DEVICE FOR PRODUCING ELECTROSPUN SHORT POLYMER FIBRES

Abstract

A device for producing electrospun polymer short fibers has a dosing electrode (1) and a collector medium (3) opposite the dosing electrode (1) in the dosing direction (2). In order to create a device that enables continuous production of electrospun polymer short fibers, a cutting grid (5), which can be heated at least to the softening temperature of the polymer and which has a mesh size that corresponds to the minimum fiber length, is arranged upstream of the collector medium (3) in the dosing direction (2).

Claims

1. A device for producing electrospun polymer short fibers, said device comprising: a dosing electrode having a dosing direction; and a collector medium opposite the dosing electrode in the dosing direction; and a cutting grid that is heated at least to a softening temperature of a polymer of which the polymer short fibers are comprised, and that has a mesh size that corresponds to a minimum fiber length, is arranged upstream of the collector medium in the dosing direction.

2. The device according to claim 1, wherein the mesh size of the cutting grid is at least 5 μm.

3. The device according to claim 1, wherein that the cutting grid is comprises an electrical heating resistor and operates as a counter-electrode to the dosing electrode.

4. The device according to claim 1, wherein the dosing electrode and/or a take-off region extending between the dosing electrode and the cutting grid is cooled by a heat-transfer fluid.

5. A method for producing electrospun polymer short fibers, said method comprising: providing a device according to claim 1; generating an electric field between the dosing electrode and the collector medium which the spun polymer short fibers are deposited; first drawing off, as a result of the electric field, a primary fiber from the dosing electrode and cutting a primary fiber into the short fibers by heating thereof in sections at least to the softening temperature of the polymer, and then depositing the short fibers on the collector medium.

6. The method according to claim 5, wherein the collector medium includes a storage fluid, and the short fibers are deposited on the storage fluid and dispersed therein.

7. The method according to claim 5, wherein the mesh size of the cutting grid is at least 5 μm.

8. The method according to claim 7, wherein the cutting grid comprises an electrical heating resistor, and the method further comprises operating the cutting grid as a counter-electrode to the dosing electrode.

9. The method according to claim 8, wherein the method further comprises cooling the dosing electrode and/or a take-off region extending between the dosing electrode and the cutting grid by a heat-transfer fluid.

10. The method according to claim 5, wherein the cutting grid comprises an electrical heating resistor, and the method further comprises operating the cutting grid as a counter-electrode to the dosing electrode.

11. The method according to claim 10, wherein the method further comprises cooling the dosing electrode and/or a take-off region extending between the dosing electrode and the cutting grid by a heat-transfer fluid.

12. The method according to claim 5, wherein the method further comprises cooling the dosing electrode and/or a take-off region extending between the dosing electrode and the cutting grid by a heat-transfer fluid.

13. The method according to claim 6, wherein the cutting grid comprises an electrical heating resistor, and the method further comprises operating the cutting grid as a counter-electrode to the dosing electrode.

14. The method according to claim 13, wherein the method further comprises cooling the dosing electrode and/or a take-off region extending between the dosing electrode and the cutting grid by a heat-transfer fluid.

15. The device according to claim 2, wherein the cutting grid comprises an electrical heating resistor and operates as a counter-electrode to the dosing electrode.

16. The device according to claim 2, wherein the dosing electrode and/or a take-off region extending between the dosing electrode and the cutting grid is cooled by a heat-transfer fluid.

17. The device according to claim 3, wherein the dosing electrode and/or a take-off region extending between the dosing electrode and the cutting grid is cooled by a heat-transfer fluid.

18. The device according to claim 13, wherein the dosing electrode and/or a take-off region extending between the dosing electrode and the cutting grid is cooled by a heat-transfer fluid.

Description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] A device according to the invention comprises a dosing electrode 1 and a collector medium 3 opposite the dosing electrode 1 in dosing direction 2. The collector medium can be a storage liquid for the short fibers produced, for example an ethanol/water mixture located in a collector vessel 4. A cutting grid 5 heated at least to the softening temperature of the polymer is arranged upstream of the collector medium 3 in the dosing direction 2, the mesh size of which corresponds to the minimum fiber length of the short fibers produced.

[0014] For the production of electrospun polymer short fibers, various polymer systems can be used as starting materials, in particular water-soluble, solvent-based and meltable polymers together with any additives and fillers. For example, to obtain fibers based on polymethyl methacrylate, the starting material can be a polymer solution comprising mass fractions of about 20% of polymethyl methacrylate, about 55% of acetic acid, and about 25% of ethyl acetate, plus any additional additives. The softening temperature, in the case of the amorphous polymethyl methacrylate, would be its glass transition temperature, which is about 100°−110° C.

[0015] A voltage, which can be between 20 kV and 30 kV, is applied between the dosing electrode 1 and the heated cutting grid 5 and/or the collector medium 3 to generate an electric field. The polymer solution is fed at a flow rate of 3 ml/hour to 9 ml/hour via the dosing electrode 1 to the take-off region 6, whereby the polymer droplet forming at the dosing electrode 1 is electrostatically charged and stretched under the influence of the electric field. This results in the development of a primary fiber 7 which, due to electrostatically induced bending instabilities, essentially describes a path curve in the take-off region 6 which has a cone extending in the dosing direction 2 as its envelope, as indicated schematically in the drawing.

[0016] The primary fiber 7 is heated by the cutting grid 5 in sections at least to the softening temperature of the polymer and thereby cut into short fibers, in that the primary fiber 7 strikes the cutting grid 5 at an acute angle of incidence relative to the cutting grid plane in such a way that the border sections enclosing the individual grid openings or grid meshes form corresponding cutting edges for the incident primary fiber 7. The short fibers produced in this way, which are not shown in detail in the drawing, are subsequently deposited on the collector medium 3 and dispersed therein, so that the short fiber dispersion thus obtained can be further processed without difficulty, for example as a spray base for the production of filter materials. For this purpose, the collector vessel 4 can have a corresponding liquid outlet via which the storage liquid together with the short fibers dispersed therein can be passed on to a filling device.

[0017] The fiber length distribution can be influenced, for example, by the mesh size of the grid meshes of the cutting grid 5. In order to increase the frequency of the generated short fibers according to a probability density function related to the fiber length distribution, the cutting grid 5 can have a mesh size of at least 5 μm.

[0018] Favorable process conditions are obtained if the cutting grid 5 is designed as an electrical heating resistor and as a counter-electrode to the dosing electrode 1. A heating current generated by two different electrical potentials applied to the cutting grid 5 flows through the cutting grid 5 between two connection poles of a supply unit 8.

[0019] According to some embodiments, the dosing electrode 1 and/or the take-off region 6 extending between the dosing electrode 1 and the cutting grid 5 can be cooled via a heat-transfer fluid. This can counteract undesirable heating of the air in the take-off region 6 due to the heated cutting grid 5, which impairs the trajectory of the primary fiber 7, as well as clogging of the dosing electrode 1, whereby a more stable manufacturing process can be achieved.