Flexibly Deformable Stopper For A Hypodermic Syringe

Abstract

A flexibly deformable stopper for a hypodermic syringe consisting of a neck having a central channel, a diaphragm at one end of the neck and an annular flange having a quadrangular cross-section at the closed end. The front face and the rear face of the flange enclose an acute angle with the neck and extend in the same direction, the outer edge projecting beyond the front side of the diaphragm in such manner that during the clamping operation of the flange the diaphragm is pre-stretched.

Description

The invention relates to a flexibly deformable stopper for a hypodermic syringe consisting of a neck having a central channel which is open at one end and is closed at the other end by a diaphragm and comprising at the closed end an annular flange having a quandrangular cross-section.

Such stoppers are used in hypodermic syringes which have a cartridge forming a piston, which may be filled with a medicament. In this syringe the stopper separates the cartridge from the injection needle which is supported by the cartridge.

Communication of the medicament between the cartridge and the needle is known to be effected by causing the diaphragm to burst as a result of a fluid pressure which is exerted on the diaphragm by means of the piston, in which the diaphragm is stretched and is or is not contacted, prior to bursting, with the sharp end of the needle or with other perforation elements. The stoppers used in said syringes should be of such a construction that, during the injection of a medicament, clogging of the needle is prevented and, during the aspiration of moisture or blood, the flow aperture of the diaphragm remains free.

Stoppers of the known type, are of such a construction that due to the deformation of the flange during the clamping-in thereof between the cooperating parts of the hypodermic syringe, the flange will expand in the direction of the center line of the stopper so that the diaphragm is compressed in the radial direction and is not tautly stretched in the clamped condition of the stopper. The compression of the diaphragm results in requiring it to be considerably stretched in order to cause it to burst. As a result of this the operation of the diaphragm during the injection and the aspiration is adversely affected.

It is the object of the invention to provide a stopper for a hypodermic syringe which will overcome the disadvantages of prior stoppers and which is of such a construction that the flow aperture of the burst diaphragm is maintained unobstructed in all circumstances, both during the injection of a medicament and during the drawing of blood or fluid.

In accordance with the present invention, the above stated object is achieved by providing that both the front face and the rear face of the flange enclose an acute angle with the neck and said faces extend in the same direction, the outer edge of the front face projecting beyond the front of the diaphragm remote from the neck, all this in such manner that, during the clamping operation of the flange, the diaphragm is pre-stretched. During the clamping operation of the stopper between two flanges of the hypodermic syringe, the flange of the stopper is deformed and bent backwards in the direction of the open end of the neck so that the diaphragm is tautly stretched (pre-stressed). Because the diaphragm is pre-stressed the relaxation after expanding the material from which the stopper is manufactured is compensated for. The burst diaphragm tends to shrink in the radial direction towards the flange, so that a flow aperture is obtained which remains free. Experiments have proved that this is possible with stoppers manufactured from various materials having different medical properties and different relaxation properties.

According to a preferred embodiment of the stopper in accordance with the present invention, the flange has a substantially rhombic cross-section the sides of which form describing lines of four conical surfaces, the apices of which are situated on the center line of the neck. As a result of the flange design, space is created on its circumference to accommodate the radial expansion of the flange during the clamping operation. During the compression the flange is pressed radially to the outside, so that the prestress of the diaphragm is increased.

According to a further preferred embodiment of the stopper according to the invention, the face of the flange which adjoins the neck adjoins the outer circumference of the neck with a rounding. The stopper at the area of the transition has an axial wall thickness which is smaller than the maximum axial thickness of the flange. Due to the rounded transition between the flange and the neck a deformation of the neck is prevented. At the area of the transition, a bending of the flange relative to the neck occurs during the clamping operation in which the surface and the rear face of the flange contact the cooperating flanges of a syringe with the whole surface so that a good seal is obtained.

According to a further preferred embodiment of the stopper according to the invention, the radial distance, viewed in the cross-section, from the vertex of the flange projecting beyond the front side of the diaphragm to the center line is larger than the radial distance to the center line of the oppositely located vertex facing the neck. Due to the difference in the radial distances of the two vertices a lever action is obtained during the clamping operation of the flange as a result of which the stretching of the diaphragm is stimulated.

According to the invention the above-described stopper can advantageously be used in a hypodermic syringe comprising a cartridge which has at one end a narrowed neck with adjoining flange, a needle holder comprising a chamber and a hollow needle and a flange part near the end of the chamber remote from the needle, a stopper having a neck being provided in the narrowed neck of the cartridge, a flange of the stopper being clamped, by means of a connection part, between the flange part of the needle holder and the flange of the cartridge in a deformed condition and in a sealing manner. In this case the flange of the stopper is bent backwards relative to the neck so that the diaphragm is under a stretched condition.

In order that the invention may be readily carried into effect, it will now be described in greater detail, by way of example, with reference to the accompanying drawings, in which

FIG. 1 is a cross-sectional view of an embodiment of the stopper according to the invention taken on the line I--I of FIG. 2,

FIG. 2 shows the stopper viewed in the axial direction taken on the line II--II of FIG. 1,

FIG. 3 is a partial longitudinal cross-sectional view of a hypodermic syringe comprising a stopper according to the invention prior to clamping the flange;

FIG. 4 is a longitudinal cross-sectional view of the hypodermic syringe with the stopper in the clamped condition, and

FIG. 5 is another embodiment of a stopper according to the invention.

The stopper 1 shown in FIGS. 1 and 2 comprises a neck 3 having a central channel 5 which is closed at one end 7 by a flat thin-walled diaphragm 9 and which is open at the other end 11. At the closed end 7 the stopper comprises an annular flange 13 which, in the example shown, has a rhombic profile 15. The four sides 17, 19, 21 and 23 of the profile 15 form describing lines of four conical surfaces which bound the front face 25, the outer circumference 27, the rear face 29 and the inner circumference 31, respectively, of the flange. The front face 25 and the rear face 29 extend in the same direction and enclose an acute angle .alpha. with the center line 33 of the neck 3, the outer edge 35 of the end face 25 projecting beyond the front side 37 of the diaphragm 9. The apices 39 of the end face 25 and the rear face 29 lie on the part of the center line 33 facing the open end 11. The outer circumference 27 and the inner circumference 31 likewise extend in a same direction and enclose an acute angle .beta. with the center line 33, their apices 41 being situated on the part of the center line 33 remote from the open end 11. The inner circumference 31 which adjoins the neck 3 is connected to the outer circumference 45 of the neck 3 by a rounded section 43 having a wall thickness d which is smaller than the maximum axial wall thickness D of the flange 13. Viewed in the cross-section, the radial distance R from the apex 35 projecting beyond the front side 37 to the center line 33 is larger than the corresponding distance r of the apex 49 facing the neck 3. The neck 3 furthermore comprises a number of longitudinal ribs 51, in the present example four such longitudinal ribs are provided.

FIG. 3 shows a part of a hypodermic syringe having a stopper, the flange of which is not yet clamped. The hypodermic syringe 53 comprises a cartridge 55 and adjoining flange 59. A hollow injection needle 61 is secured in a needle holder 63 which comprises a chamber 65 and has a flanged portion 67. During assembly, the neck 3 of the stopper 1 is inserted in the narrowed neck 57 of the cartridge 55, the longitudinal ribs 51 facilitating the insertion of the stopper. The flange 13 of the stopper 1 becomes situated between the flange portion 67 of the needle holder 63 and the flange 59 of the cartridge 55 in which, as is shown in FIG. 3, the outer edge 35 of the end face 25 contacts the flange portion 67 first, while the inner edge 49 of the rear face 29 contacts the flange 59. Due to the rhombic profile 15, free space is present between the conical surfaces of the flange and the adjacent wall parts of the hypodermic syringe in the non-deformed condition of the flange.

FIG. 4 shows the hypodermic syringe 53 with the stopper 1 in the mounted clamped condition in which the flange 13 is compressed between the flange portion 67 and the flange 59 by means of a bent-over collar 69. In this example the collar 69 forms part of the needle holder 63 which is manufactured from metal. Clamping the needle holder 63 to the cartridge 55 can be effected in any other conventional manner, for example, by means of a separate ring separated from the needle holder 63, in which the needle holder may be manufactured from a synthetic resin. During clamping of the needle holder 63 to the cartridge 55, the flange 13 experiences a bending action on the part situated at the area of the rounding 43, so that the originally conical end face 25 becomes located in the flat plane of the flange portion 67 and the rear face 29 becomes located in the plane of the flange 59. Due to this bending of the flange 13, the diaphragm 9 is tautly stretched and subjected to a pre-stress after which the stopper 1 is clamped in this condition by bending over the collar 69. As a result of the free space available between the flange 13 and the adjacent wall parts, said flange, during the clamping operation, can expand towards the outside in a radial direction remote from the center line, so that the pre-stress is increased.

When using the hypodermic syringe 53, filled, for example, with a medicament 71, a pressure is exerted on the medicament 71 in the cartridge 55 by means of the piston 73, so that the diaphragm 9 begins to bulge into the chamber 65, is subjected to a tensile stress and ultimately bursts, the tensile stress being mainly removed during bursting. On the basis of the relaxation power of flexible materials, a diaphragm tends to return to the original condition in a delayed manner. Since, however, in the stopper according to the invention the diaphragm 9 is pre-stretched, the relaxation influence is removed and even overcompensated in accordance with the material used. The diaphragm tends to shrink in a radial direction away from the center line, so that the burst diaphragm shows a flow aperture which remains free in all circumstances.

The construction of the stopper 1 is such that in most of the cases the diaphragm can be made to burst as a result of the fluid pressure. In order also to cause diaphragms having too large a wall thickness deviating from the required thickness to burst with certainty, the needle 61 comprises, at its end facing the diaphragm 9, a sharp tip 75 which extends in the chamber 65. The bursting of the diaphragm is introduced by the contact with the sharp tip. Instead of providing the needle 61 with a sharp tip 75, other sharp elements known per se may be provided in the needle holder 63.

FIG. 5 shows another embodiment of the stopper according to the invention. This stopper 1 likewise comprises a flange 13 having a rhombic profile 15, the front face 25 and the rear face 29 of which enclose an acute angle .alpha. with the center line 33 of the neck 3, said faces forming parts of conical surfaces the apices 39 of which are situated on the part of the center line facing the open end 11. The outer circumference 77 extends parallel to the center line 33, while the rear face 29 adjoins the cylindrical outer circumference 45 of the neck 3 directly or via an annular chamber 78. In this embodiment also a bending of the flange 13 relative to the neck 3 takes place during the clamping operation of the stopper 1 so that the diaphragm 9 comes under a pre-stress.

The invention is not restricted to the examples described but also comprises other constructions, for example, a stopper in which the boundary lines of the profile are curved, a stopper in which the front face and the rear face of the flange do not extend in parallel, or a stopper the flange of which has the profile of a trapezium.

Claims

What is claimed is:

1. A stopper of flexibly deformable material for a hypodermic syringe comprising a neck having a central channel being open at one end thereof and closed at its other end, a diaphragm forming the closure at the closed end of said neck, an annular flange attached to said neck at its closed end, said flange having a quadrangular cross-section, a front face and a rear face extending in parallel directions and forming acute angles with the center line of the neck in the direction of the closed end, the outer edge of the front face projecting beyond the front of the diaphragm remote from the neck whereby the diaphragm will be stretched when said flange is clamped in the syringe.

2. The stopper according to claim 1 wherein said flange has a substantially rhombic cross-section the sides of which form describing lines of four conical surfaces, the apices of which are located on the center line of the neck.

3. The stopper according to claim 1 further comprising a rounded section connecting the face of the flange with the outer circumference of the neck, the axial wall thickness of said rounded section being smaller than the maximum axial thickness of the flange.

4. The stopper according to claim 1 wherein the radial distance from said outer edge of the front face projecting beyond the front of the diaphragm to the center line of said neck is larger than the radial distance from the outer edge of the rear face closest to said neck to the center line of said neck.