HERMETICALLY SEALABLE CONTAINERS AND METHOD OF SEALING

Abstract: A container body (10) made of thermoplastic materials, and of uniform bottom and side wall thickness, after being filled with a hot liquid (50), is then hermetically sealed by a flat closure disc (55) adhesively contacting a peripheral lip (26, 28) formed around the top of the body. The bottom wall (20) of the container body (10) is formed with annular grooves (22) to de­ fine a flexible diaphragm which flexes inwardly upon cooling of the liquid (50) to substantially dissipate the internal vacuum which is formed in the container head space (62); the suction is similarly relieved by inward flexing of the disc (55). The bot­ tom (20) of the container body has a reinforced pedestal base (14) formed with stacking ledges (25) to facilitate nesting of empty bodies (10) for shipment and storage.

Description: HERMETICALLY SEALABLE CONTAINERS AND METHOD OF SEALING" This invention relates to hermetically sealable containers and method of sealing. More particularly the invention concerns the filling and hermetic sealing of plastics bodied containers with hot liquid or semiliquid products, and resides in improvements in the methods and structures for accomplishing hermetic sealing without deformation of the side wall of the container or premature breaking of the seal. A demand has arisen for a thermoplastic container for storing commestibles needing heating to a liquid or semi-liquid state at temperatures of up to about 1900F (880C) to facilitate filling the container, which must then be hermetically sealed with a heat sealed peelable closure disc. This container can be used to package foods commonly classified as hot fillable, such as jams and fruit juices, inter alia. By hot-filling at a temperature of 1900F (880C) the container and contents are sterilized and do not require additional preservatives. The higher the temperatures that must be used, the greater the likelihood of creating stresses in the container and/or its seal because of high internal vacuums developed upon subsequent cooling of the product, primarily resulting from the condensation of steam in the head space of the sealed container. It is important that the side wall of the container be kept free of deformation or paneling while at the same time maintaining the hermetic seal to prevent spoilage of the product during shipping and storage. A thermoplastic-bodied container is known for storing motor oils. This container has a flexible bottom so that depletion of gaseous components causing a change in internal pressure can be compensated for by the flexing action on the bottom - see U.S. patent 3,409,167. According to the patent, the container was formed with a relatively thick side wall and a relatively thin bottom wall to prevent paneling of the side wall while permitting flexing of the bottom wall. The invention aims to provide a hermetically sealable thermoplastic bodied container capable of holding hot filled products such as jams or the like, and which can be easily opened by simply peeling the container closure from the container body. Preferably the peelable closure has a peel strength sufficiently low to permit easy opening by the consumer, and yet high enough to prevent rupture of the seal when subjected to the conditions under which the container is filled and sealed. By providing a container according to the invention with flexible top and bottom portions which are adapted to move inwardly as the hot filled product cools, paneling or deformation of the side wall of the container and rupture of its hermetic seal is prevented. According to the present invention, there is provided an hermetically sealable container adapted to be filled with a hot liquid having a measurable vapor pressure comprising a thermoplastic cup shaped member having a side wall and a bottom wall and a closure disc attachable to the cup, characterised in that the bottom wall has annular grooves formed therein to define a diaphragm structure capable of flexing when subjected to a predetermined pressure, the said cup having an annular lip extending outwardly around the top of its side wall and the closure disc is formed of sheet material for covering said cup and is adhesively securable to the lip portion the bottom wall and the closure disc being capable of being pulled inwardly to maintain the side wall substantially undeformed after filling and sealing the container and after cooling of its contents. Also according to the invention, there is provided a method of sealing hot material with a measurable vapor pressure in a package such that breakage of the seal or deformation of a side of the package is prevented upon cooling, characterised by providing a cup shaped member of thermoplastic material including a gas barrier layer in which the bottom wall of the cup is formed with annular grooves to permit diaphragmatic flexing of the wall and in which the top of the cup is formed with a projecting annular lip therearound, filling the cup with a hot liquid material having a measurable vapor pressure, sealing the hot filled cup with a flexible, impervious closure disc by adhesively securing the disc to the top annular lip to form a peelable seal, both the bottom wall of the cup and the flexible closure disc being allowed to flex inwardly to eliminate or substantially reduce the partial vacuum within the sealed container upon cooling whereby the cup remains sealed without incurring any significant deformation to its side wall. The container body can have uniform thickness and be thermoformed from thermoplastic materials having a plurality of layers including an oxygen barrier layer. The lip portion around its rim or periphery facilitates sealing with an easily peelable heat-sealed closure disc made of a flexible flat sheet material after the container has been filled with a hot liquid. The bottom wall and the top closure disc of the container are each capable of flexing in the manner of a diaphragm to relieve the internal vacuum resulting upon subsequent cooling of the liquid and thus prevent rupture of the seal or paneling of the side wall. A preferred embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a side view of a pair of container bodies embodying the invention, the bodies being shown nested with the outer body in cross section to illustrate certain details of construction; Figure 2 is a top view of Figure 1; Figure 3 is an enlarged vertical cross-sectional view taken through the curled lip formed around the periphery of the container body, the view also showing portions of the peelable closure disc and a heated sealing plate adapted to heat-seal the disc onto the curled lip; Figure 4 is an enlarged vertical cross-sectional view taken through the multiple layer wall of the container body; Figure 5 is an enlarged vertical cross-sectional view taken through a bottom corner portion of the container body; and Figure 6 is a schematic cross-sectional view of the filled and sealed container after the top closure disc and the bottom wall of the sealed container have flexed inwardly as the result of the reduced internal pressure created upon cooling of the hot filled product. Referring to the drawings and in particular to Figure 1, nestable one piece thermoformed container bodies 10 embodying the principles of the invention are shown. Each container body 10 has a cup shape and is formed with a tapered main or side wall 12 permitting the bodies to stack, nested one in another. The bottom end of wall 12 merges into a pedestal base, generally indicated by the numeral 14, which forms the bottom end portion of the container. The base 14 includes a rounded corner portion 15 which connects the base 14 and the side wall 12, and an inwardly and downwardly angled reinforcing wall 16 which is disposed at about 450 angle to the container axis. The angled wall 16 merges into a short vertical wall 18 which in turn connects with a horizontal bottom wall 20. Wall 20 is formed with a plurality of annular grooves or corrugations 22 which permit diaphragmatic flexing of the wall 20, as will be hereinafter explained. The pedestal base 14 includes a plurality of spaced, vertical, inwardly-extending indentations 24 which at their upper ends create inwardly-extending ledge portions 25 facilitating non-wedging nesting of the container bodies 10, and also strengthening the bottom portion of the container body and helping to re-enforce it against deformation. As best shown in Figure 3, the top of container body 10 is formed with a peripheral curled lip 26 having a top portion 28. The top portion 28 provides an annular sealing surface which is important from the standpoint of ensuring proper sealing of the container as will become more apparent hereinafter. A flat annular lip, rim or flange or combination thereof with a curled portion may also be used. The materials used in the construction of container body 10 comprise multiple layers including an inner polyolefin layer 32 made preferably of polyethylene or polypropylene or blends thereof, an adhesive layer 34 made preferably of a compatible material such as a modified polypropylene or a modified polyethylene, and a barrier layer 36 made of a plastic material such as ethylene vinyl alcohol copolymer or Saran (Trade Mark) which is substantially impervious to oxygen. Next in order there is another compatible adhesive layer 38 similar or identical to the layer 34, a bulk layer 40 preferably but not necessarily consisting of reground scrap generated during manufacture of the bodies 10, and an outer polyolefin layer 42 preferably similar or identical in composition to the inner polyolefin layer 32. It will be appreciated that the barrier layer 36 serves primarily to prevent oxygen from penetrating the container after filling and sealing, although it may also serve as a barrier for other gases or fluids. The layer 40 functions primarily to add bulk and strength to the body at low cost. The thicknesses of the various body layers can be varied as desired and required, but it has been found that cup shaDed bodies constructed from these multiple layers should have a total thickness of at least 15 mils (0.38 mm) and preferably of about 20 mils (0.50=). In use of the invention, the container body 10 is filled with a hot liquid product such as jam 50 which has been heated to a temperature up to about 190 F (880C). after filling, the container is sealed with a flat imperforate and impervious closure disc 55 which is preferably made of aluminum foil 56 provided on its undersurface a heat sealable adhesive layer 57 capable of adhering to top portion 28 of the curled lip 26 of the body 10. If desired, a suitable oxygen impervious thermoplastic material such as ethylene vinyl alcohol copolymer (EVOH) or saran may be substituted for the aluminum foil 56. The closure disc 55 may be a laminate in which the alumirumfoil 56 is laminated on one or both sides to a suitable layer of a protective plastic material such as a nylon, a polyester or a polyolefin, one of which may function as the adhesive 57 which adheres the disc 55 to the annular body portion 28. Preferably, the hot melt adhesive 57 is chosen to provide a peel strength sufficiently low in magnitude to permit easy peeling of the disc 55 from the body 10 when it is desired to open the container. It has been found that T-peel strengths (ASTM D 1876-72) on the order of about three pounds per inch (0.54 kg per cm) are ideal for the present purpose, since they permit easy opening of the container while at the same time providing sufficient strength to maintain the integrity of the seal during normal processing and handling of the container, as will be morc fully described. Substantially higher T-peel strengths than the ideal peel strength such as greater than five pounds per inch (0.9 kg per cm) will provide the resistance necessary to maintain the seal integrity, but they prevent easy peelability of the closure disc. The cover disc 55 is preferably formed with a small, integral, radially projecting opening tab 58 and may be applied in any suitable manner as by a flat, heated sealing ring or plate 59 which engages the upper layer 60 of the closure disc 55 and presses its peripheral edge portion against the top surface 28, while at the same time heating the disc 55 sufficiently to soften the adhesive 57 and cause it to heat-seal to the top annular surface 28. The contacting surface of the sealing plate 59 may be coated with Teflon or the like to prevent the upper surface of the closure disc 55 from sticking to it. It will be appreciated that upon subsequent cooling of the hot filled product 50, the closure disc 55 and bottom wall 20 are pressed inwardly by atmospheric pressure, as a substantial partial vacuum is formed within the sealed container due primarily to condensation of moisture vapor which is present in the head space 62 of the filled and sealed container. For a completely rigid container, the vacuum formed upon cooling would be about 20 inches (50.8 cm) of mercury. The purpose of this container is for use with liquids that have a measurable vapor pressure when hot-filled such that upon cooling, a vacuum is generated. For commercial filling operations, head space 62 is desirable to prevent over-filling of the containers and spilling the contents just prior to the heat sealing operation. It will be further appreciated that because of this inward flexing of the closure disc 55 and bottom wall 20, the partial vacuum is substantially reduced and the stresses on the closure seal and the side wall relieved so that the container seal is maintained and deformation or paneling of the side wall 12 of the container is prevented. Annular grooves 22 provide the means for the flexing motion of bottom wall 20. Because the diameter of the pedestal wall 14 as defined is the minimum diameter of the container side, the stiffness at the juncture between the pedestal wall 14 and side wall 12 is stiffened. That stiffness is essential to permit the flexure at the annular grooves 22 and to prevent deformation at the juncture of the pedestal and side wall 12. It should be understood that the high internal vacuum formed within the sealed container also subjects the pedestal base 14 to a high pressure differential, and unless some provision is made to prevent it, could cause it to partially deform inwardly before or at the same time as the bottom wall 20 is being flexed inwardly. This undesirable result is prevented by the reinforcing wall 16 which supports the pedestal base 14 at the area of its greatest vulnerability, and thus limits the inward movement of the body 10 to the inward flexing of the bottom wall 20. After cooling, and in the proper case solidification of the product 50, the container may be easily opened by the user grasping the opening tab 58 and pulling upwardly on it, thus breaking the adhesive bond and peeling the closure disc 55 from the top sealing surface 28.

Claims: Claims: 1. An hermetically sealable container adapted to be filled with a hot liquid having a measurable vapor pressure comprising a thermoplastic cup shaped member having a side wall and a bottom wall, and a closure disc attachable to the cup, characterised in that the bottom wall (14) has annular grooves (22) formed therein to define a diaphragm structure capable of flexing when subjected to a predetermined pressure, the said cup (10) having an annular lip (26, 28) extending outwardly around the top of its side wall (12), and the closure disc (55) is formed of sheet material for covering said cup (10) and is adhesively securable to the lip portion (26, 28), the bottom wall (20) and the closure disc (55) being capable of being pulled inwardly to maintain the side wall (12) substantially undeformed after filling and sealing the container and after cooling of its contents. 2. A container according to claim 1, characterised in that the cup (10) is made from a plurality of layers including a gas barrier layer. 3. A container according to claim 2, characterised in that the combined thickness of the layers is at least about 15 mils (0.38 mm). 4. A container according to claim 1, 2 or 3, characterised in that the cup has a bottom portion of smaller than transverse dimensions than the cup (10) and is connected to the side wall (12) by a short vertical wall (18) and by a downwardly and inwardly angled reinforcing wall (16) to form a pedestal base (14). 5. A container according to claim 4, characterised by the vertical wall (18) being formed with a plurality of spaced indentations which, at their upper ends, form ledges within the cup (10). 6. A container according to any of claims 1 to 5, wherein the closure disc is an aluminum foil (56) having its bottom surface covered by a thermoplastic layer (57) which enables an outer peripheral portion of the foil to be adhesively secured to said annular lip (26, 28) forming a seal having a T-peel strength of less than 5 pounds per inch (0.9 kg per cm). 7. A method of sealing hot material with a measurable vapor pressure in a package such that breakage of the seal or deformation of a side of the package is prevented upon cooling, characterised by providing a cup shaped member (10) of thermoplastic material including a gas barrier layer (36) in which the bottom wall (20) of the cup is formed with annular grooves (22) to permit diaphragmatic fleming of the wall (20) and in which the top of the cup is formed with a projecting annular lip (26, 28) therearound, filling the cup with a hot liquid material having a measurable vapor pressure, sealing the hot filled cup (10) with a flexible, impervious closure disc (55) by adhesively securing the disc to the top annular lip (26, 28) to form a peelable seal, both the bottom wall (20) of the cup (10) and the flexible closure disc (55) being allowed to flex inwardly to eliminate or substantially reduce the partial vacuum within the sealed container upon cooling whereby the cup remains sealed without incurring any significant deformation to its side wall (12).

Inventors: CANER, ALI R., SPENCER, KENNETH B.
Applicants: AMERICAN CAN COMPANY
Application year: 1982
Main classification: B65D1
IPC codes: B65D77, B65B7, B65D79, B65D1, B65D85