Stock material or miscellaneous articles – Hollow or container type article – Flexible food casing
Reexamination Certificate
1999-11-17
2003-10-07
Beck, Shrive P. (Department: 1772)
Stock material or miscellaneous articles
Hollow or container type article
Flexible food casing
C428S034900, C428S035100, C428S035200, C428S035700, C428S036900, C426S105000, C426S135000, C426S143000
Reexamination Certificate
active
06630214
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of controlling the rewet shrinkage of a tubular film of non derivatized cellulose to enhance its value as a food casing.
BACKGROUND OF THE INVENTION
The use of tubular cellulose films as food casings is well known in the art. A non reinforced type of cellulose casing commonly is used in the manufacture of various sausage products such as frankfurters and the like. These cellulose films generally consist of a tubular film of pure regenerated cellulose having a wall thickness ranging from 0.025 to 0.038 mm and ranging in diameters from about 14 to 50 mm.
To date, the most notorious process for manufacturing cellulose food casings is the “viscose process.” In the viscose process a natural cellulose is such as cotton linters or wood pulp is converted to a soluble cellulose derivative (cellulose xanthate) by chemical reaction. The soluble cellulose derivative is extruded as a tube and contacted with reagents that react chemically with the cellulose derivative to regenerate a pure form of cellulose.
A more recent innovation for the production of cellulose food casings involves the simple dissolution of the natural cellulose without chemical reaction. In this process the natural cellulose is solubilized by a tertiary amine N-oxide such as N-methyl-morpholine-N-oxide (“NMMO”). The solution is thermoplastic in that it is solid at room temperature and has a melting point of about 65° C. The solution is extruded as a tube into a bath containing a liquid that is a non solvent for cellulose (such as water) where the solvent is extracted to regenerate a pure form of cellulose. The cellulose derived from this process is “non derivatized” in that it has not been subjected to covalent bonding with a solvent or reagent as is the “derivatized” cellulose derived from the viscose process. Instead, the non derivatized cellulose has been dissolved by association with a solvent or reagent through Van der Waals forces or by hydrogen bonding.
Regardless of the process used, the regenerated cellulose immediately after tubular extrusion and regeneration is in a gel state. This tubing of cellulose gel is contacted with a plasticizing agent such as an aqueous polyhydric alcohol solution and then is dried under inflation to produce a cellulose film. The gel tubing is initially dried down to a moisture content of less than 10% and preferably 3 to 5% moisture based on the weight of dry cellulose to form a cellulose film. The moisture content based on the weight of dried cellulose is sometimes referred to as the percent of moisture to bone dry gauge or “BDG.” Unless otherwise stated, all moisture contents mentioned hereinbelow are on a dry cellulose basis (BDG). Drying the gel tube to a moisture content of 3 to 5% BDG is believed to establish hydrogen bonding in the cellulose structure which is responsible for many end-use properties of the resulting tubular film.
After drying to establish the hydrogen bonding, the tubular cellulose film is remoisturized to a moisture content of about 10 to 20% BDG or higher to provide the film with the suppleness needed for handling and further processing the film without damaging it.
The inflation during the dring process serves to provide the cellulose film with a degree of orientation that also contributes to the properties of the cellulose film. For example, with the conventional derivatized cellulose casing, it is customary to dry the tubing of cellulose gel while holding it by inflation at a diameter that is about 20 to 30% greater than the extrusion diameter to provide transverse direction (TD) orientation. In addition, the tubing is longitudinally stretched by drawing it in the machine direction about 1 to 3% over its length in the gel state to provide a machine direction (MD) orientation.
According to U.S. Pat. No. 2,999,757, the orientation provided by this transverse and longitudinal stretching provides the casing with certain desirable properties including a lower degree of distension upon being subjected to stuffing pressures and the ability to produce a more consistent and uniform diameter of sausage. The '757 Patent further says that diametrically stretching the casing less than about 35% in the transverse direction does not appreciably improve the casing characteristics whereas stretching it more than about 55% is difficult and presents operating problems. When stretched beyond about 55%, the casing is more apt to break in the dryer. Thus, according to the teachings of the '757 Patent, the upper limit of transverse orientation for a derivatized cellulose casing is about 55%.
Orienting the film makes it less extensible so that when the casing is stuffed, a change in the stuffing pressure will not result in a substantial change in the stuffed diameter of the sausage. This is a desirable property as it contributes to the production of sausages having a uniform diameter as noted in the '757 Patent. In particular, it is customary to design a sausage casing to operate at a desired stuffing diameter. When stuffed to this desired or recommended stuffed diameter (RSD), the portion of the curve plotting casing diameter against stuffing pressure is relatively flat so the diameter of the sausage remains substantially constant over a wide range, of stuffing pressures. Sausage manufacturers take advantage of this casing property in that it allows the casing to be tightly stuffed under high pressures of up to about 250 mm of mercury without exceeding a desired diameter.
One drawback of this orientation is that the casing tends to shrink back. to its extruded diameter when it is rewet. The casing is rewet to various degrees when it absorbs moisture during processing or use. For example, the casing is rewet during the shirring of the casing as it as it absorbs moisture from the shirring solution. It also is rewet during stuffing as it absorbs moisture from the fluid products being stuffed into the casing. Excessive shrinkage of the casing during either shirring or stuffing is not desired. Shrinkage during the shirring operation causes the shirred casing to grip tightly about the shirring mandrel. Consequently, damage may result to the casing if excessive force is needed to doff the shirred casing from the mandrel. On the other hand, excessive shrinkage of the casing about the food product stuffed and processed in the casing may cause the casing to split, or the casing may adhere so tightly to the food product that it is difficult to peel the casing from the food product after processing.
Excessive shrinkage is a particular problem with respect to a casing formed of a non derivative cellulose. In this respect it has been found that a non derivatized cellulose casing is much more extensible than its derivatized counterpart. For example, U.S. Pat. No. 5,658,524 discloses that non derivatized cellulose can be diametrically stretched upwards of 200% during the drying cycle. The greater extensibility of the non derivatized casing means that during stuffing, it undergoes a greater diameter change with smaller changes in stuffing pressure than does a comparable derivatized cellulose casing. To compensate for the more extensible nature of the derivatized cellulose casing, it was found necessary to dry the tubing of cellulose gel while holding it under inflation at a diameter of 70 to 80% greater than its extruded diameter. While drying the cellulose gel under these conditions allowed for better control of the stuffed diameter of the casing, the resulting increase in the shrinkage rate upon the casing becoming rewet caused other problems.
For example, because the casing retained a relatively large amount of a shrink (due to its greater degree of orientation), the diameter of the shirring mandrel had to be reduced in order to accommodate the greater amount of shrinkage. This in turn resulted in an undesirably smaller bore diameter of the shirred casing article. Upon stuffing, the casing shrank even more which resulted in the casing being so tight around the sausage in the casing that conventional peeling operations
Mc Garel Owen Joseph
McAllister Merlan Elroy
Aceto Roger
Beck Shrive P.
Bobrowicz Donna
Tsoy Elena
Viskase Corporation
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