Coating compositions based on blocked polyisocyanates and sterically hindered aromatic polyamines

The present invention is directed to a coating composition which possesses improved storage stability and contains PA1 a) a blocked polyisocyanate prepared by blocking the isocyanate groups of an organic polyisocyanate with a blocking agent based on a di-C.sub.1 -C.sub.12 -alkyl and/or -alkoxyalkyl malonate or an acetoacetic acid C.sub.1 -C.sub.12 -alkyl and/or -alkoxyalkyl ester PA1 b) an aromatic polyamine, and PA1 c) is free from compounds having monofunctional reactivity towards isocyanate groups.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention is directed to coating compositions based on blocked 
polyisocyanates and aromatic polyamines which have good storage stability. 
2. Description of the Prior Art 
Coating compositions based on a blocked polyisocyanate component and a 
component containing isocyanate-reactive hydrogens are known. The purpose 
of the blocking agent is to prevent the polyisocyanate from reacting with 
the isocyanate-reactive component at ambient temperature conditions and 
thus allow the two components to be mixed and stored prior to their actual 
use. When the composition is baked at an elevated temperature, the 
blocking agent is released and the reaction of the two components 
commences. 
It is desirable to use blocking agents for the polyisocyanate which can be 
released at low curing temperatures in order to reduce energy costs. U.S. 
Pat. Nos. 2,801,990; 3,779,794; 4,007,215; 4,087,392; 4,101,530; 
4,132,843; and 4,332,965; British Pat. Nos. 1,442,024 and 1,523,103; 
German Offenlegungsschrift No. 2,623,081 and German Auslegeschrift No. 
2,639,491 described polyisocyanates blocked with C-H acidic compounds 
which can be reacted at lower temperatures than polyisocyanates blocked 
with other known blocking agents. The disadvantage of compositions based 
on polyisocyanates blocked with C-H acidic compounds and either aliphatic 
amine or hydroxyl co-reactants is that they must contain stabilizers in 
order to provide sufficient room temperature stability. Note U.S. Pat. 
Nos. 4,439,593 and 4,518,522. To the contrary, polyisocyanates blocked 
with oximes such as methylethylketoxime have better storage stability with 
hydroxyl co-reactants, but require higher curing temperatures. 
Accordingly, it is an object of the present invention to provide coating 
compositions which cure at low temperatures and have improved storage 
stability, especially when compared to blocking agents which require 
higher curing temperatures. It was surprisingly found that these objects 
could be achieved in accordance with the present invention as described 
hereinafter. 
SUMMARY OF THE INVENTION 
The present invention is directed to a coating composition which possesses 
improved storage stability and contains 
a) a blocked polyisocyanate prepared by blocking the isocyanate groups of 
an organic polyisocyanate with a blocking agent based on a di-C.sub.1 
-C.sub.12 -alkyl and/or -alkoxyalkyl malonate or an acetoacetic acid 
C.sub.1 -C.sub.12 -alkyl and/or -alkoxyalkyl ester, 
b) an aromatic polyamine, and 
c) is free from compounds having monofunctional reactivity towards 
isocyanate groups. 
DETAILED DESCRIPTION OF THE INVENTION 
Blocked polyisocyanates which are suitable for use in the compositions have 
an isocyanate content of about 1 to 30, preferably about 2 to 25 weight 
percent, based on the unblocked polyisocyanate, contain an average of 
about 2 to 6, preferably about 2 to 4, blocked isocyanate groups per 
molecule and may be prepared from any organic polyisocyanate, preferably 
from polyisocyanates containing 2 to 4 isocyanate groups. Preferred are 
polyisocyanates having aromatically-, aliphatically- or 
cycloaliphatically- bound isocyanate groups, or mixtures thereof. 
The polyisocyanates used for preparing the blocked isocyanates are adducts 
prepared from organic polyisocyanates, preferably diisocyanates, and 
containing biuret, allophanate, urea, urethane, carbodiimide or uretdione 
groups or isocyanurate rings. Suitable polyisocyanates which may be used 
for preparing the polyisocyanate adducts include ethylene diisocyanate, 
1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 
1,12-dodecane diisocyanate, cyclobutane-1,3-diisocyanate, cyclohexane-1,3- 
and -1,4-diisocyanate and mixtures of these isomers, 
1-isocyanato-2-isocyanatomethyl cyclopentane, 
1-isocyanato-3,3,5-trimethyl-5-iso-cyanatomethyl cyclohexane (isophorone 
diisocyanate or IPDI), 2,4- and 2,6-hexahydrotoluylene diisocyanate and 
mixtures of these isomers, 2,4'- and/or 4,4'-dicyclohexymethane 
diisocyanate, .alpha.,.alpha.,.alpha.',.alpha.'-tetramethyl-1,3- and/or 
-1,4-xylylene diisocyanate, 1,3- and 1,4-xylylene diisocyanate, 
1-isocyanato-1-methyl-4(3)-isocyanato- methyl-cyclohexane, 1,3- and 
1,4-phenylene diisocyanate, 2,4- and 2,6-toluylene diisocyanate and 
mixtures of these isomers, diphenyl methane-2,4'- and/or 
-4,4'-diisocyanate, naphthalene-1,5-diisocyanate, triphenyl 
methane-4,4',4"-triisocyanate, polyphenyl polymethlene polyisocyanates of 
the type obtained by condensing aniline with formaldehyde followed by 
phosgenation, and mixtures of the above-mentioned polyisocyanates. 
Polyisocyanate adducts containing biuret groups may be prepared from the 
previously mentioned diisocyanates according to the processes disclosed in 
U.S. Pat. Nos. 3,124,605; 3,358,010; 3,644,490; 3,862,973; 3,903,126; 
3,903,127; 4,051,165; 4,147,714 or 4,220,749 by using co-reactants such as 
water, tertiary alcohols, primary and secondary monoamines, and primary 
and/or secondary diamines. The preferred diisocyanate to be used in these 
processes is 1,6-diisocyanatohexane. 
Polyisocyanate adducts containing allophanate groups may be prepared by 
reacting the previously mentioned diisocyanates according to the processes 
disclosed in U.S. Pat. Nos. 3,769,318 and 4,160,080, British Pat. No. 
994,890 and German Offenlegungsschrift No. 2,040,645. 
Polyisocyanate adducts containing isocyanurate groups may be prepared by 
trimerizing the previously mentioned diisocyanates in accordance with the 
processes disclosed in U.S. Pat. Nos. 3,487,080; 3,919,218; 4,040,992; 
4,288,586; and 4,324,879; German Auslegeschrift No. 1,150,080; German 
Offenlegungsschrift No. 2,325,826; and British Pat. No. 1,465,812. The 
preferred diisocyanates to be used are 2,4-diisocyanatotoluene, 
2,6-diisocyanatotoluene, mixtures of the isomers, 1,6-diisocyanatohexane, 
isophorone diisocyanate and mixtures of the latter two diisocyanates. 
Polyisocyanate adducts containing urea or preferably urethane groups and 
based on the reaction product of the previously mentioned diisocyanates 
and compounds having a molecular weight of less than 400 and containing 2 
or more isocyanate-reactive hydrogens may be prepared according to the 
process disclosed in U.S. Pat. No. 3,183,112. When preparing 
polyisocyanate adducts using a large excess of diisocyanate, the average 
isocyanate functionality may be determined from the functionality of the 
compounds containing isocyanate- reactive hydrogens. For example, 
theoretically when an excess of a diisocyanate is reacted with a diol, a 
polyisocyanate with a functionality of approximately 2 will be produced, 
while a triol co-reactant will result in a polyisocyanate functionality of 
at least 3. By using mixtures of compounds containing isocyanate- reactive 
hydrogens, various functionalities can be obtained. The preferred 
isocyanate-reactive hydrogens are provided by hydroxyl groups, although 
other groups such as amino groups are not excluded. Suitable compounds 
containing isocyanate-reactive hydrogens are disclosed in U.S. Pat. No. 
3,183,112, incorporated herein by reference, and include ethylene glycol, 
1,2- and 1,3-propylene glycol, 1,3- and 1,4-butanediol, 1,6-hexanediol, 
1,8-ocatanediol, neopentyl glycol, diethylene glycol, 
2-methyl-1,3-propylene glycol, 2,2-dimethyl-1,3-propylene glycol, the 
various isomeric bis-hydroxymethyl cyclohexanes, 
2,2,4-trimethyl-1,3-pentanediol, glycerine, trimethylol propane, ethylene 
diamine, diethylene triamine, triethylene tetraamine, 1,6-hexanediamine, 
piperazine, 2,5-dimethyl piperazine, 
1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane, 
bis(4-aminocyclohexyl)methane, bis(4-amino-3-methylcyclohexyl)methane, 
1,4-cyclohexanediamine, 1,2-propanediamine, hydrazine, aminoacid 
hydrazides, hydrazides of semicarbazido carboxylic acids, bis-hydrazides 
and bis-semicarbazides. 1,3- and 1,4-butanediol, 
2,2,4-trimethyl-1,3-pentanediol, trimethylol propane and mixtures thereof 
are particularly preferred. It is also possible to use any of the 
previously described polyisocyanate adducts for the further preparation of 
polyisocyanate adducts containing urethane or urea groups. Preferred 
diisocyanates are 2,4-toluylene diisocyanate and/or 2,6-toluylene 
diisocyanate, 1,6-hexamethylene diisocyanate, isophorone diisocyanate and 
mixtures of these diisocyanates. 
In addition to using the previously described polyisocyanate adducts for 
preparing the blocked polyisocyanate component of the present invention, 
it is also suitable to prepare the blocked polyisocyanate component from 
isocyanate-terminated prepolymers. These prepolymers are formed by 
reacting an excess of the previously described polyisocyanates with high 
molecular weight isocyanate-reactive compounds and optionally low 
molecular weight isocyanate-reactive compounds. Prepolymers prepared 
exclusively from polyisocyanates and low molecular weight 
isocyanate-reactive compounds are referred to as polyisocyanate adducts 
containing urea and/or urethane groups and have previously been discussed. 
A sufficient excess of the polyisocyanate should be used to ensure that 
the prepolymers are terminated with isocyanate groups. 
It should also be ensured that the isocyanate-terminated prepolymers remain 
soluble in the commonly used polyurethane solvents and do not gel. 
Gelation may result when sufficiently cross-linked, isocyanate-terminated 
prepolymers are prepared from polyisocyanates or isocyanate-reactive 
compounds containing more than two reactive groups. Minimal amounts of 
cross-linking do not lead to gelation; however, once a sufficient 
cross-linked density is achieved, gelation occurs. The critical cross-link 
density, commonly referred to as the gel point, may be calculated by known 
methods or readily determined by simply reacting the desired components 
and observing whether gel particles form. In order to avoid gelation, it 
is preferred to prepare the isocyanate-terminated prepolymers from the 
polyisocyanates described as suitable for use in preparing the 
polyisocyanate adducts rather than using the polyisocyanate adducts 
themselves. It is additionally preferred to prepare the 
isocyanate-terminated prepolymers from high molecular weight 
isocyanate-reactive compounds which do not contain excessive amounts of 
branching in order to further reduce the possibility that gelation will 
occur. Finally, it is preferred to prepare the isocyanate-terminated 
prepolymers by adding the isocyanate-reactive compound to the 
polyisocyanate since this helps to maintain an excess of isocyanate 
throughout the formation of the prepolymer. 
The high molecular weight compounds to be used with the previously 
described polyisocyanates for preparing the isocyanate-terminated 
prepolymers are selected from the known compounds containing 
isocyanate-reactive groups, preferably hydroxyl groups, which are at least 
difunctional in the sense of the isocyanate-addition reaction. These 
compounds generally have an average functionality of about 2 to 8, 
preferably 2 to 4. The compounds containing at least two 
isocyanate-reactive hydrogen atoms generally have a molecular weight of 
400 to about 10,000, preferably 400 to about 8,000. 
Examples of high molecular weight compounds include: 
1) polyhydroxyl polyesters which are obtained from polyhydric, preferably 
dihydric alcohols to which trihydric alcohols may be added, and polybasic, 
preferably dibasic carboxylic acids. Instead of these polycarboxylic 
acids, the corresponding carboxylic acid anhydrides or polycarboxylic acid 
esters of lower alcohols or mixtures thereof may be used for preparing the 
polyesters. The polycarboxylic acids may be aliphatic, cycloaliphatic, 
aromatic and/or heterocyclic and they may be saturated and/or substituted, 
e.g. by halogen atoms. Examples of these acids include succinic acid, 
adipic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, 
isophthalic acid, trimellitic acid, phthalic acid anhydride, 
tetrahydrophthalic acid anhydride, hexahydrophthalic acid anhydride, 
tetrachlorophthalic acid anhydride, endomethylene tetrahydrophthalic acid 
anhydride, glutaric acid anhydride, maleic acid, maleic acid anhydride, 
fumaric acid, dimeric and trimeric fatty acids such as oleic acid (which 
may be mixed with monomeric fatty acids), dimethyl terephthalate and 
bis-glycol terephthalate. Suitable polyhydric alcohols include the 
polyhydric alcohols previously set forth for preparing the polyisocyanate 
adducts containing urea or urethane groups. 
2) Polylactones generally known from polyurethane chemistry, e.g., polymers 
of caprolactone initiated with the above-mentioned polyhydric alcohols. 
3) Polycarbonates containing hydroxyl groups such as the products obtained 
from reaction of the polyhydric alcohols previously set forth for 
preparing the polyisocyanate adducts containing urea or urethane groups, 
preferably dihydric alcohols such as 1,3-propanediol, 1,4-butanediol, 
1,4-dimethylol cyclohexane, 1,6-hexanediol, diethylene glycol, triethylene 
glycol or tetraethylene glycol with phosgene, diaryl carbonates such as 
diphenyl carbonate or cyclic carbonates such as ethylene or propylene 
carbonate. Also suitable are polyester carbonates obtained from the 
reaction of lower molecular weight oligomers of the above-mentioned 
polyesters or polylactones with phosgene, diaryl carbonates or cyclic 
carbonates. 
4) Polyethers include the polymers obtained by the reaction of starting 
compounds which contain reactive hydrogen atoms with alkylene oxides such 
as propylene oxide, butylene oxide, styrene oxide, tetrahydrofuran, 
epichlorohydrin or mixtures of these alkylene oxides. Suitable starting 
compounds containing at least one reactive hydrogen atom include the 
polyols set forth as suitable for preparing the polyisocyanate adducts 
containing urethane or urea groups and, in addition, water, methanol, 
ethanol, 1,2,6-hexanetriol, 1,2,4-butanetriol, trimethylol ethane, 
pentaerythritol, mannitol, sorbitol, methyl glycoside, sucrose, phenol, 
isononyl phenol, resorcinol, hydroquinone and 1,1,1- or 
1,1,2-tris(hydroxylphenyl)ethane. Polyethers which have been obtained by 
the reaction of starting compounds containing amino groups can also be 
used, but are less preferred for use in the present invention. Suitable 
amine starting compounds include those set forth as suitable for preparing 
the polyisocyanate adducts containing urethane or urea groups and also 
ammonia, methylamine, tetramethylenediamine, ethanolamine, diethanolamine, 
triethanolamine, aniline, phenylenediamine, 2,4- and 2,6-toluylenediamine, 
polyphenylene polymethylene polyamines of the kind obtained by the 
aniline/formaldehyde condensation reaction and mixtures thereof. Resinous 
materials such as phenol and cresol resins may also be used as the 
starting materials. The preferred starting compounds for the polyethers 
are those compounds which exclusively contain hydroxyl groups, while 
compounds containing tertiary amine groups are less preferred and 
compounds containing isocyanate-reactive-NH groups are much less 
preferred. Polyethers modified by vinyl polymers are also suitable for the 
process according to the invention. Products of this kind may be obtained 
by polymerizing, e.g., styrene and acrylonitrile in the presence of 
polyethers (U.S. Pat. Nos. 3,383,351; 3,304,273; 3,523,095; and 3,110,695; 
and German Pat. No. 1,152,536). Also suitable as polyethers are amino 
polyethers wherein at least a portion of the hydroxyl groups of the 
previously described polyethers are converted to amino groups. 
5) Polythioethers such as the condensation products obtained from 
thiodiglycol on its own and/or with other glycols, dicarboxylic acids, 
formaldehyde, amino carboxylic acids or amino alcohols. The products are 
either polythio mixed ethers, polythio ether esters, or polythioether 
ester amides, depending on the co-components. 
6) Polyacetals including those obtained from the above-mentioned polyhydric 
alcohols, especially diethylene glycol, triethylene glycol, 
4,4'-dioxyethoxy-diphenyldimethylene, 1,6-hexanediol and formaldehyde. 
Polyacetals suitable for use in the invention may also be prepared by the 
polymerization of cyclic acetals. 
7) Polyether esters containing isocyanate-reactive groups which are known 
in the art. 
8) Polyester amides and polyamides including the predominantly linear 
condensates obtained from polyvalent saturated and unsaturated carboxylic 
acids or their anhydrides and polyvalent saturated and unsaturated amino 
alcohols, diamines, polyamines, or mixtures thereof. 
9) Polyacrylates including those based on acrylic acid, methacrylic acid 
and crotonic acid, maleic anhydride, 2-hydroxyethyl acrylate, 
2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl 
methacrylate, 3-hydroxypropyl acrylate, 3-hydroxypropyl methacrylate, 
glycidylacrylate, glycidyl methacrylate, 2-isocyanatoethyl acrylate and 
2-isocyanatoethyl methacrylate. 
The preferred high molecular weight isocyanate-reactive compounds for use 
in the process according to the invention are the polyhydroxyl polyethers, 
polyesters, polylactones, polycarbonates and polyester carbonates. 
In addition to the high molecular weight compounds, the 
isocyanate-terminated prepolymers may also optionally be prepared from low 
molecular weight isocyanate-reactive compounds having an average molecular 
weight of up to 400. The low molecular weight isocyanate-reactive 
compounds should have an average functionality of about 2 to 8, preferably 
from about 2 to 6 and most preferably from about 2 to 4, and may also 
contain ether, thioether, ester, urethane and/or urea bonds. 
Examples of low molecular weight compounds include the polyamines and diols 
or triols used as chain lengthening agents or cross-linking agents in 
polyurethane chemistry such as those listed as suitable for preparing the 
polyisocyanate adducts containing urethane or urea groups and the 
polyester and polyether polyols. Additional examples include those set 
forth in U.S. Pat. Nos. 4,439,593 and 4,518,522, both of which are herein 
incorporated by reference in their entirety. 
Prior to their use in accordance with the present invention, the 
polyisocyanate adducts are blocked with C-H acidic compounds such as a 
di-C.sub.1 -C.sub.12 -alkyl and/or -alkoxyalkyl, preferably a C.sub.1 
-C.sub.4 -dialkyl malonate or an acetoacetic acid C.sub.1 -C.sub.12 -, 
preferably a C.sub.1 -C.sub.4 -alkyl or -alkoxyalkyl ester. Preferred 
blocking agents are ethylacetoacetate, ethoxyethylacetoacetate and most 
preferably diethyl malonate. Preferably, these blocking agents are used as 
the sole blocking component for reaction with the polyisocyanates. 
However, it is possible to use up to about 20 mole %, preferably up to 
about 10 mole %, of other known blocking agents, e.g. secondary or 
tertiary alcohols such as isopropanol or t-butanol; oximes such as 
formaldoxime, acetaldoxime, butanone oxime, cyclohexanone oxime, 
acetophenone oxime, benzophenone oxime or diethyl glyoxime; lactams such 
as .epsilon.-caprolactam or .delta.-valerolactam; phenols such as phenol 
or cresol; N-alkyl amides such as N-methyl acetamide; imides such as 
phthalimide; imidazole; or alkali metal bisulfites. While polyisocyanates 
blocked with these other known blocking agents will react normally with 
isocyanate-reactive compounds when using sufficiently elevated 
temperatures, they will not react significantly at the preferred low 
temperature baking conditions which may be employed for curing 
compositions containing polyisocyanates blocked with the C-H acidic 
compounds. Accordingly, polyisocyanates blocked with these other known 
blocking agents should only be used in the amounts specified when low 
temperature baking conditions are employed. To compensate for the low 
reactivity of these blocked polyisocyanates the amount of the 
isocyanate-reactive component to be used in combination with the 
compositions of the present invention may be correspondingly reduced. The 
unreacted blocked polyisocyanates will remain in the cured coating and 
provide a softening effect. 
The reaction between the polyisocyanates and the blocking agent is 
generally conducted at above about 50.degree. C., preferably from about 
60.degree. to 100.degree. C., optionally in the presence of a basic 
catalyst such as diazabicyclo- octane, triethyl amine, alkali metal 
alcoholates such as sodium methoxide or alkali metal phenolates such as 
sodium phenolate. 
Suitable co-reactants for use in combination with the blocked 
polyisocyanate adducts are aromatic polyamines and include 2,4- and/or 
2,6-diaminotoluylene, 2,4'- and/or 4,4'-diaminodiphenyl methane, 1,2- and 
1,4-phenylene diamine, naphthalene-1,5-diamine and 
triphenylmethane-4,4',4"-triamine. Liquid mixtures of polyphenyl 
polymethylene-polyamines, of the type obtained by condensing 
aniline/formaldehyde, are also suitable. 
Preferred co-reactants are the sterically hindered aromatic diamines which 
contain at least one linear or branched alkyl substituents in the 
ortho-position to the first amino group and at least one, preferably two 
linear branched or alkyl substituents containing from 1 to 4, preferably 1 
to 3 carbon atoms in the ortho-position to a second amino group. These 
aromatic diamines include 1-methyl-3,5-diethyl-2,4-diaminobenzene, 
1-methyl-3,5-diethyl-2,6-diaminobenzene, 
1,3,5-trimethyl-2,4-diaminobenzene, 1,3,5-triethyl-2,4-diaminobenzene, 
3,5,3',5'-tetraethyl-4,4'-diaminodiphenylmethane, 
3,5,3'5'-tetraisopropyl-4,4'-diaminodiphenylmethane, 
3,5-diethyl-3',5'-diisopropyl-4,4'-diaminodiphenylmethane, 
3,3'-diethyl-5,5'-diisopropyl-4,4'-diaminodiphenylmethane, 
1-methyl-2,6-diamino-3-isopropylbenzene and mixtures of the above 
diamines. Most preferred are mixtures of 
1-methyl-3,5-diethyl-2,4-diaminobenzene and 
1-methyl-3,5-diethyl-2,6-diaminobenzene in a weight ratio between about 
50:50 to 85:15, preferably about 65:35 to 80:20. 
It is also possible in accordance with the present invention to use high 
molecular weight compounds which contain terminal aromatic amino groups as 
co-reactants for the blocked polyisocyanate adducts in accordance with the 
present invention. Examples of these high molecular weight compounds 
include polyethers wherein the terminal hydroxyl groups have been 
converted to aromatic amino groups. Suitable methods for preparing such 
high molecular weight compounds are set forth in U.S. Pat. No. 4,515,923, 
herein incorporated by reference in its entirety. 
While minor amounts of other isocyanate-reactive compounds may be used in 
combination with the aromatic diamines, the diamines should be present in 
an amount such that at least about 80%, preferably at least about 90% and 
most preferably 100% of the reactive groups for the blocked polyisocyanate 
adducts are aromatic amino groups. The aromatic polyamine component is 
used in an amount sufficient to provide about 0.8 to 1.2 aromatic amino 
groups, preferably about 0.9 to 1.1 and most preferably about 1.0 aromatic 
amino groups for each blocked isocyanate group. 
A solvent or solvent mixture may be used during the production of the 
blocked polyisocyanates. When a solvent is employed, the solvent or 
solvent mixture preferably remains in the composition until it is used. 
However, it is of course also possible to use a solvent simply to promote 
thorough mixing of the compounds used for preparing the blocked 
polyisocyanates and subsequently to distill off this solvent (in vacuo) 
leaving a ready-to-use mixture in solvent-free form which may be 
redissolved in solvents at any later stage. 
Suitable solvents include the known polyurethane solvents, for example, 
toluene, xylene, butyl acetate, ethylacetate, ethylene glycol monoethyl 
ether acetate (EGA), ethylene glycol monomethyl ether acetate, ethylene 
glycol monobutyl ether acetate, diethylene glycol monoethyl ether acetate, 
diethylene glycol monomethyl ether acetate, diethylene glycol monobutyl 
ether acetate, propylene glycol monomethyl ether acetate, methyl ethyl 
ketone or methyl isobutyl ketone, hydrocarbon solvents such as hexane and 
heptane, aromatic solvents and also mixtures of the above solvents. 
In the compositions prepared according to the present invention, the use of 
solvents is not always necessary, the solvent being used primarily to 
reduce the viscosity of the compositions to a workable range. Generally 
the solids content of the composition is greater than 20% and may be as 
high as 100%, based on the weight of the blocked polyisocyanate. 
Additives, such as catalysts, pigments, dyes and levelling aids, may be 
added as required to the compositions of the present invention. 
The compositions produced according to the present invention may be stored 
as such for prolonged periods at room temperature without gel formation or 
any other undesirable changes occurring. The compositions according to the 
present invention do not require the presence of the stabilizers having 
monofunctional reactivity towards isocyanate groups which are disclosed in 
U.S. Pat. Nos. 4,439,593 and 4,518,522 in order to possess storage 
stability. These compositions may be diluted as required to a suitable 
concentration and applied by conventional methods, for example spraying or 
spread coating, and heated, generally to temperatures in excess of about 
100.degree. C., preferably from about 100.degree. to 150.degree. C., more 
preferably from about 120.degree. to 130.degree. C., in order to cure the 
coating. 
The coating compositions may be used as coating agents for primer, 
intermediate or surface coatings for a variety of different substrates. 
The resulting coatings possess excellent adhesion to substrates, are 
uniform and exhibit excellent mechanical and chemical properties and water 
and solvent resistance, especially hardness, impact resistance and 
elasticity. 
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 
PREATION OF THE ISOCYANATE PREPOLYMERS 
Polyisocyanate Component I 
800 parts of a polyether (MW 550) based on polypropylene oxide/bisphenol A 
were reacted with 1000 parts of 4,4'-diphenylmethane diisocyanate at a 
temperature of 70.degree. C. until an isocyanate content of 11.8% was 
obtained. 
Polyisocyanate Component II 
73 parts of diethylene glycol, 181 parts of trimethylol propane and 678 
parts of polypropylene glycol (MW 1000) were mixed with 837 parts of 
propylene glycol monomethyl ether acetate (PM Acetate) and 837 parts of 
xylene. 1000 parts of a diisocyanate mixture of 80% 2,4- and 20% 
2,6-diisocyanatotoluene were then added to the mixture and the temperature 
was increased to 80.degree. C. for 2 hours. The temperature was then 
raised to 100.degree. C. until an isocyanate content of 5.5% was obtained. 
PREATION OF THE BLOCKED ISOCYANATES TO BE USED IN THE INVENTION 
EXAMPLE 1 
814 parts of diethyl malonate and 9.4 parts of 25% sodium methoxide in 
methanol were added to 1800 parts of Polyisocyanate Component I at a 
temperature of 40.degree. C. The reaction mixture was heated to 70.degree. 
C. and maintained at that temperature until the isocyanate content was 
below 0.5%. Then 1433 parts of light aromatic solvent naphtha and 719 
parts of propylene glycol monomethyl ether acetate were added. The 
remaining isocyanate was reacted with a stoichiometric amount of 
isopropanol at a temperature of 70.degree. C. until the isocyanate content 
was essentially zero as determined by infrared spectroscopy. 
EXAMPLE 2 (COMISON) 
442 parts of butanone oxime were added dropwise to 1800 parts of 
Polyisocyanate Component I at a temperature of 30.degree.-40.degree. C. 
The temperature of the reaction mixture increased (exothermic reaction) to 
70.degree. C. The mixture was maintained at 70.degree. C. until the 
isocyanate content was essentially zero as determined by infrared 
spectroscopy. Then 1260 parts of light aromatic solvent naphtha and 620 
parts of propylene glycol monomethyl ether acetate (PM Acetate) were 
added. 
EXAMPLE 3 
177 parts of ethyl acetoacetate and 2.4 parts of 25% sodium methylate in 
methanol were added to 1000 parts of Polyisocyanate Component II at a 
temperature of 50.degree. C. The mixture was maintained at 70.degree. C. 
until the NCO content was essentially zero, as determined by infrared 
spectroscopy. 
EXAMPLE 4 
220 parts of diethyl malonate and 2.4 parts of 25% sodium methylate in 
methanol were added to 1000 parts of Polyisocyanate Component II at a 
temperature of 40.degree. C. This mixture was maintained at 70.degree. C. 
until the isocyanate content was below 0.5%. The remaining NCO was reacted 
with a stoichiometric amount of isopropanol until the isocyanate content 
was essentially zero, as determined by infrared spectroscopy. 
EXAMPLE 5 (COMISON) 
116 parts of butanone oxime were added to 1000 parts of Polyisocyanate 
Component II at a temperature of 30.degree. C. The temperature of the 
reaction mixture increased (exothermic reaction) to 70.degree. C. The 
mixture was maintained at 70.degree. C. until the isocyanate content was 
essentially zero, as determined by infrared spectroscopy. 
AMBIENT TEMPERATURE VISCOSITY STABILITY OF BLOCKED ISOCYANATE/AMINE 
CURATIVE SYSTEM PREED ACCORDING TO THE INVENTION 
EXAMPLES 6-17 
Compositions of blocked isocyanates, aromatic polyamines and optionally 
solvent were prepared as set forth in Tables I and II. These compositions 
were formulated at an isocyanate to amine ratio of 1.0:1.0. The ambient 
temperature viscosity stability of the mixtures was measured at 25.degree. 
C. at the indicated times. The fractional viscosity increases, as defined 
by the viscosity at the indicated time divided by the initial viscosity, 
are listed in parentheses below the viscosity measurements. 
FILM CURE TIME VERSUS TEMPERATURE PROFILES OF BLOCKED ISOCYANATE/AMINE 
CURATIVE SYSTEMS PREED ACCORDING TO THE INVENTION 
EXAMPLES 18 AND 19 
The film cure time versus temperature profiles for a diethyl malonate 
blocked polyisocyanate (Example 18) and a butanone oxime blocked 
polyisocyanate (Example 19) in combination with an amine curative are 
listed in Tables III and IV, respectively. The film cure was determined by 
the "MEK double-rub test." In this test, a cotton ball saturated with 
methyl ethyl ketone was rubbed back and forth across a film on a 
substrate. A double rub was defined as one back and forth motion across 
the film. The number of double rubs required to penetrate the film to the 
substrate surface was determined and was proportional to the degree of 
cure. The values in Tables III and IV are averages of at least three 
determinations. 
TABLE I 
__________________________________________________________________________ 
AMBIENT TEMPERATURE STORAGE STABILITY 
Parts 
VISCOSITY (mpa .multidot. s @ 25 degrees C.) 
by (FRACTIONAL INCREASE IN VISCOSITY) 
Example 
Components Weight 
Initial 
2 days 
4 days 
7 days 
10 days 
14 days 
17 days 
21 days 
24 
31 
__________________________________________________________________________ 
days 
6 Example 1 Blocked 
Isocyanate 200.00 
108 112 119 129 133 
146 149 164 174 220 
2,4-diaminotoluene 
12.41 (1.0) 
(1.1) 
(1.2) 
(1.2) 
(1.3) 
(1.4) 
(1.5) 
(1.6) 
(2.0) 
PM acetate 23.05 
7 Example 2 Blocked 
(Comp) 
Isocyanate 200.00 
250 263 291 319 354 
450 540 754 1054 3300 
2,4-diaminotoluene 
14.37 (1.1) 
(1.2) 
(1.3) 
(1.4) 
(1.8) 
(2.2) 
(3.0) 
(4.2) 
(13.2) 
PM acetate 26.69 
8 Example 3 Blocked 
Isocyanate 200.00 
204 312 482 540 634 
780 798 1480 7000 gel 
2,4-diaminotoluene 
13.42 (1.5) 
(2.4) 
(2.7) 
(3.1) 
(3.8) 
(3.9) 
(7.3) 
(34.3) 
PM acetate 24.92 
9 Example 4 Blocked 
Isocyanate 200.00 
1238 
1360 
1750 
1900 
2380 
2990 
3250 4200 4550 8300 
2,4-diaminotoluene 
12.37 (1.1) 
(1.4) 
(1.5) 
(1.9) 
(2.4) 
(2.6) 
(3.4) 
(3.7) 
(6.7) 
PM acetate 23.06 
10 Example 5 Blocked 
(Comp) 
Isocyanate 200.00 
484 690 984 4300 
15000 
51000 
120000 
142000 
296000 
gel 
2,4-diaminotoluene 
13.47 (1.4) 
(2.0) 
(8.9) 
(31.0) 
(105) 
(248) 
(293) 
(611) 
PM acetate 25.02 
11 Example 3 Blocked 
Isocyanate 200.00 
489 557 602 696 666 
748 1124 1570 3270 5950 
Diethyltoluenediamine 
19.58 (1.1) 
(1.2) 
(1.4) 
(1.4) 
(1.5) 
(2.3) 
(3.2) 
(6.7) 
(12.2) 
12 Example 4 Blocked 
Isocyanate 200.00 
2170 
2400 
2900 
3160 
3850 
4910 
5160 7250 8060 15700 
Diethyltoluenediamine 
18.09 (1.1) 
(1.3) 
(1.5) 
(1.8) 
(2.3) 
(2.4) 
(3.3) 
(3.7) 
(7.2) 
13 Example 5 Blocked 
(Comp) 
Isocyanate 200.00 
1584 
2288 
5260 
7600 
17680 
54000 
114000 
280000 
400000 
gel 
Diethyltoluenediamine 
19.66 (1.4) 
(3.3) 
(4.8) 
(11.2) 
(34.1) 
(72.0) 
(176) 
(253) 
__________________________________________________________________________ 
TABLE II 
__________________________________________________________________________ 
AMBIENT TEMPERATURE STORAGE STABILITY 
Parts 
VISCOSITY (mpa .multidot. s @ 25 degrees C.) 
by (FRACTIONAL INCREASE IN VISCOSITY) 
Example 
Components Weight 
Initial 
2 days 
4 days 
18 days 
40 days 
47 days 
__________________________________________________________________________ 
14 Example 4 Blocked 
Isocyanate 200.00 
750 830 950 1510 
4100 
4260 
Diethyltoluenediamine 
18.09 (1.1) 
(1.3) 
(2.0) 
(5.5) 
(5.7) 
PM acetate 37.38 
15 (Comp) 
Example 5 Blocked 
Isocyanate 200.00 
290 340 690 57000 
gel 
Diethyltoluenediamine 
19.66 (1.2) 
(2.4) 
(195) 
PM acetate 40.62 
16 Example 4 Blocked 
Isocyanate 200.00 
780 880 950 1940 
8240 
9500 
4,4'diphenylmethane (1.1) 
(1.2) 
(2.5) 
(10.6) 
(12.2) 
Diamine 20.13 
PM acetate 37.38 
17 (Comp) 
Example 5 Blocked 
Isocyanate 200.00 
320 390 540 49000 
gel 
4,4-diphenylmethane (1.2) 
(1.7) 
(153) 
Diamine 21.87 
PM acetate 40.62 
__________________________________________________________________________ 
TABLE III 
______________________________________ 
EXAMPLE 18 
FILM CURE TIME VERSUS TEMPERATURE 
(MEK DOUBLE RUBS) 
______________________________________ 
Example 4 Blocked 
Isocyanate 100.00 parts 
Diethyltoluenediamine 
9.60 parts 
______________________________________ 
Time Temperature (.degree.C.) 
(minutes) 120 140 
______________________________________ 
10 300 500+ 
20 400 500+ 
30 500+ 500+ 
50 500+ 500+ 
80 500+ 500+ 
______________________________________ 
TABLE IV 
______________________________________ 
Example 19 
FILM CURE TIME VERSUS TEMPERATURE 
(MEK DOUBLE RUBS) 
______________________________________ 
Example 5 Blocked 
Isocyanate 100.00 parts 
Diethyltoluenediamine 
10.40 parts 
______________________________________ 
Time Temperature (.degree.C.) 
(minutes) 120 140 
______________________________________ 
10 300 500+ 
20 425 500+ 
30 500+ 500+ 
50 500+ 500+ 
80 500+ 500+ 
______________________________________ 
Although the invention has been described in detail in the foregoing for 
the purpose of illustration, it is to be understood that such detail is 
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.