Disposable plastic syringe for medical use and plastic barrel, e

Details Disposable plastic syringe for medical use and plastic barrel, e Disposable plastic syringe for medical use and plastic barrel, e

1986-05-19

1987-11-03

Pellegrino, Stephen C.

Surgery

Means for introducing or removing material from body for...

Treating material introduced into or removed from body...

604221, 604228, A61M 500

Patent

active

047041056

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD OF THE INVENTION

The invention relates to a disposable syringe made of plastics, for medical purposes, consisting of a piston provided with a plunger shaft and a barrel provided at the bottom with a tapered chuck for the attachment of a cannula needle, in which the plunger shaft is guided in the barrel at a distance from the barrel wall, and the piston is releasably attached to the plunger shaft. The invention furthermore relates to a piston of thermoplastic, preferably of polyethylene, especially for disposable syringes of the above kind.


DESCRIPTION OF THE STATE OF THE ART

Disposable syringes, especially so-called two-piece disposable syringes of plastic, have long been known and widely used, which are injection-molded, assembled, sterilized and packed at low cost by modern manufacturing methods. Known disposable syringes of this kind have a plunger shaft having, as a rule, stiffening fins running offset at 90 degrees, which are guided along their edges on the inside wall of the barrel. Since in this case it is hardly avoidable that, especially when several liquids are aspirated and the indrawn air is ejected, the fins will be touched by the hand, pick up germs and transfer them to the inside wall of the barrel it has been proposed to construct disposable syringes of plastics such that the plunger shaft will be guided at a distance from the barrel wall, i.e., the largest cross-sectional dimension of the plunger shaft will be substantially smaller than the inside diameter of the barrel. This, however, creates the necessity of providing also for a centering of the plunger shaft at the plunger-shaft end of the otherwise open barrel. One known method of doing this is described in German Offenlegungsschrift No. 25 41 043. In this, two infolding projections having very thin film hinges are integrally injection molded, which, in the folded state, after the plunger has already been inserted into the barrel, produce a centering of the plunger shaft on the stroke axis by means of appropriate cutouts. One deficiency of this known solution, however, is that such syringes are difficult to assemble by machine, and at the same time the guidance afforded by the folded projections is only a centering, not a proper guidance path for the plunger shaft so as to prevent the buckling of the shaft now weakened in cross section, when an injection is given. In disposable syringes of this contamination-free kind, in which extremely slender plunger shafts are sought after with good reason, it has been found in practice to be disadvantageous that, when thin needles and especially when liquids of higher viscosity are injected, the thin plunger shaft can easily bow or buckle, and this deflection is transmitted on the one hand to the piston itself, creating sealing troubles and difficulty of movement, and on the other hand, in the fully retracted or drawn-back state of the plunger shaft the so-called starting force becomes too high, and in extreme cases the plunger shaft can even break. This is especially the case with known plastic disposable syringes in which a hard plunger of stable shape is used in combination with a relatively flexible, i.e., easily deformable, barrel. For there is a natural trend among syringe manufacturers to make the plunger shaft stiffer by selecting harder materials. In types, however, in which the piston and plunger shaft are a single injection molding of all the same material, the piston is also stiff and stable in shape, which always causes poor sealing as a source of danger. The last-named disadvantage is eliminated in known, so-called three-piece syringes by providing a substantially hard piston with a separate gasket of rubber, preferably silicone rubber. To improve the sliding and sealing properties, especially in gaskets of cheaper, silicone-free rubber, a silicone-containing wetting agent is used in the assembly of the disposable syringe. Such known disposable syringes, however, suffer from the disadvantage that on the one hand they are expensive and on the other hand the piston

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patent: 4578055 (1986-03-01), Fischer

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