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BACKGROUND OF THE INVENTION
1. Field Of The Invention
The present invention relates to rigid foams characterized by carbodiimide,
isocyanurate and urethane linkages and improved flame retardancy. More
particularly, the invention relates to rigid foams prepared by
catalytically condensing (a) an organic polyisocyanate with a polyol or
(b) a quasi-prepolymer in the presence of a blowing agent and alumina
trihydrate.
2. Prior Art
The preparation of urethane-modified carbodiimideisocyanurate foams is well
known in the art. Generally these foams are prepared by the condensation
of an organic polyisocyanate in the presence of a polyol, a blowing agent
and a catalyst system which promotes the carbodiimide, isocyanurate and
urethane reactions. The foams may also be prepared by condensing, in the
presence of a blowing agent, a quasi-prepolymer prepared by the reaction
of a stoichiometric excess of an organic polyisocyanate with a polyol.
Various catalyst systems have been described in the art as useful for the
preparation of these foams. Illustrative of the prior art in this area
include U.S. Pat. Nos. 3,887,510; 3,891,578; 3,891,579; 3,894,972;
3,922,238; 3,928,256; and 3,981,829. The present invention is directed to
an improvement in the process and compositions described in the
aforementioned patents.
SUMMARY OF THE INVENTION
In accordance with the present invention, rigid foams characterized by
carbodiimide, isocyanurate and urethane linkages and having improved flame
retardant properties are prepared by catalytically condensing (a) an
organic polyisocyanate with a polyol or (b) a quasi-prepolymer in the
presence of a blowing agent and from 20 parts to 100 parts by weight of
alumina trihydrate per 100 parts by weight of polyisocyanate. Employing
alumina trihydrate in the preparation of the foams results in foams having
improved flame retardant properties without a loss in the physical
properties or closed cell content of the foams.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The organic polyisocyanate used in the preparation of the foams in
accordance with the subject invention corresponds to the formula:
R"(NCO).sub.z
wherein R" is a polyvalent organic radical which is either aliphatic,
aralkyl, alkaryl, aromatic or mixtures thereof, and z is an integer which
corresponds to the valence of R" and is at least two. Representative of
the organic polyisocyanates contemplated herein includes, for example, the
aromatic diisocyanates such as 2,4-toluene diisocyanate, 2,6-toluene
diisocyanate, mixtures of 2,4- and 2,6-toluene diisocyanate, crude toluene
diisocyanate, methylene diphenyl diisocyanate, crude methylene diphenyl
diisocyanate and the like; the aromatic triisocyanates such as
4,4',4"-triphenylmethane triisocyanate, 2,4,6-toluene triisocyanates; the
aromatic tetraisocyanates such as
4,4'-dimethyldiphenylmethane-2,2'-5,5'-tetraisocyanate, and the like;
arylalkyl polyisocyanates such as xylylene diisocyanate; aliphatic
polyisocyanates such as hexamethylene-1,6-diisocyanate, lysine
diisocyanate methylester and the like; and mixtures thereof. Other organic
polyisocyanates include polymethylene polyphenylisocyanate, hydrogenated
methylene diphenylisocyanate, m-phenylene diisocyanate,
naphthylene-1,5-diisocyanate, 1-methoxyphenylene-2,4-diisocyanate,
4,4'-biphenylene diisocyanate, 3,3'-dimethoxy-4,4'-biphenyl diisocyanate,
3,3'-dimethyl-4,4'-biphenyl diisocyanate, and
3,3'-dimethyldiphenylmethane-4,4'-diisocyanate. These polyisocyanates are
prepared by conventional methods known in the art such as the phosgenation
of the corresponding organic amine. Quasi-prepolymers may also be employed
in the process of the subject invention. These quasi-prepolymers are
prepared by reacting an excess of organic polyisocyanate or mixtures
thereof with a minor amount of an active hydrogen-containing compound as
determined by the well-known Zerewitinoff test, as described by Kohler in
Journal Of The American Chemical Society, 49, 3181 (1927). These compounds
and their methods of preparation are well known in the art. The use of any
one specific active hydrogen compound is not critical hereto, rather any
such compound can be employed herein. Generally, the quasi-prepolymers
have a free isocyanate content of from 20% to 40% by weight.
Suitable active hydrogen-containing groups as determined by the
Zerewitinoff method which are reactive with an isocyanate group include
--OH, --NH--, --COOH, and --SH. Examples of suitable types of organic
compounds containing at least two active hydrogen-containing groups which
are reactive with an isocyanate group are hydroxy-terminated polyesters,
polyalkylene ether polyols, hydroxy-terminated polyurethane polymers,
polyhydric polythioethers, alkylene oxide adducts of phosphorus-containing
acids, polyacetals, aliphatic polyols, aliphatic thiols including alkane,
alkene and alkyne thiols having two or more --SH groups; diamines
including both aromatic aliphatic and heterocyclic diamines as well as
mixtures thereof. Compounds which contain two or more different groups
within the above-defined classes may also be used in accordance with the
process of the present invention such as, for example, amino alcohols
which contain an amino group and a hydroxyl group. Also, compounds may be
used which contain one --SH group and one --OH group as well as those
which contain an amino group and a --SH group. The active
hydrogen-containing compound will generally have an equivalent weight of
from 50 to 500 and a functionality of from 2 to 8.
Any suitable hydroxy-terminated polyester may be used such as are obtained,
for example, from polycarboxylic acids and polyhydric alcohols. Any
suitable polycarboxylic acid may be used such as oxalic acid, malonic
acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic
acid, azelaic acid, sebacic acid, brassylic acid, thapsic acid, maleic
acid, fumaric acid, glutaconic acid, .alpha.-hydromuconic acid,
.beta.-hydromuconic acid, .alpha.-butyl-.alpha.-ethyl-glutaric acid,
.alpha.,.beta.-diethylsuccinic acid, isophthalic acid, terephthalic acid,
hemimellitic acid, and 1,4-cyclohexanedicarboxylic acid. Any suitable
polyhydric alcohol, including both aliphatic and aromatic, may be used
such as ethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol,
1,4-butylene glycol, 1,3-butylene glycol, 1,2-butylene glycol,
1,5-pentanediol, 1,4-pentanediol, 1,3-pentanediol, 1,6-hexanediol,
1,7-heptanediol, glycerol, 1,1,1-trimethylolpropane,
1,1,1-trimethylolethane, hexane-1,2,6-triol, .alpha.-methyl glucoside,
pentaerythritol, and sorbitol. Also included within the term "polyhydric
alcohol" are compounds derived from phenol such as
2,2-bis(4-hydroxyphenyl)propane, commonly known as Bisphenol A.
The hydroxy-terminated polyester may also be a polyester amide such as is
obtained by including some amine or amino alcohol in the reactants for the
preparation of the polyesters. Thus, polyester amides may be obtained by
condensing an amino alcohol such as ethanolamine with the polycarboxylic
acids set forth above, or they may be made using the same components that
make up the hydroxy-terminated polyester with only a portion of the
components being a diamine such as ethylenediamine.
Any suitable polyalkylene ether may be used such as the polymerization
product of an alkylene oxide or of an alkylene oxide with a polyhydric
alcohol. Any suitable polyhydric alcohol may be used such as those
disclosed above for use in the preparation of the hydroxy-terminated
polyesters. Any suitable alkylene oxide may be used such as ethylene
oxide, propylene oxide, butylene oxide, amylene oxide, and heteric or
block copolymers of these oxides. The polyalkylene polyether polyols may
be prepared from other starting materials such as tetrahydrofuran and
alkylene oxide-tetrahydrofuran copolymers; epihalohydrins such as
epichlorohydrin; as well as aralkylene oxides such as styrene oxide. The
polyalkylene polyether polyols may have either primary or secondary
hydroxyl groups and, preferably, are polyethers prepared from alkylene
oxides having from two to six carbon atoms such as polyethylene ether
glycols, polypropylene ether glycols, and polybutylene ether glycols. The
polyalkylene polyether polyols may be prepared by any known process such
as, for example, the process disclosed by Wurtz in 1859 and Encyclopedia
Of Chemical Technology, Vol. 7, pp. 257-262, published by Interscience
Publishers, Inc. (1951) or in U.S. Pat. No. 1,922,459. Alkylene oxide
adducts of Mannich condensation products are also useful in the invention.
Alkylene oxide adducts of acids of phosphorus which may be used include
those neutral adducts prepared from the alkylene oxides disclosed above
for use in the preparation of polyalkylene polyether polyols. Acids of
phosphorus which may be used are acids having a P.sub.2 O.sub.5
equivalency of from about 72% to about 95%. The phosphoric acids are
preferred.
Any suitable hydroxy-terminated polyacetal may be used such as, for
example, the reaction product of formaldehyde or other suitable aldehyde
with a dihydric alcohol or an alkylene oxide such as those disclosed
above.
Any suitable aliphatic thiol including alkane thiols containing at least
two --SH groups may be used such as 1,2-ethanedithiol, 1,2-propanedithiol,
1,3-propanedithiol, and 1,6-hexanedithiol; alkenethiols such as
2-butene-1,4-dithiol, and alkynethiols such as 3-hexyne-1,6-dithiol.
Any suitable polyamine may be used including aromatic polyamines such as
methylene dianiline, polyarylpolyalkylene polyamine (crude methylene
dianiline), p-aminoaniline, 1,5-diaminonaphthalene, and
2,4-diaminotoluene; aliphatic polyamines such as ethylenediamine,
1,3-propylenediamine; 1,4-butylenediamine, and 1,3-butylenediamine, as
well as substituted secondary derivatives thereof.
In addition to the above hydroxy-containing compounds, other compounds
which may be employed include graft polyols. These polyols are prepared by
the in situ polymerization product of a vinyl monomer in a reactive polyol
medium and in the presence of a free radical initiator. The reaction is
generally carried out at a temperature ranging from about 40.degree. C. to
150.degree. C.
The reactive polyol medium generally has a molecular weight of at least
about 500 and a hydroxyl number ranging from about 30 to about 600. The
graft polyol has a molecular weight of at least about 1500 and a viscosity
of less than 40,000 cps. at 10% polymer concentration.
A more comprehensive discussion of the graft polyols and their method of
preparation can be found in U.S. Pat. Nos. 3,383,351; 3,304,273;
3,652,639; and 3,823,201, the disclosures of which are hereby incorporated
by reference.
Also, polyols containing ester groups can be employed in the subject
invention. These polyols are prepared by the reaction of an alkylene oxide
with an organic dicarboxylic acid anhydride and a compound containing a
reactive hydrogen atom. A more comprehensive discussion of these polyols
and their method of preparation can be found in U.S. Pat. Nos. 3,585,185;
3,639,541; and 3,639,542. As is clear from the above, the particular
polyol ingredient employed in the preparation of the quasi-prepolymer is
not a critical aspect of the present invention. Any compound containing at
least two reactive hydrogen atoms may be so used. Particularly preferred
compounds are those having an equivalent weight between 100 and 400.
As mentioned above, the process of the subject invention can also be
carried out by condensing an organic polyisocyanate in the presence of a
polyol. Any of the organic compounds containing at least two active
hydrogen-containing groups reactive with an isocyanate group described
above in connection with the preparation of the "quasi-prepolymers" may be
employed in the subject invention. Generally, the amount of polyol
employed will be from about 0.1 to 0.8 equivalent, preferably from 0.1 to
0.6 equivalent per equivalent of polyisocyanate, resulting in an NCO/OH
equivalent ratio of from about 3:1 to 50:1 or greater.
When a polyol is employed in the process of the subject invention, a
urethane catalyst may also be employed. Urethane catalysts which may be
employed are well known in the art and include the metal or organometallic
salts of carboxylic acid and tertiary amines. Representative of such
compounds are: dibutyltin dilaurate, dibutyltin diacetate, stannous
octoate, lead octoate, cobalt naphthenate, and other metal or
organometallic salts of carboxylic acids in which the metal is bismuth,
titanium, iron, antimony, uranium, cadmium, aluminum, mercury, zinc, or
nickel as well as other organometallic compounds such as are disclosed in
U.S. Pat. No. 2,846,408. Tertiary amines such as triethylenediamine,
triethylamine, diethylcyclohexylamine, dimethylethanolamine,
methylmorpholine, trimethylpiperazine, N-ethylmorpholine and
diethylethanolamine may also be employed as well as mixtures of any of the
above. The preferred urethane-promoting catalyst is dibutyltin diacetate.
Generally, the amount of the urethane-promoting catalyst employed will be
from 0.01 part to 10 parts by weight per 100 parts by weight of
polyisocyanate.
As mentioned above, the crux of the subject invention resides in the use of
alumina trihydrate as flame retardant agent. The alumina trihydrate is
employed in an amount within the range of 20 parts by weight to about 100
parts by weight per 100 parts by weight of organic polyisocyanate. The
alumina trihydrate is generally available as a free-flowing powder and may
be introduced into the foam reaction mixture by admixing it with the
polyol or polyisocyanate component.
Compounds which promote carbodiimide linkages which are employed in the
subject invention include aliphatic alcohols such as methyl alcohol and
furfuryl alcohol; amino alcohols having a molecular weight of from 89 to
304 such as N,N-dialkylaminoalkanols, triethanolamine,
N-2-hydroxyethylmorpholine and N,N,N',N'-tetrakis(2-hydroxypropyl)ethylene
diamine and s-triazine compounds such as
2,4,6-tris(diethanolamino)-s-triazine,
2,4,6-tris(diisopropanolamino)-s-triazine,
2,4,6-tris(N-methylethanolamino)-s-triazine, and unsymmetrically
substituted triazines of the formula:
##STR1##
wherein R is hydrogen or lower alkyl of from 1 to 10 carbon atoms, R.sup.1
is CR.sub.2 CR.sub.2 OH or lower alkyl of from 1 to 12 carbon atoms, X is
NR.sub.2, alkoxy of from 1 to 12 carbon atoms, phenoxy, alkyl of from 1 to
12 carbon atoms, phenyl, hydroxyl, halogen aziridyl, pyrrolidyl,
piperidyl, or N-alkylpiperazyl. Since the triazines are unsymmetrically
substituted, it is apparent that each X cannot concurrently be
##STR2##
wherein each R and R.sup.1 is the same. Generally from about 0.1 part to
10 parts by weight of carbodiimide-promoting compound per 100 parts by
weight of polyisocyanate will be employed in the subject invention.
Trimerization catalysts which are employed in the present invention include
1,3,5-tris(N,N-dialkylaminoalkyl)-s-hexahydrotriazines; the alkylene oxide
and water adducts of
1,3,5-tris(N,N-dialkylaminoalkyl)-s-hexahydrotriazines; triazines;
2,4,6-tris(dimethylaminomethyl)phenol; o-, p- or a mixture of o- and
p-dimethylaminomethylphenol and triethylene diamine or the alkylene oxide
and water adducts thereof, alkali metal carboxylates, alkali metal
alkoxides, and organic boron-containing compounds. These compounds are
well known in the art, as is their use as catalysts which promote
isocyanurate linkages.
1,3,5-Tris(N,N-dialkylaminoalkyl)-s-hexahydro-triazine compounds have
heretofore been described as useful isocyanate trimerization catalysts.
See U.S. Pat. No. 3,723,366, the disclosure of which is hereby
incorporated by reference. Preferred within this group of
hexahydrotriazine compounds is
1,3,5-tris(N,N-dimethylaminopropyl)-s-hexahydrotriazine.
The alkylene oxide and water adducts of a
1,3,5-tris(N,N-dialkylaminoalkyl)-s-hexahydrotriazine are presumably
quaternary ammonium hydroxides. These compounds are generally prepared by
reacting equimolar amounts of the hexahydrotriazine, alkylene oxide and
water at a temperature of from about 10.degree. C. to 80.degree. C. for a
period of from about five minutes to two hours. Preferred within this
group of compounds is the propylene oxide and water adduct of
1,3,5-tris(N,N-dimethylaminopropyl)-s-hexahydrotriazine. See U.S. Pat.
Nos. 3,746,709 and 3,766,103, the disclosures of which are hereby
incorporated by reference.
2,4,6-Tris(dimethylaminomethyl)phenol as well as o-, p- and a mixture of o-
and p-(dimethylaminomethyl)-phenol are known compounds which are
commercially available products sold by Rohm & Haas under the trade names
DMP-30 and DMP-10. Triethylenediamine and the alkylene oxide and water
adducts thereof are also well known. The amount of trimerization catalyst
which may be employed in the present invention is generally from 0.1 part
to 20 parts by weight of catalyst per 100 parts by weight of
polyisocyanate.
The foams of the present invention are prepared by mixing together the
organic polyisocyanate, the polyol or the quasi-prepolymer, a blowing
agent, alumina trihydrate and the catalysts at an initiating temperature
which, depending on the catalyst, will range from about 0.degree. C. to
50.degree. C. The present invention also contemplates the incorporation of
additional ingredients in the foam formulation to tailor the properties
thereof. Thus, plasticizers, surfactants, such as the silicone
surfactants, e.g. alkylpolysiloxanes, may be employed in the invention.
Also, inorganic fillers, pigments and the like can be used.
In any event, the foams prepared in accordance herewith are rigid cellular
products having a density of from about one pound to forty pounds per
cubic foot which exhibit excellent strength and flame properties, such as
fire resistance, low smoke evolution, and excellent weight retention.
Following are specific, non-limiting examples which are provided to
illustrate the enumerated principles described herein. All parts are by
weight unless otherwise indicated. In the Examples which follow, the
following abbreviations are employed:
Cmdi--crude diphenylmethane diisocyanate.
Tdh--1,3,5-tris(N,N-dimethylaminopropyl)-s-hexahydrotriazine
Dc-193--polyalkylsiloxane-polyoxyalkylene copolymer, a foam stabilizer
F-11b--trichlorofluoromethane
Fa--furfuryl alcohol
Ma--methyl alcohol
Ath--alumina trihydrate
Dbtda--dibutyltin diacetate
Polyol A--a polyol prepared by the reaction of ethylene oxide with
trimethylolpropane, said polyol having an equivalent weight of 250
Polyol B--a polyol prepared by the reaction of ethylene oxide with ethylene
glycol, said polyol having an equivalent weight of 200
In addition, the physical properties of the foams were determined in
accordance with the following test methods:
Density--ASTM D -1622-63
Compression strength--ASTM D -1621-3
Tumbling friability--ASTM C - 421
Flame retardancy--ASTM D - 3014
Smoke density--NBS smoke density test
Also, the presence of carbodiimide, isocyanurate and urethane linkages in
the foams was confined by infrared spectroscopic analyses.
EXAMPLE I
Three foams were prepared by mixing in a vessel at high speed a stream of
an organic polyisocyanate, a fluorocarbon blowing agent and alumina
trihydrate and a stream containing a blend of polyol, catalysts and
surfactant. Thereafter the resulting mixture was cast in a mold and the
mixture was allowed to foam. The ingredients employed, amounts thereof and
physical properties of the foams are presented in Table I, below.
As indicated by the data in the Table, the flame retardant properties of
foams B and C (those of the present invention) as measured by Butler
Chimney Test improved with added alumina trihydrate. The weight retention
increased and there was a significant decrease in flame height. Moreover,
a loss in closed cell content, a common occurrence associated with the use
of inorganic fillers, was not obtained.
TABLE I
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Foam A B C
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CMDI 100 100 100
F-11B 17 25 26
DC-193 1 1 1
Polyol B 40 40 40
FA 3 3 3
DBTDA 1 0.5 0.5
TDH 3 3 3
ATH 0 25 50
Density, pcf. 2.1 2.0 2.1
Closed cells, corr. %
94 98 102
Compressive strength, psi.
10% defl. 19 17 13
Tumbling friability, % wt.
loss 5 18 19
Butler Chimney Test
wt. ret. % 88 93 92
flame height, in.
10 6 5
time to SX, sec. 12 10 10
NBS Smoke Density, D.sub.m
49 61 66
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EXAMPLES II-XIII
A series of foams was prepared by mixing in a vessel at high speed a stream
of polyisocyanate, alumina trihydrate and blowing agent, and a stream
containing a polyol, catalysts, and surfactant. Thereafter the resulting
mixture was cast in a mold and the foams were allowed to "free rise". The
ingredients employed, amounts thereof and physical properties of the
resulting foams are presented in Table II, below.
TABLE II
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Example: II III IV V VI VII VIII
IX X XI XII XIII
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CMDI 300 300 300 300 300 300 300 300 300 300 300 300
F-11B 50 60 66 78 50 69 75 78 52 66 66 75
ATH -- 60 90 150 -- 60 90 150 -- 60 90 150
FA 9 9 9 9 9 9 9 9 9 9 9 9
DBTDA 3 3 1.5 1.5 3 1.5 1.5 1.5 3 1.5 1.5 1.5
TDH 9 9 9 9 9 9 9 9 9 9 9 9
Polyol B 90 90 90 90 120 120 120 120 150 150 150 150
DC-193 3 3 3 3 3 3 3 3 3 3 3 3
NCO/OH Equivalent Ratio
5.0 5.0 5.0 5.0 3.8 3.8 3.8 3.8 3.0 3.0 3.0 3.0
Density, pcf. 2.0 2.1 2.0 2.1 2.1 2.0 1.9 2.1 2.2 2.1 2.1 2.3
Closed cells, corr. %
95 98 100 99 94 98 99 102 91 95 100 101
Compressive strength,
psi., 10% defl.
20 26 16 16 19 11 15 13 11 14 15 16
Tumbling friability,
% wt. loss 8 29 27 43 5 24 24 19 1 9 11 18
Butler Chimney Test
wt. ret., % 92 94 94 94 88 88 90 92 67 86 85 87
flame height, in.
8 6 7 3 10 10 8 5 10 10 10 8
time to SX, sec.
11 10 10 10 12 10 10 10 23 13 13 10
NBS Smoke Density, D.sub.m
-- -- -- -- 49 46 41 66 -- -- -- --
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EXAMPLES XIV-XXII
A series of foams was prepared in the manner described in Example I. The
ingredients employed, amounts thereof as well as the physical properties
of the resulting foams are presented in Table III, below. In all of the
Examples that follow an NCO/OH equivalent ratio of 9.4:1 was employed.
TABLE III
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Example: XIV XV XVI XVII
XVIII
XIX XX XXI XXII
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CMDI 300 300 300 300 300 300 300 300 300
F-11B 55 67 67 67 67 67 61 58 58
FA 3 3 3 3 3 3 9 9 9
DC-193 3 3 3 3 3 3 3 3 3
TDH 9 9 9 9 9 9 9 9 9
DBTDA 0.9 0.9 0.9 0.9 0.9 0.9 3 3 3
Polyol A 60 60 60 60 60 60 60 60 60
ATH -- 45 60 75 90 150 45 60 75
Density, pcf.
2.0 1.9 2.0 1.9 2.1 2.4 1.9 2.1 2.3
Closed cells, corr. %
96 103 97 98 97 98 100 97 99
Compressive, strength,
psi., 10% defl.
24 16 15 15 17 17 18 21 20
Tumbling friability,
% wt. loss 24 40 38 52 49 53 27 25 28
Butler Chimney Test
wt. retained, %
90 92 94 93 93 95 94 94 93
flame height, in.
6 5 4 4 4 4 5 5 5
time to SX, sec.
10 10 10 10 10 10 10 10 10
NBS Smoke Density, D.sub.m
125 90 69 97 100 -- -- 101 --
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