Process and machine for packaging products with stretchable thermoplastic film

Abstract

Means are provided to ensure that during the stage of formation through the tube- forming and longitudinal welding means ( 1, 18 ) the wrapping is subjected to longitudinal stretching which causes it to adhere intimately in a direction transverse to the product and this condition is ensured by means which bring about a particular difference in velocity between the jaw ( 19, 119 ) which supports the tubular wrapping and causes it to advance and the means ( 15, 115, 17 ) which feed the film to the tube-forming means ( 1 ) which also remain suitably active during the subsequent stage in which the tubular wrapping is seized posteriorly by the appropriate posterior closing jaw ( 119, 19 ), all in such a way that the wrapping film runs over the said tube-forming means in an almost continuous movement to prevent localised appearance defects in the packaging and to assist operation of the longitudinal welding means ( 18 ) which are then able to operate substantially continuously.

1 ) Machine for the packaging of products with stretchable thermoplastic film characterised in that it comprises: 
 means ( 1 ) for making the wrapping film unwind from a spool into a tube and means ( 18 ) for longitudinally welding the overlapping edges of that film so as to produce a continuous tubular wrapping,    means ( 15 ,  115 ,  17 ) to feed the film unwound from the spool to the said tube-forming means ( 1 ) in a controlled way,    jaw means ( 19 ,  119 ) located downstream from the film-tube-forming means ( 1 ) which alternate in transverse gripping of the head and tail ends of the tubular wrapping leaving the said tube-forming means, and into which the product being packed is inserted at the appropriate stage, these jaw means being designed to support and cause the said wrapping to advance longitudinally and produce two transverse parallel leaktight welds therein, a transverse cut between the two welds and to hold the wrapping upstream and downstream from the two welded areas separated by the cut,    means for cyclically inserting a product (P) through the said tube-forming means and for accompanying it as it exits therefrom and inserting it into the tubular wrapping being formed which is held anteriorly by one of the said jaw means ( 19 ,  119 ),    means to ensure that the wrapping in the stage of being formed through the said tube-forming and longitudinal welding means ( 1 ) is subjected to longitudinal stretching in such a way as to adhere intimately to the product in a transverse direction, this condition being ensured by means which bring about a particular difference in speed between the jaw ( 19 ,  119 ) which supports the tubular wrapping and causes it to advance, and the said means ( 15 ,  115 ,  17 ) which feed the film to the tube-forming means ( 1 ), which also remain suitably active during the subsequent stage during which the tubular wrapping is gripped posteriorly by the appropriate posterior sealing jaw ( 119 ,  19 ), all in such a way that the wrapping film moves with an almost continuous movement over the said tube-forming means to prevent local unsightliness in the packaging and to assist operation of the longitudinal welding means ( 18 ) which are then able to operate substantially continuously,    means ( 23 ) for collecting and removing the packs (Z) which are cyclically formed.    
   
   
       2 ) Machine according to  claim 1) , in which the film ( 5 ) is unwound from the spool ( 105 ) by means which are expressly dedicated to that function and which are capable of constantly providing the necessary suitably stretched quantity of film to the subsequent means ( 15 ,  115 ,  17 ) for controlled delivery of that film to the tube-forming means ( 1 ), motor-driven means ( 6 ,  7 ) being provided for rotation of the spool ( 105 ) and subsequent swinging arm means ( 8 ,  108 ,  10 ) for buffer storage of the cyclically unwound film, and means ( 12 ) which detect the angular position of the swinging arm and consequently the quantity of buffer film to produce a signal which is useful for control of the said means ( 6 ,  7 ) for unwinding film from the spool.  
   
   
       3 ) Machine according to  claim 1) , in which the said means for the controlled feed of film to the tube-forming means ( 1 ) comprise at least one roller ( 15 ) with a high coefficient of friction in relation to the film, for example a rubber-coated roller, on which the film is held and delivered with an extensive contact surface area by at least one parallel opposing roller ( 115 ), which idles and can be removed when necessary, the said rubber-coated roller ( 15 ) being connected to controlled rotation means which comprise a motor ( 17 ) under electronic control of speed and phase, such as for example a stepping motor, governed by a main processor ( 13 ) of the machine which operates it in proper phase with the lateral and closure movements of the jaws ( 19 ,  119 ), which are themselves also controlled by the said processor.  
   
   
       4 ) Machine according to  claim 3) , in which the processor ( 13 ) detects the dimensions of the product being packed through suitably dedicated means ( 30 ,  2 ) and suitably automatically adjusts the function of the said film feed means ( 15 ,  115 ,  17 ) and the operation of the jaws ( 19 ,  119 ) drawing, supporting, welding and transversely cutting the wrappings to those dimensions.  
   
   
       5 ) Process for the packaging of products with stretchable thermoplastic film, characterised by the following sequence of stages: 
 formation of a tube of stretchable thermoplastic film unwound from a corresponding feed spool, with welding along its longitudinal edges in such a way as to form a continuous tube which is positioned almost horizontally and has a transverse cross-section of sufficient size for the product which is being packed to be inserted therein,    closure of the head end of the said tube of film leaving the tube-forming and longitudinal welding stage with at least one transverse weld and support of the closed head in such a way that the tube which is also supported by the tube-forming means remains in a substantially horizontal position,    insertion of the product (P), which is usually placed in a tray, within the length of tubular wrapping which is sealed and supported anteriorly in such a way as to be close to that anterior end of the tubular wrapping,    longitudinal stretching of the tubular wrapping while this is being created through the tube-forming and longitudinal welding means, as it leaves these means and while the product being packed is being inserted into the said wrapping, all in such a way that through the effect of the stretching and as a result also of the properties of the film used the tubular wrapping shrinks transversely onto the product and wraps it intimately,    closure of the posterior extremity of the longitudinally stretched tubular wrapping downstream from the product packed therein by at least one transverse weld, sealing of the end of the tubular wrapping following the packaging formed with at least one other transverse weld, transverse cutting of the tubular wrapping in the area between the said two transverse welds, while the head end of the next tubular wrapping is held while the tail end of the packaging formed is also held, while such packaging is supported horizontally and while at the appropriate time the head end of the same packaging is released in such a way that the film forming it can react longitudinally to adhere intimately to the packed product in that direction too,    release of the posterior extremity of the packaging formed from the clamp and removal of the same from the packaging area.    
   
   
       6 ) Process according to  claim 5 , in which the film unwound from the spool ( 105 ) by the dedicated means ( 6 ,  7 ,  8 ,  108 ,  10 ) is fed positively and in a controlled way from the appropriate means ( 15 ,  115 ,  17 ) to the subsequent tube-forming and longitudinal welding means ( 1 ,  18 ) both during the stage of formation and longitudinal stretching of the tubular wrapping by the jaw means ( 119 ,  19 ) operating on the head end of the packaging being formed, and during the stage of sealing by the jaw means ( 19 ,  119 ) which takes place on the tail end of the said packaging during the completion stage, stretching of the film being ensured by a suitable difference in speed between the said feed means ( 15 ,  115 ,  17 ) and the successive jaw means ( 19 ,  119 ) which operate upstream and downstream of the said means ( 1 ,  18 ) respectively.  
   
   
       7 ) Process according to  claim 6)  in which activation of the said means ( 15 ,  115 ,  17 ) feeding film to the subsequent tube-forming and longitudinal welding means is automatically correlated with the size of the product being packed.  
   
   
       8 ) Process according to  claim 5) , in which the operation of longitudinal welding of the tubular wrapping of film as it passes over the tube-forming mandrel ( 1 ) is continuous because the wrapping film runs over the said mandrel continuously during both every cycle of product packaging and the transition from one cycle to the next, provided that continuity in the cyclical feed of products to be packed is ensured upstream of the said mandrel.  
   
   
       9 ) Process according to  claim 5) , in which the lateral movement (A) of the jaw ( 19 ) supporting the head end of the packaging being formed can begin at the same time as the movement (B) of the unit ( 15 ,  115 ,  17 ) feeding the film and the difference in speed between the two movements controls the percentage stretching of the film, and the said first movement (A) can cease in phase with the said second movement (B) which is reactivated at the appropriate stage with the closing movement (C) of the jaw ( 119 ) acting on the tail end of the packaging being formed.  
   
   
       10 ) Process according to  claim 5)  in which the movement (B) of the film feed means ( 15 ,  115 ,  17 ) begins after lateral movement (A) of the upstream jaw and ends before that movement (A) so that the film wrapping is stretched to a greater extent and adheres to the product (P) and that the film is under greater tension at the beginning of the next packaging cycle when the film is unwound for the next pack.  
   
   
       11 ) Process according to  claim 9) , in which the movement (B) of the film feed means ( 15 ,  115 ,  17 ) can be stopped with a delay in relation to the stopping of closing movement (C) of the jaw acting on the tail end of the packaging at the completion stage and/or can begin in advance of the horizontal and/or vertical movements (A and/or C) of the jaws ( 19 ,  119 ).  
   
   
       12 ) Process according to claims  10 ), in which the movement (B) of the film feed means ( 15 ,  115 ,  17 ) can be stopped with a delay in relation to the stopping of closing movement (C) of the jaw acting on the tail end of the packaging at the completion stage and/or can begin in advance of the horizontal and/or vertical movements (A and/or C) of the jaws ( 19 ,  119 ).  
   
   
       13 ) Process according to  claim 5) , in which the speed of movement (B) of the film feeding means ( 15 ,  115 ,  17 ) can be progressively increased towards the end of the wrapping cycle in such a way that the tube of film wrapping the product is firmly tensioned at the start and then progressively becomes slower or more relaxed, with beneficial effects on the risk of film breakage at high packaging speeds, particularly during the stage of the start of stretching by the jaw acting on the head end of the wrapping.