Note: Descriptions are shown in the official language in which they were submitted.
2~
SPECIFICATION
PROCESS FC)R PRODUCING RUBBE~R TUBE AND RESIN
COATING DEVICE USED l~EREIN
TEC~NOLOG ICAL F I ELD
This invention relates to a process for pro-
ducing a rubber tube having a smooth outside surface, and
to a resin coating apparatus directly used for practising
the process.
BAC~G~O~ND ~c~NoLQGY .
To produce a rubber tube including a reinforc-
ing material and having a smooth outside surface, it is
the conventional practice to suppress the foaming of a
rubber material on the outside surface of the tube in the
vulcanization of the rubber material constituting the
rubber tube by using a pressurizable vulcanization device
and thereby applying pressure to the peripheral surface
of the tube, or by coating the periphery of the tube with
a synthetic resin or lead.
In the former method of suppressing the foaming
of the rubber material on the outside surface of the
vulcanization device, the foaming itself of the outside
surface of the tube can be limited, but still it is
impossible to achieve smoothening of the outside of the
tube. Moreover, since it is necessary to seal up the
inside of the vulcanization device consecutively, this
method is inconveniently unsuitable for mass-production.
In the latter method of coating the periphery
Of the tube with lead so as to smoothen the outside
surface of the tube, it is difficult to keep lead under
proper care and storage, and expenditures for facilities
and operations increase, and the product is likely to
increase in cost.
A method comprising coating the periphery of
the tube with a synthetic resin, and then vulcanizing the
rubber material constituting the rubber tube was regarded
as promising as a method for producing a rubber tube
h~ving a smooth outside ~urface. As shown in Japanese
Laid-Open Patent Publication No. 290,011/1986, a tech-
nique was developed by which the periphery of a rubber
tube is coated with a the~mally resistant resin cover
having a higher melting point than the vulcanization
temperature of the rubber material, and then ~ulcanizing
the ruhber material by using, for example, microwaves.
In the conventional method of coating the
periphery of a tube with a synthetic resin including the
one disclosed in the above patent publication, an ex-
trusion die for a resin is used as a resin coating device
2 as shown in Figure 3, and a synthetic resin 6 is ex-
truded along the periphery of a rubber material layer
coated on the periphery of a mandrel to form a resin
lS coated layer 8 continuously on the periphery of the
rubber material layer 4. Since the rubber material layer
4 as coated with the synthetic resin layer is heated and
thus vulcanized in the subsequent tep, the synthetic
resin 7 constituting the resin coated layer 8 must have a
2~ higher melting point than the vulcanization temperature
vf the rubber material~ Otherwise, during the vulcaniza-
tion of the rubber material layer 4, the resin coated
layer 8 would also be melt~d and the peripheral surface
of the rubber material layer 4 would be destroyed.
Accordingly; the synthetic resin in the molten state
flowing through the resin coating device 2 as the ex-
trusion die has to be heated at a temperature above the
vulcanization temperature of the rubber material. In the
prior art, a heater 10 is mounted on the outside of the
device 2 so as to heat the entire device~ Furthermore,
the rubber material layer 4 coated on the periphery of
the mandrel, before being fed into the device 2, is
heated by a preheater 12 so that the periphery of the
rubber material layer is covered closely with ~he resin
coated layer 8.
However, in the coventional method and device
~ ~ ~2~
2, the device 2 is heated from outside so that the syn-
thetic resin may remain flowable, and the rubber material
layer 4 is heated with the pre-heater 12. Hence, during
passage through the device 2, volatile components con-
tained in che rubber material layer 4 are likely to befoamed, and thus, the peripheral surface of the rubbery
material layer 4 is likely to be coated with the resin
coated layer 8 while it is roughened. Accordingly, even
if the surface of the rubber material layer 4 is covered
closely with the resin coated layer 8, a rubber tube
having a smooth peripheral surface is unlikely to be
obtained.
DFS~r-OS~RE OF T~E I~V~NTION
The present invention has been completed in
lS order to obviate these inconveniences of the prior art,
and has for its object the provision of a process for
producing a rubber tube having a smooth peripheral
surface efficiently, and a resin coating device directly
used for its practice.
To achieve this object, the present invention
provides a process for producing a rubber tube which
comprises forming a rubber material layer comprising
mainly an unvulcanized rubber material on the periphery
vf a mandrel, forming on the periphery of the rubber
material layer a thermally resistant resin coated layer
having a higher melting point than the vulcanization
temperature of the rubber material constituting the
rubber material layer, then heating the rubber material
layer to vulcanize the rubber material constituting the
rubber material, peeling and removing the resin coated
layer, and then pulling out the mandrel; wherein in the
formation of the resin coated layer on the periphery of
the rubber material layer, the synthetic resin in the
molten state is heated from the inner circumferential
side just before it flows out from a nozzle along the
periphery of the rubber material layerD
The resin coating device in accordance with
this invenion comprises
an insertion hole through which to insert a
mandrel coated on its periphery with a rubber material
layer comprising mainly an unvulcanized rubber material,
a resin flow passage through which a thermally
resistant synthetic resin having a higher melting point
than the vulcanization temperature of the rubber material
flows,
a nozzle for causing the synthetic resin flow-
ing through the resin flow passage to advance along the
periphery of the rubber material layer coated on the
periphery of the mandrel which is inserted through the
insertion hole, and
heating means for heating the synthetic resin
in the resin flow passage ~rom the inner circumferential
side before it flow~ out of the nozzle.
According to the process for producing the
rubber tube and the resin coating layer directly used in
the practice of this process in accordance with thi~
invention, the molten synthetic resin is heated from the
inner circumferential side just before it flows from the
nozzle. Accordingly, a resin coated layer can be formed
closely on the peripheral surface of the rubber material
layer without so much heating the entire device and
without pre-heating the rubber material layer. Moreover,
the volatile components in the rubber material layer are
not foamed before coating of the synthetic layer, and no
roughening of the peripheral surface of tbe rubber mate-
ria~ layer occurs.BRIEF DESCRIPTIO~ OF T8~ D~A~I~GS
Fig. 1 is a sectional view of the essential
parts of a resin coating device in accordance with one
embodiment of the invention; Fig. 2 is a sectional view
taken along line II-II of Fig. l; and Fig. 3 shows a
sectional view of a conventional resin coating device.
~ ~3~ ~'7~i
2, 20.. resin coating device; 4...rubber mate-
rial layer; 6.O.synthetic resin; 8.~.resin coated layer;
22...resin flow passage, 24...mandrel; 26...insertion
hole; 30...coolin~ tube; 34...heater.
5 BEST MODE OF PRACTISING THE INVENTION
The present invention will be described in
detail on the basis of the embodiments in accordance with
one embodiment of the invention.
Figu 1 is a sectional view of the es6ential
parts of the resin coating device in accordance with one
embodiment of the invention. Fig~ 2 is a sectional view
along line II-II of Fig. 1.
Before describing the process for producing a
rubber tube in accordance with this invention, the resin
coating device used directly in the practice of the
process will be described.
As shown in Fig. 1, the resin coating deYice 20
in accordance with one embodiment of the invention is an
improved version of a resin extru~ion die. The upstream
end portion of a resin flow passage 22 throu~h which a
molten synthetic resin 6 passes is connected to an ex-
truder. Various known extruders can be used a~ the
extruder for this purpose. Example are a continuous
extruder operable by screw rotation, an injection ex-
truder based on an in-line screw and an extruder based on
an accumulator method. The resin coating device 22
includes an insertion hole 2 through which a mandrel 24
coated on its periphery with a rubber material layer 4
containing mainly an un~ulcanized rubber material is
inserted. A recess 28 is formed on the inlet 26a side of
the insertion hole 26. Preferably, a cooling tube 30 is
received tberein. For example, cooling water is cir-
culated within the cooling tube 30 so as to cool the
rubber material layer 4 on the periphery of the mandrel
24. To make temperature ad~ustment by the cooling tube
30 easy, the inside diameter of the recess 28 is
maximizedO
~ resin flow passage 22 formed within the
device 20 communicates with an annulac nozzle 32 formed
nearly concentrically with the outlet 26b of the in-
sertion hole 2. ~ence, the synthetic resin in the molten
state is extruded from the nozzle 32 and flows in tubular
form and closely covers the periphery of the rubber
material layer 4.
Particularly, in the resin coating device 20 in
accordance with this invention, a heater 34 as heating
means is disposed immediately before the nozzle 32
between the resin flow passage 6 and the insertion hole
26 in order to heat the synthetic resin S in the resin
flow passage before it flows out from the nozzle 32. The
heater 34 may be, for example, an electric resistance
heating device or an electr~magnetic induction heating
device~ The heating temperature of the heater 34 can be
variously controlled according to the type, for example,
of the synthetic resin 6.
The synthetic resin to be extruded from the
nozzle 32 may be any thermally resistant resin having a
higher melting point than the vulcanization temperature
of the rubber material in the rubber material layer 4,
and examples are poly~4-methyl-1-pentene), nylon, poly-
etherimides and polysulfones. From the viewpoint of mold
releasability and thermal resistance, poly(4 methyl-l-
pentene) is most desirable. When poly(4-methyl-1-
pentene) is usPd as the synthetic resin 6, the heating
temperature of the heater 34 is preferably ~00 to 350 ~C.
In the embodiment shown in Fig. 1, no heater
for heating exteriorly of the device 20 is shownO As
required, such a heater may ~e provided. Even when a
heater is provided exteriorly of the device 20, heating
of the entire device 20 as in the prior art is not
necessary since the device includes the heater 34 in
accordance with this invention.
The process for producing a tube in accordance
6:~
with tllis invention will be described on the basis of the
embodiment shown in the drawings.
In the process of this invention, the rubber
material layer 4 which contains mainly an unvulcanized
rubber material is first coated on the periphery of the
mandrel 24. As required, a reinforcing material 36 may
be included in the rubber material layer 4~ Natural or
synthetic rubbers may be used as the rubber material
constituting the rubber material layer. The reinfor~ing
material 36 may be, for example, ~etallic wires or syn-
thetic fibers.
Generally, the mandrel 24 is a jig for forming
a hollow body, which is adapted to be pulled out in a
subsequent step. In the present invention, the outside
1~ diameter of the mandrel 24 corresponds to the inside
diameter of the rubber tube to be obtained.
Coating of the rubber material layer 4 on the
periphery may be carried out by known methods, for
example, by extrudin~ the rubber material along the
periphery of the mandrel 24.
In the next step of the process of this
invention, th~ mandrel 24 coated with the rubber material
layer 4 is inserted through the insertion hole 26 in the
resin coating device 20 shown in Fi~. 1 from the inlet
26a. When the mandrel 24 has jutted out from tbe outlet
26b or immediately before it, the synthetic resin 6 is
extruded from the nozzle 32 to coat the periphery of the
rubber material layer 4 with the resin coated layer 8.
Then, the mandrel 24 coated with the rubber
3~ material layer 4 and the resin coated layer 8 is entirely
heated to vulcanize the rubber material in the rubber
material layer 4. The heating temperature is preferably
below the vulcanization temperature of the rubber mate-
rial. This is for the purpose of preventing softening of
the resin coated layer 8. Various known means such as
microwave heating and heating by a vulcanization vessel
may be employed as heating means.
Thereafter, the resin coated layer 8 is peeled
and removed and the mandrel 24 is pulled out to give the
desired rubber tube. It should be understood that the
term ~rubber tube~, as used in the present specification
is used in a broad sense including rubber tubes and
rubber hoses.
According to the process of this invention~ the
molten synthetic resin 6 is heated from the inner cir-
cumferential side just before it flows out from the
nozzle 32 along the periphery of the rubbery material
layer 4. Accordingly, the resin coa~ed layer 8 can be
formed closely on the peripheral surface of the rubber
material layer 4 without so much heating the entire
device 20 and without pre-heating the rubber material
layer 4. Furthermore, before the coating of the syn-
thetic resin, volatile components in the rubbery ~aterial
layer 4 are not foamed to roughen the peripheral surface
of the rubber material layer. Therefore, when the rubber
material in the rubber material layer 4 is vulcanized in
a subsequent step, foaming on the peripheral surface of
the rubber m~terial layer 4 is ~uppressed to give a
smooth peripheral surface because the peripheral surface
of the rubber material layer 4 is closely covered with
the resin coated layer 8.
The following examples illustrate the present
invention. It should be noted that the invention is not
limited to these examples~
Example 1
Poly~4-mehyl-1-pentene) (to be reffered to as
PMP) having an MFR of 2 g/10 min. (tradename, TP ~ MX004,
a product of Mitsui Petrochemical Industries, Ltd.) was
coated on a nitrile-type rubber tube by using the device
shown in Fig. 1. The molding temperature conditions were
as follows:-
3s Cylinder of an extruder: 240-250 ~C
Prescribed tempera~ure of heater (reference
numeral 34): about 280 ~C
3Z~
_ 9 _
Compressed air ~or water3 was passed through
cooling tube ~reference numeral 30) to cool the raw
rubber.
After the resin coating, the coated layer was
rapidly cooled in a cooling water tank, and vulcanization
was carried out in a vulcanization device ~steam auto-
clave) or a high-frequency vulcanization device. The
resin layer was peeled, and the appearance of the rubber
hose was examined.
1~ The results are shown in Table 1 below.
The surface foaming and surface luster of the
hose were evaluated on the scale of 5 grades as follows:-
Surface foaming
5: none
4: almost none, but foaming occurred at one or
two sites per 10 m (no problem in practical use~.
3: foaming occurred 2 or 3 sites per 1-2 m~
2: on a better level than 1, but many foamings '~
occurred.
1: many foamings occurred.
Surface luster
5: Yery good
4: good but inferior to 5.
3: melt fracture began to occur, but the pro-
duct was usable.
2: melt fracture occurred slightly vigrously.
1: melt fracture occurred vigorously.
Example 2
PMP used in Example 1 was coated on a
styrene-type rubber tube. Otherwise, the molding
conditions, etc. were the same as in Example 1. The
appearance of the rubber hose was examined.
The results are shown in Table 1 below.
Comparative Example 1
Example 1 was repeated except that no heater
was provided, and no-cooling of the raw rubber w~ car-
ried out. The results are shown in Table 1.
.
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UTILIZABILITY IN INDUSTRY
~ s described hereinabove~ according to the
process for producing a rubber tube and the resin coating
device used therefor in accordance with this invention, a
~olten synthetic resin is heated from the inner circum-
ferential side just before it flows out from the no zle
in the formation of a resin eoated layer on the periphery
of the rubber material layer. Therefore, the resin
coated layer can be formed closely on the peripheral
surface of the rubber material layer without so much
heating the entire device and without preheating the
rubber material layer. Moreover, before the coating of
the synthetic resin, Yolatile components in the rubber
material layer are not foamed to roughen the peripheral
surface of the rubber material layer. Since the resin
coated layer is closely coated on the peripheral surface
of the rubber material, foaming on the peripheral surface
is suppressed at the time of vulcanizing the rubber
material in the rubber material layer in a subsequent
step, and a rubber tube having a smooth peripheral
surface can be produoed efficiently.
