Patent Application
20060159877
The present invention relates to polymer film laminates, and more particularly relates to such laminates useful in applications such as composite containers.
Composite containers comprise wound paperboard container bodies lined by an impervious liner that provides a barrier against the passage of oxygen and/or moisture. In some applications, the liner must provide a high degree of barrier performance, which is achievable with metal foil-based liners. Typical foil-based liners are laminated structures such as {paper/foil/sealant}, or {sealant/foil/sealant}. Because it is a relatively costly component of the liner, it would be desirable to eliminate the metal foil layer, while still achieving high levels of barrier performance.
The present invention addresses the above needs and achieves other advantages, by providing a non-foil-based liner for composite containers. The liner has a two-ply construction, comprising a paper outer ply adapted to be adhered to an inner surface of a body wall of a composite container, and an inner ply laminated to the paper outer ply by an intervening tie layer. The inner ply comprises a polymer film core layer having an outer surface and an inner surface, a vapor-deposited metal layer joined to the outer surface of the film core layer, and a sealant layer disposed on the inner surface of the film core layer. The sealant layer forms the innermost surface of the container and is operable for sealing opposite edges of the liner to each other at a fold seal therebetween.
The inner and outer plies can be laminated either by adhesive lamination or extrusion lamination. In the case of adhesive lamination, the tie layer in one embodiment comprises a urethane-based adhesive. Advantageously, the urethane-based adhesive comprises a polyester urethane adhesive.
In the case of extrusion lamination, the tie layer comprises a coextruded layer having an outer sublayer contiguous with the outer ply and an inner sublayer contiguous with the inner ply, the outer and inner sublayers comprising different polymer materials. The outer sublayer advantageously comprises polyethylene such as low-density polyethylene. The inner sublayer advantageously comprises an acrylic acid-based polymer such as ethylene methacrylic acid.
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 inventions 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.
With reference to
The tubular container 10 includes a wall having one or more body plies 13 (
The seams where the various plies are joined together are illustrated in
A liner structure in accordance with a first embodiment of the invention is schematically depicted in
The metallized film 50 comprises the primary barrier layer of the liner. The metallized film in this embodiment comprises a film core layer 46 and a metal layer 48. The metal layer 48 is vacuum- or vapor-deposited on the surface of the film core layer 46, which serves as the substrate for the metal layer. Various metals can be used, but aluminum is most commonly employed. Processes for metallizing film are well known and are not further described herein. The film core layer 46 can comprise various polymers, including but not limited to polyethylene, polypropylene, polyester such as polyethylene terephthalate, nylon, and the like.
The adhesive tie layer 42 comprises a urethane-based adhesive, and advantageously comprises a polyester urethane adhesive. It has been found that the barrier performance of the liner is improved when a polyester urethane adhesive is used, in comparison with other types of laminating adhesives. A suitable polyester urethane adhesive useful in the practice of the invention is Adcote® 522A/522B two-component polyester urethane adhesive available from Rohm & Haas. The 522A component is an isocyanate-terminated polyester urethane and the 522B component is a coreactant.
The liner structure of
With respect to discontinuities in the metal layer 48, although some of them can result from the metallization process itself, in other cases they can be introduced subsequent to metallization such as by inadvertently scratching the metal layer during handling of the film. To reduce the incidence of such breaches in the metal layer, it is advantageous for the metallized film to include a protective coating over the metal layer.
The liner 14″ also differs from the prior embodiments in that the paper layer 40 is extrusion-laminated to the metallized film 50″ via a coextruded layer having an inner sub-layer 51 and an outer sub-layer 52 that are different polymers. The inner sub-layer 51 advantageously comprises an acrylic acid-based polymer such as ethylene methacrylic acid. The outer sub-layer advantageously comprises a polyethylene such as low-density polyethylene. It has been found that extrusion laminating the liner using a coextruded LDPE/EMAA layer results in a liner having better barrier performance than when LDPE alone is used for extrusion laminating the liner.
The liners in accordance with the invention advantageously are two-ply structures formed by laminating two separate webs together. For instance, one web can comprise the metallized film 50, 50′, 50″ having the sealant layer 44, and the other web can comprise the paper layer 40. As such, the liners can be prepared in a single-pass laminating operation, which offers distinct advantages over multi-pass operations often required for high-barrier laminate construction. Thus, in the case of adhesive lamination, the paper web and the web having the metallized film and sealant layer are advanced toward a laminating nip and a laminating adhesive is applied to one of the webs and the webs are laminated together in the nip and the resulting laminate is wound into a roll. In the case of extrusion lamination, the two webs are advanced toward the nip and a coextruded layer is extruded between the webs as they approach the nip, and the webs are laminated together in the nip and the resulting laminate is wound into a roll.
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.
