Patent Application
20080245761
The present invention relates to pressurized plastic containers subject to pasteurization that exhibit reduced creep.
Many products (e.g., food and beverages) undergo pasteurization in order to reduce the number of microorganisms in the product. The process involves heating a filled and sealed container at an elevated temperature for a time period sufficient to a pasteurize the contents. Desirably, the physical stability of the bottle and the biological stability and flavor of the contents are minimally compromised, thereby increasing the shelf life.
For example, there are various organisms in beer that, while not pathological or dangerous to humans, can affect the taste and appearance of the beer if allowed to grow. Draft beer does not require pasteurization because it is kept refrigerated and consumed in a short period of time. However, beer packaged in glass bottles or metal cans is traditionally pasteurized to achieve a long shelf life. In a conventional pasteurization process, known as tunnel pasteurization, water is sprayed onto a series of closely spaced packages as they move on a conveyor through a pasteurization tunnel, the tunnel being divided into a series of zones which may include preheating, heating, holding and cooling zones. The temperature of the beer in the containers is progressively raised to a desired level, held at this level for a predetermined period of time, and then cooled before exiting the tunnel. Generally, in order to insure complete pasteurization, the temperature of the beer at the “cold spot” (one quarter inch from the bottom of the center of the can or bottle) must reach a temperature of at least 140° F. for a sufficient period of time to produce a cumulative heating profile (e.g., a specified number of pasteurization units (P.U.), generally defined as the amount of heat imparted into the product during the elevated temperature and time period. Because the temperature of the beer generally increases when progressing from the cold spot to the top of the package, it is desirable to pasteurize at the lowest possible cold spot temperature (above 140° F.) to avoid overheating (and thus deforming or degrading) the rest of the product and package. One example of a tunnel pasteurization process is described for example in U.S. Pat. No. 4,693,902 to Richmond et al., the contents of which are hereby incorporated by reference in their entirety.
Although products such as beer have historically been pasteurized in glass bottles, it would be desirable to use plastic containers, e.g., containers comprising polyethylene terephthalate (PET) homopolymer or copolymers, to take advantage of PET's lighter weight and shatter resistance. However, producing a pasteurizable plastic beer container that can withstand the pasteurization time/temperature profile and provide a desired shelf life, at a price that is commercially viable, has been a long-standing need in the industry based on numerous problems which must be overcome. In particular, the range of temperatures encountered during pasteurization will cause a typical plastic container to undergo permanent, uncontrolled deformation (also known as creep).
Deformation is undesirable not only from an aesthetic perspective, but because it results in a loss of carbonation pressure. The volume growth undergone by a plastic container during pasteurization produces a drop in the product fill line, which increases the head space and results in a drop in carbonation (CO2) pressure in the liquid. This drop in CO2 pressure reduces the overall shelf life because the filled and pasteurized container is effectively starting with a reduced carbonation pressure. In various applications, it would be desirable to provide a pasteurizable beer container having an initial carbonation pressure of 3.3 volumes of CO2 (where “volumes”=volume CO2 per volume water) and a shelf life of 16 weeks.
Accordingly, there remains a need to provide pressurized plastic containers that can withstand pasteurization with reduced deformation.
One embodiment provides a method of reducing creep in a pressurized pasteurizable plastic container comprising:
providing a blow-molded plastic container, the container having a biaxially-oriented wall of a structural polymer with a moisture content of no greater than a predetermined value at the start of a pressurized filling, capping, and pasteurization process,
wherein the structural polymer is present in an amount of 85% or greater by weight relative to the total weight of the container wall, and
wherein the predetermined value is selected to reduce creep in the pressurized pasteurized container.
Another embodiment provides a pasteurizable plastic container comprising a blow-molded plastic container having a biaxially-oriented wall of a structural polymer with a moisture content of no greater than a predetermined value at the start of a pressurized filling, capping and pasteurization process, the predetermined value limiting pressure loss in the pasteurized container over a desired shelf life.
Another embodiment provides a method of making a pressurized pasteurizable plastic container having reduced creep comprising;
blow molding a plastic container having a biaxially-oriented wall;
subjecting the container to filling with a pressurized liquid, capping and pasteurization, wherein the biaxially-oriented wall has a moisture content of no greater than a predetermined value at the start of the filling step, the predetermined value being selected to limit pressure loss in the pressurized pasteurized container over a desired shelf life.
Another embodiment provides a method of making pasteurizable plastic containers having reduced creep comprising providing a substantially continuous in-line process of blow molding, filling, capping and pasteurization steps, including blow molding a plastic preform to form a blow-molded plastic container having a biaxially-oriented wall, conveying the blow-molded container to a filling and capping station at which the blow-molded container is filled with a pressurized liquid and capped, and conveying the filled and capped container to a pasteurization station for pasteurization, and wherein at the start of filling the container wall has a moisture content of no greater than a predetermined value selected to reduce creep of the pasteurized container.
According to one embodiment, a method is provided for reducing creep in a pressurized pasteurizable plastic container.
When entering the housing the relatively cool bottles may first be subjected to sprays of liquid (e.g., water) at a preheating temperature, such as 120° F., to preheat the bottles before they are subjected to a relatively hot spray. The containers pass under a series of nozzles in the preheating zone which spray the bottles with the liquid; the preheating liquid sprayed onto the bottles will fall by gravity into a lower compartment and is collected for reuse.
The bottles next pass through liquid sprays at a pasteurizing temperature which brings the bottles and their contents to a desired temperature and maintains the temperature to provide the desired pasteurizing action. The maximum temperature of the sprayed liquid may be 145° F., so as to achieve a maximum internal temperature at the cold spot of the container just slightly above 140° F. (e.g., 141° F.). Here, the tunnel pasteurizer includes two successive pasteurizing zones followed by a maintaining zone, each of which may subject the bottles to a liquid spray of a different temperature to achieve a desired temperature profile. This is by way of example only and not limiting. Again the pasteurizing fluid falls by gravity into the compartment below.
After the bottles pass from the pasteurizing and holding zone(s), they can first be precooled and then subjected to a more intense cooling action. The precooling liquid may be at a temperature of 125° F., followed by successive cooling sprays at for example 75° F. and 60° F. The bottles then exit the tunnel pasteurizer at a desired temperature.
The conveyer belt can have the design of U.S. Pat. No. 2,658,608, the disclosure of which is incorporated herein by reference. Alternatively, the method of conveyance can involve a walking beam as described in U.S. Pat. No. 4,441,406.
In one embodiment, the plastic container has a biaxially oriented wall of a structural polymer with a moisture content of no greater than a predetermined value at the start of a pressurized filling, capping and pasteurization process. In one embodiment, the structural polymer is present in an amount of 85% or greater by weight relative to the total weight of the container wall.
The structural polymer can comprise those materials well known in the art. In one embodiment, the structural polymer is a polyester, such as polyethylene terephthalate homopolymers, copolymers, and blends thereof.
PU/minute=10[(T−140)/12.5]
One P.U. for beer is 1 minute at 140° F. PU begins to become significant when the beer temperature is above about 130-135° F., and most significant at 139° F. and above. However, P.U. accumulation begins at 120° F. Again, this pasteurization curve for a desired P.U. range of 12-15 is meant to be illustrative only and is not limiting. Different manufacturers will have different requirements for pasteurizing beer or other beverages (such as juice or soda), e.g., a minimum P.U. of 10, or a minimum P.U. of 8, and thus the process parameters will vary for the desired application.
In one embodiment, the desired shelf time for the pasteurized contents, e.g., beer, is at least 12 weeks, and in a further embodiment, at least 16 weeks.
The top two curves of
Accordingly, in one embodiment, one parameter, namely the moisture content of the structural polymer in the container prior to the pasteurization process, can have an effect on the volume change (and resulting carbonation loss) undergone by the pasteurized container. In prior processes, the initial moisture content of the container was not controlled and the carbonation loss during pasteurization and subsequent storage (prior to use) could be unacceptably high. In one embodiment, container deformation can be reduced by controlling the moisture content, resulting in reduction of carbonation loss.
Methods for measuring moisture content are well known in the art. In one embodiment, moisture content is determined by a Karl Fischer titration with a reagent containing iodine and sulfur dioxide. During the titration, the iodine reacts with water until the water in the sample is completely consumed. Based on the amount of reagent needed to consume the water, the moisture content is calculated. An exemplary instrument for performing a Karl Fischer titration is an Aquastar® AQ-2000.
In one embodiment, the amount of moisture present in the structural polymer prior to filling is less than 5000 ppm, such as an amount of less than 3000 ppm, independent of bottle size. Typically a blow molded bottle pick up moisture while in storage. According to one embodiment of the invention, for example, a 500 mL bottle contains 750 ppm moisture in the structural polymer immediately after it is blow molded. In another embodiment, the moisture content is less than 1500 ppm, less than 1000 ppm, or even less than 500 ppm. In yet another embodiment, the moisture content ranges from 500-1500 ppm. In yet another embodiment, the moisture content is approximately 0 ppm.
In one embodiment, the container is filled with a pressurized liquid having an initial carbonation of 2.5 to 3.7 volumes of CO2, such as an initial carbonation of 2.7 to 3.5 volumes of CO2, or an initial carbonation of 3 to 3.4 volumes of CO2.
In one embodiment, the wall of the container is a biaxially-oriented sidewall adapted to be filled at 3.3 volumes of CO2.
In one embodiment, the pasteurization process produces at least 7 pasteurization units (P.U.), such as from 7-30 P.U.'s, from 7-15 P.U.'s, or from 7-12 P.U.'s. In another embodiment, the pasteurization process produces at least 10 pasteurization units (P.U.).
In one embodiment, the amount of CO2 loss due to the reduction in moisture content of the structural polymer is 0.5 volumes CO2 or less, such as an amount of 0.4 volumes CO2 or less (from a starting amount of 3.3 volumes).
For example, filling and capping a container provides approximately 3.3 CO2 volumes. After subjecting the filled container to pasteurization, in one embodiment, it is desired that the bottle contain at least 3.0 volumes of CO2, e.g., a loss of 0.3 volumes. In one embodiment, the structural polymer has an initial moisture level (prior to pasteurization) of 2000 ppm or less, resulting in a loss of 0.4 volumes or less of CO2 (3.3 volumes CO2 before pasteurization to 2.9 volumes CO2 after pasteurization). For example, in a 500 mL bottle, the resulting volume growth would be 34 mL or less. In another embodiment, the structural polymer has an initial moisture level of 1500 ppm or less, resulting in a loss of 0.36 volumes or less of CO2 after pasteurization (e.g., a volume growth of 31 mL or less for a 500 mL bottle). In yet another embodiment, the structural polymer has a moisture content of 1000 ppm or less, resulting in loss of 0.34 volumes or less of CO2 after pasteurization (e.g., a volume growth of 28 mL or less for a 500 mL bottle).
The container can be made of structural polymer only or can include a layer of a non-structural polymer, e.g., a nylon such as MXD6. Generally, the structural polymer comprises the largest weight percent, e.g., 85% or more. In the case of multi-layer bottles containing non-structural polymers, generally the moisture content of the structural polymer has a predominant effect on the amount of volume growth of the bottle, e.g., nylons such as MXD6 may contain a larger amount of water relative to the amount in the structural polymer, but the nylon is a much lower weight percentage and does not substantially affect the creep.
Another embodiment provides a pasteurizable plastic container comprising a blow-molded plastic container having a biaxially-oriented wall with a moisture content of no greater than a predetermined value at the start of a pressurized filling, capping and pasteurization process, the predetermined value limiting pressure loss in the pasteurized container over a desired shelf life. In one embodiment, the container comprises a structural polymer in the amount of 85% or greater relative to the total weight of the container.
Exemplary wall thicknesses of the container of
A process according to one embodiment will now be described for providing a pasteurizable container having a desired shelf life (reduced deformation and/or reduced carbonation loss), as illustrated by the results disclosed herein. However, there are other methods which can be used to obtain the desired moisture level, and this is just one example.
One embodiment provides an “in-line process” for controlling the moisture content of the blow-molded containers.
blow molding
In
A conveyor belt 33 conveys a series of containers through the various blow molding, filling, capping, heating and cooling zones. In actual practice, the containers would be stacked on the conveyor in a continuous series in direct contact with adjacent containers. The schematic of
In another embodiment, the container is blow molded and stored under dry conditions to maintain a predetermined moisture content level, e.g., less than 2000 ppm.
Another embodiment provides a method of making a pressurized pasteurizable plastic container having reduced creep comprising;
blow molding a plastic container having a biaxially-oriented wall;
subjecting the container to filling with a pressurized liquid, capping and pasteurization, wherein the biaxially-oriented wall has a moisture content of no greater than a predetermined value at the start of the filling step, the predetermined value being selected to limit pressure loss in the pressurized pasteurized container over a desired shelf life. In one embodiment, the method is performed in-line. In another embodiment, the container comprises a structural polymer in the amount of 85% or greater relative to the total weight of the container.
Another embodiment provides a method of making pasteurizable plastic containers having reduced creep comprising providing a substantially continuous in-line process of blow molding, filling, capping and pasteurization steps, including blow molding a plastic preform to form a blow-molded plastic container having a biaxially-oriented wall, conveying the blow-molded container to a filling and capping station at which the blow-molded container is filled with a pressurized liquid and capped, and conveying the filled and capped container to a pasteurization station for pasteurization, and wherein at the start of filling the container wall has a moisture content of no greater than a predetermined value selected to reduce creep of the pasteurized container. The filled container is then immediately subjected to pasteurization, i.e., before the structural polymer has a moisture level greater than 2000 ppm.
Table 2 specifies the pasteurization parameters used in an example of an in-line process.
Due to the range of temperatures experienced by the container during pasteurization (e.g., from room temperature to at least 140° F.), the plastic container can experience deformations in one or more of the neck finish, shoulder, panel and base areas. During the heating phase of pasteurization, the product and head space gas expand in the sealed container. For example, when a container is filled with beer, the pressure can increase from e.g., 15 psi while cold (if the container is cold filled with beer) to approximately 45 psi at ambient temperature, and can peak at approximately 85 psi at a pasteurization temperature of 140° F. At these higher pressures and temperatures, one or more areas of the bottle may increase in diameter and/or height.
Table 3 lists the diameter changes in various portions of the container. It compares the amount of change along the various positions (21-27) for containers having different moisture contents, namely 700 ppm (“Dry”), 3,000 ppm, and 5,000 ppm as measured in a biaxially-oriented sidewall portion taken at location 23 (mid panel). The container having the lowest moisture content (700 ppm) had the lowest diameter changes in all of the various positions indicated. The container with the next greater moisture content (3000 ppm) had greater volume increases at each position, and the container having the greatest moisture content (5000 ppm) had yet greater increases in diameter at the various positions. Table 3 also specifies the wall thickness of the various positions. The greatest change in diameter occurred in the panel area, which is the thinnest wall portion of the container.
Table 3 also lists changes in base clearance for the three containers. The low moisture level (700 ppm) container had only a 1% change in base clearance, and it was a positive increase in base clearance. A reduction in base clearance is undesirable because at some point the hemispherical dome will extend down below the feet and the bottle will become unstable (a rocker). The 3,000 ppm container had a loss of base clearance of 8.3%. The 5,000 ppm container had an even more drastic loss of base clearance of 14.4%. Thus, the lower moisture content container had greater resistance to deformation in the base, as well as in the side wall.
Table 4 lists the height changes for the three containers, and is broken down by position and overall height change. Again, the height change in the dry (700 ppm) container was the lowest. The 3,000 ppm container had twice the overall height change of the dry container, and the 5,000 ppm container had four times the overall height change of the dry container. There was significant height change in each of the base, shoulder and neck areas of the higher moisture level containers.
Table 5 illustrates the carbonation loss which resulted from the volume growth (deformation) in the three containers. The dry container had a volume growth of 21.4 cc (4.1% of the overall container volume as blow-molded). The resulting carbonation loss was 0.34 volumes of CO2 (10.2% of the initial carbonation of 3.3 volumes of CO2). In contrast, the 3,000 ppm bottle had a volume growth of 29.0 cc (5.5%) and a carbonation loss of 0.43 volumes (12.7%). The 5,000 ppm container had a still greater volume growth of 33.5 cc (6.4%), and a resulting carbonation loss of 0.44 volumes (13.2%). Thus, controlling the moisture content of the container (as measured in the relatively thinnest biaxially-oriented panel section) resulted in a substantial improvement in reduced deformation and reduced carbonation loss. This example demonstrates that these changes can enable an extension of the shelf life and/or an improved performance over a designated shelf life.
These and other modifications will be readily apparent to the skilled person and are included within the scope of the claimed invention.
