Cook-in package with tight appearance

Details Cook-in package with tight appearance Cook-in package with tight appearance

1998-07-22

2003-05-13

Dye, Rena (Department: 3627)

Stock material or miscellaneous articles

Structurally defined web or sheet

Including components having same physical characteristic in...

C428S034900, C428S220000, C428S412000, C428S474700, C428S475800, C428S476100, C428S476300, C428S483000, C428S516000, C428S518000, C428S519000, C428S910000, C156S244240, C156S085000, C264S173120, C264S173130, C264S173140, C264S173150, C264S173190

Reexamination Certificate

active

06562443

ABSTRACT:

BACKGROUND INFORMATION
1. Field of the Invention
The present invention relates generally to heat-shrinkable films suitable for cook-in applications. The present invention is also directed to articles of manufacture which are useful for packaging proteinaceous products. The present invention is particularly related to a process for packaging a proteinaceous product in a heat-shrinkable film.
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 further processed by, for example, slicing and repackaging into smaller portions for retail display. 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° C. to 65° C.) water for up to about 4 hours 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.
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. 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. Also, during cook-in the film should preferably have food product adherence to restrict “cook-out,” i.e., the collection of juices between the surface of the contained food product and the food-contact surface of the packaging material. In this manner, product yield is increased by the food product retaining moisture.
Various meat products, such as pork, sausage, poultry, mortadella, bologna, beef, braunsweiger, etc. are prepared as cook-in products. Other non-meat products such as soybean also are considered to be proteinaceous. In all the above cases, it is important to obtain adequate film-to-food adhesion and provide a snug package for superior aesthetic appearance.
For cook-in applications, packaging materials typically are produced in roll form and then converted into shirred sticks, bags, pouches, etc., for the end user. In the past, heat-shrinkable packaging films which have been provided to the cook-in end-user undesirably have been characterized by inconsistent widths. This inconsistency arises because of two primary reasons. First, heat-shrinkable films have significant free shrink at temperatures as low as 50° C., in some cases 45° C., and in some cases, as low as 40° C. Thus, upon exposure to environments where the temperature exceeds 40° C. and sometimes 45° C., the heat-shrinkable film partially shrinks, causing a change in its width. Obviously, this is more of a problem during storage or transportation of heat-shrinkable films in the hotter summer months. Second, heat-shrinkable films are produced in roll-form. When films are wound into rolls, the leading edge of the film being rolled typically experiences higher tension than the outer portions of the roll. Since polymers are viscoelastic in nature, the film material at the outer portions of a roll (which is under little
o tension) tends to ‘snap back’ like a rubber band, relaxing some of the strain imparted by the orientation process. However, film material at the inner portion of the roll is under tension and therefore unable to relax or snap back. This can result in film which is the first used from the roll, i.e., the outer portions of the roll, having a significantly lower width than film at the interior of the roll. Consequently, heat-shrinkable films can vary in width as much as 5%, and in extreme situations, as much as 7% or 10%.
The marketplace continues to express a need for films which are more consistent in width and are dimensionally stable when exposed to temperatures of 40° C., 43° C., 47° C. or even 50° C. This demand arises from the need to stuff the same quantity of meat product into each casing length, especially where the film is formed into shirred casings. In such cases, the width of the packaging material preferably varies less than 3%, more preferably, less than 2%. Packages produced from shirred casings often are cooked in molds, with the cooked meat-product then being sliced. An inconsistent film width will result in an inconsistent package size and, therefore, in significantly greater yield loss.
To provide the end-user with film that is more consistent in width, film manufacturers often anneal the heat-shrinkable cook-in films. Typically, a moving web of film is heated to an elevated temperature in a continuous process. Upon heating the film to an elevated temperature (typically as high as 60° C.), the film shrinks and reduces in width. As a result of this shrinking, the film has now lost some or all of its ability to shrink at or near that elevated temperature. If the process of heat-treatment at an elevated temperature is conducted with a moving web, rather than a roll of film, the process also reduces or eliminates width variation in the film due to the viscoelastic nature of the film (as described above). Thus, the process of annealing produces a film with a more consistent width.
However, the process of annealing as described above can produce other disadvantages. For example, cooked packages produced from some annealed films can be relatively flaccid because the film does not fit snugly around the packaged product, creating an unsightly package which includes cook-out from the underlying food product. Such cook-out is evidenced even when the heat-shrinkable film includes a food-contact surface which would be expected to provide adequate film-to-meat adhesion to prevent substantial purge or cook-out.
Thus, providing a film which exhibits good width stability during transportation and storage in hot environments, yet remains suitable for cook-in applications which require adequate adhesion remains desirable. Such a film also preferably would have the ability to conform to the food product during cooking and after the cook-in process and prevent substantial purge loss/cook-out, thereby providing a tight, more aesthetically pleasing package.
SUMMARY OF THE INVENTION
Briefly, the present invention provides a heat-shrinkable multilayer film that includes at least two layers. One of these layers is an outer layer that includes a polymer that has a surface energy of at least about 0.034 J/m
2
. The other layer includes at least one of the following polymers: polyester, polyvinylidene chloride, polyamide and polyalkylene carbonate. The film of the present invention has a transverse direction free shrink of at least about 3% at 57° C. and a transverse direction free shrink of less than about 2% at 50° C. The film also can include one or more other layers. The heat-shrinkable film of the present invention is particularly useful for cook-in applications, especially those involving the packaging of meat-products. The present invention provides several unexpected and surprising advantages in the packaging of meat-products. For example, the present invention provides a tight package after the cook-in process, while still providing a film which has low shrink (i.e., is dimensionally stabilized) at temperatures as high as 50° C. The present invention also provides

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