Blocked polyisocyanates prepared from partially trimerized cyclic organic diisocyanates having (cyclo)aliphatically bound isocyanate groups and their use for the production of coatings

The present invention relates to a blocked polyisocyanate which is based on the reaction product of a polyisocyanate with a reversible, monofunctional blocking agent for isocyanate groups, wherein the polyisocyanate is prepared by trimerizing 5 to 85% of the isocyanate groups of a cyclic organic diisocyanate having (cyclo)aliphatically bound isocyanate groups and contains PA0 i) an isocyanurate group-containing polyisocyanate and PA0 ii) at least 5% by weight, based on the weight of the polyisocyanate, of unreacted diisocyanate. The present invention also relates to a one-component coating composition containing this blocked polyisocyanate and a polyhydroxyl polyacrylate and/or a polyhydroxyl polyester. Finally, the present invention relates to substrates coated with this coating composition.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to blocked polyisocyanates prepared by 
blocking partially trimerized cyclic organic diisocyanates having 
(cyclo)aliphatically bound isocyanate groups, to one-component coating 
compositions containing this blocked polyisocyanate and a polyhydroxyl 
component and to the coatings obtained therefrom. 
2. Description of the Prior Art 
There is a need in the automotive industry for a clear topcoat which can be 
applied over existing basecoats and which provides improved environmental 
etch resistance. The thermoset melamine/acrylics which are conventionally 
used as the clearcoat suffer from poor resistance to acid rain, bird 
droppings, tree sap, etc. 
Recently, two-component polyurethane coatings have increasingly been used 
as clearcoats. These coatings possess excellent environmental etch 
resistance and also possess many other excellent properties such as 
appearance, durability, hardness and flexibility. However, the 
two-component polyurethane coating compositions suffer from one major 
disadvantage. They require two-component spray equipment as opposed to the 
conventional thermoset melamine/acrylics which are applied using 
one-component equipment. Therefore, an additional capital expenditure is 
required to obtain the necessary spray equipment for applying the 
two-component polyurethane coating compositions. 
Accordingly, it is an object of the present invention to provide a 
one-component system which overcomes the disadvantages of the 
two-component polyurethane coating compositions. 
This object may be achieved in accordance with the present invention by the 
use of the blocked polyisocyanates described hereinafter. The fact that 
these blocked polyisocyanates may be used for production of coatings with 
improved environmental etch resistance is surprising because the 
polyisocyanates used for the blocking reaction contain unreacted monomer. 
It would be expected that the presence of monomer, which lowers the 
average functionality of the polyisocyanate, would reduce the amount of 
crosslinking and result in coatings with reduced environmental etch 
resistance. 
SUMMARY OF THE INVENTION 
The present invention relates to a blocked polyisocyanate which is based on 
the reaction product of a polyisocyanate with a reversible, monofunctional 
blocking agent for isocyanate groups, wherein the polyisocyanate is 
prepared by trimerizing 5 to 85% of the isocyanate groups of a cyclic 
organic diisocyanate having (cyclo)aliphatically bound isocyanate groups 
and contains 
i) an isocyanurate group-containing polyisocyanate and 
ii) at least 5% by weight, based on the weight of the polyisocyanate, of 
unreacted diisocyanate. 
The present invention also relates to a one-component coating composition 
containing this blocked polyisocyanate and a polyhydroxyl polyacrylate 
and/or a polyhydroxyl polyester. 
Finally, the present invention relates to substrates coated with this 
coating composition.

DETAILED DESCRIPTION OF THE INVENTION 
The polyisocyanate component, which is blocked with the reversible, 
monofunctional blocking agent for isocyanate groups, is a mixture of i) 
polyisocyanates containing isocyanurate groups and ii) unreacted starting 
diisocyanate. The amounts of the individual components are controlled by 
the percentage of isocyanate groups which are trimerized to form 
isocyanurate groups. The final product contains at least 5%, preferably at 
least 10% of unreacted diisocyanate. The isocyanate content of the 
polyisocyanate component increases as the amount of unreacted diisocyanate 
increases. To the contrary the isocyanate content decreases as the amount 
of component i) increases. 
In accordance with the present invention at least 5%, preferably at least 
20% and more preferably at least 25%, of the isocyanate groups are 
trimerized. The upper limit for the amount of isocyanate groups which are 
trimerized is 85% or less, preferably 75% or less and more preferably 65% 
or less. 
The polyisocyanates containing isocyanurate groups are prepared by 
trimerizing a portion of the isocyanate groups of a cyclic diisocyanate 
having (cyclo)aliphatically bound isocyanate groups. The term 
"(cyclo)aliphatic" is defined to include both aliphatically and/or 
cycloaliphatically bound isocyanate groups. The cyclic groups may be 
either aromatic or cycloaliphatic, provided that the isocyanate groups are 
(cyclo)aliphatically bound. Examples of these cyclic diisocyanates include 
cyclohexane-1,3- and -1,4-diisocyanate, 1-isocyanato-2-isocyanatomethyl 
cyclopentane, 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethyl-cyclohexane 
(isophorone diisocyanate or IPDI), bis-(4-isocyanatocyclohexyl)-methane, 
1,3- and 1,4-bis-(isocyanatomethyl)-cyclohexane (HMDI), 
bis-(4-isocyanato-3-methylcyclohexyl)-methane, xylylene diisocyanate, 
.alpha., .alpha., .alpha.', .alpha.'-tetramethyl-1,3- and/or -1,4-xylylene 
diisocyanate, 1-isocyanato-1-methyl-4(3)-isocyanatomethyl cyclohexane, and 
2,4- and/or 2,6-hexahydrotoluylene diisocyanate. Mixtures of cyclic 
diisocyanates may also be used. Preferred cyclic diisocyanates are HMDI 
and IPDI, with HMDI being especially preferred. 
The trimerization reaction is terminated when the desired percentage of 
isocyanate groups has been trimerized. However, it is possible to 
terminate the reaction before the desired percentage of isocyanate groups 
has been trimerized and then remove unreacted HMDI from the mixture, e.g., 
by distillation, until a product is obtained which contains the desired 
percentage of trimerized isocyanate groups. It is also possible to 
trimerize more than 85% of the isocyanate groups and then add starting 
diisocyanate until the percent of trimerized isocyanate groups is within 
the disclosed ranges. These latter two embodiments require additional 
process steps and, thus, are not preferred. 
In accordance with the present invention it is also possible to use a blend 
the cyclic diisocyanates with another organic diisocyanate, preferably an 
aliphatic diisocyanate, for use as the starting material for the 
trimerization reaction. The most preferred diisocyanate for this purpose 
is 1,6-hexamethylene diisocyanate. The other diisocyanates may be blended 
with the cyclic diisocyanates in an amount of up to 30 weight percent, 
preferably 20 weight percent and more preferably 10 weight percent, based 
on the total weight of the diisocyanate starting material. Most 
preferably, the cyclic diisocyanates are used as the sole starting 
material. It is also possible to blend these other diisocyanates or 
polyisocyanate adducts prepared therefrom with the partial trimer of the 
cyclic diisocyanates. 
In accordance with the present invention it is preferred to treat the 
starting diisocyanate prior to or during the trimerization reaction by 
bubbling an inert gas such as nitrogen through the starting diisocyanate 
in order to reduce the content of carbon dioxide. This process is 
discussed in German Offenlegungsschrift 3,806,276 (U.S. application, Ser. 
No. 07/311,920). 
Trimerization catalysts which are suitable for preparing the partial 
trimers according to the invention include those previously known such as 
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 DE-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; and mixtures of alkali metal fluorides and quaternary ammonium 
or phosphonium salts as described in U.S. patent Ser. No. 07/391,213. If 
it is desired to introduce allophanate groups into the resulting product, 
the trimerization catalysts should also catalyze the formation of 
allophanate groups from urethane groups. 
Phosphines, such as those described in DE-OS 1,935,763, may also be used 
for preparing the products of the present invention. The phosphines, in 
addition to promoting the trimerization reaction, also promote the 
dimerization of diisocyanates. 
Particularly suitable as catalysts for the process according to the 
invention are quaternary ammonium hydroxides corresponding to the formula 
##STR1## 
as described in U.S. Pat. No. 4,324,879 and German Offenlegungsschriften 
2,806,731 and 2,901,479. Preferred quaternary ammonium hydroxides are 
those wherein the radicals R.sub.1 to R.sub.4 represent identical or 
different alkyl or aralkyl groups having from 1 to 20, preferably from 1 
to 4 carbon atoms, which may optionally be substituted by hydroxyl groups. 
Two of the radicals R.sub.1 to R.sub.4 may form a heterocyclic ring having 
from 3 to 5 carbon atoms together with the nitrogen atom and optionally 
with a further nitrogen or oxygen atom. Also the radicals R.sub.1 to 
R.sub.3 in each case may represent ethylene radicals which form a bicyclic 
triethylene diamine structure together with the quaternary nitrogen atom 
and a further tertiary nitrogen atom, provided that the radical R.sub.4 
then represents a hydroxyalkyl group having from 2 to 4 carbon atoms in 
which the hydroxyl group is preferably arranged in a 2-position to the 
quaternary nitrogen atom. The hydroxyl-substituted radical or the 
hydroxyl-substituted radicals may also contain other substituents, 
particularly C.sub.1 to C.sub.4 -alkoxy substituents. 
The production of these quaternary ammonium catalysts takes place in known 
manner by reacting a tertiary amine with an alkylene oxide in an 
aqueous-alcoholic medium (c.f. U.S. Pat. No. 3,995,997, col. 2, lines 
19-44). Examples of suitable tertiary amines include trimethylamine, 
tributylamine, 2-dimethylamino-ethanol, triethanolamine, 
dodecyldimethylamine, N,N-dimethylcyclohexylamine, N-methylpyrrolidine, 
N-methylmorpholine and 1,4-diazabicyclo-[2,2,2]-octane. Examples of 
suitable alkylene oxides include ethylene oxide, propylene oxide, 
1,2-butylene oxide, styrene oxide and methoxy, ethoxy or phenoxy propylene 
oxide. The most preferred catalysts from this group are 
N,N,N-trimethyl-N-(2-hydroxyethyl)-ammonium hydroxide and 
N,N,N-trimethyl-N-(2-hydroxypropyl)ammonium hydroxide. Another most 
preferred catalyst is N,N,N-trimethyl-N-benzyl-ammonium hydroxide. The 
trimerization of the starting diisocyanate mixture may be carried out in 
the absence or in the presence of solvents which are inert to isocyanate 
groups. Depending upon the area of application of the products according 
to the invention, low to medium-boiling solvents or high-boiling solvents 
can be used. Suitable solvents include aromatic compounds such as toluene 
or xylene; halogenated hydrocarbons such as methylene chloride and 
trichloroethylene; ethers such as diisopropylether; and alkanes such as 
cyclohexane, petroleum ether or ligroin. 
The trimerization catalysts are generally used in quantities of about 
0.0005 to 5% by weight, preferably about 0.002 to 2% by weight, based on 
the diisocyanate used. If, for example, a preferred catalyst such as 
N,N,N-trimethyl-N(2-hydroxypropyl)-ammonium hydroxide is used, then 
quantities of about 0.0005 to 1% by weight, preferably about 0.001 to 0.02 
by weight, based on starting diisocyanate, are generally sufficient. The 
catalysts may be used in pure form or in solution. The previously named 
solvents which are inert to isocyanate groups are suitable as solvents, 
depending upon the type of catalysts. Dimethyl formamide or dimethyl 
sulphoxide may also be used as solvents for the catalysts. 
The simultaneous use of co-catalysts is possible in the process according 
to the invention, but not necessary. All substances which have a 
polymerizing effect on isocyanates are suitable as co-catalysts such as 
those described in DE-OS 2,806,731 and U.S. Pat. No. 3,487,080. 
Particularly preferred co-catalysts are monoalcohols which react with a 
minor portion of the starting diisocyanate to form urethane groups. In 
addition, these co-catalysts can be used as solvents for the trimerization 
catalyst. The co-catalysts are optionally used in an amount 0.1 to 2% by 
weight, preferably 0.2 to 0.8% by weight, based on the weight of the 
starting diisocyanate. 
The reaction temperature for isocyanurate formation in accordance with the 
present invention is about 10.degree. to 160.degree. C., preferably about 
50.degree. to 150.degree. C. and more preferably about 60.degree. to 
90.degree. C. 
The process according to the invention may take place either batchwise or 
continuously, for example, as described below. The starting diisocyanate 
is introduced with the exclusion of moisture and optionally with an inert 
gas into a suitable stirred vessel or tube and optionally mixed with a 
solvent which is inert to isocyanate groups such as toluene, butyl 
acetate, diisopropylether or cyclohexane. The optional monoalcohol 
co-catalyst may be introduced into the reaction vessel in accordance with 
several embodiments. The monoalcohol may be prereacted with the starting 
diisocyanate to form urethane groups prior to its introduction into the 
reaction vessel; the monoalcohol may be mixed with the diisocyanate and 
introduced into the reaction vessel; the monoalcohol may be separately 
added to the reaction vessel either before or after, preferably after, the 
diisocyanate has been added; or, preferably, the catalyst may be dissolved 
in the monoalcohol prior to introducing the solution into the reaction 
vessel. 
In the presence of the required catalyst or catalyst solution the 
trimerization begins and is indicated by an exothermic reaction. The 
progress of the reaction is followed by determining the NCO content by a 
suitable method such as titration, refractive index or IR analysis. From 
the NCO content it is possible to readily determine the percentage of 
isocyanate groups which have been trimerized. The reaction is terminated 
at the desired degree of trimerization. 
The termination of the trimerization reaction can take place, for example, 
by the addition of a catalyst-poison of the type named by way of example 
in the above-mentioned literature references. For example, when using 
basic catalysts the reaction is terminated by the addition of a quantity, 
which is at least equivalent to the catalyst quantity, of an acid chloride 
such as benzoyl chloride or diethylhexyl phosphate. When using heat-labile 
catalysts, for example, the previously described quaternary ammonium 
hydroxides, poisoning of the catalyst by the addition of a catalyst poison 
may be dispensed with since these catalysts decompose in the course of the 
reaction. When using such catalysts, the catalyst quantity and the 
reaction temperature are preferably selected such that the catalyst which 
continuously decomposes is totally decomposed when the desired degree of 
trimerization is reached. The quantity of catalyst or reaction temperature 
which is necessary to achieve this decomposition can be determined by a 
preliminary experiment. It is also possible initially to use a lesser 
quantity of a heat sensitive catalyst than is necessary to achieve the 
desired degree of trimerization and to subsequently catalyze the reaction 
by a further incremental addition of catalyst, whereby the quantity of 
catalyst added later is calculated such that when the desired degree of 
trimerization is achieved, the total quantity of catalyst has decomposed. 
The use of suspended catalysts is also possible. These catalysts are 
removed after achieving the desired degree of trimerization by filtering 
the reaction mixture. 
The working-up of the reaction mixture, optionally after previous 
separation of insoluble catalyst constituents, may take place in various 
ways depending upon how the reaction was conducted and the area of 
application for the isocyanates. One of the primary advantages of the 
present invention is that it is not necessary to remove unreacted HMDI 
from the reaction mixture. 
The partial trimers according to the invention are valuable starting 
materials for one-component polyurethane coating compositions in which the 
isocyanate groups are used in a form blocked by known blocking agents. The 
blocking reaction is carried out in known manner by reacting the 
isocyanate groups with suitable blocking agents, preferably at an elevated 
temperature (e.g. about 40.degree. to 160.degree. C.), and optionally in 
the presence of a suitable catalyst, for example, the previously described 
tertiary amines or metal salts. 
Suitable blocking agents include monophenols such as phenol, the cresols, 
the trimethylphenols and the tert. butyl phenols; tertiary alcohols such 
as tert. butanol, tert. amyl alcohol and dimethylphenyl carbinol; 
compounds which easily form enols such as acetoacetic ester, acetyl 
acetone and malonic acid derivatives, e.g. malonic acid diethylester; 
secondary aromatic amines such as N-methyl aniline, the N-methyl 
toluidine, N-phenyl toluidine and N-phenyl xylidine; imides such as 
succinimide; lactams such as .epsilon.-caprolactam and 
.delta.-valerolactam; oximes such as methyl ethyl ketoxime (butanone 
oxime), methyl amyl ketoxime and cyclohexanone oxime; mercaptans such as 
methyl mercaptan, ethyl mercaptan, butyl mercaptan, 
2-mercaptobenzthiazole, .alpha.-naphthyl mercaptan and dodecyl mercaptan; 
and triazoles such as 1H-1,2,4-triazole. 
Preferred blocking agents are the oximes; methyl ethyl ketoxime is 
especially preferred. 
Reaction partners for the partial trimers according to the invention are 
polyhydroxyl polyesters and polyhydroxyl polyacrylates. The polyester 
polyols contain at least 2 preferably 2 to 15 and more preferably 2 to 6 
hydroxyl groups, and have a molecular weight of 400 to 6,000, preferably 
800 to 3,000. The molecular weights are number average molecular weights 
(M.sub.n) and are determined by end group analysis (OH number). In 
accordance with the present invention the polyhydroxyl polycarbonates are 
included with the polyester polyols. 
Suitable polyester polyols include reaction products of 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 
substituted, e.g. by halogen atoms, and/or unsaturated. The following are 
mentioned as examples: 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 terephthalates and bis-glycol terephthalate. Suitable 
polyhydric alcohols include, e.g. ethylene glycol; propylene glycol-(1,2) 
and -(1,3); butylene glycol-(1,4) and -(1,3); hexanediol-(1,6); 
octanediol-(1,8); neopentyl glycol; cyclohexanedimethanol 
(1,4-bis-hydroxymethylcyclohexane); 2-methyl-1,3-propanediol; 
2,2,4-trimethyl-1,3-pentanediol; triethylene glycol; tetraethylene glycol; 
polyethylene glycol; dipropylene glycol; polypropylene glycol; dibutylene 
glycol and polybutylene glycol, glycerine, trimethlyolpropane, 1,2,6hexane 
triol, 1,2,4-butane triol, trimethylol ethane, pentaerythritol, mannitol, 
sorbitol, sucrose, hydroquinone and 1,1,1- or 1,1,2- 
tris-(hydroxylphenyl)-ethane. The polyesters may also contain a portion of 
carboxyl end groups. Polyesters of lactones, e.g. .epsilon.-caprolactone 
or hydroxycarboxylic acids, e.g. -hydroxycaproic acid, may also be used. 
Polycarbonates containing hydroxyl groups include those known such as the 
products obtained from the reaction of diols such as propanediol-(1,3), 
butanediol-(1,4) and/or hexanediol-(1,6), diethylene glycol, triethylene 
glycol or tetraethylene glycol with phosgene, diarylcarbonates such as 
diphenylcarbonate or with cyclic carbonates such as ethylene or propylene 
carbonate. Also suitable are polyester carbonates obtained form the 
above-mentioned polyesters or polylactones with phosgene, diaryl 
carbonates or cyclic carbonates. 
The polyhydroxy polyacrylates preferably have at least two alcoholic 
hydroxyl groups per molecule as a statistical average, although a small 
portion of monohydroxyl compounds may be present. The polyhydroxy 
polyacrylates may be prepared by known methods such as those described in 
European Patent Office Publication 68,383, German Patentschrift 2,460,329, 
British Patent 1,515,868, U.S. Pat. No. 3,002,959, U.S. Pat. No. 3,375,227 
or German Auslegeschrift 1,038,754. The polyhydroxy polyacrylates are 
generally prepared by the radical polymerization or copolymerization of a 
hydroxyalkyl ester of an unsaturated carboxylic acid, preferably acrylic 
or methacrylic acid, with itself or preferably together other 
hydroxyl-free unsaturated monomers. 
Suitable hydroxylalkyl esters include esters containing 2 to 8, preferably 
2 to 4 carbon atoms in the alkyl group and obtained from .alpha., 
.beta.-unsaturated carboxylic acids having 3 to 5 carbon atoms, such as 
acrylic, methacrylic, fumaric, maleic, itaconic or crotonic acid. The 
acrylic and methacrylic acid esters are preferred. Hydroxyalkyl esters of 
the above-mentioned acids containing ether bridges in the alkyl groups may 
also be used but are less preferred. The particularly preferred monomers 
with alcoholic hydroxyl groups include the 2-hydroxyethyl-, 2- and 
3-hydroxypropyl-, and 2-, 3- and 4-hydroxybutyl-acrylates and 
-methacrylates. These monomers containing alcoholic hydroxyl groups may be 
prepared, for example, by the reaction of the above-mentioned acids with 
epoxides such as alkylene or propylene oxide. 
The polyhydroxy polyacrylates which are used may also be prepared by 
reacting the corresponding polyacrylates containing carboxylic acid groups 
with alkylene oxides such as propylene oxide and/or ethylene oxide in the 
presence of suitable alkoxylation catalysts such as tetrabutylammonium 
bromide. The starting materials for this alkoxylation reaction, i.e., the 
polyacrylates containing carboxylic acid groups, are obtained in known 
manner by the copolymerization of unsaturated carboxylic acids such as 
acrylic acid and/or methacrylic acid with unsaturated comonomers which do 
not contain carboxyl or hydroxyl groups. The preferred method for 
preparing the polyhydroxy polyacrylates is the copolymerization of the 
hydroxyalkyl esters of unsaturated carboxylic acids previously set forth. 
The comonomers used for the above-mentioned hydroxyl group-containing 
monomers may be any .alpha.,.beta.-olefinically unsaturated compounds in 
the molecular weight range of 28 to 350 which are free from hydroxyl 
groups such as ethylene, propylene, butene-1, hexene-1, octene-1, styrene, 
.alpha.-methylstyrene, divinyl benzene, various isomeric vinyl toluenes, 
esters of .alpha.,.beta.-unsaturated carboxylic acids of the type 
exemplified above monohydric aliphatic alcohols having 1 to 18, preferably 
1 to 10 carbon atoms, in particular the corresponding esters of acrylic or 
methacrylic acids such as the methyl, ethyl, N-butyl, N-pentyl, N-hexyl, 
2-ethylhexyl or octadecyl esters of acrylic or methacrylic acid. 
Neutral esters of polycarboxylic acids are also suitable comonomers, for 
example, itaconic, crotonic, maleic or fumaric esters of the monohydric 
alcohols exemplified above. 
Acrylic acid, methacrylic acid, vinyl acetate, acrylonitrile, 
methacrylonitrile and dienes such as isoprene or or butadiene are all 
suitable comonomers. Vinyl chloride may in principle also be used as a 
comonomer. 
Particularly preferred polyhydroxy polyacrylates are obtained from about 10 
to 50 parts by weight of hydroxyalkyl esters of acrylic or methacrylic 
acid, 0 to 80 parts by weight of styrene and/or .alpha.-methylstyrene, 
about 10 to 90 parts by weight of an acrylic and/or methacrylic acid ester 
free from hydroxyl group of the type exemplified above and 0 to about 5 
parts by weight of an .alpha.,.beta.-unsaturated mono- or dicarboxylic 
acid of the type exemplified, in particular acrylic acid or methacrylic 
acid. 
The compositions may also contain a low molecular weight 
isocyanate-reactive component having an average molecular weight of up to 
400. The low molecular weight compounds which may optionally be used in 
combination with the high molecular weight polyhydroxyl polyesters and 
polyhydroxyl polyacrylates include the polyhydric alcohols which have been 
described for the preparation of the polyester polyols and also the low 
molecular weight polyamines which are known from polyurethane chemistry. 
The amounts of the partial trimer and polyhydroxyl compounds are selected 
to provide an equivalent ratio of isocyanate groups (whether present in 
blocked or unblocked form) to isocyanate-reactive groups of about 0.8 to 
3, preferably about 0.9 to 2.0 and more preferably about 1.0 to 1.5. 
To accelerate hardening, the coating compositions may contain known 
polyurethane catalysts, e.g., tertiary amines such as triethylamine, 
pyridine, methyl pyridine, benzyl dimethylamine, N,N-dimethylamino 
cyclohexane, N-methylpiperidine, pentamethyl diethylene triamine, 
1,4-diazabicyclo[2,2,2]-octane and N,N'-dimethyl piperazine; or metal 
salts such as iron(III)-chloride, zinc chloride, zinc-2-ethyl caproate, 
tin(II)-ethyl caproate, dibutyltin(IV)-dilaurate and molybdenum glycolate. 
The coating compositions may also contain other additives such as pigments, 
dyes, fillers, levelling agents and solvents. The coating compositions may 
be applied to the substrate to be coated in solution or from the melt by 
conventional methods such as painting, rolling, pouring or spraying. 
The coating compositions containing the polyisocyanates according to the 
invention provide coatings which adhere surprisingly well to a variety of 
materials including metal substrates and basecoats (especially those used 
in the automotive industry), and are particularly light-fast, color-stable 
in the presence of heat and very resistant to abrasion. Furthermore, they 
are characterized by high hardness, elasticity, very good resistance to 
chemicals, high gloss, excellent weather resistance, excellent 
environmental etch resistance and good pigmenting qualities. 
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. Isocyanate contents and equivalents weights 
are based on the weight of the solution unless otherwise specified. 
EXAMPLES 
Polyisocyanate I--Preparation of partially trimerized HMDI 
A round bottom flask was charged with 2990.2 g of HMDI and 747.55 g of 
xylene. A nitrogen inlet tube was placed into the solution and a slow 
stream of nitrogen was bubbled through for two hours. The solution was 
heated to 70.degree. C. and 15.94 g of a catalyst solution was added. The 
catalyst solution was prepared by mixing 47.2 g of a 40% 
benzyltrimethylammonium hydroxide solution in methanol with 59.9 g of 
1-butanol. The temperature began to rise from the exothermic reaction. The 
reaction temperature was maintained between 70.degree. and 83.degree. C. 
until an isocyanate content of 13.48 was obtained by titration. This took 
approximately 1.5 hours. 6.18 g of diethylhexyl phosphate was then added 
to inactivate the catalyst. The product had a viscosity of 190,000 mPa.s. 
To reduce the viscosity 534.0 g of xylene was added. The final product had 
a viscosity of 3,090 mPa.s at 25.degree. C., a solids content of 70%, an 
isocyanate content of 11.72%, and an equivalent weight of 358.4 g/eq. 
Polyisocyanate II 
An isocyanurate group-containing polyisocyanate prepared by trimerizing a 
portion of the isocyanate groups of 1,6-hexamethylene diisocyanate and 
having an isocyanate content of 21.6% by weight, a content of monomeric 
diisocyanate of &lt;0.2% and a viscosity at 20.degree. C. of 3000 mPa.s. 
Polyisocyanate III 
An isocyanurate group-containing polyisocyanate present as a 70% solution 
in 1:1 blend of propylene glycol monomethyl ether acetate and xylene and 
prepared by trimerizing a portion of the isocyanate groups of isophorone 
diisocyanate, wherein the solution has an isocyanate content of 11.7% by 
weight, a content of monomeric diisocyanate of &lt;0.5% and a viscosity at 
20.degree. C. of 1300 to 2700 mPa.s. 
Polyisocyanate IV 
A blend of 40% Polyisocyanate II and 60% Polyisocyanate III, wherein the 
percentages are based on solids. 
Polyisocyanate V--Preparation of partially trimerized IPDI 
A round bottom flask was charged with 1000 g of IPDI and 428.6 g of xylene. 
A nitrogen inlet tube was placed into the solution and a slow stream of 
nitrogen was bubbled through for two hours. The solution was heated to 
70.degree. C. and 5.0 g of a catalyst solution was added. The catalyst 
solution was prepared by mixing 47.2 g of a 40% benzyltrimethylammonium 
hydroxide solution in methanol with 59.9 g of 1-butanol. The temperature 
began to rise from the exothermic reaction. The reaction temperature was 
maintained between 70.degree. and 80.degree. C. until an isocyanate 
content of 12.9% was obtained by titration. This took approximately 1.5 
hours. 1.92 g of diethylhexyl phosphate the final product was 736 mPa.s at 
23.degree. C. 
Blocked Polyisocyanate I--Preparation of a blocked, partially trimerized 
HMDI 
A round bottom flask was charged with 716.8 g (2.0 eq) of the partially 
trimerized HMDI described in the preceding example. To this stirred 
solution was slowly added 175.74 (2.02 eq) of methyl ethyl ketoxime, while 
cooling the flask with a water bath. The temperature was not allowed to 
exceed 80.degree. C. After the addition was complete, the mixture was 
stirred at 70.degree. C. for 1 to 2 hours until the isocyanate content was 
0.13%. Because this product was very viscous 149.77 g of propylene glycol 
monomethyl ether acetate was added to reduce the viscosity. The final 
product had a viscosity of 23,000 mPa.s at 25.degree. C., a solids 
content of 65%, a blocked isocyanate content of 8.06%, and an equivalent 
weight of 521.1 g/eq. 
Blocked Polyisocyanate II 
Blocked Polyisocyanate I was repeated except that the methyl isobutyl 
ketone was used in place of propylene glycol monomethyl ether acetate. 
Blocked Polyisocyanate III 
A blocked polyisocyanate prepared by blocking Polyisocyanate II with methyl 
ethyl ketoxime as described for the preparation of Blocked Polyisocyanate 
I. 
Blocked Polyisocyanate IV 
A blocked polyisocyanate prepared by blocking Polyisocyanate III with 
methyl ethyl ketoxime as described for the preparation of Blocked 
Polyisocyanate I. 
Blocked Polyisocyanate V 
A blend of 40% Blocked Polyisocyanate III and 60% Blocked Polyisocyanate 
IV, wherein the percentages are based on solids. 
Blocked Polyisocyanate VI and VII--Preparation of blocked, partially 
trimerized HMDI's 
In two separate experiments a round bottom flask was charged with 69.66 g 
of HMDI and 29.86 g of xylene. A nitrogen inlet tube was placed into the 
solution and a slow stream of nitrogen was bubbled through for two hours. 
The solution was heated to 70.degree. C. and 0.348 g of the catalyst 
solution was added. The catalyst solution was prepared by mixing 47.2 g of 
a 40% benzyltrimethylammonium hydroxide solution in methanol with 59.9 g 
of 1-butanol. The temperature began to rise from the exothermic reaction. 
The reaction temperature was maintained between 70.degree. and 80.degree. 
C. until the isocyanate content set forth in the following table was 
obtained by titration. This took approximately 1.5 hours. 0.132 g of 
diethylhexyl phosphate was then added to inactivate the catalyst. 
In separate experiments a round bottom flask was charged with 1.0 eq of the 
two partially trimerized HMDI's and sufficient propylene glycol monomethyl 
ether acetate to obtain a solids content of 65%. To this stirred solution 
was slowly added 1.01 eq of methyl ethyl ketoxime, while cooling the flask 
with a water bath. The temperature was not allowed to exceed 80.degree. C. 
After the addition was complete, the mixture was stirred at 70.degree. C. 
for 1 to 2 hours until the isocyanate content was less than 0.2%. The 
viscosity and equivalent weight of the final product, which are dependent 
upon the isocyanate content of the unblocked partial trimer, are set forth 
in the table. 
______________________________________ 
Blocked Isocyanate Viscosity 
Equivalent 
Isocyanate 
Content at 25.degree. C. 
Weight 
______________________________________ 
VI 15.68 1050 422.5 
VII 13.82 3140 461.1 
______________________________________ 
Blocked Polyisocyanate VIII--Preparation of a blocked, partially trimerized 
IPDI 
A round bottom flask was charged with 1.0 eq of the Polyisocyanate V and 
sufficient propylene glycol monomethyl ether acetate to obtain a solids 
content of 65%. To this stirred solution was slowly added 1.01 eq of 
methyl ethyl ketoxime, while cooling the flask with a water bath. The 
temperature was not allowed to exceed 80.degree. C. After the addition was 
complete, the mixture was stirred at 70.degree. C. for 1 to 2 hours until 
the isocyanate content was less than 0.2%. The product had a viscosity of 
3820 mPa.s at 25.degree. C. and an equivalent weight of 485. 
Polyol I 
A polyacrylate polyol having an OH equivalent weight of 607, an OH content 
of 2.8% and an acid number of &lt;10, present as a 65% solution in a 3:1 
mixture of butyl acetate and xylene, and prepared from 41.95% styrene, 
32.53% hydroxyethyl methacrylate, 24.57% butylacrylate and 0.95% acrylic 
acid. 
Polyol II 
A polyacrylate/polyester polyol mixture having an OH equivalent weight of 
630, an OH content of 2.7% and an acid number of &lt;10, present as a 65% 
solution in xylene, and containing 20% of Polyol 3 and 45% of Polyol 4. 
Polyol III 
A polyester polyol having an OH equivalent weight of 400, an OH content of 
4.25% and a functionality of about 3.1 and prepared from 34.6 parts 
1,6-hexane diol, 9.8 parts trimethylol propane, 30.43 parts isophthalic 
acid, 5.4 parts phthalic acid anhydride and 10.7 parts adipic acid. 
Polyol IV 
A polyacrylate polyol prepared from 26.07% styrene, 26.07% hydroxyethyl 
acrylate, 46.88% butylacrylate and 0.98% acrylic acid. 
Catalyst 
A 1% solution in propylene glycol monomethyl ether acetate of dibutyltin 
dilaurate (available as T-12 from Air Products and Chemicals). 
Additive A 
A polyether modified dimethylpolysiloxane copolymer flow aid (available as 
Byk 301 from Byk Chemie). 
Additive B 
A hindered amine light stabilizer (available as Tinuvin 292 from 
Ciba-Geigy). 
Additive C 
A benzotriazole light stabilizer (available as Tinuvin 1130 from 
Ciba-Geigy). 
EXAMPLE 1 
A coating composition was prepared by mixing Blocked Polyisocyanate I with 
the polyol set forth in Table 1 at the NCO/OH equivalent ratio set forth 
in Table 1. The coating composition also contained 1% of Additive A, 1.3% 
of Additive B, 1.3% of Additive C and the amount of Catalyst set forth in 
the Table, wherein all of the percentages are based on resin solids. A 
1:1:1 blend of methyl amyl ketone, xylene and methyl isobutyl ketone was 
added until the coating composition had a viscosity of 20 sec. as measured 
using a #4 Ford cup at room temperature. 
Panels were sprayed over commercial black basecoats and placed outdoors 
laying horizontally in Florida and were rated from 0 to 10 for 
environmental etch resistance every two weeks. 
0=No Etch 
1=Very Minor Etch 
2-3=Slight Etch 
4-6=Moderate Etch 
7-10=Total Failure 
TABLE 1 
__________________________________________________________________________ 
4 6 8 10 12 14 16 18 22 
Panel 
Polyol 
NCO/OH 
Catalyst 
wks 
wks 
wks 
wks 
wks 
wks 
wks 
wks 
wks 
__________________________________________________________________________ 
1 Polyol II 
1.1 .05 1 1 1 3 3 4 1 2 1 
2 Polyol II 
1.1 .1 1 1 1 3 3 4 1 2 1 
3 Polyol II 
1.5 .1 1 0 1 3 2 2 1 2 1 
4 Polyol I 
1.5 .1 0 1 1 2 1 1 1 1 1 
5 Polyol I 
1.1 .1 1 1 1 2 2 3 1 2 1 
6 Polyol I 
1.1 .05 1 1 1 2 2 3 1 2 1 
__________________________________________________________________________ 
EXAMPLE 2 
A coating composition was prepared by mixing the blocked polyisocyanate set 
forth in Table II with Polyol II at an NCO/OH equivalent ratio of 1.1:1. 
The coating composition also contained 0.1% Catalyst, 1% of Additive A, 
1.3% of Additive B and 1.3% of Additive C, wherein all of the percentages 
are based on resin solids. A 1:1:1 blend of methyl amyl ketone, xylene and 
methyl isobutyl ketone was added until the coating composition had a 
viscosity of 20 sec. as measured using a #4 Ford cup at room temperature. 
The values set forth in Table 2 are the average for two panels. 
TABLE 2 
__________________________________________________________________________ 
Panel 
Polyisocyanate 
2 wks 
4 wks 
6 wks 
8 wks 
12 wks 
__________________________________________________________________________ 
1 Polyisocyanate IV 
2 3 5 4.5 2 
2 Blocked Polyisocyanate II 
1.5 
2 3 1 1 
3 Blocked Polyisocyanate V 
4 2.5 
4 2.5 3 
__________________________________________________________________________ 
EXAMPLE 3 
Coating compositions were prepared by mixing the polyisocyanate or blocked 
polyisocyanates set forth in Table III with Polyol II at an NCO/OH 
equivalent ratio of 1.3:1. The coating compositions also contained 0.1% 
Catalyst, 1% of Additive A, 1.3% of Additive B and 1.3% of Additive C, 
wherein all of the percentages are based on resin solids. A 1:1:1 blend of 
methyl amyl ketone, xylene and methyl isobutyl ketone was added until the 
coating compositions had a viscosity of 20 sec. as measured using a #4 
Ford cup at room temperature. The coating compositions were applied to 
panels as described in Example 1. Three panels were prepared for each 
coating composition, one was cured at 250.degree. F., one at 275.degree. 
F. and one at 300.degree. F. The cured panels were tested for 
environmental etch, solvent resistance and hardness. The panels were then 
rated best (1), second best (2) and worst (3). The results are set forth 
in Table 3. 
TABLE 3 
__________________________________________________________________________ 
Etch Resistance 
Solvent Resistance 
Hardness 
Temp., .degree.F. 
Temp., .degree.F. 
Temp., .degree.F. 
Polyisocyanate 
250 
275 
300 
250 
275 300 
250 
275 
300 
__________________________________________________________________________ 
Blocked Polyisocyanate II 
1 1 1 1 1 1 1 1 1 
Blocked Polyisocyanate V 
3 3 3 3 3 1 1 1 1 
Polyisocyanate IV 
1 2 1 1 1 1 1 3 1 
__________________________________________________________________________ 
Etch resistance was determined using 5 solutions 
______________________________________ 
Etch resistance was determined using 5 solutions 
______________________________________ 
1 Tap water 
2 1% hydrochloric acid 
3 2% hydrochloric acid 
4 0.01N sulfuric acid 
5 Acid rain spot 41% sulfuric acid 
21% nitric acid 
4% hydrochloric acid 
34% ammonium hydroxide 
pH = 3 
______________________________________ 
Solutions 1-5 were pipetted as 50 microliter droplets onto a test panel 
using a 150 microliter micropipette (3 droplets for each solution) to 
ensure uniform distribution of the test solutions. The panels were then 
placed in a 150.degree. F. oven for 1 hour. Solution 5 was repeated by 
pipetting as described previously onto a test panel and baked for 15 hours 
at 150.degree. F. 
The spots were then rated on a scale of 0-5 (0=no etch damage and 5=failure 
or severe etch damage) and a total etch number was assigned. A ranking of 
best to worst for each system was then assigned. 
Solvent resistance was determined by wetting cheesecloth with methyl ethyl 
ketone and then rubbing each panel 100 times. A double rub consists of one 
back and forth rub against the coated panel. Following a five minute 
waiting period after the rubs were completed, each panel was scratched 
with a thumb nail. If there was no evidence of film destruction, the films 
were rated as passing. 
Pendulum Hardness was determined by evaluating coated panels of a Pendulum 
Hardness Tester. The tester was levelled, and at the desired interval of 
measurement the metal plate was placed on the sample stage of the tester. 
The fulcrum points of the pendulum were lowered onto the curing film, the 
pendulum was deflected 6.degree. and released. The time for the pendulum 
to damp to a 3.degree. deflection was recorded. 
EXAMPLE 4 
Coating compositions were prepared by mixing the polyisocyanate or blocked 
polyisocyanates set forth in Table IV with Polyol II at an NCO/OH 
equivalent ratio of 1.3:1. The coating compositions also contained 0.1% 
Catalyst, 1% of Additive A, 1.3% of Additive B and 1.3% of Additive C, 
wherein all of the percentages are based on resin solids. A 1:1:1 blend of 
methyl amyl ketone, xylene, and methyl isobutyl ketone was added until the 
coating compositions had a viscosity of 20 sec. as measured using a #4 
Ford cup at room temperature. The coating compositions were applied to 
panels as described in Example 3 and cured at 300.degree. F. The cured 
panels were tested for environmental etch, solvent resistance and hardness 
using the procedures described in Example 3. The panels were then rated 
best (1), second best (2) and worst (3). The results are set forth in 
Table 4. 
TABLE 4 
______________________________________ 
Etch Solvent 
Polyisocyanate Resistance 
Resistance 
Hardness 
______________________________________ 
Blocked Polyisocyanate VI 
1 1 1 
Blocked Polyisocyanate VII 
2 1 1 
Polyisocyanate IV 
3 1 1 
______________________________________ 
The examples demonstrate that coatings prepared from one-component systems 
containing the blocked polyisocyanates of the present invention possess 
excellent acid etch resistance when compared to one-component systems 
which correspond to the existing two-component systems, i.e., systems 
prepared by blocking the isocyanate component of the two-component system 
to obtain a one-component system. The examples also demonstrate that when 
all of the properties are evaluated, the one-component systems according 
to the invention can be used to prepare coatings which possess properties 
which are equal to or better than the properties of coatings prepared from 
the corresponding two-component system. 
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.