Process for coating electrically conducting substrates, substrates coated by this process and aqueous electrocoating baths

The invention relates to a process for a cathodic electrocoating process, wherein the electrocoating bath contains at least 7.5% by weight of a polyoxyalkylenepolyamine or a mixture consisting of several polyoxyalkylenepolyamines of different chemical structures, the percentage by weight referring to the total amount of binders contained in the electrocoating bath.

The invention relates to a process for coating electrically conducting 
substrates, in which process 
(1) the substrate is immersed in an aqueous electrocoating bath which 
contains a resin capable of being cathodically deposited, 
(2) the substrate is connected as cathode, 
(3) a film is deposited on the substrate by the action of direct current, 
(4) the substrate is removed from the electrocoating bath and 
(5) the deposited paint film is baked. 
The invention also relates to substrates coated by the process according to 
the invention and to the electrocoating baths employed in the process 
according to the invention. 
The cathodic electrocoating process described above is a painting process 
frequently used primarily for priming, in particular for priming of 
automotive bodies. 
Processes of the type described above have been disclosed, for example, in 
the following patents: DE-OS 3,518,732, DE-OS 3,518,770, DE-OS 3,409,188, 
EP-A 4,090 and EP-A 12,463. 
Using processes of this type, it is possible to achieve coatings of 
excellent quality. However, surface defects (particularly craters), well 
known to a person skilled in the art, often occur in the baked paint film. 
Many attempts have been made to suppress the occurrence of surface defects 
by adding additives. It is true that the surface defects may be eliminated 
in this manner, but, instead, problems due to adhesion failure usually 
appear in the overcoated paint films (for example filler and top coat). 
Problems of this sort occur especially in overcoated paint films 
containing alkyd resins as binders. 
The object forming the basis of the present invention is to make available 
a novel process in accordance with the preamble to patent claim 1. The 
novel process should overcome or reduce, in particular, the problems 
outlined above, associated with the present state of the art. 
Surprisingly, this object is achieved by a process in accordance with the 
preamble of patent claim 1, wherein the electrocoating bath contains at 
least 7.5% by weight of a polyoxyalkylenepolyamine or of a mixture 
consisting of several polyoxyalkylenepolyamines of different chemical 
structures, the percentage by weight referring to the total amount of 
binders contained in the electrocoating bath. 
The advantages achieved by the invention are essentially to be found in the 
fact that it is possible, using the process according to the invention, to 
obtain paint films which, compared with the paint films of the present 
state of the art, exhibit fewer and/or more faintly pronounced surface 
defects and do not give rise to defects due to adhesion failure in 
overcoated paint films, especially in overcoated paint films containing 
alkyd resins as binders. 
Further important advantages achieved by the process according to the 
invention lie in the fact that, compared with the present state of the 
art, the paint films obtained by the process according to the invention 
possess greater film thicknesses and greater flexibility. 
U.S. Pat. No. 3,975,250 discloses cationic reactive plasticizers, suitable 
for use in electrocoating baths, which are prepared by the reaction of 
partly blocked polyisocyanates with polyoxypropylenediamines. However, an 
average person skilled in the art, faced with the object forming the basis 
of the present invention, is unable to infer from U.S. Pat. No. 3,975,250 
any information for achieving the object. 
U.S. Pat. No. 4,423,166 discloses an electrocoating process in accordance 
with the preamble to patent claim 1, wherein the electrocoating bath 
contains as anticratering agent an adduct of a polyoxyalkylenepolyamine 
and a polyepoxide. It is true that the paint films obtained by the process 
disclosed in U.S. Pat. No. 4,423,166 exhibit a lower tendency for surface 
defect formation, but they give rise to defects due to adhesion failure in 
the overcoated paint films. Such defects occur especially in overcoated 
paint films containing alkyd resins as binders. 
The advantages achieved by the present invention are all the more 
surprising, since U.S. Pat. No. 4,423,166, column 18, describes 
electrocoating baths which contain up to 7.0% by weight, based on the 
total amount of binders contained in the electrocoating bath, of a 
polyoxyalkylenepolyamine, adduct but produce paint films with pronounced 
surface defects (cf . Table I in U.S. Pat. No. 4,423,166). 
Electrocoating baths for cathodic electrocoating are preferably prepared by 
first preparing an aqueous dispersion which contains a resin capable of 
being cathodically deposited and, if appropriate, a crosslinking agent and 
other customary additives such as, for example, antifoams etc. 
A pigment paste is then incorporated in this aqueous dispersion. 
The pigment paste consists of a ground resin and pigments and/or fillers. 
In addition, the pigment paste may also contain other additives such as, 
for example, plasticizers, wetting agents, antioxidants etc. 
Examples of pigments and fillers which may be contained in the pigment 
paste, are: titanium dioxide, antimony oxide, zinc oxide, basic lead 
carbonate, basic lead sulfate, barium carbonate, porcelain, clay, calcium 
carbonate, aluminum silicate, silicon dioxide, magnesium carbonate, 
magnesium silicate, cadmium yellow, cadmium red, carbon black, 
phthalocyanine blue, chromium yellow, toluidyl red and hydrated iron 
oxide. 
The preparation of pigment pastes is generally known and need not be 
explained here in greater detail (cf., for example, D. H. Parker, 
Principles of Surface Coating Technology, Interscience Publishers, New 
York (1965); R. L. Yates, Electropainting, Robert Draper Ltd., 
Teddington/England (1966); H. F. Payne, Organic Coating Technology, volume 
2, Wiley and Sons, New York (1961)). 
The pigment paste is added to the aqueous dispersion described above in 
such an amount that the finished electrocoating bath possesses the 
characteristics required for the deposition. In most cases the weight 
ratio of pigment or filler to the total amount of resin capable of being 
cathodically deposited and contained in the electrocoating bath is 0.05 to 
0.5. 
After the aqueous dispersion and the pigment paste have been combined and 
the combination adjusted to a suitable solids content, an electrocoating 
bath ready-for-use is obtained. 
The electrocoating baths used according to the invention may in principle 
contain all the non-self-crosslinking or self-crosslinking resins capable 
of being cathodically deposited which are suitable for the preparation of 
electrocoating baths. The electrocoating baths used according to the 
invention may also contain mixtures of different resins capable of being 
cathodically deposited. 
However, electrocoating baths containing cationic amine-modified epoxy 
resins as the resins capable of being cathodically deposited are 
preferred. Self-crosslinking as well as non-self-crosslinking cationic 
amine-modified epoxy resins are known. Non-self-crosslinking cationic 
amine-modified epoxy resins are preferably used. 
Cationic amine-modified epoxy resins are understood to be cationic reaction 
products from 
(A) optionally modified polyepoxides and 
(B) amines. 
Polyepoxides are understood to be compounds which contain two or more 
epoxide groups in the molecule. 
Particularly preferred components (A) are compounds which may be prepared 
by reacting 
(a) a diepoxide compound or a mixture of diepoxide compounds of an epoxide 
equivalent weight below 2000 with 
(b) a compound monofunctionally reactive toward epoxide groups under the 
given reaction conditions and containing a phenol or thiol group, or a 
mixture of such compounds, 
the components (a) and (b) being used in a molar ratio of 10:1 to 1:1, 
preferably 4:1 to 1.5:1, and the reaction of the component (a) with the 
component (b) being carried out at 100.degree. to 190.degree. C. in the 
presence or absence of a catalyst (cf. DE-OS 3,518,770). 
Other particularly preferred components (A) are compounds which may be 
prepared by a polyaddition of a diepoxide compound and/or a mixture of 
diepoxide compounds, if desired in conjunction with at least one 
monoepoxide compound, to an epoxy resin in which the diepoxide compound 
and initiator are incorporated in a molar ratio greater than 2:1 to 10:1, 
the said polyaddition being carried out at 100.degree. to 195.degree. C. 
in the presence of absence of a catalyst and initiated by a 
monofunctionally reactive initiator carrying either an alcoholic OH group 
or a phenolic OH group or an SH group (cf. DE-OS-3,518,732). 
The polyepoxides which may be used for the preparation of the particularly 
preferred components (A) and may even themselves be used as the components 
(A), are polyglycidyl ethers of polyphenols prepared from polyphenols and 
epihalohydrins. The use of bisphenol A and bisphenol F, for example, as 
the polyphenols is particularly preferred. In addition, 
4,4'-dihydroxybenzophenone, bis(4-hydroxyphenyl)-1,1-ethane, 
bis(4-hydroxyphenyl)-1,1-isobutane, 
bis(4-hydroxy-tert-butylphenyl)-2,2-propane, 
bis(2-hydroxynaphthyl)methane, 1,5-dihydroxynaphthalene and phenolic 
novolak resins are also suitable. 
Other suitable polyepoxides are polyglycidyl ethers of polyhydric alcohols, 
such as, for example, ethylene glycol, diethylene glycol, triethylene 
glycol, 1,2-propylene glycol, 1,4-propylene glycol, 1,5-pentanediol, 
1,2,6-hexanetriol, glycerol and bis(4-hydroxycyclohexyl)-2,2-propane. 
Polyglycidyl esters of polycarboxylic acids, such as, for example, oxalic 
acid, succinic acid, glutaric acid, terephthalic acid, 
2,6-naphthalenedicarboxylic acid and dimerized linoleic acid may be also 
used. Glycidyl adipate and glycidyl phthalate are typical examples. 
Other suitable compounds are hydantoin epoxides, epoxidized polybutadiene 
and polyepoxide compounds which are obtained by epoxidation of an 
olefinically unsaturated aliphatic compound. 
Modified polyepoxides are understood to be polyepoxides in which some of 
the reactive groups have been reacted with a modifying compound.

Examples of modifying compounds are: 
a) compounds containing carboxyl groups such as saturated or unsaturated 
monocarboxylic acids (for example benzoic acid, linseed fatty acid, 
2-ethylhexanoic acid, versatic acid), aliphatic, cycloaliphatic and/or 
aromatic dicarboxylic acids of various chain lengths (for example adipic 
acid, sebacic acid, isophthalic acid or dimeric fatty acids), 
hydroxyalkylcarboxylic acids (for example lactic acid, dimethylolpropionic 
acid) as well as polyesters containing carboxyl groups, or 
b) compounds containing amino groups, such as diethylamine or 
ethylhexylamine or diamines with secondary amino groups, for example 
N,N'-dialkylalkylenediamines such as dimethylethylenediamine, 
N,N'-dialkylpolyoxyalkyleneamines such as 
N,N'-dimethylpolyoxypropylenediamine, cyanoalkylated alkylenediamines such 
as bis-N,N'-cyanoethylethylenediamine, cyanoalkylated polyoxyalkylene 
amines such as bis-N,N'-cyanoethylpolyoxypropylenediamine, polyaminoamides 
such as, for example, versamides, in particular reaction products 
containing terminal amino groups, obtained from diamines (for example 
hexamethylenediamine), polycarboxylic acids, particularly dimeric fatty 
acids, and monocarboxylic acids, in particular fatty acids, or the 
reaction product of one mole of diaminohexane with two moles of a 
monoglycidyl ether or monoglycidyl ester, especially glycidyl esters of 
.alpha.-branched fatty acids such as versatic acid, or 
c) compounds containing hydroxyl groups such as neopentylglycol, 
bis-ethoxylated neopentylglycol, neopentyl glycol hydroxypivalate, 
dimethylhydantoin-N,N'-diethanol, hexane-1,6-diol, hexane-2,5-diol, 
1,4-bis(hydroxymethyl)cyclohexane, 
1,1-isopropylidene-bis(p-phenoxy)-2-propanol, trimethylolpropane, 
pentaerythritol or amino alcohols such as triethanolamine, 
methyldiethanoamine or alkylketimines containing hydroxyl groups, such as 
aminomethylpropanediol-1,3-methylisobutylketimine or 
tris(hydroxymethyl)aminomethanecyclohexanoneketimine, as well as 
polyglycol ethers, polyester polyots, polyether polyols, polycaprolactone 
polyols, polycaprolactam polyols of various functionalities and molecular 
weights, or 
d) saturated or unsaturated fatty acid methyl esters which are 
transesterified with the hydroxyl groups of the epoxy resins in the 
presence of sodium methylate. 
Primary or secondary amines and their salts, salts of tertiary amines or 
mixtures of these compounds may be used as the component (B). 
Water-soluble amines are preferably used as the component (B). Examples of 
suitable amines are monoalkylamines and dialkylamines, such as 
methylamine, ethylamine, propylamine, butylamine, dimethylamine, 
diethylamine, dipropyl-amine, methylbutylamine etc. Alkanolamines, such 
as, for example, methylethanolamine and diethanolamine may also be used as 
components (B). Kerimines of polyamines with primary and secondary amino 
groups may also be used as the component (B). Furthermore, 
dialkylaminoalkylamines, such as, for example, dimethylaminoethylamine, 
diethylaminopropylamine and dimethylaminopropylamine, are also suitable as 
the component (B). 
Low-molecular amines are used in most cases as the components (B). It is 
also possible, however, to use higher-molecular monoamines. 
Secondary amines are preferably used as the components 
In many cases several different amines are used as the component (B). 
The positive charges required for water dilutabitity and capacity to be 
electrically deposited may be imparted by protonation with water-soluble 
acids (for example boric acid, formic acid, lactic acid and, preferably, 
acetic acid) and/or by the use of amine salts as the components (B) in the 
binder molecule. 
The cationic amine-modified epoxy resins used according to the invention 
are essentially free from epoxide groups, i.e. their epoxide group content 
is so low that crosslinking reactions via the epoxide groups cannot take 
place either before or after the deposition of the paint film. The 
cationic amine-modified epoxy resins used according to the invention 
preferably do not contain any free epoxide groups. 
The cationic amine-modified epoxy resins may be used both as 
non-self-crosslinking resins and as self-crosslinking resins. 
Self-crosslinking cationic amine-modified epoxy resins may be obtained, 
for example, by chemical modification of the cationic amine-modified epoxy 
resins. A self-crosslinking cationic amine-modified epoxy resin may be 
obtained, for example, by reacting the cationic amine-modified epoxy resin 
with a partly blocked polyisocyanate which has on average one free 
isocyanate group per molecule and whose blocked isocyanate groups lose 
their blocking groups only at elevated temperatures. 
Preferred electrocoating baths are obtained when non-self-crosslinking 
cationic amine-modified epoxy resins are used as resins capable of being 
cathodically deposited in combination with a suitable crosslinking agent. 
Examples of suitable crosslinking agents are phenoplasts, polyfunctional 
Mannich bases, melamine resins, benzoguanamine resins, blocked 
polyisocyanates and compounds containing at least two groups of the 
general formula R.sup.1 --O--CO--. 
The radical R.sup.1 denotes: 
R.sup.1 =R.sup.2 O--CO--CH.sub.2 --, R.sup.3 --CHOH--CH.sub.2 --, R.sup.4 
--CHOR.sup.5 --CHOH--CH.sub.2 -- 
R.sup.2 =alkyl 
R.sup.3 =H, alkyl, R.sup.6 --O--CH.sub.2 -- or R.sup.6 --CO--O--CH.sub.2 -- 
R.sup.4 =H or alkyl 
R.sup.5 =H, alkyl or aryl 
R.sup.6 =alkyl, cycloalkyl or aryl 
Preferred electrocoating baths are obtained when blocked polyisocyanates 
and/or compounds containing at least two groups of the general formula 
R.sup.1 --O--CO-- are used as crosslinking agents. 
Any polyisocyanates in which the isocyanate groups have been reacted with a 
compound in such a way that the blocked polyisocyanate formed is 
non-reactive toward hydroxyl and amino groups at room temperature, but 
becomes reactive at elevated temperatures, usually in the range from about 
90.degree. C. to about 300.degree. C., may be used as the blocked 
polyisocyanates. Any organic polyisocyanates suitable for the crosslinking 
may be used for the preparation of the blocked polyisocyanates. 
Isocyanates containing about 3 to 36, in particular about 8 to about 15 
carbon atoms, are preferred. Examples of suitable diisocyanates are 
hexamethylenediisocyanate, 2,4-toluylenediisocyanate, 
2,6-toluylenediisocyanate and 
1-isocyanatomethyl-5-isocyanato-1,3,3-trimethylcyclohexane. However, it is 
also possible to employ polyisocyanates of higher isocyanate 
functionality. Corresponding examples are trimerized 
hexamethylenediisocyanate and trimerized isophoronediisocyanate. In 
addition, mixtures of polyisocyanates may also be used. The organic 
polyisocyanates which are suitable as crosslinking agents for the 
invention may also be prepolymers derived, for example, from a polyol 
including a polyether polyol or a polyester polyol. 
Any suitable aliphatic, cycloaliphatic or aromatic alkylmonoalcohols may be 
used for the blocking of the polyisocyanates. Examples of these are 
aliphatic alcohols, such as methyl, ethyl, chloroethyl, propyl, butyl, 
amyl, hexyl, heptyl, octyl, nonyl, 3,3,5-trimethylhexyl, decyl and lauryl 
alcohol; cycloaliphatic alcohols such as cyclopentanol and cyclohexanol; 
aromatic alkylalcohols such as phenylcarbinol and methylphenylcarbinol. 
Other suitable blocking agents are hydroxylamines such as ethanolamine, 
oximes such as methyl ethyl ketonoxime, acetone oxime and cyclohexanone 
oxime or amines such as dibutylamine and diisopropylamine. The above 
polyisacyanates and blocking agents may also be used, in suitable 
proportions, for the preparation of the partly blocked polyisocyanates 
referred to above. 
Examples of compounds which contain at least two groups of the general 
formula R.sup.1 --O--CO--, are bis(carbalkoxymethyl) azelate, 
bis(carbalkoxymethyl) sebacate, bis(carbalkoxymethyl) adipate, 
bis(carbalkoxymethyl) decanate, bis(carbalkoxymethyl) terephthalate, 
bis(2-hydroxybutyl) acelate (sic) and bis(2-hydroxyethyl) terephthalate. 
The crosslinking agent is usually used in an amount from 5 to 60% by 
weight, preferably 20 to 40% by weight, based on the total amount of 
crosslinkable resin capable of being cathodically deposited contained in 
the electrocoating bath. 
It is an essential part of the invention that in the process according to 
the invention electrocoating baths are employed which contain at least 
7.5% by weight of a polyoxyalkylenepolyamine or a mixture of several 
polyoxyalkylenepolyamines of different chemical structures, the percentage 
by weight referring to the total amount of binders contained in the 
electrocoating bath. 
The polyoxyalkylenepolyamines are understood to be compounds which contain 
both oxyalkylene groups as well as at least two amino groups, preferably 
at least two primary amino groups. The polyoxyalkylenepolyamines should 
have a number average molecular weight of about 137 to 3600, preferably 
400 to 3000, particularly preferably 800 to 2500. Furthermore, the 
polyoxyalkylenepolyamines should have an amine equivalent weight of about 
69 to about 1800, preferably 200 to 1500, particularly preferably 400 to 
1250. 
The polyoxyalkylenepolyamines preferably used have a chemical structure 
according to the general formula (I) 
EQU H.sub.2 N--CHR--CH.sub.2 --O--(--CHR--CH.sub.2 --O--).sub.n --CH.sub.2 
--CHR--NH.sub.2 (I) 
in which 
R denotes H or an alkyl radical of 1 to 6 carbon atoms, preferably 
--CH.sub.3 
n denotes 5-60, preferably 20-40. 
Polyoxyalkylenepolyamines which have a chemical structure in accordance 
with the general formula (I), are disclosed in U.S. Pat. No. 3,236,895, 
column 2, lines 40-72. The processes for the preparation of these 
polyoxyalkylenepolyamines are disclosed in the patent examples 4, 5, 6 and 
8 to 12 found in columns 4 to 9 of U.S. Pat. No. 3,236,895. 
It is also possible to employ polyoxyalkylenepolyamines which contain 
different oxyalkylene groups, for example polyoxyalkylene polyamines which 
have a chemical structure in accordance with the general formula (II): 
EQU H.sub.2 N--CH(CH.sub.3)--CH.sub.2 --(O--CH(CH.sub.3)--CH.sub.2).sub.n 
--(O--CH.sub.2 --CH.sub.2 --).sub.m --O--CH.sub.2 
--CH(CH.sub.3)--NH.sub.2(II) 
in which 
n+m denotes 5 to 60, preferably 20 to 40 
m denotes 1 to 59, preferably 5 to 30 
n denotes 1 to 59, preferably 5 to 30. 
It is also possible to use polyoxyalkylenepolyamine derivatives which are 
obtainable by the reaction of the polyoxyalkylenepolyamines described in 
U.S. Pat. No. 3,236,895, column 2, lines 40-72, with acrylonitrile, 
followed by hydrogenation of the reaction product. 
These derivatives have a chemical structure in accordance with the general 
structural formula (III): 
EQU H.sub.2 N--(CH.sub.2).sub.3 --NH--CHR--CH.sub.2 --O--(--CHR--CH.sub.2 
--O--).sub.n --CH.sub.2 ----CHR--NH--(CH.sub.2).sub.3 --NH.sub.2(III) 
in which 
R denotes H or an alkyl radical of 1 to 6 carbon atoms, preferably 
--CH.sub.3 
n denotes 5 to 60, preferably 20 to 40. 
It goes without saying that the electrocoating baths used according to the 
invention may also contain a mixture of several polyoxyalkylenepolyamines 
of different chemical structures. 
The polyoxyalkylenepolyamines or the polyoxyalkylenepolyamine mixtures may 
be incorporated in the electrocoating baths at any time during the 
preparation and even to the finished electrocoating baths. The 
polyoxyalkylenepolyamines or the polyoxyalkylenepolyamine mixtures are 
preferably added either to the aqueous dispersion or a precursor of the 
aqueous dispersion which contains a resin capable of being cathodically 
deposited and, optionally, a crosslinking agent and other customary 
additives such as, for example, antifoams etc. (cf. page 4, lines 19 ff), 
or to the pigment paste or a precursor of the pigment paste (cf. page 4, 
lines 26 ff). 
The polyoxyalkylenepolyamine molecules are in all probability protonized by 
the acid contained in the aqueous dispersion or the pigment paste. 
However, it is also possible to add the corresponding 
polyoxyalkylenepolyamine or polyoxyalkylenepolyamine mixture in the 
protonized form to the aqueous dispersion under discussion or a precursor 
of this dispersion, or to the pigment paste or a precursor of the pigment 
paste. The protonized polyoxyalkylenepolyamine or polyoxyalkylenepolyamine 
mixture may be obtained by the simple addition of a Bronsted acid to the 
corresponding polyoxyalkylenepolyamine or polyoxyalkylenepolyamine 
mixture. The total amount of Bronsted acid contained in the finished 
electrocoating bath should be selected in such a manner that the pH of the 
electrocoating bath is between 4 and 8, preferably between 5 and 7.5. 
It is an essential part of the invention that the amount of 
polyoxyalkylenepolyamine or polyoxyalkylenepolyamine mixture contained in 
the electrocoating baths used according to the invention is at least 7.5% 
by weight, the percentage by weight referring to the total amount of 
binders contained in the electrocoating bath. This means in other words 
that the electrocoating baths used according to the invention must contain 
at least 7.5 parts by weight of polyoxyalkylenepolyamine or 
polyoxyalkylenepolyamine mixture per 100 parts by weight of binder. When 
electrocoating baths with a lower content of polyoxyalkylenepolyamine or 
polyoxyalkylenepolyamine mixture are used, the resultant paint films 
exhibit considerably more and/or considerably more strongly pronounced 
surface defects than when the electrocoating baths according to the 
invention are used. 
The upper limit of the amount of polyoxyalkylenepolyamine or 
polyoxyalkylenepolyamine mixture contained in the electrocoating baths 
used according to the invention is determined by the plasticizing effect 
of the added polyoxyalkylenepolyamine or polyoxyalkylenepolyamine mixture 
and is generally from 20 to 40% by weight, the percentage by weight 
referring to the total amount of binders contained in the electrocoating 
bath. 
The electrocoating baths used according to the invention preferably contain 
8 to 18, particularly preferably 10 to 15% by weight of 
polyoxyalkylenepolyamine or polyoxyalkylenepolyamine mixture, the 
percentage by weight referring to the total amount of binders contained in 
the electrocoating bath. 
The total amount of binders contained in the electrocoating bath is 
determined by adding the amount of resin capable of being cathodically 
deposited contained in the electrocoating bath, the amount of crosslinking 
agents optionally contained in the electrocoating bath, the amount of 
ground resin contained in the electrocoating bath and the amount of resins 
which crosslink under the baking conditions which may or may not be 
additionally present in the electrocoating bath. 
The solids content of the electrocoating baths used according to the 
invention is preferably 7 to 35 parts by weight, particularly preferably 
12 to 25 parts by weight. 
The electrocoating bath is brought into contact with an electrically 
conducting anode and with the electrically conducting substrate connected 
as cathode. When electric current passes between the anode and the 
cathode, a highly adherant paint film is deposited on the cathode. 
The temperature of the electrocoating bath should be between 15.degree. and 
35.degree. C., preferably between 20.degree. and 30.degree. C. 
The applied voltage may fluctuate within a wide range and may be, for 
example, between two and one thousand volt. However, typical operational 
voltages are between 50 and 500 volt. The current density is usually 
between about 10 and 100 ampere/m.sup.2. The current density tends to drop 
in the course of the deposition. 
When the deposition is completed, the coated object is rinsed and is then 
ready for baking. 
The deposited paint films are generally baked at temperatures from 
130.degree. to 200.degree. C. during a period of 10 to 60 minutes, 
preferably at 150.degree. to 180.degree. C. during a period from 15 to 30 
minutes. 
The process according to the invention may be employed for coating of any 
electrically conducting substrate, in particular, however, for coating of 
metals such as steel, aluminum, copper and the like. 
The invention is explained in greater detail in the examples below. All 
parts and percentages are parts and percentages by weight, unless 
expressly stated otherwise. 
1. Preparation of Aqueous Dispersions Containing a Resin Capable of Being 
Cathodically Deposited and a Crosslinking Agent 
1.1 Preparation of an Amine-Modified Epoxy Resin 
1780 g of Epikote 1001.sup.1), 280 g of dodecylphenol and 105 g of xylene 
are placed in a reaction vessel and molten at 120.degree. C. in an 
atmosphere of nitrogen. 
FNT .sup.1) An epoxy resin from Shell with an epoxide equivalent weight of 500. 
Traces of water are subsequently removed in a slight vacuum. 3 g of 
N,N-dimethylbenzylamine are then added, the reaction mixture is heated to 
130.degree. C. and kept at this temperature for about 3 h until the 
epoxide equivalent weight (EEW) has risen to 1162. The mixture is then 
cooled and 131 g of hexylglycol, 131 g of diethanolamine and 241 g of 
xylene are then added in rapid succession. This causes a slight 
temperature rise. The reaction mixture is then cooled to 90.degree. C. and 
further diluted by the addition of 183 g of butylglycol and 293 g of 
isobutanol. When the temperature has dropped to 70.degree. C., 41 g of 
N,N-dimethylaminopropylamine are added, the temperature is kept for 3 h 
and the mixture is then discharged. 
The resin has a solids content of 70.2% and a base content of 0.97 
milliequivalents/gram. 
1.2 Preparation of a Crosslinking Agent 
1.129 g of toluylene diisocyanate (commercial mixture of isomers consisting 
of the 2,4 and 2,6 isomers) and 490 g of methyl isobutyl ketone are placed 
in a reaction vessel in an atmosphere of nitrogen. 0.6 g of dibutyltin 
dilaurate and then, in small portions, 290 g of trimethylolpropane are 
added with stirring in such a manner that with external cooling the 
internal temperature does not exceed 50.degree. C. (duration about 2 h). 
The reaction mixture is further stirred, while cooling, until the NCO 
equivalent weight has reached a value of 215. 675 g of ethylene glycol 
monopropyl ether are then added dropwise at such a rate that the internal 
temperature does not exceed 100.degree. C. The temperature is then kept at 
100.degree. C. for 1 h, the mixture is diluted with 362 g of methyl 
isobutyl ketone and 10 g of n-butanol, and after brief cooling the mixture 
is discharged. The resin has a solids content of 71.8% (1 h at 130.degree. 
C.) and a viscosity of 1.5 dPas (50% solution in methyl isobutyl ketone, 
measured in a plate-cone viscometer). 
1.3 Preparation of the Aqueous Dispersions 
1.3.1 Dispersion (I) 
915 g of resin according to procedure 1.1, 493 g of crosslinking agent 
according to procedure 1.2 and 134 g of a polyoxypropylenediamine of the 
formula 
EQU H.sub.2 N--CH(CH.sub.3)--CH.sub.2 --(--OCH.sub.2 --CH(CH.sub.3)).sub.x 
--NH.sub.2 
x=33.1 
(Jeffamine.sup.R D 2000, commercial product from Texaco Chemical Company) 
are mixed at room temperature and stirred. As soon as the solution has 
become homogeneous, 2.2 g of an antifoam solution.sup.1) and 22 g of 
glacial acetic acid are stirred in, and 674 g of deionized water are added 
in 6 portions. The mixture is then diluted with further 960 g of deionized 
water added in small portions. 
FNT .sup.1) Surfynol (commercial product from Air Chemicals), strength solution 
in ethylene glycol monobutyl ether 
The resultant aqueous dispersion is freed from low-boiling solvents by 
vacuum distillation and subsequently diluted with deionized water to a 
solids content of 33%. 
1.3.2 Dispersion (II) 
The procedure 1.3.1 is followed, except that 67 g of 
polyoxypropylenediamine are used in place of 134 g of 
polyoxypropylenediamine. 
1.3.3 Dispersion (III) 
Procedure 1.3,1 is followed, except that no polyoxypropylenediamine is 
used. After vacuum distillation a correspondingly smaller amount of 
deionized water is added in order to adjust the solids content of 33%. 
2. Preparation of a Pigment Paste 
2.1 Preparation of a Ground Resin According to DE-OS 3,422,457 
640 parts of a diglycidyl ether based on bisphenol A and epichlorohydrin 
with an epoxide equivalent weight of 485 and 160 parts of such diglycidyl 
ether with an epoxide equivalent weight of 189 are mixed at 100.degree. C. 
452 parts of hexamethylenediamine are placed in a further vessel, heated 
to 100.degree. C. and treated with 720 parts of the above hot epoxy resin 
mixture in the course of one hour, gentle cooling being necessary in order 
to keep the temperature at 100.degree. C. After a further period of 30 
minutes the excess hexamethylenediamine is removed while increasing the 
temperature and reducing the pressure, a final temperature of 205.degree. 
C. and a final pressure of 30 mbar being reached. 57.6 parts of stearic 
acid, 172.7 parts of dimeric fatty acid and 115 parts of xylene are then 
added. The water formed is then removed by azeotropic distillation at 
175.degree. to 180.degree. C. in the course of 90 min. 58 parts of 
butylglycol and 322 parts of isobutanol are then added. The product has a 
solids content of 70% and a viscosity of 2240 mPas, measured at 75.degree. 
C. in a plate-cone viscometer. 
2.2 Preparation of the Pigment Paste 
586 parts of the ground resin are thoroughly mixed with 1162 parts of 
deionized water and 22 parts of glacial acetic acid. The mixture is 
subsequently treated with 880 parts of TiO.sub.2, 250 parts of an extender 
based on aluminum silicate, 53 parts of lead silicate and 10 parts of 
carbon black. This mixture is comminuted in a grinding unit to a Hegman 
fineness of less than 12 .mu.m. Deionized water is then added in order to 
reach the required paste consistency. 
3. Preparation of Electrocoating Baths and Deposited Coatings According to 
the Invention 
700 parts of the pigment paste according to procedure 2.2 are added to 2200 
parts by weight of the dispersions according to procedure 1.3, and the 
solids content of the bath is adjusted to 20% by weight using deionized 
water. The deposition of the paint films is carried out for 2 minutes at 
300 V on phosphated metal sheet. The bath temperature is 27.degree. C. The 
films are baked at 165.degree. C. for 20 minutes. 
Electrocoating bath 1: Dispersion according to procedure 1.3.1 with paste 
according to procedure 2.2 Polyoxypropylenediamine content (based on the 
total amount of binders): 11.9% by weight 
Electrocoating bath 2: Dispersion according to procedure 1.3.2 with paste 
according to procedure 2.2 Polyoxypropylenediamine content (based on the 
total amount of binders): 6.0% by weight 
Electrocoating bath 3: Dispersion according to procedure 1.3.3 with paste 
according to procedure 2.2 Polyoxypropylenediamine content: 0% by weight 
Deposition Results 
______________________________________ 
Electrocoating bath 
1 2 3 
______________________________________ 
Film thickness (.mu.m) 
27 20 16 
Flow-out.sup.1) 
1.5 2.5 1.5 
Craters/dm.sup.2 
1 20 10 
______________________________________ 
These films were then overcoated by a commercial aqueous fuller and a white 
alkyd topcoat, and tested in a condensed water static test for 240 h. The 
adhesion of the films was subsequently tested by the crosshatch test and 
the Tesa pull-off test. 
______________________________________ 
Electrocoating bath 
1 2 3 
______________________________________ 
Adhesion.sup.1) 
0.5 0.5 0.5 
______________________________________ 
.sup.1) Rating 0-5 (good poor)