Patent Application
20230051927
The present invention relates to a process for the production of spunbonded nonwovens, wherein a spinning mass is extruded through a plurality of nozzle holes of at least a first spinneret and a second spinneret to form filaments and the filaments are drawn, in each case, in the extrusion direction, with the filaments of the first spinneret being deposited on the conveyor belt to form a first spunbonded nonwoven and the filaments of the second spinneret being deposited on the conveyor belt to form a second spunbonded nonwoven to form the second spunbonded nonwoven over the first spunbonded nonwoven in order to obtain a multi-layered spunbonded nonwoven.
The production of spunbonded nonwovens and, respectively, nonwoven fabrics by the spunbond process, on the one hand, and by the meltblown process, on the other hand, is known from the prior art. In the spunbond process (e.g., GB 2 114 052 A or EP 3 088 585 A1), the filaments are extruded through a nozzle and pulled off and drawn by a drawing unit located underneath. By contrast, in the meltblown process (e.g., U.S. Pat. Nos. 5,080,569 A, 4,380,570 A or 5,695,377 A), the extruded filaments are entrained and drawn by hot, fast process air as soon as they exit the nozzle. In both technologies, the filaments are deposited in a random orientation on a deposit surface, for example, a perforated conveyor belt, to form a nonwoven fabric, are carried to post-processing steps and finally wound up as nonwoven rolls.
It is also known from the prior art to produce cellulosic spunbonded nonwovens according to the spunbond technology (e.g., U.S. Pat. No. 8,366,988 A) and according to the meltblown technology (e.g., U.S. Pat. Nos. 6,358,461 A and 6,306,334 A). A lyocell spinning mass is thereby extruded and drawn in accordance with the known spundbond or meltblown processes, however, prior to the deposition into a nonwoven, the filaments are additionally brought into contact with a coagulant in order to regenerate the cellulose and produce dimensionally stable filaments. The wet filaments are finally deposited in a random orientation as a nonwoven fabric.
From the state of the art (US 2018/0282922 A1), processes for the production of spunbonded nonwovens are also known, in which a spinning mass is extruded at least through a first spinneret and a second spinneret downstream of the first spinneret, so that the filaments extruded from the second spinneret are deposited over the filaments extruded from the first spinneret, forming a multilayer spunbonded web.
Especially in the production of spunbonded nonwovens and, respectively, nonwoven fabrics with very low weights per unit area, the above-mentioned processes exhibit the disadvantage that increasing the throughput without impairing the quality of the spunbonded nonwovens is possible only to a very limited extent.
Therefore, it is the object of the invention to improve a process for the production of spunbonded nonwoven of the initially mentioned type in such a way that the throughput of the process can be increased in a cost-efficient and simple manner.
The object is achieved in that the multi-layered spunbonded nonwoven is separated into at least the first spunbonded nonwoven and the second spunbonded nonwoven in a subsequent step and after separation the first and second spunbonded nonwovens each undergo a hydroentanglement and optionally a drying and/or are each wound up individually.
Namely, if the filaments of the second spinneret are deposited on the conveyor belt to form the second spunbonded nonwoven over the first spunbonded nonwoven in order to obtain a multi-layered spunbonded nonwoven, the throughput of the process can be increased in a simple way, since at least two spinnerets are provided for the simultaneous formation of at least two spunbonded nonwovens, but the multi-layered spunbonded nonwoven formed thereby can be processed further with the existing means instead of with a single spunbonded nonwoven. In this case, the second spinneret is preferably located downstream of the first spinneret in the conveying direction of the conveyor belt.
The multi-layered spunbonded nonwoven formed thereby consists of the first and the second spunbonded nonwovens, with the second spunbonded nonwoven being arranged above the first one. The first and the second spunbonded nonwovens can, in this case, be interconnected in such a way (for example, by adhesion) that the multi-layered spunbonded nonwoven forms a unit which may undergo further process steps, but can be separated into the first and the second spunbonded nonwovens essentially without causing any structural damage to them.
If the multi-layered spunbonded nonwoven is separated into at least the first and the second spunbonded nonwovens in a subsequent step, at least two independent spunbonded nonwovens can again be obtained in the course of the process. A cost-efficient process for the production of spunbonded nonwoven with an increased throughput can thus be created.
Likewise, the spinning mass can also be extruded into filaments through a third and further spinneret and the filaments can be drawn, in each case, in the extrusion direction, wherein the filaments of the third spinneret are deposited on the conveyor belt to form a third spunbonded nonwoven over the second spunbonded nonwoven in order to obtain the multi-layered spunbonded nonwoven, or, respectively, the filaments of the further spinnerets are deposited on the conveyor belt to form further spunbonded nonwovens over the respective preceding spunbonded nonwoven in order to obtain the multi-layered spunbonded nonwoven. Such a multi-layered spunbonded nonwoven may comprise a plurality of spunbonded nonwovens, which can be separated from each other in a subsequent process step.
To improve clarity, the following statements each relate to an embodiment with two spinnerets, but are in no way to be regarded as limitative. Rather, they can be applied analogously to any number of spinnerets.
The process can be particularly noteworthy if the first and the second spunbonded nonwovens each undergo hydroentanglement separately after they have been separated. By arranging the hydroentanglement after the multi-layered spunbonded nonwoven has been separated, a disadvantageous connection between the first and the second spunbonded nonwovens in the multi-layered spunbonded nonwoven can be avoided, which would hamper a subsequent non-destructive separating of the multi-layered spunbonded nonwoven. The separate hydroentanglement of the spunbonded nonwovens can then advantageously improve the internal structure and, respectively, the internal cohesion. In particular, the first and the second spunbonded nonwovens may furthermore underdo drying individually following the respective hydroentanglement so that finished spunbonded nonwovens that can be wound up are obtained.
Then, the spunbonded nonwovens that have been treated to completion or, respectively, separated can each be wound up individually so that at least two spunbonded nonwovens are obtained simultaneously.
For the purposes of the present invention, it is noted that, within the meaning of the present disclosure, a spunbonded nonwoven is understood to be a nonwoven fabric which is formed directly by depositing extruded filaments, wherein the filaments are essentially continuous filaments and are deposited in a random orientation to form the spunbonded nonwoven.
The aforementioned advantages of the process can become apparent especially if the multi-layered spunbonded nonwoven is subjected to at least one treatment step before it is separated into at least the first and the second spunbonded nonwovens. In this way, a joint treatment of the first and the second spunbonded nonwovens may, in fact, occur in the form of the multi-layered spunbonded nonwoven, and, thus, the throughput of the process can be increased considerably in comparison to the separate treatment of the spunbonded nonwovens.
This can become apparent especially if the at least one treatment step of the multi-layered spunbonded nonwoven consists in a washing or a drying.
Furthermore, the at least one treatment step of the multi-layered spunbonded nonwoven can be a hydroentanglement, whereby the first and second spunbonded nonwoven within the multi-layered spunbonded nonwoven still remain separable non-destructively.
The advantages of the process may become evident especially in case of a washing. For the manufacture of thermoplastic spunbonded nonwovens, a washing is generally not necessary, as so-called “dry” spinning processes are involved in which any solvents that may be used evaporate by themselves from the spunbonded nonwoven downstream of the calender or dryer. In the simplest case, the spunbonded nonwoven is wound up into rolls immediately upon the extrusion and the deposition in such processes. However, in case of spinning processes that require a washing, such as for cellulosic spunbonded nonwovens, the throughput is usually limited by the duration of the washing, since the spunbonded nonwovens have to achieve certain dwell times in the washing so that the solvent can be washed out. Accordingly, in case of very low weights per unit area, very long washing systems would have to be employed in order to achieve the same throughput as with higher weights per unit area. By means of the process according to the invention with a joint washing of the first and the second spunbonded nonwovens in the multi-layered spunbonded nonwoven, the duration of the washing can thus be significantly reduced, and, respectively, the throughput can be increased. Furthermore, the residual solvent content in the produced spunbonded nonwoven can be reduced.
According to the invention, it has been shown that the reduction in the production speed and the increase in dwell time obtained as a result have a very strong effect on the effectiveness of the washing and on the residual content of the solvent in the finished spunbonded nonwoven.
For example, the production speed during the production of single-layered spunbonded nonwoven having a weight per unit area of 40 g/m2 is 125 m/min at a cellulose throughput of 300 kg/h/m. In the multi-layered production according to the invention of single-layered spunbonded nonwoven, the individual spunbonded nonwovens already have a weight per unit area of 40 g/m2. With two superimposed spunbonded nonwovens and a cellulose throughput of 300 kg/h/m, the production speed then drops to 62.5 m/min. It has been shown that the effectiveness of the individual washing stages is not only doubled, but increased up to eight times. Since the dwell time has a serious impact on the efficiency of the washing, doubling the dwell time may lead to a residual solvent content in the spunbonded nonwoven which is 4 to 8 times less.
The costs of the process can be reduced further if the washing is a multi-stage countercurrent washing. Namely, in the countercurrent washing, the water used for washing circulates in several washing stages, wherein fresh water is supplied at the end of the washing and is passed along successively to the upstream washing stages, and wherein the spent washing water is discharged at the beginning of the washing.
A drawing air stream for drawing the filaments is preferably assigned to each of the first and the second spinnerets. The spinnerets can thus control the extrusion and drawing conditions of the filaments independently of each other, thus producing two first and second spunbonded nonwovens that are independent and different from each other. A particularly flexible and versatile process can thus be created. The drawing air stream is thereby directed from the respective spinneret onto the extruded filaments. In particular, the drawing air stream can have a pressure ranging from 0.05 bar to 5 bar, preferably from 0.1 bar to 3 bar, particularly preferably from 0.2 bar to 1 bar. In particular, the drawing air stream can furthermore have a temperature ranging from 20° C. to 200° C., preferably from 60° C. to 160° C., particularly preferably from 80° C. to 140° C.
The process according to the invention is particularly suitable for the production of cellulosic spunbonded nonwovens, with the spinning mass being a lyocell spinning mass, i.e., a solution of cellulose in a direct solvent for cellulose. Such a direct solvent for cellulose is a solvent in which the cellulose is present in a state of having been dissolved in a non-derivatized form. Preferably, this may be a mixture of a tertiary amine oxide, such as NMMO (N-methylmorpholine-N-oxide), and water. Alternatively, however, also ionic liquids, or mixtures with water, are, for example, suitable as direct solvents. In this case, the content of cellulose in the spinning mass may range from 3% by weight to 17% by weight, in preferred embodiment variants from 5% by weight to 15% by weight, and in particularly preferred embodiment variants from 6% by weight to 14% by weight.
Since the cellulose spinning masses in processes for the production of cellulosic spunbonded nonwovens only have cellulose contents of, at most, 17%, a larger amount of spinning mass is required in cellulosic spunbond technologies than for the production of thermoplastic spunbonded nonwovens in order to achieve the same productivity. As a result, more spinnerets or, respectively, a greater spinning mass throughput per spinneret have to be achieved in comparison to thermoplastic spunbond systems, with the productivity remaining the same. The individual layers are then washed, solidified, dried and wound up.
In WO 2018/071928 A1, a process for washing cellulosic spunbonded nonwovens is described. Therein, the link between dwell time, effectiveness of the washing and impact on the costs and, respectively, the duration of the washing is explained. Especially in case of a high cellulose throughput, which is important for the profitability of the process, and with low weights per unit area of up to 10 g/m2, which are desirable for many applications, high production speeds must be achieved. Consequently, both the requirement in terms of the effectiveness of each individual washing stage and the necessary duration of the washing and, accordingly, the expenditure for mechanical and systems engineering and the costs for the system and, respectively, the appropriately long building are increased.
However, for an economical operation of a plant for the production of cellulosic spunbonded nonwoven, a high throughput is necessary. The process according to the invention is able to ensure a higher throughput and, respectively, a shortening of the washing especially in the production of cellulosic spunbonded nonwovens.
The throughput of cellulose per spinneret may preferably range between 5 kg/h per metre of spinneret length and 500 kg/h per metre of spinneret length.
In addition, the internal structure of the spunbonded nonwovens can be controlled reliably if the filaments of the first and the second spinnerets are coagulated at least partly.
For this purpose, a coagulation air stream comprising a coagulation liquid for an at least partial coagulation of the filaments can be assigned to each of the first and the second spinnerets, whereby the internal structure of the first and the second spunbonded nonwovens can be controlled independently of each other. In this case, a coagulation air stream can preferably be a fluid containing water and/or a fluid containing coagulant, for example, gas, mist, vapour, etc.
A particularly reliable coagulation of the extruded filaments can thereby be achieved if the coagulation liquid is a mixture of water and a direct solvent for cellulose. In particular, the coagulation liquid may be a mixture of demineralized water and 0% by weight to 40% by weight of NMMO, preferably 10% by weight to 30% by weight of NMMO, particularly preferably 15% by weight to 25% by weight of NMMO.
The amount of coagulation liquid may, in this case, preferably range from 50 l/h to 10,000 l/h, furthermore preferably from 100 l/h to 5,000 l/h, particularly preferably from 500 l/h to 2,500 l/h per metre of coagulation nozzle.
The second spunbonded nonwoven may preferably have a weight per unit area different from that of the first spunbonded nonwoven, whereby a process can be created which is applicable in a particularly flexible way. In this case, the weight per unit area of the first and the second spunbonded nonwovens may range from 5 g/m2 (gsm) to 500 g/m2, preferably from 10 g/m2 to 250 g/m2, particularly preferably from 15 g/m2 to 100 g/m2.
Moreover, it is the object of the invention to improve a device for the production of spunbonded nonwoven according to the preamble of claim 12 in such a way that it enables the production throughput to be increased in a structurally simple and cost-efficient manner.
The object that is posed is achieved by the characterizing part of claim 12.
Namely, if the second spinneret of the device is arranged in the conveying direction of the conveyor belt downstream of the first spinneret in such a way that the second spunbonded nonwoven is deposited on the conveyor belt over the first spunbonded nonwoven to form a multi-layered spunbonded nonwoven, a device can be created in a structurally simple manner which forms a multi-layered spunbonded nonwoven composed of two spunbonded nonwovens on the conveyor belt. If the device additionally comprises a separation device fed via the conveyor belt for separating the multi-layered spunbonded nonwoven into individual spunbonded nonwovens, a compact and inexpensive device with an increased throughput can furthermore be provided in that the multi-layered spunbonded nonwoven that has been formed is separated into its individual spunbonded nonwovens by the separation device following a joint transportation.
The aforementioned advantages can be particularly noticeable in a device which comprises a washing to wash the multi-layered spunbonded nonwoven, which is arranged between the spinnerets and the separation device in the conveying direction of the conveyor belt. Thus, the device can, in fact, provide a joint washing with an increased throughput for the multi-layered spunbonded nonwoven before the multi-layered spunbonded nonwoven is separated into the individual spunbonded nonwovens in the separation device.
If the device comprises at least a first and a second winding device, with the winding devices being fed by the seperation device, a structurally simple device with a high throughput can be created, which allows individual spunbonded nonwovens to be obtained simultaneously.
In addition, the device may comprise at least a first and a second hydroentanglement, with a hydroentanglement being provided, in each case, between a separation device and a winding device. In this case, the hydroentanglements are each supplied with the spunbonded nonwovens from the separation device and can additionally subject them to hydroentanglement. Following the hydroentanglement, the spunbonded nonwovens are transferred to the winding device.
With the spinnerets of the process according to the invention or, respectively, the device according to the invention, single-row slot nozzles, multi-row needle nozzles or preferably column nozzles with lengths of 0.1 m to 6 m as known from the prior art (U.S. Pat. Nos. 3,825,380 A, 4,380,570 A, WO 2019/068764 A1) may preferably be used.
The embodiment variants of the invention are described in more detail below with reference to the drawings.
The device 200 comprises three spinnerets 3.1, 3.2, 3.3 for extruding a spinning mass 2 into filaments 5.1, 5.2, 5.3. In doing so, the spinning mass 2 is extruded in the spinnerets 3.1, 3.2, 3.3, in each case, through a plurality of nozzle holes 4.1, 4.2, 4.3, which are allocated to the respective spinneret 3.1, 3.2, 3.3, to form the filaments 5.1, 5.2, 5.3. In addition, each spinneret 3.1, 3.2, 3.3 comprises drawing devices 4.1, 4.2, 4.3 for drawing the extruded filaments 5.1, 5.2, 5.3, whereby a drawing air stream for drawing is allocated to each of the first, the second and the third spinnerets 3.1, 3.2, 3.3. For this purpose, drawing air 6 is supplied to the drawing devices in the spinnerets 3.1, 3.2, 3.3, and the filaments 5.1, 5.2, 5.3 are drawn by the drawing air stream in the extrusion direction as they exit from the spinnerets 3.1, 3.2, 3.3. In doing so, the drawing air 6 can emerge from openings in the spinnerets 3.1, 3.2, 3.3 between the nozzle holes 4.1, 4.2, 4.3 and can be directed as a drawing air stream directly onto the extruded filaments 5.1, 5.2, 5.3.
Preferably after or already in the course of drawing, the extruded filaments 5.1, 5.2, 5.3 are charged with one coagulation air stream 7.1, 7.2, 7.3 each, wherein, in each case, at least one coagulation air stream 7.1, 7.2, 7.3 is allocated to the spinnerets 3.1, 3.2, 3.3 and is generated by a coagulation device 8.1, 8.2, 8.3. The coagulation air streams 7.1, 7.2, 7.3 usually comprise a coagulation liquid, for example, in the form of vapour, mist, etc. Due to the contact of the filaments 5.1, 5.2, 5.3 with the coagulation air stream 7.1, 7.2, 7.3 and the coagulation liquid contained therein, the filaments 5.1, 5.2, 5.3 are coagulated at least partly, which, in particular, reduces adhesions between the individual extruded filaments 5.1, 5.2, 5.3.
The drawn and at least partially coagulated filaments 5.1 of the first spinneret 3.1 are then deposited in a random orientation on a conveyor belt 9 of the device 200 to form a first spunbonded nonwoven 1.1. The second spinneret 3.2 is arranged downstream of the first spinneret 3.1 in the conveying direction of the conveyor belt 9 in such a way that the drawn and at least partially coagulated filaments 5.2 of the second spinneret 3.2 are deposited in a random orientation on the conveyor belt 9 over the first spunbonded nonwoven 1.1 to form a second spunbonded nonwoven 1.2. In the same manner, the drawn and at least partially coagulated filaments 5.3 of the third spinneret 3.3 are deposited on the conveyor belt 9 over the second spunbonded nonwoven 3.2, namely in that the third spinneret 3.3 is arranged downstream of the second spinneret 3.2 in the conveying direction of the conveyor belt 9.
By depositing the second spunbonded nonwoven 1.2 over the first spunbonded nonwoven 1.1 and the third spunbonded nonwoven 1.3 over the second spunbonded nonwoven 1.2, a multi-layered spunbonded nonwoven 10 is formed in which the spunbonded nonwovens 1.1, 1.2, 1.3 are detachably connected to each other. The detachable connection between the spunbonded nonwovens 1.1, 1.2, 1.3 to form the multi-layered spunbonded nonwoven 10 is thereby constructed in such a way that a non-destructive separation of the multi-layered spunbonded nonwoven 10 into the individual spunbonded nonwovens 1.1, 1.2, 1.3 is possible even after further treatment steps.
Following the formation, the multi-layered spunbonded nonwoven 10 is guided across the conveyor belt 9 through a washing 11 in which the multi-layered spunbonded nonwoven 10 is washed in order to free it from residues of the solvent, namely the NMMO contained in the spinning mass 2. In a preferred embodiment variant, the washing 11 is, in this case, a multi-stage countercurrent washing, which, however, has not been illustrated in the figures. In a next step, the washed multi-layered spunbonded nonwoven 10 is then supplied to a drying 12 in order to remove the remaining moisture. In particular, the washing 11 is arranged in the conveying direction of the conveyor belt 9 between the spinnerets 3.1, 3.2, 3.3 and a subsequent separation device 13.
In a further embodiment variant, which is not shown in further detail in the figures, the multi-layered spunbonded nonwoven 10 can be subjected to an additional hydroentanglement, wherein the spunbonded nonwovens 1.1, 1.2, 1.3 within the multi-layered spunbonded nonwoven 10 still remain separable in a non-destructive way.
The washed and dried multi-layered spunbonded nonwoven 10 is separated into the first spunbonded nonwoven 1.1, the second spunbonded nonwoven 1.2 and the third spunbonded nonwoven 1.3 in a separation device 13 fed with the multi-layered spunbonded nonwoven 10 by the conveyor belt 9, wherein the spunbonded nonwovens 1.1, 1.2, 1.3 are each supplied separately to a winding device 14.1, 14.2, 14.3 in order to obtain the finished spunbonded nonwovens 1.1, 1.2, 1.3 simultaneously. In this case, the separation device 13 has an inlet for the multi-layered spunbonded nonwoven 10 and several outlets for the spunbonded nonwovens 1.1, 1.2, 1.3, with the inlet of the separation device 13 being connected to the dryer 12, and the outlets each being connected to the winding devices 14.1, 14.2, 14.3 for feeding them with the spunbonded nonwovens 1.1, 1.2, 1.3.
The drawn and at least partially coagulated filaments 5.1 of the first spinneret 3.1 are then again deposited in a random orientation on the conveyor belt 9 to form a first spunbonded nonwoven 1.1, the filaments 5.2 of the second spinneret 3.2 are deposited in a random orientation on the conveyor belt 9 over the first spunbonded nonwoven 1.1 to form a second spunbonded nonwoven 1.2, and the filaments 5.3 of the third spinneret 3.3 are deposited in a random orientation on the conveyor belt 9 over the second spunbonded nonwoven 3.2 to form a third spunbonded nonwoven 1.3. In doing so, as described above, a multi-layered spunbonded nonwoven 10 is again formed in which the spunbonded nonwovens 1.1, 1.2, 1.3 are arranged one on top of the other and are detachably connected to each other.
Across the conveyor belt 9, the multi-layered spunbonded nonwoven 10 is then passed through a washing 11 in which the multi-layered spunbonded nonwoven 10 is washed and freed from solvent residues (in particular NMMO). In contrast to the first embodiment variant of
In comparison to the device 101 according to
The spunbonded nonwovens 1.1, 1.2, 1.3 are then brought together again for a joint drying 12 and, after the joint drying 12, they are again separated into the individual spunbonded nonwovens 1.1, 1.2, 1.3 and supplied to the respective winding devices 14.1, 14.2, 14.3. Separate merging and separation devices may be provided for bringing the spunbonded nonwovens 1.1, 1.2, 1.3 together and separating them before and after the drying 12, which is not shown in the figures.
In an embodiment variant which is an alternative to the process 101 shown in
In a further embodiment of the invention, the spunbonded nonwovens 1.1, 1.2, 1.3 can be produced by the spinnerets 3.1, 3.2, 3.3 each having different weights per unit area, for example, by changing the mass throughput through the spinnerets 3.1, 3.2, 3.3.
| Number | Date | Country | Kind |
|---|---|---|---|
| 19217034.8 | Dec 2019 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2020/085772 | 12/11/2020 | WO |
