Coating composition of an acrylic polymer, a dispersed acrylic polymer and an alkylated melamine crosslinking agent

A coating composition that is used primarily as a clear finish over a colored or pigmented finish that are applied to automobile and truck bodies; the composition contains as the film forming binder PA0 (a) an acrylic polymer PA0 (b) a self stabilized dispersed resin formed by polymerizing in solution the following constituents: PA1 (1) an acrylic solution polymer, PA1 (2) monomers of alkyl methacrylate or acrylate and hydroxy ethyl acrylate or methacrylate, wherein either the acrylic solution polymer contains post reacted glycidyl methacrylate or acrylate or the monomers contain glycidyl methacrylate or acrylate, and PA0 (c) an alkylated melamine formaldehyde crosslinking agent.

BACKGROUND OF THE INVENTION 
This invention is related to a coating composition useful for finishing 
automobiles and trucks. 
One particular finish that provides an excellent aesthetic appearance is 
being used widely on automobiles and trucks has a colored base coat which 
contains pigments and a clear topcoat which is unpigmented. There is a 
need for a clear topcoating composition that has excellent durability, 
weatherability and adhesion to a colored base coat and provides a finish 
with an excellent aesthetic appearance. 
SUMMARY OF THE INVENTION 
A coating composition comprising about 20-85% by weight of film forming 
binder and 15-85% by weight of an organic liquid carrier; wherein the 
binder contains 
(a) an acrylic polymer I of polymerized monomers of alkyl methacrylate, 
alkyl acrylate, hydroxy alkyl acrylate or methacrylate and has a weight 
average molecular weight of about 3,000 to 20,000; 
(b) a self stabilized dispersed resin formed by polymerizing the following 
constituents: 
(1) an acrylic polymer II of polymerization monomers comprising alkyl 
methacrylate, alkyl acrylate, hydroxy alkyl acrylate or methacrylate, an 
ethylenically unsaturated carboxylic acid and has a weight average 
molecular weight of about 3,000-20,000; 
(2) monomers of alkyl methacrylate, alkyl acrylate, hydroxy alkyl acrylate 
or methacrylate; wherein either acrylic polymer II contains glycidyl 
methacrylate or acrylate monomers post reacted with the carboxylic acid or 
the monomers contain glycidyl methacrylate or acrylate; 
(c) an alkylated melamine formaldehyde crosslinking agent 
DETAILED DESCRIPTION OF THE INVENTION 
The coating composition has a film forming binder content of about 20-85% 
by weight and corresponding about 15-80% by weight of a liquid carrier. 
Preferably, the coating composition is a high solids composition that 
contains about 50-80% by weight of the binder and 20-50% by weight of 
organic solvent for the binder. The binder of the composition preferably 
is a blend of about 5-75% by weight of an acrylic polymer I, and 5-45% by 
weight of a self stabilized dispersed resin and 20-50%, by weight of an 
alkylated melamine formaldehyde crosslinking agent. 
The acrylic polymer I is of polymerized monomers of an alkyl methacrylate, 
an alkyl acrylate, hydroxy alkyl acrylate or methacrylate and has a weight 
average molecular weight of about 3,000-20,000. Preferably, styrene is 
used with the above monomers in acrylic polymer I. 
Molecular weight is measured by gel permeation chromatography using 
polymethyl methacrylate as a standard. 
Typical alkyl methacrylates used to form the acrylic polymer are methyl 
methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, 
isobutyl methacrylate, pentyl methacrylate, hexyl methacrylate, octyl 
methacrylate, nonyl methacrylate, lauryl methacrylate and the like. 
Typical alkyl acrylates used to form the acrylic polymer are methyl 
acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, isobutyl 
acrylate, pentyl acrylate, hexyl acrylate, octyl acrylate, nonyl acrylate, 
lauryl acrylate and the like. Typical hydroxy alkyl acrylates and 
methacrylates are hydroxy ethyl acrylate, hydroxy propyl acrylate, hydroxy 
isopropyl acrylate, hydroxy butyl acrylate, hydroxy ethyl methacrylate, 
hydroxy propyl methacrylate, hydroxy isopropyl methacrylate, hydroxy butyl 
methacrylate and the like and mixtures of the above monomers. 
Preferably, the acrylic polymer I is composed of 5-30% by weight styrene, 
10-40% by weight butyl methacrylate 10-40% by weight butylacrylate, 15-50% 
by weight of hydroxyethyl acrylate or hydroxy propyl acrylate and has a 
weight average molecular weight of about 5,000-15,000. Optionally, the 
polymer can contain about 0.1-5% by weight of acrylic acid or methacrylic 
acid. 
The acrylic polymer I is prepared by solution polymerization in which the 
monomers, conventional solvents, polymerization initiators, such as peroxy 
acetate are heated to about 90.degree.-250.degree. C. for 1-6 hours. 
The self-stabilized dispersed resin is formed by polymerizing in solution 
the following constituents: 
(1) an acrylic polymer II; 
(2) monomers of alkyl acrylate, alkyl methacrylate, and hydroxy acrylate or 
methacrylate. Conventional polymerization initiators such as t-butyl 
peracetate, and solvents are used. The constituents are heated to about 
80.degree.-250.degree. C. for about 1-6 hours to form the resin. 
The solution acrylic polymer II is composed of polymerization monomers of 
alkyl methacrylate, alkyl acrylate, hydroxy alkyl acrylate or methacrylate 
and an ethylenically unsaturated carboxylic acid and optionally, monomers 
of styrene. Any of the aforementioned alkyl acrylates, methacrylates, 
hydroxy alkyl acrylates or methacrylates can be used to prepare the 
polymer. Typical ethylenically unsaturated carboxylic acids that can be 
used are acrylic acid and methacrylic acid. Preferably, styrene is used to 
form the polymer with the above monomers. 
One preferred polymer contains about 5-25% by weight styrene, 20-40% by 
weight butyl acrylate, 20-40% butyl methacrylate, 5-15% by weight hydroxy 
ethyl acrylate, 1-5% by weight acrylic acid and 10-20% by weight ethyl 
methacrylate and has a weight average molecular weight of about 
7,000-15,000. 
Another preferred polymer contains about 5-25% by weight styrene, 25-35% by 
weight butyl methacrylate, 20-40% by weight butyl acrylate, 5-15% by 
weight hydroxy ethyl acrylate, 1-5% by weight acrylic acid, 10-20% by 
weight ethyl methacrylate and 1-5% by weight glycidyl methacrylate post 
reacted with acrylic acid and has a weight average molecular weight of 
about 7,000-15,000. 
Conventional polymerization techniques as described above for acrylic 
Polymer I are used to prepare acrylic Polymer II. 
Glycidyl methacrylate or acrylate is either post reacted with the carboxyl 
groups of acrylic polymer II or is one of the monomers that are 
polymerized with acrylic polymer II. 
Any of the aforementioned alkyl methacrylates, alkyl acrylates, hydroxy 
alkyl acrylates or methacrylates, ethylenical unsaturated acids are 
monomers that can be used to prepare the self stabilized/dispersed resin. 
Other useful monomers are styrene, acrylonitrile, methacrylonitrile, 
acrylamide, methacrylamide, perfluoro alkyl methacrylates or acrylates, 
dicarboxylic acids such as itaconic acid and the like. 
Typical solvents and diluents are used to form the above polymers and thee 
resulting coating composition. Appropriate solvents are chosen to form 
polymer solutions or dispersions and appropriate diluents are chosen to 
form coating compositions. Typical solvents and diluents are toluene, 
xylene, butyl acetate, acetone, methyl isobutyl ketone, methyl ethyl 
ketone, methanol, isopropanol, butanol, hexane, acetone, ethylene glycol 
monoethyl ether, VM and P naphtha, mineral spirits, heptane and other 
aliphatic, cycloaliphatic, aromatic hydrocarbons, esters, ethers and 
ketones and the like. 
The crosslinking agent used in the composition is a fully alkylated 
melamine formaldehyde resin that preferably is a methylated and butylated 
melamine formaldehyde resin that has a degree of polymerization of about 
1-3. Generally, this melamine formaldehyde resin contains about 50% 
butylated groups and 50% methylated groups. Typically these crosslinking 
agents have a number average molecular weight of about 300-600 and a 
weight average molecular weight of about 500-1500. 
It is possible to use other alkylated melamine formaldehyde crosslinking 
agents. Typically lower alkyl alcohols are used to form these crosslinking 
agents such as methanol, ethanol, propanol, isopropanol, butanol, 
isobutanol, hexanol and the like. 
Also, urea formaldehyde, benzoquanamine formaldehyde and polyisocyanates 
may be used as crosslinking agents. 
One preferred coating composition contains about 5-75%, by weight of a 
solution acrylic polymer I of about 5-30% by weight styrene, 10-40% by 
weight butyl methacrylate, 10-40% by weight butyl acrylate, 15-50% by 
weight hydroxy ethyl acrylate or hydroxy propyl acrylate and has a weight 
average molecular weight of about 5,000-15,000; about 5-45% by weight of a 
self stabilized dispersion resin formed by polymerizing the following 
constituents: 
(1) an acrylic solution Polymer II composed of 5-25% by weight styrene, 
20-40% by weight butyl acrylate, 20-40% by weight butyl methacrylate, 
5-15% by weight hydroxy ethyl acrylate, 1-5% by weight acrylic acid 10-20% 
by weight ethyl methacrylate and having a weight average molecular weight 
of about 7,000-15,000 and 
(2) monomers of styrene, methyl methacrylate hydroxy ethyl acrylate, 
methacrylic acid, methyl acrylate and glycidyl methacrylate; 
(3) an acrylic solution polymer II wherein the carboxyl groups of the 
acrylic acid are post reacted with glycidyl methacrylate and 
25-50% by weight of a fully methylated and butylated melamine formaldehyde 
crosslinking agent. 
Generally, an acid catalyst is used in the coating composition to enhance 
crosslinking of the components on curing. About 0.1-2% by weight, based on 
the weight of the composition, of catalyst can be used. Typically, blocked 
aromatic sulfonic acids are used. One preferred blocked acid catalyst is 
dodecyl benzene sulfonic acid blocked with dimethyl oxazolidine. Other 
acid catalysts that can be used are sulfonic acid, para-toluene sulfonic 
aid, dinonyl naphthalene sulfonic acid and the like. 
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 as follows: 
Benzophenones such as hydroxydodecyclbenzophenone, 
2,4-dihydroxybenzophenone, hydroxy-benzophenones containing sulfonic acid 
groups, 2,4-dihydroxy-3',5'-di-t-butylbenzophenone, 
2,2',4'-trihydroxybenzophenone esters of dicarboxylic acids, 
2-hydroxy-4-acryloxyethoxybenzophenone, aliphatic mono-esters of 
2,2',4-trihydroxy-4'-alkoxybenzophenone, 
2-hydroxy-4-methoxy-2'-carboxybenzophenone; 
Triazoles such as 2-phenyl-4-(2'-4'-dihydroxybenzoyl)triazoles, substituted 
benzotriazoles such as hydroxyphenyltriazoles such as 
2-(2'hydroxy-5'-methyphenyl)benzotriazole, 
2-(2'hydroxyphenyl)benzo-triazole, 
2-(2'-hydroxy-5'-octylphenyl)naphthotriazole; 
Triazines such as 3,5-dialkyl-4-hydroxyphenyl derivatives of triazine, 
sulfur-containing derivatives of dialkyl-4-hydroxyphenyltriazines, 
hydroxyphenyl-1,3,5-triazines and such triazines containing sulfonic acid 
groups, aryl-1,3,5-triazines, orthohydroxyaryl-s-triazine; 
Benzoates such as dibenzoate of diphenylolpropane, t-butyl benzoate of 
diphenylolpropane, nonyl phenyl benzoate, octyl phenyl benzoate, 
resorcinol dibenzoate. 
Other ultraviolet light stabilizers that can be used include lower alkyl 
thiomethylene-containing phenols, substituted benzenes such as 
1,3-bis(2'-hydroxybenzoyl)benzene, metal derivatives of 
3,5,-di-tbutyl-4-hydroxyphenylpropionic acid, asymmetrical oxalic acid 
diarylamides, alkylhydroxyphenylthioalkanoic acid esters, 
dialkylhydroxyphenylalkanoic acid esters of di- and tri-pentaerythritol, 
phenyl- and naphthlenesubstituted oxalic acid diamides, 
methyl-.beta.-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 
.alpha.,.alpha.'-bis(2-hydroxy-phenyl)diisopropylbenzene, 
3,5'-dibromo-2'-hydroxy-acetophenone, ester derivatives of 
4,4-bis(4'-hydroxy-phenyl)pentaonic acid wherein there is at least one 
unsubstituted position ortho to the aromatic hydroxyl groups, 
organophosphorus sulfides such as bis(diphenyl-phosphinothioyl)monosulfide 
and bis(diphenyl-phosphinothioyl)disulfide, 
4-benzoyl-6-(dialkylhydroxybenzyl)resorcinol, 
bis(3-hydroxy-4-benzoylphenoxy)diphenylsilane, 
bis(3-hydroxy-4-benzoylphenoxy)dialkylsilane, 1,8-naphthalimides, 
.alpha.-cyano-.beta.,.beta.-diphenylacrylic acid derivatives, 
bis(2-benzoxazolyl)alkanes, bis(2-naphthoxazolyl)alkanes, methylene 
malonitriles containing aryl and heterocyclic substitutes, 
alkylenebis(dithio)carbamate, 4-benzoyl-3-hydroxyphenoxyethyl acrylate. 
4-benzoyl-3-hydroxyphenoxyethyl methacrylate, aryl or alkyl-substituted 
acrylonitriles, 3-methyl-5-isopropylphenyl-6-hydroxycourmarone, 
8-acetyl-3-dodecyl-7,7,9,9-tetramethyl-1,3,8-triazaspiro(4,5)decanol-2,4-d 
ione. 
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. 
The following blend of ultraviolet light stabilizers is particularly 
preferred 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. The stabilizers can be used in any ratio 
however, a 1:1 ratio of benzotriazole to propanedioate is preferred. 
Another useful blend of ultraviolet light stabilizers is 
2-(benzotriazole-2-VL)-4,6-bis(methylethyl-1-phenyl ethyl)phenol, and 2(3 
hydroxy-3,5'-ditert amyl phenyl)benxotriazole. 
Generally, the clear coating composition of this invention is applied by 
conventional spraying techniques to a color or base coat of an automobile 
or truck and then is baked. Preferably, electrostatic spraying is used to 
apply the composition. The coatings are baked at about 80.degree. to 
200.degree. C. for about 10 to 60 minutes. The resulting clear coat is 
about 1-5 mils thick preferably 1-2 mils thick and has excellent gloss, 
good adhesion to the color coat and excellent weatherability. 
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 polymethyl methacrylate as a standard.

EXAMPLE 1 
A nonaqueous acrylic resin dispersion was prepared by charging the 
following constituents into a reaction vessel equipped with a stirrer, a 
heating source and a reflux condenser: 
______________________________________ 
Parts by 
Weight 
______________________________________ 
Portion 1 
Isopropanol 179.26 
Acrylic Polymer Solution 2254.05 
(52% solids of an acrylic 
polymer of 15% styrene, 28% 
butyl methacrylate, 30% 
butyl acrylate, 10% hydroxy 
ethyl acrylate, 2% acrylic 
acid and 15% ethyl methacrylate 
having a weight average Mw of 
10,000 in a solvent mixture of 
82.2% xylene and 17.8% butanol) 
Mineral spirits 255.65 
Heptane 1912.46 
Portion 2 
Heptane 28.75 
t-butyl peroctoate 4.68 
Portion 3 
Methylmethacrylate monomer 
1459.69 
Hydroxyethyl acrylate monomer 
784.81 
Styrene monomer 156.97 
Portion 4 
Acrylic Polymer solution (53% solids 
1126.52 
of an acrylic polymer of 15% 
styrene, 28% butyl methacrylate, 
30% butyl acrylate, 10% hydroxy 
ethyl acrylate, 2% acrylic acid 
and 15% ethyl methacrylate 2.7% 
glycidyl methacrylate having a 
weight average MW of 10,000 in a 
solvent mixture of 82.2% xylene 
and 17.8% butanol) 
Methyl methacrylate monomer 
125.57 
Methyl acrylate monomer 565.06 
Glycidyl methacrylate monomer 
47.05 
Heptane 17.25 
Portion 5 
Mineral Spirits 638.63 
t-butyl peroctoate 47.14 
Isobutanol 127.31 
Portion 6 
t-butyl peroctoate 30.96 
Isobutanol 255.65 
Portion 7 
Heptane 167.25 
Total 10,184.71 
______________________________________ 
Portion 1 is charged into the reaction vessel and heated to its reflux 
temperature Portion 2 is added to the reaction vessel mixed and held at 
reflux temperature for 2 minutes. Then portions 3 and 4 are added 
simultaneously with portions 5 over a 210 minute period to the reaction 
vessel while maintaining the resulting reaction mixture at its reflux 
temperature. Then the mixture is held at its reflux temperature for an 
additional 45 minutes. Portion 6 is added over a 90 minute period while 
maintaining the reaction mixture at its reflux temperature and then held 
at this temperature for an additional 90 minutes. Portion 7 is added and 
excess solvent is stripped off to give a 60% solids acrylic resin 
dispersion. 
A coating composition was prepared by blending together the following 
constituents: 
______________________________________ 
Parts by 
Weight 
______________________________________ 
Portion 1 
Xylene 163.00 
2(3-hydroxy-3,5'-ditert 113.20 
amylphenyl)benzotriazole 
Hindered amine U.V. light 
147.80 
stabilizer solution [40% solution 
in xylene of 8-acetyl-3-dodecyl- 
7,7,9,9-tetramethyl 2,3,8-tri- 
azaspiro(4,5)decane-2,4 dione] 
Baysilon Oil Solution 4.10 
(72.8 parts Baysilone Fluid 
OL and 655.2 parts xylene) 
Portion 2 
Methylated/butylated melamine 
2068.50 
formaldehyde resin (fully 
butylated and methylated 
melamine formaldehyde resin 
having a butyoxy/methoxy ratio 
of 1:1 and a degree of polymerization 
of about 1-1.2) 
Acrylic resin solution (75% 
4054.30 
solids in naphtha solvent of 
an acrylic resin of 15% styrene, 
30% butyl methacrylate, 25% 
butylacrylate; 30% hydroxy ethyl 
acrylate having a weight average 
Mw of 6,000) 
Blocked sulfonic acid 236.40 
Solution (33% solids in methanol 
of dodecyl benzene sulfonic acid 
blocked with dimethyl oxazolidine, 
molar ratio of acid; dimethyl 
oxazolidine is 1.52:1) 
Nonaqueous Acrylic resin 985.40 
dispersion (prepared above) 
Portion 3 
Methanol 203.80 
Methylamyl ketone 458.50 
Total 8435.00 
______________________________________ 
The constituents of Portion 1 were added in the order shown to a mixing 
vessel and agitated until in solution. Portion 2 was added to the vessel 
and mixed for 30 minutes. Portion 3 was added and mixed for 30 minutes. 
The resulting clear coating composition had 70% solids content. 
The resulting composition was sprayed onto primer coated phosphatized steel 
panels that were coated with a pigmented acrylic base coat. The 
composition was sprayed onto the panels before the base coat was baked. 
The panels were baked at 120.degree. C. for 30 minutes and a clear coat 
about 2 mils thick was formed on each panel. The clear coating had a 
hardness of 8 knoops, a gloss measured at 20 degrees of 95. The coating 
had excellent outdoor weatherability. 
EXAMPLE 2 
A coating composition was prepared that was identical to the coating 
composition of Example 1 except the following acrylic resin solution was 
used in the preparation of the coating composition: 
Acrylic resin solution (71% solids in xylene and aromatic hydrocarbon 
solvent mixture of an acrylic resin of 15% styrene, 30% butyl 
methacrylate, 17% butyl acrylate and 38% hydroxy propyl acrylate and has a 
weight average molecular weight of about 6,000). 
The resulting clear coating composition was sprayed onto primer coated 
phosphatized steel panels that were coated with a pigmented acrylic base 
coat as in Example 1 and baked as in Example 1. The resulting coating was 
about 2 mils thick and had the same hardness and gloss as the coating 
composition of Example 1 and had excellent outdoor weatherability.