Cathodically depositable resins and process of preparing same

Binders for cathodically depositable aqueous coating compositions comprising the reaction product, having an NCO-value of zero, of PA1 (A) polymers carrying reactive hydroxyl groups and having a hydroxyl number of at least about 40 mg KOH/g; and PA1 (B) compounds carrying per molecule an average of 0.8 to 1.5, and preferably 1.0, free isocyanate groups and at least one teritary basic aliphatically bound nitrogen atom. Optionally, the reaction product of (A) and (B) can include as PA1 (C) a compound carrying an average of 0.8 to 1.5, and preferably 1.0, free isocyanate groups and from 1 to 3 olefinic double bonds. Coating compositions containing the partially or totally neutralized reaction product when depositrd cathodically in an electrodeposition system will cure at relatively low temperatures and relatively short curing times to provide films having good resistance to water, chemicals, and corrosion.

The present invention is directed to synthetic resins. More particularly, 
the invention is directed to synthetic resins which are suitable for 
deposition from aqueous solutions of the resins at the cathode of an 
electrodeposition coating system. 
As known to one skilled in the art, to prepare synthetic resins which are 
depositable at the cathode of an electrodeposition system from their 
aqueous solutions in a direct current circuit, it is necessary to 
introduce into the resins basic functional groups which are at least 
partly neutralizable with inorganic or organic acids to obtain water 
solubility. The introduction of a basic functional group, such as a basic 
nitrogen atom, is carried out according to known methods, by reaction of 
an epoxy group with a secondary amine, or through copolymerization of an 
alpha,beta-ethylenically unsaturated monomer containing basic nitrogen 
functionality with alpha, beta-unsaturated monomers. Such methods, 
however, utilize raw materials which are available to only a limited 
extent and/or are expensive. Thus, cataphoretic electrodeposition coatings 
and the advantages thereof, including elimination of spot discoloration or 
other chemical changes as a result of metal ions anodically dissolved from 
the anode, are not possible for all applications. 
Accordingly, a primary object of the present invention is to provide 
synthetic resins which contain basic functional nitrogen groups so as to 
permit deposition from their aqueous solutions at the cathode of an 
electrodeposition system prepared from readily available raw materials 
which are relatively inexpensive, but which provide coating compositions 
having excellent resistance to water, chemicals, and corrosion. 
According to the present invention, basic functional nitrogen groups are 
introduced into resinlike prepolymers containing hydroxyl groups. More 
specifically, according to the present invention, heat-hardenable polymer 
binders for use in cathodically depositable coating compositions are 
provided characterized in that polymers carrying hydroxyl groups and 
having a hydroxyl number of at least about 40 mg KOH/g are reacted with 
compounds carrying per molecule an average of 0.8 to 1.5, and preferably 
1.0, free isocyanate groups and at least one tertiary basic aliphatically 
bound nitrogen atom at a temperature of from about 10.degree. to about 
100.degree. C., preferably 50.degree. to 80.degree. C., to an NCO-value of 
zero. The reaction product is partially or totally neutralized with 
inorganic or organic acids to provide an aqueous solution of the binder. 
Optionally, the reaction product can include the moiety of a molecule 
carrying an average of 0.8 to 1.5, and preferably 1.0, free isocyanate 
groups and from 1 to 3 olefinic double bonds. The reaction can be carried 
out in the presence of solvents inert to the isocyanates and of catalysts. 
Polymers containing hydroxyl groups suitable for use in the present 
invention can be prepared in a simple and convenient manner from a variety 
of raw materials. For example, polymers having a hydroxyl number of at 
least about 40 mg KOH/g can be prepared through solution polymerization of 
alkyl esters of acrylic and/or methacrylic acid and 
hydroxyalkyl(ene)esters of acrylic and/or methacrylic acids, optionally 
containing additional modifiers besides the hydroxyl groups. Suitable 
alkyl esters include methyl(meth)acrylate, ethyl(meth)acrylate, 
propyl(meth)acrylate, n-butyl(meth)acrylate, isobutyl(meth)acrylate, 
n-hexyl(meth)acrylate, and 2-ethylhexyl(meth)acrylate. Further, styrene, 
chlorostyrene, tert. butylstyrene, vinyltoluene, vinylacetate, and small 
quantities of (meth)acrylic acid, (meth)acrylamide or acrylonitrile can 
also be used to provide a copolymer. Suitable hydroxyalkyl(ene)esters 
include hydroxyethyl(meth)acrylate, 3-hydroxypropyl(meth)acrylate, 
4-hydroxybutyl(meth)acrylate, 3-hydroxybutyl(meth)acrylate, 
2-hydroxyhexyl(meth)acrylate, 6-hydroxyethyl(meth)acrylate, 
tripropyleneglycolmono(meth)acrylate, 
tetrapropyleneglycolmono(meth)acrylate. Small quantities of vinyl alcohols 
or allyl alcohols can also be used to provide a copolymer. The copolymers 
can optionally be modified, e.g., by reacting the carboxy groups present 
with, e.g., tris-hydroxymethylamine, to form oxazoline ring structures 
with free hydroxy groups. 
Basic nitrogen atoms are introduced into the preformed copolymers having a 
hydroxyl number of at least 40 mg KOH/g by reaction with compounds 
carrying in the molecule an average of from 0.8 to 1.5 isocyanate groups 
and at least one tertiary basic nitrogen atom. Preferably, the compounds 
contain an average of about one isocyanate group per molecule. These 
compounds are prepared by reacting a diisocyanate or polyisocyanate with 
less than stoichiometric quantities of an amine of the general formula 
##STR1## 
wherein R is an alkanol or hydroxyphenyl radical and R.sub.1 and R.sub.2 
are alkyl or cycloalkyl. The dialkanol amines such as dimethylethanol 
amine, diethylethanolamine and their higher homologues and isomers are 
preferred. Suitable di- or polyisocyanates include aromatic isocyanates 
such as 2,4 or 2,6-tolulenediisocyanate and blends thereof, 
4,4'-diphenylmethanediisocyanate, or cycloaliphatic isocyanates such as 
isophorone diisocyanate, cyclohexane-1,4-diisocyanate, as well as 
aliphatic isocyanates, such as trimethylhexamethylene-1,6-diisocyanate and 
tris-hexamethylenetriisocyanate. The reaction between the amine and the 
diisocyanate or polyisocyanate is effected at from about 0.degree. to 
80.degree. C., and preferably at from about 20.degree.-50.degree. C. The 
weight ratios between the reaction partners are chosen such that the 
compound formed contains from 0.8 to 1.5, preferably 1, free isocyanate 
group. The compound is at times hereinafter called the "basic isocyanate 
intermediate." 
In order to enhance the thermal crosslinking of the cathodically deposited 
coatings, it may optionally be desirable to react the reaction products 
with further compounds carrying in the molecule an average of from about 
0.8 to 1.5 free isocyanate groups and from 1 to 3 olefinically unsaturated 
double bonds. Such compounds are prepared in a separate reaction step from 
the aforementioned diisocyanates and polyisocyanates with reaction 
partners to provide in addition to the isocyanate group from 1 to 3 
olefinic double bonds. Suitable unsaturated compounds include the 
hydroxyalkylesters of acrylic acid or methacrylic acid, 
triethyleneglycolmono(meth)acrylate, trimethylolpropanedi(meth)acrylate, 
allylalcohol, tripropyleneglycolmonoabietate, oleyl alcohol or linoleyl 
alcohol. The reaction between the diisocyanate or polyisocyanate and the 
isocyanate reactive olefinically unsaturated compound can be carried out 
in solvents inert to isocyanates at temperatures of from 10.degree. to 
100.degree. C., preferably from 50.degree. to 80.degree. C., optionally in 
the presence of organic stannous compounds as catalyst. The weight ratios 
between the reaction partners are chosen in order that the compound formed 
has from 0.8 to 1.5, and preferably 1, free isocyanate groups per 
molecule. This optional compound is at times hereinafter called the 
"olefinically unsaturated isocyanate intermediate." 
The process of the invention is carried out in order that the 
above-mentioned hydroxy group containing copolymers, preferably dissolved 
in isocyanate-inert solvents, and the desired quantity of the basic 
isocyanate intermediate and, optionally, the olefinically unsaturated 
isocyanate intermediate are reacted at from 10.degree. to 100.degree. C., 
preferably 50.degree. to 80.degree. C., optionally in the presence of 
organic stannous compounds as catalyst, until an NCO-value of practically 
zero is attained. The quantity of basic isocyanate intermediate is 
normally chosen in order that the basicity of the binder system, upon 
neutralization with the acid, gives satisfactory water dilutability at a 
pH-value of from 4 to 8, preferably 5 to 7. The reaction between the 
hydroxy containing copolymers, the basic isocyanate intermediate and the 
olefinically unsaturated isocyanate intermediate can be effected in random 
sequence, separately or jointly. 
For reducing the stoving temperature or for obtaining a particularly good 
corrosion protection of the coatings, it can be advantageous to coemploy 
additional known crosslinking agents, such as the urea-, melamine-, or 
phenolformaldehyde condensates. These resins are prepared by known methods 
through condensation of formaldehyde and substances splitting off 
formaldehyde with urea, melamine, benzoguanamine, acetoguanamine, phenol, 
cresol, p-tert. butylphenol, Bisphenol A, and the like. Optionally, the 
methylol compounds may be etherified with alcohols. A preferred product is 
the reaction product of phenol with formaldehyde-containing allyl ether 
groups. If the crosslinking agent selected is not water soluble, it can be 
conveniently combined with the binder prepared according to the invention 
through careful condensation at temperatures of from 50.degree. to 
120.degree. C. The reaction is carried on to the extent that satisfactory 
dilutability with water of the total reaction mass upon neutralization 
with acids is obtained. 
The basic nitrogen atoms of the coating composition of the invention are 
partially or totally neutralized with organic and/or inorganic acids. The 
degree of neutralization in the individual case depends upon the 
properties of the binder selected. In general, sufficient acid is added to 
render the coating composition dilutable or dispersible with water at a 
pH-value of from 4 to 8, and preferably of from 5 to 7. 
The concentration of the binder depends upon the parameters at processing 
in the electrodeposition process and ranges from about 3 to 30 percent by 
weight, preferably 5 to 15 percent by weight. The composition being 
processed may optionally contain various additives such as pigments, 
extenders, surface active groups, and the like. 
Upon electrodeposition the aqueous coating composition containing the 
binder of the invention is wired to an electrically conductive anode and 
an electrically conductive cathode, the surface of the cathode being 
coated with the coating composition. A variety of electrically conductive 
substrates may be coated, such as steel, aluminum, copper, etc., or the 
metalized plastics or other materials covered with a conductive coating. 
After deposition, the coating is optionally rinsed with water and cured at 
elevated temperature. For curing, temperatures of from 130.degree. to 
200.degree. C., preferably 150.degree. to 190.degree. C., are utilized. 
The curing time is normally from about 5 to 30 minutes and preferably 10 
to 25 minutes.

The following examples illustrate the invention without limiting the scope 
thereof. Parts are by weight unless otherwise stated. 
PREATION OF THE INTERMEDIATES 
(A) Hydroxy Groups Containing Polymers 
In a reaction vessel equipped with stirrer, thermometer, inert gas supply, 
and reflux condensor, about 1/5 or 20 percent of a solution of 666 parts 
ethylglycolacetate containing the monomer mixture as hereinafter stated, 
30 parts azobisisobutyronitrile, and 50 parts dodecylmercaptan are charged 
and heated to reflux temperature while stirring. In the course of 1 to 2 
hours, the remainder of the monomer mixture as hereinafter stated is added 
dropwise. Then the batch is stirred while maintaining reflux temperature, 
until the theoretical solids content is attained, which normally is about 
four hours. 
Intermediate Component A-1 
500 parts--n-butylacrylate 
400 parts--2-hydroxyethylacrylate 
100 parts--styrene 
Intermediate Component A-2 
400 parts--n-butylacrylate 
500 parts--4-hydroxybutylacrylate 
100 parts--styrene 
Intermediate Component A-3 
360 parts--n-butylacrylate 
400 parts--2-hydroxyethylmethacrylate 
140 parts--tripropyleneglycolmonomethacrylate 
100 parts--styrene 
Intermediate Component A-4 
300 parts--n-butylacrylate 
250 parts--2-hydroxyethylacrylate 
290 parts--4-hydroxybutylacrylate 
40 parts--acrylamide 
120--styrene 
(B) Basic Isocyanate Intermediates 
Intermediate Component B-1 
In a three-neck reaction vessel equipped with reflux condensor and inert 
gas supply, 174 g of toluene diisocyanate (blend of 80 percent of the 2,4- 
and 20 percent of the 2,6-isomer) are reacted uniformly with 89 g of 
dimethylethanolamine, diluted to 60 percent with 
ethyleneglycolmonoethyletheracetate, while cooling and preventing any 
access of moisture. The reaction temperature must not exceed 30.degree. C. 
The reaction is ended when the isocyanate content has attained the 
theoretical value of 16 percent or less. 
Intermediate Component B-2 
174 g of toluene diisocyanate (blend of 80 percent of the 2,4- and 20 
percent of the 2,6-isomer) are blended with 194 g of 
ethyleneglycolmonoethyletheracetate in a three-neck reaction vessel with 
reflux condensor, inert gas supply, with absolute prevention of moisture 
access. With cooling, 117 g of diethylethanolamine are added continuously 
within one hour at 30.degree. C. The isocyanate level of the final product 
is 14.4 percent. 
(C) Olefinically Unsaturated Isocyanate Intermediates 
Intermediate Component C-1 
In a three-neck reaction vessel with reflux condensor and inert gas supply 
168 g of hexamethylenediisocyanate are mixed with 200 g of 
ethyleneglycolmonoethyletheracetate, and heated to 60.degree. C. while 
preventing access of moisture. At this temperature a blend of 130 g of 
hydroxyethylmethacrylate stabilized with 0.1 g of hydroquinone is added 
dropwise. The reaction is ended after about two hours, when the isocyanate 
level is 14.1 percent or slightly less. 
Intermediate Component C-2 
In a three-neck reaction vessel with reflux condensor and inert gas supply, 
222 g of isophorone diisocyanate and 325 g of 
ethyleneglycolmonoethyletheracetate are mixed and heated to 40.degree. C., 
preventing access of moisture. 116 g of hydroxyethylacrylate are 
continuously added and, at the end of the addition, the temperature is 
raised to 70.degree. C. and held until the isocyanate value has attained 
12.5 percent. 
Intermediate Component C-3 
In a reaction vessel 277 g of ethylglycolacetate and 174 g of toluene 
diisocyanate (blend of 80 percent of the 2,4- and 20 percent of the 
2,6-isomer) are charged and, while preventing access of moisture, 242 g of 
trimethylolpropanediacrylate are added within one hour at 
25.degree.-35.degree. C. Then the batch is heated to 60.degree.-70.degree. 
C. and stirred at this temperature, until an isocyanate value of about 10 
percent is attained. 
Intermediate Component C-4 
As in C-3; however, 193 g of ethylglycolacetate and 174 g of 
toluylenediisocyanate are charged and 116 g of hydroxyethylacrylate are 
added dropwise. 
EXAMPLES 1-9 
In a reaction vessel equipped with stirrer, addition funnel, thermometer 
and reflux condensor, the hydroxy-rich polymer (Intermediate Component A), 
optionally in the presence of a solvent inert to isocyanates such as 
ethyleneglycolmonoethyletheracetate, the basic isocyanate (Intermediate 
Component B) is added, preventing access of moisture, and subsequently, is 
completely reacted at 40.degree. to 100.degree. C. Then, the reaction 
product is mixed with an alipha,beta-olefinically unsaturated isocyanate 
intermediate (Intermediate Component C) and, at a temperature of from 
about 40.degree. to 100.degree. C., is reacted to an NCO-value of zero. 
The reaction of Intermediate Component A with Intermediate Component B and 
Intermediate Component C can also be effected in one reaction step at from 
40.degree. to 100.degree. C. without substantially different results. 
The quantities of the intermediate components and the reaction conditions 
are listed in Table 1. 
TABLE 1 
______________________________________ 
Reaction 
Example 
Intermediate Components (g).sup.+ 
Conditons.sup.++ 
Number (A) (B) (C) hours/.degree.C. 
______________________________________ 
1 1000 A-1 395 B-1 298 C-1 4/70 
2 1000 A-1 395 B-1 290 C-4 3/70 
3 1000 A-2 524 B-2 416 C-3 3/70 
4 1000 A-2 447 B-1 435 C-4 3/70 
5 1000 A-3 395 B-1 506 C-2 4/70 
6 1000 A-3 524 B-2 540 C-3 4/70 
7 1000 A-4 395 B-1 506 C-2 4/70 
8 1000 A-4 473 B-1 540 C-3 3/70 
9 1000 A-4 447 B-1 493 C-4 3/70 
______________________________________ 
.sup.+ All quantities refer to resin solids. 
.sup.++ Intermediate Components B and C are jointly reacted. 
EVALUATION OF THE BINDERS 
100 g resin solids samples of each binder were mixed with the designated 
quantity of acid and made up to 1000 g with deionized water while 
stirring. The 10 percent solutions were deposited on various substrates as 
the cathode of an electrodeposition system. Deposition time in all cases 
was 90 seconds. The coated substrates were rinsed with deionized water and 
cured at elevated temperature. The average film thickness of the cured 
films was between 13 to 17 .mu.m. Evaluation results are listed in Table 
2. 
TABLE 2 
______________________________________ 
Neutralization 
Deposition Evaluation 
Quan- Curing 
Hard- Inden- 
Resis- 
tity Type pH Min/ ness tation 
tance 
Ex. 1 2 3 Volt .degree.C. 
4 5 6 7 
______________________________________ 
1 3.5 E 5.8 180 30/190 
160 7.9 320/240 
2 2.8 A 6.2 280 20/180 
165 7.1 360/240 
3 3.0 A 6.1 300 20/180 
190 6.8 480/360 
4 3.8 E 6.0 250 25/180 
185 8.0 380/260 
5 4.6 M 5.9 200 30/190 
155 7.9 240/140 
6 3.6 E 6.1 230 30/180 
170 7.4 300/160 
7 3.0 A 6.0 220 30/180 
180 8.0 300/240 
8 3.0 A 6.0 280 20/180 
200 6.9 480/360 
9 2.8 A 6.2 240 20/180 
175 7.8 480/300 
______________________________________ 
1 quantity of acid in grams added to 100 g of resin solids 
2 E: acetic acid; M: lactic acid; A: formic acid 
3 measured on a 10% aqueous solution 
4 Konig pendulum hardness DIN 53 157 (sec) 
5 Erichsen indentation DIN 53 156 (mm) 
6 hours of water soak at 40.degree. C. until corrosion or blistering 
becomes visible 
7 salt spray ASTMB 11764: 2 mm of corrosion at the cross incision after 
the stated hours 
For this test degreased non-pretreated steel panels were coated with a 
pigmented paint consisting of 100 parts by weight of resin solids, 20 
parts by weight of aluminum silicate pigment, and 2 parts by weight of 
carbon black. 
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.