Heat-hardenable resins suitable for cathodic deposition

Heat-hardenable synthetic resins which are water soluble upon partial or total neutralization comprising the reaction products of epoxy groups containing unsaturated diene polymers and amine compounds, graft polymerized with alpha, beta-ethylenically unsaturated monomers which are free from epoxy reactive groups, the homopolymers of the monomers having a glass transition temperature of over 320.degree. K. A process of preparing the heat-hardenable resins is also described. The synthetic resins can be employed as binders for cathodically depositable aqueous coating compositions to provide coatings which will cure at relatively low temperatures and relatively short curing times to provide smooth and hard films having good resistance to water, chemicals, and corrosion; and which adhere well to the coated surface.

The present invention is directed to heat-hardenable synthetic resins. More 
particularly, the invention is directed to heat-hardenable synthetic 
resins which, in addition to being suitable for application by 
conventional methods such as spraying, dipping and brushing, are suitable 
for deposition from aqueous solutions of the resins at the cathode of an 
electrodeposition coating system. 
A substantial number of resinous binders have been proposed for deposition 
at the cathode of an electrochemical system, the majority being based on 
epoxy resins, and specifically on the polyglycidyl ethers of bisphenol A 
(2,2-bis(4-hydroxylphenyl)propane). 
Although epoxidized polymers of dienes have been suggested for cathodic 
application, no specific, practical examples are known in the prior art. 
Thus, while it is known that epoxidized polymers of dienes can be reacted 
with amine compounds to provide cathodically depositable products, coating 
compositions based on the epoxidized diene polymers have a number of 
disadvantages making them substantially useless for industrial scale 
coatings. As an example, the coatings exhibit poor throwing power; the 
freshly deposited films have a gel-like structure and, thus, cannot be 
rinsed without difficulty to remove adherent bath material; owing to their 
thermoplastic character, the coatings recede from the edges of the coated 
article with rising temperatures during the stoving process; and the 
coatings, under the conditions prevailing in industrial coating, do not 
attain the required smoothness and hardness. In spite of the noted 
disadvantages, the epoxidized diene polymers exhibit certain advantages 
over the epoxy resins based on polyglycidyl ethers of bisphenol A. For 
example, the backbone of the polymer consists of --CH.sub.2 --CH.sub.2 -- 
linkages resistent to saponification; whereas in the polyglycidyl ethers, 
the backbone of the polymer is interrupted periodically by ether linkages 
which are susceptible to splitting, particularly by acidic reactants. 
Furthermore, polymers of dienes carry a substantial number of unsaturated 
--CH.dbd.CH-- double bonds in the polymer backbone or in side chains, 
which upon crosslinking of the coating produced therefrom can be used for 
polymerization reactions or other reactions due to the action of 
airoxygen. A further substantial advantage of the epoxidized diene 
polymers is that they are liquid to viscous masses at room temperature. 
Accordingly, the solvents otherwise necessary in binder synthesis, or at 
least a substantial part of the solvents, can be omitted. This can be 
desirable from the standpoint of cost and ecology; and, further, in the 
electrodeposition process there are a number of solvents which are 
inconvenient in that they may detrimentally affect the electrochemical 
properties, e.g., the maximum attainable deposition voltage. The suitable 
(higher molecular) epoxy resins of the bisphenol glycidylether type are 
solid masses at room temperature and have to be dissolved in suitable 
solvents prior to synthesis reactions. Furthermore, the choice of solvents 
is greatly reduced owing to the reactivity of the epoxy group. As a 
result, in the prior art the ketones are preferably used although their 
presence in the coating bath, as is known, is particularly harmful to the 
cathodic electrodeposition. 
According to the present invention, it has been found that the 
disadvantages of cathodically depositable reaction products of epoxidized, 
unsaturated diene polymers and amine compounds as above stated can be 
overcome without loss of the above-mentioned advantages, provided the 
products are modified through graft polymerization with specific monomers. 
Based on the present invention, coating compositions for cathodic 
electrodeposition can be formulated using the epoxidized diene polymers 
which fully meet the requirements of large-scale industrial applications. 
The present invention, therefore, is directed to cationic binders for 
water-dilutable, heat-hardenable coating compositions comprising the 
reaction products of epoxy group containing unsaturated diene polymers and 
amine compounds, characterized in that the products are prepared by graft 
polymerization of alpha,beta-ethylenically unsaturated monomers which are 
free from epoxy-reactive groups, the homopolymers of these monomers having 
a glass transition temperature of over 320.degree. K., to reaction 
products of low molecular unsaturated diene polymers carrying at least one 
1,2-epoxy group in the molecule and amine compounds. Optionally, the 
hydroxy groups of the polymers resultant from the reaction of the epoxy 
groups with amines can be partially or totally esterified with 
monocarboxylic acids. The invention is also directed to the process of 
preparing the cationic binders, and to their use in coating compositions 
applied by cathodic electrodeposition. 
The reaction of the epoxidized unsaturated diene polymers with secondary 
amines is described in British Pat. No. 1,148,899 for the preparation of 
pressure-sensitive adhesives. According to the British patent, rubberlike 
polymers of 1,4-cis-polybutadiene or butadiene-styrene or 
acrylonitrile-butadiene copolymers serve as the starting material. The 
additional monomers are part of the copolymer skeleton and are not grafted 
to the polymer chain by a subsequent graft polymerization. Further, the 
graft polymerization of alpha,beta-ethylenically unsaturated monomers free 
from carboxy groups to macromolecules is described, for example, in H. 
Rauch-Puntigam and Th. Volker "Acrylic And Methacrylic Compounds," pages 
192 ff. (Springer, 1967). However, there is no suggestion in the 
literature of grafting to basic polymers or to use them in water-soluble 
cathodically depositable binders. Furthermore, it could not be foreseen 
that the desired properties would only be obtainable by the use of 
monomers where the glass transition temperature of the homopolymers of the 
monomers was above 320.degree. K. 
Suitable unsaturated diene polymers are in particular the liquid oligomers 
and polymers of butadiene, pentadiene, isoprene, etc., and/or with the 
coemployment of subordinate quantities of other monomers or chain end 
formers. The microstructure of such polymers is not critical in 
constitution, i.e., in the butadiene polymers 1,4-cis structures may be 
present besides 1,4-trans and 1,2-vinyl structures. In general a minimum 
of 30 percent of 1,4-cis configuration is preferred because, on the one 
hand, the epoxidizing reaction more easily occurs at this structure and, 
on the other hand, the later oxidative crosslinking reaction of the 
coating is enhanced through the 1,4-cis configuration. Suitable polymers 
have molecular weights of below 5000 and iodine numbers of between 300 and 
470, and at room temperature are preferably liquid to resinlike viscous 
masses having a pale color. The unsaturated polymers are transformed by 
known epoxidizing reactions, for example, with blends of glacial acetic 
acid and hydrogen peroxide to epoxidized unsaturated diene polymers, 
whereby preferably a small quantity only of the --CH.dbd.CH-- double bond 
is transformed to oxirane rings, the major quantity remaining unchanged. A 
number of products having varying oxirane-oxygen levels are available on 
the market. Particularly suited for use according to the present invention 
are epoxidized diene polymers with an oxygen level of from 1 to 18 
percent, with 1 to 12 percent of the oxygen level being oxirane oxygen. 
The polymers preferably have a viscosity of from 500 to 30,000 mPas at 
20.degree. C. and iodine numbers of from 150 to 450. The polymers can 
optionally contain hydroxy groups. 
The epoxidized diene polymers are reacted with amine compounds at elevated 
temperature in order to obtain a polymer with basic nitrogen atoms. 
Suitable amine compounds for use according to this invention are aliphatic 
and cycloaliphatic amines and alkanol amines. Included are the diamines 
and polyamines, as along as the primary and secondary functional groups 
reactable with oxirane groups are not substantially more than 2. The di- 
or polyamine can, without detriment, contain a random number of tertiary 
amine groups which, under the conditions chosen for the reaction, are 
inert or substantially inert to oxirane groups. The introduction of these 
tertiary amine groups enhances the basicity of the polymer molecule at low 
levels of oxirane groups. 
Suitable primary amines or alkanolamines include methylamine, ethylamine, 
and higher homologues thereof, their isomers, ethylene diamine, propylene 
diamine, monoethanolamine, monopropanolamine, their homologues and 
isomers. Suitable secondary amines and alkanolamines are, e.g., 
dimethylamine, diethylamine, their higher homologues and isomers, 
morpholine, N-methylbenzylamine, N-methylcyclohexylamine, piperazine, 
piperidine and pyrrolidine, diethanolamine, dipropanolamine, 
N-methylethanolamine, their higher homologues and isomers. Suitable di- 
and polyamines are, e.g., N',N-dimethylaminopropylamine, 
N',N-diethylaminopropylamine. Suitable polyamines include polyamines where 
the primary amine functions are masked as ketime groups. An example is the 
reaction product of one mole of diethylene trimaine and two moles of 
methylisobutylketone, being formed with the separation of two moles of 
water. At the end of the binder synthesis the ketimine groups may be split 
off by hydrolysis with the freeing of the primary amine group. 
The reaction between epoxidized diene polymer and amine compound can be 
carried out at room temperature or, preferably, at a temperature of 
between 80.degree. and 250.degree. C. The weight ratios are chosen in 
order that the finished binder, on the total, including the graft polymer 
and other optional modifying additives, has an amine number of from 30 to 
150 mg KOH/g (DIN 53 176). The presence of antioxidizing agents based on 
substituted phenols or substituted aromatic amines, in a level of up to 
two percent of the reaction mass, is advantageous in order to prevent 
undesired side reactions which can lead to a molecular size increase. 
Suitable compounds include 2,5-di-tertiary butyl-4-methylphenol and 
N,N'-diphenyl-p-phenylene diamine. 
The unsaturated epoxidized diene polymer is graft polymerized to the 
alpha,beta-unsaturated monomers during or after the reaction with the 
amine compound, the monomers being free from epoxide reactive groups and 
the homopolymers thereof having glass transition temperatures of at least 
320.degree. K. Monomers meeting the requirements as stated include 
(meth)acrylnitrile, methylmethacrylate, isopropylmethacrylate, 
tert.butylmethacrylate, styrene, vinyltoluol, indene, and vinylcarbazol. A 
survey on glass transition temperatures of various polymers is given in 
Official Digest 34, No. 445, 2, page 133. The monomers are used at a level 
of from 3 to 30 percent calculated on the sum of epoxidized diene polymer 
and amine compound. The graft polymerization is carried out in known 
manner in the presence of free radical polymerization initiators at 
temperatures of from 80.degree. to 220.degree. C. Normal initiators are 
azobisisobutyronitrile, dibenzoylperoxide, di-tertiary butylperoxide, 
dicumylperoxide, and the like. The coemployment of chain transfer agents, 
for example, mercaptans, can be desirable. In general, a conversion of 
over 80 percent is desired. The unpolymerized monomers can remain in the 
reaction mass or they can be removed, e.g., through distillation. 
Upon opening of the oxirane rings in the reaction with the amine compound 
hydroxy groups are formed. These hydroxy groups are available for further 
reactions, e.g., for esterification reactions. The esterification is 
preferably effected with monocarboxylic acids, optionally also with 
subordinate quantities of dicarboxylic acids. Suitable monocarboxylic 
acids include the drying and non-drying vegetable oil fatty acids, rosin 
acids, particularly rosin, or aromatic monocarboxylic acids such as 
benzoic acid or p-tertiary butyl benzoic acid. In a manner similar to that 
for the hydroxy groups, the excess epoxy groups not used for the reaction 
with the amine compound can be esterified with the aforementioned 
monocarboxylic acids. 
The finished reaction product can be diluted in solvents convenient for 
cationic electrodeposition, including alcohols such as ethanol, propanol, 
isopropanol, and the butanols; the glycolethers such as ethylglycol, 
isopropyl glycol and butyl glycol, and the like. It is also possible to 
dilute the finished reaction product with water, without the addition of 
solvents, upon at least partial neutralization with acids. 
Independent from the manner of dilution, the binders can be used in 
pigmented or unpigmented form. Suitable pigments and extenders are 
titanium dioxide, carbon black, iron oxides, phthalocyanines, lead 
silicate, lead oxide, lead chromate, lead silico chromate, and strontium 
chromate. Normal extenders are quartz powder, aluminum silicate, talcum, 
barium sulfate, highly dispersed silicic acid, and the like. 
The basic nitrogen atoms of the binders of the invention are partially or 
totally neutralized with organic or inorganic acids. The degree of 
neutralization depends on the individual binder system. In general, 
sufficient acid is added to permit dilution with water or dispersion of 
the coating composition in application form at a pH-value of from about 4 
to 9, preferably 5 to 7. The concentration of the binder in water may 
range from about 3 to 30 percent by weight, and preferably from 5 to 15 
percent by weight. 
The coating compositions of the binders of the invention may be applied by 
spraying, dipping, flow coating, and electrodeposition. In an 
electrodeposition process the coating composition is wired with an 
electrically conductive anode and an electrically conductive cathode, the 
surface of the cathode being coated. Suitable substrates are metallic 
substrates, in particular steel, aluminum, copper, etc., and also 
metalized plastics or other materials coated with a conductive coating. 
After deposition, the coating is optionally rinsed with water and stoved 
at 130.degree. to 220.degree. C., preferably 150.degree. to 190.degree. C. 
Curing time is from about 5 to 30 minutes, preferably 10 to 25 minutes. 
The following examples are illustrative of the invention without limiting 
the scope thereof. Parts are by weight unless otherwise stated. All 
examples utilized comparable conditions in reaction vessels equipped with 
stirrer, thermometer, inert gas duct, addition funnel, and reflux 
condensor.

EXAMPLE 1 
437 g of an epoxidized polybutadiene containing 4.2 percent by weight of 
epoxy oxygen and having a microstructure of 40 percent 1,4-cis, 13 percent 
1,4-trans, and 47 percent 1,2-vinyl configuration; and a viscosity of 4400 
mPas at 20.degree. C. are heated to 100.degree. C. together with 0.175 g 
of 2,6-di-tert.butyl-4-methylphenol. 77 g of vinyltoluol, 1.6 g of 
di-tertiary butylperoxide, and 65 g of N,N-diethylaminopropyl amine are 
added and the batch is heated to 200.degree. C. while stirring and under 
inert gas protection within 2 to 3 hours as reflux permits. After about 6 
hours of reaction time the solids content has risen to more than 98 
percent. The viscosity of a solution of 7 g of the reaction mass and 3 g 
of ethylglycol acetate is U, Gardner standard. At 180.degree. C., 120 g of 
rosin are added and reacted at this temperature for about 1 hour, until an 
acid value of 2 mg KOH/g is attained. The viscosity of a solution of 5 g 
of reaction mass and 5 g of ethylglycol acetate is T, Gardner standard. At 
100.degree. C., the resin is diluted to 70 percent solids with 
ethylglycol. The amine number of the resin is 80 mg KOH/g (DIN 53 176). 
EXAMPLE 2 
437 g of an epoxidized polybutadiene with 4.1 percent epoxy oxygen, a 
microstructure of 60 percent 1,4-cis and 40 percent 1,4-trans double 
bonds, and a viscosity of 3700 mPas at 20.degree. C. is heated to 
100.degree. C. with 0.44 g of 2,6-di-tertiary butyl-4-methylphenol. 73.5 g 
of diethanolamine are added and the temperature is raised to 180.degree. 
C. The temperature is held for about 6 hours, until a sample of the resin 
is not turbid at room temperature when applied to a glass plate. At 
150.degree. C., a blend of 77 g styrene and 0.8 g di-tertiary butyl 
peroxide is added within 1 hour, and the batch is reheated to 180.degree. 
C. After 4 hours of reaction time at 180.degree. C., a solids content of 
97 percent is attained. A sample of the resin, diluted with butylglycol 
and neutralized with lactic acid is soluble in water to give a clear 
solution. The viscosity of a 50 percent resin solution in xylene is J, 
Gardner standard. The resin is diluted at 120.degree. C. with ethylglycol 
to a solids content of 70 percent. The amine number of the resin is 63 mg 
KOH/g (DIN 53 176). 
EXAMPLE 3 
270 g of an epoxidized polybutadiene with 5.4 percent by weight of epoxy 
oxygen, with a microstructure of about 60 percent of 1,4-cis and 40 
percent of 1,4-trans double bonds, and a viscosity of 7260 mPas 
(20.degree. C.) are heated to 80.degree. C. together with 0.27 g of 
2,6-di-tertiary butyl-4-methylphenol. 67 g diisopropanol amine are added 
and the temperature is raised to 150.degree. C. At this temperature, 
within the course of 40 minutes, a blend of 38 g of vinyltoluene, 10 g of 
methylmethacrylate and 0.7 g of di-tertiary butyl peroxide are added 
dropwise. As reflux permits, the temperature is raised to 180.degree. C. 
and held for about 9 hours, until a cold sample of the resin is not turbid 
on a glass plate. The solids content is 97.2 percent. Diluted with a 
little butyl glycol and neutralized with lactic acid the reaction product 
is soluble in water to give a clear solution. The viscosity of a resin 
solution of 2 parts of resin and 1 part by xylene is W, Gardner standard. 
At 150.degree. C., 35.5 g of p-tertiary butyl benzoic acid are added and 
reacted at 160.degree. C. for about 1 hour, until the acid value is below 
4 mg KOH/g. The finished reaction product is diluted at 120.degree. C. 
with ethylglycol to a solids content of 70 percent. The amine number of 
the resin is 68 mg KOH/g (DIN 53 176). 
EXAMPLE 4 
300 g of an epoxidized polybutadiene with 5.4 percent by weight of epoxy 
oxygen, a microstructure of about 60 percent of 1,4-cis and 40 percent of 
1,4-trans double bonds, and a viscosity of 7260 mPas (20.degree. C.) are 
heated to 150.degree. C. with 0.3 g of 2,6 di-tertiary 
butyl-4-methylphenol. At this temperature a blend of 53 g of vinyltoluene 
and 0.5 g of di-tertiary butylperoxide and, separately, 42 g 
diethanolamine are added at the same time, in the course of 30 minutes. 
The batch is reheated to 180.degree. C. and the temperature is held for 
about 10 hours, until the non-volatile content of the reaction mass has 
reached more than 98 percent. At 120.degree. C., the batch is diluted with 
130 g of ethyleneglycolmonoethylether acetate to 75 percent solids. The 
amine number of the resin is 53 mg KOH/g (DIN 53 176). 
COMISON EXAMPLE A 
437 g of the epoxidized polybutadiene of Example 1 are heated to 
100.degree. C. with 0.17 g of 2,6-di-tertiary butyl-4-methylphenol. 65 g 
of N,N-diethylaminopropylamine are added and the temperature is raised to 
180.degree. C. It is held for about 10 hours, until a sample of the resin 
neutralized with lactic acid is soluble in water to give a clear solution. 
The solids content of the resin is 99 percent. At 150.degree. C., 120 g of 
rosin are added and the temperature is held until after about 3 hours the 
acid value has fallen below 3 mg KOH/g. At 120.degree. C., the batch is 
diluted to 70 percent solids with ethyleneglycol monoethylether. The amine 
number of the resin is 72 mg KOH/g (DIN 53 176). 
COMISON EXAMPLE B 
437 g of the epoxidized polybutadiene of Example 2 are heated to 
100.degree. C. with 0.44 g of 2,6 di-tertiary butyl-4-methylphenol. 73 g 
diethanolamine are added and the batch is reheated to 180.degree. C. This 
temperature is held for about 9 hours, after which time a sample of the 
batch remains clear when cooled to room temperature. At the end of the 
reaction, the solids content is 99 percent. At 120.degree. C., the batch 
is diluted to 70 percent solids with ethyleneglycol monoethylether. The 
amine number of the resin is 72 mg KOH/g (DIN 53 176). 
COMISON EXAMPLE C 
300 g of the epoxidized polybutadiene used in Examples 3 and 4 are heated 
to 150.degree. C. with 0.3 g 2,6-di-tertiary butyl-4-methylphenol. At this 
temperature, 52 g of diethanolamine are added within 30 minutes. The 
temperature is raised to 180.degree. C. and held for about 3 hours. During 
this time the batch becomes clear, the solids content is 99 percent, and 
the viscosity of a solution of 6 parts reaction mass and 4 parts of 
ethyleneglycolmonoethylether acetate is O, Gardner. At 150.degree. C., 121 
g of rosin are added and this temperature is held until the acid value has 
fallen below 10 mg KOH/g. The resin is highly viscous and is diluted at 
140.degree. C. with ethyleneglycol monoethylether acetate to 60 percent 
solids. The amine value of the resin solids is 57 mg KOH/g (DIN 53 176). 
APPLICATION OF THE BINDERS PREED ACCORDING TO THE EXAMPLES 
The resins of Examples 1-4 and of Comparison Examples A-C are passed over a 
three roll mill in the following formulation: 
100 g resin solids 
18 g aluminum silicate pigment 
2 g carbon black 
2 g lead silicate pigment 
The pigment pastes, milled to a standardized degree of fineness, are 
neutralized with diluted formic acid with the quantities listed in Table 1 
and are slowly diluted with water while stirring to give paint baths of 15 
percent solids. 
Cathodically wired steel panels are immersed into the paint batch and are 
coated with a direct current, according to the conditions set forth in 
Table 1, while the tank materials are slowly stirred. The wall of the 
metallic paint container was wired as the anode. Deposition time was 60 
seconds, bath temperature 22.degree. C. The panels were removed from the 
paint bath, rinsed with tap water, and cured at 180.degree. C. for 30 
minutes. 
Table 2 shows the evaluation results of the obtained coatings. 
As apparent from an evaluation of the data of Tables 1 and 2, the 
heat-hardenable coating compositions of the present invention, in 
comparison with Examples A, B, and C falling outside the scope of the 
present invention, are superior in respect to electrochemical 
characteristics; appearance and characteristics of the coating upon 
application; and, furthermore, have improved throwing power and other 
physical characteristics. This superiority was not predictable. 
In the above illustrative examples, various modifications can be made. Such 
modifications being within the ability of one skilled in the art are 
within the scope of the present invention and appended claims. 
TABLE 1 
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Max. Voltage (V) 
mol HCOOH 
pH-Value 
Conductivity 
Dry Film Thickness (.mu.m) 
Appearance 
Examples 
per 100 g 
Paint Bath 
.mu.S . cm.sup.-1 
On Zinc Phosphated Steel 
Of The Coating 
__________________________________________________________________________ 
1 0.06 5.05 805 220 V 24.mu. 
uniform, smooth, 
hard 
2 0.045 4.9 930 220 V 35.mu. 
uniform, smooth, 
hard 
3 0.06 4.5 1880 160 V 18.mu. 
uniform, hard, 
slight orange peel 
4 0.06 4.6 1650 180 V 20.mu. 
uniform, smooth, 
hard 
A 0.06 6.2 1220 140 V 17.mu. 
tears on vertical 
surfaces, poor edge 
covering, thermo- 
plastic 
B 0.06 5.4 1310 120 V 18.mu. 
tears, some craters, 
poor edge covering 
C 0.06 4.5 1580 100 V &gt;50.mu. 
foamy porous coating 
with poor adhesion 
__________________________________________________________________________ 
TABLE 2 
______________________________________ 
Salt Spray 
Throwing Power 
Flexibility Resistance 
Example 
(1) (2) (3) 
______________________________________ 
1 15.5 4.1 390 
2 16.3 3.8 457 
3 15.6 3.4 410 
4 17.8 4.2 624 
A 14.7 3.9 360 
B 14.2 3.6 336 
C 10.6 not recordable 
120 
owing to porous 
structure 
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(1) A steel strip 1.4 cm wide, 30 cm long and 0.3 mm thick is inserted in 
diagonal position into a steel square with 1 cm.sup.2 of interior apertur 
and a length of 30 cm. This testing device, wired as the cathode, is 
placed in vertical position into a plastic cylinder of 6 cm diameter and 
40 cm height, the bottom of which contains a steel disc as the anode. The 
distance between the electrodes is 10 cm. The cylinder is filled with the 
paint material. Deposition time is 3 minutes. The length (in cm) of the 
coating on the steel strip recordable by visual inspection is a measure 
for the throwing power. 
(2) Erichsen indentation (mm) DIN 53 156. 
(3) ASTM B 11764: Number of hours, after which 2 mm of rust appear at bot 
sides of the incision line.