NZ200879A - Tamperproof screw cap - Google Patents

Description

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NEW ZEALAND PATENTS ACT, 1953 No.: Date: COMPLETE SPECIFICATION >'■£ ' VUl^l98? r~* ■ 'TAMPER-INDICATING CLOSURE" SUBSTITUTION OF APPLICANT UNDER SECTION 24 tTHVu Ko^v >~£>t0 WoDJlCTS C 0 MCftVi y ^ ——— K/ \Vr^—ETHYL rRQ&!^-To-~GQMP.AN Y.,...a company incorporated in the State of Virginia, U.S.A., of 330 South Fourth Street, Richmond, State of Virginia, U.S.A. hereby declare the invention for which X / we pray that a patent may be granted toxg^/us, and the method by which it is to be performed, to be particularly described in and by the following statement:- (followed by page la) ?0Qg79 TAMPER-INDICATING CLOSURE This invention relates to a tamper-indicating closure suitable for use in packaging carbonated beverages.

Due to the economy of manufacture and availability 5 of raw material, the utilization of thermoplastic closures in packaging carbonated beverages is becoming more popular. To be commercially acceptable, the closure must have tamper-proof qualities. As understood in the closure art, the term "tamperproof" also has the meaning of tamper-indicating 10 qualities. A highly successful tamperproof system for use on thermoplastic closures is the one disclosed in U.S. 4,206,851. This system utilizes a fracturable band which can be heat shrunk into an interfering fit with a container flange. The fracturable band is carried by a plurality of 15 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 band as it attempts to override the container flange. There are other tamperproof systems, such as the ones ^hown in U.S. 4,033,472 20 and British Patent Specification 1,384,370, which also utilizes a tamperproof band which needs to be heated so that it can achieve a position of interfering with a container flange.

In designing the total package, either the container 25 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 the container. As the closure is turned, it moves axially upward thus 3Q breaking the seal between the top of the closure and the top 200879 of the container. Upon loss of the seal, pressurized gas from the container enters between the sidewall of the closure and the container, tending to bulge the closure sidewall outwardly. As the closure of the sidewall bulges 5 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 engage-10 ment is insufficient to contain the pressurized 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 15 cap. To aid in preventing premature release of this type of closure, the art has suggested providing a vent slot through the container threads. The slot provides a path for the pressurized gas to vent to the atmosphere, thus preventing closure bulge. See U.S. 4,007,848. In U.S. 20 4,007,851, another venting method for metal closures 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 vent-25 ing, is shown in U.S. 1,739,659? These systems, while they may work in theory, are not particularly 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 3 0 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 3"5&U.S. 3, 883,347. The width of the vent groove and the number ^ | of vent grooves utilized can be varied to provide the necessary ^Pventing rate for the conditions expected. Further, with this i? !• . "> " type of system, there will be no dirt entrapping openings *available on request 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 the packaging carbonated beverages are almost all roll formed on the container from a blank.) Desirable as it may be, the location of the vent slot in the closure presents problems itself. The use of the vent slot requires a recessed cut in the closure side-wall across the closure thread, with the result being that the closure sidewall is thinner at the vent slot and un-10 supported by a continuous thread„ 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 15 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 engagement» When the thread 20 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 25 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 gas is not trapped between the closure sidewall and the container neck, there is still 30 a chance for blow-off if the thread engagement is lessened too quickly as sufficient time will not have passed for the pressurized gas to complete its venting. For some closures, complete unscrewing of the closure from the container can take as little as one-half of a second. Clearly, in this 35 amount of time, venting has only started and pressure in the container is still high.

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 shrink inwardly and make intimate contact with the container flange or container neck. When this occurs, the function of the venting system is compromised as the shrunken portion 10 of the sidewall which is in contact with the container interferes with gas escapement.

The degree and incidence of shrinkage is increased when the lower portion of the sidewall is thinned out so that it flares outwardly from the container flange. The 15 flare configuration is desirable since it aids in placement of the cap on the container as it goes through the capping line. The flaring is also desirable as it provides a space between the closure sidewall and the container flange. Of course, by thinning out the lower portion of the closure 20 sidewall, this thinned sidewall portion will more likely reach its heat shrinking temperature if it receives tray heat from the source used to apply heat to the tamperproof band.

The problems of the prior art are overcome by 25 providing a thermoplastic closure having a heat-shrinkable tamperproof band, an extended closure thread, and a pressurized gas venting system which are compatible with each other.

This invention relates to a thermoplastic closure having a top wall with an annular, downwardly depending 30 sidewall. On the inside surface of the annular sidewall is a helical extended closure thread 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 35 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 of traverse by the venting groove with the closure 5 thread. This structure is dimensioned so that its perpendicular height, measured from the sidewall, is less than the perpendicular height of the closure thread, also measured from the inside surface of the sidewall. By having the rigidifying structure with this smaller dimension, 10 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 intersection of the vent groove and the closure thread insures that no threading interference will occur between the structure and 15 the cooperation of the closure and container threads. The vent groove(s) width and depth will be dependent upon the pressures expected to be encountered as the closure is removed from the container. The lower portion of the inside surface of the closure sidewall is preferably flared 20 slightly outward. Connected to the lowermost edge of the closure sidewall is a fracturable, heat-shrinkable, tamperproof band which is attached to the closure sidewall by means of a plurality of non-fracturable ribs. To give the lower portion of the closure sidewall resistance to 25 achieving a temperature conducive to its shrinkage, there is provided on the outside surface of this sidewall portion an annular bead which operates as a heat sink. Also provided, to prevent contact between the flared inside surface of the closure sidewall and the container, are a 30 plurality of stand-off 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 35 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 tamperproof band. 200879 These and other features of the invention contributing to satisfaction in use and economy in manufacture will be more fully understood when taken in connection with the following description of preferred embodiments .and the 5 accompanying drawings in which identical minerals refer to identical parts and in which: Figure 1 is a front elevational view of a closure of this invention; Figure 2 is a sectional view taken through 10 section line 2-2 of Figure 1; 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 1; 15 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 from a container; and Figure 6 is a partial sectional view taken through 20 section line 6-6 of Figure 2.

Referring 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 25 22. Liner keepers 24 are utilized to hold liner 22 in a position adjacent the inside surface of top wall 12. Liner 22 is utilized to effect a gas-tight seal with the top lip of the container neck. Other sealing systems may be utilized with the closure of this invention. The systems 30 utilized, whether they be liner systems or linerless systems, must fulfill the requirement that they be capable of effecting 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. Helical thread 20 is 35 dimensioned to cooperate with container helical thread 42, shown in Figure 3, to effect fitment of closure 10 to the container. r e 79 Recessed in the inside surface 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, 5 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 may be vented safely to the atmosphere within a period of time that is shorter than 10 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 15 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 surface of sidewall 14, greater than the height of closure thread 20, also measured from the inside surface of sidewall 20 14. However, the height of rigidifying structure 34 should not be so small that it is not able to achieve its required enhancement of sidewall hoop strength. Determination of the height of rigidifying structure 34 will be dependent on several factors, i.e., the pressures expected to be encountered, 25 the material of construction 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 polypropylene having a vent groove width of 30 about 1/16 inch and depth of .005 to .015 inches, a sidewall thickness of .035 to .04 0 inches, a closure thread traversing approximately 480 degrees having conventional thread engagement and a rigidifying structure height of about 2/3 of thread height. For other materials and other venting 35 channel depths and sidewall thicknesses, the sizing of rigidifying structure 34 is empirically determined by observation and experimentation, both of which are within the ;*VB7 9 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 5 in cross section. Such flaring is beneficial for the reasons stated previously. About the lowermost outside surface of sidewall 14 is provided with annular boss 30. As mentioned previously, annular boss 30 serves the function of providing a heat sink for absorption of "stray heat" from 10 the heat shrinking operation of band 16. Thus, the configuration and size of annular boss 30 is not critical so long as the heat sink function is achieved and thus the lowermost portion of sidewall 14 does not reach a temperature which would cause its shrinkage.

To further discourage contact of the lower inside surface of sidewall 14 with the container, there is additionally provided stand-off protuberances 32. These protuberances prevent any tendency of the lower portion of sidewall 14 to move towards the container. For the embodiment shown, these 20 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 fitted to the container, sidewall 14 is slightly deformed outwardly from the container. It is to be under-25 stood that other forms of protuberances may be utilized such as beads and the like.

Extending downwardly from the lowermost edge of sidewall 14 are a plurality of non-fracturable ribs 18.

These ribs are for carrying heat shrinkable tamper-indicating 30 band 16. Brand 16 is provided with at least one weakened portion so that this portion can fracture upon stress applied to the band. This fracture 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 fitted thereto by the cooperation of container threads 42 and closure threads 20. Note that heat 008 79 shrinkable band 16 has been heat shrunken so that it has moved to a position of interference with container flange 48. As can be appreciated, unscrewing of closure 10 results in upward axial movement of the closure, which movement forces 5 the fracture of band 16 as it is not able to follow 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 50 between the lowermost edge of sidewall 14 and container flange 48 has been maintained since 10 no shrinkage of sidewall 14 at its lowermost portion has occurred. Also, as pointed out previously, ribs 32 will act to accomplish this function. without annular boss 30 and ribs 32 is depicted. As can 15 be seen, the lowermost 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 of pressurized gas to the atmosphere so that premature release of the closure occurs. 20 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. 25 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 rigidifying structure 34 does not interfere with passage of the pressurized gas while at the same time the aforementioned enhancement in hoop 30 strength provided by rigidifying structure 34 is realized. As closure 10 continues its removal rotation, pressurized gas is continuously vented until the interior package pressure is equal to ambient pressure. Since there has been no loss of container thread to closure thread cooperation, 35 removal of closure 10 is done without fear of premature closure release.

In Figure 4, the results of utilizing closure 10 A particularly useful closure of this invention is ® ^ 0 0 S *7 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 5 by any well known injection molding techniques.

Illustrative of the benefits realized when utilizing boss 30 is the fact that a polypropylene closure with the features of this invention can be passed through a 52 inch long slotted forced-air heater utilizing 404°C. 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 14. To accomplish this passage through this slotted oven, annular boss 30 had a thickness measured from the inside wall of 0.037 inches.

Without annular boss 30, the thickness would normally be 0.028 inches for this portion of sidewall 14. 200879

Claims (12)

WHAT WE CLAIM IS:

1. A thermoplastic closure (10) for fitment to a container, said closure having: (a) a top wall (12); (b) an annular sidewall (14), downwardly depending from said top wall (12); (c) a closure thread (20) about the inside surface of said sidewall (14) ; (d) sealing means (22) above said closure thread (20) for" achievement of a gas- tight seal with said container; (e) gas venting means traversing said closure thread for venting gas from said container to the atmosphere subsequent to loss of said gas-tight seal when said closure (10) is loosened from its fitment to said container; and (f) heat-shrinkable tamper-indicating means attached to the lowermost end of said closure sidewall (14); said closure being characterized further by having: (i) stand-off protuberances about the inside surface of the lower portion of the closure sidewall (14) for aiding in keeping the closure sidewall (14) from making contact with the container, -11- 200879 whereby pressurized gas can pass through said venting means to the atmosphere as said closure (10) is removed from said container.

2. The closure of Claim 1 and being characterized further by having: (ii) at each point of traverse by said venting means of said closure thread, a rigidifying means (34) being dimensioned so that it has a perpendicular height measured from said sidewall less than the perpendicular height of said closure thread (20) measured from said sidewall (14).

3. The closure of Claim 1 being further characterized by having: (iii) heat sink means (30 adjacent the lowermost end of said sidewall (14).

4. The closure of Claim 1 being characterized further by having: (iv) said closure thread (20) extended to traverse from 400 to 500 degrees of rotation about the inside surface of said sidewall (14).

5. The closure of Claim 1 being further characterized by having: . (v) retaining means (24) about the inside of surface said sidewall (14) positioned below said sealing means (22), but above said closure thread (20) for preventing said sealing means (22) from moving down to said closure thread (20).

6. The closure of Claims 1, 2, 3, 4 or 5 wherein said gas venting means comprises a vent groove (26) extending from a point above §aid closure thread (20) to a point adjacent the lowermost edge of said sidewall (14).

7. The closure of Claims 1, 2, 3, 4 or 5 wherein said tamper-indicating means is a fracturable heat-shrinkable bead (16) attached to the lowermost edge of said sidewall (14) by a plurality of non-fracturable ribs (18).

8. The closure of Claims 1, 2, 3, 4 or 5, wherein said closure (10) is polypropylene.

9. The closure of Claims 1, 2, 3, 4 or 5, wherein the inside surface of the lower portion o& said sidewall (14) is flared outwardly by thinning of said lower portion from its upppermost extent to its lowermost extent.

10. The closure of Claim 3 wherein said heat sink means is an annular bead (30) extending outwardly from the outer lowermost surface of said sidewall. - / 3 7 108 7

11. The closure of Claim 2 wherein said rigidifying means (34) when viewed in cross section has the shape of a truncated pyramid.

12. The closure of Claims 1, 2, 3, 4 or 5, wherein said gas venting means is a vertically extending slot in the inside surface of said sidewall, said slot extending to the lower portion of said sidewall, and wherein said stand-off protuberances comprise at least one vertically extending rib adjacent each side of the lowermost extent of said slot. Authorised Agents, A. J. PARK & SON -