Note: Descriptions are shown in the official language in which they were submitted.
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.
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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.
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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 ~
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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:
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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~
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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.
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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
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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.
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