Injection molding system for threaded tamper indicating closures

A method of injection molding a container cap with a precision thread having a tamper indicating band depending from the bottom of the cap skirt. Collet jaws form at least a frangible connection between the bottom of the cap skirt and the top of the tamper indicating band, and these jaws are moved radially outward specified amounts during the molding process to provide clearance for stripping an inwardly directed retaining element on the band from the core and for ejection of the finished cap.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a method for forming container closures. More 
particularly, this invention relates to a method for injection molding 
threaded tamper indicating closures. 
2. State of the Art 
Many threaded closures, including tamper indicating closures having a 
threaded cap and a tamper, indicating band joined to the bottom of the cap 
by a frangible connection, are molded with a rounded thread so that the 
molding core can be stripped from the molded cap by axial movement, 
jumping the thread forming portion of the core over the internal cap 
thread. 
Where a precision thread has been required having a sharply defined thread 
apex, axially split cores have been used mandating closure design where 
the cap skirt of the closure is at least twice as long as a cap having 
jump threads in order to accommodate unthreading splines or axially 
extending teeth. This can be seen in FIG. 1 of the closure described in 
U.S. Pat. No. 4,572,387 where the threaded cap 12 of closure 10 has a 
first skirt portion 18 having a precise internal thread 20 and a second 
skirt portion 24 having unscrewing teeth or spline receiving grooves 30. A 
splined portion of the core remains stationary, to be engaged with teeth 
30, to prevent rotation of the closure as a second separate portion of the 
core forming the internal threads 20 is rotated in an unthreading 
direction. 
SUMMARY OF THE INVENTION 
The present invention provides a new method of molding a tamper indicating 
band with a precision internal thread on the cap of the closure, 
overcoming problems inherent in the prior art. The closure to be molded 
has a tamper indicating band joined to the bottom of the cap by a 
frangible connection as is well known in the art. The tamper indicating 
band has an inwardly directed retaining element which cooperates with a 
corresponding outwardly directed retaining element on the neck of the 
container. As is also well known, the retaining element can be in the form 
of a circumferentially continuous or a segmented bead, ratchet teeth, 
folding fingers or other similar stop elements. When the closure is 
unthreaded, the band is retained on the container neck by the retaining 
element, putting stress on the frangible connection to break it as the cap 
is unthreaded from the container neck. 
The new method includes the following steps: 
providing a cavity mold defining an exterior portion of the cap; 
providing a core defining an internal thread of the cap and an inwardly 
directed retaining element on the tamper indicating band; 
providing a circumferential array of radially movable jaws a concentrically 
around the core so that when the jaws are in a radially innermost position 
they define the exterior surface and bottom of the tamper indicating band, 
the bottom of the cap and the frangible connection between the tamper 
indicating band and the bottom of the cap; 
axially moving the core and the array of jaws into the cavity mold; 
moving the jaws into their radially innermost position and locking the jaws 
in this position completing delineation of a molding cavity for the 
closure; 
injecting plastic material into the molding cavity to form the closure; 
moving the jaws radially outward a predetermined amount to provide 
clearance for stripping of the retaining element on the tamper indicating 
band from the core; 
rotating the core in an unthreading direction while restraining rotation of 
the closure; 
axially advancing the array of jaws while maintaining contact between each 
of the jaws and the bottom of the tamper indicating band and the bottom of 
the cap to strip the cap from the core as the core is being rotated; and 
moving the jaws radially outward a further amount more than the 
predetermined amount and ejecting the closure. 
The cavity mold is preferably provided with a internal frusto-conical 
surface and each of the array of jaws is provided with an external 
frusto-conical surface so that during axial movement of the jaws into the 
cavity mold, the jaws can move into their radially innermost position to 
lock in this position for defining the molding cavity. The radially 
movable jaws can be biased inwardly or outwardly, and in a preferred 
embodiment a collet is provided having axially extending fingers which 
form the circumferential array of the movable jaws. When the collet jaws 
are spring biased outwardly, axial movement into the cavity mold will move 
the jaws inwardly to their molding position by the coaction of the 
frusto-conical surfaces. Axial movement between the cavity mold and collet 
will allow the jaws to spring outwardly, and this outward movement can be 
limited to the predetermined amount by a sleeve surrounding the collet. 
Axial movement of the sleeve relative to the collet a further amount can 
provide clearance for further movement of the jaws radially outward for 
ejection of the molded closure. 
In another embodiment where the collet jaws are spring biased inwardly, 
their inward movement to define the molding cavity is accomplished by the 
spring bias and their movement outwardly can be obtained by axial movement 
of the core provided with a camming surface which acts radially outward 
against the collet jaws. In this case, the movement of the jaws outwardly 
a predetermined amount can be controlled by the camming surface itself. 
In a preferred embodiment the jaws further define axially extending 
unthreading teeth on the bottom of the cap which remain engaged with the 
jaws as the jaws are moved outwardly the predetermined amount so that such 
engagement restrains rotation of the closure during unthreading of the 
core. A substantial portion of the exterior wall of the cap can be formed 
by the collet jaws. 
In another preferred embodiment, the cavity mold defines a circumferential 
array of axially extending ribs on the exterior portion of the cap. These 
ribs remain engaged with the cavity mold, restraining rotation of the 
closure during unthreading of the core.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
Referring to FIGS. 1 and 2, the threaded closure 10 formed by the methods 
of the present invention includes a cap 12 and a tamper indicating band 14 
attached to the bottom of the cap by a number of circumferentially spaced 
axially extending frangible webs 16 as seen in FIG. 2. The cap 12 has a 
top 18 and an axially extending skirt 20 formed with internal precision 
threads 22 and external ribs 24 which provide the user a grip for 
unthreading the closure. The tamper indicating band has an inwardly 
directed element shown in FIG. 2 as a continuous bead 26. In the 
particular embodiments shown in FIGS. I and 2, the band 14 is also 
connected to the bottom of the cap skirt 20 by a pair tether webs 28. 
In use, the closure 10 is threaded onto a threaded container neck with the 
bead 26 snapping over a complimentary flange on the container neck. When 
the cap is rotated in an unthreading direction, the bead 26 retains the 
band 14 on the neck fracturing the frangible webs 16 to provide evidence 
of initial opening or tampering of the container closure package. The 
tether webs 28 retain the tamper indicating band 14 attached to the cap 12 
after fracture of the webs 16. This closure structure is the subject of my 
co-pending patent application, Ser. No. 877,812, filed May 4, 1992, now 
U.S. Pat. No. 5,246,125. In other embodiments, the tether webs may be 
omitted so that when the frangible webs 16 are broken, the band 14 remains 
on the container neck. Also in other embodiments the continuous bead 26 as 
shown in FIG. 2 can be replaced by a segmented bead or other retaining 
element such as ratchet teeth. 
In the embodiment shown in FIG. 1, the bottom of the cap is formed with 
circumferentially spaced axially extending unthreading teeth 30 and slots 
32. These teeth 30 prevent rotation of the closure 10 as a core forming 
the threads 22 is unscrewed from the cap during the molding procedure. 
In the closure of FIG. 2 rotation of the closure 10 is prevented when the 
core is being unthreaded by engagement of the axially extending ribs 24 
with the cavity mold projections forming them. 
Referring to FIGS. 3-6 and the enlarged portions of these FIGS. shown in 
FIGS. 7-9, a collet unthreading embodiment of the molding method is 
sequentially shown as practiced in the molding machine 34. 
In FIGS. 3 and 8 the molding machine is shown in the closed position with 
all of the elements of the mold positioned to define the molding cavity 36 
in which the closure 10 has been formed by injection of plastic into the 
cavity. As is conventional, the cavity plate 38 and its cavity mold or 
molds 40 are stationary with the plastic being injected through the cavity 
mold into the molding cavity 36. While a single molding cavity and its 
associated parts are shown throughout the drawing, it will be appreciated 
that the cavity plate 38 may accommodate a number of vertically spaced 
rows of horizontally spaced cavity molds. The moving portion of the 
molding machine 34 includes the core 42, collet 44 having a plurality of 
axially extending fingers 46 defining a circumferential array of radially 
movable jaws 48, and a collet sleeve 50. 
It will be appreciated that many details, well known in the art, have been 
eliminated for both the stationary and moving elements of the molding 
machine 34 to simplify the showing and emphasize the components used in 
the method of the invention. Likewise, it is the relative movement between 
components that accomplishes the steps of the molding method rather than 
which components are stationary and which are moved. On the stationary 
side, a single cavity mold 40 and cavity plate 38 are shown, but the sprue 
and gate system for injecting the molten plastic into the molding cavity 
36 is omitted. With a multi-cavity mold, there would be at least an 
additional stationary runner plate for the sprue system. 
In a like manner, on the moving side, collet plate 52 and collet sleeve 
plate 54 are shown, but a core plates for imparting axial movement to the 
core has been omitted in order to shorten the views. Similarly, additional 
core plate for imparting rotation to the core have been omitted such as 
spaced roller bearing core support plates and an intermediate plate 
containing a rack for coaction with a pinion on the core (not shown). 
Other well known elements are also omitted such as cams, etc. to impart 
axial motion to the col let when it acts as a stripper against the closure 
cap and band bottoms in synchronization with the axial movement of the 
core imparted by rotation of the core. As best seen in FIG. 3, with the 
molding machine in its closed position, the cavity mold 40 forms a 
substantial portion of the external surface of cap 12, namely top 18 and 
skirt 20. Gripping ribs 24, as best seen in FIG. 8 are also formed by the 
cavity mold 40 on cap skirt 20. 
As best seen in FIGS. 3, 8 and 9, the collet jaws 48 form the exterior 
surfaces of the tamper indicating band 14, namely the band side wall, 
bottom and top. Collet jaws 48 also form the frangible connection between 
the top of the ))and 14 and the bottom of the cap skirt 20, namely, open 
window areas 56 and frangible webs 16 by inwardly directed jaw projections 
72. Jaws 48 also form collet unthreading teeth 30 with the spaces 32 
between the teeth being formed by inwardly directed jaw projections 58. 
Note in FIG. 9 that a portion of the cap skirt 20 is formed by the top 
interior wall portion 60 of the jaws 48. It will be appreciated that the 
top of the collet jaws can be axially extended to form substantially all 
of the cap skirt 20 with the axially extending ribs 24, reducing that 
portion that is shown being molded by cavity mold 40. This axial extension 
of jaws 48 is shown in phantom in FIG. 15 at 48'. 
As best seen in FIGS. 3, 7 and 8, the core forms the interior of the 
closure 10, namely, cap top interior surface 62 and thread 22, best seen 
in FIG. 7, and band 14 inside wall with inwardly projecting bead 26, best 
seen in FIG. 8. 
Collet jaws 48 have a tapered exterior surfaces 64 which cooperates with an 
internal tapered surface 66 in cavity mold 40, as seen in FIGS. 3 and 4, 
to lock the mold in its closed position. With the collet fingers 46 being 
spring biased outwardly in the embodiment of FIGS. 3-7, these cooperating 
tapered surfaces 64 and 66 will move the jaws 48 into their radially 
innermost position as the collet 44 is moved axially from a separated 
position such as in FIG. 4 to its closed position in FIG. 3. 
When the injection step has been completed as shown in FIG. 3, the core 42, 
collet 44 and collet sleeve 50 are moved axially away from cavity mold 40 
with the closure 10 being retained between core 42 and collet jaws 48 as 
seen in FIG. 4. This allows the jaws 48 to move radially outward by the 
spring bias in collet fingers 46 from the position shown in FIG. 4 to the 
position shown in FIG. 5. Collet sleeve 50 has been maintained aligned 
with collet 44 so that upper cylindrical sleeve surface 68 acting against 
cylindrical external collet jaw surface 70 limits the outward movement of 
the jaws 48 to a predetermined amount providing clearance for stripping 
the inwardly directed band bead 26 from the core 44 shown in exaggerated 
position in FIG. 7. During this outward movement of the jaws 48, the jaw 
projections 58 remain in contact with threading teeth 30 to prevent 
rotation of the closure 10 as the core 44 is rotated in an unthreading 
direction. 
During the unthreading step, the collet jaws in addition to being held in 
contact with the bottom of cap skirt 20 through teeth 30 are kept in 
contact with the bottom of the tamper indicating band 14, and the collet 
is advanced in synchronization with the axial movement of the core 42 as 
it is being rotated to provide stripping of the closure 10 from the core 
42. 
When the core 42 has been completely unthreaded from the closure 10, the 
collet sleeve 50 is moved axially relative to collet 44 to allow the jaws 
48 to move radially outward a further amount limited by contact of the 
cylindrical collet surface 70 with cylindrical sleeve surface 72 ejecting 
the closure 10 as shown in FIG. 6. 
In the cavity unthreading method of molding illustrated in FIGS. 10-13, the 
components of molding machine 34 are essentially the same as those of 
FIGS. 3-6 with the exception that the collet jaws 48 are not configured to 
form unthreading teeth at the bottom of the cap skirt 14. In the cavity 
unthreading method the axially extending ribs 24 formed on cap skirt 20 
are utilized to restrain rotation of the molded closure 10 during 
unthreading of the core 42. Thus the overall molding sequence is changed 
from axially displacing the moving components completely away f rom the 
stationary cavity mold 40 as depicted from FIG. 3 to FIG. 4 to a 
sequential or gradual axial movement away from the cavity mold as depicted 
in FIGS. 10-12 in order to maintain the cavity mold rib forming 
projections in contact with cap skirt ribs 24 to keep the closure 10 
stationary as the core 42 is unthreaded. 
In FIG. 10 the molding machine 34 is shown in its closed position. The 
collet jaws 48 are locked in the cavity mold 40 by cooperating external 
tapered surface 64 on collet jaw 48 and internal tapered surface in cavity 
mold 40. This closed position defines the molding cavity 36. In FIG. 11 
the molding machine 34 has been opened by movement of the moving elements 
core 42, collet 44 and collet sleeve 50 a short axial distance from the 
cavity mold 40 to permit the jaws 48 to expand outwardly a predetermined 
distance to provide sufficient clearance for jumping the internal bead 26 
or other inwardly directed stop element from the core 42. 
In FIG. 12 the collet jaw 48 has expanded radially outward this 
predetermined distance limited by abutment of the cylindrical collet 
sleeve surface 68 and cylindrical collet surface 70 as seen in FIGS. 12 
and 14. The rib forming projections in the cavity mold acting against ribs 
24 as best seen in FIG. 14, restrain the closure 10 from rotation as 
unthreading rotation of the core 42 takes place. 
While there are no collet unthreading teeth in this embodiment, the window 
forming portion 72 of collet jaw 48 remains in contact with the bottom of 
the cap skirt 20 and contact is maintained between the jaw 48 and the 
bottom of the tamper indicating band to strip the closure 10 in 
synchronization with the axial movement of the core 42 during the 
unthreading rotation of core 42. 
In FIG. 13 the core 42 has been completely unthreaded from the closure 10, 
and the collet sleeve 50 has been moved axially relative to the collet 44 
so that the collet jaw 48 has moved outwardly an amount more than the 
predetermined amount to bring the collet surface 70 into abutment with the 
collet sleeve surface 72 releasing the collet from the closure for 
ejection as shown. 
Another collet unscrewing embodiment is shown in FIGS. 15 and 16 in which 
the collet fingers 46 are spring biased radially inwardly so that they are 
in their radially innermost position as the collet is advanced into the 
cavity mold 40. Here the abutment of the cooperating externally tapered 
surfaces 64 of the collet jaws 48 with the internally tapered surface 66 
of the cavity mold 40 merely locks the collet in its molding cavity 36 
defining position. Core 42 has a frusto-conical cam surface 74 which 
coacts with frusto-conical cam surfaces 76 and 78 on collet 44 to effect 
radially outward movement of collet jaws 48 when core 42 is moved axially 
relative to collet 48. 
FIG. 15 shows the molding machine 34 in its closed position with the 
injection step having been completed to form closure 10. 
As the core 42 is rotated in an unthreading direction the axial 
displacement of the core relative to the collet 44, as seen in FIG. 16, 
causes the core cam surface 74 to coact with the upper internal 
frusto-conical cam surface 76 of the collet, forcing the jaws 48 outward a 
predetermined amount to the position shown in full line where the bead 26 
has cleared the core 42 and is stripped from it. This displacement a 
predetermined amount is maintained by the coaction of the cylindrical core 
surface 80 with the internal cylindrical collet surface 82. When the core 
has been completely unthreaded from the closure as shown in the phantom 
position at 42' in FIG. 16 the conical cam surface 74 on core 42 will have 
moved to its position shown at 74' to coact with the lower conical surface 
78 on the collet to move the collet fingers 46 and jaws 48 to the position 
shown at 46' and 48' respectively. The collet jaws 48 are now free of the 
collet 42, for ejection of the closure 10. 
It will be readily apparent from the foregoing description of the presently 
preferred embodiments of the invention that various modifications can be 
made to the overall molding process without departing from the essence of 
the invention as set forth in the claims.