Patent ID: 7390138

Claim:
A ballpoint pen comprising: an ink accommodation cylinder; a ballpoint pen tip in which a ball is rotatably held, the pen tip being attached to a tip end of an ink-accommodation cylinder directly or through a tip holder; and ballpoint oil-based ink comprising at least a coloring agent, organic solvent, a lubricant comprising organic acid and phosphoric ester, and organic amine, the ink having ink viscosity at shearing speed 6.8 sec −1 of 500 to 6000 mPa·s (20° C.) and directly being accommodated in the ink-accommodation cylinder, wherein the ballpoint pen satisfies 2.5×10 −3 ≧Z≧1.0×10 −3 where ink amount per 1 mm 2 is Z mg/mm 2 which is calculated from Y=X×10 5 ×Z where writing width of the ballpoint pen is X mm and ink consumption per 100 m is Y mg.