The surfactant to be used is a surfactant having a carboxy group, sulfo group, or phosphate group.

The anionic functional groups are at least one group selected from a carboxy group, a sulfo group and a phosphate group.

In formula (2), R5 indicates a sulfo group, etc., and R6 indicates and amino group or a carboxy group, etc.

In formula (6), R represents a hydrogen atom or a sulfo group.

R2 represents a hydrogen atom, sulfo group, carboxyl groups, substituted or unsubstituted carbamoyl group, or cyano group.

In formula (3), R represents a hydrogen atom or a sulfo group.

In formula (3), m represents 0 or 1; R101 to R103 independently represent a hydrogen atom, a sulfo group or a C1-C4 alkoxy group; and a group D represents a phenyl or naphthyl group substituted by 1 to 3 sulfo groups.

In formula (1), R1 and R2 independently represent a hydrogen atom, a sulfo group or the like; R3 and R4 independently represent a halogen atom, a sulfo group or the like; and n represents 0 or 1.

In formula, A indicates a sulfo group or a carboxy group, and x indicates an integer between 2 and 4.

In formula (6), Z represents a hydrogen atom, a caboxy group, or a sulfo group, and k represents an integer from 0 to 2.

In formula (2), Ra represents C1-C4 alkyl group or the like, and X represents an aliphatic amino group substituted by a carboxy group or a sulfo group.

In formulas (2) and (3), R2, R3, R4, and R5 each independently represents a sulfo group or a carboxy group, etc.

In formula (5), n represents an integer between 0 and 2, and Z represents a hydrogen atom, a carboxy group, or a sulfo group.

In formula (5), n represents an integer of 0 to 2, and z represents a hydrogen atom, a carboxy group, or a sulfo group.

It is a polybenzazole compound containing units to which an aromatic dicarboxylic acid having a sulfo group and/or a phosphono group has been bonded.