Abstract: The present invention provides a reversibly thermochromic aqueous inkjet printer ink composition which can form print images of high resolution and rich color development. The composition comprises: a reversibly thermochromic microcapsule pigment, water, and a polyalcohol organic solvent. Microcapsules which are comprised in the composition have a volume-based mean particle size (X) of 0.1 to 2 ?m and a mean cross-sectional membrane thickness (Y) of 0.02 to 0.4 which is average of cross-sectional membrane thickness defined by the formula: cross-sectional membrane thickness=(outer section diameter?inner section diameter)/2.

Abstract: The present invention provides a thermochromic color-memory composition including (a) an electron-donating color-developing organic compound, (b) an electron-accepting compound, and (c) an ester compound represented by the following formula (1) or (2), as a reaction medium which controls color reaction of the component (a) and the component (b); and a thermochromic color-memory microcapsule pigment encapsulating the thermochromic color-memory composition.

Abstract: To provide a reversibly thermochromic aqueous ink composition excellent in dispersion stability of a reversibly thermochromic microcapsule pigment and a writing instrument using the same. Disclosed is a reversibly thermochromic aqueous ink composition comprising a reversibly thermochromic microcapsule pigment encapsulating a reversibly thermochromic composition comprising (a) an electron-donating color-developing organic compound, (b) an electron-accepting compound, and (c) a reaction medium to determine an occurrence temperature of a coloring reaction of the component (a) and the component (b), and a vehicle comprising water and a specific gravity adjuster selected from the group consisting of an oxyacid belonging to Group 6 having an atomic weight of 90 to 185 or salt thereof.

Abstract: To provide a reversibly thermochromic aqueous ink composition excellent in dispersion stability of a reversibly thermochromic microcapsule pigment and a writing instrument using the same. Disclosed is a reversibly thermochromic aqueous ink composition comprising a reversibly thermochromic microcapsule pigment encapsulating a reversibly thermochromic composition comprising (a) an electron-donating color-developing organic compound, (b) an electron-accepting compound, and (c) a reaction medium to determine an occurrence temperature of a coloring reaction of the component (a) and the component (b), and a vehicle comprising water and a specific gravity adjuster selected from the group consisting of an oxyacid belonging to Group 6 having an atomic weight of 90 to 185 or salt thereof.

Abstract: The present invention provides a thermochromic color-memory composition including (a) an electron-donating color-developing organic compound, (b) an electron-accepting compound, and (c) an ester compound represented by the following formula (1) or (2), as a reaction medium which controls color reaction of the component (a) and the component (b); and a thermochromic color-memory microcapsule pigment encapsulating the thermochromic color-memory composition.