KR100463192B1 - Single-use device for injection - Google Patents

Abstract

The present invention relates to a disposable injection device, wherein the disposable injection device is housed in a protective cover 7 and a rear body 24 made up of the rear and front bodies 9, 8 and means for locking the syringe 1 ( A conventional syringe (1) comprising a ring (24) with 29,31 and a protective mechanism of the injection needle (2) of the syringe (1) after use, with the front and rear bodies extending to another It is designed to be integral to the part, and the ring is between the first position for injection and the second position for protection after use of the injection needle 2 by means of a spring 42 which remains compressed in the injection position. Deployed and released when scanning is complete.

Description

Single-use device for injection

Disposable injection devices currently in common use are designed to protect the needle before use, then be removed so that the injection can be made, and finally returned to its place after the injection is performed to prevent the serious risk of being stuck to the contaminated needle. It consists of a prefilled syringe with a cap.

However, this type of design has been found to have a major drawback resulting from the fact that the cap should be placed opposite the needle tip when the needle is covered more than once. This requirement is in fact known to cause relatively frequent sticking accidents, and all risks are involved in being stuck in this way by contaminated needles. Moreover, these types of syringes do not have any safeguards designed to prevent them from being used again, so special care must be taken to destroy them.

In order to eliminate these drawbacks, the prior art provides a syringe opening with a protective cover which can slide along the body of the syringe or the syringe can be retracted therein, so that the injection position or injection needle at which the needle is released One of the post-use protection positions accommodated and protected inside this protective cover can be obtained.

According to this principle, a conventional solution is an injection mechanism having elastic means fitted between the syringe body and the protective cover, which elastic means maintains compression to ensure that the protective cover and syringe are placed in the injection position before and during the injection. It is designed to weaken when the injection is complete so that the protective cover or syringe automatically slides towards the post-use protective position.

This solution makes it possible to produce an injection device as described in international patent applications WO-91.13634, WO-93.23089, WO-93.25254 and European patent application EP-446.551, EP-307.367, which firstly have a protective cover or syringe Since is made to slide automatically by the relaxation of the elastic means after the injection is made, it prevents the risk of accidental sticking before and after the injection is made and secondly prevents the syringe from being used again.

However, these injection instruments require the manufacture of certain syringes, and therefore require significantly higher prices than conventional syringes, such as glass syringes, which are now mass produced at very low prices.

In fact, there was no means to solve the problem of this type of injection device which cannot be used again after injection and is equipped with a conventional syringe.

Current syringes of this type for injection are said to be completely empty because of the tolerances received in relation to the length of the syringes when the syringes are manufactured when the release of the resilient means controlled by the release means arranged on the piston rod occurs. Another drawback is the fact that it cannot be guaranteed. Since this type of injection device is designed to be used for the purpose of injection of very small amounts of injection liquid (approximately 1 μs) in which the quantity is strictly controlled, this technical solution is not suitable for fulfilling the appropriate requirements.

It is an object of the present invention to obviate these drawbacks, and the real object of the present invention is to provide an injection device which comprises a conventional syringe and is easily manufactured and cannot be reused after the injection is performed.

It is a further object of the present invention to provide an injection mechanism that ensures injection of every single dose of injection liquid.

The present invention relates to a disposable injection device designed to be prefilled with a single dose of injection to be injected.

Further features of the objects and advantages of the invention are apparent from the following detailed description, which is provided by reference to the accompanying drawings. And the figures are shown through examples of selected non-limiting embodiments. The figures show the following.

1 is a longitudinal cross section through an axial plane of an injection device according to the invention, shown before use;

2 is a perspective view of a protective cover of the injection mechanism;

3 is a longitudinal sectional view through the axis plane A of the protective cover.

4 is a longitudinal cross section through the axis plane B of the protective cover.

5 is a cross-sectional view through the plane C of the protective cover.

6 is a cross-sectional view through the plane D of the protective cover.

7 is a longitudinal sectional view through the axial plane E of the locking ring of the injection mechanism.

8 is a perspective view of a fixing ring;

9 is a longitudinal sectional view through the axial plane F of the engaging piece in the form of a claw of the injection mechanism.

10 is a perspective view of the engaging piece in the form of a claw.

11A-11F are schematic diagrams illustrating successive manufacturing steps of the injection device.

12 is a longitudinal sectional view through the axial plane of the injection device showing the initiation step of removal of the protective cap for use of the injection device.

13 is a longitudinal cross section through the axial plane showing the injection mechanism at the completion of scanning;

14 is a longitudinal cross section through the axial plane showing the injection mechanism in the protected position after it has been used.

To this end, the present invention relates to a disposable injection mechanism comprising a front nose for supporting an injection needle and a syringe with a rear collar, the syringe being filled with a single injection to be injected and pressed against the opposite end. The chamber defines a chamber sealed by a piston integrally provided at one of the ends of the piston rod provided with the dog.

According to the invention, such injection mechanisms comprise a protective mechanism after the syringe has been used, said protective mechanism comprising:

An assembly means consisting of two tubular bodies known as anterior body and a posterior body, the assembly of which allows one of the tubular bodies to be integrated in the extension of the other, wherein the anterior body is in relation to the diameter of the syringe A protective cover having a mating diameter, the length of which is designed to partially receive the syringe, the rear body having a diameter greater than the diameter of the collar of the syringe;

A ring disposed on the rear body and including collar locking means of the syringe for inserting the syringe by positioning an injection needle opposite the rear body of the protective cover;

The ring and the rear body,

By placing the ring facing the assembly surface of the front body and the rear body and defining the first locking position known as the injection position when the injection mechanism is assembled, it is possible to make the ring fit in the rear body. First relative locking means in translating;

• second relative locking means in translation, known as a protective position after use and defining a second locking position obtained after the rearward sliding of the ring inside the rear body and in which the injection needle is received in the front body;

The ring and the front body are provided with stopper means capable of maintaining the compression of the resilient means in the first locking position for injection;

The ring or the rear body comprises a rear portion which is radially deformable and supports the first locking means in translation, the portion being deformed by the push of the piston rod at the path end of the piston rod, so that the first Release the locking means and allow movement of the ring towards the second locking position for protection after use.

Thus, the device according to the invention for the protection of a syringe comprises four main elements (rings, the front and rear bodies of the protective cover, and elastic means, which constitute a pre-assembled assembly, after which a conventional syringe Is inserted and designed to provide protection of the needle after use and to prevent any reuse.

In addition, the protective mechanism is manufactured in a very simple way by means of steps that can be easily automated. In practice, this assembly is performed according to the following steps:

Inserting the ring into the rear body of the protective cover until it is in the first locking position;

Positioning the uncompressed elastic means in place in the ring; And

Assembling the rear body and the front body to cause compression of the elastic means by means of the stopper means and the ring of the front body.

This pre-assembled assembly is moved to a protective position to enable a conventional prefilled syringe to continuously position the prefilled syringe locked in place in this manner in the collar and to prevent any reuse after the injection is made.

According to a preferred embodiment, the ring is made of a material with a color different from that of the protective cover, especially for safety reasons, making it possible to identify already used injection instruments.

In addition, preferably, the front body of the protective cover is made of a transparent material to see the syringe.

On the other hand, the rear body of the protective cover is made of an opaque material to hide the view of the release mechanism, and the view of the release mechanism can confuse the doctor and the patient.

In addition, the locking means at the time of translation of the rear body of the ring and the protective cover,

At least one longitudinal groove provided in the rear body and extending to the rear locking cavity;

It includes two rear and front locking clasps for each groove provided in the ring and designed to slide in the groove and to be received in the locking cavity.

In addition to defining the first and second locking positions in translation, this arrangement results in relative locking in the translation of the ring and the rear body.

In addition, each locking cavity preferably consists of a gap provided in the outer circumferential wall of the rear body, which is delimited in the form of asymmetric teeth in the rear by the inner shoulder and in the front by the inner latch. A photographic front face is provided and supported by a deformable tab provided on the outer circumferential wall of the rear body.

Furthermore, according to a preferred embodiment, the means for assembling the front and rear bodies of the protective cover comprises an inner annular groove provided on the rear body and an outer clip ring provided on the front body.

In addition, for each groove in the rear body, the front body of the protective cover includes an external protrusion that can be received in the groove. This arrangement provides relative locking upon rotation of both bodies of the protective cover.

Means for locking the collar of the syringe include at least one rear inner clasp provided in the ring and an asymmetrical tooth and a front inner shoulder provided in the ring at a distance equal to the thickness of the collar from each clasp, the tooth being The photo has a rear face.

The stop means of the resilient means comprise the shoulder portion provided in the ring and the inner shoulder portion provided in the front body at the rear portion of the front body, the inner shoulder portion having an inner diameter larger than the prescribed inner diameter.

Furthermore, preferably, the deformable parts supporting the first locking units in translation consist of two tabs which are radially deformed and extend in the rear extension of the ring, with the rear locking clasp being arranged on the respective tabs.

In addition, each rear locking clasp is disposed at an intermediate position along the length of the tab so that a slope is provided to the rear of the clasps, which absorbs a change in the length of the syringe while a force acts on the cuff when the injection is complete. This ensures that a single injection is injected.

In addition, the pusher of the piston rod has the shape of a bowl provided with an edge with an inclined contour and each tab has a rear region with an additional inclined contour.

The instrument according to the invention shown in FIG. 1 firstly comprises a prefilled syringe 1 of conventional form, for example made of glass, the syringe having a front nose 1a into which the needle 2 is fitted in a conventional manner. And a collar 1b at its rear end.

This syringe 1 also comprises a cap 3 for protecting the needle 2 in a conventional manner, the cap being designed to fit on the front nose 1a of the syringe.

In addition, the syringe delimits the chamber in which a single injection is filled in a conventional manner, the chamber comprising a closed threaded hole to which the threaded end 5a of the piston rod 5 is fastened, the piston rod on the other side of the chamber. A stopper 6 is provided at the end.

According to the invention, the sealer 6 has the form of a bowl having an area 6a with an inclined contour for the purpose to be described later.

The injection device according to the invention also comprises an assembly for the protection of the syringe 1, which is designed to be assembled in its entirety before the initially filled syringe is placed in the protective assembly.

This protective assembly first comprises a protective sheath 7 consisting of two tubular bodies, a front tubular body 8 and a rear tubular body 9, as shown in FIGS. It is designed to fit into the extension of the thing.

The anterior body 8 has an inner diameter paired with the outer diameter of the syringe 1, the length of which is designed to receive the needle 2 provided with the protective cap 3, and substantially of the length of the syringe 1. 80%.

At its rear end, this anterior body 8 comprises a posterior region 8a having a substantially ovoidal contour with an outer diameter greater than the prescribed outer diameter of the anterior body, having a hollow interior, An inner longitudinal rib 10 defining an inner diameter equal to the prescribed inner diameter of the front body 8 is included.

Each rib 10 additionally has a shoulder 10a delimiting the rear end with an inner diameter greater than the diameter of the syringe 1.

This rear region 8a comprises an annular groove 11 bordered by a rear clip ring 12 on its outer side. In addition, as shown in FIG. 5, this groove 11 is blocked by two projections 13 facing diagonally and projecting radially relative to the clip ring 12.

The anterior body 8 includes a front region 8b that can be separated at the front end, the front region being a breakable annular region positioned to be placed in the front nose 1a of the syringe 1 when the syringe is positioned ( 14) the boundary is determined.

The separable area 8b has an inclined contour 15 which forms a slope at its rear end, which contour constitutes a neck 50 having a diameter smaller than the prescribed inner diameter of the anterior body 8. Delimit the rear part.

The separable region 8b comprises a plurality of longitudinal clasps 16 in front of the rear portion of which the inner surface of the region is circumferentially distributed, the clasps delimiting an inner diameter equal to the inner diameter of the rear portion. The bases of the catches define the shoulder 17 together with the front end of this rear part.

Finally, for this region 8b that can be separated, the front part of the region disposed in front of the clasps 16 has the same details as the diameter separating the bases of the clasps.

The rear body 9 has an oval shape paired with the shape of the rear region 8a of the front body 8 and is designed to fit into the rear region 8a.

For this purpose, the rear body 9 first comprises an inner annular groove 18 designed to receive the clip ring 12. The rear body also includes two diagonally opposed longitudinal grooves 19, which grooves each receive a projection 13 to ensure locking upon rotation of the two bodies 8, 9, the grooves being rearward. Blocked at a short distance from the rear end of the sieve 9, the rear end of the rear body has an inner shoulder 20 at the level of the end of these grooves 19.

As shown in FIG. 7, grooves 19 are provided along the larger diameter of the rear body 9 to minimize the wall thickness of the rear body.

The rear body additionally has two deformable tabs 21, each tab being provided in the groove at the rear end of the groove 19 and formed from a U-shaped cut provided in the wall of the rear body.

Each of these tabs 21 includes a cross hook 22 that protrudes inward of the rear body 9 at its rear end. Each of these hooks comprises a substantially radial non-returning rear face 22a and an inclined front face 22b forming a slope.

Finally, the rear body 9 comprises a conventional finger support outer collar 23.

Secondly, the protective assembly comprises a locking ring 24 having a shape that is designed to be inserted into the rear body when positioned opposite the front face of the rear body 9.

This locking ring 24 having a length designed to be inserted into the rear body 9 is in the form of a cylindrical sleeve 25 extending rearwardly by two tabs 26 facing each other diagonally in the form of a cylindrical region. have.

Each of the two tabs 26 first has a rear end face 26a with an inclined contour, which is complementary with respect to the contour of the region 6a of the pusher 6 of the piston rod 5.

In addition, at an intermediate point along its length, each of these tabs 26 includes transverse outer ribs 27 designed to slide in one of the grooves 10 of the rear body 9.

Cylindrical sleeve 25 of this locking ring 24 concentrated at the same parent point as the transverse ribs 27 is designed to slide in the groove 10 of the rear body 9 and is provided at the front end of the sleeve. Transverse ribs 28.

This cylindrical sleeve 25, aligned axially with the ribs 27, 28 described above along its length, also includes two diagonally opposed inner ribs 29, each of the inner ribs. Downward from there, the outer circumferential wall of the sleeve has a gap to allow for discharge of the undercut piece.

Each of these inner ribs 29 has a rear face with an inclined contour defining a slope and a non-returning locking radial front face 29b.

Finally, at some distance downstream from the gap 30 and from the inner ribs 29 mated with respect to the thickness of the collar 1b of the syringe 1, the cylindrical sleeve 25 has an annular inner shoulder ( 31).

Finally, the injection device according to the invention comprises the connecting piece 32 with claws shown in FIGS. 9 and 10 and designed to cover the protective cap 3, so that the front body 80 of the protective cover 7. Causes the retraction of the protective cap 3 after breakage of the damaged area 14.

This connecting piece 32 with claws has a cylindrical front wall 33 having a diameter designed to penetrate in the detachable area 8b, and at its outer periphery four regularly distributed in relation to the axis of the wall. The longitudinal tabs 34, 35, 36, 37 extend at right angles:

Two tabs 34 and 35 are provided at the free end with two lateral claws 38 and 39 respectively designed to face diagonally and penetrate the protective cap 3;

The two different diagonally facing tabs 36 and 37 each have an outer boss 40 having an outer surface with a longitudinal clasp 41 at an intermediate position along its length, and of the separable area 8b. Paired against clasps 16. In addition, each boss 40 has a cylindrical rear portion 40a preceded by an inclined front portion 40 forming a slope.

As shown in FIG. 9, when seated, the tabs 34-37 are in a substantially open position, ie they are inclined outward with respect to the axis of the front wall 33.

The interconnection of the various units of the components, as well as the fabrication of the injection mechanism described above, is described with reference to FIGS. 11A-11F.

The first step is to lock the locking ring into the rear body 9 of the protective cover 7 by positioning the protective cover opposite the front face of the rear body until the ribs 27 abut the shoulders 20. 24) is fitted (FIG. 11A). It should be noted that this arrangement is allowed by the elasticity of the tabs 21 and by the shape of the front face 22a of the ribs 22 forming the slope allowing the ribs to be bypassed.

It should be noted that when the locking ring is placed in place, it locks in relative rotation relative to the rear body 9 as a result of the positioning of the ribs 27 in the grooves 19.

The second step is to partially fit the inside of the locking ring 24 by positioning the locking ring 24 opposite the front face of the same ring until one of the ends abuts the shoulder 31. (FIG. 11B).

The third step involves fitting the front body 8 onto the rear body by the interaction of the groove 18 and the clip ring 12 (FIG. 11C). During this operation, the spring 42 is operatively compressed between the shoulder 10a and the shoulder 31 of the ribs 10. In addition, the front body 8 and the rear body are locked in rotation with respect to each other as a result of the positioning of the projections 13 in the groove 19.

With the completion of these three operations, which can be easily automated, a completely assembled protective assembly can be obtained, in which the previously mentioned prefilled syringe can be fitted.

As shown in FIG. 11D, prior to this fitting, the connecting piece 32 with the claws is positioned in the protective cap 3 of the syringe 1, in this step no piston rod 5. During this position selection, the tabs 34-37 of the connecting piece 32 with the claws are secured around the protective cap 3 without the risk of pushing the protective cap and without damaging the syringe 2 and / or breaking the seal. Simply located.

The syringe 1, which is provided with a connecting piece 32 with claws, is then placed on the rear body 9 of the protective cover 7 until the collar 1b is secured between the ribs 29 and the shoulder 31. ) (Fig. 11E). This fit is possible due to the fact that the ribs 29 can be deformed and due to the oblique shape of the rear face 29a of the ribs 29 which allows the rear face of the ribs to be bypassed by the collar 1b. Note that it is made.

In addition, during this fitting, the connecting piece 32 with the claw passes through the level of the slope 15 and the neck 50 of the region 8b where the bosses 40 of the protective cap 3 can be separated. Clamped on the protective cap 3, the passage is also easily made by means of the mission form of the front part 40b of the boss.

As shown in FIG. 1, during this clamping, the claws 38, 39 penetrate the protective cap 3 downstream from a glass cone provided in the front nose of a conventional syringe 1 and designed to ensure sealing. Therefore, any risk of sliding in the protective cap 3 and damaging the needle 2 and / or breaking the seal is eliminated.

When this step is carried out, as a result of the cooperation of the respective clasps 16, 41 of the protector, the connecting piece 32 with the claws and the protective cover 7 are locked in rotation with respect to each other. In addition, the protective cap 3 is first locked in relative rotation with respect to the connecting piece 32 with the claws due to the penetration of the connecting pieces of the claws 38 and 39, and secondly, this connecting piece 32 with the claws. ), The protective cover 7 and the locking rings 24 are also locked in rotation relative to each other as previously described.

The final step shown in FIG. 11F includes the step of making the piston rod 5 integral with the piston 4 in a conventional manner. This provides an injection device that is easy to use, the use of which will be described with reference to FIGS.

First, as shown in FIG. 12, the initial step includes breaking the damaged area 14 in a conventional manner by rotating and pulling the area that can be separated. During the movement, since the assembled elements (protective cap 3, protective cover 7, locking ring 24) are locked in rotation with respect to each other, the protective cap 3 is made to rotate first, thus protecting The detachable cap is easy and the connecting piece 32 with the claws can be locked in translation relative to the area 8b which can be separated by pushing the boss 40 towards the shoulder 17, The protective cap 3 is removed simultaneously with the connecting piece 32 with the claws and the detachable area.

The injection is then performed in a conventional manner by means of opposing actions on the hand holding 6 and the finger support collar 23. Upon completion of the scan, as shown in FIG. 13, the outer edge 6a of the seal 6 cooperates with the outer edge 26a of the tabs 26 of the locking ring 24 so that the ribs 27 release. Until the tabs 26 are radially deformed inwards.

Since the ribs 27 are placed in an intermediate position on the tabs 26, the tabs have a slope to the rear of the ribs, which can absorb the manufacturing confluence of the syringe 1 and ensure that the total injection is injected. To be.

As shown in FIG. 14, when the injection is completed, the force on the seal 6 is stopped, and the locking ring 24 pressed by the spring 42 is pushed into the protective cover 7 to inject the syringe ( 1) Ribs are locked between the ribs 22 and the shoulder 20 until they are loaded into the ribs 28 and bypass the slopes 22b of the ribs 22, thus further use of an injection device. To prevent.

Finally, the front body 8 of the protective cover 7 is made of a transparent material, so that the syringe 1 can be seen from the outside. On the other hand, the rear body 9 of this protective cover is made of an opaque material, so that the release mechanism is hidden from the view of the user and the patient.

The locking ring 24 has a different color from the rear body 9, making it possible to immediately identify the injection mechanism already used.

Claims (13)

A piston rod (5) having a front nose (1a) for supporting the injection needle (2) and a rear collar (1b), the syringe being filled with a single injection liquid to be injected and provided with a seal (6) at the opposite end. In a disposable injection device comprising a syringe delimiting a chamber sealed by a piston 4 provided integrally at one of the ends of A protective mechanism after the syringe has been used, the protective mechanism comprising: Consisting of two tubular bodies 8, 9, known as the front body and the rear body, having assembling means 12, 18 which allow one of the tubular bodies to be integrated in the extension of the other; The front body 8 has a diameter paired with the diameter of the syringe 1, the length of which is designed to partially receive the syringe, and the rear body 9 of the collar 1b of the syringe. A protective cover 7 having a diameter larger than the diameter and including a finger support unit 23; Locking the collar 1b of the syringe 1 which is arranged on the rear body 9 and inserts the syringe by positioning the injection needle opposite the rear body 9 of the protective cover 7. A ring 24 comprising means 29, 31; The ring 24 and the rear body 9, It is possible to fit the ring in the rear body by placing the ring facing the assembly surface of the front body 8 and the rear body and defining the first locking position known as the injection position when the injection mechanism is assembled. First relative locking means (20, 22, 27) during translation; At the time of translation, which is known as a protective position after use and which is obtained after the rearward sliding of the ring 24 on the inside of the rear body 9 and defines a second locking position in which the injection needle 2 is received in the front body 8. Second relative locking means (20, 22, 28); The ring 24 and the front body 8 have stopper means 10a, 31 which are able to maintain the compression of the resilient means 42 in the first locking position for injection, The ring 24 or the rear body 9 comprises a rear portion 26 which is radially deformable and supports the first locking means 27 during translation, which part at the path end of the piston rod Deformed by the seal 6 of the piston rod 5, the disposable injection mechanism is characterized in that it releases the first locking means and allows the movement of the ring 24 towards the second locking position for protection after use. . 2. Disposable injection device according to claim 1, characterized in that the ring (24) is made of a material having a different color from the protective cover (7). 2. Disposable injection device according to claim 1, characterized in that the front body (8) of the protective cover (7) is made of a transparent material. 2. Disposable injection device according to claim 1, characterized in that the rear body (9) of the protective cover (7) is made of an opaque material. The front body (8) and the rear body (9) of the protective cover (7) are provided with an inner annular groove (18) provided in the rear body (9) and an outer clip provided in the front body (8). Disposable injection device comprising a ring (12). The locking means according to claim 1, wherein the locking means at the time of translation of the rear body (9) of the ring (24) and the protective cover (7), At least one longitudinal groove 19 provided in the rear body 9 and extending to the rear locking cavities 20, 22; Disposable injection device, characterized in that it comprises two rear and front locking clasps (27,28) for each groove (19) provided in the ring (24) and designed to slide in the groove to be received in the locking cavity. 7. The locking cavity according to claim 6, wherein each locking cavity consists of a gap provided in the outer circumferential wall of the rear body (9), by the inner shoulder (20) in the form of asymmetric teeth and from the rear and by the inner clasp (22). A border is defined at the front, wherein the tooth is provided with an inclined front face (22b) and is supported by a deformable tab (21) provided on the outer circumferential wall of the rear body (9). 8. The front body (8) of the protective cover (7) according to claim 6 or 7, for each groove (19) in the rear body (9) has an outer projection (13) which can be received in the groove. Disposable injection device comprising a. 2. The device according to claim 1, wherein the means for locking the collar (1b) of the syringe (1) is provided in the ring (24) and comprises at least one rear inner clasp (29) consisting of an asymmetric tooth and from each clasp (29) Disposable injection device, characterized in that it comprises a front inner shoulder (31) provided to the ring (24) at a distance equal to the thickness of the collar, the teeth have an inclined rear surface (29a). 10. The shoulder (31) of claim 9, wherein the stop means of the elastic means (42) are provided with the shoulder (31) provided on the ring (24) and the inner shoulder (10a) provided on the front body at the rear part of the front body (8). And an inner shoulder portion having an inner diameter larger than the prescribed inner diameter. 8. The deformable portions of claim 6 or 7, wherein the deformable portions supporting the first locking units 27 during translation consist of two tabs 26 that are radially deformed and extend in the rear extension of the ring 24. And a rear locking latch (27) disposed on each of the tabs. 12. Disposable injection device according to claim 11, characterized in that each rear locking clasp (27) is arranged in an intermediate position along the length of the tab (26). 12. The seal 6 of the piston rod 5 has the shape of a bowl provided with an edge 6a with an inclined contour, with each tab 26 having an additional inclined contour. Disposable injection device having a back region (26a).