Patent ID: 7771523

Claim:
An inkjet ink comprising an aqueous vehicle, a colorant, and a first and second cationic species wherein: i) said aqueous vehicle comprises water and a first humectant wherein said first humectant is any member or combination of members selected from the group consisting of 2-pyrrolidone, di-(2-hydroxyethyl)-5,5-dimethyl hydantoin, sulfolane, tetramethylene sulfoxide, 1,3-dimethyl-2-imidazolidinone and imidazolidinone; ii) said colorant comprises self-dispersed pigment with anionic carboxylate dispersibility-imparting surface groups; iii) said first cationic species is Li + , and has a molar concentration per unit weight of ink of M1; iv) said second cationic species is any member or combination of members selected from the group consisting of Na + , K + , Rb + and Cs + , and has a molar concentration per unit weight of ink of M2; and v) the molar ratio of M1 to 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=M1+M2).