The present invention relates to tapered thread structures on a container finish and a corresponding closure.
Thread structures used on containers can take a wide variety of designs. The details of any one particular thread structure on a container is influenced by many factors, including the contained contents, operational aspects of the complimentary closure, materials, methods of package manufacture and consumer use.
A particularly useful and widely accepted closure/seal system for packages is to position external threads on the container which mate with internal threads positioned on the interior wall of a closure. As is well known, the closure is removed and reapplied by rotary threading action.
One factor requiring attention with threaded closure systems is the circumferential extent of mating thread engagement between closure and container. One may desire to minimize circumferential thread engagement to only that required for adequate closure retention for a number of reasons. These include avoiding requirements for excessive turning during closure manipulation by the consumer. Moreover, equipment associated with rotary capping operations is normally restricted in the number of “turns” of the closure allowed during initial application. On the other hand, there must be enough thread engagement for proper threading and sealing on application. A common “rule-of-thumb” in classic packaging technology is that at least a single turn of thread engagement should be incorporated into the designed thread engagement between the fully applied closure and container. This “rule-of-thumb” is most often adequate for packaging using classic materials and fabrication, such as combinations of rigid glass containers and rigid polystyrene or polypropylene closures. In these cases the complimentary threads have been designed to be relatively massive (such as the familiar modified buttress design) with substantial thread depth. In this way the required surface contact between the topside of the closure thread and the underside of the container thread is normally achieved with one turn (360 degrees) of complimentary thread engagement.
It is common to deviate from the “classical” packaging designs, materials, and fabrication for a myriad of reasons, such as, to provide lightweight packaging by thinning the wall sections and structural improvements. However, when providing lightweight packaging other concerns such as part flexibility and distortion are increased. Another example is the choice of alternate materials such as low density polyethylene (LDPE) for the closure, taking advantage of the unique properties of LOPE. In these cases, if one wishes to employ a threaded closure, the classic one turn “rule-of-thumb” may not be adequate to ensure proper retention of the applied closure. This is a result of the added flexibility of thin walling or the inherent relative flexibility of the LDPE materials. In some cases a minimal amount of internal container pressure, such as that experienced when the container may be dropped, is sufficient to cause the closure skirt to expand to the point where the closure simply pops off. This flexibility can also allow localized distortion of the closure to the point where the closure threads “strip” relative to the mating container threads. This stripping action normally initiates at the bottom end of the closure thread where the hoop strength of the closure is at a minimum. At that position, radial distortion of the closure skirt allows disengagement of the mating threads. Continued torquing causes the disengagement to proceed helically upward in a “tiring” manner until finally the mating threads “jump” over each other. This stripping mechanism is not only of concern on initial application, where such stripping can result in an unseated closure, but also in the hands of the consumer expecting reseal integrity.
In order to adjust for the inherent flexibility of LDPE materials, designers have often chosen to dramatically increase the circumferential extent of mating thread engagement. However, when maintaining a single lead thread, the amount of turning required to apply and remove the closure can become excessive for rotary capping and/or convenient consumer manipulation. These concerns can be addressed by using multiple lead threads. In this case, the total thread engagement approximates the sum of the circumferential extent of each of the multiple leads. In addition, the multiple leads are circumferentially distributed around the lower portion of the closure skirt to thereby balance the distortional forces involved in closure torquing. On the other hand, multiple lead threads normally require an increased helical angle (vs. horizontal) for the thread and/or an uniformly finer thread. An increased helical angle can lead to closure back-off or unintentional unthreading or even loosening of the thread. In addition, an uniformly finer thread will decrease the amount of radial thread overlap thereby reducing the ability of the system to withstand closure distortions. Such threads will also promote cross threading during application due to the decrease target presented to the closure thread lead by the reduced container thread pitch.
It is clear to those skilled in the art that substitution of LDPE materials for more rigid materials, while accomplishing benefits unique to LDPE, also involves performance tradeoffs which cannot always be recovered by the alternate designs advanced to date.
Additional problems have arisen recently when attempts have been made to employ certain closure designs using certain capping practice. These problems can be broadly categorized as associated with the capping process as opposed to the material choices for the package components.
A first method of capping, known in the industry, involves a “pick and place” operation. This method includes positive positioning of a closure within a gripping chuck which is then moved directly over a container. The chuck is simultaneously turned and moved axially toward the container to screw the closure onto the container finish. This application method is similar to actual manual application. Further details of this application method appear in the “Detailed Description Of Preferred Embodiments” which follows in the Specification.
An alternate, less expensive, approach to closure application can be characterized as a “pickoff” operation. During “pickoff” a closure is held in a chute and positioned at an angle relative to the axis of a container finish that passes beneath the closure. The container finish comes into contact with the closure and picks it off the chute. Unfortunately, the “pickoff” approach can lead to certain difficulties associated with structural design and material selection as will be more fully explained herein in association with prior art
In a first embodiment of the present invention, a unique neck finish for a container is provided. The neck finish includes a substantially cylindrical exterior wall surface surrounding an orifice defined in the container and includes a thread structure positioned about the exterior wall surface. The thread structure has at least a first portion and a second portion. Each portion has a corresponding effective maximum diameter, wherein the effective maximum diameter of the first portion is less than the effective maximum diameter of the second portion.
Further elements of the first embodiment may include providing a neck finish wherein the first portion is positioned axially above the second portion. Alternatively, the thread structure may have a convex surface projecting radially outwardly from the exterior wall surface. The thread structure may also have an effective maximum diameter that continuously increases from the first portion to the second portion, or that incrementally increases from the first portion to the second portion, or that selectively increases from the first portion to the second portion.
In a second embodiment of the present invention a neck finish for a container is provided and has a substantially cylindrical exterior wall surface surrounding an orifice and has a thread structure. The thread structure has multiple portions of convex surface regions projecting radially outwardly from the exterior wall surface. Each of the portions has a point of maximum separation from the exterior wall surface. The point of maximum separation also defines an effective maximum diameter associated with the portion. A selected first portion has an effective maximum diameter less than a selected second portion positioned axially below the first portion.
Additional elements of the second embodiment may provide for multiple portions being positioned to form a helical path extending circumferentially around the exterior wall surface and being characterized by having a maximum effective diameter of a portion positioned at an upper segment of the helical path being less than the maximum effective diameter of a portion positioned at a lower segment of the helical path.
In a third embodiment of the present invention a neck finish for a container is provided in combination with a container closure. The neck finish is defined as having an upper orifice that defines an opening, a downward extending neck wall below the opening, a thread structure positioned on the exterior of the neck wall, and a first bead-like structure surrounding the neck wall positioned axially below the thread structure. The thread structure has a first portion and a second portion positioned axially below the first portion. The first and second portions have a corresponding effective maximum diameter such that the effective maximum diameter of the first portion is less than the effective maximum diameter of the second portion. The container closure has a top, a downwardly extending skirt portion depending from the top. The skirt portion has an interior, and a radially inwardly projecting member adapted for engagement with the first bead-like structure, such as a second bead-like structure or a J-band structure, positioned within the interior of the skirt portion.
The third embodiment may include other elements such as providing a thread structure to include multiple portions positioned to form a helical path extending circumferentially around the exterior of the neck wall and characterized by having a maximum effective diameter of a portion positioned at an upper segment of the helical path being less than a maximum effective diameter of a portion positioned at a lower segment of the helical path. Alternatively, a clearance space may be provided when the container closure is initially applied to the container neck for closing. The clearance space would be disposed between an upper edge of the exterior of the neck wall and a free edge of the interior of the skirt portion. The clearance space may provide decreased interference or increased clearance with said first portion, and/or provide resistance to stripping under the action of torque applied to said container closure.
The radially inwardly projecting member on the container closure may include a tamper-evidencing band frangibly connected to the downwardly extending skirt portion and having an inwardly and upwardly turned retaining rim adapted for engagement with the first bead-like structure.
In a fourth embodiment of the present invention, a method of applying a threaded cap to a threaded neck of a container is disclosed. The method includes providing a threaded neck of a container that includes thread structure having a first portion and a second portion positioned axially below said first portion. The first and second portions have a corresponding effective maximum diameter such that the effective maximum diameter of the first portion is less than the effective maximum diameter of the second portion. The threaded neck further includes a neck wall having an exterior with a bead-like structure surrounding the neck positioned axially below the thread structure. Next, a threaded cap is placed at an angle offset from a vertical axis defined by the threaded neck. Then, the container and/or the cap are moved towards each other such that a neck edge defined by the exterior of the neck wall comes into contact with a cap edge defined by an interior wall of the cap, wherein upon contact a clearance space is defined between an upper edge of the exterior defined by the neck wall and a free edge of the interior wall of the cap. Next, the container and/or cap are further moved towards each other with the cap in contact therewith. Last, the cap is leveled onto the threaded neck of the container such that the cap axis is urged towards a substantially vertical position on the threaded neck. The fourth embodiment may further include contacting the cap with a skid plate or roller to level and align the cap and container to one another. Additionally, it may include urging a tamper-evidencing band defined on the cap vertically downward past the thread structure and/or urging the tamper-evidencing band over the bead-like structure surrounding the neck wall. In addition, a step may be included to screw the cap on the container in complimentary threaded engagement, or to snap the cap on the container in complimentary threaded engagement by axial force,
The present invention has a number of embodiments any one of which may or may not include a number advantages over the prior art. One advantage is to teach an inventive container finish contributing to the facile application of closures incorporating depending tamper evidencing band structure. Another advantage is to improve the integrity, seal, and reliability of threaded closure systems while maintaining consumer ease of use. A further advantage is to permit choice of low density materials for threaded closures while eliminating some detrimental consequences previously accompanying such a choice.
Numerous other advantages and features of the invention will become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims, and from the accompanying drawings.
A fuller understanding of the foregoing may be had by reference to the accompanying drawings, wherein:
a is a side elevational view, partially in section, of a novel container finish according to an embodiment of the present invention wherein the variable outward projection of the thread structure incrementally increases as it traverses its vertical helical path.
b is a side elevational view, partially in section, of a novel container finish according to an embodiment of the present invention wherein the variable outward projection of the thread structure selectively increases as it traverses its vertical helical path.
a is a side elevational view showing the combination of a closure having a bead-like engagement structure after complete application to the container finish of
The embodiments of the invention will now be described in detail in conjunction with the descriptive figures. While the invention is susceptible to embodiments in many different forms, there are shown in the drawings and will be described herein, in detail, the preferred embodiments of the present invention. It should be understood, however, that the present disclosure is to be considered an exemplification of the principles of the invention and is not intended to limit the spirit or scope of the invention and/or the embodiments illustrated.
Referring now to
The thread structure 18 can take many sectional forms as is known in the art. In addition, the thread structure 18 can comprise multiple leads and various pitches as is known in the art. The diameter defined by the exterior projection of the thread structure 18 is commonly referred to as the “T diameter”. The effective “T” diameter is twice the radial distance from the finish axis to the point of maximum projection at a particular position along a helical thread path or horizontally directed bead. The upper portion of the thread structure 18 has an upper thread start indicated by numeral 20. The vertical distance between the uppermost point of thread structure 18 and the uppermost point on top surface 22 of base structure 12 is commonly referred to as the “S dimension” of the finish 10, as shown.
Below the thread structure 18 there is often present a retention bead-like structure 19 outwardly projecting from the “E wall”. As is known in the art, this retention bead-like structure 19 serves as a retention feature, cooperating with suitable structure defined on a cap, as later discussed herein, such as a closure tamper evidencing band to retain the band during initial closure removal. The diameter defined by the maximum extent of this retention bead-like structure is commonly referred to as the “A diameter” as shown.
Referring now to
When combining a prior art closure, such as that of
Turning now to
An alternate, less expensive, approach to this closure application can be characterized as a “pickoff” application as illustrated at prior art
In the case of a screw-on closure, the application station following “pickoff” may consist of various mechanisms to impart relative rotation between the closure and container. In many cases rotation alone is expected to result in proper threading and seating of the closure. Thus if the pickoff is not adequately “square” cross-threading can be a problem. In other cases, if the closure is insufficiently seated during pickoff, the closure and container threads may have insufficient vertical overlap to properly mesh as a result of simple rotation. In these cases more complicated top loading may be required. Those skilled in the art will recognize that while the “pickoff” method employs relatively simple, inexpensive equipment compared to rotary chuck application, many more closure/container design factors must be proper to achieve satisfactory “pickoff” closure application.
Regarding the “pickoff” method of closure application, some closure designs, particularly certain tamper evident closure designs, present additional difficulties. Many of the tamper evident closure concepts incorporate a tamper evidencing band depending from the lower edge of the primary closure skirt through a frangible connection.
One such design that is particularly effective in its tamper evidencing performance is the “i-Band” design illustrated in the simplified embodiment of
One skilled in the art will recognize that in general there will exist an optimal value for the difference in effective diameters for the flange free edge between the fully expanded and relaxed conditions. However, as will be shown, the appropriate diameter in the relaxed condition has considerable influence on the ability of such a closure to be properly applied by the “pickoff” method.
Turning now to
However, as is seen in the prior art
One will understand that, while the “pickoff” problems illustrated in the snapshot view of prior art
Turning now to
In
Referring now to
The latter resting position of the closure following pickoff is illustrated in
A further aspect of one or more of the embodiments is an increase in the ability of threaded closures to resist stripping under the action of applied torque. This feature is illustrated in conjunction with the situational embodiment of
Classical methods of plastic closure manufacture included unscrewing threads from the mold and use of relatively rigid materials such as polypropylene. In these classic cases the closure could be made very resistant to stripping. However, if one wishes to manufacture closures using a simpler molding process wherein threads are simply stripped from the mold, thread design and material selection must be considered. These considerations, in general, reduce the ability of the closure to resist stripping when applied to a container.
The novel container finishes of one or more of the embodiments can be adopted to recover some of the ability of certain closure systems to resist stripping. This is a result of the variable effective “T” dimension of the novel finishes taught here. These finishes incorporate a reduced effective “T” dimension in the upper portions of the container finish while expanding the effective “T” dimension as the thread descends vertically to its lower thread start (see
When using low density polyethylene closures, typically about 0.020 inch diameter interference at the lower thread start, changing to 0.007 inch clearance at the upper thread start has given positive results. These dimensions are only typical and could vary considerably depending on structural design and material selection.
It is noted here that a classic “rule-of-thumb” for closure design is to ensure there be at least 0.001 inch of clearance between the finish “T” diameter and the closure thread root diameter in all cases. The current specification teaches a novel consideration of purposely designing in selective thread interference in those contact regions sensitive to closure stripping. Such selective interference may give particular advantage to systems employing thin walled closures or closures fabricated from relatively flexible materials such as low density polyethylene.
From the foregoing and as mentioned above, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of the novel concept of the invention. It is to be understood that no limitation with respect to the specific methods and apparatus illustrated herein is intended or should be inferred.
The present invention is a divisional application of U.S. patent Ser. No. 11/379,101.
Number | Date | Country | |
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Parent | 11379101 | Apr 2006 | US |
Child | 12775712 | US |