Partially Crystalized Polyester Containers

Abstract

A clear polyester container ( 1.0 ) comprising a base and upwardly extending side walls terminating in a continuous flange projecting from the side walls is described. Said multilayer container comprises an inner layer ( 1.1 ) in amorphous phase and an outer layer comprising a nucleating agent in the polymer composition in order to be crystallized in at least one portion of the flange.

1 ) A clear multilayer polyester container comprising a base and upwardly extending side walls terminating in a continuous flange projecting from the side walls, said multilayer container comprising at least an inner layer of an amorphous polyester and a bulk outer layer comprising a polyester in admixture with a nucleating agent, said bulk outer layer being crystallized in at least one portion of said flange. 
     
     
         2 ) The container according to  claim 1  wherein said bulk outer layer is continuously crystallized all along the flange. 
     
     
         3 ) The container according to  claim 1  wherein the polyester is selected among polyethylene terephthalate, polylactic acid, and polyethylene terephthalate-glycol. 
     
     
         4 ) The container according to  claim 3  wherein the polyester is polyethylene terephthalate or polyethylene terephthalate-glycol. 
     
     
         5 ) The container according to  claim 1  having two or three layers of polyester film. 
     
     
         6 ) The container according to  claim 1  wherein the flange has a thickness of from 100 μm to 1000 μm. 
     
     
         7 ) The container according to  claim 1  wherein the percentage of crystallization of the crystallized portion of the flange is equal to or higher than about 10%. 
     
     
         8 ) The container according to  claim 1  wherein the crystallization of the flange is obtained by heating at least one portion of said flange at a temperature of from 270° C. to 300° C. for a time from 5 seconds to 10 seconds. 
     
     
         9 ) The container according to  claim 1  wherein the nucleating agent is selected among alkali metal salts of organic acids; lithium or sodium salts of aliphatic, cycloaliphatic, aromatic carboxylic acids or heterocyclic polycarboxylic acids, containing up to 20 carbon atoms; DBS-Dibenzylidene Sorbitol; trygliceride oil and triglyceride oil in combination with organic acid metal salts or chemically bonding to organic metal salts. 
     
     
         10 ) A package comprising a container according to  claims 1 , including a product loaded into said container and a lid sealed onto the flange of said container. 
     
     
         11 ) The package according to  claim 10  wherein the container and the lid are made of polyesters. 
     
     
         12 ) The package according to  claim 10  wherein said lid is made of a shrinkable film. 
     
     
         13 ) The package according to  claim 10  having one or more films covering it. 
     
     
         14 ) Use of a container according to  claim 1  for tray lidding applications. 
     
     
         15 ) A process for manufacturing a container, comprising the steps of:
 a) providing a multilayer polyester sheet comprising an inner amorphous polyester layer and a bulk outer layer comprising a polyester in admixture with a nucleating agent;   b) pre-heating said multilayer polyester sheet at a temperature between 90 and 120 ° C.; and   c) forming said pre-heated polyester sheet in a mold suitable for inducing crystallization of the bulk outer layer in at least one portion of the flange.