Closure Having Improved Resistance To Unseating

Abstract

A closure is provided with a retention bead structure for engaging a corresponding bead retention groove in a packaging container. At least a portion of the surface of the upper portion of the retention bead structure which contacts the upper portion of the bead retention groove is provided with a rough texture to increase the coefficient of friction thereof, thereby increasing the resistance of the closure against unseating after the closure has been inserted into the container. The coefficient of friction of the lower portion of the retention bead structure can be significantly lower than the coefficient of friction of the upper portion thereof to minimize resistance against the insertion of the closure into the container.

Description

This invention relates to improvements in closures and in packages utilizing such closures with containers.

One of the greatest uses of thermoformed containers and closures is for the packaging of cottage cheese which has been coated with a cream dressing. When the containers are filled with the cottage cheese, a portion of this dressing spatters into the closure retention groove of the container, thereby reducing the coefficient of friction of the wall of the closure retention groove. It is generally customary to fill the containers to the point where there will be little or no air space between the product and the closure, since air causes oxidation of the product. This frequently results in the container being slightly overfilled. When the closure is applied to such an overfilled container, the cottage cheese curd is slightly compressed, causing a buildup of pressure in the container. This excess pressure is a primary cause of closures popping off containers during handling and shipping. Although such closures have been fabricated with venting grooves in the retention bead of the closure for the purpose of venting gases, such venting grooves are ineffective with respect to the pressure caused by compressed product. In addition, such venting grooves do not contribute to the force which retains the closure in the container, but rather detracts therefrom due to a reduction in contact area and an increase in the flexibility of the closure.

Accordingly, it is an object of the present invention to provide an improved closure for a packaging container. Another object of the invention is to increase the retentive force on a closure releasably secured in a container. A further object of the invention is to decrease the frequency of occurrence of thermoformed closures popping off of containers which have been slightly overfilled. Other objects, aspects and advantages of the invention will be apparent from a study of the specification, the drawings and the accompanying claims.

In accordance with the present invention, it has been discovered that the disadvantages of the prior art can be avoided and the desired objectives achieved by providing a rough texture on at least a portion of the surface of the upper portion of the retention bead structure of the closure which contacts the upper portion of the wall ofthe bead retention groove of the container. In a presently referred embodiment, an at least substantially circumferentially continuous band of grainy texture is formed on the upper portion of the retention bead structure of a thermoformed closure by sandblasting the corresponding portion of the female mold. It is hightly desirable that the coefficient of friction of the lower portion of the retention bead structure be significantly less than that of the upper portion of the retention bead structure to minimize resistance against the insertion of the closure into the container while maximizing the resistance against unseating of the closure.

In the drawings,

FIG. 1 is a side elevational view of a container and closure constructed in accordance with the present invention.

FIG. 2 is a top plan view of the closure and container of FIG. 1;

FIG. 3 is a side elevational view of the closure of FIG. 1; and

FIG. 4 is a fragmentary cross-sectional view taken along line 4--4 in FIG. 2.

Referring now to the drawings in detail, and to FIGS. 1 and 4 in particular, the package 10 comprises a packaging container or cup 11 and a closure 12. The container 11 is a one-piece integral structure, and can be fabricated by thermoforming a sheet of thermoplastic material. Container 11 comprises a bottom wall 13 of any suitable configuration; a circumferentially continuous sidewall 14 extending upwardly and outwardly from the periphery of bottom wall 13; stacking ring 15; and rim 16. Where container 11 has substantially circular horizontal cross-sections, sidewall 14 will have a substantially frusto-conical configuration. The rim 16 can be in the form of a rolled rim having at least 270.degree. curvature, as illustrated, or a generally U-shaped configuration can be utilized. Stacking ring 15 comprises flange 17, closure retention groove section 18, spacer section 19, and upper stacking shoulder 21. Annular flange 17 is circumferentially continuous and extends outwardly in a substantially horizontal direction from the upper extent of sidewall 14 to the lower extent of closure retention groove 18. Spacer section 19 is circumferentially continuous and extends substantially vertically from the upper extent of closure retention groove section 18 to the inner extent of upper stacking shoulder 21. In the illustrated container 11, the spacer section 19 has a substantially cylindricll configuration, and closure retention groove sectiofn 18 is circumferentially continuous and is in the form of an inwardly opening, outwardly directed, concavely contoured wall section extending substantially vertically from the outer periphery of flange 17 to the lower edge of spacer section 19. The lower portion of groove section 18 serves as the lower stacking shoulder. The upper stacking shoulder 21 curves outwardly and upwardly from the upper extent of spacer section 19 to rim 16. The inner diameter of spacer section 19 is less than the outer diameter of groove section 18 while the inner diameter of rim 16 is greater than the outer diameter of groove section 18.

Closure 12 is a one-piece thermoformed structure having horizontal cross-sections corresponding at least generally to the horizontal cross-sections of the upper portion of container 11. Where container 11 has a generally frusto-conical configuration, closure 12 has substantially circular horizontal cross-sections. Closure 12 comprises a closure disc or diaphragm 22, a retention bead 23, upwardly and outwardly sloping wall section 24, rim 25 and depending flange or skirt 26. Disc 22 is illustrated as being planar, but can be bowed upwardly or dished downwardly and/or provided with an annular expansion groove, if desired. In the illustrated closure, the retention bead 23 is an inwardly opening, outwardly directed, concavely shaped groove section extending generally upwardly from the periphery of disc 22 to the lower extent of wall section 24. Other outwardly directed inwardly opening configurations can be employed for the retention bead, for example, a vertical wall section extending upwardly from the outer periphry of a horizontal flange to the lower edge of an upwardly and inwardly inclined surface. The horizontal flange can be an extention of disc 22 or vertically spaced therefrom. The upwardly and inwardly inclined surface can be a frusto-conical surface or a curved surface.

Retention bead 23 can be interrupted at circumferentially spaced locations by a plurality of inwardly directed, outwardly opening notches or venting grooves 27. Each notch 27 will generally be disposed with the elongated axis thereof in a substantially vertical plane. The innermost wall portion of each notch 27 can extend outwardly and inwardly from wahl section 24 to a point on disc 22 which has a significantly smaller diameter than the inner diameter of flange 17. Wall 24 of closure 12 can be spaced inwardly from the wall formed by spacer section 19 and stacking shoulder 21 of container 11 to form a continuous annular space 28. The upper portion of each notch 27 opens into the annular space 28. This provides continuous fluid access between the annular space 28 and the packaging space 29 within wall 14 of co1tainer 11 below disc 22.

Stacking lugs 31 can be provided in the circumfrrentially spaced positions in sidewall 24. Stacking lugs 31 are generally inwardly directed, outwardly opening embossments. Each of the illustrated lugs 31 has a substantially vertical or upwardly and slightly inwardly inclined backwall 32, a generally horizontal shoulder 33, and substantially vertical sidewalls 34. Shoulder 33 extends outwardly in a generally horizontal direction from the upper extent of the back or inner wall 32 to wall 24. Shoulder 33 can be curved outwardly and upwardly in conformance with the contour of the lower portion of bead 23 for purposes of stacking one closure upon another.

Upon insertion of closure 12 into container 11, bead 23 cams inwardly on the curved upper shoulder 21 and then snaps into the closure retention groove 18. Notches 27 permit continuous outflow of air from the interior of the package during the insertion of closure 12 into container 11 thereby preventing a buildup of excessive gas pressure in the package during the capping operation. The upper outer surface of bead 23 contacts the inner surface of the upper portion of retention groove 18 along a band of contact 35. This band of contact 35 is circumferentially continuous excpet in the area of the venting grooves 27. In accordance with the present invention, at least a portion 30 of the outer surface of the upper portion of bead 23 which is involved in the band of contact 35 is provided with a rough texture to significantly increase the coefficient of friction thereof. Preferably the portion 30 includes all of the surface of bead 23 involved in the band of contact 35. Although the roughtly textured portion 30 can be produced by any technique known in the art, a presently preferred procedure involves thermoforming a sheet of synthetic organic thermoplastic material in a famale mold to produce the closure, the portion of the mold which forms the upper portion of the retention bead structure having a rough surface while the remainder of the mold surface is polished. One suitable procedure for providing the rough surface portion of the mold is sandblasting that area. The lower surface of the resulting thermoformed closure will have a glossy smooth finish except for portion 30 which will have a grainy texture. The glossy smooth finish on the lower portion of bead 23 minimizes frictional resistance to the insertion of closure 12 into container 11, whereas the rough texture of portion 30 significantly increases the resistance of the closure 12 to being popped out of the container 11. The employment of a single treating operation on the mold has obvious advantages over techniques which involve individual treatment of each closure. While sandblasting is a presently preferred technique for providing a rough mold surface, other techniques can be employed, for example, etching, grinding or cutting grooves or other indentations, and the like.

The underside or rim 25 can contact the top of container rim 16 at point 36. This results from the formation of closure 12 in such a manner that the distance between points 35 and 36 in the unstressed closure is less than the distance between points 35 and 36 on the uncapped container. Thus, the upper portion of bead 23, wall 24 and rim 25 can act as a C-clamp to grip the mating surfaces of container 11 to thereby removably secure closure 12 to the container 11. The C-clamp configuration also increases the resistance of the closure 12 to undesired removal from container 11. The contact of closure rim 25 and container rim 16 can be circumferentially continuous to serve as a seal for the capped container. This provides sanitary conditions for the entire interior of the container.

Closure 12 can be provided with a plurality of circumferentially spaced venting cams 37, bridging rim 25 and depending flange 26. Cams 37 project inwardly from flange 26 and downwardly from rim 25 to form a camming surface which is inclined downwardly at an acute angle to the horizontal reference. The cams 37 are preferably positioned at least closely adjacent the outwardly and downwardly curving portion of rim 16, and camming contact therebetween occurs during venting of the package. Preferably this contact is made in the first 45.degree. of curvature of rim 16 outwardly and downwardly from the horizontal.

While the invention has been illustrated with the container and clousre having substantially circular horizontal cross-sections, other configurations can be utilized, for example, oval, rectangular with at least the corners being rounded and more preferably with the side being bowed outwardly, and the like. Other reasonable variations and modifications are possible within the scope of the foregoing disclosure, the drawings and the appended claims to the invention.

Claims

I claim:

1. In a closure for a container having a bead retention groove disposed in the wall thereof, said closure comprising a diaphragm, a side wall extending generally upwardly from the periphery of said diaphragm and a rim extending generally outwardly from the upper extent of said side wall, said side wall having forward therein an outwardly directed, inwardly opening retention bead structure adapted to snap into the bead retention groove of the container to releasably secure the closure to the container by the engagement of the upper portion of said retention bead structure against the upper portion of the bead retention groove of the container, the improvement comprising at least a portion of the outer surface of the upper portion of the retention bead structure which contacts the upper portion of the bead retention groove of the container being textured to increase the coefficient of friction thereof, the coefficient of friction of the textured portion of the retention bead structure being significantly higher than the coefficient of friction of the surface of the lower portion of the retention bead structure.

2. A closure in accordance with claim 1 the closure having been fabricated by thermoforming a sheet of synthetic organic thermoplastic material in a polished female mold, the portion of the mold which forms the upper portion of the retention bead structure having been sandblasted to provide a rougher surface texture for said upper portion of the retention bead structure than for the remainder of the closure.

3. A closure in accordance with claim 1 wherein said upper portion of the retention bead structure has a grainy texture, and the lower portion of the retention bead structure has a glossy smooth surface to minimize frictional resistance to the insertion of the closure into the container.

4. A package comprising a closure in accordance with claim 1 and further comprising a container having a bottom wall, an upstanding side wall extending generally upwardly and outwardly from the periphery of said bottom wall, a rim forming the mouth of the container, and a ring section extending generally upwardly from the upper extent of said upstanding side wall to said rim and having a circumferentially continuous outwardly directed, inwardly opening retention groove formed therein, said ring section also having an upwardly and outwardly extending camming wall section between said bead retention groove and said rim adapted to serve as a centering guide for said closure upon the contact of the lower portion of retention bead structure of the closure therewith, the outer diamter of the outermost portion of said retention bead structure being greater than the inner diameter of the lower end of said camming wall section and the innermost diameter of the upper portion of said bead retention groove and less than the inner diameter of the upper end of said camming wall section and the inner diameter of the laterally adjacent portion of said bead retention groove.

5. A package in accordance with claim 4 wherein said container and said closure have substantially circular horizontal cross-sections, and wherein the textured portion of said retention bead structure is at least substantially circumferentially continuous.