Abstract: Provided are a reversibly thermochromic aqueous ink composition having excellent writability and few problems such as aggregation of a colorant, an increase in viscosity of the composition, or a decrease in handwriting density, and a refill or an aqueous ballpoint pen using the reversibly thermochromic aqueous ink composition. A reversibly thermochromic composition is a reversibly thermochromic aqueous ink composition containing a reversibly thermochromic microcapsule pigment encapsulated in a microcapsule formed from an organic resin, an N-vinyl-2-pyrrolidone polymer, glycerin, and water, in which when contents (% by mass) of the reversibly thermochromic microcapsule pigment, the N-vinyl-2-pyrrolidone polymer, and the glycerin with respect to a total mass of the ink composition are PMC, PPVP, and PG, respectively, 0.3?PMC/(PPVP+PG)?4, and 0.2?PPVP/PG?5, and a refill or an aqueous ballpoint pen incorporating the reversibly thermochromic aqueous ink composition.

Abstract: [Problems] Provided are a highly marketable reversibly thermochromic composition that provides a black color during color development by using a fluoran derivative having a specific structure as an electron-donating color-developing organic compound, turns colorless during decoloration, and is excellent in contrast between a colored state and a decolored state and a microcapsule pigment encapsulating the same. [Solution] Disclosed are a reversibly thermochromic composition including: (a) a fluoran derivative having a specific structure as an electron-donating color-developing organic compound; (b) an electron-accepting compound; and (c) a reaction medium which reversibly induces an electron transfer reaction between the component (a) and the component (b) in a specific temperature range, and a reversibly thermochromic microcapsule pigment encapsulating the same.

Abstract: A writing instrument excellent in handwriting density and temporal stability. The writing instrument includes a ball-point pen tip attached to the front end portion of the ink storage cylinder; and a ball-point pen refill having an ink composition for a writing instrument loaded therein. The ink composition for the writing instrument is a thermochromic ink containing at least a thermochromic microcapsule pigment. The writing instrument includes a pressurization mechanism for applying a pressure to the back end of the ink composition for the writing instrument.

Abstract: A writing instrument excellent in handwriting density and temporal stability. The writing instrument includes a ball-point pen tip attached to the front end portion of the ink storage cylinder; and a ball-point pen refill having an ink composition for a writing instrument loaded therein. The ink composition for the writing instrument is a thermochromic ink containing at least a thermochromic microcapsule pigment. The writing instrument includes a pressurization mechanism for applying a pressure to the back end of the ink composition for the writing instrument.

Abstract: A writing instrument includes a pen point retaining member, a pen point that is attached to a first end of the pen point retaining member, an ink tank that is attached to a second end of the pen point retaining member, and an ink that is accommodated in the ink tank. The ink includes a lubricating interface layer-forming compound, and a carbonaceous film is formed on at least one of a surface of the ball or a contact portion of the ball holding portion with the ball.

Abstract: [Problem to be Solved] Provided is a writing instrument, in which stable writing performance can be maintained for a long term, and a feeling of writing and handwriting are favorable. [Solution] A writing instrument including: a pen point retaining member; a pen point that is attached to a first end of the pen point retaining member; an ink tank that is attached to a second end of the pen point retaining member; and an ink for a writing instrument that is accommodated in the ink tank. The ink includes a lubricating interface layer-forming compound, and a carbonaceous film is formed on at least one of a surface of the ball or a contact portion of the ball holding portion with the ball.