Method for extruding catheter tubing

Method and apparatus for making hollow catheter tubes or tubing from silicone rubber in which silicone rubber X-ray opaque flexible thread is introduced into a wall of the tubing during the extrusion of the tubing. The flexible thread enters the extruded silicone rubber in the extruding die close to the outer diameter of the tube at a line where the extruded silicone material changes from a varying to a constant cross-section. The apparatus is constructed to locate the terminating forward end of the tube through which the silicone thread passes at a line at the entrance to the constant cross-sectional area. The extruded tubing with the thread in one wall thereof is then cured into a final product.

BACKGROUND OF THE INVENTION 
The invention is directed to tubes for use as catheter tubes or the like of 
varying shapes and sizes which are ordinarily employed by medical 
personnel to drain fluids from body cavities or to distend body passages. 
It is desirable to know the location of the tube within the body. 
Elastomeric material such as silicone rubber is extruded to form the tube 
and simultaneously a silicone X-ray opaque thread is introduced into one 
wall of the tube as the latter is extruded which readily is exposed when 
the tube is located in a body and is X-rayed. The method and apparatus 
produces an extremely effective working catheter tube or the like. 
SUMMARY OF THE INVENTION 
There is provided by this invention a hollow tube or tubing of inherently 
flexible elastomeric material such as, for example, silicone rubber of 
varying sizes and shapes by an extrusion operation followed by curing to 
complete the tubes. 
To provide an X-ray marking member in the tubing, a thread-like member, 
also of inherently flexible elastomeric X-ray opaque material, such as 
silicone rubber, is introduced into the outer diameter of a wall of the 
tube during the extrusion operation at a line at which the die of the 
extrusion apparatus changes from a varying extent to a constant extent. 
After the extrusion of tubing and the introduction of the thread, which may 
be of various colors, the tubing is cured into a final product. 
The invention has several embodiments. Under the first embodiment the 
flexible elastomeric thread is introduced into the tubing extruding 
material via a guide tube extending through an extruding pin or inner die 
which forms the hollow inside of the tubing. 
In the second embodiment, the tubing which carries the flexible elastomeric 
thread extends through the outer extruding die rather than through the 
extruding pin.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1 there is shown an extruder 1 within which is located an 
extruding screw 2 and an adjustable breaker plate 3 disposed forwardly of 
screw 2. Extruder 1 extends forwardly of breaker 3 and has a conical 
shaped hollow opening 4 formed by the extruder member 5 threaded into the 
body of extruder 1 and having an inner downwardly tapered wall. 
The breaker plate 3 has a plurality of apertures 6 extending therethrough 
to provide passages for the flow of the extruded material shown in part at 
7 in FIG. 1. The inner side of breaker plate 3 is covered by a screen 8 to 
thereby remove undesirable deposits from the extruded material. 
Breaker plate 3 has an internally threaded forwardly extending collar 9 
located generally centrally of the forward side of breaker plate 3 and 
within which is threaded the forwardly extending extruder pin 10 which 
terminates commensurate with the forward end of extruder 1 and operates as 
an inner die. Pin 10 has a central passage 11 therethrough which connects 
with the vertical passage 12 through breaker plate 3 and extruder 1 for 
flow of air. 
The forward end of extruder 1 which initially is open, surrounds extruder 
pin 10 and receives an outer extruder die 13 which is secured by bolts 14 
to the forward end of extruder 1. Die 13 surrounds pin 10 and has a 
conical inner surface 15 tapered in line with and in accord with the 
downwardly tapered extruder member 5 of extruder 1. The conical varying 
cross-section of the inner surface 15 of die 13 terminates generally 
abruptly in a straight extending surface 16 having a constant 
cross-section which extends forwardly of extruder 1 and surrounds the 
outer end portion of pin or inner die 10 in predetermined spaced relation 
therewith. The spacing between die 13 and pin 10 regulates the thickness 
of the wall of the tube 17 which is extruded between pin 10 and die 13. 
Tube 17 is of an elastomeric material such as silicone and may be of 
various shapes such as oblong, round and the like. 
In order to encase a flexible marking thread 18 in the wall 19 of the tube 
17 as tubing 17 is extruded, a passage or guide tube 20 is provided in the 
wall of extruder pin 10. Tube 20 at the outer end extends through and out 
of the wall of pin 10 and terminates in the area of line 21 which is the 
dividing line between the tapered and varying surface 15 of extruding die 
13 and the constant or straightly extending surface 16 of extruding die 
13. This introduces marking thread 18 into extruded material 7 at that 
critical area. If thread 18 is introduced too far before line 21, the raw 
extruded material 7 tends to enter guide tube 20 and block guide tube 20 
which can cause thread 18 to stretch as the extrusion operation proceeds. 
If marking thread 18 is introduced too far beyond line 21, air may enter 
extruded material 7 with thread 18 and produce an undesirable air passage 
in catheter tube 17 adjacent to thread 18. Both of the described 
undesirable introductions of thread 18 into extruded material 7 creates an 
extruded tube 17 which must be rejected. 
Thread 18 may be of any color and by way of example a blue color has been 
found to be very satisfactory. Thread 18 which may be radio-opaque 
elastomeric material such as silicone is very flexible and is only 
partially cured when introduced into the wall of tube 17 so that a good 
bond is obtained between thread 18 and tube 17 when tubing 17 is finally 
cured. The thread 18 being of a flexible nature and not stiff enough to be 
forced into die 13 so that when the extruder 1 is placed in operation the 
extrusion operation tends to automatically draw thread 18 into the wall of 
tube 17 as the latter is extruded. For example, thread 18 may have a 
diameter of approximately 0.040 of an inch and a hardness of 30 to 60 
Durometer Shore A scale. 
The rear portion of guide tube 20 projects from extruder pin 10 into 
central passage 11 within the area of collar 9 of breaker plate 3 to 
receive thread 18 from the vertical passage 12 of breaker plate 3 arriving 
from a source, not shown. Passage 12 is aligned with the passage 22 
extending through a guide member 23 secured to extruder 1. 
After tube or tubing 17 with thread 18 encased in the wall 19 is extruded 
the tubing 17 is then heated to partially cure tubing 17 and thread 18 and 
then is baked for four or five hours to complete the cure and bond thread 
18 to tubing 17. The tubing 17 may then be cut into the lengths of tubes 
17 desired. 
FIG. 3 illustrates a tube or tubing 17 and thread 18 shown as it projects 
from the wall of tube 17 which has been partially broken away. The edge of 
the tubing 17 may be notched if desirable. 
FIG. 2 is directed to another embodiment of the invention. This embodiment 
has the usual extruder 1 enclosing screw 2 and breaker plate 3 and screen 
8 with plate 3 having passage 12 extending therethrough and through 
extruder 1 to entry passage 22 for flow of air. Similarly, extruder pin 10 
is threaded into central collar 9 of breaker plate 3 and extends forwardly 
and has a hollow central passage 11 therein for receipt of air from 
passage 12. 
Forwardly of breaker plate 3 extruder 1 in general is open and in which is 
lodged an extruder member 24 having a conical inner downwardly tapered 
surface 25. The extruding die 26 is disposed within the forward end of 
extruder 1 and is secured to member 24 by a ring 28 through which extend 
the bolts 28 and into threaded engagement with extruder member 24. 
Extruding die 26 tapers downwardly in line with the tapered surface 25 of 
extruder member 24 and in general abruptly changes from a varying extent 
to a straight line extent at line 29 around the outer end portion of 
extruder pin 10. 
In this embodiment guide tube 30 extends vertically through extruding die 
26 and then turns forwardly so that the marking thread 18 is discharged 
into the extruded material 7 at line 29 in the area where die 26 rather 
abruptly changes from the varying extent to a constant or straight line 
extent. This overcomes the problems discussed with respect to the first 
embodiment caused by entry of thread 18 into the extruded material too 
soon or too late. 
The tubing 17 provided by the second embodiment is then cured to complete 
the tube and encasing of thread 18. 
The invention provides a method and apparatus for introducing an X-ray 
opaque marking thread or line into the wall of a catheter tube or tubing 
whereby rejection of the tubing for use for medical purposes is kept to a 
minimum. 
Various modes of carrying out the invention are contemplated as being 
within the scope of the following claims particularly pointing out and 
distinctly claiming the subject matter which is regarded as the invention.