Process for laying fibrous webs from a centrifugal spinning process
A method for laying down a nanoweb of nanofibers from a centrifugal spinning process by a combination of an air flow field and a charging arrangement. Fibrous streams in the form of fibrils of molten polymer or polymer solution are discharged from a rotating member into an air flow field that is essentially parallel to the direction of discharge of fibrils at the point of discharge of the fibrils. The fibrous streams are attentuated and directed by means of the air flow field onto the surface of a collector to form a nanoweb. The fibrous streams are charged along all or at least a portion of their route from the point of discharge to the surface of the collector.
1. A method for laying down a web of nanofibers from a centrifugal spinning process comprising the steps of
(i) discharging fibrous streams in the form of fibrils or fibers of molten polymer or polymer solution from a rotating member into an air flow field that is essentially parallel to the direction of discharge of fibrils at the point of discharge of the fibrils,
(ii) attenuating the fibrous streams, and
(iii) directing the attenuated fibrous streams by means of an air flow field onto the surface of a collector to form a nanoweb,
wherein the air flow field of step (iii) further comprises a flow of air into at least a portion of the collector surface where the flow of air is essentially perpendicular to the collector from a region between the body of the rotating member and the collector surface, and
wherein the fibrous streams are charged along all or at least a portion of their route from the point of discharge to the surface of the collector.
2. The method of claim 1 in which the web has a uniformity index range 0.1 to 5 when measured on a sample size of 90 by 60 cm at 3000 by 2000 pixels.
3. The method of claim 1 wherein the attenuation of step (ii) is caused by the centrifugal force of ejection of fibrils from the point of discharge.
4. The method of claim 1 in which the nanofibers are directed to the collector by a shaping air flow that is essentially perpendicular to the collector surface.
5. The method of claim 1 in which the air flow field at step (i) comprises air from a nozzle that has an opening that is located on a radius of the cup or disk, and the air flow is directed at an angle to the radius of between 0 and 60 degrees and in a direction opposite to the direction of rotation of the disk.
6. The method of claim 1 in which the rotating member comprises a disk or cup and fibrils are discharged from the edge of the surface of said disc or cup or from orifices located in or on the surface or cup.
7. The method of claim 1 in which the spinning process further comprises the step of attenuating the fibrils with centrifugal force and cooling the attenuated fibrils or allowing the attenuated fibrils to cool and form nanofibers.
8. The method of claim 1 in which the fibrils attain their charge relative to the collector by the application of a charge to the rotating member, the fibrils, the collector surface, a structure located in the vicinity of the collector surface, or any combination of these locations and the charge is relative to a ground located on rotating member, the fibrils, the collector surface, a structure located in the vicinity of the collector surface, or any combination of these locations.
9. The method of claim 8 in which the charge is applied to the fibrils by an ion flow produced by a corona discharge.
10. The method of claim 1 wherein a charge is applied to the collector only and the polymer is a polar polymer.
11. The method of claim 1 in which vacuum is applied to the collector in the shape of an annulus.
12. The method of claim 1 further comprising a step of fabricating an article from the web as obtained therein.
13. The method of claim 12 wherein the article comprises a battery separator.