CA1038522A - Aqueous thermosetting acrylic enamel - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

The aqueous thermosetting acrylic coating composition contains the following film-forming constituents:
(1) an acryllc polymer of styrene and/or methyl methacrylate, sn alkyl acrylate or an alkyl methacrylate other than methyl methacrylate, a bydroxy alkyl acrylate or a hydroxy alkyl methacrylate and an .alpha.,.beta.-unsaturated carboxylic acid wherein the polymer has an acid numbor of 35-150 and carboxyl/hydroxyl ratio of 1:0.2 to 1:1.8; and (2) a water soluble or water dispersible alkylated melamine formaldehyde resin;

the novel coating composition is useful as an exterior finish for automobile and truck bodies.

Description

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BACKGROUND OF THE INVENTION ~f~

This invention relates to an aqueous based ~ :
coatlng compositlon and in particular to an aqueous thermosetting acrylic enamel that provides a high quality ~ :f finish for the exterior of automobile and truck bodies.
Thermosetting acrylic enamels are well known in ~ :~
, ~
., the art as shown by Frazier et al. U.S. Patent 2,681,897 issued June 22, 1954; Vasta U.S. Patent 3,338,860, issued August 29, 1967; Fisk ~t al. U.S. Patent 3,365,414, issued .~ 10 January 23, 1968; Vasta U.S. Patent 3,622,651, issued November 23, 1971; and Parker U.S. Pate~t 3~637J546~
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issued January 25, 1972. These acrglic enamel~ are all X~ solvent based systems and do not provide a non-air-polluting ~ finish. Ta~t U.S. Patent 3,661,827, issued May 9, lg72 is ,1 : " ':
directed to a process for preparing a water disper~ible acrylic enamel composition but this product doe~ not meet .:~ the needs of the automobile and truck manufacturing industry for a high quality water based finish. ~;~
The novel aqueous thermosetting acryllc enamel .:, ~ 20 coating composition of this invention utilized a particular .. :
,b, acrylic polymer having a uniform composition and haYing a ~.
q balance of hydroxyl and carboxyl groups in combination with a water disperslble or water s~luble cross-linking agent .
such as an alkylated melamine formaldehyde resin to form a ~ ::
high quality finlsh useful for the exterior of auto~obile and truck bodies.
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SUMMARY OF THE INVENTIO~

The aqueous thermosettin~ acrylic enamel coating composition comprises 10-60% by welght of ~llm-~ormlng constltuen~s and correspondingly 90-50% by weight o~ water : ~ :
~ 5 ~nd up to 20% by weight of a so~.vent ~or the film-forming ;~ constituents; whereln the film-ro~ming constituent~ consis~ - -essentially o~
(1) 60-go~ by weight, based on the weight of the -film-forming constituents, of an acrylic polymer . 10 havin~ a uniformity factor of at least 75~ which consist& essentially of a) ~0 60~ by weight, ba~ed on tho weight of the acrylic polymer, of a hard ; .
constituent which ls elther methyl ~ methacrylate. or a blend of methyl : ~:
.~ 15 methacrylate and ~tyrene wherein the ~ ~tyrene comprlse~ up to 40~ by weight ~
~ o~ the acrylic polymer; ~ :
. tb) 20-40% by weight, ba~ed on the weight of the acrylic polymer, of a 50~t `~ 20 acrylic constltuent that i8 either an alkyl acrylate havlng 2-12 carbon atoms in the / alkyl group, an alkyl methacrylate havlng ;`
¦: . 4-12 carbon atoms in the alkyl group, or :`? ~`
~ ~ mlxture of the above alkyl acrylate and ~ 25 alkyl methacrylate; -:
.:, (c) 4-20~ by weight, ba~ed on the weight .J o~ the acrylic polymer, o~ a hydrox~-containlng .-~
~ constituent which is either a hydroxyalkyl ~.
-~, ~ethacrylate or a hydroxyalkyl acrylate or a ~;30 mixture thereo~ ln whlch the alkyl groups :.
have 2-4 carbon atomfi, ~, .

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(d) 4-20~ by welght, based on the weight o~ the acrylic polymer, o~ a,~-uns~turated carboxylic acld;

wherein the polymer has ~ carboxyl to hydroxyl ratio of 1:0.2 to 1:1.8 and an acid number of about 35-150 and a welght average molecular weight of 5,000-80~000;
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(2) 10-40% by wei~ht, based on the weight of ;,:, . . .
the film-forming constituentJ of a water dispersible !~
or water soluble cross-linking resln, preferably, an alkylated melamine ~ormaldehyde resin having 1-4 carbon atoms in the alkyl group; and the compositlon is at least partiall~ neutrallzed i `15 with a ~ater-soluble amine and ~as a pH o~ about ~-9.
"J. ~', , ' '; ': ' ' DESCRIPTION OF THE I~VE~ION

The novel coatlng composition Or this inventlon has a sollds content o~ ~llm-formlng constituents of about 10-60%
, by weight and preferably about 20-50~ by weight. The novel 20 composition is usually pigmented and contains about 0.1-40%
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~ by weight o~ pigment and preferably, 0.1-30% by weight ;~
`~ pigmen~
The fllm-forming constituents of the novel coatlng composition comprise 60-go~ by weight o~ acryllc polymer and 25 correspondingly, 40-10~ by weight of a water dispersible or .~r `
water soluble cross-linklng resin, preferably an alkylated melamine ~ormaldehyde resin whlch is compatible with the acrylic polymer i8 u8ea. Pre~erably, the novel compositlon -',';1 ~ , .~, , , ~" ;:
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'~ contains 65-85~ of the acrylic resin an~ ~5-15~ by weight of an alkylated melamine formialdehy~e resin and more preferably about 70~ by weight of the acryllc polymer is used ln combination with about 30~ by weight of an alk~lated ,~ 5 melamine formaldehyde resin.
'J~ The acrylic polymer used in the novel coating compositlon of thls invention is partially soluble and partially dispersed in the aqueous medium. About 30-5Q~
by weight o~ the acrylic polymer is dispersed and has a particle size of about 0.01-0.10 mlcrons preferably about 0.02-0.06 microns and the residual 50-70~ by weight of the ¦ acrylic polymer is soluble and dissoJ.ved ln the aqueous medium. To obtain w~ter solubility and disperslbility the ~! &cryllc polymer has a carboxyl to hydroxyl ratio of 1:0.2 to 1:1.8 which i6 the molar ratio of carboxyl groups to ! hydr~xyl groups of the polymer.

~, The acrylic polymer used in the novel coating composition of this invention has a uniformity factor of at least 7~ and preferably 80-95~. The uniformity factor is the per cent o~ the polymer in which the constituents are within plu5 or minus 15~ of the average amount given for the polymer~ For example, if the average composition of the acrylic polymer i8 54% methyl methacrylate, ~4% butyl acrylate, 6~ 2-hydroxyethyl acryla~e and 6% acrylic acid, 25 75% o~ the polymer will be within plus or minus 15% of ^
these average values or 54 ~ 8~ methyl methacrylate, ., ' ;. 5 :
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34 ~ 5% butyl acrylate, 6 -~ 0.9~ ~-hydroxyethyl acryl~te, and 6 + 0.9% acr~lic acid.

The acrylic polymer utilized ln the novel composi- I
tion Or this inventlon i8 prepared by a progra~med addition ~ ~ -of the monomers, polymerization catalyst~ ~nd 801vent8 This programmed addltlon process is an attempt to form polymer at all stages of the polymerizat~on proce~s which is essentially the same as the predetermined compos~tion, and re~ult~ ln a pol~ner composltion upon completion of the process which has a uni~ormity factor o~ at least 75%.
This proce6s allows ~or high percentage conver~lon of ;-monomer~ to polymer and ~lso provides a polymer h~ving a relatively uniform molecular weight. These polymer~ wh~n used in the novel composition of this invention pro~ide hlgh quality finishes.
Cpnventional polymerization proce~6e~, ~uch a~
batch polymerization, commonly used ln the art provide ~~
polymer~ ~ith a wide range o~compoæitions and molecular weights which are not ~ultable for the novel coating composltion of this lnventlon.
The above programmed addltion polymerization 1 process ls baged on a computer program which uses known polymerlzation equations and activity ratlog o~ monomers to determine the monomer additlon rates and ratio6 and ` polymer polymerizatlon temperatures and times. Thls ~orms ,,! a polymer that has a uniform composltion throughout. The bove programmed addition procedure can be based on a computer program which u~es a polymerization equation in which the polymeriza~ion values of the monomers are used.
~o ~n general, the programmed polymerlzation procedure comprises an initial charge of monomers and solvent~ which , ~
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are heated to the reflux temperature in the polymerization vessel, then at glven lntervals monomers and polymerlzatlon inltiator are charged into the vessel while maintaining a re~lux temperature according to the programmed polymerlza-tion procedure. Throughout the polymerization reaction, the polymer being for~ed has a uniformity factor o~ at least ` 75~ In general, the polymerlzatlon ls conducted at about ;
; 75-125C. over a 2-4 hour period to ~orm a polymer that has '~ a weight average molecular weigh~ of about 5,ooo-80~000, -and preferably, about 10,000-50,000 determined by gel per- :
meation chromotography. The polymer has an acid number of -about 35-150, preferably about 35-80. ~;
In one preferred process which prepares a polymer o~ 52-56~ by weight methyl methacrylate, 32-36% by weight ;
butyl acrylate, 5-7~ by weight of hydroxyethyl acrylate and 5-7% by weight of acrylic acid, the constituents are J reacted as follows:
Step (1) .-.~ . .
! The following constituents are charged into a ,:.j .
;~ 20 reaction vessel and are heated to reflux temperature:
; 13-15% by weight of the total amount of methyl methacrylate, 52-54~ by weight of the total amount o~ butyl acrylate, `~
28-30% by weight of the total amount of hydroxy ethyl acrylate, ~ ~
23-25% by weight of the total amount of acrylic acid, ~ ~ -l, water miscible solvents such as isopropanol and ethylene glycol monobutyl ether and a chain trans~er agent such as lauryl mercaptan.

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The following lngredlents are then charged into the reaction ve~æel~
polymerlzation catalyst ~uch as b~nzoyl peroxlde and optionally, 14-16% by weight of the total amount of methyl .
methacrylate,

3 the addition o~ the methyl methacrylate in thiæ ~tep ~;
is optional since this amo~nt of methyl methacrylate may be added in the fir~t ~tep and a solvent may be used ~or the benzoyl - ~.
peroxide.
Step (3) The ~ollowing ingredlents are then slowly and j continuously charged into the reuction vessel over a 1 14-16 minute perlod ¦ 20-21~ o~ the total amount o~ me-thyl methacrylate, . 13-15% of the total amount of7 butyl acrylate, `~
31-33% of the total amount of hydroxy ethyl :~ 20 acrylate, ;;~
22-24~ of the total amount of acrylic acid, and ~.
polymerization inltiator of benzoyl peroxide and ;
maintaining the react~on mixure at a reflux temperature ~or about 10-20 minutes.
Step (4) !~ , The ~ollowing ingredients are then slowly and continuouæly charged into the reaction veæsel over a 49-51 ~ -~
minu~e period while maintaining the reactlon mix~ure at a re~lux temperature, ., . .~ .
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31-33~ of the total amount of methyl methacrylate~
20-22% of the total àmount of butyl acrylate, 31-33% o~ the total amount of hydroxy ethyl acrylatej 33-35~0 of the total amount of acrylic acid, and polymerization initiator of benzoyl peroxide~

Step (5) ~ ;
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The ~ollowing ingredients are then slowly and continuously charged into the reaction vessel over a 75-80 minute period~
17-19~ of the total amount of methyl methacrylate, , . . 11-13% of the total amount of butyl acrylate, 6-8~ of the total amount of hydroxyethyl acrylate, 17-19~ of the total amount of acrylic acld, ~`~

and polymerlzatlon initiator o~ benzoyl peroxide; `;
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the reaction mixture is held at reflux temperature for ~ ; f ~ about 25-35 minutes to form a polymer.

.SIf Step (6) . ~ i ~, . .
Tne polymer is then neutralized with an amine and 3 then di}uted with water to form a dispersion.
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Water miscible solvents are used in the polymeriza-3 tion process such as isopropanol n-propyl alcohol, diacetone ':`~ ~, . ..
alcohol and other alcohols, acetone, acetyl acetone, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether and ethylene glycol monomethyl ether acetate. Minor amounts o~
solvents of limited water solubility can be used such as methyl :, ethyl ketone, ethylene glycol monoethyl ether acetate. The ! ~
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i novel composition can contain up to ~bout 20~ by weight o~
w~ter miscible solvent but preferably contains 5-15% by weight of ~olvent. If desired the novel composition may be made ;~
solvent free.
- 5 About 0.1-4~ by weightJ ba~ed on the weight o~ the ~ monomer used to prepare the acrylic polymer,o~ the polymeriza-J tion catalyst iB utilized~ T~pical catalysts are azo-bis-obutyronitrile, azo-bis-t~, ~~dimethylvaleronitrile), benzoyl peroxide, t-butyl peroxypivalate, t-butgrl peracetate and the llke. Chain transfer agents such as lauryl mercaptan are also used. ;

il The acrylic polymer contains 20-60% by weight of ,' a hard constituent which can be methyl methacrylate or a mixture of methyl methacrylate and styrene; up to 40% by 15 welght of the polymer can be styrene. The acrylic polymer can ~ -contaln 5 to 30% by weight of styrene in combination with 15 to 30~ by weight of methyl methacrylate. Preferabl~, the polymer contains about 52-57% by weight of methyl methacr~late.
~ The acrylic polymer contains 20-40~ by weight of .. , 20 ~ so~t acrylic constituent whlch is either an alkyl acrylate ~ `
-~ that has 2-12 carbon atoms in the alkyl group, an al~yl ~ -~
methacrylate having 4-12 carbon atoms ln the alkyl group or ~ a mixture o~ these two constituents~ Pre~erab}y, the -?j acrylic polymer contains 28 to 38% by weight o~ the 1 ?5 ~o~t acryllc con~tituent, preferably, an alkyl a~rylate ;; having 2-8 carbon atoms in the alkyl group. The followin~
are typical so~t acrylic monomers which can be utilized:
~; ethyl acrylate, propyl acrylate~ isopropyl acrylate, butyl .... .
~ acrylate, isobutyl acrylate~ hexyl acrylate, 2-~thylhexyl ... .
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~crylate, octyl acrylate, nonyl acrylate, lauryl acrylate and the llkeJ butyl methacrylate, lsobutyl methacrylate, pentyl meth~crylate, hexyl methacrylate, octyl meth~crylate, 2-ethyl-hexyl methacrylateJ decyl methacrylate, lauryl methacrylate and the like. But~l acrylate i~ the pre~erred 30ft acryllc con~tituent since it forms a hlgh quallty polymer that has excellent physlcal properties.
The acrylic polymer contain~ 4-20% by weight o~ a hydroxy containing constltuent 8uch as a hydroxy alkyl ¦~
acrylate or a hydroxy alkyl methacrylate or a ml~ture o~
these two compound~. Preferably, the polymer contains about 5-10~ o~ the hydrox~l containing con~tituent. These ~ constituents contain 2-4 carbon atoms in the alkyl groups and ``I are, ~or example, hydroxyethyl acrylate, hydroxybutyl i, 15 acrylate7 hydroxyethyl methacrylate, hydroxypropyl methacrylate, ~ ~and hydroxy!Du~yl me~nacryia~e.
-~ The acrylic polymer also contains 4-20~ by weight, based on the weight of the acrylic polymer, of an a,~-unsaturated carboxylic acld. T~plcally useful acids are ' 20 acrylic acid, methacrylic acid, crotonic acid, itaconic acid, ; propyl acrylic acid, and the like. Pre~erably, acrylic acid and methacrylic acid are used in amount~ of 4-10~ by weight since these aclds form high quality polymers use~ul in the novel compo~ition of this lnvention.

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One pre~erred acrylic polymer used in the novel coating composition of this invention contains 50-60~ by : weight of methyl methacrylate, 30-40~ by weight of a soft : acrylic constituent, preferably butyl acrylate, 5-10% by , welght of the hydroxy containing constituent, preferab~y -hydroxyethyl acrylate or hydroxypropyl methacrylate, and

4-12~ by weight of acrylic acid, methacrylic acid, or itaconic acid. These preferred acrylic polymers have a . . . .
I weight average molecular welght of about 20,000~50~000, l an acld number of about 35-100 and a carboxyl to hydroxyl I ratio of about 1:1.03 to 1:1.5.

Another particularly use~ul acrylic polymer which ~.;
.. gives a high quality ~inish contains about z8-~o~ by weight - of styreneJ 22-26% by weight of methyl methacrylate, 30-35%
:1 by weight of butyl acrylate, 7-9% by welght of hydroxy ethyl ~-acrylate and 4-6~ by weight of acrylic acid and has an acid number of about 30 to 50, a carboxyl to hydroxyl ratio of- :~
. 1:0.4 to 1:1.5 and a weight average molecular weight of about i 20,000-50,000.
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~33~5~2 To form the aqueous dlspersion) the acrylic i~
polymer is at lsast partially neutrali~ed wlth a water- ~
soluble amine and then dlspersed in water. ~yplcal water ! : ~:
soluble am~nes that can be used are primary ~mines, secondary ! 5 amines, tertlary amlnea, polyamlnes and hydro~yamines, such a8 ethanolamlne, diethanolamine7trlethanolamineJ n-methylethanol amine, N,N-diethylethanolamine, N-amlnoethanolaminel N-methyl-t diethanolamine~ monoisopropanolamine, dii~opropanol~mine~
triisopropanolamine, hydroxyamlne, butanolamine, hexanol~
amine, methyl diethanolamine, N,N-diethylaminoethylamine, ethylene diamine, diethylene triamine, diethylene tetramine, .. ~ , .
hexamethylene tetramine, triethylamine and the like. The acrylic polymer i8 usually 50-60~ neutralized and can be 100~
neutrallzed. Neutralizatlon of 50-60~ is preferred since this d~g~e~ of ~utralization ~orms an a~ueous d~per~ion whleh `~ permits enamel formulation at high solids. The pH o~ the `l resulting aqueous coating composition is generally ad~usted ~ to a pH o~ 6-9, preferably 7.1-7.5.
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!~ The novel coating composition of this lnvention ` :'~
contains 10-~0~ by weight, based on the weight of the film-forming constituents, o~ a water dlspersible or water soluble cross-linking resln. Preferably, alkylated melamine formaldeh~de r0s1ns are used ln an amount of about 20 40~ by welght of this ~;
resin. The alkylated melamlne formaldehyde resin has 1-4 ?5: carbon atoms in the alkyl group and is prepared by conventional , . . . .
techniques ln which an alkanol such as methanol, ethanol, propanol, isopropanol o~ butanol is reacted with melamine formaldehyde resln. One preferred resin ls hexamethoxymethyl `~ ~ melamine. Melamine formaldehyde resin reacted with isopropanol is another useful res1n. Urea ~ormaldehyde resins can ~l~o be used as a cross-linklng resin.
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~; Generally the novel coating compo~ition of thi~
invention contains pigments in amounts of 0.1-40~ by weight~
A wide variety of pigments can be used such as metallic : : :
oxide~, for example, titanium dioxide~ iron oxide, zinc oxide, and the like, metal hydroxide3, metal ~lake3, metal ~; powders, chromates~ sul~ates, carbonates, carbon black, - , silica, t~lc, phtalocyanine blues and greens, indolinone pigments and other organic pigments and dye~
The novel coat~ng composition of this invention can be applied to a var~ety of substrate~ such as glass, plastic substrate3 reinforced with glass ~ibersg metal and the like, by any of the usual application methods such as ~ spraying, electrostatic spraying, dipping, brushing, ~low i - coating and the like. These coatings are baked according ; ;~
to conventional procedures. One preferred baklng cycle comprl~es ~ prebake at about 75-95C, ~or about 5-30 mlnute~ ~;
~ and then a bake at about 125-200C. to provide a high quality .. ~ , , ,i~ finish. The re~ulting finish is about 0.5-3.5 mlls thick, preferably 1-2.5 mils in thickne~q, and can be rubbed or ~ 20 polished in accordance wlth conventional techniques to lmprove j smoothness or gloss or bothO
-i The novel coating composition of this invention is preferably applied over a primed metal substrate. Typlcal alkyd primers and epoxy primers pigmen~ed with iron oxide, carbon black~ titanium dioxide can be used. The primer can be applied by electrodeposition or can be applied by conven~
~ tional spraying or dipping of the metal substrate, Also~
`~ the novel composition can be used directly Gver galvanized ~;~
steel to form a durable coatlng.
The novel composition of this invention can be -~
applied directly over a primed metal substrate without the use o~ an intermediate sealer coat. However, a sealer coat j 14 ., .
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can be used to provide a finish with excellent ~dhesion and smoothness. These sealers may be water based or solvent ~ .
based. One typlcally useful sealer composition is disclosed in Rohrbacher U.S. Patent 3,509,086, issued April 2~, 1970. ' The ~inish of the novel coating compositlon of this invention is characterized by a glossy and smooth appearance that has water spot resistance, excellent craze resistance, good durability and weatherability and gloss retention and has good gasoline resist~nce. These charac-, 10 teristics make the novel composition particularly attractive ~, as an exterior finish for automobiles and trucks.

' The ~ollowing Examples illustrate the inventlon.
i~ The parts and percentages are by weight unless otherwise ', specified.

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_ 15 _ A coating composition i8 prepared by ~ir~t If ~1 : formlng the following acrylic polymer ~
Part6 By ¦, 5Weight Portion 1 `~1 .
. Methyl methacrylate monomer 170080 i,:~ ~
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Bu~yl ac~r}ate monomer l9ol~0 ~ 2-Ethyl hexyl acrylate monomer 2.720 ~ :~
,~, 10 Acryllc acid monomer 1.150 Isopropanol 6,140 .- ;~
~;: Ethylene glycol monobutyl ether 9.680 Lauryl mercaptan 0.294 `:~
Portion 2 .. . .
Benzoyl peroxlde 0.672 I Methylethyl ketone 1.580 j Ethy~.en~ ~1ycol monomethyl ~her ~ce~te1~580 :~ Ethylene glycol monobutyl ether 2.360 ~ Portion :~, 20 Methyl methacrylate monomer 24.530 Butyl acrylate monomer 11.520 '~ 2-Hydroxyethyl acrylate 3.910 Acr~ylic acld 2.090 Benæoyl peroxide 0.906 Isopropyl alcohol 3.000 .~ Ethylene glycol monobutyl ether 9.800 ~; Portion 4 : Methyl methacrylate monomer 25.720 Butyl acrylate 12.080 i~ 30 2-Hydroxyethyl acrylate monomer 4-090 j Acrylic acid monomer 2.200 ,1 `
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- Parts By Wei~ht Portion 4 (Continued) Benzoyl peroxide 1.248 Iqopropanol 4.120 Ethylene glycol monobutyl ether 1~ o l50 i Portlon~
Ethyl methacrylate 9.570 Butyl acrylate 4.~90 2-Hydroxyethyl acrylate 1.520 Acrylic acid monomer 0.820 Benzo~l peroxide 0.440 Isopropanol 1.460 Ethylene glycol monobutyl ether 4.760 Portion 6 Diethylethanoli~mine 7.900 ' ~smineral~zed ~a~er 101,~0 -; Portion 7 I
Deminer~lized water l69.ogo Total 4920100 Portion 1 ~s charged into a reaction vessel equlpped wlth a stirrer, a heating mantel, and a re~lux condenser and then heated to the re~lux temperature which i8 about 160C. Portion 2 is premixed and then added and then ~ 25 Portion 3 is premixed and added at a unlform rate over a 20-I minute period, while maintaining the reaction mlxture at its ~1~ - re~lux temperature. Portion 4 1~ premixed and added at a `1 uniform rate over a 60-mlnute period whi-e the reaction mixture is maintained at lts reflux temperature. Portion 5 is premlxed .,, ~

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and added at a unlform rate over a 100-minute periodJ then the reaction mixture i~ main~ained at lts re~lux tempera~
ture for an additional 1/2 hour. Portion 6 i8 premixed and then added to the reaction mixture and then Portion 7 is added to the reaction mixture and the reactLon mixture is cooled to room temperature and filtered to remove any ` coagulum.

- The resulting polymer disperslon ~las a 34~ polymer ~olids content in which the particle size is about 0.02-0.06 `
,~ 10 microns. The polymer has a relative viscosity of 1.16 measured at 25C. in dimethyl formamide at about 0.5~ polymer solids and has an acid number of about 3~ to 35 and ~
carboxyl to hydroxyl ratio o~ 1 to 1~5. The polymer has the ~ollowing composition: methyl methacrylate/butyl acrylate/
'~ 15 2-hydroxyethyl acrylate/acrylic acid in a weight ratio o~
, about 54.2j33.1/8.4/4.3 and uniformity ~actor of about , 75-85%.
' A phthalocyanlne blue mill base is prepared as follows:
' 20 Parts By Weight Portion 1 Hexa(methoxymethyl) melamine 546 Isopropanol 630 Portion 2 Phthalocyanine blue pigment 210 Portion 3 Hexa(methoxymethyl~ melamine 285 Isoprop~nol 426 , 3 Total 2097 .
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. minute per~od and then Portion 3 i~ added and the constituents `;, are mlxed ~or 30 minutes. The resulting composition 1~
passed through a standard Qand mill and ground two passeg ~, to provlde a uni~orm mill base. ~ Y ~ .

A blue mlll base i~ prepared a~ follows~
Part By Welght Portion 1 Hexa(methoxymethyl) melamine 78 ;
Isopropanol 90 Portion 2 MONASTRAL* blue pigment 30 Portion 3 . ~
Hexa(methoxymethyl) melamine 41 ~ ;:
Isopropanol 61 Total 300 ~ :
Portion 1 i~ mixed with Portion 2 over Q 30-mlnute .~
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period ~nd then Portion 3 i~ ~dded and the constituents are mixed for 30 minutes. The result~ng composltlon is pas~ed :~

. through a ~tandard sand-mlll and ground ior two passes to provide a unl~orm bl~e mill base.

A vlolet mill ba~e is prepared as follows~
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Portion 1 :~
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Hexa(methoxymsthyl) melamine 13.6 I~opropanol 45,1 Portion 2 ~::
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~s MONASTRAL violet plgment 7.0 ~
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Hexa(methoxymethyl) melamine 7.6 Isopropanol 26.7 Total lOO.O i~
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Portions 1 and 2 are blended together and then mixed ~:~
~r~for 30 mlnutes and then Portion 3 i5 added and the composltlon is mixed for an additional 15 minutes. The resulting composition is then ground two pa~se~ ln a ~tandard sand-grindlng mill to form a un~form mill base.
~A green-yellow mill base i8 formed as follow~
:~Part~ By -:
Welght . ~ -Portion I
Hexa(methoxymethyl) melamine 78 ;:~ ;
I~opropanol 90 Portion 2 '. -:
I Phthalocyanine green-yellow pigment 30 :~
.~ Portion 3 ~3l Hexa(methoxymethyl) melamine 41 Isopropanol 61 Total 300 . ~ 1~ ' ~ . . .

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; Portion 1 i8 blended with Portlon 2 ln a mlxing - vessel ~or 30 minutes and then Portion 3 is added and blended to an additional 15 minutes. The resultlng composltion is then ground two pas~es in a standard s~nd-grinding mill to form a unlform mill bQse. ~ ~ :
An aluminum flake disperslon is prepared as follows:
Parts By - Weight -~ .
; 10 Aluminum flake 1~71 ,~ , Hexa(methoxymethyl) melamine 5~75 I~opropanol 11.05 Total 18.51 I
The above con~tituents are thoroughly blended , 15 together ~or 30 mlnutes to form a unl~orm disperslon.
!
. A paint composition is prepared by blendlng . ~ , . together the following ingredients: .
Parts By _Weight Portion 1 i Phthalocyanine Blue mill base . (prepared above) 6.35 l Blue mill base (prepared above) 0.20 .1 Vlolet mill base (prepared ~bove) 0.70 ., Phthalocyano green-yellow mlll ba~e (prepared .'., 25 above) 45 1 Aluminum flake mill base (prepared above)11.05 ~ ~;
;' Portion 2 .
Hexa(methoxymethyl) melamlne 2Q.40 : :
Portion 3 .~ 30 Acryl1c polymer dispersion (prepared above) 272.40 ;~
~ .
.

.j .

,.

- 21 ~

: . - ~ -.

- 103~2Z Parts By Wei~ht Portion 4 Deionized water 18.00 Portlon 5 .: Butyl acrylate/acrylic acid copolymer .;
~olution - (80~ polymer solids in alcohol - of an 85/15 butyl acrylate/acrylic acid copolymer) 3-3 ~ 10 Silicone anti-cratering agent solution : ~10~ low molecular weight silicone resin in water) 3.35 . Deionized water 31.00 ~- Total 367010 : .
;
~ 15 Portion 1 is charged in a mixing vessel and , thoroughly blended together and then Portion 2 is added ;l then blended with Portion 1 and Portions ~, 4 and 5 are , added consecutively wlth blending a~ter each addition, The ,, resulting composltion has a ~0 second viscosity using a :
' 20 No. 2 Fisher cup and a total solids content o~ 28,1 .3 A standard suction gun is used to apply the paint ~
.,' composition at an air pressure of about ~0 pounds. The .~:
1 composition is applied to a steel panel primed with 1.5 mil . ' thick iron oxide pigmented alkyd resin primer. Six passes ~, 25 are used to apply the paint applied and the panel is prebaked for 15 minutes at 90C0 and then baked for 30 minutes at 150C. ~ ~;
~ . .
The resulting ~ilm is about 2 mils thick and has j good gloss~ excellent hardness, excellent appearance, and is .:
.~, resistant to blistering at high humldity, hsas excellent i, 30 resistance to water spotting good chip resistance, good . gasoline resistance and excellent resistance toward deteriora- :~
,~j , .~ tion by weatherling.

:

., -, , 1 , '' :, ` ,, ! , ... , ', ~ ' , .. ' , ' ,' ' 103852Z ~:
. EXAMPLE 2 ~: ~
~:
A coatlng compositlon ls prepared first by ~orming : ~:
the follo~ing a~rylic polymer solution; `:
Parts By ` ;~ `
Weight : :~
.. ' 5 :
-, Portion 1 :
j Methyl methacrylate monomer s8.0 ~
Butyl acrylate monomer 98.o :;
~ 2-Hydroxyethyl acrylate monomer 9.0 :
:, 10 Acrylic acid monomer 8.o :
opropanol 30.0 I
, Methylene glycol monobutyl ether 75.o ~ :
;l Dodecyl mercaptan 4.3 :
Portion 2 .
Methyl methacrylate monomer 27.0 ,~ Benzo~l p.eroxide 3 i Portion 3 , .
Methyl methacrylate monomer 293.0 !.
Butyl acrylate monomer 142.0 ~ ~:
2-Hydroxyethyl acrylate monomer 31.0 :
~ Acrylic acid monomer 35.0 .l Isopropanol .42.0 .'~ Ethylene glycol monobutyl ether acetate 137.0 ,, .l Ben~oyl peroxlde 17.0 '~j 25 ~ Total1009!6 Portion 1 is charged into a reaction vessel e~uipped with a ~tirrer> a heating mantel, and a reflux condenser and then the constituents are heated to a re~lux te~perature.
' Portion 2 ~s premixed and then ~dded to the re~ction ~essel ? 3o and then the reaction mixture 1~ brought to ~ts re~lux tempera-ture. Portion 3 is then premixed and 40% of Portion 3 ls ~:., added over a 20-minute period while maintalning the reaction ,;, mixture at its reflux temperature~ The remainin~ 6o~ o~
, 1 ..
, 23 - ~ :
: i . , , ~;
.~ .

~38522 I Portion 3 i6 added continuou~ly over an 80-minute perlod ~I
and then the reaction mlxture is held at lts re~lux temperature for a~} additional hour and then cooled to room temperature and filtered.
. 5 The resultlng polymer disperslon haa a solids content ;;
; of about 70% and the polymer has a rel~tlve vlscosity of about -~ 1.09 measured at 25 in dimethyl formamide and about 0.5% polymer solids and the polymer has an acid number of about 47 and a carboxy to hydroxyl ratio of 1 to o.58. The ~ :
.
.. 10 polymer has the following composition: methyl methacrylate/
; .~ -., butyl acrylate/2-hydroxyethyl acrylate/acrylic acid in ~
~`~ weight ratio of about 54/34.2/5.7/6,1 and a uniformity factor of about 75-85~
., ~ . . .
A coating composition ls then prepared as follows:
Parts By _ ~eight :! ~ .
Portion 1 j Polymer solution (prepared above) 200 . ", . . ...
i Portion 2 ;j . - , Dlethylamlnoethanolamine 14 Portion 3 ~ ~:
Deionized ~ater 318 ~: .
Portion 4 . ~
.
Hexa(methoxymethyl)melamine 60 ~ ~
., , ~-, 3 25 Tot~l 592 ~-Portion 1 ls charged into a mixing vessel and then :~
Portion 2 is added and blended with Portion 1. Portion 3 is ~ then slowly added with constant agitation. A~ter Portion 3 :-~ ls added, all of Portlon 4 is th~n added ~nd mixed in. The ~0 resulting coating compoæition has a sol~ds of content of j~ about 33~ and a spray viscosity of abouk 30 seconds using a ;1 No. 2 P~rlin cup.
, I :.
:. _ 21 ;1 :
~::
~03~ Z
; A standard spray gun is used to apply the coatlng ;
composition to a steel panel primed with 1.5 mil thick iron oxlde pigmented alkyd resin prlmer. After the coating is applied, the panel i8 baked for 15 minute~ at 90C. and then ~or 30 minutes at about 1~0C. to prov~de a coating of about `
2 mils thick that ha~ a good appearanceJ good gloss, excellent ~:
', hardness, and good chip resistance. :
.. ~. , EXAMPLE 3 -~
~' ~
A coating composition is prepared by first forming ;~ ;
the following acrylic polymer solution:
,., Parts By :
, , Wei~t i Portion 1 ,; .
:. Methyl methacrylate monomer 55.0 i 15 Butyl acrylate monomer 81.0 ~ : :
',Jl 2-Hydroxyethyl acrylate monomer 9.O : ;
,~ Acrylic acid monomer 15-Isopropanol ~0.0 Ethylene glycol monobutyl ether 75.0 ~! 20 Dodecyl mercaptan 1.4 Portion 2 ~ Ben~oyl peroxide 3.3 ~:
,~ Methyl methacrylate monomer 30.0 : ;~
, Portion 3 :
Methyl methacrylate monomer 29200 Butyl acrylate monomer 116.
. 2 Hydroxyethyl acrylate monomer 3~.0 Acrylic acid monomer 69.0 ,, .
Benzoyl peroxide 13.0 Isopropanol 42.0 Ethylene glycol monobut~l ether 132._ :
` Total 99~7 , .. .
~ -25 ~ 1~38522 ; Portion 1 1~ charged lnto a re~ction vessel - equipped wi~ a s~irrer, a heating man~el and a reflux condenser and then heated to lts reflux temperature. ~ -Portion 2 1~ premixed and then added to the reaction mixture.
Portion 3 is premixed and 46% of Portion 3 is continuously ~ ~;
~! added over a 20-minute period, and then the remainder of ;~~ Portion 3 is continuously added over a 60 minute period j whlle malntaining the reaction mixture at lts reflux tempera-- ture. The reflux o~ the reaction mixture is continued for an additional 90 minutes. The reaction mixture is then coo:Led to room temperature and filtered.
.
The resulting polymer dlspersion has a solids content about 71% and the polymer has a relative viscoslty of 1.0~6 measured at 25C. ln dimethyl ~ormamide at about 0.5~
i 15 polymer solids, and the polymer has an acid n~unber o~ about 93 to 94 and a c~rboxyl to hydroxyl ratio of 1 to 0.31. The :
polymer has the following composition: methyl methacrylate/
butyl acrylate/hydroxyethyl acrylate/acrylic acid - -,"~
53.8/28.2/6.0/12.0 and a uniformity ~actor of about 75-85~.

A coatlng compo~ition i8 prepared by blending the followlng ingredients:
Parts By Welght Portlon l Polymer solut~on prepared above 200 Portion 2 Diethylaminoethanolamine 15 ~; Portion 3 -1 Delonized water 31 Portion 4 '~ Hexa(methoxymethyl) melam~ne 60 ' Total 593 ~.
."~ ,.
. .

, , ~

. ., .: :: .. :: .' . :' : ' ',, ,, : .

l;

3~95ZZ
Portion 1 ls charged lnto a mixing ~e~sel and , .
then Portion 2 iB added wlth constant agitation and then .
Portion 3 is 810wly added to the reaction m:lxture and after Portion 3 ha3 been added, Portion 4 i6 added and blended with ; 5 the reactlon mixture. The resul~ing compos:ltion has a 33%
polymer solids content and a spray viscosity o~ 30 seconds measured in a No. 2 Parlin cup. The compos:ltion is then sprayed :
onto a steel panel prim~d a~ in Example 1 and baked according i to the procedures described in Example 1. The resulting ~inish i8 about 2 mils thick, has good appearance and is an .
-, acceptable finish for the exterior of automob~le bodies and ~ ~ .
truck bodle~.

EXAMPLE 4 ..

~ A coating compo~ition i~ prepared by first ~orming ! 15 the following acrylic polymer ~olution:
~a.t~ ~y Wei~ht Portion 1 .
Methyl methacrylate monomer lR.210 :
~, 20 Butyl acrylat2 monomer 21.050 ! 2-Hydroxyethyl acrylate monomer 1.900 . Acrylic acid monomer 1.810 Isopropanol 6.55 Ethylene glycol monobutyl ether 8.73 Lauryl mercaptan 0.310 '~ Portlon 2 .
.i . Benzoyl peroxide 0.716 ` Ethylene glycol monobutyl ether 5.880 ~ . ~

,,~ .
. '. .
27 _ ' . . . .. : . . . - .

; ~0~2Z Parts By Wei~ht Port1on 2 (Continued) .
, Methylethyl ketone 1.600 5Portlon ~ :
. Methyl methacrylate monomer 26.800 ~:
Butyl acrylate monomer 130030 :.
2-Hydroxyethyl acrylate monomer 2.860 :~
Acryllc acid monomer ~.18 ;
Benzoyl peroxide 10150 Isopropanol 3.8 :~
Ethylene glycol monobutyl ether 12.400 ~, Portion 4 .~ -Methyl methacrylate monomer 26.800 i: .
Butyl acrylate monomer 13.030 :
2-Hydroxyethyl acrylate monomer 2.850 I Acrylic acid monomer ~-17 -~ Benzoyl peroxi~e 1.150 . . ~ :
Isopropanol . ~.800 i 20 Ethylene glycol monobutyl ether 12.400 ,~ Portion 5 } Methyl methacrylate monomer 10.210 ~ ~
~i Butyl acrylate monomer 4.880 ~ ;
2-Hydroxyethyl acrylate monomer 1.160 -~. :
~' Acrylic acid monomer 1.200 ; -Benzoyl peroxlde o.474 ~ ~.
;~ Isopropanol 1.550 :~ Ethylene glycol monobutyl ether 5.o80 .~ portion 6 Dleth~lethanol~mine 10.500 Demlneralized water . 128.000 :~ , . 9 , ;,~ . .
,,'.1 . ,.j .

~, .
~ 8 ~
. ,,. ~

.. . . . " .. , _ `~

Parts By _~Weii~ht Portion 7 Demineralized water 209.60 . ~
, 5 Total 566~730 Portion 1 i8 charged into a reaction vessel equipped with a stirrer, a heating mantel and a ref:Lux condenser and the ingredients are heated to the reflux temperature.
Portion 2 is premixed and then added to the reaction mixture ` 10 and then Portion 3 is added at a uniform rate over a ,'lf 20 minute period while maintaining the reaction mixture t at a reflux temperature. Portion 4 is premixed and then about ~4~ of Portion 1~ is added at a continuous rate to the ~J~ reaction mixture over a 20-minute period. Then the remainder of Portion 4 is added at a continuous rate over the next 60-~,' minute period while maintaining the reaction mixture at its ,~ reflux temperature. Portion 5 is premixed and thën added at .,., : . :- .
l a uni~orm rate over a 100-minute period keéping the réaction ,j mixture at its re~lux temperature and then thé reâction mixture is held at its reflux temperature for an additional 1/2 hour. Portion 6 is then added to the reaction mixture ¦ and then Portion 7 is added and the mixture is cooled and ~iltered to remove coa~ulum. ~ ;
.. ,~, . . . . . .. .
The resulting polymer dispersion has a po~ymër ~solids content of about 26% by weight and the polymer has a reiative viscosity of about 1.15 measured at ~5C. in dimethyl ;~ ~ormamide solvent at about 0.5% polymer solids. The po-lymer ~-has an acid number of about 46 to 47 and a carboxyl to hydroxyi ;' ratio o~ 1 to 0.62. The polymer has the ~oi~owing compositioni ;i~ 3o met~yl methacrylate~ but~l acrylate/2-hydroxyethyl acryiate/
' acrylic acid in a weight ratio of about 54/34j6/6 and a ;~ unlformity factor of about 75-85~.

, .,;~, .Q3~9S2~
A paint compo~ition is then prepared by blending together the following lngredients:
Parts By Weight Portion . Mill base (described in Example 1) :. MONASTRAL Blue mill base (prepared ln ~ample 1) 0.20 MONhSTRAL Violet mill base (prepared in Example ; "~
1) 0.70 . :
. Phthalocyanine green-yellow mill base ::
(prepared in Example 1) 0.45 ~ Alumlnum Flake mill baæe (prepared in Example ;~ 1) 11.05 Ii Portion 2 ;~ Hexa(methoxymethyl) melamine 20.40 . .
Portion 3 . .
. Acrylic polymer dispersion (prepared above) 272.1~0 Portion 4 Deionized water 18.00 Portlon 5 Butyl acrylate/acrylic acid copolymer ~:
solution (described ln Example 1) 3.30 Anti-cratering solutlon (10~ silicone solution) 3,35 ~ ~.
Deioni~ed water 31.00 $~ Total 367.20 , Portlon 1 i8 chargcd into a mixing vessel and `; thoroughly blended together and then Portion 2 i~ added and ~ bl~nded and then Portion 3 i~ added and the constituents are , ,, thoroughly blended together. Po~tion 4 i9 added and blended ~: with the mixture and then Portion 5 is added and thoroughly bler~ded with the mixture. me resulting paint composition has a 28~ ~ollds content and a ~pray visco~ity of 31 seconds using a No, 2 Zahn Cup.

J ~ ~

,`?
` .

. ., . ~ . ~ . , .

: ~ 1038S~Z ~ ~ ~
The paint is sprayed onto ~ steel panel . prlmed with 1.5 mil thick lron oxide pigment alkyd resin ~, primer as in Example 1. The coating is baked as in Example 1 . ~
providlng a film about 2 mils thick which has good gloss, : ;
good appearance, good adhesion to the substrate, good chip -.` resistance, good gasoline reslstance and resistance to .
-i. deterioration by weathering.

EXAMPLE 5 .

~; A coating composition is p-epared by first forming ;l 10 the following acrylic polymer solution~
~ Parts By ~`
I Weight ~ ~
Portion 1 ~ `
;~ ,' `I
., ,, ~ .
Methyl methacrylate monomer 47 Styrene monomer 30 utyl Acrylate monomer ; 112 .
`.. `!~: 2-Hydroxyethyl acrylate monomer 15 : ;~,~ Acrylic acid ~onomer 6 ..
Ethylene glycol monobutyl ether 190 ~ 20 Isopropanol 30 `; Dodecyl mercaptan 2 ~ Portion 2 .
~ Eth~lene glycol monobutyl ether 30 `,~ Tertiary butyl peracetate solution 9.5 .:
(75~ solution in mlneral spirits) ~ ~
Portion 3 ~.
~:~ :
~.x ~ Methyl methacrylate monomer 117 ~ Styrene monomer ~ 174 ~ Butyl acrylate monomer 112 ~;
: 2-Hydroxyethyl acrylate monomer 42 .~ Acrylic acid monomer : : 23 ., ~1 : .
~ 31 _ i ;
.;J`~ ::
! :~
. , ~ . . ; ~

4~ `
~ `Portion 4 la3ss2~ 4,o ~ ~
Isopropanol Tertiarybutyl peracetate solution (described above) 3.9 Total 983.4 Portion 1 is charged into a reaction vessel equipped ; with a stirrer, a heating m~ntel and a refl~ condenser and ,~ heated to its reflux temperature. Portion 2 is then adde~ and ir the reactlon mixture is held at its reflux temperature ~or 5 ... .
minutes. Portions 3 and 4 are premixed and added s~multaneously in the following order: 85% of portion 3 i6 slowly added over ~ ~ , a 25 minute period alon~ with 75~ of portion 4 then the remainder of portion 3 is added over a 60 minute perlod while the remainder of portion 4 is added over a 90 minute period. During these ', addltions, ths reactlon mixture is held at its re~lux tempera-~ ture and after the additions the reaction mixture is re~luxed ~ ;}~ for one hour.
The resulting polymer dispersion has a solids content ~( of 70~, the polymer has a relative viscosity mea~ured a+ 25C.
; ~ 20 in dimethyl forma~ide at 0.5~ polymer solids of about 1.15;
,~ the polymer has an acid number of 33-35 and a carboxyl to hydroxyl ratio of 1 to 1.5. m e polymer has the following composition: styrene/methyl methacrylate~butyl acrylate/
2-hydroxyethyl acrylate/acrylic acid - 30.0/24.2/33.1/8.~/4.3 and has a unlformlty factor of about 75-85%. ~ ;
A coating composition is prepared as in Exa~ple 3 ~ -~
. . ~, except the above prepared polymer solution is used. The ~ ;
` composition is sprayed onto a prlmed steel panel and ba~ed ~ as ln Example 3. m e resulting finish is a~out 2 mils thick, '~ 30 has a good appearance and is an acceptable finish for the exterlor of automob1le and truc~ bodies.
- 32 ~

, ~ , .; ,~

.", ~ . , . . , . . . ~ ~ . ..

~ Example 6 :: t.. -A coa,'-;ing composition is prepared by ~lrst ~orming the followlng polymer solution by a programmed polymerization l,-. i`:
process: l~
Parts by l ~.
-., Welght ~i Portion 1 -~
;~-' Methyl methacrylate monomer 241 .! Butyl methacrylate monomer 571 `` ~`:
'., 10 2-Hydroxy ethyl acrylate monomer 55 .~ Acrylic acid monomer 46 .
Isopropanol 402 Ethylene glycol monobutyl ether 771 Lauryl mercaptan 14 ~ .
l 15 Portion 2 Benzoyl peroxide 7 Methyl methacrylate monomer 254 .
!~ Portion 3 ' Methyl methacrylate monomer 1211 ~:
l 20 Butyl acrylat~e monomer 504 " 2-Hydroxy ethyl acrylate monomer 135 Acrylic acid monomer 144 Benzoyl peroxide 72 .¦ Portion 4 25. N~N-diethyl aminoethyl amine 185 Water 310 ~ :

: i....... /~

,', j: ," ~ ` ' ~ :
~ ? ,: .

~:, 33 ~
'.,, " ~:

~L03~ Z Pwrtishtby r ;
Portion 5 ~i~
`', Water 1600 Portion 6 ~ Water 16~0 , ',~ Portion 7 ~;1 Water 1878 ;
~) Total 10,000 i 10 Portion 1 is premixed and charged into a reaction vessel equipped with a stirrer, a heating mantel and a reflux condenser and heated to its re~lux temperature~ Portion 2 is then added. Portlon 3 is premixed and 30~ added over a 15 minute period while maintaining a reflux temperature9 45% of ;~
Portion 3 is then added over a 50 minute period while main~
~ taining a reflux temperature and the re~ainder of Portion 3 :,: , : ::
is added over the next 80 minutes while maintaining a reflux .. , -! temperature and the reaction mixture is held at its reflux , ;.,, . ;
; :! temperature for another 30 minutes. Portion 4 is added and -i' 20 mixed for 10 minute~ then Portion 5 is added over a 10 minute period with mixing. Portions 6 and 7 are then added ., with mixing between each addition. `~ ;

. The resulting polymer dispersion has a ~olids content ~ v~ 32%~ About 40~ of the polymer is dispersed and th0 dispersed m~ 25 polymer particles have a partlcle size of about o.o2-0.06 microns and the remainlng 60~ o~ the polymer is dissolved. The polymer has a rela~ive viscosity of 1.15-1.16 measured as in Example 1, the polymer has an acid number of 47 and a carboxyl to `' hydroxyl ratio of 1 to 0.62. The polymer has the following .~.~ . .. ..

',,', , s~ ~ - 34 ~
.,, ~Q~522 `;
- composition: methyl methacryl~te/butyl acrylate/2-hydrox~- 1 ethyl acrylate/acrylic acid _ 54/34/6/6~ and has ~ uniformity factor at about 75-85 A coating composition i8 prepared as in Example 4 except the above prepared polymer solution :ls used. The composition is sprayed onto a primed steel panel and baked as in Example 4. The resulting finish is about 2 mils ~ .
-, thick~ has a ~ood appearance and i8 an acceptable finish .. for the exterior of automobile and truck bodies. : .
,.~ , .
, ~ :
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'~ - 35 .. . .

Claims (8)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An aqueous thermosetting acrylic enamel coating composition comprises 10-60% by weight of film-forming constituents and correspondingly 90-40% by weight of water and up to 20% by weight of a solvent for the film-forming constituents; wherein the film-forming constituents consist essentially of (1) 60-90% by weight, based on the weight of the film-forming constituents, of an acrylic polymer having a uniformity factor of at least 75%
and consisting essentially of (a) 50-60% by weight, based on the weight of the acrylic polymer, of methyl methacrylate;
(b) 30-40% by weight, based on the weight of the acrylic polymer, of butyl acrylate, (c) 5-10% by weight, based on the weight of the acrylic polymer, of hydroxy-ethyl acrylate;
(d) 4-12% by weight, based on the weight of the acrylic polymer, of acrylic acid or methacrylic acid;
wherein 30-50% by weight of the acrylic polymer is dispersod and has a particle size of 0.01-0.10 microns and the remaining 50-70% is soluble and dissolved and the polymer has a carboxyl to hydroxyl ratio of 1:0.3 to 1:1.5 and an acid number of about 35-80 and weight average molecular weight of 10,000 -50,000 and (2) 10-40% by weight, based on the weight of the film-forming constituent, of a hexa(methoxymethyl) melamine; and the composition is at least partially neutralized with a water-soluble amino and has a pH of about 7.1 - 7.5.

2. The coating composition of Claim 1 containing 0.1-40% by weight pigment and having a polymer solids content of about 20-50% by weight.

3. The coating composition of Claim 2 in which the acrylic polymer consists essentially of 54% methyl methacrylate, 34% butyl acrylate, 6% 2-hydroxyethyl acrylate and 6% acrylic acid and has an acid number of about 45-50 and a carboxyl to hydroxyl ratio of about 1:0.6.

4. The aqueous thermosetting acrylic enamel coating composition of Claim 1 comprises 20-50% by weight of film-forming constituents and correspondingly 80-50%
by weight of water and up to 20% by weight of a solvent for the film-forming constituents; and additionally contains about 0.1-20% by weight of pigment; wherein the film-forming constituents consist essentially of (1) 60-90% by weight, based on the weight of the film-forming constituents, of an acrylic polymer having a uniformity factor of 80-95% and consisting essentially of (a) 50-60% by weight, based on the weight of the acrylic polymer, of methyl methacrylate, (b) 30-40% by weight, based on the weight of the acrylic polymer, of butyl acrylate;

(c) 5-10% by weight, based on the weight of the acrylic polymer, of hydroxy-ethyl acrylate;
(d) 4-12% by weight, based on the weight of the acrylic polymer, of acrylic acid or methacrylic acid;
wherein 30-50% by weight of the acrylic polymer is dispersed and has a particle size of 0.01-0.10 microns and the remaining 50-70% is soluble and dissolved and the polymer has a carboxyl to hydroxyl ratio of 1:0.3 to 1:1.5 and an acid number of about 35-80 and a weight average molecular weight of 10,000-50,000, and (2) 10-40% by weight, based on the weight of the film-forming constituent, of a hexa(methoxymethyl) melamine; and the composition is at least partially neutralized with a water-soluble tertiary amine and has a pH of about 7.1 - 7.5.

5. A metal substrate coated with about 0.5-3.5 mils of the dry coalesced layer of the coating composition of Claim 1.

6. A ferrous metal substrate having a pigmented primer coating and a finish layer about 0.5-3.5 mils of the dried coalesced coating composition of Claim 1.

7. A plastic substrate reinforced with glass fibers coated with 0.5-3.5 mils thick dried layer of the coalesced coating composition of Claim 1.

8. A process for preparing a coating composition of an acrylic polymer of 52-56% by weight of methyl meth-acrylate, 32-36% by weight of butyl acrylate, 5-7% by weight of hydroxy ethyl acrylate and 5-7% by weight of acrylic acid;
the acrylic polymer having a uniformity factor of at least 75%, carboxyl to hydroxyl ratio of 1:0.2 to 1:1.8, an acid number of about 35-80 and a weight average molecular weight of about 10,000-50,000 comprising the following steps:
Step (1) Charging the following constituents into a reaction vessel and heating the constituents to reflux temperature:
13-15% by weight of said total amount of methyl methacrylate, 52-54% by weight of said total amount of butyl acrylate, 28-30% by weight of said total amount of hydroxy ethyl acrylate 23-25% by weight of said total amount of acrylic acid, water miscible solvents and a chain transfer agent;

Step (2) Charging the following constituents into the reaction vessel and maintaining the reaction mixture at a reflex temperature:
a polymerization catalyst, 14-16% by weight of said total amount of methyl methacrylate;
Step (3) Charging the following constituent slowly and continuously into the reaction vessel over a 14-16 minute period:

20-21% of said total amount of methyl methacrylate, 13-15% of said total amount of butyl acrylate, 31-33% of sald total amount of hydroxy ethyl acrylate, 22-24% of said total amount of acrylic acid, and polymerization initiator and maintaining the reaction mixture at a reflux temperature for about 10-20 minutes;
Step (4) Charging the following ingredients slowly and continuously into the reaction vessel over a 49-51 minuto period and maintaining the reaction mixture at a reflux temperature, 31-33% of said total amount of methyl methacrylate, 20-22% of said total amount of butyl acrylatc, 31-33% of said total amount of hydroxy ethyl acrylate, 33-35% of sald total amount of acrylic acid, and a polymerization initiator;
Step (5) Charging the following ingredients slowly and continuously into the reaction vessel over a 75-80 minute period:
17-19% of said total amount of methyl methacrylate, 11-13% of said total amount of butyl acrylate, 6-8% of said total amount of hydroxy ethyl acrylate, 17-19% of said total amount of acrylic acid and a polymerization initiator maintaining the reaction mixture at a reflux tomperature for about 25-35 minutes to form said polymer;
Step (6) Adding a sufficient amount of an amine to said polymer to provide a resulting pH of about 6-9 and then adding water to provide an aqueous coating composition.