Hardness taper tube and production method and device therefor

Details Hardness taper tube and production method and device therefor Hardness taper tube and production method and device therefor

2002-01-02

2004-10-26

Davis, Robert (Department: 1722)

Plastic article or earthenware shaping or treating: apparatus

Means feeding fluent stock from plural sources to common...

Extrusion shaping means

C425S208000, C425S209000, C425S381000, C425S467000, C366S090000, C366S322000

Reexamination Certificate

active

06808380

ABSTRACT:

TECHNICAL FIELD
This invention relates to stiffness-taper tubing, that is formed by joining two or more resin materials having different stiffness such that the stiffness along its length gradually changes, and to the manufacturing method and manufacturing apparatus for such tubing. The stiffness-taper tubing of this invention is suitable for use in medical applications such as a catheter.
BACKGROUND ART
Conventionally, a two-layer extrusion-type formation apparatus was used when using two types of resin materials having different stiffness to form stiffness-taper tubing. The stiffness-taper tubing was formed such that there was a stiff section made from a first resin, having much stiffness in the longitudinal direction, a soft section made from a second resin, having little stiffness, and a transition section between these two sections in which the stiffness gradually changed (stiffness taper section). For this kind of stiffness-taper tubing, the first resin and then the second resin is supplied to the two-layer extrusion-type formation apparatus, and the transition section is formed when switching between resins and the first resin is gradually replaced by the second resin.
When this kind of stiffness-taper tubing is used in medical applications such as a catheter, a joint between both resin materials in the transition section that is adequately strong is required, and it is desired that the length of the transition section be long enough to be able to maintain its function as a catheter, but also be as short as possible in order to improve operability.
FIG. 7
is a horizontal cross-sectional diagram of a two-layer extrusion-type formation apparatus that the inventors used before developing the present invention.
This two-layer extrusion-type formation apparatus
30
comprises a die having an extrusion hole
31
, a die holder
34
for holding the die by way of a bolt
33
, and a mandrel
35
that is mounted such that it faces the extrusion hole
31
. The mandrel
35
is attached to and held by the die holder
34
by way of an inner-layer mandrel holder
36
and outer-layer mandrel holder
37
. The inner-layer and outer-layer mandrel holders
36
,
37
are nearly conical shaped, and there is a guide cavity
38
formed all the way around the tip of the cone for supplying resin to the mandrel
35
.
On both of the outer sides of the die holder
34
there are switching devices
39
,
49
for switching between and supplying the different types of resins A and B. The switching devices
39
,
40
are connected respectively to the resin A supply port
43
and resin B supply port
45
, that are located on the die holder
34
. There are heaters
47
on the die holder
34
and switching devices
39
,
40
for keeping the resins soft.
The switching device
39
for supplying resin A comprises a switching valve
41
, and a resin A inlet
42
that is connected to the resin A extruder. Resin A is supplied to the resin A supply port
43
on the die holder
34
as the switching valve
41
turns. The resin A, that is supplied to the resin A supply port
43
, is supplied to a channel
49
in the outer-layer mandrel holder
37
by way of a connection path
44
, and then supplied to the guide cavity
38
on the tip by way of this channel
49
and drawn out from the extrusion hole
31
by way of a ring-shaped space on the outer surface of the mandrel
35
.
Similarly, resin B passes through the resin B supply port and connection path
46
and is supplied to the guide cavity
38
by way of the channel
49
in the inner-layer mandrel holder
36
, and then is drawn out from the extrusion hole
31
by way of the ring-shaped space on the outer surface of the mandrel
35
.
When either resin A or resin B is selected by the switching device
39
,
40
and supplied to the die holder
34
, the resin that is not selected passes through the switching valve
41
of the respective switching device
39
or
40
and is discharged through the resin discharge port (not shown in the figure). At that time, part of the resin that was not selected remains in the resin supply ports
43
,
45
of the switching devices
39
,
40
and the die holder
34
, in the connection paths
44
,
46
, in the channels in the inner-layer and outer-layer mandrel holders
36
,
37
and in the guide cavity
38
, and remains there until the resin is switched and fed again.
The mandrel
35
is fastened to the end of a shaft
48
. The center axis of this shaft
48
is coaxial with the center axis of the extrusion hole
31
in the die
32
. This shaft
48
is fastened to and held inside the die holder
34
by fastening it on the inside of the inner-layer mandrel holder
36
. During use, a core member passes along the axis of, for example the shaft
48
, mandrel
35
and extrusion hole
31
, and melted resin, that was selected by the switching device, is supplied from the extrusion hole
31
and flows around this core member to form tubing.
In this kind of two-layer extrusion-type formation apparatus
30
, two kinds of resin are mixed at the point C in the figure where the respective cavity
38
opens up to the conical-shaped inlet of the extrusion hole
31
in the die
32
, and the mixed resin is discharged in a formed shape from the outlet of the extrusion hole
31
at point D in the figure. Moreover, when the two kinds of resins are alternately switched and supplied to the die
32
, at the time of switching, the first resin fills the space from the extrusion hole
31
, between the mixing point C at the die inlet and it the discharge point D at the die outlet, and the mandrel
35
. The resin that fills the space between this mixing point C and discharge point D is then replaced by the next resin after switching. The transition section becomes the part from the start of replacement to the end of replacement.
However, in the inventor's prior 2-layer extrusion-type device, the cavities
38
for both the inner-layer
36
and outer layer
37
open up at the mixing point C, so the volume between this mixing point C and discharge point D becomes large, and as a consequence the length of the transition section becomes long.
The length of the transition section is proportional to the time required for resin replacement. By taking the volume between the mixing point C and the discharge point D (called the joint-flow volume below) to be V, and taking the inflow rate of resin B, when going from 100% resin A to 100% resin B in this joint-flow volume V to be q, then the time T required for replacement is given by the following equation:
 
T=V/q+T
1
(T
1
is a constant that is determined by the mixing efficiency of resin A and resin B.) Moreover, the time T required for replacement becomes longer as the joint-flow volume V becomes larger. In other words, when the joint-flow volume V is large, the time T required for replacement becomes long and the length of the transition section becomes long in accordance.
Furthermore, in the prior two-layer extrusion-type formation apparatus, the resin supply path from the respective supply ports
43
,
45
for resin A and resin B to the mixing point C becomes long and its volume becomes large. In addition, the amount of resin that remains in the resin supply path during switching becomes large, and while waiting, this residual resin is heated by the heaters and there is a possibility that its quality could be altered or become degraded.
Moreover, when forming stiffness-taper tubing with the prior two-layer extrusion-type formation apparatus, the second resin is supplied such that it pushes the residual first resin when the resin is switched, so there is hardly any mixing between the two resins at the interface between them, and the tubing is formed with a clear interface (contact plane) between the two resins. The two resins are joined with the two resins in contact with each other through this kind of distinct interface, so it is not possible to obtain adequate bonding strength, and there is the possibility that the tubing will come apart at the joint surface in the transition section.
On the othe

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