Stock material or miscellaneous articles – Hollow or container type article – Shrinkable or shrunk
Reexamination Certificate
1999-12-23
2002-06-18
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Hollow or container type article
Shrinkable or shrunk
C428S035400, C428S036600, C428S036700, C428S213000, C428S214000, C428S215000, C428S216000, C428S336000, C428S474400, C428S514000, C428S515000, C428S516000, C428S520000, C426S112000, C426S113000, C426S127000, C426S392000, C426S407000, C426S412000
Reexamination Certificate
active
06406763
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to multiple layer films for food packaging, and more particularly to films that are useful for packaging food products to be pasteurized after packaging.
There are generally two types of heat shrinkable bags for packaging processed (i.e., cooked) food products: i) barrier bags and ii) cook-in bags. A “barrier bag” protects a food product (e.g., meat) that is cooked before packaging. The barrier bag protects the product from spoilage and contamination and prevents leakage of the packaged product's juice or liquid. The barrier bag may also display printed information regarding the packaged product. The barrier bag is sealed and usually heat shrunk tightly about the cooked product. Accordingly, the thermoplastic film from which the barrier bag is made (i.e., the “barrier bag film”) is heat shrinkable, having a high total free shrink. Further, the barrier bag film is preferably capable of quickly forming a heat seal that will hold at or below the heat shrinking temperature. The barrier bag film also presents pleasing optical characteristics (i.e., high gloss and low haze). For example, a widely used barrier bag film sold by Sealed Air Corporation under the B620 product code has typical values of about 66% total free shrink, 5.7% haze, and 78% gloss.
Alternatively, a “cook-in bag” protects a food product that is cooked while packaged. In this process, an uncooked food product is heat sealed within a cook-in bag formed from a thermoplastic film (i.e., “cook-in film”). The cook-in film is designed to maintain heat seal integrity, resist delamination, and maintain acceptable optical properties (e.g., gloss, low haze, and clarity) during and after exposure to the cook-in conditions. In a typical cook-in process, the cook-in bag is immersed in hot water or a steam-heated environment for a period of time to cook the packaged product to the desired level. During cooking, the cook-in film is also subjected to abuse, for example rubbing against the walls of a metal container that holds the hot water in which the cook-in bag is immersed. Cook-in time and temperature conditions typically involve a long, slow cook—for example, submersion in hot water at about 55° C. to 65° C. for about 1 to about 4 hours. Submersion in water or steam at 70° C. to 100° C. for up to 12 hours is also possible. Cook-in films are also heat shrinkable so that the heat exposure step shrinks the cook-in bag tightly about the product. Examples of cook-in bag and film constructions are disclosed, for example, in U.S. Pat. No. 4,469,742 issued Sep. 4, 1984 to Oberle entitled “Pasteurizable, Cook-In Shrink Film,” which is incorporated herein in its entirety by reference.
However, even a food product cooked in a cook-in bag may eventually be packaged in a barrier bag. This is because a processor may desire to remove the cook-in bag from the cooked food product to further process the cooked food product. For example, the processor may wish to apply a food modifier or slice the packaged food into smaller portions. Food modifiers are used to impart seasoning, color, flavor, glazing, or pleasing odor to the outer surface of the cooked food product. This further processing typically requires stripping the cook-in film from the cooked food product, applying the modifier to the surface of the food product, and then repackaging the modified food product in a barrier bag. The packaged food is then refrigerated for shipment to a retailer, who stores or displays the packaged product until sale to the consumer.
The cooking process—either before the food product is packaged in a barrier bag or while the food product is packaged in a cook-in bag—typically kills or significantly reduces the population of undesirable microorganisms such as the listeria organism that may contaminate the food product. However, the handling of cooked food before it is eventually sealed within a barrier bag may reintroduce undesirable microorganisms to at least the surface of the cooked food.
To return the handled, cooked food product to a safe condition for consumption, a processor may expose the packaged food to a heat treatment to reduce the bacterial load that was reintroduced to the surface of the food product after cooking. This heat treatment subsequent to packaging is known as “post packaging pasteurization” or simply “post pasteurization.” Post pasteurization typically involves submersion of the packaged product in hot water (160° F. to 205° F.; i.e., 71° C. to 96° C.) for from about 30 seconds to about 10 minutes. See, for example U.S. Statutory Invention Registration H1762 to DeMasi entitled “Post-Pasteurization,” which is incorporated herein in its entirety by reference.
However, a barrier bag often does not withstand the exposure to post pasteurization conditions without failure of the heat sealed seams or delamination of the barrier bag film. To overcome this problem, the processor may package or repackage the cooked food product in a cook-in bag to survive the post pasteurization conditions. A cook-in bag will not fail under post-pasteurization conditions—which typically are much less rigorous than the cook-in conditions for which a cook-in bag is designed. However, cook-in bag films have several disadvantages compared to barrier bag films. Cook-in bags typically cost more, display poorer presentation characteristics (e.g., gloss, haze, and clarity), and possess lower heat shrink capability.
SUMMARY OF THE INVENTION
The aforementioned problems are overcome in the present invention of a post pasteurization film. More specifically, the multilayer heat-shrinkable film includes a first outer layer formed from a resin composition having a Vicat softening point of at least 100° C. The film includes a second outer layer having one or more thermoplastic gloss materials selected from polyester, ethylene/alpha-olefin copolymer having a melt index of greater than 1 g/10 minutes, styrene/butadiene block copolymer, and ethylene/styrene random copolymer. The film also includes one or more inner layers between the first and second outer layers. At least one of the inner layers includes an ethylene/&agr;-olefin copolymer. The film has a total free shrink of at least 40% at 85° C. If the second outer layer includes polyester, then: i) each of the inner layers of the multilayer film is devoid of a weight amount of polyamide greater than the weight amount of polyester in the second outer layer and ii) each of the inner layers of the multilayer film is devoid of a weight amount of polyester greater than the weight amount of polyester in the second outer layer.
In preferred embodiments, the second outer layer includes an amount of the thermoplastic gloss material sufficient to impart a gloss of greater than 60%. The film may also include an oxygen barrier internal layer. Also preferably, the film includes at least one layer that is cross-linked.
The film of the present invention may be used to form a food package or bag suitable for post pasteurization. Such a bag may be used in a method of post pasteurization, in which the processor: i) forms a bag from the inventive film, ii) encloses a food product within the bag to create a packaged food product, and iii) exposes the packaged food product to conditions sufficient to pasteurize at least the surface of the packaged food product to a desired level.
Such a bag may also be used in a method for imparting a food modifier to a cooked food product. In such case, a processor: i) encloses a food product in a cook-in bag to form a packaged food product, ii) at least partially cooks the packaged food product in the cook-in bag to form a cooked food product, iii) removes the cook-in bag from the cooked food product, iv) applies a food modifier to the cooked food product to form a modified, cooked food product, v) forms a post-packaging pasteurization bag from the inventive film, vi) encloses the modified, cooked food product within the post-packaging pasteurization bag to create a packaged modified cooked food product, and vii) exposes the packaged, modified coo
Childress Blaine C.
Wofford George D.
Wolf John R.
Cryovac Inc.
Kiliman Leszek
Ruble Daniel B.
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