CA1195290A

CA1195290A - Closure for pressurized containers

Info

Publication number: CA1195290A
Application number: CA000404733A
Authority: CA
Inventors: Efrem M. Ostrowsky
Original assignee: Precise TMP Inc
Current assignee: Precise TMP Inc
Priority date: 1981-06-08
Filing date: 1982-06-08
Publication date: 1985-10-15
Also published as: EP0149198A3; EP0149198A2; EP0149198B1; NZ200879A; EP0067650B1; DE3272712D1; EP0067650A1; AU8466382A

Abstract

Abstract of the Disclosure A thermoplastic closure (10) for fitment to a container for packaging product capable of producing internal container pressure, e.g., carbonated beverages, is disclosed. The closure (10) comprises a top wall (12) and an annular sidewall (14) downwardly depending from the top wall (12). An extended closure thread (20) on the inside surface of the sidewall (14) which requires the user to make two turning motions to achieve removal is provided for cooperation with the container neck thread (42) to achieve fitment of the closure (10) to the container neck (40). A sealing system (22) adjacent the top wall of the closure provides sealing of the closure to the container.
Venting structure is provided on the closure for venting of pressurized gas from the container upon loss of the seal when the closure is rotated to remove it from the container. A rigidifying means (34) having a perpendicular height less than the perpendicular height of the closure thread is provided at the point of traverse of the venting groove (26) and the closure thread (20). A heat-shrinkable tamper-indicating means (16) is attached to the lowermost edge of the sidewall of the closure (10). Application of heat to the tamper indicating means (16) causes it to shrink towards the container and to a point of interference with a container flange (48). A heat sink structure (30), such as an annular bead about the outside surface of the sidewall (14), is utilized to keep the sidewall at a temperature below that temperature which would normally cause the sidewall (14) to shrink.

Description

5~

~AMPER-INDICATING CLGSURE

~s~r~ t,~
This invention relates to a t~mFer~hndieRt*n~r I closure suitable for use in packaging carbonated ,~
beverages.
Due to the economy of manufacture and avail-ability of raw material~ the utilization of thermo-plastic closures in packaging carbonated beverages is becoming more popular. To be commercially acceptable, the closure must have tamperproof qualities. As understood in the closure art~ the terrn "tarnperproof~
also has the meaning of tamper-indicating qualities. A
highly successful tamperproof system for use on thermoplastic closures is the one disclosed in U. S.
4,206,~51. This system utilizes a fracturable band which can be heat shrunk into an interfering fit with a container ~lange. The fractwrable band is carried by a plurality of non- fracturable ribs attached to the lowermost end of the closure sidewall. Attempted removal of the closure from the container results in fracture of the banc3 as it attempts to override the container flange. There are other tamperproof systems, ~uch as the ones shown in U. S. ~,033,472 and British Patent Specificatlon l,38~/370, which also utllizes a tamperproof band which needs to he heated so that it can achieve a position of interfering with with a container ~lanc3e.

'~

In designing the total package, either the container and/or the closure must be designed to prevent premature release of the closure from the container. This premature release phenomenon is most often experienced as the user turns the closure to begin its removal from ~he container. As the closure is turned, it moves axially upward thus breaking the seal between the top of the closure and the top of the container. Upon loss of the seal, pressurized gas from the container enters between the sidewall of the closure and the CGntainer; tending to bulge the closure sidewall outwardly. As the closure of the sidewall bulges outwardly, the closure threads are pulled away from engagement with the container threads and the connection between the container and closure is tenuous at best. If the gas is under sufficient pressure, the closure will be released from the container since the container-closure thread engagement is insufficient to contain the pressurlzed gas. This release is oftentimes with great force thereby presenting danger to the user.
One of the most popular threaded closures used in packaging carbonated products is the nearly ubiquitous metal cap~ To ald in preventing premature release o this type of closure, the art has suggested providing a vent slot through the container threads.
The slot provides a path for the pre~lsurized gas to vent to the atmosphere, thus preventing closure bluge.
Se~ V. S. ~,007,8~8. In U. S. 4,007,8Sl, another ventlng method for metal clo~ures is shown. The closure is constructed to have, at a point adjacent the intersection of the sidewall and the top wall, at least one vent through which the pressurized gas may pass.
Another type of system, one which uses circumferential venting, is shown in U S. 1~739~659. ~hese systems~
while they may work in theory, are not partlcularly desirable as either they require modification in the design of the container threaded neck portion, they have dirt trapping openings in the closure itself, or they do not provide a sufficient amount of venting.
These problems can be solved by the utilization of thermoplastic closures. Thermoplastic closures can be designed so that a vent groove is cut on the inside surface of the closure sidewall across the closure threads. See U. S. 3,888,347. The width of the vent groove and the number oE vent grooves utilized can be varied to provide the necessary ventiny rate for the conditions expected. Further, with this type of system, there will be no dirt entrapping openings exposed to the outside of the closure. (The use of such a groove on a metal closure is not practical as the metal closures used in packaging carbonated beverages are almost all roll Pormed on the container from a blank ) Desirable as it may be, the location of the vent slot in the closure presents problems itselP~ The use of the vent slot requires a recessed cut in the closure sidewall acorss the closure thread, with the result belng that tha closure sidewall is thinner at the vent slot and unsupported by a continuous thread.
I

~, . . .

2~ `

Upon tightening the closure to the container, the weakened sidewall will expand outwardly as, in its weakened configuration, it cannot support the forces applied on it by the engagement of the container and closure threads. Also, when the closure is loosened from its seal position, the pressurized gas can cause the weakened closure sidewall to expand. Both, the closure expansion realized upon tightening and the closure expansion caused by the pressurized gas, jeopardize the closure-container thread engagem~nt.
When the thread engagement is compromised to the extent that the pressure inside the closure cannot be held by the threads, then premature release of the closure occurs. Using a closure with thickened sidewalls is not an answer as such a closure uses more thermoplastic material per closure and could not compete economically in the marketplace.
Although venting can be accomplished, for example, by using a vertical vent slot on the container or closure because with the vent slot, the yas is not trapped between the closure sidewall and the container neck, there is still a chance for blow-off if the thread engagement is lessened too quickly as sufficient time will not have passed or the pressurized gas to complete its venting. ~or some closures, complete unscrewin~ oE the closure from the container can take as little as one-half of a second. Clearly, in thi~
amount of time, venting has only started and pressure in the container is still high.

5~9~

Combining a tamperproof system which utilizes heat application with a venting system, such as the one described above, can present another difficult problem. The problem lies in the fact that application of heat to the tamperproof band cannot be done very precisely and that, oftentimes, heat intended for the band also reaches the lower closure sidewall. Heating of the sidewall can cause it to shirnk inwardly and make intimate contact with the container Elange or container neck. When this occurs, the function of the venting system is compromised as the shrunken portion of the sidewall which is in contact with the container interfere~ with gas escapement.
The degree and incidence of shrinkage is increased when the lower por~ion of the sidewall is thinned out so that it flares outwardly from the container ~lange. The flare configuration is desirable since it aids in placement of the cap on the container as it goes through the capping line. The flaring ls also desirable as it provides a space between the closure sidewall and the container flange. Of course, by thinning out the lower portion fo the closure sidewall, this thinned sidewall portion will rnore likely reach lts heat shrinking temperature i it receives tray heat frorn the souce used to apply heat to the tamperproof ban-3.
~ he problems of the prior art are overcorne by providlng a thermoplastic clo~ure havLny a heat-~hrlrlkable tamperproof band, an extended closure thread, and a pressurized c3a~ venting system which are compatible with each other.

2S~ `

This invention relates to a thermoplastic closure having a top wall with an annular, downwardly dependin~ sidewall. On the inside surface of the annular sidewall is a helical extended closure ~hread traversing from 400 to 500 degrees and dimensioned for cooperation with a similar container thread for fitment of the closure to the container neck. A sealing system is utilized above the closure thread to achieve a gas-tight seal when the closure is fitted to the container. A venting system provides at least one vent groove which intersects the closure thread and extends from the bottom of the closure sidewall to a point above the-closure thread. Rigidifying structure is also provided to enhance the hoop strength of the closure sidewall at the venting groove(s). The structure is located at each point o~ traverse by the venting groove with the closure thread. This structure is dimensioned so that its perpendicular height, measured from the sidewall, is less than the perpen-dicular height of the closure thread, also measured from the inside surface of the sidewall. By having the rigidifying structure with this smaller dimension, the pressurized gas is able to find sufficient escapement cross sectional area in the venting groove. Location of the rigidifying structure at the point(s) of inter-se-tion of the vent groove and the closure thread lnsures that no threading interference will occur between the structure and the cooperat:ion of the closure and container threads. The vent groove(s) width and depth will be depell-2ent upon the pressures expected to be encountered as the closure is removea fro~ the container. The lower portion of the inside surEace o~
the closure sidewall is preferably flared slightly ~J outward. ~ ~onnected to the lowermost edge o~ the closure sidewall is a fracturable, heat-shri~kabler tamperproof band which is attached to ~he closure sidewall by means of a plurality of non-~racturable ribs. To give the lower portion of the closure side-wall resistance to achieving a temperature conducive to its shrinkage, there is provided on the outside surface of this sidewall portion an annular ~ead which operates as a heat~sink. Also provided, to prevent contact between the flared inside surface of the closure side-wall and the container, are a plurality of ~tand o~f protuberances positioned about the flared inside surface of the closure sidewall. Preferably, these protuberances will take the form of vertical ribs.
By utilizing the annular bead to provide a large heat sink and the protuberances on the inside wall of the flared portion of the container sidewall, it has been found that the container sidewall will not shrink and/or contact the container due to heat received by it during the heating of the tampeLproof band.
, s G~ r` te rn p ~at ~
'' ' ' ~ - 7 ~

29~

Therefore, in accordance with the present invention there is provided in a thermoplastic closure suitable for fitme~l to a thre-de~ containe~ neck where~n the closure includes: a top wall, an annular sidewall aownwardly dependi;.g from the top wall, a closure thread carried on the inside surface of the annular sidewall for cooperatlon with the container neck thread, a sealing system above the closure thread for eflecting a gas-tight seal between the closure and the container, and at leas. one venting groove in the sidewall traversing the closure thread. The improvement according to the present invention whi~h comprises a rigidifying means at e~ch point of traverse by the venting groove oi the closure thread. The rigidifyina means is di~ensioned so that it has a per~endicular height measured from the inside surface of the sidewall less than the perpendicular height of the ciosure thread me_sured from the inside sur ace of the sidewall but havir.a a perpendicular height suf~icient to enc;.ance the hoo~ strenath of the annular sidewall. Pressurized gas can pass through the ventinq groove to the a~mosphere as the closure is removed from the container.

These and other eatures or this invention ontributlng to satisfaction in use and economy ln manufacture will be more fully understood when taken in connection with the following description of preferred emoodiments and the accompanying drawings in which iden~ical numerals rerer to identical parts and in which:

- 7a -25~Q

FIGURE 1 is a front elevational view of a closure of this invention;
FIGURE 2 is a sectional view taken through section line 2-2 of Figure l;
FIGURE 3 is a vertical sectional view of the closure shown in Figure 1 fitted to a container;
FIGURE 4 is a vertical sectional view of a closure not incorporating features of the closure shown in Figure l;
FIGURE 5 is an enlarged sectional view showing the path of escapement for the - pressurized gas as the closure shown in Figures 1, 2 and 3 is removed Erom a container; and FIGURE 6 is a partial sectional view taken through section line 6-6 of Figure 2.

ReEerring now to Figures 1-2, the closure of this invention, generally designated by the numeral 10, has a top wall 12 and a downwardly depending annular sidewall 14. Nested against the inside surface of top wall 12 is a liner 22. Liner keepers 24 are utilized to hold liner 22 in a position adjacent the inside sur~ace of top wall 12. ~iner 22 is utiliæed to effect a ga~-tlght ~eal wlth the top lip of the contairler neck. other ~ealing ~ystems may be utilized with the closure of this invention. The systerns utiliæed, whether they be liner ~y3teMs or linerless sy3tem~, mu~t ~ul~ill the requirernent that they be capable o~

, ' ' , efecting a gas-tight seal under the pressures expected in the package. About the inside surface of sidewall 14 there is provided a helical thread 20. ~elical thread 20 is dimensioned to cooperate with container helical thread 42, shown in Figure 3, to effect fitment of closure 10 to the container.
Recessed in the inside surEace of sidewall 14 is vent groove 26. As can be seen in Figure 2, vent groove 26 intersects closure thread 20. For the embodiments shown in the drawings, a single vent groove is utilized. However, it is to be understood that more than one vent groove may be used. The width and depth of vent groove 26 should be such that sufficient passageway is provided for the pressurized gas so that it rnay be vented safely to the atmosphere within a period oE time that is shorter than the time necessary for removal of closure 10 from the container by the user.
Traversing vent groove 26 at each point of its intersection with closure thread 20 is rigidifying structure 34. For the embodiment shown in Figures 2 and 6, rigidifying structure 34 has a cross sectional shape resembling a truncated pyramid. Whatever the form of rigidifying structure 34, it cannot have a height, measured from the inside surEace of sidewall 14, greate~ than the height of closure thread 20, also measured feom the inside surface of sidewall 14.
However, the height of rigidifying st,ructure 34 should not be so ~mall that lt ls not able to achieve Lts required enhallcement of sidewall hoop strength.
Determinatlon of the height of rigidifying structure 34 will be dependent on several factors, i.e. t the pressures expected to be encountered, the material of cons~ruction for the closure, the width and depth venting groove~s) 26, the length of closure thread 20 and the degree of engagement between closure thread 20 and container thread 42. An example of a useful closure is one made of polypropy~ene having a vent groove width of about 1/16 inch and depth of .005 to .015 inches, a sidewall thickness of .035 to .040 inches, a closure thread traversing appro~imately 480 degrees having conventional thread engagement and a rigidifying structure height of about 2/3 of thread height. For other materials and other venting channel depths and ~idewall thicknesses, the sizing of rigidifying structure 34 is empirically determined by observation and experimentation, both of which are well within the ability of those skilled in the art having the disclosure of this invention before them.
The inside surface of sidewall 14, at its lowermost end, is provided with a flared profile when viewed in cross section. Such flaring is beneficial for the reasons stated previously. About the lowermost outside surface of sidewall 14 is provided with annular hoss 30. As mentioned previously, annular boss 30 ~erves the function of providinc3 a heat sink for ab~orption of "stray heat~ from the heat shrinking operation of band 16. Thus, the configuration and size of annular boss 30 is not critical so long as the heat ~ink function is achieved and thus the lowermo~t portion of sidewall 14 cdoes not reach a temperature which ~ould cause its shrinkage.

To further discourage contact of the lower inside surface o~ sidewall 14 with the container, there is additionally provided stand-off protuberances 32.
These protuberances prevent any tendency o the lower portion of sidewall 14 to move towards the container.
For the embodiment shown, these protuberances are vertical ribs grouped in pairs and spaced each pair every ninety degrees. In fact, it has been found desirable to dimension ribs 32 so that when the closure is ~itted to the container, sidewall 14 is slightly deformed outwardly from the container~ It is to be understood that other forms of protuberances may be utilized such as beads and the like.
Extending downwardly from the lowermost edge of sidewall l4 are a plurality of non-fracturable ribs 18. These ribs are for carrying heat shrinkable tamper-indicating band 16. Band 16 is provided with at least one weakened portion so that this portion can fracture upon stress applied to the band. This ~racture of the band is a clear indication to the user that the closure has been tampered with.
In Figure 3, closure 10 is shown fitted to a container. As can be seen in this figure, container neck 40 has closure 10 ~itted thereto by the cooperation o~ container threads 42 and closure threads 20. Note that heat shrinkable band 16 has been heat shrunken so that it has moved to a position o~
inter~erence with container Elange 48. As can be appreciated, unscrewlng oE closure 10 re~ult.s in upward axial movement of the closure, which movement forces the fracture of band 16 as it is not able to follow 2~

this axial movement without fracturing due to its interference with container flange 48. Also, it is to be seen from Figure 3 that the spacing sn between the lowermost edge of sidewall 14 and container Elange 48 has been maintained since no shrinkage of sidewall 14 at its lowermost portion has occurred. Also, as pointed out previously, ribs 32 will act to accomplish this functiori.
In Figure 4, the results of utilizing closure 10 without annular boss 30 and ribs 32 is depicted. As can be seen, the lower most portion of sidewall 14 has shrunk inwardly and is in intimate contact with container-flange 48. As mentioned previously, this contact often results in restriction of the passage oE
pressurized gas to the atmosphere 50 that premature release of the closure occurs.
In Figure 5, the venting of pressurized gas from the package is shown. Note that as closure 10 is rotated about container neck 40, closure 10 moves axially upward. This axial upward movement results in liner 22 being removed from its nesting position on the top 44 of container neck 40~ Pressurized gas in the interior of the container begins movement through vent groove 26 as indicated by the arrows. As can be seen, the utilization of rlgidl~ying structure 34 does not interfere with pas~age of the pressurized gas while at the same time the aforementioned enhancement in hoop strength provided by rigidifylny structure 34 is reallzed. As closure 10 continues its rernoval rotation, pressurized ga~ is continuously vented until the interior package pre~sure is equal to ambient pressure. Since there has been no loss of container thread to closure thread cooperation, removal of closure lO is done without fear of premature closure release.
A particularly useful closure of this invention is one made of polypropylene. However, it is to be understood that other materials may be utilized such as polyethylene terephthalate, polyvinyl chloride, high density polyethylene, and the like. The closure of this invention may be made by any well known injection molding techniques.
Illustrative of the benefits realized when utilizing-annular boss 30 is the fact that a prolypropylene closure with the features of this invention can be passed through a 52 inch long slotted forced-air heater utilizing 404C. air with a passage time of two seconds and a package rotation of 3-1/4 revolutions per pass without shrinkage of the lower portion of sidewall l4. To accomplish this passage through this slotted oven, annular boss 30 had a thickness measured from the inside wall to the outside wall of 0~037 inches. Without annular boss 30, the thickness would normally be 0~028 inches ~or this portion of sldewall 14.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a thermoplastic closure suitable for fitment to a threaded container neck wherein the closure includes:
(a) a top wall (12);
(b) an annular sidewall (14), downwardly depending from the top wall (12);
(c) a closure thread (20) carried on the inside surface of the annular sidewall (14) for cooperation with the container neck thread, (d) a sealing system (22) above the closure thread (20) for effecting a gas-tight seal between the closure and the container, and (e) at least one venting groove (26) in the side-wall traversing the closure thread, the improvement which comprises a rigidifying means (34) at each point of traverse by said venting groove (26) of said closure thread (20), said rigidifying means being dimensioned so that it has a perpendicular height measured from the inside surface of said sidewall less than the perpendicular height of said closure thread measured from the inside surface of said sidewall but having a perpendicular height sufficient to enhance the hoop strength of said annular sidewall, whereby pressurized gas can pass through said venting groove to the atmosphere as said clo-sure is removed from said container.

2. The closure of Claim 1 wherein said rigidifying means (34) when viewed in cross section has the shape of a trun-caked pyramid.

3. The closure of Claim 1 wherein said rigidifying means (34) is a structure having a height of about 2/3 of the height of said closure thread (20), both heights being measured from the inside surface of said sidewall.

4. The closure of Claim 1 wherein the number of said venting grooves (26) in said sidewall and the depth of said grooves in said sidewall is such that sufficient venting groove cross section area is provided for venting the pressurized gas at a rate so that conventional removal of said closure from said threaded neck will occur only after the venting is substantially accomplished.

5. The closure of Claim 3 wherein said venting groove has a width of about 1/16 inch, a depth of from about 0.005 inch to about 0.015 inch, and said sidewall has a thickness of from about 0.035 inch to about 0.040 inch.