Patent ID: 11951289
Assignee: WEST PHARMACEUTICAL SERVICES, INC.
Field: Medical technology (Instruments)
Classification: CPC A | IPC A

Claim 13:
14. A syringe comprising a barrel and a piston within the barrel, the piston manufactured by a method comprising:
placing a first rubber sheet and an inert film between die plates of a first forming tool;
vulcanizing the first rubber sheet and the inert film between the die plates of the first forming tool to form a first piston body, the first piston body comprising a central face portion at a distal axial end of the first piston body, and an annular curved portion, the central face portion and at least a part of the annular curved portion being enclosed by the inert film;
blanking out the first piston body from the first rubber sheet and the inert film;
placing the first piston body into a second forming tool;
placing a second rubber sheet into the second forming tool;
vulcanizing the second rubber sheet and the first piston body together to form a second piston body and joining the second piston body to the first piston body to form the piston, the second piston body comprising a proximal axial end that circumscribes the second piston body; and
blanking out the piston from the second rubber sheet at a trim edge, wherein:
the trim edge is spaced apart from the inert film between the inert film and the proximal axial end,
the central face portion is oriented coaxially with respect to a longitudinal axis of the piston, the piston defining a first piston diameter measured perpendicularly to the longitudinal axis, the first piston diameter is a maximum diameter of the central face portion and is less than an inner diameter of an inner wall of the barrel,
the first piston body further comprises a cylindrical portion oriented coaxially with the longitudinal axis, the cylindrical portion defining a first axial end, a second axial end, and a wall extending a distance along the longitudinal axis between the first axial end and second axial end, the wall defining a second piston diameter measured perpendicularly to the longitudinal axis, the second piston diameter is larger than the inner diameter of the barrel,
the annular curved portion extends between the first axial end of the cylindrical portion and the central face portion,
the annular curved portion comprises:
a first portion defining a curve and a diameter that is less than the second piston diameter; and
a second portion with a diameter that is substantially equal to the second piston diameter, the second portion of the annular curved portion extends a distance along the longitudinal axis,

the inert film defines an outer boundary that does not extend axially beyond the first axial end of the cylindrical portion to minimize contact between the inert film and the inner wall of the barrel, and
the distance that the wall of the cylindrical portion extends along the longitudinal axis is greater than the distance that the second portion of the annular curved portion extends along the longitudinal axis.