US20020166837A1

US20020166837A1 - Container side wall with ribs causing a predefined varying thickness

Info

Publication number: US20020166837A1
Application number: US09/852,186
Authority: US
Inventors: Frank Gonzalez
Original assignee: Liquid Container Corp
Current assignee: Liquid Container Corp
Priority date: 2001-05-09
Filing date: 2001-05-09
Publication date: 2002-11-14
Also published as: WO2002090213A1

Abstract

A container with an improved container side wall is disclosed. The improved container side wall including a top end and a bottom end, an open top and a bottom wall. The top of the container merges with the top end of the side wall and the bottom wall merges with and closes the bottom end of the side wall. The side wall also includes a plurality of ribs which protrude radially outward from an inside surface of the side wall and which are integrally displaced upon the inside surface of the side wall. These ribs cause the inside surface of the container side wall to form a varying thickness. In this manner, an improved container side wall is provided that increases the resistance of the side wall to deformation caused by internal/external positive or negative pressures without significantly increasing the overall amount of material needed to manufacturer the container. The container side wall may assume a cylindrical, rectangle, oval, or square geometry.

Description

BACKGROUND OF THE INVENTION

The present invention relates generally to hollow plastic containers and, more particularly, to an injection stretch-blow-molded plastic container with an improved side wall design.

Plastic containers for use in storing and transporting a variety of materials are well known in the art and hundreds of millions of plastic containers are used each year to distribute goods to consumers. The large number of plastic containers being shipped to consumers has resulted in increased competition and the need for plastic containers capable of being shipped in large quantities. Thus, the plastic container industry has been faced with the challenge of producing cheaper plastic containers that are structurally sound and that are capable of meeting the filling line, distribution system and consumer performance requirements. In order to be competitive within the container industry, manufacturers have continued to reduce the cost of plastic containers. Many manufacturers have determined that the best way to accomplish that goal is by using thinner walls and therefore, less material per container. However, since the thickness of the container walls directly affects the structural integrity of the container, manufacturers are limited in their ability to reduce the thickness of the container walls.

There are various factors that need to be considered and which ultimately define the limits on any variance in the thickness of container side walls. For example, in addition to the actual load conditions that the container is subjected to and the physical properties of the material, the production process must also be considered in combination with the performance requirements.

While it is common for the container wall thickness to vary in plastic articles, the magnitude of the variations is different dependent upon the process and the size of the article. Injection molding generally produces containers with the least amount of dimensional variation in the side walls. However, since injection stretch blow molded containers consist of generally uniform, but thin side walls, it is not uncommon to observe variations in the side wall thickness of plus or minus 30% of the nominal or average side wall thickness. For example, an 18 oz. cylindrical stock container for hot or vacuum filled products typically requires an average wall thickness of 0.025 in. Thus, the side wall thickness can vary from 0.0175 in. to 0.0325 in. This variance in the side wall thickness may result from either a one step or two step multi-cavity injection stretch blow process.

To achieve the goal of producing containers with the requisite degree of structural integrity, while also minimizing the amount of material included therein, manufacturers have designed containers with different shapes and structures. These different designs allow manufacturers to produce stronger plastic containers. Typically, the design of the uniform side wall is altered in order to incorporate different shapes that, through geometry alone, will increase the strength of the container with respect to certain load conditions. These geometric changes may vary in shape, location and design to meet the actual load conditions that are to be addressed, such as internal or external pressures versus direct mechanical axial loads, also commonly referred to as top load in the container industry.

For example, U.S. Pat. No. 4,892,205 to Powers et al., which is incorporated herein by reference in its entirety, describes an improved plastic container comprised of a base that includes a plurality of concentric ribs on the inner surface of the base. The concentric ribs are of decreasing thickness as they move radially outward from the center of the base. A concentric ribbed preform is used to manufacture that container. This improved plastic container design was intended to provide a container with improved base strength.

While the container disclosed in the '205 patent provides a stronger and more economical container base, it does not allow a manufacturer to reduce the thickness of the container side wall, which makes up the majority of the plastic container while also increasing the strength of the side wall. For improving side wall strength in containers for certain load conditions, without significantly increasing the thickness of the side wall, it is known to form beads or other similar shapes on the container side wall. This method, however, suffers the disadvantage of causing the side walls to form uneven inner and outer surfaces which, in turn, creates unacceptable problems with regard to removal of the product from the container and the application/aesthetics of labeling.

SUMMARY OF THE INVENTION

To overcome the disadvantages noted above, the present invention is directed to a container with an improved container side wall. More specifically, the improved container in a preferred embodiment includes a side wall with a top end and a bottom end, an open top and a bottom wall. The open top merges with the top end of the side wall and the bottom wall merges with and closes the bottom end of the side wall. The side wall also includes a plurality of inwardly protruding ribs integrally disposed upon the interior surface of the side wall between thinner intermediate side wall sections. These ribs and intermediate side wall sections cause the side wall to exhibit a generally smooth exterior surface, while also producing a side wall cross section of a varying thickness. In this manner, an improved container side wall is provided that increases the strength of the side wall with respect to internal and external pressures, without substantially increasing the overall amount of material needed to manufacturer the container. Therefore, an objective of the invention is to generally redistribute the material, which defines the side wall, to localized thicker sections, or ribs, interspersed between localized thinner sections, or intermediate side wall sections.

A better understanding of the objects, advantages, features, properties and relationships of the invention will be obtained from the following detailed description and accompanying drawings which set forth an illustrative embodiment and which are indicative of the various ways in which the principles of the invention may be employed.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, reference may be had to a preferred embodiment shown in the following drawings in which: [0010]
FIG. 1 shows a side view of an exemplary container embodying the present invention; [0011]
FIG. 2 shows a sectional view of the container shown in FIG. 1; [0012]
FIG. 3 shows a side view of an exemplary injection molded preform for use in forming a blow molded plastic container which embodies the present invention; [0013]
FIG. 4 shows a sectional view of the preform illustrated in FIG. 3, along line AA; [0014]
FIG. 5 shows a sectional view of an injection mold, a preform and an injection core for producing the preform shown in FIG. 3; and [0015]
FIGS. [0016] 6 shows an sectional view of the injection core and the preform shown in FIG. 5.

DETAILED DESCRIPTION

Turning now to the figures, wherein like reference numerals refer to like elements, there is illustrated an improved [0017] container 20 comprised of a container side wall of varying thickness, which is capable of producing a container 20 with a stronger side wall. The improved side wall strength is particularly advantageous as it allows the container 20 to meet the need for manufacturers of containers to reduce the thickness of container side walls without negatively affecting the structural integrity of the container 20. As will be understood by those of ordinary skill in the art, the container 20 is manufactured using standard injection blow-molding techniques.
As shown in FIG. 1, the [0018] container 20 includes an open top 22 that merges with a top end 24 a of a cylindrical side wall 24, and a bottom wall 26 that merges with and closes a bottom end 24 b of the side wall 24. The top 22 of the container 20 may also include threads 28 on the outside to engage a container cap or similar means for releasably closing the open top 22 of the container 20.
For increasing the strength of the [0019] container side wall 24, the side wall 24 includes a plurality of one or more ribs 30 that protrude radially outward from the inside surface of the container side wall 24. These ribs 30 may be of a thickness generally between 20% and 150% greater than the thickness of the intermediate side wall sections 31. The container side wall 24 also includes intermediate side wall sections 31 where the side wall 24 thickness is deliberately thinner than the average thickness of the side wall 24. Thus, the thickness of the container side wall 24 varies beyond general variations associated with the production of containers.
By varying the thickness of the [0020] side wall 24 in this deliberate manner, a side wall 24 is created that provides increased mechanical strength without a significant increase in the total amount of material that is used to form the side wall 24. Moreover, by deliberately forming the ribs 30 on the inside surface of the container side wall 24, this approach alleviates the labeling and product removal problems associated with containers that include bead designs and similar geometric variations in the shape of the container.
While the overall material usage for the [0021] side wall 24 may increase slightly in cases where the container 20 size, or conditions associated with the process for forming the container 20, limit the minimum thickness which can be utilized for the intermediate side wall sections 31, methods will be described below where the increase in wall thickness of the improved container 20 will use significantly less material than would normally be used to produce an equivalent increase in strength in a container having a uniform side wall thickness.
For producing a [0022] container 20 with a side wall 24 of varying thickness, a preform, or parison, 40 is provided that includes an open top 42 formed at a top end 44 a of a side wall 44, and a bottom wall 46 that merges with and closes the bottom end 44 b of the side wall 44. The side wall 44 of the preform also includes a plurality of ribs 48 that protrude radially outward from the inside surface of the preform side wall 44. Interspersed between the ribs are intermediate side wall sections 47 where the side wall thickness is deliberately thinner than the average thickness of the side wall 44. The combination of these features will cause the preform side wall 44 to be of a varying thickness. Since these features of the preform side wall 44 are generally maintained during the stretching process associated with stretch-blow molding plastic containers, the side wall 24 of the finished container 20 will maintain a varying thickness.
It should also be understood that the thinner intermediate [0023] side wall sections 31, 47 and the corresponding thicker ribs 30, 48 can have different angular relationships with respect to the side wall 24, 44. For example, angular displacement of up to approximately 45° will provide usable strength increases for internal or external pressure applications. To address internal or external pressure resistance ribs 30, 48 and intermediate side wall sections 31, 47 will be generally disposed in a horizontal manner.
To improve top load or direct axial strength performance it is possible to utilize [0024] ribs 30, 48 and intermediate side wall sections 31, 47, such that the ribs 30, 48 and intermediate side wall sections 31, 47 are generally vertically disposed or assume an angular relationship which is greater than 45° from the horizontal.
As shown in FIG. 5, for manufacturing a [0025] container side wall 24 with ribs 30 a mold 60 is provided that is comprised of a first half 62, a second half 64 and a core 65. The first half 62 and the second half 64 of the mold 60 cooperate to form a cavity 66 and a mold shell 67. The cavity 66 is used to form the preform 40 for the container 20. The cavity 66 is used to form the outside surface of the preform 40 and includes an open top 68 a, a side wall 70 a, a bottom wall 72 a and an aperture 74, the aperture 74 being capable of receiving molten plastic. In the preferred embodiment of the present invention, the cavity 66 may also include threaded grooves 76 at its top 68 a for forming threads 28, 50 on the outer portion of the top 22, 42 of the container 20 and the preform 40, respectively. The top 68 a merges with the top end 71 a of the side wall 70 a and the bottom wall 72 a merges with and closes the bottom end 73 a of the side wall 70 a. The molten plastic can be injected into the cavity 66 using standard techniques such as ram feeding or screw feeding.
The [0026] mold 60 further includes a core 65. The core 65 cooperates with the mold shell 67 to form the preform 40 for the container 20. More specifically, the core 65 is used to form/mold the inside surface of the preform 40, including an open top 68 b, a side wall 70 b and a bottom wall 72 b and the mold shell 67 and the core 65 may have a cooperating diameter and length ratio such that the ribs 48 do not generate a point of interference that prevents the preform 40 from being removed from the mold 60. The top 68 b merges with the top end 71 b of the side wall 70 b and the bottom wall 72 b merges with and closes off the bottom end 73 b of the side wall 70 b. The side wall 70 b of the core further includes a plurality of channels 78. The channels 78 vary in depth generally between 5% and 50% of the greatest distance between the core 65 and mold shell 67. Thus, the channels 78 are used to form the ribs 30, 48 on the container 20 and preform 40, respectively.
For producing a [0027] hollow container 20 with an improved side wall 24 using a single-step method, a preform 40 may be injection molded, the preform being comprised of a side wall 44 with an open top 42 and a closed bottom end 46, the side wall 44 also including a plurality of ribs 48 protruding radially outward from the inside surface of the preform side wall 44 thereby causing the side wall 44 to assume a varying thickness. Once the preform 40 has been produced, the preform 40 must be cooled to a predetermined temperature. Typically, this predetermined temperature is between 95° C. and 120° C. degrees. The preform 40 can be cooled in a variety of manners. For example, as is generally known in the art, the preform 40 may be cooled by conductive cooling through the side walls 68 a, 68 b of the core 65 and cavity 66 using chilled fluids.
After the [0028] preform 40 has reached the predetermined temperature, the preform 40 is stretched to a desired length. The preform 40 may be stretched by using a stretch rod to mechanically stretch the preform 40. More specifically, the stretch rod is inserted into the open top 42 of the preform 40 and then pressure is applied at the bottom end 44 b of the preform 40 in a direction away from the top end 44 a of the preform 40. Since the intermediate side wall sections 47 have a thinner cross-section than the ribs 48 of the preform side wall 44, the intermediate side wall sections 47 will cool at a faster rate. Since these intermediate side wall sections 47 are colder than the rest of the preform 40, the intermediate side wall section 47 will stretch less. Thus, the intermediate side wall sections 47 will retain the majority of their thickness during the stretching of the preform 40; hence, the intermediate side wall sections 47 of the preform 40 will be transferred into the ribs 30 on the container side wall 24 as a result of the stretching process. This will produce a container side wall 24 of a varying thickness.
Meanwhile the [0029] ribs 48 on the preform 40, or the thicker regions, will retain more heat and will be more pliable. As a result, the ribs 48 will stretch and thin to a greater extent, as compared to the intermediate side wall sections 47, and be transformed into the thinner intermediate side wall sections 31 on the container 20, as described above.
After the [0030] preform 40 has been stretched to the desired length, the preform 40 may be blow molded to a desired shape. The side wall 44 will continue, however, to maintain a varying thickness on the inside surface of the side wall. The varying thickness of the side wall 44 will allow the container side wall 44 to achieve greater structural integrity without requiring a significant amount of additional material to be added to the container side wall 44.
For producing a [0031] hollow container 20 with an improved side wall 24 using the two-step method, a preform 40 may be injection molded, the preform 40 being comprised of a side wall 44 with an open top 42 and a closed bottom end 46. The side wall 44 also includes a plurality of ribs 48 which protrude radially outward from the inside surface of the preform side wall 44, which cause the side wall 44 to assume a varying thickness. Once the preform 40 has been produced, the preform 40 may be allowed to cool to the ambient room temperature, generally between 8° C. to 50° C. After the preform 40 has reached room temperature, the preform 40 may be re-heated to a designated temperature. As is known in the art, the preform 40 may be re-heated using electrical means, hot-air heating techniques or other similar methods. This occurs because the two-step process utilizes two independent pieces of equipment, one for forming the preform and a separate independent machine for stretch blow molding.
After the [0032] preform 40 is heated to the designated temperature, the preform 40 may be stretched to a desired length and the blow molding process may be initiated. The designated temperature used to stretch the preform 40 is generally between 95° C. and 120° C. A stretch rod may be used to mechanically stretch the preform 40. More specifically, the stretch rod is inserted into the open top 42 of the preform 40 and then pressure is applied at the bottom wall 46 of the preform 44 and in a direction away from the top end 42 a of the preform 44. The ribs 48 in the two-step preform 40 have a thicker cross-section than the other portions of the preform side wall 44 and therefore, the ribs 48 will remain at a lower temperature than the rest of the side wall 44 during the reheating process. Further, since these ribs 48 are colder than the rest of the preform 40, the ribs 48 will stretch less. Thus, the ribs 48 on the stretched preform 40 will maintain their thicker cross-section as compared to the rest of the preform 40. This will produce a container side wall 24 of a varying thickness.
As the [0033] preform 40 is being stretched to the desired length, the blow molding process may begin and the preform 40 may be blow molded to a desired shape. Again, the side wall 44 will continue to maintain a varying thickness. The varying thickness of the side wall 44 will allow the container side wall 24 to achieve greater structural integrity without requiring a significant amount of additional material to be added to the container side wall 24.
When employing injection stretch blow molding techniques, a [0034] container side wall 24 of a varying thickness can be produced by several methods. This feature can be molded into the preform 40 by selectively shaping specific regions of the mold 60 for forming the preform 40. The design of these regions will vary depending upon the process that is employed. For example, to produce ribs 30, 48 that extend radially outward from the inner surface of the container side wall 24, the core 65 will include specifically shaped regions. On the other hand, to produce ribs 30, 48 that extend radially outward from the outer surface of the container side wall 24, the mold cavity 66 will include specifically shaped regions.
It is also possible to produce a [0035] container side wall 24 with a varying thickness by employing localized heating/cooling techniques. In this approach, after the preform 40 is molded but before stretching, the preform 40 is brought into contact with a shaped cooling/heating tool. This tool will have regions that will only contact specific areas of the preform for the purpose of producing a localized cooling/heating effect on the preform side wall 44. Therefore, sections with substantially colder or hotter temperatures than the average preform side wall temperature may be generated. As mentioned before, the hotter regions will stretch and thin at a greater rate than the colder. By the use of this zoned heating/cooling approach, a conventional preform can produce articles exhibiting features similar to those obtained by using a preform 40 comprised of ribs 30, 48 and intermediate side wall sections 31, 47, as described above. Since narrow diameter containers, such as water and beverage bottles have smaller tapers, or shallower draft angles, use of localized cooling/heating techniques would be particularly advantageous in forming ribs in narrow diameter containers.
It should be understood by those skilled in the art that the order of all steps disclosed in the figures and discussed above need not be performed in the exact order set forth and the measurements relating to the thickness of the side wall and the temperature ranges listed for the preform and container are provided for exemplary purposes only. In addition, it should be understood that including ribs and intermediate side wall sections and varying the side wall thickness as described herein can be employed in a variety of containers, including non-cylindrical containers. It should also be appreciated that, as an alternative embodiment of the present invention, the ribs may protrude radially outward from and be disposed on the outside surface of the preform and the container side walls. All patents discussed in this document are to be incorporated herein by reference in their entirety. [0036]
While specific embodiments of the present invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangement disclosed is meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any equivalents thereof. [0037]

Claims

What is claimed is:

1. A plastic container comprising:

a side wall;

an open top formed at a top end of the side wall;

a bottom wall merging with a bottom end of the side wall and closing the bottom end of the side wall; and

a plurality of ribs which protrude radially outward from an inside surface of the side wall and which are integrally displaced upon the inside surface of the side wall, where the ribs cause the side wall to form a varying thickness.

2. A plastic container comprising:

a side wall, where an inside surface of the side wall is of a predefined varying topography; and

a bottom wall merging with a bottom end of the side wall and closing the bottom end of the side wall.

3. A plastic container comprising:

a side wall, where an inside surface of the side wall is of a varying topography and arranged in a predefined pattern; and

4. The plastic container according to claim 3, wherein the side wall further comprises a plurality of ribs causing the side wall to form the varying thickness.

5. A preform for blow molded containers comprising:

a side wall, where an inside surface of the side wall is of a predefined varying topography;

an open top formed at a top end of the side wall; and

6. The preform according to claim 5, wherein the side wall further comprises a plurality of ribs providing the side wall with the predefined varying thickness.

7. A mold for use in an injection molding machine, comprising:

a first half and a second half of a mold shell, the first half and the second half cooperating to form a cavity therebetween, the cavity defining an exterior side wall and bottom wall, the cavity further including an aperture being capable of receiving molten plastic;

a core for cooperating with the mold shell and for defining an interior side wall and bottom wall; and

a plurality of channels formed upon the side wall of the core, where the channels are used to mold the molten plastic to form a preform side wall having a predefined varying thickness.

8. The mold according to claim 7, wherein the channels vary in depth generally between 5% and 50% of the greatest distance between the core and the mold shell.

9. A method for producing a hollow-structured injection molded plastic container, comprising:

injection molding a preform comprised of a side wall with a closed bottom end, where an inside surface of the side wall is of a predefined varying topography;

cooling the preform to a predetermined temperature;

stretching the preform to a desired length; and

blow molding the preform to a desired shape, where the side wall maintains a varying thickness.

10. The method as recited in claim 9, wherein the preform further comprises a plurality of ribs providing the side wall with the varying thickness.

11. The method as recited in claim 9, wherein cooling the preform comprises liquid cooling the preform to the predetermined temperature.

12. The method as recited in claim 9, wherein cooling the preform comprises air cooling the preform to the predetermined temperature.

13. A method for producing a hollow-structured injection molded plastic container, comprising:

injection molding a preform comprised of a side wall and a closed bottom end, where the side wall is of a predefined varying thickness;

heating the preform to a desired temperature;

stretching the preform to a desired length; and

14. The method as recited in claim 13, wherein the preform side wall further comprises a plurality of ribs providing the side wall with the varying thickness.

15. The method as recited in claim 13, wherein heating the preform comprises electrically heating the preform to the desired temperature.

16. The method as recited in claim 13, wherein heating the preform comprises heating the preform to the desired temperature with hot air.

17. A plastic container comprising:

a side wall, the side wall being comprised of a plurality of ribs, which protrude radially outward from an inside surface of the side wall, the ribs causing the side wall to have a predefined varying thickness; and

18. The plastic container according to claim 17, wherein the side wall is cylindrical.

19. The plastic container according to claim 17, wherein the side wall is rectangular.

20. The plastic container according to claim 17, wherein the ribs are uniformly spaced on the inside surface of the side wall.

21. The plastic container according to claim 17, wherein the ribs lie in a plurality of spaced, generally horizontal planes.

22. The plastic container according to claim 21, wherein the ribs extend so as to form a continuous protrusion on the inside surface of the side wall.

23. The plastic container according to claim 21, wherein the ribs extend so as to form a non-continuous protrusion on the inside surface of the side wall.

24. The plastic container according to claim 17, wherein the ribs lie in a plurality of spaced, generally vertical planes.

25. The plastic container according to claim 17, wherein the ribs lie in a plurality of spaced planes that are angled with respect to the horizontal.

26. A plastic container comprising:

a side wall, the side wall being comprised of a plurality of ribs, which protrude radially outward from an inside surface of the side wall, and a plurality of intermediate side wall sections interleaved between the ribs, the combination of the ribs and the intermediate side wall sections causing the side wall to form a predefined varying thickness; and

27. The plastic container according to claim 26, wherein the ribs will have a thickness generally between 20% and 150% greater than the thickness of the intermediate side wall sections.

28. A mold for use in an injection molding machine, comprising:

a mold shell; and

a core, wherein the mold shell and the core cooperate to form ribs having a predefined pattern on a side wall of a preform and wherein the mold shell and the core have a cooperating diameter and length ratio such that the ribs do not generate a point of interference that prevents the preform from being removed from the mold.