Technical field

The invention relates to a method of producing a linear nanofibrous structure in an AC electric field from a polymer solution or melt, in which a spinning area with a supercritical AC electric field intensity is formed on a spinning electrode. In the spinning area, nanofibers are formed, which are carried away from the spinning electrode by the action of an electric wind in the direction of the maximum values of the gradient of the generated electric fields.

The invention also relates to a device for producing a linear nanofibrous structure in an AC electric field from a polymer solution or melt, wherein a spinning area with a supercritical value of AC electric field intensity is created on a spinning electrode mounted in a spinning chamber and connected to a source of high alternating voltage and coupled to a means for applying the polymer solution or melt to the surface of the spinning electrode,

Background art

In the preparation of nanofibrous yams, oriented nanofibers are the basis for the construction of nanofibrous yarns. Currently, numerous methods have been developed in the field of DC electrospinning to obtain longitudinally oriented fiber bundles which can be attributed to two main aspects, that is, obtaining highly ordered nanofibers by improving a collecting device or by influencing the electric field by means of auxiliary electrodes.

CN111118677 discloses production of nanofibrous yarn by DC electrostatic spinning. The device comprises a cylindrical collector which consists of a cavity and a throat which is rotatable about its axis, wherein the diameter of the upper opening of the throat is smaller than the diameter of the lower opening of the cavity. Mounted inside the lower opening of the cavity is a DC electrostatic rotating spinning electrode connected to a high voltage DC source into which a solution to be subjected to electrospinning is fed. In the upper part of the collector cavity, pressurized air inlets open into the inner space of the collector and above them is arranged a counter electrode which can be grounded or connected to a voltage source of opposite polarity to the rotating spinning electrode.

The nanofibers formed on the rotating spinning electrode are carried by the action of the electrostatic field to the counter electrode and by the action of airflow, they are carried up into the throat of the cylindrical collector which rotates and due to its rotation and the supplied air flow, a vortex is generated, which twists the nanofibers into yarn, which is subsequently withdrawn and wound on a bobbin.

The nanofibers are twisted immediately after their formation due to the rotation of the spinning electrode and the subsequent action of the vortex, so that there is no parallelization of the nanofibers before twisting, the twisting takes place unevenly and, as a result, their strength and appearance is variable.

CN111286792 describes a horizontal arrangement of a DC electrostatic spinning device comprising a rotating jet spinning electrode and a collecting electrode formed by a hollow cylinder which is arranged coaxially against the jet spinning electrode, wherein a DC electric field is formed between the spinning electrode and the collecting electrode. At least two air jets directed towards the axis of the collecting electrode are arranged around the rotating jet spinning electrode. Due to an electric wind, the nanofibers formed by the rotating jet spinning electrode are carried to the hollow cylinder forming the collecting electrode, wherein due to the rotation of the jet spinning electrode and the air currents from the jets, they are twisted into yam which, after passing through the cavity of the collecting electrode, is drawn off and wound on a bobbin.

In this solution, too, the aim is to twist the nanofibers as soon as possible after they are formed without achieving their parallelization.

In both cases, the disadvantages of DC electrostatic production of nanofibrous yarn include low yarn cohesion, irregular twist and poor orientation of the nanofibers.

Currently, a method of continuous preparation of nanofibrous yarns is also known, for example from CN110644080, in which nanofibers are formed from a polymer solution in a jet head from which the nanofibers are drawn off by the action of high-speed air flow generated in a Venturi tube and, through a funnel- shaped collection tube, enter a Venturi collection system, where they are straightened and oriented into oriented bundles of nanofibers by sucking the bundle of nanofibers using the Venturi effect. The oriented bundles of nanofibers are subsequently twisted and agglomerate by the action of the twisting device into a nanofibrous yarn, which is in the next step wound on a bobbin. The twisting device comprises air jets for supplying the air flow in the tangential direction towards the yarn to be twisted.

From the point of view of the subsequent processing and use of nanofibrous yarns, it is not enough to only obtain oriented fibers in order to meet the current requirements for their preparation, but it is necessary to be able to obtain oriented fibers or fiber bundles continuously and to impart evenly a certain degree of twist to them in order to ensure their length and degree of orientation. In order to optimize the strength of the nanofibrous yarn, it is advantageous if the nanofibers in the nanofiber bundle are already oriented longitudinally due to the method of their formation, i.e., they are oriented in agreement with the axis of the bundle. Existing DC electrospinning technologies for the continuous production of nanofibrous yarns have a low yield and poor quality of the produced nanofibrous yarn. Therefore, core yams are currently produced by DC electrospinning.

For example, CZ PV 2007-179 discloses a linear fibrous structure comprising polymeric nanofibers which form a coating on the surface of a core formed by a supporting linear fibrous structure, at least some of the nanofibers being trapped between the fibers of the surface portion of the core. Nanofibers are produced by DC electrostatic spinning (i.e., using high voltage DC sources), wherein the supporting linear structure is guided through a spinning space between a spinning electrode and a collecting electrode and outside the spinning space it is imparted with a false twist. Therefore, the supporting linear structure in the spinning space rotates about its axis and individual nanofibers carried through the spinning space to the collecting electrode are deposited on its surface. Not all the nanofibers are trapped on the supporting linear structure, but some of them fly past and are trapped only on the collecting electrode. This problem has not been eliminated even by an embodiment in which the collecting electrode is formed by a conductive supporting linear structure. In this embodiment, too, a large part of the nanofibers fly past the linear supporting structure and are trapped on the walls of the spinning space.

Although the nanofibers are trapped among the fibers of the surface portion of the core, during their unwinding, the nanofibrous coating is torn away from the core due to the forces acting between the surfaces of adjacent fibers in a package, these forces being greater than the cohesive force between the coating of nanofibers and the core.

The above-mentioned problems were partially solved by CZ PV 2009-797, where the nanofibers are fixed to the core with at least one cover thread. The wrapping by a cover thread ensures a sufficiently strong and durable fixation of the nanofibers to the core for the majority of possible applications, and at the same time, it allows full use of the specific properties of the nanofibers, as it does not hinder access to them.

The actual fibrous structure is produced by the passage of the supporting linear structure through the spinning space several times, wherein the supporting linear structure outside the spinning space is returned through part of the circumference of at least one cylinder, onto which it approaches obliquely, so that after returning, the supporting linear structure faces the spinning electrode with its opposite side. In this embodiment, there is no false twist, and consequently, when passing through the spinning space, the supporting linear structure does not rotate about its axis, and so the nanofibers are deposited during each passage on the side of the supporting linear structure that faces the spinning electrode. Due to the multiple passage of the supporting linear structure through the spinning space, a larger amount of nanofibers is deposited on it than in the previous solution, yet some of the nanofibers fly over as far as to the collecting electrode. The nanofibers are deposited on the surface of the supporting linear structure in a disorderly manner as individual nanofibers in layers, and their cohesion with the core surface is low. Fixation of the nanofibers to the surface of the supporting linear structure is achieved by subsequent wrapping with at least one cover thread.

EP2931951 B1 discloses a method of producing polymeric nanofibers, in which polymeric nanofibers are formed by applying an electric field to a polymer solution or melt placed on the surface of a spinning electrode, wherein the electric field for spinning is alternately formed between the spinning electrode to which an AC voltage is applied and air and/or gas ions generated and/or supplied to the vicinity of the spinning electrode, without a collecting electrode, whereby, depending on the phase of the AC voltage on the spinning electrode, polymeric nanofibers with opposite electric charge and/or with sections with opposite electric charge are formed, which, after their formation due to the action of electrostatic forces, aggregate into a linear structure in the form of a cable or belt which moves freely in space away from the spinning electrode in the direction of the gradient of the electric fields.

Spinning by the AC high electric voltage method is another way of producing nanofibers, alternative to electrostatic spinning. However, its yield is not yet at a level to produce purely nanofibrous yarns by this method. Therefore, EP3303666 proposed a method of producing a core yarn with a coating of polymer nanofibers enveloping a supporting linear structure forming the core during its passage through a spinning chamber. In this method, a spinning electrode connected to the inlet of a polymer solution and powered by AC high voltage is arranged below the supporting linear structure on the face of which nanofibers are formed in a spinning space in the immediate vicinity of the face of the spinning electrode and above it, wherein the supporting linear structure rotates in the spinning space about its own axis. Nanofibers are formed around the circumference of the face of the spinning electrode and in the spinning space. They are formed into a hollow electrically neutral nanofibrous plume in which the nanofibers are arranged in an irregular lattice structure in which nanofibers in short sections change their direction, wherein the hollow electrically neutral nanofibrous plume is carried by the electric wind towards the supporting linear structure and change into a flat strip which is brought to the circumference of the supporting linear structure, wherein the strip created from a hollow electrically neutral nanofibrous plume wraps around the rotating and/or ballooning supporting linear structure in the shape of a helix, creating a nanofiber coating on it, in which the nanofibers are arranged in an irregular lattice structure, in which the individual nanofibers in short sections change their direction. The nanofibrous plume represents an ideal material for the coating of the core yarn, because due to its electrical neutrality and irregular lattice structure, in which the individual nanofibers in short sections change their direction, it is capable of forming a solid coating enveloping the yarn core, whereby the coating is inert to its surroundings when wound on a bobbin and during subsequent unwinding during processing. However, if a pure nanofibrous yam were to be produced from the nanofiber plume, there would be a problem both with an insufficient quantity of the nanofibers as well as with the lattice structure of the plume, which does not allow parallelization of the nanofibers.

At present, there is no satisfactory method of producing nanofibrous yam with potential for industrial applications. Current methods of preparing nanofibrous yams are hampered by low productivity, low reliability and limited choice of materials. Their production is realized only on a laboratory scale as part of research work.

See, for example, Zhou B. et al. Developments in Electrospinning of Nanofibrous yams, Journal of Physics: Conference Series 1790 (2021 ) 012081 doi: 10.1088/1742-6596/1790/1 /012081 ).

The object of the invention is to provide a method of producing a nanofibrous yam by AC electrospinning of a polymer solution or melt, in which nanofibers would be produced in sufficient quantity, before twisting would be partially parallelized and after twisting would be adequately strong to allow winding on a bobbin and subsequent use or processing into textile structures by known textile technologies.

In addition, the object of the invention is to provide a device for performing this method.

Summary of the invention

The object of the invention is achieved by a method of producing a linear nanofibrous structure in an alternating electric field by spinning a polymer solution or melt, wherein the principle of the invention consists in that at least one spinning area is created on a spinning electrode with a supercritical AC electric field intensity and a finite length, from which the emerging nanofibers are carried by the effect of the electric wind in the direction of the maximum values of the electric field gradient away from the spinning area towards a moving electrically neutral collector on whose circumferential surface which is located opposite the spinning area and which forms the collection area of the moving electrically neutral collector, are deposited in the form of a fluffy band of nanofibers, which is moved by the movement of the electrically neutral collector into a withdrawal area, in which it is withdrawn from the surface of the electrically neutral collector by a tensile force and subsequently wound onto the bobbin of the winding device, the nanofibers being at least partially parallelized by the tensile force.

In a preferred embodiment, the fluffy band of nanofibers is rounded during transfer to the withdrawal area on the surface of the electrically neutral collector, thereby tapering it so that it can be wound directly or is more easily formed into a twist triangle during the taper when imparting a twist without the risk of damage to the edges of the fluffy band of nanofibers.

The tensile force for withdrawing the fluffy band of nanofibers is generated by a winding device, or a drawing-off device arranged between the withdrawal area and the winding device. This separates the technological tensile force from the winding force, so that appropriate tensile force can be selected for winding with respect to the construction of the bobbin.

Prior to winding or drawing-off, the fluffy band of nanofibers is acted upon by a twisting device which tapers the fluffy band of nanofibers into a twist triangle and then imparts a twist to it, thereby forming a nanofibrous yarn.

A significant feature of the method is that the twist is imparted to the fluffy band of nanofibers between two clamping points, that is between the withdrawal area of the electrically neutral collector and the point of the winding or drawing- off of the nanofibrous yarn on the bobbin, wherein residual amount of twists imparted to the fluffy band of nanofibers by the twisting device is retained in the nanofibrous yarn being wound after leaving the twisting device.

An important feature of the method according to the invention is also the fact that the spinning area of the spinning electrode is formed on the circumference of a disk spinning electrode, or at a bending point of the belt spinning electrode, where the spinning area is arranged transversely to the direction of movement of a spinning belt, or on a linear flexible structure of a linear spinning electrode.

To perform the method, a device for producing a nanofibrous yarn by AC electrospinning of a polymer solution or melt is provided, the principle of which consists in that an electrically neutral collector coupled to a drive is arranged above a spinning electrode in the path of the nanofibers, wherein the area of the surface of the electrically neutral collector against the spinning electrode forms a collection area of nanofibers for continuous deposition of nanofibers in the form of a fluffy band of nanofibers, wherein a withdrawal area of the fluffy band of nanofibers is formed on the surface of the electrically neutral collector in the direction of movement of the collector downstream of the collection area, downstream of which a winding device is arranged in the direction of the withdrawal of the fluffy band of nanofibers. The winding device serves to generate a tensile force for withdrawing the fluffy band of nanofibers from the surface of the electrically neutral collector.

The tensile force can also be generated by a drawing-off device located between the withdrawal area and the winding device. In this manner, it is possible to separate the technological tensile force, i.e., the tension associated with ballooning the yarn and the withdrawal strength, and the winding tensile force, i.e., the winding tension. Appropriate winding tensile force can be then selected with respect to the construction of the bobbin.

In a preferred embodiment, a twisting device is arranged in the direction of the withdrawal of the fluffy band of nanofibers upstream of the winding device or the drawing-off device, so that nanofibrous yam is fed into the winding device.

The spinning electrode can be formed by a disk spinning electrode, a belt spinning electrode or a linear spinning electrode or by another type of a spinning electrode.

The electrically neutral collector may consist of an electrically neutral drum collector or an electrically neutral belt collector.

If the electrically neutral collector is formed by an electrically neutral drum collector, a collection area of nanofibers is formed on it against the spinning electrode in a preferred embodiment, and in the area of the surface of the drum collector facing away from the spinning electrode, a withdrawal area of the drum collector is formed for withdrawing the fluffy band of nanofibers.

In this embodiment, it is advantageous if rounding means are assigned to the fluffy band of nanofibers between the collection area and the withdrawal area of the electrically neutral drum collector. The rounding means reduce the width/thickness of the fluffy band of nanofibers and thus simplify its twisting and/or winding.

If the electrically neutral collector is formed by a belt collector, this collector is an endless conveyor belt encircling two upper cylinders and two lower cylinders, at least one of which is a drive cylinder. The lower branch of the endless conveyor belt forms a collection area for the nanofibers which are deposited thereon in a fluffy band of nanofibers.

In a preferred embodiment, the fluffy band of nanofibers is fed by the movement of the endless conveyor belt into the upper branch of the endless conveyor belt the end of which in the direction of movement of the endless conveyor belt forms a withdrawal area for withdrawing the fluffy band of nanofibers from the electrically neutral belt collector. This embodiment allows rounding means to be assigned to the fluffy band of nanofibers on the upper branch of the endless conveyor belt, which tapers the fluffy band of nanofibers and improves its properties for withdrawing and subsequent twisting.

In another preferred embodiment, the withdrawal area is formed in the direction of movement of the endless conveyor belt at the end of its lower branch for withdrawing the fluffy band of nanofibers from the electrically neutral belt collector which is connected to the collection area formed by the lower branch of the endless conveyor belt on which the nanofibers are deposited in the form of a fluffy band.

The device according to the invention is schematically represented in the enclosed drawings, wherein Fig. 1 shows a side view of a device with a rotating disk spinning electrode and an electrically neutral drum collector, Fig. 2 shows the device of Fig. 1 in front view, Fig. 3 shows the device of Fig. 1 in top view, Fig. 4 shows the distribution of electric field intensity on the circumference of the disk electrode, Fig. 5 represents a side view of a device with a rotating disk spinning electrode and an electrically neutral belt collector, Fig. 6 shows the device of Fig. 5 in front view, Fig. 7 shows the device of Fig. 5 in top view, Fig. 8a shows the device with the belt spinning electrode and the electrically neutral belt collector with the withdrawal area of the fluffy band of nanofibers in the upper branch of the collector in side view, Fig. 8b shows the device of Fig. 8a in front view, Fig. 8c shows the device with the belt spinning electrode and the electrically neutral belt collector with the withdrawal area of the fluffy band of nanofibers in the lower branch of the collector in side view, Fig. 8d shows a front view of the device of Fig. 8c, Fig. 9a shows a side view of the device with the linear spinning electrode and the electrically neutral belt collector with the withdrawal area of the fluffy band of nanofibers in the upper branch of the collector, Fig. 9b shows a front view of the device of Fig. 9a, Fig. 9c shows a side view of the device with the linear spinning electrode and the electrically neutral belt collector with the withdrawal area of the fluffy band of nanofibers in the lower branch of the collector, Fig. 9d shows a front view of the device of Fig. 9c.

Examples of embodiment

A device for producing nanofibers by AC electrospinning of a polymer solution or polymer melt comprises a spinning electrode 1., which, in the embodiment of Figs. 1 to 7, consists of a rotating disk spinning electrode 11 which is mounted with the lower part of its circumference in a reservoir 2 of the polymer solution 21 or melt and is coupled to a known unillustrated drive. Since the spinning of a polymer melt takes place in the same manner as the spinning of a polymer solution 21 , the only spinning of a polymer solution will be described hereinafter. The polymer solution usually consists of a solution of PVB, PCL, PVA, or other spinnable polymer solutions. The spinning electrode 1 and the reservoir 2_of the polymer solution are mounted in a spinning chamber 3.

The spinning electrode 1 is connected to an unillustrated high voltage AC source, for example, with an effective voltage of 32 kV and a frequency of 50 Hz. Connected to the AC voltage source may also be the polymer solution to be spun, through which the spinning electrode 1 and the AC voltage source are interconnected. According to the first exemplary embodiment, the spinning electrode 1 is formed by a rotating disk spinning electrode 11 with a horizontal axis of rotation. The rotating disk spinning electrode 11 is mounted with the lower part of its circumference in the polymer solution 21, which is in the reservoir 2. The rotating disk spinning electrode 11 is coupled to a known unillustrated rotary drive, so that during its rotation, it carries out the polymer solution 21 to the circumferential parts of its surface. The amount of the polymer solution 21 is normally adjusted by a known unillustrated wiping device. In the vicinity of the upper part of the circumference of the disk spinning electrode 11 and above it, in the spinning chamber 3, there is a spinning space 31. Above the spinning electrode 1 in the spinning chamber 3, an electrically neutral collector 4 coupled to an unillustrated known drive is rotatably mounted. The upper part of the disk spinning electrode 11 forms a spinning area 110, in which nanofibers 5_are formed, the nanofibers 5 being carried through the spinning space 31 to the surface of the electrically neutral collector 4, which is covered with a suitable coating, for example by a flat textile made of a material which allows easy withdrawing of the nanofibers from the surface of the electrically neutral collector 4.

In the embodiment of Figs. 1 to 3, the collector 4 is formed by an electrically neutral drum collector 41. The axis of the electrically neutral drum collector 41 is parallel with the axis of the disk spinning electrode 11. The area of the surface of the electrically neutral drum collector 41 against the disk spinning electrode 11 forms the collection area 410 of nanofibers, on which nanofibers 5 are deposited in the form of a fluffy band 51 of nanofibers. The area of the surface of the electrically neutral drum collector 41 which faces away from the disk spinning electrode 11 forms the withdrawal area 4101 of the fluffy band 51 of nanofibers.

Outside the spinning space 31 , in the tangential direction to the circumference of the electrically neutral drum collector 41 and in the direction of the flow of the nanofibers 5 being withdrawn, is arranged a twisting device 6 which consists, for example, of a rotating guide eyelet located outside the axis of rotation of the twisting device 6, or another known twisting device. A winding device 7 with a bobbin 71 is arranged downstream of the twisting device 6, in the direction of the flow of the withdrawn nanofibers 5 and in the direction of the drawing-off of yarn 54. In an unillustrated exemplary embodiment, a drawing-off device is arranged between the withdrawal area 4101 and the winding device 7, which serves to create a tensile force for withdrawing the fluffy band 51 of nanofibers from the surface of the electrically neutral collector.

Neither the effective value of the voltage, for example 32 kV, the waveform of the voltage function, for example sine, sawtooth, step, nor the frequency, for example 50 Hz, are limiting, and other suitable values can be used in a very wide range.

During rotation, the disk spinning electrode 11 on its circumference and parts of the faces in the vicinity of its circumference carries out the polymer solution 21 from the reservoir 2. During spinning in an AC electric field, the aim is to produce, per unit of time, the largest possible amount of nanofibers 5, which are formed throughout the spinning area 110 of the disk spinning electrode 11 and are carried away from the disk spinning electrode 11 by an electric wind in the direction of the gradient of the generated electric fields, optionally also by auxiliary air streams, to the electrically neutral drum collector 41 , which is neither grounded nor connected to a source of electric voltage. The formation of nanofibers 5 starts at a critical value of electric field intensity E, which varies according to the type of the polymer solution 21 to be spun, the value of the voltage, the waveform, the frequency of AC voltage, the quality of the gas in the spinning chamber 3 and other parameters. At a lower value of the electric field intensity E than the critical value, nanofibers 5 are not formed, or their formation ceases.

The critical value of the electric field intensity E for the purposes of AC electrospinning means the smallest value of the electric field intensity_E, which will provide a sufficient amount of nanofibers for further technological processing for the given shape of the spinning electrode, the type of polymer solution and the value of the frequency and waveform.

Therefore, during conventional spinning in an AC electric field using a specific design of the spinning electrode 1., a higher electric field intensity E_than the critical intensity, i.e. , supercritical, is used for the selected frequency of the electric field and its waveform, which creates an electric field of high intensity E on the spinning electrode 1., in order to prevent the danger of interrupting the spinning process, to ensure sufficient evaporation of the solvent from the emerging Taylor cones of the polymer solution, and to provide a sufficiently strong electric wind to transport the formed nanofibers 5 to the electrically neutral collector 4.

The distribution of the electric field intensity E for the above-mentioned conventional spinning of the polymer solution 21 on the disk spinning electrode 11 is shown in Fig. 4 for a disk diameter of 300 mm, a disk thickness of 1 mm, the polymer solution layer thickness of 0.2 mm and a voltage amplitude of 50 kV. The supercritical value of the electric field intensity E for the PVB polymer solution is equal to or greater than 3000 MV/m. It is clear from the figure that the supercritical value the electric field intensity E is obtained in a wide region around the circumferential part of the disk spinning electrode 11. Spinning of the polymer solution 21 therefore takes place on the entire width of the circumferential surface of the disk spinning electrode 11 and on a part of its faces in the vicinity of its circumference and the nanofibers 5 formed are carried away from the disk spinning electrode 11 in the direction of the gradient of the generated electric fields through the spinning space 31 to the surface of the electrically neutral drum collector 41 to its collection area 410 and, if necessary, the effect of the electric wind is assisted by flowing the air in the required direction. Given the size of the area of supercritical electric field intensity E, it is clear that a sufficient amount of nanofibers 5 will be produced for further processing thereof.

Nanofibers 5 are deposited on the collection area 410 of the circumference of the electrically neutral drum collector 41 into a narrow fluffy band 51 of nanofibers and by rotating the drum collector 41, the fluffy band 51 of nanofibers is carried to the upper part of the electrically neutral drum collector 4, that is to the withdrawal area 4101 , in which it is withdrawn. The fluffy band 51 of nanofibers created by AC electrospinning consists of a three-dimensional layer of nanofibers 5, which are deposited on the surface of the electrically neutral drum collector 41 due to the action of the electric wind and attractive forces between the oppositely polarized parts of the nanofibers 5 and are partially parallelized during the deposition, wherein the fluffy band 51 of nanofibers represents a linear nanofibrous structure. The fluffy band 51 of nanofibers can be withdrawn from the surface of the withdrawal area 4101 of the electrically neutral drum collector 41 in a three-dimensional shape and, by subsequently drawing-off and twisting it, a twisted triangle 52 and a nanofibrous yarn 54 can be formed from it in a similar way as when processing a strand of fibers with a permanent twist on the yarn.

If nanofibers were produced by DC electrospinning on a similar device, the drum collector would function as a collecting electrode connected to the opposite polarity of the DC voltage to the spinning electrode, and the nanofibers would be deposited on it in a flat, very thin band, which, after being withdrawn from the drum and subsequently subjected to twisting, would behave as a solid flat structure and would twist into a spiral formed by this band.

The circumferential speed of the electrically neutral drum collector 41 is regulated so that the fluffy band 51 of nanofibers created on the drum collector 41 is sufficiently mechanically resistant when it is withdrawn from the surface of the electrically neutral drum collector 41 in its withdrawal area 4101 and for the subsequent imparting of a twist, or for direct winding on the bobbin 71 of the winding device 7.

The fluffy band 51 of nanofibers is withdrawn from the rotating electrically neutral drum collector 41 and guided to the twisting device 6, wherein after the withdrawal, it tapers into a twist triangle 52, from which, under the action of the twisting device 6 and the moment of force transmitted by the partially twisted nanofibers 5 from the twisting device 6, the fluffy band 51 of nanofibers tapers and simultaneously twists into a nanofibrous yarn 54. Since the nanofibers 5 of the fluffy band 51 of nanofibers are deposited on the surface of the electrically neutral drum collector 41 with a certain degree of adhesion, tensile forces are generated in the nanofibers 5 when they are released from the surface of the electrically neutral drum collector 41 in the withdrawal area 4101 , the tensile forces being necessary to parallelize the nanofibers 5 prior to twisting, so that the formation of the twists, and thus the formation of the nanofibrous yarn 54, occurs after the nanofibers are partially parallelized. In addition, the withdrawal of the fluffy band 51 of nanofibers from the surface of the electrically neutral drum collector 41 occurs due to the drafting between the two clamping points, namely between the surface of the drum collector 41 and the winding point on the bobbin 71 , the nanofibers 5 are elongated and partially parallelized in the direction of their flow, which, when they are being subsequently twisted, facilitates the arrangement of the nanofibers 5 into a helix and thus ensures sufficient strength of the produced nanofibrous yarn 54.

During twisting, the nanofibers no longer parallelize, but twist into a helix. If withdrawal is performed at a speed greater than the speed of the collector, then at the moment of withdrawing, the nanofibers will straighten and stretch/elongate, but then immediately start twisting in the twist triangle into a helix.

After withdrawing the nanofibers 5 from the withdrawal area 4101 of the electrically neutral drum collector 41, the fluffy band 51 of nanofibers being withdrawn is formed by the twisting device 6 into a twist triangle 52 and from it into a nanofibrous yarn 54, wherein the nanofibrous yarn 54 balloons before entering the twisting device 6. The twist propagates from the twisting device 6 against the technological direction of the flow of nanofibers 5 towards the electrically neutral drum collector 41 , thus assisting the withdrawal of the fluffy band 51 of nanofibers from the withdrawal area 4101 of the drum collector 41.

The twisting device 6 imparts the nanofibrous yarn 54 with a twist between two clamping points, namely between the withdrawal area and the point of winding or drawing-off, so that in the case of yams from conventional fibers, a false twist would occur, which would be cancelled out in the case of yams from conventional fibers after passing through the twisting device. This does not apply to the twisting of the nanofibrous yam 54, because due to the high surface area of the nanofibers 5, the binding forces between the individual nanofibers 5 and the low twist coefficient, a relatively high degree of twist is retained as a residual amount of twist on the nanofibrous yam 54 downstream of the twisting device 6. According to the experiments performed on nanofibers made of different types of polymers, it is 10 to 60 % of the twists, so it is a permanent twist. In the specific tests, at a twisting device speed of about 10,000 rpm, the residual twist was about 1 ,400 twists per one meter of yam length. Subsequently, the nanofibrous yarn 54 is wound onto the bobbin 71 in the winding device 7 in a known manner.

To increase the strength and uniformity of the produced nanofibrous yam 54, it is advantageous to round the fluffy band 51 of nanofibers on the surface of the drum collector 41 before withdrawing the fluffy band 51 of nanofibers from the electrically neutral drum collector 41 , thereby achieving the narrowing of the fluffy band 51 of nanofibers, a more uniform action of the forces holding the nanofibers 5 on the surface of the electrically neutral drum collector 41 and the easier withdrawing of the nanofibers 5 in the withdrawal area 4101 of the electrically neutral drum collector 41 in the entire cross section of the fluffy band 51 of nanofibers and their smooth transition into a twist triangle 52. At the same time, the rounding reduces the base of the twist triangle 52, thereby reducing the tensile forces in the circumferential parts of the fluffy band 51 of nanofibers, and thus reducing the risk of breaking of the fluffy band 51 of nanofibers during the withdrawal from the withdrawal area 4101 of the electrically neutral drum collector 41. The linear structure formed by the rounding of the fluffy band 51 of nanofibers can be used also for direct winding onto the bobbin 71 of the winding device 7 without twisting on the twisting device 6.

A further increase in the strength of the nanofibrous yam 54 produced can be achieved, for example, by twisting the nanofibrous yam 54 with a permanent twist on a suitable device (not shown).

The amount of the nanofibers 5 formed, the circumferential speed of the electrically neutral drum collector 41 and the drawing-off speed of the fluffy band 51 of nanofibers determine the linear mass of the nanofibrous yam 54 which is critical to the resulting strength of nanofibrous yam 54.

Another alternative variant of an embodiment of the device according to the invention in which the electrically neutral collector 4 is formed by a belt collector 42 arranged in the spinning chamber 3 above a rotating disk spinning electrode 11 , as shown in Figs. 5 to 7. The belt collector 42 comprises an endless conveyor belt 421 engirdling two upper cylinders 422 and two lower cylinders 423, of which at least one cylinder 422, 423 is a drive cylinder. The axes of rotation of all cylinders 422, 423 of the belt collector 42 are parallel with the axis of rotation of the disk spinning electrode 11. In the embodiment according to Figs. 5-7, the endless conveyor belt 421 moves counter-clockwise, wherein its lower branch 4211 situated between the lower cylinders 423 is arranged against the spinning area 110 of the rotating disk spinning electrode 11 and the nanofibers 5 formed in the spinning area 110 of the rotating disk spinning electrode 11 ae deposited on the lower branch of the endless conveyor belt 421 into a fluffy band 51 of nanofibers. The lower branch 4211 of the endless conveyor belt 421 thus forms the collection area 420 of the electrically neutral belt collector 42. Due to the direction of movement of the endless conveyor belt 421, in this embodiment, the fluffy band 51 of nanofibers transported to the upper branch 4212 of the endless conveyor belt 421 , whose end forms the withdrawal area 4201 of the electrically neutral belt collector 42, from which the fluffy band 51 of nanofibers is withdrawn and guided to the twisting device 6, by which a twist is imparted to it. After withdrawal, the fluffy band 51 of nanofibers tapers into a twist triangle 52 due to the action of the twist and subsequently and is subsequently formed into a nanofiber yam 54, as described in the previous variant of the device with the electrically neutral drum collector 41. This arrangement allows a larger amount of nanofibers 5 to be deposited on the electrically neutral belt collector 42, thereby forming a fluffy band 51 of nanofibers of greater thickness and weight. In addition, this arrangement provides sufficient space on the upper branch 4212 of the endless conveyor belt 421 for rounding the fluffy band 51 of nanofibers by known unillustrated rounding means. If the endless conveyor belt 421 moves in the opposite direction, the withdrawal area 4201 will be formed again at the end of the upper branch 4212 of the endless conveyor belt 421 , but according to the figures it will be on the right-hand side.

In an alternative embodiment of this arrangement which is not shown, it is possible to change the location of the withdrawal area 4201 of the fluffy band 51 of nanofibers by changing the direction of rotation of the drive cylinder of the cylinders 422, 423, around which the endless conveyor belt 421 is wrapped, and place the withdrawal area 4201 of the fluffy band 51 of nanofibers at the end of the lower branch 4211 in the direction of movement of the endless conveyor belt 421. Consequently, the deposition of nanofibers 5, formation of the fluffy band 51 of nanofibers, as well as their withdrawal takes place on the lower branch 4211 of the endless conveyor belt 421 of the electrically neutral belt collector 42, the upper branch 4212 being empty.

In the arrangement of the device according to Figs. 5 to 7, the rotating disk spinning electrode 11 can be replaced with a spinning electrode with a direct spinning area, which may consist of a belt spinning electrode 12 or a linear spinning electrode 13 formed by a linear flexible structure, which will be described hereinafter. The device with a belt spinning electrode 12 is shown in Figs. 8a to 8d. The device comprises a reservoir 2 of a polymer solution 21 , into which a rewinding shaft 8 coupled to the drive 81 extends with part of its circumference. Above the rewinding shaft 8, a blade is 121 is fixedly mounted in the spinning chamber 3 on the device frame, for example, by means of struts 82. The rewinding shaft 8 together with the blade 121, is wrapped with a spinning belt 122, 122 which extends from the polymer solution 21 and bends over the blade 121 above the rewinding shaft 8. The spinning belt 122 carries the polymer solution 21 out of the reservoir 2 and the bending of the spinning belt 122 forms the spinning area 120 of the belt spinning electrode 12, which is connected to an AC voltage source. Above the spinning area 120 of the belt spinning electrode 12, at least along its entire width, is arranged the lower branch 4211 of the endless conveyor belt 421 of the electrically neutral belt collector 42, as shown in Fig. 8b.

The electrically neutral belt collector 42 is configured in the same manner as in the embodiment according to Figs. 5-7. The belt collector 42 comprises an endless conveyor belt 421 engirdling two upper cylinders 422 and two lower cylinders 423, of which at least one cylinder 422, 423 is a drive cylinder. The axes of rotation of all cylinders 422, 423 of the belt collector 42 are perpendicular to the axis of rotation of the rewinding shaft 8. The endless conveyor belt 421, in the embodiment of Figs. 8a, 8b, moves counter-clockwise, wherein its lower branch 4211 which is situated between the lower cylinders 423 is arranged against the spinning area 120 of the belt spinning electrode 12 and the nanofibers 5 formed in the spinning area 120 of the belt spinning electrode 12 are deposited into a fluffy band 51 of nanofibers on the lower branch of the endless conveyor belt 421. The lower branch 4211 of the endless conveyor belt 421 represents the collection area 420 of the electrically neutral belt collector 42. In this embodiment, with respect to the direction of the movement of the endless conveyor belt 421 , the fluffy band 51 of nanofibers is transported to the upper branch 4212 of the endless conveyor belt 421 , whose end forms the withdrawal area 4201 of the electrically neutral belt collector 42, from which the fluffy band 51 of nanofibers is withdrawn and guided in the direction of the arrow to the twisting device 6, by which it is imparted a twist. After withdrawal, the fluffy band 51 of nanofibers is tapered into a twist triangle 52 due to the twist action and subsequently a nanofibrous yarn 54 is formed from it, as described in the previous variant of the device with the electrically neutral drum collector 41. As already described above, the direction of the movement of the endless conveyor belt can be reversed and the above- mentioned arrangement is only side reversed.

An alternative embodiment of this arrangement of the device for producing nanofibrous yam is shown in Figs. 8c and 8d. In this embodiment, the direction of rotation of the drive cylinder of the cylinders 422, 423, around which the endless conveyor belt 421 is wrapped so that the endless conveyor belt moves clockwise, as shown in Fig. 8d. The other parts of the device and their functions remain the same as in the embodiment of Figs. 8a and 8b. As a result, the deposition of nanofibers 5, formation of the fluffy band 51 of nanofibers, as well as their withdrawal take place on the lower branch 4211 of the endless conveyor belt 421 of the electrically neutral belt collector 42, the upper branch 4212 being empty. The withdrawal area 4201 of the electrically neutral belt collector 42, in which the fluffy band 51 of nanofibers is withdrawn from the endless conveyor belt 421 is therefore at the end of the lower branch 4211 of the endless conveyor belt 421. From the withdrawal area 4201, the fluffy band 51 of nanofibers is fed in the direction of the arrow to the twisting device, where it is twisted into a nanofibrous yam 54, as described above. As already described above, the direction of the movement of the endless conveyor belt can be reversed and the above-mentioned arrangement is only side reversed.

In the embodiment with the linear spinning electrode 13, the linear spinning electrode 13 consists of an endless linear flexible structure which is in the embodiment shown in Figs. 9a to 9d mounted on two rotatably mounted pulleys 131 coupled to an unillustrated drive. At least one of the pulleys 131 extends with part of its circumference to the reservoir 2 of the polymer solution 21. In the embodiment shown, each pulley 131 has its reservoir_2 of the polymer solution 21

The linear flexible structure consisting of the linear spinning electrode 13 may be formed by, for example, a string, a belt, a strap, or a structure with a more fragmented surface composed of several mutually intertwined parts, such as a cable, a cord, a multi-core formation, etc. Similar to the previous embodiments, a spinning area 130 of finite length is formed on the linear spinning electrode 13 between the pulleys 131. The spinning area 130 is connected to an AC electric voltage source by one of known methods.

Above the spinning area 130 of the linear spinning electrode 13 is arranged an electrically neutral belt collector 42, whose lower branch 4211 is arranged at least above the entire length of the spinning area 130 of the linear spinning electrode 13, as shown in Figs. 9b and 9d. The electrically neutral belt collector 42 is configured similarly as in the previous embodiments and comprises an endless conveyor belt 421 engirdling two upper cylinders 422 and two lower cylinders 423, of which at least one cylinder 422, 423 is a drive cylinder. The axes of rotation of all cylinders 422, 423 of the belt collector 42 are parallel with the axes of the pulleys 131. In the embodiment according to Figs. 9a, 9b, the endless conveyor belt 421 moves counter-clockwise, wherein its lower branch 4211 situated between the lower cylinders 423 is arranged against the spinning area 130 of the linear spinning electrode and the nanofibers 5 formed in the spinning area 130 of the linear spinning electrode 13 are deposited on the lower branch of the endless conveyor belt 421 into a fluffy band 51 of nanofibers. The lower branch 4211 of the endless conveyor belt 421 thus represents the collection area 420 of the electrically neutral belt collector 42. In this embodiment, with respect to the direction of movement of the endless conveyor belt 421, the fluffy band 51 of nanofibers is transported to the upper branch 4212 of the endless conveyor belt 421 , whose end forms the withdrawal area 4201 of the electrically neutral belt collector 42, from which the fluffy band 51 of nanofibers is withdrawn and guided in the direction of the arrow into the twisting device 6 and by twisting it, a nanofibrous yam is formed. As described above, the direction of the movement of the endless conveyor belt can be reversed and the above-mentioned arrangement is only side reversed.

An alternative embodiment of this arrangement of the device for producing nanofibrous yam is shown in Figs. 9c and 9d. In this embodiment, the direction of the movement of the endless conveyor belt 421 is changed, and so it moves clockwise, as shown in Fig. 9d. The other parts of the device and their functions remain the same as in the embodiment according to Figs. 9a and 9b. As a result, the deposition of nanofibers 5, formation of the fluffy band 51 of nanofibers and their withdrawal on the lower branch 4211 of the endless conveyor belt 421 of the electrically neutral belt collector 42, the upper branch 4212 being empty. The withdrawal area 4201 of the electrically neutral belt collector 42 is thus at the end of the lower branch 4211 of the endless conveyor belt 421. From the withdrawal area 4201, the fluffy band 51 of nanofibers is fed in the direction of the arrow to the twisting device and a nanofibrous yam is formed by twisting it. As described above, the direction of movement of the endless conveyor belt can be reversed and the above-mentioned arrangement is only side reversed.

In the embodiment with the linear spinning electrode 13, the endless linear flexible structure can be replaced with a linear flexible structure of finite length, which is wound on pulleys 131. Both pulleys 131 extend in this embodiment with their lower parts of its circumference to the polymer solution 21. The pulleys 131 are coupled to a known unillustrated reciprocating drive and rotate alternately in both directions, wherein the linear flexible structure is held in tension between them.

Industrial applicability

Yarns and threads made of fibers are the most commonly used construction elements in the textile industry for the production of various types of textiles, e.g., fabrics and knitwear. The use of 100% nanofibrous yarns in the conventional way of textile production means significant potential for the production of so-called nanotextiles, which exhibit excellent optical, electrical, mechanical and biological properties due to the effects associated with their extremely large specific surface area and low flexibility (bending modulus).

Nanofibrous yams will find application as structural units of surgical threads, tissue carriers for the repair of nerves, tendons, bones and blood vessels. They have the potential to become structural elements for harvesting and storage of energy, for actuators of mechatronic devices, for sensors and filters. List of references

1 spinning electrode

11 rotating disk spinning electrode

110 spinning area of the rotating disk spinning electrode

12 belt spinning electrode

120 spinning area of the belt spinning electrode

121 blade

122 spinning belt

13 linear spinning electrode

130 spinning area of the linear spinning electrode

131 pulley

2 reservoir of polymer solution

21 polymer solution

3 spinning chamber

31 spinning space

4 electrically neutral collector

40 collection area of the electrically neutral collector

401 withdrawal area of the electrically neutral collector

41 drum collector

410 collection area of the drum collector

4101 withdrawal area of the drum collector

42 belt collector

420 collection area of the belt collector

4201 the withdrawal area of the belt collector

421 the endless conveyor belt

4211 lower branch of the endless conveyor belt

4212 upper branch of the endless conveyor belt

422 upper cylinders

423 lower cylinders

5 nanofibers

51 fluffy band of nanofibers

52 twist triangle

54 nanofibrous yam

6 twisting device

7 winding device

71 bobbin

8 rewinding shaft

81 drive

82 struts

E electric field intensity