A METHOD OF PRODUCING A LINEAR NANOFIBROUS STRUCTURE IN AN ALTERNATING ELECTRIC FIELD, A DEVICE FOR PERFORMING THIS METHOD AND A DEVICE FOR PRODUCING A NANOFIBROUS THREAD

A method of producing a linear fibrous structure in an alternating electric field by spinning of a polymer solution or polymer melt on a spinning electrode, in which nanofibers are formed from the polymer solution or melt in a spinning area created on the spinning electrode and are carried away from it by the action of the electric wind. In the spinning area, a narrow flat linear structure of polymer solution is formed with a finite length. The spinning area is open in the spinning direction and in the central part thereof. The nanofibers are formed and move away from the spinning area in a flat structure in which they gradually lose their kinetic energy. In a place with zero kinetic energy, nanofibers form a linear virtual collector in which nanofibers are formed into a ribbon of nanofibers.

TECHNICAL FIELD

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

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

In addition, the invention relates to a device for producing a nanofibrous thread.

BACKGROUND ART

In the preparation of a nanofibrous threads, oriented and twisted nanofibers are the basis for their construction. Currently, numerous methods have been developed in the field of electrospinning to obtain oriented and twisted nanofiber bundles. This development can be attributed to two main aspects, that is, to obtaining highly ordered nanofibers by improving a collecting device or by adding an auxiliary electrode.

CN111118677 discloses production of nanofibrous yarn by 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. Inside the lower opening of the cavity is mounted an electrostatic rotating spinning electrode connected to a high voltage 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.

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 air flow, they are carried up into the throat of the cylindrical collector, which rotates, and due to its rotation and the supplied air flow, an air vortex is created, which twists the nanofibers into yarn, which is further 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 air vortex, so there is no parallelization of the nanofibers before twisting, the twisting is uneven and, as a result, their strength and appearance is variable.

CN111286792 describes a horizontal arrangement of an electrostatic spinning device comprising a rotating jet spinning electrode and a coaxially arranged collecting electrode formed by a hollow cylinder and arranged against the jet spinning electrode, wherein a DC electric field is formed between the spinning and collecting electrodes. At least two air jets directed towards the axis of the collecting electrode are arranged around the rotating jet spinning electrode. The nanofibers produced by the rotating jet spinning electrode are carried by the electric wind to the hollow cylinder forming the collecting electrode, wherein due to the rotation of the jet spinning electrode and air flows from the jets, they are twisted into yarn 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.

The disadvantages of electrostatic production of nanofibrous yarn are in both cases 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 created 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 using vacuum adsorption in the Venturi collection system. 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 the length and degree of orientation of the fibers in the nanofibrous yarn. Existing electrospinning technologies for the continuous production of nanofibrous yarns have a low yield and poor quality of the produced nanofibrous yarns.

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 located 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 the 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 electrical charge and/or with sections with opposite electrical 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 strip which moves freely in space away from the spinning electrode in the direction of the gradient of the electric fields.

Spinning by the alternating high electrical voltage method is another way of producing nanofibers, alternative to electrostatic spinning. However, its yield is not yet at a level to produce purely nanofiber 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 alternating 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 nanofiber yarn 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 yarn with potential for industrial applications. Current methods of preparing nanofibrous yarns 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.

Classic yarn with a permanent twist is produced, for example, on ring or rotor spinning machines, where at first, a ribbon of parallel fibers is formed and subsequently the ribbon is twisted, creating yarn with high tensile strength and uniform twist. However, it is not yet possible to create yarn from nanofibers in this way.

The object of the invention is to propose a method of producing nanofibers by AC electrospinning of a polymer solution or melt, in which nanofibers would be produced in sufficient quantity and carried away from the spinning area so as to form a ribbon of nanofibers at a certain location, in which the nanofibers would be at least partially parallelized, wherein the nanofibers would have sufficient strength allowing them to be drawn off and wound on a bobbin for subsequent use or processing into textile structures using known textile technologies.

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

SUMMARY OF THE INVENTION

The object of the invention is achieved by a method of producing a linear nanofibrous structure from a polymer solution or melt in an alternating electric field on a spinning electrode, in which nanofibers are formed from the polymer solution or melt in a spinning area created on the spinning electrode and are carried away from it by the action of the electric wind, wherein the principle of the invention consists in that on the spinning electrode is formed at least one spinning area with a supercritical AC electric field intensity and a final length, from which the emerging nanofibers are carried away by the effect of the electric wind in the direction of the maximum values of the electric field gradient from the spinning area in a flat structure whose initial width is the same as the width of the linear spinning area, wherein as the electric field gradient decreases, the nanofibers lose their kinetic energy until, after losing their kinetic energy, they stop, gather and are compacted into a linear nanofibrous structure which is drawn off, with the linear weight of the linear nanofiber structure gradually increasing, while the nanofibers are at least partially parallelized and a ribbon of nanofibers is formed. Due to the high specific surface area of the nanofibers and the binding forces between the individual nanofibers, the nanofiber ribbon created in this way has sufficient cohesion, which enables it to be wound on a bobbin for subsequent technological operations, such as twisting, elongation, heat fixation, etc. By being imparted a twist, the nanofiber ribbon is formed into a nanofibrous thread.

At the point of the loss of kinetic energy of the nanofibers, a force balance of electric and gravitational forces acting on the formed nanofibers is created, thereby creating a virtual collector. Gravitational forces are caused by the mass of nanofibers and electric forces represent the sum of all electric forces acting on the nanofibers, i.e., the force of the electric wind from the spinning electrode, the force of the electric wind from other charged parts of the spinning device, the force from ionized air ions and the force from oppositely charged parts of nanofibers formed in the previous half-wave of the alternating electric field.

According to an alternative embodiment of the invention, the spinning area of the belt and linear spinning electrode is straight and the nanofibers emerging therefrom move in a planar flat structure whose thickness corresponds to the width of the spinning area and whose length corresponds to the length of the spinning area.

To produce large quantities of nanofibers, in another alternative of this embodiment, a double spinning area can be formed by increasing the width of the spinning electrode, wherein nanofibers emerging from both spinning areas move in planar flat structures which move away from each other in the direction of movement of the nanofibers. In this manner, two ribbons of nanofibers are formed on one spinning electrode, which can be further processed separately, or combined before processing.

In another alternative embodiment of the invention, the spinning area is formed by a part of a circle on the circumference of a disk spinning electrode nanofibers emerging from it move in a planar flat structure which is perpendicular to the axis of rotation of the disk spinning electrode, wherein the linear virtual collector is formed by a part of a circle.

Also in this embodiment, to produce a larger number of nanofibers, it is possible to increase the width of the spinning electrode and form a double spinning area, wherein nanofibers emerging from the two spinning areas move in conical flat structures which move away from each other in the direction of the movement of the nanofibers until the formation of virtual collectors, where they form two ribbons of nanofibers which can be further processed separately or combined before further processing.

In all the embodiments described, the created ribbon of nanofibers is wound on a bobbin, being capable of unwinding and further processing.

In order to speed up the production process, according to another alternative embodiment of the invention, a twist can be imparted to the ribbon of nanofibers before it is wound, thereby creating a nanofibrous thread. The twist imparted can be false or permanent.

The principle of the device for producing a linear nanofibrous structure in an alternating electric field from a polymer solution or polymer melt is that by setting the supercritical intensity of the alternating electric field, at least one linear spinning area is created on the surface of the spinning electrode, and above it, in the direction of the maximum values of the electric field gradient, a virtual collector is created in the area of force balance of electric and gravitational forces acting on the formed nanofibers, for stopping, collecting and compacting the nanofibers into a linear fibrous structure, to which a draw-off mechanism and winding device for winding the ribbon of nanofibers are assigned.

According to one alternative embodiment, the spinning area may be straight, with the maximum electric field gradient directed vertically upwards so that the formed nanofibers are carried vertically upwards as far as to the virtual collector.

Furthermore, the spinning electrode can be formed by a strip spinning electrode, or a linear spinning electrode formed by a linear flexible structure, for example a string, a thin tape, or a thin strap, on which the polymer solution is only on the spinning area.

If the linear flexible structure forming the spinning electrode is composed of several interlaced or intertwined parts, a shielding bar is placed under the spinning area, which can also cover the edges of the linear flexible structure, so that spinning takes place only on its upper side, open in the spinning direction.

By increasing the width of the linear flexible structure forming the linear spinning electrode and by suitably setting the intensity of the electric field, the creation of two spinning areas near the edges of the linear flexible structure is achieved. These spinning areas can be formed by protrusions on the edges of the strip, or on the edge of this strip.

In another alternative device, the spinning electrode is formed by a narrow rotating disk spinning electrode, which with the lower part of its circumference extends into the polymer solution or the melt in a reservoir, and on the free part of the circumference of the disk spinning electrode, a spinning area is formed, which is formed by part of a circle, wherein the maximum gradient of the electric field is directed from the spinning area in the radial direction and the nanofibers are carried in a planar flat structure from which a ribbon of nanofibers is formed in a virtual collector.

To increase the quantity of the nanofibers produced, the rotating disk spinning electrode is mounted on a common shaft with at least one other rotating disk spinning electrode.

An increase in the quantity of the nanofibers produced can also be achieved by arranging several rotating disk spinning electrodes one behind the other.

In another embodiment, the rotating disk spinning electrode has a larger disk width, and so two spinning areas are formed on its edges, which are formed by a part of a circle, and the maximum gradient of the electric field creates conical surface structures on the edges of the disk spinning electrode. The nanofibers in the conical surface structures are carried into virtual collectors, in which a ribbon of nanofibers is formed, wherein the conical surface structures of nanofibers move away from each other and create the letter “V” in cross-section.

According to another alternative embodiment, the spinning electrode is formed by an overflow spinning electrode, wherein the device comprises a reservoir of a polymer solution, in which the inlet of the polymer solution is placed vertically. At the upper end of the inlet, an overflow electrode is arranged, wherein the inlet is opened on its upper face and an overflow area is formed around its mouth, sloping slightly from the mouth of the inlet of the polymer solution to the edge of the overflow electrode and is terminated with a circumferential edge which forms the spinning area of the overflow spinning electrode on which nanofibers are elongated. The elongated nanofibers are carried by the action of the electric wind in the direction of the maximum electric field gradient through the spinning space in the radial direction from the circumferential edge of the overflow electrode and collected in the area of the virtual collector, where they are compacted into a material structure forming a ribbon of nanofibers, which is drawn off from the virtual collector in the tangential direction with respect to the virtual collector and further wound onto a bobbin or processed into a thread.

The created ribbon of nanofibers is taken from any of the above-mentioned spinning devices to a device for producing a nanofibrous thread which comprises a twisting means for creating a false or permanent twist and is then guided to the winding device and wound onto a bobbin.

EXAMPLES OF EMBODIMENT

The method of producing nanofibers by spinning a polymer solution or polymer melt in an alternating electric field will be described hereinafter. Since the spinning of a polymer melt proceeds in the same manner as the spinning of a polymer solution, it is only the spinning of a polymer solution that will be described further on.

In the production of nanofibers from a polymer solution to create a linear nanofiber formation, the technology of spinning in the alternating electric field is used, which is created by an alternating voltage with an amplitude of, for example, 25 to 50 kV, depending on the geometry and arrangement of the spinning electrode 1 at a frequency of, for example, 10 to 1000 Hz. The polymer solution usually consists of a solution of PVB, PCL, PVA, or other spinnable solutions.

In conventional spinning in an alternating electric field, the aim is to produce per unit of time the largest possible quantity of nanofibers, which are created over the entire working surface of a spinning electrode and are carried away from the spinning electrode by the electric wind, or possibly also by auxiliary air currents, to a collector which is neither grounded nor connected to an electric voltage source and which can be, for example, a flat textile or a linear fibrous structure which, after being coated with a nanofibrous plume, forms core composite nanofibrous yarn. The formation of nanofibers begins at a critical value of the electric field intensity, which varies depending on the type of polymer solution being spun, voltage value, gas quality in the spinning chamber and other parameters. At a lower value of the electric field intensity than the critical one, nanofibers are not formed, or their formation ceases. Therefore, in conventional spinning in an alternating electric field, using a specific design of the spinning electrode, a higher electric field intensity than the critical one, i.e. supercritical, is used, which creates an alternating electric field of high intensity on the spinning electrode, in order to eliminate the risk of interruption of the spinning process, as well as to ensure sufficient evaporation of the solvent and a sufficiently strong electric wind to transport the nanofibers to the collector.

The distribution of supercritical intensity E of the electric field for the above-mentioned conventional spinning of polymer solution Z on a narrow rotating disk spinning electrode 11 is shown in FIG. 1a for a disk diameter of 300 mm, a disk thickness of 1 mm, a polymer solution layer thickness of 0.2 mm, and a voltage amplitude of 50 kV. The supercritical value of the intensity E of the electric field for PVB polymer solution is equal to or greater than 3000 V/mm2. It is clear from the figure that the supercritical value of the intensity E of the electric field is achieved in a wide area around the circumferential part of the disk. Spinning of polymer solution Z therefore takes place on the entire circumferential surface of the disk and on the part of the disk faces near the disk circumference, and the created nanofibers are carried through the spinning space to the surface of an unillustrated collector.

In order to achieve the formation of nanofibers 5 in the alternating electric field by spinning polymer solution Z to produce a ribbon 6 of nanofibers according to the invention, it is necessary to create a linear spinning area with supercritical intensity E on the spinning electrode 1 covered with polymer solution Z, which has a finite length and is open in the spinning direction. The spinning area 10 can be straight, for example in the case of a belt, strip or cable spinning electrode, or it can be formed by a part of a circle, for example in the case of a rotating disk spinning electrode 11. At the same time, it is necessary to set the alternating electric power supply of the spinning electrode to a value at which supercritical intensity E of the electric field on the linear spinning area 10 of the respective spinning electrode 1 is created especially above its central part, so that spinning takes place predominantly in the central part of the above-mentioned spinning area 10.

This is achieved in an exemplary embodiment by distributing supercritical intensity E of the electric field for spinning polymer solution Z on the narrow rotating disk spinning electrode 11 shown in FIG. 1b for a disk diameter of 300 mm, a disk thickness of 1 mm, a polymer solution layer thickness of 0.2 mm, and a voltage amplitude of 30 kV. Compared to the previous embodiment intended for conventional spinning, due to reduction in the voltage amplitude, the area of supercritical intensity E has significantly decreased and is only above the central part of the circumferential surface of the disk. All the nanofibers 5 being formed emerge above the central part of the circumferential surface of the disk and are carried away from the rotating disk spinning electrode 11 in a planar flat structure, which is perpendicular to the axis of rotation of the disk. The nanofibers 5 stop at the same distance from the spinning electrode 11 in the region of the so-called virtual collector 7 and are not carried further.

This generally means that Taylor cones begin to form on the surface of polymer solution Z in the linear spinning area 10 of the spinning electrode 1, from which, due to the effect of a sufficiently strong alternating electric field, nanofibers 5 begin to elongate and are carried away from the spinning area of the spinning electrode in the direction of the maximum values of the electric field gradient, i.e. in the plane of the greatest density of electric field lines, in one flat structure, whereas in the area in which the repeated natural slowing down to stopping of the nanofibers occurs, a virtual collector 7 is formed, i.e. a area where the nanofibers gather and are compacted to form a ribbon 6 of nanofibers and this ribbon 6 is drawn off. As a result of the periodic change of polarity of the power supply of the spinning electrode 1, the formed nanofibers 5 in the region of the virtual collector 7 are compacted into a material structure due to the loss of speed. Since these nanofibers 5 are formed in one flat structure, a linear nanofiber structure called a ribbon 6 of nanofibers is created due to this compaction. The flat structure of nanofibers has a thickness corresponding to the width of the spinning area, which is narrow and its width varies in the interval of up to 5 mm. The length of the virtual collector 7 corresponds to the length of the spinning area on the spinning electrode 1.

If the spinning process takes place in a vertical plane as described above, the flat structure of nanofibers 5 is planar, because all the forces acting on it act in the vertical direction.

If the spinning process takes place in a plane inclined from the vertical plane, for example on both edges of belt or strip electrodes, nanofibers 5 are created in the direction of the maximum values of the electric field gradient, i.e. in a plane inclined from the vertical plane, but by the action of gravitational forces and mutual repulsive forces of nanofibers with the same charge, the nanofibers 5 are deflected and, consequently, a virtual collector 7 is formed under the surface of the electric field gradient.

If the spinning process takes place by way of forming nanofibers in a conical surface, for example, on both edges of a wide rotating disk spinning electrode 11, nanofibers 5 are formed in the direction of the maximum values of the electric field gradient. The distribution of regions of electric field intensity E is shown in FIG. 1c on the wide rotating disk spinning electrode 11, with a width of, for example, 6 mm, on the circumference of which a recess 111 is formed in the middle, whereby protrusions 112 are formed on the edges of the disk spinning electrode circumference, on which supercritical intensity E of the electric field is concentrated. As a result, two spinning areas 110 are created, one on each protrusion 112. Due to the distribution of supercritical intensity E, the nanofibers 5 in this embodiment are carried in two conical flat structures that move away from each other in the direction of movement of the nanofibers 5. The movement of the nanofibers from each other is also aided by the fact that the nanofibers 5 formed on both protrusions 112 of one disk spinning electrode 11 have the same residual electric potential at a specific time, and so they repel each other. In addition, a gravitational force acts on the nanofibers, deforming the conical flat structures, and so a virtual collector 7 is formed under the surface of the electric field gradient.

For a rotating disk spinning electrode 11 without a circumferential recess, supercritical intensity E of the electric field will be concentrated on the edges of the circumferential surface of the disk, and so the nanofibers 5 will be formed as described above. It will only be necessary to set the voltage amplitude more accurately so as to create an electric field with the supercritical intensity E in the area of the edges of the circumferential surface of the disk.

The virtual collector 7, i.e., the area with a concentration of density of nanofibers 5, is formed at the point of force balance of all electric and gravitational forces acting on the formed nanofibers 5. Electric forces represent the sum of all electric forces acting on the nanofibers 5, i.e., the force of the electric wind from the spinning electrode 1, the force of the electric wind from other charged parts of the spinning device, the force from ionized air ions and the force from oppositely charged parts of the nanofibers 5 formed in the previous half-wave of the alternating electric field and the repulsive force from consensually charged parts of nanofibers 5. By the virtual collector 7 is meant a narrow region terminating the planar structure of the nanofibers 5, being formed, where the nanofibers 5 being formed lose their movement speed when moving from the spinning area 10 of the spinning electrode 1. The reason for their slowing down is the re-polarization of the spinning electrode 1 in the second half of the period of the supplied AC voltage. The already formed nanofibers 5 carried towards the virtual collector 7 or the nanofibers 5 collected in the virtual collector 7 are left with a residual electric charge of the polarity of the previous half-wave of electric voltage, and so they are now reversed charged relative to the current polarity of the spinning electrode 1. Thus, the electric potential difference required for the initialization and progress of the spinning process in the alternating electric field is created. When starting the spinning process, an electric potential is created between polymer solution Z in the spinning area 10 of the spinning electrode 1 and the air ions in the vicinity of the spinning electrode 1.

The nanofibers slowing down to stopping in the region of the virtual collector 7 is due to the change in polarity of the supplied electrical voltage, wherein the distance of the virtual collector 7 from the spinning area 10 of the spinning electrode 1 is determined by the frequency of the supplied electrical voltage. A suitable configuration of the spinning electrode 1 and suitable setting of the amplitude, frequency and shape of the supplied electrical signal enables to create of a linear ribbon 6 of nanofibers and to ensure its uniform continuous withdrawal outside the spinning space 41 for further operations. The position of the virtual collector 7, i.e., the area where the ribbon 6 of nanofibers is formed, is mainly determined by the frequency and amplitude of the supplied electric voltage. Stable formation of the ribbon 6 of nanofibers is ensured by the creation of a force balance of all electric, mechanical and gravitational forces acting on the ribbon 6 of nanofibers in the alternating electric field. The quantity of the nanofibers 5 formed and thus the weight of the ribbon 6 of nanofibers depends on the configuration of the spinning electrode 1, the value of the electric field intensity E and the size of the spinning area 10, i.e., the surface of the spinning electrode 1 on which the above-mentioned the supercritical intensity E is achieved, i.e., on the value of the amplitude of the supplied alternating electric voltage. With the balance of electric, gravitational and mechanical forces, the weight of the ribbon 6 of nanofibers is ensured by the drawing-off speed, which can be regulated according to technological requirements.

An important element in the formation of the ribbon 6 of nanofibers is the waveform of the applied AC electrical voltage. For a more stable formation of the ribbon 6 of nanofibers, it is advantageous to shorten the time of the transition region between the positive and negative half-wave of the electric voltage, so it is most advantageous to use a rectangular or at least a trapezoidal waveform of the electric voltage, when the transition regions are shorter and the production process is therefore more stable. In the case of a rectangular waveform of the electric voltage, the magnitude of the intensity E of the electric field in the respective half-wave is constant, in the case of a sinusoidal waveform it changes.

A major advantage of the proposed method of producing nanofibers for forming the ribbon 6 of nanofibers is the homogeneity of the ribbon 6 of nanofibers, because the formation of the ribbon 6 of nanofibers in the virtual collector 7 is not influenced by any frictional forces which would affect the homogeneity. The homogeneity of the formed ribbon 6 of nanofibers is ensured by the invariability in time and an adequate amount of Taylor cones on the surface of the polymer solution in the spinning area 10 of the spinning electrode 1, from which nanofibers 5 are formed by the action of the alternating electric field. When maintaining a constant supply of the polymer solution to the surface of the spinning electrode 1 in the spinning area, the number of Taylor cones is constant, which leads to the formation of a constant quantity of nanofibers 5 and thus to obtaining a uniform ribbon 6 of nanofibers.

The ribbon 6 of nanofibers is held together due to the high specific surface area of the nanofibers 5 and the intermolecular binding forces between the individual contacting nanofibers 5. Another reason is the natural entanglement of the positively and negatively charged sections of nanofibers 5 in the area of the virtual collector 7. The cohesion of the ribbon 6 of nanofibers allows it to be wound on a bobbin for further technological operations, such as imparting a twist, stretching, heat fixation, etc. By imparting a twist, a nanofiber thread is formed from the ribbon 6 of nanofibers.

In a close-up view, the ribbon 6 of nanofibers in the virtual collector 7 area oscillates due to changes in the polarity of the AC electric voltage, electric field changes induced by changes in the electric wind and gravity. During each such movement, possibly uncompacted, i.e., insufficiently fixed or insufficiently entangled, nanofibers 5 stick to the surface of the ribbon 6 of nanofibers, from where they will not separate due to the high specific surface area, mutual entanglement and intermolecular binding forces between the individual nanofibers 5.

The weight of the ribbon 6 of nanofibers increases along its length, and thus the ratio of electric and gravitational forces changes. Therefore, for long spinning areas, or for several spinning areas which are repeated in succession and through which one ribbon 6 of nanofibers passes, a variable electric field is generated by one of the known methods, for example, by shielding the surroundings above the ribbon 6 of nanofibers being formed, or by shielding the spinning electrode 1, or by the variable shielding of the surroundings above the ribbon 6 of nanofibers being formed. The goal is to adapt the intensity of the electric field to the variable weight of the ribbon 6 of nanofibers. So, for example, in places with a higher weight of the ribbon 6 of nanofibers, increase the intensity of the electric field.

The method of producing nanofibrous thread consists in twisting the prepared ribbon 6 of nanofibers either imparting a false twist to it or a permanent twist. When being imparted with a false twist, the ribbon 6 of nanofibers passes between two clamping points, between which a twisting device is arranged, consisting of, for example, a twisting tube. The twisting device imparts the ribbon 6 of nanofibers a false twist which is untwisted downstream of the twisting device, wherein due to the high specific surface of the nanofibers 5 and the binding forces between the individual nanofibers 5, a relatively high degree of twist is preserved on the nanofibrous thread as a residual twist.

The ribbon of nanofibers can also be subjected to a permanent twist.

Imparting a twist to the ribbon 6 of nanofibers can be performed before winding it onto the bobbin, following the formation of the ribbon 6 of nanofibers, or additionally by conventional methods, when a greater twist can be imparted to the ribbon 6 of nanofibers so as to achieve a higher strength of the produced thread, which will be even better processable into textile products by classic textile technologies on textile products.

Nanofibrous threads and textile products made from them can serve as carriers of drugs or other biologically active substances for use in medicine and biomedicine, for example in the form of biological probes, skin covers, grafts, tissue carriers, the so-called scaffolds, bandages, surgical and oral threads, etc. In addition, nanofibrous threads/yarns can be used for filter media, for example for producing coil filters.

The device for performing the method described above, i.e., for producing nanofibers 5 by AC electrospinning of polymer solution Z for producing a ribbon 6 of nanofibers, comprises a spinning electrode 1, which in the first exemplary embodiment is formed by a thin 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 a reservoir 2 of the polymer solution and is coupled to a known rotary drive (not shown).

Furthermore, in the exemplary embodiment described hereinafter, the disk spinning electrode 11 rotates about a horizontal axis and is connected to a high AC voltage source 3 which has, for example, an effective voltage of 35 kV and a frequency of 50 Hz and which carries the polymer solution onto its circumference as it rotates. However, neither the effective voltage or frequency is limiting and other suitable values may be used. The surroundings of the free part of the circumference of the disk spinning electrode 11 in a spinning chamber 4 is called a spinning space 41, in which a spinning area 110 is formed on the spinning electrode 11. After delivering polymer solution Z to be spun to the spinning area 110 on the free part of the circumference of the disk spinning electrode 11, during the spinning by AC voltage, Taylor cones are formed on the surface of the polymer solution in the central part of the spinning area 110, from which nanofibers are elongated by the action of a strong electric field. The nanofibers rise radially from the spinning area 110 from the circumference of the disk spinning electrode 11 and are carried by the electric wind in one planar structure away from the free part of its circumference in the direction of the maximum gradient of the generated electric fields, wherein in the area in which repeated natural slowing down to stopping of nanofibers occurs, a virtual collector 7 is formed above the spinning area 110 around the circumference of the disk spinning electrode 11, i.e., the area where the nanofibers 5 gather, are compacted into a mass and are drawn off in the form of a ribbon 6 of nanofibers.

The virtual collector 7 is formed at the point of balance of the electric and gravitational forces acting on the formed nanofibers 5. The virtual collector 7 is the area around the disk spinning electrode 11, where the formed nanofibers 5 lose their kinetic energy when moving from the surface of the disk spinning electrode 11. The reason for their stopping is the polarity reversal of the disk spinning electrode 11 in every other half of the period of the supplied AC voltage. The formed nanofibers 5 are left with a residual electric charge of the polarity of the previous half-wave of electric voltage, so that they are now oppositely charged with respect to the current polarity of the disk spinning electrode 11. In this manner, the electric potential difference required for the initialization and progress of the AC electrospinning process is created.

For a specific spinning solution, with a constant diameter of the disk spinning electrode 11 and a constant speed of its rotation, the place of creation of the virtual collector 7 can be influenced by the frequency of the supplied AC voltage and its magnitude.

According to the technological requirements for the spinning of the processed polymer solution and the weight of the ribbon 6 of nanofibers, the intensity E of the electric field can be varied by configuring the disk spinning electrode 11, i.e., by changing the diameter of the disk, the thickness of the disk, the relief of the surface of the circumferential part of the disk, by changing the speed and direction of rotation of the disk and the speed of drawing off the ribbon 6 of nanofibers from the virtual collector 7. However, care must be taken to ensure that polymer solution Z does not dry on the circumference of the disk spinning electrode 11.

In the illustrated embodiment, the disk spinning electrode 11 rotates against the direction of drawing off the ribbon 6 of nanofibers. In this embodiment, there is a longitudinal orientation of the nanofibers 5 in the ribbon 6 and their partial parallelization, whereby by changing the ratio of the speed of rotation of the disk spinning electrode 11 and the withdrawal speed of the ribbon 6 of nanofibers, these properties can be changed according to the requirements for further use of the ribbon 6 of nanofibers. The disk spinning electrode 11 can also be rotated in the same direction as the drawing-off direction of the ribbon 6 of nanofibers, in this case the parallelization of nanofibers 5 in the ribbon 6 of nanofibers will be smaller and the nanofibers 5 will not be so oriented longitudinally.

As part of the verification of production possibilities, disk spinning electrodes with diameters of up to 500 mm and thickness of up to 5 mm were tested at rotation speeds from 10 to 30 min−1. The alternating electric field was formed by AC voltage with an amplitude of 20 to 50 kV depending on the geometry and arrangement of the spinning electrode 1 at frequencies ranging from 10 to 100 Hz. Polymer solution Z usually consists of a solution of PVB, PCL, PVA, or other polymer solutions spinnable in an alternating electric field.

The thin rotating disk spinning electrode 11 is shown in cross-section in FIGS. 1b and 2a, and in a view in FIG. 3, from which it can be seen that the nanofibers 5 formed on the circumference of the electrode 11 are carried away from the electrode 11 in a radial direction, that is, perpendicularly to its axis of rotation in the direction of the maximum gradient of electric forces, which is indicated by an arrow.

FIG. 2b shows a cross-section of a rotating disk spinning electrode 11 with a greater thickness, for example 6 mm, where one spinning area 110, is formed on each edge of the disk spinning electrode 11 in which Taylor cones are formed. In view, this electrode is shown in FIG. 4. Nanofibers 5 are formed at both edges and are carried away from them by the electric wind in the direction of the maximum values of the electric field gradient, which are indicated by arrows, and form two conical flat structures that move away from each other, as shown in FIG. 4. In addition, the nanofibers 5 produced on both edges of the disk spinning electrode 11 have the same residual electric potential, so they tend to repel each other and not connect to each other, further aiding the movement of the two conical flat structures away from each other. It is evident from the cross-section of FIG. 2b and the view of FIG. 4 that the nanofibers 5 are carried in a “V” shape away from the disk spinning electrode 11, their path being perpendicular to the surface of the polymer solution in the nanofiber forming region. Thus, the nanofibers 5 are not carried away from the surface of the disk spinning electrode 11 in flat planar structures, but in two conical flat structures which move away from the surface of the disk spinning electrode 11. Consequently, the mutual distance of the virtual collectors 7 is greater than the thickness of the disk spinning electrode 11, as shown in FIG. 4. In addition, the gravitational force acts on the nanofibers 5 and deforms the conical flat structures. As a result, the virtual collector 7 is formed below the surface of the electric field gradient. Both ribbons 6 of nanofibers produced in virtual collectors 7 have the same properties as described above and can be further wound separately, or combined and wound together, or brought to a device for producing a nanofibrous yarn which will be described further on.

The wide disk spinning electrode 11 can be further improved by a recess 111 formed in the middle of the circumferential surface, so that the edges of the circumferential surface adjacent to the faces form protrusions 112 on which the intensity E of the electric field is concentrated, thereby creating two spinning areas 110. Since the intensity E of the electric field is concentrated at the protrusions 112, the spinning areas 110 with the supercritical electric field intensity are narrowed compared to the previous embodiment of the wide disk spinning electrode 11. Also in this embodiment, the nanofibers 5 are carried away from the surface of the disk spinning electrode 11 in two conical flat structures in the direction of the maximum gradients of electric forces, which are indicated by arrows. The conical flat structures move away from the surface of the disk spinning electrode 11, so consequently, the mutual distance of the virtual collectors 7 is greater than the thickness of the disk spinning electrode 11. This is also aided by the repulsive forces between the equally charged nanofibers 5. In addition, the gravitational force acts on the nanofibers 5, deforming the conical flat structures, and so the virtual collector 7 is formed below the surface of the electric field gradient. Both ribbons 6 of nanofibers have the same properties as described above and can be further wound separately, or combined and wound together, or brought to the device for producing nanofibrous yarn, which will be described hereinafter.

Another alternative arrangement of the device for producing a ribbon 6 of nanofibers is shown in FIG. 5, where two disk spinning electrodes 11 are arranged on a common shaft. Each of the disk spinning electrodes 11 works in the same way as a separate disk spinning electrode 11, as is shown in FIG. 1 and described above. The device produces two ribbons 6 of nanofibers that can be wound separately or combined and wound together. From the illustrated arrangement, it is apparent that the number of disk spinning electrodes 11 can be greater.

In this embodiment, a different polymer solution may be used for each disk spinning electrode 11, so that when the fabricated ribbons 6 of nanofibers are combined, a composite of nanofibers is formed from the nanofibers 5 from two or more different polymers.

To produce one ribbon 6 of nanofibers with a higher specific gravity, the disk spinning electrodes 11 can be arranged one behind the other, as shown in FIG. 6a in front view and in FIG. 6b in a plan view, showing three disk spinning electrodes 11a, 11b, 11c, each of which operates in the same way as a separate disk spinning electrode 11 as shown in FIG. 1b, 2a and FIG. 3 and described above. In particular, due to the shortening of the length of the spinning device, the disk spinning electrodes 11a, 11b, 11c are partially offset from each other, so that in the front view, the second disk spinning electrode 11b overlaps the front part of its circumference with the rear part of the circumference of the first disk spinning electrode 11a and with its rear part it overlaps the front part of the circumference of the third disk spinning electrodes 11c. By the mutual offset of the disk spinning electrodes 11a, 11b, 11c, the sagging of the ribbon 6 of nanofibers between the disk spinning electrodes 11a, 11b, 11c is reduced. Spinning takes place in the upper part of the individual disk spinning electrodes 11a, 11b, 11c, wherein the ribbon 6 of nanofibers is drawn off from the first disk spinning electrode 11a over the second disk spinning electrode 11b and the third disk spinning electrode 11c to be wound on a bobbin or to be processed subsequently. Increasing the electric field intensity along the length of the unwound ribbon 6 of nanofibers is achieved, for example, by reducing the thickness of successive disk spinning electrodes 11a, 11b, 11c, or by adjusting the high AC voltage on the individual disk spinning electrodes.

Another alternative of the device for producing a ribbon 6 of nanofibers by AC electrospinning is a device with a belt spinning electrode 12 shown in FIGS. 7a, 7b. The device comprises a reservoir 2 of the polymer solution, into which extends a rewinding shaft 8 by the lower part of its circumference, the rewinding shaft 8 being coupled to a drive 81. Above the rewinding shaft 81, in the spinning chamber 4 on the frame of the device, a blade 121 is fixedly mounted for example by means of struts 82. The rewinding shaft 81, together with the blade 121, is wrapped by an endless belt 122 which emerges from the polymer solution 21 and bends over the rewinding shaft 8 over the blade 121. The belt 122 carries polymer solution Z from the reservoir 2, wherein the bending of the belt 122 forms the spinning area 120 of the belt spinning electrode 12, which is connected to an AC voltage source. An AC voltage can be supplied to polymer solution Z in the reservoir 2 or to the blade 121. Taylor cones are formed on the spinning area 120 of the belt spinning electrode 12, from which nanofibers 5 are elongated, which are carried upwards to the virtual collector by the electric wind 7, moving through the spinning space 41 in one planar flat structure. In the place of the virtual collector 7, the nanofibers 5 gather and are compacted into a material formation forming a ribbon 6 of nanofibers, which is drawn from the virtual collector 7 in a known manner, not shown in detail, and wound on a bobbin, or is brought to the device for producing a nanofiber thread, which will be described below.

Similar to the disk spinning electrode 11, the width of the edge 122 can be greater, so that on the wide strip spinning electrode 12, two spinning areas 120 on both of its edges, on which Taylor cones are formed, and the nanofibers 5 are carried away from the spinning areas 120 in the direction of the maximum gradient of the electric fields, in two planar flat structures that form the letter “V” in cross-section, to the regions of virtual collectors 7, the mutual distance of which is greater than the width of the edge 122 of the belt spinning electrode 12. In this device, two ribbons 6 of nanofibers are formed, which have the same properties and can be further wound separately or can be combined and wound together or can be fed to a device for producing a thread. This embodiment is not shown. The conical surfaces will be deformed by the action of gravity as in the previous cases.

Another alternative of the device for producing a ribbon 6 of nanofibers by AC electrospinning is a device with an overflow spinning electrode 13 shown in FIGS. 8a, 8b. The device comprises a reservoir 2 of polymer solution Z, in which an inlet 131 of polymer solution Z is vertically arranged. An overflow electrode 13 is arranged at the upper end of the inlet 131 of the polymer solution, and the inlet 131 opens into the upper face of the overflow electrode 13. Around the mouth of the inlet 131 of the polymer solution, an overflow surface 132 is formed, sloping slightly from the mouth of the inlet 131 of the polymer solution to the edge of the overflow electrode 13 and ending in a circumferential edge 133 on which are formed Taylor cones from which the nanofibers 5 are elongated. The elongated nanofibers 5 are carried by the electric wind through the spinning space 41 in the radial direction away from the circumferential edge 133 of the overflow electrode 13 and gather in the region of the virtual collector 7, where they are compacted into a material structure forming a ribbon 6 of nanofibers, which is drawn off from the virtual collector 7 in the tangential direction and further wound onto an unillustrated bobbin or processed into a thread. In fact, the virtual collector 7 is formed at a point of balance of electric and gravitational forces, wherein the electric wind force from the inlet 131 of polymer solution Z acts in an upward direction, so that a conical flat structure directed upwards is formed. This structure is further deformed by the action of the gravitational force.

Another alternative of the device for producing a ribbon 6 of nanofibers by AC electrospinning is a device in which the linear spinning electrode 14 is formed by an infinite linear flexible structure which, in the first embodiment, is mounted on two rotatably mounted bobbins 141 coupled to an unillustrated drive. At least one of the bobbins 141 extends with a part of its circumference into the reservoir 2 of polymer solution Z. In the illustrated embodiment, each bobbin 141 has its own reservoir 2 of the polymer solution.

The linear flexible structure which constitutes the linear spinning electrode 14 can be formed, for example, by a string, a strip, a strap, or a structure with a more fragmented surface composed of several mutually intertwined or interlaced parts, such as a cable, a cord, a multi-core structure, etc. As in previous embodiments, on the linear spinning electrode 14 is formed a spinning area 140 having a finite length, which is open in the spinning direction. In the central part of the spinning area 140, a narrow flat structure of polymer solution Z is formed, and the intensity E of the electric field is set to a supercritical value at which nanofibers 5 are formed. The nanofibers 5 move from the spinning area 140 in a flat structure in the direction of the maximum gradient of electric forces, that is, in the illustrated embodiment, in a vertical plane. The nanofibers 5 gradually lose their kinetic energy and at the point of zero kinetic energy the nanofibers 5 form a linear virtual collector 7 in which the nanofibers 5 stop, gather and are compacted into a ribbon 6 of nanofibers. The linear flexible structure forming the linear spinning electrode 14 is endless and, in the embodiment according to FIG. 9, it is arranged on two bobbins 141 which are provided with grooves for the temporary mounting of the linear spinning electrode 14, wherein the dimensions and shape of the cross-section of the groove corresponds to the dimension and shape of the linear spinning electrode 14. The bobbins 141 are mounted with a part of their circumference in polymer solution Z. The section of the linear spinning electrode 14 between the bobbins 141 forms the spinning area 140. In an embodiment of the linear spinning electrode 14 in which polymer solution Z is in the spinning area 140 on the entire circumference of the linear spinning electrode 14, as shown in FIG. 9c, a shielding bar 142 is arranged below the spinning area 140. The shielding bar 142 prevents the creation of supercritical value E of the electric field outside the upper part of the linear spinning electrode 14, so that in some cases the shielding bar 142 also surrounds the side parts of the linear spinning electrode 14. All the formed nanofibers 5 then arise especially in the middle of the spinning area 140, which is straight, and are carried upwards from the spinning area 140 in the direction of the maximum gradient of the electric field in a planar flat structure in the vertical direction, wherein they gradually lose their kinetic energy and at a point with zero kinetic energy, the nanofibers 5 form a linear virtual collector 7, in which the nanofibers 5 stop, gather and are compacted into a linear ribbon 6 of nanofibers, which is drawn off.

In FIGS. 10a, 10b, the linear spinning electrode 14 is also formed by an endless linear flexible structure. In this embodiment, one common reservoir 2 of the polymer solution is used, into which both pulleys 141 extend with a part of their circumference. The linear spinning electrode 14 moves in one direction and at the end of the spinning area 140 wraps around a return pulley 141, returns to the reservoir 2 of the polymer solution and re-enters the spinning area 140 through a delivery pulley 141. In this embodiment, too, the shielding bar 142 can be used for some linear flexible structures. The part described above applies to linear spinning electrodes 14 formed by narrow linear flexible structures to which polymer solution Z is applied to their entire circumference.

In the embodiment according to FIG. 11, the linear spinning electrode 14 is formed by a wide strip 143 in the central part of which is formed a recess 1431 which creates protrusions 1432 on the edges of the strip. On the protrusions 1432, similarly to the embodiment according to FIG. 2c, spinning areas are formed. From both spinning areas 140, the nanofibers are entrained in the direction of the maximum gradient of the electric fields, in two flat planar structures that form the letter “V” in cross-section, to the areas of virtual collectors 7, the mutual distance of which is greater than the distance of the protrusions 1432. In this device, two ribbons 6 of nanofibers are created, which have the same properties and can be further wound separately, or they can be combined and wound together, or they can be fed to the device for producing thread.

In the embodiment according to FIG. 12, the linear spinning electrode 14 is formed by a flat strip 144, in which the spinning areas are formed on its edges 1441. Since the thickness of the strip 144 is small in comparison to its width, the maximum electric field gradient is directed from the edges of the strip to the sides. Another reason is the fact that the environment above and below the flat strip 144 is the same, so there is no deviation of the maximum electric field gradient.

Thus, two planar flat structures are formed from the produced nanofibers which end in the corresponding virtual collectors (not shown), where two ribbons of nanofibers are formed and drawn off as in the previous embodiments. Due to the action of gravitational forces, the planar flat structures will be deformed by these forces, as in the other embodiments.

The device for continuous production of a nanofibrous thread 60 from a ribbon 6 of nanofibers will be explained and described in combination with a rotating disk spinning electrode 11 for producing a ribbon of 6 nanofibers, as shown in FIG. 13. The ribbon 6 of nanofibers is conveyed from the virtual collector 7 of the disk spinning electrode 11 to the device 9 for producing a nanofibrous thread 60, which in the illustrated embodiment comprises a transfer pulley 91 downstream of which a first draw-off mechanism of the ribbon 6 of nanofibers is arranged in the direction of movement of the ribbon 6 of nanofibers. A twisting device 93 for creating a false twist is arranged downstream of a first draw-off mechanism of the ribbon 6 of nanofibers, downstream of which is arranged a second draw-off mechanism 94, downstream of which a drying and/or fixing unit 95 is included, downstream of which there is a third draw-off mechanism 96, downstream of which a winding device 97 is arranged.

The ribbon 6 of nanofibers is drawn off from the virtual collector 7 of the disk spinning electrode 11 through the transfer pulley 91 by the first draw-off mechanism 92 and enters the twisting device 93, in which it passes through a twisting member 931, for example, through a twisting pipe by which a false twist is imparted to it. From the twisting device 93, the twisted ribbon 6 of nanofibers is drawn off by the second draw-off mechanism 94. The twist is imparted to the ribbon 6 of nanofibers by the twisting member 931 of the twisting device 93 between two clamping points, formed by the first draw-off mechanism 92 and the second draw-off mechanism 94. Between the first draw-off mechanism 92 and the twisting device 93 the twist is formed and between the twisting device 93 and the second draw-off mechanism 94 the twist is untwisted, wherein due to the high specific surface area of the nanofibers 5 and the binding forces between the nanofibers 5, even after untwisting, a relatively high degree of twist is retained as a residual twist, thereby forming a nanofibrous thread 60. The nanofibrous thread 60 is withdrawn from the second draw-off mechanism 94 by the third draw-off mechanism 96 through the drying and/or fixing unit 95, in which the remaining solvent is evaporated and, if necessary, the nanofibrous thread 60 is thermally fixed. From the third draw-off mechanism 96, the nanofibrous thread 60 is led to the winding device 97, in which it is wound onto a bobbin by some of the known methods.

The ribbon of nanofibers may be produced on any of the above-described devices.

The device 9 for producing a nanofibrous thread 60 from a ribbon 6 of nanofibers may be configured also in another suitable manner, for example, it may comprise a device for forming a permanent twist.

Alternatively, the production of a nanofibrous thread from a ribbon of nanofibers may be performed on a special device from a ribbon of nanofibers wound on a bobbin in the subsequent operation.

INDUSTRIAL APPLICABILITY

Using the method of producing nanofibers by AC electrospinning according to the invention it is possible to produce a sufficient quantity of nanofibers and create a ribbon of nanofibers from them, which is capable of being drawn off and wound onto a bobbin, wherein it is also capable of being unwound from the bobbin for the purpose of its use or further processing.

LIST OF REFERENCES