TITLE METALIZED SEAM SEAL FOR SINGLE WRAP CONTAINER BACKGROUND This patent relates to a single wrap container for holding foodstuffs or other oxygen or moisture sensitive products. More particularly, this patent relates to a single wrap container having a seam having an exposed underlying edge enclosed by tape having a metalized layer.

Single wrap containers, formed from a single ply of material, can be used to hold drink mixes, snacks and other foods. The single wrap container body typically is formed from a blank comprising layers of, from the inside out, polyolefin, paper stock, polyolefin, metal foil, polyolefin, printed paper and overlacquer. The blank is die cut to the desired silhouette and then formed into a tubular shape by wrapping it once around a mandrel. The overlapping ends of the blank form a straight seam. The seam has an underlying portion and an overlying portion.

The edge of the underlying portion of the seam, and therefore an edge of the paper layer, is exposed to the container contents. Air and moisture can migrate through the paper layer into or out of the container.

One solution to this problem involves covering the exposed edge of the blank with a strip of barrier tape. Such a solution is taught in Stahlecker U. S. Patent No. 5,620, 135, wherein the underlying seam edge of the container is enclosed by a protective covering. In Stahlecker, the edge is less thick than the rest of the body wall so that the total

thickness of the inner edge segment, including the protective covering, is approximately equal to that of the rest of the wall.

Known materials for protecting the raw edges of paperboard'containers include low density polyethylene (LDPE), ethylene vinyl alcohol copolymer (EVOH), polyethylene terephthalate (PET), glycol modified PET (PETG), nylon, and combinations thereof.

The inventor made single wrap straight seam cans and covered the underlying body wall exposed edge with seam tape comprising a layer of PET interposed between LDPE layers. The sealed containers were tested for air migration levels and the resulting levels were unacceptably high (0.10 cc of oxygen per container per day). What is needed is an improved side seam tape for preventing migration of air and moisture into or out of a sealed container.

SUMMARY OF THE INVENTION The present invention is an improved seam tape for protecting the underlying exposed edge of single wrap containers. The tape comprises a layer of metalized PET interposed between layers of LDPE. The seam tape is especially useful with containers designed to hold products sensitive to oxygen and water.

DRAWINGS Figure 1 is a perspective view of a single wrap blank formed into a tubular container.

Figure 2 is an enlarged partial sectional view of the single wrap container of Figure 1.

Figure 3 is an enlarged partial sectional view of the single wrap container of Figure 1 showing the seam tape of the present invention.

DETAILED DESCRIPTION OF THE INVENTION Turning to the drawings, there is shown in Figure 1 a blank formed into a single wrap straight walled tubular container. The container 10 has a straight overlap seam 12 having an underlying portion 14 and an overlying portion 16.

As best seen in Figure 2, the edge 18 of the underlying portion 14 is exposed to the inside contents of the container 10.

The blank used to form the single wrap container typically comprises layers of, from the inside out, polyolefin, paper stock, polyolefin, metal foil, polyolefin, printed paper and overlacquer. Usually the polyolefin layers are low density polyethylene (LDPE), but any suitable polyolefin, including high density polyethylene (HDPE), may be used. Because the tubular container has an exposed edge, air can migrate through the paper layer into the container and moisture from the contents can wick into the paper layer.

To prevent air from getting into the container and moisture from getting out, seam tape 20 can be used to cover the underlying exposed edge 18 of the container wall, as shown in Figure 3. Conventional seam tape comprises one or more layers of low density polyethylene (LDPE), ethylene vinyl alcohol copolymer (EVOH), polyethylene terephthalate (PET), PETG, nylon, or combinations thereof. However, these materials may not be satisfactory in sealing the container edge.

The present invention is a seam tape comprising, in a first embodiment, a metal layer disposed between layers of polyolefin. The polyolefin may be LDPE, HDPE or any other suitable polyolefin. The polyolefin must match the polyolefin

used in the blank for seal integrity. Preferably, the metal layer is PET coated with metal such as aluminum ("metalized aluminum PET"). The coating may be accomplished by blade coating, spray coating, or any other suitable method.

Alternatively, the metal layer can be a metal foil, such as aluminum foil or tin foil.

To use, the seam tape with metal layer is applied to the underside of the blank and wrapped around the exposed edge prior to wrapping the blank around the mandrel.

Alternatively, the seam tape may be applied to the inside of the tubular container after the container has been formed.

EXAMPLE Single wrap straight seam cans were made from blanks comprising layers of HDPE, paper, LDPE, foil and HDPE. The exposed underlying wall edge was covered with either a first seam tape comprising a layer of 48 gauge PET interposed between layers of 18 lb/ream (8.16 kg/ream) LDPE or a second seam tape comprising 48 gauge metalized aluminum PET interposed between layers of 18 lb/ream (8.16 kg/ream) LDPE.

Both sets of sealed cans were tested for oxygen migration with a Mocon, Inc. oxygen transmission analyzer.

The average level of oxygen migration in the first set of containers (with the LDPE/PET/LDPE seam seal) was 0.10 cc of oxygen per container per day. The average level of oxygen migration in the second set of containers (with the seam seal of the present invention) was 0.01 cc of oxygen per container per day. These results demonstrate the superior barrier properties of a seam tape comprising a metal layer interposed between polyolefin layers.

Other modifications and alternative embodiments of the invention are contemplated which do not depart from the scope of the invention as defined by the foregoing teachings and appended claims. It is intended that the claims cover all such modifications that fall within their scope.