Self-blocking hypodermic syringe for once-only use, comprising a needle protection cap

Claim 2

A self-blocking hypodermic syringe for once-only use comprising a cylindrical body which at its front end carries means for connection to a hypodermic needle and is open at its opposite end, and contains a plunger which slides in a fluid-tight manner and is provided with a gripping rod, characterised by also comprising elastic means for blocking the intake stroke of the plunger (2) which are initially located in an inactive position and are transferred into an active position during the first syringe intake and injection operation, when in said active position the elastic means being disposed in a position secured to the cylindrical body (1) of the syringe and interfering with the plunger intake stroke.

Claim 3

A syringe according to claim 1, characterised in that the elastic means for blocking the plunger (2) intake stroke consist of a split-ring (7) which before the syringe is initially used embraces the minor diameter region of a frusto-conical portion (6) of the rod (4) of the plunger (2) which converges in the direction in which the plunger (2) is driven for injection, the minor diameter region of the frusto-conical portion (6) having a diameter less than the diameter of the rod (4) and the major diameter region having a diameter substantially equal or slightly less than the inner diameter of the cylindrical body (1), the syringe cylindrical body (1) comprising an annular bulge (9) which is able to receive the split-ring (7) when this is drawn in front of it during the initial liquid intake stage, said bulge (9) having an inner diameter greater than the diameter of the major diameter region of the frusto-conical portion (6) plus the thickness of the split-ring (7) and being positioned at a distance from that end of the cylindrical body (1) carrying the needle which exceeds the distance between the front end of the plunger (2) and the rear surface of its frusto-conical portion (6), when in its undeformed state the split-ring (7) having an inner diameter less than the maximum diameter of the frusto-conical portion (6) and an outer diameter greater than the inner diameter of the cylindrical body (1), and being elastically deformable to widen out into the bulge (9) under the action of the frusto-conical surface as the plunger (2) is driven in.

Claim 4

A syringe according to claim 2, characterised in that before the syringe is initially used, the split-ring (7) is in a position forward of the bulge (9) in the cylindrical body (1) and is in an elastically deformed contracted state.

Claim 5

A syringe according to claim 3, characterised in that the distance between the split-ring (7) when in its initial position, i.e. embracing the minor diameter region of the frusto-conical portion (6), and the bulge (9) in the cylindrical body (1) is less than that stroke of the plunger (2) which corresponds to the minimum scheduled liquid dosage for which the syringe can be used.

Claim 6

A self-blocking hypodermic syringe for once-only use according to claim 1, characterised by comprising a slidable cap (109) coaxial to the syringe body (1) and covering the body itself, and being provided at its front with an exit hole (109 a ) for the needle (101 a ), and further having members for its fastening to the syringe body (1), and elastic thrust means, said cap (109) when in its retracted position leaving the needle (101 a ) exposed and when in its advanced position covering the needle, the fastening members being moved into their released position by release means associated with the first forward movement of the plunger.

Claim 7

A syringe according to claim 5, characterised in that the cap fasten­ing members consist of elastic tongues (110) provided in the rear part of the cap (109) and having their ends (110 a ) turned inwards to form a hook so that when the cap (109) is in its retracted position they become inserted into corresponding slots (111) in the syringe body (1) to axially lock the cap (109), the release means consisting of elastic means for blocking the intake stroke of the plunger (2), which are provided within the syringe in a position corresponding with the slots (111) in the syringe body (1) which house the hook-shaped ends (110 a ) of the tongues (110) provided on the cap (109), and are arranged to be radially deformed by the forward stroke of the plunger (2) during the first injection, so urging the hook-shaped ends (110 a ) out of the relative slots (111).

Claim 8

A syringe according to claim 6, characterised in that the syringe body (1) also possesses one or more recesses (113) for receiving the fastening elements on the tongues (110) of the cap (109) when the cap (109) is in its advanced position in which it encloses the needle (101 a ), to thus block any further sliding of the cap (109) and prevent its escape.

Claim 9

A syringe according to claim 6, characterised in that the elastic element inside the syringe, which urges the hook-shaped ends (110 a ) out of the relative slots (111), consists of a split-ring (7) which before the syringe is used embraces the minor diameter region of a forwardly converging frusto-conical portion (6) of the rod (4) of the plunger (2), and is arranged to be dragged during the first intake stroke into an inner annular cavity (108) in the cylindrical syringe body (1) into which the slots (111) in the body (1) which house the hook-shaped ends (110 a ) of the tongues (110) open, the split-ring (7) being radially deformable outwards under the action of the frusto-conical portion (6) during forward movement of the plunger (2).

Claim 10

A syringe according to claim 5, characterised in that the elastic means for urging the cap (109) into its advanced position consist of a spiral spring (112) interposed between the front surface of the syringe body (1) and the front end of the plunger (2), said elastic means being preloaded by the cap being placed in its retracted position, before the syringe is used.

Claim 11

A syringe according to any claim from 5 to 9, characterised in that under the initial conditions, before the syringe is used, the front end of the cap (109) is rearward of the base of the needle (101 a ) by a distance equal to the distance through which the cap (109) has to be advanced in order to completely release the hook-shaped ends (110 a ) of the tongues (110) on the cap (109) from the respective slots (111) in the syringe body without their re-insertion into the slots (111) being possible.

Claim 12

A syringe according to claim 7, characterised in that the hook-­shaped ends (110 a ) of the cap (109) tongues have their outer surface bevelled towards the rear of the syringe, and in correspondence with these the recesses (113) in the syringe body (1) which receive the cap (109) tongue (110) fastening elements (110 a ) when the cap (109) is in its advanced position have an undercut rear wall to cause the tongues (110) to deflect inwards should the cap (109) receive a rearward thrust.

Claim 13

A syringe according to any claim from 5 to 11, characterised in that the needle (101 a ) has its axis oblique to the axis along which the cap (109) slides on the syringe body (1), and is elastically flexible during the sliding of the cap (109), after completion of this sliding it returning to its initial oblique axis position within the cap (109) with its free front end laterally displaced from the axis of the front hole (109 a ) in the cap (109).

Claim 14

A syringe according to any claim from 5 to 12, characterised in that the cap (109) is constructed of transparent material, to allow the quantity of liquid present in the syringe body (1) to be seen.