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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to rigid polyurethane foams and a method for
manufacturing the same.
2. Description of the Prior Art
Rigid polyurethane foam is fabricated from
organic polyisocyanate;
organic polyol;
halogenated alkane blowing agents;
surfactants;
catalysts for the reaction of --OH and --NCO radicals.
Rigid polyurethane foam can be produced by combining the listed ingredients
in a free-rise environment or by combining the listed ingredients in a
closed mold. When manufactured in a free-rise environment, rigid
polyurethane foam is customarily employed as a filler material wherein its
compressive strength and shear strength are not usually significant
factors. Because the resulting rigid polyurethane foam is intended to be
used as a filler, the lowest feasible densities are usually desirable for
free-rise foam.
When rigid polyurethane foam is employed in a closed mold, there is a
tendency for the material to have a greater density at the skin of the
mold than at the interior. The resulting molded foam article has a
differential density; the core has a density which may be substantially
lower than the skin density.
Where polyurethane foam products are intended for fire retardant
applications, it is customary to employ halogenated organic polyols, at
least in part, as a component of the organic polyol ingredients. The
resulting rigid polyurethane foam is evaluated by ASTM E84 to determine
its flame spread and smoke generation properties.
Rigid polyurethane foam products have included a variety of organic polyol
ingredients including polyethers, polyesters and mixtures thereof.
The use of a polyalkylene terephthalate digestion product in flexible
polyurethane foam is described in U.S. Pat. No. 4,048,104. Therein, the
digestion product and its preparation are described. However in that
instance the digestion product is employed to prepare polyisocyanate
prepolymers--and not as a polyol ingredient in the fabrication of flexible
polyurethane foam.
STATEMENT OF THE INVENTION
A principal object of this invention is to provide a rigid polyurethane
foam and method for making the same which has, for the same overall
density as a corresponding rigid polyurethane foam of the prior art,
equivalent or superior strength properties.
A converse object of the invention is to produce a rigid polyurethane foam
which has, for the same strength properties as a corresponding rigid
polyurethane foam of the prior art, a lower overall density.
A further object of the invention is to provide a molded rigid polyurethane
foam containing from 5 to 30 percent of its weight in the form of a
polyalkylene terephthalate digestion product wherein the molded foam will
have a higher core density than a corresponding polyurethane foam
fabricated to the same overall density from identical ingredients except
for the said digestion product.
A further object of this invention is to prepare a fire retardant rigid
polyurethane foam wherein the organic polyol ingredient includes
polyhalogenated polyol and also includes from 5 to 30 percent of its
weight in the form of the polyalkylene terephthalate digestion product and
wherein the resulting rigid fire retardant foam has a lower flame spread
and lower smoke generation than a corresponding foam prepared from the
same ingredients except for the said digestion product.
A further object of the invention is to provide a polyurethane foam which
can be molded to produce a rigid flame retardant polyurethane foam having
a flame spread less than 25 and a smoke generation less than 450 in the
ASTM E84 test.
A particular related object is to provide a rigid polyurethane foam having
a flame spread less than 25 and a smoke generation less than 100 in the
ASTM E84 test.
A still further object of this invention is to provide a double metal (or
other incombustible material) skin, rigid polyurethane foam core
construction panel having a flame spread less than 25 and a smoke
generation has than 100 in the ASTM E84 test.
A particular related object is to provide a double metal (or other
combustible material) skin, rigid polyurethane foam core construction
panel having a flame spread less than 25 and a smoke generation less than
25 in the ASTM E84 test.
According to the invention, in its broadest embodiment, polyurethane foam
is prepared by combining
organic polyisocyanate;
organic polyol;
halogenated alkane blowing agent;
surfactant;
catalyst for the reaction of --OH and --NCO radicals.
The organic polyol ingredient includes 5 to 30 percent of its weight of a
digestion product of polyalkylene terephthalate which is obtained by
digesting polyalkylene terephthalate having a molecular weight greater
than 15,000 in a reactive solvent selected from the class consisting of
organic diols and triols having a molecular weight from 62 to 500 until
the digestion product is soluble in acetone at room temperature. By
including this digestion product in the organic polyol ingredient of the
polyurethane foam, the resulting polyurethane foam in a free-rise
fabrication will have a lower density than a corresponding rigid
polyurethane foam fabricated from the same ingredients except for the
polyalkylene terephthalate digestion product. An alternative comparison is
between (a) the rigid polyurethane foam obtained from a polyol mixture
containing 5 to 30 percent by weight of the digestion product with (b) the
rigid polyurethane foam obtained from corresponding ingredients without
the said digestion product, wherein both foams (a) and (b) are formulated
to the same overall density. In this circumstance, the polyurethane foam
(a) which contains the said digestion product will have a greater
compression strength and shear strength than the corresponding foam (b).
When the rigid polyurethane foam forming ingredients are fabricated in a
closed mold according to this invention, the rigid foam which contains the
said digestion product will have a more uniform density, i.e., a higher
core density, than a corresponding rigid foam of the same overall density
which does not contain the digestion product.
When fire retardant rigid polyurethane foams are prepared, a foam
containing 5 to 30 percent of the organic polyol in the form of the
digestion product will have a lower flame spread and a lower smoke
generation, ASTM test E84, than a corresponding rigid polyurethane foam
which does not contain the digestion product.
A building construction panel, fabricated in accordance with U.S. Pat. No.
4,037,377, and containing a fire retardant polyol composition as herein
set forth can achieve a flame spread of 20 and a smoke generation of 15
when tested in ASTM E84.
DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
In its broadest embodiment the present invention concerns polyurethane
foams, both fire retardant foams and others. Rigid polyurethane foams are
prepared by combining the following ingredients:
an organic polyisocyanate--which can be a monomeric polyisocyanate, a
polymeric polyisocyanate or a polyisocyanate prepolymer;
an organic polyol which may be a polyether, a polyester, a mixed
polyether-polyester, or a mixture of polyethers and polyesters;
a halogenated alkane blowing agent such as trichlorofluoro methane;
a surfactant, usually an alkoxylated silicone;
a catalyst for the reaction of --OH and --NCO
radicals, usually an amine or a tin catalyst.
Polyalkylene terephthalate polymers, principally polyethylene terephthalate
polymers, are available in the form of photographic films and synthetic
fibers. Waste or scrap films and fibers of polyethylene terephthalate are
inexpensively available. In addition polyalkylene terephthalate polymers
are available as sludges which are obtained as by-products from
polyalkylene terephthalate manufacturing plants. In all cases the
polyalkylene terephthalate contains recurring units of
##STR1##
wherein G represents a divalent organic radical containing from 2 to 10
carbon atoms attached to the adjacent oxygen atoms by saturated carbon
atoms. The molecular weight of such polyalkylene terephthalate polymers is
greater than 15,000, frequently greater than 100,000. According to the
present invention such polyalkylene terephthalate polymers are digested
with low molecular weight polyols selected from the class consisting of
diols and triols. Typical diols include ethylene glycol, propylene glycol,
butylene glycol, diethylene glycol, polyethylene glycol, dipropylene
glycol, polypropylene glycol, other alkylene glycols and glycol ethers,
hydroxy-terminated polyesters, bis(2-hydroxy-ethoxyethyl) glutarate,
bis(2-hydroxy-ethyl) terephthalate, and in general any hydroxy-terminated
ether, ester or mixed etherester having a molecular weight of 500 or less.
The digesting polyol can be aliphatic or aromatic. The digesting polyol
may include substituents which are inert in the digestion reaction, for
example, chlorine or bromine substituents.
A preferred digesting polyol is bis(2-hydroxy-ethoxyethyl) glutarate. The
glutarate may be prepared initially by transesterification of diethylene
glycol and dimethyl glutarate. Alternatively the glutarate may be made by
transesterification contemporaneously with the desired digestion by
combining the polyalkylene terephthalate digested by heating the polymer
at temperatures from about 200.degree.-250.degree. C. for several hours
with the selected digesting polyol solvent. The digestion is carried out
in a nitrogen atmosphere to minimize oxidation reactions. Periodically
samples are taken from the digestion kettle and deposited in acetone at
room temperature. The digestion process is considered to be complete when
the sample digested product is soluble in the acetone. After completion of
the digestion, the reaction kettle contents are allowed to cool and may be
used directly or may be stored in suitable containers such as metal cans.
While the digestion product of polyalkylene terephthalate is soluble in
acetone, it may be possible to produce the acetone soluble digestion
product by observing the changes in viscosity and/or acid value of the
materials in the digestion process, without actually carrying out an
acetone solubility test.
Some polyalkylene terephthalate materials contain dispersed solids which
can be catalyst particles (left over from the processing by which the
terephthalate was produced); or may be insoluble fragments of other
organic films which have been incompletely separated from the
terephthalate; or may be pigments or other foreign substances. Such
dispersed solids may remain in the digestion product, so long as they are
substantially inert in the subsequent preparation of rigid polyurethane
foam. Such dispersed substances, in general, are not soluble in acetone
and their presence in an acetone solution of the digested polyol may
create cloudiness.
For the purposes of the present invention in its broadest scope, the
digestion product constitutes 5 to 30 percent of the weight of the organic
polyol ingredient. Appropriate revisions must be made to satisfy the
stoichiometric requirements of the urethane reaction--the reaction between
the --NCO radicals of the polyisocyanate and the --OH radicals of the
organic polyol. Apart from that adjustment, the polyurethane reaction is
carried out exactly in the same manner that it would be carried out for
making any other rigid polyurethane foam. The ingredients may be mixed in
advance--at least in those instances where the digestion product is
compatible with the other organic polyols and halogenated alkane blowing
agent. In those instances where the digestion product is not compatible
with the remaining organic polyols, the polyurethane reaction may be
carried out by combining three ingredient streams, namely, the
polyisocyanate stream, the digestion product stream and the remaining
organic polyols as a separate stream. The halogenated alkane blowing agent
and surfactant may be included in any or all of the three streams. The
catalyst may be added in any stream which does not contain isocyanate
groups. The polyurethane foam may employ spray techniques, pouring
techniques or frothing techniques, all of which are well-known in the
polyurethane foam art.
EXAMPLE 1
PRIOR ART
A rigid polyurethane foam was prepared by combining the following
ingredients as a polyol mixture:
75 grams Multranol-E9136, a polyoxypropylene aromatic amine having a
hydroxyl value of 480;
5 grams Fyrol-6, a halogen-containing polyol having the following
structural formula
##STR2##
1 gram surfactant, alkoxylated silcone; 1 gram dimethyl ethanol amine,
catalyst;
0.35 grams triethylene diamine (33% by weight in dipropylene glycol
solvent) catalyst;
31 grams trichlorofluoro methane (Freon-11).
100 grams of the above-described polyol mixture was combined with 89.5
grams Mondur--MR, a polymethylene polyphenyl polyisocyanate having an
--NCO value of 31-32. The mixed materials were allowed to rise freely in
an open-top box to produce a rigid polyurethane foam having a density of
1.60 pounds per cubic foot. This rigid foam was identified as foam 1.
EXAMPLE 2
Example 1 was repeated except that the organic polyol was 55 grams of the
Multranol E-9136 and 20 grams of the digested polyol described in Example
6 having an --OH value of 220. Also the formulation included 30 grams of
trichlorofluoro methane. This mixture was combined with 76 grams
Mondur--MR, a stoichiometric equivalent, and allowed to rise freely in an
open-top box to produce a rigid polyurethane foam having a density of 1.60
pounds per cubic foot, identified as foam 2.
Foam 1 and foam 2 were compared in compressive strengths parallel to the
direction of rise and perpendicular to the direction of rise. The results
are set forth in the following Table 1.
TABLE 1
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COMPRESSION TESTS
Foam Parallel Perpendicular
Example Density To Rise To Rise
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1 1.60 pcf 17.4 psi 12.5 psi
2 1.60 pcf 27.6 psi 14.1 psi
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It will be observed that for the same density of product, the foam (Example
2) containing digested polyalkylene terephthalate exhibited greater
compressive strength than the corresponding foam (Example 1) which did not
contain the digestion product.
EXAMPLE 3
PRIOR ART
A fire retardant rigid polyurethane foam is prepared from the following
ingredients:
Polyol Mixture
65.3 grams RF230 which is a trichloro butylene oxide adduct of a starter
polyol. The adduct has an --OH value of 365;
13.40 grams of a glycerine-based adduct of propylene oxide capped with
ethylene oxide having a molecular weight of about 3000 and a hydroxyl
value of 56;
0.30 grams Ferrocene which is dicyclopentadienyliron, used as a smoke
suppressant;
1.0 grams surfactant, a polyalkoxylated silicone;
20 grams trichlorofluoro methane (Freon 11).
100 grams of the foregoing polyol mixture is combined with 69 grams of
polyphenyl polymethylene polyisocyanate having an --NCO value of 30-31
percent by weight and a catalyst consisting of 1.6 grams of dimethyl
cyclohexyl amine. The ingredients were allowed to foam in a closed
aluminum mold having a rectangular mold cavity measuring
12".times.12".times.2". The resulting foam is identified as foam 3.
EXAMPLE 4
The fire retardant polyurethane foam of Example 3 was duplicated except
that the polyol mixture contained
59.31 grams RF230 (supra);
20 grams of the digested polyol of Example 6 having an --OH value of 220;
0.84 grams surfactant, the same polyalkoxylated silicone;
1.30 grams catalyst, dimethyl cyclohexyl amine; and
19.85 grams trichlorofluoro methane (Freon 11).
100 grams of the polyol mixture was combined with 72 grams of polyphenyl
polymethylene polyisocyanate having an --NCO value of 30-31 percent by
weight. The resulting mixture was charged into the same
12".times.12".times.2" aluminum mold at 100.degree. F. to produce a rigid
polyurethane foam, identified as foam 4.
The comparative properties of the foams 3 and 4 are set forth in Table 2.
TABLE 2
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Foam
Foam Example 4
Example 3
Sample A Sample B
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Overall Density
(pounds/cu.ft.)
3.6 3.6 3.6
Core Density (pcf)
2.81 2.95 2.89
Compression Strength
(Room Temp.) psi
30.2 40.2 39.5
Compression Strength
(130.degree. F.) psi
29.0 -- 38.1
Compression Modulus
(Room Temp.) 963 1190 1363
Compression Modulus
(130.degree. F.)
790 -- 1194
Peak Exotherm, .degree. F.
198 216 218
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It will be observed from Table 2 that the core density of foam 4 is greater
than the core density of foam 3 although the overall density of both
examples is the same. It will be observed that the compression strength
and modulus are greater for foam 4 than foam 3. Similarly the peak
exotherm of foam 4 greatly exceeds the peak exotherm of foam 3 indicating
that the polyurethane foam forming reaction occurs more vigorously with
foam 4.
The polyol mixture of Example 4 exhibited compatibility--that is, no phase
separation occurred when the material was stored for extended periods. As
a consequence, a polyurethane foam forming polyol mixture can be prepared
so that the polyurethane foam can be produced in conventional
two-component systems rather than three or more component systems.
While polyol compatibility was demonstrated in Example 4, it is possible
that the polyalkylene terephthalate digestion product might not be
compatible with other polyols. In such instances, the benefits of the
present invention can be obtained by employing three-component mixing
devices for mixing (a) the other polyols; (b) the polyalkylene
terephthalate digestion product; (c) the polyisocyanate.
EXAMPLE 5--BUILDING PANEL
A building panel of the type described in U.S. Pat. No. 4,037,377 was
prepared utilizing the polyurethane foam forming ingredients of Example 4.
The resulting panel, 8'3" long; 2" thick; 24" wide, was enclosed in 20
gauge galvanized steel facing sheets. The rigid polyurethane foam itself
was tested for fire properties by peeling away one of the metal skins and
exposing the remaining polyurethane foam core in an ASTM E84 fire test.
The exposed foam core was sanded until smooth, as is normal in such fire
testing.
A similar building panel was tested without removing either metal skin. The
results of the ASTM E84 test are set forth in Table 3.
TABLE 3
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ASTM E84 TESTS
Flame Smoke
Spread Generation
______________________________________
Foam Core - Foam Exposed
Test A 23 99
Test B 20 107
Test C 20 100
Rating 20 100
Foam Panel - Both Metal
Liners Retained
Test D 18 19
Test E 20 12
Test F 18 13
Rating 20 15
______________________________________
It will be observed that the exposed foam alone (without the covering metal
skin) achieves a flame spread less than 25 and a smoke generation of 100
in the ASTM E84 test. When the panel was tested (two incombustible skins
separated by a foamed-in-place rigid polyurethane foam core), the flame
spread was less than 25 and the smoke generation was less than 25,
specifically, the smoke generation was 15.
EXAMPLE 6--PREPARATION OF DIGESTION PRODUCT
Two moles of diethylene glycol and one mole of dimethyl glutarate are mixed
and heated to 320.degree.-330.degree. F. Methanol is recovered as a vapor
as the ingredients are further heated to 440.degree. F. to produce a
transesterification glutarate having an --OH value of 365.+-.5.
One hundred pounds of the glutarate is combined with 63 pounds of
polyethylene terephthalate photographic film chips and heated at
420.degree..+-.10.degree. F. for six hours. The final acid value is less
than 3. The final --OH value is 220.+-.10. The viscosity is 5,000.+-.1,000
CPS at 70.degree. F. (Number 3 spindle).
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