MXPA98002394A - Manufacturing method of cellulose wrapping for alime - Google Patents

Abstract

The present invention relates to a method for forming a seamless tubular cellulose film from a thermoplastic solution composed of a non-derivatized cellulose, a solvent of tertiary amine cellulose and water by extruding the solution down through of an air space and inside an external bath of a non-solvent liquid, the method comprising the steps of: a) extruding the solution down from an annular die to form a seamless extruded tube of said solution, the extrusion being through an air space of at least 304 mm as measured between the side and surface of the non-solvent liquid in the external bath: b) the extrusion that occurs around a mandrel that depends on said die, the mandrel having a small diameter arrow and a longer lower end, and the mandrel arrow that is extendable from the die to change the lower end clearance of the mandrel from the die c) remove the arrow from the mandrel inside the die to locate the lower end of the mandrel in the air space so that the lowermost end of the mandrel is on the surface of the non-solvent liquid in the external bath, d) start the extrusion of the seamless tube when the lower end of the mandrel is placed on the surface of the non-solvent liquid in said bath: e) extract the front end of the extruded tube along the mandrel, on the lower end of the mandrel, through the space between the end lower the mandrel and the surface of the non-solvent liquid in the external bath and then in the external bath, and f) extend the arrow of the mandrel from the die during the course of extrusion to move the lower end of the mandrel through the inside of the tube extruded until the lower end of the mandrel is placed in the non-solvent liquid of the external bath

Description

MANUFACTURING METHOD OF CELLULOSE FOOD PACKAGING TECHNICAL FIELD The present invention relates to a method and apparatus for forming a seamless cellulose tube, suitable for use as a food wrap, using a non-derivatized cellulose solution, tertiary amine N'-oxide and water.

BACKGROUND OF THE INVENTION Cellulose wrappers for food are well known in the art and are widely used in the production of stuffed products such as sausages and the like. Cellulose food wrappers are generally seamless tubes formed of a regenerated cellulose and contain a plasticizer such as water and / or a polyol such as glycerin. Plasticizing is necessary because otherwise the cellulose tube is too fragile for commercial use and handling. Cellulose food wrappers are generally used in one of two ways. In one form, the wrap consists of a tubular film of pure and unreinforced 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 envelope wherein the tubular wall of the envelope consists of a regenerated cellulose attached to a paper web. Such reinforced casings are commonly called "fibrous" casings to distinguish them from unreinforced cellulose casings. The fibrous casings have a wall thickness in the range of 0.050 mm to 0.102 mm in thickness and are made in diameters of approximately 40.6 mm to 193 mm or greater. The present invention relates to the manufacture of the unreinforced cellulose casing type, hereinafter referred to simply as "cellulose casing". The cellulose to make the wrapper is most commonly produced by the known "viscous process" wherein the viscose, a soluble cellulose derivative, is extruded as a tubular film through an annular die into coagulation and regeneration baths to produce a regenerated cellulose tube. This tube is subsequently washed, plasticized with glycerin and another polyol and dried. Drying is usually achieved while the tube is inflated with air at a pressure sufficient to maintain a constant tube diameter and to orient the film. The present invention involves an alternative cellulose production method in which the cellulose solution is formed by means of a simple solution instead of requiring the formation of a cellulose derivative before forming a soluble substance (as in the process of viscose). A cellulose dissolving process is described, for example, in U.S. Patent 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 not derived" in that the natural cellulose did not react chemically before dissolution to produce a soluble cellulose derivative as would occur for example in the viscose process. U.S. Patent No. 3,447,939 describes the use of N-methyl-morpholine N-oxide (NMMO) as the tertiary amine N-oxide solvent wherein the resulting solutions having low solids content can be used in reactions Chemicals that involve the dissolved compound or, to precipitate the cellulose to form a film or filament. More recent patents such as U.S. Patent No. 4,145,532 and 4,426,288 improve the teachings of the '939 patent. U.S. Patent No. 5,277,857 describes a method and apparatus for manufacturing cellulose casing for food from a solution comprising non-derivatized cellulose, NMMO and water. In the '857 patent, cellulose not derived in a molten state is extruded as a tubular film into a non-solvent liquid such as a water bath. In the water bath, the NMMO solvent is removed to regenerate or precipitate the non-derived cellulose. This forms a gel tube that is treated with water, a polyhydric alcohol such as glycerin, or other water-soluble softening agent such as a polyalkylene oxide or a polyalkylene glycol before drying. More specifically, in the method of manufacturing the '857 patent, the following steps are employed: a) providing a solution comprising cellulose not derived in an amine oxide solvent; b) extrude down the solution from an annular hole to form a seamless tube of at least 14.5 mm in diameter; c) passing the seamless tube extruded from the solution down from the first hole through an air space and then into a bath of non-solvent liquid; d) introducing a non-liquid solvent into the interior of the extruded seamless tube in a location below the annular orifice and on the surface of the non-solvent liquid bath; e) flowing the non-solvent liquid down concurrently with the inner surface of the extruded seamless tube moving down the solution and into the bath as the tube moves through the air gap, and contacting the inner surface of the seamless tube extruded with non-solvent liquid in the course of the countercurrent flow to precipitate the non-derived cellulose on the inner surface from the solution; f) keeping the seamless tube extruded from the solution in the bath with its internal and external surfaces in direct contact with the non-solvent liquid thereby precipitating the non-derivatized cellulose from the solution and forming a non-derived cellulose tube; and g) removing the non-derived cellulose tube from the bath and contacting it with a water-soluble softener. In U.S. Patent No. 5,451,364 the manufacturing method as described in the '857 patent is improved by the discovery that extruding the thermoplastic cellulose solution through a large air gap improves the properties of the film. tubular cellulose resulting. In particular, the '364 patent discloses that the air gap should be more than 152.4 mm and preferably from 152.4 mm to 304.88 mm long and perhaps larger. Both patents '364 and' 857 further describe the use of a mandrel that depends on the extrusion die and around which the thermoplastic cellulose solution is extruded. This mandrel extends through the air space and has its lower end face below the level of the non-solvent liquid bath. The mandrel for most of its length is a thin arrow. However, the lower portion is of a longer diameter and is as large or larger than the diameter of the extruded tube so that it contacts about the entire inner circumference of the extruded tube. The mandrel shaft, which is smaller in diameter, is radially spaced from the inner surface of the extruded tube. The lower diameter portion of the mandrel serves to size the tube as it enters the bath. Also, since it makes contact with the extruded tube, the elongated lower portion of the mandrel together with the extrusion die provide the separate support points to stabilize the extruded tube and prevent it from deflecting. The mandrel is also used to introduce a non-liquid solvent into the interior of the extruded tube. One function of this non-solvent liquid introduced, among others, is to lubricate around the circumference of the lower portion of the mandrel to prevent the extruded tube from flexing as it passes over the surface of the lower portion or locking when the end is compressed to a flat width. In this regard, a non-solvent liquid or "internal bath" is introduced into the extruded tube through ports in the mandrel shaft. The inner bath flows under the mandrel and stagnates where the extruded tube meets the elongate lower end of the mandrel. This stagnation distributes the non-solvent around the mandrel so that the entire outer circumference of the lower portion of the mandrel is moistened. The non-solvent liquid then flows out of the mandrel and into the bath inside the extruded tube. It has been found that an even larger air gap will improve the properties of the resulting tubular cellulose film. However, in the air space length of more than 304.8 mm and up to 500 mm or more, problems have been encountered at the start of the extrusion operation with the mandrel structure as described in the '857 patents and '364.

In particular, with a longer mandrel of about 304.8 mm to 381 mm it is difficult to guide the leading end of the extruded tube down the full length of the mandrel shaft without contacting the surface of the mandrel. If the extruded tube contacts any non-lubricated portion of the mandrel shaft, it will flex immediately toward the mandrel and prevent the start. It has also been found that with a large mandrel that surface tension causes the non-solvent liquid that is introduced through the mandrel to travel in downward currents instead of providing a uniform coating around the entire surface of the mandrel shaft. Therefore, with a large mandrel there are sections of the mandrel surface that are free of the non-solvent lubricating liquid. Accordingly, the leading end of the extruded tube must be kept open and separated from the mandrel surface as it is drawn toward the elongated lower end to avoid accidental contact with any dry portion of the mandrel shaft. The length of the air space of 381 mm to 500 mm or more can also cause the extruded tube to be reduced as it falls by gravity or is extracted from the die. This reduction decreases the diameter of the free space between the mandrel shaft and the internal diameter of the extruded tube and increases the likelihood that any abandonment of the tube during the start of extrusion will cause its inner surface to make contact with a dry or non-lubricated portion. of the mandrel shaft and bend towards the surface of the mandrel. Once the open end of the tube is pulled over the elongated lower portion of the mandrel, the tube is less likely to come into contact with the arrow because the tube, in effect, is held in two separate locations, i.e. extrusion die and the elongated lower end of the mandrel. It is also important that the extruded tube does not contact the non-solvent until there is uniform contact around the entire inner and outer circumference as the tube first passes over the elongate mandrel end and then into the non-solvent bath. It has been found that the point contact of the inner surface of the extruded tube with the non-solvent introduced along the arrow of the mandrel produces a weak point in the resulting cellulose film. Therefore, insofar as the non-solvent will prevent the tube from flexing towards the mandrel arrow, it is preferred that no contact between the extruded tube and a wet or dry surface of the mandrel arrow occurs before entering the liquid reservoir. non-solvent around the elongated lower end of the mandrel. A further problem of using the mandrel from 381 mm to 500 mm or more is that the internal bath tends to flow in a spiral path down and around the mandrel shaft, due to a coriolis effect. With a long arrow, as described above, the spiral flow is fast enough to cause the drops of the internal bath to dissipate from the arrow and against the inner surface of the extruded tube. The point contact, as previously observed, affects the properties of the resulting cellulose film. Therefore, the use of a large air space of 381 mm up to 500 mm or more presents severe problems. One is how to allow easy removal of the forward end of the extruded tube along the arrow of the mandrel and over the elongated lower end of the mandrel without contacting any dry or unlubricated portion of the mandrel surface at the start. Another is how to introduce the internal bath to avoid large drops in height so that the internal bath does not stain the internal surface of the extruded tube. The exit of the possible adhesion to the mandrel or dripping of the internal bath are sharper when extruded tubes of small diameters of approximately 12.7 mm. In those tube diameters. There is little free space between the outer diameter of the mandrel shaft and the internal diameter of the extruded tube and the free space that is reduced by reducing the extruded tube as described above. ThereforeIt is an object of the present invention to provide an improvement in the apparatus for extruding a seamless tube from a non-derived thermoplastic cellulose solution. A further object of the present invention to provide an improved method and apparatus for forming a seamless cellulose tube from a non-derived thermoplastic cellulose solution and particularly to facilitate the initiation of extrusion where extrusion is through a space of big air. Another object is to provide an improved method and apparatus as described above which facilitates the extrusion of the front end of the extruded tube onto a mandrel extending through the air space. Still another object of the present invention is to provide an improved method and apparatus for extruding down a non-thermoplastic cellulose solution down through a large air gap and around a mandrel which prevents staining of the inner surface of the tube by a non-solvent liquid that moves down the surface of the mandrel. A further object of the present invention is to provide a method and apparatus for extruding a seamless tube composed of a non-derived thermoplastic cellulose solution using a mandrel structure that prevents the flow of an internal non-solvent bath through large droplets. Still another object of the present invention is to provide a method and apparatus for extruding a thermoplastic cellulose solution such as a tube whose method and apparatus use an extendable mandrel to facilitate the start of the extrusion operation.

BRIEF DESCRIPTION OF THE INVENTION In the present invention, a thermoplastic non-derived cellulose tube is extruded down through an air space and into a non-solvent liquid bath as generally described in U.S. Patent No. 5,277, 857. and 5,451,364, the descriptions of which are incorporated herein by reference. For purposes of the "non-derivatized" cellulose specification it means a cellulose that has not been subjected to covalent bonding with a solvent or reagent although it has been dissolved by association with a solvent or reagent through the Van der Waals forces such as bonding. hydrogen. "Non-solvent" means a liquid that is not solvent in cellulose. The extrusion is approximately a mandrel that depends on the extrusion die. The mandrel has an arrow portion and a lower end portion that is longer in diameter than the arrow. The mandrel is long enough to extend through the air space and into the bath of a non-solvent liquid. However, the mandrel is extendable from the die so that at the beginning, the mandrel is in an elevated position. This locates the lower end of the mandrel on the level of the non-solvent liquid in the bath and presents a relatively short mandrel for the start operation.

Since the mandrel has a relatively short length at this point, the leading end of the extruded tube of the thermoplastic non-derivatized cellulose solution can be kept open and relatively easily conducted along the mandrel rod and on the elongated lower end of the mandrel. . A non-solvent liquid comprising an internal bath that is introduced through the mandrel rod, moves the rod down and is deposited around the elongated bottom end. This allows the front end of the extruded tube to be easily removed over the elongated end of the mandrel. The extruded tube is then led into the bath and wound around driving rollers to remove the extruded tube through the bath. After the leading end of the extruded tube is removed past the lower end of the mandrel, the mandrel is extended from the die until the mandrel expands the entire air space and the lower end of the mandrel is below the level of the non-solvent liquid in the bathroom . During the course of the mandrel extension, the location where the internal bath is introduced through the mandrel is displaced. In this regard, the flow from the first location is terminated and the flow is initiated from a second point that is lower than the first. This avoids the disadvantage of having the internal bath flowing down substantially the entire length of the mandrel when the mandrel is extended to its full length. Accordingly, the present invention can be characterized in one aspect thereof by a method of forming a seamless tubular cellulose film from a thermoplastic solution composed of non-derived cellulose, a tertiary amine cellulose solvent and water extruded to down through an air space and into an external bath of a non-solvent liquid, the method comprising the steps of: a) extruding the solution down from an annular die to form a seamless extruded tube of said solution, the extrusion being through an air gap of at least 304 mm as measured between the die and the internal surface of the non-solvent liquid in the external bath; b) the extrusion that occurs around a mandrel that depends on said die, the mandrel having a small diameter arrow and a longer lower end, and the mandrel arrow that is extendable from the die to change the lower end spacing of the mandrel from the die; c) removing the arrow from the mandrel inside the die to locate the lower end of the mandrel in the air space so that the lowermost end of the mandrel is on the surface of the non-solvent liquide in the external bath; d) starting the extrusion of the seamless tube when the lower end of the mandrel is located on the surface of the non-solvent liquid in said bath; e) extracting the leading end of the extruded tube along the mandrel, on the lower end of the mandrel, through the space between the lower end of the mandrel and the surface of the non-solvent liquid in the external bath and then into the external bath; and f) extending the arrow of the mandrel from the die during the course of extrusion to move the lower end of the mandrel through the interior of the extruded tube until the lower end of the mandrel is located in the non-solvent liquid of the external bath. In another aspect, the present invention is characterized by an apparatus for forming a seamless tubular cellulose film comprising: a) an annular extrusion die positioned and adapted to extrude down a seamless tube composed of a non-cellulose thermoplastic solution derivative, a tertiary amine oxide solvent and water through an air space and inside an external bath of non-solvent liquid; b) a mandrel that depends on the extrusion die and that is inside the extruded tube; c) the mandrel having a small diameter arrow and a large diameter lower end and the arrow that is extendable through the extrusion die from and between a first position where the lower end of the mandrel is above the level of the non-solvent liquid for the start of the extrusion process of your bo yu in the second position where the lower end of the mandrel is in the external bath for the continuation of the extrusion process of the tube. Other objects and advantages of this invention will be apparent from the following detailed description and the appended claims.

DESCRI PTION OF THE DRAWINGS Figure 1 is a schematic view showing the apparatus of the present invention during the course of stable state extrusion; Figures 2 and 3 are views similar to Figure 1 showing only the apparatus after the start and before the steady state operation; Figure 4 is a view on an enlarged scale, partially broken away and in section showing the mandrel structure at the start of the extrusion operation; and Figure 5 is a view similar to Figure 4 showing only the mandrel structure after the start and during the course of the steady state operation.

DETAILED DESCRIPTION OF THE INVENTION Referring to the drawings, Figure 1 shows the apparatus indicated generally at 10 during the course of the steady-state operation. The apparatus includes a die 12 positioned to extrude down a thermoplastic cellulose solution. The die inlet 14 receives the molten solution under pressure from any suitable source (not shown). The source, for example, may be an extruder as described in the patents '857 and' 364 which melts and pumps the ground pellets of the thermoplastic solution or a pumping system which supplies the thermoplastic solution to the die as it is made. The solution is generally a solution of natural cellulose (such as wood pulp) dissolved in a cellulose solvent comprising N-methyl-morpholine N-oxide (NMMO) and water. Methods for making an appropriate solution (hereinafter referred to as "additive") for extrusion as a tubular film are well known in the art and do not form part of the present invention. It is also within the skill of the skilled person to alter the composition and properties of such a solution to obtain the desired properties of the cellulose article formed from the solution. The process parameters also affect the properties of the resulting article and reference is made to an additional discussion of such parameters as set forth, for example, in the '857 and' 364 patents and in the United States Patent No. descriptions. of which are incorporated herein by reference. The die has an annular extrusion hole 15 so that the molten additive is extruded as a seamless tube indicated at 16. For purposes of extruding a small diameter food wrap, the extrusion orifice is approximately 12-14. mm in diameter. As shown in Fig. 1, the die is placed on the container 18 containing a bath 20 (sometimes referred to as an "external bath") comprising non-solvent liquid. For the purposes of the present invention, "non-solvent" means a liquid that is not solvent in cellulose. Water or an aqueous solution containing a low concentration of NMMO are preferred non-solvents for the purposes of the present invention. The die is separated above the level 22 of the bath so that the tube is extruded down through a large air gap 24. This air gap can be 381 mm to 500 mm or more in length. Depending on the die there is a mandrel, indicated generally at 26, which extends from the die to below the level of the bath 22. The mandrel has an arrow portion 28 and a lower end 30. The lower end is longer in diameter than the arrow and preferably is equal or more preferably is larger in diameter than the diameter of the annular extrusion orifice 15 of the die 12. The lower end of the mandrel, which includes a conical transition section 32 is preferably made of a hydrophobic material such as Teflon and has its lowermost end face 34 placed below the level of the bath 22. As the extruded tube 16 enters the bath, the NMMO solvent is extracted from the tube causing the regeneration of the dissolved cellulose to form the so-called "gel tube" 36 of pure cellulose. This gel tube is compressed to a flat width by a series of limbs or diverters 38. The diverters 38 function as a scale to compress the tube to its flat width. Preferably, the horizontal position of each diverter 38 as seen in Fig. 1 is adjustable. By adjusting the horizontal relationship between the deviators, the correct position can be found to compress the gel tube to its flat width in a wrinkle-free manner. After compression to a flat width, the gel tube is withdrawn through an S-fold formed by the driving rollers 40. S-folding and drive rolls serve to extract the extruded tube 16 in the machine direction which causes a thinning of the wall of the tube and imparts a degree of orientation of the machine direction towards the extruded tube in the air space. The gel tube is then directed up and out of the bath container 18 for further processing. For example, it should be understood that the gel tube can still contain NMMO after leaving the bath container so that a further operation would be washing to remove as much NMMO from cellulose solvent as possible. Subsequent operations would also include contacting the cellulose gel tube with a plasticizer such as glycerin or the like and then drying the tube to a desired water content while holding the tube to a desired inflated diameter. These subsequent operations also do not form part of the present invention. The tubular extrusion process, as described in the '857 and' 364 patents, includes the introduction of air and a non-solvent liquid into the interior of the extruded tube 16. Both the air and the non-solvent liquid, hereinafter called the "internal bath" are introduced through the mandrel. An air line 43 connected to the upper end of the mandrel shaft 28 provides air flow through the mandrel to the openings (not shown) that vent air within the interior of the extruded tube. One function of this air is to hold the extruded tube open at the start of the extrusion process. The non-solvent liquid for the internal bath is contained in a container 42. From the container, it is pumped through the flow line 44 into a conduit (not shown) that travels through the mandrel. One or more ports in the mandrel allow the internal bath to exit the mandrel and flow towards the surface of the mandrel shaft 28. The internal bath is colder than the extruded tube 16 so as to extract heat from the extruded tube 16 and it helps to cool the extruded tube in the air space. It is considered that cooling in the air space improves the properties of the resulting tubular film. The inner bath flows down the mandrel shaft 28 and forms a reservoir 46 around the lower end of the mandrel. This reservoir provides lubrication to allow the passage of the extruded bo onto the elongated lower end of the mandrel 30. This reservoir further initiates the regeneration of the cellulose on the inner surface of the extruded tube. The inner bath passes down between the lower end of the mandrel and the extruded tube and flows into the volume 48 of the liquid bath within the tube. Part of the liquid in this volume 48 remains within the tube gel when compressed to a flat width by diverters 38. This portion of the liquid from the volume 48 prevents blockage of the flattened gel tube and is carried out with the flattened tube between the rollers 40. During the course of the operation, an excessive amount of the inner bath liquid accumulates in the volume 48. Therefore, it may be necessary to remove the liquid from the volume by suction through a conduit (not shown) having an inlet (not shown) on the lower end face 34 of the mandrel. In this way, the liquid from this volume can be drawn through the mandrel as indicated by arrow 49. With an air gap 24 of 381 mm to 500 mm or even greater, the start of extrusion is difficult using a mandrel 26 which expands the entire length of the air space. It was observed before, that at the beginning of the extrusion the front end of the extruded tube 16 should not make contact with the mandrel shaft as the front end is lowered to the mandrel, on the elongated lower end of the mandrel 30 and inside the bath 20. This is difficult to achieve with a large mandrel. While the lubrication of the shaft of the mandrel with an internal bath facilitates the removal of the front end of the extruded tube under the mandrel, the introduction of the internal bath above the mandrel so that it can lubricate the entire length of the arrow also presents a problem discussed above. These problems are solved by the method and apparatus of the present invention. In this aspect, the mandrel shaft 28 is positioned to extend slidably through the die 12, as shown in FIG. 2, the mandrel shaft 28 is raised so that the lower end face 34 of the mandrel is located in the shaft. air space 24 and above the level of the bath 22. When the extrusion of the tube 16 begins, air through line 43 and an internal bath through line 44 are introduced through the mandrel towards the mandrel openings ( not shown) in a location close to the extrusion orifice 15 of the die 12. The air initially helps to keep the extruded tube open and the introduced internal bath lubricates the small mandrel structure depending on the die 12. The small mandrel structure, as shown in FIG. shown in Fig. 2, makes it easier to remove the front end 50 of the extruded tube along the mandrel and on the elongated lower end of the mandrel 30. As the front end passes over end elongate 30, the internal bath starts forming the reservoir 46 about the elongate end of the mandrel. The leading end 50 then extends into the bath 20 and is wrapped around the diverters 38 and through the fold rollers at S 40. After the leading end 50 of the extruded tube is past the lowermost end 34 of the mandrel , the arrow of the mandrel 28 moves downward, as shown in Figure 3, as the effective length of the mandrel increases. The arrow continues to move downward until the elongated lower end of the mandrel 30 is below the level of the bath 22 for steady-state operation, as shown in Figure 1. As the lower end of the mandrel moves downward, the is introduced through line 43 maintains a desired positive pressure inside the extruded tube. In the course of the mandrel movement downwards, the location of the internal bath is interposed from a location near the die 12 to a location much lower than the mandrel. This avoids the previously observed problem of the internal bath flowing in a spiral current around the arrow with such a velocity that it descends and makes contact with the inner surface of the extruded tube. However, as the mandrel arrow is lowered, the air is introduced into a higher location to fill the increasing volume between the inner surface of the extruded tube and the outer surface of the mandrel shaft. This introduction of air replacement provides a positive pressure that prevents the extruded tube from compressing against the mandrel and alters the extrusion operation. The mandrel structure is illustrated in greater detail in Figs. 4 and 5. It will be appreciated that the components are not necessarily drawn to scale in order to facilitate the illustration of the mandrel structure. As seen in Fig. 4, the mandrel 26 has a fixed sleeve 52 that supports the moveable mandrel shaft 28. The sleeve is fixed at its upper end 54 to the die 12. Openings 56 and 58 in the sleeve provide the outputs initials for the air and the internal bath respectively, as stated below.

The moving arrow 28 extends concentrically through the sleeve so that the sleeve and the arrow define an annular space 60 therebetween. At its upper end, this space communicates with the air supply 43 shown in Figures 1-3. At its lower end, this space 60 is closed by an internal shoulder 62 which abuts against the arrow 28. This shoulder not only closes the lower end of the space 60 but also provides the support support for the arrow when the arrow extends. down. The mandrel shaft 28 is formed by concentric tubes that include an outer tube 64 and an inner tube 66. Those tubes 64, 66 define an annular space 68 therebetween. The space 68 is closed at its lower end 70 by a cover 72 on the end of the outer tube. The upper end of the space 68 is in communication with the internal bath flow line 44 of FIGS. 1-3. The inner tube 66 extends through the end cap 72. Attached around the lower end of the inner tube is the elongated bottom end of the mandrel 30 that includes its conical transition section 32. The inner tube 66 has its lowermost end 76 which opens through the lowermost end face 34 of the lower end of the mandrel 30. The upper end of the inner tube 66 is connected to a vacuum source (not shown) for the purposes of sucking the liquid bath through the inner tube as shown in FIG. shows by arrow 49.

The conical transition section 32 at the end 74 has a diameter approximately equal to the diameter of the sleeve 52. The conical section protrudes outwardly at its other end to the total diameter of the elongated lower end of the mandrel 30. Preferably, the elongated lower end of the mandrel and its conical transition section are made of a low friction material such as Teflon. The diameter of the elongated lower end of the mandrel 30 is preferably between about 1.5 and 2.5 times the diameter of the extrusion orifice 15. This imparts a transverse extension to the extruded tube and helps fix the desired diameter of the gel tube. The length of the lower end 30 also contributes to the dimensional stability of the gel tube that was formed. A length to full diameter of approximately 50 mm is preferred. The outer surface of the longer lower end 30 is provided with a series of vertically spaced circumferential grooves 33 which are connected by vertical channels 35. These grooves and channels allow air to escape from around the sizing portion as described below. uation.

Placed at the smaller end 74 of the conical section 32 is an O-ring or other suitable seal member 78. With the arrow in position, as shown in Fig. 4, the seal member 78 bears against the bottom end 79 of sleeve 52 to seal the lower end of the sleeve.

To complete the structure, the outer tube 64 of the mandrel shaft 28 has a plurality of vertically spaced ports 80, 82 along its length. When the arrow 28 is in the position as shown in Fig. 2 and 4 so that the mandrel 26 is at its shortest dependent length from the die 12, the lower ports 82 are closed by the sleeve tubular internal shoulder 62 (Fig. 4) considering that the upper ports 80 located on the inner shoulder open within the space 60. The operation will be described starting with the reference to Figures 2 and 4. At the beginning of the extrusion, the mandrel arrow 28 is in an elevated position so as to extend through the die 12 as shown in Fig. 2. This places the mandrel 26 in its shortest dependent position locating the lower end face 34 of the mandrel above the bath level 22 (Fig. 2). The mandrel components are positioned as seen in Figure 4. A non-solvent comprising the internal bath is pumped through line 44 and into space 68 between the internal and external conduits., 64 respectively comprising the arrow 28. The internal bath fills this space and passes through the ports 80 within the space 60 between the arrow 28 and the surrounding sleeve 52. The internal bath fills the space 60 up to the level of the openings 58. The inner bath then drains from the openings 58, travels down the outer surface of the sleeve 52 and over the longer lower end of the mandrel 30. The liquid dripping from the lower end of the mandrel falls into the bath 20.

At the same time, the air is introduced through the line 43 and into the space 60. The air introduced in this way is vented from the sleeve through at least the openings 56 that are slightly higher on the sleeve than the opening 58. Extrusion is started and the leading end of the extruded tube 16 is withdrawn downwardly and over the sleeve 52. The liquid in the internal bath that drains from the openings 58 flows down along the external surface of the sleeve. This provides lubrication to prevent contact of the extruded tube that is attached to the sleeve from occurring. The air from the openings 56 helps to hold the extruded tube open and away from the surface of the sleeve as the tube is pulled out along the sleeve. When the leading end 50 of the extruded tube is extended and pulled on the lower end of the mandrel 32 (Fig. 2), the inner bath is collected in the reservoir 46 which forms around the lower end of the mandrel. The non-solvent liquid from this reservoir is brought from between the inner surface of the extruded tube and the external surface of the elongate end to lubricate this area and allows the extraction of the extruded tube 16 passing the lower end of the mandrel. The anterior end 50 of the extruded tube then passes into the external bath 20 to form the gel tube 36 (Figure 3). The gel tube is wound around the deviators to flatten the tube. The flattened gel tube 36 is then placed through the folding rollers at S 40 and possibly led out of the container 18 (Fig. 1). After the front end of the extruded tube is beyond the lower end 34 of the mandrel, the arrow of the mandrel 28 is lowered by sliding through the die 12. As the arrow 28 extends, the O-ring seal 78 is disengages the lower end 79 of the sleeve. When the ports 82 move past the inner sleeve shoulder 62, the internal bath liquid floods the sleeve volume 84 below the shoulder which is dislodged by the lid 72. Some infiltration of the internal bath bath can occur from around the top. However, the main flow continues through those ports 80 located on the inner shoulder and within the space 60 so that the internal bath exits from the sleeve openings 58.

When the lid 72 is free of the lower end of the sleeve 79 (Fig. 5), the internal bath liquid contained in the volume 84 spills and flows on the lid. The internal bath liquid from the space 68 can now flow directly from the ports 82 below the sleeve shoulder and downwardly along the arrow 28 and the cap towards the lower end of the mandrel 30. Clearing the lid 72 through of the lower sleeve end 79 terminates the internal bath flow through the opening 58 on the sleeve because the internal bath liquid can now exit directly into the air space 24 from the openings 82 in the mandrel shaft 28. The air it continues to exit from the sleeve openings 56. Continuous introduction of air into the extruded tube is important as the arrow 28 is extended downward. In this regard, the introduction of air into the rising volume between the mandrel shaft and the extruded tube 16 maintains a differential pressure through the extruded tube to prevent the extruded tube from being compressed against the mandrel shaft 28. When the shaft is fully extended, the lower end of the mandrel 30 is below the bath level 22 of the external bath 20, as shown in Figs. 1 and 5, for the operation of stable state extrusion. During steady-state extrusion, the level of the reservoir 46 around the lower end of the mandrel is maintained slightly higher than the level 22 of the external bath 20 by approximately 50-60 mm. At this level, the deposit 46 exerts sufficient internal pressure on the extruded tube 16 to keep the tube radially separated from the sleeve end 79 as the extruded tube is reduced. This reservoir level also maintains the lower end of the extruded extruded tube to facilitate the transition of the extruded tube over the larger diameter of the lower end of the mandrel 30. This larger reservoir or internal bath level is maintained primarily by controlling the air pressure within the Extruded tube as provided by the introduction of air from line 43. In this regard, the reservoir level 46 is monitored visually and the volume of the air introduced through the line 43 (Fig. 1) is manually adjusted to maintain the reservoir at the desired level.

During the course of the extrusion, gas bubbles may appear at the interface of the extruded tube and the lower end of the mandrel. The circumferential grooves 33 and the vertical channels 35 connecting these grooves provide means for the passage of gas bubbles into the volume 48 below the lowermost end face of the mandrel 34. When the gas or the internal bath liquid becomes excessive. , can be removed by suction through the inner tube 66 as described herein. Thus, as shown in Figure 5, in the steady-state operation through the large air gap, the internal bath exits from the ports 82 in the mandrel shaft 28. Those ports 82 are considerably smaller on the mandrel structure. that the openings 58 from which the internal bath flowed at the beginning. This avoids the problem presented by the spiral flow of the internal bath substantially the full length of the mandrel as noted above. The sleeve 52, with its upper end 54 rigidly connected to the die, remains stationary. This allows the inner shoulder 62 to provide support support for the extended mandrel shaft at a location separate from the die. The stability provided by this support support is especially preferred in cases where the arrow is small enough in diameter to provide clearance from the inner surface of a small diameter extruded tube. For example, on exiting the die 12, the extruded tube 16 can be as small as 12 mm in diameter. The extruded tube cools in the air space so that the tube becomes smaller in diameter. Extracting through the air gap in the machine direction causes the tube to be reduced which further reduces the diameter. Consequently, the extruded tube 16 having an initial diameter of 12.7 mm, at some point along the arrow 28 can have a diameter of about 6.55 mm. This means that the arrow must be even smaller in diameter to provide radial clearance between it and the extruded tube 16. At the lower end of the mandrel, the diameter of the extruded tube is extended as it passes over the elongated end 30. The depth of the reservoir and the pressure of the resulting head assists with the opening and stretching of the extruded tube to facilitate passage over the lower end of the mandrel. Therefore, it will be appreciated that the method and apparatus of the present invention achieve its intended objects. The extendable mandrel facilitates initial operation in that it provides stability and support for the extruded tube during stable state extrusion through an air gap of up to 500 mm or more. At the beginning, the internal bath is introduced at a higher elevation to ensure that the starting length of the mandrel is lubricated to avoid bending the front end of the extruded tube must make contact with the mandrel. Subsequently, the introduction is switched to a lower elevation to prevent the internal bath having to assume a spiral flow down and around the long mandrel shaft. As noted above, such a spiral flow can allow drops of the internal bath that rotate from the mandrel and strike the inner surface of the extruded tube. This results in subsequent weaknesses in the resulting tubular cellulose film product. Although a preferred embodiment of the present invention has been described in detail, it is understood that modifications thereto can be made without changing the spirit and scope of the invention as claimed. For example, the sleeve 52 can also be slidable through the die instead of having a fixed end 54 as shown. Also, the exact composition of the extruded additive, extrusion rates, extrusion ratios and other process parameters can be altered as desired to achieve the desired properties of the resulting tubular film. Similarly, altering the dimensions of the mandrel structure can result in the alteration of the properties of the film and are within the experience of the technique. For example, increasing the length of the lower end of the elongated mandrel extending within the external bath can provide the resulting film with improved diametral uniformity. Such changes are not part of the present invention.

Claims (25)

1. A method for forming a seamless tubular cellulose film from a thermoplastic solution composed of a non-derivatized cellulose, a tertiary amine oxide cellulose solvent and water by extruding the solution down through an air space and inside an external bath of a non-solvent liquid, the method comprising the steps of: a) extruding the solution down from an annular die to form a seamless extruded tube of said solution, the extrusion being through a space of air of at least 304 mm as measured between the die and the internal surface of the non-solvent liquid in the external bath; b) the extrusion that occurs around a mandrel that depends on said die, the mandrel having a small diameter arrow and a longer lower end, and the mandrel arrow that is extendable from the die to change the lower end spacing of the mandrel from the die; c) removing the arrow from the mandrel inside the die to locate the lower end of the mandrel in the air space so that the lowermost end of the mandrel is on the surface of the non-solvent liquid in the external bath; d) starting the extrusion of the seamless tube when the lower end of the mandrel is located on the surface of the non-solvent liquid in said bath; e) extracting the leading end of the extruded tube along the mandrel, on the lower end of the mandrel, through the space between the lower end of the mandrel and the surface of the non-solvent liquid in the external bath and then into the external bath; and f) extending the arrow of the mandrel from the die during the course of extrusion to move the lower end of the mandrel through the interior of the extruded tube until the lower end of the mandrel is located in the non-solvent liquid of the external bath.

A method as in claim 1, comprising initiating extrusion after the mandrel has its lowest end face located at its shortest distance from the die.

3. A method as in claim 1 comprising: a) introducing an internal bath of non-solvent liquid into the interior of the extruded tube at a first location adjacent to the die before the time when a leading end of the extruded tube is pulled over the end lower the mandrel and flow the non-solvent liquid introduced downwards and over the lower end of the mandrel into the external bath; b) continuing the introduction of the internal bath in the first location after the leading end of the extruded tube is removed over the lower end of the mandrel; c) extending the mandrel shaft from the die and moving the lower end of the mandrel through the interior of the extruded tube until the lower end of the mandrel is below the level of the non-solvent liquid in the external bath; d) finish the introduction of the external bath of the non-solvent liquid from the first location; and e) introducing the internal bath of the non-solvent liquid into the interior of the extruded tube at a second, separate location below the first location and on the lower end of the mandrel.

4. A method as in claim 3, comprising introducing air into the interior of the extruded tube at a location adjacent to the die and above the first location for introducing the internal bath into the interior of the extruded tube.

A method as in claim 3, which includes introducing air into the interior of the extruded tube while extending the mandrel shaft from the die.

6. A method as in claim 3, comprising forming a reservoir of the internal bath around the lower end of the mandrel and maintaining the level of the reservoir above the level of the non-solvent liquid in the external bath.

A method as in claim 3, wherein introducing the internal bath of the non-solvent liquid into the interior of the extruded tube in the first location comprises the steps of: a) locating the mandrel shaft in a sleeve having one end upper fixed to the die, the sleeve and the mandrel arrow defining an annular channel between them and the sleeve having openings defining the first location for the introduction of the internal bath of the non-solvent liquid; b) transport the internal bath of the non-solvent liquid through a conduit in the arrow of the mandrel towards the ports that communicate with the annular channel; c) making a seal between the sleeve and a portion of the arrow of the mandrel below the ports to seal the lower end of the annular channel; d) flowing the internal bath of the non-solvent liquid through the ports and into the annular channel and filling the annular channel with the non-solvent internal bath liquid up to the level of the openings in the sleeve; and e) pouring the internal bath of non-solvent liquid from the openings and into the interior of the extruded tube.

A method as in claim 7, wherein introducing the internal bath of non-solvent liquid into the interior of the extruded tube at the second location comprises the steps of: a) extending the arrow through the sleeve until the mandrel ports are below the seal; and b) discharging the internal bath of non-solvent liquid through the ports and directly into the interior of the extruded tube and the internal bath flowing down the mandrel shaft to form a deposit of non-solvent liquid around the lower end of the mandrel .

A method as in claim 8, comprising a step of terminating the flow of the internal bath of non-solvent liquid from the first location by moving the ports under the seal.

10. A method as in claim 8, comprising maintaining the level of the non-solvent liquid in the reservoir above the level of the non-solvent liquid in the external bath.

A method as in claim 10, comprising controlling the level of the non-solvent liquid in the reservoir by controlling the air pressure inside the extruded tube.

A method as in claim 1, comprising removing the non-solvent liquid from a volume below the lower end of the mandrel and into the extruded tube by pulling upward through an axial conduit in the mandrel shaft.

A method as in claim 1, which comprises extruding the thermoplastic solution through an air gap of about 381 mm to about 500 mm.

A method as in claim 1, wherein the diameter of the lower end of the mandrel is larger than the extruded diameter of the extruded tube to extend the diameter of the extruded tube as it passes over the lower end of the mandrel.

15. An apparatus for forming a seamless tubular cellulose film comprising a) an annular extrusion die positioned and adapted to extrude downwardly a seamless tube composed of a non-derivatized cellulose thermoplastic solution, a tertiary amine oxide solvent and water through an air space and inside an external bath of non-solvent liquid; b) a mandrel that depends on the extrusion die and that is inside the extruded tube; c) the mandrel having a small diameter arrow and a large diameter lower end and the arrow that is extendable through the extrusion die from and between a first position where the lower end of the mandrel is above the liquid level is not solvent for the start of the pipe extrusion process and a second position where the lower end of the mandrel is in the external bath for the continuation of the pipe extrusion process.

16. The apparatus as in claim 15, wherein the mandrel comprises means for introducing an internal bath of a non-solvent liquid into the interior of the extruded tube in a first location adjacent to that given at the beginning of the tube extrusion process and subsequently the introduction of the internal bath in a second separate location below the first location to the extension of the arrow through the extrusion die.

The apparatus as in claim 15, wherein the mandrel comprises: a) a sleeve that depends on the extrusion die and positioned around the arrow so that the sleeve and the arrow define an annular space therebetween; b) the sleeve having an upper end fixed to the extrusion die and the arrow that is extendable through the sleeve; c) the sleeve having a separate internal shoulder from the upper end providing supporting support for the arrow as the arrow extends from and between the first and second positions.

18. The apparatus as in claim 17, wherein: a) the annular space forms a channel for the non-solvent liquid of the internal bath; b) seal means between the arrow and the sleeve to close a lower end of the channel; and c) the sleeve having a first set of openings adjacent to the die for the passage of the inner bath liquid out of the channel and the openings defining the first location for introducing the internal bath into the interior of the extruded tube.

The apparatus as in claim 18, wherein: a) the arrow has an internal conduit for the non-solvent liquid of the internal bath and the conduit has an upper end connected to a source of the non-solvent liquid; and b) the arrow having a plurality of ports that provide communication between the inner conduit and the channel, the ports that are located on the arrow above the seal means when the arrow is not extended from such a die so that the liquid does not solvent flowing from the source and through the inner conduit passes through said ports, fills the channel to the level of the openings in the first location and then drains from the openings within the interior of the extruded tube.

20. The apparatus as in claim 19, wherein the internal shoulder comprises the seal means.

The apparatus as in claim 19, wherein the ports, when the arrow extends from the die, are located below the seal means and provide direct communication from the conduit to the interior of the extruded tube thereby comprising the second location for the introduction of the non-solvent liquid of the internal bath inside the extruded tube.

22. The apparatus as in claim 19, wherein the arrow comprises an inner tube and a concentric outer tube, the space between the inner and outer tubes comprising the inner conduit for the non-solvent liquid of the inner bath.

The apparatus as in claim 22, wherein the inner tube has an inlet opening in a lower end face of the lower end of the mandrel, the outer tube extending through the die and having its upper end connected to a vacuum source.

24. The apparatus as in claim 18, wherein the lower end of the mandrel is larger in diameter than the sleeve and the seal means includes an O-ring that is conveyed over the lower end of the mandrel and sits against the lower end of the sleeve when the arrow is in the first position.

25. The apparatus as in claim 17, wherein the space between the arrow and the sleeve is connected to a source of pressurized air and the sleeve having a second set of openings on the first assembly for introducing air into the interior of the extruded tube.