Biodegradable composite barrier film

Abstract

The present invention is directed to a multilayer film having, as its main component, a hydroxy acid polymer with improved gas barrier and optional heat sealability. The oriented film of predominately hydroxy acid polymer having controlled shrink can be produced by melting and coextruding a hydroxy acid polymer with a much thinner layer of an amorphous aromatic copolyester to form a multilayer film that is quench cooled, then biaxially stretched at a process temperature above the glass transition and below the cold crystallization temperature of the hydroxy acid polymer. A heat-setting treatment with a controlled relaxation of the film above the hydroxy acid polymer glass transition temperature and below its melt temperature may be used to control shrinkage. The films thus obtained are vacuum metallized on the aromatic copolyester surface to produce environmentally friendly packaging from predominately renewable resources having improved gas barrier properties.

1 . A multilayer film comprising (i) a core layer comprising a major fraction by weight of the core layer of a poly(hydroxy acid), (ii) a polymeric barrier receiving layer adjacent to one side of the core layer and comprising a major fraction by weight of the polymeric barrier receiving layer of an amorphous aromatic copolyester, and (iii) a barrier layer adjacent the polymeric barrier receiving layer opposite the core layer, the barrier layer consisting of an inorganic compound,
 in which the poly(hydroxy acid) is at least about 85% by weight of the total in the multilayer film of the poly(hydroxy acid) and the amorphous aromatic copolyester.   
     
     
         2 . The multilayer film of  claim 1  in which the amorphous aromatic copolyester is at least about 90 wt % of the polymeric barrier receiving layer. 
     
     
         3 . The multilayer film of  claim 1  in which crystallinity of the amorphous aromatic copolyester is at most about 10%. 
     
     
         4 . The multilayer film of  claim 1  in which the inorganic compound is selected from the group consisting of Al, Mg, Zn, Sn, Ni, Ti, Si, C, an oxide, carbide, nitride, alloy of these elements, and a mixture thereof. 
     
     
         5 . The multilayer film of  claim 5  further comprising a metal seeding layer positioned between and in direct contact with both of the polymeric barrier receiving layer and the barrier layer,
 in which the inorganic compound of the barrier layer is aluminum, and 
 in which the metal seeding layer consists essentially of a seeding metal present in amount of about 0.1-0.5 mg/m 2 , the seeding metal being selected from the group consisting of Cu, Ni and a mixture thereof. 
 
     
     
         6 . The multilayer film of  claim 1  which further comprises on a side of the film opposite the barrier layer at least one additional layer of which the farthest from the core layer is a heat seal layer comprising a major fraction by weight of the heat seal layer of an amorphous polyester having at most about 10% crystallinity. 
     
     
         7 . The multilayer film of  claim 1  in which the core layer is free of amorphous aromatic copolyester.