EP4448428A1

EP4448428A1 - A method for joining together two sheets of packaging material

Info

Publication number: EP4448428A1
Application number: EP22818121.0A
Authority: EP
Inventors: Alessandro CRISTOFORI; Enrico Bernardi; Salvatore Carboni
Original assignee: GD SpA
Current assignee: GD SpA
Priority date: 2021-12-14
Filing date: 2022-12-01
Publication date: 2024-10-23
Anticipated expiration: 2042-12-01
Also published as: ES3061484T3; EP4448428C0; IT202100031250A1; WO2023111744A1; US20250051122A1; EP4448428B1

Abstract

A method is described for joining a first sheet (110) and a second sheet (120) of packaging material, which comprises: preparing the first sheet (110) with a first joint edge (111) transverse to a longitudinal axis (Y1) of the first sheet, and having a particular configuration with a non-straight edge; arranging the second sheet (120) with a second joint edge (121) transverse to a longitudinal axis (Y2) of the second sheet; superimposing the first and second joint edges (111, 121) to join the first and second sheets (110, 120) so that the longitudinal axes (Y1, Y2) are aligned, and the second sheet (120) constitutes a continuation of the first sheet (110) along the longitudinal axes; welding together the first and second joint edges (111, 121) superimposed on each other.

Description

“A method for joining together two sheets of packaging material

****

DESCRIPTION

Field of the invention

The present invention relates to a method for joining a first sheet of packaging material to a second sheet of packaging material.

In particular, the method described here has been implemented for an application in the context of a process for forming containers filled with a liquid and sealed, starting from a sheet of packaging material unwound from a bobbin along a work path.

In the context of a process of this type, it is known to replace a bobbin about to finish with a new bobbin during the execution of the process and without interrupting the process itself.

In this regard, a machine for forming the aforesaid containers is - in fact - commonly provided with a buffer area wherein there is an accumulation of the sheet of packaging material of the bobbin in use, which is used during the bobbin-change operation.

This operation involves cutting the sheet of packaging material of the bobbin in use, at a section thereof upstream of the accumulation area, and joining the end edge thus obtained with the end edge of the sheet of the new bobbin by means of a welding operation.

At the end of the aforesaid operation, the sheet of packaging material of the previous bobbin is joined to the sheet of packaging material of the new bobbin, and the latter actually constitutes an extension of the first sheet.

In this way, the formation process of the containers normally proceeds without interruption and, at some point, it will start working directly on the sheet of packaging material of the new bobbin.

In a per se known manner, a process for forming containers filled with a liquid and sealed envisages wrapping the sheet of packaging material according to a tube conformation around a main axis parallel to the direction of advancement of the sheet, and sealing the sheet wound in tube-form along this axis, with the aid of a tape of thermosealable material.

The tube thus produced is filled with the liquid product to be packaged. On the lower end of the tube, transverse seals are carried out, in succession and in a synchronized manner with the advancement of the sheet, which generate on the tube, one after the other, individual containers filled with the liquid product and sealed. The individual containers are separated from the tube by means of cutting.

In such a process it is essential to keep the inside of the aforesaid tube in a sterile condition, in order to safeguard the liquid product from possible external contamination.

In the present description and in the claims attached thereto, some terms and expressions are deemed to have, unless otherwise explicitly indicated, the meaning given in the following definitions.

The expression "longitudinal edge" of a sheet means an edge of that sheet that extends along the length of the sheet; in particular cases wherein a sheet is unwound from a bobbin, the longitudinal edge extends along the feed direction of the sheet.

The terms "weld", "fasten", "fastening", "union", "joint", referring to two edges of a sheet mean the operation of making the two edges adhere together in a definitive way or the result of this operation.

The term "width" referring to an area or an element means the smallest dimension of that area or element; in the particular cases wherein reference is made to the "width" of a sheet or of a part or area thereof, it means the smallest dimension of that sheet or of its part or area.

In a processing unit, for example, for forming a sheet advancing along a feed direction, a first station is considered "upstream" of a second station when this first station precedes the second station with reference to the feed direction of the sheet, conversely, the second station is considered "downstream" of the first station since it follows the first station, again with reference to the feed direction of the sheet.

The "inner side" of a sheet of packaging material means the side intended to be found inside the package or final container, or rather the side of the sheet intended to come into contact with the packaged product.

The term "parallel" means a substantial parallelism between two elements, including both the ideal case wherein these elements are arranged with respect to each other so as to form a zero angle, and more frequent cases wherein the two elements are arranged with respect to each other in such a way as to form an angle that is not zero but - in any case - negligible or not relevant for the purposes of the operation of the present solution.

The term "aligned" means a particular condition of parallelism wherein the two elements extend along the same ideal straight line or - in any case - have respective parts that extend along the same ideal line.

“Section” means a portion of a continuous line, open and not intertwined; in the present discussion a "section" may be equally straight, curvilinear, mixed, or broken. By "segment", on the other hand, we mean a straight "section", or rather, a portion of a straight line between its two end points.

The Applicant has found that the tube made by wrapping and sealing the sheet of packaging material is - in some cases - subject to breakage, or rather, opening and a consequent loss of sterility, which requires the process to be stopped immediately to restore the necessary aseptic conditions. Before being able to restart the process, it may take more than one hour and, therefore, such interruptions significantly affect production volumes as well as production costs.

The Applicant has noted that in the known solutions these interruptions occur, in particular, in concomitance with the change of the bobbin of the sheet of packaging material.

Following an intense analysis activity, the Applicant has, therefore, found that the openings of the tube occur on the longitudinal sealing band, which closes the sheet of packaging material in the tube configuration, and precisely at the point wherein this band intersects with the joint between the sheet of the replaced bobbin and the sheet of the new bobbin.

The Applicant has, therefore, understood that to prevent the tube from opening, it is necessary to find a new solution to join the two sheets of packaging material, in particular, which allows a greater sealing of the longitudinal welding of the tube at the joint between the two sheets to be obtained.

In particular, the Applicant has perceived that the welding devices, which carry out the longitudinal welding to form the tube, generate a non-uniform heat distribution at the joint between the sheet of the replaced bobbin and the sheet of the new bobbin. As a consequence of this, the tape of thermoseal able material is not uniformly heated and, precisely at this joint, tends not to adhere, or rather, weakly adhere to the packaging material, causing the aforesaid breaks and openings of the tube. Finally, the Applicant has found that by suitably shaping at least one of the edges which form the joint between the sheet of the replaced bobbin and the sheet of the new bobbin, the heat generated by the welding devices is suitably distributed along the entire surface affected by the welding, so that the tape of thermosealable material is uniformly heated and adheres entirely to the packaging material.

Therefore, in a first aspect, the present invention relates to a method for joining a first sheet of packaging material to a second sheet of packaging material.

The method comprises:

- preferably, providing said first sheet with a first joint edge extending transversally to a longitudinal axis of said first sheet;

- preferably providing said second sheet with a second joint edge extending transversally to a longitudinal axis of said second sheet;

- preferably, superimposing said first and said second joint edges to join said first and said second sheets; preferably, in this way, the longitudinal axes of said first and said second sheet are parallel; even more preferably, in this way the longitudinal axes of said first and said second sheet are aligned; preferably, in this way said second sheet constitutes a continuation of said first sheet along said longitudinal axes;

- preferably, welding together said first and said second joint edge superimposed on each other.

Preferably, said first joint edge comprises, along a direction transverse to said longitudinal axis of said first sheet, a first lateral portion and a second lateral portion opposite to each other with respect to said longitudinal axis. Preferably, said first joint edge comprises, along a direction transverse to said longitudinal axis of said first sheet, an intermediate portion located between said first lateral portion and said second lateral portion. Preferably said intermediate portion protrudes with respect to at least one of said first and said second lateral portions, preferably in a direction parallel to said longitudinal axis of said first sheet.

Thanks to these characteristics, the problem mentioned at the beginning concerning the possible openings of the tube made with the sheet of packaging material in the context of the formation process of the containers discussed above is resolved.

In particular, the configuration described above of the joint edge of the first sheet allows obtainment, during the welding operation for producing the longitudinal sealing band of the tube, a heating of the joint of the first and second sheets, which is substantially uniform on the entire width of the joint involved in the welding operation. In this way, an optimal sealing of the tube is guaranteed also at the joint of the first and second sheets.

In a second aspect, the present invention relates to a process for forming containers filled with a liquid and sealed, starting from a sheet of packaging material, preferably unwound from a bobbin along a work path.

Preferably, the process comprises the step of providing, when the sheet is to be replaced with a new sheet of packaging material of a new bobbinjoining the sheet and the new sheet by means of a method, as indicated above. Preferably, one of said sheet and new sheet is said first sheet; still preferably, the other of said sheet and new sheet is said second sheet.

In a third aspect, the present invention relates to an apparatus for joining a first joint edge of a first sheet of packaging material to a second joint edge of a second sheet of packaging material.

The apparatus preferably comprises a cutting device. Preferably, the cutting device includes a cutting blade intended to make a first cutting line, preferably transverse to a longitudinal axis of said first sheet, to make said first joint edge.

Preferably, said first joint edge comprises, along a direction transverse to said longitudinal axis, a first lateral portion and a second lateral portion, opposite to each other with respect to said longitudinal axis. Preferably, said first joint edge comprises, along a direction transverse to said longitudinal axis, an intermediate portion located between said first lateral portion and said second lateral portion. Preferably the intermediate portion protrudes with respect to at least one of said first and said second lateral portion, in a direction parallel to said longitudinal axis of said first sheet.

Preferably, the apparatus comprises a welding device for welding together said first and said second joint edge superimposed on each other.

Thanks to the aforesaid characteristics, it is possible to implement in an automated manner a method of joining a first and a second sheet, which is capable of resolving the problem mentioned at the beginning concerning the possible openings of the tube produced with the sheet of packaging material in the context of the formation process of containers discussed above.

In a fourth aspect, the present invention relates to a machine for forming containers filled with a liquid and sealed, preferably starting from a sheet of packaging material unwound from a bobbin along a work path. Preferably, the machine comprises an apparatus as indicated above.

Thanks to the aforesaid characteristics, it is possible to implement - in an automated manner - a method of joining a first and a second sheet, which is capable of resolving the problem mentioned at the beginning concerning the possible openings of the tube produced with the sheet of packaging material in the context of the formation process of containers discussed above.

In a fifth aspect, the present invention relates to a bobbin of packaging material.

Preferably, the bobbin comprises a central support. Preferably, the bobbin comprises a sheet of packaging material extending along a longitudinal axis, preferably wound along the same axis, preferably around the central support.

Preferably, an end edge of said sheet comprises, along a direction transverse to said longitudinal axis, a first lateral portion and a second opposite lateral portion. Preferably, an end edge of said sheet comprises, along a direction transverse to said longitudinal axis, an intermediate portion located between said first lateral portion and said second lateral portion, preferably protruding with respect to at least one of said first and said second lateral portion, preferably along a direction parallel to said longitudinal axis.

Thanks to the aforesaid characteristics, the simple use of such a bobbin allows resolving the problem mentioned at the beginning concerning the possible openings of the tube made with the sheet of packaging material in the context of the formation process of the containers discussed above.

In one or more of the aforesaid aspects, the present invention may comprise one or more of the following characteristics. In one or more embodiments, said intermediate portion projects with respect to said first and said second lateral portions, in a direction parallel to said longitudinal axis of said first sheet.

In one or more embodiments, in a direction transverse to said longitudinal axis of said first sheet, said intermediate portion has a length at least equal to half of a width of said first sheet.

In one or more embodiments, providing said first sheet with said first joint edge includes cutting said first sheet along a first cutting line, preferably transverse to said longitudinal axis of said first sheet.

In one or more embodiments, said first cutting line comprises a first section, which delimits said first lateral portion. In one or more embodiments, said first cutting line comprises a second section, which delimits said second lateral portion. In one or more embodiments, said first cutting line comprises a third section, which delimits said intermediate portion. Preferably, said third section joins said first section and said second section. Preferably, said third section defines a profile with variable progression of the relative distance from at least one of said first lateral portion and second lateral portion in said direction parallel to said longitudinal axis of said first sheet. Preferably, said variable profile comprises a maximum point or region.

In one or more embodiments, said first cutting line comprises a first segment, which delimits said first lateral portion. In one or more embodiments, said first cutting line comprises a second segment, which delimits said second lateral portion. In one or more embodiments, said first cutting line comprises at least one third segment and one fourth segment, which delimit said intermediate portion. Preferably, said third segment is joined to said first segment, and preferably inclined with respect thereto. Preferably, said fourth segment is joined to said second segment, and preferably inclined with respect thereto.

In one or more embodiments, said first and said second segments are aligned, in particular along the same straight line.

In one or more embodiments, said first cutting line comprises a fifth segment, preferably interposed between said third and said fourth segment. Said fifth segment is preferably parallel to said first segment. Said fifth segment is preferably parallel to said second segment.

In one or more embodiments, providing said second sheet with the second joint edge includes cutting said second sheet along a second cutting line, preferably inclined with respect to a direction perpendicular to said longitudinal axis of said second sheet.

In one or more embodiments, the formation process of containers comprises the steps of:

- preferably folding said sheet or said new sheet about a main axis along which said work path extends, for obtaining a tube,

- preferably, sealing said sheet or said new sheet wound in tube-form along said main axis.

Preferably, the sealing step includes superimposing two opposite longitudinal edges of said sheet or said new sheet wound in tube-form. Preferably, the sealing step includes making a longitudinal sealing band at said two superimposed edges.

Preferably at least one of said first lateral portion and said second lateral portion of said first sheet has a length along a direction transversal to said longitudinal axis of said first sheet substantially equal to a width of said longitudinal sealing band.

In one or more embodiments, the formation process of containers includes, before wrapping the sheet or the new sheet to obtain a tube, applying a tape of thermosealable material to a longitudinal edge of said sheet or said new sheet. Preferably, making said longitudinal sealing band includes welding the other longitudinal edge of said sheet or said new sheet to said tape of thermosealable material.

Preferably, in said first sheet, said longitudinal edge ends at said first lateral portion or said second lateral portion of said joint edge.

In one or more embodiments, the machine comprises:

- preferably, a forming apparatus for wrapping the sheet into tube-form around a main axis along which said work path extends; and

- preferably, a welding device for making a longitudinal sealing band on two opposite longitudinal edges of said sheet wound into a tube and superimposed on each other.

Preferably, a cutting blade of said cutting device of said joining apparatus is arranged to produce at least one of said first lateral portion and second lateral portion, preferably with a length along a direction transverse to said longitudinal axis of the sheet substantially equal to the width of said longitudinal sealing band. Preferably, said sheet is said first sheet. In an equally preferred manner, said new sheet is called first sheet.

In one or more embodiments, the machine comprises a unit for applying a tape of thermosealable material along a longitudinal edge of said sheet. Preferably, said longitudinal edge ends at said first lateral portion or said second lateral portion of said joint edge, before wrapping the sheet to obtain a tube. Preferably, the welding device makes said longitudinal sealing band, welding the other longitudinal edge of said sheet to said tape of thermosealable material.

Further characteristics and advantages of the present invention will become evident from the description that follows with reference to the attached drawings, provided purely by way of non-limiting example, wherein:

- Figure 1 represents - in a schematic manner - the method described here according to a preferred embodiment;

- Figure 2 illustrates in detail a joint edge of a first sheet of packaging material, and a joint edge of a second sheet of packaging material;

- Figure 3 represents an example of an apparatus for implementing the method described here;

- Figure 4 represents a step of a process for forming containers filled with a liquid and sealed, starting from a sheet of packaging material;

- Figure 5 represents an additional step of a process for forming containers filled with a liquid and sealed, starting from a sheet of packaging material.

In the following description various specific details are illustrated aimed at a thorough understanding of the embodiments. The embodiments may be implemented without one or more of the specific details, or with other methods, components, materials, etc. In other cases, known structures, materials or operations are not shown or described in detail to avoid obscuring various aspects of the embodiments.

The references used here are only for convenience and do not therefore define the field of protection or the scope of the embodiments.

With reference to Figure 1, the solution described here relates to a method for joining a first sheet 110 of packaging material, for example, of a first bobbin 210, to a second sheet 120 of packaging material, for example, of a second bobbin 220.

In one or more preferred embodiments, such as the one illustrated, the first bobbin 210 and the second bobbin 220 are bobbins of packaging material, which comprise a central support and a sheet of packaging material, corresponding to the first sheet 110 and the second sheet 120, respectively, wound along a longitudinal axis of the respective sheet around the central support. The first bobbin 210 is a bobbin in use, and is running out, in a process for the formation of containers filled with a liquid and sealed, while the second bobbin 220 is a new bobbin intended to replace the bobbin 210 (step A of Figure 1).

In a per se known manner, the first sheet 110 of packaging material is unwound from the first bobbin 210, and is fed along a work path wherein it is subjected to a series of operations until the aforesaid containers are formed.

With reference to Figure 1, the method of joining the two sheets 110, 120 comprises:

- providing the first sheet 110 with a first joint edge 111 extending transversally to a longitudinal axis Y1 of the first sheet (step B of Figure 1);

- providing the second sheet 120 with a second joint edge 121 extending transversally to a longitudinal axis Y2 of the second sheet (step B of Figure 1);

- superimposing the first joint edge 111 and the second joint edge 121 to join the first sheet 110 and the second sheet 120 so that the respective longitudinal axes Yl, Y2 are aligned or - in any case - parallel and the second sheet 120 constitutes a continuation of the first sheet 110 along the longitudinal axes Yl, Y2 (step C of Figure 1); and

- welding together the first joint edge 111 and the second joint edge 121 (step D of Figure 1).

At the end of the welding operation, a joint 130 is obtained, which extends at an area Al wherein the two joint edges 111, 121 are superimposed on each other, and which permanently connects the two sheets 110 of packaging material together.

According to an important characteristic of the solution described here (see Figure 2), the first joint edge 111 comprises, along a direction transverse to the longitudinal axis Yl of the first sheet, a first lateral portion 111A and a second lateral portion 111C, opposite to each other with respect to the longitudinal axis Y 1 of the first sheet, and an intermediate portion 11 IB, placed between the first lateral portion 111 A and the second lateral portion 111C, and protruding with respect to at least one of the two lateral portions 111A, 111C along a direction parallel to the longitudinal axis Yl of the first sheet.

In one or more preferred embodiments, such as the one illustrated, the intermediate portion 11 IB projects with respect to both the two lateral portions 111 A, 111C, along a direction parallel to the longitudinal axis Yl of the first sheet. In one or more preferred embodiments, such as that illustrated, the first joint edge 111 is delimited by a first cutting line C, transverse to the longitudinal axis Yl. The cutting line C comprises a first section, which delimits the first lateral portion 111 A, a second section, which delimits the second lateral portion 111C, and a third section, which joins the first section and the second section, and delimits the intermediate portion 11 IB. Furthermore, in the direction parallel to the longitudinal axis Yl of the first sheet, the third section defines a variable profile of a distance from at least one of the first lateral portion 111A and the second lateral portion 111C, and said profile comprises a maximum point or region.

With particular reference to the illustrated embodiment, the first section includes a first segment Cl, which delimits the first lateral portion 111 A, the second section includes a second segment C2, which delimits the second lateral portion 111C, and the third section includes a third segment C3, a fourth segment C5 and a fifth segment C4, which delimit the intermediate portion 11 IB. The third segment C3 and the fourth segment C5 are joined to the first segment Cl and the second segment C2, respectively, and are inclined with respect to them. The first segment C 1 and the second segment C2 are aligned along the same straight line and the fifth segment C4, which is interposed between the third segment C3 and the fourth segment C5, is parallel to the first segment Cl and the second segment C2.

On the other hand, the second joint edge 121 has a known type configuration, or rather, is delimited by a second straight cutting line C, perpendicular to the longitudinal axis Y2 of the second sheet or slightly inclined with respect to a direction perpendicular to the longitudinal axis Y2 of the second sheet.

Preferably, the first joint edge 111 is arranged internally in the joint 130 (with respect to the inner side of the second sheet 120), for the reasons that will become evident below.

The configuration described above of the first joint edge 111 allows the problem to be resolved that was mentioned at the beginning concerning the possible openings of the tube made with the sheet of packaging material in the context of the formation process of the containers discussed above.

In this regard, Figure 4 schematically represents an example of a forming step of the tube of such a process.

In a per se known manner, a sheet of packaging material, which - in this case - corresponds to the first sheet 110, is wound around a main axis I along which the work path K extends, to obtain a tube 140, and two opposite longitudinal edges 112, 112' of the sheet are heated and superimposed to produce a longitudinal sealing band 142. A tape of thermosealable material (not visible) is applied to a longitudinal edge or inner edge 112', which extends longitudinally along the same edge, and is positioned so as to protrude laterally from the inner edge 112' itself.

Again in a per se known manner, the two longitudinal edges 112, 112' are heated by means of an induction welding device 50, which is designed to generate a magnetic field such as to induce in the metal layer that makes up the sheet 110 localized currents on the two superimposed longitudinal edges 112, 112', and which heat the metal layer by thermoelectric effect and, indirectly, the inner coating of the sheet on which the tape of thermosealable material is applied.

Downstream of the induction welding device 50, a fastening device 52 presses the two heated longitudinal edges 112, 112’ and the tape of thermosealable material against each other, so as to produce the longitudinal sealing band 142.

When the joint 130 of the two joint edges 111, 121, obtained as described above, reaches this portion of the work path K, it intersects with the longitudinal sealing band 142 being formed.

The configuration described above of the first joint edge 111 allows heating of the longitudinal edges 112, 112' to be obtained at the joint 130, which is substantially uniform over the whole width of these edges involved in the welding operation, and in this way it is possible to guarantee an optimal sealing even at the joint 130.

In particular, the configuration of the first joint edge 111 is capable of distributing the currents generated by induction in the metal layer of the sheet 110 so that they extend at least over the entire area of the two lateral portions 111A, 111C, and this is achieved thanks to the intermediate portion 11 IB that extends in the direction of the longitudinal axis Y1 of the first sheet so as to protrude with respect to the two lateral portions 111 A, 111C.

In one or more preferred embodiments, the two lateral portions 111A, 111C of the first joint edge 111 have a length along the direction transverse to the longitudinal axis Y1 of the first sheet substantially equal to the width of the longitudinal sealing band 142. Therefore, at the joint 130, the longitudinal sealing band 142 essentially consists of the two lateral portions 111 A, 111C of the first joint edge 111 and the corresponding portions of the second joint edge 121. The specific shape of the first joint edge 111 may - in any case - vary with respect to that illustrated in the figures. For example, the first cutting line C, which delimits the first joint edge 111 may have a curvilinear and not broken profile.

In general, the shapes and dimensions of the portions 111A, 11 IB and 111C of the first joint edge 111 may vary according to the requirements of the specific applications.

With reference now to Figure 5, a step of the formation process of the containers will now be illustrated in detail by means of a machine for the formation of containers filled with a liquid and sealed, wherein on a sheet of packaging material, corresponding to the first sheet 110, the tape of thermosealable material mentioned above is applied and indicated in the Figure with the reference number 146.

The machine comprises a forming unit, which includes the induction sealing device 50 and the fastening device 52, and a unit for applying the tape 146 on the inner edge 112' of the first sheet 110, placed upstream of the forming unit, and comprising an initial induction welding device 54 and an initial fastening device 56.

The aforesaid step involves heating the inner edge 112' of the first sheet 110 and applying the tape 146 of thermosealable material on the heated inner edge 112'.

The inner edge 112' is heated by means of the initial induction welding device 54, according to the same method described above with reference to the induction welding device 50. The initial fastening device 56 presses the tape 146 against the heated inner edge 112’ causing their mutual fastening.

The connection between the tape 146 and the inner edge 112' is made on a attachment area A2, which extends along the longitudinal direction of the two same elements.

When the joint 130 of the two joint edges 111, 121 reaches the section of the work path K wherein the indicated step takes place, it intersects with the attachment area A2 being formed.

Similarly to the above, the configuration of the first joint edge 111 allows an optimal welding to be produced of the tape of thermosealable material 146 on the inner edge 112' of the sheet 110 also at the joint 130. This result is obtained for the same technical reasons discussed above, or rather, thanks to the ability of the first joint edge 111 to distribute the currents generated by induction in the metal layer of the sheet so that these invest the entire area of the sheet affected by the welding operation.

In one or more preferred embodiments, the first lateral portion 111 A has a length in the direction transverse to the longitudinal axis Y1 of the first sheet substantially equal to the width of the attachment area A2.

The configuration described above for the first joint edge 111 of the first sheet 110 may alternatively be made on the second joint edge 121 of the second sheet 120 of the new bobbin 220. In this case, it is preferably the same second joint edge 121 of the second sheet 120 to be arranged internally in the joint 130 (with respect to the inner side of the first sheet 110).

In an embodiment not illustrated, a bobbin of packaging material may be made already prepared with an end edge corresponding to the first joint edge 111 in the configuration described above. According to this embodiment, the bobbin comprises, in general: a central support and a sheet of packaging material extending along the longitudinal axis of the sheet and wound along the same longitudinal axis around the central support, wherein the end edge of the sheet comprises, along a direction transverse to the longitudinal axis, a first lateral portion and a second opposite lateral portion and an intermediate portion located between said first lateral portion and said second lateral portion and protruding with respect to at least one of said first and second lateral portions along a direction parallel to the longitudinal axis.

With reference to Figure 3, this illustrates an example of an apparatus for implementing a method as described above.

This apparatus - indicated as a whole with the reference number 10 - comprises a first seat 11 and a second seat 12 for each receiving a bobbin of a sheet of packaging material.

Each seat 11, 12 comprises a shaft 13, which can rotate around a preferably horizontal rotation axis on which the respective bobbin is arranged. Preferably, the shaft 13 is equipped with rentention means to constrain the bobbin in rotation to the shaft itself.

The apparatus 10 also comprises a guide 14, which can be selectively positioned above the first seat 11 or the second seat 12, and which has the function of guiding the sheet unwound from the bobbin in use, located in one of the two seats, to place it in the predefined starting point (not illustrated) of the work path K. In the example shown, the bobbin in use 210 is arranged in the first seat 11 and the new bobbin 220, which will replace the bobbin 210, is arranged in the second seat 12.

In one or more preferred embodiments, such as that illustrated, the apparatus 10 further comprises a cutting device 15, which is integral with the guide 14 and is designed to produce on the sheet of the bobbin in use 210, which is running out, the first j oint edge 111.

In one or more preferred embodiments, such as that illustrated, the cutting device 15 comprises an outer casing 15B, which defines a narrow passage for the sheet of packaging material and is provided with a slit 15C within which a cutting blade is linearly movable (not visible), perpendicularly to the plane of the sheet. In one or more preferred embodiments, the cutting blade is movable according to a cutting stroke, which extends in a direction outwards of the apparatus 10 (or rather, in a direction leaving the plane of illustration of the figure). The outer casing 15B has the function of retaining the sheet during the cutting operation.

Preferably, the cutting blade 15A is arranged to form a cutting line on the sheet of the bobbin in use 210, corresponding to the first cutting line C described above.

The first joint edge 111 made by the cutting device 15 is intended to be joined to the sheet of the new bobbin 220.

In one or more preferred embodiments, such as that illustrated, the apparatus 10 comprises an additional cutting device 16, which can be positioned, manually, above each of the two seats 11, 12 and is designed to form a joint edge on the sheet of the new bobbin 220. The additional cutting device 16 can be operated manually. In the example shown, the additional cutting device 16 is positioned above the second seat 12 to make the second joint edge 121 on the sheet of the new bobbin 220.

Preferably, the additional cutting device 16 comprises a cutting blade (not visible) designed to produce a cutting line on the sheet of packaging material corresponding to the second cutting line C.

Furthermore, the apparatus 10 described herein comprises at least one sealing device for fastening together the joint edges of the two sheets of packaging material. This device comprises, for example, a welding plate operable to press the aforesaid joint edges against each other. In view of the above, the operation of the apparatus 10 envisages, first of all, stopping the rotation of the bobbin in use 210, which is positioned in the first seat 11. When the sheet of the bobbin in use 210 is stationary, the cutting device 15 is operated to produce the first j oint edge 111. In the meantime, after the new bobbin 220 has been loaded on the second seat 12, the second joint edge 121 is made on the sheet of the new bobbin 220 by means of the additional cutting device 16.

At this point, the guide 14 is moved above the second seat 12, taking with it the sheet of the bobbin in use 210 and the relative first joint edge 111. Finally, the two joint edges 111, 121 are welded together by means of the welding device so as to form the joint 130. At the end of the process, the sheet of the new bobbin 220 constitutes the extension of the sheet of the bobbin in use 210 and the new bobbin 220 is then rotated to feed the relative sheet along the work path K.

Of course, without prejudice to the principle of the invention, the details of construction and the embodiments may vary, even significantly, with respect to those illustrated here, purely by way of non-limiting example, without departing from the scope of the invention as defined by the attached claims.

Claims

1. A method for j oining together a first sheet ( 110) of packaging material to a second sheet (120) of packaging material, the method comprising: providing said first sheet (110) with a first joint edge (111) extending transversally to a longitudinal axis (Yl) of said first sheet; providing said second sheet (120) with a second joint edge (121) extending transversally to a longitudinal axis (Y2) of said second sheet; superimposing said first joint edge (111) and second joint edge (121) for joining said first sheet (110) and second sheet (120), so that said longitudinal axis (Yl) of said first sheet and said longitudinal axis (Y2) of said second sheet are parallel with respect to one another, and said second sheet (120) forms an extension of said first sheet (110) along said longitudinal axes (Yl, Y2); welding together said first joint edge (111) and said second joint edge (121) superimposed to one another; wherein said first joint edge (111) comprises, along a direction transversal to said longitudinal axis (Yl) of said first sheet, a first lateral portion (111 A) and a second lateral portion (111C), which are opposite to one another with respect to said longitudinal axis (Yl) of said first sheet, and an intermediate portion (11 IB), which is located between said first lateral portion (111 A) and said second lateral portion (111C) and projects with respect to at least one of said first and second lateral portions (111 A, 111C) in a direction parallel to said longitudinal axis (Yl) of said first sheet.

2. A method according to claim 1, wherein said intermediate portion (11 IB) projects with respect to said first and second lateral portions (111 A, 111C), along a direction parallel to said longitudinal axis (Yl) of said first sheet.

3. A method according to any one of the preceding claims, wherein in a direction transversal to said longitudinal axis (Yl) of said first sheet, said intermediate portion (11 IB) has a length at least equal to half of a width of said first sheet (110).

4. A method according to any one of the preceding claims, wherein providing said first sheet (110) with said first joint edge (111) includes cutting said first sheet (110) along a first cutting line (C) transversal to said longitudinal axis (Yl) of said first sheet.

5. A method according to claim 4, wherein said first cutting line (C) comprises a first section delimiting said first lateral portion (111 A), a second section delimiting said second lateral portion (111C), and a third section joining together said first and second sections and delimiting said intermediate portion (11 IB), wherein said third section defines a variable profile of a relative distance from at least one of said first lateral portion (111 A) and second lateral portion (111C) in said direction parallel to said longitudinal axis (Yl) of said first sheet, wherein said profile comprises a maximum point or region.

6. A method according to claim 4 or 5, wherein said first cutting line (C) comprises a first segment (Cl) delimiting said first lateral portion (111 A), a second segment (C2) delimiting said second lateral portion (111C), and at least one third segment (C3) and one fourth segment (C5) delimiting said intermediate portion (11 IB), wherein said third segment (C3) and said fourth segment (C5) are joined to said first segment (Cl) and second segment (C2), respectively, and are inclined with respect to them.

7. A method according to claim 5, wherein said first and second segments (Cl, C2) are aligned to one another.

8. A method according to claims 6 or 7, wherein said first cutting line (C) comprises a fifth segment (C4), which is interposed between said third and forth segments (C3, C5) and is parallel to said first and second segments (Cl, C2).

9. A method according to any one of the preceding claims, wherein providing said second sheet (120) with said second joint edge (121) includes cutting said second sheet (120) along a second cutting line (C’), which is inclined with respect to a direction perpendicular to said longitudinal axis (Y2) of said second sheet.

10. A process for forming containers filled with a liquid and sealed, starting from a sheet of packaging material unwound from a bobbin (210) along a work path (K), the process comprising the steps of providing, when the sheet must be replaced with a new sheet of packaging material of a new bobbin (220), joining said sheet and new sheet by means of a method according to any one of the preceding claims, wherein one of said sheet and new sheet is said first sheet (110) and the other of said sheet and new sheet is said second sheet (120).

11. A process according to claim 10, further comprising the steps of: folding said sheet or new sheet about a main axis (I) along which said work path extends, for obtaining a tube (140), sealing along said main axis (I) said sheet or said new sheet folded in tube-form, wherein said step of sealing includes superimposing two opposite longitudinal edges (112, 112’) of said sheet or said new sheet folded in tube-form and making a longitudinal sealing band (142) at said two superimposed longitudinal edges (112, 112’); wherein at least one of said first and second lateral portions (111 A, 111C) of said first sheet (110) has a length along a direction transversal to said longitudinal axis (Yl) of said first sheet (110) substantially equal to a width of said longitudinal sealing band (142).

12. A process according to claims 10 or 11, which includes, before folding said sheet or said new sheet for obtaining a tube, applying a strip (146) of thermosealable material on a longitudinal edge (112’) of said sheet or new sheet and wherein making said longitudinal sealing band (142) includes welding the other longitudinal edge (112) of said sheet or said new sheet to said strip of thermosealable material (146), wherein in said first sheet (110) said longitudinal edge (112’) terminates at one of said first and second lateral portions (111 A, 111C) of said first joint edge (111).

13. An apparatus ( 10) for j oining a first j oint edge ( 111 ) of a first sheet (110) of packaging material to a second joint edge (121) of a second sheet (120) of packaging material, the apparatus comprising: a cutting device (15), which includes a cutting blade intended to make a first cutting line (C) transversal to a longitudinal axis (Yl) of said first sheet, for making said first joint edge (111) comprising, along a direction transversal to said longitudinal axis (Yl), a first lateral portion (111 A) and a second lateral portion (111C) opposite to one another with respect to said longitudinal axis (Yl) of said first sheet, and an intermediate portion (11 IB) arranged between said first lateral portion (111 A) and second lateral portion (111 C) and projecting with respect to at least one of said first and second lateral portions (111 A, 111C) in a direction parallel to said longitudinal axis (Yl) of said first sheet;

19 a welding device for welding together said first and second joint edges (111, 121) superimposed to one another.

14. A machine for forming containers filled with liquid and sealed, starting from a sheet (110, 120) of packaging material unwound from a bobbin along a work path, the machine comprising an apparatus (10) according to claim 13.

15. A machine according to claim 14, further comprising a forming apparatus for wrapping said sheet to form a tube around a main axis (I) along which said work path extends, and a welding device (50) for making a longitudinal sealing band (142) on two longitudinal edges (112, 112’) of said sheet folded to form a tube, which are opposite and superimposed to one another, wherein a cutting blade of said cutting device (15) of said joining apparatus is configured to make at least one of said first lateral portion (111 A) and second lateral portion (111 C) with a length along a direction transversal to said longitudinal axis (Yl) of said sheet substantially equal to a width of said longitudinal sealing band (142), said sheet being said first sheet (110).

16. A machine according to claim 15, comprising a unit for applying a strip of thermosealable material (146) along a longitudinal edge (112’) of said first sheet (110) terminating at one of said first and second lateral portions (111 A, 111C) of said first joint edge (111), before wrapping said sheet to form a tube, said welding device (50) making said longitudinal sealing band (142) by welding the other longitudinal edge (112) of said first sheet (110) to said strip (146) of thermosealable material (146).