Processes and apparatus for making transversely drawn films with substantially uniaxial character

Abstract

An apparatus for processing a film includes a conveyor and an isolated takeaway device. The conveyor includes gripping members that hold opposing edge portions of the film and convey, under influence of a drive member, the film along a machine direction within a stretching region of the apparatus. The conveyor, over substantially the entire stretching region, is configured and arranged to provide diverging, substantially parabolic paths along which the gripping members move to stretch the film. The isolated takeaway device receives the film from the conveyor and includes gripping members to grasp opposing takeaway regions of the film directly from the stretching region and convey the film in the machine direction. In another embodiment, the conveyor provides diverging curvilinear paths along which the gripping members move to stretch the film. An isolated takeaway device includes opposing flexible, continuous gripping mechanisms for grasping opposing takeaway regions of the film.

1 . An apparatus for processing a film, the apparatus comprising: 
 a conveyor comprising gripping members that hold opposing edge portions of the film and convey, under influence of a drive member, the film along a machine direction within a stretching region of the apparatus, wherein the conveyor, over substantially the entire stretching region, is configured and arranged to provide diverging, substantially parabolic paths along which the gripping members move to stretch the film; and    an isolated takeaway device that receives the film from the conveyor and comprising gripping members to grasp opposing takeaway regions of the film directly from the stretching region and convey the film in the machine direction.    
     
     
         2 . The apparatus of  claim 1 , wherein the isolated takeaway device is configured and arranged to convey the film without substantial stretching of a region of the film between the opposing take-away regions.  
     
     
         3 . The apparatus of  claim 1 , wherein the diverging, substantially parabolic paths have a functional form:  
           x/x   0 =±((¼)( y/x   0 ) 2 +1)  
       wherein an x-axis is defined in a plane of the film and orthogonal to the machine direction with x=0 at a center axis of the film, a y-axis is defined in the plane of the film and along the machine direction with y=0 where stretching of the film commences within the stretcher, and x 0  is a distance of the edge portions from the center axis of the film when y=0.  
     
     
         4 . The apparatus of  claim 1 , wherein at least a portion of the diverging, substantially parabolic paths have a functional form:  
         ( x+c )/( x   1   +c )=±((¼)( y/ ( x   1   +c )) 2 +1)  
       wherein the film is a multilayer film, an x-axis is defined in a plane of the multilayer film and orthogonal to the machine direction with x=0 at a center axis of the multilayer film, a y-axis is defined in the plane of the multilayer film and along the machine direction with y=0 where stretching of the multilayer film commences within the stretcher, c is any number, and x 1  is a distance of the edge portions from the center axis of the multilayer film when y=0.  
     
     
         5 . The apparatus of  claim 1 , further comprising an extruder in-line with the conveyor, wherein the extruder is configured and arranged to provide the film to the conveyor.  
     
     
         6 . The apparatus of  claim 1 , wherein the gripping members of the isolated takeaway device comprise opposing belts or treads.  
     
     
         7 . The apparatus of  claim 1 , wherein the isolated takeaway device further comprises a system for machine direction tension control of the film.  
     
     
         8 . An apparatus for processing a film, the apparatus comprising: 
 a conveyor comprising gripping members that hold opposing edge portions of the film and convey, under influence of a drive member, the film along a machine direction within a stretching region of the apparatus, wherein a portion of the conveyor in the stretching region is configured and arranged to provide diverging curvilinear paths along which the gripping members move to stretch the film; and    an isolated takeaway device that receives the film from the conveyor and comprises opposing flexible, continuous gripping mechanisms that grasp opposing takeaway regions of the film directly from the stretching region and convey the film in the machine direction.    
     
     
         9 . The apparatus of  claim 8 , wherein each flexible, continuous gripping mechanism comprises a belt.  
     
     
         10 . The apparatus of  claim 8 , wherein each flexible, continuous gripping mechanism comprises a tread.  
     
     
         11 . The apparatus of  claim 8 , further comprising 
 a slitting member positioned within the apparatus to slit the stretched portion of the film between the opposing edge portions of the film and the opposing takeaway regions of the film to form selvages that continue along the diverging paths while a remainder of the stretched portion of the film is conveyed in the machine direction.    
     
     
         12 . The apparatus of  claim 11 , wherein the slitting member is configured and arranged to slit the stretched portion of the film after the takeaway device has grasped the opposing takeaway regions.  
     
     
         13 . The apparatus of  claim 11 , wherein the slitting member is re-positionable.  
     
     
         14 . The apparatus of  claim 11 , wherein the slitting member utilizes hot slitting of the selvages from the remainder of the stretched portion of the film.  
     
     
         15 . The apparatus of  claim 8 , wherein the isolated takeaway device further comprises a system for machine direction tension control of the film.  
     
     
         16 . The apparatus of  claim 8 , wherein the isolated takeaway device is configured and arranged to convey the film without substantial stretching of a region of the film between the opposing take-away regions.  
     
     
         17 . The apparatus of  claim 8 , wherein the diverging curvilinear paths are substantially parabolic.  
     
     
         18 . The apparatus of  claim 17 , wherein the diverging, substantially parabolic paths have a functional form:  
           x/x   0 =±((¼)( y/x   0 ) 2 +1)  
       wherein an x-axis is defined in a plane of the film and orthogonal to the machine direction with x=0 at a center axis of the film, a y-axis is defined in the plane of the film and along the machine direction with y=0 where stretching of the film commences within the stretcher, and x 0  is a distance of the edge portions from the center axis of the film when y=0.  
     
     
         19 . The apparatus of  claim 17 , wherein at least a portion of the diverging, substantially parabolic paths have a functional form:  
         ( x+c )/( x   1   +c )=±((¼)( y/ ( x   1   +c )) 2 +1)  
       wherein the film is a multilayer film, an x-axis is defined in a plane of the multilayer film and orthogonal to the machine direction with x=0 at a center axis of the multilayer film, a y-axis is defined in the plane of the multilayer film and along the machine direction with y=0 where stretching of the multilayer film commences within the stretcher, c is any number, and x 1  is a distance of the edge portions from the center axis of the multilayer film when y=0.  
     
     
         20 . The apparatus of  claim 8 , further comprising an extruder in-line with the conveyor, wherein the extruder is configured and arranged to provide the film to the conveyor.