Patent Publication Number: US-2011062274-A1

Title: Peel off device for unwinding a web of material from a roll

Description:
FIELD OF THE INVENTION 
     The invention refers to a peel off device for unwinding a web of material from a stock or forming roll, especially for high speed unwinding a web of a thin polymer film or the like. 
     BACKGROUND OF THE INVENTION 
     The problem underlying the present invention arises in the field of continuous production of e.g. baby or feminine hygiene care products like diapers or sanitary napkins, where thin polymer films such as a backing sheet or a topsheet have to be peeled off from a stock roll at a high speed. As production practice shows, such as a polymer web may tend to adhere to the stock roll for several reasons, such as interlocking phenomena due to microstructures in the web (e.g. apertures) or adhesion due to the surface properties of the web material. 
     Due to prior use it is known to provide for an idler at the periphery of the stock roll to support the unwind process of the web from the roll. The web is guided around the circumference of the idler along an angle of contact of about 90° to 120°, then running to the so-called unwind dancers which are a balancing means for the web as concerns instabilities or irregularities in the following in-line production process of any product. The problem is that due to the interlocking phenomena and/or adhesion the web nevertheless tends to stick to the roll leading to a phenomenon, already mentioned above, called “blocking” which occurs whenever a web presents high tendency to stick to itself during unwinding. This can be caused by surface forces, electrostatic forces or mechanical interlocking of apertures, adhesive coating etc. 
     Said blocking is a severe problem for downstream processes as it introduces sudden changes of tension, cross-direction tracking issues and wrinkle formation within the web. In most critical cases a web breakage can occur leading to a complete production line stop. 
     The problems in unwinding a rolled web of material are already addressed in U.S. Pat. No. 3,368,771 A which discloses a method and an apparatus for unwinding a rolled web of material. The apparatus comprises two rollers which are in contact with each other and supported on a rocker arm by means of which a first idler is pivoted onto the stock roll. The web is led around the flexible surface of the first idler, runs through a gap between the first and a second idler and then is led away via the second idler. The latter has a surface with venting passages at the periphery which together with a surface layer of elastic material on the first idler helps to enable the air between the web of material and the surface of the roller to escape completely to the side. The overall object of the prior art apparatus on the one hand is to compensate for the local distortions that are inherent in a particular web of material and which extend in the longitudinal direction and are due, for example, to variations in thickness. On the other hand the air introduced between the web and the rollers is removed owing to a slight contact pressure between the first and second roller which displaces the film of air which is drawn between the web of material and the second roller. Important is the fact that the first idler is in a “out of pressure contact”, this means that the stock roll and the first idler have a space between them or may just touch so long as no appreciable pressure is exerted by the roller on the stock roll. 
     It was found out that with this “pressureless” concept and the two contacting idlers no significant improvement in avoiding web blocking in modern high speed applications can be reached. 
     FR 2 573 059 A1 discloses a peel off device for unwinding a web of material from a stock roll especially for high speed unwinding a web of a thin polymer film or the like. This peel off device comprises a base associated to the roll and a linear guiding device mounted on the base. On the linear guiding device several rolls are positioned offset to each other providing for a meandering path of the web between the rolls. Two of the rolls are driven to unwind the web material from the stock roll. 
     The problem of this known construction is the fact that the heavy stock roll has to be driven indirectly via the traction forces applied by the driven rolls onto the web. High tension forces could lead to a tearing of the web and thus to a disruption of the peeling off process. 
     It is therefore an object of the invention to provide a peel off device for unwinding a web material from a stock roll in a reliable and undisturbed manner, avoiding web blocking to a high extent. 
     SUMMARY OF THE INVENTION 
     This object is achieved by a peel off device and method for unwinding a web of material from a roll as indicated in the claims. In particular a device comprising:
         a base associated to the roll,   a linear guiding device mounted on the base,   an idler support linearly guided on the base by the linear guiding device in a direction towards the roll, and   a pair of idlers for the web to be unwound wherein
           the idlers are mounted offset with respect to each other on the idler support to provide for a meandering path of the web between the idlers,   the axes of rotation of the idlers are parallel to the bearing axis of the roll, and   a first one of the idlers is pushed towards the roll so that a contact force is maintained between the first idler and the surface of the roll while the web is peeled off the roll
 
is provided.
   
               

     This two-idler peeling system significantly differentiates the invention from the known unwinding devices. Firstly, the first idler is maintained in permanent contact with the surface of the roll while the web is peeled off which helps to maximize and maintain constant the peel force even at high speed. Secondly, the separate, offset second idler provides immediate restraining action to prevent the web from passing underneath the first (peeling) idler without being peeling off. Furthermore, the span between the two idlers and the next span of the web path can be maintained at a constant angle. 
     Finally, the invention only needs a limited layout space due to the compact construction elements involved. 
     Preferred embodiments are subject matter of the depending claims, the features and advantages of which are explained in detail in the following description of a preferred embodiment referring to the accompanying drawing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic elevation of a peel off device according to the invention in a first embodiment. 
         FIG. 2  shows an enlarged partial schematic elevation of a peel off device according to the invention in a second embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     The first embodiment of a peel off device depicted in  FIG. 1  is associated to a stock roll  1  of material, e.g. a thin plastic web  2 . The stock roll  1  is supported on a driven central reel  3  on which it rotates in the direction R when the web  2  is unwound and supplied to a production line via common unwind dancers (not shown) after leaving the second idler  10 . The web may then be used in a converting line for example to be used as topsheet or backsheet in an absorbent article. 
     To peel off the web  2  from the stock roll  1  in a reliable manner, a peel off device  4  is provided which comprises a base  5  associated to the stock roll  1 , i.e. in the case shown the beamlike base  5  extends behind the stock roll  1 . 
     A linear guiding device  6 , such as a guiding rail, is mounted on the base  5  in lengthwise direction. This guiding rail  6  holds the idler support  7  via a guide block  8  which is linearly guided along the guiding rail  6 . 
     First and second idlers  9 ,  10  are mounted offset with respect to each other on the idler support  7  to provide for a meandering path of the web  2  between the two idlers  9 ,  10 . The idlers can freely rotate in relation to the idler support. The idlers  9 ,  10  respectively comprise axes of rotation A 9  and A 10  which are parallel to the bearing axis A 3  of the stock roll reel  3 . 
     The first idler  9  is kept in surface contact with the circumference  11  of the stock roll  1  by being pushed towards the stock roll  1  by the idler support  7  to generate a contact force F between the first idler  9  and the circumference  11  of the stock roll  1  as the web is peeled off. This force F can be generated by a pneumatic drive system using a pressurized air cylinder  12  abutting on the base  5  and pushing the idler support  7  along the guiding rail  6 . The contact force F may be desired to be maintained in a range between 2 N and 5 N, and may be set up to remain approximately constant during the peeling off process. This may be equivalent to an air pressure of about 1.5 bars when using a pneumatic system. It may be desirable to use lower force for particularly soft material, or higher forces relatively sturdy material, so that the force may also be in the range of between 1 N and 15 N for example. 
     When peeling off the web  2  from the stock roll  1  the web  2  is led around the first idler  9  by a peel off angle of contact which is about 90° because the first idler is maintained in contact with the surface of the roll (the peel off angle is defined as the angle between the tangent of the roll at the point of peeling off and the line tangent with the surface of the first idler guiding the web and passing through the center of the roll). It is believed that a peel off angle of about 90° maximizes the peeling force and reduces the risk of breakup of the web. 
     Then the web  2  is led to the second idler  10  which is mounted with a fixed offset with respect the first idler  9 . The center to center distance of the two idlers can be a multiple of the (first) idler diameter, e.g. three to six times the diameter. The first and second idlers may advantageously be formed by identical pieces to simplify installation and maintenance but this is not necessary. The angle C between the tangent of the surface  11  of the roll  1  at the point of contact with the idler  9  and the line passing through the centers of the first and second idlers is of more than 270° to provide a meandering path for the web between the idlers. Advantageously, the angle C may be of from 300° to 360°, more advantageously between 320° to 350°, or more precisely from 330° to 350°. The two idlers can be advantageously mounted in a fixed position relative to each other on the idler support so that their distance and angle are advantageously kept constant during the peel off process. 
     A magnetic position tracking system  13  may be incorporated into the guiding rail  6  for detecting the position of the guide block  8  along the guiding roll  6 . This serves to record the position of the guide block  8  and thus of the first idler  9 , i.e. this gives a signal for the current size of the stock roll  1 . A magnetic position tracking system may be advantageous to provide a robust system against natural occurring dust formation. 
     The position tracking system  13  may also be used to detect an anomalous blocking of the movement of the idler support towards the roll  1 . In this case a control unit (not shown) may give a signal to push the idler support  7  by means of a short burst of pressurized from the air cylinder  12  in a direction towards the roll  1 . In this connection a force impulse is applicable which exceeds the continuous pushing force F. The pressure burst may exemplarily generate a force F of 8 N in a time of 0.5 s. 
     The dot and dash lines in the drawing show the situation when the stock roll  1  has decreased in diameter considerably versa the initial state depicted in full lines. As can be seen, the idler support  7  has moved linearly along the guiding rail  6  thus moving the idler  9  in a more or less radial direction as concerns the stock roll  1  in synchronism with the diminishing stock on the roll  1 . The idler  9  is kept in contact with the stock roll  1  during the complete unwinding process. 
     The second embodiment of the peel off device as it is shown in  FIG. 2  again includes a stock roll  1  of e.g. a thin plastic web  2 . The support and drive of the stock roll  1  may be the same as the embodiment of  FIG. 1 . Also, the peel off device  4 ′ of the second embodiment comprises a base  5  associated to the stock roll  1 , on which a linear guiding device  6 , such as a guiding rail, is mounted in lengthwise direction. This guiding rail  6  holds the idler support  7 ′, the guide block  8 ′ of which—contrary to the first embodiment—rotatably supports only the second idler  10 . 
     The first idler  9  is rotatably supported on the pivoting end  15  of a lever arm  16  which is pivotably mounted on the idler support  7 ′ via a pivot axis A 17 . The latter is provided by a rotary pneumatic cylinder  17  which biases the lever arm  16  and thus the idler  9  towards the surface of the stock roll  1  to generate the contact force F. The pivot axis A 17  of the lever arm  16  is parallel to the axis of rotation A 9  of the idler  9 . 
     A further difference compared to the embodiment shown in  FIG. 1  is the drive of the roller support  7 ′ with guide block  8 ′. Whereas in the first embodiment the pressurized air cylinder  12  biases the roller support  7  and thus guide block  8  towards the roll, thus creating the contact force F, within the second embodiment the roller support  7 ′ with the guide block  8 ′ are linearly driven along the guiding rail  6  by a stepper motor  18 . By means of this stepper motor  18 , the roller support  7 ′ and guide block  8 ′ are basically positioned according to the decreasing roll diameter by tracking the roller support  7 ′ and guide block  8 ′ to the right referring to  FIG. 2 . 
     Due to the support of the idler  9  on the pivotable lever arm  16 , any unroundness of the stock roll  1  can be compensated, as the lever arm  16  with the idler  9 , as having a relatively low mass, can easily track any deviations of the surface of the stock roll  1  from the ideal round shape. 
     The control of the tracking of the roller support  7 ′ and guide block  8 ′ is provided by position sensors, e.g. proximity sensors  19 , which monitor the position of the lever arm  16  within its pivot range P. When the lever arm  16  increasingly pivots in clockwise direction related to  FIG. 2 , this is an indication that the stock roll  1  decreases in diameter. Accordingly, the roller support  7 ′ and guide block  8 ′ are moved to the right, thus pivoting the lever arm  16  in the counterclockwise direction again until the lever arm  16  on average stands upright and centrally between the pair of proximity sensors  19 . 
     To limit the pivot range P of the lever arm  16 , a pair of stoppers  20  is provided on the roller support  7 ′. 
     Summing up the advantages of the embodiment of  FIG. 2 , both the decreasing roll diameter and the unroundness of the roll are compensated. Further on, the idler  9  mounted on the lever arm  16  is well controllable as to the contact force F which is approximately 8 N. The angle of the lever arm stays within a certain operating range which is smaller than the pivot range P never touching the end positions defined by the stoppers  20 . When the lever arm tends to move outside of this operation range due to the decreasing roll diameter, the stepper motor  18  will advance the roller support  7 ′ and guide block  8 ′ forward by a certain distance against the stock roll  1 . 
     The controller of the stepper motor  18  “knows” where the roller support  7 ′ and guide block  8 ′ are, as it comprises a counter for the moving steps of the motor. Thus, additional information for the machine control is provided. 
     Features described in relation to one embodiment may of course be used with the apparatus or method of another embodiment unless they are mutually excluding. 
     The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and functionally equivalent range surrounding that value. For example, a dimension disclosed as “40 mm” is intended to mean “about 40 mm”. 
     Every document cited herein, including any cross referenced or related patent or application, is hereby incorporated herein by reference in its entirety unless expressly excluded or otherwise limited. The citation of any document is not an admission that it is prior art with respect to any invention disclosed or claimed herein or that it alone, or in any combination with any other reference or references, teaches, suggests or discloses any such invention. Further, to the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern. 
     While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.