Plunger kit, syringe kit, and prefilled syringe

A plunger kit comprising:

• a piston configured to be slidably inserted into a liquid medicine storage chamber of a syringe main body part, and a plunger rod mountable to the piston;
• wherein the plunger rod has a rod main body that extends in an axial direction and transmits drive force to the piston, and a mounting part that projects from a tip end of the rod main body and is for mounting the plunger rod to the piston;
• the mounting part includes a shaft part that projects from a tip end part of the rod main body to a tip end side with a substantially constant diameter, an engagement part that projects from a tip end part of the shaft part in a radial direction and forms an engagement surface formed substantially perpendicular to the axial direction, and a conical part disposed on a tip end side of the engagement part and reduced in diameter in a tapered manner toward a tip end;
• a recess is formed on the piston, the recess having an opening part opened in a base end direction, a narrow part communicating with a tip end side of the opening part and extending in the axial direction, and a storage part communicating with a tip end side of the narrow part and capable of storing the engagement part and the conical part, the storage part being formed in a hollow shape;
• and
• the piston has a first side wall part forming the storage part, and a second side wall part forming the narrow part and thicker than the first side wall part.

A prefilled syringe comprising:

• a plunger kit, the plunger kit comprising:
• a piston configured to be slidably inserted into a liquid medicine storage chamber of a syringe main body part, and a plunger rod mountable to the piston;
• wherein the plunger rod has a rod main body that extends in an axial direction and transmits drive force to the piston, and a mounting part that projects from a tip end of the rod main body and is for mounting the plunger rod to the piston;
• the mounting part includes a shaft part that projects from a tip end part of the rod main body to a tip end side with a substantially constant diameter, an engagement part that projects from a tip end part of the shaft part in a radial direction and forms an engagement surface formed substantially perpendicular to the axial direction, and a conical part disposed on a tip end side of the engagement part and reduced in diameter in a tapered manner toward a tip end;
• a recess is formed on the piston, the recess having an opening part opened in a base end direction, a narrow part communicating with a tip end side of the opening part and extending in the axial direction, and a storage part communicating with a tip end side of the narrow part and capable of storing the engagement part and the conical part, the storage part being formed in a hollow shape;
• and
• the piston has a first side wall part forming the storage part, and a second side wall part forming the narrow part and thicker than the first side wall part;
• and
• a syringe main body part having a liquid medicine storage chamber with a liquid medicine, a nozzle provided on a tip end of the liquid medicine storage chamber, and a cap that seals a tip end opening part of the nozzle.