Process for producing modified polyisocyanurate foams

A modified polyisocyanurate foam is produced by reacting an organic polyisocyanate, a polyol and water in the presence of three catalyst, i.e. two particular trimerization catalysts and a carbodiimidation catalyst. There can be produced, without using any evaporating type blowing agent, a modified polyisocyanurate foam which is suitably used for continuous production of laminate boards, siding boards, insulation boards, etc.

This invention relates to a process for producing a modified 
polyisocyanurate foam and, more particularly, to a process for producing a 
modified polyisocyanurate foam suitable for continuous production of 
laminate boards, insulation boards and the like which process does not 
involve the use of evaporating type blowing agent such as CFC, HCFC, HFC, 
pentane and methylene chloride. 
It is known to produce a modified polyisocyanurate foam by reacting an 
organic polyisocyanate and a polyol in the presence of a blowing agent and 
using an trimerization catalyst and a carbodiimidation catalyst in 
combination (cf., for example, U.S. Pat. No. 3,657,161). It has also been 
proposed to produce a modified polyisocyanurate foam by reacting an 
organic polyisocyanate and a polyol in the presence of a blowing agent and 
using methanol, furfuryl alcohol or phosphorene oxide (carbodiimidation 
catalyst) and an alkali metal salt (trimerization catalyst) in combination 
(U.S. Pat. No. 4,166,164, and European Patent No. 381,324). U.S. Pat. No. 
3,887,501, U.S. Pat. No. 3,928,256, U.S. Pat. No. 3,998,776, U.S. Pat. No. 
3,994,837, U.S. Pat. No. 3,981,829, U.S. Pat. No. 3,994,839 and so on have 
reported a process for producing modified polyisocyanurate foam using a 
tertiary amine and an alcohol such as an amino alcohol as cocatalysts, a 
process in which a Mannich polyol, a phosphorus containing polyol or the 
like is used catalytically, a method in which s-triazine and phenol are 
used. 
For producing these (modified) polyisocyanurate foams, it is a general 
measure to use flon as a blowing agent. However, the use of CFCs has a 
problem of breaking the ozone layer, and in near future the use of CFC and 
HCFC will be prohibited completely. While there is a possibility to use 
carbon dioxide gas generated by the reaction between water and isocyanate 
as a substitute for CFC, this is disadvatageous since increase in the 
amount of water with view to making low density foam leads to increase in 
the amount of urea bonds generated (--NCO+H.sub.2 O.fwdarw.--NH.sub.2 
+CO.sub.2 .Arrow-up bold., --NH.sub.2 +OCN--.fwdarw.--NHCONH--), and 
therefore there arises a problem of giving only those foams that have low 
strength, deteriorated dimensional stability, and poor adherability with 
surface materials. Also, in the above-described conventional method using 
an trimerization catalyst and a carbodiimidation catalyst in combination, 
it is difficult to control the reaction when water is used as a blowing 
agent, and in particular, it is impossible to produce, at economically 
acceptable speeds, a low density rigid foam which has a free rise density 
of not more than 40 kg/m.sup.3 and a density when molded, of not more than 
60 kg/m.sup.3, required for laminate boards or insulation boards. 
The present inventors made a study on a process which can industrially 
produce, from an organic polyisocyanate and a polyol without using any 
evaporating type blowing agent typified by CFCs, a modified 
polyisocyanurate foam of low density having a free rise density of not 
more than 40 kg/m.sup.3 and a density when molded into a board (said 
density is hereinafter referred to as "density when molded into a board of 
22 mm thickness"), of not more than 60 kg/m.sup.3. As a result, it was 
found that by using a combination of two particular trimerization 
catalysts and a carbodiimidation catalyst together with water, a 
trimerization reaction of polyisocyanate, a carbodiimidation reaction of 
polyisocyanate, a reaction of polyisocyanate and water, etc. proceed 
quickly at a favorable balance, whereby a modified polyisocyanurate foam 
of low density having a free rise density of not more than 40 kg/m.sup.3, 
preferably 20-40 kg/m.sup.3 and a density when molded into a board, of not 
more than 60 kg/m.sup.3, preferably 30-50 kg/m.sup.3 can be obtained in a 
short time without using any evaporating type blowing agent such as CFC or 
the like. The finding has led to the completion of the present invention. 
According to the present invention, there is provided a process for 
producing a modified polyisocyanurate foam, which process comprises 
reacting an organic polyisocyanate, a polyol and water in the presence of: 
(a) a trimerization catalyst selected from a hydroxyalkyl quaternary 
ammonium compound represented by formula (I) 
##STR1## 
wherein R.sub.1, R.sub.2 and R.sub.3 are each a substituted or 
unsubstituted alkyl group, and R.sub.4 and R.sub.5 are each a hydrogen 
atom or a substituted or unsubstituted alkyl group, and an alkali metal 
salt of a C.sub.1-8 aliphatic monocarboxylic acid, represented by formula 
(II) 
EQU R.sub.6 --COOM (II) 
wherein R.sub.6 is a hydrogen atom or a substituted or unsubstituted 
C.sub.1-7 aliphatic hydrocarbon group, and M is an alkali metal, 
(b) a trimerization catalyst selected from the compounds of formulas (III), 
(IV), (V) and (VI) 
##STR2## 
and (c) a carbodiimidation catalyst selected from phosphorene oxides 
represented by formulas (VII) and (VIII) 
##STR3## 
wherein R.sub.7 is a substituted or unsubstituted alkyl, phenyl, naphthyl 
or benzyl group, and R.sub.8, R.sub.9, R.sub.10, R.sub.11, R.sub.12 and 
R.sub.13 are each a hydrogen atom, a chlorine atom or a C.sub.1-4 alkyl 
group. 
Hereinafter, this invention will be described in more detail. 
The organic polyisocyanates used in the process of this invention as 
starting materials may be any of aliphatic, alicyclic, and aromatic types, 
and mixtures of these. Those conventionally used in the production of 
polyurethanes and polyisocyanurates can be used similarly. To be specific, 
suitable examples thereof include aromatic diisocyanates such as 
2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, crude tolylene 
diisocyanate, diphenylmethane diisocyanate, and crude diphenylmethane 
diisocyanate; aromatic triisocyanates such as 4,4', 4"-triphenylmethane 
triisocyanate, and 2,4,6-tolylene triisocyanate; aromatic tetraisocyanates 
such as 4,4'-dimethyldiphenylmethane-2,2', 5,5'-tetraiisocyanate, 
aliphatic isocyanates such as hexamethylene-1,6-diisocyanate; alicyclic 
isocyanates such as hydrogenated diphenylmethane diisocyanate; and other 
diisocyanates such as m-phenylene diisocyanate, 
naphthylene-1,5-diisocyanate, 1,-methoxyphenyl-2,4-diisocyanate, 
4,4'-biphenyl diisocyanate, 3,3'-dimethoxy-4,4'-biphenyl diisocyanate, and 
3,3'-dimethyldiphenylmethane-4,4'-diisocyanate. Among them, preferred are 
2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, crude tolylene 
diisocyanate, diphenylmethane diisocyanate, crude diphenylmethane 
diisocyanate, hexamethylene-1,6-diisocyanate, hydrogenated diphenylmethane 
diisocyanate, etc. The above-described organic polyisocyanates may be used 
singly or two or more of them may be combined. 
The polyols include aliphatic, saccharide, aromatic compounds having two or 
more hydroxyl groups in the molecule, and mixtures thereof, such as 
polyether polyols, polyester polyols, and castor oil. Those conventionally 
used in the production of polyurethanes can also be used similarly. Those 
polyols may be of either lower molecular weight or high molecular weight. 
Specific examples thereof include, as polyether polyols, those compounds 
having structures of active hydrogen-containing compounds such as 
polyhydric alcohols, polyhydric phenols, amines, or polycarboxylic acids 
to which alkylene oxides are added. As the polyhydric alcohols, there can 
be cited, for example, dihydric alcohols such as ethylene glycol, 
propylene glycol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, and 
neopentyl glycol; trihydric or higher polyhydric alcohols such as 
pentaerythritol, and surcrose. As the polyhydric phenols, there can be 
cited, for example, polyhydric phenols such as pyrogallol, and 
hydroquinone; bisphenols such as bisphenol A; condensates of phenol and 
formaldehyde; and so on. As the amines, there can be cited, for example, 
ammonia, alkanolamines such as mono-, di- and triethanolamines, 
isopropanolamine, and aminoethylethanolamine; C.sub.1 -C.sub.22 
alkylamines, C.sub.2 -C.sub.6 alkylenediamines, polyalkylenepolyamines, 
aromatic amines such as aniline, phenylenediamine, diaminotoluene, 
xylenediamine, methylenedianiline, and diphenyletherdiamine, alicyclic 
amines such as isophoronediamine, and cyclohexylenediamine, heterocyclic 
amines, and so on. As the polycarboxcylic acids, there can be cited, for 
example, aliphatic polycarboxylic acids such as succinic acid, adipic 
acid, sebacic acid, maleic acid, and dimeric acid, aromatic polycarboxylic 
acids such as phthalic acid, terephthalic acid, trimellitic acid, and 
pyromelitic acid, etc. These active hydrogen-containing compounds may also 
be used as a mixture of two or more of them. As the alkylene oxides to be 
added to the active hydrogen-containing compounds, there can be cited, for 
example, propylene oxide, ethylene oxide, butylene oxide, tetrahydrofuran, 
etc. These alkylene oxides may be used singly or two or more of them may 
be used in combination. In the latter case, there may be blocked adducts 
or randomly added products. As the polyester polyols, there can be cited, 
for example, condensed polyester polyols obtained by the reaction between 
polyhydric alcohols (the aforementioned alcohols, trimethylolpropane, 
glycerol, etc.) and carboxylic acids (the aforementioned polycarboxylic 
acids, etc.), polyester polyols obtained by ring opening polymerization 
lactone, scrap PET to which ethylene oxide adduct of nonylphenol is added, 
and the like. Among them, aliphatic, aromatic, aliphatic or aromatic 
amine, pentaerythritol, or sucrose based polyether polyols; aromatic or 
aliphatic carboxylic acid polyester polyols; lactone polyester polyols; 
etc. are particularly preferred. The aforementioned polyols may be used 
singly or two or more of them may be used in combination. 
The aforementioned polyols may have a hydroxyl number within the range of 
generally 20 to 600 mgKOH/g, preferably 25 to 500 mgKOH/g, more preferably 
50 to 400 mgKOH/g. 
According to the process of this invention, polyisocyanurate foams can be 
generated by the reaction of the aforementioned organic polyisocyanate 
with the aforementioned polyol together with water as a blowing agent. To 
perform the reaction, compounding proportions of the organic 
polyisocyanate, the polyol and water are not limited strictly, and may 
vary widely depending on desired physical properties and uses of final 
products of modified polyisocyanurate foams. Generally, it is preferred to 
react the aforementioned components after blending them such that 
isocyanate index expressed as NCO/OH equivalent ratio can become within 
the range of not below 1.8, preferably from 1.8 to 5, more preferably 2 to 
4. 
The amount of water to be used as a blowing agent can be controlled 
depending on the density and the like desired for final products of the 
modified polyisocyanurate foam. In particular, the process of this 
invention has a feature that a low density rigid foam can be produced by 
using only water and without using volatile blowing agents. According to 
the process of this invention, addition of water in amounts within the 
range of, for example, 0.3 to 1.8% by weight, preferably 0.8 to 1.5% by 
weight, based on the total weight of organic polyisocyanate, polyol and 
water enables production of a low density foam having a free rise density 
of generally not more than 40 kg/m.sup.3, preferably 20-30 kg/m.sup.3 and 
a density when molded into a board of 22 mm thickness, of generally not 
more than 60 kg/m.sup.3, preferably 30-50 kg/m.sup.3, with ease without 
using any volatile blowing agent. 
The present process is characterized in that the reaction for producing a 
modified polyisocyanurate foam from the above-mentioned polyisocyanate, 
the above-mentioned polyol and water is carried out in the presence of the 
following catalysts: 
(a) a trimerization catalyst selected from a hydroxyalkyl quaternary 
ammonium compound represented by formula (I) 
##STR4## 
wherein R.sub.1, R.sub.2 and R.sub.3 are each a substituted or 
unsubstituted alkyl group, and R.sub.4 and R.sub.5 are each a hydrogen 
atom or a substituted or unsubstituted alkyl group, and an alkali metal 
salt of a C.sub.1-8 aliphatic monocarboxylic acid, represented by formula 
(II) 
EQU R.sub.6 --COOM (II) 
wherein R.sub.6 is a hydrogen atom or a substituted or unsubstituted 
C.sub.1-7 aliphatic hydrocarbon group, and M is an alkali metal, 
(b) a trimerization catalyst selected from the compounds of formulas (III), 
(IV), (V) and (VI) 
##STR5## 
and (c) a carbodiimidation catalyst selected from phosphorene oxides 
represented by formulas (VII) and (VIII) 
##STR6## 
wherein R.sub.7 is a substituted or unsubstituted alkyl, phenyl, naphthyl 
or benzyl group, and R.sub.8, R.sub.9, R.sub.10, R.sub.11, R.sub.12 and 
R.sub.13 are each a hydrogen atom, a chlorine atom or a C.sub.1-4 alkyl 
group. 
These catalysts are described in more detail below. 
Trimerization Catalyst (a) 
In formula (I), "alkyl group" may be any of straight chain or branched 
chain type, and can be exemplified by methyl, ethyl, n-propyl, isopropyl, 
n-butyl, tert-butyl, n-pentyl, isoamyl, n-hexyl, n-heptyl, 1-ethylpentyl, 
n-octyl and 2-ethylhexyl. Each of the alkyl groups represented by R.sub.1 
-R.sub.3 is preferably a lower alkyl group of six or less carbon atoms, 
preferably four or less carbon atoms. Each of the alkyl groups represented 
by R.sub.4 and R.sub.5 may be not only a lower alkyl group but also a 
higher alkyl group of up to 18 carbon atoms. 
The hydroxyalkyl quaternary ammonium compound of formula (I), used as the 
trimerization catalyst (a) in the present process is known per se as a 
catalyst used in production of polyurethane, polyisocyanurate, 
polyurethane-polyisocyanurate resin, etc. (U.S. Pat. No. 4,040,992). 
Specific examples thereof include the followings: 
##STR7## 
Of these hydroxyalkyl quaternary ammonium compounds, the compounds 1 and 2 
are used preferably. 
The alkali metal salt of a C.sub.1-8 aliphatic monocarboxylic acid, of 
formula (II) also used as the trimerization catalyst (a) is known per se 
as a catalyst used in production of polyurethane, polyisocyanurate, 
polyurethane-polyisocyanurate resin, etc. Specific examples thereof 
include the followings: 
______________________________________ 
(1) Potassium acetate 
CH.sub.3 COOK 
(2) Potassium 2-ethylhexanoate 
##STR8## 
(3) Potassium propionate 
CH.sub.3 CH.sub.2 COOK 
(4) Potassium formate 
HCOOK 
(5) Potassium isobutyrate 
(CH.sub.3).sub.2 CHCOOK 
(6) Potassium methacrylate 
##STR9## 
(7) Potassium surbate 
CH.sub.3 CHCHCHCHCOOK 
(8) Sodium acetate CH.sub.3 COONa 
(9) Sodium 2-ethylhexanoate 
##STR10## 
(10) Sodium propionate 
CH.sub.3 CH.sub.2 COONa 
(11) Sodium butyrate CH.sub.3 CH.sub.2 CH.sub.2 COONa 
(12) Sodium formate HCOONa 
(13) Sodium caprylate CH.sub.3 (CH.sub.2).sub.6 COONa 
______________________________________ 
Of these alkali metal salts of C.sub.1-8 aliphatic monocarboxylic acids, 
the compounds (1) and (2) are used preferably. 
Trimerization Catalyst (b) 
Salts of 1,8-diaza-bicyclo[5.4.0]undecene-7 (hereafter abbrebiated as DBU) 
represented by the above formula (III) are known per se as a catalyst for 
preparation of polyurethane, polyisocyanurate and 
polyurehtanepolyisocyanurate resins, etc. (refer to Japanese Patent 
Publication No. 37503/1971 and Japanese Patent Publication No. 
25017/1971), and can be obtained by reaction of DBU with acids such as 
phenols or fatty acids. 
As phenols usable for formation of these salts, there can, for example, be 
mentioned monohydric phenols such as phenol, cresols, xylenols, naphthols, 
trimethylphenols, tetramethylphenols, pentamethylphenols, ethylphenols, n- 
and iso-propylphenols, n- and iso-butylphenols, clclohexylphenols, n- and 
iso-amylphenols, iso-octylphenols, iso-nonylphenols, iso-dodecylphenols, 
di- and poly-substituted phenols (for example, thymol, carbacrol, 
di-iso-alkylphenols) and methoxylphenols (e.g., eugenol, guaiacol); 
dihydric phenols such as catechols, resorcinols, hydroqinones and 
bisphenols; and polyhydric phenols such as pyrogallol and phyloroglucinol. 
Further, as fatty acids, there can, for example, be mentioned saturated 
fatty acids such as formic acid, acetic acid, propionic acid, butyric 
acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic 
acid, capric acid, undecylic acid, lauric acid, tridecyl acid, myristic 
acid, pentadecylic acid, palmitic acid, heptadecylic acid and stearic 
acid; unsaturated fatty acids such as acrylic acid, crotonic acid, 
iocrotonic acid, undecylenic acid, oleic acid, elaidic acid, cetoleic 
acid, erucic acid, brassidic acid, sorbic acid, linolic acid, linolenic 
acid, arachidonic acid, propiolic acid and stearolic acid; isoalkyl fatty 
acids such as 2-ethylhexanoic acid; oxyfatty acids such as lactic acid, 
glycolic acid, ricinolic acid and oxystearic acid. In addition, it is also 
possible to use weak acids such as, for example, benzoic acid, salicylic 
acid, enolic acid (e.g., barbituric acid), carbonic acid and phosphoric 
acid. Particularly preferably used among these acids are phenol, 
2-ethylhexanoic acid, oleic acid, formic acid, etc. 
Any of the compounds (IV), (V) and (VI) each used as the trimerization 
catalyst (b) is known per se as a catalyst used in production of 
polyurethane, polyisocyanurate, polyurethane-polyisocyanurate resin, etc. 
Incidentally, the trimerization catalyst (a) used in the present process 
generally has a degree of trimerization of more than 15%, and the 
trimerization catalyst (b) generally has a trimerization ratio of not more 
than 15%. Herein, the degree of trimerization is a value measured by the 
method of C. M. Bartish et al. [SPI Summary, pp. 157-162 (1989)]. 
Carbodiimidation Catalyst (c) 
On the other hand, as for the compounds represented by the formula (VII) or 
(VIII) used in combination with the aforementioned trimerization catalysts 
(a) and (b), the alkyl group represented by R.sub.7 may be either straight 
chain or branched chain, or partially substituted with halogen or other 
functional groups. Examples of such an alkyl group include methyl, ethyl, 
propyl, isopropyl, n-butyl, tert-butyl, 2-phenylethyl, 2-chloroethyl, 
2-methoxyethyl, etc. groups. The substituted or unsubstituted phenyl, 
naphthyl and benzyl group include benzyl, phenyl, o-, p- or m-tolyl, 
xylyl, naphthyl, 4-diphenyl, o-, p- or m-chlorphenyl, etc. R.sub.7 may 
preferably be a C.sub.1 -C.sub.4 alkyl group, a phenyl group, or a benzyl 
group. The groups represented R.sub.8 -R.sub.13 of formula (VII) or (VIII) 
include hydrogen, chlorine, methyl, ethyl, propyl, isopropyl, butyl, etc., 
preferably hydrogen and methyl. 
Specific examples of phosphorene oxide represented by formula (VII) or 
(VIII) include the following: 1-methylphosphorene oxide, 
3-methyl-1-phenylphosphorene oxide, 3-methyl-1-benzyl-phosphorene oxide, 
3-methyl-1-ethylphosphorene oxide, 3-methyl-1-ethylphenylphosphorene 
oxide, 1-phenyl-3-(4-methyl-3-pentenyl)phosphorene oxide, 
1-phenyl-3-chlorophosphorene oxide, etc. Among these phosphorene oxides, 
especially 3-methyl-1-phenylphosphorene oxide, 
3-methyl-1-phenyl-2-phosphorene oxide and 3-methyl-1-phenyl-3-phosphorene 
oxide are used suitably. These phosphorene oxides are known per se as a 
catalyst for accelerating the reaction for producing carbodiimide linkage 
form organic isocyanates (cf., for example, U.S. Pat. No. 3,657,161). 
Production of Modified Polyisocyanurate Foam 
The present invention is characterized in that in producing a modified 
polyisocyanurate foam from an organic polyisocyanate, a polyol and water, 
there is used, as a catalyst, a combination of the three catalysts, i.e. 
the trimerization catalyst (a), the trimerization catalyst (b) and the 
carbodiimidation catalyst (c). By using a combination of the three 
catalysts, it has been made possible to industrially produce a modified 
polyisocyanurate foam of low density without using any evaporating type 
blowing agent such as CFC or the like which has problems. 
The amounts of the trimerization catalyst (a), the trimerization catalyst 
(b) and the carbodiimidation catalyst (c) used are not strictly restricted 
and can be varied depending upon the reaction conditions used, etc. 
However, the preferable amount of the trimerization catalyst (a) is 
generally 0.1-10% by weight, particularly 0.5-5% by weight based on the 
weight of the organic polyisocyanate; the preferable amount of the 
trimerization catalyst (b) is generally 0.1-5% by weight, particularly 
0.5-3% by weight on the same basis; and the appropriate amount of the 
carbodiimidation catalyst (c) is generally 0.05-5% by weight, particularly 
0.1-2% by weight on the same basis. 
The relative proportions of the trimerization catalyst (a) and the 
trimerization catalyst (b) and the relative proportions of [the 
trimerization catalyst (a)+the trimerization catalyst (b)] and the 
carbodiimidation catalyst (c) can be varied in a wide range,depending upon 
the desired properties of final product, etc. However, the preferable 
weight ratio of [the trimerization catalyst (a)]/[the trimerization 
catalyst (b)] is generally 0.3/1 to 20/1, particularly 1/1 to 15/1. When 
the ratio is smaller than 0.3/1, the resulting foam has low curing, which 
adversely affects the production of boards; further, the resulting foam 
has a low trimerization ratio and consequently low flame retardancy. When 
the ratio is larger than 20/1, it is difficult to control the reaction and 
the resulting foam has inferior flowability. Specifically, the resulting 
foam has a high overpack ratio (50% or higher) [the overpack ratio 
indicates the proportions of a free rise density and a density when molded 
into a board and is defined by (density when molded into board/free rise 
density--1).times.100] and has deteriorated properties in dimensional 
stability, etc. 
The desirable weight ratio of [the trimerization catalyst (a)+trimerization 
catalyst (b)]/[the carbodiimidation catalyst (c)] is generally 1/1 to 
25/1, particularly 2/1 to 15/1. When the ratio is smaller than 1/1, the 
resulting foam has a high overpack ratio. When the ratio is larger than 
25/1, it is difficult to obtain a foam of low density. The overpack ratio 
is preferably 15-50%, particularly preferably 20-35%. 
In the process of this invention, there can be used various additives in 
combination in amounts usually used. Such additives include, for example, 
urethanation catalysts (for example, triethylenediamine, 
dimethylethanolamine, triethylamine, trimethylaminoethylethanolamine, 
dimethylaminoethylether, pentamethyldiethylenetriaime, 
N-methyl-morpholine, dibutyltin dilaurate, tin octanoate, lead octanoate, 
etc.), surfactants (for example, dimethylsiloxane/polyether block 
copolymer, etc.), crosslinking and chain extender agent (for example, 
ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, 
diethylene glycol, triethanolamine, diethanolamine, ethylenediamine, 
toluenediamine, etc.), flame retardants (for example, triphenyl phosphate, 
triethyl phosphate, trimethyl phosphate, cresyldiphenyl phosphate, 
tris(cresyl) phosphate, tris(chloroethyl) phosphate, tris(dichloropropyl) 
phosphate, tris(.beta.-chloropropyl) phosphate, tris(.beta.-chloroethyl) 
phosphate, tris(2,3-dibromopropyl) phosphate, tris(bromocresyl) phosphate, 
melamine, antimony triolxide, etc.), colorants, etc. 
As the process for producing modified polyisocyanurate foams from the 
components described above, there can be cited, for example, a process in 
which first there are provided an isocyanate component composed of the 
aforementioned organic polyisocyanate or an isocyanate-terminated 
prepolymer component obtained by reacting an organic polyisocyanate with a 
polyol, and a polyol component composed of the above-described polyol, 
water, trimerization catalysts (a) and (b), and carbodiimidation catalyst, 
and optionally one or more of the urethanation catalyst, surfactant, 
crosslinking agent, flame retardant, colorant and other additives, and 
then upon use, the both components are put together, rapidly stirred and 
mixed. The resulting mixture is foamed and cured. 
It is sufficient to set the reaction temperature at room temperature. In 
some cases, the reaction temperature may be elevated up to a temperature 
of about 90.degree. C.