Biaxially oriented polyolefin film for cold seal application

Abstract

The present invention relates to multi-layered polyolefin films that provide excellent adhesion to cold seal cohesive formulations. In a preferred embodiment, a film of the present invention is characterized as having a polyolefin resin layer with a discharge-treated surface on one side. It has been found that when the discharge-treated surface has at least 0.3% nitrogen functional groups, it provides an excellent cold seal receptive surface. A biaxially oriented polypropylene film of the present invention may also have a second skin layer, opposite the first layer, which may be used for metallizing, laminating, or printing.

1 . A polyolefin film comprising: 
 a polyolefin resin layer having a discharge-treated surface on one side of said polyolefin resin layer, said discharge-treated surface comprising at least 0.3% nitrogen functional groups.    
   
   
       2 . The polyolefin film of  claim 1  wherein said polyolefin resin layer is a propylene homopolymer.  
   
   
       3 . The polyolefin film of  claim 1  wherein said polyolefin resin layer is a propylene homopolymer, ethylene homopolymer, propylene-ethylene copolymer, propylene-ethylene-butene terpolymer, propylene-butene copolymer, or blends thereof.  
   
   
       4 . The film according to  claim 1  wherein said discharge-treated surface is imparted by a corona discharge in a controlled atmosphere of nitrogen and carbon dioxide.  
   
   
       5 . A polyolefin film comprising: 
 a polyolefin core layer;    a first coextruded skin layer of polyolefin resin on one side of said polyolefin core layer;    a second coextruded skin layer of polyolefin resin on one side of said polyolefin core layer opposite said first coextruded skin layer;    said second coextruded skin layer of polyolefin resin having a charge-treated surface comprising at least 0.3% nitrogen functional groups on said discharge-treated surface.    
   
   
       6 . The film of  claim 5  wherein the polyolefin core layer is a propylene homopolymer.  
   
   
       7 . The film of  claim 5  wherein the first coextruded layer is a metallizable layer having a thickness of about 0.5 to 5.0 μm.  
   
   
       8 . The film of  claim 7  wherein said metallizing layer comprises an anti-blocking agent of about 0.01 to 0.5 percent by weight of said metallizing layer.  
   
   
       9 . The film of  claim 7  wherein said metallizing layer composition is selected from the group consisting of: polypropylene, low isotactic polypropylene, ethylene propylene random copolymer, butene propylene copolymer, ethylene-propylene-butene terpolymer, or blends thereof.  
   
   
       10 . The film of  claim 7  wherein said metallizing layer is treated to provide a surface for metallizing.  
   
   
       11 . The film of  claim 5  wherein said second skin layer composition is selected from the group consisting of polypropylene, low isotactic polypropylene, ethylene-propylene copolymer, propylene-butene copolymer, ethylene-propylene-butene terpolymer, and blends thereof.  
   
   
       12 . The film of  claim 5  wherein said second skin layer has a thickness of about 0.5 -5.0 μm.  
   
   
       13 . The film of  claim 5  wherein said second skin layer comprises an anti-blocking agent of about 0.01 to 0.5 percent by weight of said second skin layer.  
   
   
       14 . The film according to  claim 5  wherein said discharge-treated surface of the second skin layer is imparted by a corona discharge in a controlled atmosphere of nitrogen and carbon dioxide.  
   
   
       15 . The film of  claim 7  wherein said metallizable layer has an optical density of 2.0 to 5.0.  
   
   
       16 . The film of  claim 7  wherein said metallizable layer comprises aluminum.