Note: Descriptions are shown in the official language in which they were submitted.
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MOLDED POLYURETHANE FOAM WITH
ENHANCED PHYSICAL PROPERTIES
Technical Field
The present invention pertains to molded,
flexible polyurethane foam prepared by the prepolymer
process. More particularly, the present invention
pertains to molded polyurethane flexible foams prepared
from isocyanate-terminated prepolymers derived from the
reaction of an excess of di- or polyisocyanate with a
polyol or polyol component having an unsaturation of
less than 0.03 milliequivalents of unsaturation/per gram
of polyol (meq/g). The molded foams display enhanced
physical properties in addition to displaying excellent
processing latitude. The foams are preferably all-water
blown.
Background Art
High resiliency (HR) polyurethane slab foam is
now a high volume commercial product. HR slab foam is
generally all-water blown and may be made by either
prepolymer or one-shot technology. However, slab foam,
while eminently suitablefor applications such as carpet
underlay and flat cushioning material for.furniture, is
unsuitable for applications which require contoured
parts, for example automotive seating. For such appli-
cations, molded polyurethane foam is generally used. In
molded foam, the foam forming ingredients are mixed and
injected into a closed mold, which may be heated to 150-
~ 300 C (hot molding) or 30-70 C (cold molding). The
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admixture of multiple streams into the mix head is
termed a "one-shot" process.
Because molded foam cannot rise unrestrained,
as is the case with slab foam, the respective formula-
tions are quite different. Even with different formula-
tions, processing of molded foam is considerably more
difficult than processing of slab foam, and often gives
rise to a high scrap rate. A further difference between
molded foam and slab foam is that the former must be
crushed mechanically prior to complete cure, either by
hand or by the use of rollers or similar devices.
Alternatively, the foam may be "crushed" in situ through
the use of timed pressure release (TPR) as disclosed in
U.S. Patent No. 4,579,700; by timed partial pressure
release (TPPR); or by a combination of TPR and reduced
mechanical crushing as disclosed in U.S. Patent No.
4,717,518. The foregoing TPR patents are licensed
worldwide.
Prepolymer technology has certain advantages
over one-shot technology. Foams produced by prepolymer
technology are subject to less processing related
variation due to the use of fewer reactive chemical
streams as opposed to one-shot foams. The polymer
structure is also more controllable in prepolymer foams.
Moreover, the use of prepolymer techniques allows the
foam manufacturer to inventory fewer components.
Although much earlywork in polyurethane foam technology
centered on prepolymer techniques, today most flexible
foam is produced by one-shot technology. With respect
to molded foams, virtually all systems are one-shot.
The reasons why prepolymer technology is not in wide-
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spread use in molded foam have to do with the nature of
the molding process as opposed to the slab process.
For example, in the well known treatise on
pCly,urethanes: "P(1T,VTTRF.THA7~TES: C_'HF.MT~TRY ANI~ TECHNnL(~-
GY", J.H. Sanders and K.C. Frisch, Interscience Publish-
ers, N.Y., p.99, the authors indicate that even one-shot
technology was difficult with molded foam, and that
completely satisfactory prepolymer systems were never
fully achieved. Not only is the scrap rate cited as
being high, particularly with regard to surface defects,
but cure cycles are inordinately long in molded foams
prepared from prepolymers. One-shot technology has
reduced material usage due to decreased scrap rates,
reduced labor costs, and eliminated lengthy curing
cycles.
R.E. Knox, in "Molding of Prepolymer Based
Resilient Urethane Foam", RusBER WORLD, February 1959, pp.
685-692, has documented some of the defects, particular-
ly surface defects, associated with prepolymer molded
foam. Cited as assisting elimination of surface defects
is the use of brushing or spray-coatingthe mold surface
with surface active agents. However, this process
involves additional steps which increase manufacturing
costs.
-- - Attempts to overcome the problems associated
with molded polyurethane foams via prepolymers have
generally focused on adjusting such variables as type of
catalyst, catalyst levels, catalyst combinations, type
and amount of cross-linker, isomer content of the
isocyanate component, polyether polyol blends, and the
like. However, while isolated, successful systems have
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been sometimes prepared, these systems still suffer in
terms of processing latitude as well as lacking the
flexibility to readily accommodate desired changes in
such physical properties such as density, foam softness,
and the like. Fundamental changes in the nature of the
prepolymer ingredients have not been.proposed.
An example of the types of formulation adjust-
ments referred to above is disclosed in U.S. Patent No.
5,070,114, wherein water-blown, molded polyurethane
foams are prepared from isocyanate-terminated prepoly-
mers derived from methylenediphenylenediisocyanate (MDI)
blends containing minimally 2 weight percent of 2,4'-MDI
isomers. However, no molded foams are exemplified, only
free rise foams having been produced.
In "Production of Soft Block Foams and TDI-
Based Cold Cure-Molded Foams With No Use of CFCs", 32ND
ANNULAR POLYURETHANE TECHNICAL MARKETING CONFERENCE, October 1-4,
1989, G.F. Lunardon et al., hypersoft molded foams are
prepared from toluene diisocyanate-based prepolymers and
a special polyether polyol having a high ethylene oxide
content, supplied as a separate stream. Polyether
polyols with high terminal oxyethylene content are
commonly utilized in one-shot molded foams due to the
higher reactivity associated with_high primary hydroxyl
content, generally above 70 mol percent. However,
appreciable amounts of such high ethylene oxide content
polyols may undesirably affect numerous physical proper-
ties in humid environments. The resulting foams had
relatively low resiliency and high compression set.
Polyoxyalkylene polyether polyols utilized in
polyurethane foam production are conventionally manufac-
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tured by the base-catalyzed oxyalkylation of a two to
eight-functional initiator molecule, generally using
propylene oxide or mixtures of propylene oxide and
ethylene oxide as the alkylene oxide. For one-shot
molded polyurethane foams where high primary hydroxyl
content is required, i.e., higher than 70 mol percent,
the polyols are capped with polyoxyethylene moieties by
employing solely ethylene oxide during the last stages
of oxyalkylation. Use of such polyols often leads to
problems in humid environments where_absorption of water
plasticizes the polyurethane.
During preparation of polyoxypropylene poly-
ether polyols by base catalysis, a competing rearrange-
ment of propylene oxide to allyl alcohol introduces
unsaturated monols into the reaction mixture which
themselves serve as mono-functional initiator molecules.
The result is a gradual dilution of functionality and
continued production of polyoxyalkylene monol of lower
molecular weight. As a result, base-catalyzed polyol
equivalent weight is limited to about 2000 Daltons (Da).
Even at this modest equivalent weight, the functionality
of a polyoxypropylene diol may be reduced from its
nominal, or theoretical, functionality of 2 to the range
of 1.5 - 1.7 or less. The product may contain as much
as 40-45 or more mol percent monol, the monol fraction
having a broad molecular weight distribution as well.
In the decade of the 60's, double metal
cyanide complex catalysts (DMC catalysts) were developed
= for alkylene oxide polymerization. However, due to
their greatly increased cost as compared to simple basic
catalysts, and limited polymerization rate, such cata-
lysts had not been widely used, despite their ability to
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produce polyoxyalkylene polyols with low unsaturation and low monol
content. Non-stoichiometric metal cyanide complex catalysts, as
disclosed, for example, in U.S. Patent Nos. 5,100,997, 4,477,589,
5,158,922, and 5,248,833 have exhibited increased polymerization rates
as compared to the first generation DMC catalysts and have lowered
unsaturation to the range of 0.015 - 0.018 meq/g in polyols in the c.a.
2000 Da equivalent weight range. However, the amount of catalyst
required is still relatively high in view of the catalyst cost. Most recently,
however, the assignee of the present invention has developed highly
efficient double metal cyanide complex catalysts which not only may be
used in much smaller amounts than previously possible, but moreover
provide polyoxyalkylene polyols with exceptionally low unsaturation, i.e.,
in the range of 0.002 to 0.007 meq/g. The measured functionality of such
polyols closely approaches the nominal initiator functionality. Moreover,
the polyols display a very narrow molecular weight distribution, as
reflected by polydispersities (MdMn)) generally less than c.a. 1.2. Suitable
methods of preparation are disclosed in U.S. Patent Nos. 5,470,813 and
5,482,908.
Double metal cyanide catalysis has certain drawbacks with respect
to polyoxyethylene capped polyols, however. It has been discovered that
terminating DMC-catalyzed alkylene oxide polymerization with ethylene
oxide, rather than resulting in high primary hydroxyl, oxyethylene capped
polyols, results in complex products believed to contain considerable
quantities of homopolyoxyethylene. Thus, preparation of ethylene
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oxide capped polyethers employing double metal cyanide
catalysts has required denaturing the double metal
cyanide catalyst with base such as potassium hydroxide
and continuing addition of ethylene oxide in a tradi-
tional base-catalyzed oxyalkylation. This adds signifi-
cant cost and complexity to the polyol preparation
process.
Although numerous benefits have been ascribed
to the use of DMC-catalyzed polyoxyalkylene polyols,
such polyols are not drop-in replacements for conven-
tionally catalyzed polyols, for reasons not completely
understood, but at least in major part due to the
differences in monol content, actual functionality, and
molecular weight distribution which lead to different
polymer microstructure.
For example, as shown by R.E_ Bolin et al.,
"Properties of Urethane Foams Related to Molecular
Structure", J. CHEM. AND ENG. DATA, v.4, No. 3, July 1959,
pp. 261-265, use of higher molecular weight polyols
increases the molecular weight between branch points in
the cross-linked polyurethane structure, and as a
result, increases tensile elongation while decreasing
tensile strength. At the same time, compression
strength decreases as well, resulting in softer, more
extensible foams. Thus, use of higher equivalent weight
polyols, made possible through DMC-catalyzed oxyalkyla-
tion, should result in a softer, more extensible foam.
However, R.L. Mascioli, "Urethane Applications for Novel
High Molecular Weight Polyols", 32ND ANNUAL POLYURETHANE
TECHNICAL/MARKETING CONFERENCE, OCt. 1-4, 1989, pp. 139-142,
indicates that substitution of a double metal cyanide
complex-catalyzed, low unsaturation_ 10,000 Da triol in
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a typical flexible foam formulation, rather than produce
a softer, more- extensible foam, produced a stiff and
boardy product. J.W. Reisch et_al. in "Polyurethane
Sealants and Cast Elastomers With Superior Physical
Properties", 33RD ANNUAL POLYURETHANE TECHNICAL MARKETING
CONFERENCE, Sept. 30 - Oct. 3, 1990, on page 368, indi-
cates that substitution of a low unsaturation polyether
polyol for a conventional, base-catalyzed polyol of
higher unsaturation led to increased hardness in elasto-
mers prepared from such polyols. While not directed to
the present field of endeavor, the increased hardness of
the elastomers mitigates against use of such polyols in
polyurethane foams, where decreased hardness is general-
ly the goal. Moreover, as the inventors of the present
invention disclose below, in a one-shot molded polyure-
thane foam formulation, substitution for a conventional-
ly catalyzed triol having a measured functionality of
2.2 by a DMC-catalyzed diol/triol blend having similar
(2.3) functionality led to total foam collapse.
It would be desirable to provide to the
polyurethane foam industry, a prepolymer composition
suitable.for preparing molded polyurethane foams with
acceptable processing time and latitude. It would be
further desirable to provide foam formulations which
result in enhanced physical properties of the molded
foam product. It would be yet further desirable to
offer prepolymer foam formulations which allow for
taking advantages of the unique properties of double
metal cyanide-catalyzed polyoxyalkylene polyols, without
requiring high primary hydroxyl content. =
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Summary Of The Invention
it has now been surprisingly discovered that
prepolymer-based molded polyurethane foams may be
prepared from isocyanate-terminated prepolymers based on
low-unsaturation polyoxyalkylene polyols. Moreover, it
has been further surprisingly discovered, that not only
do these prepolymers offer wide processing latitude and
short cure cycles, but moreover, the molded polyurethane
foams thusly prepared exhibit superior physical proper-
ties in virtually all categories, including vastly
improved 50% wet compression set (wet set). Seldom is
it possible to increase nearly all foam physical proper-
ties without a trade-off in terms of other properties.
Description of the Preferred Embodiments
The prepolymer foams of the subject invention
are prepared by introducing the prepolymer formulations
of the subject invention together with water and option-
ally auxiliary blowing agents and additives into a
closed mold, allowing the reactive ingredients to foam,
and recovering a molded, foamed polyurethane product.
The isocyanate index of the reactive ingredients is
advantageously between 70 and 130, preferably between 90
and 110, and most preferably c.a. 100. By the term
"closed mold" is meant a mold which prevents unrestrain-
ed rise of foam. Such molds may be clamped in a closed
condition following which__the polyurethane reactive
ingredients are injected into the mold cavity, or may be
open molds into which the reactive ingredients are
poured or metered, the mold being subsequently closed.
Most such molds contain one or more vents which may be
monitored to ascertain progress of the reaction. Such
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molds are closed molds as viewed by one skilled in the
art.
The prepolymers of the subject invention are
prepared by conventional prepolymer techniques employing
an excess of di- or polyisocyanate or mixture thereof,
but employing as the polyol component, a polyol compo-
nent having a measured unsaturation of less than 0.03
meq/g, preferably less than 0.02 meq/g, and most prefer-
ably, less than 0.01 meq/g as measured by ASTM D-2849-
69, "Testing of Urethane Foam--Polyol Raw Materials".
The polyol component used to prepare the prepolymers may
comprise polyoxyalkylene polyether polyols in their
entirety, mixtures of polyoxyalkylene polyether polyols
with polymer-modified polyoxyalkylene polyether polyols
as hereinafter described, or minor quantities of other,
hydroxyl-functional polyols such as polyester diols,
amino-terminated polyoxyalkylene polyether polyols, and
other isocyanate-reactive polyols.
By polyoxyalkylene polyether polyol is meant
a polyol derived from the additional polymerization of
a vicinal alkylene oxide. Polyols prepared entirely
from non-vicinal cyclic oxides such as oxetane and
tetrahydrofuran are not polyoxyalkylene polyether
polyols as that term is defined herein, although such
polyols may be_ included inthe polyol component. The
"measured unsaturation" of the polyol component is the
measured value, or weight average of measured values of
the polyoxyalkylene polyether polyol portion of the
polyol component only.
The polyoxyalkylene polyether polyols of the
prepolymer polyol component are preferably prepared by
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the double metal cyanide complex-catalyzed oxyalkylation
of a suitable initiator molecule or mixture thereof.
Non-limiting examples of suitable initiator molecules
are di- to octa-functional initiators such as water,
ethylene glycol, propylene glycol, diethylene glycol,
dipropylene glycol, hydroquinone, bisphenol A, neo-
pentylglycol, cyclohexanediol, cyclohexanedimethanol,
2,2,4-trimethyl-1,5-pentanediol, glycerine, trimethylol-
propane, pentaerythritol, dipentaerythritol, a-methyl-
glucoside, sorbitol, mannitol, sucrose, methylol group-
containing phenol/formaldehyde condensates, and the
like.
Preferred nominal initiator functionality is
from 2-6, preferably 2-4, and most preferably 2-3.
Particularly when metal naphthenates or other low-
unsaturation producing catalysts are used, amino-group
containing initiators such as the various toluence
diamine isomers, ethylene diamine, propylene diamine,
tetrakis [2-hydroxyethyl- and 2-hydroxypropyl]ethylene
diamine, alkanol amines such as triethanol amine,
diethanol amine, and monoethanol amine, aniline, methyl-
enedianiline, diethylene triamine, and the like may be
used as well. Thus, while it is preferred to employ
DMC-catalysis to produce the polyoxyalkylene polyether
polyols, other catalysts capable of producing low-
unsaturation polyols may be used as well. Blends of
initiator molecules may also be used, as well as blends
of polyoxyalkylene polyether polyols individually
prepared from single or multiple initiators. The
preferred overall functionality of the polyol component
used to form the isocyanate-terminated prepolymers of
the subject invention ranges from about 2.3 to about 4,
more preferably about 2.5 to 3.5.
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Because low molecular weight initiators,
particularly those with vicinal hydroxyl groups, may
cause undesirably long induction periods and/or lower
rates of oxyalkylation when oxyalkylation is catalyzed
by DMC catalysts, polyoxyalkylene oligomers prepared
from the foregoing or other initiators may advantageous-
ly be employed rather than the monomeric, low molecular
weight initiators themselves. Thus, oligomeric polyoxy-
alkylene polyol initiators having equivalent weights of
from 100 to 1000 Da, preferably 100-600 Da are pre-
ferred. Such oligomeric polyoxyalkylene polyol initia-
tors may be prepared by conventional base catalyzed
oxyalkylation of the respective monomeric, low molecular
weight initiator, following which the basic catalyst
residues are removed or inactivated by neutralization,
treatment with an adsorbent such as magnesium silicate
followed by filtration, removal using ion exchange, etc.
Other methods of preparing the oligomeric polyoxyalkyl-
ene polyol initiators are suitable as well.
The oxyalkylation of the initiator molecules
is conducted with one or more higher alkylene oxides,
optionally in admixture with ethylene oxide. By "higher
alkylene oxide" is meant an alkylene oxide having 3 or
more carbon atoms, for example, propylene oxide, 1,2-
and 2,3-butylene oxide, C5-C18 a-olefin oxides, epi-
chlorohydrin, and the like. Preferred are propylene
oxide and butylene oxide, the former being most pre-
ferred. Use of mixtures of ethylene oxide and one or
more higher alkylene oxides leads to essentially random
copolymers. The ratio of higher alkylene oxide to
ethylene oxide may be changed during oxyalkylation to
produce multiple block polyols containing blocks of all
higher alkylene oxide-derived moieties and/or one or
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more blocks of higher alkylene oxide/ethylene oxide
moieties. Polymerization solely with ethylene oxide
should be avoided when employing_DMC catalysis.
The polyoxyalkylene polyols preferably contain
from 0 to 25 weight percent more preferably 5 to 25
weight percent, and most preferably 5 to 20 weight
percent oxyethylene moieties, present randomly or as a
cap. Random oxyethylene moieties, as explained previ-
ously, may be incorporated simply by adding ethylene
oxide along with higher alkylene oxide during oxyalkyl-
ation in the presence of a DMC-catalyst or other low-
unsaturation producing catalyst. To prepare polyoxy-
ethylene capped polyols, it is necessary to conduct
oxyethylation with other than DMC catalysts, preferably,
but not limited to, basic catalysts such as sodium or
potassium hydroxides or alkoxides.
When oxyethylene-capped polyoxyalkylene
polyols are desired, and the propylene oxide or mixed
propylene oxide/ethylene oxide polymerization has been
effected with DMC-catalysts, the DMC catalysts or
catalyst residues may be removed prior to introduction
of conventional oxyalkylation catalysts if desired, but
preferably, a basic catalyst is simply added without
resort to DMC catalyst removal. The basic catalyst
deactivates the DMC catalyst, permitting capping with
oxyethylene moieties to prepare polyoxyalkylene poly-
ether polyols having primary hydroxyl content ranging up
to 100 mol percent. Preferably, however, the primary
= hydroxyl content is from 0 mol percent to about 70 mol
percent, more preferably 0 mol percent to 50 mol per-
cent, and most preferably 0 to 30 mol percent. It is
most surprising that polyoxyalkylene polyether polyols =
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prepared by DMC--catalyzed polymerization of mixtures of
higher alkylene oxide and ethylene oxide, having no "cap"
and having primary hydroxyl content less than 50 mol
percent, advantageously less than 30 mol percerit, are
suitable for preparation of molded polyurethane foam,
allowing polyol preparation without a separate
oxyethylene capping step.
Regardless of their manner of preparation, the
polyoxyalkylene polyether polyols, whether capped or not,
have a weight average measured unsaturation of less than
0.03 meq/g polyol as measured by ASTM D-2849-69,
preferably less t.han 0.02 meq/g, more preferably less
than 0.01 meq/g. If the weight average unsaturation of
the polyoxyalkylene polyether polyol portion of the
polyol component, as herein defined, is not less than
0.03 meq/g, foams having the desired properties will not
be obtained. Preferably, each polyol has an unsaturation
of less than 0.01.5 meq/g. More preferably, each polyol
has an unsaturatiori of less than 0.010 meq/g.
Polyme-r--modified polyols, when employed in the
polyol component, are preferably prepared from the low-
unsaturation polyoxyalkylene polyols previously de-
scribed. Preferred polymer-modified polyols are prepared
by the in situ polymerization of one or more vinyl
monomers in the polyoxyalkylene polyol, variously termed
the "base" or "carrier" polyol. Preferred vinyl monomers
are acrylonitrile and. styrene, although other monomers
such as the various acrylates, methacrylates, and other
vinyl monomers may be used as well. Methods for the in
situ polymerization are well known to those skilled in
the art, for example as evidenced by U.S. Patent Nos.
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3,383,351, 3,953,393, and 4,119,586. The polyoxyalkylene
polyether base or carrier polyol is included when
measuring or calculating the average unsaturation of the
polyoxyalkylene polyether polyol portion of the polyol
component.
In addition to the aforementioned polyvinyl
polymer-containing polymer-modified polyols, polymer
polyols may also be prepared by the addition of finely
ground polymer particles or the in situ size-reduction of
larger particles to form stable dispersions. Dispersions
prepared by the reaction of isocyanates with various
amino-functional, hydroxyl-functional, or combined
amino/hydroxyl furictional monomers to form the so-called
PUD (polyurea di_spersion) polyols, PID (polyisocyanurate
dispersion) polyols, PIPA (reaction product of
isocyanates with alkanolamines), PHD polyols, and the
like, may also be used. All these polyols are well
described in the literature. PHD and PIPA polyols are
recognized commercial products.
The polyol component should have an average
equivalent weight of 800 Da to 5000 Da, preferably from
1000 Da to 5000 Da, more preferably 1.500 Da to 5000 Da,
and most preferably about 1500 Da to 3000 Da. Equivalent
weights and molecl.Elar weights expressed herein in Daltons
(Da) refer to number average weights unless otherwise
specified. The average hydroxyl number of the polyol
component may ranqe from 10 to 80, more preferably 10 to
56, and most preferably 15 to 35.
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The polyol component may comprise but a single
polyoxyalkylene polyol, a blend of polyoxyalkylene
polyols, a single polyoxyalkylene polymer-nlodified
polyol, or a blend of polyoxyalkylene polyols and
polymer-modified polyoxyalkylene polyols. Pref'erably,
polyoxyethylene capped polyoxypropylene/polyoxyethylene
polyols having primary hydroxyl contents in excess of 50
mol percent are used in not more than a minor amount in
the polyol component. The pol.yol
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component may further comprise hydroxyl functional
polyesters, amino-functional polyoxyalkylene polyols and
the like. The polyoxyalkylene polyols of the polyol
component, whether conventional (non-polymer-modified)
or polymer-modified polyols, are_all preferably prepared
with catalysts such that unsaturation is minimized.
However, polyoxyalkylene polyols or polymer-modified
polyoxyalkylene polyols prepared by base catalysis or
other methods of catalysis which result in higher levels
of unsaturation than 0.03 meq/g may be used, provided
that the total unsaturation of the polyoxyalkylene
polyether polyol portion of the polyol component is less
than the previously defined limits, i.e., less than 0.03
meq/g, most preferably less than 0.01 meq/g.
The isocyanate components useful in preparing
the isocyanate-terminated prepolymers of the subject
invention include the known aromatic and aliphatic di-
and polyisocyanates, for example 2,4- and 2,6-toluene-
diisocyanates and mixtures thereof (TDIs), 2,2'-, 2,4'-
and 4,4'-methylene diphenylene diisocyanates and mix-
tures thereof (MDIs), polymethylene polyphenylene poly-
isocyanates (PMDIs), 1,6-hexanediisocyanate, isophorone-
diisocyanate, and mixtures of such isocyanates. Other
isocyanates may be used as well. Also suitable are the
so-called modified isocyanates prepared by reacting a
di- or polyisocyanate with _ an isocyanate-reactive
monomer or oligomer or with themselves. Examples are
urethane-modified isocyanates prepared by reacting a di-
or polyisocyanate or mixture thereof with one or more
glycols, triols, oligomeric polyoxyalkylene diols or
polyols or mixtures thereof; urea modified isocyanates
prepared by reacting the isocyanate with a diamine or
amino-terminated polyoxyalkylation polyether oligomer;
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and carbodiimide, polyisocyanurate, uretonimine, allo-
phanate and uretdione modified polyisocyanates prepared
by reacting the isocyanate or modified isocyanate with
itself in the presence of a suitable catalyst. Such
isocyanates and modified isocyanates are well established
items of commerce.. Particularly, preferred di- and/or
polyisocyanates include TDIs, MDIs, PMDIs and mixtures of
these, particularly mixtures of TDIs and MDIs, the latter
preferably conta.in.ing a substantial majority of the 4,4'-
isomer.
The prepolymers of the subject invention are
prepared in the conventional manner by reacting the
polyol component with the i.socyanate component with or
without urethane promoting catalysts, as described, for
example, in the POLYURETHANE HANDBOOK, Gunter Oertel, Hanser
Publishers, Munic7-~ 1985, POLYURETHANES: CHEMISTRY AND
TECHNOLOGY, J.H. Saunders anci K.C. Frisch, INZ'ERSCIENCE
PUBLISHERS, New York, 1963, and in U.S. Patent No.
5,070,114. Cont.inuous and batch processes for the
preparation of isocyanate-terminated prepolymers are
disclosed in "Continuous Processing of Urethane Foam
Prepolymers", J.R. Wall, CHEMICAL ENGR. PROGRESS, V. 57, No.
10, pp. 48-51; Sariders, op.cit., Part II, pp. 38-43; U.S.
Patent No. 5,278,274; European published application EP 0
480 588 A2; and Canadian Patent No. 2,088,521.
The prepolymers of the subject invention have a
free isocyanate (NCO) group content of from 5 weight
percent to 35 weiqht percent, preferably 6 weight percent
to 25 weight percent, and advantageously 8 to 20 weight
percent.
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The isocyanate-terminated prepolymers comprise
the A-side (iso side) of the molded polyurethane foam
system. The B-side (resin side) of the subject inven-
tion molded polyurethane foam system employs isocyanate
reactive components, blowing agent(s), surfactant(s),
and other additives and auxiliaries, for example chain
extenders, cross-linkers, catalysts, dyes, pigments,
fillers, etc. One or more of the B-side components
may, in the alternative, be included with the A-side
components.
Catalysts are generally necessary. The
catalysts may be selected from conventional urethane-
promoting catalysts, for example, tin catalysts such as
dibutyltin diacetate, dibutyltin dilaurate, stannous
octoate, and the like; amine catalysts such as NIAX A-1,
diethylene triamine, 1,4-diazabicyclo[2.2.2]octane, and
the like.- Mixtures of metal catalysts and amine cata-
lysts may be used as well. Preferred are amine cata-
lysts. Amounts of catalysts may be readily determined
by one skilled in the art, and may range, for example,
from 0.1 to 5 weight percent based on the weight of the
foam.
Suitable chain extenders include the various
alkylene glycols and oligomeric polyoxyalkylene glycols
with molecular weights up to about 300 Da, for example
ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-
hexanediol, diethylene glycol, dipropylene glycol,
tripropylene glycol, and the like. The amount of chain
extender may be adjusted to provide the necessary
processing or physical parameters of the foam. Prefera-
bly, only most minor amounts of chain extenders are
used, for example less than 10% by weight and preferably
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less than 5% by weight relative to foam weight. Amino-
functional chain extenders such as MOCA, toluene
diamine, and hindered aromatic amines may also be
suitable.
Suitable cross-linkers include polyhydroxyl
functional monomeric compounds such as glycerine, but
preferably alkanolamines such as monoethanolamine,
diethanolamine (DEOA) and triethanolamine (TEOA). As
with the chain-extenders, cross-linkers, when used, are
preferably used in most minor amounts, for example less
than 10 weight percent and most preferably less than 5
weight percent relative to total foam weight. Both
chain extenders and cross-linkers, when used, are
preferably dissolved in water which serves as the
blowing agent.
A cell-stabilizing surfactant is generally
required. Suitable cell-stabilizing surfactants include
the various organopolysiloxanes and polyoxyalkylene
organopolysiloxanes as are well known to those skilled
in the art. Suitable surfactants include DC5043 avail-
able from Air Products, and Y-10,515 available from OSi,
Inc. Additional surfactants are available from Wacker
Silicones, Adrian, MI, and Goldschmidt A.G., Germany.
Combinations of surfactants may also be used, for
example, a blend of Tergitol 15-S-9 available from the
Union Carbide Corporation and DC5043. The amount of
surfactant should be an amount effective to avoid foam
collapse, and is readily ascertained by one skilled in
the art. Amounts of from 0.1 to about 5 weight percent,
preferably 0.5 to 2 weight percent based on the weight
of the foam may be suitable.
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The B-side may further contain polyoxyalkylene
polyols and/or polymer-modified polyoxyalkylene polyols
wherein the polyo:l.s have molecular weights of c.a. 300 Da
or higher, preferably equivalent weights of from 500 to
5000, more preferably 1000 to 3000. Up to about 50
weight percent of total polyol, preferably up to 25% of
total polyol may be contained i_n the B-side as opposed to
the prepolymer, as, the polyol contained in the prepolymer
does not have to react, being already incorporated into
the prepolymer. Most preferably, the prepolymer contains
in excess of 90'; of total polyol, and in particular
virtually all polyol. For the same reason, high primary
hydroxyl content is not necessary for any B-side polyol.
However, B-side polyols may advantageously contain
greater than 50 mol percent, and more preferably greater
than 70 mol percerit primary hydroxyl groups. Pref'erably,
no additional polyoxyalkylene polyol is contained in the
B-side formulatiori. Preferably, polyols contained in the
B-side (isocyanate reactive component) have unsaturations
such that the total unsaturation of the polyoxyalkylene
polyols contained in the B-side is less than 0.03 meq/g.
The B-side contains one or more blowing agents
of the chemical and/or physical type. The preferred
blowing agent is water, which reacts with isocya:nate to
generate urea linkages with coricomitant release of carbon
dioxide gas. Physical blowing agents may also be used,
either alone or in conjunction with water. Non-limiting
examples of additional blowing agents include the lower
alkanes, e.g., butane, isobutane, pentane, cyclopentane,
hexane, and the like; the chlorofluorocarbons (CFCs),
e.g. chlorotrifluoromethane, dichlorodifluoromethane, and
the like; the hydrochlorofl.uorocarbons (HCFCs) such as
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fluorodichloromethane and chlorodifluoromethane; the
perfluorinated C3-C8 aliphatic and cycloaliphatic hydro-
carbons (PFCs) and substantially fluorinated analogous
(HPFCs); chlorinated hydrocarbons such as
methylenedichloride, liquid C02, and the like. CFC's are
preferably avoided due to environmental concerns. As
stated previously, the preferred blowing agent is water,
which is most preferably used as the sole blowing agent.
Frothing agents such as CO2, nitrogen, and air may be
introduced as well.
The amount of blowing agent is selected so as
to provide a foam density of from about 1.0 lb/ft3 or less
to 4.0 lb/ft3 or more, more preferably 1.0 lb/ft3 to 3.0
lb/ft3, and most preferably about 1.2 lb/ft3 to about 2.8
lb/ft3. Amounts of water ranging from 1.0 part to 7.0
parts per 100 parts of total polyol component, preferably
2.0 parts to about 6.0 parts are especially preferred.
The A-side and B-side are combined in conven-
tional fashion employing a low pressure or high pressure
mix head and introduced into the mold which is optionally
and preferably maintained above ambient temperature. The
mold temperature may be maintained at a temperature
suitable for either hot or cold molding. The mold may be
closed, with foam forming ingredients introduced into a
suitable charging port, or may be an open mold which is
closed following introduction of the foam formulation.
The foam is cured, demolded, TPRed and/or crushed, and
cured in the conventional manner. It has been surpris-
ingly discovered that not only do the foam formulations
of the subject invention process well, but moreover, the
foams are of supex:-ior quality as compared to conventional
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foams from similar systems. Moreover, these results are
achievable from polyols independent of primary hydroxyl
content normally required t:o produce molded foam. The
foams preferably have wet sets of less than 15%,
preferably less than 10%.
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Having generally described this invention, a
further understanding can be obtained by reference to
certain specific examples which are provided herein for
purposes of illust:;rati.on only and are not intended to be
limiting unless otherwise specified.
Comparative Examples 1 and 2
Two "one-shot" formulations as set forth in
Table 1, one containing a low monol polyol in the B-side,
the second containing a conventional EO-capped, KOH-
catalyzed polyol with much higher unsaturation but
similar pol.yol functionality. As can be seen, low
unsaturation polyols of low primary hydroxyl content do
not produce foam in typical HR fashion.
TABLE 1 Low
Foam Composition: Unsat. Conventional
Low Unsaturation Base Polyol 74
Conventional Polvol. 74
Polymer Polyol 26 26
Water 4.1 4.1
DEOA 1.2 1.2
Niax A-107 0.20 0.20
Niax A-33 0.40 0.40
OSi Y-10,515 1.00 1.00
TDI 100 index 100 index
Polyol Properties
Hydroxyl Number (mgKOH/g) 28 28
Polyol Functionality 2.3 2.2
Ethylene Oxide Content (wt.%) 15 15
Primary Hyd.roxyl Content (mol%) 22 75
Polyol Unsaturation (meq/g) 0.003 0.070
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Foam Properties:
Low Unsat. Conventional
Molded Part Density (lb/ft3) 1.80
Resiliency (%) 69
25% IFD (lbs) Total 24
50% IFD (lbs) Collapse 44
65% IFD (lbs) 68
Tensile Strength (psi) 22
Elongation at Break (psi) 186
Tear Strength (lb/in) 1.55
75% Dry Compression Set (%) 7
50% Humid-Aged Compression Set (%) 18
50% Wet Compression Set (o) 32
Comparative Examples 1 and 2 illustrate that
substitution of low monol, exclusively DMC-catalyzed
polyol having low unsaturation for -a conventional
polyurethane molding polyol (high primary hydroxyl),
despite having the same overall oxyethylene content,
results in a foam system in which the foam totally
collapses in one-shot molded foam.
Example 1 and Com,parative Example 3
Molded foams were produced utilizing a pre-
polymer process with low unsaturation and conventional
(high unsaturation, high monol content) polyether
polyols of similar overall functionality. Two low
monol, low unsaturation polyols, a triol and a diol,
were blended to produce a base polyol composition which
has an actual functionality similar to the control.
Note that actual, or measured functionality_is a measure
of the actual polyol functionality and is not the
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"nominal" functionality, or functionality of the polyol
starter, as is normally reported. These examples
compare foams which are either entirely low monol or
conventional (i.e., both base polyol and polymer polyol
are either low unsaturation or conventional). The
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are either low unsaturation or conventional). The
polymer solids content of each foam was identical, the-
difference in polymer polyol content the result of
normalization of solids levels (the low unsaturation
polymer polyol was 43 weight percent solids, the conven-
tional polymer polyol, 38 weight percent solids).
The results shown below indicate significant
and surprising improvements in firmness, tensile
strength, elongation, tear strength, dry compression
sets, humid-aged compression sets, wet sets, and the
durability parameters: creep, load loss, and height
loss, when prepolymers prepared from low unsaturation
polyols are employed. Testing of dynamic properties is
discussed in several articles, including "New Dynamic
Flex Durability Test. 1", K. D. Cavender, 33RD ANNUAL
POLYURETHANE TECHNICAL/MARKETING CONFERENCE, Sept. 3 0-Oct . 3, 1990,
pp. 282-288; "Real Time Foam Performance Testing", K. D.
Cavender, 34TH ANNuAL POLYURETHANE TECHNICAL /MARKETING CONFERENCE,
Oct. 21-24, 1992, pp. 260-265; and "Real Time Test for
Auto Seating Foam", SAE INTL. CONGRESS & EXPOSITION, Paper No.
930634, 1993.
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TABLE 2
Prepol,vmer Composition Low Unsaturation Conventional
0 0 0 0
Low Unsaturation Base
Polyol' (0H=28) 73 -
Conventional Base Polyol2(0H=28) - 70
Arcol 25804 4 4
Low Unsaturation Polymer Polyol3 23 -
Conventional Polymer Polyol5 - 26
TDI/MDI (80/20) 42 42
Polymer Solids Content -10% -10%
Base Polyol Functionality -2.3 -2.2
Base Polyol Unsaturation (meq/g) 0.003 0.07
Foam Composition
Low Unsaturation Prepolymer (above) 100 -
Conventional Prepolymer (above) - 100
Water 2.5 2.5
OSi Niax A-1 Catalyst 0.25 0.25
Surfactant Blend
(Tergitol 15-S-9/DC5043) 1.1 1.1
Foam Pro en rties
Molded Part Density (lb/ft3) 2.3 2.3
Resiliency (%) 61 62
25% IFD (lbs) 38 33
50% IFD (Ibs) 62 59
65% IFD (lbs) 84 83
Tensile Strength (psi) 20.2 14.7
Elongation at Break (psi) 178 135 _
Tear Strength (lb/in) 2.20 1.91
50% Dry Compression Set (%) 4.5 8.4
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75% Dry Compression Set (%) 3.1 6.8
50% Humid-Aged Compression Set (%) 8.0 11.1
50% Wet Compression Set (%) 9.0 24.1
Dynamic Fatigue Properties
Creep, % 8.0 9.2
Load Loss, % 15.6 21.8
Height Loss, % 1.4 2.4
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t A polyoxypropylene/polyoxyethylene polyol containing 15 weight percent
oxyethylene moieties prepared by the DMC-catalyzed oxyalkylation of a mixed
diol/triol starter, having an unsaturation of c.a. 0.005 meq/g, a primary
hydroxyl content of c.a. 30%, and a functionality of 2.3.
2 A base (KOH) catalyzed polyoxypropylene/polyoxyethylene polyol having an
unsaturation of 0.07 meq/g, a measured functionality of 2.2, and containing
15%
by weight oxyethylene moieties as a cap.
3 A polymer-modified polyol containing 43 weight percent of 37/63 acryloni-
trile/styrene solids polymerized in situ in a 6000 Da mx. polyoxypro-
pylene/polyoxyethylene, DMC-catalyzed low unsaturation polyol containing 15%
random oxyethylene moieties.
4 A cell-opening polyol, conventionally catalyzed, having 75% oxyethylene and
25%
oxypropylene moieties co-fed (random), and a hydroxyl number of 40.
5 Polymer modified polyol similar to the low-unsaturation polymer modified
polyol, but containing 38% solids, the base polyol unsaturation being c.a.
0.04
meq/g.
Example 1 and Comparative Example 3 illustrate
the unexpected and surprising increases in foam physical
properties achieved when employing prepolymers based on
low unsaturation polyols as compared to conventionally
base-catalyzed polyol-derived prepolymers. Both foam
formulations had the same solids content, contributed by
the polymer-modified polyol used in prepolymer prepara-
tion. Noteworthy is the increase in 25% IFD, and the
considerable improvements in both tensile strength (37%
increase) and elongation at break (32% increase). The
prior art suggests that improvement in one of the latter
two properties would be expected to result in a decrease
in the other of_the two properties. The tear strength
is increased also, but perhaps the most notable improve-
ments are in both the dry and humid aged compression
sets, and particularly the wet set performance, the
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latter showing a 67 percent improvement! Wet set is
particularly important in molded seating, e.g. automo-
tive seating, where exposure to hot, humid environments
such as are found in the Southern United States and the
tropics is expected.
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In addition to the static properties discussed
above, the subject foams also displayed noticeably
improved dynamic fatigue properties, such as resistance
to creep, load loss, and height loss, and demonstrated
superior composite durability as well.
Exumple 2
A molded foam was prepared from an isocyanate
terminated prepolymer prepared by reacting 73 parts of
a glycerine-initiated polyoxypropylene polyol having an
unsaturation of 0.003 meq/g containing 15 weight percent
random oxyethylene moieties and a primary hydroxyl
content of 30 percent; 23 parts of a polymer polyol
having 43% acrylonitrile/styrene (37/63)solids as the
dispersed phase in a conventionally catalyzed base
polyol having a hydroxyl number of 35 and 19% oxyethyl-
ene content; 4 parts AR.COL 2580 polyether polyol, a
conventionally catalyzed 40 hydroxyl number 75% oxy-
ethylene/25% oxypropylene random polyol; with 42 parts
of an 80/20 blend of TDI/MDI. The prepolymer was
reacted with water, 3.5 parts; diethanolamine, 1.0 part;
NIAX A-i amine catalyst 0.25 part; and Air Products
DC5043 silicone surfactant, 1.0 part. Foam test results
are presented below.
Foam Results:
Molded Part Density (lb/ft3) 2.3
Resiliency (%) 66
25% IFD (lbs) 31
50% IFD (lbs) 53
65% IFD (lbs) 77
Tensile Strength (psi) 16.9
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Elongation at Break (psi) 125
Tear Strength (lb/in) 1.52
50% Dry Compression Set (%) 5.8
75% Dry Compression Set M 5.3
50% Humid-Aged Compression Set (%) 8.5
50% wet Compression Set (%) 11.0
Exam-ple 4 and Comparative Example 6
In a manner similar to that disclosed in
Example 1, further prepolymer formulations employing low
unsaturation polyols and base-catalyzed polyols of
similar functionality were employed to produce molded
foam. The formulations and foam physical properties are
given below in Table 4.
TABLE 4
Low Unsaturation Conventiona
Polvol o ol
Prepo1ymer Composition
Low Unsaturation, 28 OH triol' 36_5
Low Unsaturation, 28 OH diol2 36.5
Conventional Polyol, 28 OH triol3 73
Arcol 2580 (40 OH polyol) 4 4
Polymer Polyol4 23 23
80/20 TDI/MDI Isocyanate Blend 42 42
Base Polyol Functionality -2.5 -2.5
Foam rormulation
Low Unsaturation Polyol 100
Conventional Polyol Prepolymer 100
Water 2.5 2.5
OSi Niax A-1 Catalyst 0.18 0.18
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Surfactant Blend (UCC Tergitol
15-S-9/DC5043) 0.35 0.35
Foam Properties
Molded Density (lb/ft3) 2.3 2.3
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25% IFD (lbs.) 37 37
= 65% IFD (lbs.) 84 82
Tensile Strength (psi) 20.2 18.0
Elongation (%) 178 161
Tear Strength (lb/in) 2.20 1.89
50% Compression Set (%) 4.5 7.6
75% Compression Set (%) 3.1 6.3
50% Humid Compression Set (%) 8.0 11.2
50% Wet Set (%) 9.0 30.3
1 A polyoxypropylene/polyoxyethylene, oxypropylated glycerine oligomer
initiated, random
copolymer prepared by DMC catalysis containing 15% by weight oxyethylene
moieties, a
primary hydroxyl content of 30 mol percent, and an unsaturation of 0.005
meq/g.
2 A polyoxypropylene/polyoxyethylene, oxypropylated propylene glycol oligomer
initiated
random copolymer prepared by DMC catalysis containing 15% by weight
oxyethylene
moieties, a primary hydroxyl content of 30 mol percent, and an unsaturation of
0.005
meq/g.
3 A base-catalyzed (KOH) glycerine initiated polyoxypropylene/polyoxyethvlene
triol having
an unsaturation of 0.07 meq/g, a functionality of 2.2, and containing 15
weight percent
oxyethylene moieties as a cap.
4 Polymer-modified polyol containing 43% solids, the base polyol unsaturation
being c.a.
0.04 meq/g.
As can be seen, consistent with prior exam-
ples, foam properties are considerably improved when
molded foam is prepared from prepolymers derived from
1ow unsaturation polyols are utilLzed.
Having now fully described.the invention, it
will be apparent to one of ordinary skill in the art
that many changes and modifications can be made thereto
without departing from the spirit or scope of-- the
invention as set forth herein.
SUBSTITUTE SHEET (RULE 26)
