Abstrict The present invention relates to a disposable syringe the barrel
(4) of which is provided with a blob (6) of a cured adhesive substance
on the barrel that prevents the piston (5) from being pulled out
of the open rear end (8) of the barrel (4), for example when operated
by an unexperienced person.
Claims We claim:
1. In a disposable hypoderamic syringe of the type comprising a
barrel having an inner surface and an open end, means for connecting
a hypodermic needle to the barrel, a piston disposed in the barrel,
and a piston rod secured to the piston and extending out of the
open end of the barrel, the improvement comprising:
a quantity of a cured adhesive substance formed of a material dissimilar
to that of the barrel and secured to the inner surface between the
open end of the barrel and the piston, said quantity of cured adhesive
substance sized to prevent the piston from moving past the quantity
of cured adhesive substance, out of the open end of the barrel.
2. A disposable hypodermic syringe according to claim 1 characterized
in that the syringe barrel is made of glass.
3. A disposable hypodermic syringe according to claim 1 characterized
in that the syringe barrel is coated with silicone.
4. A disposable hypodermic syringe according to claim 1 characterized
in that the syringe barrel is made of a thermoplastic material.
5. A disposable hypodermic syringe according to claim 4 characterized
in that the syringe barrel is made up of a material selected from
the group consisting of PMP (Poly-4-methylpenten-1) and polyamide.
6. A disposable hypodermic syringe according to claim 4 characterized
in that the syringe barrel is made of a material selected from the
group consisting of polyethylene and polypropylene.
7. A disposable hypodermic syringe according to claim 1 or 2 or
3 or 4 or 5 or 6 characterized in that the adhesive substance is
a silicone sealant.
8. A disposable hypodermic syringe according to claim 2 4 5 or
6 characterized in that the adhesive substance is a cyanoacrylate
based adhesive substance.
9. A disposable hypodermic syringe according to claim 2 or claim
5 characterized in that the adhesive substance is an epoxy based
adhesive substance.
10. A method for assembling a disposable hypodermic syringe comprising
the following steps:
(a) providing a hypodermic syringe comprising a barrel having an
inner surface and an open end, means for connecting a hypodermic
needle to the barrel, a piston disposed in the barrel, and a piston
rod secured to the piston and extending out of the open end of the
barrel;
(b) applying a quantity of an uncured adhesive to the inner surface
of the barrel between the piston and the open end of the barrel;
and
(c) allowing the quantity of uncured adhesive to cure to form an
obstruction sized to prevent the piston from moving past the obstruction,
out of the open end of the barrel.
11. The method of claim 10 wherein the providing step comprises
the step of providing the hypodermic syringe having a glass barrel.
12. The method of claim 10 further comprising the step of coating
the inner surface with silicone prior to step (b).
13. The method of claim 10 wherein the providing step comprises
the step of providing the hypodermic syringe having a thermoplastic
barrel.
Description BACKGROUND OF THE INVENTION
The present invention relates to a disposable hypodermic syringe
comprising a barrel the front end of which is equipped with a firmly
connected hypodermic needle or with a gland for fixing a hypodermic
needle, in which barrel a tightly fitting piston can be displaced
by means of a piston rod.
Various kinds of disposable syringes are known. Most frequently
used are disposable syringes having a barrel made of a thermoplastic
material. However, in some instances disposable syringes having
a barrel made of glass are preferred in spite of the higher price.
For both types of barrels the piston can be made of a suitable type
of elastomer and the piston can be equipped with a piston rod made
of a thermoplastic material. Alternatively the piston and the piston
rod can be made in one piece of a suitable thermoplastic material
possibly to be equipped with a gasket made of a suitable elastomer.
A common feature with these disposable syringes is that the piston
may slip out of the barrel during the filling of the syringe so
that the contents will be spilled or the sterility spoiled or both
if the piston rod is pulled too strongly.
Some barrels made of thermoplastic materials do have a circumferential
bead on the inside of the rear part of the barrel in order to reduce
the risk that the piston may slip out. However, since the bead is
an integral part of the barrel its size must be moderate enough
to allow the passage of the piston during the assembly of the syringe.
Therefore, the bead cannot effectively prevent the piston from being
pulled out of the barrel.
From DE patent application publication No. 2329390 it is known
to weld or otherwise fix an inwardly protroding flange to the rear
end of the barrel of a hypodermic syringe after the piston has been
placed in the barrel. The flange prevents the piston from being
pulled out of the barrel. During the welding process the flange
and the barrel must be carefully positioned relative to each other.
For barrels of different diameters different flanges have to be
produced.
The purpose of the present invention is to provide a disposable
syringe which eliminates the above-mentioned drawbacks connected
with the disposable syringes according to the known art.
SUMMARY OF THE INVENTION
According to the present invention there is provided a disposable
syringe which is characterized in that the barrel is provided with
a small blob of a cured sealant or other adhesive substance, which,
after the piston or piston and piston rod has been placed in the
barrel, is applied in uncured form to the inner surface of the barrel
at a position between the open rear end of the barrel and the piston
in its rearmost position. The use of a small blob of a cured sealant
or other adhesive substance to restrict the movement of the piston
has several advantages. By the use of the syringe according to the
invention the spillage and contamination which may occur with other
disposable syringes is avoided. The sealant is cheap and it can
be applied automatically on a packing line. In contradiction to
a flange or the like to be mounted on a syringe in order to achieve
a similar result the blob of sealant according to the present invention
is universal to syringes of all sizes, except for a possible adjustment
of the size of the blob of sealant. No investments in expensive
tools for the manufacture of said flange are necessary.
The syringe barrel can be made of glass and the glass barrel can
be coated with silicone. Alternatively the syringe barrel can be
made of thermoplastic material, for example of polyethylene, polypropylene,
PMP (poly-4-methylpenten-1) or a polyamide or any other suitable
thermoplastic material.
The sealant or adhesive substance used for the blob can for example
be a silicone sealant, a cyanoacylate based adhesive or an epoxy
based adhesive, but other types of sealants or adhesives may also
be used. The sealant or adhesive substance preferably is so viscous
that it only runs insignificantly if at all when it is applied to
the syringe barrel.
In some cases it will be possible to apply the sealant or the adhesive
substance in such a precisely measured quantity and at a so well-defined
position in the syringe barrel that the blob will not come in contact
with the piston or the piston rod. Consequently, these will not
adhere to the blob. However, if adhesion is a potential problem
it can also be avoided by treating the piston and/or the piston
rod with a repellant, for example an oil solution, or by mounting
a sleeve made of paper, plastic foil or metal foil on the piston
rod.
According to one preferred embodiment of the invention the syringe
barrel is made of glass and coated with silicone prior to the application
of the sealant and the sealant is a silicone sealant. The silicone
sealant has a suitable viscosity and adheres well to the glass whereas
it does not adhere to the piston and the piston rod when these are
made of suitable materials or suitably treated materials. Coating
with silicone is a usual measure taken with glass barrels for syringes
to prevent the piston from sticking even after long storage and
to make the piston move more smoothly in operation. Also in other
connections silicone coating of glass and other materials serves
as an anti-adhesion measure. Surprisingly, however, silicone coating
of the syringe barrels made of glass does not adversely influence
the adhesion of the silicone sealant to the glass.
According to another preferred embodiment of the invention the
syringe barrel is made of glass which is not coated with silicone
and the sealant or adhesive substance is a silicone sealant, a cyanoacrylate
based adhesive substance or an epoxy based adhesive substance.
According to a further preferred embodiment of the invention the
syringe barrel is made of a thermoplastic polyamide and the sealant
or adhesive substance is a silicone sealant, a cyanoacrylate based
adhesive substance or an epoxy based adhesive substance.
According to a further preferred embodiment of the invention the
syringe barrel is made of PMP (poly-4-methylpenten-1) and the sealant
or adhesive substance is a silicone sealant, a cyanoacrylate based
adhesive substance or an epoxy based adhesive substance.
According to a further preferred embodiment of the invention the
syringe barrel is made of polyethylene and the adhesive substance
is a cyanoacrylate based adhesive.
According to a still further preferred embodiment of the invention
the syringe barrel is made of polypropylene and the adhesive substance
is a cyanoacrylate based adhesive.
BRIEF DESCRIPTION OF THE DRAWING
The drawing shows a sectional view along the longitudinal axis
of a disposable hypodermic syringe according to the invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
A syringe barrel 4 which can be made of glass or a suitable thermoplastic
material is equipped at the front end 3 with a hypodermic needle
2 and a cap 1 which protects the hypodermic needle. Alternatively
the syringe barrel can be equipped with a gland for fixing a hypodermic
needle, which gland may also be protected by a suitable cap. A piston
5 is displaced in the syringe barrel by means of a piston rod 9.
A small blob 6 of cured sealant or adhesive substance secures the
piston 5 against slipping out of the open rear end 8 of the syringe
barrel 4. The exact amount of sealant or adhesive substance in the
blob is not critical but will of course to some degree depend on
the size of the syringe and especially on the diameter of the barrel
and the piston. A guide to the amount of sealant or other adhesive
substance will be found in Example 1.
The disposable hypodermic syringe according to the invention is
especially useful when injections are to be performed by lay people,
unexperienced in handling a hypodermic syringe. For example the
syringe can form part of an emergency kit to be used for treating
hypoglycemic diabetics. Hypoglycemia can be relieved by injection
of glucagon, and the emergency kit can thus consist of a vial containing
the required amount of lyophilized glucagon and a disposable syringe
according to the invention containing the required amount of sterile
water. In use the contents of the syringe is transferred to the
vial and after complete dissolution of the glucagon the solution
is drawn back into the syringe. If an ordinary disposable syringe
were used for this operation there would be a risk that the piston
would slip out of the barrel since the operation would typically
be performed by an unexperienced and possibly nervous person. When
in a syringe according to the invention the piston hits the blob
of cured sealant or other adhesive substance it can go no further
back and thus cannot slip out of the barrel.
The use of the disposable syringe according to the invention is
not limited to the above emergency kit. Rather the disposable syringe
according to the invention can be used for the same purposes as
any ordinary disposable syringe.
Example 1 illustrates the production of disposable syringes according
to the invention and containing 1 ml of sterile water.
EXAMPLE 1
Silicone coated glass barrels having an internal diameter of 8.5
mm and an internal length of 35 mm and having a fixed hypodermic
needle were cleaned and equipped with a clean cap to protect the
needle. The barrels were placed on a filling line with the rear
end of the barrel pointing upwards. One ml of purified water was
transferred to each barrel and a piston made of bromobutyl rubber
was pushed down to the surface of the water. The ensemble was then
autoclaved in order to obtain sterility. Finally a polypropylene
piston rod with a threaded end was screwed into the piston and a
blob of Silastic.RTM. 732 RTV silicone sealant weighing about 250
mg (corresponding to a volume of about 240 mm.sup.3 of sealant)
was delivered from an automatic dispensing unit to the inner surface
of the barrel at a position between the piston and the open rear
end of the barrel (Silastic.RTM. is a registered trade mark of Dow
Corning Corporation). After curing, the sealant neither adhered
to the piston nor to the piston rod whereas it adhered well to the
glass barrel.
EXAMPLE 2
A blob of an epoxy based adhesive substance (about 300 mg, "Super
Epoxy", obtained from Plastic Padding) was applied to the inner
surface near the open rear end of the barrel of a complete disposable
hypodermic syringe with a barrel made of PMP. The barrel had an
internal diameter of 17 mm and an internal length of 65 mm. After
curing the blob of adhesive substance adhered well to the wall of
the barrel and the piston could not be pulled beyond the blob.
EXAMPLE 3
A blob of a cyanoacrylate based adhesive substance (about 300 mg,
"Loctite 409", obtained from Loctite Corp.) was applied
to the inner surface near the open rear end of the barrel of a complete
disposable hypodermic syringe with a barrel made of polypropylene.
The barrel had an internal diameter of 17 mm and an internal length
of 65 mm. After curing the blob of adhesive substance adhered well
to the wall of the barrel and the piston could not be pulled beyond
the blob. |