An aqueous ink contains a titanium oxide particle, poly(acrylic acid) and potassium ions, in which the titanium oxide particle contains titanium oxide, at least part of the surface of the titanium oxide is covered with alumina and silica, and the poly(acrylic acid) content is 0.05 times or more to 0.40 times or less the alumina content in terms of a mass ratio.

Provided is a semiconductor nanoparticle complex dispersion liquid in which semiconductor nanoparticles are dispersed in a polar dispersion medium at a high mass fraction, and in which high fluorescence quantum efficiency (QY) is maintained. A semiconductor nanoparticle complex dispersion liquid according to an embodiment includes a semiconductor nanoparticle complex dispersed in an organic dispersion medium, wherein: the semiconductor nanoparticle complex is composed of two or more ligands including an aliphatic thiol ligand and a polar ligand, and a semiconductor nanoparticle with the ligands coordinated to the surface thereof; the ligands are composed of an organic group and a coordinating group; the organic group of the polar ligand includes a hydrophilic functional group; and an SP value of the organic dispersion medium is 8.5 or more.

Provided is a semiconductor nanoparticle complex dispersion liquid in which semiconductor nanoparticles are dispersed in a polar dispersion medium at a high mass fraction, and in which high fluorescence quantum efficiency (QY) is maintained. A semiconductor nanoparticle complex dispersion liquid according to an embodiment includes a semiconductor nanoparticle complex dispersed in an organic dispersion medium, wherein: the semiconductor nanoparticle complex is composed of two or more ligands including an aliphatic thiol ligand and a polar ligand, and a semiconductor nanoparticle with the ligands coordinated to the surface thereof; the ligands are composed of an organic group and a coordinating group; the organic group of the polar ligand includes a hydrophilic functional group; and an SP value of the organic dispersion medium is 8.5 or more.

A resin solution for printing, including: a nonpolar solvent having a boiling point of 125° C. or higher; a thermoplastic elastomer; and a particle having a primary particle diameter of 1 nm or more and 200 nm or less, the resin solution having a viscosity of 1 cP or more and 50 cP or less. Preferably, the thermoplastic elastomer is a hydrogenated aromatic vinyl compound-conjugated diene block copolymer or a modified product of the hydrogenated aromatic vinyl compound-conjugated diene block copolymer with a silicon atom-containing polar group.

A treatment liquid which is applied to a substrate by an inkjet system, and includes water, a coagulant, and a surfactant, in which the coagulant contains a polycondensate of an aliphatic amine and an epihalohydrin, and a diallyldialkylammonium halide-based polymer, at a mass ratio of 20:80 to 90:10, and the surfactant contains a fluorine-based surfactant and a silicone-based surfactant.

An ink which comprises a water-insoluble colorant, a dispersant, a polymer resin, and water. The polymer resin is one of four monomers which are methacrylic acid and three monomers selected respectively from among C1- to C4-alkyl methacrylates, C6- to C10-alkyl acrylates, and unsaturated C2- to C4-alkyl methacrylates; and a reactive emulsifier having a radical-polymerizable double bond in the molecule. An ink-jet recording method in which the ink is used; a recording medium to which the ink has been adhered; and an ink-jet printer including a vessel filled with the ink.

An ink which comprises a water-insoluble colorant, a dispersant, a polymer resin, and water. The polymer resin is one of four monomers which are methacrylic acid and three monomers selected respectively from among C1- to C4-alkyl methacrylates, C6- to C10-alkyl acrylates, and unsaturated C2- to C4-alkyl methacrylates; and a reactive emulsifier having a radical-polymerizable double bond in the molecule. An ink-jet recording method in which the ink is used; a recording medium to which the ink has been adhered; and an ink-jet printer including a vessel filled with the ink.

An aqueous ink for ink jet recording includes a titanium oxide particle containing titanium oxide, at least part of the surface of the titanium oxide being covered with alumina and silica in specific proportions, in which the titanium oxide particle is dispersed at least by the action of the silica, and the ratio (η.sub.1/η.sub.1,000) of the viscosity (η.sub.1) of the aqueous ink at a shear rate of 1 (1/s) to the viscosity (η.sub.1,000) at a shear rate of 1,000 (1/s) is 1.10 times or less.

An aqueous ink for ink jet recording includes a titanium oxide particle containing titanium oxide, at least part of the surface of the titanium oxide being covered with alumina and silica in specific proportions, in which the titanium oxide particle is dispersed at least by the action of the silica, and the ratio (η.sub.1/η.sub.1,000) of the viscosity (η.sub.1) of the aqueous ink at a shear rate of 1 (1/s) to the viscosity (η.sub.1,000) at a shear rate of 1,000 (1/s) is 1.10 times or less.

A radiation-curable ink jet composition includes a polyfunctional monomer containing a predetermined acrylic compound, and a monofunctional monomer containing vinyl methyl oxazolidinone.