WO1991002556A1

WO1991002556A1 - Disposable syringe

Info

Publication number: WO1991002556A1
Application number: PCT/DK1990/000209
Authority: WO
Inventors: Finn Toft Madsen
Original assignee: Pharma-Plast A/S
Priority date: 1989-08-16
Filing date: 1990-08-15
Publication date: 1991-03-07
Also published as: AU6278990A; DK402689D0

Abstract

A disposable syringe preferably for injection comprises a barrel (1) and a piston rod (3) displaceable forwards and backwards inside said barrel, where the piston rod carries a resilient piston (5) on a pin (4), said piston sealingly abutting on the wall (1) of the barrel. The pin (4) comprises a circumferential, radially extending front and rear, respectively, abutment surface (8, 9) at each end, said abutment surfaces in the axial direction of the piston rod (3) being mutually spaced such that the piston (5) can be displaced between two positions in which the ends of the piston (5) alternately form a sealing connection with the adjacent abutment surface (8, 9). At the end farthest from the outlet end of the barrel (1) the piston (5) comprises a foldable, circumferential collar (17), said collar being hinged to the piston (5) and receivable in a circumferential recess (20) while abutting on the piston rod pin (4). The collar (17) comprises a plurality of passages. The piston rod pin (4) comprises a circumferential groove (11) receiving the circumferential collar (17) on the piston (5) when said piston sealingly cooperates with the rear abutment surface (9), and in addition the groove turns out the collar (17) into a position in extension of the piston (5) when said piston (5) moves away from the end of the pin (4).

Description

Title: Disposable S yr in g e

Technical Field

The invention relates to a disposable syringe preferably for injection and comprising a barrel and a piston rod displaceable forwards and backwards inside said barrel, where the piston rod carries a resilient piston on a protruding pin, said piston sealingly co-operating with the wall of the barrel and comprising a through hole receiving the protruding pin of the piston rod, where said pin comprises a circumferential, radially extending front and rear, respectively, abutment surface at each end, said abutment surfaces in the axial direction of the piston rod being mutually spaced a distance greater than the axial distance between mating abutment surfaces at the ends of the piston so as to allow a relative displacement of the .piston between two positions in which the ends of the piston alternately form a sealing connection with one of the abutment surfaces.

Background Art It is a well-known fact that injection syringes involve a risk of infection if the syringe is reused. Accordingly a great demand exists for a guarantee that the syringe cannot be reused despite various attempts in this respect. Previously known disposable injection syringes turned out not to meet the above demand because a skilled manipulation of such syringes allows a reuse thereof. The lack of such disposable syringes has sometimes resulted in a decision not to vaccinate in order to avoid dissemination, which inter alia has caused a relatively high infant mortality in certain areas of the world.

Disclosure of the Invention The disposable syringe according to the invention is characterised in that the piston comprises a foldable and circumferentially extending collar at the end farthest from the outlet end of the barrel, said collar being hinged to the piston and receivable in a mating circumferentially extending recess in the piston at the opening of the hole while abutting on the piston rod pin, whereby said collar comprises a plurality of perforations or passages, and that the piston rod pin comprises a circumferential groove at the rear abutment surface situated farthest from the outlet end of the barrel, whereby the circumferential groove receives the collar on the piston when said piston sealingly co-operates with the rear abutment surface, and whereby said groove turns out said collar into a position substantially in extension of the piston when said piston moves away from the end of the pin in a direction towards the front abutment surface at the opposite end.

The resulting disposable syringe cannot be used twice. During the mounting procedure where the piston rod pin is inserted through the piston from the end provided with the collar, the piston enters a position in which it directly engages the front abutment surface with the collar folded downwards into its position in the associated recess. The latter is obtained by initially placing the piston in the bottom of the barrel whereafter the piston rod is inserted. As a result, the piston does not come near the rear abutment surface before the disposable syringe has been used once. When the disposable syringe is to be used, the liquid dose in question is sucked in a conventionally known manner into the syringe by retracting the piston rod while the piston remains sealingly engaging the front abutment surface. During the following expelling of air bubbles and initiation of the injection by displacing the piston rod forwards towards the outlet end of the barrel, the piston enters the sealing engagement with the rear abutment surface and remains in said engagement until the injection has been completed. Attempts at sucking a liquid dose into the barrel again have the effect that the piston slides forwards on the piston rod pin towards the front abutment surface simultaneously with the collar being folded axially backwards in extension of the piston by engaging the circumferential groove in the piston rod pin. Succeeding attempts at injection starting with an expelling of air have the effect that the collar engages the rear abutment surface and/or adjacent surfaces in the bottom of the circumferential groove in the piston rod pin. The perforations or passages provided in connection with the collar cause a ieaking which prevents a sealing connection from being reestablished at the rear end of the piston. According to the invention the front abutment surface on the piston rod pin adjacent the outlet end of the syringe may be formed by a circumferential flange, which by applying a low pressure can pass through the hole of the piston during the mounting procedure, the piston comprising a recess adjacent the outlet end of the syringe, said recess receiving the circumferential flange, and the abutment surface on said flange may co-operate with a substantially conical surface in the bottom of the recess and provided about the hole, said conical surface being adapted to sealingly engage the abutment surface adjacent the centre of the hole. As a result, an extremely good sealing connection is obtained between the piston and the front abutment surface during the suction procedure. Furthermore it is ensured, that the piston rod pin cannot be retracted from the piston in connection with attempts at repeating the mounting procedure and reusing the syringe.

Furthermore according to the invention, the circumferential front flange may comprise an axially extending projection engaging the front end portion of the syringe and preventing the piston rod from passing so far through the piston during the mounting procedure that the foldable collar of said piston is caused to engage the circumferential groove. In this manner it is ensured that the piston is correctly positioned relative to the piston rod pin during the mounting procedure despite a possible narrowing of the cross section of the barrel cavity towards the outlet opening.

Moreover according to the invention, the piston may be formed in one piece with the foldable collar of a plastic material, where the collar is moulded with such a built-in memory that the collar tends to automatically enter a position in which it projects radially inwards in extension of the remaining portion of the piston. In this manner a particularly high security is obtained that the collar engages the groove in the piston rod pin.

According to the invention it is particularly preferred that the hole of the piston comprises a portion of such a reduced radius in the front end adjacent the injection opening that inside said portion the front end sealingly abuts on the pin of the piston rod, and that the pin of the piston rod comprises recessed portions situated a distance from the front abutment surface and ensuring a passage of air and liquid between the piston and the pin of the piston rod when the piston has left the sealing connection with the front abutment surface.

Moreover according to the invention it is particularly advantageous that the collar is of a substantially rectan gular cross section, which in the unstressed state forms a ring coaxially arranged relative to the piston, said ring being defined by two substantially parallel, radial planes, of which one plane is placed a distance from the end of the piston and the other plane coincides with the end of the piston, and that the collar is hinged to the piston along the outer circumferential rim adjacent the p i s t o n .

According to the invention the hinged connection between the piston and the collar may form a circumferential ridge to be used by the sealing co-operation with the rear abutment surface on the piston rod when the collar has been received in the mating recess in the piston at the opening of the hole, whereby a particularly good sealing connection is obtained between the piston and the rear abutment surface during the injection. Finally according to the invention the collar may be received in the mating recess in the piston, whereafter said collar tends to project radially, inside the adjacent portion of the wall in the hole through the piston, whereby the collar easily engages the rim of the groove when the piston moves forward at attempts at reuse of the syringe.

Brief Description of Drawing

The invention is described in greater detail below with reference to the accompanying drawing, in which

Fig. 1 is an axial, sectional view through a preferred embodiment, of a syringe according to the invention,

Fig. 2 is a side view on a larger scale of the lower portion of the piston rod with a pin carrying a piston,

Fig. 3 is a cross-sectional view of the pin taken along the line I-I of Fig. 2, Fig. 4 is an axial, cross-sectional view on a larger scale of the piston arranged inside the barrel of the syringe, the inner wall of said barrel being indicated,

Fig. 5 illustrates the front portion of the piston rod provided with the pin and the rear portion of the piston immediately before the pin is inserted through the piston during the mounting procedure,

Fig. 6 corresponds to Fig. 5 apart from the fact that the front end of the pin has been partially inserted in a through hole in the piston, said piston being shown full size in an axial view and arranged in the interior of the barrel of the syringe, where the inner wall of the barrel is Indicated, Fig. 7 illustrates the piston rod pin completely inserted through the entire piston at the end of the mounting procedure and ready for the suction in of a dose of liquid, also shown in the lower portion of the barrel of the injection with the inner wall of said barrel being indicated,

Fig. 8 corresponds to Fig. 7 except for the fact that Fig. 8 illustrates the termination of an injection, and

Fig. 9 corresponds to Fig. 7 except for the fact that Fig. 9 illustrates the starting of another injection in connection with an attempt at reusing the syringe.

Best Mode for Carrying Out the Invention

The embodiment of Fig. 1 of a syringe to be used for injections comprises a barrel 1 carrying a needle 2 at the front. A piston rod 3 is provided inside the barrel 1. When seen in the direction towards the needle 2 or the outlet end of the syringe, the front end of the piston rod comprises a pin 4. A piston 5 of resilient material, such as silicon rubber, is axially displaceably mounted on the pin 4. The pin 4 is defined by a front flange 6 and a rear flange 7, of. Fig. 2, said flanges forming a front radial, circumferential abutment surface 8 and a rear radial, circumferential abutment surface 9, respectively. The piston 5 can move between the flanges by being axially displaced. As illustrated in Fig. 1, the barrel comprises a circumferential narrowing 10 at the end placed opposite the needle 2. The narrowing is formed after insertion of the piston rod 3 and the piston 5 into the barrel 1. Together with the rear flange 7, the narrowing prevents the p i s ton r o d 3 f rom b e ing pul l e d out aga in a t the s ame t ime as it assists in defining the maximum dose of the syringe.

Between the two abutment surfaces, the piston rod pin is formed like a rod of a circular cross section. However, adjacent the rear abutment surface 9 the pin comprises a circumferential recess or groove 11 and a short distance from the front abutment surface 3, said pin comprises two diametrically opposing plane portions 12 and 13, respectively, of. Fig. 3.

As illustrated in Fig. 4, the piston 5 is a cylindrical body of rotation with an axially extending through hole 14 adapted to receive the pin 4 of the piston rod 3. On the outside, the piston 5 comprises a circumferential, axial abutment surface 15 and 16, respectively, at each axial end. The abutment surfaces co-operate sealingly with the inner wall of the barrel 1. The piston 5 comprises a circumferential collar 17 at the end farthest from the front end of the syringe in the mounting position. Fig. 4 illustrates how the collar 17 in the unstressed state forms a ring of a substantially rectangular cross section defined by two radial planes. The radial planes are mutually spaced along the axis of the piston 5, one plane coinciding with the adjacent end of the piston 5 and the other plane being spaced from said end in a direction away from the opposite end of the. piston. The collar is formed integral with the remaining portion of the piston 5 through a hinge - forming film 18 with the result that the collar is connected to the piston 5 by a hinge. The collar is furthermore slightly rounded, of the drawing, at the side facing away from the piston 5. The collar 17 comprises two diametrically opposing through passages 19 adjacent the hinge 18, the function of said passages being explained in greater detail below.

The piston 5 comprises a circumferential recess 20 immediately inside the collar 18, said recess receiving the collar 17 when said collar is folded downwards as indicated inter alia in Fig. 6. The dimension of the collar 17 and the recess 20 is such that when the collar 17 is not stressed but only folded downwards Into the recess 20, said collar projects a short distance radially inside the adjacent inner wall of the piston in the hole 14.

When seen in the axial direction of the piston 5, a cylindrical portion 21 is provided immediately inside the recess 20 of the piston 5, said cylindrical portion being of a diameter slightly larger than the diameter of the pin 4. The cylindrical portion 21 continues through a conical portion 22 into a second cylindrical portion 23 of a diameter slightly smaller than the diameter of the pin 4. The second cylindrical portion 23 ends at a recess 24 for receiving the front flange 6 of the pin 4. The bottom of the recess 24 is formed by a conical surface 26. The portion of the conical surface 26 of the smallest diameter is placed closer to the adjacent end of the piston 5 than the portion of the largest diameter. The piston rod 3 and the piston 5 are interconnected by initially inserting the piston 5 into the interior of the barrel 1, whereafter the piston rod 3 with the pin 4 in front is inserted so as to engage the piston 5. Fig. 5 illustrates the situation during the mounting procedure where the front flange 6 of the piston rod pin 4 comes into contact with the collar 17 on the piston 5 through a conical narrowing frusto-conical point 26. By a continued axial displacement of the piston rod 3, the pin 4 is pressed through the hole 14 of the piston 5 while said piston 5 rests against the front end of the barrel 1, of. Fig. 6. The dimensions of the piston 5 and the pin 4 as well as the resilience of the piston 5 are such that the above displacement is allowed despite the dimensions in the unstressed state.

When the flange 6 passes the collar 17, said collar is folded into the recess 20, where it is retained as shown in Fig. 6 while abutting on the cylindrical portion of the pin 4. The displacement of the piston rod 3 continues through the hole 14 of the piston 5 until the front flange 6 is received in the front recess 24 in the piston 5, of Fig. 7. The front frusto-conical point 26 of the front flange 6 on the pin 4 ensures that the pin 4 of the piston rod 3 does not proceed so far through the piston 5 that the collar 17 opposes the circumferential groove 11 on the pin 4 because before then the point 26 comes into contact with the front end of the barrel. Accordingly, the piston 5 and the pin 4 are of a mutually adjusted axial extension which ensures that the collar 17 during the mounting procedure is positioned a suitable distance from the groove 11, of. Fig. 7.

Now the syringe is ready for use, and from the position shown in Fig. 7 the piston rod 3 is moved backwards away from the front end of the syringe while sucking in a dose of a liquid. While the piston rod travels backwards, the piston 5 sealingly abuts on the front abutment surface 8.

When the dose in question has been sucked into the syringe, the injection is initiated by first expelling air out of the syringe in a conventional manner whereafter the injection is performed. Hereby the piston rod 3 is initially pressed towards the front end of the syringe while the piston 5 is displaced relative to said piston rod in such a manner that the rear abutment surface 9 of said piston rod is caused to engage the piston 5, of. Fig. 8. As a result the portion about the hinge 18 of the collar 17 sealingly abuts on the rear abutment surface 9, said hinge forming a circumferential ridge. In this manner the liquid is expelled from the syringe, of. Fig. 8 showing the termination of the injection. Fig. 8 further illustrates how the collar 17 is radially arranged opposite the groove 11 on the pin 4. Subsequently, if it is tried to reuse the syr inge , the suction in of another dose of liquid causes the piston 5 to move relative to the piston rod 3 and forwards towards the front abutment surface 8. As a result, the collar 17 engaging the rim of the groove 11 is unfolded from the recess 20 into a position in which it projects away from the piston 5 towards the rear abutment surface 9 on the piston rod 3.

Successive attempts at initiating the injection by expelling air followed by expelling the liquid cause the piston 5 to enter the position in Fig. 9 with the collar 17 abutting on the bottom of the groove 11 and the rear abutment surface 9. The passages 19 in the collar 17 imply that no sealing connection exists at the rear end of the piston 5. In addition, the positioning of the plane portions 12 and 13 of the pin 4 opposite the narrowest portion 23 of the hole 14 of the piston 5 prevents the piston 5 from sealingly abutting on the pin 4 in this position. Accordingly, it is impossible to expel air and subsequently liquid from the front end of the syringe by means of the inventive disposable syringe. It is noted, that the groove 11 of the piston rod pin 44 must be of such a dimension in radial direction that the collar 17 does not automatically return to its position in the unstressed state, but remains substantially in a position extending upwards towards the rear abutment surface 9 when the injection is initiated in connection with atttempts at reuse.

The members of the syringe are suitably made by injection moulding and of materials compatible with the injection liquid in question. The dimensions are adapted to the size of the injection dose and the above conditions in order to ensure the desired function. As mentioned, the piston 5 is suitably made of silicon rubber preserving both a high flexibility and a built-in memory in such a manner that the piston always try to enter the position in which it is moulded. In other words when the collar 17 has been moulded in the position shown in Fig. 4, it tries automatically to return to said position and out of the recess 20 when positioned opposite the groove 11 on the pin 4 of the piston 5.

The invention has been described with reference to preferred embodiments. Many modifications may, however, be carried out without thereby deviating from the scope of the invention. The Invention is based on the fact that leaking paths are established which make it impossible to reuse the syringe. The above plane portions 12 and 13 on the piston rod pin 4 may for instance be replaced by a plurality of axial grooves extending into connection with the circumferential groove 11. The collar 16 may also be shaped with a number of passages 19 exceeding two or a plurality of perforations, optionally in such a number or of such an extent in circumferential direction that the collar is almost shaped like separated flaps.

Claims

C lai ms

1. Disposable syringe preferably for injection and comprising a barrel and a piston rod displaceable forwards and backwards inside said barrel, where the piston rod carries a resilient piston on a protruding pin, said piston sealingly co-operating with the wall of the barrel and comprising a through hole receiving the protruding pin of the piston rod, where said pin comprises a circumferential, radially extending front and rear, respectively, abutment surface at each end, said abutment surfaces in the axial direction of the piston rod being mutually spaced a distance greater than the axial distance between mating abutment surfaces at the ends of the piston so as to allow a relative displacement of the piston between two positions in which the ends of the piston alternately form a sealing connection with one of the abutment surfaces, c h a r a c t e r i s e d in that the piston (5) comprises a foldable and circumferentially extending collar (17) at the end farthest from the outlet end of the barrel (1), said collar being hinged to the piston (5) and receivable in a mating circumferentially extending recess (20) in the piston at the opening of the hole (14) while abutting on the piston rod pin (4), whereby said collar comprises a plurality of perforations or passages (19), and that the piston rod pin (4) comprises a circumferential groove (11) at the rear abutment surface (9) situated farthest from the outlet end of the barrel (1), whereby the circumferential groove receives the collar (17) on the piston (5) when said piston sealingly co-operates with the rear abutment surface (9), and whereby said groove turns out said collar (17) into a position substantially in extension of the piston (5) when said piston (5) moves away from the end of the pin (4) in a direction towards the front abutment surface (7) at the opposite end.

2. Disposable syringe as claimed in claim 1, c h a r- a c t e r i s e d in that the front abutment surface (8) on the piston rod pin (4) adjacent the outlet end of the syringe is formed by a circumferential flange (6), which by applying a low pressure can pass through the hole (14) of the piston (5) during the mounting procedure, the piston

(5) comprising a recess (24) adjacent the outlet end of the syringe, said recess receiving the circumferential flange (6), and that the abutment surface (8) en said flange co-operates with a substantially conical surface (25) in the bottom of the recess (24) and provided about the hole (14) said conical surface (25) being adapted to sealingly engage the abutment surface (8) adjacent the centre of the hole (14).

3. Disposable syringe as claimed in claim 2, c h a ra c t e r i s e d in that the circumferential front flange

(6) comprises an axially extending projection (26) engaging the front end portion of the syringe and preventing the piston rod (3) from passing so far through the piston (5) during the mounting procedure that the foldable collar of said piston is caused to engage the circumferential groove (11).

4. Disposable syringe as claimed in claim 1, 2 or 3, c h a r a c t e r i s e d in that the piston (5) is formed in one piece with the foldable collar (17) of a plastic material, where the collar is moulded with such a built-in memory that the collar (17) tends to automatically enter a position in which it projects radially inwards in extension of the remaining portion of the piston (5).

5. Disposable syringe as claimed in claim 1, 2, 3 or 4, c h a r a c t e r i s e d in that the hole (14) of the piston (5) comprises a portion of such a reduced radius in the front end adjacent the injection opening that inside said portion the front end sealingly abuts on the pin (4) of the piston rod (3), and that the pin (4) of the piston rod (3) comprises recessed portions (12, 13) situated a distance from the front abutment surface (8) and ensuring a passage of air and liquid between the piston (5) and the pin (4) of the piston rod (3) when the piston (5) has left the sealing connection with the front abutment surface (8).

6. Disposable syringe as claimed in one or more of the preceding claims 1 to 5, c h a r a c t e r i s e d in that the collar (17) is of a substantially rectangular cross section, which in the unstressed state forms a ring coaxially arranged relative to the piston (5), said ring being defined by two substantially parallel, radial planes, of which one plane is placed a distance from the end of the piston (5) and the other plane coincides with the end of the piston, and that the collar (17) is hinged to the piston (5) along the outer circumferential rim adjacent the piston (5).

7. Disposable syringe as claimed in one or more of the preceding claims 1 to 6, c h a r a c t e r i s e d in that the hinged connection (18) between the piston and the collar (17) forms a circumferential ridge to be used by the sealing co-operation with the rear abutment surface (9) on the piston rod (3) when the collar (17) has been received in the mating recess in the piston at the opening of the hole (14).

8. Disposable syringe as claimed in one or more of the preceding claims l to 7, c h a r a c t e r i s e d in that when the collar (17) has been received in the mating recess (20) in the piston (5), said collar (17) tends to project radially inside the adjacent portion of the wall in the hole (14) through the piston (5).