Flame retardant composition, flame retardant fiber treated with flame retardant composition, and method for increasing amount of flame retardant component adhered onto fibers using said composition

A flame retardant composition, comprising:

• at least one phosphorus compound of the following formula (1);
• a cationic surfactant comprising a polyether group-containing cationic surfactant, wherein the cationic surfactant comprises one or both of an amine of the following formula (6) and a quaternary ammonium salt of the following formula (8);
• and
• a nonionic surfactant comprising a nonionic surfactant having an aromatic ring in a molecule thereof:
• wherein A represents a divalent hydrocarbon group having 1 to 20 carbon atoms, n represents a number of from 1 to 10, and R1 to R8 each independently represent a hydrogen atom or an alkyl group having 1 to 20 carbon atoms;
• wherein R15 to R17 each independently represent a hydrocarbon group having 1 to 20 carbon atoms, a group represented by -(G-O)m—H where G represents an alkylene group having 2 carbon atoms and m represents a number of from 1 to 100, or a group that has 1 to 20 carbon atoms and has one or more substituents selected from the group consisting of an ester group, an amide group, and a hydroxyl group, provided that one or two groups represented by -(G-O)m—H are necessarily included;
• wherein R18 to R21 each independently represent a hydrocarbon group having 1 to 20 carbon atoms, a group represented by -(L-O)q—H where L represents an alkylene group having 2 to 4 carbon atoms and q represents a number of from 1 to 100, or a group that has 1 to 20 carbon atoms and has one or more substituents selected from the group consisting of an ester group, an amide group, and a hydroxyl group, and Y represents an anionic atom or an anionic group, provided that the compound of formula (8) contains at least one group represented by -(L-O)q—H.