Patent Application
20220049375
The invention relates to a molding tool for the extrusion of cellulosic molded bodies from a spinning dope, having an entry side and an exit side for the spinning dope, with at least one nozzle body including a planar carrier with extrusion openings that penetrate the carrier from the entry side to the exit side and have a mouth diameter at the exit side and through which the spinning dope is extruded into the cellulosic molded bodies.
The invention also relates to a method for producing the molding tool and to a method for producing cellulosic molded bodies by using the molding tool.
Typically, molding tools used for the extrusion of cellulosic molded bodies of the afore-mentioned type (also known as “spinning nozzles” or “spinnerets”) must meet numerous high quality criteria in order to be suited for spinning of highly viscous cellulose solutions. For instance, high standards with respect to the quality and dimensional accuracy (profile shape, mouth diameter, and positioning) of the extrusion openings must be satisfied in order to obtain a homogeneous bundle of molded bodies and avoid any sticking together of the individual molded bodies in the bundle of molded bodies. Furthermore, the roughness of the inner walls of the extrusion openings as well as the edge sharpness and freedom from burrs of the extrusion openings play a crucial role in shaping the molded bodies (that are formed from the extruded spinning dope at the exit side of the extrusion opening) and in avoiding spinning defects (such as breaking, tearing, or sticking together of molded bodies) caused, for example, by irregularities or burrs of the extrusion openings at their exit side. High standards must also be satisfied in terms of the strength of the molding tools, as they are exposed to very high pressures of up to 150 bar during the extrusion of the spinning dope.
From EP 0 430 926 B1 and WO 94/28211 A1, molding tools for the extrusion of cellulosic molded bodies from a spinning dope are known, which can be used in methods for producing cellulosic molded bodies—such as the viscose or lyocell processes. In these cases, the extrusion openings are typically formed in a carrier by means of mechanical drilling or punching. However, this presupposes that the material of the carrier meets special requirements, as it must have sufficient ductility, on the one hand, so that it can be machined with the drilling or punching tool, and must permanently withstand the very high pressures of up to 150 bar in the viscose or lyocell process, on the other. In EP 0 430 926 B1, these requirements are met, for example, by inserting a small plate made of a softer, easy-to-machine material (such as gold, silver, or tantalum), in which the extrusion openings have been formed, into a stainless steel carrier. The special combination of materials makes it easy to form the extrusion openings in the molding tool and yet obtain a high level of strength. However, such molding tools have the disadvantage that the materials used for them are very expensive and that the composite molding tools require a high-effort manufacturing process, as the small plates need to be inserted into and connected to the carrier at a subsequent stage. Furthermore, mechanical machining processes such as drilling or punching create burrs at the extrusion openings, which need to be removed in additional effortful finishing steps (e.g., by polishing). Also, such mechanical machining processes are able to achieve only limited positioning accuracy and reproducibility, which will generally result in large tolerances at the extrusion openings.
WO 2005/005695 A1 shows a method for producing molding tools of the afore-mentioned type, the extrusion openings being formed in a carrier of the molding tool by means of electron beams. Molding tools produced in such a manner solve the problem of the choice of materials, as the extrusion openings can be formed directly in the carriers, whereby the separate formation of extrusion openings in a small plate and the effortful subsequent assembly of the components become unnecessary. In addition, such extrusion openings formed in the molding tools by using electron beams exhibit advantageously reduced roughness and high edge sharpness with minimal burr. Yet, the extrusion openings formed in the carrier by using electron beams are highly limited in their profile shapes and have a high variation or tolerance regarding their mouth diameters, as the effect of the electron beams can be controlled and reproduced only to a limited extent. In addition, the formation of the extrusion openings by using electron beams must take place in a high vacuum, which in turn implies an effortful manufacturing method.
Therefore, it is an object of the invention to provide a molding tool of the afore-mentioned type, which can be produced more easily and inexpensively while also offering excellent strength and pressure stability, and whose extrusion openings have smaller tolerances in regard to mouth diameter, position, and profile shape.
The invention solves the defined object in that the ratio of the thickness of the carrier to the mouth diameter of the extrusion openings at the exit side is at least 6:1 and that the extrusion openings are formed in the carrier by applying laser energy.
If the ratio of the thickness of the carrier to the mouth diameter of the extrusion openings at the exit side is at least 6:1, then a particularly pressure-stable nozzle body of high strength can be created which guarantees a long service life at high pressure. This pressure stability means that plastic deformations of the nozzle body during its service life can be avoided under normal operating conditions, whereas a small amount of load-dependent elastic deformations is unavoidable. This strength can be improved further if the above-mentioned ratio is at least 10:1, or more preferably at least 12:1 or at least 15:1. Furthermore, if the extrusion openings are formed in the carrier by applying laser energy, then the molding tool can prove advantageous by being very easy to manufacture. In this case, the extrusion openings can be formed in the carrier of the molding tool with very high dimensional accuracy, whereby a molding tool can be created that meets the high quality requirements and narrow dimensional tolerances in regard to mouth diameter and positioning. In particular, the use of laser radiation makes it possible to obtain dimensional tolerances of less than 2% for the critical parameters such as mouth diameter, hole geometry and cross-section of the extrusion openings, as well as distance between the extrusion openings. The laser radiation also makes it possible to directly create smooth and burr-free extrusion openings, as a consequence of which further finishing steps on the molding tool can be omitted. Such finishing steps such as grinding or polishing involve high mechanical loads and can generate adverse stress effects in the carrier. It is therefore possible to create a molding tool with small dimensioning tolerances that is particularly easy to manufacture and reliable.
Within the scope of the invention, the term ‘molded bodies’ particularly denotes the filaments exiting the extrusion openings, which can subsequently be used for the production of continuous or staple fibers. Within the scope of the invention, such filaments or fibers preferably have titers greater than or equal to 0.7 dtex.
Generally, it is noted that the invention relates to molding tools for the production of regenerated cellulose molded bodies, having a mouth diameter of the extrusion opening at the exit side of greater than or equal to 40 μm, particularly of greater than or equal to 45 μm, preferably of greater than or equal to 50 μm, more preferably of between 70 μm and 150 μm. If the mouth diameters are less than 40 μm, then the molding tools are particularly suited for the production of microfibers having a fiber titer of less than 0.7 dtex. However, the molding tools of the present invention are used in the production of cellulosic fibers typically having a titer of greater than or equal to 0.7 dtex for which extrusion openings having a mouth diameter greater than 40 μm are suitable.
If the thickness of the carrier is at least 600 μm, then a molding tool featuring sufficient strength and service life of the nozzle body can be created, which can also be designed large enough in order to provide for an advantageous production throughput. In particular, the preferred thickness of the carrier is at least 800 μm, and more preferably 1000 μm. If the carrier has a thickness in this range, then it can be ensured that there will be no plastic deformation of the carrier in regular operation, at operating pressures up to 100 bar that are usually encountered, for example, in a method for producing regenerated cellulose molded bodies of the lyocell type (lyocell process). After all, plastic deformation of the carrier can adversely alter the geometry of the extrusion openings and also negatively influence the discharge behavior of the molded bodies from the molding tool. In addition, it can be ensured that the carrier can even be loaded with a pressure of up to 150 bar in overpressure events without causing the carrier to break or suffer irreversible structural damage. Molding tools including a carrier with a thickness of less than 600 μm are only of limited suitability for use in such methods, as they do not have the necessary strength in order to permanently withstand the high pressures and allow only a very limited throughput, respectively.
If the extrusion openings at the exit side are free from burrs, then a molding tool can be created in which detrimental sticking together of the molded bodies after exiting the extrusion openings can be avoided. After all, burrs at the extrusion openings can entail the disadvantage that the extruded molded bodies will not exit the extrusion openings in a straight orientation, but be diverted by the burr and come into contact and stick together with a neighboring molded body, thereby causing spinning defects that require an interruption and restart of the process (renewed spin-up) or lead to rejects being produced.
Particularly versatile molding tools for use in different methods for the extrusion of cellulosic molded bodies can be created when configuring the nozzle body as being of annular or rectangular shape. In addition, the molding tool can include several of such nozzle bodies. Thus, it is possible, for example, that the molding tool includes several rectangular nozzle bodies adjoining one another. Such a molding tool, for example, is particularly easy to manufacture and can be more cost-effective.
If the molding tool has at least a first web firmly connected to the nozzle body by material bonding and protruding from the nozzle body toward the entry side, then the stability and strength of the carrier can be improved further, on the one hand, as the web counteracts a pressure load of the nozzle body and especially of the carrier, and the web provides a guide surface for the spinning dope, on the other hand, as it can ensure the efficient transport of the spinning dope to the extrusion openings. In addition, suitably configuring the web helps avoid the formation of dead spaces and thus improves the quality of the molded bodies extracted thereby.
The strength of the carrier can yet be substantially increased, if the molding tool has at least a second web, the nozzle body extending between the first web and the second web. Like the first web, the second web is firmly connected to the nozzle body by material bonding and protrudes from the nozzle body toward the entry side. Thus, the first and second webs can particularly serve as edge-side support of the nozzle body and thus reliably absorb the pressure loads acting on the carrier during the extrusion. In addition, the first and second webs together can form a passage for guiding the spinning dope at the entry side. This way, a particularly reliable and durable molding tool can be created.
The molding tool can prove particularly advantageous if at least portions of the web extend substantially normal to the nozzle body. Due to the part that extends substantially normal to the nozzle body, the spinning dope can be directed heavily toward the extrusion openings, and a directional mass flow can thus be maintained.
If the distance normal to the lengthwise extension of the nozzle body between the first and second webs is at least less than 100 times the thickness of the carrier, then the molding tool will be able to prove effective through excellent stability and resistance against deformation by the high pressure of the spinning dope.
Advantageously, the first web can fully encircle the second web and thus provide a molding tool of a particularly simple design. This can be particularly suited, for example, for use in a molding tool having an annular nozzle body, the annular nozzle body in this case extending between the first and second webs.
If, at the entry side, the molding tool also includes a flange with at least one flange limb, the flange limb adjoining the web, then an easy-to-handle and flexible-to-replace molding tool can be created which can be attached fast and easily to a spinning machine via the flange. If the flange limb protrudes outward from the molding tool, then it can also be ensured that the spinning dope can flow freely, without impediments, from the entry side to the nozzle body, thereby ensuring uniform extrusion by the molding tool.
As regards the method for producing the molding tool as claimed in one of claims 1 through 11, the object of the invention is to provide a simple and cost-effective method which nevertheless achieves high precision.
The object regarding the production method is solved by the subject-matter of claim 12.
If a molding tool is produced according to one of claims 1 through 11, in which the extrusion openings are formed in the carrier by applying laser energy thereto from the entry side of the molding tool and burr-free extrusion openings are created in the carrier without any further finishing at the exit side, then a particularly simple and reproducible production method for molding tools can be created. By using laser radiation, the effortful finishing of the extrusion openings becomes obsolete as well, as the extrusion openings directly formed in the carrier are able to meet all quality criteria required of the molding tools. This is true for the roughness and freedom from burrs of the extrusion openings as well as for the positioning accuracy and opening diameter. If the laser energy is applied to the carrier in the form of pulsed laser radiation, then particularly small manufacturing tolerances of the extrusion openings can be met. Laser radiation with a pulse duration between 100 fs and 100 ns and pulse energies between 1 μJ and 1000 μJ has proved particularly suitable. In this connection, the pulsed laser radiation can preferably be applied to the carrier in a percussion drilling process or a helical drilling process and thus create extrusion openings with high precision and small manufacturing tolerances.
If the extrusion openings are formed in the carrier after the carrier has been firmly connected to a web by material bonding, then a particularly reliable and reproducible manufacturing method can be provided. The creation of a firm material bonding connection between the carrier and a web inexorably subjects the carrier material to mechanical loads and thus leads to an undesired deterioration or alteration of the extrusion openings. By subsequently forming the extrusion openings in the completely assembled or completed formed molding tool, such mechanical loading of the extrusion openings can be avoided, especially if forming of the extrusion openings takes place as the last, final procedural step.
The molding tool according to the invention as claimed in one of claims 1 through 11 can prove particularly advantageous when used in a method for producing regenerated cellulose molded bodies wherein cellulose-containing spinning dope is extruded by the molding tool and precipitated in a spinning bath in order to produce the molded bodies.
Preferably, such a method can be a lyocell process wherein the spinning dope contains a tertiary amine oxide in which the cellulose is dissolved and the spinning bath includes a mixture of water and tertiary amine oxide.
The embodiments of the invention are described hereinafter with reference to the drawings, wherein:
The carrier 9 includes extrusion openings 10 that penetrate it from the entry side 6 to the exit side 7. At the exit side 7, the extrusion openings 10 form a mouth 11 having a mouth diameter 12. In this case, the size of the mouth diameter 12 decisively influences the titer (or diameter) of the extruded cellulosic molded body 4. In addition, the extrusion behavior and the geometry of the molded bodies 4 can be controlled via the cross-sectional shape of the extrusion opening 10. For example, this can be used to change the discharge behavior of the spinning dope 2 from the extrusion openings 10 in order to prevent sticking together of the extruded spinning dope 3 prior to precipitation in the spinning bath 5. In this case, preferred cross-sectional shapes of the extrusion openings 10 may have a configuration that is tapering toward the exit side 7, as is shown in
The extrusion openings 10 have a mouth diameter 12 between 70 and 150 μm. Such mouth diameters 12 can ensure that fibers or filaments having a titer greater than 0.7 dtex are produced as the extruded cellulosic molded bodies 4. In another preferred embodiment of the invention, regenerated cellulose fibers having a titer between 1.0 and 2.5 dtex are produced.
The ratio of the thickness 13 of the carrier 9 to the mouth diameter 12 of the extrusion opening 10 is at least 6:1, thereby ensuring sufficient resistance of the carrier 9 to the high pressures exerted by the spinning dope 2. In further preferred embodiments of the invention, a ratio of at least 10:1, of at least 12:1, or of at least 15:1, is chosen.
The thickness 13 of the carrier 9 is at least 600 μm. This way, the carrier 9 is able to permanently withstand a pressure load of up to 150 bar from the entry side 6. In another embodiment, the preferred thickness 13 of the carrier 9 is at least 800 μm, or preferably 1000 μm, in order to ensure a particularly high resistance of the carrier 9.
The extrusion openings 10 were formed in the carrier 9 by applying laser energy to it, and allowing laser energy to act on it. This makes it easy to produce the molding tool 1 in technical processes. In addition, with the laser radiation acting on the material of the carrier 9, particularly high dimensional accuracy in the positioning, the dimensions, and the geometry of the extrusion openings 10 is achieved. In particular, the extrusion openings 10 have a constant average distance 14 from one another that is between 50 and 1000 μm, the standard deviation of the distance 14 being no more than 1%. In order to avoid sticking together of the fibers as they exit the extrusion openings 10, larger distances 14 from 250 to 800 μm are usually employed. In this connection, the extrusion openings 10 can be disposed as distributed over the carrier 9 in an arbitrary, regular pattern (e.g., radial, grid-shaped, etc.) or irregularly. Also, the laser radiation makes it possible to obtain a standard deviation of the mouth diameters 12 of less than 2%. In addition, the extrusion openings 10 formed in the carrier 9 by using laser radiation do not have burrs at the exit side 7 right after being formed and thus do not have to be subjected to any further finishing steps such as grinding or polishing which might adversely affect the geometry of the extrusion openings 10. In particular, the burr-free and smooth extrusion openings 10 also ensure that the individual strands of the extruded spinning dope 3 will not stick together before being precipitated into the molded bodies 4 in the spinning bath 5.
The molding tool 1 shown in
In the interior of the molding tool 1, the webs 15 and 16 act as guide surfaces 19 for the spinning dope 2, which advantageously support the flow behavior of the highly viscous spinning dope 2 and prevent the formation of dead spaces within the molding tool 1. Thus, the webs 15, 16 form a guide passage 20 for the spinning dope 2 starting from the entry side 6. Preferably, the webs 15 and 16 extend, as shown in
In addition, the molding tool 1 includes a flange 23 by means of which the molding tool 1 can be—as is shown in
In this case, the molding tool 51 includes three nozzle bodies 58a, 58b, and 58c, each of which comprises a planar carrier 59a, 59b, 59c. Generally, it is to be mentioned that a molding tool 51, as shown in
In this case, the nozzle bodies 58a, 58b, 58c are firmly connected to the remaining molding tool 51 by material bonding, preferably by welds 73. The carriers 59a, 59b, 59c include respective extrusion openings 60 which penetrate them from the entry side 56 to the exit side 57 and are formed in them through the action of laser radiation. At the exit side 57, each of the extrusion openings 60 forms a mouth 61 having a mouth diameter 62. As described for the first embodiment, the mouth diameters 62 can be varied in order to change the titer of the extruded cellulosic molded bodies 4. The preferred mouth diameter 62 of the extrusion openings 60 is between 70 and 150 μm in order to produce cellulosic molded bodies 4, particularly fibers, having a titer greater than 0.7 dtex. In addition, by forming the extrusion openings 60 by means of laser radiation, a standard deviation of the mouth diameters 62 of less than 1% is obtained. More preferably, this is used to produce regenerated cellulose fibers having a titer between 1.0 and 2.5 dtex. Also, as described for the first embodiment, the cross-sectional shapes of the extrusion openings 60 can be changed in order to control the exit behavior of the extruded spinning dope 3.
The carriers 59a, 59b, 59c of the nozzle bodies 58a, 58b, 58c have a preferred thickness 63 of at least 600 μm. In other advantageous configurations of this embodiment, the thickness 63 is at least 800 μm, or at least 1000 μm, in order to obtain a particularly permanently resistant molding tool 51 that withstands the high pressures of up to 150 bar acting from the entry side 56. Here, the ratio of the thickness 63 of the carriers 59a, 59b, 59c to the mouth diameter 62 of the extrusion openings 60 is at least 6:1 in order to obtain the necessary resistance. In preferred configurations of the invention, the ratio is at least 10:1, at least 12:1, or at least 15:1.
Very high dimensional accuracy in the positioning and the dimensions of the extrusion openings 60 is obtained by forming the extrusion openings 60 in the carriers 59a, 59b, 59c by applying laser energy to them. As is shown in
The molding tool 51 includes first webs 65a, 65b, 65c, 65d, provided at the outside of the molding tool 51. Inside the molding tool 51 second webs 66a, 66b are provided that extend in a rib-like manner between the first webs 65c and 65d and are firmly connected to them by material bonding. In this case, each of the nozzle bodies 58a and 58c extends transversely to its lengthwise extension 68 between a first web 65a, 65b and a second web 66a, 66b. The nozzle body 58b extends between the second webs 66a, 66b. The webs 65a, 65b, 65c, 65d, 66a, 66b and the carriers 59a, 59b, 59c of the nozzle bodies 58a, 58b, 58c are firmly material-bond-connected to one another via welds 73. Preferably, the webs 65a, 65b, 65c, 65d, 66a, 66b are configured as one integral piece (for example, as a milled, deep-drawn, rolled piece, etc.), and protrude from the nozzle bodies 58a, 58b, 58c toward the entry side 56.
The webs 65a, 65b, 66a, 66b extend parallel to one another and maintain a constant normal distance 67 (normal to the lengthwise extension 68) to one another along the carriers 59a, 59b, 59c. In this case, the normal distance 67 is no more than 100 times the thickness 63 of the carriers 59a, 59b, 59c so that the highest possible stability of the nozzle bodies 58a, 58b, 58c is obtained.
Inside the molding tool 51, the webs 65a, 65b, 65c, 65d 66a, 66b act as guide surfaces 69 for the spinning dope 2. Thus, the webs 65a, 65b, 65c, 65d, 66a 66b create a guide passage 70 starting from the entry side 56, through which the spinning dope 2 is guided to the extrusion openings 60.
In addition, the molding tool 51 includes a flange 73, by means of which the molding tool 51 can be connected to a spinning device 100 in a force-locking engagement. In this case, four flange limbs 71a, 71b, 71c, and 71d, each of which adjoins a first web 65a, 65b, 65c, 65d, form the flange 73 which protrudes outward from the molding tool 51 at the entry side 56 and encircles the molding tool 51.
| Number | Date | Country | Kind |
|---|---|---|---|
| 19159270.8 | Feb 2019 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2020/054331 | 2/19/2020 | WO | 00 |
