Systems and methods for making fiber webs
Systems and methods for forming fiber webs, including those suitable for use as filter media and battery separators, are provided. In some embodiments, the systems and methods involve a first system for forming a fiber web (e.g., a wet laid system or non-wet laid system) and additionally one or more coating units. The first system for forming a fiber web may be used to form one or more fibrous layers of the fiber web, and the coating unit may be used to form an additional fibrous layer of the fiber web. In some embodiments, the systems and methods can be used to form fiber webs having a gradient in a property across a portion of, or the entire, thickness of the fiber web.
1. A method of forming a fiber web, comprising:
forming a first fibrous layer using a fiber web-forming system; and
forming a second fibrous layer on the first fibrous layer using a coating unit,
wherein the step of forming the second fibrous layer comprises depositing a coating layer on the first fibrous layer, and removing a solvent from the coating layer to form the second fibrous layer.
2. The method of claim 1 , wherein forming the first fibrous layer comprises:
dispensing a fiber mixture comprising a first fiber and a second fiber into a flow zone of the fiber web-forming system; and
collecting a plurality of first and second fibers downstream of the flow zone in a fiber web forming zone to form the first fibrous layer, wherein the first and second fibers are different.
3. The method of claim 1 , comprising forming a third fibrous layer using the fiber web-forming system.
4. The method of claim 1 , wherein the coating unit is a gravure.
5. The method of claim 1 , wherein the coating unit is a slot die coating unit.
6. The method of claim 1 , wherein the coating unit is a sizepress.
7. The method of claim 1 , wherein the coating unit is a filmpress.
8. The method of claim 1 , further comprising removing a solvent from at least the first fibrous layer using a dewatering system positioned upstream of the coating unit.
9. The method of claim 1 , further comprising removing a solvent from the first fibrous layer and/or the coating layer using a dewatering system positioned downstream of the coating unit.
10. The method of claim 9 , wherein removing a solvent comprises pulling the solvent from underneath the fiber web.
11. The method of claim 9 , wherein removing a solvent comprises pulling the solvent from above the fiber web.
12. The method of claim 1 , wherein the first layer comprises fibers having a first diameter, and the second layer comprises fibers having a second diameter, and the first diameter is larger than the second diameter.
13. The method of claim 1 , wherein the second fibrous layer comprises fibers having a fiber diameter of less than about 2 microns.
14. The method of claim 13 , wherein the fibers having a diameter of less than about 2 microns comprise synthetic fibers.
15. The method of claim 1 , wherein the second fibrous layer comprises fibers having a fiber diameter of less than about 1 micron.
16. The method of claim 1 , wherein the second fibrous layer comprises fibers having a fiber diameter of less than about 0.5 microns.
17. The method of claim 1 , wherein the fiber web-forming system is a wet laid system.
18. The method of claim 1 , wherein the fiber web-forming system is a non-wet laid system.
19. The method of claim 1 , wherein a mixer or agitator is connected to the coating unit.
20. The method of claim 1 , wherein the second fibrous layer comprises fibers having a fiber diameter of less than about 5 microns.
21. The method of claim 20 , wherein the fibers having a diameter of less than about 5 microns comprise synthetic fibers.
22. The method of claim 1 , wherein the second fibrous layer comprises fibers having a fiber diameter of less than about 3 microns.
23. The method of claim 22 , wherein the fibers having a diameter of less than about 3 microns comprise synthetic fibers.
24. The method of claim 1 , wherein the coating layer comprises a surfactant and wherein the solvent comprises water.
25. A method of forming a fiber web, comprising:
forming a first fibrous layer using a fiber web-forming system, wherein the fiber web-forming system is a wet laid system; and
forming a second fibrous layer on the first fibrous layer using a coating unit.
26. The method of claim 25 , wherein the coating unit is a gravure, a slot die coating unit, a sizepress, or a filmpress.
27. The method of claim 25 , further comprising removing a solvent from the first fibrous layer and/or the coating layer using a dewatering system positioned downstream of the coating unit.
28. The method of claim 27 , wherein removing a solvent comprises pulling the solvent from underneath the fiber web.
29. The method of claim 27 , wherein removing a solvent comprises pulling the solvent from above the fiber web.
30. The method of claim 25 , wherein the first layer comprises fibers having a first diameter, and the second layer comprises fibers having a second diameter, and the first diameter is larger than the second diameter.
31. The method of claim 25 , wherein the second fibrous layer comprises fibers having a fiber diameter of less than about 5 microns.
32. The method of claim 31 , wherein the fibers having a diameter of less than about 5 microns comprise synthetic fibers.
33. The method of claim 25 , wherein the second fibrous layer comprises fibers having a fiber diameter of less than about 3 microns.
34. The method of claim 33 , wherein the fibers having a diameter of less than about 3 microns comprise synthetic fibers.
35. The method of claim 25 , wherein the second fibrous layer comprises fibers having a fiber diameter of less than about 2 microns.
36. The method of claim 35 , wherein the fibers having a diameter of less than about 2 microns comprise synthetic fibers.
37. The method of claim 25 , wherein the second fibrous layer comprises fibers having a fiber diameter of less than about 1 micron.
38. The method of claim 25 , wherein the second fibrous layer comprises fibers having a fiber diameter of less than about 0.5 microns.
39. A method of forming a fiber web, comprising:
forming a first fibrous layer using a fiber web-forming system;
forming a second fibrous layer on the first fibrous layer using a coating unit; and
removing a solvent from the first fibrous layer and/or the second fibrous layer using a dewatering system positioned downstream of the coating unit.
40. The method of claim 39 , wherein the coating unit is a gravure, a slot die coating unit, a sizepress, or a filmpress.
41. The method of claim 39 , wherein removing a solvent comprises pulling the solvent from underneath the fiber web.
42. The method of claim 39 , wherein removing a solvent comprises pulling the solvent from above the fiber web.
43. The method of claim 39 , wherein the first layer comprises fibers having a first diameter, and the second layer comprises fibers having a second diameter, and the first diameter is larger than the second diameter.
44. The method of claim 39 , wherein the second fibrous layer comprises fibers having a fiber diameter of less than about 5 microns.
45. The method of claim 44 , wherein the fibers having a diameter of less than about 5 microns comprise synthetic fibers.
46. The method of claim 39 , wherein the second fibrous layer comprises fibers having a fiber diameter of less than about 3 microns.
47. The method of claim 46 , wherein the fibers having a diameter of less than about 3 microns comprise synthetic fibers.
48. The method of claim 39 , wherein the second fibrous layer comprises fibers having a fiber diameter of less than about 2 microns.
49. The method of claim 48 , wherein the fibers having a diameter of less than about 2 microns comprise synthetic fibers.
50. The method of claim 39 , wherein the second fibrous layer comprises fibers having a fiber diameter of less than about 1 micron.
51. The method of claim 39 , wherein the second fibrous layer comprises fibers having a fiber diameter of less than about 0.5 microns.