Patent Application
20070131750
The present invention relates to composite containers, and particularly relates to liners for composite containers.
Traditionally, liners for composite containers have included a layer of paper on the back side that faces outward toward the paperboard body wall of the container. Such liners have been termed “supported” liners because the paper layer serves as a structural support for the liner, which imparts substantial tensile strength to the liner and makes the handling of the liner during the container manufacturing process relatively easy. The paper layer also facilitates gluing the liner to the paperboard body wall.
While the paper layer thus serves useful purposes, it also necessitates an “anaconda” fold seal of the liner so that the paper layer is not exposed to the container contents at the edge of the liner ply. The innermost surface of the liner comprises a sealant material. The folded edge of the liner places the sealant on the folded edge in contact with sealant on the opposite unfolded edge of the liner ply, and the liner edges are sealed together by the sealant.
Such supported liners tend to be quite thick, and the anaconda fold seal represents three layers of the liner, such that the fold seal is extremely thick. This extreme thickness of the fold seal can create problems in forming a hermetic seal between a container end and a membrane lid because the fold seal creates a large bump on the container end. Accordingly, efforts have been made to develop “unsupported” liners that do not have a paper backing. Instead of the paper backing, the back side of current unsupported liners comprises an extruded polymer layer. However, this necessitates the use of a special adhesive for adhering the liner to the paperboard body wall, because the types of wet adhesives typically used for adhering conventional supported liners are not suitable.
The present invention addresses the above needs and achieves other advantages, by providing an unsupported, lap-sealable liner for a composite container, a method of making such a liner, and a composite container incorporating the liner. The liner is compatible with wet adhesives for attaching the liner to a paperboard body wall of a container. Because the liner is lap-sealable, the liner joint represents only two thicknesses of the liner, and because the liner is unsupported, the liner is thin. Therefore, the liner joint is much thinner than a fold seal of a conventional supported liner.
In accordance with one embodiment of the invention, an unsupported lap-sealable liner comprises a heat seal layer, a barrier web having a first surface attached to the heat seal layer and having an opposite second surface, and a sealable primer applied as an aqueous dispersion to the second surface of the barrier web and then dried. The sealable primer comprises a polymer having bonding affinity with wet adhesive used for bonding the liner to a paperboard surface of a composite container. The sealable primer furthermore is heat-sealable to the heat seal layer such that the liner is lap-sealable.
Various materials can be used for the sealable primer, including but not limited to modified ethylene polymers, modified acrylic primers, acrylic heat seal coatings, and vinyl primers or washcoats. The heat seal layer forming the opposite surface of the liner can comprise any of various heat seal materials including but not limited to ionomer resins such as SURLYN® or TRANCEND®, high-density polyethylene (HDPE), ionomer/HDPE coex, or the like. The heat seal layer can be a separately manufactured film that is adhesively laminated to the barrier web, or can comprise an extrusion coating on the barrier web.
The barrier web can comprise a metal foil layer, a layer of metallized polymer film (i.e., a polymer film on which a thin layer of metal in substantially pure form, such as aluminum, is vapor-deposited), a layer of barrier polymer such as ethylene vinyl alcohol copolymer (EVOH), or combinations thereof.
A composite container in accordance with one embodiment of the invention comprises a tubular body wall defining an inner paperboard surface facing toward an interior of the container, and an unsupported liner free of paper layers and adhered to the inner paperboard surface of the body wall via a wet adhesive interposed between the liner and the inner paperboard surface. The liner comprises a heat seal layer defining an innermost surface of the container, a barrier web attached to a radially outer surface of the heat seal layer, and a sealable primer applied as an aqueous dispersion to a radially outer surface of the barrier web and then dried. The sealable primer comprises a polymer having bonding affinity with the wet adhesive and furthermore being heat-sealable to the heat seal layer of the liner, and the liner has opposite edges that form a lap joint therebetween via heat sealing of the heat seal layer to the sealable primer.
The invention also provides a method of making an unsupported, lap-sealable liner for a composite container. The method comprises the steps of providing a barrier web having opposite first and second surfaces, attaching a heat seal layer to the first surface of the barrier web, and applying an aqueous dispersion of a sealable primer to the second surface of the barrier web and allowing the aqueous dispersion to dry such that a layer of the sealable primer covers the second surface of the barrier web, the sealable primer comprising a polymer having bonding affinity with wet adhesive used for bonding the liner to a paperboard surface of a composite container, the sealable primer furthermore being heat-sealable to the heat seal layer whereby the liner is lap-sealable.
Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:
The present inventions now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, these inventions may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.
The container body 12 also includes a liner 18 adhered against an inwardly facing surface of the innermost body ply 14. The liner 18 is provided for forming a barrier substantially impervious to moisture and/or gases such as oxygen. In the packaging of food and drink products in particular, it is often important to ensure that the container wall have a water vapor transmission rate (WVTR) below a certain specified value, and/or to ensure that the container wall have an oxygen transmission rate (OTR) below a certain specified value. Depending upon the requirements in a particular case, the material(s) that are suitable for the liner 18 may vary
The present invention particularly concerns containers in which the liner 18 is an unsupported, lap-sealable liner. By “unsupported” is meant that the liner does not include any paper layer as a backing. The liner 18 includes a web 20 of material that forms the barrier to moisture and/or gases. The barrier web 20 can comprise one or more layers of barrier material. Suitable barrier materials include but are not limited to metal foil, metallized polymer film (i.e., polymer film having a thin layer of substantially pure metal vapor-deposited thereon), barrier polymers such as ethylene vinyl alcohol copolymer (EVOH), polyvinylidene chloride, polyethylene, and polypropylene, silicon dioxide or aluminum oxide coatings, or combinations thereof. The liner 18 further comprises a heat seal layer 19 attached to the radially inward surface of the barrier web 20. The heat seal layer 19 forms the innermost surface of the container adjacent the container contents. Various materials can be used for the heat seal layer, including but not limited to ionomer resins such as SURLYN® or TRANCEND® (ethylene acid copolymers having acid groups partially neutralized by zinc or sodium ions), high-density polyethylene (HDPE), and others. A coextruded heat seal layer comprising a layer of ionomer resin and a layer of HDPE can also be used.
The liner 18 also comprises a layer of sealable primer 21 that forms the radially outermost surface of the liner facing the paperboard body wall of the container. The liner 18 is adhered to the inner paperboard surface of the body wall ply or plies 14 by a wet adhesive 23. The wet adhesive can comprise, for example, a PVA type adhesive such as XR-6520M available from the H.B. Fuller Company. The sealable primer comprises a material that has good bonding affinity with the wet adhesive 23 and is also heat-sealable to the heat seal layer 19 of the liner. Various materials are suitable for the sealable primer, including modified ethylene polymers, modified acrylic primers, acrylic heat seal coatings, and vinyl primers or washcoats. Examples of suitable commercially available materials include: Sovereign 87XW134 (water-based vinyl primer) available from Sovereign Specialty Chemicals, Inc.; H.B. Fuller SC8062 (solvent-based acrylic primer/heat seal coating) available from H.B. Fuller Company; and MICA M1164 (water-based, modified acrylic primer/heat seal coating) available from Mica Corporation of Shelton, Conn.
Thus, as shown in
The container 10 can also include a rolled bead 22 at a top end of the container body 12, formed by rolling the top edge of the wall of the container body 12 radially outwardly and then downwardly toward a lower end of the container body. The bead 12 can be formed by providing a die of suitable configuration and forcing the top end of the container body axially against the die to roll an upper portion of the body outwardly and then downwardly. The bead 12 is provided in part so that a removable and replaceable overcap 24 can be snap-fit onto the top end of the container in engagement with the bead. The overcap provides a way to re-close the container after it has initially been opened.
The primary or original sealing of the top end of the container, however, can be provided by a flexible membrane closure 26 that is bonded to the end surface of the bead 22 after the container is filled. The membrane closure 26 can be of various constructions, but generally includes at least a moisture and/or gas barrier layer 28 and can include one or more further layers 30 if desired. To bond the membrane closure 26 to the bead, the membrane closure includes on its under surface a sealant 32 that is heat-sealable to the heat seal layer 19 of the liner. The greatly reduced thickness of the liner lap joint relative to conventional anaconda fold seals means that there is a much smaller profile variance on the end of the bead. This potentially can allow the thickness of the sealant layer 32 on the membrane to be reduced, since a lesser amount of sealant is needed to fill in any gap between the membrane and the bead created by the lap joint.
After the membrane closure 26 is bonded to the bead 22, the overcap 24 is then placed over the membrane and engaged with the bead. When the consumer wishes to open the sealed container, the overcap 24 is removed and then the membrane closure 26 is peeled off the bead as depicted in
The liner 18 can be manufactured in a number of ways.
After application of the aqueous primer composition, the laminate is passed through a dryer 60 to dry the coating of primer. The finished liner 18 is then wound into a roll 18a in a reel-up 70.
Variations can be made in the process depicted in
Another embodiment of a liner manufacturing method in accordance with the invention is shown in
After the application of the aqueous primer composition, the web is advanced through a dryer 60 to dry the primer coating, and then the finished liner 18 is wound into a roll 18a in a reel-up 70.
Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
