MXPA96006144A - Tubular film stretched to preserve alimentic products - Google Patents

Abstract

The present invention relates to a tubular film for coating food. The tubular film comprises a material, which has been regenerated from a cellulose solution in a solvent comprising carbon disulfide. The tubular material is longitudinally stretched from 8 to 30% and transversely stretched from -3 to + 10%, while it is humid, and the stretch is maintained during drying, said transverse stretch being less than 75% of the longitudinal stretch, to obtain an orientation longitudinal crystalline. In general, the tubular material has a wall thickness of 75 to 90% of a tubular material, which is identical, except that it is longitudinally unstretched. The invention also includes a method for making the tubular material by stretching the tubular material, while it is moist, and maintaining the stretch during the dry

Description

TUBULAR FILM STRETCHED TO PRESERVE FOODSTUFFS BACKGROUND OF THE INVENTION This invention relates to a tubular film for coating food products such as sausage and cheese. More particularly, this invention relates to said wrapping material made of regenerated cellulose. Food wraps made of regenerated cellulose have been known for a long time and can be made using methods well known to those skilled in the art. In particular, it is made xanthan viscose by treating cellulose of cotton, wood or other plant fiber, with alkali, then dissolving in carbon disulfide. The resulting viscose is then extruded through a die to form a tube. The resulting tube is then regenerated, usually by passing it through a coagulation bath containing coagulant materials such as sodium sulfate, and sulfuric acid. Afterwards, the envelope is dried. The patents of E.U.A. 2,999,756 and 3,835,113 describe said methods in detail. It is also known that casings containing cellulose can be made by extruding the viscose onto a web of cellulose fiber, usually a non-woven paper, configured in the shape of a tube, followed by regeneration. Such casings are known as "fibrous" casings. The term "regenerated cellulose casings for food", as used herein, is intended to include both types of casings. Regenerated cellulose casings for food have been very successful for several reasons, including a relatively low cost, permeability to smoke, resistance and dimensional stability. Despite the advantages of regenerated cellulose casings for food, there are a number of areas where the properties can be improved. In particular, the longitudinal dimensional stability is not as good as desired, especially when the wrapper is wet, i.e., a wrapper for stuffed foods will have an unacceptable longitudinal stretch, when hung vertically, eg, in a smokehouse or for healing purposes. Said stretching may be 10% or more. Since regenerated cellulose wrappers for food have considerable permeability, it is not as good as desired. And, in order to obtain sufficient strength, the wall of the envelope has become thicker than desired. Thicker walls use more viscose material than desired, decrease permeability and reduce the amount (unshinded length) of shirred wrap (longitudinally folded and compressed) to a normal unit of shirred length. Attempts have been made to make said wrappings with thinner walls, by a variation of processing conditions, eg, chemical changes in the regeneration bath, as described in the US patent 4,590,107. Unfortunately, such thin walled casings have had insufficient burst strength and tensile strength for commercial application.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a perspective view of a tubular film of the invention. Figure 2 shows a block diagram of the method of the invention.

BRIEF DESCRIPTION OF THE INVENTION This invention comprises a tubular film for coating food. The tubular film comprises a material, which has been regenerated from a cellulose solution in a solvent comprising carbon disulfide. The tubular material is longitudinally stretched from 8 to 30% and transversely stretched from -3 to + 10%, while wetting, and the stretching is maintained during drying, said transverse stretching being less than 75% of the longitudinal stretch, to obtain a longitudinal crystalline orientation. In general, the tubular material has a wall thickness of 75 to 90% of a tubular material, which is identical except that it is longitudinally unstretched. The invention also includes the method for making the tubular material by stretching the tubular material, while wetting, and maintaining the stretch during drying.

DETAILED DESCRIPTION OF THE INVENTION According to the invention, the tubular material 10 comprises regenerated cellulose 11 and is a food wrapper for food products such as sausage and cheese. The wrap is made by extruding viscose (cellulose dissolved in carbon disulfide) either to the shape of a tube or to impregnate a fiber band configured to the shape of a tube. While still wet, the tubular material is longitudinally stretched from 8 to 30%, and usually from 10 to 20%, and transversely stretched from -3 to + 10%, and the stretch is maintained during drying, said transverse stretch being less than 75% and preferably less than 50% of the longitudinal stretch, to obtain a longitudinal crystalline orientation. In general, the tubular material has a wall thickness of 75 to 90% of a tubular material, which is identical except for being longitudinally unstretched.

In general, for a food wrap of a usual diameter for a hot dog sandwich, the envelope has a wall thickness of between 18 and 25 microns, and usually between 21 and 23 microns. In addition, the food wrapper of the invention has a permeability to smoke and other vapors, which is 20 to 50% greater than the same envelope except that it is not longitudinally stretched, to obtain the thin wall. The other physical properties of the envelope of the invention, despite having a significantly thinner wall, are surprisingly close to the longitudinally unstretched envelope. For example, the bursting pressure is at least 88%, and usually at least 95% of the bursting pressure.of a longitudinally unstretched wrapper * The longitudinal tensile strength is at least 85%, usually at least 90% and commonly over 100% of the longitudinal tensile strength of the same envelope, except that it is longitudinally unstretched. The following example serves to illustrate, and not limit, the present invention.

EXAMPLE In general, the tubular film of the invention was made by the following steps shown in the process blocks of Figure 2 1 to extrude a viscose tube; 2 coagulate the tube in a bath comprising acid and salt to form a tubular film of regenerated cellulose; 3. longitudinally stretching the film from 8 to 30% and transversely stretching the film from -3 to + 10%, while wet, said transverse stretch being less than 75% of the longitudinal stretch; and 4. maintaining said stretch during drying, to form a tubular film having a wall thickness of 75 to 90% of a tubular film, which is identical, except for being longitudinally unstretched. The viscose was made essentially as described in the patent of E.U.A. 3,835,113 and, except as otherwise indicated, it was substantially extruded and regenerated as described in the US patent. 2,999,756. The die was for a code wrap 24 (a width of approximately 25.4 mm in wet planar storage). The extrusion speed was set at 39.01 meters per minute, the final wet machine speed was 37.52 meters per minute, allowing a shrinkage of 3.8% at the wet end to the dryer. The speed at the end of the dryer was varied from 36.57 to 48.76 meters per minute to vary the dryer stretch from -2.5% to + 30%. The coagulation bath (regeneration) contained a sulfuric acid concentration of 132 grams per liter and a sodium sulfate salt concentration of 253 grams per liter. For plasticizing purposes, the envelope is passed through tanks containing glycerin twice. at the wet end, to obtain a glycerin content of approximately 15.4%. The flow of the viscose at the extrusion point is sufficient to produce a thickness of approximately 25.4 microns, if it is not stretched. After the extrusion, the envelope is inflated with air to expand the diameter to approximately 20 mm. The results are shown in the Table. The Table clearly shows the effects of maintaining the longitudinal stretch in the drying. The strength properties are not significantly altered, but the thickness of the sheath is substantially less and the vertical stretch is greatly reduced. Permeability studies show better permeability in reduced thickness. In the Table, the following abbreviations are used: BDG = total caliber in dry, the thickness of the dry film in grams of cellulose per ten meters in length. DFW = dry flat width, 0.24 means code 24, as used in industry, which is a width of approximately 32.7 mm, mpm = meters per minute, Ipm = liters per minute.

Claims (2)

1 - . 1 - A tubular film for coating food products comprising a material, which has been regenerated from a solution of cellulose in a solvent comprising carbon disulfide, characterized in that said tubular film is longitudinally stretched from 8 to 30% and transversely stretched from -3 to + 10%, while wet, said stretch being maintained during drying, said transverse stretch being less than 75% of the longitudinal stretch, said tubular film having a wall thickness of 75 to 90% of a tubular film , which is identical, except that it is longitudinally unstretched.

2 - The tubular film of claim 1, wherein said film is longitudinally stretched from 10 to 20%. 3. The tubular film of claim 1, having a wall thickness of 18 to 25 microns. 4. The tubular film of claim 1, having a wall thickness of 21 to 23 microns. 5 - The tubular film of claim 1, having a permeability, which is 20 to 50% greater than the same film, except that it is longitudinally unstretched. 6. The tubular film of claim 1, wherein the film has a bursting pressure of at least 88% of the burst pressure of the same film, except that it is longitudinally unstretched. 7. - A method for making the tubular film of claim 1, which comprises: extruding a tube from the viscose; and coagulating the tube in a bath comprising acid and salt to form a tubular film of regenerated cellulose; characterized in that the film is longitudinally stretched from 8 to 30% and transversely stretched from -3 to + 10%, while wet, said transverse stretch being less than 75% of the longitudinal stretch; and said stretching is maintained during drying, to form a dry tubular film having a wall thickness of 75 to 90% of a tubular film, which is identical, except that it is longitudinally unstretched.