Abstract: A set of an ink containing a self-dispersible pigment and a water-soluble resin, which is a copolymer having a unit derived from (meth)acrylic acid, and a reaction liquid containing a surfactant, which is an ethylene oxide adduct of a higher alcohol of a linear primary or secondary alcohol or an isoalkyl alcohol and has a HLB value of 13.0 or more determined by the Griffin method, and having buffering ability in an acid region. Content of the surfactant in the reaction liquid is 0.20 times or more in terms of mass ratio as much as total content of the pigment and water-soluble resin.

Abstract: An aqueous ink for ink jet contains a self-dispersible pigment in which a first functional group including a phosphonic acid group and a second functional group including at least one of a carboxylic acid group and a sulfonic acid group are bonded to a particle surface, wherein a surface charge amount derived from the phosphonic acid group included in the above-described first functional group is 0.3 micromoles/m2 or more, a total surface charge amount derived from the carboxylic acid group and the sulfonic acid group included in the above-described second functional group is 1.0 micromoles/m2 or more, and a total surface charge amount derived from anionic groups included in the above-described first functional group and the above-described second functional group is 2.0 micromoles/m2 or more and 8.0 micromoles/m2 or less.

Abstract: The present invention preferably provides an ink including an organic pigment, a water-soluble resin and a surfactant that allows images having high color developability to be obtained independently of the type of recording medium, even when a small amount of ink is applied. Preferably, the organic pigment is a phosphonic acid-type self-dispersible pigment, the acid value of the water-soluble resin is 100 mg KOH/g to 160 mg KOH/g, the surfactant is an ethylene oxide adduct of a higher alcohol selected from the group consisting of a linear primary alcohol, a linear secondary alcohol and an isoalkyl alcohol, the HLB value of the surfactant as determined by the Griffin method is 13.0 or more, and the mass ratio of the content (% by mass) of the surfactant in the ink to the content (% by mass) of the water-soluble resin in the ink is 0.07 to 0.70.

Abstract: A set of an ink containing a self-dispersible pigment and a water-soluble resin, which is a copolymer having a unit derived from (meth)acrylic acid, and a reaction liquid containing a surfactant, which is an ethylene oxide adduct of a higher alcohol of a linear primary or secondary alcohol or an isoalkyl alcohol and has a HLB value of 13.0 or more determined by the Griffin method, and having buffering ability in an acid region. Content of the surfactant in the reaction liquid is 0.20 times or more in terms of mass ratio as much as total content of the pigment and water-soluble resin.