Recessed, Rim-Locking Container Closure

As is well understood in the packaging art, many relatively short shelf-life products, especially dairy products such as cottage cheese, yogurt, sour cream and the like, may be satisfactorily and advantageously packaged in relatively inexpensive, frusto-conically shaped, wide-mouth nestable containers in which the mouth is surrounded by an annular externally projecting curled rim or bead. At one time, two-piece waxed paperboard containers were very widely used for such purposes and in recent years one-piece seamless containers produced from a suitable thermoplastic sheet material by thermoforming have also gained a substantial measure of popularity for such purposes. In any case, any such container must be suitably closed by a separate closure member after the intended product has been packaged therein, and it is important, for economic reasons, that such closure be of such a type that it can be rapidly applied to a filled container, by mechanical closure-applicating equipment, in order to permit the rapid capping of a great number of such containers.

One-piece thermoplastic closures of the recessed rim-locking type are relatively inexpensive and have proven to be functionally satisfactory for the closing of externally rimmed, nestable cottage cheese and other food product containers of the type described above. However, to provide the radially outermost skirt of such a closure with inwardly projecting locking beads of sufficient depth to securely engage the rim of the associated container, it has proven to be quite desirable to form such closures in a female die, where the natural shrinkage of the formed closure, on cooling, will cause the closure to shrink away from the die, thereby facilitating removal of closure from the die in spite of the outwardly projecting locking bead forming portions of the die. In order to get the sheet from which such closure is formed to draw properly into such a die, however, it has been found necessary to maintain a ratio of no more than about 1:1 between the depth of the outer closure skirt and the annular width of the web that extends between such skirt and the peripheral wall which surrounds the recessed central portion of the closure. Because of the substantial width of such web, however, difficulty has been experienced in properly centering the recessed portions of such closures on the open mouths of filled containers when applying such closures mechanically. Likewise, because of the width of such web, heretofore such closures were not always resistant to turning relative to a filled container, when assembled thereto, since the frictional contact between the closure and the container was inherently limited to the contact at the outer skirt of the closure.

In accordance with the present invention, however, there is provided a recessed, rim-locking closure for a wide-mouth container with an externally projecting rim or bead surrounding the mouth thereof, such closure being of a design suitable to permit it to be manufactured from thermoplastic material in one-piece configuration by thermoforming a thermoplastic sheet material in a female die, such closure having improved centering characteristics during capping of a filled container and thereby being suitable for application by mechanical applicating devices, such closure also being adapted to frictionally engage the inside of the associated container for added resistance to turning relative thereto. A closure according to the present invention has the usual degree of lateral spacing between the outer skirt and the recessed central portion of the closure to permit proper forming of the closure by thermoforming in a female die, the improved centering characteristics and resistance to turning of such closure being obtained by a circumferentially spaced apart series of arcuately short, radially outwardly projecting, suitably contoured lugs on the peripheral wall which surrounds the recessed central portion of the closure. These lugs, which do not interfere with proper thermoforming of such a closure, each have a lower tapered portion which extends upwardly and outwardly from the recessed central panel of the closure and which aids in the centering of the closure on a container during capping. Each of these closure lugs also has an upper, generally vertical section which is adapted to frictionally contact the inside of the mouth of a capped container to increase the resistance of the closure to turning on the container.

Accordingly, it is an object of the present invention to provide an improved container closure of the recessed, rim-locking type. More particularly, it is an object of the present invention to provide a one-piece, recessed, rim-locking container closure which can be thermoformed from thermoplastic sheet material in a female die and which has improved centering characteristics, relative to the associated container, when being applied thereto. More particularly yet, it is an object of the present invention to provide such a closure which will also be adapted to frictionally engage the inside of the mouth of the associated container, when in place thereon, for improved resistance to turning relative thereto. It is also an object of the present invention to provide a package comprising a wide-mouth container with an externally projecting rim or bead and a female die-thermoformed, plastic one-piece closure in place over the mouth of such container, such closure being of the recessed rim-locking type and contacting the inside of the container mouth at a plurality of circumferentially spaced apart points for improved frictional resistance to turning relative to the container.

For a further understanding of the present invention and the objects thereof, attention is directed to the drawing and the following description thereof, to the detailed description of the invention and to the appended claims.

FIG. 1 is a horizontal plan view of a preferred embodiment of a closure in accordance with the present invention;

FIG. 2 is a sectional view taken on line 2--2 of FIG. 1;

FIG. 3 is a vertical elevation view, partly in section, of a typical nestable container to which the closure of FIGS. 1 and 2 may be applied;

FIG. 4 is a view similar to FIG. 3 showing the closure of FIGS. 1 and 2 affixed to the container of FIG. 3; and

FIG. 5 is a fragmentary sectional view, at an enlarged scale, illustrating more clearly the manner in which the closure of FIGS. 1 and 2 engages the container of FIG. 3 when it is affixed thereto.

A closure in accordance with the present invention, as identified generally by reference character 11 in the drawing, may be made in one-piece by thermoforming a sheet of a suitable thermoplastic material, preferably in a female die for reasons which will be hereinafter explained more fully. Impact resistant grades of thermoplastic material are preferred for such closures, for example, medium impact polystyrene for closures for cottage cheese and yogurt containers and ABS for soft margarine containers because of its good grease resistance.

In its construction, closure 11 comprises a central panel portion 12 which is adapted to substantially span the mouth of the container to which such closure is adapted to be affixed, as will be hereinafter described more fully. So that central panel portion 12 of closure 11 will be recessed within the head space of the associated container, to reduce the volume of air in the head space of the container and to thereby preserve the freshness of the packaged product, as is well understood in the art, panel portion 13 is surrounded by a peripheral wall portion 13 which extends axially outwardly from central panel portion 12 for a distance substantially equal to the distance it is desired to recess central panel within the mouth of the associated container. Peripheral wall portion 13, in turn, is surrounded by an annular portion 14 which is attached thereto above the juncture of panel portion 12 with wall portion 13 and which extends laterally outwardly from wall portion 13. Annular portion 14 is sized and positioned so as to be adapted to rest on the beaded or flanged rim portion of the container to which it is intended to be affixed, and has attached thereto, at a location laterally outwardly of its juncture with wall portion 14, a peripheral skirt portion 15 which extends axially downwardly, or, in other words, back toward the plane of central panel portion 12.

Closure 11 is adapted to be affixed to a wide-mouth, thin wall container such as the conventional one-piece, seamless container of nestable shape which is identified by reference character 21 in FIG. 3. Such containers are quite popular for many short shelf life food packaging applications, and they may be produced relatively inexpensively from a sheet of a suitable thermoplastic material, such as general purpose polystyrene for cottage cheese containers, by known types of thermoforming. A container of this type is customarily provided with an annular, laterally outwardly projecting rim 22 reinforcing and surrounding the open mouth thereof, and comparable two-piece paperboard containers have an equivalent projection, usually in the form of a curled bead of generally circular cross-section.

To firmly retain closure 11 in place on the rimmed mouth of the container 21 to which it is adapted to be affixed, as is shown in FIGS. 4 and 5, where the product to be packaged in container 21 is omitted for the sake of clarity, the peripheral skirt portion 15 of the closure is provided with a series of spaced apart, inwardly projecting beads 16. Beads 16 are located near the lower or free end of skirt portion 15, below the plane of the lowermost portion of the rim 22 which surrounds the mouth of the associated container 21 when the closure is affixed thereto, and the radial distance from the vertical central axis of the assembled container and closure to the radially innermost portion of beads 16 is at least slightly less than the radial distance to the outermost portion of the rim 22 of container 21. This relationship between such radial distances results in interference between the beads 16 and the container rim 22 thereby making it possible for the beads to securely grip the container rim when assembled thereto, the inherent flexible nature of the thin skirt portion 15 making it possible to force the closure on to the container mouth by capping equipment of conventional character. In fact, to obtain optimum rim gripping or locking properties, closure 11 should preferably be formed in a female mold, since normal shrinkage of the formed closure, on cooling, will make it possible to provide beads 16 of greater radial extent without interfering with removal of the closure from the mold.

In order to properly thermoform a closure 11 as described above, it is important to maintain the ratio of the radial or lateral extent of annular portion 14 to the axial extent of skirt portion 15 at not substantially less than about 1:1; otherwise, the sheet from which such closure is formed will not properly fill the mold when using conventional thermoforming practices. Such lateral extent of annular portion 14 is normally considerably greater than the lateral extent of the container rim over which it is adapted to lie, making it difficult to properly center a closure on its associated container during capping, especially when using high-speed mechanical capping devices. To overcome such centering difficulties, peripheral wall portion 13 of closure 11 is provided with a circumferentially spaced apart series of outwardly projecting lugs 17 which project into the space between wall portion 13 and skirt portion 15, terminating short of skirt portion by a distance sufficient to receive rim portion 22 of container 21. Such lugs, which do not interfere with proper thermoforming of closure 11, preferably have at least a lowermost portion of substantial axial extent, identified as portion 17a in the drawing, which tapers at a substantial angle, e.g. of the order of 40.degree.-45.degree., upwardly and outwardly from the juncture of wall portion 13 with panel portion 12 to further aid in the centering of closure 11 on container 21. Lugs 17 can also advantageously be provided with an upper portion of substantial axial extent, identified as portion 17b in the drawing, which has a generally vertical orientation for frictional engagement with the inside of the mouth of container 21. This increases the frictional resistance to turning of the closure on the container to which it is affixed over that characteristic of other rim-gripping closures which engage the container only at points on the outside thereof.

The best mode known to me to carry out this invention has been described above in terms sufficiently full, clear, concise and exact as to enable any person skilled in the art to make and use the same. It is to be understood, however, that it is within my contemplation that certain modifications of the above-described mode of practicing the invention can be made by a skilled artisan without departing from the scope of the invention and it is, therefore, desired to limit the invention only in accordance with the appended claims.