U.S. patent application number 10/831188 was filed with the patent office on 2004-10-07 for method and system for the production of a plastic needle.
Invention is credited to Hansen, Henrik Egesborg, Jensen, Soren, Nielsen, Poul E. B., Papsoe, Mogens, Sorensen, Anne.
Application Number | 20040199127 10/831188 |
Document ID | / |
Family ID | 8097254 |
Filed Date | 2004-10-07 |
United States Patent
Application |
20040199127 |
Kind Code |
A1 |
Jensen, Soren ; et
al. |
October 7, 2004 |
Method and system for the production of a plastic needle
Abstract
A method and a system is provided for producing a needle of
plastic, as well as a needle of plastic, in particular a needle for
medical purposes. The method produces a needle having at least the
outer diameter of one end being less than 0.50 mm using a moulding
system having an assembly comprising a feed system and a mould
cavity. The method includes introducing a melt of plastic into the
feed system, increasing the melt pressure gradually during melt
passage through the feed system, passing the melt into the mould
cavity whereby the melt substantially fills the mould cavity,
cooling the melt in the mould cavity whereby the melt solidifies to
a needle, and removing the needle from the mould cavity.
Inventors: |
Jensen, Soren; (Taastrup,
DK) ; Papsoe, Mogens; (Horsholm, DK) ;
Nielsen, Poul E. B.; (Vedbaek, DK) ; Hansen, Henrik
Egesborg; (Hellerup, DK) ; Sorensen, Anne;
(Holte, DK) |
Correspondence
Address: |
STITES & HARBISON PLLC
1199 NORTH FAIRFAX STREET
SUITE 900
ALEXANDRIA
VA
22314
US
|
Family ID: |
8097254 |
Appl. No.: |
10/831188 |
Filed: |
April 26, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10831188 |
Apr 26, 2004 |
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09979779 |
Nov 27, 2001 |
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6767496 |
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09979779 |
Nov 27, 2001 |
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PCT/DK00/00286 |
May 26, 2000 |
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Current U.S.
Class: |
604/272 ;
264/328.1; 425/542; 425/577 |
Current CPC
Class: |
A61M 5/32 20130101; B29L
2031/7544 20130101; B29C 45/46 20130101; B29C 45/00 20130101; B29C
2045/2714 20130101; B29K 2105/0079 20130101; B29C 45/261
20130101 |
Class at
Publication: |
604/272 ;
264/328.1; 425/542; 425/577 |
International
Class: |
A23P 001/00; B29C
045/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 28, 1999 |
DK |
PA 1999 00760 |
Claims
What is claimed:
1. A method for producing a plastic needle, the needle having two
ends, and having at least the outer diameter of one end being less
than 0.50 mm, the needle having a longitudinal lumen extending
between two openings of the needle, said method using a moulding
system having an assembly comprising a feed system, a mould cavity,
and an insert corresponding to and for forming the lumen in the
needle, said method comprising the following steps: introducing a
melt of plastic into the feed system; increasing the melt pressure
gradually during melt passage through the feed system; passing the
melt into the mould cavity whereby the melt substantially fills the
mould cavity; cooling the melt in the mould cavity whereby the melt
solidifies to form a needle; and removing the needle from the mould
cavity.
2. The method according to claim 1, wherein the mould cavity is
substantially filled in a period of time from 0.1 to 10 msec.
3. The method according to claim 2, wherein the mould cavity is
substantially filled in a period of time from 1 to 2 msec.
4. The method according to claim 1, wherein the melt is introduced
into the feed system with a rate of from 0.10 to 100 ccm/sec.
5. The method according to claim 1, wherein the melt is introduced
into the feed system with a rate of from 1 to 10 ccm/sec.
6. The method according to claim 1, wherein the mould temperature
is from 50 to 350.degree. C.
7. The method according to claim 6, wherein the mould is from
120.degree. C. to 140.degree. C.
8. A system for producing a plastic needle, said plastic needle
having an outer diameter of one end being less than 0.5 mm and
having a longitudinal lumen extending between two openings of the
needle, said system comprising: an assembly comprising a feed
system, a mould cavity, and an insert corresponding to and forming
the lumen in the needle, said feed system being arranged for
increasing the melt pressure gradually during melt passage through
the feed system; and means for passing the melt into the mould
cavity, so that the melt substantially fills the mould cavity.
9. The system according to claim 8, wherein the feed system is at
least partly conical shaped with the narrow part being downstream
of the melt flow passage.
10. The system according to claim 8, wherein the feed system
comprises cylindrical parts having a respective cylindrical flow
passage of different diameters separated by conical parts.
11. The system according to claim 8, wherein a ring gate is
arranged in front of the mould cavity, whereby melt is introduced
into the ring gate before entering the mould cavity.
12. The system according to claim 11, wherein the ring gate is of
conical shape.
13. The system according to claim 11, wherein the melt of plastic
is introduced radially into the ring gate.
14. The system according to claim 8, wherein the feed system and
the mould cavity are adapted to exhibit a temperature in the range
of 50-350.degree. C.
15. The system according to claim 8, wherein the feed system and
the mould cavity are adapted to exhibit a temperature in the range
of 120-140.degree. C.
16. The system according to claim 8, wherein the insert is a wire
substantially centered in the mould cavity.
17. The system according to claim 16, further comprising means for
removing the wire after moulding is arranged.
18. The system according to claim 8 wherein said means for passing
the melt into the mould cavity is adopted to fill the mould cavity
in a period of time from 0.1 to 10 msec.
19. The system according to claim 18, wherein said means for
passing the melt into the mould cavity is adapted to substantially
fills the mould cavity in a period of time from 1 to 2 msec.
20. A system for producing a hollow plastic needle, the needle
having two ends and at least the outer diameter of one end being
less than 0.50 mm, the needle having a longitudinal lumen extending
between two openings of the needle, said system comprising: a feed
system; a mould cavity; an insert corresponding to and forming the
lumen in the needle; means for introducing a melt of plastic into
the feed system, said feed system being arranged for increasing the
melt pressure gradually during melt passage through the feed
system; and means for passing the melt into the mould cavity, so
that the melt substantially fills the mould cavity in a period of
time from 0.1 to 10 msec.
21. The system of claim 20, wherein said means for passing the melt
into the mould cavity substantially fills the mould cavity in a
period of time from 1 to 2 msec.
22. A system for producing a hollow plastic needle, the needle
having two ends and at least the outer diameter of one end being
less than 0.50 mm, the needle having a longitudinal lumen extending
between two openings of the needle, said system comprising: a feed
system, said feed system being arranged for increasing the melt
pressure gradually during melt passage through the feed system; a
mould cavity; an insert corresponding to and forming the lumen in
the needle; a thermal conduit associated with the feed system for
introducing a melt of plastic into the feed system; and a mould
cavity fill conduit connecting the feed system with the mould
cavity, said mould cavity fill conduit adapted to provide the melt
to substantially fill the mould cavity in a period of time from 0.1
to 10 msec.
23. The system of claim 22 wherein the mould cavity fill conduit is
adapted to permit the melt to substantially fill the mould cavity
in a period of time from 1 to 2 msec.
24. A plastic needle having two ends, said needle being produced by
injection moulding from a plastic melt, wherein the outer diameter
of the moulded needle in at least one end of the needle is less
than 0.50 mm, said needle comprising a lumen, said needle having an
inner diameter corresponding to the diameter of the lumen which is
no greater than 60% of the outer diameter of the needle.
25. The plastic needle according to claim 24, wherein the inner
diameter of the needle in the range of from 20% to 50% of the outer
diameter.
26. The plastic needle according to claim 24, wherein the at least
one end of the needle is less than 0.45 mm.
27. The plastic needle according to claim 24, wherein said needle
is composed from an injection moulded liquid crystalline polymer
melt.
28. The plastic needle according to claim 27, wherein the liquid
crystalline polymer is a polymer comprising monomer units selected
the group consisting of hydroxybenzoic acid, hydroxynaphtoic acid,
terephtalic acid, p-aminophenol and p-biphenol alone or in
combination.
29. The plastic needle according to claim 28, wherein the polymer
is a random copolymer comprising 70-80% hydroxybenzoic acid and
20-30% hydroxynaphtoic acid.
30. The plastic needle according to claim 24, wherein the plastic
melt comprises fiber reinforcement.
31. The plastic needle according to claim 30, wherein the
reinforcement is selected from the group consisting of glass fiber
or carbon fiber and aramid fiber.
32. The plastic needle according to claim 30, wherein the
reinforcement fibers constitute from 15 to 40% by weight of the
solid plastic.
33. A plastic needle having two ends, said needle being produced by
injection moulding from a plastic polymer melt, said polymer being
a random copolymer comprising 70-80% hydroxybenzoic acid and 20-30%
hydroxynaphtoic acid, said needle having an outer diameter in at
least one end of the needle being less than 0.50 mm and comprising
a lumen.
34. A plastic needle according to claim 31, wherein the at least
one end of the needle is less than 0.45 mm.
35. The plastic needle according to claims 31, wherein the plastic
melt comprises fiber reinforcement.
36. The plastic needle according to claim 35, wherein the
reinforcement is selected from the group consisting of glass fiber,
carbon fiber and aramid fiber.
37. The plastic needle according to claim 36, wherein the
reinforcement fibers constitute from 15 to 40% by weight of the
solid plastic.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation of application Ser. No. 09/979,779,
filed Nov. 27, 2001, now pending.
FIELD OF THE INVENTION
[0002] This invention relates to a method for producing a needle of
plastic, a system for same as well as a needle of plastic, in
particular a needle for medical purposes.
BACKGROUND OF THE INVENTION
[0003] Needles or cannulas for medical purposes, such as injections
of medicine, have been produced in various sizes depending on their
intended use. For medicine to be injected frequently, such as
several times a day, it is preferable to use the thinnest possible
needle taking into account the viscosity of the medicine to be
injected. Diabetics injecting insulin several times a day would
preferably use a very thin needle, such as from gauge 26 to gauge
30, in order to reduce the pain as well as reduce the tissue damage
resulting from each injection. In the present context the term
"thin" refers to the diameter of the needle in question. Usually
needles and other medical tubings are sized in gauges, wherein
gauge 8 corresponds to 4.19 mm, and gauge 30 corresponds to 0.30
mm, for example.
[0004] In order to obtain a needle exhibiting the necessary
strength for penetrating the skin and subcutis as part of the
injection the very thin needles have usually been made from metal.
Like many other medical articles it is of interest to produce the
needles of a plastic material.
[0005] EP 452 595 discloses a method for producing a plastic
medical tubing, such as a catheter, wherein a liquid crystalline
polymer has been shear-thinned to such a viscosity allowing the
melt to flow into and fill a mould. The plastic tubings produced
have a gauge size of from 8 to 26, preferably from 14 to 20. The
shear-thinning is provided by passing the plastic melt through an
orifice before the melt reaches the mould. The patent describes a
method for preparing the tubing by extruding the shear-thinned
polymer into a mould, and describes further that the polymer melt
may be forced under pressure through the orifice and thence
directly into the mould.
[0006] However, in order to obtain very thin needles of the length
relevant for injection of medicine, very small volumes of plastic
melt is used. It has been found, that merely extruding the melt,
optionally under pressure will not result in the moulding of a
needle of the dimensions in question with sufficient strength.
[0007] Injection moulding systems are often used for the production
of large amount of articles. Injection moulding is a periodical
process, in which a plastic granulate is being homogenized and
melted by heating as well as by mechanical working. The plastic
melt is injected into a mould cavity. The mould cavity has a
temperature which is controlled to be lower than the melting point
of the plastic. Hereby the melt injected into the mould cavity will
solidify from the wall of the mould cavity to the center of the
article.
[0008] In the known injection moulding systems a screw may be used
to the mechanical working of the melt as well as to introduce the
melt into the mould cavity at a certain injection speed.
[0009] The screw movement or injection stroke is normally set to 1
to 4 times of the diameter of the screw. As a result, a right
quality of the melt as well as a uniform shot volume will be
ensured, where "shot volume" is defined as the amount of melt
necessary to at least fill the mould cavity to obtain a needle of
predetermined dimensions.
[0010] The inertia of the screw as well as the hydraulic pressure
transferred to the screw ensures a pressure which is sufficient to
fill large shot volumes in the known systems.
[0011] However, due to the small amount of melt necessary for
producing a small article, pressure applied to the screw cannot be
timely transferred to the melt at the entrance of the mould cavity.
The problem with known injection moulding systems is that the
hydraulic pressure behind the screw does not build up a pressure
from the screw to the entrance of the mould cavity in approximately
1 to 10 msec. Therefore, it has not previously been possible to
obtain plastic needles or cannulas for medical purposes, for which
the outer diameter of the needle or the cannula is 0.5 mm or
less.
[0012] Furthermore, needles or cannulas of a 0.5 mm outer diameter
have a very thin wall, e.g., a wall thickness of approximately
0.10-0.18 mm. This provides the problem of introducing the melt
into the mould cavity in such a short time, that "freezing" of the
melt is avoided. By "freezing" is meant that the melt solidifies
rapidly due to the small thickness of the material. In case melt
freezes in the first part of the mould cavity, the melt will not be
able to fill the entire mould cavity and thereby a needle of
predetermined dimensions will not be obtained.
[0013] By the known methods of injection moulding it has therefore
not previously been possible to mould needles or cannulas having a
wall thickness of material of approximately 0.10-0.18 mm.
[0014] The needles or cannulas have a very large L/D ratio (wherein
L is the length, and D is the diameter of the article) which
further provides the problem of not only requiring a small shot
volume but also of filling the "long" mould cavity as compared to a
small diameter. Thus, in order to ensure that the mould cavity is
filled totally with melt, a very precise control of the energy
reserve in the melt at the entrance of the mould cavity is
necessary.
[0015] Certain requirements must be met for needles or cannulas for
medical purposes irrespective of the material used. One requirement
is that the needle must not bend during insertion of the needle
into the patient. Many plastic needles have lacked sufficiently
strength when the diameter of the needle is decreased, so that in
practice it has not been possible to use plastic needles for
medical purposes unless very large needles, such as needles having
a diameter of 1 mm or above.
SUMMARY OF THE INVENTION
[0016] One aspect of the invention relates to a method for
producing a plastic needle wherein at least the outer diameter of
one end is less than 0.5 mm and the needle has a longitudinal lumen
extended between two openings of the needle. The method employs a
moulding system having an assembly comprising a feed system, a
mould cavity and an insert corresponding to and for forming the
lumen in the needle. The method includes introducing a melt of
plastic into the feed system and increasing the melt pressure
gradually during the melt passage through the feed system. The melt
passing into the mould cavity whereby the melt substantially fills
the mould cavity. The melt is cooled in the mould cavity whereby
the melt solidifies to form the needle. Subsequently the needle is
then removed from the mould cavity.
[0017] The invention in another form thereof concerns a system for
producing a plastic needle which includes an assembly which
includes a feed system, a mould cavity and an insert corresponding
to and forming the lumen of the needle. The system further includes
means for introducing a melt of plastic into the feed system and
the feed system is arranged for increasing the melt pressure
gradually during melt passage through the feed system. An insert
corresponds to and forms the lumen in the needle. Further means are
provided for passing the melt into the mould cavity so that the
melt substantially fills the mould cavity. In one form thereof the
system produces a needle having two ends and an outer diameter of
one end which is less than 0.5 mm and the needle has a longitudinal
lumen extending between two openings of the needle.
[0018] The invention in another form thereof concerns a system for
producing a hollow plastic needle wherein at least the outer
diameter of one end is less than 0.5 mm and the needle includes a
longitudinal lumen extending between two openings of the needle.
The system includes means for introducing a melted plastic into a
feed system where the feed system is arranged for increasing the
melt pressure gradually during melt passage through the feed
system. Means are provided for passing the melt into the mould
cavity so that the melt substantially fills the mould cavity in a
period of time from 0.1 to 10 msec.
[0019] The present invention in another form thereof concerns a
plastic needle having two ends produced by injection moulding from
a plastic melt wherein the outer diameter of the moulded needle on
one end is less than 0.5 mm. The needle includes a lumen wherein
the inner diameter of the needle corresponding to the diameter of
the lumen is no greater than 60% of the outer diameter of the
needle.
[0020] The present invention in another form thereof concerns a
system for producing a hollow plastic needle wherein at least one
end has an outer diameter less than 0.5 mm and a longitudinal lumen
extending between two openings of the needle. The system includes a
thermal conduit associated with the feed system for introducing a
melt of plastic into the feed system. The feed system is arranged
for increasing the melt pressure gradually during melt passage
through the feed system. A mould cavity fill conduit connects the
feed system with the mould cavity. An insert corresponds to and
forms the lumen of the needle. The mould cavity fill conduit is
adapted to provide the melt to substantially fill the mould cavity
in a period of time from 0.1 to 10 msec.
[0021] The present invention in yet another form thereof concerns a
plastic needle produced by injection moulding from a plastic melt
in which the needle has an outer diameter of at least one end of
the needle being less than 0.5 mm. The needle includes a lumen and
is comprises of a polymer which is a random copolymer comprising
70-80% hydroxybenzoic acid and 20-30% hydroxynaphtoic acid.
[0022] By the present invention it has been found that in order to
produce small, thin and elongated articles by injection moulding
whereby the shot volume is very small, it is preferable to have a
high energy reserve in the melt at the entrance of the mould cavity
itself.
[0023] By gradually increasing the pressure through the feed system
it is possible to meet the specific pressure demands at the
entrance of the mould cavity in order to mould the thin and
elongated articles in spite of the small shot volume, because the
melt will then reach a sufficient pressure before it enters the
mould cavity.
[0024] During injection moulding the melt is in motion in the feed
system, i.e., flows, whereby the flow front of the melt has a
pressure of approximately 0.1 MPa whereas the pressure in front of
the screw is high. Accordingly, a high pressure gradient is
present.
[0025] The high pressure gradient in the feed system ensures the
high energy reserve in the melt. This energy reserve in the melt
has the same function as for example a biased spring.
[0026] When the melt is introduced into the entrance of the mould
cavity the energy reserve in the melt ensures, that the spring
effect in the melt when released will substantially fill the mould
cavity in a very short time. By "substantially fill" is meant that
the mould cavity is filled with melt within predetermined
tolerances for needles produced.
[0027] Surprisingly, it has been found, that due to the energy
reserve in the melt, the high melt pressure in front of the screw
can be transferred to the flow front of the melt in approximately 1
msec. Hereby, the solidification or freezing of the melt before the
melt actually has substantially filled the entire mould cavity is
avoided.
[0028] Accordingly, the entire mould cavity will substantially be
filled by the melt, so the predetermined length and diameter of the
needles is obtained.
[0029] A third object of the invention relates to a plastic needle
having two ends, the needle being produced by injection moulding
from a plastic melt, wherein the outer diameter of the moulded
needle in at least one end of the needle is less than 0.50 mm,
preferably less than 0.45 mm, the needle comprising a lumen.
[0030] Hereby, a plastic needle is obtained having an outer
diameter, which diameter is so thin that the pain as well as the
tissue damage resulting from injections is reduced. The thin needle
is especially useful for diabetics who are injecting insulin
several times a day.
[0031] In an embodiment according to the invention the inner
diameter of the needle, e.g., the diameter of the lumen, may
correspond to at most 60% of the outer diameter of the needle,
preferably from 20% to 50% of the outer diameter. Hereby, a high
strength of the needle is obtained compared to the size of the
inner diameter.
[0032] The lumen may be formed in many different ways. In one
embodiment according to the invention an insert in the mould cavity
corresponding to the lumen of the needle may form the lumen.
[0033] In another embodiment the insert may comprise a wire
substantially centered in the mould cavity for forming the lumen in
the needle. According to the invention the wire may be fixed
extending through the entire mould cavity. Hereby, the melt flows
around the wire and the lumen is formed.
[0034] After the melt has solidified and the needle is formed, the
wire is removed from the needle. For example, means may be arranged
for removing the wire after moulding. The removal of the wire may
be carried out before or after the needle leaves the mould
cavity.
[0035] The pressure is increased gradually through the feed system
to meet the specific pressure demands at the entrance of the mould
cavity. The pressure increase may be carried out by any suitable
means.
[0036] In one embodiment, the specific design of the feed system,
i.e., the geometry of the feed system, leads to an increase of the
pressure.
[0037] The feed system may be comprised of a long tube having a
small diameter, optionally with parts of decreasing diameter.
[0038] The diameter of the feed system may be decreased in many
suitable ways such as stepwise or continuously. In one embodiment
according to the invention the feed system is at least partly of
conical shape, or in another embodiment the feed system comprises
cylindrical parts of different diameters separated by conical
parts, whereby the pressure is increased gradually through the feed
system. It is of importance to ensure that a sudden increase of
pressure is avoided in the feed system.
[0039] The amount of melt being introduced into the feed system
shall be of a rate sufficient to fill at least the feed system
completely in a predetermined time interval, so the design of the
feed system can increase the pressure to a level which is enough
for completely filling the mould cavity.
[0040] If the rate introduced is too small, the feed system will
not be timely filled and accordingly the pressure will not be
increased sufficiently to eventually fill the mould cavity. In
cases where the rate introduced is too large, it is not possible to
control the increase of the pressure and thereby the complete
filling of the mould cavity. Therefore, the melt is preferably
introduced into the feed system with a rate of from 0.10 to 100
ccm/sec, preferably from 1 to 10 ccm/sec.
[0041] The feed system and mould cavity may exhibit many different
temperatures according to the material used in moulding process.
The temperature of the feed system and mould cavity has a direct
influence on the viscosity of the melt and thereby the ability of
the melt to flow easily through the feed system and the mould
cavity. However, the temperature may not be to high as this will
influence on the strength of the produced needle.
[0042] According to the invention the temperature of the feed
system and of the mould cavity may be from 50 to 350.degree. C.,
preferably from 120 to 140.degree. C. Hereby, the flow length of
the melt in the feed system and in the mould cavity is optimal in
relation to the strength of the produced needle.
[0043] In a preferred embodiment according to the invention a ring
gate is arranged in front of the mould cavity, so the melt is
introduced into the ring gate before entering the mould cavity. The
melt will in this embodiment be completely confluent along the
periphery of the ring gate before entering the mould cavity in
order to avoid a burr or any other moulding defects due to lack of
confluence.
[0044] The ring gate may have many different shapes. In one
embodiment the ring gate is of a conical shape. When the ring gate
have an elongated conical shape, no sudden changes in the thickness
of the melt material will occur and the melt flow will not
stop.
[0045] Especially in cases where a wire is substantially centered
in the ring gate and the mould cavity for forming the lumen, the
melt may be introduced radially into the ring gate. A suitable
balance of the melt in the ring gate is hereby obtained. The melt
will flow equally around the wire and will have a uniform flow
front and thereby distribution in the mould cavity. Hereby, the
produced needle avoid having a burr or any other moulding
defects.
[0046] In order to avoid that the plastic melt will freeze or
solidify in the mould cavity, the melt has to be introduced into
the mould cavity in a short time. According to the present
invention the mould cavity may be substantially filled in a period
of time from 0.1 to 10 msec, preferably from 1 to 2 msec. Hereby,
the entire mould cavity will be filled with the melt before it
starts to solidify or to freeze.
[0047] The plastic needle is preferably produced from a liquid
crystalline polymer melt. The material, liquid crystalline polymer,
may be used due to the fact, that it has a high degree of molecular
orientation. During moulding the molecules of the liquid
crystalline polymer melt are aligned substantially in the direction
of the main flow of the melt. After solidification of the liquid
crystalline polymer the molecular orientation is maintained. This
high degree of orientation of the material ensures that the needles
obtained exhibits high strength compared to needles made of other
plastic materials.
[0048] The liquid crystalline polymer may be a polymer comprising
monomer units selected from hydroxybenzoic acid, hydroxynaphtoic
acid, terephtalic acid, p-aminophenol and p-biphenol alone or in
combination.
[0049] In an embodiment according to the invention the polymer may
be a random copolymer comprising 70-80% hydroxybenzoic acid and
20-30% hydroxynaphtoic acid.
[0050] The passage of the melt in the feed system ensures a
gradually increase in pressure. The passage further ensures that an
optimal orientation of the material particles in the plastic melt
is obtained. Hereby, a needle with the necessary strength is
obtained.
[0051] In order to increase the strength of the needle, the plastic
melt may comprise fiber reinforcement. The reinforcement may be
selected from glass fiber, carbon fiber, aramid fiber or any
suitable fibers.
[0052] When the melt comprises fiber reinforcement the viscosity of
the melt is increased and thereby it's ability to flow is
decreased. For obtaining a sufficient strength of the needle in
relation to the viscosity of the melt, the reinforcement fibers may
constitute from 15 to 40% by weight of the solid plastic,
preferably from 25 to 35%, such as approximately 30%.
BRIEF DESCRIPTION OF THE DRAWINGS
[0053] The invention will be explained more fully below with
reference to particularly preferred embodiments as well as the
drawings, in which:
[0054] FIG. 1 is a schematic view of an injection moulding system
according to the invention;
[0055] FIG. 2 is a schematic view of an assembly comprising the
mould cavity and the feed system;
[0056] FIG. 3 is a schematic view of the mould cavity and a ring
gate;
[0057] FIG. 4 is a schematic view of a first embodiment of the feed
system according to the invention;
[0058] FIG. 5 is a schematic view of a second embodiment of the
feed system according to the invention;
[0059] FIG. 6 is a sectional view of the ring gate shown in FIG.
3;
[0060] FIG. 7 is a schematic sectional view of the plastic
needle;
[0061] FIG. 8 is a schematic sectional view of the vertical section
A-A shown in FIG. 6; and
[0062] FIG. 9 is a view of a diagram showing the pressure as
function of the time.
[0063] All the figures are highly schematic and not necessarily to
scale, and they show only parts which are necessary in order to
elucidate the invention, other parts being omitted or merely
suggested.
DETAILED DESCRIPTION OF THE INVENTION
[0064] The moulding system 1 may be any injection moulding system
suitable for injection moulding of small articles. FIG. 1 shows a
schematic view of a injection moulding system 1. The system 1
comprises a granulate reservoir 2, which reservoir 2 contains the
plastic in a solid phase.
[0065] The granulate is at the bottom 3 of the reservoir 2 which
leads through a feed tube 4 into a chamber 5. In this embodiment a
thermal conduit in the form of a chamber 5, comprises a screw 6.
The screw 6 is rotated by a driving shaft 7 connected to a motor 8.
An instrument for measuring pressure 9 is connected to the chamber
5 in front of the screw 6, for monitoring the pressure building by
the screw 6. As the screw 6 rotates, the granulate is led towards
the entrance of an assembly 10. During the rotation of the screw 6,
the granulate is being heated and becomes a plastic melt. The
temperature is monitored by a temperature sensor 11.
[0066] The temperature of the assembly 10 is monitored by a
temperature sensor 12 and is controlled to be from 50 to
350.degree. C., preferably from 120 to 140.degree. C. according to
the material used in the moulding process. Hereby, the flow length
of the melt in the assembly 10 is optimal in relation to the
strength of the produced needle.
[0067] The assembly 10 is shown schematic in FIG. 2. The assembly
10 comprises in this embodiment a mould cavity 13 and a feed system
14.
[0068] The melt from the chamber 5 is introduced into the feed
system 14. From the feed system 14 the melt is introduced radially
into the mould cavity 13 by passing through a mould cavity fill
conduit such as a first cylindrical port 15 and a second
cylindrical port 16. In the feed system 14 the melt pressure is
gradually increased before the melt enters the mould cavity 13.
[0069] In the embodiment shown in FIG. 2 the pressure is increased
due to the distance the melt has to flow. The pressure is increased
due to the flow resistance of the melt. The pressure is further
increased by decreasing the diameter of the feed system 14. The
feed system 14 comprises a first cylindrical part 15 having a first
diameter and a second cylindrical part 16 having a second diameter,
smaller than the first diameter. The first cylindrical part 15 is
separated from the second cylindrical part 16 by a conical part
17.
[0070] The melt pressure in this embodiment is already increased
from the start of the feed system 14 and afterwards increased
gradually by the passage of the melt through the feed system 14 due
to the distance the melt has to flow as well as due to the
decreasing of the diameter of the feed system 14.
[0071] The melt pressure is increased sufficiently so the high
energy reserve in terms of pressure in the melt is ensured. Hereby,
the melt pressure can be transferred to the flow front of the melt
in approximately 1 msec.
[0072] In FIG. 3 is the mould cavity 13 shown separated from a ring
gate 18, the function of the ring gate 18 will be explained more
fully below. The melt is in this embodiment introduced radially
from the feed system 14 into the ring gate 18 with respect to the
melt flow in the mould cavity 13. The mould cavity 13 comprises a
first part 19 having a first diameter and a second part 20 with a
second diameter smaller than the first diameter. The first part 19
is separated from the second part 20 by a conical part 21. The
diameter of the second part 20 corresponds to the outer diameter of
the needle and is less than 0.50 mm.
[0073] A wire 22 is substantially centered in the mould cavity 13
for forming the lumen in the needle. In this embodiment the wire 22
is fixed and extends through the mould cavity 13 and further
extends through the ring gate 18. Hereby the melt flows equally
around the wire during moulding and the lumen is formed in the
center of the needle.
[0074] In FIG. 4 another embodiment of the feed system 14 according
to the invention is shown. The feed system 14 has in this
embodiment a first diameter D.sub.entrance at the entrance to the
feed system 14 and a second diameter D.sub.exit at the exit of the
feed system 14. The diameter of the feed system 14 is in this
embodiment gradually decreasing along the entire length L.sub.feed
system, so the feed system 14 exhibits a conical geometry.
[0075] FIG. 5 shows the feed system 14 in the same way as in FIG.
2. In this embodiment, the feed system 14 has two cylindrical parts
separated by conical parts. The first cylindrical part 15 has a
diameter corresponding to the diameter D.sub.entrance at the
entrance to the feed system 14. The second cylindrical part 16 has
a diameter D.sub.middle, which diameter D.sub.middle is smaller
than the diameter D.sub.entrance. At the end of the feed system 14
the diameter corresponds to the diameter D.sub.exit, which diameter
corresponds to the entrance of the mould cavity. The first
cylindrical part 15 is separated from the second cylindrical part
16 by a first conical part 17. The second cylindrical part 16 is
further separated from the mould cavity by a second conical part
23. The diameter of the feed system 14 is in this embodiment
decreased in steps along its entire length L.sub.feed system.
[0076] FIG. 6 is a schematic sectional view of the ring gate 18.
The arrow B indicates the main melt flow direction in the feed
system. The melt is introduced radially into the ring gate 18
(indicated by arrow B) with respect to the melt flow in the mould
cavity (indicated by arrow A). A first part 24 of the ring gate 18,
where the melt is introduced, is formed with a large volume around
the circumference of the ring gate 18, whereby the melt is forced
to flow firstly along the circumference of the first part 24
filling the large volume with melt before entering a second part 25
of the ring gate 18. In the second part 25 the melt flows in
direction of arrow A. The second part 25 of the ring gate 18 is
designed with an elongated conical geometry to avoid any sudden
changes in geometry that otherwise could lead to melt stop.
[0077] FIG. 7 is a schematic sectional view of a plastic needle 26.
The needle 26 has a longitudinal lumen 27 extending between one
opening 28 at a first end 29 of the needle 26 and a second opening
30 at a second end 31.
[0078] FIG. 8 shows a sectional view of the vertical section A-A of
the needle 26. In this embodiment the needle 26 is round and has an
outer diameter D.sub.needle as well as an inner diameter
D.sub.lumen.
[0079] A plastic needle produced according to the invention has an
outer diameter of 0.40 mm and a length of 8.00 mm. The needle
further has a lumen with a diameter of 0.16 mm. The wall of the
needle in this embodiment is 0.12 mm.
[0080] The plastic melt used is a liquid crystalline polymer, which
is a random copolymer comprising 73% hydroxybenzoic acid and 27%
hydroxynaphtoic acid.
[0081] The needle in accordance with this embodiment is produced
using an injecting moulding system having an assembly comprising a
feed system, a ring gate, and a mould cavity.
[0082] The screw used in the injecting moulding system has a 15 mm
screw. The injection moulding system is set to introduce
approximately 2.6 ccm of melt into the feed system with an
injection speed of 3 ccm/sec. The temperature of the assembly is
controlled to 130-140.degree. C.
[0083] The geometrical form of the feed system includes an entrance
diameter of 4.00 mm, a first cylindrical part with a diameter of
2.50 mm for distance of 449.00 mm, and a second cylindrical part
with a diameter on 1.60 mm for a distance of 10.00 mm, separated by
a conical part for a distance of 10.00 mm.
[0084] The diagram in FIG. 9 shows an abscissa and an ordinate. At
the abscissa, the time is indicated as seconds, and at the
ordinate, the pressure is indicated as MPa. The diagram shows the
melt pressure at the entrance to the feed system as a function of
the time during filling of the assembly. The diagram shows that the
pressure increased gradually for about a second during the melts
passage of the feed system. At about 1 sec on the abscissa, the
pressure had a high increase due to the small diameter of the mould
cavity. The high pressure in the melt was due to the energy reserve
be transferred to the flow front of the melt, so the entire mould
cavity will be filled before the melt starts to solidify.
[0085] As will now be apparent to one skilled in the art, the
pressure of the melt will be increased during passage of the feed
system, so the energy reserve in the melt will be sufficient to
fill the entire mould cavity in approximately 1 msec. Accordingly,
the produced needle will obtain the predetermined size as mentioned
before.
[0086] Although the invention has been described in considerable
detail with respect to preferred embodiments, it will be apparent
that the invention is capable of numerous modifications and
variations, apparent to those skilled in the art, without departing
from the spirit and scope of the invention
* * * * *