Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a rapid curing polyurethane elastomer.
More particularly, this invention prGvides a polyurethane elastomer which is
curable and releasable at a relatively low temperature and in a short time.
The so-called casting polyurethane elastomers, which have been wide-
ly used in roller, belt, solid-tire applications on account of its excellent
mechanical characteristics, wear resistance, and resistance to oils, includes
two types. One is the TDI (tolylene diisocyanate) prepolymer type which
employs MOCA ~3,3'-dichloro-4,4'-diaminodiphenylmethane) as curing agent and
employs as polyol polytetramethylene ether glycol (hereinafter simply refer-
red to as PTMEG), polyester diol, polyoxypropylene glycol (hereinafter simply
referred to as PPG) and the like, and the other is a type obtained according
to the so-called semi-one shot process in which a 1,5-naphthylenediisocyanate
or diphenylmethanediisocyanate/polyester diol system is employed and glycol
is employed as curing agent.
However, both processes for preparing the two types mentioned above
have such drawbacks that curing takes several hours at about 100C and work-
ability is extremely low.
In both types mentioned above, pot life on mixing the prepolymer
with the curing agent can be shortened by the use o~ a catalyst, but it is
2n quite impossible to shorten curing time to several minutes. Moreover, it is
necessary to raise the temperature of the raw material up ~o around 100 C
for reasons such as high viscosity of the prepolymer, high melting-point of
MOCA, and the like. However, a high pressure casting machine, to which the
raw material at such a high temperature is applicable, is not available at
present. Even if such a high pressure casting machine should be available,
it would be impossible to shorten the curing time to several minutes.
With respect to high density polyurethane foam, which is also call-
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ed micro-cellular elastomer, and is used as soles and automobile parts such
as bumpers, Japanese published examined patent applications Nos. 22711/1972,
38587/1971 and 1386/1972 discloseprocesses in which curing is effected more
rapidly at lower temperatures compared with the so-called casting elastomer
process mentioned above. All the processes disclosed as above follow the so-
called one shot process, in which modified diphenylmethanediisocyanate ~MDI)
is used as polyisocyanate.
With respect to rapid curing polyurethane elastomer, Japanese pub-
lished unexamined patent applications Nos. 118795/1974 and 125199/1976
disclose the use of a prepolymer as polyisocyanate, and particularly the lat-
ter discloses the use of PTMEG in the prepolymer and as a curing agent.
In accordance with the processes disclosed as above, however, it
is very difficult to satisfy simultaneously both rapid curability and satis-
factory physical properties of the cured product, and no elastomer has yet
been obtained with high physical properties equal to an elastomer obtained
from the PTMEG/TDI prepolymer represented by Adiprene L-100 ~produced by E.
I. Du Pont de Nemours ~ Co.), where MOCA is employed as a curing agent.
The present invention provides a -rapid curing polyurethane elastomer
; which is curable and releasable in a short period of time of -from one minute
to about a dozen minutes at a temperature of from room temperature to a
relatively low temperature. Accordingly the invention provides a rapid cur-
ing polyurethane elastomer, which is prepared by mixing to cure a prepolymer
(A~, which is liquid at room temperature and is prepared by reacting 4 to ~
equivalents of a mixture of diphenylmethanediisocyanate (hereinafter referr-
ed to as MDI) and a carbodiimide modified material of said compound, which is
liquid a~ room temperature, with one equivalent of polytetramethylene ether
glycol having a mean molecular weight of from 650 to 2000 or a mixture there-
-- 2 --
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of with an aliphatic diol having a molecular weight less than 250, and a cur-
ing agent (B) essentially consisting of a mixture of one equivalent of said
polytetramethylene ether glycol, 1 to 4 equivalents of a diol having a
molecular weight less than 2S0 as chain-elongating agent, and an organometal-
lic catalyst at an NCO/OH equivalent ratio of from 1.00 to 1.10, preferably
1.03 to 1.07.
Thus, the present invention relates to a rapid curing polyurethane
elastomer which is curable and releasable in a short period of time of from
one minute to about a dozen minutes at a temperature of from room temperature
to a relatively low temperature.
More particularly, the present invention relates to a rapid curing
polyurethane elastomer curable and releasable in a short period of time at a
temperature of from room temperature to a relatively low temperature, said
polyurethane elastomer being prepared by mixing with agitation by use of a
high pressure casting machine, a low pressure casting machine, a batch type
agitator~ or the llke depending on the pot life on mixing a prepolymer and a
curing agent which is controlled in the range of from about a dozen seconds
: to several minutes by selecting a prepolymer of a suitable composition, and
a curing agent, particularly the amount of a catalyst for urethane formation.
The present i-nventors made an extensive study in order to obtain
an elastomer having rapid curability and such high physical properties as to
be equal to those of a casting type elastomer represented by Adiprene L-100
produced by E. I. Du Pont de Nemours ~ Co. which is cured on heating by the
use of MOCA and found out that such an elastomer can be obtained by satis-
factorily selecting the composition of the prepolymer so that the viscosity
thereof may be lowered to such an extent as to be applicable to a casting
machine at a temperature of from room temperature to a relatively low temper-
ature.
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The rapid curing polyurethane elastomer of the present invention
is a rapid curing polyurethane elastomer, which is curable and releasable in
a short period of time of from one minute to about a dozen minutes at a rela-
tively low temperature of from room temperature to 60C by controlling the
amount of the catalyst so that the pot life on mixing ingredients ~A) and ~B)
may be in the range of from about a dozen seconds to several minutes.
Carbodiimide modified material of MDI, which is liquid at room temp-
erature, includes material prepared according to the processes disclosed in
Japanese published examined patent application Nos. 4576/1963 and 2908/1977.
Examples of aliphatic diols having a molecular weight less than 250
include ethylene glycol ~hereinafter simply referred to as EG)~ propylene
glycol ~hereinafter simply referred to as PG), dipropylene glycol ~hereinafter
simply referred to as DPG), diethylene glycol ~hereinafter simply referred to
as DEG), 1,4-butane-diol and cyclohexane dimethanol, and aromatic diol such
as bishydroxyethoxybenzene and p-xylylene-diol.
Examples of the organometallic catalyst used include known catalysts
for urethane formation such as dibutyltin dilaurate ~hereinafter simply refer-
red to as DBTDL), lead octylate and cobalt naphthenate. Explaining in more
detail control of the pot life on mixing a prepolymer and a curing agent by
the amount of the catalyst for urethane formation, the pot life can readily
be controlled simply be increasing or decreasing the amount of the catalyst
as shown by the fact that 0.05 parts ~hereinafter all parts are parts by
weight), 0.2 parts, and 0.6 parts respectively of DBTDL based on lO0 parts of
a curing agent result in 5 minutes, one minute, and about 20 seconds of the
pot life, respectively.
The pot life means the period of time required from the time at
which two solutions are mixed to the time at which the fluidity thereof is
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almost lost with the viscosity thereof increasing to 1000 ps.
The high pressure casting machine is, for example, a casting machine
such that two stock solutions are circulated under a circulating pressure of
from 150 to 200 kg/cm2 by a high pressure pump, such as an axial piston pump
or a Bosch pump, and these high pressure streams impinge directly on to each
other in a small mixing zone and cause an intimate mixing of liquids, which
is then subjected to casting. The low pressure casting machine is a casting
machine in which two stock solutions are sent to a mixing part respectively
by a low pressure pump such as a gear pump, and these solutions are mixed
with agitation by a rotor mixer or a static mixer, and the mixture is then
subjected to cas-ting. The batch type agitator used is most preferably of
such a type that air bubbles are not involved therein on agitation, for
example, the AJITER ~trade mark of Shimazaki Equipment Co., Ltd.).
In 'he practice of the present invention, the prepolymer ~A) and
the curing agent (B) may be used at room temperature as they are, or they
may be warmed up to abo~lt 60C in order that the viscosity thereof may be low-
ered depending on the case required. Examples of the casting process applic-
able include various casting processes applicable to the so-called casting
elastomer, Reaction Injection Molding Process (simply referred to as RIM
process), in ~hich a high pressure casting machine is used, and a process in
which a thick coating is effected by use of an airless spray machine.
The present invention will be further illustrated by way of the
following Examples and Comparative Examples. Hereinafter, % and parts repre~
sent % by weight and parts by weight respectively.
Example 1
One equivalent of PTMEG having an average molecular weight o 1000
and 5.~ equivalents of polyisocyanate mixtures prepared by mixing MDI and
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carbodiimide-modified MDI ~liquid at room tempera~ure and hereinafter simply
referred to as liquid MDI) at a ratio be weight of 7 to 3 are reacted at 80 C
for 3 hours to obtain a prepolymer ~C) having a free isocyanate radical con-
tent of 14.8% and a viscosity of 2000 cps at 25C.
Separately therefrom, one equivalent of PTMEG having an average
molecular weight of 1000, 2 equivalents of 1,4-butane-diol, and 0.05 g of
DBTDL are mixed to obtain a curing agent (D).
The prepolymer ~C) and the curing agent ~D) are subjected to vacuum
degassing, both solutions are then mixed throughly for one and half minutes
in such a manner that bubbles are not involved therein, by the use of an agita-
tor at such a blend ratio that the NCO/OH equivalent ratio is 1.05, and the
mixture is cast into a mold to form a sheet of 2 mm in thickness in an oven
maintained at 60C. The period of time from the time at which the mixing of
two solutions is started to the time at which the viscosity of the mixture
reaches 1000 ps is five minutes, and the cured material has neither bubbles
included therein nor cracks and is releasable in 10 minutes after commence-
ment of mixing of the two solutions.
The physical properties of the product showed values equal to those
of elastomers prepared by curing Adiprene L-lOO with MOCA as shown in Table
1 which follows.
Example 2
A curing agent prepared by mixing one equivalent of PTMEG having
an average molecular weight of 1000, 2 equivalents of 1,4-butane-diol, and
0.2 g of DBTDL and the prepolymer (C) obtained in Example 1 are mixed by a
low pressure casting machine ~AF-206 Type of Toho Machinery Co. Ltd.; Foaming
machine for urethane foam in which a gear pump of a maximum discharge amount
of 3 ~/min is used for both solutions and the solutions are mixed by a mixing
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rotor) are mixed with agitation at a blend ratio such that the NCO/OH equiva-
lent ratio is 1.05 to be cast into a mold to form a sheet of 2 mrn in thick-
ness maintained at 50C at a discharge amount of 2 kg/min. The period of
time from starting discharge from the mixing head to the time when the visco-
sity thereof reaches 1000 ps at 25C is one minute, and the cured product is
releasable in 5 minutes and has neither bubbles involved therein nor cracks.
The product shows the same values for physical properties as in the case of
the batch type agitation of Example 1 as shown in Table 1.
Example 3
A curing agent prepared by mixing one equivalent of PTMEG having
an average molecular weight of 1000, 2 equivalents of 1~4-butane-di~ol~ and
0.6 g of DBTDL and the prepolymer ~C) obtained in Example 1 is subjected to
casting under the conditions of an NCO/O~I equivalent ratio of 1.05 and a dis-
charge amount of 7.5 kg/min ~125 g/sec) by the use of a high pressure casting
machine ~NR-215 Type of Toho Machinery Co. Ltd.; where an axial piston pump
having a maximum discharge amount of 7.5 Q/min is used for both solutions).
The period of time from starting discharge from the mixing head to the time
when the viscosity thereof reachss lOOO ps is approximately 20 seconds, and
the cured product is releasable in one and one half minutes.
The cured product thus obtained is free from bubbles, voids and
cracks. The physical properties of the cured product are found to be not
greatly different from those achieved in Examplesl and 2 as shown in Table 1.
Comparative Example 1
One equivalent of PTMEG having an average molecular weight of 1500
and 7.1 equivalents of polyisocyanate mixtures prepared by blending MDI and
the liquid MDI in a ratio by weight of 7 to 3 are reacted at 80 C for 3 hours
to obtain a prepolymer ~E) having a free NCO of 14.8% and a viscosity of 2800
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cps at 25C.
The prepolymer (E) thus obtained and the curing agent (D) obtained
in Example 1 are subjected to a casting test at an NC0/OH equivalent ratio
of 1.05 in the same manner as in Example 1.
The period of time from starting to mix two solutions of (E) and
(D) to the time when the viscosity of the mixture reaches 1000 ps is three
and half minutes, and it takes 20 minutes for release.
Fine cracks were found in a part of the cured product. The physical
properties of the portion free from cracks are good as shown in Table 1, but
the cured product shows poor moldability characteristics such as a prolonged
time for release, development of cracks, and the like as described above.
Comparative Example 2
One equivalent of a glycol mixture prepared by blending PTMEG hav-
ing an average molecular weight of 1000 and DPG to make the average molecular
weight of the mixture 500 and 3.6 equivalents of polyisocyanate mixture pre-
pared by blending MDI and liquid MDI in a ratio by weight of 7 to 3 are
reacted at 80C for 3 hours to obtain a prepolymer (F) having a free NC0 of
14.8% and a viscosity of 7500 cps at 25C.
The prepolymer (F) and the curing agent (D) obtained in Example 1
are subjected to a casting test at an NCO/OH equivalent ratio of 1.05 in the
same manner as in Example 1.
The period of time from the moment at which mixing of two solutions
is started -to the time when the viscosity of the mixture reaches 1000 ps is
five and half minutes, and it takes 10 minutes for release.
Neither bubbles nor cracks are found in the cured product, but the
high viscosity of the prepolymer requires a prolonged mixing time. Resilience,
which is very important as a physical property of the elastomer, is greatly
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lowered.
That is, according to Comparative Example 2~ no lowering in mold-
ability characteristics such as development of cracks, and the like, took
place, but it exhibited difficulties in handling due to an increase in visco-
sity of the prepolymer, lowing in physical properties of the elastomer, and
the like.
Comparative Example 3
Hiprene L-100 (Trade mark of Mi~sui-Nisso Corporation for a pre-
polymer from PTMEG/TDI having an NCO of 4.2% and a viscosity of 18,000 cps
at 25C, and equal to Adiprene L-100) is subjected to thorough degassing at
80C, and then is thoroughly mixed with fused MOCA at 120C in such a manner
that bubbles are not involved therein, for one minute in a blend ratio of
100 to 12.5, that is, a~ an NCO/OH equivalen~ ratio of 1.07, and then is cast
into a mold in an oven maintained at 100C. One hour after casting, a cured
elastomer is released from the mold, and is subjected to post curing for
about 20 hours in an oven at 100C. The physical properties of the elastomer
obtained after post curing are shown in Table 1.
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Table 1
~-~ Example Comparative
\ ExamplesExamples
Physical ~
: Properties \ 1 2 3 1 2 3
_ ,
Hardness ~JIS-A type 88 88 87 88 89 90
durometer)
Modulus 100% ~kg/cm2) 75 78 74 73 83 77
300% 136 144 133134 200 148
Tensilestrength ~kg/cm2) 350 370400 380 410 350
Elongation at breakage (%) 520 500490 540 410 450
Tear strength ~kg/cm) 89 90 90 92 81 89
Resilience ~%) 58 56 55 59 36 55
Compression set ~%) 32 35 33 31 37 27
~10C, 22 hours) L L_____ L _ L l I
, ;
