Stock material or miscellaneous articles – Hollow or container type article – Flexible food casing
Reexamination Certificate
1998-09-01
2003-12-02
Nolan, Sandra M. (Department: 1772)
Stock material or miscellaneous articles
Hollow or container type article
Flexible food casing
C428S034900, C428S035700, C428S036300, C428S036900
Reexamination Certificate
active
06656547
ABSTRACT:
The invention relates to flat or tubular cellulose-based food casings which are produced by extruding (“spinning”) cellulose dissolved in N-methylmorpholine N-oxide. The casings are particularly suitable as sausage casings.
Cellulose is insoluble in the usual solvents. It does not have a melting point or melting range and cannot therefore be melt-processed either. Therefore, it is usually chemically modified for producing food casings. However, these processes are associated with a breakdown of the cellulose, i.e. the mean degree of polymerization of the cellulose becomes lower. In addition, the processes are highly technically complex and correspondingly expensive.
Currently, the viscous process is preferred. In this process, the cellulose is reacted with sodium hydroxide solution and then with carbon disulfide. This produces a yellow-orange-colored cellulose xanthogenate solution which is extruded through a spinneret. The cellulose is then regenerated using precipitation and washing baths. A variety of apparatuses have had to be developed for this for cleaning up exhaust air and wastewater.
As early as 1936 it was discovered that cellulose is soluble in oxides of tertiary amines (DE 713 486); however, this discovery was not pursued further until 30 years later. In the course of this, N-methylmorpholine N-oxide (NMMO) was identified as the most suitable solvent. The cellulose dissolves therein without being chemically modified. No breakdown of the cellulose chains takes place. Preparation of the corresponding spinning solutions has also been disclosed (DD 218 104; DD 298 789; U.S. Pat. Nos. 4,145,532; 4,196,282; 4,255,300). Yarns may be produced from the solutions by extrusion into a spinning bath (DE-A 44 09 609; U.S. Pat. No. 5 417 909). WO 95/07811 (=CA 2 149 218) also discloses a process for producing tubular cellulose films by the amine oxide process. A characteristic of this process is cooling the extruded film by cooling gas immediately below the annular gap of the extrusion die. According to EP-A 662 283, the extruded tubular film is cooled internally using liquid.
Recovery and purification of the NMMOs are described in DD 274 435. Since the cellulose is not chemically modified in the process, less equipment is required. In the amine oxide process, no gaseous or aqueous waste products are produced, so that there are no problems with respect to the exhaust air or the wastewater. It is therefore achieving increasing importance.
EP-A 0 686 712 describes the production of flexible cellulose fibers by the N-methylmorpholine N-oxide (NMMO) spinning process. In this process, a cellulose solution in aqueous NMMO is forced through a spinneret, conducted via an air section into an NMMO-containing aqueous precipitation bath and then washed, post-treated and dried.
According to WO 93/13670, a seamless tubular food casing is produced by extruding a solution of cellulose in NMMO/water using a special extrusion die. An air section is situated between extrusion die and precipitation bath. A characteristic of this process is a specially shaped hollow mandrel through which the precipitation liquid can also circulate in the interior of the tube. In the air section, the interior of the extruded tube is virtually completely filled by a hollow mandrel and precipitation liquid. The film is not stretched transversely in the course of this.
WO 95/35340 describes a process for producing blown cellulose films in which an underivatized cellulose dissolved in NMMO is used.
However, the amine oxide process also has disadvantages. The underivatized cellulose molecules are already preorientated in the NMMO solution and are substantially more tightly packed than is the case with chemically modified (“derivatized”) molecules. On extrusion, the orientation in the longitudinal direction is still more pronounced. The yarns thus produced therefore exhibit a high strength in the longitudinal direction, but only low strength in the transverse direction. They have a strong tendency to split on being mechanically stressed in the wet state. Films or other shaped bodies, which must be able to be loaded in the longitudinal and transverse direction, may thus scarcely be produced by this method.
The object was therefore to modify the amine oxide process in such a manner that sufficiently load-bearing films or shaped bodies, in particular tubular food casings, can be produced. The process should succeed in this case with as few steps as possible, and should remain inexpensive and environmentally compatible.
The object can be achieved if the wet treatment is combined with a blow molding. The present invention thus relates to a seamless tubular cellulose-based film, which is obtainable by extruding a cellulose-, N-methyl-morpholine N-oxide- and water-containing spinning solution through an annular die and treating the tubular film in an N-methylmorpholine N-oxide-containing aqueous spinning bath, wherein the spinning solution comprises 0.2 to 50% by weight, based on the weight of the cellulose, of modifying compounds which increase the suppleness, strength, clipping stability and shear stability of the tubular casing.
The spinning solution preferably comprises 7 to 15% by weight, particularly preferably 9 to 12% by weight, cellulose, in each case based on the total weight of the spinning solution. The mean degree of polymerization of the cellulose in this case is preferably 300 to 700, particularly preferably 400 to 650. As solvent, the spinning solution preferably comprises 90.5 to 92.5% by weight NMMO and 9.5 to 7.5% by weight water. The parameters mentioned in this paragraph, together with the temperature, essentially determine the viscosity and fluid behavior of the spinning solution.
Processes for preparing the spinning solution are generally familiar to those skilled in the art. Customarily, cellulose is mashed in a 60% strength by weight aqueous NMMO solution at room temperature. The cellulose usually originates from wood or cotton. As the temperature increases, water is then distilled off in a heated stirred tank under reduced pressure until the residue consists of cellulose and NMMO monohydrate. This is the case at an NMMO content of 87.7% by weight, based on the total weight of NMMO and water. The ratio of NMMO to water may be readily determined by the refractive index. In the NMMO monohydrate, the cellulose dissolved completely at a temperature of 85 to 95° C. with intensive stirring. The refractive index of the solution is 1.4910 to 1.4930. The water content has decreased to 7.5 to 9.5% by weight. The spinning solution is degassed, filtered and transferred to the spinning vessel.
The modifying compounds for improving the suppleness must be miscible with the cellulose/NMMO/water solution. The content of these compounds is preferably 0.5 to 20% by weight, particularly preferably 1 to 15% by weight, in each case based on the weight of the cellulose. The compounds may be mixed homogeneously with the spinning solution at a temperature of 85 to 105° C., preferably 90 to 100° C. Particularly suitable modifying compounds are starch, starch derivatives and cellulose derivatives (in particular esters or ethers of the starch or cellulose), as well as sugar esters, and in addition hydrophilic naturally occurring polymers (preferably alginic acid and alginates, chitosan and carrageenan). Suitable compounds are also hydrophilic synthetic polymers (preferably vinyl alcohol, vinyl acetates and acrylates) and polymers which simultaneously possess hydrophilic and hydrophobic properties (preferably esters from a sugar-such as sucrose-and fatty acids, the esters having an HLB of 1 to 15; HLB=hydrophilic-lipophilic balance). If appropriate, fatty acids and salts thereof, for example stearic acid or calcium stearate, waxes and paraffins are also suitable. Finally, polyvinylpyrrolidone, copolymers of vinylpyrrolidone and 2-(dimethylamino)ethylmethacrylate, copolymers of methyl vinyl ether and maleic anhydride or of methyl vinyl ether and maleic acid monoalkyl ester may also be used. The modifying compounds may al
Berghof Klaus
Gord Herbert
Grolig Gerhard
Hammer Klaus-Dieter
Maron Reinhard
Foley & Lardner
Kalle Nalo GmbH & Co. KG
Nolan Sandra M.
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