Prior art beverage containers designed for use in a pasteurization process have typically been made of glass because glass can withstand the extended high temperatures and high internal pressures of this process. FIG. 1 illustrates graphically, as a function of time, the increasing internal temperature and pressure for a pasteurizable 16-ounce glass container. The pasteurization cycle has five components:
(1) emersion in bath 1 for a period of about 12.5 minutes in order to raise the container and contents up to about the bath temperature of 43.degree. C.; PA1 (2) emersion in bath 2 during a time period from about 12.5 to 21 minutes in order to raise the container and contents up to about the bath temperature of 77.degree. C.; PA1 (3) emersion in bath 3 during a time period from about 21 to 31.5 minutes in order to hold the container and contents at about the bath temperature of 73.degree. C.; PA1 (4) emersion in bath 4 during a time period from about 31.5 to 43 minutes in order to lower the container and contents down to about the bath temperature of 40.degree. C.; and PA1 (5) emersion in quench bath 5 for a time period from about 43 to 60 minutes in order to cool the container and contents down to about 10.degree. C.
The top curve shows that the temperature of the container (and contents) remains above 70.degree. C. for roughly ten minutes, during which time there is a significant increase in internal pressure to about 20 psi. There is a slight negative internal pressure at the end of the cycle. A glass container can withstand these temperatures and pressures without deformation.
There is a need to provide a plastic container able to withstand pasteurization in order to gain the advantages of plastic over glass, i.e., light-weight, shatter-resistance, etc. However, known carbonated beverage and/or hot fill polyester containers can not be expected to withstand these temperatures and pressures without substantial deformation. The prior art teaches that a plastic container for pasteurization would require a very high level of average crystallinity in the panel section (e.g., 35-40%), achievable either by high-temperature heat setting or an expensive double-blowing process. It would be desirable, however, to provide a less expensive method of making a pasteurizable polyester container having a relatively low level of crystallinity, i.e., below 30%.
USPTO Backgrounds
USPTO Backgrounds