Aqueous compositions containing an at least partially blocked polyisocyanates and a trimerization catalyst and coatings and binders prepared therefrom

The present invention relates to an aqueous composition containing PA1 a) an at least partially blocked, aqueously dispersed polyisocyanate PA2 i) having an isocyanate content prior to blocking of at least 12% by weight, based on the weight of the unblocked polyisocyanate and PA2 ii) containing at least 2 equivalent percent, based on the total equivalents of isocyanate groups, of blocked isocyanate groups, and PA1 b) a trimerization catalyst. The present invention also relates to coatings or binders prepared by heating the aqueous compositions to evaporate water and initiate trimerization.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention is directed to aqueous compositions containing an at 
least partially blocked, water dispersible polyisocyanate and a 
trimerization catalyst and to coatings or binders prepared by heating 
these compositions to evaporate water and initiate trimerization. 
2. Description of the Prior Art 
It is known from U.S. Pat. No. 4,904,522 to use aqueous dispersions of 
polyisocyanates as binders for fiberglass. When compared to known 
phenol/formaldehyde resins, the polyisocyanate binders cure at a much 
lower temperature, do not split off volatile monomers, provide at least 
the same strength, are not a potential formaldehyde source and do not 
require an amino alkoxy silane adhesion promoter. However, the 
polyisocyanate binders disclosed in this patent have relatively high 
quantities of unmodified monomeric diisocyanates. Because the presence of 
monomeric diisocyanates may lead to industrial hygiene problems, it would 
be beneficial to reduce the content of monomeric diisocyanates as much as 
possible. 
Another deficiency of the polyisocyanate binders disclosed in U.S. Pat. No. 
4,904,522 is that it is difficult to achieve complete cure during 
subsequent heating of the fiberglass mats in the oven zone. During the 
production of fiberglass mats, the fibers are treated with the aqueous 
polyisocyanate binders and continuously run through an oven zone in order 
to evaporate water and to cure the polyisocyanate resins. 
When aqueously dispersed polyisocyanates are used as binders, the water 
serves as the co-reactant for the isocyanate groups to form polyureas. If 
the isocyanate content of the polyisocyanate binder is too high, water is 
evaporated in the oven zone before the reaction is complete and as a 
result, an uncured, unusable fiberglass mat is obtained. 
A further disadvantage is that even though the preferred polyisocyanates of 
U.S. Pat. No. 4,904,522, i.e., polyphenyl polymethylene polyisocyanates, 
exhibit a low vapor pressure at ambient temperature, they still contain 
high amounts (as much as 70% by weight) of monomeric diphenyl methane 
diisocyanates. Upon exposure to the high temperatures in the oven zone 
these monomeric diisocyanates can be volatilized which results in high 
concentrations in the exhaust gases. This represents an environmental 
hazard if these exhaust gases escape into the atmosphere of the workplace 
or the air surrounding the manufacturing facility. 
One method for lowering the isocyanate content of the polyisocyanate 
binders would be to react the polyisocyanates with polyols to form 
isocyanate-terminated prepolymers prior to dispersing in water. However, 
this results in products which have high viscosities at the desired low 
isocyanate content, i.e., an isocyanate content of less than 10% by 
weight, based on solids, and thus are too viscous to disperse in water 
even if they have been hydrophilically modified. 
One method of avoiding uncured polyisocyanate binders is to incorporate 
catalysts which promote the isocyanate/water reaction in the aqueously 
dispersed polyisocyanate binders. However, this method also does not 
result in a complete cure of the polyisocyanate prior to evaporation of 
water in the oven zone. 
Accordingly, it is an object of the present invention to provide aqueous 
binders which overcome the deficiencies of the previously described 
binders. It is an additional object to provide aqueous compositions which 
do not require water to cure, but which can be fully cured without giving 
off monomeric diisocyanates. It is an additional object of the present 
invention to provide aqueously dispersed binders that possess excellent 
adhesion, especially to glass fibers. 
Surprisingly, these objects may be achieved in accordance with the present 
invention as described hereinafter. 
SUMMARY OF THE INVENTION 
The present invention relates to an aqueous composition containing an at 
least partially blocked, aqueously dispersed polyisocyanate having an 
isocyanate content of at least 12% by weight, based on the weight of the 
unblocked polyisocyanate, and a trimerization catalyst. 
The present invention also relates to coatings or binders prepared by 
heating the aqueous compositions to evaporate water and initiate 
trimerization. 
DETAILED DESCRIPTION OF THE INVENTION 
Suitable polyisocyanates for use in preparing the polyisocyanates to be 
dispersed in water in accordance with the present invention include the 
known aliphatic, cycloaliphatic, araliphatic, aromatic and heterocyclic 
polyisocyanates. Suitable examples of these polyisocyanates include those 
described by W. Siefken in Justus Liebigs Annalen der Chemie, 562, pages 
75 to 136. Prior to being dispersed in water, the polyisocyanates have an 
isocyanate content of at least about 12%, preferably at least about 15% 
and more preferably at least about 20% by weight, based on the weight of 
the polyisocyanate. Polyisocyanates having a lower isocyanate content and 
prepared, e.g., by reacting a monomeric polyisocyanate with a high 
molecular weight polyol, have sufficiently high viscosities that it is 
difficult to disperse them in water even if they are hydrophilically 
modified. 
Examples of suitable monomeric polyisocyanates include 1,6-hexamethylene 
diisocyanate, 1,12-dodecane diisocyanate, cyclobutane-1,3-diisocyanate, 
cyclohexane-1,3-and/or -1,4-diisocyanate, 
1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl cyclohexane (isophorone 
diisocyanate), 2,4-and/or 2,6-hexahydrotoluylene diisocyanate, 
hexahydro-1,3-and/or -1,4-phenylene diisocyanate, perhydro-2,4'- and/or 
-4,4'-diphehylmethane diisocyanate, 1,3- and/or 1,4-phenylene 
diisocyanate, 2,4- and/or 2,6-toluylene diisocyanate, 
diphenylmethane-2,4'- and/or -4,4'-diisocyanate, 
naphthalene-1,5-diisocyanate, triphenylmethane-4,4', 4"-triisocyanate and 
polyphenyl polymethylene polyisocyanates obtained by phosgenating 
aniline/formaldehyde condensation products. Also suitable are 
polyisocyanates adducts containing urea, biuret, urethane, allophanate, 
uretdione or carbodiimide groups or isocyanurate rings. These adducts may 
be prepared from any known monomeric polyisocyanates, especially those set 
forth above, by known methods. When using low molecular weight, highly 
volatile diisocyanates, it is especially preferred to convert these 
diisocyanates into adducts with lower monomeric diisocyanate contents 
prior to dispersing them in water. It is also possible to use mixtures of 
any of these monomeric polyisocyanates and/or polyisocyanate adducts. 
In general, it is particularly preferred to use readily available 
polyisocyanates such as polyphenyl polymethylene polyisocyanates ("crude 
MDI") and polyisocyanate adducts containing carbodiimide groups, urethane 
groups, allophanate groups, isocyanurate groups, uretdione groups or 
biuret groups, especially those based on 2,4- and/or 2,6-toluylene 
diisocyanate ("TDI"), 1,6-hexamethylene diisocyanate, isophorone 
diisocyanate and mixtures thereof. 
The polyisocyanates or polyisocyanate adducts used to prepare the aqueous 
dispersions of the present invention may be used in their unmodified, 
hydrophobic form or preferably they may be rendered hydrophilic by 
admixture with external emulsifiers or by reaction with cationic, anionic 
and/or nonionic compounds containing isocyanate-reactive groups. The 
reaction components which ensure the dispersibility of the polyisocyanates 
include compounds containing lateral or terminal, hydrophilic ethylene 
oxide units and compounds containing ionic groups or potential ionic 
groups. 
The compounds containing lateral or terminal, hydrophilic ethylene oxide 
units contain at least one, preferably one, isocyanate-reactive group and 
are used in an amount sufficient to provide a content of hydrophilic 
ethylene oxide units of up to about 40% by weight, preferably about 5 to 
40% by weight and more preferably about 10 to 35% by weight, based on the 
weight of the polyisocyanate. The compounds containing ionic groups or 
potential ionic groups contain at least one, preferably two, 
isocyanate-reactive groups and are used in an amount of up to about 120 
milliequivalents, preferably about 8 to 80 milliequivalents, more 
preferably about 10 to 60 milliequivalents and most preferably about 15 to 
50 milliequivalents per 100 grams of polyisocyanate. 
Hydrophilic components having terminal or lateral hydrophilic chains 
containing ethylene oxide units include compounds corresponding to the 
formulae 
##STR1## 
wherein 
R represents a difunctional radical obtained by removing the isocyanate 
groups from a diisocyanate corresponding to those previously set forth, 
R' represents hydrogen or a monovalent hydrocarbon radical containing from 
1 to 8 carbon atoms, preferably hydrogen or a methyl group, 
R" represents a monovalent hydrocarbon radical having from 1 to 12 carbon 
atoms, preferably an unsubstituted alkyl radical having from 1 to carbon 
atoms, 
X represents the radical obtained by removing the terminal oxygen atom from 
a polyalkylene oxide chain having from 5 to 90 chain members, preferably 
20 to 70 chain members, wherein at least about 40%, preferably at about 
65%, of the chain members comprise ethylene oxide units and the remainder 
comprises other alkylene oxide units such as propylene oxide, butylene 
oxide or styrene oxide units, preferably propylene oxide units, 
Y represents oxygen or --NR"'--wherein R"' has the same definition as R" 
and 
Z represents a radical which corresponds to Y, but may additionally 
represent --NH--. 
The compounds corresponding to the above formulae may be produced by the 
methods according to U.S. Pat. Nos. 3,905,929, 3,920,598 and 4,190,566 
(the disclosures of which are herein incorporated by reference). The 
monofunctional hydrophilic synthesis components are produced, for example, 
by alkoxylating a monofunctional compound such as n-butanol or N-methyl 
butylamine, using ethylene oxide and optionally another alkylene oxide, 
preferably propylene oxide. The resulting product may optionally be 
further modified (although this is less preferred) by reaction with 
ammonia to form the corresponding primary amino polyethers. 
The compounds containing ionic groups or potential ionic groups for 
providing hydrophilicity to the polyisocyanates may be cationic or 
anionic. Examples of anionic groups include carboxylate groups and 
sulphonate groups. Examples of cationic groups include tertiary and 
quaternary ammonium groups and tertiary sulphonium groups. The ionic 
groups are formed by neutralizing the corresponding potential ionic groups 
either prior to, during or after their reaction with the polyisocyanate. 
When the potential ionic groups are neutralized prior to forming the 
modified polyisocyanate, ionic groups are incorporated directly. When 
neutralization is performed subsequent to forming the prepolymer, 
potential ionic groups are incorporated. Suitable compounds for 
incorporating the previously discussed carboxylate, sulphonate, tertiary 
sulphonium and tertiary or quaternary ammonium groups are described in 
U.S. Pat. Nos. 3,479,310, 4,108,814, 3,419,533 and 3,412,054, the 
disclosures of which are herein incorporated by reference. 
In addition to the previously discussed hydrophilic modifiers, which are 
chemically incorporated into the polyisocyanates, it is also possible to 
use external emulsifiers which may be anionic, cationic or nonionic. 
Further, when dispersion stability is not a specific requirement, it is 
possible to disperse the polyisocyanate in water in the absence of 
emulsifiers by using high shear mixers, for example, those disclosed in 
British Patents 1,414,930, 1,432,112 and 1,428,907 as well as German 
Offenlegungsschrift 2,347,299. Low shear mixers may also be used to 
disperse the polyisocyanates in water such as the stator-rotor dynamic 
mixer disclosed in U.S. Pat. No. 4,742,095. 
The polyisocyanates to be dispersed in water preferably have a 
functionality of at least 2, more preferably at least 2.2. These compounds 
may be prepared by reacting polyisocyanates having functionalities of 
greater than 2 with a monofunctional compound containing hydrophilic 
groups, provided that the average functionality remains at least 2. When 
diisocyanates are used as the polyisocyanate, it is preferred to use 
difunctional compounds containing hydrophilic groups in order to maintain 
a functionality of at least 2. The treatment of diisocyanates with 
monofunctional compounds containing hydrophilic groups is less preferred 
since this reduces the functionality to less than 2. Accordingly, the 
functionality of the component containing hydrophilic groups and the 
functionality of the polyisocyanate must be taken into consideration in 
order to ensure that the modified polyisocyanates have functionalities of 
at least 2. 
The polyisocyanate dispersions generally have a solids content of about 2 
to 50, preferably about 10 to 30 weight percent. 
Either before, during or after the polyisocyanates have been dispersed in 
water, a trimerization catalyst is also incorporated into the aqueous 
compositions of the present invention. Trimerization catalysts which are 
suitable in accordance with the present invention include those previously 
known such as phosphines of the type described in DE-OS 1,935,763; alkali 
phenolates of the type described in GB-PS 1,391,066 or GB-PS 1,386,399; 
aziridine derivatives in combination with tertiary amines of the type 
described in U.S. Pat. No. 3,919,218; quaternary ammonium carboxylates of 
the type described in U.S. Pat. Nos. 4,454,317 and 4,801,663; quaternary 
ammonium phenolates with a zwitterionic structure of the type described in 
U.S. Pat. No. 4,335,219; ammonium phosphonates and phosphates of the type 
described in U.S. pat. No. 4,499,253; alkali carboxylates of the type 
described in E-OS 3,219,608; basic alkali metal salts complexed with 
acyclic organic compounds as described in U.S. Pat. No. 4,379,905 such as 
potassium acetate complexed with a polyethylene glycol which contains an 
average of 5 to 8 ethylene oxide units; basic alkali metal salts complexed 
with crown ethers as described in U.S. Pat. No. 4,487,928; aminosilyl 
group-containing compounds such as aminosilanes, diaminosilanes, 
silylureas and silazanes as described in U.S. Pat. No. 4,412,073; mixtures 
of alkali metal fluorides and quaternary ammonium or phosphonium salts as 
described in U.S. application Ser. No. 07/391,213; Mannich bases, for 
example, those based on i-nonylphenyl, formaldehyde and dimethylamine of 
the type described in U.S. Pat. Nos. 3,996,223 and 4,115,373; and 
quaternary ammonium hydroxides containing hydroxyalkyl substituents as 
described in U.S. Pat. No. 4,324,879. 
One specific advantage of the present invention is that it is not necessary 
to form complexes of the highly active trimer catalysts because they are 
soluble in the aqueous media. Therefore, preferred trimerization catalysts 
for use in accordance with the present invention are basic alkali metal 
compounds whose aqueous solutions at a 1 molar concentration have a pH of 
at least 7.5. Preferred alkali metals are sodium and potassium, more 
preferably potassium. Suitable anions include carboxylates preferably 
having 1 to 12 carbon atoms, alcoholates preferably having 1 to 8 carbon 
atoms, phenolates preferably having 6 to 10 carbon atoms, carbonates, 
hydroxides, cyanates, enolates and cyanides. Examples of these anions 
include formates, acetates, propionates, 2-ethylhexanoates, 
n-dodecanoates, caprylates, methylates, ethylates, butylates, hexylates, 
phenolates, tert.-butyl-phenolates, carbonates, hydroxides, cyanates, 
thiocyanates, cyanides and N-methylacetamides. Included among the 
preferred anions are carboxylates, alcoholates, phenolates, carbonates, 
hydroxides, cyanates and cyanides. More preferred anions are the 
hydroxides and carboxylates having 1 to 4 carbon atoms. 
Especially preferred trimerization catalysts are potassium acetate and 
potassium hydroxide. 
Because certain of the trimerization catalysts also promote the reaction 
between isocyanate groups and water, a portion of the isocyanate groups 
are blocked with a monofunctional blocking agent to prevent these groups 
from reacting with water. In addition, the reaction between isocyanate 
groups and water gives off carbon dioxide which can cause the aqueous 
compositions to foam. If it is desired to cure the aqueous compositions 
before the foam has dissipated, then in those instances when the foam may 
cause subsequent processing problems it is also recommended to block at 
least a portion of the isocyanate groups. Finally, if increased storage 
stability is required, it may be necessary to block a portion of the 
isocyanate groups to ensure that isocyanate groups can be regenerated for 
the trimerization reaction which takes place when the aqueous composition 
is cured. 
Suitable monofunctional blocking agents are those which are more reactive 
with isocyanate groups than water. Examples of suitable blocking agents 
include secondary aromatic amines such as N-methylaniline; the N-methyl 
toluidines, N-phenyl toluidine and N-phenyl xylidene; N-alkyl amides such 
as N-methyl acetamide; imides such as succinimide; lactams such as 
.epsilon.-caprolactam and .delta.-valerolactam; mercaptans such as 
methylmercaptan, ethyl mercaptan, butyl mercaptan, 
2-mercapto-benzothiazole and dodecyl mercaptan; triazoles such as 
1H-1,2,4-triazole; preferably alkali metal bisulfites and more preferably 
oximes. 
The oximes preferably correspond to the formula 
EQU HO--N.dbd.C(R.sub.1)(R.sub.2) 
wherein 
R.sub.1 and R.sub.2 may be the same or different and represent hydrogen or 
an alkyl or aralkyl group having 1 to 10 carbon atoms, provided that both 
R.sub.1 and R.sub.2 are not hydrogen, or the two groups together with the 
oxime carbon atom may form a cycloaliphatic ring containing 4 to 8 carbon 
atoms. 
Suitable oxime blocking agents include methyl ethyl ketoxime, methyl 
isobutyl ketoxime, acetone oxime, cyclohexanone oxime and methyl n-amyl 
ketoxime, methyl n-propyl ketoxime, methyl isopropyl ketoxime, diethyl 
ketoxime, methyl sec-butyl ketoxime, ethyl butyl ketoxime and acetophenone 
oxime. 
The equivalent ratio of monofunctional blocking groups to isocyanate groups 
is at least 0.02:1, preferably at least 0.25:1, more preferably at least 
0.6:1 and most preferably about 1:1. With regard to the latter ratio if an 
excess of the blocking agent is used, the excess may be removed after the 
blocking reaction is complete. However, to avoid the necessity of removing 
excess blocking agent, it is preferred not to use an excess of the 
blocking agent. 
During subsequent curing of the aqueous composition at elevated temperature 
the blocking agent will be released and the reformed isocyanate groups 
will be available for trimerization. Any isocyanate groups which are not 
blocked by the blocking agent may be left to react with water. If the 
aqueous composition will be cured shortly after its preparation, the 
unblocked isocyanate groups will take part in the trimerization reaction. 
Any isocyanate groups which react with water to form urea groups will not 
be available for trimerization. 
In accordance with another, less preferred embodiment of the present 
invention, a portion of the isocyanate groups of the dispersed 
polyisocyanate may also be reacted with compounds having at least two 
isocyanate-reactive groups, preferably groups which are more reactive with 
isocyanate groups than water. Examples of these compounds are the 
polyamines having a molecular weight of less than 400 and containing two 
or more primary and/or secondary amino groups which are disclosed in 
copending application, U.S. application Ser. No. 07/677,010, filed Mar. 
28, 1991, the disclosure of which is herein incorporated by reference; and 
the primary or secondary monoamines containing at least one hydroxyl group 
disclosed in copending application, U.S. application Ser. No. 07/529,056, 
filed May 25, 1990, the disclosure of which is herein incorporated by 
reference; or mixtures of these compounds as disclosed in copending 
application, U.S. application Ser. No. 07/676,670, filed Mar. 28, 1991, 
the disclosure of which is herein incorporated by reference. 
It is also possible in accordance with the present invention to add 
compounds which are not more reactive with isocyanate groups than water, 
such as polyhydroxyl compounds, to the aqueous compositions. Suitable 
polyhydroxyl compounds are disclosed in copending applications, U.S. 
application Ser. No. 07/676,670 filed Mar. 28, 1991, the disclosures of 
which are herein incorporated by reference. If polyhydroxyl compounds are 
added and the aqueous composition is cured shortly after its preparation, 
then the reaction between the hydroxyl groups and isocyanate groups will 
not be complete. In this case the hydroxyl groups will react with a 
portion of the isocyanate groups during the subsequent trimerization 
reaction. 
The amount of the these isocyanate-reactive compounds is chosen to provide 
an equivalent ratio of isocyanate-reactive groups to isocyanate groups of 
the dispersed polyisocyanate of less than 0.4:1.0, preferably less than 
0.2:1.0 and more preferably less than 0.1:1.0. Lower limits for the amount 
of these compounds are chosen to provide an equivalent ratio of 
isocyanate-reactive groups which are more reactive than water to 
isocyanate groups of 0.02:1.0, preferably 0.05:1.0. 
It is believed that amino groups react with the isocyanate groups on the 
surface of the dispersed polyisocyanates to form urea groups which 
encapsulate the dispersed polyisocyanates. Because this encapsulation may 
interfere with the reaction between the isocyanate groups and the blocking 
agent, it is preferred not to add significant amounts of the polyamines 
for reaction with the dispersed polyisocyanate. If the incorporation of 
urea groups is desired, it is possible to react the polyamines with the 
polyisocyanate before the polyisocyanate is dispersed in water as 
previously described. 
The trimerization catalyst, the blocking agent and the optional 
isocyanate-reactive compound may be added to the water either before, 
during or after the polyisocyanate has been dispersed. Preferably, the 
polyisocyanate is first dispersed in water and then the trimerization 
catalyst, blocking agent and optional isocyanate-reactive compound are 
added to the dispersed polyisocyanate. In one embodiment of the present 
invention the polyisocyanate may be dispersed in water in a first mixing 
step, and subsequently the remaining components can be added to this 
mixture in a second mixing step. Suitable apparatus for performing these 
mixing steps have previously been disclosed for dispersing the 
polyisocyanate in water and also include the mixing apparatus disclosed in 
copending application, U.S. application Ser. No. 07/677,002, filed Mar. 
28, 1991, the disclosure of which is herein incorporated by reference. 
In accordance with the present invention, it is also possible to 
incorporate additives into the aqueous compositions. The additives may be 
present in the form of a solution or in the form of an emulsion or 
dispersion. These additives are known and include catalysts such as 
tertiary amines, aminosilanes having carbon-silicon bonds, ammonium 
hydroxides and organo metallic compounds; surface-active agents; reaction 
retarders; and adhesion promoters. Examples of suitable additives which 
may optionally be used in accordance with the present invention and 
details on the way in which these additives are to be used and how they 
function may be found in Kunststoff-Handbuch, Vol. VII, published by 
Vieweg and Hochtlen, Carl-Hanser-Verlag, Munich 1966, for example on pages 
103 to 113. 
The aqueous compositions prepared in accordance with the present invention 
may be used alone, e.g., as binders for fiberglass, or they may be used as 
crosslinkers for aqueously dispersed polyurethanes which may optionally 
contain hydroxyl and/or amino groups. The dispersions according to the 
present invention are also suitable to improve the properties (such as 
adhesion, solvent resistance and abrasion resistance) of many other 
aqueous polymer dispersions such as acrylic, epoxy, polyvinyl acetate and 
styrene/butadiene rubber dispersions. 
The invention is further illustrated but is not intended to be limited by 
the following examples in which all parts and percentages are by weight 
unless otherwise specified.

EXAMPLES 
EXAMPLE 1 
Preparation of an aromatic water-dispersible polyisocyanate 
A three liter round bottom flask equipped with a thermometer, drying tube, 
condenser, and stirrer was charged with 549 parts of Crude MDI.sup.1 and 
274.5 parts of a monofunctional poly(ethylene oxide) ether.sup.2. The 
temperature of the reaction flask was increased to 70.degree.. The 
reaction preceeded at this temperature for four hours at which time the 
isocyanate content was determined by titration to be 20.42% (theoretical 
NCO=20.75%). The modified polyisocyanate was cooled to ambient temperature 
and placed in dry containers. 
1 An aniline/formaldehyde condensation product containing 
4,4'-diphenylmethane diisocyanate and about 50% of higher functionality 
homologs and having an isocyanate content of about 31.5% and a viscosity 
at 25.degree. C. of 200 mPa.s. 
2 A polyether monohydric alcohol having a molecular weight of 2200 and 
prepared from n-butanol, ethylene oxide and propylene oxide (molar ratio 
of ethylene oxide to propylene oxide - 83:17). 
EXAMPLE 2 
Trimerization of a partially blocked (75%), aqueous, aromatic olyisocyanate 
with potassium acetate catalyst 
125 grams of the water dispersible polyisocyanate of Example 1 were 
dispersed in a two liter resin flask containing 192.53 grams of 
demineralized water at ambient temperature and under agitation. To the 
dispersed polyisocyanate was added a mixture of butanone oxime (MEKO, 
39.62 grams) and potassium acetate (1.25 grams of a 1% aqueous solution). 
The result was a thin, off-white dispersion. After 3 days the dispersion 
was stable, and still contained traces of free isocyanate. The films (3 
and 10 mils wet, oven cured at 150.degree. C. for 45 minutes) from this 
dispersion were clear, yellow and not continuous. IR analysis of these 
films showed both trimer and urea. 
EXAMPLE 3 
(Comparison) Trimerization of an aqueous, aromatic polyisocyanate with 
potassium hydroxide catalyst 
125 grams of the water dispersible polyisocyanate of Example 1 were 
dispersed in a two liter resin flask containing 232.14 grams of 
demineralized water at ambient temperature and under agitation. To the 
dispersed polyisocyanate was added potassium hydroxide (1.25 grams of a 1% 
aqueous solution). The off-white dispersion foamed badly, had a viscosity 
of 700 mPa.s at 25.degree. C. and a pH of 3.4. A film (5 mils wet, cured 
at 150.degree. C. for 45 minutes) was clear, yellow and continuous. It had 
a pencil hardness of 2 H, adhesion by tape test of 5 B, MEK double rub of 
&gt;200, and was not sensitive to the water-spot test. 
EXAMPLE 4 
Trimerization of a partially blocked (75%), aqueous, aromatic 
polyisocyanate with potassium hydroxide catalyst 
125 grams of the water dispersible polyisocyanate of Example 1 were 
dispersed in a two liter resin flask containing 192.53 grams of 
demineralized water at ambient temperature and under agitation. To the 
dispersed polyisocyanate was added a mixture of butanone oxime (MEKO, 
39.62 grams) and potassium hydroxide (1.25 grams of a 1% aqueous 
solution). The reaction exothermed to 40.degree. C. and foamed less 
severely than the comparative example due to the fact that a portion of 
the isocyanate groups were blocked. The dispersion had a viscosity of 1500 
mPa.s at 35.degree. C. and a pH of 3.2. A film (10 mils wet, cured at 
150.degree. C. for 45 minutes) from this dispersion was clear, yellow and 
continuous. It had a pencil hardness of 2 H, adhesion by tape test of 5 B, 
MEK double rub of &gt;200, and was not sensitive to the water-spot test. 
EXAMPLE 5 
Trimerization of a blocked (100%), aqueous, aromatic polyisocyanate with 
potassium hydroxide catalyst 
125 grams of the water dispersible polyisocyanate of Example 1 were 
dispersed in a two liter resin flask containing 178.08 grams of 
demineralized water, 52.82 grams of butanone oxime, 1.25 grams of a 1% 
aqueous solution of potassium hydroxide and 0.20 grams of a silicone 
containing flow agent (SILWET L-77, available from Union Carbide) at 
ambient temperature and under agitation. The reaction exothermed to 
38.degree. C. and did not foam. The off-white dispersion had a viscosity 
of 280 mPa.s at 25.degree. C. and a pH of 4.75. A film (5 mils wet, cured 
at 150.degree. C. for 45 minutes) from the dispersion was clear, yellow 
and continuous. It had a pencil hardness of 2 H, adhesion by tape test of 
5 B, MEK double rub of &gt;200, and was not sensitive to the water-spot test. 
IR analysis of the film showed both timer and urea formation. 
Film testing procedures: 
Pencil Hardness - ASTM D3363 
Adhesion to Tape Test- ASTM D3359-83 
MEK Double Rubs - Number of double rubs with a cotton cheese cloth 
saturated with MEK that were necessary to begin to remove the coating from 
the glass plate. Water Spot Sensitivity - One drop of water was placed on 
the coating for one hour, then the film was checked to see if the water 
had any effect. If the film had a haze or was easier to remove from the 
glass where the water was, it would be considered sensitive. 
Although the invention has been described in detail in the foregoing for 
the purpose of illustration, it was to be understood that such detail was 
solely for that purpose and that variations can be made therein by those 
skilled in the art without departing from the spirit and scope of the 
invention except as it may be limited by the claims.