| 摘要 |
PROBLEM TO BE SOLVED: To achieve easier injection molding while preventing the infiltration of air and the spillage of the contents by protrusively arranging a plurality of inscribed surface parts with a specified value of width axially along a side which inscribes a circular arc of a circular arc-shaped section of the internal surface of an outer cylinder base end part while circumscribing a virtual concentric circular arc with the diameter thereof smaller than that thereof. SOLUTION: A plurality of inscribed surface parts 8 are protrusively arranged with a fixed value of the width on the internal surface 7 of a base end part 2 of an outer cylinder 1 in the direction of a circular arc of a circular arc-shaped section thereof axially along a side equivalent to one side portion which inscribes the circular arc-shaped section of the internal surface 7. A tapered opening part 9 is smoothly formed continuously at an opening side end part of the inscribed surface part 8. The axial lengths of the inscribed surface part 8 and a piston part 14 should be almost equal. For example, four of the inscribed surface parts 8 are arranged at an interval of 90 deg. and the interval of the inscribed surface parts 8 facing each other should be made to almost coincide with a virtual inscribed circle inscribing the opposed inscribed surface parts 8. |
