Acid-epoxy-melamine coating composition modified with a silane polymer

A coating composition useful for a finish for automobiles and trucks in which the film forming binder comprises an acrylic polymer having at least two reactive acid groups, an epoxy-containing crosslinker, a melamine resin, and an epoxy-silane modifying agent. The composition may be used as a one-package system with a reasonable pot life. The composition is characterized by improved environmental resistance.

FIELD OF THE INVENTION 
This invention is related to a coating composition comprising an 
acid-epoxy-melamine composition modified with a silane polymer. 
BACKGROUND 
There are a wide variety of coating compositions available for finishing 
automobiles and trucks. Various coating compositions comprising 
anhydride-epoxy or acid-epoxy containing compositions are known. For 
example, U.S. Pat. No. 4,906,677 discloses a composition comprising an 
acrylic anhydride polymer, a glycidyl component, and a phosphonium 
catalyst. U.S. Pat. No. 4,681,811 discloses a composition comprising a 
polyepoxide and a polyacid curing agent. 
A problem with present coating compositions for automobiles and trucks, or 
parts thereof, is that durability is not as good as desired. An important 
aspect of durability is environmental resistance. The present invention 
offers a high quality finish exhibiting superior environmental resistance. 
Another problem with epoxy-containing systems has been that, due to 
limited pot life, they have been used as a two package system, which 
packages are conventionally mixed shortly before use. The present 
composition is a potential one-package system. Such a coating composition 
exhibits excellent adhesion to the substrate to which it is applied, good 
outdoor weatherability, etch resistance, and gloss. 
SUMMARY OF THE INVENTION 
An essentially anhydride-free coating composition containing 20-80% by 
weight of binder components and 80-20% by weight of solvent. The binder 
contains, as separate molecules or components of the mixture, the 
following: 
(a) an acid polymer having at least two acid (carboxyl) groups and having a 
weight average molecular weight of about 2,000-50,000; 
(b) an epoxy component having at least two reactive glycidyl groups; 
(c) a melamine crosslinker; 
(d) an acrylosilane polymer; and 
(e) an effective amount of a curing catalyst. 
In one embodiment of the invention, the acrylosilane polymer has reactive 
epoxy groups as well as silane groups. 
DETAILED DESCRIPTION OF THE INVENTION 
The composition of the present invention forms a durable environmental 
resistant coating. The composition is especially useful for finishing the 
exterior of automobiles and trucks. 
The composition can also be pigmented to form a colored finish, although 
the composition is especially useful as a clearcoat. 
Preferably, the coating composition has a high solids content and contains 
about 20-80% by weight binder and 20-80% by weight of organic solvent. The 
binder of the composition contains about 25-90%, preferably 35 to 65% by 
weight of binder, of an acid polymer containing at least two acid groups; 
5-30%, preferably 10 to 20% by weight of binder, of a glycidyl containing 
component; 5-30%, preferably 10-20% of polymer comprising silane groups 
and optionally epoxy groups; and 2-15% of a polymeric melamine resin, 
preferably 3-9% by weight of binder. 
Optionally, the composition may, in addition, comprise 5-30%, preferably 10 
to 25% by weight of binder of an acrylic or a polyester or a polyester 
urethane which may contain hydroxyl and/or acid functionality. If hydroxy 
functional, the hydroxy number is 20 to 120. If acid functional, the acid 
number is 20 to 120. The binder should contain a maximum of 25%, based on 
the weight of the binder of aromatic vinyl. 
The acid polymer employed in preparing the present composition has a weight 
average molecular weight of about 2,000-50,000, determined by gel 
permeation chromatography using polymethyl methacrylate as a standard. 
Preferably the acid polymer has a weight average molecular weight of 
3,000-25,000. 
The acid polymer may be prepared by conventional techniques in which the 
monomers, solvent, and conventional catalysts such as t-butyl perbenzoate 
are charged into a polymerization vessel and heated to about 
75.degree.-200.degree. C. for about 0.5-6 hours to form the polymer. 
The acid polymer can be formed by polymerizing monomers of alkyl 
methacrylates, or alkyl acrylates or mixtures thereof, where the alkyl 
groups have 1-12 carbon atoms, preferably 1-6 carbon atoms, and 
ethylenically unsaturated acids. Optionally, the acid functional polymer 
can also contain other components such as styrene, methyl styrene, and/or 
acrylonitrile, methacrylonitrile in amounts of about 0.1-50% by weight. 
Typically useful ethylenically unsaturated acids are acrylic acid, 
methacrylic acid, itaconic acid, maleic acid, isobutenyl succinic acid, 
and the like. 
This acid resin may also contain hydroxyl functionality by using monomers 
such as hydroxyethylacrylate, hydroxyethyl methacrylate and hydroxypropyl 
acrylate. The hydroxy functionality may be introduced by a post reaction 
of the acid with epoxy containing compounds such as Cardura E.RTM. from 
Shell Chemical Company (a glycidyl ester of versatic acid) and propylene 
oxide. 
Typical alkyl acrylates and methacrylates that can be used to form the acid 
acrylic polymer are methyl methacrylate, ethyl methacrylate, propyl 
methacrylate, butyl methacrylate, isobutyl methacrylate, pentyl 
methacrylate, hexyl methacrylate, octyl methacrylate, nonyl methacrylate, 
decyl methacrylate, lauryl methacrylate, methyl acrylate, ethyl acrylate, 
propyl acrylate, butyl acrylate, octyl acrylate, nonyl acrylate, decyl 
acrylate, lauryl acrylate, and the like. Cycloaliphatic methacrylates and 
acrylates also can be used, for example, such as trimethylcyclohexyl 
methacrylate, trimethylcyclohexyl acrylate, iso-butyl methacrylate, 
t-butyl cyclohexyl acrylate, or t-butyl cyclohexyl methacrylate. Aryl 
acrylate and aryl methacrylates also can be used, for example, such as 
benzyl acrylate and benzyl methacrylate. Of course, mixtures of the two or 
more of the above mentioned monomers are also suitable. 
Other components that can be used to form the acid acrylic polymer are 
acrylamide and methacrylamide. 
It is also possible to impart the acid functionality to the acid acrylic 
polymer by using an ethylenically unsaturated acid anhydride which can be 
converted completely or substantially completely to the corresponding add 
polymer. 
A preferred acid acrylic polymer comprises styrene, butyl methacrylate, 
n-butyl acrylate, and methacrylic acid. 
The epoxy component preferably contains at least two glycidyl groups and 
can be an oligomer or a polymer. Typical glycidyl components are sorbitol 
polyglycidyl ether, mannitol polyglycidyl ether, pentaerythritol 
polyglycidol ether, glycerol polyglycidyl ether, low molecular weight 
epoxy resins such as epoxy resins of epichlorohydrin and bisphenol A, di- 
and polyglycidyl esters of acids, polyglycidyl ethers of isocyanurates, 
such as Denecol EX301.RTM. from Nagase. Sorbitol polyglycidyl ethers, such 
as DCE-358.RTM. from Dixie, Inc., and di- and polyglycidyl esters of 
acids, such as Araldite CY-184.RTM. from Ciba-Geigy or XUS-71950.RTM. from 
Dow Chemical form high quality finishes. Cycloaliphatic epoxies such as 
CY-179.RTM. from Ciba-Geigy may also be used. 
Glycidyl methacrylate or acrylate containing acrylic polymers can be used, 
such as random and block polymers of glycidyl methacrylate/butyl 
methacrylate. The block polymers can be prepared by anionic polymerization 
or by group, transfer polymerization. 
The melamine crosslinker is suitably a conventionally known alkylated 
melamine formaldehyde resin that is partially or fully alkylated, for 
example a methylated and butylated or isobutylated melamine formaldehyde 
resin that has a degree of polymerization of about 1-5. Polymeric 
melamines are preferred because they are catalyzed by weak acids such as 
carboxylic acids versus strong acids such as sulfonic acids and are not 
hindered by amines. 
The silane polymer portion of the binder has a weight average molecular 
weight of about 1000 to 30,000. (All molecular weights disclosed herein 
are determined by gel permeation chromatography using a polystyrene 
standard.) The silane polymer is suitably the polymerization product of 
about 5-70%, preferably 40-60%, by weight of polymer, of ethylenically 
unsaturated silane containing monomers, and 30-95%, preferably 40-60%, by 
weight of non-silane containing monomers. Suitably non-silane containing 
monomers are the alkyl acrylates and alkyl methacrylates mentioned above 
with respect to the acid polymer, as well as styrene, methyl styrene, 
acrylamide, acrylonitrile, methacrylonitrile, and the like. 
In addition to alkyl acrylates or methacrylates, other 
non-silane-containing polymerizable monomers, up to about 50% by weight of 
the polymer, can be used in an acrylosilane polymer for the purpose of 
achieving the desired physical properties such as hardness, appearance, 
mar resistance, and the like. Exemplary of such other monomers are 
styrene, methyl styrene, acrylamide, acrylonitrile, methacrylonitrile, and 
the like. Styrene can be used in the range of 0-50% by weight. 
A suitable silane containing monomer useful in forming an acrylosilane 
polymer is an alkoxysilane having the following structural formula: 
##STR1## 
wherein R is either CH.sub.3, CH.sub.3 CH.sub.2, CH.sub.3 O, or CH.sub.3 
CH.sub.2 O; R.sub.1 and R.sub.2 are CH.sub.3 or CH.sub.3 CH.sub.2 ; 
R.sub.3 is either H, CH.sub.3, or CH.sub.3 CH.sub.2 ; and n is O or a 
positive integer from 1 to 10. Preferably, R is CH.sub.3 O or CH.sub.3 
CH.sub.2 O and n is 1. 
Typical examples of such alkoxysilanes are the acrylatoalkoxy silanes, such 
as gammaacryloxypropyltrimethoxy silane and the methacrylatoalkoxy 
silanes, such as gamma-ethacryloxypropyltrimethoxy silane, and 
gamma-methacryloxypropyltris(2-methoxyethoxy) silane. 
Other suitable alkoxy silane monomers have the following structural 
formula: 
##STR2## 
wherein R, R.sub.1 and R.sub.2 are as described above and n is a positive 
integer from 1 to 10. 
Examples of such alkoxysilanes are the vinylalkoxy silanes, such as 
vinyltrimethoxy silane, vinyltriethoxy silane and 
vinyltris(2-methoxyethoxy) silane. 
Other suitable silane containing monomers are acyloxysilanes, including 
acrylatoxy silane, methacrylatoxy silane and vinylacetoxy silanes, such as 
vinylmethyl diacetoxy silane, acrylatopropyl triacetoxy silane, and 
methacrylatopropyltriacetoxy silane. Of course, mixtures of the 
above-mentioned silane-containing monomers are also suitable. 
Consistent with the above mentioned components of the silane polymer, an 
example of an organosilane polymer useful in the coating composition of 
this invention may contain the following constituents: about 15-25% by 
weight styrene, about 30-60% by weight methacryloxypropyltrimethoxy 
silane, and about 25-50% by weight trimethylcyclohexyl methacrylate. 
One preferred acrylosilane polymer contains about 30% by weight styrene, 
about 50% by weight methacryloxypropyltrimethoxy silane, and about 20% by 
weight of nonfunctional acrylates or methacrylates such as 
trimethylcyclohexyl methacrylate, butyl acrylate, and iso-butyl 
methacrylate and any mixtures thereof. 
Silane functional macromonomers also can be used in forming the silane 
polymer. These macromonomers are the reaction product of a silane 
containing compound, having a reactive group such as epoxide or 
isocyanate, with an ethylenically unsaturated non-silane containing 
monomer having a reactive group, typically a hydroxyl or an epoxide group, 
that is co-reactive with the silane monomer. An example of a useful 
macromonomer is the reaction product of a hydroxy functional ethylenically 
unsaturated monomer such as a hydroxyalkyl acrylate or methacrylate having 
1-4 carbon atoms in the alkyl group and an isocyanatoalkyl alkoxysilane 
such as isocyanatopropyl triethoxysilane. 
Typical of such above mentioned silane functional macromonomers are those 
having the following structural formula: 
##STR3## 
wherein R, R.sub.1, and R.sub.2 are as described above; R.sub.4 is H or 
CH.sub.3, R.sub.5 is an alkylene group having 1-8 carbon atoms and n is a 
positive integer from 1-8. 
Curing catalysts for catalyzing the crosslinking between silane moieties of 
a silane polymer and/or between silane moieties and other components of 
the composition include dibutyl tin dilaurate, dibutyl tin diacetate, 
dibutyl tin dichloride, dibutyl tin dibromide, triphenyl boron, 
tetraisopropyl titanate, triethanolamine titanate chelate, dibutyl tin 
dioxide, dibutyl tin dioctoate, tin octoate, aluminum titanate, aluminum 
chelates, zirconium chelate, and other such catalysts or mixtures thereof 
known to those skilled in the art. Tertiary amines and acids or 
combinations thereof are also useful for catalyzing silane bonding. 
In one embodiment of the present invention, the silane polymer optionally 
also has epoxy groups, that is, a portion of the monomers reacted to form 
the polymer contain an epoxy group. An example of a suitable epoxy 
functional monomer is glycidyl methacrylate and the like. Suitably, the 
silane polymer may be the reaction product of a monomer mixture comprising 
up to 40% by weight of an epoxy functional monomer, preferably 5 to 20%, 
and most preferably 10 to 15% by weight of an epoxy functional monomer. 
As indicated above, the binder of the present composition may further 
comprise from about 5 to 30%, preferably 10 to 25%, based on the weight of 
the binder, of an acrylic or polyester or a polyester urethane or 
copolymer thereof having a hydroxy number of about 20 to 120, preferably 
70 to 100, or an acid number of about 20 to 120, preferably 75 to 95. This 
polymer has a weight average molecular weight of about 2,000 to 20,000, 
preferably 4,000-10,000. Unless otherwise indicated, all molecular weights 
mentioned herein are measured using gel permeation chromatography using 
polymethyl methacrylate as a standard. 
Polyester urethanes are a reaction product of a hydroxyl terminated 
polyester component and a polyisocyanate component, preferably, an 
aliphatic or cycloaliphatic diisocyanate. A polyester, which may be used 
alone or as a component of the polyester urethane, may be suitably 
prepared from linear or branched chain diols, including ether glycols, or 
mixtures thereof or mixtures of diols and triols, containing up to and 
including 8 carbon atoms, or mixtures of such diols, triols, and 
polycaprolactone polyols, in combination with a dicarboxylic acid, or 
anhydride thereof, or a mixture of dicarboxylic acids or anhydrides, which 
acids or anhydrides contain up to and including 12 carbon atoms, wherein 
at least 75% by weight, based on the weight of dicarboxylic acid, is an 
aliphatic dicarboxylic acid. 
Representative saturated and unsaturated polyols that can be reacted to 
form a polyester include alkylene glycols such as neopentyl glycol, 
ethylene glycol, propylene glycol, butane diol, pentane diol, 1,6-hexane 
diol, 2,2-dimethyl- 1,3-dioxolane-4-methanol, 1,4-cyclohexane dimethanol, 
2,2-dimethyl 1,3-propanediol, 2,2-bis(hydroxymethyl)propionic acid, and 
3-mercapto-1,2-propane diol. Preferred are 1,6-hexanediol and butylene 
glycol. 
Polyhydric alcohols, having at least three hydroxyl groups, may also be 
included to introduce branching in the polyester. Typical polyhydric 
alcohols are trimethylol propane, trimethylol ethane, pentaerythritol, 
glycerin and the like. Trimethylol propane is preferred, in forming a 
branched polyester. 
Polycaprolactone polyols may be also be used in making the polyester. A 
preferred polycaprolactone, a triol, is Tone.RTM. FCP 310 (available from 
Union Carbide). 
The carboxylic acids used in making the polyester component of the 
polyester urethane include the saturated and unsaturated polycarboxylic 
acids and the derivatives thereof. Aliphatic dicarboxylic acids that can 
be used to form the polyester are as follows: adipic acid, sebacic acid, 
succinic acid, azelaic acid, dodecanedioic acid, 1,3 or 1,4-cyclohexane 
dicarboxylic acid and the like. A preferred acid is adipic acid. Aromatic 
polycarboxylic acids include phthalic acid, isophthalic acid, terephthalic 
acid, and the like. Anhydrides may also be used, for example, maleic 
anhydride, phthalic anhydride, trimellitic anhydride, and the like. 
Typical polyisocyanates that may be used to form the polyester urethane are 
as follows: isophorone diisocyanate which is 
3-isocyanatemethyl-3,5,5-trimethyl-cyclohexyl-isocyanate, 
propylene-1,2-diisocyanate, butylene-1,2-diisocyanate, 
butylene-1,3-diisocyanate, hexamethylene diisocyanate, 
methyl-2,6-diisocyanate, methyl-2,6-diisocyanate caproate, octamethlyene 
diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, nonamethylene 
diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, decamethylene 
diisocyanate, 2,11-diisocyano-dodecane and the like, meta-phenylene 
diisocyanate, para-phenylene diisoxyanate, toluene-2,4-diisocyanate, 
toluene-2,6-diisocyanate, xylene-2,4-diisocyanate, 
xylene-2,6-diisocyanate, dialkyl benzene diisocyanates, such as 
methylpropylbenzene diisocyanate, methylethylbenzene diisocyanate, and the 
like: 2,2'-biphenylene diisocyanate, 3,3'-biphenylene diisocyanate, 
4,4'-biphenylene diisocyanate, 3,3'-dimethyl-4,4'-biphenylene 
diisocyanate, and the like; methylene-bis(4-phenyl isocyanate), 
ethylene-bis(4-phenyl isocyanate), isopropylidene-bis(4-phenyl 
isocyanate), butylene-bis(4-phenylisocyanate), and the like; 
2,2'-oxydiphenyl diisocyanate, 3,3'-oxydiphenyl diisocyanate, 
4,4'-oxydiphenyl diisocyanate, 2,2'-ketodiphenyl diisocyanate, 
3,3'-ketodiphenyl diisocyanate, 4,4'-ketodiphenyl diisocyanate, 
2,2'-thiodiphenyl diisocyanate, 3,3'-thiodiphenyl diisocyanate, 
4,4'-thiodiphenyl diisocyanate, and the like; 2,2'-sulfonediphenyl 
diisocyanate, 3,3'-sulfonediphenyl diisocyanate, 4,4'-sulfonediphenyl 
diisocyanate, and the like; 2,2,-methylene-bis(cyclohexyl isocyanate), 
3,3'-methylene-bis(cyclohexyl isocyanate), 4,4'-methylene-bis(cyclohexyl 
isocyanate), 4,4'-ethylene-bis(cyclohexyl isocyanate), 
4,4'-propylene-bis-(cyclohexyl isocyanate), 
bis(paraisocyano-cyclohexyl)sulfide, bis(para-isocyano-cyclohexyl)sulfone, 
bis(para-isocyano-cyclohexyl)ether, bis(para-isocyano-cyclohexyl)diethyl 
silane, bis(para-isocyano-cyclohexyl)diphenyl silane, 
bis(para-isocyano-cyclohexyl)ethyl phosphine oxide, 
bis(para-isocyano-cyclohexyl)phenyl phosphine oxide, 
bis(para-isocyano-cyclohexyl)N-phenyl amine, 
bis(para-isocyano-cyclohexyl)N-methyl amine, 3,3'-dimethyl-4,4'-diisocyano 
biphenyl, 3,3'-dimethoxy-biphenylene diisocyanate, 
2,4-bis(b-isocyano-t-butyl)toluene, 
bis(para-b-isocyano-t-butyl-phenyl)ether, 
para-bis(2-methyl-4-isocyanophenyl)benzene, 3,3-diisocyano adamantane, 
3,3-diisocyano biadamantane, 3,3-diisocyanoethyl-1'-biadamantane, 
1,2-bis(3-isocyano-propoxy)ethane, 2,2-dimethyl propylene diisocyanate, 
3-methoxy-hexamethylene diisocyanate 2,5-dimethyl heptamethylene 
diisocyanate, 5-methyl-nonamethylene diisocyanate, 
1,4-diisocyano-cyclohexane, 1,2-diisocyano-octadecane, 
2,5-diisocyano-1,3,4-oxadiazole, OCN(CH.sub.2).sub.3 O(CH.sub.2).sub.2 
O(CH.sub.2).sub.3 NCO, OCN(CH.sub.2).sub.3 NCO or the following: 
##STR4## 
Aliphatic diisocyanates are preferred, forming urethanes that have 
excellent weatherability. One aliphatic diisocyanate that is particularly 
preferred is trimethyl hexamethylene diisocyanate. 
A preferred polyester urethane is the reaction product of 
trimethylhexamethylene diisocyanate and a hydroxy terminated polyester of 
1,3-butylene glycol, 1,6-hexanediol, adipic acid, trimethylolpropane, and 
Tone.RTM. FCP 310. 
It is noted that a hydroxy functional polyester urethane can be converted 
to the corresponding acid functional polyester urethane by reaction with 
methylhexahydropthalic anhydride or other mono-anhydride such as succinic 
anhydride. Converting the hydroxy to the acid may result in longer pot 
life. 
A polyester may be prepared by conventional techniques in which the 
component polyols and carboxylic acids and solvent are esterified at about 
110.degree. C.-250.degree. C. for about 1-10 hours to form a polyester. To 
form a polyester urethane, a diisocyanate may then be added and reacted at 
about 100.degree. C. for about 15 minutes to 2 hours. 
In preparing the polyester urethane, a catalyst is typically used. 
Conventional catalysts include benzyl trimethyl ammonium hydroxide, 
tetramethyl ammonium chloride, organic tin compounds, such as dibutyl tin 
diaurate, dibutyl tin oxide stannous octoate and the like, titanium 
complexes and litharge. About 0.1-5% by weight of catalyst, based on the 
total weight of the reactants, is typically used. 
The stoichiometry of the polyester preparation is controlled by the final 
hydroxyl number and by the need to obtain a product of low acid number; an 
acid number below 10 is preferable. The acid number is defined as the 
number of milligrams of potassium hydroxide needed to neutralize a 1 gram 
sample of the polyester. Additional information on the preparation of 
polyester urethanes is disclosed in commonly assigned U.S. Pat. No. 
4,810,759, hereby incorporated by reference. 
Another optional component of the present composition is the half ester of 
an anhydride compound, as distinguished from a polymer, for example the 
reaction product of an acid anhydride such as hexahydrophthalic anhydride 
or a succinic anhydride, which may be substituted, for example with a 
C.sub.1 -C.sub.8 alkyl group, with a monofunctional or polyfunctional 
alcoholic solvent such as methanol or ethylene glycol. A preferred half 
ester is the reaction product of methylhexahydrophthalic anhydride and an 
alcohol. Other alcoholic solvents are propanol, isobutanol, isopropanol, 
tertiary butanol, n-butanol, propylene glycol monomethyl ether, ethylene 
glycol monobutyl ether, and the like. Such half esters are useful for 
boosting the solids content of the composition. More particularly, such a 
half ester is chosen to be a good solvent for the preferred phosphonium 
catalyst. The half ester is suitably present in the mount of 2 to 25 
percent by weight of binder, preferably 4-12 percent. 
About 0.1-5% by weight, based on the weight of the binder of the coating 
composition, of a catalyst is added to enhance curing of the composition. 
Typical catalysts are as follows: triethylene diamine, quinuclidine, 
dialkyl alkanol amines such as dimethyl ethanolamine, diethyl ethanol 
amine, dibutyl ethanol amine, diethyl hexanol amine and the like, lithium 
tertiary butoxide, tri(dimethylaminomethyl)phenol, 
bis(dimethylamino)propan-2-ol, N,N,N.sup.1,N.sup.1 
-tetramethylethylenediamine, N-methyldiethanolamine, 
N,N-dimethyl-1,3-propanediamine and 1-dimethylamino-2-propanol or 
quaternary ammonium salts such as tert-butyl ammonium bromide, benzyl 
trimethyl ammonium formate and the like. Preferred catalyst, however, are 
phosphonium compounds such as are disclosed in U.S. Pat. No. 4,906,677, 
hereby incorporated by reference in its entirety. 
Typical solvents used as a diluent for the coating composition include 
toluene, xylene, butyl acetate, ethyl benzene, higher boiling aromatic 
hydrocarbons, amyl acetate, ethyl acetate, propyl acetate, ethylene or 
propylene glycol mono alkyl ether acetates. 
Generally, the present composition is applied as a coating to a substrate 
by conventional techniques such as spraying and electrostatic spraying. 
The composition may be applied as a one-package system. The resulting 
coating can be dried and cured at elevated temperatures of 100.degree. to 
200.degree. C. Coatings are applied to form a finish typically about 0.5-5 
mils thick, and preferably 1-2 mils thick. 
To improve the pot life or stability of the composition it is desirable to 
include a trialkyl orthoacetate or orthoformate, wherein the alkyl group 
has 1-6 carbon atoms. Preferred compounds are trimethyl or triethyl 
orthoacetate. A suitable range of such a stabilizer is 1 to 6% by weight 
of composition, preferably about 3 to 4% by weight. Such a stabilizer also 
serves to keep the viscosity of the composition low. 
To improve weatherability of the clear finish of the coating composition, 
about 0.1-5%, by weight, based on the weight of the binder, of an 
ultraviolet light stabilizer or a combination of ultraviolet light 
stabilizers can be added. These stabilizers include ultraviolet light 
absorbers, screeners, quenchers and specific hindered amine light 
stabilizers. Also, about 0.1-5% by weight, based on the weight of the 
binder, of an antioxidant can be added. 
Typical ultraviolet light stabilizers that are useful are listed in U.S. 
Pat. No. 4,906,677, previously incorporated by reference. Particularly 
useful ultraviolet light stabilizers that can be used are hindered amines 
of piperidyl derivatives such as those disclosed in Murayama et al., U.S. 
Pat. No. 4,061,616, issued Dec. 6, 1977, column 2, line 65, through column 
4, line 2, and nickel compounds such as [1 
-phenyl-3-methyl-4-decanoylpyrazolate(5)]-Ni, 
bis[phenyldithiocarbamato]-Ni(II), and others listed in the above patent, 
column 8, line 44 through line 55. 
An applicable blend of ultraviolet light stabilizers comprises 
2-[2'-hydroxy-3',5'-1(1-1-dimethyl-propyl )phenyl]benzotriazole and 
bis-[4-(1,2,2,6,6-pentamethylpiperidyl)]2-butyl-2-[(3,5-t-butyl-4-hydroxyp 
henyl)methyl]propanedioate. Although the stabilizers can be employed in any 
ratio, a 1:1 ratio of benzotriazole to propanedioate is preferred. 
The composition can be pigmented to form a colored finish or primer. About 
0.1-200% by weight, based on the weight of the binder, of conventional 
pigments can be added using conventional techniques in which a mill base 
containing pigment, dispersant and solvent is first formed. The mill base 
is then mixed with the composition to form a colored composition. This 
composition can be applied and cured as shown above. 
The present composition can be used in a one-package system with a pot life 
of up to several weeks, depending on conditions.

The following examples illustrate the invention. All parts and percentages 
are on a weight basis unless otherwise indicated. The weight average 
molecular weight of polymers was determined by GPC (gel permeation 
chromatography) using polyethyl methacrylate as a standard,unless stated 
otherwise. 
EXAMPLE 1 
This example illustrates, as a component for use in the present 
composition, an acid polymer, more specifically a methacrylic acid resin, 
which may be prepared by charging the following constituents into a 
reactor equipped with a thermometer, stirrer, dropping funnel, and 
condensor: 
______________________________________ 
Parts by Weight 
______________________________________ 
Portion 1 
Propylene glycol monomethyl ether acetate 
155.3 
(PM acetate) 
Xylene 103.5 
Portion 2 
n-Butyl methacrylate 174.8 
Methacrylic acid 97.1 
Butyl acrylate 140.8 
Styrene 72.8 
Portion 3 
Tertiarybutyl peroxyacetate 
35.0 
Propylene glycol monomethyl ether acetate 
41.7 
(PM acetate) 
Xylene 27.8 
Total 849.0 
______________________________________ 
Portion 1 was charged into the reactor and heated to its reflux 
(approximately 140.degree. C). Portion 2 was premixed and added to the 
reactor dropwise over a 240 minute period. Portion 3 was premixed and 
added to the reactor over a 270 minute period concurrent with Portion 3. 
After the addition was complete, the reactor was held at reflux and filled 
out. 
The resulting acid polymer composition had a composition of 15% styrene, 
36% butyl methacrylate, 29% n-butyl acrylate, and 20% methacrylic acid. 
The solids content was 60% and the polymer had a Gardner-Holdt viscosity 
of Z-1. The polymer had a weight average molecular weight of 5000. 
EXAMPLE 2 
This example illustrates one embodiment of an acrylosilane polymer which 
may be employed in a composition according to the present invention. A 
solution of the polymer is prepared by charging the following constituents 
into a polymerization reactor equipped with a heat source and a reflux 
condensor: 
______________________________________ 
Parts by Weight 
______________________________________ 
Portion I 
"Solvesso" 100 75.00 
Portion II 
Methacryloxypropyltrimethoxy silane 
300.00 
Styrene monomer 173.00 
Isobutyl methacrylate monomer 
103.86 
"Solvesso" 100 45.02 
Portion III 
2,2'-azobis(2-methyl) butanenitrile 
57.32 
"Solvesso" 100 85.80 
Total 840.00 
______________________________________ 
The "Solvesso" 100 is a conventional aromatic hydrocarbon solvent. Portion 
I is charged into the reactor and heated to its reflux temperature. 
Portion II, containing the monomers for the organosilane polymer, and 
Portion III, containing the polymerization initiator, are each premixed 
and then added simultaneously to the reactor while the reaction mixture is 
held at its reflux temperature. Portion II is added at a uniform rate over 
a 6 hour period and Portion II is added at a uniform rate over a 7 hour 
period. After Portion II is added, the reaction mixture is held at its 
reflux temperature for an additional hour. The resulting acrylosilane 
polymer solution is cooled at room temperature and filtered. 
The resulting acrylosilane polymer solution has a polymer solids content of 
about 70%, the polymer has a weight average molecular weight of about 
3,000, and has the following constituents: 30% styrene, 18% isobutyl 
methacrylate, and 52% methacryloxypropyl trimethoxysilane. 
EXAMPLE 3 
This example illustrates an epoxy-silane polymer, more particularly an 
epoxy functional acrylosilane polymer which was prepared by charging the 
following constituents into a polymerization vessel equipped with a 
heating mantle, reflux condenser, thermometer, nitrogen inlet, and 
stirrer: 
______________________________________ 
Parts by Weight 
______________________________________ 
Portion 1 
Xylol (135-145.degree. C.) 
363.2 
"Aromatic" 100 363.2 
Portion 2 
Styrene 530.9 
gamma-Methacryloxypropyl trimethoxy silane 
1380.3 
Methyl methacrylate 318.5 
Butyl methacrylate 79.6 
2-Ethylhexyl acrylate 79.6 
Glycidyl methacrylate 265.4 
Aromatic 100 40.9 
Xylol 40.9 
Portion 3 
t-Butyl peroxyacetate 132.7 
Aromatic 100 99.6 
Xylol 99.7 
TOTAL 3794.5 
______________________________________ 
Portion 1 was charged into the polymerization vessel and heated under 
nitrogen to 149.degree. C. Portion 2 was then added over 360 minutes and 
Portion 3 over 420 minutes to the vessel. The resulting polymer solution 
had the following characteristics: 
______________________________________ 
Gallon wt. 8.56 lbs./gal. 
% wt. solids 72.2% 
% volume solids 68.6 
M.sub.w of polymer 5000 
M.sub.n of polymer 1650 
______________________________________ 
The polymer composition was, by weight, 20 percent styrene, 52 percent 
gamma-methacryloxylpropyl trimethoxy silane (A-174 commercially available 
from Union Carbide, Inc., Danbury, Conn.), 12 percent methyl methacrylate, 
3 percent butyl methacrylate, 3 percent 2-ethylhexyl acrylate, and 10 
percent glycidyl methacrylate, represented as follows: 
STY/A-174/MMA/BMA/2-EHA/GMA in the ratio of 20/52/12/3/3/10. 
EXAMPLE 4 
This example illustrates, as an optional component for a composition 
according to the present invention, a polyester urethane solution which 
may be prepared by charging the following constituents in order into a 
reaction vessel equipped with a stirrer, a heating source and a reflux 
condenser: 
______________________________________ 
Parts by Weight 
______________________________________ 
Portion 1 
1,3-butylene glycol 173.4 
1,6-hexanediol 163.1 
Trimethylol propane 78.8 
Adipic acid 403.7 
Toluene 20.0 
Portion 2 
Propylene glycol monomethyl ether acetate 
294.4 
Portion 3 
Tone .RTM. FCP 310 (caprolactone polyol from 
934.9 
Union Carbide) 
Propylene glycol monomethyl ether acetate 
185.3 
Hydrocarbon solvent 706.1 
Portion 4 
trimethylhexamethylene diisocyanate 
290.3 
dibutyl tin dilaurate 0.5 
Portion 5 
Hydrocarbon solvent 69.8 
Total 3320.3 
______________________________________ 
Portion 1 is charged in order into the reaction vessel, and the 
constituents of Portion 1 are heated to distill water at 
140.degree.-230.degree. C. The distillation is continued until the acid 
number is 6.5 to 8.5. The product is thinned and cooled to 98.degree. to 
102.degree. C. by charging Portion 2 into the vessel. While the 
constituents in the vessel are maintained at the above temperature, 
Portion 3 was charged to the reactor in order. Portion 4 is added to the 
composition at a uniform rate over a 30 minute period while the batch 
temperature is maintained at 98.degree.-102.degree. C. A sample is removed 
and tested for unreacted isocyanate NCO by infrared analysis. The 
composition is held at the above temperature until there is no unreacted 
isocyanate in the composition. Portion 5 then is added as a rinse and the 
resulting composition was allowed to cool to ambient temperatures. 
Following this procedure, the resulting composition had a polymer weight 
solids content of about 61.0%. The polyester urethane had a Gardner-Holdt 
viscosity of L. The M.sub.n (number average molecular weight) was 3734.0 
and the M.sub.w (weight average molecular weight) was 7818.0 (by gel 
permeation chromatography using polystyrene as the standard). The acid 
content was determined to be 4.9 Meq/g. The hydroxy number was 92. 
EXAMPLE 5 
This example illustrates a clearcoat coating composition according to the 
present invention. The following was thoroughly blended: 
______________________________________ 
Components Parts 
______________________________________ 
Acid Resin (prepared as described above) 
35.1 
Propylene glycol monomethyl ether acetate 
27.28 
DISLON 1984 acrylic flow additive (50%) 
0.17 
in xylene, from King Industries 
XU-71950 (diglycidylester from Dow) 
10.04 
Catalyst solution 5.92 
CYMEL 325 (Melamine) 4.76 
Epoxy-silane polymer (prepared as described above) 
10.92 
TINUVIN 384 (UV Screener from Ciba-Geigy) 
0.72 
TINUVIN 123 (HALS from Ciba-Geigy) 
0.53 
Trimethyl orthoacetate 4.56 
TOTAL 100.00 
______________________________________ 
In the above list, fully capitalized names indicate trademarks of 
commercially available products. The UV screener and hindered amine light 
stabilizer (HALS) are commercially available from Ciba-Geigy as indicated 
above. The catalyst solution refers to a solution of benzyl triphenyl 
phosphonium chloride, which may be prepared from a mixture of 62.8 parts 
of ethylene glycol-MHHPA half-ester, 29.9 parts of xylene, and 7.3 parts 
of benzyl triphenyl phosphonium chloride, in which the solution was heated 
to 50.degree.-60.degree. C. to dissolve the phosphonium chloride catalyst. 
The MHHPA half-ester was prepared as follows: 578.7 parts of methyl 
hexahydrophthalic anhydride and 249.7 parts of xylene were heated to 
160.degree. F. and 106.2 parts of ethylene glycol were added over 45 
minutes. After the feed was complete, the reaction was maintained at 
250.degree..+-.10.degree. F. for 5 hours to complete the reaction. 
Finally, the reaction product was cooled to 150.degree. F. and 8.8 parts 
of methanol was added. The mixture was stirred for 60 minutes and heated 
to reflux to remove solvent, cooled to 160.degree. F., and filtered (75 
weight percent solids). 
The coating composition was sprayed onto primed metal panels coated with a 
basecoat and cured at 265.degree. F. The coating exhibited excellent 
humidity resistance, chemical resistance, durability and other film 
properties. 
Various modifications, alterations, additions, or substitutions of the 
components of the composition of this invention will be apparent to those 
skilled in the art without departing from the scope and spirit of this 
invention. This invention is not limited to the illustrative embodiments 
set forth herein, but rather the invention is defined by the following 
claims.