Patent ID: 6919452

Claim:
4,4′-Bis(1,3,5-triazinylamino)stilbene-2,2′-disulfonic acid derivative having the following formula: in which each of R 11 and R 12 independently is hydrogen, methyl, ethyl, n-propyl, n-butyl, or 2-sulfoethyl; each of R 21 and R 22 independently is hydrogen, methyl, ethyl, n-propyl, isopropyl, 2-hydroxyethyl, 2-hydroxypropyl, 3-hydroxypropyl, 2,3-dihydroxypropyl, 2-sulfoethyl, 2-(2-hydroxyethoxy)ethyl, 2-[2-(2-hydroxyethoxy)ethoxy]ethyl, phenyl, naphthyl, 4-hydroxyphenyl, 3,5-dicarboxyphenyl, 4-methoxyphenyl, and 3-isopropylphenyl; each of L 1 and L 2 is an alkylene group having 2 to 8 carbon atoms, which alkylene group has one or more substituents selected from the group consisting of hydroxyl and hydroxyalkyl having 1 to 3 carbon atoms; and M is a hydrogen atom, an alkali metal atom, or pyridinium group.