Patent Publication Number: US-8119055-B2

Title: Method and apparatus for corrugating and winding up rolls of plastic film

Description:
BACKGROUND OF THE INVENTION 
     This invention refers to the formation of rolls in film plastic material, in particular to a method and an apparatus for corrugating and winding up rolls of a plastic film which is provided with a plurality of crosswise corrugations or pleats, extending between opposite open-end side edges, as the plastic film is wound up into a roll. 
     Although the invention finds its application in the production of rolls of plastic films for packing and/or wrapping loads, the aforementioned method and apparatus prove to be particularly suitable for winding up coreless rolls, or rolls with a soft core made of thin cardboard, for example 1 or 2 mm thick, by an extensible stretchable plastic film. 
     STATES OF THE ART 
     It is well known that stretchable plastic films are widely used for packing and wrapping palletized loads, in order to give the load the necessary protection and stability. 
     Usually a plastic film can be produced by linear or circular extrusion heads, and subsequently wound up into rolls having weight and size suitable for the manual wrapping of a load, or by an automatic wrapping machine. 
     The plastic film can be wound up into rolls either around a rigid tubular core, generally of cardboard or plastic material, having a wall thickness of 3 or 4 mm, or made of thin cardboard, or directly wound around itself thereby forming a so-called “coreless” roll. 
     In the production of rolls of a stretchable plastic film, several problems arise caused by the natural adhesiveness of the plastic material, and by the elastic memory of the same plastic film after has been stretched; these problems can lead to the production of faulty rolls, or to the implosion of the rolls themselves if wound up without any internal supporting core, or with a core of a thin cardboard. 
     In order to partially solve these problems, EP 0.728.102 suggests the use of a textured roller provided with a peripheral teething for partially deforming the plastic film, embossing a plurality of small pockets suitable to trap air in the rolled film, during the winding; the trapped air will tend to prevent adhesion between the turns of the roll, and facilitates the subsequent unwinding of the film. This solution however does not prevent any possible deformation and implosion of the rolls both at the winding and over time, caused by the shrinkage due to the elastic memory of the film. 
     In turn, WO 05/123555 suggests the use of a grooved drawing drum having a peripheral surface provided with a plurality of longitudinally extending grooves to shape or fold the plastic film with a plurality of crosswise pleats, or open-end corrugations, which extend crosswise between the opposite side edges of the film; the plastic film is urged and folded into longitudinal grooves of the drawing roller, by air jets as it is continuously made to move towards a roll being wound. 
     Although this solution has allowed a substantial improvement and the formation of rolls of regular diameter and shape, in which any incidental yielding or implosion of the turns is substantially compensated by a controlled flattening of the crosswise pleats, made possible by venting air from the open ends of the pleats, further improvements are however possible in the method of corrugating or folding the crosswise pleats, as well as in the apparatus. 
     In the case of extensible or stretchable films, a different behaviour was in fact noted, both during the winding up of the rolls and subsequently, depending upon whether the plastic film is extruded in a flat or tubular form, due to the different molecular orientation resulting from the different stretching conditions, and from the different elastic memory of the plastic films. 
     While on the one hand, the use of air jets to fold and cause the plastic film to penetrate into the longitudinal grooves of a drawing and corrugating drum, as proposed in WO 05/123555, has enabled the production of wholly regular rolls, reducing any risk of implosion, from tests and experiments subsequently carried out it was found that in certain cases, or with certain types of plastic film, it does not allow an adequate control of the corrugations, in the forming of the pleats, and in the winding up of the film. On the contrary, the tests carried out proved that this control of the corrugations is necessary in order to compensate a different shrinkage degree of the plastic material both during the winding up of the roll, and over time, due to the different elastic memory of the same films; it was also noted that the action of the air jets some times is opposed by the cushioning of air that remains trapped between the film and the grooved drum, especially at high winding revolutions, which causes a certain lateral instability in the positioning of the film both on the grooved drum and on the roll being wound. 
     OBJECTS OF THE INVENTION 
     The main object of this invention is therefore to provide a method and an apparatus for corrugating and winding up plastic film into rolls, capable of obviating the drawbacks of the previously known methods and devices, by means of which it is possible to wind up rolls with or without an internal supporting core, in a controlled manner and of a wholly regular shape. 
     A still further object of the invention is to provide a method and an apparatus of the aforementioned kind, by means of which it is possible to control the effect and the corrugation depth of the plastic film, depending upon the characteristics of the same film to be wound, and of the rolls. 
     A still further object is to provide a method and an apparatus for corrugating and winding up plastic films into rolls, by which it is possible to further reduce any deformation risk of the rolls caused by an implosion of its turns, or by an uncontrolled shrinkage of the film itself, over the time. 
     The invention is particularly applicable for producing rolls of stretchable plastic films wound either around a rigid or soft tubular core, or for producing coreless rolls. 
     BRIEF DESCRIPTION OF THE INVENTION 
     According to a main feature of the invention, use is made of a grooved drawing drum for corrugating a plastic film material to be wound onto a roll, said grooved drum with a plurality of longitudinally extending grooves and air suction holes opening into the corrugating grooves and means to connect the air suction holes to an air suction source and to allow a controlled penetration and folding of the plastic film into the grooves of the drawing drum during the winding up of the film onto the roll. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and further characteristics of a method, a corrugating drum, and an apparatus for winding up rolls of plastic films, as well as a preferential embodiment, will be more clearly evident from the following description, with reference to the drawings, in which: 
         FIG. 1  shows a schematic representation of an apparatus according to the invention; 
         FIG. 2  shows a longitudinal cross-sectional view of a grooved drum, along the line  2 - 2  of  FIG. 1 ; 
         FIG. 3  shows a partially enlarged cross-sectional view of the grooved drum, along the line  3 - 3  of  FIG. 2 ; 
         FIG. 4  shows an enlarged detail of  FIG. 3 ; 
         FIG. 5  shows a schematic representation of a possible disposition of the air intake holes, on the grooved drum. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIG. 1 , a description will now be given of the essential parts of an apparatus for winding up rolls of plastic films, comprising the improvements according to the invention. 
     In  FIG. 1 , the reference number  10  indicates a plastic film for example fed from a large pre-wound roll, or directly from an extrusion head (not shown), to form a roll  11  of limited dimensions, by winding up the film  10  around a tubular core, or directly onto a mandrel  12 , in the form of a coreless roll. 
     The film  10 , preferably in a pre-stretched state, is made to move between a first drawing assembly  13  and a second drawing assembly  14 , between which a tension control device  15  is disposed for controlling the tensioning of the film, before to be wound. 
     In particular, the first drawing assembly  13  comprises a pair of drawing rollers  16 ,  17  one of which is operatively connected to a driving motor  17 ′; the control device  15  suitable for balancing the tensioning of the film  10  in turn comprises a pair of spaced apart and parallely arranged idle rollers  18 ,  19 , between which an upwardly oriented loop  20  of the film  10  is formed and supported, in a freely floating condition, by an air jet generated by a nozzle  21 ; reference number  22  in  FIG. 1  has been used to indicate a film sensing device for controlling the position and depth of the loop  20  of the film. 
     The second drawing assembly  14  in turn comprises a grooved and perforated drawing drum  23  rotatably and pivotally supported to be urged against the roll  11 ; the drawing drum  23  in turn is connected to a respective driving motor, not shown, to cause the plastic film  10  to move towards the roll  11  drawing the same roll  11  into rotation. 
     As more clearly shown in the remaining figures, the drawing drum  23  is conformed with a plurality of longitudinally extending outer grooves  31  open frontally and at both ends, into which the plastic film  10  is made to penetrate to form a plurality of pleats or cross corrugations, open at both ends, which extend between the two opposite side edges of the film  10 . 
     As shown in  FIG. 2 , the drawing drum  23  comprises a hollow body defining an air suction chamber  23 ′ closed at both ends by rings  23 ″, being supported by a tubular shaft  24  which extends between the two rings  23 ″; the tubular shaft  24  is closed at one end  24 ″, while is connected at its other end to an air suction source  25 , for example a suction pump, by a rotary joint  26 , and a control valve device  27  for controlling and adjusting the flow at the sucked air. 
     The tubular shaft  24  has a side wall provided with through holes  24 ′ which put into fluid communication the suction chamber  23 ′ of the hollow body of the drum  23  with the tubular shaft  24 , thereby enabling the air into the outer grooves  31  of the drum  23  to be sucked into the suction chamber  23 ′ through radial holes  28 , and consequently the plastic film  10  to be sucked and folded into the grooves  31 , in correspondence with a contact area of the film  10  with the drawing drum  23 , as shown in  FIG. 1 , providing the same film  10  with suitable open-end cross corrugations  10 A. 
     The quantity of air sucked through the holes  28  in the drum  23 , can be changed and appropriately adjusted in any suitable manner, for example by means of the valve control device  27  for changing the air flow, or by adjusting the speed of the suction pump  25 , or by any other suitable means. 
     As shown in  FIG. 3  and in the enlarged detail of  FIG. 4 , the drawing drum  23  comprises a hollow cylinder body  29  provided with a coating or sheathing  30  of rubber or synthetic material, defining a peripheral contact surface  30 , for the plastic film  10 ; in the case shown, the peripheral contact surface  30 ′ of the sheathing  30 , is provided with a plurality of longitudinal grooves  31  angularly spaced apart, in which air suction holes  28 ′ axially aligned with corresponding air suction holes  28  in the peripheral wall of the hollow body  29  of the cylinder  23 , open out. 
     The suction of the air in the contact area between the drawing drum  23  and the plastic film  10 , tends to cause the plastic film to adhere and be sucked into the longitudinal grooves  31 , thereby shaping the plastic film  10  with corrugations consisting in a plurality of crosswise pleats or folds  10 A open at both ends which, during the progressive winding up of the film onto the roll  11 , retain a small quantity of cushioning air to prevent the superimposed turns of the wound film to adhere each other, as well as a slight stress relieving and relaxation of the film, both during the winding onto the roll  11 , and subsequently. 
     In fact, the formation of open-end crosswise pleats  31 , makes it possible to compensate any elastic shrinkage of the plastic film, both during and after the winding of the roll  11 ; consequently it makes possible to obtain perfectly cylindrical rolls of regular shape, preventing their implosion and tightening of the internal turns which, in the case of coreless rolls or rolls with a soft core would cause a deformation of the central hole of the same roll which tends to prevent the insertion of a mandrel, for unwinding the film during the wrapping of a load. 
     The air suction holes  28 ,  281  can be anyway shaped and disposed along the longitudinal grooves  31  of the drum  23 ; one possible example is shown in  FIG. 5  where the longitudinal lines represent the grooves  31 , in which the transversal lines represent cross planes at right angle to the longitudinal axis of the drum and in which the radial air suction holes  28 ,  28 ′ are circumferentially arranged. 
     Schematically, in the example of  FIG. 5  the drum  23  has a first perforated central area L 1  with the holes  28  disposed closer than the side areas, for example spaced apart by a first pitch P 1 , and second intermediate perforated areas L 2  at both sides of the central area L 1 , having holes  18  spaced apart by a second pitch P 2 ; a third area L 3  devoid of holes  28  is provided at each end of the drum. 
     In particular, the holes  28  of the central area L 1  have a pitch P 1  of a pre-established value, while the holes  28  in the intermediate areas L 2  have a pitch P 2  equal to or greater than P 1 , for example double the length. This can be obtained by any disposition of the holes  18 ; for example, it can be achieved by maintaining a same axial space between the holes along the grooves  31 , and staggering the holes of each groove with respect to the holes of the adjacent ones, or providing suction holes  28 , differently spaced apart on all or some of the grooves  31 . 
     Obviously, it is possible to contemplate any other disposition of the suction holes, of such kind as to maintain a greater number or concentration of holes  28  along a central section of the drum  23 , and a smaller number of suction holes on the opposite side areas  42 . 
     A greater concentration of suction holes  28  in the central area L 1 , has proved to be particularly advantageous in that it offers the possibility of causing, at the central portion of the drum  23 , a greater suction force on the plastic film  10  and penetration into the grooves  31 , allowing a certain air to flow from the ends towards the centre of the grooves themselves, thereby avoiding the formation of air pockets and, consequently, of irregular pleats or corrugations in the wound up film. 
     In the example of  FIG. 5 , the suction holes  18  are spaced apart by two pitches P 1  and P 2  along the areas L 1  and L 2 , over sections of a pre-established length of the drum  23 . However, without departing from the general teaching of the invention, the pitches, and the disposition of the holes  18  could also differ from those shown; for example, the pitch P of the holes along part or all of the grooves in the drum  23  could progressively increase from the centre towards the two ends of the drum; conversely a different conformation, for example a spiral disposition of the grooves could be contemplated in the drum. 
     The diameter of the holes  2 S, the length, the depth and the width of the grooves  31 , as well as the angular space between adjacent grooves can be of any size whatsoever, and must be chosen each time depending on specific requirements, and the characteristics of the plastic film to be wound. 
     Successful experiments have been carried out with perforated drums having a maximum diameter ranging from 150 to 180 mm, in which the holes  28  had a diameter ranging from 1.5 to 2.5 mm, an angular pitch between grooves ranging from 2° to 3°, and a pitch P between holes  28  along the same groove  31  ranging from 30 to 50 mm. 
     In the tested drums, the holes  28  all had a same diameter, however the use of holes of different diameters in the same drum could be also considered. 
       FIG. 2  of the drawings shows a further characteristic of the apparatus according to the invention, which contemplates the use of air jets in correspondence with the two external areas L 3  devoid of suction holes of the drum, to give stability to the plastic film  10  during winding, maintaining the same film  10  in contact with the peripheral surface of the drum  23 , to prevent side moving or telescoping and irregular winding of the film. 
     In fact, depending upon the working conditions of the apparatus, for example the speed and/or the thickness of the film, or for other causes, the plastic film  10  could have a certain instability or tendency to shift sideways, with the consequent winding of faulty rolls. 
     Consequently, according to a further feature of the invention, in correspondence with each end of the drawing drum  23 , use of one or more nozzles  32  has been made for the ejection of air jets which urge and maintain the lateral edges of the plastic film  10  against the drum  23 , preventing the same film from shifting sideways. Both nozzles  32  are connected, by a pressure adjusting valve  33 , to a pressurised air source  34 . 
     From what has been described and shown in the accompanying drawings it will be clear that a method and an apparatus are provided for winding up rolls of plastic film, wherein use is made of a grooved and perforated drum, connectable to a vacuum source, both in order to corrugate and to draw the plastic film, forming a plurality of cross folds or corrugations which extend between the opposite side edges of the film, as the latter is wound up around into a roll. 
     It is understood therefore that what has been described and shown with reference to the drawings, has been given purely by way of example in order to illustrate the general characteristics and those of preferential embodiments of the invention; consequently, other modifications or changes may be made, to the grooved and perforated drum, to the apparatus and to the film winding method, without departing from the claims.