CLOSURE FOR RETORTABLE PLASTIC CONTAINER

Abstract: A closure is described of particular value for sealing containers formed of barrrier plastic. The closure has a disc shaped central portion (2) of barrier material which has an upwardly and outwardly extending sealing portion (7) at its outer edge coated with sealant. A clamping means (10) holds the sealant against a tapered rim of the container (3).

Description: The invention relates to a package comprising the combination of a composite closure and a container having a rim with an annular inner sealing surface and an annular outer surface, said composite closure having a disc a radially outer annular portion with a first surface which extends upwardly and outwardly forming an annular sealing surface for cooperation with the annular inner sealing surface of the rim of the container, and the second surface extending downwardly and outwardly forming an annular outer sealing surface with the outer surface of the rim, and said disc configured such that said outer annular portion tightly engages the annular sealing surface of said rim; sealant material disposed on said outer annular portion of said disc for sealing engagement with the container rim; and a moulded plastic ring including a skirt with container-engaging means and a top portion having a downwardly opening C-shaped radial cross section, said cross section having a downwardly extending inner annular leg segment which is substantially parallel to the center axis of said ring, and an outer segment which is also substantially parallel to the center axis of said ring, wherein said inner annular leg segment engages and retains said annular inner sealing surface of said disc with said sealant material thereon in sealing engagement with the annular inner sealing surface of said rim. A package of this type is know from US-A- 1921016. In this package the rim has a circular cross-section so that there is no sealing effect when the closure is shifted upwardly. The sealing of the known package does not have any clamping action because only lateral pressure is created. If a vertical displacement of the closure takes place, no sealing is maintained. Accordingly, an object of the present invention is to provide an improved closure for plastic containers. Another object of the present invention is to provide an improved closure particularly for barrier plastic containers. Another object of the present invention is to provide an improved resealable closure for barrier plastic containers which retains its seal during retorting. Other and further objects of the present invention will become apparent upon an understanding of the illustrative 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. BRIEF DESCRIPTION OF THE DRAWINGS A preferred embodiment of the invention has been chosen for purposes of illustration and description and is shown in the accompanying drawings, forming a part of the specification, wherein: FIG. 1 is a perspective view of the upper portion of a sealed plastic container. FIG. 2 is an exploded perspective view of the sealed package of FIG. 1. FIG. 3 is a vertical cross-sectional view of a preferred embodiment of a closure in accordance with the present invention. FIGS. 4 and 5 are vertical sectional views of the preferred embodiment of a closure sealing a container and having a ratchet-type tear strip and a differing locked tear strip respectively. FIG. 6 is a vertical sectional view of another and thermoformed embodiment of the closure cap sealing a container and having a ratchet-type tear strip. DESCRIPTION OF THE PREFERRED EMBODIMENT This is a closure for sealing plastic containers and particularly those known as barrier plastic containers which are impervious to oxygen penetration and thereby spoil resistant. Such plastic containers are often cup shaped or in the form of large mouth bottles and there is a need for an inexpensive and barrier sealing closure or disc. In addition to the requirements of low cost and barrier seals, the closure must also be of the type which retains its seal through the retorting or heat treating steps used in food packaging. FIGS. 1 thru 4 illustrate a preferred embodiment of a composite closure 1 of this type. It consists of a barrier sealing disc 2 which is held in sealing position on the container 3 by a sealing ring 4. A preferred disc 2 is illustrated in FIG. 3 which consists of a multi-layer extruded plastic material with the barrier layer 5 cut and stamped into the illustrated form comprising the disc-like inner portion 6 and a generally C-shaped outer sealing portion 7. The material is formed by a simultaneous extrusion of the outer and the barrier layers and an additional outer or bottom layer comprising a sealant such as plastisol-layer 8. The plastic ring 4 has a skirt portion 9 and a generally C-shaped clamping portion 10 for engaging the outward C-shaped sealing portion 7 of the disc 2. Suitable container engaging threads 11 are provided on the inner surface of the skirt 9 and preferably a tamper indicating strip 12 is provided at the lower edge of the ring skirt 9. This tamper strip 12 is of the known type whose teeth 13 engage ratchet teeth 14 on the container 3. The tamper indicating strip 12 is torn from the remaining portion of the ring 4 upon closure removal using a tear tab 15. A line of weakness 16 is provided between the tamper indicating strip 12 and the remaining portion of the skirt 9. The radially outer edge of the disc 2 has the above described C shape as illustrated at 7. This shaping of the disc 2 edge provides for elongated and tightly gripped annular contact areas on the inner and the outer surfaces of the container 3 rim 17, which preferably has an upwardly tapered shaping. In addition to the clamping and sealing forces on the closure edge 7, the relatively thick clamping section 10 of the ring 4 maintains the sealing pressure on the disc 2 sealing surfaces both initially and during any of the positioning or dimensional changes which occur during retorting. Even though the disc 2 may move upwardly on the rim 17, the seal remains effective. This clamping action maintains the sealing pressures in spite of the barrier plastic becoming more flexible at the retorting temperatures of 220° to 260°F. The plastic such as polypropylene of the outer ring 4 is selected to maintain substantial rigidity at these and slightly higher temperatures by maintaining its tight grip. In order to provide tamper indication for the closure 1, a tamper indicating strip 12 is provided on the lower portion of the ring skirt 9. The embodiment illustrated at 23 in FIG. 5 is generally similar to that of FIG. 4 with the exception of the tamper strip 18 and in this embodiment, the tamper strip 18 has a container engaging bead 19 which interlocks with a bead 20 on the container 21. The strip 18 is removed using the tear tab 22 before closure removal. The closure 23 is a press-on closure engaging container 21 at bead 24 by its locking bead 25. The closure 23 is thumbed of using thumb tab 26. FIG. 6 illustrates another embodiment with a closure 90 having a downwardly opening sealing channel 91 held in sealing engagement with the tapered rim 92 of the container 93. This is a one-piece closure formed from barrier layer plastic by a thermoforming operation. A C shaped sealing portion 99 is provided at the top outer corner of the closure 90 and threads 94 are formed for engaging the cooperating container threads 95. The one-piece thermoformed closure 90 also includes a ratchet-type tamper evident cut tear strip 96 including a thumb tab 97 for removal. A relatively thick barrier plastic is used to insure a satisfactory type clamping effect at the sealing channel. The barrier plastic is preferably formed by extrusion including an extruded plastisol sealing membrane 98. Alternatively, the sealing membrane may be sprayed into the sealing channel 91.

Claims: An improved package comprising the combination of a composite closure (1; 60; 80; 90; 100) and a container (3; 21; 39; 50; 62; 93; 106) having a rim (17; 34; 65; 92) with an outwardly and upwardly tapered annular inner sealing surface and an inwardly and upwardly tapered annular outer surface, said composite closure having a disc (2; 30; 63) having a radially outer annular portion with a first surface which extends upwardly and outwardly forming a tapered annular sealing surface for cooperation with the outwardly and upwardly tapered annular inner sealing surface of the rim (17; 34; 65; 92) of the container (3; 21; 39; 50; 62; 93; 106) and a second surface extending downwardly and outwardly forming a tapered annular outer sealing surface with the outwardly and downwardly tapered outer surface of said rim, and said disc (2; 30; 63) configured such that said outer annular portion tightly engages the tapered annular sealing surface of said rim (17; 34; 65; 92); sealant material (8; 31; 68; 98; 102) disposed on said outer annular portion of said disc (2; 30; 63) for sealing engagement with the container rim (17; 34; 65; 92); and a moulded plastic ring (4; 35; 52; 61; 83) including a skirt (9) with container-engaging means (11; 25; 37; 51; 82; 94) and a top portion (10) having a downwardly opening C-shaped radial cross section, said cross section having a downwardly extending inner annular leg segment which is substantially parallel to the center axis of said ring (4; 35; 52; 61; 83) and an outer segment which is also substantially parallel to the center axis of said ring, wherein said inner annular leg segment engages and retains said tapered annular inner sealing surface of said disc (2; 30; 63) with said sealant material (8; 31; 68; 98; 102) thereon in sealing engagement with the tapered annular inner sealing surface of said rim (17; 34; 65; 92) and wherein said outer segment engages and retains said tapered annular outer surface of said disc, with said sealant material thereon in sealing engagement with the tapered annular outer sealing surface of said rim, such that said inner and outer leg segments of said ring (4; 35; 52; 61; 83) exert a clamping action on said tapered annular first and second sealing surfaces of said disc (2; 30; 63) to maintain a continuous seal and to cause the seal to be relatively insensitive to vertical movement of the closure. The package as claimed in claim 1 in which said disc (2; 30; 63) comprises a barrier plastic layer.

Inventors: OCHS, CHARLES, S.
Applicants: ANCHOR HOCKING CORPORATION
Application year: 1987
Main classification: B65D41
IPC codes: B65D41, B65D51