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BACKGROUND OF THE INVENTION
This invention relates to a molding process and apparatus for producing
hollow articles, particularly full length Foley catheters. In the past,
hollow articles have been produced by a variety of dipping, molding and
extrusion apparatus and processes. However, each of these prior art
processes and apparatus have suffered from disadvantages that are
substantially overcome by the present apparatus and process.
In the dipping processes known in the prior art, a wire is dipped into a
liquified material to be formed into the hollow article. With each dip of
the wire more product from the bath adheres to the coated wire until
eventually the desired amount of material is built up onto the wire. Then
the material coated on the wire is sufficiently hardened so as to permit
the hollow article surrounding the wire to be peeled or stripped
therefrom. One disadvantage of the dipping process is the large number of
dips and great amount of time sometimes required to build up the desired
amount of material on the wire. Additionally, when the hollow article to
be manufactured requires small diameter wires, many materials are too
viscous in a liquified state for the wire to be dipped therein without
bending of the wire.
As with the above described prior art dipping processes, other prior art
processes also have disadvantages. For instance, extrusion processes are
not advantageously employed to obtain products with a closed end. Further,
while many molding processes may be employed to obtain products with
closed ends, the processes are generally not advantageously employed when
the article is relatively long and slender. The reason for this is that
the portion of the mold defining the hollow portion of the final product
is often unstable and bends at the high pressures employed in the molding
process.
The above noted deficiencies in prior art processes and apparatus are
substantially overcome by the process and apparatus disclosed in United
States Patent Application Ser. No. 580,881, filed May 27, 1975 now U.S.
Pat. No. 4,005,166 . The apparatus of the above-noted application
comprises a mold cavity with a first wire longitudinally disposed therein.
A second wire may be spaced distally from the distal end of the first wire
in longitudinal alignment therewith. Upon injection of molding material
into the mold, said material flows longitudinally toward the distal end of
the mold cavity pushing the follower ahead of it. When the follower
reaches the distal end of the first wire, it continues to move distally
into the mold onto the second wire thereby bridging the gap between the
first wire and the second wire. Eventually, the follower disengages
entirely from the first wire to provide a hollow article with a solid tip.
If a hollow article without a solid tip is desired, only one wire is used
and the follower does not disengage from the wire.
The process and apparatus described in the above-noted application has two
disadvantages. First, it is difficult to produce long articles with
relatively small hollow portions according to the process and apparatus
disclosed because the small wire required is distorted by the high
pressures required. For example, full length Foley catheters can not be
produced by the process and apparatus disclosed in U.S. application Ser.
No. 580,881 because the small inflation lumen wire is distorted by the
high process pressures required to such an extent that the wire touches
the mold wall to provide a useless inflation lumen with a hole in it.
Second, when a hollow article with a solid tip is produced according to
the process and apparatus of the above-noted application, the follower is
transferred from a first wire to a second wire, However, the first wire
may be twisted with respect to the second wire by the high pressures
required, thereby preventing the smooth transfer of the follower from the
first wire to the second wire. As described in U.S. application Ser. No.
580,881, the seriousness of this problem may be diminished by using
specially designed followers and second wires in which the cross sectional
area defined by the inside wall of the distal end of the follower is
larger than the cross sectional area defined by the proximal end of the
second wire. However, the specially designed follower and second wire of
the above-noted application may not always accomplish their intended
function, and at any rate, an apparatus and process that do not require a
specially designed follower and second wire would be most desirable.
The process and apparatus of the present invention may be used to produce
hollow articles from a wide variety of materials, including materials
which are too viscous in a liquid state to be used to produce hollow
articles by prior art dipping processes. Additionally, the process and
apparatus of the present invention may be employed to produce hollow
products with one of the ends closed by a solid tip. Further, the process
and apparatus of the present invention may be used to produce long
articles with relatively small, long hollow portions, such as Foley
catheters. Finally, the process and apparatus of the present invention may
be used to produce hollow articles with a solid tip without requiring the
use of a specially designed follower and second wire.
SUMMARY OF THE INVENTION
The apparatus of one embodiment of the present invention comprises a mold
with at least a first wire longitudinally disposed therein. First and
second followers are slidably disposed about the first wire in close
abutment with both the wire and inside wall of the mold. A set of gates in
fluid communication with a source of molding material is provided in the
walls of the mold. At the beginning of the molding process, the second
follower is spaced distally of the first follower and is positioned to
seal the set of gates. Molding material is then introduced through a gate
into the annular space defined by the wire and inside of the mold
proximally of the proximal end of the first follower. The molding material
thus introduced into the annular space flows longitudinally toward the
distal end of the mold while pushing the first follower along the wire
ahead of it. As the follower proceeds toward the distal end of the mold,
the first follower reaches the second follower and pushes it toward the
distal end of the mold. As the first follower proceeds to push the second
follower distally, the followers will eventually no longer seal the set of
gates. At such time, molding material will flow into the annular space
through the gates thereby pushing the followers toward the distal end of
the mold. It will be appreciated by those skilled in the art that process
pressures are reduced by providing multiple inlets into the mold as
described above. The lower process pressures required, in turn, reduce
distortion of the wire in the mold.
In a second embodiment of the invention, a hollow article with a solid tip
may be produced. In the second embodiment, there is provided a second wire
spread distally from the distal end of a first wire and longitudinally
aligned therewith. A first follower is slidably disposed about the first
wire in a close abutment with the first wire and inside of the mold. A
second follower is provided which bridges the gap between the first wire
and second wire. Molding material is then injected through a gate into the
annular space defined by the first wire and the mold and flows
longitudinally toward the distal end of the mold while pushing the first
follower ahead of it. As the follower proceeds along the wire toward the
distal end of the mold, the first follower reaches the second follower and
proceeds to push the second follower toward the distal end of the mold.
Eventually, the first follower disengages from the first wire and entirely
engages with the second wire. Because the first follower is substantially
aligned with the second follower when they first touch, the transfer from
the first wire to the second wire may frequently be smooth. However, the
transition from the first wire to the second wire may be facilitated by
notching the first follower and second follower so that they will not
twist with respect to each other once they are engaged.
It is within the scope of the present invention to employ both a follower
which initially seals gates and a follower which bridges wires in the same
apparatus. Additionally, multiple wires may be employed to provide
articles with multiple hollow portions therein. The above noted features
are concurrently used in the most preferred embodiment of the present
invention to produce a full length Foley catheter.
To produce a full length Foley catheter, there is provided a mold with
drainage lumen and inflation lumen wires longitudinally disposed therein.
Two receiving wires are spaced distally from the distal ends of the
drainage lumen and inflation lumen wires and are longitudinally aligned
therewith.
Preferably three followers are slidably disposed about the drainage lumen
and inflation lumen wires in close abutment with the wires and inside wall
of the mold, and a fourth follower is positioned so that it bridges the
space between the lumen wires and receiving wires. The four followers are
preferably about evenly spaced between widened funnel forming portions of
the lumen wires and the end of the lumen wires. The first three followers
located along the longitudinal axis of the mold are initially transversely
aligned with three sets of opposing gates. As noted supra, the fourth
follower bridges the space between the lumen wires and the receiving
wires.
In operation, molding material is introduced into the mold through a gate
proximally of the first follower. The molding material then flows toward
the distal end of the mold pushing the first follower ahead of it. As the
follower is pushed distally, the first set of gates which was initially
sealed by the first follower is opened and molding material flows into the
molding channel through these gates.
The first follower continues toward the distal end of the mold in response
to the pressure of molding material injected through the first set of
gates until the first follower meets and engages with a second follower.
The two followers then continue together distally in the mold until the
second set of gates is no longer sealed. Thereafter, molding material
flows into the molding channel through the second set of gates.
We have found that if at least two sets of gates are not employed when
producing a full length Foley catheter, the inflation lumen wire is
distored by the forces in the mold until it touches the wall of the mold.
This, of course, results in a useless inflation lumen with holes in it.
Moreover, to insure wire stability, it is preferred that a third follower
and a third set of gates be used in the mold. Initially the third follower
is aligned with and seals a third set of gates in the same fashion
described above in connection with the first two followers. After the
first three followers have proceeded in the mold cavity past the third set
of gats, eventually, the distal end of the third follower reaches and
engages the proximal end of the fourth follower. Unlike the previous three
followers, the fourth follower is not transversely aligned with a set of
gates but, rather, bridges the space between the drainage lumen and
inflation lumen wires and the receiving wires. In this fashion it is
insured that the lumen forming wires are aligned with the receiving wires
at the time the proximal end of the fourth follower disengages from the
lumen forming wires.
To insure that the lumen forming wires and the followers remain aligned
with the receiving wires as the followers proceed through the space
between the lumen wires and receiving wires, the followers may be
interlockingly notched so that they will not twist with respect to each
other. Thus, if the lumen wires or any follower is twisted slightly in
response to process pressures, then all the followers and the proximal
ends of the receiving wires are twisted in the same fashion to insure that
the followers remain aligned with the receiving wires.
As the followers continue to proceed distally in the mold, eventually the
first follower disengages totally from the drainage lumen and inflation
lumen wires and continues distally until finally it is totally engaged
with the receiving wires. In this fashion, molding material is permitted
to flow inwardly across the entire cross section of the mold between the
distal end of the drainage lumen and inflation lumen wires and the
proximal ends of the receiving wires thereby forming the solid tip of the
Foley catheter. Desirably, the proximal ends of the first follower and the
receiving wires are concave so as to provide a rounded, smooth tip.
During the molding process the mold is preferably maintained at a suitable
temperature so that shortly after the followers reach the distal end of
the mold the molding material will be cured or hardened. After the molded
material is sufficiently cured or hardened, the mold is opened and the
hollow article is stripped or peeled from the lumen forming wires. Molding
material will also have hardened in the gates and inputs thereto in the
mold. This material may be easily removed from the catheter by a cutting
operation either before or after the catheter is peeled from the lumen
forming wires. Thereafter, holes are provided in the catheter in
communication with the drainage and inflation lumens by conventional
techniques. Finally, a balloon is attached near the distal end of the
catheter to obtain the completed Foley catheter.
The number of followers used in the present invention may be increased
indefinitely until a substantial portion of the mold is filled with
followers, in which case it is preferred to use a single continuous
follower. The single continuous follower functions substantially in the
same manner as the followers described above, except that it may
simultaneously block more than one set of gates and bridges the space
between lumen wires and receiving wires.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the mold employed in one embodiment of the present invention.
FIG. 1A shows a cross section of FIG. 1 along line 1-A--1-A.
FIG. 2 shows the mold employed in another embodiment of the invention.
FIG. 3 shows three notched followers about to engage one another used in
the preferred embodiments of the present invention.
FIG. 4 shows the mold used to manufacture Foley catheters according to a
preferred embodiment of the present invention.
FIG. 4A shows a cross-section of FIG. 4 along lines 4A--4A.
FIG. 5 shows another embodiment of the present invention.
FIG. 6 shows the orientation of wires and followers at one time during the
process using the apparatus shown in FIG. 2.
FIG. 7 shows two notched followers about to engage one another.
FIG. 8 shows the mold used in another embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, there is shown in cross section mold 10 with wire 11
and followers 12 and 13 provided therein. As shown in FIG. 1, wire 11 is
hung from a source 17 and terminates at 18 close to the distal end 14 of
mold 10. However, it is to be understood that any suitable means for
providing the wire in the mold may be used in the invention. For instance,
the wire 11 may be imbedded into or adhesively attached to the distal end
14 of mold 10.
As shown in FIG. 1, followers 12 and 13 fit snugly into the annular space
15 in close abutment with wires 11 and the inside wall of mold 10. As
described more fully in U.S. application Ser. No. 580,881, now U.S. Pat.
No. 4,005,166 the followers 12 and 13 fit into the mold 10 so that in use
the followers will not move prematurely or permit the flow of material
into the spaces between the followers 12 and 13 and the inside wall of
mold 10 or wire 11.
As the start of the process, molding material is injected from a source
(not shown) through line 16 to two runners 19 and 20 that extend along
opposed sides of the mold. Runners 19 and 20 are preferably identically
designed and symmetrically oriented with respect to the mold so that in
use, the flow of molding material will be substantially the same in each
runner. As molding material proceeds to flow along the runners 19 and 20,
eventually some of the molding material will flow via lines 21 and 22
through gates 23 and 24 into annular space 15 proximally of follower 12.
While opposed gates 23 and 24 are used to introduce molding material
proximally of first follower 12 in the embodiment shown in FIG. 1 (and in
other embodiments described below), it is to be understood that a single
gate may be used to introduce molding material proximally of follower 12.
It is further to be understood that the source of molding material for
each gate 23 and 24 (and for the other gates used in this embodiment and
other embodiments described below) need not be the same as shown in FIG.
1.
The molding material injected into the mold 10 flows through annular space
15 pushing follower 12 ahead of it until the distal end of follower 12
reaches the proximal end of follower 13. In the meantime runners 19 and
20, as well as lines 124 and 125 and gates 26 and 27, have been filled
with molding material. Injection of molding material into the mold via
gates 26 and 27 is prevented up to this point however, because follower 13
is initially positioned in the mold 10, as shown in FIG. 1, to seal gates
26 and 27. However, when follower 12 reches follower 13, it continues
along the mold pushing follower 12 ahead of it until eventually gates 26
and 27 are unsealed when the proximal end of the follower 12 passes gates
26 and 27. At this time, molding material is injected into mold 10 via
gates 27 and 27 and flows through annular space 15, pushing followers 12
and 13 toward the distal end 14 of mold 10.
In the embodiment shown in FIGS. 1 and 1A (and in other embodiments
described below) runners 19 and 20, lines 21, 22, 124 and 125, and gates
23, 24, 26 and 27 are preferably identically designed and symmetrically
oriented with respect to mold 10. The reason for this is that when a small
wire is used in the invention, it is important the wire is not subjected
to any pressure that might distort it. Therefore, gates 26 and 27
oppositely oppose each other at the same longitudinal distance along the
mold as shown in FIGS. 1 and 1A so that opposing forces from material
injected through the gates 26 and 27 tend to cancel each other cut. It
will be appreciated that when a small wire is used in the invention more
than two gates may be suitably arranged symmetrically around the periphery
of the mold within the scope of the present invention. Further, it will be
appreciated that a ring gate enveloping the entire mold may be used
pursuant to the present invention. Finally, it will be appreciated that in
some circumstances, e.g., where thick wires are used, single gates may be
used instead of sets of gates along the length of the mold. A single gate
may also be used when it is desired to introduce molding material through
the proximal end wall of the mold.
It should be recognized that the rlative dimensions of the component parts
of the mold assembly shown in FIG. 1 (as well as in FIGS. 2 and 4 to 6)
are distorted for the purposes of illustration. In practice it is
contemplated that the cross sectional area of runners 19 and 20 will be
substantially larger than the cross sectional area of annular space 15.
Thereby, the pressure drops that occur in the runners will be
substantially lower than the pressure drops that occur in the mold itself
with the result being that substantially lower pressures can be employed
in molds that employ multiple sets of gates. The reduction of process
pressures permitted by the apparatus and process of the present invention
is particularly advantageous when small wires (e.g., 0.035 inch diameter),
which can be easily distorted, are used.
It will be appreciated by those skilled in the art that the manner in which
the gates are sealed by a movable follower is characterized by its
relative simplicity. Other methods and means of sealing the gates, e.g.,
by valves actuated by pressure transducers, could be used, but these other
methods and means would be much more complicated and costly than the
memthod and means used in the present invention.
As was noted supra, the gates used in the present invention are preferably
identially designed so that the forces exerted by molding material
injected into the mold via the opposing gates tend to balance each other.
The preferred dimensions of the gate used, of course, will vary depending
on the particular process and apparatus parameters employed, e.g., width
of wires, length of the mold, molding material, etc. However, when
producing Foley catheters, as described in more detail below, the gates
are preferably 0.100 inch long and have a cross sectional area of 0.050
inch by 0.100 inch.
Preferably, each follower used in the present invention is provided with at
least one air vent and most preferably two air vents 28 and 29, as shown
in FIG. 1A. The purpose of these air vents is to relieve air pressure
caused by the compression of the air space in the mold during the molding
process. At least one air vent (not shown) is also located at the distal
end of the mold. The design of the air vents is not particularly critical,
but the vents 28 and 29 should preferably be out of alignment with gates
26 and 27, as shown in FIG. 1A, and should be small enough to prevent the
passage of substantial amounts of molding material into the space defined
by the vents 28 and 29 and the inside wall of the mold 10.
As is apparent from FIG. 1, when followers 12 and 13 reach the distal end
of mold 10, follower 12 is still on wire 11. As a result, a hollow article
with an open end is produced. However, it is to be understood that the
mold may be designed so that both followers 12 and 13 disengage entirely
from wire 11 to provide a hollow article with a pigtailed tip. As
described in U.S. application Ser. No. 580,881, the pigtail on the tip
results from molding material flowing into the holes provided in followers
12 and 13.
After follower 13 reaches the distal end of mold 10, the molding material
is hardened by known processes. Thereafter, the mold is opened and the
hollow article is stripped from the wire. When the molding material is
catalyzed silicone rubber, it is desirable to heat the mold as described
in U.S. application Ser. No. 580,881 to partially cure the molding
material during the molding process.
Referring now to FIG. 2, there is shown an apparatus for producing a closed
ended hollow article according to the present invention. More
specifically, and for purposes of illustration, there is shown an
apparatus for producing a non-retention urinary catheter.
Urinary catheters, as is well known to physicians, are used in the
treatment of individuals who have lost control of their urinary function.
One generally accepted medical practice involves inserting a tube or
catheter into the urinary passage until the remote or distal end is
located within the bladder. The near or proximal end of the catheter
remains outside the body. Often the most proximal end of the catheter is
in the shape of a funnel. The funnel is in communication with a path or
drainage lumen that is provided along the longitudinal axis of the
catheter. The distal end of the catheter contains a hole in communication
with the drainage lumen such that in use the bladder may drain through the
hole into the drainage lumen and out through the funnel into a suitable
receptacle. While the invention is described with respect to urinary
catheters, it is to be understood that other types of catheters, e.g.,
tracheal catheters, venous catheters, etc. operate on similar principles
and may be manufactured according to the present invention.
As shown in FIG. 2, there is provided mold 30 with first wire 31
longitudinally disposed therein. A second wire 34 is also provided and is
longitudinally aligned with the first wire. Wire 31 is attached to a
suitable source which, as shown in FIG. 2, may be the proximal end of mold
30. As shown, the distal end of the first wire 31 is spaced from the
proximal end of the second wire. The proximal end of the first wire 31 is
preferably widened so that a catheter with a funnel at its proximal end is
provided by the process of the present invention.
At the beginning of the molding process, a first follower 32 is preferably
positioned a short distance from the widened portion of wire 31. A second
follower 33 is positioned so that it bridges the space between the distal
end of the first wire 31 and the proximal end of the second wire 34, as
shown in FIG. 2. The followers 32 and 33 are again fitted snugly into
annular space 36 closely abutting wires 31 and 34 and the inside of mold
30 as described above in connection with FIG. 1.
With the followers so positioned, molding material, e.g., catalyzed
silicone rubber, is introduced into the mold from a source not shown via
line 37, runners 38 and 39, lines 40 and 41 and gates 42 and 43. Again,
for reasons discussed above in connection with FIG. 1, it is preferred
that the runners, lines and gates are identically designed and
symmetrically oriented with respect to mold 30, although such design and
orientation is not essential when employing the relatively thick wires
(about 0.150 inch diameter) used to form the drainage lumens of
nonretention urinary catheters.
The catalyzed silicone rubber which has been injected into the mold via
gates 42 and 43 flows through annular space 36 and pushes follower 32
ahead of it. Eventually, the distal end of follower 32 reaches the
proximal end of follower 33. At this point, the follower 32 continues to
slide along wire 31 in response to the pressure of injected silicone
rubber pushing follower 33 ahead of it. Eventually, both the first
follower 32 and second follower 33 are entirely disengaged from the first
wire 31 so that molding material may spread throughout the cross section
defined by the inner wall of mold 30 thereby providing a solid tip for the
catheter. When the distal end of the second follower 33 reaches the distal
end of mold 30, the movement of the two followers stops. At this point,
desirably the rounded proximal edges of first follower 32 are aligned with
rounded proximal end of second wire 34 as shown in FIG. 5 of U.S.
application Ser. No. 580,881 to provide a continuous smooth tip for the
catheter. To complete the molding process, the molding material is
hardened, the mold is opened and the catheter is stripped or peeled from
the wire 31 as described above in connection with the description of FIG.
1. Thereafter, at least one drainage hole is provided toward the distal
end of the catheter in communication with the drainage lumen.
It will be appreciated by those skilled in the art that the proportions
shown in FIG. 2 are not the proportions which would be employed normally
in the manufacture of urinary catheters. That is, a typical urinary
catheter may be about 16 inches long and about 0.24 inches in diameter.
The catalyzed silicone rubber composition used in this embodiment of the
invention (as well as the other embodiments described herein) may be
prepared in the same manner and from the same materials as described in
U.S. application Ser. No. 580,881. Additionally, the silicone rubber is
suitably injected at the same temperatures and pressures described in the
above-noted application. Even further, the materials used for the wires
and followers in all embodiments of the present invention are preferably
the same as the materials used in the above-noted application.
In the above-noted application, a second follower 33 was not used to bridge
the space between first wire 31 and second wire 34. Rather, a specially
designed first follower was used to insure a smooth transition of the
first follower 32 from the first wire 31 to the second wire 34. In the
present invention, however, second follower 33 stabilizes the first wire
31 with respect to the second wire 34 thereby helping to insure the smooth
transition of the first follower 32 from the first wire 31 to the second
wire 34. As a result, specially designed followers, such as those
described in the above-noted application, are not required in the present
invention.
It will be appreciated by those skilled in the art that the embodiments
shown in FIGS. 1 and 2 may be combined to give a process and apparatus
with three or more followers. It will further be appreciated by those
skilled in the art that when the wires and followers are oriented as shown
in FIG. 6, the hole in the first follower 32 will be longitudinally
aligned with second wire 34. That is, as long as the distal end of the
first follower 32 is aligned with the distal end of wire 31, the first
follower 32 will still be aligned with second wire 34. However,
particularly when the wires are not concentric with the inner wall of the
mold (as described infra in connection with FIG. 5), as the followers
proceed distally in the mold beyond the orientation shown in FIG. 6,
second follower 33 will no longer be engaged with the first wire 31 and
therefore will be free to twist with respect to the distal end of first
wire 31. As a result, the distal end of first wire 31 may no longer remain
longitudinally aligned with the proximal end of second wire 34.
Thus, in the embodiment shown in FIG. 2, first follower 32 may become
misaligned with the second wire 34 thereby preventing the smooth
transition of the first follower 32 onto the second wire 34. The
misalignment problem noted above may be overcome, however, by notching the
followers used in the present invention so that they will interlock with
each other thereby preventing the twisting of one follower with respect to
another follower. One manner of interlockingly notching the followers is
shown in FIG. 3.
Referring to FIG. 3, there is shown first follower 90, second follower 91
and third follower 92 arranged in the same order as they would be provided
in a mold containing three followers. The followers are provided with
holes 93, 94 and 95 represented by the dotted lines. It will be observed
that the distal end of follower 90 and | | |
