Nonwoven fabric and filter
A nonwoven fabric, including fibers, in which the fibers have an elongational viscosity, as measured under conditions at an elongational strain rate of 2.5×10 2 (1/s) and a temperature of 160° C., of from 430 Pa·s to 1200 Pa·s, and a ratio of the elongational viscosity (Pa·s) to a shear viscosity (Pa·s) of the fiber, as measured under conditions at a shear strain rate of 2.5×10 2 (1/s) and a temperature of 160° C., is from 35 to 65.
1. A meltblown nonwoven fabric, comprising resinous polypropylene fibers, wherein the fibers have an elongational viscosity, as measured under conditions at an elongational strain rate of 2.5×10 2 (1/s) and a temperature of 160° C., of from 430 Pas to 1200 Pa-s, and a ratio of the elongational viscosity (Pa-s) to a shear viscosity (Pa-s) of the fiber, as measured under conditions at a shear strain rate of 2.5×10 2 (1/s) and a temperature of 160° C., is from 35 to 65.
2. The nonwoven fabric according to claim 1 , wherein the shear viscosity is from 10 Pas to 20 Pa-s.
3. The nonwoven fabric according to claim 1 , wherein the resin composition contains a long-chain branched polypropylene.
4. The nonwoven fabric according to claim 3 , wherein a content of the long-chain branched polypropylene is from 0.7% by mass to 5% by mass with respect to a total mass of the resin composition.
5. The nonwoven fabric according to claim 1 , wherein the resin composition further contains a linear polypropylene.
6. The nonwoven fabric according to claim 5 , wherein a content of the linear polypropylene is from 95% by mass to 99.3% by mass with respect to a total mass of the resin composition.
7. The nonwoven fabric according to claim 5 , wherein the linear polypropylene comprises a linear polypropylene having a weight-average molecular weight of 20,000 or more.
8. The nonwoven fabric according to claim 7 , wherein a content of the linear polypropylene having a weight-average molecular weight of 20,000 or more is 50% by mass or more with respect to a total mass of the linear polypropylene.
9. The nonwoven fabric according to claim 5 , wherein the linear polypropylene comprises a linear polypropylene having a weight- average molecular weight of less than 20,000.
10. The nonwoven fabric according to claim 9 , wherein a content of the linear polypropylene having a weight-average molecular weight of less than 20,000 is 50% by mass or less with respect to a total mass of the linear polypropylene.
11. The nonwoven fabric according to claim 1 , wherein the fibers have an average fiber diameter (Da) of 2.7 μm or less.
12. The nonwoven fabric according to claim 11 , wherein a ratio of a standard deviation (Dd) of the average fiber diameter to the average fiber diameter (Da) (Dd/Da) is from 70 to 100.
13. The nonwoven fabric according to claim 1 , wherein, in the fibers, a content of fibers having a fiber diameter that is 5 or more times as large as the average fiber diameter is 20% by mass or less.
14. A filter, comprising the nonwoven fabric according to claim 1 .