Multilayer container resistant to elevated temperatures and pressures, and method of making the same

Abstract

A multilayer plastic container having enhanced strength for high temperature and pressure applications such as the pasteurization of carbonated juice drinks. The container is commercially cost-effective in comparison to prior art pasteurizable glass containers, and provides all of the advantages of plastic over glass, i.e., lightweight, shatter-resistant, etc. In a particular embodiment, the multilayer container includes inner and outer layers of a relatively high IV virgin PET, e.g., 0.85-0.90 dl/g, and a core layer of post-consumer PET having a substantially lower IV. The container has a relatively tall and slender profile, with high orientation levels in the panel and shoulder, and an oriented thick-walled base with feet. The base preferably has a high profile and angled foot pads which are allowed to move outwardly under creep. According to a method of making a multilayer preform for such container, an enhanced injection rate and mold pressure are utilized to enhance interlayer bonding and prevent separation of the layers in spite of their substantial differences in IV.

1 . A method of making a multilayer container, the method comprising the steps of: 
 injecting a first thermoplastic material having a first intrinsic viscosity (IV) into a preform mold cavity at a first injection rate to form a first layer of a preform;    injecting a second thermoplastic material having a second IV, which differs by at least about 0.10 dl/g from the first IV, into the mold cavity at a second injection rate to form a second layer of the preform adjacent the first layer;    applying a pressure to the first and second layers in the mold cavity, the injection rates and the pressure being selected to promote layer adhesion between the first and second layers; and    blow molding a container from the preform which can withstand a 1 meter drop onto a hard rigid surface without layer separation.    
     
     
         2 . The method of  claim 1 , wherein the second IV differs by at least about 0.20 dl/g from the first IV.  
     
     
         3 . The method of  claim 1 , wherein the first and second thermoplastic materials are polyesters.  
     
     
         4 . The method of  claim 1 , wherein the first thermoplastic material comprises virgin polyethylene terephthalate (PET) and the first IV is at least about 0.85 dl/g.  
     
     
         5 . The method of  claim 4 , wherein the first IV is at least about 0.90 dl/g.  
     
     
         6 . The method of  claim 4 , wherein the second thermoplastic material comprises post-consumer PET (PC-PET) and the second IV is no greater than about 0.75 dl/g.  
     
     
         7 . The method of any one of  claims 3  to  6 , wherein the pressure is at least about 9000 psi.  
     
     
         8 . The method of  claim 7 , wherein the pressure is on the order of 9000 to 12,000 psi.  
     
     
         9 . The method of  claim 8 , wherein at least one of the first and second injection rates is on the order of 16-20 grams per second.  
     
     
         10 . The method of  claim 9 , wherein both injection rates are on the order of 16-20 grams per second.  
     
     
         11 . The method of  claim 7 , wherein the temperature of blow molding is selected to reduce inter-layer shear during expansion of the multilayer preform.  
     
     
         12 . The method of  claim 11 , wherein the blow molding temperature is on the order of 110 to 118° C.  
     
     
         13 . The method of  claim 1 , wherein the first IV is higher than the second IV.  
     
     
         14 . The method of  claim 13 , wherein the first material forms an exterior preform layer and the second material forms an interior preform layer.  
     
     
         15 . The method of  claim 1 , further including: 
 injecting a third thermoplastic material at a third injection rate to form a layer adjacent one of the first and second layers, the third material having a third IV which differs by at least 0.10 dl/g from the IV of the material of the adjacent one of the first and second layers.    
     
     
         16 . The material of  claim 15 , wherein the first and second materials form at least a sidewall-forming portion of the preform, and the third material is included in a base-forming region of the preform.  
     
     
         17 . The method of  claim 16 , wherein the first and third materials have a higher IV than the second material.  
     
     
         18 . A biaxially-oriented multilayer expanded preform container having a first layer of a first thermoplastic material having a first intrinsic viscosity (IV), and a second layer adjacent to the first layer of a second thermoplastic material having a second IV which differs by at least about 0.10 dl/g from the first IV, which container can withstand a 1 meter drop onto a hard rigid surface without separation of the first and second layers.  
     
     
         19 . The container of  claim 18 , wherein the second IV differs by at least about 0.20 dl/g from the first IV.  
     
     
         20 . The container of  claim 18 , wherein the first and second thermoplastic materials are polyesters.  
     
     
         21 . The container of  claim 18 , wherein the first thermoplastic material comprises virgin polyethylene terephthalate (PET) and the first IV is at least about 0.85 dl/g.  
     
     
         22 . The container of  claim 21 , wherein the second thermoplastic material is post-consumer PET (PC-PET), and the second IV is no greater than about 0.75 dl/g.  
     
     
         23 . The container of  claim 18 , wherein the container when filled with a pressurized liquid of 2.5 volumes, sealed and then exposed to an elevated temperature of 75° C. for 10 minutes, undergoes an overall volume change of no greater than about 3%.  
     
     
         24 . The container of  claim 23 , wherein the overall volume change is no greater than about 2%.  
     
     
         25 . The container of  claim 1 , wherein the first IV is higher than the second IV.  
     
     
         26 . The container of  claim 25 , wherein the first material forms an exterior preform layer and the second material forms an interior preform layer.  
     
     
         27 . The container of  claim 18 , further including: 
 injecting a third thermoplastic material at a third injection rate to form a layer adjacent one of the first and second layers, the third material having a third IV which differs by at least 0.10 dl/g from the IV of the material of the adjacent one of the first and second layers.    
     
     
         28 . The container of  claim 27 , wherein the first and second materials form at least a sidewall-forming portion of the preform, and the third material is included in a base-forming region of the preform.  
     
     
         29 . The container of  claim 28 , wherein the first and third materials have a higher IV than the second material.  
     
     
         30 . The container of  claim 20 , having a generally cylindrical panel portion with a height-to-diameter ratio on the order of 2.0 to 3.0, a panel wall thickness on the order of 0.25 to 0.38 mm, and an average planar stretch ratio in the panel portion on the order of 13.0 to 14.5, and a base having a substantially hemispherical bottom wall and a plurality of legs, wherein the bottom wall has a thickness on the order of 0.60 to 2.5 mm.  
     
     
         31 . The container of  claim 30 , wherein the bottom wall extends from about θ=60° to θ=90° from a vertical centerline of the container.  
     
     
         32 . The container of  claim 31 , wherein each leg has an angled foot pad which is disposed at an angle of about 5 to 10° with a flat surface on which the container rests.  
     
     
         33 . The container of  claim 32 , wherein the angled foot pads as formed are disposed at about 60 to 75% of the panel diameter.  
     
     
         34 . The container of  claim 30 , wherein the container has an outwardly protruding and substantially rounded shoulder section above the panel section.  
     
     
         35 . The container of  claim 30 , wherein the first thermoplastic material is virgin PET and forms exterior inner and outer layers, and the second thermoplastic material is post-consumer PET and forms an interior core layer between the inner and outer layers.  
     
     
         36 . The container of  claim 35 , wherein the second thermoplastic material comprises on the order of 30 to 60% of a total weight of the container.  
     
     
         37 . The container of  claim 36 , wherein the first thermoplastic material comprises on the order of 40 to 70% of the total weight of the container.  
     
     
         38 . The container of  claim 18 , having a relatively tall and slender profile, a shoulder portion and a panel portion with an average planar stretch ratio at least on the order of 13.0, and a footed base including a substantially hemispherical bottom wall wherein the bottom wall has a thickness greater than that of the panel portion.  
     
     
         39 . The container of  claim 38 , wherein the bottom wall has a base profile of θ=60° to 90°, where θ is an angle that a radius, defining the substantially hemispherical bottom wall, extends from a vertical centerline of the container.  
     
     
         40 . A multilayer preform for blow molding a container, the preform having a first layer of a first polyester material having a first intrinsic viscosity (IV), and a second layer adjacent the first layer of a second polyester material having a second intrinsic viscosity (IV) which differs by at least about 0.20 dl/g from the first IV, the multilayer preform being injection molded without separation of the first and second layers.