Barrier film for food packaging

Abstract

Barrier films are prepared from a blend of two high density polyethylene blend components and a high performance organic nucleating agent. The two high density polyethylene blend components have substantially different melt indices. Large reductions in the moisture vapor transmission rate of the film are observed in the presence of the nucleating agent when the melt indices of the two blend components have a ratio of greater than 10/1. The resulting barrier films are suitable for the preparation of packaging for dry foods such as crackers and breakfast cereals.

What is claimed is: 
     
         1 . A barrier film comprising at least one extruded polyethylene layer, wherein said at least one extruded polyethylene layer comprises:
 I) an organic barrier nucleating agent and   II) a high density polyethylene blend composition comprising:
 II-i) from 5 to 60 weight % of at least one high density polyethylene blend component a) having a high melt index, I 2 ; and 
 II-ii) from 95 to 40 weight % of at least one high density polyethylene blend component b) having a low melt index, I 2 ′, wherein:
 w) said organic barrier nucleating agent is added in an amount of from 100 to 3000 parts per million based on the weight of said high density polyethylene blend composition; 
 x) each of said blend component a) and blend component b) has a density of from 0.950 to 0.975 g/cc; 
 y) the melt index, I 2 , of said high density polyethylene blend composition is from 0.5 to 10 grams/10 minutes; and 
 z) the I 2  ratio, obtained by dividing the I 2  value of said blend component a) by the I 2 ′ value of said blend component b) is greater than 10/1. 
 
   
     
     
         2 . The barrier film of  claim 1  wherein said high density polyethylene blend composition comprises from 10 to 40 weight % of said component a) and from 90 to 60 weight % of said component b). 
     
     
         3 . The barrier film of  claim 1  wherein said high density polyethylene blend composition comprises from 20 to 40 weight % of said component a) and from 80 to 60 weight % of said component b). 
     
     
         4 . The barrier film of  claim 1  wherein said blend component a) is further characterized by having a molecular weight distribution, Mw/Mn, of from 2 to 4. 
     
     
         5 . The barrier film of  claim 1  wherein said high density polyethylene blend composition has a density from 0.955 to 0.965 g/cc. 
     
     
         6 . The barrier film of  claim 1  wherein said high density polyethylene blend composition has a melt index, I 2 , of from 0.8 to 8 grams/10 minutes. 
     
     
         7 . The barrier film of  claim 1  wherein said nucleating agent has a melting/decomposition temperature of greater than 300° C. 
     
     
         8 . The barrier film of  claim 6  wherein said nucleating agent is a salt of a dicarboxylic acid. 
     
     
         9 . The barrier film of  claim 8  wherein said dicarboxylic acid is a cyclic dicarboxylic acid having a hexahydrophtalic structure. 
     
     
         10 . The barrier film of  claim 9  wherein said salt is selected from the group consisting of calcium and zinc salts. 
     
     
         11 . A process to prepare a barrier film for food packaging, said process comprising the film extrusion of a composition comprising:
 I) an organic barrier nucleating agent; and   II) a high density polyethylene blend composition comprising:
 II-i) from 5 to 60 weight % of at least one high density polyethylene blend component a) having a high melt index, I 2 ; and 
 II-ii) from 95 to 40 weight % of at least one high density polyethylene blend component b) having a low melt index, I 2 ′, wherein:
 w) said organic barrier nucleating agent is added in an amount of from 100 to 3000 parts per million based on the weight of said high density polyethylene blend composition; 
 x) each of said blend component a) and blend component b) has a density of from 0.950 to 0.975 g/cc; 
 y) the melt index, I 2 , of said high density polyethylene blend composition is from 0.5 to 10 grams/10 minutes; and 
 z) the I 2  ratio, obtained by dividing the I 2  value of said blend component a) by the I 2 ′ value of said blend component b) is greater than 10/1. 
 
   
     
     
         12 . The process of  claim 11  wherein said high density polyethylene blend composition comprises from 10 to 40 weight % of said component a) and from 90 to 60 weight % of said component b). 
     
     
         13 . The process of  claim 11  wherein said blend component a) is further characterized by having a molecular weight distribution, Mw/Mn, of from 2 to 4. 
     
     
         14 . The process of  claim 13  wherein said nucleating agent is a salt of a dicarboxylic acid. 
     
     
         15 . The process of  claim 11  wherein conducted at a blow up ratio of from 1.5/1 to 4/1.