Composite closure cap with removal torque control

A composite closure cap is described comprising a molded plastic ring and a separate disc-like cover. The cover includes a gasket for sealing. Tapered friction surfaces on the plastic ring and on the cover interact to provide for the control of the closure cap removal torque.

BACKGROUND OF THE INVENTION 
The present invention relates to closure caps for sealing glass or plastic 
containers and more particularly to an improved composite closure cap 
having a metal cover and molded plastic container engaging ring. The metal 
cover and the plastic ring have tapered and engaging surfaces for a 
controlled closure cap removal torque. 
Composite closure caps are well known and are widely used. They include a 
disc-like cover portion inserted into a circular molded plastic ring with 
the ring providing threaded or other means for attaching the composite cap 
to the container. A sealing gasket is provided on the metal cover and 
tamper indicating means are sometimes provided in the form of a vacuum 
indicator button on the cover with or without an additional tamper 
indicating band provided as a portion of the molded plastic ring. 
While such composite closures have found acceptance in various packaging 
uses, including the vacuum packaging of food, prior composite closures 
have proven unsatisfactory for certain food packages where heat is applied 
during the sealing operations in retorting and otherwise. A serious 
drawback to certain of these prior closures has been a significant 
reduction in torque during the package handling and/or shelf life. The 
removal torque for the closure cap can become significantly reduced 
resulting in potential problems with consumer confidence and reduced 
resistance to abuse. Even where attempts have been made to increase this 
torque by the application of excess rotational force to the cap during 
application, the result has been creepage of portions of the plastic ring 
and container causing a loss of removal torque between the ring and 
threads and between the ring and the separate closure cover. 
An object of this invention is to minimize this drop in removal torque by 
reducing the force in the plastic threads which cause it. 
Other and further objects of the present invention will become apparent 
upon an understanding of the illustraive embodiments about to be 
described, or will be indicated in the appended claims, and various 
advantages not referred to herein will occur to one skilled in the art 
upon employment of the invention in practice.

Composite closures, as noted above, are in wide use particularly for 
sealing food packages. The following United States patents, for example, 
have been issued to the assignee of the present invention and these 
illustrate prior composite caps with a plastic sealing ring mounting a 
metal or plastic disc-like cover, i.e. U.S. Pat. No. 3,930,589 of Jan. 6, 
1976; U.S. Pat. Nos. 3,913,772 and 3,913,771 both of Oct. 21, 1975. 
DESCRIPTION OF THE PREFERRED EMBODIMENT 
A preferred embodiment of the improved closure and package will now be 
described with particular references to the figures. 
The closure 1 is applied to and seals a glass or plastic container 2. As 
illustrated in FIGS. 3 and 4, the molded plastic ring 4 is formed with a 
skirt portion 5 including inwardly directed threads 6 for engaging 
cooperating threads 7 at the container mouth. A radially inwardly directed 
flange 8 is formed at the top of the plastic ring 4. Together with the 
skirt portion 5 it forms a cover engaging corner with the inner edge 9 
engaging and forcing the cover 10 into sealing engagement with the 
container rim 11. A tamper indicating band may form the lower portion of 
the plastic ring 4 and it is attached to the skirt portion 5 of the 
plastic ring 4 at a line of weakness as described in the above noted 
patents. 
As illustrated at 12 in the figures, there is an inwardly and upwardly 
tapered surface near the top of the plastic band. Upon assembly of the 
closure 1, the cover 10 is inserted at the top of the ring 4 and the 
preferred embodiment of the cover 10 includes a downwardly facing gasket 
receiving channel 13 having a tapered radial outermost surface 14 shaped 
to conform to the ring taper for engagement therewith. The engaged 
surfaces 12 and 14 form a torque control means. The frictional engagement 
between these surfaces 12 and 14 upon closure cap application provides for 
a removal torque adjustment as will be described further below. Either the 
plastic surface 12 or the metal cover surface 14 or both may be roughened 
or scored as illustrated in FIG. 8 to increase the frictional engagement 
therebetween. 
These engaged frictional surfaces 12 and 14 provide an adjustable amount of 
ring 4 retention torque which is set by controlling the sealing torque 
force during container sealing. The relative flared or "inclined plane" 
engagement between the cover and the plastic ring increases as the cap and 
the container threads draw the closure cap into sealing relation with the 
advantage resulting from the taper reducing the stress on the ring 4 
threads 6. This is advantageous because the reduced thread and ring 
stresses permit them to remain in their original molded position without 
creepage during package storage and cause the removal torque as determined 
by the frictional engagement between the tapered surfaces to remain 
substantially constant and at the level obtained during the sealing. 
FIGS. 6 and 7 illustrate a closure cap 1 including the ring 4 and the cover 
10 in sealing positions. FIG. 5 illustrates a seal made to provide a low 
degree of closure removal torque so that the cover and the ring are not 
screwed fully down on the container and are relatively higher on the 
sealed package. Nevertheless, the relatively thick channel 13 with the 
sealing gasket 20 are fully engaged with the rim 11 to form an effective 
top and side seal. The downward force generated at the ring threads 6 has 
been transferred to the upper portion of the ring 4 including the ring 
edge 9 and the flared ring and cover torque control surfaces 12 and 14. 
FIG. 6 illustrates a seal where the ring 4 has been turned further down on 
the container rim resulting in an increase in the amount of removal torque 
created between the taper surfaces 12 and 14. In this case the ring inner 
edge 9 flexes upwardly to accommodate the change in ring position and an 
excellent top and side seal results between the gasket 20 and the 
container rim 11. 
FIG. 7 is an enlarged perspective view showing the rotation of the ring 4 
on the container threads 7 and showing the ring inner edge 9 forcing the 
cover 10 into sealing position as an additional sealing and torque 
controlling force is generated between the engaged tapered ring and cover 
torque control surfaces 12 and 14. 
FIG. 9 is an enlarged sectional view showing the engaged and roughened 
tapered portions 12 and 14 in the embodiment of FIG. 8 and illustrating 
the generation of the significant and controllable torque removal force 
between the two engaged and roughened surfaces 12 and 14. One or the other 
of these surfaces may be left smooth where a satisfactory friction force 
is generated by a single roughened surface. 
Enlarged sectional views 10 and 11 illustrate differing angular positions 
of the tapered surfaces with respect to the container axis. FIG. 10 
illustrates a relatively small angle A in a situation where a relatively 
low degree of stress is placed on the ring threads 6 when drawing the 
cover 10 into its sealed position as illustrated. This sharper angular 
relationship maximizes the more radially directed component of force 
between the plastic ring 4 and the cover 10 to provide a relatively high 
closure retention and removal torque while the low stress on the plastic 
threads minimizes plastic creep and unintentional closure loosening. 
FIG. 11 illustrates a wider angle B providing for a minimized radially 
directed component of the force between the ring and the cover providing a 
still effective removal torque control without a significantly increased 
stress on the ring threads. 
It will be seen that an improved composite closure is provided which 
provides a package with minimized creep in the plastic ring of the closure 
and with a predetermined torque control. 
As various changes may be made in the form, construction and arrangement of 
the parts herein without departing from the spirit and scope of the 
invention and without sacrificing any of its advantages, it is to be 
understood that all matter herein is to be interpreted as illustrative and 
not in a limiting sense.