Envelopes – wrappers – and paperboard boxes – Paperboard box – Including tearing or breaking means for opening a nonunitary...
Reexamination Certificate
1999-10-11
2001-05-22
Elkins, Gary E. (Department: 3727)
Envelopes, wrappers, and paperboard boxes
Paperboard box
Including tearing or breaking means for opening a nonunitary...
C053S478000, C229S005500
Reexamination Certificate
active
06234386
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to food containers and methods and apparatus for making food containers, and more particularly relates to heat seals used to seal such containers.
BACKGROUND OF THE INVENTION
Food and drink products and other perishable items are often packaged in tubular containers, which are sealed at both ends. These tubular containers typically include at least one structural body ply and are formed by wrapping a continuous strip of body ply material around a mandrel of a desired shape to create a tubular structure. The body ply strip may be spirally wound around the mandrel or passed through a series of forming elements so as to be wrapped in a convolute shape around the mandrel. At the downstream end of the mandrel, the tube is cut into discrete lengths and is then fitted with end closures to form the container.
Tubular containers of this type typically include a liner ply on the inner surface of the paperboard body ply. The liner ply prevents liquids, such as juice, from leaking out of the container and also prevents liquids from entering the container and possibly contaminating the food product contained therein. Preferably, the liner ply is also resistant to the passage of gasses, such as oxygen and nitrogen, so as to prevent odors of the food product in the container from escaping and to prevent atmospheric air from entering the container and spoiling the food product. Thus, the liner ply provides barrier properties and the body ply provides structural properties.
In addition, current commercial containers often have membrane-type lids or end closures heat sealed to a curled or bead-shaped rim of the composite container wall to form a peelable seal. The rim is formed by turning outwardly the end of the container to position the inner layer of the liner material on the outwardly curved surface.
A major difficulty in developing a usable heat seal between the container lid and the rim of the container wall is balancing bond strength with ease of opening for the end user. During transport, the sealed containers experience temperature and pressure extremes that stress the heat seal and can lead to rupturing of the container. The bond strength must be sufficient to withstand the rigors of transportation. In particular, when containers packaged and sealed at one elevation are then subjected to lower ambient air pressure, such as during air transportation or when transported to consumers at higher elevations, a relative positive pressure is created within the container which could cause the seal between the lid and the container to rupture. Further, environmental temperature changes could adversely affect the container seal and cause a seal rupture. This ability of the container to avoid rupturing under such conditions is known as burst strength. However, as the burst strength increases, there is generally a concomitant increase in difficulty of opening of the container, which is exhibited by the peel strength or peel resistance of the container. The higher burst strength indiscriminately prevents both rupturing during transport and opening by the end user.
It would be advantageous to provide a sealed container and method for sealing a container that combine improved ease of opening and an attractive appearance after opening with the seal strength and barrier properties required for protection of the products within the container.
SUMMARY OF THE INVENTION
The composite container of the present invention successfully balances the need for ease of opening with the burst strength necessary to maintain a hermetic seal despite changes in pressure or temperature routinely experienced during transportation of the container. The present invention provides a sealed composite container, wherein the heat seal surface of the container includes a substantially planar portion. The substantially planar portion of the heat seal surface provides a wider heat seal area that results in increased heat seal strength. The sealed composite containers of the present invention are capable of maintaining a hermetic seal at elevated altitudes and/or extreme temperatures.
In one embodiment, the present invention provides a sealed composite container having a tubular body member comprising at least one paperboard body ply. A liner ply is adhered to the inner surface of the tubular body member and comprises a barrier layer. At least one end of the body member and the liner ply are rolled outwardly to form a rim and expose the liner ply. The rim defines a heat seal surface having a substantially planar portion. A lid is operatively positioned adjacent to the rim and heat sealed thereto. The lid comprises a barrier layer and at least one of the lid and liner ply further comprise a seal layer comprising a heat sealable composition. The seal layer forms a heat seal between the lid and the liner ply.
Preferably, the heat seal comprises an inner bead formed of the heat sealable composition and facing the interior of the container and an outer bead formed of the heat sealable composition on the opposite side of the heat seal from the inner bead. Advantageously, the inner bead comprises a larger amount of heat sealable composition in cross section than the outer bead.
The substantially planar portion of the heat seal surface is about 0.05 to about 0.11 inches in width. More preferably, the substantially planar portion is about 0.07 inches in width. In a preferred embodiment, the heat seal surface further comprises an inner portion sloping away from the substantially planar portion and toward the interior of the container and an outer portion sloping away from the substantially planar portion and toward the exterior of the container. The inner portion slopes away from the substantially planar portion at a greater rate than the outer portion. In this manner, a heat seal is formed comprising an inner bead and an outer bead as described above, wherein the inner bead extends further along the inner portion of the heat seal surface toward the interior of the container then the outer bead extends along the outer portion of the heat seal surface toward the exterior of the container.
A method of manufacturing a sealed container is also provided. The method includes providing a tubular member comprising at least one paperboard body ply and a liner ply adhered to the inner surface of the body ply, the liner ply comprising a barrier layer. At least one end of the tubular member is rolled outwardly to form a rim. The rim is shaped such that the rim defines a heat seal surface having a substantially planar portion. A lid for closing the end of the tubular container is also provided, the lid comprising a barrier layer. At least one of the lid and the liner ply further comprise a seal layer comprising a heat sealable composition, the seal layer being operatively positioned to form a heat seal between the lid and the liner ply. The rim and the lid are contacted and the seal layer is heated under conditions sufficient to render the heat sealable composition of the seal layer flowable. The rim and the lid are pressed together to form a hermetic heat seal therebetween.
Preferably the pressing step comprises pressing the rim and the lid together such that flow of the heat sealable composition forms an inner bead and an outer bead of the heat sealable composition. In one embodiment, the flow of heat sealable composition is preferentially encouraged in the direction of the interior of the container so that the inner bead comprises a larger amount of the heat sealable composition in cross section than the outer bead.
The shaping step used to form the substantially planar portion of the heat seal surface preferably includes supporting the undersurface of the rim and applying pressure to the exposed heat seal surface of the rim to flatten the heat seal surface and form the substantially planar portion of the heat seal surface. Preferably, the rim is also shaped such as the heat seal surface further comprises an inner portion sloping away from the planar portion and toward the interior of the container
Drummond Michael T.
Gentile Michael
Krishnaraj Varadarajan
Osman Rick A.
Williams Alan D.
Alston & Bird LLP
Elkins Gary E.
Sonoco Development Inc.
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