| 摘要 |
PROBLEM TO BE SOLVED: To prevent cracks from developing in a cap even after the repeated attachment and detachment of the cap to and from a writing utensil main body by a method wherein engaging undercuts to the writing utensil main body are provided at the positions rotated peripherally by proper angles in the peripheral wall of a cap main body, which is produced by injection-molding plastic. SOLUTION: A cap main body 1 with both upper and lower ends open is produced by injection-molding plastic under the condition that engaging undercuts 7 to a writing utensil main body are provided on the inner surface part near to the lower end opening part 6 of the cap main body. These undercuts 7 are provided at four positions in total on the peripheral wall of the cap main body 1 or positions, which are positioned by being further turned respectively by 45 deg. both to left and right sides from a position E turned by 180 deg. peripherally from a position on an axial extension line of a site G facing to the gate of a mold at molding, and positions, which are positioned by being further turned respectively by 90 deg. from the just-mentioned positions. In addition, the molds for molding the cap main body 1 is so constituted as to produce the weld-line of the cap main body at the same position as the position of E. |
