Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a flame retardant
rigid polyurethane syntactic foam.
Compositions which contain hollow beads,
bubbles or microballoons have been known for many
years. The concept of using these hollow beads in a
composition is designed to reduce the density and also
reduce the high cost of the matrix material. It was
observed, however, that a reduction in density also
resulted in a reduction of the structural strength of
the product and it was difficult to retain maximum
strength with reduced density.
From the prior art, it is well known to use
liquid reactants to make polyurethanes, both foams and
solid products. It is also well known that flame
retardants, such as tris(2-chloroethyl)phosphate can
be used in polyurethanes as a flame retardant. It is
also apparent from the prior art that if such a flame
retardant material is used there are too many
disadvantages associated with this low molecular weight
material to be broadly useful in making flame retardant
polyurethane foams. It is also known from the prior
art to use solvents or diluents for compositions which
contain large amounts of microballoons. However, it has
not been known heretofore that a rigid polyurethane syntactic
foam could be made which is pourable or castable, have
a relatively low density, contain a large amount of micro-
balloons, cures to a product which is structurally as
strong as wood or stronger, could be cast and cured in thick
section and ha~e a flame retardant property which exceeds
prior art rigid polyurethanes.
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This invention relates to a flame retardant rigid
polyurethane syntactic foam which is made from a mixture of
microballoons, an organic polyol, a polyisocyanate, a catalyst
and a flame retardant which also acts as a flow promoter.
The flame retardant provides the composition with sufficient
fluidity to allow it to be cast into molds, flow into crevices
to duplicate mold detail and provides composition which when
cured will be flame retardant and structurally strong. The
flexural strength can be improved by adding to the mixture
noncombustible flexible fibers, such as glass fibers. The
composition cures in large molds and will provide a cured
product which can be substituted for wood with the added
advantage that it is flame retardant.
It is therefore an object of this invention
to provide a flame retardant syntactic foam which can
be cast in a mold and cures to a product which is a
substitute for wood and is also flame retardant. These
and other ob~ects will become more apparent in the
following detailed discussion.
This invention relates to a rigid polyurethane
syntactic foam consisting of a cured product obtained
from a mixture consisting essentially of the composition
obtained by mixing an organic polyol, a polyisocyanate,
microballoons, a catalyst for the reaction between the
organic polyol and polyisocyanate, and a substantially
colorless, compatible flame retardant having a viscosity
less than 100 centipoise at 24C., having a volatility
such that the flame retardant does not evaporate from
the exotherm generated by reacting ingredients and
said flame retardant is non-reactive in the mixture to
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the extent that the physical properties of the :Eoam are
not substantially changed compared to the physical
properties of the foam ~ithout the :Elame retardant
presenk J a combination of the organic polyol and the
poly.isocyanate being a liquid at 25C., there being
present in the mixture a su~ficient amount of micro-
balloons to provide a non-castable mixture in the absence
of the flame retardant and the amount of flame retardant
present in the mixture being sufficient to provide a
castable mixture which will flow in a mold cavity to
the extent that mold details are filled, and the mixture
cures to a rlgid polyurethane syntactic foam which is
flame retardant.
The organic p~lyols and polyisocyanates which
are liquids at 25C. are well known in the prior art. The
specific polyQls or isocyanates are not critical except
that a combination of the two are liquid at 25C. The
organic polyol can be either of the polyether type or
the polyester type. It is also w:ithin the scope of this
in~ention to use some prereacted combinations of organic
polyol and polyisocyanate. The organic polyol and poly-
isocyanate, however, are those combinations of organic
polyol and polyisocyanate which gi~e rigid polyurethane.
The microb~lloons can be made from any
material known in the art, but are preferably made from
glass which provides the optimum physical properties
for strength The particle size of the microballoons are
those ~rdinarily found in the prior art.
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The catalysts are those conventionally used
to cure polyurethanes, especially those which catalyze
the reaction between organic polyols and polyisocyanate,
such as amines and tin catalyst.
The flame retardants suitable for the rigid
polyurethane syntactic foams of th~s invention are those which
have a viscosity of less than 100 centipoise at 24C. Flame
retardants which are solids or have viscosities greater
than 100 centipoise at 24C. do not provide all the
properties of the mixture as well as of the cured foam,
however, small amounts of these other flame retardants can
be used with the low viscosity flame retardants for some
additional benefits but their amounts should not interfere
with the overall property profile of the mixture or cured
foam. The flame retardant should also be compatible with
the polyurethane reactants and with the cured foam to the
extent that it does not exude from the cured foam or separate
from the mixture. The volatility of the flame retardant
must be sufficiently high so that it does not evaporate from
the mixture during the exotherm generated by the reacting
ingredients. The flame retardant should also be non-reactive
in the mixture to the extent that the physical properties of
the cured syntactic foam are not substantially changed
compared to the physical properties of the cured syntactic
foam without the flame retardant present. The preferred
flameIretardant is tris(betachloroethyl)phosphate~
A foam with a combination of properties of low
density, strength, fluidity and flame retardancy result
from using liquid organic polyol and polyisocyanate
combinations and using a sufficient amount of microballoons
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to make the resulting mixture non-castable, non-flo~ing and
then using enough flame retardant as described above to
make the mixture castable to the extent that ~t will flow
in a mold cavity such that the mold details are filled. By
using these amounts, the resulting cured rigicl polyurethane
syntactic foam is strong, low in density and flame retardant.
The amounts of each ingredient will depend upon the
particular organic polyol, polyisocyanate and microballoon
used. These ingredients vary broadly in characteristics and
thus the amount of each will vary likewise. The relative
amounts of organic polyol and polyisocyanate are used in
the stoichiometric amounts of the prior art.
The mixture can also contain noncombustible
flexible fibers which are less than 25 mm in length.
These noncombustible flexible fibers improve the flexural
strength of the rigid polyurethane syntactic foam. A
preferred noncombustible flexible fiber is glass fiber.
These noncombustible flexible fibers can be a single
monofilament or fiber of multi-filament which are herein
referred to as bundles. The fibers can be chopped into
the desired lengths from longer strands. Preferably,
the fibers are about 6 mm in length. These noncombustible
fibers improve the flexural strength of the rigid
polyurethane syntactic fo~m without disturbing the flame
retardant properties or the casting properties of the mixture.
The amount of noncombustible flexible fiber will
vary in accordance with the particular mixing and molding
equipment available. The amount should not be such that
it reduces the fluidity of the mixture to a point where
the mixture is no longer suitable for casting into a mold.
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Amounts of from 5 to 15 weight percent based on the total
weight of the mixture have been ound suitable to increase
the flexural strength without reducing the ability of the
mixture to be cast into a mold.
The ingredients are combined in the manner usually
used in the prior art in that the polyisocyanate is usually
added last. Any other method of combining the ingredients
is applicable as long as the final mixture can be cast into
a mold. ~nce all the ingredients are combined, the mixture
will cure at room temperature to a rigid polyurethane
synt~ctic foam.
The syntactic foams of this invention are suitable
for structural purposes, such as a replacement for wood and
have the added advantage of being flame retardant.
The following examples are presented for
illustrative purposes only and should not be construed as
limiting the invention which is properly delineated in the claims.
Example 1
A mixture of 6 parts by weight of a commercial organic
polyol ~Voranol RS-350, trademarked and sold by Dow Chemical
Company), 6 parts by weight of polymethylene polyphenyldi-
isocyanate, 6 parts by weight of tris~betachloroethyl)-
phosphate, 2.5 parts of glass microballoons and 0.1 part
by weight of a mixture of 1 part by weight of triethylene
diamine and 2 parts by weight of dipropylene glycol was
prepared. The above mixture was prepared by adding the
isocyanate ingredient last. The resulting mixture was
fluid and could readily be cast into a mold and when cured
to a rigid polyurethane syntactic foam, was non-burning.
A mixture was prepared as described above except the
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tris~betachloroethyl)phosphate was let out. This mixture
was a wet powder, was not castable and when cured, burned.
This mat0rial had a limiting oxygen index ~LOI) o-f 17% oxygen
whereas the mixture containing the tris(betachloroethyl)-
phosphate had an LOI of 80~ oxygen.
Example 2
A mixture o 100 parts by weight of the commercial
organic polyol employed in ~xample 1, 42 parts by weight glass
microballoons, 75 parts by weight of tris(betachloroethyl)-
phosphate, 1 part by weight of the catalyst mixture of Example 1,and 100 parts by weight of polymethylene polyphenyl diisocyanate
was prepared by adding the isocyanate ingredient last. The
mixture was castable and cured at room temperature to a
rigid polyurethane syntactic foam which did not burn, in that
no burning occured after the flame was removed.
Example 3
(A) A mixture of 100 parts by weight of a commercial
organic polyol (Voranol 370, trademarked and sold by Dow
Chemical Company), 75 parts by weight of tris(betachloroethyl)-
phosphate, 35 parts by ~eight of glass microballoons, 1.5parts by weight of a silicone surfactant and 1.0 part by
weight of a mixture of one part by weight triethylene
diamine and two parts by weight dipropylene glycol was
prepared. To this mixture, 100 parts by weight polymethylene
polyphenyldiisocyanate was added and the mixture was allowed
to cure in a test sample.
(B) ~ mixture was prepared as described in (A)
above except 5 parts by weight of chopped glass fiber
strands o about 6 mm in length were pre~ent in the mixture~
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(C) A mixture was prepared as described in (A)
abo~e except 10 parts by weight o~ chopped glass ~iber
strands of about 6 mm in length were present in the mixture.
The ~lexural strength was determined on each
cured sample of (h), (B) and (C) in accordance with the
procedure ASTM-D-790 with the results as shown in the
Table below in kilopascals (kPa).
Table
Com~ tion Flexural Strength~ kPa
(A) 6674
(B) 7584
(C) 9067
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