Process for forming a high efficiency nanofiber filter
A process for forming a high efficiency filter containing the steps of forming a non-woven layer having pores from a plurality thermoplastic fibers having a median diameter of less than about 2 micrometers, saturating the non-woven layer in a wetting liquid, and drying the wetted non-woven layer.
1. A process for forming a high efficiency filter comprising:
forming a non-woven layer having pores from a plurality of thermoplastic fibers having a median diameter of less than about 2 micrometers, wherein the formed non-woven layer contains no electrostatic charge;
saturating the non-woven layer in a wetting liquid, wherein the wetting liquid has a surface tension of less than the surface tension of the thermoplastic making up the thermoplastic nanofibers, wherein the wetting liquid completely wets the pores in the non-woven layer;
drying the wetted non-woven layer forming a dried non-woven layer at room temperature such that size and shape of at least a portion of the pores change, wherein the dried non-woven layer has higher filtration efficiency than the formed non-woven layer, and wherein the dried non-woven layer contains no electrostatic charge.
2. The process of claim 1 , wherein the thermoplastic fibers have a median diameter of less than about 1 micrometers.
3. The process of claim 1 , wherein the thermoplastic fibers have a median diameter of less than about 100 nanometers.
4. The process of claim 1 , wherein the thermoplastic fibers have a median diameter of less than about 70 nanometers.
5. The process of claim, wherein the formed non-woven layer further comprises a plurality of micron-sized fibers.
6. The process of claim 1 , wherein the wetting liquid is selected from the group consisting of isopropanol, ethanol, methanol, DMF, alcohol/water mixtures, and mixtures thereof.
7. The process of claim 1 , wherein the formed non-woven layer further comprises a plurality of binder fibers.
8. The process of claim 1 , wherein the formed non-woven layer further comprises a plurality of fire resistant or fire retardant fibers.
9. The process of claim 1 , wherein the forming the non-woven layer further comprises attaching a support substrate to at least one surface of the non-woven layer.
10. The process of claim 1 , wherein the formed non-woven layer has a density of between about 5 and 200 g/m 2 .
11. The process of claim 1 , wherein the drying of the wetted non-woven layer comprises drying the wetted non-woven layer in a horizontal orientation.
12. The process of claim 1 , wherein the drying of the wetted non-woven layer comprises drying the wetted non-woven layer in a vertical orientation.
13. The process of claim 1 , wherein the thermoplastic fibers comprise a polymer are selected from the group consisting of polypropylene, polyester, polybutylene terephthalate, and polyethylene.
14. The process of claim 1 , wherein the dried non-woven layer has a filtration efficiency of greater than MERV 11.
15. The process of claim 1 , wherein the dried non-woven layer has lower pressure drop efficiency than the formed non-woven layer.
16. The process of claim 1 , wherein the process further comprises pleating the filter.
17. The process of claim 1 , wherein the process further comprises placing the filter in a frame.
18. A high efficiency filter formed from the method of claim 1 .