Oriented polyolefin processing

Abstract

The present invention relates to improved processability of polyolefin films through the addition to the basic isotactic polypropylene (iPP) polymer of a resin or rosin modifier in an amount within the range of 1 to 30 weight percent. Alternatively, the composition could contain from about 5 to about 10 weight percent of a resin or rosin. Preferably the mixture should contain resin or rosin modifiers in an amount of about 10 percent by weight. The invention encompasses both the resulting polyolefin films and the process for producing such film. The improved processability of the film includes fewer web breaks and drawability at higher line speeds, resulting in fewer shut downs of the processing line and a decrease in manufacturing time. These improvements are measured in terms of variable machine direction orientation draw ratios and transverse direction orientation oven temperatures.

We claim:  
     
         1 . In a process for producing a polyolefin film, the steps comprising: 
 a. providing a polymer mixture comprising a propylene selected from the group consisting of isotactic propylene homopolymer and isotactic propylene-ethylene copolymer containing no more than 1.0 weight percent ethylene, and having incorporated therein: 
 a modifier selected from the group consisting of a resin and a rosin, in an amount within the range of 1 to 30 weight percent; and  
   b. forming said polymer mixture into a film layer.    
     
     
         2 . The process of  claim 1 , wherein the amount of said modifier is within the range of 5 to 10 weight percent.  
     
     
         3 . The process of  claim 1 , wherein the amount of said modifier is about 10 weight percent.  
     
     
         4 . The process of  claim 3 , wherein said modifier is a hydrogenated hydrocarbon resin having a molecular weight of about 750 g/mol, a softening point within the range of 136° C. to 140° C. and a glass transition temperature of about 90° C.  
     
     
         5 . The process of  claim 3 , wherein the propylene polymer mixture of step (a) is an isotactic propylene-ethylene co-polymer containing no more than 1.0 weight percent ethylene.  
     
     
         6 . The process of  claim 3 , wherein the propylene polymer of step (a) is an isotactic propylene homopolymer.  
     
     
         7 . The process of  claim 4 , further comprising the step of stretching said film layer in the machine direction and separately stretching said film layer in the transverse direction to produce a biaxially oriented polyolefin film.  
     
     
         8 . The process of  claim 4 , wherein the isotactic propylene homopolymer is produced by the method of polymerizing propylene in the presence of a metallocene catalyst.  
     
     
         9 . The process of  claim 5 , wherein said modifier is a hydrogenated hydrocarbon resin having a molecular weight of about 750 g/mol, a softening point within the range of 136° C. to 140° C. and a glass transition temperature of about 90° C.  
     
     
         10 . The process of  claim 5 , further comprising the step of stretching said film layer in the machine direction and separately stretching said film layer in the transverse direction to produce a biaxially oriented polyolefin film.  
     
     
         11 . The process of  claim 5 , further comprising the step of stretching said film layer in the machine direction and separately stretching said film layer in the transverse direction to produce a biaxially oriented polyolefin film.  
     
     
         12 . The process of  claim 5  wherein the isotactic propylene homopolymer is produced by the method of polymerizing propylene in the presence of a metallocene catalyst.  
     
     
         13 . The process of  claim 6  wherein the isotactic propylene homopolymer is produced by the method of polymerizing propylene in the presence of a metallocene catalyst.  
     
     
         14 . The process of  claim 6 , wherein said modifier is a hydrogenated hydrocarbon resin having a molecular weight of about 750 g/mol, a softening point within the range of 136° C. to 140° C. and a glass transition temperature of about 90° C.  
     
     
         15 . The process of  claim 14 , further comprising the step of stretching said film layer in the machine direction and separately stretching said film layer in the transverse direction to produce a biaxially oriented polyolefin film.  
     
     
         16 . The process of  claim 14  wherein the isotactic propylene homopolymer is produced by the method of polymerizing propylene in the presence of a metallocene catalyst.  
     
     
         17 . In a polyolefin film, the combination comprising: 
 a. a film layer formed of a mixture of: 
 a propylene polymer selected from the group consisting of isotactic propylene homopolymer and an isotactic propylene-ethylene co-polymer containing no more than 1.0 weight percent ethylene, and  
 a modifier selected from the group consisting of a resin and a rosin; and  
   b. said modifier present in said mixture in a relative amount effective to produce a biaxially oriented polyolefin film capable of being stretched up to 9 times its original length in the machine direction and stretched in the transverse direction at a temperature equal to or less than about 166° C.    
     
     
         18 . The combination of  claim 17 , wherein said modifier is a hydrogenated hydrocarbon resin having a molecular weight of about 750 g/mol, a softening point within the range of 136° C. to 140° C. and a glass transition temperature of about 90° C.  
     
     
         19 . The combination of  claim 18 , wherein said modifier is present in said mixture in an amount within the range of about 1 to 30 weight percent.  
     
     
         20 . The combination of  claim 18 , wherein said modifier is present in said mixture in an amount with the range of about 5 to 10 weight percent.  
     
     
         21 . The combination of  claim 18 , wherein said modifier is present in said mixture in an amount of about 10 weight percent.