Device and method for production of nanofibrous and/or microfibrous layers having an increased thickness uniformity

Abstract

Device for the production of nanofibrous and/or microfibrous layers having an increased thickness uniformity by spinning a liquid material (3), said device comprising: a collecting electrode (6), a spinning nozzle (1) for dispensing the liquid material (3) to be spun, an assembly for guiding the collecting electrode (6) and/or for guiding a base strip (5) along the collecting electrode (6) or adjacent to it, such that—in the area faced by the outlet orifice (10) of the spinning nozzle (1)—the collecting electrode (6) and/or the base strip (5) move(s) in the direction (MD) spaced from the outlet orifice (10) of the spinning nozzle (1), a power supply for generating a voltage of 10 to 150 kV between the collecting electrode (6) and the spinning nozzle (1), at least one body (2), which moves along the liquid surface to destabilize the locations of the points where fibres (4) are formed on the surface of the liquid material (3) at the outlet orifice (10) of the spinning nozzle (1). The nanofibrous and/or microfibrous layers having an increased thickness uniformity are produced by spinning a liquid material (3) in an electrostatic field, wherein a body (2) is moved along the surface of the spun liquid in order to destabilize positions of locations, where the fibers originate.

Claims

1. A device for the production of nanofibrous and/or microfibrous layers having an increased thickness uniformity by spinning a liquid material, said device comprising: a collecting electrode, a spinning nozzle for dispensing the liquid material to be spun, the spinning nozzle being provided with at least one outlet orifice, which faces the collecting electrode, an assembly for guiding the collecting electrode and/or for guiding a base strip along the collecting electrode or adjacent to it, such that—in an area faced by the outlet orifice of the spinning nozzle—the collecting electrode and/or the base strip move(s) in the direction (MD) spaced from the outlet orifice of the spinning nozzle, a power supply for generating a voltage of 10 to 150 kV between the collecting electrode and the spinning nozzle, at least one body for destabilizing locations of points where fibres are formed on the surface of the liquid material at the outlet orifice of the spinning nozzle, and an assembly for repeated guiding of the body along the outlet orifice or orifices of the spinning nozzle.

2. The device according to claim 1, wherein the collecting electrode has a form of a foil having a surface resistivity ranging between 0.1 and 100,000 Ohm/square.

3. The device according to claim 1, wherein the assembly for repeated guiding of the body along the outlet orifice or orifices of the spinning nozzle comprises a driving unit and an element for guiding the body along a trajectory extending in parallel to that edge of the spinning nozzle which comprises the outlet orifice or orifices, at a distance from that edge of the spinning nozzle ranging between 0 and 50 mm.

4. The device according to claim 1, wherein the assembly for guiding the collecting electrode and/or for guiding the base strip comprises a driving unit adapted for guiding the collecting electrode and/or for guiding the base strip at least in the area, which is faced by the outlet orifice or orifices of the spinning nozzle, at a speed of at least 18 m/h.

5. The device according to claim 1, wherein the assembly for repeated guiding of the body in along the outlet orifice or along a plurality of the outlet orifices of the spinning nozzle comprises a pneumatic driving unit for the body and/or further comprises at least one sensor for scanning the position of the body in at least one range of movement thereof.

6. A method for producing nanofibrous and/or microfibrous layers having an increased thickness uniformity by spinning a liquid material, said method comprising the following steps: preparing a collecting electrode and a spinning nozzle, the latter being provided with at least one outlet orifice facing the collecting electrode, and an assembly for guiding the collecting electrode and/or for guiding a base strip along the collecting electrode or adjacent to the collecting electrode, feeding the liquid material to be spun into the spinning nozzle, generating voltage ranging between 10 and 150 kV between the spinning nozzle and the collecting electrode to enable formation of nanofibres and/or microfibres, the collecting electrode and/or the base strip being guided in the direction (MD) and spaced from the outlet orifice of the spinning nozzle, and repeatedly guiding a body along the outlet orifice or orifices of the spinning nozzle and along the surface of the liquid material to cause repeated displacement of the locations of the points, where the fibres are formed on the surface of the liquid material being fed into said outlet orifice or orifices.

7. The method according to claim 6, wherein the body is guided along the outlet orifice at least once in 10 seconds.

8. The method according to claim 6, wherein the base strip is guided between the collecting electrode and the outlet orifice of the spinning nozzle at a speed of at least 18 m/h.

9. The method according to claim 6, wherein the liquid to be spun, which is fed into the spinning nozzle, is a homogeneous or heterogeneous mixture containing a spinnable polymeric substance selected from the group comprising hyaluronic acid, polyethylene oxide, polyethylene glycol, polyvinyl alcohol, polyvinyl pyrrolidone, collagen, gelatin, chitin, chitosan, heparin, inulin, fibrin, fibrinogen, pullulan, lignin, starch, agar, alginate, dextran, glycogen, beta-glucan, chondroitin sulphate, cellulose, polycaprolactone, polymers and co-polymers of lactic and glycolic acids, polyurethane, polyacrylonitrile, nylon or a combination thereof.

10. The method according to claim 6, wherein the collecting electrode and/or the base strip is guided in the machine direction (MD) in the form of an endless belt.

11. The device according to claim 4, wherein the speed is at least 50 m/h.

12. The device according to claim 4, wherein the speed is at least 60 m/h.

13. The method according to claim 8, wherein the speed is at least 50 m/h.

14. The method according to claim 8, wherein the speed is at least 60 m/h.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is further described with reference to the exemplary embodiments and to the accompanying drawings, where FIG. 1A to 1D schematically show the exemplary arrangements described in the present document and the results obtained by means of such arrangements, including graphs.

(2) FIG. 2A schematically shows the principle of destabilizing the locations of the points, where fibres are formed, by moving a body immediately under the surface of the solution to be spun; FIG. 2B shows a similar scheme where the body is moved immediately over the surface of the solution to be spun; and FIG. 2C schematically shows an aperture-type spinning nozzle along with a movable body.

(3) FIG. 3 shows a spinning nozzle comprising an array of outlet orifices in a schematical view.

(4) FIG. 4 shows an exemplary embodiment of the device according to the invention in a schematical view, the viewing direction being from the collecting electrode.

(5) FIG. 5 shows a backlight photograph of a layer that has been obtained in a process described with reference to the Example 1.

(6) FIG. 6 shows a backlight photograph of a layer that has been obtained in a process described with reference to the Example 2.

(7) FIG. 7 shows a backlight photograph of a layer that has been obtained in a process described with reference to the Example 3.

(8) FIG. 8 shows a backlight photograph of a layer that has been obtained in a process described with reference to the Example 4.

(9) FIG. 9 shows a backlight photograph of a layer that has been obtained in a process described with reference to the Example 5.

(10) FIG. 10 shows a backlight photograph of a layer that has been obtained in a process described with reference to the Example 6.

EXEMPLARY EMBODIMENTS OF THE INVENTION

(11) FIG. 1A illustrates a spinning process wherein the material coming out of the nozzle 1 is deposited on a stationary base strip 5, FIG. 1B illustrates a spinning process wherein the material coming out of the nozzle 1 is deposited on the base strip 5 being unwound at a speed, which is higher than critical speed v.sub.k, thus over critical speed (which substantially corresponds to the Example 2), FIG. 1C illustrates a spinning process wherein the material coming out of the nozzle 1 is deposited on the base strip 5 being unwound at a speed, which is lower than critical speed, thus an undercritical speed, and wherein the deposition is influenced by the integrated body 2 (which substantially corresponds to the Example 3), and FIG. 1D illustrates a spinning process wherein the material coming out of the nozzle 1 is deposited on the base strip 5 being rapidly unwound at an overcritical speed and wherein the deposition is also influenced by the integrated body 2 (which substantially corresponds to the Example 4). The top row of each of FIGS. 1A to 1D includes graphs of the obtained weight profiles along the lateral direction CD, the middle row indicates possible shapes of the patterns formed on the surface of the base material and the bottom row shows the individual arrangements, each being composed of a nozzle 1, a base strip 5 and a collecting electrode 6 as seen in the direction MD. The imaginary cones, which are also indicated in the bottom row, delimit the areas within which a flying fibre 4 is expected to pass through.

(12) FIG. 2C schematically shows the aperture-type spinning nozzle 1 that forms the spinning electrode and has its outlet orifice 10 facing the base strip 5 for depositing the fibres 4 formed during the process. The longitudinal axis of the outlet orifice 10 extends substantially in parallel to the direction CD, which is perpendicular to the direction MD, the latter direction corresponding to that of the movement of the base strip 5 in the place which is faced by the outlet orifice 10. In the vicinity of the edge of the outlet orifice 10, a body 2 is arranged, said body being capable to carry out a reciprocating motion in the lengthwise direction of the respective outlet orifice 10. In the present exemplary embodiment, a motion from one end of the outlet orifice to the other one and vice versa is concerned, the constant distance between the body and the respective edge of the outlet orifice 10 being, for example, 5 mm.

(13) When the device is in operation, the liquid material 3 to be spun is forcibly fed into the aperture in order to cause the level of the surface of liquid material 3 to be spun to approximately correspond to the level of the edge of the outlet orifice 10 or to lie immediately above or below that edge. Thereby, the body 2 moves immediately above the surface of the liquid. The fibres 4 being formed are being thus disrupted in the close vicinity to the surface, i.e., in the close vicinity to the points where the fibres are being formed during the eruption of the spun liquid material 3 towards the opposite collecting electrode 6. This situation corresponds to that shown in FIG. 2B, while FIG. 2A illustrates a situation where the moving body 2 is partly submerged under the surface of the liquid material and where the motion of the body also interferes with the locations of the points where Taylor cones are formed or, as the case may be, causes the latter cones to be displaced.

(14) The above described aperture-type spinning nozzle 1 can be advantageously replaced with a spinning nozzle 1 provided with an array of outlet orifices 10 arranged across the outlet face of the spinning nozzle 1, the latter face forming a groove 9 for collecting the possibly spilled liquid material 3 during spinning, as schematically shown in FIG. 3. The size of the outlet orifices 10 of such spinning nozzle can be, for example, 2×1 mm, the number of the orifices depending on the length of the spinning nozzle 1 or on that of the groove 9.

(15) The movable body 2 can be guided, for example, by means of pneumatically driven mechanisms provided with non-electrical end-position control sensors (such as pneumatic sensors, optical sensors, or the like). An apt exemplary embodiment is shown in FIG. 4, where a pair of mutually parallel spinning nozzles 1 is recognizable, said nozzles being electrically interconnected with a high-voltage or very-high-voltage supply by means of an intermediate coupling line 14. Simultaneously, the spinning nozzles 1 are fluidly connected to the supply 13 of the liquid material 3 to be spun. Furthermore, the embodiment shown comprises an elongated body 2 for destabilizing the locations of the points where fibres 4 are formed on the surface of the liquid material 3 in the vicinity of the outlet orifice 10 of the spinning nozzle 1. One of the ends of the movable body 2 extends over the line of arrangement of the outlet orifices 10 of the first spinning nozzle 1 (or, as the case may be, adjoins said line), while the other end of said movable body extends over the line of arrangement of the outlet orifices 10 of the other spinning nozzle 1.

(16) Inside the intermediate space between the spinning nozzles 1, a pneumatic driving unit 12 is arranged, said pneumatic driving unit 12 being connected with the movable body 2 and adapted for guiding the movable body 2 in a direction that is parallel to the longitudinal axes of the spinning nozzles 1 (i.e., that extends along the array of the spinning orifices 10), said direction advantageously corresponding to the direction CD. The pneumatic drive 12 is connected to the compressed air supply 7.

(17) The illustrated device further comprises a pair of optical sensors 16, which are interconnected with a control unit (not shown) assigned to the pneumatic driving unit 12 and adapted for transmitting a signal containing information on the proximity of the movable body 2 to the respective end position or on reaching the end position of the movable body 2 for the purpose of changing the direction of the reciprocating movement thereof.

(18) Advantageously, the spinning nozzle 1 or the pair of spinning nozzles 1 is arranged in a manner causing the orthogonal projection of the longitudinal axis of the outlet orifice 10 or of the edge, which incorporates the outlet orifices 10, into the plane of the collecting electrode 6 and/or into that of the base strip 5 to extend perpendicularly to the direction MD, thus corresponding to the direction CD; nevertheless, it is also possible to arrange the spinning nozzle in a manner causing the angle formed between said projection and the direction MD to be acute rather than perpendicular.

(19) Preferably, the device comprises two or more spinning nozzles 1 arranged with a mutual spacing in the direction MD.

Example 1

(20) According to this exemplary embodiment, a 12% polyvinyl alcohol (PVA) solution was processed by spinning. The solution was fed at a speed of 2.4 ml/min in total into a pair of needleless spinning nozzles 1 constituting spinning electrodes, the longer sides of the latter extending in the direction CD (i.e., the lengthwise direction of the outlet orifice/outlet edge was parallel to the direction CD). The length of the outlet orifice 10 of each spinning nozzle 1 was 600 mm, the mutual spacing of the spinning nozzles being 400 mm (as measured in the direction MD). An electric potential of +45 kV was applied to the spinning nozzles 1. The spinning process took place in an air-conditioned spinning chamber, the relative humidity and the temperature inside the latter being (20±5) % RH and (23±2) ° C., respectively. The fibres 4 were deposited onto the surface of the base strip 5 consisting of a knitted 100% polyester fabric, the distance between the strip and the spinning nozzles 1 being 18 cm. The above base strip 5 was attached to a foil having reduced electrical conductivity and forming a collecting electrode 6. An electric potential of −30 kV was applied to the above foil. Then, both the above materials were unwound at a speed of (25±5) cm/min in the direction MD, thereby forming a so-called endless strip having a total length of 120 cm. The deposition was taking place during a period of time totalling 20 minutes. The image of the final layer obtained by means of the backlight photography technique is shown in FIG. 5.

Example 2

(21) According to an exemplary embodiment, a 12% polyvinyl alcohol (PVA) solution was processed by spinning. The solution was fed at a speed of 2.4 ml/min in total into a pair of needleless spinning nozzles 1 constituting spinning electrodes, the longer sides of the latter extending in the direction CD. The length of the outlet orifice 10 of each spinning nozzle 1 was 600 mm, the mutual spacing of the spinning nozzles being 400 mm (as measured in the direction MD). An electric potential of +45 kV was applied to the spinning nozzles 1. The spinning process took place in an air-conditioned spinning chamber, the relative humidity and the temperature inside the latter being (20±5) % RH and (23±2) ° C., respectively. The fibres 4 were deposited onto the surface of the base strip 5 consisting of a knitted 100% polyester fabric, the distance between the strip and the spinning nozzles 1 being 18 cm. The above base strip 5 was attached to a foil having a reduced electrical conductivity and forming a collecting electrode 6. An electric potential of −30 kV was applied to the above foil. Both the above materials were reeled at a speed of (100±5) cm/min in the direction MD forming a so-called endless strip having a total length of 120 cm. The deposition was taking place for 20 minutes. The image of the final layer obtained by means of the backlight photography technique is shown in FIG. 6.

Example 3

(22) According to an exemplary embodiment, a 12% polyvinyl alcohol (PVA) solution was processed by spinning. The solution was fed at a speed of 2.4 ml/min in total into a pair of needleless spinning nozzles 1 constituting spinning electrodes, the longer sides of the latter extending in the direction CD. The length of the outlet orifice 10 of each spinning nozzle 1 was 600 mm, the mutual spacing of the spinning nozzles being 400 mm (as measured in the direction MD). At a distance of (10±5) mm from the upper edge of each spinning nozzle 1, a body 2 made of an electrically non-conductive material was moved above the upper edge along the whole length of the outlet orifice 10 of the spinning nozzle 1 continuously and during the whole process, the speed of the latter being (15±5) cm/s. An electric potential of +45 kV was applied to the spinning nozzles 1. The spinning process took place in an air-conditioned spinning chamber, the relative humidity and the temperature inside the latter being (20±5) % RH and (23±2) ° C., respectively. The fibres 4 were deposited onto the surface of the base strip consisting of a knitted 100% fabric, the distance between the strip and the spinning nozzles 1 being 18 cm. The above base strip 5 was attached to a foil having a reduced electrical conductivity and forming a collecting electrode 6. An electric potential of −30 kV was applied to the above foil. Both the above materials were reeled at a speed of (25±5) cm/min in the direction MD forming a so-called endless strip having a total length of 120 cm. The deposition was taking place for 20 minutes. The image of the final layer obtained by means of the backlight photography technique is shown in FIG. 7.

Example 4

(23) According to an exemplary embodiment, a 12% polyvinyl alcohol (PVA) solution was processed by spinning. The solution was fed at a speed of 2.4 ml/min in total into a pair of needleless spinning nozzles 1 constituting spinning electrodes, the longer sides of the latter extending in the direction CD. The length of the outlet orifice 10 of each spinning nozzle 1 was 600 mm, the mutual spacing of the spinning nozzles being 400 mm (as measured in the direction MD). At a distance of (10±5) mm from the upper edge of each spinning nozzle 1, a body 2 made of an electrically non-conductive material was moved above the upper edge along the whole length of the outlet orifice 10 of the spinning nozzle 1 continuously and during the whole process, the speed of the latter being (15±5) cm/s. An electric potential of +45 kV was applied to the spinning nozzles 1. The spinning process took place in an air-conditioned spinning chamber, the relative humidity and the temperature inside the latter being (20±5) % RH and (23±2) ° C., respectively. The fibres 4 were deposited onto the surface of the base strip 5 consisting of a knitted 100% polyester fabric, the distance between the strip and the spinning nozzles 1 being 18 cm. The above base strip 5 was attached to a foil having a reduced electrical conductivity and forming a collecting electrode 6. An electric potential of −30 kV was applied to the above foil. Both the above materials were reeled at a speed of (100±5) cm/min in the direction MD, thereby forming a so-called endless strip having a total length of 120 cm. The deposition was taking place during a period of time totalling 20 minutes. The image of the final layer obtained by means of the backlight photography technique is shown in FIG. 8.

Example 5

(24) According to an exemplary embodiment, an aqueous 8% polyethylene oxide (PEO) solution was processed by spinning. The solution was proportioned at a speed of 3.0 ml/min into a pair of needleless spinning nozzles 1 constituting spinning electrodes, the longer sides of the latter extending in the direction CD. The length of the outlet orifice 10 of each spinning nozzle 1 was 600 mm, the mutual spacing of the spinning nozzles being 400 mm (as measured in the direction MD). At a distance of (10±5) mm from the upper edge of each spinning nozzle 1, a body 2 made of an electrically non-conductive material was moved above the upper edge along the whole length of the outlet orifice 10 of the spinning nozzle 1 continuously and during the whole process, the speed of the latter being (15±5) cm/s. An electric potential of +45 kV was applied to the spinning nozzles 1. The spinning process took place in an air-conditioned spinning chamber, the relative humidity and the temperature inside the latter being (20±5) % RH and (23±2) ° C., respectively. The fibres 4 were deposited onto the surface of the base strip 5 consisting of a 100% knitted fabric, the distance between the strip and the spinning nozzles 1 being 18 cm. The above base strip 5 was attached to a foil having a reduced electrical conductivity and forming a collecting electrode 6. An electric potential of −30 kV was applied to the above foil. Both the above materials were reeled at a speed of (200±5) cm/min in the direction MD forming a so-called endless strip having a total length of 120 cm. The deposition was taking place for 20 minutes. The image of the final layer obtained by means of the backlight photography technique is shown in FIG. 9.

Example 6

(25) According to an exemplary embodiment, an aqueous 6% solution based on the mixture of hyaluronic acid and polyethylene oxide (PEO) was processed by spinning, the mixing ratio of the underlying mixture being 4:1. The solution was fed at a speed of 2.5 ml/min into a pair of needleless spinning nozzles 1 constituting spinning electrodes, the longer sides of the latter extending in the direction CD. The length of the outlet orifice 10 of each spinning nozzle 1 was 600 mm, the mutual spacing of the spinning nozzles being 400 mm (as measured in the direction MD). At a distance of (10±5) mm from the upper edge of each spinning nozzle 1, a body 2 made of an electrically non-conductive material was moved above the upper edge along the whole length of the outlet orifice 10 of the spinning nozzle 1 continuously and during the whole process, the speed of the body being (15±5) cm/s. An electric potential of +45 kV was applied to the spinning nozzles 1. The spinning process took place in an air-conditioned spinning chamber, the relative humidity and the temperature inside the latter being (20±5) % RH and (23±2) ° C., respectively. The fibres 4 were deposited onto the surface of the base strip 5 consisting of a knitted 100% polyester fabric, the distance between the strip and the spinning nozzles 1 being 18 cm. Subsequently, the above base strip 5 was attached to a foil having a reduced electrical conductivity and forming a collecting electrode 6. An electric potential of −30 kV was applied to the above foil. Then, both the above materials were unwound at a speed of (200±5) cm/min in the direction MD, thereby forming a so-called endless strip having a total length of 120 cm. The deposition was taking place for 20 minutes. The image of the final layer obtained by means of the backlight photography technique is shown in FIG. 10.

(26) The results of the analyses of the layers prepared according to the exemplary embodiments 1 to 6 are summarized in the Table 1.

(27) TABLE-US-00001 TABLE 1 Exemplary Use of the Speed of the base Standard deviation of embodiment body 2 strip 5 (cm/min) the pixel intensity 1 No 25 12.5 2 No 100 10.0 3 Yes 25 11.8 4 Yes 100 6.6 5 Yes 200 2.6 6 Yes 200 3.2

INDUSTRIAL APPLICABILITY

(28) The invention is particularly useful in the fields of the production of nanostructured and/or microstructured layers or, as the case may be, nanofibrous and/or microfibrous layers obtained by means of the electrostatic spinning method, such layers being produced in the form of self-supporting layers or in the form of layers deposited on a base material.