Emulsion binder, aqueous pigment ink for inkjet containing same, and method for producing emulsion binder

An emulsion binder comprising an A-B block copolymer formed of a polymer block A and another polymer block B, at least 90 mass % of constituent monomer units of said A-B block copolymer having been derived from at least one (meth)acrylate-based monomer, wherein:

• the A-B block copolymer has a number average molecular weight of equal to or less than 100,000 and a polydispersity index (weight average molecular weight/number average molecular weight) of not greater than 1.7,
• the polymer block A has a number average molecular weight of equal to or greater than 22,000, an acid value of 0 to 30 mgKOH/g and a glass transition point of not higher than 60° C,
• the polymer block B has an acid value of 75 to 250 mgKOH/g, and
• the A-B block copolymer has been neutralized with an alkaline material, and has been allowed to self-emulsify in an aqueous medium to form emulsion particles having a number average particle size of 30 to 300 nm.