Opaque films for use in packaging

Abstract

An opaque polymer film is prepared by admixing high crystalline polypropylene with a microvoid causing filler and extruding to form a sheet that is then biaxially stretched to form an opaque film. End uses for these films include soda bottles, candy wrappers and synthetic paper.

1 . An opaque biaxially oriented polymer film comprising an opaque biaxially oriented polymer film prepared from high crystalline polypropylene wherein the film has a thickness of less than 1.25 mil (32 micrometres).  
   
   
       2 . The opaque biaxially oriented polymer film of  claim 1  wherein the high crystalline polypropylene is prepared using a Ziegler-Natta catalyst and has a heat of fusion of at least 100 joules/g or is prepared using a metallocene catalyst and has a heat of fusion of at least 70 joules/g.  
   
   
       3 . The opaque biaxially oriented polymer film of  claim 1  wherein the high crystalline polypropylene have a melting point of from about 155° C. to about 170° C.  
   
   
       4 . The opaque biaxially oriented polymer film of  claim 1  wherein the opaque biaxially oriented polymer film has a light transmittance, measured according to ASTM D1003-00, of less than 80 percent due to the presence of microvoids.  
   
   
       5 . The opaque biaxially oriented polymer film of  claim 4  wherein the opaque biaxially oriented polymer film has a light transmittance, measured according to ASTM D1003-00, of less than 70 percent due to the presence of microvoids.  
   
   
       6 . The opaque biaxially oriented polymer film of  claim 5  wherein the opaque biaxially oriented polymer film has a light transmittance, measured according to ASTM D1003-00, of less than 50 percent due to the presence of microvoids.  
   
   
       7 . The opaque biaxially oriented polymer film of  claim 1  wherein the opacity of the film results from microvoids, which are cause by a microvoid producing filler.  
   
   
       8 . The opaque biaxially oriented polymer film of  claim 7  wherein the microvoid producing filler is an inorganic solid.  
   
   
       9 . The opaque biaxially oriented polymer film of  claim 8  wherein the inorganic solid is selected from the group consisting of aluminum oxide, aluminum sulfate, barium sulfate, calcium carbonate, magnesium carbonate, aluminum silicate (kaolin clay), magnesium silicate (talc), silicon dioxide, titanium dioxide, and mixtures thereof.  
   
   
       10 . The opaque biaxially oriented polymer film of  claim 9  wherein the inorganic solid is CaCO 3 .  
   
   
       11 . The opaque biaxially oriented polymer film of  claim 7  wherein the microvoid producing filler is an organic solid.  
   
   
       12 . The opaque biaxially oriented polymer film of  claim 1  wherein the high crystalline polypropylene has a recrystallization temperature of from about 105° C. to about 125° C.  
   
   
       13 . The opaque biaxially oriented polymer film of  claim 1  wherein the polymer film additionally includes a pigment.  
   
   
       14 . The opaque biaxially oriented polymer film of  claim 13  wherein the pigment is TiO 2 .  
   
   
       15 . The opaque biaxially oriented polymer film of  claim 1  wherein the polymer film additionally includes a conventional additive selected from the group consisting of antioxidants, orientation stress modifiers, flame retardants, antistatic agents, antiblock agents, antifoggants, slip agents, and mixtures thereof.  
   
   
       16 . The opaque biaxially oriented polymer film of  claim 1  wherein the opaque biaxially oriented polymer film has a density of from about 0.44 to about 0.55 g/cm 3    
   
   
       17 . A label wherein the label is an opaque biaxially oriented polymer film of  claim 1 .  
   
   
       18 . The label of  claim 17  additionally comprising a transparent film having printing thereon.  
   
   
       19 . A packaging material comprising an opaque biaxially oriented film of  claim 1 .  
   
   
       20 . The packaging material of  claim 19  wherein the packaging material is a soda bottle.  
   
   
       21 . The packaging material of  claim 19  wherein the packaging material is a food wrapper.  
   
   
       22 . The packaging material of  claim 21  wherein the food wrapper is a candy wrapper.  
   
   
       23 . An opaque biaxially oriented polymer film comprising an opaque biaxially oriented polymer film prepared from high crystalline polypropylene wherein the film has a density of less than 0.55 g/cm 3 .  
   
   
       24 . The opaque biaxially oriented polymer film of  claim 23  wherein the film is a synthetic paper.