Adducts of oxazolidine compounds, such as the reaction product of monoethanol amine with cyclohexanone, are adducted with an organic polyepoxide and the adduct is reacted with an acid to protonate at least 50% of the amine groups in the adduct. These protonated adducts can be dispersed in water to form dispersions which cure with various curing agents. When all the epoxy groups are consumed by reaction with the oxazolidine, aqueous electrocoating baths can be formulated which may contain aminoplast resin or phenoplast curing agents.

DESCRIPTION 
1. Technical Field 
This invention relates to water dispersible cationic resins based on 
polyepoxides, their production, and to the cationic electrocoating of such 
resins from an aqueous bath containing the same. 
2. Background Art 
It is known to react polyepoxides with ketimine-blocked amines which 
include a single secondary amino hydrogen atom. The reaction products can 
be reacted with an acid to quaternize the tertiary amine groups in the 
reaction product, and the quaternized reaction product can be dispersed in 
water. The water reacts with the ketimine groups to release ketone into 
the water medium and this provides primary amine groups. The resulting 
amine-functional resin is electrodepositable from aqueous medium at the 
cathode of a unidirectional electrical system, and it can be cured with a 
curing agent which is introduced into the water medium for this purpose. 
The curing agents primarily selected in the prior art have been blocked 
polyisocyanates. When electrodeposited coatings containing the 
amine-functional resin and the blocked polyisocyanate are baked, the 
blocking agent is removed and the amine resin cures. All of the foregoing 
is illustrated in U.S. Pat. No. 4,031,050. 
It would be desirable to replace the blocked polyisocyanate curing agent 
with an aminoplast resin because these are less costly, but the amine 
functionality (which is largely constituted by primary amine groups) 
creates a strongly alkaline environment which inhibits cure with an 
aminoplast resin. 
Another point of importance is the fact that the ketimine-blocked secondary 
amines which are used in the prior process are derived from diethylene 
triamine, and it is desired to use less costly materials. 
DISCLOSURE OF INVENTION 
In this invention, a monoalkanol amine, such as monoethanol amine, is 
reacted with a ketone or an aldehyde (preferably selected as described 
hereinafter) and water is removed to generate an oxazolidine which 
contains a single reactive secondary amino hydrogen atom. This oxazolidine 
is adducted through its secondary amino hydrogen atom with a polyepoxide 
resin containing an average of at least 1.2 epoxy groups per molecule, 
sufficient oxazolidine being preferably used to consume all of the epoxy 
groups in the polyepoxide so as to provide superior stability in the 
aqueous baths which are formed. However, the invention includes adducts in 
which some of the epoxy groups are retained for cure. Upon protonation of 
at least about 50% of the amine groups in the adduct with an acid which 
may be nonvolatile when electrocoating is intended, and dispersion in 
water, hydrolysis of the oxazolidine occurs, and this generates a 
secondary amine group and an alkylol group. The ketone or aldehyde which 
formed the oxazolidine is released into the water. 
The protonated secondary amine groups enable cathodic electrodeposition and 
provide stability in the aqueous medium in the presence of a curing agent, 
even when the curing agent is not an expensive blocked polyisocyanate 
which provides stability through its own reluctance to react while 
blocked. The alkylol groups provide reactive hydroxy groups which may be 
of primary character to supplement the secondary hydroxy groups in the 
polyepoxide. These alkylol groups also provide improved compatibility with 
water without raising the amine value which detrimentally increases the 
conductivity of an electrocoating bath to impair electrodeposition 
performance. 
The water dispersions of the protonated adducts of this invention are cured 
using external curing agents. The blocked polyisocyanates, like 
butanol-blocked toluene diisocyanate,can be used as the curing agent, but 
these are costly, as previously noted. It is preferred herein to use 
phenoplast or aminoplast curing agents. These curing agents are not easily 
used in accordance with the prior art procedures. 
The good solubility in water of the protonated adducts of this invention 
assists in the practical use of water insoluble, heat-hardening 
phenol-formaldehyde curing agents, such as the reaction product of one mol 
of formaldehyde with one mol of ortho-cresol. 
The reduced amine content and the limitation of the amine functionality to 
secondary amine groups also facilitates cure with an aminoplast resin, it 
being well known that cure with aminoplast resins is hindered in an 
alkaline medium. The capacity to satisfactorily cure the coatings of this 
invention with an aminoplast resin is an important advantage. More 
particularly, larger amounts of amine functionality or the presence of 
primary amine groups creates an excessively alkaline environment which 
interferes with the reactivity of the N-methylol groups of the aminoplast 
resin, and this problem is minimized herein. 
Primary amine groups also contribute instability in aqueous medium which 
the acid protonating agent cannot fully overcome, and this is detrimental 
to commercial electrocoating operations unless an expensive blocked 
polyisocyanate is used. Reliance upon protonated secondary amine improves 
long term stability in aqueous medium which is vital to practical 
electrocoating operations. 
In preferred practice, the oxazolidine is formed using cyclohexanone. This 
is an unhindered ketone which forms the desired ring structure easily. 
Also of importance is the fact that cyclohexanone is water immiscible. It 
remains associated with the dispersed resin particles and is codeposited 
therewith at the cathode. As a solvent, the cyclohexanone assists film 
coalescence, especially as the deposited films are baked. This tends to 
enhance film gloss and to minimize film defects, like pinholes. Also, the 
cyclohexanone is reactive, and some of it may be incorporated into the 
final cured film, which desirably minimizes volatiles in the coating 
process. 
The monoalkanol amine is preferably monoethanol amine because of its 
favorable cost and availability, but 2-amino-2-methyl-1-propanol is also 
useful. It is preferred that the hydroxy group in the alkanol amine be a 
primary hydroxy group, but this is not essential. Isopropanol amine is an 
illustration of a useful amino alcohol in which the hydroxy group is of 
secondary character. 
The ketones and aldehydes which are selected for reaction with the 
monoalkanol amine to cause the production of an oxazolidine in a reaction 
involving the removal of water are unhindered. Hindered ketones, for 
example, form ketimides with the primary amine group, and these are not 
reactive with epoxy resins and release the primary amine group in water. 
Suitable ketones and aldehydes for use herein, in addition to the 
preferred cyclohexanone are; formaldehyde, acetaldehyde, benzaldehyde, 
acetone, and methyl ethyl ketone. 
The oxazolidines which are used herein have the formula: 
##STR1## 
where R.sub.1, R.sub.2 and R.sub.5 are selected from hydrogen and C.sub.1 
-C.sub.10 alkyl, especially methyl or ethyl, and R.sub.3 and R.sub.4 are 
the residue of the ketone or aldehyde used to form the oxazolidine 
compound by a reaction involving the removal of water. 
The reactive resin having at least 1.2 epoxy groups per molecule which is 
used in this invention is subject to wide variation, it being preferred to 
use those polyepoxides having a 1,2-epoxy equivalency up to about 2.0 and 
having an average molecular weight (by calculation) of 800 to 4000, 
preferably 1000 to 3000. Diglycidyl ethers of a bisphenol are particularly 
desirable, these being illustrated by the commercially available bisphenol 
A. Especially preferred polyepoxides are diglycidyl ethers having a 
1,2-epoxy equivalency of from about 1.6 to 2.0. The Shell products Epon 
1001, 1004 and 1007 are all useful. These can be purchased, or they can be 
approximated by reacting Epon 829 with a stoichiometric deficiency of 
bisphenol A. 
Volatile acids, like acetic acid, are preferred to protonate at least 50% 
of the amine groups. Dimethylol propionic acid can be used for 
electrocoating systems. 
It will be observed that the secondary amino nitrogen of the oxazolidine is 
directly reactive with the 1,2-oxirane functionality (the epoxy groups) of 
the polyepoxide. In the reaction, one can use an excess of epoxy 
functionality over amine functionality. The resulting adduct thus contains 
unreacted epoxy groups. After protonation with an acid and dispersion in 
water, the protonated amine is only very slowly reactive, so the aqueous 
medium containing a reactive curing agent is relatively stable even though 
hydrolysis produces a secondary amino hydrogen atom. Upon coating and 
evaporation of water, volatile acid and volatile solvent, the amino 
hydrogen atoms will react with the epoxy groups for cure. Additional 
polyepoxide may be added to assist this cure. These systems, however, are 
not sufficiently stable for electrocoating due to the presence of 
unreacted epoxy groups. 
When all the epoxy groups in the polyepoxide are consumed in the initial 
adduction with the oxazolidine, then sufficient stability for 
electrocoating is obtained, even when reactive curing agents are used. 
This is an important feature of this invention. It is stressed that the 
phenoplast and aminoplast curing agents are reactive materials, even when 
their reactive groups are etherified (especially with methanol) but the 
absence of epoxy groups and the fact that the amine functionality is 
secondary permits one to have either adequate stability with phenoplast 
resins or adequate cure with aminoplast resins.

Throughout this specification and claims, and in the examples which follow, 
all proportions are by weight, unless otherwise specified. These examples 
show preferred operation to provide an electrocoating system in accordance 
with this invention. 
EXAMPLE 1 
(Preparation of 1-Oxa-4-azaspiro[4.5]decane which is the oxazolidine of 
cyclohexanone and monoethanol amine) 
Monoethanol amine (61.08 grams--1.0 mole), cyclohexanone (126.69 
gram--1.291 moles), benzene (1 liter--874 gram and Dowex 50W-X12 ion 
exchange resin (5.0 grams--0.025 equiv.) were charged into a 2000 ml. 
one-neck flask equipped with a Dean-Stark trap, cold finger reflux 
condenser, magnetic stir bar and drying tube. The flask was heated to 
reflux temperature and and held there overnight to collect water (18.7 
gram--1.04 equiv.). The mixture was then cooled and the ion exchange resin 
was removed by filtration through a glass wool plug. Solvent was then 
removed on a rotary evaporater under aspirator vacuum. The infrared 
spectrum of the product confirmed the desired structure and indicated the 
presence of traces of residual cyclohexanone and ketimine; NMR 
spectroscopy also confirmed the product structure and indicated less than 
one percent of ketimine. An equivalent weight of 183.9 grams per 
equivalent of amine was determined by titration, and this can be compared 
with a theoretical equivalent weight of 141.2 grams per equivalent. 
EXAMPLE 2 
(Preparation of oxazolidine-functional polyepoxide derivative) 
Epon 829 (85.72 grams--0.43 equiv.) 2-butoxy ethanol (75.0 grams) and 
bisphenol A (28.42 grams--0.25 equiv.) were charged into a 500 ml. flask 
equipped with stirrer, thermometer, nitrogen inlet and condenser (with 
drying tube). The contents were heated to 170.degree. C. and held there 
under a nitrogen blanket until an epoxy value of 1.03 meq./g. sample was 
reached. This took three hours. 
The reaction mixture was then cooled to 60.degree. C. and then the 
oxazolidine prepared in Example 1 (35.86 grams--0.1950 equiv.) was slowly 
added over a period of 1 hour while the temperature was raised to 
110.degree. C. The reaction mixture was then held at 110.degree. C. until 
the epoxy value reached zero, which occurred in three hours. The product 
was then cooled to 60.degree. C. and 35.86 grams of diacetone alcohol were 
added. 
EXAMPLE 3 
(Preparation of water dispersion, incorporation of curing agent and 
electrodeposition and cure) 
The oxazolidine-functional resin solution of Example 2 (36.36 grams--0.0274 
equiv.) was mixed with an etherified hexa-N-methylol melamine (American 
Cyanamid product Cymel 1130 which is partially methylated and partially 
butylated) in an amount to provide 30 parts by weight of the melamine 
resin for 70 parts by weight of the oxazolidine resin. The mixture was 
then neutralized to an extent of about 60% with acetic acid (0.99 
gram--0.0165 equiv.). Then 2% by weight of total resin solids of catalyst 
was added and mixed into the solution. The catalyst was bis-2-ethylhexyl 
phosphoric acid. This solution was then dispersed in deionized water (163 
grams) using a high speed mixer. 
The resulting solution was then electrodeposited on a steel cathode by the 
application of 50 volts for 90 seconds. The deposited film had a thickness 
of from 1 to 2 mils and was baked in an oven maintained at 375.degree. F. 
for 20 minutes. The resulting cured film was hard and resisted 100 double 
rubs with a methyl ethyl ketone-saturated cloth. 
While 30% of curing agent based on total resin solids is used in the above 
example, this component may vary from 5% to 50% of total resin solids, 
preferably from 15% to 40%. 
Comparable results were also obtained by replacing the monoethanol amine 
used in the foregoing examples by an equimolar proportion of aminomethyl 
propanol and also with isopropanol amine. The oxazolidine of aminomethyl 
propanol and formaldehyde is available in commerce and has been used 
successfully herein.