Plastic and nonmetallic article shaping or treating: processes – Direct application of fluid pressure differential to... – Production of continuous or running length
Reexamination Certificate
2000-05-19
2002-09-03
Eashoo, Mark (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Direct application of fluid pressure differential to...
Production of continuous or running length
C264S102000, C264S187000, C264S203000, C264S209500, C264S211110, C425S071000, C425S380000
Reexamination Certificate
active
06444161
ABSTRACT:
TECHNICAL FIELD.
The present invention relates to a method and apparatus of forming a seamless cellulose tube, suitable for use as a food casing, using a solution of nonderivatized cellulose, tertiary amine N-oxide and water.
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 used in the manufacture of small diameter sausages such frankfurters and the like generally are seamless tubes formed of a regenerated cellulose and contain aplasticizer such as water and/or a polyol such as glycerine. Plasticization is necessary because otherwise the cellulose tube is too brittle for handling and commercial use.
Cellulose food casings of pure regenerated and non-reinforced cellulose for the manufacture of frankfurters generally have a wall thickness ranging from about 0.025 mm to about 0.076 mm and are made in tube diameters of about 14.5 mm to 203.2 mm. These casings are hereinafter referred to simply as “cellulose casing”.
Cellulose casing is most commonly produced by the well known and so called “viscose process” wherein viscose, a soluble cellulose derivative, is extruded as a tubular film. The annular extrusion die extends through the bottom of a coagulating and regenerating bath so that the extrusion proceeds in an upward direction through the bath. By extruding upwardly directly into the regenerating bath, the bath liquid supports the extrusion which is fragile and not self supporting during the initial phase of regeneration. After sufficient regeneration to be self supporting, the tube undergoes additional processing steps and is then washed, plasticized with glycerine or other polyol, and dried. Drying usually is accomplished while the tube is inflated with air at a pressure sufficient both to maintain a constant tube diameter and to orient the film.
The present invention involves an alternate cellulose production method in which a cellulose solution is formed by means of a simple dissolution rather than: requiring the formation of a cellulose derivative prior to forming a soluble substance (as in the viscose process). A cellulose dissolution process is described, for example, in U.S. Pat. No. 2,179,181 wherein a natural cellulose is dissolved by a tertiary amine N-oxide to produce solutions of relatively low solids content. The cellulose in the resulting solution is “nonderivatized” in that the natural cellulose was not chemically reacted prior to dissolution to produce a soluble cellulose derivative as would occur for example, in the viscose process. U.S. Pat. No. 3,447,939 discloses use of N-methyl-morpholine-N-oxide (NMMO) as the tertiary amine N-oxide solvent wherein the resulting solutions, while having a low solids content, nevertheless can be used in chemical reactions involving the dissolved compound, or 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. 5,277,857 discloses a method and apparatus for manufacturing cellulose food casing from a solution comprising nonderivatized cellulose, NMMO and water.
In the '857 Patent, nonderivatized cellulose in a molten state, and contrary to the viscose process, is extruded as a tubular film downwardly through an air space and into a non solvent liquid such as a water bath. In the water bath, the NMMO solvent is removed to regenerate or precipitate the nonderivatized cellulose which is then washed of residual solvent plasticized and dried.
In U.S. Pat. No. 5,451,364 the manufacturing method as disclosed in the prior '857 Patent is improved by the discovery that extruding the thermoplastic cellulose solution through a long air gap improves the properties of the resulting tubular cellulose film. In particular, the '364 Patent discloses that the air gap should be over 152.4 mm and preferably from 152.4 mm to 304.88 mm long and perhaps longer.
Both the '364 and '857 Patents further disclose the use of a mandrel which depends from the extrusion die and about which the thermoplastic cellulose solution is extruded. This mandrel extends through the air gap and has its lower end face disposed below the level of the non solvent liquid bath. The mandrel for most of its, length is a slender shaft. The lower portion, however, is larger in diameter and is as large as, or larger than, the extruded tube diameter so it contacts around the entire inner circumference of the extruded tube. The mandrel shaft, being smaller in diameter, is radially spaced from the inner surface of the extruded tube.
The large diameter lower portion of the mandrel serves to size the tube as it enters the bath. Also, since it contacts the extruded tube, the enlarged lower portion of the mandrel together with the extrusion die provide spaced bearing points for stabilizing the extruded tube and preventing it from wandering.
The mandrel also is used to introduce a non solvent liquid into the interior of the extruded tube. One function of this introduced non solvent liquid, among others, is to lubricate around the circumference of the lower portion of the mandrel to prevent the extruded tube from binding as it passes over the surface of the lower portion or blocking when it later is collapsed to a flat width.
In this regard, a non solvent liquid or “inner bath” is introduced inside the extruded tube through ports in the mandrel shaft. This inner bath flows down the mandrel and pools where the extruded tube meets the enlarged lower end of the mandrel. This pooling distributes the non solvent around the mandrel so the entire outer circumference of the mandrel lower portion is wetted. Non solvent liquid then flows off the mandrel and to the bath within the extruded tube.
U.S. Pat. No. 5,766,540 discloses a mandrel structure allowing extrusion through even longer air gaps of up to 500 mm or more.
U.S. Pat. No. 5,759,478 discloses that certain properties of the cellulose film formed by the tubular extrusion as described in the '857 Patent are enhanced by increasing the length of the enlarged lower or “sizing portion” of the mandrel. It is speculated that maintaining the extruded tube in a stretched condition for a longer time by keeping it in contact with the sizing portion of the mandrel allows desirable orientation characteristics of the gel tube to “set” during the solvent extraction process: Whatever the reason, a longer contact time with the sizing portion of the mandrel was desirable and the '478 Patent indicates that a preferred length of the sizing portion is about 50 mm.
However, as disclosed in the '478 Patent, increasing the length of the sizing portion of the mandrel gives rise to another problem. This involves the removal of gas bubbles from the interface between the surface of the sizing portion and the inside surface of the extruded tube that likely are formed by out gassing of air from the extruded tube. In the '478 Patent, these bubbles are removed through a series of interconnected circumferential grooves formed in the surface of the sizing portion.
It now has been found that both the stability of the extrusion process and properties of the casing are further improved when the length of the sizing portion is increased to lengths greater than the 50 mm disclosed in the '478 Patent. Increasing the length of the sizing portion necessitated additional circumferential grooves to provide for the removal of gas bubbles. However, adding more grooves made difficult the drawing of the leading end of the extrusion over the sizing portion on the start-up of extrusion. This is because the increase in the number of grooves increased the likelihood of the leading end of the extrusion snagging on the edge of a groove.
Also, contrary to the disclosure of the '478 Patent, the additional grooves did not act as air bearings to facilitate the passage of the extrusion over the sizing portion. Instead, each additional groove added an amount of friction
Albert James Joseph
Jerantowski Ronald Joseph
Long Larry Clyde
Mc Garel Owen Joseph
Williams Mark Griffith
Aceto Roger
Bohrowicz Donna
Eashoo Mark
Viskase Corporation
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