CPC B01D 69/02 (2013.01) [B01D 65/08 (2013.01); B01D 67/0009 (2013.01); B01D 67/0083 (2013.01); B01D 69/08 (2013.01); B01D 71/22 (2013.01); B01D 71/34 (2013.01); B01D 71/40 (2013.01); B01D 71/44 (2013.01); B01D 71/48 (2013.01); B01D 71/52 (2013.01); B01D 71/56 (2013.01); B01D 71/66 (2013.01); B01D 2323/12 (2013.01); B01D 2325/022 (2013.01); B01D 2325/0283 (2022.08); B01D 2325/04 (2013.01); B01D 2325/20 (2013.01); B01D 2325/24 (2013.01)] | 15 Claims |
1. A separation membrane comprising, as a main component A, a thermoplastic polymer selected from the group consisting of a cellulose ester and a polyamide,
wherein, when regions obtained by dividing a cross-sectional surface perpendicular to a longitudinal direction of the separation membrane into 5 at an equal interval in order from one surface of the separation membrane in a thickness direction of the separation membrane are defined as regions 1 to 5,
an average pore diameter obtained by weighting with a pore area ratio of pores extracted in each region to a total area of all the pores is defined as an area average pore diameter Ds in each region,
an average pore diameter obtained by weighting with a number ratio of pores extracted in each region to the number of all pores is defined as a number average pore diameter Dn in each region,
a pore having a pore diameter larger than the area average pore diameter Ds is defined as a coarse pore,
a pore having a pore diameter smaller than the number average pore diameter Dn is defined as a fine pore,
an average of closest distance between coarse pores is defined as La, and
a number average W of the fine pores that are located at a distance smaller than La from a center of the respective coarse pores is calculated,
all the regions 1 to 5 have a number average pore diameter changing rate αi defined by the following Formula of −0.25 or more and 0.25 or less, and
at least one of the regions 1 to 5 is a region P that satisfies the following conditions (a) and (b):
(a) a value of the area average pore diameter Ds/the number average pore diameter Dn is 2.50 or more and 6.00 or less; and
(b) the number average W of the fine pores is 10 or more and 30 or less,
αi=(Di−Di+1)/Di
(Di: Number average pore diameter of region i),
it is noted that the number average pore diameter changing rate in the region 5 is defined by the following formula,
α5=(D5−D4)/D5.
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