| 摘要 |
PROBLEM TO BE SOLVED: To prevent the increase of the rotational resistance of a ball having an arithematic mean roughness of a specific surface roughness and a specific outside diameter by preventing the increase in amount of ink that adheres to the outwardly exposed surface of the ball by specifying the amount of outward protrusion of the ball from its tip edge portion. SOLUTION: A tip main body 1 is formed by forming an ink passage hole 4 in the center of a bottom wall 3 of a ball holding chamber 2 and providing radial grooves 5 extending radially from the ink passage hole 4. Next, A ball 6 is inserted into the ball holding chamber 2 which ball has a ball diameter D of 1.2 to 3.0mm and a surface roughness in which the arithematic mean roughness (Ra) is 0.005 to 0.15μm so that it is brought into abutment with the bottom wall 3 for formation of a ball seat 7. Furthermore, a tip distal end portion 8 is inwardly caulked in such a manner that a projection amount H from the tip distal end portion 8 of the ball 6 becomes less than 25 to 30% of the ball diameter and the ball 6 is rotatably held, whereby a ballpoint pen tip 9 is prepared. Due to this construction, a phenomen is prevented from happening in which the tracing of writing disappear in the middle of writing and the deterioration of the performance at the start of writing is also prevented. |
