A method for joining together two sheets of packaging material

Abstract

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

1 . A method for joining together a first sheet of packaging material to a second sheet of packaging material, the method comprising:
 providing said first sheet with a first joint edge extending transversally to a longitudinal axis of said first sheet;   providing said second sheet with a second joint edge extending transversally to a longitudinal axis of said second sheet;   superimposing said first joint edge and second joint edge for joining said first sheet and second sheet, so that said longitudinal axis of said first sheet and said longitudinal axis of said second sheet are parallel with respect to one another, and said second sheet forms an extension of said first sheet along said longitudinal axes;   welding together said first joint edge and said second joint edge superimposed to one another;   wherein said first joint edge comprises, along a direction transversal to said longitudinal axis of said first sheet, a first lateral portion and a second lateral portion, which are opposite to one another with respect to said longitudinal axis of said first sheet, and an intermediate portion, which is located between said first lateral portion and said second lateral portion and projects with respect to at least one of said first and second lateral portions in a direction parallel to said longitudinal axis of said first sheet.   
     
     
         2 . The method according to  claim 1 , wherein said intermediate portion projects with respect to said first and second lateral portions, along a direction parallel to said longitudinal axis of said first sheet. 
     
     
         3 . The method according to  claim 1 , wherein in a direction transversal 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. 
     
     
         4 . A method according to  claim 1 , wherein providing said first sheet with said first joint edge includes cutting said first sheet along a first cutting line transversal to said longitudinal axis of said first sheet. 
     
     
         5 . A method according to  claim 4 , wherein said first cutting line comprises a first section delimiting said first lateral portion, a second section delimiting said second lateral portion, and a third section joining together said first and second sections and delimiting said intermediate portion,
 wherein said third section defines a variable profile of a 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, wherein said variable profile comprises a maximum point or region.   
     
     
         6 . A method according to  claim 4 , wherein said first cutting line comprises a first segment delimiting said first lateral portion, a second segment delimiting said second lateral portion, and at least one third segment and one fourth segment delimiting said intermediate portion, wherein said third segment and said fourth segment are joined to said first segment and second segment, respectively, and are inclined with respect to them. 
     
     
         7 . A method according to  claim 5 , wherein said first and second segments are aligned to one another. 
     
     
         8 . A method according to  claim 6 , wherein said first cutting line comprises a fifth segment, which is interposed between said third and fourth segments and is parallel to said first and second segments. 
     
     
         9 . A method according to  claim 1 , wherein providing said second sheet with said second joint edge includes cutting said second sheet along a second cutting line, which is inclined with respect to a direction perpendicular to said longitudinal axis of said second sheet. 
     
     
         10 . A process for forming containers filled with a liquid and sealed, starting from a first sheet of packaging material unwound from a bobbin along a work path, the process comprising the steps of;
 providing, when the first sheet must be replaced with a new sheet of packaging material of a new bobbin, the new sheet of packaging material of the new bobbin and   joining said first sheet and said new sheet by means of a method according to  claim 1 , wherein new sheet is said second sheet.   
     
     
         11 . A process according to  claim 10 , further comprising the steps of:
 folding said first sheet or second sheet about a main axis along which said work path extends, for obtaining a tube,   sealing along said main axis said first sheet or said second sheet folded in tube-form, wherein said step of sealing includes superimposing two opposite longitudinal edges of said first sheet or said second sheet folded in tube-form and making a longitudinal sealing band at said two superimposed longitudinal edges;   wherein at least one of said first and second lateral portions 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.   
     
     
         12 . A process according to  claim 11 , comprising, before folding said first sheet or said second sheet for obtaining the tube, applying a strip of thermosealable material on a longitudinal edge of one of said first sheet or second sheet and wherein making said longitudinal sealing band includes welding a longitudinal edge of the other of said first sheet or said second sheet to said strip of thermosealable material,
 wherein in said first sheet said longitudinal edge terminates at one of said first and second lateral portions of said first joint edge.   
     
     
         13 . 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 comprising:
 a cutting device, which includes a cutting blade configured to make a first cutting line transversal to a longitudinal axis of said first sheet, for making said first joint edge comprising, along a direction transversal to said longitudinal axis, a first lateral portion and a second lateral portion opposite to one another with respect to said longitudinal axis of said first sheet, and an intermediate portion arranged between said first lateral portion and second lateral portion and projecting with respect to at least one of said first and second lateral portions in a direction parallel to said longitudinal axis of said first sheet; and   a welding device for welding together said first and second joint edges superimposed to one another.   
     
     
         14 . A machine for forming containers filled with liquid and sealed, starting from the first sheet of packaging material unwound from a bobbin along a work path, the machine comprising the apparatus according to  claim 13 . 
     
     
         15 . A machine according to  claim 14 , further comprising a forming apparatus for wrapping said first sheet to form a tube around a main axis along which said work path extends, and
 a welding device for making a longitudinal sealing band on two longitudinal edges of said first sheet folded to form the tube, which are opposite and superimposed to one another, wherein the cutting blade of said cutting device of said joining apparatus is configured to make at least one of said first lateral portion and second lateral portion with a length along a direction transversal to said longitudinal axis of said first sheet substantially equal to a width of said longitudinal sealing band.   
     
     
         16 . A machine according to  claim 15 , comprising a unit for applying a strip of thermosealable material along a longitudinal edge of said first sheet terminating at one of said first and second lateral portions of said first joint edge, before wrapping said sheet to form the tube, said welding device making said longitudinal sealing band by welding the other longitudinal edge of said first sheet to said strip of thermosealable material.