An electrocoating composition useful for electrocoating a paint coating from an aqueous solution onto an anode electrical conductive substrate. The electrocoating composition is based upon a fatty acid ester and .alpha.,.beta.-unsaturated dicarboxylic acid modified styrene-allyl alcohol copolymer further modified with an acid-functional acrylic copolymer. The electrocoated film can be air dried or heat cured.

BACKGROUND OF THE INVENTION 
Electrocoating compositions are well known and disclosed in Gilchrist 
patents, U.S. Pat. Nos. 3,351,675; 3,362,899; 3,575,909; and 3,351,575 and 
the same are incorporated herein by reference. Electrocoating compositions 
are dispersed in dilute water baths and then electrocoated onto cathodic 
or anodic substrates submerged in the electrocoating bath. The 
electrocoated films can be heat cured with catalysts or cured by 
ultraviolet energy as disclosed in U.S. Pat. No. 4,040,925. 
It now has been found that particularly useful anodic electrocoating 
compositions based on a fatty acid and unsaturated acid modified 
styrene-allyl alcohol polymers, further modified with acid functional 
acrylic copolymers, provide excellent electrocoating compositions for 
anode substrates. The electrocoating compositions exhibit high hydrophobic 
properties which impart excellent plating properties such as shut down, 
throwing power, as well as excellent cured film properties such as good 
water resistance and salt spray resistance. The electrocoating composition 
polymer is substantially free of readily hydrolysable ester groups in 
addition to contributing considerably to good electrical resistance 
properties and bath stability. The electrocoating compositions are 
particularly well suited to air-drying or force-drying wherein good post 
flow is obtainable. The electrocoated film quickly dries to handle or 
stack if desired. Baking at higher temperatures may also be used to cure 
the coating in which case an aminoplast curing agent may be advantageously 
employed. These and other advantages are achieved by the electrocoating 
composition of this invention. 
SUMMARY OF THE INVENTION 
A composition for electrocoating a paint film onto an anode electrically 
conductive substrate is primarily based upon a binder polymer composition 
comprising on a weight basis: 
(a) 20% to 40% styrene-allyl alcohol copolymer; 
(b) 20% to 50% fatty acid esterified with a portion of the hydroxyl groups 
on (a); 
(c) 0% to 3.0% .alpha.,.beta.-unsaturated dicarboxylic acid or anhydride 
esterified with a portion of the allyl alcohol groups on (a); and 
(d) 20% to 50% acid-functional acrylic copolymer having double bonds 
coreacted with the fatty acid and unsaturated acid modified styrene-allyl 
alcohol polymer formed in (a), (b), and (c). 
DETAILED DESCRIPTION OF THE INVENTION 
The electrocoating composition of this invention is primarily based on a 
polymer comprising coreaction between (a) styrene-allyl alcohol copolymer, 
(b) fatty acid, (c) .alpha.,.beta.-unsaturated dicarboxylic acid or 
anhydride, and (d) acid-functional acrylic copolymer. 
(a) Referring first to the styrene-allyl alcohol copolymer, the copolymer 
can contain by weight between about 2.8 and 4.3 parts styrene 
copolymerized with one part allyl alcohols having the general structural 
formula of: 
##STR1## 
wherein R is an aliphatic chain containing 1 to 9 carbon atoms. Examples 
of suitable allyl alcohols are allyl alcohol and methallyl alcohol. 
Styrene and allyl alcohols are coreacted together to provide a 
styrene-allyl alcohol copolymer having the general structural formula of 
##STR2## 
wherein m=8 through 13 inclusive and n=5 through 6 inclusive. The 
equivalent hydroxyl weight of the copolymer is between about 197 and 328, 
and the molecular weight of the copolymer is between about 1120 and 1700. 
(b) Referring now to the fatty acid modification of the styrene-allyl 
copolymer, between about 0.5 and 1.3 weight parts of unsaturated aliphatic 
fatty acid are esterified with one weight part of the styrene-allyl 
copolymer by esterification with part of the available hydroxyl groups on 
the styrene-allyl alcohol copolymer (a). In the resulting fatty acid 
modified styrene-allyl copolymer, suitable aliphatic fatty acids contain 
between about 8 and 20 carbon atoms and include for example, oleic, 
linoleic, linolenic acids and mixtures thereof. The fatty acid can be 
esterified with the hydroxyl containing styrene-allyl copolymer at 
temperatures of about 350.degree.-500.degree. F. (180.degree.-260.degree. 
C.) to produce a structural copolymer generally illustrated as follows. 
##STR3## 
wherein: m=8 to 13 moles of styrene, 
n=5 to 6 moles of allyl alcohol, and 
p=moles of fatty acid wherein R is the aliphatic fatty chain. 
The resulting fatty acid modified styrene-allyl copolymer can have an 
hydroxyl number between 0 and 90 and a molecular weight between about 1600 
and about 3000. The unreacted hydroxyl groups can be further reacted with 
an .alpha.,.beta.-unsaturated acid anhydride as hereinafter described. 
(c) Referring next to the .alpha.,.beta.-unsaturated dicarboxylic acid 
modification of the styrene-allyl copolymer, between about 0 and about 6.0 
weight parts of .alpha.,.beta.-unsaturated dicarboxylic acid or anhydride 
is esterified with the remaining available hydroxyl groups on 100 parts by 
weight of the fatty acid modified styrene-allyl copolymer. Useful 
.alpha.,.beta.-unsaturated carboxylic acid anhydrides include for example, 
maleic anhydride, and/or itaconic anhydride and the like. The resulting 
polymer has the following structural formula: 
##STR4## 
wherein: m=8 to 13 moles of styrene 
n=5 to 6 moles allyl alcohol 
p=moles of unsaturated fatty acid 
r=moles of .alpha.,.beta.-unsaturated dicarboxylic acid 
The resulting fatty acid and .alpha.,.beta.-unsaturated acid modified 
styrene-allyl copolymer has a molecular weight between about 1600 and 
about 3000. 
(d) Referring next to the acid-functional acrylic copolymer, said acrylic 
copolymer comprises acrylic monomer copolymerized with styrene or vinyl 
toluene and acrylic or methacrylic acid. On a weight basis, the 
acid-functional acrylic copolymer contains polymerized monomer of between 
about 0% and 60% acrylic monomer, 30% and 90% styrene or vinyl toluene and 
10% and 50% acrylic or methacrylic acid. Acrylic monomers include for 
example, lower alkyl esters of acrylic or methacrylic acid such as ethyl 
acrylate, propyl acrylate, butyl acrylate, methyl methacrylate, and ethyl 
methacrylate. The acid-functional acrylic polymer is copolymerized in 
presence of peroxide initiator with the copolymer (a)-(b)-(c) formed 
hereinabove by reacting the acid-functional acrylic monomer mixture (d) 
with the maleic unsaturation in copolymer (a)-(b)-(c) and/or by reacting 
with active methylene group alpha to a fatty acid double bond. 
The foregoing electrocoating composition comprises by weight: 
(a) 20% to 40% styrene-allyl alcohol copolymer; 
(b) 20% to 50% fatty acid esterified with a portion of the hydroxol groups 
in (a); 
(c) 0% to 3% .alpha.,.beta.-unsaturated dicarboxylic acid esterified with a 
portion of the hydroxyl groups on (a); and 
(d) 20% to 50% acid-functional acrylic copolymer having double bond 
coreacted with the double bonds of copolymer of (a)-(b)-(c). 
Stable aqueous dispersions are obtained by neutralization of both the 
.alpha.,.beta.-unsaturated dicarboxylic acid ester acidity and the 
methacrylic acid carboxyls using alkali-metal hydroxides or amines. At 
least about 1% by weight of alkali-metal hydroxide or amine is coreacted 
with the electrocoating polymer (a)-(b)-(c)-(d) to neutralize carboxyl 
groups pendant and attached to the polymer backbone. Useful amines are 
selected from aliphatic, aromatic, and alkanolamines generally indicated 
--NH.sub.2, .dbd.NH, .tbd.N, --N--(ROH).sub.2, .dbd.N--(ROH), and 
N--(ROH).sub.3. Useful solubilizing bases are bases such as NaOH and KOH. 
Neutralization of the polymer is based on the actual measurable acid value 
of the polymer. The acid number of the polymer should be at least about 20 
and preferably between about 40 and 80. Among the amines that can be used 
are those amines which form water dispersible salts with the polymers and 
have a carbon content of less than about 10 carbon atoms per amine 
molecule. Suitable amines include, for example, diethyl amine, triethyl 
amine, monoisopropanol amine, monoethanol amine, diethanol amine as well 
as ammonia and aqueous ammonia commonly called ammonium hydroxide, and 
other amines as set forth in the examples. Useful amines are disclosed in 
U.S. Pat. No. 3,759,807, and the same are incorporated herein by 
reference. The preferred amines are diisopropanol amine, 
dimethylethanolamine, methyldiethanol amine, diethylethanol amine, 
triethanolamine. Preferably just enough base or amine is added to form a 
water dispersible salt of the polymer, and preferably between about 1 and 
30% by weight base or amine is added based on the polymer. For example, 
polymers having an acid value of about 40 to 60 require about 0.7 to 1.0 
equivalents of amine for each equivalent of acid found in the polymer, 
although polymers having an acid value greater than 100 can require as 
little as 0.3 equivalent of amine per each equivalent of acid. 
Solubilization of the polymers can be effected by reacting the carboxyl 
groups on said polymer with the required amount of amine, and then adding 
water to the amine salt of the polymer. The resulting mixture thereof can 
be agitated to form a stable water dispersion. A preferred method of 
solubilizing the polymers is to add slightly warmed polymer to a water 
amine solution and agitate and warm the solution, if necessary, until a 
good dispersion compatible in water is obtained. The solids content of 
such aqueous solution of solubilized polymer is generally about 5 to 25 
weight percent, and preferably about 5 to 15 weight percent. 
The water solutions of polymer can be applied to a substrate in a 
conventional manner but is particularly suitable for electrocoating onto a 
conductive metal anode which is the object to be coated with a paint film. 
The anode substrate is an electrically conductive metal such as iron, 
steel, aluminum, galvanized steel, zinc, and the like. The coating 
composition can be electrocoated onto the anode workpiece by passing a 
direct electric current between the anode and the cathode of the 
electrocoating bath to deposit a coating composition on the anode. 
The method of electrocoating is carried out at a voltage above the 
threshold voltage of the electrocoating paint composition being 
electrocoated onto the anode workpiece. The threshold voltage is the 
voltage at which deposition of the solubilized binder composition is 
initiated upon the workpiece when a direct electric current is passed 
through the electrocoating bath between the workpiece and a second 
electrode referred to as a cathode. The cathode is electrically negative 
in relation to the workpiece and spaced therefrom wherein both the cathode 
and the anode electric workpiece is in electrical contact with the 
electrocoating bath. The maximum tolerable voltage is slightly below the 
rupture voltage of the paint coating being applied to the substrate. The 
rupture voltage is commonly understood to be that voltage at which a paint 
film already applied to the substrate ruptures upon continued application 
of such voltage across the terminals during the immersion of the workpiece 
within the electrocoating bath. The minimum desirable voltage should range 
between about 20 and about 500 volts, and preferably between about 50 and 
300 volts. The temperature of the electrocoating bath normally is between 
about 15.degree. and about 50.degree. C. Preferably the temperature for 
electro-deposition is between about 20.degree. and about 35.degree. C. and 
maintenance of the bath temperature between this temperature range is 
preferred. Electrocoating bath agitation is desirable to maintain 
uniformity of composition as well as uniform temperatures at the anode 
surfaces. 
The electrocoating bath can be replenished continuously or incrementally 
with a replenishing composition so as to maintain the electrocoating bath 
approximately at a pre-determined composition wherein the total 
replenishment is substantially equal over a sustained operating period. 
The replenished composition can be concentrated having a higher level of 
solids to water content as suggested in U.S. Pat. No. 3,575,909.

The merits of the electrocoating composition of this invention are further 
illustrated by the following examples. 
EXAMPLE 1 
Into a suitable reaction vessel equipped with stirrer, thermometer, 
dean-stark water-trap, condenser and nitrogen inlet tube there are charged 
2398 grams of a styrene-allyl alcohol copolymer of molecular weight 1100 
and hydroxy equivalent wt. 220, and 2398 grams of a mixed fatty acid 
containing predominantly linoleic acid. This ester was processed along 
with xylol (191 grams) as a water removal assist during resin 
esterification at a maximum reactor temperature of 240.degree. C. and to 
an acid no. of 4-5 mg. KOH per gram. This "base ester" was cooled to 
140.degree. C. Then 69 grams of maleic anhydride was added and reacted in 
at 140.degree.-145.degree. C. for 15 minutes. To this maleinized ester, 
1763 grams of solvent ethylene glycol mono butyl ether (EGMBE) was added 
and a temperature of 140.degree.-145.degree. C. was regained. A monomer 
premix comprising the following: 
______________________________________ 
Styrene 1794 grams 
Methacrylic acid 453 grams 
Ditertiary butyl peroxide 
90 grams 
______________________________________ 
was then added dropwise to the reaction mixture at 140.degree.-145.degree. 
C. over a period of 4 hours. The batch was held at 140.degree.-145.degree. 
C. for 4 hours at which time the polymerization was substantially complete 
as indicated by a non-volatile content of at least 79% and a free styrene 
content less than 0.6%. To the batch was then added 70 grams Ionol, an 
antioxidant tank stabilizer, and 70 grams of a solution of cobalt 
napthenate containing 6% cobalt, a curing accelerator, and 512 grams of a 
mineral spirits, boiling range 150.degree.-200.degree. C. The purpose of 
the mineral spirits was to assist post-flow of the coating and to improve 
electrical resistance of the deposited film to allow higher application 
voltages. Final constants on the resin were as follows: 
______________________________________ 
Non-volatile 73.0% 
Viscosity (reduced to 
50% NV in EGMBE) H-L (Gardner Scales) 
Acid No. of non-volatile 
46 
______________________________________ 
EXAMPLE 2 
Into a reaction vessel equipped as in Example 1, there were charged 2138 
grams styrene-allyl alcohol copolymer (Ex. 1), 2138 grams mixed linoleic 
fatty acid (Ex. 1), and 171 grams xylol. This base ester was processed 
exactly as in Example 1. The base ester was maleinized by reacting with 61 
grams of maleic anhydride at 140.degree.-145.degree. C. for 15 minutes. 
The ester was then cut with 1769 grams solvent EGMBE and 705 grams mineral 
spirits having a boiling range of 150.degree.-200.degree. C. To this 
solution was added at reflux (155.degree. C.) the following monomer 
premix: 
______________________________________ 
Styrene 2262 grams 
Methacrylic acid 504 grams 
Ditertiary butyl peroxide 
110 grams 
______________________________________ 
over a period of 4 hours. The batch was held for 4 hours at 
145.degree.-150.degree. C. at which time the polymerization was 
substantially complete as indicated by a non-volatile content of at least 
72%. To the batch was then added 70 grams 6% cobalt solution and 70 grams 
Ionol. Final constants of the batch were: 
______________________________________ 
Non-volatile 73.0% 
Viscosity (50% NV in EGMBE) 
I-M (Gardner Scale) 
Acid No. (on solids) 48 
______________________________________ 
EXAMPLE 3 
A base ester was prepared exactly as in Example 1 from 2619 grams 
styrene-alcohol copolymer (Ex. 1), and 2619 grams mixed linoleic fatty 
acid (Ex. 1), and 209 grams toluene; the toluene was removed by a vacuum 
distillation. The base ester was then maleinized with 75 grams maleic 
anhydride by reacting at 140.degree.-145.degree. C. for 15 minutes. 1926 
grams EGMBE was added and the following monomer premix grafted onto this 
maleinized base ester solution: 
______________________________________ 
Styrene 1959 grams 
Methacrylic acid 495 grams 
Ditertiary butyl peroxide 
98 grams 
______________________________________ 
by adding it dropwise over a 4-hour period at 160.degree. C. falling to 
145.degree. C. The batch was then held for 4 hours at 145.degree. C. Final 
batch constants were: 
______________________________________ 
Non-volatile 80% 
Viscosity (at 50% NV 
in EGMBE) L-P (Gardner Scale) 
Acid No. (on solids) 
46 
______________________________________ 
EXAMPLE 4 
The base ester prepared as in Example 1, using 2468 grams styrene-alcohol 
copolymer (Ex. 1), 2468 grams mixed linoleic fatty acid (Ex. 1), and 198 
grams toluene. Toluene was removed by vacuum distillation. The base ester 
was maleinized at 140.degree.-145.degree. C. for a period of 15 minutes 
with 157 grams of maleic anhydride. To this was then added 2412 grams 
EGMBE as solvent. To this base ester solution was then added at 
140.degree.-145.degree. C. over a period of 4 hours the following monomer 
premix: 
______________________________________ 
Styrene 1291 grams 
Methyl Methacrylate 556 grams 
Methacrylic acid 384 grams 
Dicumyl peroxide 67 grams 
______________________________________ 
The polymerization was substantially completed within a 4-hour hold period 
at 140.degree.-145.degree. C. Final constants were as follows: 
______________________________________ 
Non-volatile 74.6% 
Viscosity (50% NV in 
EGMBE) I-J (Gardner Scale) 
Acid No. (on solids) 
45.5 
______________________________________ 
PAINT EXAMPLES 
EXAMPLE 5 
A black pigmented electrocoat tank composition was prepared from Example 1 
resin in the following parts by weight: 
______________________________________ 
Example 1 Resin 109.6 
Di-isopropanolamine (85%) 
13.3 
Non-ionic surface active 
agent 0.1 
Hydrated aluminum silicate 
16.0 
Furnace black 4.0 
Deionized water 857.0 
______________________________________ 
This electrocoat paint has a non-volatile content of 10%, a pigment to 
binder ratio of 1/4, and a pH of 9.5 to 10.0. By applying a coating 
voltage of 100-150 V, a film thickness of 0.3 to 0.5 mils is obtained. The 
coating was able to withstand a voltage of greater than 250 V before 
rupture occurred. The coated part, upon being removed from the tank and 
water rinsed, was dry enough to be handled and stacked within 20 minutes 
when exposed to forced air circulation at a temperature of 
20.degree.-25.degree. C. A tough coating developed on over-night dry. 
EXAMPLE 6 
A black pigmented electrocoat tank composition was prepared from the resin 
of Example 2 in the following parts by weight: 
______________________________________ 
Example 2 Resin 164.3 
Potassium Hydroxide (85%) 
6.5 
Non-ionic surface active 
agent 0.2 
Hydrated aluminum silicate 
18.0 
Furnace black 12.0 
Deionized water 799.4 
______________________________________ 
This paint has a non-volatile content of 15%, a pigment to binder ratio of 
1/4 and a pH of 9.8-10.2. A film thickness of 0.2-0.3 mils was obtained by 
applying a voltage of 80-100 V although the coating will withstand greater 
than 250 V before film rupture occurs. The rinsed coated part was dry 
enough to be handled and stacked within 20 minutes of forced-air drying at 
20.degree.-25.degree. C. A tough coating was the result of an overnight 
dry. No deterioration in coating application or performance was observed 
by constant vigorous agitation of the electrocoat solution using a Teal 
pump for a period of 3 weeks. 
EXAMPLE 7 
A buff-colored electrocoat tank composition was prepared from the resin of 
Example 3 in the following parts by weight: 
______________________________________ 
Example 3 Resin 99.9 
Ionol 0.3 
(2-6 ditertiary butyl 
4-methyl phenol) 
Cobalt napthenate (6% cobalt) 
5.3 
Pine oil 7.0 
Non-ionic surface active agent 
1.6 
Resinous organo-phosphate 0.3 
Di-isopropanolamine (85%) 11.3 
Dimethylethanolamine 0.7 
Hydrated aluminum silicate 
5.6 
Strontium chromate 0.3 
Yellow Iron Oxide 1.1 
Rutile Titanium Dioxide 13.0 
Phthalocyanine Green 0.04 
Deionized water 851.5 
Ethylene glycolmono-butyl ether 
2.0 
______________________________________ 
This paint has a non-volatile content of 10%, a pigment to binder ratio of 
1/4 and a pH of 9.3-9.7. The coating was applied at a film thickness of 
0.8-1.0 mils by an applied voltage of 175 V although it will withstand 200 
V before film rupture occurs. The coating applied on phosphate-treated 
steel panels (EP-10) and force-dried at 82.degree. C. for 20 minutes 
exhibited excellent gloss and post-flow properties. After 1 week at 
ambient temperature, the coating had a pencil hardness of 2B and withstood 
240 hours of a 5% salt-fog test. 
The deposited resin is very hydrophobic which provides excellent plating 
properties such as shut-down and throwing power. The cured films exhibit 
excellent water and salt spray resistance. The electrocoating polymer 
(a)-(b)-(c)-(d) composition of this invention is substantially free of 
readily hydrolyzable ester groups which provide good resistance properties 
and electrocoating bath stability. The electrocoated resin Tg can be 
advantageously adjusted to provide good handling properties such as good 
post-flow, dry-to-handle, or dry-to-stack properties. The polymer 
(a)-(b)-(c)-(d) contains sufficient residual unsaturation in the fatty 
acid chains whereby an air oxidation cure or a heat cure can be obtained 
with a cobalt napthenate or other conventional dryer salt. 
The foregoing examples of the electrocoating composition are not intended 
to be limiting except as defined by the appended claims.