Thermoformed food trays having improved toughness

Abstract

A continuous process for making a thermoplastic article comprises extruding a sheet of thermoplastic and contacting the sheet with a mold surface while the sheet is in a substantially non-oriented state. The mold surface is selectively heated and/or cooled during thermoforming to maintain the sheet in a molten or thermoformable state. A stripper plate adjacent to the mold surface is maintained at different temperature for inducing a predetermined degree of crystallinity to the sheet, for increasing web stiffness and improving web alignment, and optionally for assisting in the separation of the articles from the mold. A continuous apparatus for making thermoformed articles has co-extruders for extruding at least two distinct layers, which can have dissimilar properties (e.g., polar and non-polar), and a temperature controlled molding surface. Preferred thermoplastic compositions of the present invention have improved toughness and retained intrinsic viscosity.

1 - 23 . (canceled)  
     
     
         24 . A multi-layered thermoformed food tray comprising first, second, and third layers heat-set into a rigid, dimensionally stable article having a bottom portion and a flange portion, wherein the first, second, and third layers comprise: 
 a first polymeric layer comprising an alkylene terephthalate or naphthalate polymer, the first polymeric layer containing up to about 30 wt % mineral filler;    a second intermediate layer comprising a glycidyl or maleic functional co-polymer of ethylene or ter-polymer of ethylene and an acrylate, or both; and    a third polymeric layer comprising a substantially non-polar thermoplastic.    
     
     
         25 . The food tray of  claim 24  wherein the first layer comprises a blend of (i) virgin polymer and (ii) reprocessed polymeric materials from the first, second, and third layers.  
     
     
         26 . The food tray of  claim 24  wherein said first polymeric layer is selected from the group consisting of PET, PEN, PETG, PCT, PCTA, PBT, PTT, and mixtures thereof, and comprises one or more linear or branched homo-polymers, co-polymers, reprocessed polymers, recycled polymers, or a mixture thereof.  
     
     
         27 . The food tray of  claim 24  wherein said second intermediate layer is selected from the group consisting of ethylene/glycidyl methacrylate co-polymer, ethylene/maleic anhydride co-polymer, ethylene/glycidyl methacrylate/methacrylate ter-polymer, ethylene/glycidyl methacrylate/ethylacrylate ter-polymer, ethylene/glycidyl methacrylate/butylacrylate ter-polymer, ethylene/glycidyl methacrylate/ethylhexyl acrylate ter-polymer, ethylene/maleic anhydride/methacrylate ter-polymer, ethylene/maleic anhydride/ethylacrylate ter-polymer, ethylene/maleic anhydride/butylacrylate ter-polymer, ethylene/maleic anhydride/ethylhexyl acrylate ter-polymer, and mixtures thereof.  
     
     
         28 . The food tray of  claim 27  wherein said second intermediate layer comprises a grafted co-polymer or ter-polymer.  
     
     
         29 . The food tray of  claim 27  wherein said second intermediate layer comprises a blend of (i) said co-polymer or ter-polymer and (ii) a co-polymer of ethylene and an acrylate.  
     
     
         30 . The food tray of  claim 27  wherein said second intermediate layer comprises a blend of (i) said co-polymer or ter-polymer and (ii) polyethylene or co-polymers of ethylene and an alpha olefin.  
     
     
         31 . The food tray of  claim 24  wherein said third polymeric layer is a substantially non-polar polyolefin.  
     
     
         32 . The food tray of  claim 24  wherein said first polymeric layer is dimensionally distorted when the food tray is filled with food and is exposed to microwave radiation.  
     
     
         33 . The food tray of  claim 24  wherein said first polymeric layer is heat set and wherein said food tray is suitable for cooking in a microwave oven.  
     
     
         34 . The food tray of  claim 24  wherein said food tray contains foodstuff and is sealed with an elastic polyolefin-based lidding stock using modified atmosphere packaging.  
     
     
         35 . A multi-layered thermoformed microwavable food tray comprising first, second, and third layers heat-set into a rigid article which is dimensionally stable at elevated temperatures encountered in cooking applications, the article having a bottom portion and a flange portion, wherein the first, second, and third layers comprise: 
 a first polymeric layer comprising polyethylene terephthalate, the first polymeric layer containing up to about 30 wt % mineral filler;    a second intermediate layer selected from the group consisting of ethylene/glycidyl methacrylate co-polymer, ethylene/maleic anhydride co-polymer, ethylene/glycidyl methacrylate/methacrylate ter-polymer, ethylene/glycidyl methacrylate/ethylacrylate ter-polymer, ethylene/glycidyl methacrylate/butylacrylate ter-polymer, ethylene/glycidyl methacrylate/ethylhexylacrylate ter-polymer, ethylene/maleic anhydride/methacrylate ter-polymer, ethylene/maleic anhydride/ethylacrylate ter-polymer, ethylene/maleic anhydride/butylacrylate ter-polymer, ethylene/maleic anhydride/ethylhexylacrylate ter-polymer, and mixtures thereof; and    a third polymeric layer comprising a substantially non-polar polyolefin;    wherein the first layer comprises a blend of (i) virgin polymer and (ii) reprocessed polymeric materials from the first, second, and third layers.    
     
     
         36 . The multi-layered thermoformed microwavable food tray of  claim 35  wherein: 
 said first polymeric layer has an average thickness of from about 5 to about 35 mils;    wherein said second intermediate layer has an average thickness of from about 0.1 to about 2 mils;    wherein said third polymeric layer has an average thickness of from about 1 to about 5 mils; and    wherein said container has an area stretch ratio of from about 1.5:1 to about 3:1.