CA2080999C

CA2080999C - Disposable syringe

Info

Publication number: CA2080999C
Application number: CA002080999A
Authority: CA
Inventors: Erwin Wimmer
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-10-22
Filing date: 1992-10-20
Publication date: 1995-12-19
Anticipated expiration: 2012-10-20
Also published as: PL170226B1; FI924733A; DE59203566D1; JPH05237188A; ES2079843T3; FI924733A0; NO924079L; RU2075314C1; PL296299A1; ATA210291A; CZ319592A3; KR930007469A; EP0539348B1; KR970009715B1; HUT67260A; NO924079D0; EP0539348A1; CZ279916B6; ZA928059B; US5275582A

Abstract

A disposable syringe comprising a syringe cylinder and a syringe piston. The syringe cylinder is open at one end and at its other end has an end wall, which is closed with the exception of a region adjacent to a needle holder. The syringe piston comprises a piston skirt, which protrudes from the syringe cylinder, and a piston head which is disposed within the syringe cylinder and provided with an annular seal.
The annular seal is connected to the piston head by an annular peripheral flange. So that the syringe can easily be actuated and is nevertheless absolutely tight, the flange is frusto-conical and flares toward the piston skirt. The radial distance from the inside peripheral surface of the hollow frustoconical flange to the piston skirt increases continu-ously. The flange is adjoined by the annular seal which consists of a coaxial cylinder and freely protrudes on the side of the piston head.

Description

- 1 _ 2080ggg DISPOSABLE SYRINGE

BACKGROUND OF THE lNV~NlION

1. ~ield of the Invention This invention relates to a disposable syringe comprising a syringe cylinder and a syringe piston, wherein the syringe cylinder is open at one end and at the other end has an end wall, which is closed with the e~ception of a region adjacent to a needle holder, and the syringe piston comprises a piston skirt, which has a free end that protrudes from the syringe cylinder and at that free end carries a 15 h~n~l e, and said piston also comprise~ a piston head, which is disposed within the syringe cylinder and is provided with an annular seal, which contacts the inside surface of the cylinder and is connected to the piston head by a peripheral annular flange.

2. Description of the Prior Art Such disposable syringes are generally made of plastic and are intended to ensure an absolutely tight contact between the annular seal and the inside ~urface of the cylinder during the intake and delivery strokes of the piston and to permit the piston to be actuated gently and with a min;mum of force during the actual injection. These two requirements are not satisfactorily met by the existing disposable syringes, in which the annular seals consist of ~e~lin~ beads integrally formed on the piston head or of flanges provided with two-legged seAling lips (Published 20~0999 German Application 20 25 379; French Patent Specifica-tion 15 00 009) so that the seal proper is supported by means which are rather stiff in a r~ 1 direction and a sufficiently strong pressure force is exerted between the seal and the inside surface of the cylinder. But that design has a result that the cylinder wall will expand during a storage of the syringe for considerable time so that the sealing action is more or less lost and it is no longer possible to actuate the piston as uniformly a~ is desired because the strain has re~ulted in a variation of the diameter of the cylinder. That situation cannot be i~-Gved even by a closer fit between the seal and the inside surface of the cylinder because this would result only in a requirement for a stronger force for actuating the piston so that a sensible actuation of the piston would no longer be possible. It has been attempted to e1;m;n~te that disadvantage by an incorporation of a solid lubricant in the material of the cylinder. But in that case a long time must be permitted to elapse after the m~nufacture of the syringe before said solid lubricant emerges from the material for a lubricating action.

In other known syringes the piston head is caplike and fitted on the adapter end of the piston skirt (Swiss Patent Specification 366,126; French Patent Specification 1,228,933) and constitutes a protruding conical se~1 ;ng lip because its peripheral surface defines a forwardly open annular wedge-~haped gap and ~aid sealing lip is integrally formed with an oppositely directed, second se~ ing lip. In order to ensure the required tightness in both directions in ~80999 which the piston is actuated, the 8e~1;n~ lipS must contact the inside surface of the cylinder under a sufficiently strong pressure force so that the seal has a high stiffness, with all the disadvantages involved therein. That stiffness is further increased by the fact that the piston head must be sufficiently firmly fitted on the piston skirt.

All said known disposable syringe~ also i~volve the risk that a leak may result from a canting of the piston as the syr~ ge is actuated.
Such a canting cannot be prevented because there is a r~;al clearance between the piston skirt a~d the syringe cylinder and because the syringe is made of flexible material.

STJ~MABY 0~ TF~3 lN V~ '1' ION

For this reason it is an object of the invention to el;~in~te said disadvantages and to provide a disposable syringe which is of the kind described first hereinbefore and distinguishes in that it can be actuated with ease and that it is absolutely tight.
That object is accomplished in accordance with the in~ention in that the flange has a frusto-conical outside surface, which faces the inside surface of said syringe cylinder and said end wall of said syringe cylinder, and a frustoconical inside surface, which faces said piston skirt and said open end of ~aid syringe cylinder, said flange flares toward said open end of said syringe cylinder, the r~

_ 4 _ 208 ~g 9 clearance between ~aid frustoconical inside surface and the piston skirt increases continuously, and the annular seal is cylindrical and is joined to and co~Y;~l to said flange and freely protrudes toward said end wall. Owing to said shapes of the flange and the ~nnular seal, the seal iB relatively softly supported in a radial direction and a resilient sealing system is provided so that the biasing forces being exerted will be very weak and an expansion of the syringe cylinder need not be feared even during a prolonged storage and, besides, the reciprocation of the syringe piston in the syringe cylinder will involve only low frictional forces and for this reason can be effected by a small actuating force.
The conical shape of the flange and the provision of the unsupported and freely protruding portion of the annular seal will ensure a compliance and resiliency in a r~
direction so that the syringe can be actuated as easily as is desired and the syringe is absolutely tight. Owing to the special shapes of the flange and the seal the pressure conditions existing in the cylinder space will influence the se~l;n~ forces and will ensure that the pressure force under which the seal must contact the inside surface of the cylinder will match said pressure conditions. Any expansion of the syringe cylinder or any canting of the piston can easily be compensated owing to the resilience of the seal of the piston without any risk of a leak.

The compliance and resiliency of the me~n~
for supporting the seal will be improved further if the piston head consists of a conical member, which is mounted on the piston skirt and is continued by the flange, and the included angle of the conical 20~999 member exceeds the included angle of the flange.

The resiliency of the seal of the piston can also be influenced in that the ~nnular seal, in a _anner known per se, and optionally also the flange has a ~m~ller wall thicknesæ than the syringe cylinder and the wall thickness of the annular seal preferably decreases in known m~nner toward its free rim and, in addition, the wall thickness of the flange also decreases toward the annular ~eal.

In a desirable arrangement, the annular seal is provided in known manner on the outside with peripheral ~nn~ r se~l ;ng bead~ at both end portions of its cylindrical shape because the l;ne~r contact between the se~1;ng beads and the inside ~urface of the cyl~nder will result in more uniform and more accurate se~l;n~ conditions.

In an embodiment in which the end wall of the syringe cylinder, with the exception of the region adjacent to the needle holder, has an inside surface which conforms to the end face of the piston head, and the needle holder is eccentrically disposed in the generally triangular space between the flange and the annular seal and interrupts the opposing generally triangular portion of the end wall of the cylinder, the re~idual volume rem~;n;ng ~n the syringe after the injecting operation will be m;n;m;zed and the removal of inleaked air before an Injecting operation will be facilitated.

~080999 BRIEF DESCRIPTION OF THE DRAWING

Figures 1 and 2 are, respectively, an ~
sectional view and an end elevation showing a disposable syringe in accordance with the invention.

Figure 3 is an ~ 1 sectional view showing on a larger scale as a detail the forward end of that disposable syringe.
n~ATT~ DESCRIPTION OF THE PREFERRED EMBODIMENT

~ n illustrative embodiment of the invention will now be described in more detail with reference to the schematic drawing.

~ disposable syringe 1 is composed of a syringe cylinder 2 and a syringe piston 3. The syringe cylinder 2 and the syringe piston 3 consist each of a single piece made of a synthetic thermoplastic material.
~he syringe cylinder 2 comprises at one end an end wall 5, which is closed with the exception of the region adjacent to a hollow needle holder 4. At its other end, the syringe cylinder 2 constitutes a h~l e 6. The syringe piston 3 comprises a piston head 7 and a piston skirt 8, which at its free end protruding from the syringe cylinder 2 comprises a handle 9. The piston head 7 is provided with a flange 10, which carries an ~nular seal 11 that contacts the inside surface of the cylinder. ~he flange 10 has a frustoconical inside surface, which faces the piston skirt 8 and the open end of the syringe cylinder 2, and a frustoconical outside surface, which faces the 2~80gg9 inside surface of the syringe cylinder 2 and the end wall 5 of said cylinder. The fl~nge 10 flares toward the open end of the syringe cylinder 2. The ~nn~ r seal consists of a cylinder, which freely protrudes from the flange toward the end wall 5. The piston head 7 comprises a conical member 12, which is mounted on the piston skirt 8 and is continued by the flange 10 but has a much larger included angle than said flange.
The two end portions of the cylindrical annular seal 11 are formed on the outside with peripheral annular se~ling beads 13, 14 in se~ling contact with the inside surface of the cylinder. Besides, the end wall 5 of the syringe cylinder 2, with the exception of the region adjacent to the needle holder, has an inside surface which conforms to the end face of the piston head. ~he needle holder 4 is eccentrically disposed in the peripheral ~nnular space 15 that is defined by the flange 10 and the annular seal 11 and is generally triangular in radial section. ~he needle holder 4 has an opening 16, which intersects the peripheral ~nt~l~r portion 17 that is formed in the end wall of the cylinder and is generally triangular in radial section.

The special design of the syringe piston 3 provides a resilient, soft piston seal, which ensures an absolutely tight contact between the piston and the cylinder and nevertheless permits the syringe to be actuated easily. The pressure conditions occurring in the syringe cylinder 2 will influence the contact pressures exerted between the annular seal 11 and the syringe cylinder 2 and will cause said forces to match the preV~il;ng pre~sure conditions. For instance, the injection operation will cause an overpressure to be built up in the generally triangular space 15 adjacent to the piston head 7 so that a force will be exerted which urges the annular seal 11 ræ~ ly outwardly and 5 the se~l ;n~ bead 13 at the free end portion of the seal will be forced more strongly ~;n~t the inside surface of the cylinder so as to ensure a tight seal. During the intake operation the negative pressure being built up in the generally triangular space 15 will act on the flange 10 so that the sen-l ;ng bead 14 at the other end portion of the seal 11 will be strongly forced against the in~ide surface of the cylinder and a tight seal will thus be ensured also during the intake stroke.
Even variations of the diameter of the syringe cylinder 2 as a result of an expansion of said cylinder or a canting of the syringe piston 3 during an actuation of the syringe will readily be 20 taken up and compensated without any risk of a leak by the resiliency and compliance of the annular seal 11.

Because the end face of the piston head 25 and the inside surface of the end wall conform to each other, the residual volume left after an injection operation will be m;n;m;zed and that conformity and the eccentric arrangement of the needle holder will facilitate the escape of inleaked air because any air bubbles will migrate along the generally triangular space 15 into the opening 16 of the holder ~o that such bubbles can reliably be ejected.

Claims

1. A disposable syringe comprising:
a syringe cylinder having an inside peripheral surface, an open first end and a second end, an end wall at said second end, the end wall being provided with a hollow needle holder and being closed with the exception of the region adjacent to said needle holder, a syringe piston comprising a piston skirt that protrudes out of said open first end of said cylinder and is provided with a handle outside said cylinder and a piston head disposed within said cylinder and facing said second end thereof, the piston head having an end face facing said second cylinder end and carrying a peripheral annular flange that is provided with an annular seal in sliding contact with said inside peripheral surface of said cylinder, said end wall of said cylinder having an inside surface which, except adjacent to said needle holder, conforms to said end face of said piston head, said flange having a frustoconical inside surface facing said first end of said cylinder and said piston skirt and a frustoconical outside surface facing said inside peripheral surface of said cylinder and said second end of said cylinder, said flange flaring toward said first end of said cylinder, said inside surface of said flange and said annular seal defining a peripheral annular space which is generally triangular in radial section, said end wall of said cylinder comprising a peripheral annular portion which is generally triangular in radial section and conforms to said annular space, said needle holder being eccentrically disposed with respect to said end wall and extending through said annular portion and opening into said annular space, the radial distance from said frustoconical inside surface to said piston skirt continuously increasing toward said first end of said cylinder, and said annular seal being cylindrical and being joined to, and coaxial with, said flange and freely protruding therefrom toward said end wall of said cylinder.

2. The syringe set forth in claim 1, wherein said annular seal has a smaller wall thickness than said cylinder and decreases toward said second end of said cylinder.

3. The syringe set forth in claim 1, wherein said flange has a smaller wall thickness than said cylinder.