WO2002026582A1

WO2002026582A1 - Thin-walled skirt for cap

Info

Publication number: WO2002026582A1
Application number: PCT/US2001/030586
Authority: WO
Inventors: Charles L. Williams; David Jochem
Original assignee: Berry Plastics Corp
Current assignee: Berry Global Inc
Priority date: 2000-09-29
Filing date: 2001-09-28
Publication date: 2002-04-04
Anticipated expiration: 2003-03-29
Also published as: AU2001293194A1

Abstract

A cap skirt (22) formed from high density polyethylene which has an annular wall thickness (38a) of less than 0.035 of an inch, and at least one thread (26) formed in the interior surface (25) of the annular wall (23) of engaging a threaded neck (34) on the container. Preferably, the thickness of the annular wall is less than 0.031 of an inch and may range as low as 0.024 of an inch. The reduction in the thickness of the annular side wall results in a skirt which can be formed using significantly less resin than used to form conventional closure skirts of similar size. This reduction can lead to a significant cost savings for the manufacturer.

Description

Thin-Walled Skirt for Cap

FIELD OF THE INVENTION

The invention relates to a novel skirt for a closure or cap for sealing a container, more specifically, to a lightweight cap skirt having a thin annular side-wall.

BACKGROUND OF THE INVENTION

It is well known to use a plastic closure or cap having a top, downwardly extending skirt, and threads arranged on the skirt which are designed to engage a threaded neck on the container. Typically, such container caps have been made of low-density polyethylene (LDPE). That material has been deemed advantageous because it has sufficient flexibility to provide a "snap-on" feature in which the threads on the closure can jump over the threads on the neck of the container when downward axial pressure is placed on the cap. This allows a filler or bottler to close and seal the container by applying downward pressure on the cap, yet allows the end user to twist the cap to remove it from the bottle. Such "snap-on", "screw-off style caps typically utilize multiple fine threads having multiple leads which can more readily jump the threads on the neck of the container during bottling than a single coarse thread. U.S. Patent No. 4,625,875 issued to Carr discloses a "snap-on," "screw-off cap. The caps made in accordance with the Carr patent require a slight rotation after the cap is snapped on by axial pressure to ensure a tight seal.

It has been recognized that light weight caps are desirable due to cost savings resulting from the decreased amount of plastic resin needed to make such caps. One way to attempt to reduce the weight of a cap is to reduce the thickness of the annular side wall forming the skirt. It has been found that the prior LDPE caps required a skirt having a minimum thickness of about .037 of an inch as measured along the annular wall at a location remote from the threads. This skirt thickness was necessary to provide sufficient strength to the skirt to ensure that the threads of the skirt firmly engage the threads of the neck to form and maintain a secure seal. LDPE caps of this thickness have also been found to provide sufficient flexibility to allow their multiple threads to jump over threads on a container neck to provide a "snap-on" capability in response to a downward axial pressure.

The .037 inch minimum skirt thickness were also deemed necessary for LDPE caps in order to prevent an "over-torque" situation in which over-tightening of the cap causes the threads on the cap to jump past the threads of the container. This tendency can make it more difficult than desirable for the bottler to properly seal the container. Even caps with skirt thickness in excess of .041 of an inch have been found to be more susceptible to "over-torque" than is desirable.

Another problem with fluid containers is that they are sometimes roughly handled by retailers or consumers, e.g., by violently tipping them over or dropping them. Prior caps had a tendency to become loosened more often than is desirable during such rough handling of the container. This loosened condition was usually due to prior LDPE caps' insufficient resistance to deformation of the container to maintain proper contact between the threaded surface of the cap and container. Thus, it would be desirable to have a threaded skirt which provides increased resistance to over- torque and to deformation during rough handling.

Another problem with prior LDPE caps is that the frangible bridges used to hold a tamper-evident band onto the skirt can become stretched or broken during bottling or handling of the container. Such partial breakage or visible stretching of the bridges may be treated as evidence of tampering with the fluid of the container by retailers or consumers when, in fact, the seal is still intact and no tampering has occurred. Such "false-positive" evidence of tampering can lead to rejection and disposal of otherwise perfectly acceptable container of fluid products. Accordingly, there is a need for a cap skirt having a tamper-evident band that is less susceptible to breakage or stretching during bottling or handling of a container.

One patent refers to the use of high density polyethylene in the manufacture of a portion of a plastic cap. For example, U.S. Patent No. 5,213,224 issued to Luch discloses the use of high-density polyethylene (HDPE) for use in the tear band of a closure. Luch does not disclose the use of HDPE for forming the remainder of a container cap, such as a cap skirt and does not disclose the use of a reduced weight cap made of HDPE. U.S. Patent No. 5, 762,218 discloses a plastic seal for bottle having an inner sealing ring with a plurality of reinforced ribs. The plastic seal may be formed from HDPE. The side walls of the cap disclosed in the '218 patent are believed to be at least .041 inch thick since the sealing cap is designed for use with a carbonated beverage which can be subject to an internal pressure of up to 25 bar. Thus, the side wall skirt of the '218 patent has a thick, substantially rigid skirt to prevent deformation due to internal pressure from the carbonated beverage. Further, due to this rigid design, the cap of the '218 patent is not believed to be capable of providing a "snap-on" function.

U.S. Patent No. 5,553,727 issued to Molinaro discloses a "snap-on" cap which, in one embodiment, is disclosed to have been made of HDPE. Both the LDPE and HDPE caps are disclosed and are shown as having the same side wall thickness which is believed to be about .041 of an inch. Thus, the HDPE skirt disclosed in Molinaro would use an undesirably large quantity of plastic resin to form the skirt.

SUMMARY OF THE INVENTION

The present invention is directed to a cap skirt formed from HDPE which has an annular wall thickness of less than .035 of an inch, and at least one thread for engaging a threaded neck on the container. Preferably, the thickness of the annular wall is less than .031 of an inch and may range as low as .024 of an inch. The reduction in the thickness of the annular side wall results in a skirt which can be formed with as much as 27% less resin than used to form conventional closure skirts of similar size. This reduction can lead to a significant cost savings for the manufacturer. Moreover, HDPE resin is typically less expensive than LDPE resin which can result in additional cost savings. For purposes of this application, the thickness of the annular wall is defined as one half of the difference between the exterior wall dimension and the thread major dimension of the skirt. Preferably, the cap skirt of the invention may also include seventy-five or fewer gripper ribs located on the exterior surface of the annular side wall of the skirt. Prior cap skirts frequently had as many as 100 gripper ribs to facilitate gripping of the exterior surface of the skirt during twisting on or twisting off a cap. Lightweight skirt caps of one preferred embodiment of the invention having thinner side walls and fewer gripper ribs may be formed with as much as one-third less resin than prior cap designs for use on a similar sized container.

In one embodiment of the invention, a snap-on, twist-off skirt is provided having improved over torque resistance characteristics. Such cap skirts have an annular wall formed from HDPE, a plurality of multi-lead threads, and a torque resistance of at least 10 inch pounds, preferably more than 13 inch pounds, to thread jumping after rotation into sealing position. The skirt of this embodiment of the invention provides the bottler with a substantially greater margin for enor for twist- tightening a cap without fear of over-tightening to the point that the skirt threads jump the threads of the neck. Preferably, such a skirt also provides improved removal torque characteristics which helps prevent inadvertent loosening of the cap during rough handling.

In another embodiment of the invention, a skirt is provided which includes an annular side wall having a bottom edge, a tamper-evident band extending downwardly from said bottom edge of said annular wall, and a plurality of bridges formed from HDPE joining the band and annular wall. Such bridges are significantly more resistant to breaking or visibly stretching during bottling or handling which may give rise to a "false positive" tamper-evident condition and may cause the otherwise acceptable fluid product to be discarded. The HDPE bridges have sufficient rigidity and strength to resist at least three inch pounds of torque prior to severing when the skirt is removed from a container.

BRIEF DESCRIPTION OF THE FIGURES

FIGURE 1 is a perspective view of a cap skirt according to one embodiment of the present invention along with a cap and container.

FIGURE 2 is an enlarged perspective view of the cap skirt, cap and container of Figure 1 with the cap removed and tamper-evident band seated on the neck of the container.

FIGURE 3 is a cross-sectional view of the skirt and cap of Figure 1.

FIGURE 4 is a top plan view of the cap of Figure 1. FIGURE 5 is a bottom plan view of the cap of Figure 1 with tamper-evident band removed.

FIGURE 6 is a cross-sectional view of a cap skirt of another embodiment of the present invention.

FIGURE 7 is an enlarged cross-sectional view of the cap of Figure 1.

FIGURE 8 is an enlarged cross-sectional view of a prior art LDPE cap.

FIGURE 9 is a cross-sectional view of the container of Figure 1 taken along lines 9-9.

FIGURE 10 is an enlarged partial cross-sectional view of the cap of Figure 4 taken along lines 10—10 with the size of the ribs enlarged for ease of viewing.

DETAILED DESCRIPTION

Referring generally to the embodiment of the invention shown in FIGS. 1-5, a container closure or cap 20 is shown having a top 21 and a downwardly extending skirt 22 with a plurality of threads 26 formed in the inner surface 25 of its annular wall 23. A tamper-evident band 28 extends below the annular wall 23 and is connected thereto by frangible bridges 30. As shown in FIG. 1, cap 20 is designed to seal a container 32 by seating on a container neck 34 with skirt threads 26 engaging neck threads 35.

As shown in FIG. 3, the skirt 22 has a total of four threads 26 having four leads 36 formed in the inner surface 24 of the annular wall 23 of the skirt 22. In this embodiment, the multiple threads and multiple thread leads assist in providing a skirt 22 with sufficient flexibility to provide a snap-on/twist-off capability. The multiple threads 26 are preferably sized, angled and pitched so that they can slide over neck threads 35 in response to downward axial pressure applied during bottling. A wide variety of numbers of threads having differing length, height, pitch and angle of opposite faces may be utilized in the skirt of the present invention. Preferably, for snap-on, twist-off skirts, the number of threads is between four and eight, the height of the threads is about .027 of an inch and may be between about .025 to about .035 of an inch; the pitch of the threads is preferably .047 of an inch but may vary from about .045 to about .060 of an inch; the angle defined by opposite faces of the threads 26a and 26b of the threads is preferably 30°, but may be from about 25° to about 40°; and, each thread preferably extends about 220° around the inner surface 24 of the annular wall 25, but may extend between 180° and 240°.

The skirt 22 is made of high density polyethylene ("HDPE") material and formed by a conventional injection molding process. The use of HDPE material allows the use of a substantially thinner annular wall 23 for the skirt 22 and therefore requires significantly less material to form than the annular wall of conventional LDPE caps. Surprisingly, skirts designed in accordance with the embodiment shown in FIGS. 1-5 are flexible enough to jump threads during application of downward axial pressure in the course of bottling and have improved resistance to over-torque, "false positive" tamper evidence, as well as deformation during rough handling. As set forth previously, the thickness 38 of the annular side wall is defined as one-half of the distance between exterior wall dimension 39 and the thread major 40 dimension See FIG. 3). As illustrated in FIGS. 3, 7 and 8, the side-wall skirt of the present invention is preferably about .027 of an inch, but may range from about .024 to about .035 inches. Whereas the prior caps made of an LDPE material had a lower limit of about .037 of an inch for the side-wall thickness. The reduction in thickness of the annular side- wall 23 is illustrated by a comparison of dimension 38a of FIG. 7 with dimension 38b of FIG. 8. This reduction in the thickness of the annular wall 23 results in a cap which may weigh as much as 27% less than a conventional skirt made of LDPE of similar design. The result is an HDPE skirt which preferably weighs as little as .73 grams (excluding the weight of the tamper-evident band), but can range between .65 and .80 grams. In contrast, conventional LDPE cap skirts of similar design typically weighed at least .93 grams.

As shown in FIGS. 2 and 10, the skirt 22 has a number of ribs 42 formed on the exterior surface 25 of the annular wall 23. As shown in FIG. 10, the ribs 42 preferably extend about .014 of an inch radially outwardly from the exterior surface 25 of the skirt to a flattened rib outer surface 44. Ribs 42 have angled side surface 46a and 46b which are preferably angled at about 60° from one another. The ribs are preferably slightly drafted about 2° from their base 42a to their upper end 42b to assist in removal from an injection mold. The ribs provide a high-friction surface to assist in gripping the skirt 22 of the cap 20 when it is rotated during bottling or opening/closing by the end user. Preferably, the skirt 22 of the present invention has a total of 75 ribs on the exterior surface 25 of the annular wall 23, but may have from about 70 to about 100 ribs. Many prior cap designs included over 100 ribs on the exterior of the skirt. Applicant has found that removal of 25 ribs can provide up to an additional 10% decrease in skirt weight while maintaining a suitable high- friction surface on the exterior surface 25 of the skirt 22. By combining the reduced ribs feature and thin walls feature, applicant has formed HDPE skirts weighing as little as .73 grams (excluding the weight of the tamper-evident band) that exhibit superior torque resistance, resistance to deformation and tamper evidence performance than prior LDPE caps.

As can be best seen in FIG. 3, the frangible bridges 30 include both angled bridges 30a and vertical bridges 30b connecting the annular wall 23 to the tamper- evident band 28. Preferably, the band 28 included at least eight bridges, including two pairs of angled bridges and two pairs of vertical bridges, although other combinations of bridges may be used. The use of HDPE material provides frangible bridges which are significantly more resistant to inadvertent breaking or stretching which can lead to "false positive" evidence of tampering than bridges of formed from LDPE. This resistance is illustrated in protocol II below. The lower edge 58 of the annular wall 23 is defined by a shelf 61 extending axially outwardly so that it has a slightly greater exterior diameter than the remainder of the annular wall 23. A plurality of spaced apart pads 59 extending down from the lower edge 58 of the shelf 61 of annular wall 23. The outer diameter of the shelf 61 and pads 59 preferably match the outer diameter of the band 28. The pads 59 provide a surface for the upper edge 60 of the band 28 to bear against when downward axial pressure is applied to the cap during bottling and when upward axial pressure is applied to the bottom edge 62 of the band 28 to assist in ejection of the skirt from the injection mold.

The exterior and interior diameters of the band 28 are slightly larger than those of the annular wall 23 (other than at the pads 54 and shelf 61) to allow the band 28 to fit over the rim 68 (See FIG. 9) on the neck. The band 28 has a plurality of ridges 48 formed on its interior surface 50. The ridges 48 have an angled lower surface 52 and a bridge severing surface 54 extending transversely from the interior surface 50. The lower surface 52 of the ridges 48 are angled to ease passage of the skirt and band over the rim 68 on neck 34 during the application of downward axial pressure on the cap in the course of bottling. The bridge severing surface 54 of the ridges 48 are designed to engage the rim 68 on the neck 34 of the container 32 when the cap is twisted for removal. The engagement between the bridge severing surface 54 and rim 68 on the neck as the skirt 22 is lifted and rotated breaks the frangible bridges 30 so that the band 28 is retained on the neck 34 of the container 20. Although bridge severing surface 54 is shown in Figs. 1-10 as being disposed on a series of spaced apart ridges, it is contemplated that a continuous bridge severing surface could be provided by use of a continuous rim extending transversely from the interior surface of the band, rather than spaced apart ridges.

HDPE skirts designed in accordance with the present invention show greatly improved over-torque resistance than similar configured LDPE skirts. This point is illustrated by the results of the experimental Protocol A set forth in Tables 1 and 2 below.

PROTOCOL A

Two sets of twenty one caps of a design typically used to seal one gallon milk and juice containers were manufactured. The caps had an internal diameter of about 38mm to match the outer neck diameter of the container. The skirts of both sets of caps generally included multiple threads allowing for a"snap on/screw off capability, a tamper evident band joined by frangible bridges to the annular wall similar to that shown in FIG.3, a total of seventy- five gripper ribs, and a resilient plastic liner on the top surface of the cap. The two sets of caps were of identical design with the following exceptions, (a) the LDPE caps were formed from low density polyethylene, while the HDPE caps were formed of high density polyethylene, (b) the skirt of the LDPE cap had a side-wall thickness of about .037 inch, while the HDPE skirt had a side-wall thickness of about .027 inch.

Forty-one, one-gallon containers of a type typically used in milk and juice containers were filled with room temperature water. The containers had multiple threads designed to engage the threads of the caps and outwardly extending rim to engage the tamper evident band during removal of the caps from the container. A cap was lightly placed on each container. The container was placed onto the rotatable table of a Secure Pak Torque Tester, Model, Digital; Serial number, Cl 907. The cap was hand tightened onto the container and the maximum torque applied was recorded on a Secure Pak Torque Tester, Model, Digital; Serial number, Cl 907. For the LDPE caps, the tester recorded the maximum torque required to cause the threads of the skirt to jump the threads of the neck after being fully tightened. The HDPE caps did not jump the neck threads and the torque recorded is the maximum that could be achieved by hand tightening. The results of the testing are shown in Tables I and II.

Table I

PROTOCOL B

Each of the LDPE caps was manually re-tightened after completion of Protocol A until the caps were again fully tightened. The maximum removal torque required to take the cap off the container was then recorded using the same caps and same torque tester. The caps were completely removed from the container neck such that the tamper evident bands were severed from the caps upon removal. It was observed that the maximum torque readings occurred just prior to the severing of the frangible bridges from the skirt

Table III

Table IN

Referring generally to an alternate embodiment of the invention shown in Figure 6, a cap skirt 122 is provided which extends downwardly from a top 121 of cap 120. A single thread 126 is formed in the inner surface 124 of the annular side wall of the skirt 122. A tamper-evident band 128 extends below the annular side wall 123 which is connected thereto by frangible bridges 130. The cap 120 is designed to seal a container (not shown) by seating on its neck with the skirt thread 126 engaging a single neck thread (not shown). The skirt 122 is designed to seal a container similar to that shown in FIGS. 1 and 9 with the exception that the neck of the container has a single thread rather than the multiple threads shown in FIGS. 1 and 9.

More specifically, as shown in Figure 6, the annular wall 123 has a single thread 126 with a single lead 136 formed in its inner surface 124. The single thread 126 has a height, length, and pitch which is greater than the multiple threads shown in Figure 3. As further shown in Figure 6, the thread 126 extends around the inner surface 124 about 800 degrees or about two and one/half revolutions. Similar to the skirt 22 shown in Figures 1-3, the skirt 122 is made of as HDPE material by a conventional injection molding process. This results in a skirt with a substantially thinner sidewall than conventional caps LDPE. The thickness 138 of the annular sidewall 123 of the present invention is preferably .027 of an inch but may vary from .024 to about .035. The reduction in thickness results in a cap which typically weighs as much as 27% less than a conventional cap of similar design formed from LDPE. The cap of FIG. 6 lacks ribs on its exterior surface unlike the skirt shown in FIGS. 1-3. As can be seen in FIG. 5, the tamper-evident band 128 and bridges 130 are similar to those shown in Figure 3 and described above. More specifically, the pads 159, lower edge 158, band 128, ridges 148, top edge of band 160, bottom edge of band 162, shelf 161 are all similar to the corresponding portions of the skirt 20 shown in FIG. 3.

The thin-walled skirt of the present invention may also be used with caps having an annular plug seal descending from the top surface of the cap which is designed to engage and deform an inner lip 70 (FIG. 9) on the container neck. Such annular plugs typically have an exterior diameter which is dimensioned to be slightly larger than the interior diameter dimension of the opening in the neck of the container. As the cap is pressed axially downwardly onto the container during bottling, the exterior wall surface of the plug presses radially outwardly against the interior of the lip formed at the opening of the container neck. Applicant has found that the use of HDPE plugs in combination with an HDPE skirt provides superior deformation of the inner edge of the lip of the container opening and thereby a superior seal. This is particularly advantageous where the container has some degree of flash present at the parting line of the molded plastic container. The more rigid HDPE plug is combined with HDPE skirt can accommodate a larger amount of flush than conventional LDPE caps in forming an acceptable seal which allows the bottler to increase dimension tolerances and thereby decease costs. Although the skirts 22 and 122 have been shown with a tamper-evident band 28, such a tamper-evident band may be excluded if desired.

The applicant has provided description and figures which are intended as an illustration of certain embodiments of the invention, and are not intended to be construed as containing or implying limitation of the invention to those embodiments. It will be appreciated that, although applicant has described various aspects of the invention with respect to specific embodiments, various alternatives and modifications will be apparent from the present disclosure which are within the spirit and scope of the present invention as set forth in the following claims.

Claims

CLAIMSWhat is Claimed:

1. A reduced thickness skirt for a container closure, said container including a neck with at least one neck thread formed therein, said skirt comprising: an annular wall having an inner surface and outer surface, said annular wall having a thickness of less than about .035 of an inch as measured between said inner and outer surface of said annular wall; and at least one skirt thread formed in the inner surface of said annular wall for engaging the neck thread of the container to secure the skirt to the container.

2. The skirt of Claim 1 wherein said annular wall is formed from high density polyethylene.

3. The skirt of Claim 1 wherein said annular wall weighs less than about .8 grams.

4. The skirt of Claim 1 wherein said at least one skirt thread is a plurality of skirt threads and said at least one neck thread is a plurality of neck threads, said skirt threads are dimensioned to slide past said plurality of neck threads when downward axial pressure is applied to said annular wall.

5. The skirt of Claim 1 wherein said annular wall has a bottom edge and has a plurality of frangible bridges extending therefrom, and wherein an annular tamper- evident band is joined to said annular wall by said frangible bridges.

6. The skirt of Claim 5 wherein said tamper-evident band has an inner surface with a frangible bridge severing surface extending transversely therefrom, said frangible bridge severing surface being dimensioned to engage a rim formed in an exterior surface of said container neck during removal of said skirt from said container.

7. The skirt of Claim 1 wherein the annular wall has a thickness of less than .028 of an inch, the annular side wall being further formed from a material including high density polyethylene.

8. The skirt of Claim 1 where the annular side wall has an arcuate exterior surface which is substantially unobstructed along its periphery, the annular side wall provides sufficient rigidity to the skirt to maintain contact between the at least one skirt thread and the at least one neck after application of the closure to the container.

9. A reduced weight side wall skirt for a container closure, said container having a neck with a neck thread formed therein, said side wall skirt comprising: an annular wall formed from high density polyethylene and having an inner surface and outer surface; and a plurality of skirt threads formed in said inner surface of said annular wall for engaging the plurality of neck threads, said plurality of skirt threads being shaped and dimensioned to slip over at least one of a plurality of neck threads upon application of axial downward pressure of said annular wall, said annular wall having sufficient thickness to maintain contact between at least one thread of the plurality of skirt threads and the neck thread during the application of at least about 10 inch/pounds of torque to said annular wall during tightening of the skirt onto the container.

10. The skirt of Claim 9 wherein said annular wall has a thickness of less than .035 of an inch as measured between said inner surface and outer surface of said annular wall.

11. The skirt of Claim 9 wherein said annular wall has an upper end, a lower end, and an exterior surface with less than seventy-five gripper ribs formed in said exterior surface and extending between said upper and lower end.

12. The skirt of Claim 9 wherein said annular wall weighs less than about 0.8 grams for a cap height of greater than 0.5 inches.

13. The annular skirt of Claim 9 wherein said annular wall has a bottom edge and has at least one frangible bridge extending therefrom, said at least one frangible bridge being formed from high density polyethylene, and wherein an annular tamper- evident band is joined to said annular wall by said at least one frangible bridge.

14. A skirt for a container closure, the container having a neck with a tamper- evident band engaging surface, said skirt comprising: an annular wall having a bottom edge; at least one frangible bridge formed from high density polyethylene extending downwardly from said bottom edge of said annular wall; a tamper-evident band extending downwardly from said at least one frangible bridge, said tamper-evident band having an interior surface with at least one bridge severing surface extending therefrom, said plurality of frangible bridges being dimensioned to withstand at least about 3 inch/pounds of torque prior to breaking when said bridge severing surface is rotated into engagement with the tamper-evident band engaging surface of the container neck.

15. The skirt of Claim 14 wherein said annular wall is formed from high density polyethylene.

16. The skirt of Claim 14 wherein said annular wall weighs less than about 0.8 grams.