Safety minute dose hypodermic syringe

A safety minute dose hypodermic syringe which includes a locating stopper mounted inside the front end of the barrel and connected to the locking tip, which holds the needle cannula, and an arrowhead-like retainer rod fixed secured to the movable rubber stopper and connected to the plunger, the arrowhead-like retainer rod being forced into engagement with an arrowhead-like retaining hole on the locating stopper after the injection, for permitting the locating stopper and the locking tip with the needle cannula to be pulled backwards by the plunger to the inside of the barrel and retained in place by inside annular flanges of the barrel, and for permitting the needle cannula to be deformed by the plunger when the plunger is disconnected from the retainer rod and inserted into the front end of the barrel.

BACKGROUND OF THE INVENTION 
The present invention relates to minute dose hypodermic syringes, and 
relates more particularly to a safety minute dose hypodermic syringe which 
permits the needle cannula to be pulled back inside the barrel after the 
injection, and then deformed by the plunger by removing the plunger out of 
the rear end of the barrel and then inserting it into the front end of the 
barrel. 
In order to prevent contamination, regular hypodermic syringes are commonly 
made disposable. FIG. 1 shows a regular minute dose hypodermis syringe 
which is generally comprised of a barrel, a locking tip fixedly secured to 
the front end of the barrel on the outside to hold a needle cannula, and a 
plunger having a front end coupled with a rubber stopper moved in the 
barrel. The needle cannula must be damaged by a syringe crusher or the 
like after the injection, to prevent possible contamination. FIG. 2 shows 
a safety minute dose hypodermic syringe according to the prior art in 
which the locking tip is coupled to the front end of the plunger. After 
the injection, the plunger is pulled backwards to move the needle cannula 
to the inside of the barrel, and then the front end of the plunger is 
broken and retained on the inside of the barrel. However, because the 
needle cannula is still maintained intact, it may injure someone when the 
barrel is broken. 
SUMMARY OF THE INVENTION 
The present invention has been accomplished to provide a safety minute dose 
hypodermic syringe which permits the needle cannula to be received inside 
the barrel and then deformed after the use of the syringe. According to 
one aspect of the present invention, the safety minute dose hypodermic 
syringe comprises a locating stopper mounted inside the front end of the 
barrel and connected to the locking tip, which holds the needle cannula, 
and an arrowhead-like retainer rod fixed secured to the movable rubber 
stopper and connected to the plunger, the arrowhead-like retainer rod 
being forced into engagement with an arrowhead-like retaining hole on the 
locating stopper after the injection, for permitting the locating stopper 
and the locking tip with the needle cannula to be pulled backwards by the 
plunger to the inside of the barrel. According to another aspect of the 
present invention, the barrel has a first inside annular flange at the 
front end for holding the locking tip in the working position, a second 
inside annular flange and a third inside annular flange at the rear end 
for holding the locking tip with the needle cannula inside the barrel. 
According to still another aspect of the present invention, the plunger 
can be disconnected from the retainer rod by breaking the retainer rod, 
and then inserted into the barrel from its front end to deform the needle 
cannula.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 3, a safety minute dose hypodermic syringe in accordance 
with the present invention is generally comprised of a stepped barrel 10, 
a plunger 20, a locking tip 4 fastened to the front end of the stepped 
barrel 10, and a needle cannula 5 fastened to the locking tip 4 outside 
the stepped barrel 10. A locating stopper 24 is mounted inside the stepped 
barrel 10 and fixedly secured to one end of the locking tip 4 remote from 
the needle cannula 5, having a conical retaining hole 230 at one end 
remote from the locking tip 4. The conical retaining hole 230 slightly 
slopes in one direction from the longitudinal center axis of the locating 
stopper 24 and is disposed in communication with the needle cannula 5 for 
delivery of liquid medicine. The stepped barrel 10 comprises a first 
inside annular flange 11 near the front end, a second inside annular 
flange 110 and a third inside annular flange 120 near the rear end. The 
inner diameter of the front end of the stepped barrel 10 is relatively 
smaller than that of the rear end thereof. When the locking tip 4 is 
fastened to the front end of the stepped barrel 10, the first inside 
annular flange 11 of the stepped barrel 10 engaged an annular locating 
groove 41 around the periphery of the locking tip 4. The plunger 20 is 
inserted into the stepped barrel 10, having two collars 21 around the 
periphery near the front end, and a tapered flange 202 around the 
periphery in the middle. A movable rubber stopper 22 is inserted into the 
stepped barrel 10 to hold an arrowhead-like retainer rod 23. The 
arrowhead-like retainer rod 23 has a front end extended out of the movable 
rubber stopper 22, and a rear end connected to the front end of the 
plunger 20. The arrowhead-like retainer rod 23 further has a breaking neck 
201 adjacent to the plunger 20. 
Referring to Figures from 4 to 7, when the movable rubber stopper 22 is 
moved forwards by the plunger 20 to squeeze liquid medicine out of the 
needle cannula 5 into the body of the patient, the arrowhead-like retainer 
rod 23 is simultaneously forced into engagement with the conical retaining 
hole 230 of the locating stopper 24 (see FIG. 4). When the plunger 20 is 
pulled backwards after injection, the locating stopper 24 with the locking 
tip 4 and the needle cannula 5 are simultaneously pulled backwards to the 
inside of the stepped barrel 10. Because the conical retaining hole 230 is 
made sloping from the longitudinal axis of the locating stopper 24 in one 
direction, the needle cannula 5 is tilted slightly when the locating 
stopper 24 with the locking tip 4 and the needle cannula 5 are pulled to 
the inside of the stepped barrel 10 (see FIG. 5). When the annular 
locating groove 41 of the locking tip 4 is moved to the position between 
the second inside annular flange 110 and the third inside annular flange 
120, the breaking neck 201 is disposed at the orifice of the rear end of 
the stepped barrel 10 (see FIG. 5). At the same time, the locking tip 4 is 
stopped from backward movement by the third inside annular flange 120, and 
therefore the locking tip 4 and the needle cannula 5 is completely 
received inside the stepped barrel 10. The plunger 20 is then turned 
sideways to break the breaking neck 201 of arrowhead-like retainer rod 23 
and to disconnect from the arrowhead-like retainer rod 23 (see FIG. 6). 
The plunger 20 is then inserted into the barrel 10 from the front end to 
damage the needle cannula 5 (see FIG. 7). Because the needle cannula 5 
tilts in one direction when it is moved back to the inside of the stepped 
barrel 10, it can be easily squeezed into a curved configuration when the 
plunger 20 is inserted into the stepped barrel 10 from the front end. When 
the plunger 20 is inserted into the stepped barrel 10 from the front end, 
the tapered flange 202 is forced into engagement with first inside annular 
flange 11 of the stepped barrel 10 to stop backward movement of the 
plunger 20. Furthermore, because the plunger 20 has two collars 21 near 
the front end, when the needle cannula 5 pierces one collar 21 during the 
insertion of the plunger 20 into the barrel 10 from the front end, the 
second collar 21 is still effective for squeezing the needle cannula 5 and 
deforming it. 
It is to be understood that the drawings are designed for purposes of 
illustration only, and are not intended as a definition of the limits and 
scope of the invention disclosed.