Method for providing a thermally-processed commodity within a plastic container

IS 2 227 239 T3

DESCRIPTION

Method of providing a heat-treated product within a plastic container.

Cross reference to associated requests

This is a continuation application in part to US Patent Application No. 09/607, 262 filed June 30, 2000, the disclosure of which is incorporated herein by reference.

Technical field of the invention

This invention relates generally to methods of providing a heat-treated product. More specifically, the invention relates to a method of providing a heat-treated product contained within a plastic container having an end section to which a closure is properly applied.

Background

Recently, manufacturers of polyethylene terephthalate (PET) containers have started supplying plastic containers for products that were previously packaged in glass containers. Manufacturers, as well as consumers, have recognized that PET containers are lightweight, inexpensive, recyclable, and can be manufactured in large quantities. Manufacturers currently supply PET containers for various liquid products, such as juices. They also want to supply PET containers for solid products, such as pickles. Many solid products, however, require pasteurization or retort treatment, which represents a huge challenge for manufacturers of PET containers.

Pasteurization and retort treatment are both methods of sterilizing the contents of a container after it has been filled and capped with a closure. Both processes include heating the contents of the container to a specified temperature, usually above 70 ° C, for a specified period of time. In low temperature pasteurization, the bottle is generally exposed to temperatures up to 75 ° C. In high temperature pasteurization, the bottle is generally exposed to temperatures above 75 ° C. Retort chamber treatment differs from pasteurization in that external pressure is applied to the vessel in the retort chamber. This overpressure is necessary, because a hot water bath is often used, and the overpressure keeps water in liquid form above its boiling point temperature at atmospheric pressure. During pasteurization or retort treatment, the end section of a typical PET container shrinks considerably. This shrinkage of the end section prevents the end section from being properly engaged with the closure, which can lead to leakage or deterioration of the product within the PET container. It has been found that the end section can be stabilized by inducing spherolytic crystallization within the finish.

PET is a crystallizable polymer, which means that it is available in an amorphous or semi-crystalline form. The ability of a PET container to resist shrinkage is relative to the percentage of the PET container that is in the crystalline form, also known as the "crystallinity" of the PET container. Crystallinity is characterized as a volume fraction by the equation:

% Crystallinity = ——— x100

Pc ^{- p}where p is the density of the PET material, p_to is the density of the pure amorphous PET material (1.333 g / cc); And p_c is the density of the pure crystalline material (1.455 g / cc). The crystallinity of a PET container can be increased by mechanical treatment and by heat treatment.

Mechanical treatment involves orienting the amorphous material to achieve strain hardening. This treatment commonly involves stretching a PET container along a longitudinal axis and expanding the PET container along a transverse axis. The combination favors biaxial orientation. Manufacturers of PET bottles make use of mechanical treatment to produce PET bottles that have approximately 25% crystallinity (average crystallinity of the side wall).

Thermal treatment involves heating the material (either amorphous or semi-crystalline) to promote crystal growth. Applied on amorphous material, the heat treatment of the PET material results in a spherolytic morphology that interferes with the transmission of light. In other words, the resulting crystalline material is opaque (and generally undesirable on the side wall of the container). Applied after mechanical treatment, however, heat treatment results in higher crystallinity and excellent clarity. Heat treating an oriented PET container, which is known as thermal stabilization, typically includes blow molding a PET preform against a heated blow mold, at a temperature of 120-130 ° C, and holding the container blown against the mold for approximately three seconds. Manufacturers of PET juice bottles, which must be hot filled at a temperature of about 85 ° C, currently use heat stabilization to produce PET juice bottles that have a margin of up to 25-39% of crystallinity in its lateral walls and of more than 30% in its terminal sections. Although these

ES 2 227 239 T3 hot filled PET containers present a significant improvement over non-hot filled PET containers, they cannot adequately prevent shrinkage of the end section to be properly applied with closure. Depending on the diameter of the terminal section and on the temperature and duration of the heat treatment, these crystallized terminals have been measured and have exhibited contractions in the range of 0.4% to 0.8%. With contractions in that range, an induction seal is required, in addition to the closure cap, to ensure seal integrity. This increases the cost and complexity of treating the container.

Therefore, manufacturers of PET containers desire an efficient and inexpensive method of providing a PET container for a heat-treated product within a PET container that has a properly dimensioned end section and is applied with a closure. It is therefore an object of this invention to provide such a method.

Summary of the invention

The present invention includes a method for providing a PET container, which, after heat treatment of the product within the plastic container, has a terminal section defining a terminal diameter of a predetermined value, so as to ensure correct sealing. of the container. The invention also includes a method of providing a heat-treated product that overcomes the problems and disadvantages of the usual techniques in the art.

The present invention, in a preferred embodiment, is a method of providing a heat-treated product that includes providing a plastic container having a terminal section that defines a diameter of the terminal greater than the predetermined value. Then, dispense a product into the plastic container and cover the container with a lid designed for application with a terminal having a diameter of the predetermined value. Then, heat treating the product inside the plastic container and shrinking the diameter of the terminal during heat treatment from being greater than the predetermined value to approximately the predetermined value. With a terminal diameter of approximately the predetermined value, the terminal section will properly engage with the closure, seal the closure, and prevent deterioration of the product within the plastic container.

The present invention, in an alternative preferred embodiment, is a method of providing a heat-treated product that includes providing a plastic container having a terminal section that defines a diameter of the terminal that is within a predetermined range. Next, dispense a product into the plastic container, and cover the container with a lid designed to engage with the terminal section that defines the diameter of the terminal. Then, heat treating the product inside the plastic container, the terminal section defining the diameter of the terminal at the end of the heat treatment, which is also within the predetermined range. With the end section within the predetermined range, the closure maintains a tight seal, to prevent spillage of the product due to rupture of the seal.

Other features and advantages of the present invention will become apparent from the study that follows and the accompanying drawings.

Brief description of the drawings

Figure 1 is a side view of the plastic container system of the preferred embodiment of the invention, shown with the plastic container and closure of the preferred embodiment of the invention.

Figure 2 is a side view of the plastic preform of the preferred embodiment of the invention.

Figure 3 is a side view of the plastic container system of an alternative embodiment of the invention, with an initial end section and the closure.

Figure 4 is a side view of the plastic container system of the alternative embodiment of the invention with an intermediate end section and the closure.

Figure 5 is a side view of the plastic blank of the alternative embodiment of the invention.

Detailed description of the preferred embodiment

The description that follows of the preferred embodiment is by way of example only, and is in no way intended to limit the invention or its application or uses.

As illustrated in Figure 1, the plastic container system 10 of the preferred embodiment of the invention includes a plastic container 12 and a closure 14. The plastic container system 10 has been specifically designed to hold a product for a period of time. heat treatment, such as a high temperature pasteurization or retort treatment. The plastic container system 10 can be used to hold a product during other heat treatments as well.

IS 2 227 239 T3

The plastic container 12 of the preferred embodiment of the invention includes a terminal section 16 with thread members 22 that include a diameter of the initial terminal 17. The plastic container 12 also preferably includes a side wall section 18 that extends generally downward from the end section 16 and a base section 20 that extends generally inwardly from the side wall section 18 and closes the bottom end of plastic container 12. The plastic container 12 may alternatively include other sections, such as a handle section, a grip section, a panel section, or a label section. The plastic container 12 is preferably made of a PET material, but may alternatively be made of other suitable materials, including, for example, polyethylene naphthalate (PEN) and a PET / PEN blend or copolymer.

The closure 14 of the preferred embodiment of the invention functions to engage with the end section 16 of the plastic container 12. To achieve this, the closure 14 preferably includes thread members corresponding to the thread members 22 of the end section 16, but alternatively It may include other suitable devices to be applied to the terminal section 16 of the plastic container 12. The closure 14 is preferably made of a plastic or metallic material usual for the closure industry and suitable for subsequent heat treatment, including high temperature pasteurization and retort treatment.

The preferred use of the plastic container system 10 includes dispensing a product into the plastic container 12, applying the closure 14 with the end section 16, and heat treating the product within the plastic container system 10. After application of closure 14 to end section 16, but prior to heat treatment of the product, closure 14 and end section 16 require a first torque to remove closure 14 from end section 16. The first torque is preferably about 57.61 kg-cm, which is greater than the maximum torque that a typical person can generate. In other words, most people would not be able to remove the closure 14 from the end section 16 prior to heat treatment. After heat treatment of the product, removing the closure 14 from the end section 16 requires a second torque. The second torque is preferably about 17.28 to 23.04 kg-cm, which is less than the maximum torque that can be generated by a typical person. In other words, most people will be able to remove the closure 14 from the end section 16 after the heat treatment.

Detailed description of the preferred method

The preferred method of the invention provides a heat-treated product that is contained within the plastic container system 10. The system 10 includes providing the plastic container 12, inducing crystallinity in the end section 16 of the plastic container 12, dispensing a product into the plastic container 12, capping the container 12, heat treating the product within the plastic container 12, and allowing the end section 16 to contract such that the closure 14 and end section 16 are properly engaged to produce an acceptable seal. The preferred method has been specifically designed to provide a heat treated product contained within the plastic container 12 made of a PET material. The preferred method may also provide a heat-treated product contained within the plastic container 12 made of other equally suitable materials.

To provide the plastic container in accordance with the preferred method of the invention, the plastic container 12 is provided with the terminal section 16 defining a diameter of the initial terminal 17 greater than a predetermined value. The diameter of the initial terminal 17 is preferably calculated based on the outer diameter T of the thread members 22 in the terminal section 16 of a blank 24, as illustrated in Figure 2. The diameter of the initial terminal 17 may alternatively be calculated on the basis of the outer diameter E of the terminal section 16 of the blank 24. The predetermined value is preferably one of several commercially acceptable values, such as 63mm or 82 mm, so that it can be applied with the closure 14 of a similar size. The default values ​​of 63mm or 82mm qualify the plastic container 12 as a “wide-mouth” plastic container, since the diameter of the initial terminal 17 will be greater than one third (1/3) of the total diameter. of the container. The predetermined value may alternatively take other suitable values ​​depending, among other factors, on the product contained within the plastic container 12. To provide the plastic container, the plastic preform 24 may be provided or inserted into a mold cavity, and expanded and stretched to substantial conformity with the mold cavity to form the plastic container 12.

After the plastic container is formed, crystallinity is induced in the end section. To accomplish this, a high temperature fluid is circulated over, or directed to, the outer portion 26 of the end section 16. The high temperature fluid is also caused to be directed to, or circulated over, a containment plug. (not shown), which is applied to an inner portion 28 of the end section 16. The use of the containment plug contains the end section 16 to substantially prevent shrinkage of the end section 16 beyond a secondary predetermined size, as determined by the diameter of the containment plug, while inducing crystallinity in the section. terminal. When these steps are followed, crystallinity greater than 30% crystallinity, such crystallinity and 40% crystallinity are achieved. Induction of crystallinity in end section 16 may alternatively include other suitable steps.

After the terminal section 16 has crystallized, a product is dispensed into the plastic container and the closure 14 is applied to the terminal section 16. The closure 14 is designed to be applied to the terminal section 16 that has a terminal diameter of the final default value. However, terminal section 16, when applied

ES 2 227 239 T3 first with closure 14, has a terminal diameter greater than the final predetermined value. For this reason, it is difficult to apply the closure 14 to the end section 16 and the aforementioned increased torque is required for this. To apply the closure 14 to the terminal section 16 of that predetermined secondary size, the closure 14 may be softened prior to applying it to the terminal section 16. The softening to thus make expansion of the closure 14 possible is preferably effected by heating the closure 14 with steam, but may alternatively be carried out by other suitable heat treatments.

With the product sealed in the plastic container 12, the product is heat treated, thereby inducing shrinkage of the end section from the second predetermined value to the final predetermined value. During heat treatment, such as a retort chamber treatment at 121 ° C for 60 minutes, a terminal diameter of 63 mm (38% crystallinity) was found to shrink by approximately 0.4%. Actual terminal diameter shrinkage is a function of several factors, including terminal diameter, terminal crystallinity, heat treatment temperature, and duration of heat treatment. Due to the use of the diameter of the wide-mouth terminal and the exposure to high temperature during the long period of heat treatment, the contraction of the terminal section 16 may prevent proper application of the terminal section 16 with the closure 14. This can lead to deterioration or leakage of the product contained in the container. To overcome these problems, the preferred method of the invention includes forming the plastic container 12, prior to heat treatment, with the terminal section 16. The terminal section 16 has a secondary terminal diameter (after crystallization) that is greater than the default value. This allows the diameter of the secondary terminal to shrink, during heat treatment, to the predetermined value. Counting with these steps, the preferred method of the invention provides a heat-treated product within the plastic container 12 having the end section 16 properly engaged with the closure 14.

According to this method, a container with a diameter of the injected molded terminal is further manufactured in such a way that the diameter of the terminal is formed into a diameter of the secondary terminal. As mentioned above, this additional fabrication may include crystallization of the terminal section and containment of shrinkage during crystallization, such that the diameter of the secondary terminal is larger than the diameter of the final terminal desired. . Depending on the factors influencing shrinkage, as noted above, the diameter of the secondary terminal will be within a predetermined range greater than the diameter of the desired terminal. During heat treatment, the end section will contract from the diameter of the secondary end to within a predetermined range of the diameter of the end end. The phrase "predetermined margin", as used herein, means the predetermined value of the diameter of the end terminal, which is the ideal value for the correct application between the terminal section 16 and the closure 14, plus or minus a predetermined tolerance. This tolerance balances the need for a correct application of the closure 14 with the end section 16 against the need for a high performance manufacture of the plastic container 12.

Due to the shrinkage of the end section during heat treatment, the fit between the closure 14 and the end section 16 is within an acceptable range, and the typical consumer can easily manipulate the closure 14 to open the plastic container 12.

Detailed Description of an Alternative Preferred Embodiment

The description that follows of an alternative preferred embodiment is by way of example, and is not intended in any way to limit the invention or its applications or uses.

In Figures 3-5, an alternative preferred embodiment of the plastic container system is depicted. Referring specifically to Figure 3, the alternative preferred embodiment plastic container system 200 includes a plastic container 112 and closure 14. As with the preferred embodiment, the plastic container system 200 is designed to contain a product during heat treatment, such as, for example, high temperature pasteurization or retort treatment. As with the preferred embodiment, the plastic container system 200 can also be used to contain a product during other types of methods and heat treatments.

Returning to Figure 3, the plastic container 112 of the alternate preferred embodiment includes an end section 116 having thread members 122 and a diameter 117 of the end. The plastic container 112 of the alternate preferred embodiment further includes the side wall 18 that extends downwardly from the end section 116 and the base section 20 that extends generally inward from the side wall 18, closing the lower end of the plastic container 112. As in the preferred embodiment, the plastic container 112 may alternatively include other sections, such as a handle section, a grip section, a panel section, or a label section. The plastic container 112 is preferably constructed of a PET material, but may alternatively be made of any other suitable material to form a plastic container.

The closure 14 of the alternative preferred embodiment is configured, constructed and applied to the plastic container 112 as previously described.

Similar to the preferred use of the plastic container system 10, the plastic container system 200 includes dispensing a product into the plastic container 112, applying the closure 14 to the intermediate end section 116a, and heat treating the product within the plastic container system 200. Unlike

ES 2 227 239 T3 plastic container system 10, however, plastic container system 200 requires approximately the same torque to remove closure 14 from end section 116 following heat treatment of the product as before treatment thermal product. More particularly, the torque required to remove the closure 14 from the terminal section 116 in the plastic container system 200 is such that most people could remove the closure 14 from the intermediate terminal section 116a prior to treatment. product heat as well as after heat treatment.

Detailed description of the alternative preferred method

With reference to Figures 3-5, the alternate preferred method of forming the alternate preferred embodiment is carried out through a two-step process. More particularly, generally speaking, the plastic container 112 depicted in Figure 4 is formed from a preform 124 depicted in Figure 5, through any one of several acceptable processes. After forming the container 112 depicted in Figure 4, an intermediate end section 116a is formed by inducing crystallinity through the application of thermal energy, resulting in an appropriate degree of shrinkage. Optionally, to achieve in addition to the desired shrinkage the disappearance of the stresses within the material, the intermediate terminal section 116a is subjected to annealing by applying thermal energy. The plastic container 112 is then filled with a product, the closure 14 is applied, and the product is heat treated. Following heat treatment, end section 116 and end diameter 117 of plastic container 112 are within the predetermined range. The predetermined range has been defined as that of acceptable shrinkage that end section 116 can result without affecting sealing of closure 14 following heat treatment. This range is preferably +12.7 microns to -25.4 microns. It is to be understood that this margin may vary based on numerous parameters, as described herein. It should also be understood that the margin takes into account growth in certain directions, including, for example, changes in ovalization.

Continuing with reference to the plastic container 112, as referenced in Figure 4, the intermediate end section 116a is first formed through the preform 124 shown in Figure 5. The preform 124 has the initial diameter 117 of the end, which is preferably calculated based on the outside diameter T of the thread members 122, or alternatively based on the outside diameter E, as illustrated in Figure 5. As noted above, the intermediate terminal section 116a, and therein the intermediate diameter 117a of the terminal, undergoes a predetermined amount of shrinkage following induced crystallization through the application of thermal energy. The predetermined range, as described in detail herein, is the acceptable range for which any further shrinkage of intermediate end section 116a to end section 116 during heat treatment of the product does not result in rupture of the seal. . The predetermined range is determined based on the most suitable values ​​and factors, including the material used in the construction of the plastic container 112, the product retained within the plastic container 112, the heat treatment method used, and other factors.

Finally, it should be understood that the alternative preferred embodiment is achieved through a two-step process that results in obtaining the desired shrinkage of the intermediate terminal section 116a, and therein of the intermediate diameter 117a of the terminal, such so that after a product is dispensed and the closure 14 is applied, the heat treatment can produce additional shrinkage and / or growth of certain dimensions, within the predetermined range, to get the terminal section 116 having the diameter 117 of the terminal.

Returning to Figure 4, the plastic container 112 having the intermediate end section 116a is subjected to known methods to induce crystallinity. An example of achieving crystallinity is to circulate high temperature fluid over, or directed to, the outer portion 126 of the intermediate end section 116a. The high temperature fluid may also be directed to, or circulated over, a containment plug (not shown), applied to an interior portion 128 of the intermediate end section 116a. Therefore, crystallization can be carried out without any containment plug (free crystallization), or with a containment plug (contained crystallization). Free crystallization requires that a cooling plug (sizing), not shown, be inserted into and applied with end section 116 after crystallization has been completed. As already described in the preferred embodiment and in the method for the preferred embodiment, the use of these types of steps results in a crystallinity greater than 30 percent. Optionally, the container 112 represented in Figure 4, which has the intermediate end section 116a, can be further treated in order to achieve a greater degree of contraction and stability of the end section 116, as reflected in Figure 3 .

According to conventional crystallization techniques, since the intermediate end section 116a is actively cooled after crystallization is complete, stresses can be introduced into the plastic container 112. For certain applications that exist today, ie hot fill ( up to 97 ° C), the intermediate end section 116a remains adequately dimensionally stable to function properly. However, treating crystallized end containers under high temperature pasteurization or retort treatment may expose the intermediate end section 116a to a sufficient time and temperature to cause the dimensions to change enough to interfere. with a correct closing function. In order to better control shrinkage and induce stability, an annealing of the intermediate end section 116a is optionally desirable. Specifically, the induced crystallization takes place in a contained (plug) mode as described. Instead of cooling the intermediate end section 116a, it is kept at a high temperature (eg, 90-150 ° C) until the moment of expulsion of the plug. This so-called annealing temperature must

ES 2 227 239 T3 should preferably be 5 to 60 ° C higher than the end-use temperature to which the terminal will subsequently be exposed, for example, in a retort treatment at 121 ° C, an annealing temperature appropriate may be 150 ° C. Removal of the containment plug produces the free annealing effect of the terminal. Since injection stresses equalize during the crystallization process, the shrinkage that occurs is dictated by the diameter of the containment plug. Since all the containment plugs used are of a similar diameter, the final dimensions achieved after that annealing step are considered. Subsequent reheating of intermediate end section 116a, such as occurs during pasteurization (or hot fill) treatment, or retort treatment, results in little or no additional dimensional change in end section 116, i.e. , that the terminal section 116 remains within the predetermined range, making the terminal section 116 and therein the diameter 117 of the terminal, shown in Figure 3, are appropriate to maintain a seal after heat treatment of the product.

According to an alternative approach to the optional annealing treatment described above, after crystallization, free or contained, the container 112 is removed from the crystallization machine, and a further heat treatment is performed on the intermediate end section 116a. The container 112 may be taken directly from the crystallization machine (i.e., the intermediate end section 116a at a temperature above room temperature), or at a later time (or place) when the intermediate end section 116a has balanced its temperature with that of the surrounding environment. In either case, the intermediate end section 116a is exposed to elevated temperatures, eg, 90 ° C-150 ° C, for a short period of time, eg, 1-30 seconds. This results in the stresses in the terminal created by the cooling operation being removed by annealing, such that subsequent heat treatment results in little or no dimensional change in the intermediate terminal section 116a, that is, the section terminal 116 remains within the predetermined range. This heating method may consist of using infrared (IR) lamps, hot air, or any other suitable source as sources. This operation can be carried out, for example, by conducting the parts through an annealing furnace as they are led from the blow molds downstream.

An example of the treatment dimensions for one or other of the methods referred to in the alternate preferred embodiment is shown in Table I below.

TABLE I

<td>Contained crystallization Treatment involves removing the containment plug while the terminal is at elevated temperature, for example 150 ° C, using residual heat to anneal</td><td>82mm CT terminal Change (microns) T 90</td><td>Average (mm) T PL T90</td><td>Average T PL</td>

<td></td><td>'Crystallized *</td><td> 80,167 80,046</td><td></td>

<td></td><td>'After Treatment *</td><td> 79,421 79,273</td><td> -746,76</td>

<td></td><td> -77,21</td><td></td><td></td>

<td></td><td>'After the Process *</td><td> 79,317 79,284</td><td> -104,14</td>

<td></td><td> 10,16</td><td></td><td></td>

<td></td><td colspan="3">The process consists of 30 minutes of exposure to a water bath at 97 ° C</td>

<td>Contained crystallization The treatment involves exposure to 127 ° C</td><td>83mm terminal 4-wire Average Change (microns) T 90</td><td>Average (mm) T PL T90</td><td></td>

<td></td><td>'crystallized *</td><td> 62,073</td><td> 62,098</td>

<td></td><td>'After the Process *</td><td> 61,836</td><td> 61,808</td>

<td></td><td colspan="3">The process consists of cooking for 30 minutes at 121 ° C in a retort chamber</td>

CT = continuous thread

T = dimension of the outside diameter of the thread

PL = division line

T 90 - 90 ° from measurement T PL

IS 2 227 239 T3

It should be understood that although the study made above has been carried out on blown bottles, the methods described are equally applicable to preform terminals. More particularly, the preform 124 having the initial end section 116 can be crystallized to a certain intermediate diameter and optionally annealed as described above. This can be achieved by the same methods and treatments described herein, expressed differently, the preform 124 can be treated to include an intermediate terminal section 116a, as illustrated in Figure 4, having a diameter of the intermediate terminal 117a before that the preform 124 is treated (blown) into a plastic container 112. It should also be understood that the methods and processes described herein can be carried out separately, such as, for example, crystallizing the initial end section 116 of the preform 124 and the annealing of the intermediate end section 116a of the plastic container 112. , after the plastic container 112 has been formed.

Returning to the method of forming the plastic container 112 shown in Figure 4, the container 112 is filled with a product and the closure 14 is secured to the intermediate end section 116a to seal the container 112. Optionally, closure 14 may be heat treated to an appropriate temperature, such as by steam or hot air, to radially expand or soften closure 14 to form an intermediate closure (not shown) if the torque required to secure closure 14 to container 112 is too large. Thermal energy is then transferred to the plastic container 112, and therein to the product, to heat the plastic container 112 above the glass transition temperature. This can cause another part of the amorphous material to crystallize and contract slightly. Whether or not shrinkage occurs, the dimensions of end section 116, including thread members 122 and end diameter 117, remain within the predetermined range for one of several commercially available bottle end sections, such as those available. 63 mm and 82 mm, so that it is applicable with the closure 14 of a similar size. The resulting plastic container 112 has the end section 116 that ensures a tight seal maintained with the closure 14.

The two-step crystallization process described above compensates for the contraction of the end section 116 in a controlled manner, and ensures the correct sealing function of the closure 14 in the container 112 during the heat treatment of the product.

Certain preferred methods and preferred embodiments of the invention have been set forth and described in the above study. Those skilled in the art will recognize, in light of such study and the accompanying drawings and claims, that changes and modifications may be made to the invention without departing from the true spirit or going beyond the true scope of the invention, such as this is defined in the claims that follow.