1. Field of the Invention
This invention relates generally to the field of manufacturing plastic containers through the blow molding process. More specifically, this invention relates to an improved hot-fill type blow molded plastic container that exhibits improved resistance to deformation as a result of the considerable heat and pressure stress that is applied thereto during and after the nitrogen dosing type hot-fill process, and to processes and materials for manufacturing such a container.
2. Description of the Related Technology
Containers made of biaxially oriented or bioriented polyethylene terephthalate (PET) are in wide use throughout the world for packaging carbonated and non-carbonated beverages and other liquids. Biaxially oriented PET has good mechanical strength, a good appearance, and forms an effective barrier to the gases contained in the liquids and to the oxygen in the air, thus providing good protection against oxidation.
Perishable food and beverage products such as fruit juices are typically filled at elevated temperatures, such as 180 to 190 degrees Fahrenheit, under variable pressure conditions into specially designed PET containers in what is conventionally referred to as the hot-fill process. Container designs that are intended for use with this process are referred to as hot fill type containers. After filling, the containers are sealed by the application of a closure, preventing mass transfer into and out of the container. As the product within the containers cools, the volume that is occupied by the product decreases, thereby inducing a partial vacuum within the container that exerts an inward force upon the sidewall of the container.
The design of hot fill type containers is heavily influenced by the necessity of managing this shrinkage during cooling. Typically, the shrinkage has most commonly been accommodated by molding one or more concave vacuum panel areas into the sidewall of the container that are designed to deflect inwardly as the product cools. By substantially limiting the deformation to the vacuum panel areas, unwanted distortion of other portions of the container is prevented. In the manufacture of such containers, it is often desirable to have relatively more plastic material flow during the molding process to those areas of the container sidewall that are designed to remain rigid, and relatively less to those areas that are designed to flex. An optimal distribution of the plastic material will ensure the desired strength and flexibility characteristics for the container while avoiding waste of material.
One type of hot-fill technology that is currently under development is known as the nitrogen dosing type hot-fill process. The nitrogen dosing type hot-fill process involves injecting a dose of liquid nitrogen into the container during the hot-fill process. The liquid nitrogen gasifies, pressuring the container after application of the closure to an initial elevated pressure, which is typically on the order of about 20-25 psi. As the container cools, this pressure differential between the inside and the outside of the container will reduce itself to a slight internal overpressure. The initial pressurization and subsequent pressure adjustment, in conjunction with the heat that is inherent to the hot-fill process, places a great deal of stress on the walls of the container. Since, unlike the conventional hot-fill process, the pressure is positive, the stress that is placed on the container is different than the stress that is normally applied during a hot-fill procedure in which no nitrogen dosing is used. Conventional container designs that have worked well with the conventional hot-fill process tend to unexpectedly deform and/or fail under the overpressurization that is inherent to the nitrogen dosing process.
Typically, a blow molded PET container includes a threaded finish portion, a neck portion, a main body portion, a base portion that is either a champagne-type base, a footed base or a modified champagne-type base that has some of the characteristics of a footed base, and what is known as a heel portion connecting the main body portion to the base portion. It has been determined by the inventor that the heat and stress applied to the sidewall of the container, and particularly to the heel portion, during the nitrogen dosing hot-fill process is instrumental in causing unwanted permanent deformation of the heel portion and sidewall of the container. In designing such containers, the diameter of the base portion is normally limited to that which is needed to provide a stable contact ring for supporting the container on a flat surface. By minimizing the size of the base portion, material is conserved. At the same time, the diameter of the main body portion needs to be maximized in order to provide the required total container volume. The greater the differential between the sidewall diameter of the main body portion and the outer diameter of the contact ring of the base portion, the steeper the inclination of the heel portion. The inventor has determined that the inclination of the heel portion, and particularly the lower end of the heel portion, is material to the amount of deformation that takes place as a result of the overpressured environment within the container as a result of the nitrogen dosing process.
In forming certain types of plastic containers from a preform, it is known to utilize a preform that has a thickened sidewall portion toward the closed end of the preform in order to provide additional material that is designed to flow into the container base, usually a footed base, during molding. However, this procedure is not known in the manufacture of hot-fill type containers or nitrogen dosing type hot fill containers, which are considered separate technical areas of container manufacturing because of the different design requirements and characteristics of such containers.
A need exists in this area of technology for an improved hot-fill type container that exhibits an improved resistance to deformation during the hot-fill process, and particularly during the nitrogen dosing hot-fill process, as well as for an improved process of manufacturing such a container.
Accordingly, it is an object of the invention to provide an improved hot-fill type container that exhibits an improved resistance to deformation during the hot-fill process, and particularly during the nitrogen dosing hot-fill process, as well as for an improved process of manufacturing such a container.
In order to achieve the above and other objects of the invention, a plastic hot-fill type container that is constructed according to a first aspect of the invention includes a finish portion; a main body portion; a base portion, the base portion defining a push-up area and a chime oriented about the pushup area for supporting the container on a horizontal surface, the base portion further comprising a generally convex heel portion positioned between the chime and the main body portion, and wherein the heel portion includes a first zone having a first sidewall thickness and a second zone having a second sidewall thickness that is less than the first sidewall thickness.
According to a second aspect of the invention, a plastic hot-fill type container includes a finish portion; a main body portion having an average sidewall thickness; a base portion, the base portion defining a push-up area and a chime oriented about the pushup area for supporting the container on a horizontal surface, the base portion further comprising a generally convex heel portion positioned between the chime and the main body portion, and wherein the heel portion includes a first zone having a first sidewall thickness, the first sidewall thickness being thicker than the average sidewall thickness of the main body portion.
A plastic hot-fill type container according to a third aspect of the invention includes a finish portion; a main body portion; a base portion, the base portion defining a push-up area and a chime oriented about the pushup area for supporting the container on a horizontal surface, the base portion further comprising a generally convex heel portion positioned between the chime and the main body portion, and wherein the heel portion includes a first radiused lower portion having a first radius of curvature, a second radiused upper portion having a second radius of curvature that is greater than the first radius of curvature and a transition area where the first radiused lower portion intersects the second radiused upper portion, and wherein a line intersecting said heel portion at the transition area and intersecting an outermost edge of the chime forms an angle Φ with respect to a longitudinal axis of the container, and wherein the angle Φ is within a range of about 30° to about 42.5°.
According to a fourth aspect of the invention, a plastic hot-fill type container includes a finish portion; a main body portion; a base portion, the base portion defining a push-up area and a chime oriented about the pushup area for supporting the container on a horizontal surface, wherein the push-up area comprises an annular step ring that is segmented into a plurality of bottom steps and a plurality of concave circumferentially extending top steps, the base portion further comprising a generally convex heel portion positioned between the chime and the main body portion, the heel portion including a first radiused lower portion having a first radius of curvature and a second radiused upper portion having a second radius of curvature that is greater than the first radius of curvature; and wherein a line that is tangent to an inwardinost extension of the bottom steps and intersecting an innermost edge of the chime forms an angle β with respect to a longitudinal axis of the container, and wherein the angle β is within a range of about 30° to about 42.5°.
A method of making a hot-fill type plastic container according to a fifth aspect of the invention includes providing a preform having an open end and a closed end, the preform having a first wall portion having a first wall thickness and a second wall portion having a second wall thickness that is thicker than the first wall thickness, the second wall portion being proximate to the closed end; and blow molding the preform into a hot-fill type plastic container of the type including a main body portion, a base portion including a chime, a push-up area and a generally convex heel portion connecting the main body portion to the base portion, and wherein the step of blow molding comprises utilizing material from the second wall portion in forming the generally convex heel portion of said hot-fill type plastic container.
These and various other advantages and features of novelty that characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to the accompanying descriptive matter, in which there is illustrated and described a preferred embodiment of the invention.
Referring now to the drawings, wherein like reference numerals designate corresponding structure throughout the views, and referring in particular to
With the exception of the details described below in relation to the heel portion 17, base portion 16 is generally identical to the base portion described in U.S. Pat. No. 6,634,517 to Cheng, the disclosure of which is hereby incorporated by reference as if set forth fully herein. It should be noted that the Cheng patent is not directed to hot-fill type containers or nitrogen dosing and the design challenges presented thereby, but rather to pasteurizable plastic beer bottles.
As may best be seen in
Looking to
As may best be seen in
A plurality of integrally molded radially extending ribs 30, each having a length LR and a maximum depth DR, are spaced at regular angular intervals within the concave transition region 28. In the preferred embodiment, each rib 30 has a width that subtends an angle α, which is preferably about 30 degrees. Preferably, the ratio of the length LR of the radially extending ribs divided by the radial length LS is within a range of about 1.0 to about 4.0. More preferably, the ratio of the length LR of the radially extending ribs divided by the radial length LS is within a range of about 2.5 to about 3.0. Most preferably, this ratio is about 2.7. Preferably, maximum depth DR is within a range of about 0.05 to about 0.25 of the length LR of said radially extending ribs, and more preferably within a range of about 0.1 to about 0.18 of the length LR of said radially extending ribs. Most preferably, maximum depth DR is about 0.13 of the length LR of said radially extending ribs.
Looking again to
As may be seen in
Each of the top steps 34 of the annular step ring 24 has a radius of curvature RST, each of the bottom steps 32 similarly have a convex radius of curvature RSB. Preferably, a ratio RSB/RST is within a range of about 0.5 to about 1.0, and more preferably this ratio is within a range of about 0.65 to about 0.85. Most preferably, the ratio is about 0.75. In addition, a ratio Ra/Rb of the radius of the push-up area 26 divided by the radius of the entire base portion 16 is preferably within a range of about 0.15 to about 0.25, and most preferably is about 0.19.
The contact diameter of a champagne type base or a modified champagne type base for a molded plastic container is a major factor in the stability performance of the base both under high-pressure conditions and during filling of the container. With a given radius of contact, it has in the past been very important, but difficult, to design a base having the proper relationship between the push-up height and the overall height of the base. In determining this relationship, attention must be given to the desired material distribution and the contact point and the stress and loading distribution in the entire base. Another particularly advantageous feature of the invention is that a unique and beneficial methodology has been created for determining the optimum relative dimensions of the base portion of a champagne type base for a molded hot-fill type plastic container. Preferably, the optimum relative dimensions are determined and selected substantially according to the formula:
wherein:
Moreover, it has been found that this methodology is particularly effective when a ratio Rc/Rb is within a range of about 0.65 to about 0.74, and when Tc is within a range of about 0.06 to about 0.09 inches.
Additional details of the preferred construction of the base portion 16, and particularly the heel portion 17 of container 10 are depicted in
Preferably, the first sidewall thickness is at least 0.025 inches, and more preferably is at least 0.030 inches. The first sidewall thickness could be substantially greater than these values, with prototypes having been tested at thicknesses up to 0.070 inches. The greater the thickness, the more dimensional stability that will be imparted to the heel portion 17, with the trade-off that material costs will increase at greater thicknesses as well.
As is further depicted in
As
Preferably, first radiused lower portion 44 has a radius of curvature RH1 that is preferably within a range of about 0.05 inches to about 0.1 inches, and more preferably within a range of about 0.06 inches to about 0.08 inches. The radius of curvature RH2 of the second upper radiused portion 46 is preferably within a range of about 1 inch to about 3 inches, and more preferably within a range of about 1.5 inches to about 2.0 inches.
Additionally, it has been discovered that favorable dimensional stability is more likely to be achieved when a line that is tangent to an inwardmost extension of the bottom step 32 in the pushup region and intersecting the innermost edge of the chime 22 forms an angle β with respect to a longitudinal axis of the container 10, and the angle β is within a range of about 30° to about 42.5°. More preferably, the angle β is within a range of about 35° to about 40°.
A method of making a hot-fill type plastic container according to the preferred embodiment of the invention preferably includes a first step of providing a preform 50, best shown in
The preferred method further includes a step of blow molding the preform 50 into a hot-fill type plastic container 10 of the type described above. Preferably and advantageously, the blow molding step is performed so that material from the thickened second wall portion 58 will be used to form the generally convex heel portion 17 of the container 10. More specifically, the material from the thickened second wall portion 58 is intended to facilitate and create the increased wall thickness within the first zone 40 of the heel portion 17.
It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.
Number | Name | Date | Kind |
---|---|---|---|
4024975 | Uhlig | May 1977 | A |
4108324 | Krishnakumar et al. | Aug 1978 | A |
4134510 | Chang | Jan 1979 | A |
4249666 | Hubert et al. | Feb 1981 | A |
4785948 | Strassheimer | Nov 1988 | A |
4889752 | Beck | Dec 1989 | A |
4892205 | Powers et al. | Jan 1990 | A |
4969563 | Strassheimer | Nov 1990 | A |
4981736 | Feddersen et al. | Jan 1991 | A |
4993566 | Eberle | Feb 1991 | A |
5038947 | Strassheimer | Aug 1991 | A |
5198248 | Krishnakumar et al. | Mar 1993 | A |
5269437 | Gygax | Dec 1993 | A |
5713480 | Petre et al. | Feb 1998 | A |
5829614 | Collette et al. | Nov 1998 | A |
6077554 | Wiemann et al. | Jun 2000 | A |
6085924 | Henderson | Jul 2000 | A |
6176382 | Bazlur Rashid | Jan 2001 | B1 |
6595380 | Silvers | Jul 2003 | B2 |
6634517 | Cheng et al. | Oct 2003 | B2 |
20010002662 | Rashid | Jun 2001 | A1 |
Number | Date | Country |
---|---|---|
0 225 155 | Jun 1987 | EP |
0 413 924 | Feb 1991 | EP |
0494098 | Jul 1992 | EP |
0 668 831 | Aug 1995 | EP |
2003155015 | May 2003 | JP |
Number | Date | Country | |
---|---|---|---|
20060118508 A1 | Jun 2006 | US |