System and method for winding polymeric films, such as low modulus, polyolefin films

Abstract

A method and system of winding polymeric film includes providing a length of polymeric film (e.g., low modulus, optical grade film) along with at least one small diameter strand. The film and the strand are simultaneously wound about a cylinder to form a wound roll, with strand being interposed between successively wound layers of film. The strand establishes a gap between the outermost and immediately underlying wound layers of film. The gap facilitates natural movement (e.g., relaxation) of the outermost wound layer relative to the immediately underlying wound layer, thereby compensating for any winding-related stress or tension. The strand can be laterally moved (e.g., oscillated) relative to a width of the film with continuous winding.

1 . A method of winding a polymeric film, the method comprising:
 providing a length of polymeric film;   providing at least one small diameter strand apart from a polymeric film;   simultaneously winding the film and the strand about a cylinder to form a wound roll having   successively wound layers of film with the strand continuously interposed between the successively wound layers of film;   wherein the strand establishes a gap between an outermost wound layer of film and an immediately underlying wound layer of film.   
   
   
       2 . The method of  claim 1 , wherein the film and the strand are continuously wound about the cylinder and the strand continuously establishes the gap between the outermost and immediately underlying wound layers of film. 
   
   
       3 . The method of  claim 1 , wherein the strand establishes an air gap between the outermost and immediately underlying wound layers of film during winding. 
   
   
       4 . The method of  claim 1 , wherein the film defines an unwound segment leading to the outermost wound layer such that relative to the cylinder, a wind interface is established at a transition of the film from the unwound segment to the outermost wound layer, and further wherein simultaneously winding the film and the strand includes:
 changing a lateral position of the strand relative to a width of the film at the wind interface.   
   
   
       5 . The method of  claim 4 , wherein changing a lateral position of the strand includes:
 moving the strand laterally at a point upstream of the wind interface.   
   
   
       6 . The method of  claim 5 , wherein changing a lateral position of the strand further includes:
 oscillating the strand back-and-forth upstream of the wind interface.   
   
   
       7 . The method of  claim 6 , wherein with continuous winding of the film and the strand, a lateral position of the strand relative to an edge of the roll at the wind interface continuously changes. 
   
   
       8 . The method of  claim 6 , wherein a distance of lateral oscillation of the strand relative to the wind interface is not more than 10 percent of a width of the film. 
   
   
       9 . The method of  claim 6 , wherein a distance of lateral oscillation of the strand relative to the wind interface is not more than 6 inches. 
   
   
       10 . The method of  claim 1 , further comprising:
 providing a plurality of small diameter strands apart from the film;   discretely positioning the plurality of strands relative to a width of the film; and   simultaneously winding the film and the plurality of strands about the cylinder.   
   
   
       11 . The method of  claim 10 , wherein a first one of the strands is positioned adjacent a first edge of the film and a second one of the strands is positioned adjacent a second, opposed edge of the film. 
   
   
       12 . The method of  claim 10 , further comprising:
 continuously changing a lateral position of each of the strands relative to the film at a wind interface of the cylinder during continuous winding of the film and the strands.   
   
   
       13 . The method of  claim 12 , wherein continuously changing a lateral position of the strands includes simultaneously oscillating a lateral position of each of the strands relative to the film at the wind interface. 
   
   
       14 . The method of  claim 1 , wherein the strand has a major dimension that is at least 100 times less than a width of the film. 
   
   
       15 . The method of  claim 1 , wherein the strand is a monofilament material. 
   
   
       16 . The method of  claim 1 , wherein the strand is a multifilament material. 
   
   
       17 . The method of  claim 1 , wherein the strand is a yarn material. 
   
   
       18 . The method of  claim 1 , wherein the film is a polyolefin optical film. 
   
   
       19 . The method of  claim 18 , wherein the film is an optical grade film. 
   
   
       20 . The method of  claim 1 , wherein the film is a low modulus polypropylene film. 
   
   
       21 . The method of  claim 1 , wherein the film has a thickness of less than 25 microns. 
   
   
       22 . The method of  claim 1 , wherein the film is a simultaneous biaxially stretched polyolefin film. 
   
   
       23 . The method of  claim 1 , wherein providing a length of film includes:
 continuously supplying an extruded film from an extruder to the cylinder.   
   
   
       24 . A system for winding a polymeric film, the system comprising:
 a polymeric film supply device having an exit;   a winding device including a rotatable cylinder positioned to receive polymeric film from the film supply device such that a wind interface is defined relative to the cylinder; and   a film spacer supplying a continuous length of a small diameter strand to the wind interface;   wherein the system is configured to simultaneously wind a polymeric film from the film supply device and a strand from the film spacer about the cylinder such that the strand is continuously interposed between successively wound layers of film.   
   
   
       25 . The method of  claim 24 , wherein the film spacer includes:
 a source of strand material; and   an oscillation device for moving the strand material laterally relative to the cylinder.   
   
   
       26 . The method of  claim 24 , wherein the film spacer further includes:
 a plurality of small diameter strands discretely positioned relative to a width of the cylinder.   
   
   
       27 . The method of  claim 24 , wherein the polymeric film supply device includes:
 an extruder for extruding a film sheet from a resin;   wherein the extruder is located in-line with the winding device and the film spacer is positioned between the extruder and the winding device.