Stock material or miscellaneous articles – Hollow or container type article – Shrinkable or shrunk
Reexamination Certificate
2000-09-18
2003-12-02
Pyon, Harold (Department: 1772)
Stock material or miscellaneous articles
Hollow or container type article
Shrinkable or shrunk
C428S034800, C428S035400, C428S035200, C428S036900, C428S036910, C428S475800, C428S476100, C428S516000, C428S518000
Reexamination Certificate
active
06656548
ABSTRACT:
BACKGROUND INFORMATION
1. Field of the Invention
This invention relates generally to food packaging films, more particular to films in which packaged food products can be cooked.
2. Background of the Invention
Many food products are processed in thermoplastic film packages by subjecting the packaged product to elevated temperatures produced by, for example, immersion in hot water or exposure to steam. Such thermal processing often is referred to as cook-in, and films used in such processes are known as cook-in films.
A food product that is packaged and processed in this manner can be refrigerated, shipped, and stored until the food product is to be consumed or, for example, sliced and repackaged into smaller portions for retail display.
Many sliced luncheon meats are processed in this fashion. Alternatively, the processed food can be removed immediately from the cook-in package for consumption or further processing (e.g., sliced and repackaged).
A cook-in film must be capable of withstanding exposure to rather severe temperature conditions for extended periods of time while not compromising its ability to contain the food product. Cook-in processes typically involve a long cook cycle. Submersion in hot (i.e., about 55° to 65° C.) water for up to about 4 hours at is common; submersion in 70° to 100° C. water or exposure to steam for up to 12 hours is not uncommon, although most cook-in procedures normally do not involve temperatures in excess of about 90° C. During such extended periods of time at elevated temperatures, any seams in a package formed from a cook-in film preferably resist failure (i.e., pulling apart).
Following the cook-in process, the film or package preferably conforms, if not completely then at least substantially, to the shape of the contained food product. Often, this is achieved by allowing the film to heat shrink under cook-in conditions so as to form a tightly fitting package. In other words, the cook-in film desirably possesses sufficient shrink energy such that the amount of thermal energy used to cook the food product also is adequate to shrink the packaging film snugly around the contained product. Alternatively, the cook-in film package can be caused to shrink around the contained food product prior to initiating the cook-in procedure by, for example, placing the package in a heated environment prior to cooking.
The cook-in film also preferably possesses sufficient adherence to the food product to inhibit or prevent “cook-out” (sometimes referred to as “purge”), which is water and/or juices that collect between the surface of the contained food product and the food-contact surface of the packaging material during the cook-in process. Preventing cook-out can increase product yield, provide a better tasting product, improve shelf life and provide a more aesthetically appealing packaged product. Films that adhere well to the packaged food product help reduce cook-out.
Many cook-in films are corona treated to increase the surface energy of their food-contact layers. However, corona treatment can be inconsistent, can result in a film with inconsistent adhesion, can result in a film having a surface energy that decays over time, and can interfere with the sealability of a film.
Many types of meat are processed by a cook-in procedure. Common examples include ham, sausage, some types of poultry, mortadella, bologna, braunschweiger, and the like. However, such meats can vary substantially in fat and protein content. Obtaining adequate film-to-meat adhesion becomes more difficult with respect to meats that are high in fat, low in protein, or have substantial levels of additives (starch, water, etc.). Adhesion of the film to the meat product is believed to be due to polar functionalities of the protein being attracted to polar functionalities on the surface of the cook-in film. For example, poultry has a relatively low fat content and a relatively high protein content; therefore, obtaining adequate film-to-poultry meat adhesion is relatively easy. However, ham, sausage, mortadella, bologna, braunschweiger and the like have relatively high fat contents and relatively low protein content; therefore, obtaining adequate film-to-meat adhesion for such meat products (especially sausage, mortadella, bologna, and braunschweiger) is more difficult.
Some presently available cook-in films provide excellent adhesion with the meat product and do a good job of reducing cook-out. Additionally, most presently used films are able to withstand extended time periods at the elevated temperatures described supra; accordingly such films are adequate for many cook-in applications. However, some cook-in applications impose even more stringent performance requirements. For example, some food products that are processed via cook-in procedures are oxygen sensitive. Cook-in films for these products need to include one or more oxygen barrier layers. Other cook-in applications require that the film or the package made therefrom be printable and be able to retain any image printed thereon.
One of the most troublesome of these performance requirements is durability when used in conjunction with a forming shoe (during the package forming process). Where a film has a high degree of shrinkability in the transverse direction, it tends to “neck down” on the forming shoe during the sealing step of the process. This often causes such highly shrinkable films to rupture.
No presently available cook-in film is believed to possess all of the following characteristics: (1) good adherence to protein, (2) an extremely low permeance to oxygen, (3) an ability to shrink around a packaged product in a controlled fashion, (4) a seal layer with a softening point that is sufficiently high to survive cook-in conditions, (5) an ability to be sealed around a forming shoe without necking down, (6) good resistance to clip cuts, and (7) an ability to be printed in such a manner that the printed image is protected during the cook-in process as well as in subsequent transport and handling.
SUMMARY OF THE INVENTION
Briefly, the present invention provides a multilayer structure that includes a first polymeric film laminated to a second polymeric film. At least one of the films includes a barrier layer with an oxygen permeance of no more than about 150 cm
3
/m
2
·atm·24 hours at about 23° C. and 0% relative humidity. (The units for oxygen permeance as used herein throughout are fairly common in the industry. To convert these to SI units, mol/m
2
·s·Pa, one need only multiply by a factor of 5.097×10
−15
.) Each of the polymeric films include an outer layer that forms an outer surface of the multilayer structure (i.e., an outer layer of the first polymeric film forms one outer surface of the multilayer structure while an outer layer of the second polymeric film forms the other outer surface of the multilayer structure). The aforementioned outer layer of the first polymeric film, even when untreated, has a surface energy of at least 0.034 J/m
2
and includes at least about 10% (by wt.) of a polymer having a Vicat softening point of at least about 65° C. The outer surface of the multilayer structure formed from the outer layer of the first polymeric film (i.e., the first outer surface) can be sealed to itself, the opposite outer surface (i.e., the second outer surface), or an optional adhesive tape applied over a butt-seam juncture formed by contacting the first outer surface with itself. Each of the foregoing sealing techniques can result in the formation of a tube which, through further sealing and cutting techniques well known to those of ordinary skill in the art, can result in packages.
In another aspect, the present invention provides a multilayer structure that includes a first polymeric film laminated to a second polymeric film, at least one of which includes a barrier layer with an oxygen transmission coefficient of no more than about 150 cm
3
/m
2
·atm·24 hours at about 23° C. and 0% relative humidity. Each of the polymeric films includes an outer layer that forms an outer surface of the multilayer struc
Beckwith Scott W.
Ramesh Ram K.
Rosinski Michael J.
Cryovac Inc.
Miggins Michael C.
Pyon Harold
Ruble Daniel B.
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