Method and apparatus for interdigitally stretching polymer films and nonwoven webs

Abstract

The method and apparatus prevent the formation of pin-holes or other breakage during stretching of polymeric films, non-woven fibrous webs or laminates in the cross machine direction. Pin-holes and other breakage are prevented by creating slack areas along the length of the product where the edges of the non-woven strips meet with the polymer film, pressing the slack areas into the interdigital stretching rollers without stretching the slack areas, and stretching the remainder of the web in a typical manner. The slack regions are formed prior to interdigitation by, for example, formation of a furrow, a fold or a corrugation.

What is claimed is:  
     
         1 . A method of forming a polymeric film or nonwoven fibrous web including the steps of: 
 providing a polymeric film or nonwoven fibrous web; and    interdigitally stretching the film or web throughout its depth along a plurality of lines while controlling said film or web in a substantially unstretched condition adjacent said lines to reduce breakage.    
     
     
         2 . The method of  claim 1  wherein controlling the film or web in the substantially unstretched condition is performed by creating slack areas along the length of the film or web prior to interdigital stretching.  
     
     
         3 . The method of  claim 2  wherein the slack is created by passing a preselected area of the film or web between opposed rollers.  
     
     
         4 . The method of  claim 2  wherein the slack is created by passing a preselected area of the film or web over a bar.  
     
     
         5 . The method of  claim 2  wherein the step of creating the slack areas is selected from the group consisting of folding, corrugating, furrowing, gathering, creasing and overlapping a preselected area of the film or web.  
     
     
         6 . The method of  claim 1  wherein the film or web is thermoploastic which is heated during stretching.  
     
     
         7 . The method of  claim 1  which includes the step of making a laminate of said film or web prior to said interdigitally stretching.  
     
     
         8 . The method of  claim 1  wherein the polymeric film is a thermoplastic film having a polymer selected from the group consisting of a biodegradable polymer, an elastomer and a polyolefin.  
     
     
         9 . The method of  claim 8  wherein the thermoplastic polymer is selected from the group consisting of polyethylene, polypropylene and copolymers thereof.  
     
     
         10 . The method of  claim 8  wherein the thermoplastic polymer is an elastomeric polymer.  
     
     
         11 . The method of  claim 10  wherein said elastomeric polymer is selected from the group consisting of poly(ethylene-butene), poly(ethylene-hexene), poly(ethylene-octene), poly(ethylene-propylene), poly(styrene-butadiene-styrene), poly(styrene-isoprene-styrene), poly(styrene-ethylene-butylene-styrene), poly(ester-ether), poly(ether-amide), poly(ethylene-vinylacetate), poly(ethylene-methylacrylate), poly(ethylene-acrylic acid), poly(ethylene butylacrylate), polyurethane, poly(ethylene-propylene-diene), and ethylene-propylene rubber.  
     
     
         12 . The method of  claim 1  wherein said nonwoven fibrous web contains fibers selected from the group consisting of polypropylene, polyethylene, polyesters, cellulose, rayon, nylon and blends or coextrusions of two or more such fibers.  
     
     
         13 . The method of  claim 1  wherein the polymeric film comprises a blend of linear low density polytheylene and low density polyethylene.  
     
     
         14 . The method of  claim 13  wherein the polymeric film additionally comprises calcium carbonate filler particles.  
     
     
         15 . The method of  claim 14  wherein the polymeric film comprises: 
 about 35% to about 45% by weight of a linear low density polyethylene,  
 about 3% to about 10% by weight of a low density polyethylene,  
 about 40% to about 50% by weight calcium carbonate filler particles, and  
 up to about 6% by weight of a rubber compound.  
 
     
     
         16 . The method of  claim 1  wherein the interdigital stretching of the film or web is performed across the width or length thereof.  
     
     
         17 . A device for preventing breakage in a polymeric film or nonwoven web during stretching comprising: 
 a first interdigital roller;    a second interdigital roller, intersecting the first interdigitating roller, the intersection of said first and second interdigital roller serving to interdigitally stretch a length of the film or web along a plurality of lines across its width except in a substantially unstretched area of the film or web adjacent said lines along its length; and    at least one disc for contacting said film or web area and pressing said area into the first interdigital roller without substantially stretching the film or web in said area adjacent said lines during said interdigital stretching.    
     
     
         18 . The device of  claim 17 , further comprising at least one set of interengaging spaced rollers for creating the substantially unstretched area along the length of the film or web.  
     
     
         19 . The device of  claim 17  further comprising a bar for creating the substantially unstretched area along said length of film or web.  
     
     
         20 . The device of  claim 17  further comprising a member for creating the substantially unstretched area along said length of film or web selected from the group consisting of a folder, corrugater, furrower, gatherer, creaser, progressive roll former, and overlapper of said film or web.  
     
     
         21 . A device for preventing breakage in a polymeric film or nonwoven fibrous web during stretching comprising: 
 a first interdigital roller;    a second interdigital roller, intersecting the first interdigitating roller, the intersection of said first and second interdigital roller serving to interdigitally stretch a length of the film or web along a plurality of lines across its width except in a substantially unstretched area of the film or web adjacent said lines along its length; and    a controller for creating at least one substantially unstretched area along the length of the film or web adjacent said lines during said interdigital stretching.    
     
     
         22 . The device of  claim 21  comprising a plurality of said controllers.  
     
     
         23 . The device of  claim 21  further comprising a presser for forcing the substantially unstretched film or web area into the first interdigital roller.  
     
     
         24 . The device of  claim 23 , wherein the presser includes at least one rotatable disc for contacting the substantially unstretched film or web area and pressing said area into the first interdigital roller without substantially stretching said area.  
     
     
         25 . The device of  claim 21 , further comprising a member for creating the substantially unstretched film or web area wherein the controller is selected from the group consisting of a folder, corrugater, furrower, gatherer, creaser, progressive roll former, and overlapper of said film or web.  
     
     
         26 . The device of  claim 21 , wherein the controller is laterally adjustable.