Note: Descriptions are shown in the official language in which they were submitted.
' FILE, PM!-tN THUS AM~I'Bfa
T~~ TRANSLATION
PAT 96482 12.10.1996
Electrodeposition coating material and
additive for cathodic el.ectrodeposition coating
The invention relates to a. process for preparing an
electrodeposition coating material, to an
electrodeposition coating material prepared by the
process and to its use for improving edge coverage in
connection with electrodeposition coating materials.
In electrodeposition coating, especially cathodic
electrodeposition coating (C:ED), the process concerned
is one which in recent years has been employed ever
more frequently for the coating of electrically
conductive articles, involving as it does the
electrophoretic deposition on the surface to be coated
of preferably water-thinnable synthetic resins which
carry cationic groups. CED finds preferred application
in connection with the priming of instrument casings
and car bodies.
Electrodeposition baths suitable for said utilities are
described, for example, in the following patent
documents: US-3,799,854; US-3,984,299; US-4,031,050;
US-4,252,703; US-4,332,711; DE-31 08 073; DE-27 01 220;
DE-31 03 642; DE-32 15 891; EP-0 505 445; EP-0 074 634;
EP-0 358 221.
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Resins which can be deposited electrically at the
cathode are described, for example, in US-A 3,617,458.
These are crosslinkable coating compositions which
deposit at the cathode. There coating compositions are
derived from an unsaturated polymer, which contains
amine groups and carboxyl groups, and an epoxidized
material.
US-A 3,663,389 describes cationically electro-
depositable compositions which are mixtures of certain
amine-aldehyde condensates and a large number of
cationic resinous materials, it being possible to
prepare one of these materials by reacting an organic
polyepoxide with a secondary amine and solubilizing
with an acid.
US-A 3,640,926 discloses aqueous dispersions which can
be deposited electrically at the cathode and which
consist of an epoxy resin ester, water and tertiary
amino salts. The epoxy ester is the reaction product of
glycidyl polyether and a basic unsaturated oleic acid.
The amine salt is the reaction product of an aliphatic
carboxylic acid and a tertiary amine.
Epoxy-based and polyurethane-based binders for the use
of binder dispersions and pigment pastes are disclosed,
furthermore, in numerous embodiments. By way of
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example, reference may be made to DE-27 01 002,
EP-A-261 385, EP-A-004 090 a:nd DE-C-36 30 667.
On the basis of good material yield and the substantial
renunciation of organic solvents, CED offers great
advantages over other prior art methods. A problem
which has not been solved satisfactorily to date,
however, is that of so-callE~d edge coverage, i . a . , the
production of a uniform coating even over edges or,
generally, sharp curvatures of the article to be
coated. In fact, although the electrophoretic
deposition of resin on the workpiece generally takes
place within approximately uniform, sufficient coat
thickness, the coating pul:Ls back in an undesirable
manner from the edge regions and bend regions of the
workpiece in the course of the subsequent stowing of
the coating. In order to achieve crosslinking of the
binders deposited during deposition coating it is in
fact necessary to stove the coating film subsequently
at temperatures of up to 180°C. During the heating of
the coating film, however, it initially becomes liquid
and at a certain temperature reaches its so-called
viscosity minimum. Subsequently, as the temperature
increases further, the viscosity of the applied coating
material goes up again owing to the ensuing
crosslinking of the binders. In the mobile phase in the
region of the viscosity minimum, the effect then occurs
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that the coating film, owing to surface forces, flows
away from the edges of the workpiece. This results in a
decrease in the thickness of the coating film remaining
on the edge, and in the worst case the edge is even
exposed completely.
For these reasons various measures have been used in
the attempt to raise the viscosity minimum so that the
lowest level attained by the viscosity in the course of
stowing is in any case sufficiently high to keep the
flow away from the edges, as described, within
tolerable limits. DE-43 32 014, for example, proposes
achieving such an effect by using microgels in the
electrodeposition coating material.
A disadvantage of the processes depicted, however, is
that they are relatively expensive and complicated.
Furthermore, an increase in the edge coverage is
accompanied by a deterioration in the leveling. This is
because a uniform, smooth leveling of the
electrodeposition coating film is brought about not
least by virtue of the fact that, during stowing, the
coating film liquefies and in doing so distributes
itself in a uniform manner. The above-described raising
of the viscosity minimum of the electrodeposition
coating film therefore generally results in a
deterioration in film leveling.
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In the light of the known prior art, the object of the
present invention is to achieve a considerable
improvement in the edge coverage with a simple and
cost-effective process for preparing the
electrodeposition coating materials from aqueous binder
dispersions.
This object is achieved in accordance with the
invention by adding catalysts, if desired, to the
binder dispersions comprising the electrodeposition
coating material and adding one or more aldehydes of
the formula R-CH=O or one or more compounds which
donate such aldehydes, R being a hydrogen atom or an
alkyl radical having 1-10 carbon atoms.
The aldehydes in question, accordingly, are not only
aldehydes per se but also compounds which are able to
donate aldehydes or aldehyde groups. The invention
gives particular preference i=o the use of formaldehyde.
In one form which is particularly preferred in
accordance with the invention, the aldehyde is added as
a 35-45~ strength aldehyde solution. Solutions of this
kind are obtainable commercially - in the case of the
invention's preferred formaldehyde, for example, under
the designation Formalin~. The level of aldehydes in
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the solution, or aldehyde donor compounds, is dependent
on the intended use. In principle, however, the
additives can consist of up to 100 aldehyde.
In one variant of the process of the invention, a
mixture comprising one or more aldehydes of the formula
R-CH=0 or one or more compounds which donate such
aldehydes, R being a hydrogen atom or an alkyl radical
having 1-10 carbon atoms, is prepared and stored
separately from the electrodeposition coating material.
Where the electrodeposition coating material contains
few or no compounds having amino groups, it is
preferred first of all to prepare a mixture of organic
compounds which do contain amino groups, preferably
primary amino groups, and then to add the mixture to
the binder or coating materi<~1.
The amino-containing compounds which can be employed in
the context of the invention are preferably reactive
with the aldehydes, i.e., they have primary or
secondary amino groups. If reactive amino-containing
compounds are indeed added, an improvement in the edge
coverage is based on the following relationships. In
the course of curing at relatively high temperatures, a
deposited film undergoes a reduction in its viscosity,
and does so before the crosslinking reaction has
started or sufficiently advanced. As a result, the film
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runs undesirably away from the edges in the course of
curing, owing to surface forces. The use of aldehydes
and aldehyde-reactive amino-containing compounds,
either an amino-containing binder or a different,
additional, amino-containing compound, exerts an
advantageous influence on the abovementioned time-
dependent and/or temperature-dependent development of
the viscosity in the course of curing. The amino-
containing compound and thf~ aldehyde react with one
another and the reaction product raises the viscosity
of a deposited film in t:he initial phase of the
temperature increase in the course of curing. However,
this increase in viscosity is presumably only
intermediate in nature, since as temperature increase
advances there is apparently a reduction in viscosity
(compared with the course of. viscosity when microgels,
for example, are used) with the consequence of good
leveling. This subsequent reduction in viscosity can
probably be attributed to the fact that at a further
increased temperature (and, .consequently, with further-
advanced crosslinking) the :reaction product of amino-
containing compound and aldehyde breaks down again. To
this extent, curing takes place in the following
phases: i) initial temperature increase for curing in
the deposited film, with reaction between amino-
containing compounds and aldehydes, or by means of a
reaction product thereof, and viscosity increase
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relative to the same curing sequence without addition
of aldehydes; ii) progressive curing or temperature
increase in the deposited film, with reduction in
viscosity relative to other, known viscosity-increasing
measures; iii) final curing.
The mixture then, can be added to commercially
customary deposition coating materials in an amount
which can be controlled by the user. Preferably, the
amounts are such that the aldehyde content in the
electrodeposition coating material is from 50 to
1000 ppm, preferably from 200 to 500 ppm.
The addition of the aldehydes or aldehyde mixtures of
the invention to electrodeposition coating materials
has surprising, unforeseeab=Le positive effects on the
edge coverage achieved. In connection with the
evaluation of edge coverage' quality using customary,
standardized test procedures (microscopic analysis;
climatic cycling test on phosphated metal panels:
VDA 621/415; salt spray tE:st (360 h): DIN50021 SS;
outdoor weathering with salt:: VDA 621/414), ratings in
the region of 4 (within a ratings spectrum from 0 to 5)
are obtained in accordance with the prior art, whereas
with a deposition coating material according to the
invention, using formaldehyde in the form of Formalin~,
ratings in the region of 1 to 2 are always obtained.
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Measurement of the coating film produced by using the
coating material of the invention, with formaldehyde,
gave a film thickness at the edges of from 5 to 9 dun
under conditions in which in the absence of
formaldehyde the edge coverage is nil (film thickness =
0 um) . Even with the minimtun film thickness of 5 dun,
therefore, the edge protection achieved was still
sufficient for practical purposes.
In order to improve edge protection, the aldehydes or
aldehyde mixtures of the invention, as described, can
be added in principle to ,all commercially customary
electrodeposition coating materials or binders.
Where the electrodeposition coating material contains
no catalyst, accordingly, t:he catalyst can be added
separately to the electrodeposition coating material.
The catalyst generally comprises metals, especially
heavy metals, metal compounds, or mixtures. They can
preferably be present as divalent cations in the
electrodeposition coating material. The presence of
lead has been found to be particularly advantageous in
accordance with the invention. Mixtures containing
lead, or compounds which donate lead cations, inter
alia, are suitable here. The catalysts are added in
amounts of from about 200 to 800 ppm, with particular
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preference 350-650 ppm, based on the electrodeposition
coating material.
It should be noted here that lead is often present in
pigments and under certain circumstances is therefore
already present in the electrodeposition coating
material. In this case, the added amounts of lead or
other catalysts must be matched to the lead-containing
substances already present :in the form of pigment. If
desired, the addition of catalyst can be omitted if it
is present in a suf:Eicient amount in the
electrodeposition coating material.
In the case of the preparation process described it is
essential to the invention that the electrodeposition
coating material used comprises the required compounds
having amino groups: for instance, in the form of
binders having primary amino groups. It is, however,
also possible to add the compounds which carry amino
groups to the electrodeposition coating material
separately. It is likewise possible first of all to mix
these compounds with the aldehyde - as already
described above - and then to add the reaction adduct
produced in this mixture to the electrodeposition
coating material.
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Suitable electrodeposition coating materials include
those which can be depo:>ited at the anode, but
preferably those which can be deposited at the cathode.
Examples of anodically depositable electrodeposition
binders and coating materials (AED), containing anionic
groups, which can be employed in accordance with the
invention are knov,rn and are described, for example, in
DE-A-28 24 418. For example, they comprise binders
based on polyesters, epoxy resin esters,
poly(meth)acrylates, maleate oils or polybutadiene
oils. The binders carry, for example, -COOH, -S03H
and/or P03H2 groups. Follovuing neutralization of at
least some of the acidic groups, the resins can be
transferred to the aqueous phase. The coating materials
may also include commonly employed crosslinkers,
examples being triazine resins, crosslinkers with
transesterifiable and/or t:ransamidatable groups, or
blocked polyisocyanates.
The cathodically depositablE~ synthetic resins present
in the cathodically depositable electrodeposition
coating materials can in principle comprise any aqueous
cathodically depositable synthetic resin that is
suitable for aqueous electrodeposition coating
materials. Examples of binders and crosslinkers which
can be employed in CED coating materials are described
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in EP-A-82 291, EP-p,-234 395, EP-A-209 857,
EP-A-227 975, EP-A-178 531, EP-A-333 327, EP-A-310 971,
EP-A-456 270, EP-A-261 385, EP-A-245 786, EP-A-414 199,
EP-A-476 514, DE-A-33 24 211 and US-A-3,922,253.
These electrodeposition coating materials comprise
preferably cationic, amine--modified epoxy resins as
cathodically depositable synthetic resins. Synthetic
resins of this kind are known and are described, for
example, in DE-A-35 18 770, DE-A-35 18 732,
EP-B-102 501, DE-A-27 01 002, US-A-4,104,147,
EP-A-4090, EP-A-12 463, US-A.-4,031,050, US-A-3,922,253,
US-A-4,101,486, US-A-4,038,,232 and US-A-4,017,438.
These patent documents also describe in detail the
preparation of cationic, amine-modified epoxy resins.
By cationic, amine-modified epoxy resins are meant
cationic reaction products o:E
(a) modified or unmodified polyepoxides and
((3) amines and, if desired,
(y) polyols, polycarboxyl~_c acids, polyamines or
polysulfides.
These cationic, amine-modii:ied epoxy resins can be
prepared by reaction of components (a), ((3) and, if
used, (y) along with subsequent protonation if
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required. However, it is ,also possible to react an
unmodified polyepoxide with an amine and to carry out
further modifications on the resultant amine-modified
epoxy resin.
By polyepoxides are meant compounds which contain two
or more epoxide groups in the molecule.
Particularly preferred components (a) are compounds
which can be prepared by reacting
(i) a diepoxide compound or a mixture of diepoxide
compounds having an epoxide equivalent weight of
less than 2000 with
(ii) a phenol or thiol compound which reacts
monofunctionally with respect to epoxide groups
under the given reaction conditions, or a mixture
of such compounds,
components (i) and (ii) being employed in a molar ratio
of from 10:1 to 1:1, preferably from 4:1 to 1.5:1, and
the reaction of component (i) with component (ii)
taking place at from 100 to 190°C in the presence or
absence of a catalyst (cf. Dl~-A-35 18 770).
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Further particularly preferred components (a) are
compounds which can be prepared by polyaddition of a
diepoxide compound and/or a mixture of diepoxide
compounds, alone or together with at least one
monoepoxide compound, which is conducted at from 100 to
195°C in the presence or absence of a catalyst and is
initiated by a monofunctionally reacting initiator
which carries alternatively an alcoholic OH group, a
phenolic OH group or an SH group, to give an epoxy
resin in which diepoxide compound and initiator are
incorporated in a molar ratio of more than 2:1 to 10:1
(cf. DE-A-35 18 732).
Polyepoxides which can be employed to prepare the
particularly preferred components (a) and also as
components (a) themselves a.re polyphenol polyglycidyl
ethers prepared from polyp:henols and epihalohydrins.
Polyphenols which can be employed are, for example,
with very particular preference, bisphenol A and
bisphenol F. Also suit=able, furthermore, are
4,4'-dihydroxybenzophenone, 1,1-bis(4-hydroxyphenyl)-
ethane, 1,1-bis(4-hydroxyphenyl)isobutane, 2,2'-bis(4-
hydroxy-tert-butylphenyl)propane, bis(2-hydroxy
naphthyl)methane, 1,5-dihydroxynaphthalene and phenolic
novolak resins.
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Further 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
2,2-bis(4-hydroxycyclohexyl)propane. It is also
possible to employ 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. Typical examples a.re glycidyl adipate and
glycidyl phthalate.
Also suitable are hydant:oin epoxides, epoxidized
polybutadiene, and polyepox:ide compounds obtained by
epoxidizing an olefinically unsaturated aliphatic
compound.
By modified polyepoxides are meant polyepoxides in
which at least some of the reactive groups have been
reacted with a modifying compound.
Examples of modifying compounds are the following:
- carboxyl-containing compounds, such as saturated
or unsaturated monocarboxylic acids (e. g., benzoic
acid, linseed oil fatty acid, 2-ethylhexanoic
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acid, Versatic acid), aliphatic, cycloaliphatic
and/or aromatic dicar:boxylic acids of various
chain lengths (e. g., adipic acid, sebacic acid,
isophthalic acid or dimeric fatty acids),
hydroxyalkylcarboxylic acids (e. g., lactic acid,
dimethylolpropionic acid), and carboxyl-containing
polyesters, or
amino-containing compounds, such as diethylamine
or ethylhexylamine or diamines having secondary
amino groups, e.g., N,N'-dialkylalkylenediamines,
such as dimethylethy:lenediamine, N,N'-dialkyl-
polyoxyalkyleneamines, such as N,N'-dimethyl-
polyoxypropylenediamine, cyanoalkylated alkylene-
diamines, such as bis-N, N'-cyanoethylethylene-
diamine, cyanoalkylat~sd polyoxyalkyleneamines,
such as bis-N,N'-cyanoethylpolyoxypropylene-
diamine, polyaminoamide;s, such as Versamides, for
example, especially terminal-amino-containing
reaction products of diamines (e. g.,
hexamethylenediamine), polycarboxylic acids,
especially dimeric fatty acids and monocarboxylic
acids, especially fatty acids, or the reaction
product of one mole of diaminohexane with two
moles of monoglycidyl ether or monoglycidyl ester,
especially glycidyl esters of branched fatty
acids, such as of Versat:ic acid, or
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hydroxyl-containing compounds, such a neopentyl
glycol, bisethoxylated neopentyl glycol, neopentyl
glycol hydroxypivalate, dimethylhydantoin-N,N'-
diethanol, 1,6-hexanediol, 2,5-hexanediol,
1,4-bis(hydroxymethyl)cyclohexane, 1,1-iso-
propylidenebis(p-phenoxy)-2-propanol, trimethylol-
propane, pentaerythritol or amino alcohols, such
as triethanolamine, methyldiethanolamine or
hydroxyl-containing a:Lkyl ketimines, such as
aminomethyl-1,3-propanediol methylisobutyl
ketimine or tris(hydroxymethyl)aminomethane
cyclohexanone ketimine, and also polyglycol
ethers, polyesterpo:lyols, polyetherpolyols,
polycaprolactonepolyols and polycaprolactampolyols
of various functionality and molecular weights, or
- saturated or unsaturated fatty acid methyl esters
which are transesterified with hydroxyl groups of
the epoxy resins in the presence of sodium
methoxide.
Primary and/or secondary amines can be employed as
component ( (3 ) .
The amine should preferably be a water-soluble
compound. Examples of such amines are mono- and
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dialkylamines, such as methylamine, ethylamine,
propylamine, butylamine, d_imethylamine, diethylamine,
dipropylamine, methylbutylamine and the like. Likewise
suitable are alkanolamines, such as methylethanolamine,
diethanolamine and the like, for example. Also suitable
are dialkylaminoalkylamines, such as, for example,
dimethylaminoethylamine, diethylaminopropylamine,
dimethylaminopropylamine and the like. It is also
possible to employ amines which contain ketimine
groups, such as, for example, the methyl isobutyl
diketimine of diethylenetriamine. In the majority of
cases use is made of amin~=s of low molecular mass,
although it is also possib7_e to employ monoamines of
higher molecular mass.
The amines may also include other groups as well,
although these should not interfere with the reaction
of the amine with the epoxide group and should also not
lead to gelling of the reaction mixture.
It is preferred to employ secondary amines as component
((3) .
The charges required for water thinnability and
electrodeposition can be generated by protonation with
water-soluble acids (e. g., boric acid, formic acid,
lactic acid, preferably acetic acid). A further
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possibility for introducing cationic groups is to react
epoxide groups of component (a) with amine salts.
As component (y), use is made of polyols,
polycarboxylic acids, polyaunines or polysulfides, or
mixtures of these classes of substance. The polyols
which are suitable include diols, triols and higher
polymeric polyols, such as polyesterpolyols and
polyetherpolyols. For further details and further
examples of suitable components (y) reference may be
made to EP-B2-301 293, especially page 4 line 31 to
page 6 line 27.
The cathodically depositabl~~ synthetic resins present
in the electrodeposition coating materials are
generally either self-crossl.inking and/or are combined
with a crosslinking agent: or with a mixture of
crosslinking agents.
Self-crosslinkable synthetic' resins are obtainable by
introducing into the synthetic-resin molecules reactive
groups which react with one another under stowing
conditions. For example, in hydroxyl- and amino-
containing synthetic resins, blocked isocyanate groups
can be introduced which deblock under stowing
conditions and react with the hydroxyl and/or amino
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groups to form crosslinked coating films. Self-
crosslinkable synthetic resins can be obtained, for
example, by reacting a hydroxyl- and/or amino-
containing synthetic resin with a partially blocked
polyisocyanate containing on average one free NCO group
per molecule.
The electrodeposition coating materials can in
principle include any crosslinking agent suitable for
electrodeposition coating materials, examples being
phenolic resins, polyfunctional Mannich bases, melamine
resins, benzoguanamine resins, blocked polyisocyanates,
and compounds containing activated ester groups. The
electrodeposition coating materials preferably comprise
blocked polyisocyanates as crosslinking agents. The use
of blocked polyisocyanates in electrodeposition coating
materials comprising cathodically depositable synthetic
resins has been known for a long time and is described
in detail, inter alia, in the patent documents cited
above, as for example in EP--B2-301 293, page 6 line 38
to page 7 line 21.
The electrodeposition coating materials of the
invention are prepared by methods which are common
knowledge. The cathodically depositable binders are
synthesized by well-known methods (cf. e.g.,
DE-C-27 Ol 002 and the like;l in organic solvents. The
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binder solutions or disper~~ions obtained in this way
are transferred in neutra:Lized form to an aqueous
phase.
In addition to the components described above, the
aqueous electrodeposition coating materials of the
invention may also include further customary coatings
constituents, such as, for .example, pigments, fillers,
wetting agents, leveling agents, polymer
microparticles, antifoams, anticrater additives,
catalysts, etc.
The solids content of the electrodeposition coating
materials of the invention is generally from 5 to 40,
preferably from 10 to 40 and, with particular
preference, from 20 to 40 percent by weight.
The nonvolatiles content of the electrodeposition
coating materials of the invention comprises from ...
to ..., preferably from ... to ...~ by weight of an
electrophoretically depositable binder or a mixture of
electrophoretically depositable binders, from 0 to ...,
preferably from ... to ...~ by weight of a crosslinking
agent or a mixture of different crosslinking agents,
and from ... to ..., preferably from ... to ...~ by
weight of pigments and/or fi:Llers.
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Pigments are preferably incorporated in the form of a
pigment paste into the aqueous binder solution or
binder dispersion. The preparation of pigment pastes is
common knowledge and need not be discussed further here
(cf. D.H. Parker, Principles of Surface Coating
Technology, Interscience Publishers, New York (1965)
etc.).
To prepare the pigment pastes, epoxy-amine adducts
containing quaternary ammonium groups, for example, are
employed. Examples of suitable resins are also
described, for example, in EP-A-183 025 and
EP-A-469 497.
The pigment pastes can in principle comprise any
pigments and/or fillers that are suitable for
electrodeposition coating materials, examples being
titanium dioxide, zinc oxide, antimony oxide, lead
sulfate, lead carbonate, barium carbonate, porcelain,
clay, potassium carbonate, aluminum silicate, silicon
dioxide, magnesium carbonate and magnesium silicate,
cadmium yellow, cadmium red, carbon black,
phthalocyanine blue, chromiu~,m yellow, toluidyl red and
iron oxides, and also anticorrosion pigments, such as,
for example, zinc phosphate, lead silicate, or organic
corrosion inhibitors.
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Furthermore, the electrodeposition coating materials
can also comprise customary additives, such as, for
example, the homopolymers or copolymers of an alkyl
vinyl ether that are described in EP-B2-301 293 (cf.
EP-B2-301 293, page 7 lines 21 to 51), polymer
microparticles, anticrater agents, wetting agents,
leveling agents, antifoams, catalysts and the like in
customary amounts, preferably in amounts from ... to
...$ by weight, based on the overall weight of the
electrodeposition coating material.
The electrodeposition coating materials of the
invention can be used for coating electrically
conductive substrates, where
(1) the electrically conductive substrate is immersed
in an aqueous electrodeposition coating material,
(2) the substrate is connected as one electrode,
(3) a film is deposited on the substrate by means of
direct current,
(4) the coated substrate is removed from the
electrodeposition coating material, and
(5) the deposited coating film is stowed.
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The process described above is known and has already
been widely used for many years (compare also the
above-cited patent document~~). The applied voltage can
vary within a wide range and can, for example, be
between 2 and 1000 V. Typically, however, voltages of
between 50 and 500 V are employed. The current density
is generally between about 10 and 100 A/m2. In the
course of deposition the current density tends to drop.
As soon as the coating film has been deposited on the
substrate, the coated substrate is removed from the
electrodeposition coating material and rinsed.
Subsequently, the deposited coating film is stowed. The
stowing temperatures are usually from 130 to 200°C,
preferably from 150 to 180°C, and the duration of
stowing is generally between 10 and 60 minutes,
preferably between 15 and 30 minutes.
The process described above can be used in principle to
coat any electrically conductive substrate. Examples of
electrically conductive substrates are, in particular,
substrates of metal, such as steel, aluminum, copper
and the like. In particular, motor vehicle bodies and
parts thereof are coated in accordance with the
invention with the electrodeposition coating materials
in question. The electrodeposition coating materials
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are preferably used for priming in the context of a
multicoat paint system.
Using two examples, the text below describes the
preparation of cathodic electrodeposition coating
materials:
Example 1:
The example which follows :shows the preparation of a
cationic resin comprising primary amino groups.
Bisphenol A, bisphenol A diglycidyl ether and a
bisphenol A-ethylene oxide adduct are heated together
and form a modified polyepoxy resin. A blocked
isocyanate is added as crosslinker. This is followed by
a reaction with a mixture of secondary amines. The
resin is partially neutralized with lactic acid and is
dispersed in water.
Ingredients Parts by weight
Epikote 8281 682.4
Bisphenol A 198.4
Dianol 2652 252.7
Methyl isobutyl ketone 59.7
Benzyldimethylamine 3.7
Blocked isocyanate3 1011.3
Diketimine4 65.4
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Methylethanolamine 59.7
1-Phenoxy-2-propanol 64.8
Lactic acid 88~ 60.9
Emulsifier mixtures 15.2
Demineralized water 3026.6
1 Liquid epoxy resin prepared by reacting bisphenol A
and epichlorohydrin, having an epoxide equivalent
weight of 188 (Shell Chemicals)
2 Ethoxylated bisphenol A having an OH number of 222
(Akzo)
3 Polyurethane crosslin.ker prepared from
diphenylmethane diisocyan<~te, where, of 6 moles of
isocyanate, 4.3 are first reacted with butyldiglycol
and the remaining 1.'7 mol are reacted with
trimethylolpropane. The crosslinker is present in the
form of an 80~ strength :solution in methyl isobutyl
ketone and isobutanol (weight ratio 9:1)
4 Diketimine from the reaction of diethylenetriamine
and methyl isobutyl ketone, 75~ strength in methyl
isobutyl ketone
5 Mixture of 1 part of buty:Lglycol and 1 part tertiary
acetylene glycol (Surfynol 104; Air Products)
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The Epikote 828, bisphenol A and Dianol 265 are heated
to 130°C in a reactor under- nitrogen blanketing. Then
1.6 parts of the benzyldirnethylamine (catalyst) are
added, and the reaction mixture is heated to 150°C,
held between 150 and 190°C for about half an hour and
then cooled to 140°C. Subsequently, the remainder of
the benzyldimethylamine is added and the temperature is
held at 140°C until, after about 2.5 h, an epoxide
equivalent weight of 1120 is established. Directly
thereafter, the polyurethanes crosslinker is added and
the temperature is lowered i.o 100°C. Subsequently, the
mixture of the secondary amines is added and the
reaction is maintained at 1.15° for about 1 h until a
viscosity of about 6 dPas is reached (50~ dilution in
methoxypropanol, ICI cone and plate viscometer).
Following addition of the phenoxypropanol, the resin is
dispersed in the water, in which the lactic acid and
the emulsifier mixture are present in dissolved form.
The desired primary amino groups form from the ketimine
adduct by hydrolysis.
Following this step, the :>olids content is 35~ but
increases to 37~ after the low-boiling solvents have
been stripped off.
The dispersion is characterized by a particle size of
about 150 nm.
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Example 2:
This example shows the preparation of an aqueous
dispersion comprising a cathodically depositable
synthetic resin and a crosslinker:
In a reactor, 589 parts of epoxy resin based on
bisphenol A, having an epox:ide equivalent weight (EEW)
of 188, together with 134 parts of bisphenol A and
108 parts of nonylphenol, a:re heated to 125°C under a
nitrogen atmosphere and stirred for 10 minutes. The
mixture is subsequently heated to 130°C and 2.3 parts
of N,N-dimethylbenzylamine are added. The reaction
mixture is held at this temperature until the EEW has
reached the level of 851 g%eq. Then 723 parts of the
crosslinker (80~ strength; blocked isocyanate, see
Example 1) are added. Half an hour after the addition
of the crosslinker, a mixt=ure of 21 parts of butyl
glycol and 102 parts of sec,-butanol is added and the
mixture is maintained at 95°C. Subsequently a mixture
of 50 parts of methylethanolamine and 48 parts of
precursor diketimine (cf. Example 1: diethylenetriamine
diketimine in methyl isobutyl ketone) is introduced
into the reactor. The reaction mixture warms up
(exothermic reaction) and i.s held at 100°C. After a
further half an hour, 1.5 parts of N,N-dimethyl-
aminopropylamine are added to the reaction mixture.
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Half an hour after the commencement of the addition,
93 parts of Plastilit 3060 (propylene glycol compound
from BASF), 52 parts of prc>pylene glycol phenyl ether
and 20 parts of sec-butanol .are added.
The mixture is cooled to 80°C and, after 10 minutes
more, 1327 parts of the reaction mixture are
transferred to a dispersing vessel. In that vessel,
45 parts of lactic acid (88~ strength in water) in
728 parts of deionized wat~=r are added in portions,
with stirring. The mixture is subsequently homogenized
for 20 minutes before being diluted further with an
additional 1400 parts of deionized water in small
portions.
The dispersion has the following characteristics:
Solids content: 30~ (1 h at 130°C)
Base content: 0.68 milliequivalent/g solids
Acid content: 0.3'7 milliequivalent/g solids
Example 3
300 ppm of formaldehyde in the form of the commercially
customary 37~ strength Formalin solution are added to a
cathodically depositable electrodeposition bath in
accordance with Examples 1 and 2, and stirred in for
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between 2 and 20 h. Following the reaction time, bright
steel panels ST 1405 and phosphated steel panels Bo 25
are subjected to deposition and stowing in the
customary manner.
The edge coverage can be determined using an edge
quality measuring instrument. The isolation ability of
the edge from an untreated C:ED bath is 10-20~. Through
the addition of formaldehyde, this figure increases to
about 90~, i.e., the edge is almost fully covered. This
is confirmed by the ASTM corrosion test. ST 1405 panels
were exposed for 360 h and showed an improvement in
edge corrosion rating from 5 to 1-2.
Example 4;
In a procedure similar to that of Example 3, the same
cathodically depositable electrodeposition coating
material is admixed with 500 ppm of a hemiacetal formed
from formaldehyde and urea or butanediol, and
deposition is carried out following the reaction time
of one day. In the weakly acidic medium, the hemiacetal
is cleaved and reactive formaldehyde is liberated.
Similar results are obtained. An edge quality figure of
90-100 is obtained. In addition, the ASTM corrosion
ratings at the edge are improved from 5 to 1.
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