An improved electrocoating composition is described for cathodic electrodepositions, which composition comprises a water-miscible mixture of a substituted conjugated diene polymer or copolymer of a specific general formula, with not more than 30 parts by weight for 100 part of said diene of an epoxy resin, a petroleum resin or mixtures thereof, the mixture being neutralized with an acid.

FIELD OF THE INVENTION 
The present invention relates to a cathode deposition type electrocoating 
composition which is excellent in wettability and affords a coated film 
excellent in impact-resistance, mechanical resistance and 
chemicals-resistance. 
DESCRIPTION OF THE PRIOR ART 
According to the prior art water-soluble paints, especially 
electrodeposition paints, are used as resin component resins possessing 
acid groups such as maleinized oils, maleinized polybutadiene and alkyl 
resin or acrylic resins containing acrylic acid or methacrylic acid as 
copolymeric component, which resins have been neutralized with a base such 
as ammonia, an amine or caustic potash to render them water-soluble. 
These resins are dissociated in water to afford resins with anion. In 
electrodeposition operations, therefore, an article to be coated is used 
as anode and the resin with anion is then deposited on the anode to effect 
the coating. 
However, in such anode deposition type electrocoating method wherein a 
metal to be coated is used as anode, a problem arises in that the metal to 
be coated is oxidized by the oxygen generated at the anode by electrolysis 
of water whereby a part of the metal is dissolved in water. As a part of 
the dissolved metal remains in the electrodeposited film, the coated 
article is contaminated and colored with such oxidized metal. In case an 
article to be coated is made of iron, for example, a white paint will be 
contaminated with iron ions and colored brown. In case an article to be 
coated is made of aluminum, for example, a white paint will be colored 
yellow. In addition, metal ions remaining in the coated film cause serious 
reduction in corrosion-resistance of the film. The paint solution is also 
contaminated with the metal ions, thus resulting in serious reduction in 
stability of the electrocoating bath. 
The above mentioned problem of dissolution and contamination also arises in 
the event that a metal to be coated has been treated with a phosphate for 
preventing rust. Furthermore, a phosphate film once formed on the metal is 
dissolved, thus resulting in considerable reduction in rust-preventing 
effect. In general, the film of a paint of this type is not satisfactory 
in alkali-resisting property. 
If electrodeposition can be effected with an article to be coated as 
cathode, dissolution of a metal or a surface-treated film from the article 
will no longer take place, affording an electrodeposited film free from 
coloration with dissolved metal ions and excellent in 
corrosion-resistance. In the cathode deposition type electrocoating 
method, various additional advantages can be expected. For example, 
electrodeposition can be applied also to metals which tend to dissolve in 
water and thus are unsuited for electrodeposition when treated according 
to the anode deposition type electrocoating method. 
For carrying out the cathode deposition type electrocoating method, it is 
necessary to use a water-soluble resin which is capable of forming a 
cationic resin in water and being deposited on a cathode. 
Hitherto, various researches have been made in this art for developing the 
process for producing the water-soluble resins which are capable of being 
deposited on a cathode, and as a result, modified epoxy resins (Japanese 
Patent Publns. Nos. 23807/74 and 31736/74) and modified acrylic resins 
obtained by radical-copolymerization of an acrylic monomer having a 
tertiary amine group such as one represented by the formula: 
##STR1## 
with various acrylic monomers or other monomers (Japanese Patent Publns. 
Nos. 37147/73, 12396/70, 12395/73 and 39351/70) have been proposed. 
In the known conventional cathode deposition type electrocoating paints 
using the above resins, however, there are many drawbacks including too 
high curing temperatures and poor crosslinking densities. Thus, these 
known paints have not yet been put into practice on industrial scale. 
In general, the film of a water-soluble paint tends to dissolve in water 
unless the film be modified. Thus, the film has to be cured by 
crosslinking according to a certain chemical means. After application of 
the paint, curing of the resultant film should satisfactorily be effected 
by a baking treatment usually conducted at 150.degree.-200.degree. C. for 
about 30 minutes. In the prior art, a method wherein a melamine 
formaldehyde resin or phenol formaldehyde resin is mixed or preliminarily 
condensed with the paint, or a method wherein the paint is modified with a 
drying oil was adopted to satisfy the above requirement. However, neither 
of such methods is suitable for resins for cathode deposition type 
electrocoating paints because the resins free from said group are not 
satisfactorily cured even in the presence of the mixed melamine 
formaldehyde resin or phenol formaldehyde resin nor fully cooperated 
therewith in electrophoresis to permit undesirable fluctuation in the 
composition of the film. 
Even if a water-soluble basic resin can be synthetized and deposited on the 
cathode in the electrocoating operation, such resin is of a low value in 
practical use for electrodeposition unless it can be deposited in good 
state and the resultant coated film can exhibit good film characteristics. 
Stability of the paint should be good even at a low concentration when 
diluted or in a paint solution before dilution or during storage or 
running. 
As a result of extensive researches made to overcome the above 
disadvantages in the prior art, the present inventors already invented a 
coating composition useful for a cathode deposition type electrocoating 
paint which is excellent in curability and stability during storage and 
capable of affording a corrosion-resisting film excellent in resistance to 
external mechanical force such as impact or bending and in 
chemicals-resistance such as alkali-resistance, water-resistance or 
solvent-resistance, by neutralizing a polymer or copolymer containing 
basic groups of the general formula: 
##STR2## 
wherein R.sub.1 stands for a hydrogen atom, a halogen atom or an organic 
residue with 1-3 carbon atoms; R.sub.2 and R.sub.3 may be the same or 
different and each stands for an organic residue with 1-20 carbon atoms; 
R.sub.4 stands for a hydrogen atom or an organic residue with 1-20 carbon 
atoms; and X for a hydrogen atom or a bond with the proviso that when X 
stands for the bond, the carbon atom to which R.sub.1 is attached and the 
carbon atom adjacent to said carbon atom and carrying the hydrogen atom 
may form a part of the main chain, 
with an organic or inorganic acid and then dispersing or dissolving the 
neutralized polymer or polymer in water (Japanese Patent Applns. Nos. 
44802/75 and 138406/76). This electrocoating paint affords the above 
mentioned excellent film characteristics but is still unsatisfactory in 
wettability, one of the important characteristics of the electrocoating 
paints, which warrants complete application of the paint to complicated 
parts or invisible hidden parts of an article to be coated. 
In electrodeposition operations, wettability is a very important 
requirement for improving the rust-preventing property of a whole article 
to be coated. 
BRIEF SUMMARY OF THE INVENTION 
As a result of further extensive researches made to improve wettability of 
the cathode deposition type electrocoating paint without damaging the 
excellent film characteristics thereof, the present inventors have 
accomplished the present invention. 
It is an object of the present invention to provide a cathode deposition 
type electrocoating paint which is excellent in curability, applicability 
such as wettability and stability during storage and capable of affording 
a coated film excellent in resistance to external mechanical force such as 
impact and in chemicals-resistance such as alkali-resistance, 
water-resistance, solvent-resistance or corrosion-resistance. 
The above object of the present invention can be attained by neutralizing a 
mixture of (A) 100 parts by weight of a substituted conjugated diene 
polymer or copolymer having a number average molecular weight of 300-5000 
and containing basic groups of the general formula: 
##STR3## 
wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4 and X have the same meanings as 
given above, and (B) one or more resins selected from epoxy resin in an 
amount not greater than 30 parts by weight and petroleum resins with a 
softening point of 80.degree.-180.degree. C. in an amount not greater than 
30 parts by weight with an organic or inorganic acid and dispersing or 
dissolving the neutralized product into or in water. 
The conjugated diene polymer or copolymer containing the above specific 
basic groups which is used in the present invention is synthetized by the 
imidation reaction between a butadiene homopolymer or copolymer having 
succinic acid group or acid groups derived from maleic acid or its 
anhydride and a diamine of the general formula: 
##STR4## 
wherein R.sub.2 and R.sub.3 may be the same or different and each stands 
for an organic residue with 1-20 (preferably 1-4) carbon atoms and R.sub.4 
stands for a hydrogen atom or an organic residue with 1-20 (preferably 
1-4) carbon atoms. 
The conjugated diene polymer or copolymer having a molecular weight of 
300-5000 which is used in the present invention as a starting material is 
produced according to a method known per se. For example, a typical method 
comprises subjecting one or more conjugated dienes or preferably a 
conjugated diene, especially butadiene or isoprene together with an 
aromatic vinyl monomer such as styrene, .alpha.-methylstyrene, 
vinyltoluene or divinylbenzene in an amount not greater than 50 mol % 
based on the conjugated diene to anionic polymerization conducted at 
0.degree.-100.degree. C. in the presence of an alkali metal an 
organoalkali metal compound as a catalyst. In this case, the chain 
transfer polymerization method wherein an organoalkali metal compound such 
as benzyl sodium is used as catalyst and a compound containing an alkaryl 
group such as toluene is used as chain transfer agent (U.S. Pat. No. 
3,789,090), the living polymerization method wherein a polynuclear 
aromatic compound such as naphthalene in tetrahydrofuran solvent is used 
as activator and an alkali metal such as sodium is used as catalyst 
(Japanese Patent Publns. No. 17485/67 and 27432/68), or a polymerization 
method wherein the molecular weight of the polymer or copolymer is 
controlled by using an aromatic hydrocarbon such as toluene or xylene as 
solvent and a dispersion of a metal such as sodium as catalyst and adding 
an ether such as dioxane to the reaction system (Japanese Patent Publns. 
Nos. 7446/57, 1245/58 and 10188/59) are preferable for controlling the 
molecular weight to obtain a lightly colored low polymerization product 
poor in a gel content. A low polymer produced by the coordinated anionic 
polymerization method wherein an acetylacetonate of a metal belonging to 
Group VIII of the Periodic Table such as cobalt or nickel and an 
alkylaluminum halide are used as catalyst (Japanese Patent Publns. Nos. 
507/70 and 30300/71) can also be used for the present invention. 
The conjugated diene polymer or copolymer containing acid groups such as 
succinic acid groups which is the next starting material is produced 
according to a method known per se wherein maleic acid, maleic anhydride, 
citraconic acid or citraconic anhydride is added usually at a temperature 
of 100.degree.-300.degree. C. to the conjugated diene polymer or copolymer 
referred to above (Japanese Patent Publn. No. 11195/71). In the case of 
performing such addition reaction, a method wherein a phenylenediamine, a 
pyrogallol, a naphthol or the like is allowed to be present in the 
reaction system to prevent a gel-forming reaction (DT-OS P2 362 534) is 
preferably adopted. The amount of the acid to be added to the conjugated 
diene polymer or copolymer, such as maleic acid, maleic anhydride, 
citraconic acid or citraconic anhydride, is 0.05-0.5 mol, preferably 
0.1-0.25 mol per 100 g of the polymer or copolymer. 
If the amount of the acid is less than 0.05 mol per 100 g of the polymer or 
copolymer, water-solubility of a resin obtained by reacting the polymer or 
copolymer containing the acid groups with the diamine compound will become 
poor. On the other hand, if the amount of the acid is more than 0.5 mol, 
water-solubility of the resin will become so good that the coated film 
obtained from the paint using such resin will be poor in water-resistance 
and will be unsuited for practical use. 
Illustrative of the diamine compound used in the present invention are, for 
example, diamine compounds (III) combining a structure of primary amine 
with that of secondary amine such as .beta.-hydroxyethylaminoethylamine, 
.beta.-hydroxyethylaminopropylamine, methylaminoethylamine, 
ethylaminoethylamine, methylaminopropylamine, ethylaminopropylamine and 
butylaminopropylamine and/or compounds (IV) combining a structure of 
primary amine with that of tertiary amine such as dimethylaminoethylamine, 
diethylaminoethylamine, dimethylaminopropylamine, diethylaminopropylamine 
and dibutylaminopropylamine. 
In the present invention, the conjugated diene polymer or copolymer 
containing the acid groups is reacted with the diamine compound alone or 
as a mixture of at least two. This reaction is an imidation reaction 
between the succinic acid group and the primary amino group. The amount of 
the diamine compound used is preferably equimolar to the succinic acid 
groups in the conjugated diene polymer or copolymer containing the acid 
groups. However, it is possible to use the diamine compound in excess and 
to remove excess diamine compound by distillation after the reaction. In 
case a diamine compound (III) having structures of primary amine and 
secondary amine is used in mixture with a diamine compound (IV) combining 
a structure of primary amine with that of tertiary amine, the ratio of 
(IV)/(III)+(IV) is usually 0-90%, preferably 20-80% in terms of molar 
ratio. In the reaction of this type the molar ratio of the diamines 
consumed for the reaction and that of the diamines introduced are almost 
equal. 
The imidation reaction between the conjugated diene polymer or copolymer 
containing the acid groups and the diamines is carried out at a 
temperature within the range of 50.degree.-300.degree. C., preferably 
100.degree.-200.degree. C. 
This imidation reaction can be carried out in the presence or absence of a 
solvent. When the conjugated diene polymer or copolymer containing the 
acid groups used for the imidation reaction has a low viscosity, the 
reaction is carried out preferably in the absence of a solvent. In the 
case of using a solvent for the reaction, any of the solvents miscible 
with the conjugated diene polymer or copolymer containing the acid groups, 
for example, hydrocarbons such as benzene, toluene, cyclohexane and 
xylene, alcohols such as butyl cellosolve and ethers such as 
ethyleneglycol diethyl ether can be used, but it is preferable to use a 
hydrophilic solvent such as butyl cellosolve for the imidation reaction 
and successively to perform the water-solubilizing reaction as will be 
referred to hereinafter. 
By the term "epoxy resin" is meant herein a compound having at least two 
reactive .alpha.-epoxy groups in its molecule. In the present invention, 
an epoxy resin having a molecular weight of 300-3,000 and an epoxy 
equivalent of 150-3,500 is effectively used. 
A typical one of the epoxy resins is obtained as a reaction product of an 
active hydrogen compound and epichlorohydrine. Examples of the active 
hydrogen compound include compounds having at least two phenolic hydroxy 
groups such as bisphenol A, novolac resin and derivatives thereof. 
Compounds having carboxyl groups or amino groups are also used as the 
active hydrogen compound. 
In the present invention, an epoxy resin obtained by the reaction between 
bisphenol A and epichlorohydrin is most effectively used. Typical examples 
of this epoxy resin include Epikote (Shell Chemical) and Araldite 
(Ciba-Geigy). 
In the present invention, the epoxy resin is used in an amount not greater 
than 30 parts by weight, preferably 5-25 parts by weight per 100 parts by 
weight of the conjugated diene polymer or copolymer containing the basic 
groups. 
If the amount of the epoxy resin used is greater than 30 parts by weight 
per 100 parts by weight of the conjugated diene polymer or copolymer 
containing the basic groups, the surface of the coated film will become 
too bad in smoothness to be suitable for practical use. 
By the term "petroleum resin" is meant herein a resin with a softening 
point of 80.degree.-180.degree. C. obtained by heat polymerization or 
catalytic polymerization of a fraction containing olefins and diolefins 
with 4.5-10 carbonatoms which has been formed as by-product in the 
production of lower olefins such as ethylene and propylene from petroleum 
by thermal cracking or steam cracking. Utilizable as a catalyst for the 
catalytic polymerization are Friedel-Crafts catalysts and radical-forming 
catalysts. Among the petroleum resins, those of aliphatic or aromatic 
hydrocarbon series are representative which are obtained by polymerizing 
in the presence of a Friedel-Crafts catalyst such as boron trifluoride, 
aluminum chloride or a complex thereof a fraction boiling at 
20.degree.-280.degree. C. in a residuum formed on cracking petroleum. In 
addition, a resin obtained by polymerizing in the presence of a catalyst 
such as a Friedel-Crafts catalyst terpenes per se or those formed by 
heating a fraction containing C.sub.5 -diolefins in a residuum formed on 
cracking petroleum, a resin obtained by polymerizing under heat or by the 
aid of a radical catalyst a fraction containing cyclic C.sub.5 -diolefins 
such as cyclopentadiene and dicyclopentadiene and Diels-Alder addition 
reaction products thereof in a residuum formed on thermal cracking of 
petroleum, and a hydrogenated product of these resins in which a part or 
almost all of unsaturated bonds in the resin molecule has been 
hydrogenated can also be used as the petroleum resin referred to herein. 
Representative of these resins are, for example, Neopolymer (Nisseki 
Chemical, Japan), Mitsui Petrosine (Mitsui Petrochemical, Japan) and the 
like commercially available resins. The amount of the petroleum resin 
added is not greater than 30 parts by weight, preferably 5-25 parts by 
weight per 100 parts by weight of the conjugated diene polymer or 
copolymer containing the basic groups. If the amount of the petroleum 
resin is greater than 30 parts by weight, the electrocoating composition 
will become too bad in dispersibility into water to be useful for 
practical use. 
The epoxy resin and the petroleum resin are very preferably used together 
respectively in an amount not greater than 30 parts by weight, desirably 
5-25 parts by weight per 100 parts by weight of the conjugated diene 
polymer or copolymer containing the basic groups. 
In the present invention, the conjugated diene polymer or copolymer 
containing the basic groups is mixed with the epoxy resin and/or the 
petroleum resin. The mixing treatment of these components may be carried 
out merely by mixing under heat but is preferably carried out by mixing in 
good solvent for these components. Most preferable as the solvent is an 
organic solvent which is soluble in water and capable of dissolving the 
mixture. 
The mixture of the present invention is then rendered soluble in water. A 
method of neutralizing the mixture with an inorganic acid such as 
hydrochloric acid or sulfuric acid or a water-soluble organic acid such as 
formic acid, acetic acid or propionic acid in an amount of 0.2-1.0 molar 
equivalent to the secondary and tertiary amino groups in the mixture is 
suitably adopted for solubilizing the mixture. 
On solubilizing the mixture of the present invention, an organic solvent 
which is soluble in water and capable of dissolving the individual polymer 
and resins and has two groups selected from a hydroxyl group, an ether 
group and a carbonyl group in the molecule, such as ethyl cellosolve, 
propyl cellosolve, butyl cellosolve, ethyleneglycol dimethyl ether, 
diethyleneglycol dimethyl ether, diacetone alcohol or 
4-methoxy-4-methylpentanone-2, is preferably used in an amount of 10-100 g 
per 100 g of the mixture for the purposes of facilitating solubilization 
of the mixture into water, improving stability of an aqueous solution of 
the mixture and improving fluidity of the resins and smoothness of the 
coated film. 
The present invention will now be illustrated in more detail by way of 
examples and comparative examples in which the tests for examining the 
physical properties of the coated films were performed in accordance with 
JIS-K-5400. 
The electrocoating composition of the present invention may be incorporated 
with a proper pigment such as titania, red oxide or carbon black and a 
rust-preventing pigment such as strontium chromate. 
The composition of the present invention may further be incorporated with a 
drier such as cobalt naphthenate or manganese naphthenate for the purposes 
of depressing the baking temperature after application of the composition 
and shortening the curing time. 
Experiment 1 
In a 30-liter autoclave were placed 1 mol of benzyl sodium, 14 mols of 
toluene and 15 liters of n-hexane in a nitrogen stream. After maintaining 
the temperature at 30.degree. C., 10 liters of butadiene was introduced 
into the autoclave in 2 hours while maintaining the temperature of 
30.degree. C. Then, 200 ml of methanol was added to stop the 
polymerization reaction. To the reaction mixture was added 1 kg of clay 
and the whole was stirred vigorously and then filtered whereby a 
transparent solution of the polymer free from alkali was obtained. 
Unreacted butadiene, toluene and n-hexane were then removed by 
distillation from the polymer solution to synthetize polybutadiene (A) 
having a number average molecular weight of 800, an iodine value of 410 
and a 1,2-bond content of 55%. 
In a 2-liter autoclave were placed 1000 g of the polbutadiene (A), 212 g of 
maleic anhydride, 300 g of xylene and 2 g of Antigen 3C (trade name of 
N-phenyl-N'-isopropyl-p-phenylenediamine, prepared by Sumitomo Chemical, 
Japan). The mixture was reacted under nitrogen atmosphere at 190.degree. 
C. for 8 hours. Unreacted maleic anhydride and xylene were distilled off 
under reduced pressure from the reaction mixture whereby a liquid 
maleinized polybutadiene (A') having an acid number of 100 was 
synthetized. 
The most of the acid groups contained in the maleinized polybutadiene (A') 
is shown by the structure. 
##STR5## 
but a part of the acid groups was hydrolyzed with moisture in the air and 
changed to have the following structure: 
##STR6## 
In a 2-liter separable flask were placed 1000 g of the maleinized 
polybutadiene (A'), 200 g of butyl cellosolve, 9.13 g of 
dimethylaminopropylamine and 92.9 of .beta.-hydroxyethylaminoethylamine. 
The mixture was heated at 140.degree. C. for 3 hours and then the water 
formed by the reaction, butyl cellosolve and unreacted amines were 
distilled off under reduced pressure whereby imidated polybutadiene (A") 
having the secondary amino group, the tertiary amino group and hydroxyl 
group was synthetized. 
Then, 400 g of the imidated polybutadiene (A") was dissolved in 80 g of 
butyl cellosolve and neutralized with 18 g acetic acid whereby an aqueous 
solution having a solid concentration of 30% was prepared. 
In a 2-liter stainless steel beaker were placed 600 g of the 30% aqueous 
solution, 774 g of titania, 24 g of carbon black and 1000 g of glass 
beads. The mixture was stirred vigorously for 2 hours with a high speed 
rotating mixture and then the glass beads were filtered off whereby a 
pigment paste (A) excellent in dispersibility into water was produced.

EXAMPLE 1 
Into a 30-liter autoclave were charged 1 mol of benzyl sodium, 6 mols of 
toluene and 15 liters of benzene in nitrogen atmosphere. After maintaining 
the temperature at 30.degree. C., 10 liters of butadiene was introduced 
into the autoclave in 4 hours while maintaining the temperature at 
30.degree. C. After decomposing the catalyst with water, the residue of 
the catalyst was removed by washing with water. Then, toluene, benzene and 
unreacted butadiene were removed by distillation whereby polybutadiene (B) 
having a number average molecular weight of 1400, an iodine value of 430 
and a 1,2-bond content of 64% was synthetized. 
In a 2-liter separable flask were placed 1000 g of the polybutadiene (B), 
212g of maleic anhydride, 10 g of xylene and 2 g of Antigen 3C. The 
mixture was reacted in nitrogen atmosphere at 200.degree. C. for 5 hours 
and then xylene and unreacted maleic anhydride were distilled off under 
subatmospheric pressure to synthetize maleimized polybutadiene (B') having 
an acid number of 100 and a viscosity of 25,000 poise (25.degree. C.). In 
the same manner as described in Experiment 1 concerning the method for 
synthetizing imidated polybutadiene, the maleinized polybutadiene (B') was 
treated to synthetize imidated polybutadiene (B"). In a 2-liter separable 
flask were placed 100 g of the imidated polybutadiene (B"), 20 g of 
Epikote 1004 (an epoxy resin derived from bisphenol A, Shell Chemical) and 
24 g of butyl cellosolve. The mixture was well stirred and dissolved in 
aqueous acetic acid to prepare a 20% aqueous solution of the mixture. To 
this aqueous solution was added 75.7 g of the pigment paste (A) produced 
in Experiment 1. The mixture was well mixed and diluted with pure water to 
prepare an electro-deposition coating liquid having a solid concentration 
of 12%. 
This electrodeposition coating liquid was placed in 1-liter beaker and a 
solid component was electrodeposited as a film on a mild steel panel as 
cathode which had been treated with Bondelite #137 (Nippon Test Panel Co., 
Japan), using a carbon plate electrode as anode. The result of this test 
is shown in Table 1. 
EXAMPLE 2 
In a 2-liter separable flask were placed 100 g of the imidated 
polybutadiene (B") produced in Example 1, 20 g of a petroleum resin 
(Nisseki Neopolymer #120 having a softening point of 120.degree. C., 
Nisseki Chemical, Japan) and 24 g of butyl cellosolve. The mixture was 
well stirred and then dissolved in aqueous acetic acid to form a 20% 
aqueous solution of the mixture. To this aqueous solution was added 75.7 g 
of the pigment paste (A) produced in Experiment 1. The mixture was well 
mixed and diluted by addition of pure water to prepare an 
electrodeposition coating liquid having a solid concentration of 12%. 
This electrodeposition coating liquid was placed in a 1-liter beaker and a 
solid component of the liquid was electrodeposited as a film on a mild 
steel panel as cathode which had been treated with Bondelite 190 137 
(Nippon Test Panel Co., Japan), using a carbon plate electrode as anode. 
The result of this test is shown in Table 1. 
EXAMPLE 3 
In a 2-liter separable flask were placed 100 g of the imidated 
polybutadiene (B") produced in Example 1, 10 g of an epoxy resin (Epikote 
1004), 10 g of a petroleum resin (NP 120) and 24 g of butyl cellosolve. 
The mixture was well stirred and then dissolved is aqueous acetic acid to 
form a 20% aqueous solution of the mixture. To this aqueous solution was 
added 75.7 g of the pigment paste (A) produced in Experiment 1. The 
mixture was well mixed and then diluted by addition of pure water to 
prepare an electrodeposition coating liquid having a solid concentration 
of 12%. 
This electrodeposition coating liquid was placed in a 1-liter beaker and a 
solid component of the liquid was electrodeposited as a film on a mild 
steel panel as cathode treated with Bondelite 190 137 (Nippon Test Panel 
Co., Japan), using a carbon plate electrode as anode. The result of this 
test is shown in Table 1. 
Comparative Example 1 
In a 2-liter separable flask were placed 100 g of the imidated 
polybutadiene (B") produced in Example 2 and 20 g of butyl cellosolve. The 
mixture was well stirred and then dissolved in aqueous acetic acid to form 
a 20% aqueous solution of the mixture. To this aqueous solution was added 
63.1 g of the pigment paste (A) produced in Experiment 1. The mixture was 
well mixed and then diluted by addition of pure water to prepare an 
electrodeposition coating liquid having a solid concentration of 12%. 
This electrodeposition coating liquid was placed in a 1-liter beaker and a 
solid component of the liquid was electrodeposited as a film on a mild 
steel panel as cathode treated with Bondelite #137 (Nippon Test Panel Co., 
Japan), using a carbon plate electrode as anode. The result of this test 
is shown in Table 1. 
A comparison of Examples 1, 2 and 3 with Comparative Example 1 in Table 1 
clearly demonstrates that even in the case of using the same imidated 
polybutadiene (B") as starting material, addition of the petroleum resin 
or the epoxy resin derived from bisphenol A serves to improve wettability, 
especially addition of both the petroleum resin and the epoxy resin 
derived from bisphenol A as seen in Example 3 serves to improve not only 
wettability remarkably but also corrosion-resistance of the coated film. 
Thus, it is evident that a coated film with excellent physicochemical 
characteristics can be obtained according to the composition of this 
invention. 
Table 1 
__________________________________________________________________________ 
Results of the tests made on the electrodeposition 
coating paints 
Compara- 
tive 
Test items Example 1 
Example 2 
Example 3 
Example 1 
__________________________________________________________________________ 
Coating conditions: 
Voltage (V) 100 75 250 45 
Time (min.) 3 3 3 3 
Baking condition (.degree.C. .times. 
200 .times. 30 
200 .times. 30 
200 .times. 30 
200 .times. 30 
min.) 
Thickness of coated 
20 20 20 20 
film (.mu.) 
Physical tests: 
Penical hardness H-2H HB-H H-2H HB-H 
Sketching Passed 
Passed 
Passed 
Passed 
Passed 
Cross-cut adhesion 
100/100 
100/100 
100/100 
100/100 
test (tape test) 
Erichsen (mm) &gt;9 &gt;9 &gt;9 &gt;9 
Front*.sup.1 &gt;50 &gt;50 &gt;50 &gt;50 
Impact strength (cm) 
Back &gt;50 &gt;50 &gt;50 &gt;50 
Wettability*.sup.2 
16 12 21 7 
Chemical tests: 
Alkali resistance (hr)*.sup.3 
60 60 &gt;100 &gt;100 
Acid resistance (hr)*.sup. 4 
60 50 60 60 
Solvent resistance (day)*.sup.5 
&gt;30 &gt;30 &gt;30 &gt;30 
Water resistance (day)*.sup.6 
&gt;30 &gt;30 &gt;30 &gt;30 
Corrosion resistance (mm)*.sup.7 
3 3 1 3 
__________________________________________________________________________ 
Remarks: 
*.sup.1 The maximum height of the extruded portion where the coated film 
is not destroyed (500g, 1/2B) 
*.sup.2 In accordance with Ford test 
*.sup.3 The time elapsed until imperfections such as blistering were 
observed in the coated film (immersion in 5% NaOH). 
*.sup.4 The time elapsed until imperfections such as blistering were 
observed in the coated film (immersion in 5% H.sub.2 SO.sub.4). 
*.sup.5 The time elapsed until imperfections such as blistering were 
observed in the coated film (immersion in pure water at 40.degree. C.). 
*.sup.6 The time elapsed until imperfections such as blistering were 
observed in the coated film (immersion in a mixed solvent (1:1) of toluen 
and xylene). 
*.sup.7 The maximum rust width from a cut portion in the coated film (200 
hours after spraying a 5% aqueous solution of NaCl).