Plastic and nonmetallic article shaping or treating: processes – Forming articles by uniting randomly associated particles – With subsequent cutting – grooving – breaking – or comminuting
Reexamination Certificate
1999-10-18
2003-04-15
Pyon, Harold (Department: 1772)
Plastic and nonmetallic article shaping or treating: processes
Forming articles by uniting randomly associated particles
With subsequent cutting, grooving, breaking, or comminuting
C428S034800, C241S028000, C106S164010, C426S138000, C426S135000
Reexamination Certificate
active
06547999
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to cellulose food casings, cellulose compositions, and production methods therefor.
BACKGROUND OF THE INVENTION
Cellulose food casings are well known in the art and are widely used in the production of stuffed food products such as sausages and the like. Cellulose food casings generally are seamless tubes formed from regenerated cellulose and contain a plasticizer such as water and a humectant such as a polyalkylene oxide, a polyalkylene glycol, and/or a polyol such as glycerin. Typically, plasticization is required because otherwise the cellulose tube is too brittle for handling and commercial use.
Cellulose food casings generally are used in one of two forms. In one form the casing consists of a tubular film of pure regenerated cellulose having a wall thickness ranging from about 0.025 mm to about 0.076 mm and is made in tube diameters of about 14.5 mm to 203.2 mm. The second form is a reinforced casing wherein the tubular wall of the casing consists of regenerated cellulose bonded to a paper web. Such reinforced casings are commonly called “fibrous” casings to distinguish them from the non-reinforced cellulose casings. Fibrous casings have a wall in the range of 0.050 mm to 0.102 mm thick and are made in diameters of about 40.6 mm to 193 mm or greater.
The cellulose for making both types of casings is most commonly produced by the so called “viscose process” wherein viscose, a soluble cellulose derivative, is extruded as a tubular film through an annular die into coagulating and regenerating baths to produced a tube of regenerated cellulose.
The viscose process for making cellulose is well known in the art. Briefly, in the viscose process a natural cellulose source (e.g., wood pulp or cotton linters) is treated with a caustic solution to form alkali cellulose. The alkali cellulose then is reacted with carbon disulfide to form cellulose xanthate which is a cellulose derivative. The cellulose xanthate is dissolved in a weak caustic solution. The resulting solution or “viscose” is ripened, filtered, deaerated and extruded.
For food casing the viscose is extruded as a tube into coagulation and regenerating baths containing salts and sulfuric acid. In the acidic bath the cellulose xanthate, e.g. viscose, is converted back to cellulose. In this respect, the acid bath decomposes the cellulose xanthate in a chemical reaction with the result that a pure form of cellulose is coagulated and regenerated.
Initially, the coagulated and regenerated cellulose is in a gel state. In this gel state the cellulose tube first is run through a series of rinse water dip tanks to remove by-products formed during regeneration. The gel tube then is treated with a glycerin humectant and dried to about 10% moisture or less based on total casing weight. The gel tube preferably is inflated during the drying process to a pressure sufficient to provide a degree of orientation to the dried cellulose tube.
Both nonreinforced cellulose casings and fibrous casings are produced in this fashion except in the case of fibrous casings the viscose is extruded onto a tube of paper prior to entering the coagulation and regenerating baths.
An alternate cellulose production method involves forming a cellulose solution by means of a simple dissolution rather than requiring prior derivatization to form a soluble derivative (as in the viscose process). This avoids drawbacks normally attendant to the viscose process such as the problems associated with the generation of gases and sulfur compounds during the chemical reactions to derivative and regenerate the cellulose.
U.S. Pat. No. 2,179,181 describes the dissolution of natural cellulose by a tertiary amine oxide to produce solutions of relatively low solids content, for example 7 to 10% by weight cellulose dissolved in 93 to 90% by weight of the tertiary amine oxide. The cellulose in the resulting solution is nonderivatized (i.e., it is not derivatized prior to dissolution). U.S. Pat. No. 3,447,939 discloses use of N-methylmorpholine-N-oxide (NMMO) as the cyclic amine oxide solvent wherein the resulting solutions, while having a low solids content, nevertheless can be used to precipitate the cellulose to form a film or filament.
More recent patents such as U.S. Pat. Nos. 4,145,532 and 4,426,288 improve upon the teachings of the '939 patent. U.S. Pat. No. 4,145,532 discloses a process for making a solution of cellulose in a tertiary amine oxide such as NMMO which contains 10-35% by weight of cellulose. The higher solids content, achieved in part by including an amount of water (from 1.4% to about 29% by weight) in the tertiary amine oxide solvent, provides a solution adapted for shaping into a cellulosic article such as by extrusion or spinning. In U.S. Pat. No. 4,426,288, the NMMO-cellulose solution contains an additive which reduces decomposition of the cellulose polymer chain so that molding or spinning substances are obtained with only slight discoloration and which will yield molded shapes distinguished by improved strengths upon precipitation in a nonsolvent such as water. U.S. Pat. No. 5,707,783 describes the use of nonderivatized cellulose solutions in the production of nonreinforced and reinforced cellulose food casing.
However, while nonderivatized cellulose resulting from the process of dissolving cellulose in NMMO eliminates certain problems associated with the viscose process, significant obstacles remain regarding the commercial production of nonderivatized cellulose for use in the production of cellulose food casing.
Among the numerous challenges involved in the manufacture of cellulose food casing is the practical utilization of alternative natural cellulose sources. Wood pulp is a common source of cellulose in the viscose process. The wood source from which the pulp is obtained is significant in the viscose process. Morphologically, wood is a heterogeneous cellular structure consisting of zones or annular rings, each representing the radial or transverse growth for a single year.
Generally, hardwoods are distinguished from softwoods. Hardwoods typically include the broad-leafed species, also known as the angiosperms. Examples of hardwoods include the oaks, poplars, ashes, gums, and birches. By contrast, softwoods typically include the needle-leafed species, also known as the gymnosperms. Examples of softwoods include pines, firs, hemlocks and spruces. Hardwoods and softwoods share some similarities. The relative sizes of the cell cavities of wood are quite variable in both the longitudinal and transverse direction relative to the longitudinal axis of the tree for both hardwoods and softwoods. Thus, both softwoods and hardwoods have cellular systems arranged both longitudinally and perpendicularly to the vertical axis of the tree.
The longitudinal vertically oriented fibers in hardwoods are separated by vessels that have relatively large diameters compared to the fibers themselves. Also in hardwoods, there are short ray cells arranged with their long axis oriented radially in the tree. By contrast, the longitudinal fibers in softwoods are more regularly aligned than the fibers in hardwoods. Moreover, softwood fibers have short blunt ray cells oriented in the transverse direction. There are other significant differences between hardwoods and softwoods, particularly in the structure and composition of the fibers that lend to their use either in the viscose process or in the NMMO solvent process.
Hardwood fibers are much shorter than softwood fibers. Hardwood fiber length varies between species but generally, on average, hardwood fibers are about 1.5 mm long. Softwood fibers, on average, generally are about 3.5 mm long and even much longer in some species. Hardwood fibers also have a higher content of hemicelluloses (i.e., short or incompletely formed cellulose chains or selected alkali soluble sugar residues) than soft wood fibers. The molecular weight of hardwood fibers also is lower than softwood fibers.
The properties of softwood fiber promotes the use of a softwood pulp in the viscose process for
Ducharme, Jr. Paul Edmund
Nicholson Myron Donald
Portnoy Norman Abbye
Aceto Roger
Bobrowicz Donna
Hon Sow-Fun
Pyon Harold
Viskase Corporation
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