| 摘要 |
PROBLEM TO BE SOLVED: To provide a seal structure of a synthetic resin cap having a sealing part integrated with an inner surface side of a top plate part in which the cap can be easily opened/closed by a small force, and sealability at a seal part between a vessel mouth part and the cap can be reliably ensure. SOLUTION: In the synthetic resin cap 1 with an annular plug 16 integrally suspended from a top plate part of the cap so as to be abutted on an inner surface of the vessel mouth part 2, a part in the vicinity of the seal part abutted at least on the vessel mouth part 2 of an outer surface of the annular plug 16 is formed into a projecting curved surface 16a of arc-shape in longitudinal section which is outwardly protruded on the whole circumference, and a cap 1 is fitted to the vessel mouth part 2. In this condition, a most projecting part of the projecting curved surface 16a of the outer surface of the annular plug 16 is abutted on the inner surface of the vessel mouth part 2 as the seal part so that the annular plug 16 is deflected inwardly, and a part from a root 16c of the inner surface of the annular plug 16 to a back side of the seal part is formed into a projecting curved surface 16b of arc-shape in longitudinal section in a downwardly tapered manner around the whole circumference.
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