Patent ID: 7799121

Claim:
An ink-jet ink comprising an aqueous vehicle, a colorant, and a first and second cationic species wherein: i) said colorant comprises self-dispersed pigment with anionic dispersibility-imparting surface groups; ii) said first cationic species is a member or any combination of members selected from the group consisting of tetrabutylammonium, benzyltriethylammmonium, butyltrimethylammonium cations, and has a molar concentration per unit weight of ink of M 1 ; iii) said second cationic species is any member or any combination of members selected from the group consisting of Na + , K + , Rb + Cs + , and has a molar concentration per unit weight of ink of M 2 ; and iv) the molar ratio of first cationic species to total cation concentration (Mtot) satisfies equation 1 as follows: 0.01 ≦M 1/ M tot≦0.5 (eq. 1) wherein Mtot is the cumulative molar concentration of first and second cationic species per unit weight of ink (Mtot=M 1 +M 2 ).