| 摘要 |
PROBLEM TO BE SOLVED: To provide a pipe type ballpoint pen tip which obtains an enough ink outflow property even by adopting an extremely small ball and enables writing over a long period without dropping out the ball.SOLUTION: A ball 3 is rotatably held by a plurality of inward projecting portions 5 for a ball receiving seat formed by press-deforming a tip vicinity of a metal pipe 2 inward in a radial direction and a tip edge portion 4 formed by press-deforming the tip of the metal pipe 2 inward in the radial direction to form a ring. When a diameter of the ball 3 is 0.4 mm or less, a tilt angle α of a conical concave plane 6 of a front face of the inward projecting portion 5 is 75-90°and when a minimum inside diameter of the tip edge portion 4 is denoted by A, an inside diameter of the ball 3 is denoted by C, and an inside diameter of the metal pipe 2 between the tip edge portion 4 and the inward projecting portion 5 is denoted by B, [(A-C)/2]<[(B-C)/2] is satisfied, and a carbonaceous film is provided on an inner face of the tip edge portion 4 and/or on a surface of the ball 3, and the carbonaceous film has a carbon atom and an oxygen atom bonded to the carbon atom. |
