Note: Descriptions are shown in the official language in which they were submitted.
21~3~
PROCESS AND APPARATUS FOR THE MANUFACTURE ~F A MOLDED PART
The invention relates to the manufacture of molded parts of
non-porous, elastic polyurethane which are made by a casting process.
In conventional processes for the manufacture of such molded part~,
a pre-polymer or adduct is first manufactured which is the result of a
reaction between diisocyanate and polyol. This pre-polymer or adduct is
then transported to a mixing head through conduits and exactly metering
gear pumps. Cros~-linking or chain extending agents and, if requlred,
catalysts are also transported to the mixing head by metering gear
pumps. The mixing ratio between pre-polymer or adduct and cross-linking
or chain extending agent~ i~ thereby 100:1 to 100:10. Usually, the
mixing pressure in the conduits does not exceed the output pressure of
the gear pumps and, thus, is sub~tantially below 20 bar and must be
mechanically assisted by way of spike or worm mixers. The mixture of
pre-polymer and cross-linking or chain-extending agents is continuously
discharged from the mixing head lnto open molds which are passed
thereunder.
The diisocyanates used are especially toluylenediisocyanate
1,5-naphthylenedii~ocyanate or 4,4'-diphenyl-methanediisocyanate.
Conventionally used polyols are, for example, polycaprolactone diol,
polyester diol or polyether diol respectively having a molecular weight
of 1,000 to 5,000 or polycarbonate diol having a molecular weight of 600
to 2,000. The molded part~ which are manufactured with this convent~onal
process and in the convent~onal apparatus must b0 baked in heated tools
for 10 to 40 minutes. This is usually, followed by an annealing process
of one or more days.
One prior art proces~ is described in Oertel, Polyurethane Handbook,
Carl-Hanser-Verlag, Miinrhen (1985), page 378, example 2.
The conventional process has the following disadvantage3. The low
achievable output pre~qure of the transporting pumps reQults in a long
casting time and requires the use of an open mold, which limitq the range
of poss~ble geometric shapes of the molded part. Furthermore, the
reaction time is between 1 and 40 minutes at about 130~C and the
subsequent annealing, which depending on the wall thickness of the molded
part may last several days, 910ws the process and increases its c03t.
2107~3~
-- 2 --
It is now an ob~ect of the present invention to substantially
overcome or reduce these problems in the manufacture of molded parts of
non-porous, elastlc polyurethane. In particular, it is an ob~ect of the
present invention to reduce the casting time and the time required for
S completion of the reaction of the mixed ingredients to a fini3hed molded
part.
This ob~ect is achieved according to the present invention by
~eparately heating the diisocyanate and polyol components prior to mixing
to a temperature above their respective melting temperature but below
their respective decomposition temperature, mixing the components under
pressure in the mixlng head and transferring ~he mixture into a mold.
Preferably, at least two separate component flows are generated
which flow from at least two heated storage containers for the ~tarting
materials to be processed, the diisocyanate and the polyol components
through closed-loop conduits and pumps and into the m~xing head. In the
storage containers and the separate flow circuits, these component flows
are respectively malntained at a constant temperature which lies above
the melting temperature and below the decomposition temperature of the
respective component. These temperatureQ are selected so that the
viscosity of each component flow is below 900 Pa s as measured by DIN
51562. The component flows are ~oined in a high pressure mixing head
which forms part of the isothermal temperature circuit of the
diisocyanate and, thu~, is heated to ~he temperature of the diisocyanate
component. The mixing head, the pumps and the circulation conduits are
constructed 90 that a mixing of the starting products st a pressure of at
least 150 bar i~ achieved.
Accordingly, the invention provides a process for the manufacture of
a molded part from a non-porous, elastic poly~rethane, wherein a
diisocyanate c; ~nt solid at room temperature and a polyol component
which may also be solid at room temperature are mixed in the liquid
condition, transferred ~nto a hollow mold and solidified. The
diisocyanate and polyol components are separately heated to a temperature
which is above the melting temperature but below the decomposition
temperature of the respective component and provides a component
35 viscosity below 900 Pa s, measured according to DIN 51562. The heated
components are then mixed with each other in a high pressure mixing head
2107~3~
-- 3 --
at a pressure of at least 150 bar, expelled from the mixing head and
transferred into the molding tool. The temperature of the heated
~omponents is maintained constant during the process until entry into the
mixing head which iY heated to the temperature of the diisocyanate. The
mixed components which are connected by a chemical reaction are no longer
sub~ect to this isothermal reaction control and the high pressure after
e~ection from the high pressure mixing head.
High pressure mixing heads are known, but not for use in a process
of this type, 3ince an isothermal temperature control of the type
disclosed herein could not be guaranteed, since in conventional apparatus
using high pressure mixing head~, portions of the components, and
especially of the diiqocyanate component which is solid at room
temperature, would come in contact with solidified, cooled down material
at some point in the conduits which was not heated and would immediately
clog the conduits. Therefore, the mixing ratio required for the
achievement of a reproducible reaction could not be maintained with
sufficient accuracy which iq also the reason why only low pressure
arrangements were used. Consequently, the operation of a high pressure
arrangement as in the present invention was previously not possible.
Only the combination of the respectively isothermal component
transport all the way from the storage containers through the conduitA
and pumps and, in case of the diisocyanate, in the mixing head, when
combined with the component control under pressure allows the operation
of a process in accordance with the invention. Maintaining the pressure
in the separate component circuits up to the mixing head at at least 150
bar provides for an optimal mixing of the st~rting component~ within only
a few seconds even at a feed rate of the component flows of up to 2 1/8
and promotes the chemical reaction of the componen~s to the end product
in such a way that in many cases, especially ~ith component parts for
couplings, the annealing required in conventional processes is obviated.
This results in production time savings of several dayq, which i8 a
further important advantage of the present invention.
The individual components of an apparatus in accordance with the
invention are known. However, it is important that the apparatus include
means for maintaining all parts in contact with the respective components
at a constant temperature and that the apparatus be constructed to
2~07~g
-- 4 --
withstand high pressures. The measures requ~red to achieve ~his do not
pose any technical problems:
The isothermal control can be guaranteed wlth conventional heating
arrangements surrounding the conduits for the respective components, for
example in~rared radiators, heating bands or liguid heating media. The
pressure required for a process in accordance with the invention is
preferably achieved by pistons which compress the components. The
sealing of the conduits, the pumps and the mixing head also does not po~e
a problem, since known hydraulic component~ can be u~ed.
Accordingly, the invention further provides apparatus for carry~ng
out the process described above which includes a~ least two ~torage
containers for the components to be used, which containers are
individually connected to a mixing head by closed loop conduits including
pumps for liquefaction of the components. All part~ of the apparatus
which are contacted by the components and especially the closed loop
conduits are provlded with heating arrangements for liquefaction of the
components. The heating arrangements further guarantee an isothermal
temperature control of the respective component and that the mixing
head. The pumps and the closed loop conduits are constructed to
withstand a pressure of at least 150 bar for the mixing of the components.
The following example is used to further describe the invention:
Two ce ponpnts were maintained in constant movement in ~eparate
~torage tanks heated to the respectlve component circulation temperature
in order to prevent dc l~1ne. Component A consisted of:
di-functional epsilon-polycaprolactonediol 9
Molecular weight 2,000 2,000 g
Diethyltoluoldiamine 445 g
Diaza-bicyclooctane (2,2,2) 2,44 g
Component B was:
4,4'-diphenylmethanedlisocyanate 901.25 g
The circuit for component A including the storage container, pumps
and the closed loop conduit was isothermally heated to 100~C by way of an
oil mantle. Component B, the diisocyanate, was heated in $he same way ~o
55~C while being transported from its storage container through the pumps
and the closed loop conduit and into the mixing head. The whole heated
system which held the starting materials was sub~ected to a pressure of
2~07~3g
-- 5 --
about 200 bar by way of an in~ec~ion cylinder. Thi9 pressure was the
same throughout the apparatus even in the mi~ing head.
The molding tool was filled for the manufacture of a test plate with
different wall thick~lesses up to 6 mm by opening valves for the
respective components for an in~ection interval of 1.14 second~. These
valves were also appropriately heated. The components were mixed in the
high pressure mixing head in cross flow at high speed and subsequently
after exiting the mixing head directly filled the cavities of the molding
tool. The mixed material recelved in the tool was thereafter exposed to
a pres~ure of about S0 bar by way of an integrated piston at a tool
temperature of 70~C. This process step lasted for 10 seconds. The
molded part was thereby consolidated. The finished molded part, the test
plate, had a weight of 114 g. Corresponding molded parts can be produced
with a cycle time of 15 to 30 seconds. The annealing 3tep required in
conventional proces~e3 can be omitted from the present process without a
re~ulting quality loss.
Changes and modifications in the ~pecifically described embodiments
can be carried out without departing from the scope of the invention
which is intended to be limited only by the scope of the appended claims.
