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.

What is claimed is:  
     
         1 . A coextruded, biaxially oriented film structure comprising a base layer comprising a thermoplastic polymer and a first outer layer comprising a thermoplastic polymer that has a melting point of not more than 230° F.  
     
     
         2 . The film structure of  claim 1 , wherein the thermoplastic polymer of the base layer is a polyolefin 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.  
     
     
         3 . The film structure of  claim 1 , wherein the thermoplastic polymer of the first outer layer 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.  
     
     
         4 . The film structure of  claim 1 , wherein an intermediate layer is applied on one side of the base layer and the first outer layer is applied on a side of the intermediate layer opposite the base layer.  
     
     
         5 . The film structure of  claim 4 , wherein the intermediate layer comprises an ethylene polymer.  
     
     
         6 . The film structure of  claim 1 , wherein a second outer layer is disposed on a side of the base layer opposite the first outer layer.  
     
     
         7 . The film structure of  claim 1 , wherein the film structure has been oriented from 1.5 to 8 times in the machine direction and from 2 to 12 times in the transverse direction.  
     
     
         8 . The film structure of  claim 1 , wherein the film structure has been prepared by a process comprising the steps of: 
 preparing and coextruding melts corresponding to each individual layer of the film structure through a die to form a coextruded film sheet; and    simultaneously biaxially orienting the coextruded film sheet to form the film structure.    
     
     
         9 . The film structure of  claim 8 , wherein the simultaneous biaxial orientation proceeds on a line that utilizes linear motors to directly propel opposed pairs of tenter clips synchronously.  
     
     
         10 . The film structure of  claim 1 , wherein the film structure has been prepared by a process comprising the steps of: 
 preparing and coextruding melts corresponding to each individual layer of the film structure through a die to form a coextruded film sheet; and    sequentially biaxially orienting the coextruded film sheet with a sequential biaxial orientation apparatus that employs a radiant-heated machine-direction orientation stretcher.    
     
     
         11 . The film structure of  claim 10 , 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.  
     
     
         12 . The film structure of  claim 1 , wherein at least one outer surface of the film structure is surface-treated by one of corona discharge treatment, flame treatment or plasma treatment.  
     
     
         13 . The film structure of  claim 1 , wherein an outer surface of a side of the film structure opposite the first outer layer has a coating applied thereon.  
     
     
         14 . The film structure of  claim 1 , wherein an outer surface of a side of the film structure opposite the first outer layer is metallized.  
     
     
         15 . The film structure of  claim 1 , wherein the first outer layer is heat-sealed to a substrate.  
     
     
         16 . A laminate comprising a substrate laminated to the first outer layer of the film structure of  claim 1 .  
     
     
         17 . A metallized film structure comprising a metal layer deposited on the first outer layer of the film structure of  claim 1 .  
     
     
         18 . A film structure comprising a base layer comprising a propylene polymer, an intermediate layer on one side of the base layer, the intermediate layer comprising an ethylene polymer, and a first outer layer extrusion-coated on a side of the intermediate layer opposite the base layer.  
     
     
         19 . The film structure of  claim 18 , wherein the ethylene polymer of the intermediate layer is medium density polyethylene (MDPE).  
     
     
         20 . The film structure of  claim 18 , wherein the extrusion-coated first outer layer comprises an ethylene-vinyl acetate (EVA) copolymer.  
     
     
         21 . The film structure of  claim 18 , wherein the film structure does not comprise a primer between the base layer and intermediate layer or between the intermediate layer and first outer layer.  
     
     
         22 . The film structure of  claim 21 , wherein the film structure possesses an adhesion peel strength of at least 0.3 N/15 mm.  
     
     
         23 . The film structure of  claim 18 , wherein the first outer layer is heat-sealed to a substrate.  
     
     
         24 . A laminate comprising a substrate laminated to the first outer layer of the film structure of  claim 18 .  
     
     
         25 . A metallized film structure comprising a metal layer deposited on the first outer layer of the film structure of  claim 18 .  
     
     
         26 . A method of manufacturing a coextruded, biaxially oriented film structure comprising a base layer comprising a polyolefin and a first outer layer comprising a polymer that has a melting point of not more than 230° F. (110° C.), wherein the method comprises the steps of: 
 preparing and coextruding melts corresponding to each individual layer of the film structure through a die to form a coextruded film sheet; and  
 simultaneously biaxially orienting the coextruded film sheet to form the film structure.  
 
     
     
         27 . The method of  claim 26 , wherein the simultaneous biaxial orientation proceeds on a line that utilizes linear motors to directly propel opposed pairs of tenter clips synchronously.  
     
     
         28 . A method of manufacturing a coextruded, biaxially oriented film structure comprising a base layer comprising a polyolefin and a first outer layer comprising a polymer that has a melting point of not more than 230° F. (110° C.), wherein the method comprises the steps of: 
 preparing and coextruding melts corresponding to each individual layer of the film structure through a die to form a coextruded film sheet; and—sequentially biaxially orienting the coextruded film sheet with a sequential biaxial orientation apparatus that employs a radiant-heated machine-direction orientation stretcher.  
 
     
     
         29 . The method of  claim 28 , 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.  
     
     
         30 . A film structure prepared as a substrate for an extrusion-coated outer layer, wherein the film structure comprises (i) a base layer comprising a propylene polymer and (ii) an additional layer on one side of the base layer comprising an ethylene polymer, wherein the additional layer is receptive to an extrusion-coated outer layer on a side of the additional layer opposite the base layer.  
     
     
         31 . The film structure of  claim 30 , wherein the film structure does not comprise a primer between the base layer and additional layer.  
     
     
         32 . The film structure of  claim 31 , wherein the film structure does not comprise a primer on the side of the additional layer opposite the base layer.  
     
     
         33 . The film structure of  claim 30 , wherein the ethylene polymer of the additional layer is medium density polyethylene (MDPE).  
     
     
         34 . A method of preparing a substrate for an extrusion-coated outer layer, comprising the step of preparing the film structure of  claim 30  by coextruding melts corresponding to the base layer and additional layer through a die to form a coextruded film sheet, wherein the additional layer maximizes the adhesion between the base layer and an outer layer when an outer layer is extrusion-coated on a side of the additional layer opposite the base layer.  
     
     
         35 . A coextruded, biaxially oriented film structure comprising a base layer comprising a thermoplastic polymer and a first outer layer comprising a thermoplastic polymer that has a Vicat softening point of not more than 85° C. (185° F.).