Abstract:
A method includes steps for forming an intermediate composition. The intermediate composition is to be added to a polymer, or to a polymer precursor, in a process of manufacturing a low permeability container formed of the polymer or polymer precursor. The method includes forming an intermediate composition which, if added to the polymer or polymer precursor, will inhibit the permeability of the low permeability container subsequently formed of the polymer or polymer precursor. The forming step includes mixing a solid dispersant with clay to form the intermediate composition as a solid.

Description:
FIELD OF THE INVENTION 
     The present invention relates to plastic containers for beverages. 
     BACKGROUND OF THE INVENTION 
     Food containers, including beverage bottles, can be molded from a plastic, such as polyethylene terephthalate (PET). Permeability of such bottles may be undesirable, since ingress of oxygen and egress of carbon dioxide can degrade food quality. Permeability can be reduced by blending the plastic with permeability-inhibiting additive before molding the plastic into the food container. For example, clay is sometimes used as such an additive. 
     SUMMARY OF THE INVENTION 
     The present invention comprises a method of forming an intermediate composition. The intermediate composition is to be added to a polymer, or to a polymer precursor, in a process of manufacturing a low permeability container formed of the polymer or polymer precursor. One manner of performing the method comprises forming an intermediate composition which, if added to the polymer or polymer precursor, will inhibit the permeability of the low permeability container subsequently formed of the polymer or polymer precursor. The forming step comprises mixing a solid dispersant with clay to form the intermediate composition as a solid. 
     In a preferred embodiment, the intermediate composition is free of the polymer or polymer precursor and is also free of water. It is advantageous for the clay to be exfoliated within the dispersant in the forming step. The clay is preferably a smectite, and is most preferably montmorillonite. The dispersant is preferably a wax, and is most preferably castor wax. The polymer is preferably a thermoplastic, and is most preferably a polyester, such as PET. 
     In another manner of performing the method, a permeability-inhibiting additive is mixed with a dispersant that is solid at room temperature to form a mixture which comprises the additive and the dispersant. The method further comprises dispersing the additive within the dispersant while maintaining the mixture at a temperature above the melting point of the dispersant. The method still further comprises cooling the mixture to a temperature below the melting point of the dispersant to form an intermediate composition which is solid and which, if added to the polymer or polymer precursor, will inhibit the permeability of the low permeability container subsequently formed of the polymer or polymer precursor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a container produced according to the present invention; 
     FIG. 2 is a flow diagram showing steps of a process according to the present invention; 
     FIG. 3 is a schematic view of an apparatus used to perform steps of the process of FIG. 2; 
     FIG. 4 is a flow diagram showing steps of another process according to the present invention; and 
     FIG. 5 is a flow diagram showing steps of yet another process according to the present invention. 
    
    
     DESCRIPTION OF THE INVENTION 
     FIG. 1 shows a plastic container  10 . In this embodiment, the container  10  is a beverage container, and is preferably used for holding pressurized carbonated beverages. The container  10  has a cylindrical side wall  12 , a closed bottom wall  14 , and an opening  16  at the top. Extending between the opening  16  and the side wall  12  is a tapered neck  18 . The neck  18  has an external screw thread  19  for receiving a bottle cap (not shown). 
     In accordance with the present invention, the container  10  is formed of a plastic having low permeability to gases. This is especially desirable for carbonated beverages, in which egress of pressurized carbon dioxide and ingress of oxygen are undesirable. Migration of gas through the container walls  12 ,  14  and  18  is impeded by a dispersion of nanocomposite clay within the plastic. Microscopic platelets of the clay serve as barriers to gas molecules migrating through the plastic. 
     The container  10  is manufactured through a process shown schematically in FIG.  2 . The process utilizes clay  20 . In the preferred embodiment, the clay  20  is montmorillonite, which is in the smectite family of nanocomposite clays. Before processing, the clay  20  comprises agglomerates of platelet layers. The process also utilizes a dispersant  22 . In the preferred embodiment, the dispersant  22  is castor wax, which is a solid hydrogenation product of castor oil. 
     The clay  20  is mixed with the dispersant  22  at room temperature to form a first mixture  24 . The first mixture  24  preferably does not include water or any structural polymer. 
     Referring to FIG. 3, the first mixture  24  is heated in a barrel  26  of an extruder  28 . In this heating step  30  (FIG.  2 ), the first mixture  24  is heated to a processing temperature above the melting point of the castor wax. The melting point is typically in the range of about 82° C. to about 104° C. In an agitating step  34  (FIG.  2 ), a deep flighted screw  38  within the barrel  26  agitates the heated first mixture  24 . During the heating and agitating steps  30  and  34  (FIG.  2 ), the platelet layers are dispersed and preferably exfoliated within the melted castor wax  22 . “Dispersed” means delaminated from neighboring layers and separated from neighboring layers by dispersant molecules interspersed between neighboring layers. Layers are “exfoliated” when the separation between layers is sufficiently large such that there is insufficient attraction between layers to cause uniform spacing between the layers. 
     The screw  38  moves the first mixture  24  to an extrusion die opening  42  (FIG.  3 ). The first mixture  24  is extruded out the die opening  42  in the form of a hot slurry. Next, two chilled chrome-plated rollers  46  and  48  are used to calender the first mixture  24  to a predetermined thickness. The thickness is determined by the spacing between the rollers  46  and  48 . In a cooling step  50  (FIG.  2 ), contact with the chilled rollers  46  and  48  cools the first mixture  24  to a temperature below the melting point of the castor wax  22 . 
     In a crumbling step  52  (FIG.  2 ), a portion of the first mixture  24  is scraped off of the rollers  46  and  48  by stationary scrapers  54  and  56 . The first mixture  24  falls onto a conveyer belt  58  in the form of flakes  60 . From the conveyer belt  58 , the flakes  60  drop into an opening  62  of a rotatable drum  64 . The drum  64  has a cylindrical wall  66  partially comprised of a filtering mesh  68 . The drum opening  62  is closed, and then the drum  64  rotates. As the drum  64  rotates, the flakes  60  tumble within the drum  64  and break apart into flakes of smaller size. The flakes  60  ultimately reach a size enabling the flakes  60  to fall through the mesh  68  and into a hopper (not shown). 
     The flakes  60  may or may not be stored, depending upon the preference of the manufacturer and/or user. In the optional storing step  70 , shown in FIG. 2, the flakes  60  are stored in a sealed storage container  72  such as a drum or the like. While in dry solid form within the storage container  72 , the flakes  60  are easily shipped to a facility where beverage bottles are manufactured. 
     At the facility, beverage bottles, such as the container  10  (FIG.  1 ), are molded from pellets of a structural polymer  74  (FIG.  2 ). The structural polymer  74  in this embodiment is PET. This is a type of polyester which, in turn, is a type of thermoplastic. 
     As shown in FIG. 2, the optionally stored flakes  60  and the polymer  74  are mixed to form a second mixture  76 . The second mixture  76  is preferably formed as a stream of the flakes  60  and a stream of the polymer  74  are combined at an inlet of a molding machine (not shown). In step  80 , the second mixture  76  is molded into the container  10  (FIGS. 1 and 2) as a finished product, in a manner known in the art. The container  10  has a single-layer wall composed of the clay  20 , the dispersant  22 , and the polymer  74 . 
     In producing the first mixture  24  (FIG.  1 ), the amount of the clay  20 , relative to the amount of the dispersant  22 , is specified based on the ultimate use of the flakes  60 . Specifically, the, amount of clay  20  is specified such that the flakes  60 , when added to the polymer  74 , inhibit the permeability of the container  10  subsequently formed of the polymer  74 . In this embodiment, about 30 parts of the clay  20  are mixed with about 70 parts of the dispersant  22 . 
     As described above with reference to FIG. 2, the optionally stored flakes  60  are mixed with the polymer  74 . Alternatively, as illustrated in FIG. 4, the flakes  60  may be mixed with a monomer  84 , which is a precursor of PET polymer, to form a third mixture  86 . The third mixture  86  is thus composed of the clay  20  (FIG.  2 ), the dispersant  22  (FIG. 2) and the monomer  84 . In step  88 , the monomer  84  is polymerized in situ within the third mixture  86  to form the PET polymer. This yields a fourth mixture  90  comprising the clay  20  (FIG.  2 ), the dispersant  22  (FIG. 2) and the PET polymer. In a manner similar to that described above, the fourth mixture  90  is molded, in step  92 , into a container  94 . 
     As described above with reference to FIG. 2, the polymer  74  is combined with the flakes  60 . The flakes  60  are formed from the first mixture  24  through the steps of heating  30 , agitating  34 , cooling  50  and crumbling  52 . Alternatively, as illustrated in FIG. 5, the steps of heating  30  (FIG. 2) and agitatinng  34  (FIG. 2) to disperse platelet layers of the clay  20  within the dispersant  22  are not performed. Therefore, the steps of cooling  50  (FIG. 2) the heated slurry and crumbling  52  (FIG. 2) the slurry after cooling are not required. In this process, in step  100 , the first mixture  24  is stored in the storage container  72  and shipped to a facility where bottles are molded from the polymer  74 . Again, storage in a storage container and shipment to a separate facility are optional and are based on the preference of the manufacturer and/or user. At the facility, the polymer  74  is combined with the first mixture  24  at the throat of the molding machine to form a fifth mixture  102 . In step  104 , the fifth mixture  102  is molded into a finished container  106 . 
     Permeability of plastic bottles produced according to the present invention was measured. A process similar to that shown in FIG. 2 was used to produce the flakes. The flakes were composed of 70% montmorillonite clay and 30% castor wax. The castor wax was Maxsperse® obtained from M. A. Hanna Company of Cleveland, Ohio. The montmorillonite clay was Cloisite® 25A obtained from Southern Clay Products of Gonzales, Tex. A typical dry particle size distribution of Cloisite® 25A is 10% less than 2 microns, 50% less than 6 microns, and 90% less than 13 microns. Four bottles were produced using PET as the structural plastic. The amount of flakes added to the PET polymer was 0%, 0.5%, 1.0% and 1.5% for the four bottles, respectively. The bottles were tested on a Mocon OX-TRAN 10/50A oxygen permeability tester. In the test, the inside cavity of each bottle is flushed with nitrogen and the outside of each bottle is exposed to ambient air. Oxygen ingress is determined by measuring the oxygen concentration in the nitrogen flush gas exiting the bottle. The test conditions are listed in Table 1. The test results are listed in Table 2. Oxygen ingress is reported in cc/bottle/day. Table 2 clearly shows that oxygen ingress is lower for the bottles that include the clay/dispersant flake according to the present invention than for the bottle that does not. 
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 TEST CONDITIONS 
               
             
          
           
               
                   
                 INSIDE 
                 OUTSIDE 
               
               
                   
                 THE CONTAINER 
                 THE CONTAINER 
               
               
                   
                   
               
             
          
           
               
                 Purge gas 
                 nitrogen with 1% hydrogen 
                 ambient air 
               
               
                 Temperature 
                 71° F. +/− 2° F. 
                 71° F. +/− 2° F. 
               
               
                 Humidity 
                 65% 
                 50% 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
             
               
               
               
               
               
             
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 OXYGEN PERMEABILITY 
               
             
          
           
               
                   
                 Concentration of flake in PET 
                   
               
             
          
           
               
                   
                 0% 
                 .5% 
                 1.0% 
                 1.5% 
               
             
          
           
               
                 Time (days) 
                 cc/bottle/day 
               
               
                   
               
             
          
           
               
                 9 
                 .0474 
                 .0305 
                 .0297 
                 .0294 
               
               
                 10 
                 .0470 
                 .0298 
                 .0286 
                 .0280 
               
               
                 11 
                 .0468 
                 .0292 
                 .0285 
                 .0274 
               
               
                 15 
                 .0450 
                 .0281 
                 .0275 
                 .0266 
               
               
                 17 
                 .0443 
                 .0280 
                 .0278 
                 .0270 
               
               
                   
               
             
          
         
       
     
     The invention has been described with reference to preferred embodiments. Those skilled in the art will perceive improvements, changes and modifications. Such improvements, changes and modifications are intended to be within the scope of the claims.