Thermoplastic Film Structures With A Low Melting Point Outer Layer

Abstract

A film structure including at least a base layer containing a thermoplastic polymer and at least an outer layer containing a low melting point polymer. Methods of manufacturing the film structure, including the steps of coextruding melts corresponding to the individual layers of the film structure through a die and thereafter: simultaneously biaxially stretching the coextruded film sheet; or sequentially biaxially stretching the coextruded film sheet, wherein the machine-direction orientation (MDO) is performed with a radiant-heated MDO stretcher. An extrusion-coated film structure exhibiting strong bond adhesion, and a method of manufacturing the same are also provided.

1 . A method of manufacturing a coextruded, biaxially oriented film structure comprising a base layer and a first outer layer, the base layer comprising a polyolefin, and a first outer layer comprising a ethylene polymer that has a melting point of not more than 230° F. (110° C.), wherein the method comprises the steps of: 
 a) preparing and coextruding melts corresponding to each individual layer of the film structure through a die to form a coextruded film sheet; and    b) simultaneously biaxially orienting the coextruded film sheet in a machine direction and a transverse direction to form the coextruded, biaxially orientated film structure.    
     
     
         2 . The method of  claim 1 , wherein the simultaneous biaxial orientation proceeds on a line that utilizes linear motors to directly propel opposed pairs of tenter clips synchronously.  
     
     
         3 . The method of  claim 1 , wherein the coextruded, biaxially oriented film structure is oriented from 1.5 to 8 times in the machine direction and from 2 to 12 times in the transverse direction.  
     
     
         4 . The method of  claim 1 , wherein the ethylene polymer of the first outer layer of the coextruded, biaxially oriented film structure is selected from the group consisting of ethylene plastomer, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-methacrylate copolymer, ethylene-butyl acrylate copolymer, ethylene-ethyl acrylate copolymer, ethylene-acrylic acid terpolymer, ethylene-methacrylic acid terpolymer, ethylene homopolymer, ethylene copolymer and blends thereof.  
     
     
         5 . The method of  claim 4 , wherein the coextruded, biaxially oriented film structure does not comprise a primer between the base layer and the first outer layer.  
     
     
         6 . The method of  claim 1 , wherein the thermoplastic polymer of the base layer of the coextruded, biaxially oriented film structure is selected from the group consisting of isotactic propylene polymer, syndiotactic propylene polymer, ethylene-propylene copolymer, ethylene-propylene-butene-1 terpolymer, ethylene-butylene copolymer, ethylene copolymer, high density polyethylene, low density polyethylene, very low density polyethylene, ethylene plastomer, linear low density polyethylene and blends thereof.  
     
     
         7 . The method of  claim 1 , wherein the coextruded, biaxially oriented film structure further comprises an intermediate layer applied on one side of the base layer, the first outer layer is applied on a side of the intermediate layer opposite the base layer, the intermediate layer of the coextruded, biaxially oriented film structure comprises an ethylene polymer.  
     
     
         8 . The method of  claim 1 , wherein the coextruded, biaxially oriented film structure further comprises a second outer layer disposed on a side of the base layer opposite the first outer layer.  
     
     
         9 . The method of  claim 8 , wherein at least one outer surface of the film structure is surface-treated by one of corona discharge treatment, flame treatment or plasma treatment.  
     
     
         10 . The method of  claim 8 , wherein the second outer layer of the coextruded, biaxially oriented film structure has a coating applied thereon or is metallized.  
     
     
         11 . The method of  claim 8 , wherein the second outer layer of the coextruded, biaxially oriented film structure is heat-sealed or laminated to a substrate.  
     
     
         12 . The method of  claim 1 , wherein the first outer layer of the coextruded, biaxially oriented film structure has a Vicat softening point of not more than 85° C. (185° F.).  
     
     
         13 . The method of  claim 1 , wherein the first outer layer of the coextruded, biaxially oriented film structure is comprised of ethylene-vinyl acetate (EVA) copolymer.  
     
     
         14 . A method of manufacturing a coextruded, biaxially oriented film structure comprising a base layer comprising a polyolefin and a first outer layer comprising a ethylene polymer that has a melting point of not more than 230° F. (110° C.), wherein the method comprises the steps of: 
 a) preparing and coextruding melts corresponding to each individual layer of the film structure through a die to form a coextruded film sheet; and    b) sequentially biaxially orienting the coextruded film sheet in a machine direction with a sequential biaxial orientation apparatus that employs a radiant-heated machine-direction orientation stretcher and in a transverse direction, to form the coextruded, biaxially oriented film structure.    
     
     
         15 . The method of  claim 14 , wherein the machine-direction orientation stretcher comprises a radiant-heating section in a non-contacting free span between a last slow roll and a first fast roll.  
     
     
         16 . The method of  claim 14 , wherein the coextruded, biaxially oriented film structure is oriented from 1.5 to 8 times in the machine direction and from 2 to 12 times in the transverse direction.  
     
     
         17 . The method of  claim 14 , wherein the ethylene polymer of the first outer layer of the coextruded, biaxially oriented film structure is selected from the group consisting of ethylene plastomer, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-methacrylate copolymer, ethylene-butyl acrylate copolymer, ethylene-ethyl acrylate copolymer, ethylene-acrylic acid terpolymer, ethylene-methacrylic acid terpolymer, ethylene homopolymer, ethylene copolymer and blends thereof.  
     
     
         18 . The method of  claim 17 , wherein the coextruded, biaxially oriented film structure does not comprise a primer between the base layer and the first outer layer.  
     
     
         19 . The method of  claim 14 , wherein the thermoplastic polymer of the base layer of the coextruded, biaxially oriented film structure is selected from the group consisting of isotactic propylene polymer, syndiotactic propylene polymer, ethylene-propylene copolymer, ethylene-propylene-butene-1 terpolymer, ethylene-butylene copolymer, ethylene copolymer, high density polyethylene, low density polyethylene, very low density polyethylene, ethylene plastomer, linear low density polyethylene and blends thereof.  
     
     
         20 . The method of  claim 14 , wherein the coextruded, biaxially oriented film structure further comprises an intermediate layer applied on one side of the base layer and the first outer layer applied on a side of the intermediate layer opposite the base layer, the intermediate layer of the coextruded, biaxially oriented film structure comprises an ethylene polymer.  
     
     
         21 . The method of  claim 14 , wherein the coextruded, biaxially oriented film structure further comprises a second outer layer disposed on a side of the base layer opposite the first outer layer.  
     
     
         22 . The method of  claim 21 , wherein at least one outer surface of the film structure is surface-treated by one of corona discharge treatment, flame treatment or plasma treatment.  
     
     
         23 . The method of  claim 21 , wherein the second outer layer of the coextruded, biaxially oriented film structure has a coating applied thereon or is metallized.  
     
     
         24 . The method of  claim 21 , wherein the second outer layer of the coextruded, biaxially oriented film structure is heat-sealed or laminated to a substrate.  
     
     
         25 . The method of  claim 14 , wherein the first outer layer of the coextruded, biaxially oriented film structure comprises ethylene-vinyl acetate (EVA) copolymer.