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

BACKGROUND OF THE INVENTION

[0001] The present invention relates to an improved closure for sealing plastic containers and more particularly for a closure for sealing barrier plastic containers and for retaining the seal during a retorting of the sealed package.

[0002] There is a type of container for foods and similar products which is molded or otherwise formed from a plastic known as a barrier plastic, which is formed with layers separated by an oxygen barrier layer. These plastic con­tainers are excellent for food packaging including vacuum food packaging and the barrier provides long shelf life.

[0003] The plastic containers are characterized by being relatively thin and having precision rims which facilitate cover attachment.

[0004] The closure of the present invention is also formed of a barrier plastic material similar to that of the con­tainer in some cases and of metal in other cases.

[0005] The closure is essentially a disc formed from the barrier plastic or metal sheets and having a clamp-like or curved edge coated with wide band of sealant for being held in tight gripping engagement with the container rim. In several of the embodiments the clamp on the closure has a substantial gripping action itself due to its C-shape form and in this embodiment and in the more simple curved embodiments, a substantial portion of the sealant on the closure is held against the container rim in a broad annular band causing the seal to be relatively insensitive to vertical movements of the closure during a retorting process.

[0006] Accordingly, an object of the present invention is to provide an improved closure for plastic containers.

[0007] Another object of the present invention is to provide an improved closure particularly for barrier plastic con­tainers.

[0008] Another object of the present invention is to provide an improved resealable closure for barrier plastic containers which retains its seal during retorting.

[0009] 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

[0010] 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.

FIGS. 6 and 7 are vertical sectional views of another embodiment of the closure sealing a container and having a ratchet-type tear strip and a differing locking tear band respectively.

FIGS. 8 and 9 are vertical sectional views of another and metal embodiment of the closure cap sealing a container and having a ratchet-type tear band and a differing locking tear strip respectively.

FIG. 10 is a vertical sectional view of another and thermoformed embodiment of the closure cap sealing a con­tainer and having a ratchet-type tear strip.

FIG. 11 is a vertical sectional view of an injection molded embodiment with a barrier layer and sealing a barrier.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0011] This is a closure for sealing plastic containers and particularly those known as barrier plastic containers which are impervious of 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.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] FIGS. 6 and 7 illustrate additional closure embodiments. Thus, FIG. 6 illustrates a disc 30 formed from barrier plastic with a Lowermost extruded plastisol sealing membrane 31. The closure 30 has sealing means at its outer rim comprising an upwardly and outwardly curved sealing portion 32 which holds the sealing membrane 31 against the tapered inner sealing zone 33 of the container rim 34. The closure 30 is formed in this shape by a cutting and stamping operation which leaves a resilient sealing force in the closure itself between the outwardly urged sealing portion 32 on the closure 30 and the flared and contacting container rim sealing zone 33. A molded plastic ring 35 has container 39 engaging threads 37 on a skirt portion and a C-shaped closure gripping portion 36 at its top with the innermost edge 38 of the gripping portion 36 tightly engaging the disc 30 as illus­trated in FIG. 6.

[0016] FIG. 6 illustrates the plastic ring 35 with a tamper evident tear strip 40 including cooperating ratchet teeth 41 and 42 on the container and the tear strip respectively. A tear tab 43 is provided on the strip 40 to facilitate its removal from the ring 35 when the container 39 is opened.

[0017] The embodiment illustrated in FIG. 7 with a similar disc 30 and sealing members has a tear strip 44 engaging a container bead 45 with its own bead 46. The tear strip 44 also includes a gripping tab 47 for removal. The composite closure 48 illustrated in FIG. 7 is a snap-on closure which is held in place by a circular bead 49 on the container 50 and a cooperating circular bead 51 on the plastic ring 52. In order to facilitate removal of the closure 48 after the tear strip 44 is removed, a radially extending thumb tab 53 is formed on the plastic ring 52.

[0018] FIG. 8 illustrates a still further embodiment of a composite closure 60 having a plastic ring 61 such as a polypropylene ring for sealing the container 62 with a metal disc 63. The metal discs 63 are cut and formed to provide a downwardly opening sealing channel 64 at the outer edge of the discs for engaging the tapered rim 65 of the container 62 along wide annular sealing areas 66 and 67 on the inner and outer side sealing surfaces at the container rim 65. A plastisol or other suitable sealant 68 is sprayed into the sealing channel. The sealing channel 64 in the metal disc is proportioned to provide a tight gripping or sealing action with the container rim 65 and because of this sealing action which is insensitive to significant vertical movement of the metal disc 63 on the sealed container 62 during retorting or otherwise. This characteristic of the metal disc 63, together with the gripping forces of the rounded top 69 of the plastic ring 61 holding the sealing channel 64 in place provides for an excellent initial and continuing container seal.

[0019] Fig. 8 illustrates a tamper evident tear strip 70 with ratchet teeth 71 engaging cooperating teeth 72 on the container 62 and having a tear strip removing pull tab 73.

[0020] The generally similar closure 80 of FIG. 9 is a press-on closure sealed by engagement of the container bead 81 with the sealing bead 82 on a plastic ring 83 and having a locked tamper evident tear strip 84 engaging a projecting bead 85 on the container 86. The tear strip 84 includes a pull tab 88 for removal and a thumb tab 69 for facilitating the removal of the closure is provided on the ring 83.

[0021] FIG. 10 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 thermo-­formed 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 carrier 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.

[0022] FIG. 11 illustrates an injection molded barrier-type closure 100 having a downwardly facing container rim gripping sealing channel 101. A plastisol sealant 102 is sprayed into this channel. The one-piece closure 100 includes a tear strip 103 with a pull tab 104 for removal as well as a thumb tab 105 for facilitating removal of the closure 100 from the container 106.

[0023] It will be seen that an improved resealable closure has been provided for sealing containers such as those formed from barrier-type plastic and capable of maintaining a tight seal through retorting operations.

[0024] As various changes may be made in the form, construction and arrangement of the parts herein without departing from the spirit and scope of the invention and without sacrificing any of its advantages, it is to be understood that all matter herein is to be interpreted as illustrative and not in a limiting sense.

Claims

1. An improved closure for a container having am outwardly and upwardly tapered annular sealing surface on the inner rim comprising the combination of:
a disc;
a portion of said annular outer edge of said disc extending upwardly and outwardly for engaging the inner tapered annular sealing surface;
a sealant on the said portion of said disc; and
a clamping means creating a pressure contact between said inner tapered surface and the sealant on said disc.

2. The closure as claimed in Claim 1 in which the container and said disc comprise barrier plastic.

3. The closure as claimed in Claim 1 in which said container and said disc comprise extruded barrier plastic with an extruded outer coating of sealant.

4. The closure as claimed in Claim 3 in which said sealant comprises plastisol.

5. The closure as claimed in Claim 1 in which said clamping means comprises a molded plastic ring having container engaging means.

6. The closure as claimed in Claim 5 in which said plastic ring comprises a tamper indicating tear strip.

7. The closure as claimed in Claim 6 in which there are means releasably interlocking said strip with the container.

8. The closure as claimed in Claim 5 in which said container engaging means comprises thread means.

9. The closure as claimed in Claim 5 in which said container engaging means comprises a container engaging bead.

10. The closure as claimed in Claim 5 in which said clamping means comprises a C-shaped top on said ring.

11. The closure as claimed in Claim 1 in which said disc is metallic.

12. The closure as claimed in Claim 11 in which said sealant is sprayed on said disc.

13. The closure as claimed in Claim 1 which further comprises said annular outer edge of said disc terminating in an outwardly and downwardly curved portion having a sealant thereon providing dual inner and outer sealing zones on the tapered container rim.

14. The closure as claimed in Claim 1 in which said closure comprises a unitary barrier plastic thermoformed closure with integral container engaging means and a tamper-evident tear strip.

15. The closure as claimed in Claim 14 in which said barrier plastic is extruded with an outer simultaneously extruded coating of plastisol forming said sealant.

16. The closure as claimed in Claim 1 which comprises an injection molded closure of barrier plastic with integral container engaging means and tamper evident tear strip means.

17. An improved package comprising the combination of a barrier proof plastic container with a thin tapered rim and a closure:
said closure comprising a disc;
a portion of said annular outer edge of said disc extending upwardly and outwardly for engaging an inner tapered sealing surface at the container rim;
a sealant on said portion of the disc edge; and clamping means creating a pressure seal between said tapered rim and the sealant on said disc.

18. The package as claimed in Claim 17 in which said disc comprise barrier plastic.

19. The package as claimed in Claim 17 in which said container and said disc comprise extruded barrier plastic with an extruded outer coating of sealant.

20. The package as claimed in Claim 19 in which said sealant comprises plastisol.

21. The package as claimed in Claim 17 in which said clamping means comprises a molded plastic ring having container engaging means.

22. The package as claimed in Claim 21 in which said plastic ring comprises a tamper indicating tear strip.

23. The package as claimed in Claim 22 in which there are means releasably interlocking said strip with the container.

24. The package as claimed in Claim 21 in which said container engaging means comprises thread means.

25. The package as claimed in Claim 21 in which said container engaging means comprises a container engaging bead.

26. The package as claimed in Claim 21 in which said clamping means comprises a C-shaped top on said ring.

27. The package as claimed in Claim 17 in which said disc is metallic.

28. The package as claimed in Claim 27 in which said sealant is sprayed on said disc.

29. The package as claimed in Claim 17 which further comprises said annular outer edge of said disc terminating in an outwardly and downwardly curved portion having a sealant thereon providing dual inner and outer sealing zones on the container rim.

30. The package as claimed in Claim 17 in which said closure comprises a unitary barrier plastic thermoformed closure with integral container engaging means and a tamper-evident tear strip.

31. The package as claimed in Claim 30 in which said barrier plastic is extruded with an outer simultaneously extruded coating of plastisol forming said sealant.

32. The package as claimed in Claim 17 which comprises an injection molded closure of barrier plastic with integral container engaging means and tamper evident tear strip means.

Drawing