Press Type Closure

Abstract

A closure suitable of insertion over the opening of a tubular or similarly constructed member and adapted to hermetically seal that opening. The closure construction includes a sloping, corrugated top wall dimensioned according to a plurality of design parameters such that particularly adapts it for placement upon the tubular member by the application of pressure to the approximate center of the top wall.

Parent Case Text

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation-in-part of copending application, Ser. No. 8,228 filed Feb. 3, 1970.

Description

This invention relates to containers and container closures which, preferably, are formed from distortable materials of construction. More particularly, the invention concerns reusable, plastic container closures for open-mouthed containers that are quickly and easily effectable and which assures a lasting reliable hermetic seal.

Food storage containers, including those formed of plastic materials, have been available for many years and have generally employed a bowl, cylinder or similarly shaped tubular vessel and a separate closure or lid made of a relatively flexible material. The closures for such vessels have normally been of several types. One of these types includes an inverted peripheral groove that is placed upon the top edge or rim of a container wall and is pressed onto or expanded over that edge to form a hermetic seal between the two parts. The application of such a closure usually requires that the user apply pressure all around the periphery of the closure to effectively seat same upon the container. Another typical closure is the two-position type which may be flexed to either of two stable positions. In one of these positions, the closure may be easily placed over the rim or within the open-mouth of a container, and then may be flexed to the second position. This flexing action either expands or contracts the peripheral portions of the closure and forces it into tight locking contact with the rim or inside container wall. Others, of course, include the cork-like and toggle action closures which loosely fit into the open mouth of a container and which are thereafter pressed or expanded into contact with the container inside wall surfaces.

In contrast to those mentioned, the closure of this construction is more simple in its operation, gives a lasting hermetic seal, and is of a construction that reduces stress concentrations and susceptibility to heat distortion. In particular, the construction enables the user to apply a closure to a container simply by applying pressure at the approximate center of the closure top wall.

This new closure further includes several distinctive constructional features which enhance its applicability for use in the food storage container area and in other related fields. Among these is a sloping corrugated top wall arrangement which contributes to the contraction of the center wall peripheral edge and the recovery thereof toward or to its extended position with minimum development of internal stresses. This edge, of course, includes as an integral part a sealing wall portion which in its sealed relationship with a container retains the contained materials out of contact with those parts of the closure that lie above the portion or overlie the container edge or rim. Thus, because of this internal sealing arrangement, the hygienic features of this closure are considerably improved over those where sealing was obtained on the outside wall of the container.

The invention also encompasses variable construction parameters affecting the efficient operability of such closures. Therefore, the construction described in detail below has as its principle objectives to minimize both internal stresses within the container closure, as well as the force required to properly assemble a closure and container. At the same time, it is an objective to maximize the sealing pressure between the closure and container and the lateral contraction of the closure sealing wall portion per unit of applied force.

Further objectives of the invention are to provide: an improved closure that is easily applicable to a container and yet will effectively hermetically seal that container; a closure construction which may be molded by compression or injection techniques and which will be economical to manufacture and durable in operation.

Other objectives and advantages will become ore apparent upon further reference to the specification, drawing and claims which describe the invention in more detail and wherein:

FIG. 1 is a top view of a closure construction incorporating the concepts of this invention;

FIG. 2 is a cross-section of the closure taken along line 2--2 in FIG. 1 and a partial cross-section of a container showing the closure in sealing relationship with the container;

FIG. 3 is a partial bottom view of the closure as is depicted in FIG. 1;

FIG. 4 is an enlarged partial cross-section of the peripheral edge of a typical closure and another container shown in dis-assembled relationship; and,

FIG. 5 is a partial cross-section of a closure of this invention taken along line 5--5 of FIG. 1.

Referring now to FIGS. 1-4, it can be seen that in this preferred embodiment, the closure member 10 includes essentially three functional parts, a peripheral inverted U-shaped groove or lip 12, a conical and corrugated top wall 14 and a centrally positioned substantially planar area 16 in the approximate center of the top wall. These corrugations (FIG. 5) emanate from the substantially planar area 16 and terminate at or closely adjacent the peripheral edge 18 of the center top wall 14. The lip 12 is integrally attached to edge 18 and portions of this lip effect the seal between the closure 10 and container 20.

It can be seen that at the peripheral edge 18 of the center main wall, there is an integral upwardly extended side wall 24. Further, as indicated, the side wall 24 normally extends above the corrugated top wall 14 and forms the inside wall of the inverted peripherally disposed groove of lip 12 in closure member 10. This lip and groove are completed by an outer downwardly directed wall 26 and an interconnecting substantially horizontally disposed top wall 28. The outer portion 30 of wall 24 is adapted for mating engagement with the inner wall area of the projecting wall 32 which forms the open mouth in container 20. This engagement, of course, creates the hermetic seal spoken of and thus produces a highly desirable storage container especially suited for the storage of foodstuffs. Likewise, the outer and top walls 26 and 28, respectively, function to properly position the closure on the container 20 and to provide a suitable means for grasping the closure 10 to effect its removal from the container.

In addition, it should be pointed out that in obtaining the mating engagement between the inner area of projecting wall 32 and the outer portion 30 of wall 24, it is particularly important to maintain the innermost peripheral corner area of wall 32 in close proximity to the upper-innermost corner area of wall 24. Such close proximity or abutment can be helpful in producing a moment arm reaction against any tendency of wall 14 to assume an upward convex configuration.

The top wall 14 as indicated includes a corrugated structure such as is exemplified by the plurality of upwardly and outwardly tapered ridges 34. As can be readily seen in FIGS. 1 and 2, the upper portion 38 of these ridges are angularly directed with respect to planar area 16 and therefore the respective peripheral edges 36 thereof lie in a plane removed from that of planar area 16. Similarly, the bottom portions 40 of these corrugations lie in a substantially parallel plane approximate to that of area 16 when the closure is in a relaxed or as molded condition. However, when the closure is in place upon a container, even the bottom portion 40 will be angled toward the container center. The corrugated dimensions are dependent upon the size of the closure as well as other parameters more fully discussed below.

With continued reference to FIGS. 1 and 4, in particular, one will recognize that in operation the locally distortable closure member is contractably and distensibly constructed so that the wall 24 will be displaceable with the peripheral edge 18 of top wall 14. In accomplishing this, the resiliency and elastic memory of the particular materials of construction must be considered and, in particular, the top wall shape should be carefully constructed to take advantage of these inherent physical characteristics of the materials employed. This wall, because of its corrugated construction, tends to collapse upon itself upon the application of pressure to area 16. This collapse substantially uniformly displaces the peripheral edge 18 inwardly and thus draws the side wall 24 inwardly with it. Seemingly, the entire center main wall 14 would continue to collapse with an umbrella-like result if it were not for the reinforcing and stiffening effect of the side wall 24 and lip 12. Despite this restraining effect, the corrugated wall 14 continues to function as described and, in fact, the resilient return of the closure to its approximate as molded size and shape after each distortion is presumably aided by the noted side wall 24.

Another aspect of construction which may be employed with closures of this type is clearly exhibited in FIGS. 2 and 4. There the ribs 42 are exposed and may be seen to extend from wall 24 along the underside of wall 28 and then downwardly along the inside of outer wall 26. These ribs are spaced at selected intervals around the lip 12 so that air can be easily expelled from container 20 as the closure 10 is applied. Note in particular that by extending the ribs 42 down the outer wall 26 sealing between that wall and the container 20 is prevented during the application of the closure. This enables a maximum of air to be displaced from the container and thus creates a more desirable inside condition in the container subsequent to its being sealed by closure wall 24.

As mentioned above, one prime objective of this invention is to optimize forces for applying closures, sealing pressures and stresses in the closures. Ideally, a high sealing pressure, a small push-down force and a low stress level in the structure are desirable. Based upon the intended use of the closures of this type and conditions under which such closures are used, it appears that tensile and compressive stresses approaching 2,000 to 2,500 psi may be tolerable. However, a reduction of these stresses below 1,000 psi is highly desirable to extend the usable life of the closure.

Therefore, it becomes significant to analyze the relationship among the applied axial force (push-down force), the lateral contraction or displacement of the side wall 24, the stresses within the closure, and the sealing pressure. For the purpose of such an analysis, the corrugated plate is treated as a shallow orthotropic thin elastic conical shell of revolution with the side wall 24 acting as an edge stiffener. The orthotropicity of the shell is computed from the corrugation of the closure. The following symbols designate the noted parameters:

P = Push-down force

f.sub.o = flute height at the side wall

l.sub.o = flute base width at the side wall

h.sub.o = flute thickness at the side wall

h.sub.d = thickness of the planar area

h = thickness of the seal lip

r = radial distance from the axis of revolution

r.sub.o = radius at the side wall

r.sub.i = radius of the planar area 16

.rho. = r/r.sub.o

.rho..sub.i = r.sub.i /r.sub.o

E = Young's modulus

.nu. = Poisson's ratio

.delta. = radial displacement of side wall in the sealed condition on the container

u.sub.r = mid surface radial displacement from the undeformed position

u.sub.o = radial displacement at the side wall during the push-down phase

U.sub.P = .pi.Eh.sub.o f.sub.o u.sub.r /Pr.sub.o, dimensionless radial displacement during the push-down phase

U.sub.o = the value of U.sub.P at the side wall (at .rho.=1)

.sigma..sub.rP = peak radial stress in the structure during the push-down phase

.sigma. .sub.P = peak circumferential (hoop) stress during the push-down phase

.sigma..sub.r = radial stress at the side wall during sealed phase, a measure of the sealing pressure

In terms of the above parameters, the shell analysis gives the following formula for the push-down force, P, required to seat this closure: ##SPC1##

where the dimensionless quantity of U.sub.o depends only on the structural parameters f.sub.o /h.sub.o .sup.. f.sub.o /l.sub.o, .rho..sub.i, .nu., h.sub.d /h.sub.o, h /h.sub.o, h.sub.o /r.sub.o, and is generated by a computer program.

In studying the stress patters in closures of this type, it was found that the peak stresses occur during the push-down phase as the closure is applied to the container. Further, the dominant stresses occur at the edge of the planar area 16 and are radially and circumferentially directed. Shear stresses are found to be of secondary importance. The radial and circumferential peak stresses .sigma..sub.rP and .sigma. .sub.P are calculated from the following formulas: ##SPC2##

where .sigma..sub.rP and .sigma. .sub.P are obtained by a computerized structural analysis and depend only on the same seven structural parameters as U.sub.o.

By varying the structural parameters, one learns from Formulas [1], [2], [3] and [4] that the radial contraction per unit push-down force for a corrugated seal is much larger than that for a flat seal even if the latter is determined by a nonlinear plate analysis. The radial contraction for smooth conical seal, an isotropic shell, whose meridional slope is about one-half of the uppermost flute portion 38, approximates that of the corrugated seal only when the side wall is very stiff and is only one-third of the latter if the side wall is relatively flexible. The smooth conical arrangement, however, has at least one possible disadvantage in that the peak stresses produced in it are about twice as high as those created in the corrugated seal.

These behaviors are all due to an important property of the corrugated construction, its relatively low bending and stretching stiffness in the circumferential direction. This property is also characterized by the fact that the radial or lateral displacement per unit push-down force u.sub.o /P, increases with flute height and with the number of flutes. It follows that, for a given lateral displacement, a seal with a larger number of flutes will in general require a smaller push-down force and therefore the peak stresses will be reduced. However, there is a limit to the number of flutes beyond which the push-down force and the peak stresses become insensitive to a further increase in the number of flutes. They may actually become slightly larger (by a few per cent) beyond a certain optimal number of flutes. The optimal flute number for a minimum pushdown force (per unit lateral displacement) is in general smaller than that for minimum peak stresses. Both optimal numbers decrease as the stiffness of the side wall increases.

A reduction in peak stresses may also be effective by increasing the radius or area of planar area 16. The reason for this seems to be that the reduced effects of stress concentration gained by making the area larger, overcomes corresponding losses due to a higher stretching stiffness. Additional reductions in stresses may be accomplished by making the seal lip 12 more flexible, or by increasing the ratio f.sub.o /h.sub.o. It should be noted, however, that such reductions of peak stresses are not without limit and that at some point, the peak stresses will no longer occur at the edge of the planar area 16.

Peak stresses may also be reduced significantly by reducing the lateral displacement in effecting placement of the closure on a container. However, this also reduces the sealing pressure between the two and therefore somewhat modifies the extent that this approach may be employed. A measure of the sealing pressure of the closure is the radial stress at the outer edge of the corrugated seal after the closure is fitted with the container and the push-down force is removed:

The dimensionless quantity .sigma. in [5] depends on the same seven structural parameters as U.sub.o and is obtained by a computerized structural analysis.

By varing these structural parameters, it becomes apparent that the sealing pressure will increase as f.sub.o /l.sub.o and/or .rho..sub.i increase. Contra to this, sealing pressure will decrease as h /h.sub.o and/or f.sub.o /h.sub.o increase.

Having learned how the push-down force, the lateral displacement, peak stresses and sealing pressure vary with the structural design, the various noted design parameters may then be chosen to achieve the appropriate desired results.

Also, as is discussed briefly above, the closure member 10 is presently preferably formed from a distortable thermoplastic, for example, low density polyethylene; however, high density polyethylene, polypropylene, polyolefin blends or similar materials may be suitably employed in effectuation of the inventive concept. Likewise, the open-mouthed containers 20 (FIGS. 2, 4, 5 and 6) with which these closures are primarily intended for use, are also generally formed from the same or similar materials. It should be pointed out, however, that such closures may well be adapted for use with containers including diversified types of materials.

In this new method of operation, closures of this invention tend to experience a lateral displacement within the conical, corrugated top wall 14 as pressure is applied to the planar area 16. The corrugated construction accentuates this displacement as the top wall 14 folds upon itself in an accordion-like fashion. This then similarly tends to enable the side wall 24 to draw inwardly, thereby facilitating entry of the top wall 14 into the open-mouth end of the container or tubular member 20. After insertion and upon release of the applied pressure, the resilient closure material due to its elastic memory, attempts to assume its relaxed or as molded orientation and thus expands the side wall 24 against the inner portion of the container wall to hermetically seal the container. To remove the closure, it is only necessary to apply an upward pressure against the U-shaped seal lip 12 thus prying the closure off from projecting edge 30 of the container.

From the foregoing description, it should be apparent that the invention encompasses an advantageous advance in the art. Further, it should be clear that the invention may be embodied in other specific forms without departing from the spirit of the essential characteristics thereof. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims

We claim:

1. A locally distortable plastic closure contractably and distensibly constructed and having an elastic memory such that it is adapted to hermetically seal an open-mouthed member and comprising:

a. a top wall including an area having contiguous corrugations emanating from a center portion there of and extending to a peripheral edge, said top wall being adapted for the application of pressure, of from about between 2 and 200 psi as is computed using the formula:

where the dimensionless quantity U.sub.o depends only on the structural parameters f.sub.o /h.sub.o, f.sub.o /l.sub.o, .rho..sub.i, .nu., h.sub.d /h.sub.o, h /h.sub.o, h.sub.o /r.sub.o, and such pressure is applied to the approximate center thereof in such manner that said corrugated area tends to collapse upon itself and substantially uniformly displace said peripheral edge until said closure is easily positionable on an open-mouthed member; and,

b. integral extended sealing means positioned around said peripheral edge of the center main wall, said sealing means being displaceable in like manner with said peripheral edge such that at least a portion of said sealing means is closely engageable with and sealable against the walls of an open-mouthed member due to the resiliency and elastic memory of said closure upon the discontinuance of applied pressure to said center main wall.

2. In combination an open-mouthed container and a locally distortable, contractably and distensibly constructed plastic closure having an elastic memory such that it is adapted to hermetically seal said container and comprising:

a. a container including a projecting wall construction forming the open mouth thereof;

b. a closure having a top wall including an area having contiguous corrugations emanating from a center portion thereof and extending to a peripheral edge, said top wall being adapted for the application of pressure of from about between 2 and 200 psi as is computed using the formula:

where the dimensionless quantity U.sub.o depends only on the structural parameters f.sub.o /h.sub.o, f.sub.o /l.sub.o, .rho..sub.i, .nu., h.sub.d /h.sub.o, h /h.sub.o, h.sub.o /r.sub.o, to the approximate center thereof in such manner that said corrugated area tends to collapse upon itself and substantially uniformly displace said peripheral edge until said closure is easily positionable on said container; and,

c. integral extended sealing means positioned around said peripheral edge of the center main wall, said sealing means being displaceable in like manner with said peripheral edge, such that at least a portion of said sealing means is closely engageable with and sealable against the walls of said container due to the resiliency and elastic memory of said closure upon the discontinuance of applied pressure to said center main wall.

3. In combination an open-mouthed container and contractable and distensible closure member having an elastic memory such that it is adapted to hermetically seal said open-mouthed container and comprising:

a. a container including a projecting wall construction forming the open mouth thereof;

b. a closure having a top wall including laterally extending contiguous corrugated portions terminating in a peripheral edge, at least segments of said edge lying in a different plane than that of the centralmost area of said top wall; and,

c. an extended integral sealing member positioned around said peripheral edge, which member is distortably responsive to a substantially centrally applied force of from about between 2 and 200 psi as is computed using the formula

where the dimensionless quantity U.sub.o depends only on the structural parameters f.sub.o /h.sub.o, f.sub.o /l.sub.o, .rho..sub.i, .nu., h.sub.d /h.sub.o, h /h.sub.o, h.sub.o /r.sub.o, on the top wall enabling placement of said closure upon the open-mouthed container and which is distensibly responsive to any reduction in said force, such that it seals against said projecting walls.

4. A locally distortable plastic closure according to claim 1 wherein said sealing means includes a substantially U-shaped groove having connected inner, outer and top walls, said top and outer walls having inside surfaces upon which there are disposed a plurality of integral ribs selectively spaced therearound.

5. A locally distortable plastic closure according to claim 3 wherein said sealing means includes a substantially U-shaped groove having connected inner, outer and top walls, said top and outer walls having inside surfaces upon which there are disposed a plurality of integral ribs selectively spaced therearound.