Abstract: Provided is an aqueous ink composition for a writing instrument which is excellent in storage stability of particles, such as pigments, a writing property with the passage of time, followability, and quality of the drawn lines, though having a low viscosity, as compared with aqueous ink compositions prepared by using conventional thickeners and gelling agents, such as xanthan gum. The ink composition for a writing instrument described above includes an aqueous ink composition for a writing instrument containing 0.05 to 1.5% by mass of an oxidized cellulose and having a limiting viscosity of 16 mPa·s or less derived from Casson's equation, a viscosity value of 100 to 3000 mPa·s at a shear rate of 3.83 s?1 and a viscosity value of 10 to 40 mPa·s at a shear rate of 383 s?1.

Abstract: Provided is an aqueous ink composition for a writing instrument which is excellent in storage stability of particles such as pigments, a writing property with the passage of time, and quality of the drawn lines, though having a low viscosity, as compared with conventional thickener and gelling agents such as a xanthane gum. The above ink composition for a writing instrument is characterized by containing 0.05 to 1.5% by mass of an oxidized cellulose and having a limiting viscosity of 10 mPa·s or less derived from a Casson's equation.

Abstract: Provided is an aqueous ink composition for a writing instrument which is inhibited in time-dependent heterogeneity (difference in viscosity between up- and down-sides) in viscosity distribution in an aqueous ink composition containing an oxidized cellulose and which is excellent in time-dependent viscosity distribution stability. The above aqueous ink composition for a writing instrument includes, for example, an aqueous ink composition containing at least 0.05 to 1.5% by mass of an oxidized cellulose and 0.001 to 30% by mass of sugars having a weight average molecular weight of 5000 or less.