheet feeding direction. Preferably, the detecting device for detecting the position of the wrapping sheets or the web material is an encoder, but it is also possible to use other suitable devices. [0029] The use of a sensor for detecting the position of the sheets, or of the web material unwound from a reel, enables the dispensing device to apply the sealant in phase with the position of the paper wrapping sheets, or the paper web material.

[0030] The sealant is preferably an activatable adhesive.

[0031] The product feeding station comprises an elevator to lift the groups of products towards the wrapping station. In the lifting movement, the groups of products meet the paper wrapping sheet arranged parallel to a plane transverse to the group lifting direction. In this way, when the elevator has lifted the group of products up to the level of the wrapping station, the paper wrapping sheet forms a partial wrapping, shaped like an overturned "U", around the group of products.

[0032] The wrapping station comprises a bottom folding device that completes the partial overturned-U-shaped wrapping of the paper wrapping sheet around the groups of products, thus forming a tube or parallelepiped with approximately rectangular faces, open on two opposite parallel sides of the groups of products. Each of the two opposite parallel sides has projecting flaps that shall be folded to complete the wrapping.

[0033] The fold under the group of products made by the bottom folding device is stabilized through a transverse sealing device.

[0034] The wrapping of the paper wrapping sheets around the groups of products is completed by forming a top fold, a bottom fold, a back side fold and a front side fold for each of the two opposite sides of the group of products that makes up the package. The wrapping station therefore comprises: o a front side folding device for each of the two sides of the groups of products, to fold against each side a portion of the flaps of paper wrapping sheet, thus forming a front fold; o a back side folding device for each of the two sides of the groups of products, to fold against each side a portion of the flaps of paper wrapping sheet, thus forming a back fold; o a top side folding device for each of the two sides of the groups of products, to fold against each side a portion of the flaps of paper wrapping sheet, thus forming a top fold; o a bottom side folding device for each of the two sides of the groups of products, to fold against each side a portion of the flaps of paper wrapping sheet, thus forming a bottom fold.

[0035] To increase flexibility and productivity, the sealing station comprises an adjusting device for adjusting the mutual distance of the sealing members. The distance between the sealing surfaces can be adjusted, for example, according to the size of the groups of products.

[0036] Preferably, the inductor associated with each sealing element is supplied with an induction current having a frequency comprised between 10 Hz and 500 kHz.

[0037] In this document, the term “uniform surface” refers to a surface that has no protuberances, projections, depressions, knurls, or holes in the part in contact with the paper wrapping sheet. A uniform surface may be, for example, a surface that is smooth in the area of contact with the package to be sealed. The term “uniform” preferably means a surface that is smooth and continuous in the area of contact with the groups of rolls. Specifically, in this document “smooth sealing surface” refers to a surface that is not capable of marking, notching, or embossing the wrapping sheet during the sealing process, i.e. when the group of rolls is in contact, with a certain pressure, with the sealing members. A continuous sealing surface is a surface that in contact with the packages to be sealed has no discontinuities, i.e., edge areas, breaks or the like.

[0038] In other words, a uniform surface can be defined as a surface having a roughness of less than 200 Ra. In particular, the sealing surface, when in contact with the packages, shall be a continuous surface with a roughness of less than 200 Ra.

[0039] Advantageously, the sealing member and the channel have sufficient length for optimal sealing of the package. In other words, the contact time between the sealing members and the package to be sealed is sufficiently long, unlike other solutions where the contact time is inevitably short, such as when sealing rollers are used. Even more specifically, the length of the sealing member and the channel is such that the sealing is sufficiently stable at the maximum production speed of the machine or, in general, at the maximum feed rate of the packages to be sealed, which is a function of the package format and cycle time i.e., the maximum number of packages per minute for the format that the machine has to perform. A uniform sealing surface allows for stable homogeneous contact, at approximately constant temperature, between the package to be sealed and the sealing members for the whole time the package passes through the channel. When a sealing pressure is applied between sealing members and packages to be sealed, thanks to the homogeneity i.e. uniformity of contact, there is a stretching effect on the lateral folds of the package to be sealed, which stabilizes the package regardless of whether or not a sealant is used, in addition to greatly improving the quality of the package from an aesthetic point of view.

Brief description of the drawing

[0040] The invention will be better understood by following the description below and the attached drawing, showing a non-limiting embodiment of the invention. More specifically, in the drawing: o Fig. l is a schematic side view of a feeding station for feeding products, such as rolls, in a machine according to the invention; o Fig. 2 is a schematic side view of a wrapping station for wrapping products, such as rolls, in a machine according to the invention; o Figs. 3 to 6 show the schematic sequence of lifting a group of products and beginning wrapping the wrapping sheet in the station of Fig. 2; o Fig. 7 is a schematic perspective view of a feeding station for feeding wrapping sheets in a machine according to the invention; o Fig. 8 is a side view of the wrapping sheet feeding station of Fig. 7; o Figs. 9A to 9G show a schematic sequence of folding a wrapping sheet around a group of products with distribution of glue; o Fig. 10 shows a schematic view, different than that of the previous figure, of the glue distribution on the wrapping sheet; o Figs. 10A and 10B respectively show a schematic perspective view and a top view of a package consisting of a single layer of rolls, with the wrapping sheet having a glue distribution according to Fig. 10; o Figs. 11A and 11B respectively show a schematic top view of a wrapping sheet with a glue distribution different than that in the previous figures, and a schematic view of a closure face of the package with the wrapping sheet with such a different glue distribution; o Fig. 12 is a schematic axonometric view of a sealing station of a machine according to the invention; o Fig. 13 is a schematic front view of the sealing station of Fig. 12; o Fig. 14 is a schematic plan view of the sealing station of Fig. 12; o Fig. 15 is a further schematic perspective view from the bottom of the sealing station of Fig. 12; o Fig. 16 is a schematic axonometric view of a portion of a variant of sealing station, in which the sealing members along the channel for moving forward the groups of products are highlighted; o Fig. 17 shows a schematic cross-sectional view of a series of sealing plates forming a sealing member of the station of Fig. 16.

Detailed description of embodiments

[0041] In Fig. 1, a packaging machine 1 for packaging products R, for example paper rolls, is shown. The rolls are made of tissue paper, for example toilet rolls or kitchen towel rolls. The rolls may have either a cardboard core around which the tissue paper is wound, or not, i.e. they could be made of paper wholly wound from the center thus forming a solid cylinder (so-called solid rolls) or they could have a cylindrical cavity, such as in the case of winding around a center hole without the core (so-called coreless rolls).

[0042] The packaging machine 1 is fed by a product feeding station, which is indicated as a whole with the reference number 2 and may comprise devices for grouping products and feeding groups of products to other devices arranged downstream. In particular, the feeding station 2 may include a launcher device 3, as disclosed in EP2763917B1. In this case, the launcher 3 is comprised of one or more feeding belts 4 co-acting with motorized belts 5 that laterally engage the products R. In this specific case, the motorized belts 5 are shown arranged laterally but it is understood that they could also be provided in a different configuration, for example above and below the products R. The feeding station 2 may consist of a plurality of feeding channels arranged side by side, wherein each feeding channel feeds a line of products R. To each feeding channel there is generally associated a launcher device 3. The launcher 3 is controlled by a central control unit 45, such as PCs, PCLs, microprocessors, or the like, so as to dose sequentially groups G of products R, in this case rolls, arranged side-by-side towards subsequent conveying members that are also part of the feeding station 2 and will be described below.

[0043] In the described example, the launcher device 3 sequentially doses groups G of products R, arranged side by side, to a conveyor 7 that may have a slide surface 8, where the groups G of products R slide, and a pair of flexible members 9, e.g., chains or belts, to which push bars 10 are constrained, so spaced as to accommodate the groups G of products R. The push bars 10 extend approximately transverse to the feeding direction fR of the products R. Each push bar 10 is constrained, at its ends, to the flexible members 9. In this way, by appropriately moving the flexible members 9, the groups G of products R are moved forward, i.e. pushed forward by means of the push bars 10 synchronously with the feeding rate of the packaging machine 1 along the feeding direction fR. The launcher device 3 and the conveyor 7 are then configured to group and dose groups G of products R of desired size in a cadenced manner towards the downstream stations.

[0044] From the conveyor 7, the groups G of products R are transferred to a layering station 6, which is also part of the product feeding station 2. The layering station 6 may include a conveyor 11 provided with a swinging motion according to the double arrow fl 1 to distribute individual groups G of products R, or layers, into the feeder device 12. In this specific case, the feeder device 12 comprises two layers, but it is understood that layering can have more than two layers, such as three or even more layers of products. If the packaging machine 1 is configured to produce single-layer packages, the layering station 6 is obviously not necessary. [0045] The feeder device 12 is represented herein with pushing members for each product layer. Similarly to the conveyor 7, for each layer the pushing members are respectively formed by a slide surface 13A, 13B and a push bar 14A, 14B carried forward by a respective flexible member 15 A, 15B. The feeder device 12 synchronously inserts each layer of products onto an elevator 16. The individual layers can be deposited simultaneously on the elevator 16 or one after the other forming, on the elevator 16, a group G of products R to be packaged.

[0046] This embodiment of the feeder device 12, like that of the launcher 3 and the conveyor 7, is given just by way of non-limiting example, as completely different configurations can be used to group, to dose, and to layer the products. The devices described above are connected to the central control unit 45 that is configured to handle different format grouping of products R. For example, the number of layers of products R may vary, or the number of side-by-side channels used, or the number of products R dosed by the launcher 3 onto each side-by-side channel, or a combination of these variants. In the shown example, the launcher device 3, together with the conveyor 7, group two products R for each channel, but it is evident that, as mentioned, it is also possible to group a single product R or more than two products for each channel.

[0047] The elevator 16 consists of a plate 16A that receives and supports the groups G of layered products R. The elevator 16 is vertically movable along a lifting and lowering direction according to the double arrow fl 6. The movement of the plate 16A can be achieved by a mechanism of the rod-crank type, not shown in detail for the sake of simplicity, driven by an electric motor 17. Advantageously, the elevator 16 also comprises a bottom stop 18, which can be adjusted according to the double arrow fl 8 according to the length or depth of the group G of products R. The depth of the group G of products R is variable depending on the number of products R of which each row of each layer of products R is composed, or on the length of the individual product R. As shown in the side view of Fig. 2, the elevator 16 can also comprise side banks 21 A, 2 IB, 21C, 2 ID provided along the two side flanks of the group G of products R in order to contain and to accompany the group G of products R during lifting.

[0048] The elevator 16 sequentially lifts groups G of products R from a layering height Qs to a wrapping height Qa of a wrapping station 19, arranged higher than the product feeding station. During the lifting motion along the double arrow fl 6, the group G of products R encounters a paper wrapping sheet F arranged along a plane orthogonal to the lifting and lowering direction fl 6. The contact between the group G of products R and the paper wrapping sheet F starts the wrapping cycle that will be described in more detail from Fig. 3 to Fig. 6 and from Fig. 9A to Fig. 9G. The paper wrapping sheet F is advantageously arranged at a level between the layering height Qs and the wrapping height Qa.

[0049] The paper wrapping sheet F can be inserted into and positioned in the wrapping station 19 through two openings 22 made between the side banks 21 A, 21C and 2 IB, 2 ID, respectively, while it is held at two edges Bl, B2 by sheet feeding members 20, for example belts. The formation and of the paper wrapping sheets and the feeding thereof to the wrapping station 19 will be described in more detail below.

[0050] The wrapping cycle is now described with reference to Figs. 3 to 6 and Figs. 9A to 9G. In particular, Fig. 3 shows the group G of products R arranged at the layering height Qs. In Fig. 4, the group G of products R touches the paper wrapping sheet F, starting the wrapping of the paper wrapping sheet F around the top face Fs and the side faces Fl of the group G of products R. In Fig. 5 and Fig. 9B, the group G of products R is at the wrapping height Qa and is completely wrapped with the paper wrapping sheet around the top face Fs and the side faces Fl, leaving the two edges Bl, B2 of the paper wrapping sheet F projecting vertically downward, if necessary, with different lengths. At this time, the paper wrapping sheet F, partially wrapped around the group G of products R, forms a kind of overturned "U". Finally, in Fig. 6 and Fig. 9C, the edges Bl, B2 have been put over each other to complete the wrapping of the bottom face Fi of the group G of products R. The two edges B 1, B2 have been put over each other by two bottom folding devices 25, 26, which are part of the wrapping station 2 and at least one of which is movable. In preferred embodiments, both the two folding devices 25 and 26 can be horizontally movable, with mutual movement along respective arrows f25 and f26. Once the two edges B 1 and B2 have been put over each other, while the group G of products R is supported by the movable bottom folding devices 25, 26, the elevator 16 can reverse the upward movement and descend back to the layering height Qs to receive a new group G of products R. Now, as shown in Fig. 9C, the front face Fa and the back face Fp, facing each other, of the group G of products R are free and the side flaps LI, L2 of the paper wrapping sheet F project from the group G of products R approximately orthogonally to the front face Fa and the back face Fp.

[0051] The overlapping edges Bl, B2 are then stabilized by a transverse sealing device 30 provided along a wrapping direction fA. The transverse sealing device 30 can have a heated active surface 30A that touches the group G of products R at the point where the two edges B 1, B2 are overlapped to be sealed. The shape of the active surface 30A is, just by way of example, a rectangle, whose length is orthogonal to the wrapping direction fA. Preferably, the transverse sealing device 30 moves along a direction f30 of movement towards and away from the group G of products R. In this example, the double arrow f30 is approximately parallel to the double arrow fl 6 of the elevator 16. Specifically, when the transverse sealing device 30 has been brought to the group G of products R, partially wrapped with the paper wrapping sheet F, it seals the package in the overlapping area of the edges Bl, B2. The active surface 30A of the transverse sealing device 30 can be smooth or dotted and can be heated to temperatures between 100° C and 350° C. In some cases, the sealing of the overlapping edges Bl and B2 can occur when the group G of products R is stationary, i.e. it does not move forward along the wrapping direction fA, thus allowing the transverse sealing device 30 to remain into contact with the overlapping edges B 1 and B2 for the necessary time. In this way, the heat of the active surface 30A allows a sealant S to activate and seal, i.e., irreversibly close, the paper wrapping sheet F around the faces Fi, Fl and Fs of the group G of products R, leaving protruding the side flaps LI and L2, orthogonal to the front face Fa and back face Fp of the group G of products R.

[0052] In other embodiments, it is possible to have a transverse sealing device 30 that, in addition to having a movement according to the double arrow f30, also has a movement approximately orthogonal to the double arrow f30 and parallel to the wrapping direction fA, so as to seal the group G of products R while moving forwards along the wrapping direction fA.

[0053] Again with reference to the wrapping station 19 of Fig. 2, the lifting motion of the elevator 16 allows the groups G of products R to be inserted, at the wrapping height Qa, into a space Sp of width equal to, or slightly smaller than, the width of the group G of products R, defined by consecutive teeth 27.2, of a conveyor 27, that is part of the wrapping station 19. The conveyor 27 moves the groups G of products R, supported by a slide surface 23, along a wrapping direction fA to complete the wrapping of the paper wrapping sheet F around the group G of products R. The teeth 27.2 are constrained to a flexible member 27.1, for example a belt or a chain, driven between two pulleys 27.3, at least one of which is suitably motorized, to move the teeth 27.2 along a closed path, the active branch of which, i.e. the branch where the wrapping of the paper wrapping sheet F is completed, is the lower branch.

[0054] The conveyor 27 may be also realized differently. For example, the teeth 27.2 can be transported by carriages movable along rails. A linear electric motor, controlled by the central control unit 45, can be associated with each carriage in order to receive and to transport groups G of products R. An example of this kind of conveyor 27 is described in TH 426528.

[0055] In other embodiments, the conveyor 27 can be configured to constrain consecutive teeth 27.2 to a plurality of belts, each of which is independently motorized so as to have consecutive teeth 27.2 movable independently of each other. This kind of configuration is disclosed in the Italian patent no. 102015000084892.

[0056] Once the group G of products R, inserted into the space Sp, is moved forward by the conveyor 27 along the wrapping direction fA, it passes through a folding device 28 that comprises, for each face Fa and Fp, a top side folding device Pls, a bottom side folding device Pli, a front side folding device Pla, and a back side folding device Pip. When the side flaps Ll and L2 comes into contact with the top side folding device Pls, the bottom side folding device Pli, the front side folding device Pla, and the back side folding device Pip, a top side fold Pis', a bottom side fold Pli', a front side fold Pla' and a back side fold Pip' are respectively formed, as shown in the sequence of Figs. 9D- 9G. The top side folding device Pls, the bottom side folding device Pli and the front side folding device Pla are generally fixed while the back side folding device is movable along the double arrow Fplp. The movement of the back side folding device can be coordinated with the movement of the movable bottom folding devices 25, 26 in order to create the respective folds at the same time or to create the back side fold Pip' immediately after the overlapping of the two edges Bl, B2. Furthermore, a single motorization can be used for moving the movable bottom folding devices 25, 26 and the back side folding device Pip. In some cases, the back side folding device Pip can complete the respective fold before the group G of products R is moved by the conveyor 27. In other cases, the back side folding device Pip can complete the fold while the group G of products R has been already put in motion by the conveyor 27 along the wrapping direction fA.

[0057] The side folding members disclosed above may be also realized, for example, as described in EP1228966.

[0058] Here below, with reference to Fig. 7 and Fig.8, a sheet feeding station 31 for feeding paper wrapping sheets F will be described, which sequentially feeds one sheet at a time to the wrapping station 19.

[0059] The sheet feeding station 31 comprises an unwinding device 38 to unwind a reel B of paper web N formed from virgin or recycled fiber or a mix thereof. Preferably, the grammage of the paper web N is between 20g/m ² and 100g/m ² , and the thickness is between 20 pm and 100 pm. The unwinding device 38 can include a support device 38A to keep the reel B rotating about its longitudinal axis, and an actuating device 38B to put the reel B into controlled rotation, for example by means of belts in contact with the outer surface of the reel B or by connecting the longitudinal axis of the reel B with a motorized system. The unwinding device can be of any known type, as shown for example in IT1274081.

[0060] The paper web N can be conveyed by idle rollers 32.1, 32.2, 32.3, 32.4, 32.5, and 32.6 along a feed path P in the feed direction fN to a cutting unit 37 arranged to cut the paper web N into paper wrapping sheets F of predetermined length. Along the feed path P of the paper web N, upstream of the cutting unit 37, there is a dispensing device 33 arranged to apply a sealant S, such as glue, onto the paper web N. The sealant S may preferably be a heat-reactivated glue, i.e. it may have the characteristic of not remaining sticky once applied to the paper web N and of being activated only when heat-treated. The advantage of this type of sealant is that, in case of even accidental contact between the sealant and the elements that make up the packaging machine 1, it does not dirty the downstream devices, such as the wrapping station 19. Other types of glues can also be used, such as heat-activated glues or glues that are immediately active and can no longer be reactivated once dried, although these solutions are less preferred because the use of these types of glues dirties the machine much more than the heat-activated glues. [0061] The dispensing device 33 may comprise one or more dispensers 33.1, 33.2 33.3 provided above the feed path P to apply the sealant S to the paper web N in a controlled manner. Preferably, the dispensers 33.1, 33.2 33.3 are of the spreading type, although other types of dispensers, such as sprays, cannot be excluded. The feed path P in the section where the sealant is applied may preferably be flat. The dispensers

33.1, 33.2 33.3, as schematically shown, can be supported by a support structure 34 consisting of brackets 39, for example L-shaped brackets, constrained to a crossbar 39A whose ends are attached to two uprights 40. The support structure 34 is not binding for the purposes of the invention and may be of any other suitable type. The support structure 34 may comprise means, not shown, for adjusting the transverse position of the dispensers 33.1, 33.2, 33.3 relative to the feed direction fN of the paper web N. For example, the brackets 39 can slide along a linear guide and be blocked thereon by means of screws or other suitable systems. In a further configuration, also not shown for the sake of simplicity, the brackets 39 or in general the dispensers 33.1,

33.2, 33.3 can be adjusted by means of motors in order to simplify the product changeover, i.e., the switching to packages that require different sizes of paper wrapping sheets F. Additionally, dispensing device 33 can be height-adjustable, either manually or automatically, with respect to the feed path P. For this purpose, the dispensers 33.1, 33.2, 33.3 can be connected to an electronic control unit 45 that manages the dispensing phase, i.e., the instants when the dispensers should apply the sealant material S to the paper tape N and when they should not dispense it.

[0062] The dispensing device 33 may comprise, upstream of the dispensers 33.1,

33.2, 33.3 along the feed direction fN, a phase detection system 36 for coordinating the application of the sealant S with the paper web N. In fact, the paper web N may comprise prints, lettering, bar codes, and marks for phase detection. In fact, the N paper tape may include prints, lettering, bar codes, and phase detection marks. In the case of prints or marks visible on the final package C, the position thereof with respect to the faces of the package must be precise and predetermined. Therefore, the sealant S must also be applied in a synchronized manner with the feeding of the paper web N in order to obtain paper wrapping sheet F with sealant S and prints in phase, i.e., in a well- determined mutual position. In the example of Fig. 7, the phase detection system 26 is realized by an encoder 43 that can measure the amount of paper web N moving forward along the feed direction fN. Alternatively, the encoder 43 can detect the position of the paper web N, thus determining the position of a particular print design. Instead of the encoder 43, other systems or sensors can be used, such as photocells that detect given points of the paper web N, or vision systems that detect and recognize the position of the paper web N and especially recognize a distinctive sign such as a print or a sign specifically printed for the phase detection. Moreover, a combination of these sensors can be used, for example, a photocell and an encoder, a photocell and a vision system, etcetera. The phase detection system 36 is also connected to the electronic control unit 45 in order to coordinate the application of the sealant S in phase with the forward movement of the paper web N.

[0063] A cutting unit 37, not shown in detail, is provided downstream of the dispensing device 33 to cut the paper web N into wrapping sheets F of predetermined length. The cutting unit 37 may be of the type described in EP1052209B 1. The cutting unit 37 is preferably connected to and controlled by the electronic control unit 45 to obtain paper wrapping sheets F of predetermined length, from the cutting of the paper web N in phase with the prints, if any, and with the sealant S. Preferably, the cutting is of the "scissor" type and is performed by a rotating blade co-acting with a fixed counter-blade, both blades being at least as wide as the paper web to be cut. Once cut and exiting the cutting unit 37, the paper wrapping sheets F are fed along a sheet feeding direction fF, generally concordant with the feed direction fN for the paper web N, but it can be also different, for example orthogonal, when using cutting units having a different configuration from the preferred one, as shown in EP1052209B1.

[0064] In a different configuration, not specifically shown in the figure, the cutting unit 37 can be provided upstream of the dispensing device 33 which, in this case, must be phased directly with the paper wrapping sheets F. It is evident that, in this case again, phase detection devices 36 are provided, the operation of which is similar to that described above. In this configuration, it is also possible to phase the dispensing of the sealant S and the feeding of the paper wrapping sheets F by means of a photocell that detects the transverse edge of the sheets moving forward along a sheet feeding direction fF.

[0065] In general, to obtain sheets of the desired size, in phase with any prints, and in phase with the sealant S, it is necessary alternatively: o applying the sealant S in phase with any prints or marks provided on the paper web N and then cutting the paper web N into sheets of predetermined length in phase with respect to the sealant S o cutting the paper web N into sheets of predetermined length in phase with any prints or marks and then applying the sealant S on the paper wrapping sheets F in phase.

[0066] The application of the sealant S on the paper web N can take place in more than one configuration, as shown in Fig. 10 and Fig. 11. A first example is shown in Fig. 10, where on a paper wrapping sheet F, defined by two parallel sides and two sides transverse to the feed direction fN, the dispensing device 33 has applied a line SCP of sealant along a side parallel to the feed direction fN and a line SCT of sealant along each side transverse to the feed direction fN. The lines SCP and SCT of sealant can be continuous or discontinuous, for example, dashed. In the case of Fig. 10, the line SCP is continuous while both the lines SCT are formed by two strokes SMI, SM2 of sealant alternating with two strokes ZL1 (and possibly ZL2) without sealant, respectively. Advantageously, the strokes ZL1 (ZL2) devoid of sealant of a same line SCT respectively correspond to the sheet portion of the top side fold Pis' and of the bottom side fold Pli' of each face Fa, Fp of the package C. In Fig. 10A and Fig. 10B a sealed package C is shown, where the sealant S has been distributed according to what shown in Fig. 10. In this particular case, the sealant S forms a kind of "H" on each face Fa, Fp of the package C, as portions of sealant of the strokes SMI and SM2 of each line SCT, applied in corresponding segments of the top side fold Pis' and the bottom side fold Pli', overlap in the horizontal section of the "H" shape. The horizontal stroke of the "H" shape can be wider or narrower or even double, depending on the overlap of the lines of sealant S. The vertical strokes of the "H" shape are formed by the portions of strokes SMI and SM2 of each line SCT corresponding to the front side fold Pla' and the back side fold Pip'. In this case, the front side folding devices Pla and the back side folding devices Pip, when folding the paper wrapping sheet F, do not touch the sealant S thus leaving the packaging machine 1 cleaner and more efficient.

[0067] In the sequence of complete wrapping shown in Figs. 9A-9G, the lines SCT are formed by a single continuous stroke. In this case again, the line SCT on each side face of the package C can form an "H"-shaped seal as described above. [0068] In general, the lines SCT are applied so that between the front side folds Pla', the back side folds Pip', the bottom side folds Pli', and the top side folds Pis' there is a stroke of sealant S, whose activation by means of a sealing station 40 permanently stabilizes the package C of products R. The line SCP is applied to the paper wrapping sheet F so as to be between the overlapping edges Bl, B2, so that the sealant S can be heated, and therefore activated, by the transverse sealing device 30.

[0069] The line SCP and each line SCT are generally applied approximately parallel to the edge sides of the wrapping sheet F, although this is not strictly necessary. The width of the lines SCP and SCT can be between 5 mm and 80 cm. The width of the lines can be adjusted also based on the desired size of the package C. For example, packages C of larger size may require wider lines of sealant S than packages C of smaller size. The lines SCP and SCT can be applied at a distance from the edge of one side of the paper wrapping sheet F comprised between 0.5 mm and 50 mm, preferably between 1 mm and 25 mm.

[0070] The dispensers 33.1, 33.2, 33.3 can be configured so as to have different distributions of the sealant S. For example, instead of the continuous or discontinuous strokes of the lines SCT, it is possible to apply dotted strokes or other shapes such as triangles SI, S2, S3 or other, that coincide with the overlapping areas of the side folds obtained from the folds of the flaps LI and L2, as schematically shown in Fig. 11A and Fig. 11B. In this case again, the purpose of applying the sealant S is to obtain a stably sealed package C for most of the areas to be closed. In a preferred solution, the distribution of the sealant S is such that the package C is completely stably closed, preventing the products R from being contaminated by coming into contact with external agents. The package C may have facilitated opening systems or handles to facilitate transportation of the package C, without however changing the objects of the invention. Examples of handles are described in EP1535846, while facilitated opening systems are disclosed in EP2225159.

[0071] Once the paper wrapping sheets F have been prepared with the sealant S applied in one of the previously described ways, the sheets are sequentially moved forward, one after the other, along the sheet feeding direction fF toward the wrapping station 19. In a preferred solution, the paper wrapping sheets F are held at the two edges Bl and B2 by feeding members 20, for example belts, and positioned orthogonal to the lifting and lowering direction fl 6, as previously described. A solution of this kind is described for example in the patent document W02021009339.

[0072] In Figs. 12 to 15 a sealing station 40 is shown, configured to seal the paper wrapping sheet F wrapped around the groups G of products R forming the package C to be sealed. Sealing is achieved by heat treatment of the folds of the paper wrapping sheet F that have been previously formed in the wrapping station 19. In practice, once the folds of the side flaps LI and L2 have been completed, it is necessary to stabilize the front side fold Pla', the back side fold Pip', the bottom side fold Pli', and the top side fold Pis', obtained, for example, according to the packaging cycle described in Figs. 9A-9G, by heat treating the faces Fa, Fp of the package C of Fig. 9G.

[0073] The sealing station 40 comprises a channel 41 to move the package C to be sealed forward along a sealing direction indicated by the arrow fS. The moving forward channel 41 is delimited, at the side edges, by a pair of opposite sealing members 42 A, 42B provided on the two sides of the channel 41. The sealing members 42A, 42B have a preferably uniform sealing surface 43A, 43B, respectively. The sealing surface 43A, 43B is the surface facing the packages C to be sealed i.e., the surface that touches the packages C to be sealed. The sealing members 42A, 42B can be made of ferromagnetic material.

[0074] For example, in the case shown in Fig. 13 and Fig.14, the sealing members 42A, 42B are made from tapes 54A and 54B, respectively.

[0075] For example, such tapes are made of, or may include, a ferromagnetic material, e.g., steel, iron, or alloys thereof.

[0076] In other examples, these tapes may be made of, or may include, a paramagnetic material, such as aluminum or alloys thereof. For example, such tapes may contain an aluminum core or band, whose thickness is preferably comprised between 5 pm and 100 pm and more preferably between 20 pm and 25 pm. The aluminum core or band may include, also on the sealing surface, a material adapted to facilitate the surface sliding on the products, for example Teflon.

[0077] In a variant of the invention, not shown, it is possible to use two or more tapes for each sealing member 42A, 42B, arranged vertically preferably contiguous one after the other. The sealing members 42A, 42B can have an overall height at least equal to the height of the package C to be sealed of largest size that the packaging machine 1 can realize.

[0078] Each sealing member 42A, 42B can be driven between return members 44A, 45 A, 46A and 44B, 45B, 46B, such as pulleys or rollers, at least one of which for each sealing member is preferably motorized. In this specific case, the return members 44A and 44B are driven by a respective actuation device Ml and M2, such as a gear motor, provided to feed the package C to be sealed along the sealing direction fS. In a different configuration, it is possible to leave the sealing members 42A, 42B idle, i.e., without an actuation device, particularly when the channel 41 includes a motorized conveyor 47 to feed the packages C to be sealed along the sealing direction fS. In a preferred embodiment of the invention, both the sealing members 42A, 42B and the conveyor 47 are motorized. When the conveyor 47 is not motorized, it can be replaced with a simple feed plane, such as an extension of the slide surface 23. The conveyor 47 can be provided at the wrapping height Qa so as to receive the package C to be sealed without discontinuities with respect to the slide surface 23 that can move and deform the folds yet to be sealed, compromising the final quality of the packages C.

[0079] The sealing members 42 A, 42B can be provided close to, i.e., in continuity with, the outlet of the wrapping station 19, so as to receive the package C to be sealed while the folding device 28 is still partially in contact with the newly formed folds, making a continuous, or nearly continuous, passage between the folding device 28 and the sealing members 42A, 42B. This prevents the deformation of the newly formed front side fold Pla', back side fold Pip', bottom side fold Pli', and top side fold Pis'. Preferably, the sealing members 42A, 42B and/or the conveyor 47, when motorized, receive the package C to be sealed by feeding it along the sealing direction fS at a speed equal to, or preferably higher than, the speed along the wrapping direction fA so as to move the package C to be sealed away from the conveyor 27 and to prevent the rotation of the teeth 27.2 around the pulley 27.3 from causing deformation of the package C, that shall still be sealed and thus stabilized.

[0080] The sealing members 42A, 42B are respectively heated by induction through an electromagnetic induction device 48A, 48B that includes one or more induction coils 49A, 49B or other circuit capable of generating a time-varying electromagnetic flux. The time-varying electromagnetic field generates eddy currents in the sealing members 42A, 42B, which cause the Joule-heating thereof. As a result, also the sealing surfaces 43 A, 43B, and/or parts thereof close to the sealing surfaces, are also heated.

[0081] The induction coils 49A, 49B can be arranged facing the sealing surfaces 43A, 43B or in the opposite side i.e., inside the area delimited by the closed path determined by the sealing members 42A, 42B. The induction coils 49A, 49B can be provided in the straight section between respective return members 45 A, 46A and 45B, 46B. In other configurations, the induction coils 49A, 49B can be provided elsewhere, for example, between the return members 44A, 46A and 44B, 46B or between the return members 44A, 45A and 44B, 45B. In the latter case, the induction coils 49A, 49B cannot be placed in front of the sealing surfaces 43 A, 43B as they would be inside the channel 41; therefore, they shall be provided on the opposite side i.e. inside the area delimited by the sealing members 42A, 42B. The distance between the induction coils 49A, 49B and the sealing members 42A, 42B can be comprised between 1 mm and 80 mm.

[0082] Associated with the electromagnetic induction devices 48A, 48B there are respective generators or inverters, 50A, 50B, controlled to supply the induction coils 49A, 49B with electromagnetic induction currents adapted to generate a time-varying electromagnetic flux, passed by the sealing members 42A, 42B Joule-heated by the eddy currents generated by the time-varying electromagnetic flux.

[0083] The inverters 50 A, 50B operate at an operating frequency approximately equal to the resonance frequency of the electric circuit formed by the respective induction coil 49 A, 49B. The operating frequency of the electromagnetic induction current generated by the inverters 50A, 50B is comprised between 10 Hz and 500 kHz, and more preferably between 100 Hz and 100 KHz.

[0084] In order to adjust the operating temperature of the sealing members 42A, 42B, a closed-loop control system can be used, comprising the inverters 50A, 50B and at least one temperature sensor of any kind, such as thermocouples, pyrometers, thermocameras, or other suitable device, associated with the respective sealing member 42A, 42B, and connected to a control unit that, based on an appropriate control algorithm, controls the inverters 50A, 50B so as to regulate the temperature of the sealing surfaces 43A, 43B. The temperature control system can be run by the central control unit 45, or by a different control device, such as another PC or PLC or an industrial computer, a microprocessor, a computer network, or any other suitable device.

[0085] The operating temperature of the sealing members 42A, 42B can be comprised between 100° C and 400° C, and preferably between 150° C and 300° C. The operating temperature can be highly variable because it is a function of the operating condition of the packaging machine 1, the production speed, the type of paper wrapping sheet F, and the type and quality of the sealant S.

[0086] In order to increase the production flexibility of the packaging machine 1, the sealing station 40 comprises adjusting means for adjusting the transverse distance of the sealing members 42A, 42B, which allow the machine to be adapted to the format of the packages C to be made. The adjusting means for adjusting the transverse distance of the sealing members 42A, 42B may include a base 51 A, 5 IB, movable along guides 52, 53, transverse, i.e., preferably orthogonal to the sealing direction fS. The bases 51 A, 5 IB are constrained in slidable way to rails 52, 53 by respective shoes 70, 71. While the packaging machine 1 operates, the distance between the bases 51 A, 5 IB is blocked to keep the sealing members 42A, 42B in the desired position. The distance between the bases 51 A, 5 IB is unlocked only when it is necessary to adjust the transverse position of the sealing members 42A, 42B, thus widening or narrowing the channel 41. In order to adjust the distance of the sealing members, an actuator 73 is provided, in this case a manual hand wheel, that rotates a worm 72 engaging nut screws 74, 75, integral with the bases 51 A, 5 IB, respectively. The worm 72 is preferably made up of two parts 72' and 72” with respectively opposite thread direction, so that the rotation of the worm 72 causes the bases 51 A, 5 IB, and thus the respective sealing members 42A, 42B, to move towards and away from each other. The actuator 73 can also be an electric motor so as to adjust automatically the cross- sectional dimension of the channel 41.

[0087] To have an optimal sealing, members 76 can be provided for adjusting the sealing pressure i.e., for applying a predetermined side sealing pressure to the package C as it moves along the channel 41. As better shown in Fig. 15, the sealing pressure adjusting members 76 are attached to each of the sealing members 42A, 42B and may comprise a slide guide 77, integral with the base 51 A, 5 IB. The slide guide 77 can be approximately parallel to the rails 52, 53. A shoe 78, integral with a plate 80 on which the sealing parts 42A, 42B are installed, is associated with the slide guide 77. The bases 51 A, 5 IB are respectively connected to an actuator 82, 83, preferably a pneumatic or electric actuator, or any other type of actuator suitable for pushing the sealing members 42A, 42B toward each other. If the actuator is pneumatic, it is possible to adjust the sealing pressure by varying the air pressure, while, if the actuator is electric or electromechanical, the control unit 45, or another dedicated control device, can move the actuator by moving each base 51 A, 5 IB, and consequently the sealing members 42A, 42B, towards or away from each other.

[0088] A tensioning device 60 can be provided for each sealing member 42A, 42B for tensioning it. In the case where each sealing member 42A, 42B consists of two or more tapes of ferromagnetic or paramagnetic material, a tensioning device 60 is provided for each tape. The tensioning devices 60 can be realized by an idle roller 61, pressed against the respective sealing member 42A, 42B by a pneumatic actuator 62. Other types of actuators can also be used, for example an electric linear motor or other equivalent electromechanical devices. If pneumatic actuators are used, the tensioning of the respective sealing member 42A, 42B can be adjusted by adjusting the air pressure of each pneumatic actuator.

[0089] Preferably, in order to keep the distance between the sealing members 42A, 42B and the respective induction coils 49A, 49B constant, the tensioning device 60 can act on the respective sealing members 42A, 42B in a section delimited by two consecutive return members 45A, 46A and 45B, 46B, that does not include the respective induction coil 49 A, 49B. For example, as shown in the figures, the tensioning devices 60 act on the section comprised between the return members 44A, 46A and 44B, 46B while the induction coils 49A, 49B are placed in the section between the return members 45A, 46A and 45B, 46B. In this way, the deformation caused by the tensioning devices 60 on the sealing members 42A, 42B does not affect the section of the sealing members 42A, 42B over which the induction coils 49A, 49B face.

[0090] The fact of having uniform sealing members 42A, 42B made of ferromagnetic material such as steel, iron or derivatives thereof, results in better heat conduction and transfer from the sealing surfaces 43 A, 43B to the paper wrapping sheet F. If a compression, albeit very light, is applied to the package C to be sealed as it moves forward in the channel 41, a stretching effect is generated on the folds of the paper wrapping sheet F, increasing the aesthetic quality thereof and facilitating the stabilization of the folds. In this way, it is possible to improve the packages both when they are sealed with sealant S and when the paper wrapping sheet is devoid of sealant, as the stretching effect stabilizes the folds of the flaps LI, L2 regardless of the use of sealant S. Finally, a ferromagnetic material such as steel, iron, or alloys thereof, allows for significantly greater durability than the prior art systems mentioned in the introduction.

[0091] Finally, and optionally, contrast means 90 can be provided to balance any bending of the sealing members 42A, 42B when in contact with the packages C to be sealed, especially when the sealing members 42A, 42B are formed by tapes 54A and 54B of ferromagnetic or paramagnetic material. The contrast means 90 are placed on the opposite side with respect to the sealing surfaces 43 A, 43B and may include sliding devices, on which the tapes 54A and 54B slide. The sliding devices are preferably Teflon-coated or entirely made of Teflon, so as to reduce friction with the tape. The sliding devices can be installed with elastic elements such as springs, to allow a movement in direction orthogonal to the sealing direction fS.

[0092] In an alternative embodiment, shown for example in Figs. 16 and 17, the sealing members 42A, 42B can be formed by a flexible 70 member, such as one or more belts or chains, to which a plurality of sealing elements is constrained. The sealing elements may consist, for example, of plates 71 made of, or containing, ferromagnetic or paramagnetic material, arranged side by side. The flexible member 70 can be driven around return members 44A, 45A, 46A and 44B, 45B, 46B, completely similarly to what described above. The induction coils, not shown in this example, can face the active surfaces of the sealing elements. The eddy currents can be induced only on the sealing elements and not on the flexible members of the sealing members 42A, 42B when the flexible member is made of non-ferromagnetic material, such as plastic or rubber. In this solution again, tensioning devices (not shown in the figures) may be provided, for example quite similar to those described above, to tension each flexible member of the sealing members 42 A, 42B. [0093] As shown in the schematic view of Fig. 17, in order to facilitate the heat transfer by conduction from a plate 71 to the adjacent plate 71, the plates have contact zones 72, at least when they move along the sealing section inside the channel 41. The contact zones 72 are provided, for example, near the sides of the plates 71 orthogonal to the feed direction in the channel 41 and are realized, for example, by means of side recesses 73 and corresponding side projections 74 (which are part of the uniform sealing surface of each plate of which they are a part) coupled together so that the adjacent plates are overlapping (with reference to the orientation of the sealing surface of the plates). For example, the side recesses and projections 73-74 have respective faces parallel to the sealing surface of the plate, which face each other; during the forward movement in the channel, the side projections 74 are in contact with the side recesses 73 at these faces. For example, the area and shape of the cross section of a projection can approximately match the area and shape of the cross-section of a recess.

[0094] Moreover, also in this solution, contrast means 90’ (schematically shown only in Fig. 17) may be provided to balance any bending of the sealing members 42A, 42B when in contact with the packages C to be sealed. The contrast means 90’ are arranged on the opposite side with respect to the sealing surfaces 43 A, 43B and realize a relative thrust on the plates, so that the plates are in contact with each other at contact zones 72.

[0095] To limit or to avoid contact discontinuities, it is also possible to phase the sealing elements with the packages C to be sealed, so that the surface of each sealing element 43A, 43B matches with respective faces Fa and Fp of the package C to be sealed. To this end again, the surface of each sealing element is preferably uniform i.e. smooth and continuous, i.e. without protuberances, projections, depressions, holes in the part of contact with the paper wrapping sheet.

[0096] It is understood that what is illustrated purely represents possible non-limiting embodiments of the invention, which may vary in forms and arrangements without departing from the scope of the concept on which the invention is based. Any reference numerals in the appended claims are provided for the sole purpose of facilitating the reading thereof in the light of the description above and the accompanying drawings and do not in any way limit the scope of protection.