An aqueous ink composition for writing instruments containing an aqueous dispersion of colored resin fine particles, the colored resin fine particles containing at least a cyclohexyl (meth)acrylate monomer and a basic dye or an oil-soluble dye, the cyclohexyl (meth)acrylate monomer being contained in an amount of 30 mass% or greater relative to an amount of a polymerizable polymer component in the colored resin fine particles, and the colored resin fine particles further containing a terpene phenol resin.

Provided is an ink composition for an aqueous ballpoint pen, the composition having excellent ink discharging performance even if a pen point is exposed for a long period of time. The ink composition for an aqueous ballpoint pen according to the present invention is characterized by containing at least from 1 to 35 mass % of titanium oxide having an average particle size of greater than 0.1 μm and smaller than or equal to 1 μm, and from 1 to 35 mass % of non-tacky urethane particles having an average particle size from 0.1 to 6 μm.

Provided is an ink composition for an aqueous ballpoint pen, the composition having excellent ink discharging performance even if a pen point is exposed for a long period of time. The ink composition for an aqueous ballpoint pen according to the present invention is characterized by containing at least from 1 to 35 mass % of titanium oxide having an average particle size of greater than 0.1 μm and smaller than or equal to 1 μm, and from 1 to 35 mass % of non-tacky urethane particles having an average particle size from 0.1 to 6 μm.

There is a compound represented by the following formula (I):

##STR00001##

in which R1 and R2, identical or different, represent a C.sub.2-C.sub.30 alkyl group, a C.sub.2-C.sub.30 alkenyl group, a C.sub.2-C.sub.30 alkynyl group, or a C.sub.2-C.sub.30 alkoxy group, the alkyl, alkenyl, alkynyl, or alkoxy groups being optionally substituted with at least one hydroxy, halogen, amino, C.sub.1-C.sub.8 alkyl, or C.sub.1-C.sub.8 alkoxy group, as a temperature change regulating agent in a thermochromic ink composition. There also are thermochromic pigment microcapsules having a compound of formula (I) according to the disclosure, to ink compositions having such thermochromic pigment microcapsules, and to writing instruments comprising such ink compositions.

Provided are an oil-based ink composition for writing utensils, a writing utensil using the same, and an airbrush unit using the same. The oil-based ink composition for writing utensils has good writing properties on writing surfaces of various materials and improved scratch resistance to scratches repeated or to scratches with stronger force on a marking after writing. The subject oil-based ink composition for writing utensils contains at least an aluminum pigment, a colorant, a resin, an organic solvent, and a polydimethylsiloxane, the polydimethylsiloxane having polyether-modifying groups at both ends, and a total number of hydroxyl groups on the polyether-modifying groups being 3 or greater.

A ballpoint pen is disclosed. In the ballpoint pen, an oil-based ballpoint pen ink composition has an ink viscosity with a range of 500 mPa.Math.s to 15000 mPa.Math.s inclusive at 20° C. and a shear rate of 500 sec.sup.-1. A ball has a ball diameter of 0.5 mm or less. A tip distal end portion includes a first swaged portion and a second swaged portion. The first swaged portion has an inclination angle with a range of 90 degrees to 100 degrees inclusive. The second swaged portion is provided closer to a distal end side of a ballpoint pen tip than the first swaged portion and has an inclination angle with a range of 110 degrees to 130 degrees inclusive. An angle of a bottom wall of a ball holding chamber is the same as the inclination angle of the second swaged portion.

A ballpoint pen is disclosed. In the ballpoint pen, an oil-based ballpoint pen ink composition has an ink viscosity with a range of 500 mPa.Math.s to 15000 mPa.Math.s inclusive at 20° C. and a shear rate of 500 sec.sup.-1. A ball has a ball diameter of 0.5 mm or less. A tip distal end portion includes a first swaged portion and a second swaged portion. The first swaged portion has an inclination angle with a range of 90 degrees to 100 degrees inclusive. The second swaged portion is provided closer to a distal end side of a ballpoint pen tip than the first swaged portion and has an inclination angle with a range of 110 degrees to 130 degrees inclusive. An angle of a bottom wall of a ball holding chamber is the same as the inclination angle of the second swaged portion.

Provided is an aqueous ink composition for writing instruments which is excellent in an antibacterial property and an antifungal property without damaging storage stability and writing performances. The aqueous ink composition for writing instruments according to the present invention is characterized in that at least particles comprising principally a polymer represented by the following Formula (I) are contained as an active ingredient and that a content thereof is 0.1 to 30 mass %:

##STR00001##

wherein R is an alkyl group having 2 to 8 carbon atoms.

An oil-based ballpoint pen includes: an ink container configured to accommodate an ink composition for the oil-based ballpoint pen, the ink composition containing colorant, alkylene glycol alkyl ether, and polyacrylic resin; and a ballpoint pen tip configured to rotatably hold a ball at one end thereof in an extending direction of the ink container. A ratio of an ink consumption (mg) per writing distance of 100 m to a diameter (mm) of the ball is 30 or more.

An oil-based ballpoint pen includes: an ink container configured to accommodate an ink composition for the oil-based ballpoint pen, the ink composition containing colorant, alkylene glycol alkyl ether, and polyacrylic resin; and a ballpoint pen tip configured to rotatably hold a ball at one end thereof in an extending direction of the ink container. A ratio of an ink consumption (mg) per writing distance of 100 m to a diameter (mm) of the ball is 30 or more.