Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
.
This invention pertains, in general, to improved poly-
urethane elastomer compositions which are used in contact with
phosphate-ester-based hydraulic fluids.
DESCRIPTION OF THE PRIOR ART
. .
The term "polyurethane elastomers" is generally applied
to elastomeric or rubberlike polymers which contain significant
numbers of urethane groups, which have the characteristic
structure O
11
N - C - O -,
whether the urethane group repeats regularly throughout the
macromolecule or not. Such elastomers are ordinarily prepared
by the reaction of a polyisocyanate compound with compounds hav-
ing two or more "active hydrogens". Such active-hydrogen com-
pounds include polyhydroxy compounds, generally termed polyols,
and compounds containing amino groups or carboxyl groups. The
active hydrogen compound can contain functional groups in addi-
tion to groups which supply replaceable hydrogens. Thus
hydroxyl-terminated polyethers and polyesters have been used to
react with polyisocyanates to prepare polyurethanes, as have poly-
caprolactone polyols, which contain both ester and ether groups
in addition to hydroxyl groups. A detailed discussion of prior-
art polyurethane compositions may be found in Kirk-Othmer,
Encyclopedia of Chemical Technology, 2nd ed., (Interscience, 1970),
Vol. 21, pp. 56-106.
Generally in commercial practices a "prepolymer" tech-
nique is utilized to prepare polyurethane elastomers, in which
a diisocyanate is reacted with a polyol, usually a hydroxyl-
terminated polyester or polyether, to form an isocyanate-
terminated prepolymer. The polyols used in forming the poly-
.~, , ~
/~,1 ~
1 78~3
urethane elastomers generally have molecular weights in therange of about 1,000 to about 3,000. The diisocyanates em-
ployed are ordinarily aromatic compounds, because their bulky
molecular structure contributes rigidity and tensile strength
to the polymer. Two aromatic diisocyanates commonly used in
the preparation of polyurethane elastomers are 4,4'-diphenyl-
methane diisocyanate, designated MDI, and 3,3'-dimethyl-4,4'-
diphenyl diisocyanate, designated TODI. A partial listing of
other aromatic diisocyanates particularly useful in the pre-
paration of polyurethane elastomers is set forth in Table 16,page 77 of Kirk-Othmer, cited above. During the prepolymer
formation step the molecular weight of the material is in-
creased to the range of 25,000 to 50,000.
This prepolymer is then further reacted with a second
active-hydrogen compound, ordinarily of lower molecular weight
than the polyol used to prepare the prepolymer. This second
step is referred to as a "chain extension" reaction, and the
second active-hydrogen reactant is termed a "chain extender".
Gylcol (1,2 ethanediol); 1,4 butanediol; diamines; and tri-
hydroxy compounds have been used as chain extenders. The chainextension reaction causes the segments of prepolymer to join
together to produce a very high molecular weight linear material.
Chain extension normally does not provide any cross-linking.
However, if a trihydroxy compound such as trimethyolpropane is
used for chain extension, branching of the polymer will occur.
The above steps are usually carried out at elevated temp-
eratures in the vicinity of about 100C and may or may not be
catalyzed.
Up to this point the polyurethane polymer exists mainly
as a very high molecular weight polymeric material. In order
to provide the final physical properties associated with a
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thermoset elastomeric material, the polymer must be cross-
linked. This is accomplished by joining the long polymer chains
together through the reaction of free (unreacted) diisocyanate
groups on one macromolecule with urethane and/or substituted
urea groups on another macromolecule to form allophanate and/or
biuret cross-links respectively.
In addition to the prepolymer method discussed above for
preparing polyurethane elastomers, a "one-shot" technique is
also sometimes used. l'he one-shot method involves mixing active-
hydrogen compounds of different molecular weights and reactingthe resultant mixture with a polyisocyanate.
Within the polyurethane elastomer family, it is possible
to obtain a wide range of values for the physical and chemical
properties of the elastomer by appropriate selection of the
specific raw materials, their formulation, or their relative
amount within the formulation, as is well known in the art.
Conventional polyurethane elastomers have advantages
not possessed by other elastomeric materials; namely: 1)
excellent abrasion resistance; 2) higher tear strength; 3) high
tensile modulus; 4) high tensile strength at break; 5) outstand-
ing toughness; 6) excellent resistance to oxygen and ozone;
and 7) excellent resistance to mineral oil.
Because of their overall good abrasion resistance, high
coeffecient of friction, low noise level, and particularly their
excellent resistance to mineral oils, polyurethane elastomers
have found wide use as gaskets, wiper rings, valve seats, and
other such seals in hydraulic systems which employ mineral-oil
hydraulic fluids.
Seals for hydraulic systems made of conventional poly-
urethane elastomers, however, suffer a serious limitation whichhas become increasingly important in recent years. Because of
the fire hazard which attends the use of mineral-oil hydraulic
;3
fluids, users and manufacturers of hydraulic systems often
employ phosphate-ester hydraulic fluids in place of mineral oils.
Phosphate esters,however, attack conventional polyurethane
elastomeric materials, causing them to swell and lose strength.
A conventional polyurethane-elastomer seal in contact with a
phosphate-ester hydraulic fluid will weaken and have a substan-
tially shortened useful life compared to the same seal in con-
tact with a mineral-oil hydraulic fluid. In high-pressure
hydraulic systems employing phosphate-ester hydraulic fluids,
there is a significant risk that a seal made of a conventional
polyurethane elastomer will fail catastrophically.
Other elastomeric materials, such as certain highly
fluoronated polymers, are available which can withstand attack
by fluids containing phosphate esters, but generally these mat-
erials are significantly more expensive than conventional poly-
urethane elastomers and, moreover, have a lower abrasion resist-
ance.
I have invented an elastomeric polyurethane composition
which is highly resistant to fluids containing phosphate esters,
yet retains without significant impairment the advantages of
conventional polyurethane elastomers. This composition is
particularly adapted for use in fabricating elastomeric seals
which avoid the problems associated with conventional polyure-
thane elastomeric seals in contact with phosphate-ester hydraulic
fluids.
SUMMARY OF THE INVENTION
-
This invention relates to an improved elastomeric poly-
urethane composition which is resistant to fluids containing
phosphate esters, such as phosphate-ester hydraulic fluids. The
composition includes the reaction product of 3,3'-dimethyl-4,4'-
diphenyl diisocyanate (TODI), one or more polycaprolactone polyols,
and a chain extender which includes a linear aliphatic compound
! -4-
11~78~3
defining a chain of carbon atoms, each end of the chain being
attached to a hydroxyl group, and the chain having an unsatur-
ated carbon-carbon bond.
A preferred chain extender of the present invention,
particularly for applications in which the elastomeric poly-
urethane composition will not contact mineral oils, is 1,4-
dihydroxy-2,3-dibromo-2-butene. A second chain extender,
preferred for applicat:ions in which resistance to both mineral
oils and phosphate esters is required, is a mixture of 1,4-
butanediol and 1,4-dihydroxy-2,3-dibromo-2-butene. For
example, a mixture of about 12 percent by weight 1,4-butanediol
and about 88 percent by weight 1,4-dihydroxy-2,3-dibromo-2-
butene used as a chain extender in the present invention lead
to an elastomeric polyurethane composition with excellent re-
sistance to both mineral-oil and phosphate-ester hydraulic
fluids.
The present invention further relates to an elastomeric
seal which is resistant to fluids containing phosphate esters.
The seal is made of an elastomeric polyurethane composition of
the present invention. Seals of the present invention may be
incorporated to advantage in hydraulic machines to seal reser-
voirs, lines, and other containers of hydraulic fluids contain-
ing phosphate esters.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Elastomeric polyurethane compositions of the present
invention can be synthesized by substantially the same techniques
as conventional polyurethane elastomers. The two-step prepolymer
method is ordinarily preferred for preparing the composition, al-
though it is contemplated that for some applications it may be
advantageous to premix the polycaprolactone polyol with the chain
extender before reacting the mixture with the diisocyanate in a
one-shot process. Other sequences of reaction steps may also be
X
i~7~3
used to prepare the composition.
One ingredient used to synthesize elastomeric poly-
urethane compositions of the present invention is 3,3'-di-
methyl-4,4'-diphenyl diisocyanate (TODI), which is commercially
available.
Polycaprolactone polyols are generally made by reacting
an~ -caprolactone with an initiator such as diethylene glycol
(2,2'-oxydiethanol). Polycaprolactone polyols of various mole-
cular weight distributions are commercially available. Pre-
ferred polycaprolactone polyols for the present invention havemolecular weights in the range of from 1,000 to 3,000.
Preferred chain extenders for the present invention
include one or more of the following compounds: 1,4-dihydroxy-
2-butene; 1,4-dihydroxy-2-butyne; and 1,4-dihydroxy-2,3-dibromo-
2-butene. Any of these compounds can be used alone or mixed
with a conventional chain extender. Significantly, each of
these three preferred chain extenders is a hydroxyl-terminated
linear aliphatic compound which includes a double bond or a
triple bond between two carbon atoms in the chain. The ratio
of the effective equivalent weight of such hydroxyl-terminated,
unsaturated compound or mixture of such compounds to the equiv-
alent weight of the diisocyanate TODI preferably lies in the
range of from about 0.3 to about 0.9.
As will be recognized by those skilled in this art, the
elastomeric polyurethane composition of the present invention
can include stabilizers, plasticizers, pigments, fillers, ex-
tenders, and the like in addition to the reaction product of
the ingredients set forth above.
The elastomeric polyurethane compositions can be cast
and formed by conventional methods. Thus elastomeric seals of
the present invention such as gaskets, wiper rings, and valve
seats are preferably manufactured by the same techniques as are
7~3~3
used to fabricate seals from conventional polyurethane elasto-
mers.
EXAMPLES
EXAMPLE 1
Two samples of elastomeric polyurethane compositions
were prepared: a control sample of a conventional polyurethane
elastomer, designated A, and a test sample of a elastomeric
polyurethane composition of the present invention, designated B.
Table I lists the ingredients and proportions (in parts
by weight) used.
Table I
Ingredient Proportion (parts by weight)
Sample ASample B
"Niax Diol D-560" 100 100
TODI 48 48
1,4-butanediol 10.26 --
1,4-dihydroxy-2,3-
dibromo-2-butene -- 27.8
"Niax Diol D-560" is the trade name of a polycaprolactone poly-
ol having a mean molecular weight of about 2000 sold by Union
Carbide Corporation. TODI designates 3,3'-dimethyl-4,4'-di-
phenyl diisocyanate.
Sample B, the test sample, was prepared according to the
following procedure. The polycaprolactone polyol was dehydrated
by melting and heating it with stirring under a vacuum of about
10-20 Torr. After dehydration, the polycaprolactone polyol was
heated to 148C, the diisocyanate TODI was added, and the re-
sultant mixture was stirred for 15 minutes under a vacuum to
form a prepolymer. The temperature of the prepolymer was then
adjusted to 120C and the chain extender 1,4-dihydroxy-2,3-
dibromo-2-butene was stirred in. Standard test specimens were
formed by casting this mixture in a steel mold heated to 125C.
After the specimens solidified, they were cured for 48 hours
in an oven maintained at 100C.
Test specimens of the control sample A were prepared by
the same procedure, except that the chain extender 1,4-butane-
diol was substituted for 1,4-dihydroxy-2,3-dibromo-2-butene.
To compare the physical properties of these two samples,
a series of standard tests were run which are commonly used in
the polyurethane industry to characterize polyurethane elasto-
mers. The results of the tests are set forth in Table II below.
Table II
Test Units or Results
Symbol
Sample A Sample B
Hardness (Shore A) points 93/40 96/45
Tensile Strength psi 4322 2075
Elongation percent 463 381
Elongation Set percent 22 80
25% Modulus psi 1103 1283
50~ Modulus psi 1225 1351
100% Modulus psi 1402 1496
200% Modulus psi 1802 1736
300% Modulus psi 2418 1938
Tear Strength
(C, Nicked) PLI 389 338
Tear Strength
(Die C) PLI 693 525
Resilience percent 31 35
The tensile, elongation, and modulus measurements were carried
out on a ring specimen 52.6mm OD x 44.6mm ID x 3.2mm thick.
The samples were tested using an x head speed of 20 in./min.
Tear measurements were made according to the procedures of ASTM
test D-624.
To compare the compatibility of the two samples to
phosphate esters, specimens of each were submerged for 168 hours
at about 70C in a typical phosphate-ester hydraulic fluid,
"Pydraul 50-E" sold by Monsanto Company. Table III lists the
changes in three significant physical properties after sub-
mergence in the phosphate ester hydraulic fluid.
Table III
Test Units or Results
Symbol
Sample A Sample B
Increase in Volume percent +16 +8.4
10Decrease in Hardness
(Shore A) points -4 -2
Loss in Tear
Strength (Die C) percent -30 0
The compatibility tests were performed using Die C tear speci-
mens as described in ASTM test D-624 and the procedure specif-
ied in ASTM test D-471.
As demonstrated by Table III above, the control sample A
exhibited a greater degree of swelling, more reduction of hard-
ness, and a greater loss of tear strength then test Sample B
after extended exposure to a phosphate ester hydraulic fluid. t
In fact, the sample of elastomeric polyurethane composition of
the present invention exhibited no loss of tear strength after
contact with the fluid. Thus the elastomeric polyurethane com-
position of Sample B is proven to be more resistant to phosphate-
ester hydraulic fluids than the conventional polyurethane
elastomer of Sample A.
EXAMPLE 2
Five batches of polyurethane elastomer were prepared
according to the procedure set forth in Example 1, except that
the relative proportions of 1,4-butanediol and 1,4-dihydroxy-
2,3-dibromo-2-butene in the chain extender were varied between
0 and 100 mole percent in 25 mole percent increments. The
reaction ingredients and proportions in parts by weight are set
forth in Table IV below.
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Table IV
Ingredient Proportion (parts by weight)
Sample _ D _ _ G
"Niax Diol D-560" 100 100 100 100 100
TODI 48 48 48 48 48
1,4-butanediol 10.2 7.6 5.05 2.5 0
1,4-dihydroxy-2,3-dibromo-
2-butene 0 6.9 13.8 20.8 27.6
"Staboxol I" 0 0 0 0
"Staboxol I" is an additive for polyurethane sold by Farben-
fabriken Bayer A. G. and identified as a carbodumide.
The physical characteristics of these five samples are
set forth in Table V below. The test procedures were the
same as those set forth in Example 1. Sample C, whose chain
extender is pure 1,4-butanediol, was the control sample.
Table V
Units or
Test Symbol Results
Sample _ _ E
Hardness (Shore A) points 89 87 89 93 95
Tensile Strength psi3137 3216 49833870 3621
Elongation percent 367319 368 353402
Elongation Setpercent 13 6 9 15 43
25% Modulus psi 829748 814 9771261
50% Modulus psi 937814 917 10671305
100% Modulus psi 1142986 1140 12891439
200% Modulus psi 150714941679 17781800
300% Modulus psi 219628032798 28342475
Tear Strength
(C, Nicked)PLI 324185 203 277374
Tear Strength
(Die C) PLI 568462 519 548617
Resilience percent 30 35 36 37 30
Spec. Gravity -- 1.17 1.19 1.22 1.24 1.26
--10--
. ~
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The compatibility of these samples with the phosphate-ester
hydraulic fluid "Pydraul 50-E" was tested by immersing specimens
formed from the samples in the fluid for 168 hours at 70C.
The changes induced by this treatment are set forth in Table VI.
Table VI
-
Units or
Test _ymbol Result
Sample _ _ E F G
Increase in Volume percent +21 +21 +21 +17 +11
10Decrease in Hardness
(Shore A) points -4 -3 -4 -3 -2
Loss of Tear Strength
(Die C) percent -35 -31-25 -27 -14
As can be seen from Table VI above, any 1,4-dihydroxy-
2,3-dibromo-2-butene in the chain extender is beneficial, and
substantial resistance to deterioration caused by contact with
phosphate-ester containing fluid is obtained when the two-
component chain extender of this example contains greater than
25 mole percent 1,4-dihydroxy-2,3-dibromo-2-butene.
EX~MPLE 3
The following elastomeric polyurethane composition,
Sample H, was prepared generally according to the procedure set
forth in Example 1:
"Niax Diol D-560" 100 parts by weight
(28 parts by equivalent weight)
TODI 48 parts by weight
(100 parts by equivalent weight)
1,4-dihydroxy-2,3- 20.59 parts by weight
dibromo-2-butene (47 parts by equivalent weight)
1,4-butanediol 2.69 parts by weight
(17 parts by equivalent weight)
"Staboxol I" 1 part by weight.
Specimens of this composition were immersed for 168
hours in four different hydraulic fluids, two mineral-oil based
and two phosphate-ester based. The temperatures at which the
hydraulic fluids were maintained during the exposure of the
specimens to the fluids and the changes in volume, hardness, and
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tear strength induced by the exposure are set forth in Table VII.
Table VII
Temperature Increase Decrease Loss in
Hydraulic in Volume in Hardness Tear Strength
Fluid (C) (percent) (points) (percent)
"Pydraul 5OE" 70 32 -3 -4
"Pydraul 5OE" 100 35 -4 0
"Monsanto 230" 70 26 -2 0
"Monsanto 230" 100 28 -3 0
ASTM Oil #170 0 +1 0
ASTM Oil #1100 7 -1 0
ASTM Oil #370 6 +1 0
ASTM Oil #3100 0 0 0
"Monsanto 230" is the trade name of a phosphate-ester hydraulic
fluid sold by Monsanto Company. ASTM Oils #1 and 3 are standard
mineral oils. The test procedures were the same as were carried
out in connection with Tables III and VI above.
Table VII demonstrates that the elastomeric polyurethane
composition of Sample H is resistent to both mineral-oil hydraul-
ic fluids and phosphate-ester hydraulic fluids. Note that the
hardness of the composition actually increases upon exposure to
the mineral oils at 70C.
Similar tests were carried out on the following elasto-
meric polyurethane composition, Sample I:
"Niax Diol D-560" 100 parts by weight
(28 parts by equivalent weight)
TODI 48 parts by weight
(100 parts by equivalent weight)
1,4-dihydroxy-2,3- 25.87 parts by weight
dibromo-2-butene (58 parts by equivalent weight).
This composition exhibited superior resistance to phosphate
esters compared to Sample H, but significantly lower resistance
to mineral oils.
--12--
!~
11~7~3~3
EXAMPLE 4
Four batches of elastomeric polyurethane composition
were prepared generally according to the procedure of Example
1, except that 1,4-dihydroxy-2-butene and 1,4-dihydroxy-2-
butyne were used as chain extenders in addition to the two
chain extenders of Example 1. The reaction ingredients and
proportions in parts by weight are set forth in Table VIII
below. Equimolar amounts of chain extender were employed in
the four samples.
Table VIII
Ingredient Proportion (parts by weight)
Sample J K L M
"Niax Diol D-560" 100 100 100100
TODI 48 48 48 48
1,4-butanediol 10.00 -- -- --
1,4-dihydroxy-2-butene -- 9.69 -- --
1,4-dihydroxy-2-butyne -- -- 9.47 --
1,4-dihydroxy-2,3-
dibromo-2-butene -- -- -- 25.87
Physical characteristics of these samples are set
forth in Table IX below. The test procedures were the same
as those set forth in Example 1. Sample J was a control sample.
Table IX
Units or
Test Symbol Results
Sample J K _ M
Hardness (Shore A)points 93 91 87 95
Tensile Strength psi 3137 3026 2842 3549
Elongation percent 367 421 333 431
Elongation Set percent 13 12 10 55
300% Modulus psi2196 1928 2460 2545
Tear Strength
(Die C) PLI 568 463 440 717
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!
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The compatibility of these four samples with the
phosphate-ester hydraulic fluid "Pydraul 50-E" was tested by
immersing specimens formed from the samples in the fluid for
168 hours at three different temperatures. The changes induced
by this treatment are set forth in Table X.
Table X
.
Units or Tempera-
Test Symbol ture (C) Results
_
Sample _ K L M_
Increase in Volumepercent 20 9 4 3 4
36 18 17 14
100 47 37 37 24
Decrease in Hardnesspoints 20 -2 -1 -1 0
(Shore A)
-7 -4 -2 -3
100 -9 ~5 ~3 ~4
Loss of Tear Strengthpercent 20 -11 0 -4 -6
(Die C)
-44 -14 -13 -18
100 -59 -25 0 -17
As may be seen in Table X, Samples K, L, and M all
exhibit substantially improved resistance to attack by phosphate-
ester hydraulic fluids compared to the control Sample J.
It is not intended to limit the present invention to
the specific embodiments described above. For example, the
composition of the present invention can be made in a one-shot
process, and the polymerization reactions can be catalyzed with
conventional catalysts such as tertiary amines or metallic
catalysts. It is recognized that these and other changes may be
made in the compositions and processes specifically described
herein without departing from the scope and teachings of the
instant invention, and it is intended to encompass all other
embodiments, alternatives and modifications consistent with
the present invention.
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