PHOTOCURABLE CATHODIC ELECTROCOATING

ELECTRODEPOSITION CATHODIQUE D'UN PRODUIT PHOTOCURABLE

English Abstract

A B S T R A C T
An electrocoating composition containing a polymer having pendant
amine groups, an alpha-, beta- ethylenically unsaturated carbonyl cross-
linking agent, and an ultraviolet photosensitizer can be electrodeposited
onto a cathode substrate disposed within an aqueous electrocoating bath.
The amine groups of the polymer are protonated to render the polymer water
dispersible prior to electrodeposition and upon electrodeposition the amine
groups become de-protonated. The cross-linking agent cross-links the polymer
upon ultraviolet irradiation of the electrocoated cathode substrate for form
a fully-cured electrodeposited coating on the cathode substrate.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for the electrodeposition of an electrocoating composition
onto a cathode substrate to form a curable coating on said cathode substrate,
which comprises: cathodically electrodepositing said electrocoating compo-
sition onto said cathode substrate under cathodic electrocoating conditions,
said electrocoating composition comprising: a water-dispersed electrocoating
polymer having at least about 5% by weight pendant amine groups, each said
amine group being attached to an alpha carbon relative to each said amine
group, at least about 5% by weight of said polymer of an alpha-, beta-ethylenic-
ally unsaturated carbonyl cross-linking agent having at least two alpha-,
beta-ethylenically unsaturated carbonyl groups, and at least about 0.5% by
weight of said polymer of an ultraviolet photosensitizer; and irradiating said
curable coating on said cathode substrate with ultraviolet radiation to cross-
link said alpha carbon of said amine groups of said polymer with said cross-
linking agent to cure said coating.
2. The electrodeposition process of claim 1 wherein each said alpha-,
beta-ethylenically unsaturaged carbonyl group of said cross-linking agent is
represented by the following general structure:
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and each said group is pendantly attached to a radical selected from the
group consisting of an alkyl, an aryl, an alkyl-aryl, and polymers having a
molecular weight up to about 3,000.
3. The electrocoating process of claim 1 wherein said electrocoating
polymer is rendered water-dispersible by protonating said amine groups with
proton-donating acid and said protonated amine groups become deprotonated by

electrodeposition of said polymer having protonated amine groups onto said
cathode substrate.
4. An uncured electrocoated cathode substrate having an ultraviolet
radiation curable coating thereon of the electrocoating composition of
claim 1.
5. A cathode substrate prepared by the process of claim 1.
6. A process for the electrodeposition of an electrocoating composition
dispersed in an aqueous electrocoating bath onto a cathode substrate disposed
within said bath to form a curable electrodeposited coating on said cathode
substrate, which comprises: cathodically electrodepositing said electrocoat-
ing composition onto said cathode substrate under cathodic electrocoating
conditions, said electrocoating composition comprising: a water-dispersed
electrocoating polymer having at least about 5% by weight pendant amine groups,
each said amine group being attached to an alpha carbon relative to each said
amine group, at least about 5% by weight of said polymer of an acrylate cross-
linking agent having at least two pendant acrylate groups, and at least about
0.5% by weight of said polymer of an ultraviolet photosensitizer; and irradi-
ating said curable coating on said cathode substrate with ultraviolet radiation
to cross-link said alpha carbon of said amine groups of said polymer with
said cross-linking agent to cure said coating.
7. A process for the electrodeposition of an electrocoating composition
dispersed in an aqueous electrocoating bath onto a cathode substrate disposed
within said bath to form a curable electrodeposited coating on said cathode
substrate, which comprises: cathodically electrodepositing said electrocoat-
ing composition onto said cathode substrate under cathodic electrocoating
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conditions, said electrocoating composition comprising: a water-dispersed
electrocoating polymer having at least about 5% by weight pendant amine groups,
each said amine group being attached to an alpha carbon relative to each said
amine group, at least about 5% by weight of said polymer of an acrylamide
cross-linking agent having at least two pendant acrylamide groups, and at
least about 0.5% by weight of said polymer of an ultraviolet photosensitizer;
and irradiating said curable coating on said cathode substrate with ultra-
violet radiation to cross-link said alpha carbon of said amine groups of said
polymer with said cross-linking agent to cure said coating.
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Description

~ ~Sfi~
This invention relates to electrodeposition of water-dispersed
polymers onto a cathode substrate and more particularly to cross-linking said
electrodeposited polymers with alpha-, beta-ethylenically unsaturated
carbonyl.
United States Patent ~o. 3,975,251 of applicant, Vincent D.
~cGinniss, describes an electrocoating composition of a polymer having pendant
amine groups and an alpha-, beta ethylenically unsaturated carbonyl cross-
linking agent. The electrocoating composition is electrodeposited onto a
cathode substrate and heat cured.
rhe present invention is directed to an electrocoating process
which utilized the ethylenically unsaturated cross-linking agent for curing
a polymer which has been electrodeposited onto a cathode substrate and where
the ethylenically unsaturated carbonyl cross-links the polymer upon ultra-
violet irradiation of the electrocoated cathode substrate.
According to the present invention, there is provided a process
for electrodeposition of an electrocoating composition onto a cathode substrate
to form a curable electrodeposited coating on said cathode substrate, which
comprises:
cathodically electrodepositing said electrocoating composition
onto said cathode substrate under cathodic electrocoating conditions~ said
electrocoating composition comprising (a) a water-dispersed electrocoating
polymer having at least about 5% by weight pendant amine groups, each said
aminc group being attached to an alpha carbon relative to each said amine
group, (b~ at least about 5% by weight of said polymer of an alpha-, beta-
ethylenically unsaturated carbonyl cross-linking agent having at least two
alpha-, beta-ethylenically unsaturated carbonyl groups, ~c) at least about
0.5% by weight of said polymer of an ultraviolet photosensitizer; and
irradiating said curable coating on said cathode substrate with ultraviolet

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radiation to cross-link said cross-linking agent with said alpha carbon to cure
said coating. According to a further aspect of the present invention there is
provided a cathode substrate when prepared by the above process.
The elec*rocoating composition contains an electrocoating polymer or
resin selected according to final desired use from a wide variety of known poly-
mers in the electrocoating art.
The polymers contain pendant amine groups. The amine groups can be
primary, secondary, or tertiary for present purposes. By protonating such amine
groups, the polymer can be water dispersed. Electrodeposition of the polymer de-
protonates the amine groups. Amine groups can be attached to the polymer by re-
acting free carboxyl groups on a polymer (polyester, acrylic, urethane, etc.)
containing available carboxyl groups with alkyleneimine or substituted alkylenei-
mine, as proposed in United States 3,679,564 and United States 3,617,458. Simi-
larly, amine groups can be introduced into the polymer by reacting pendant car-
boxylic acid groups on a polymer with ethylene imine or derivatives of ethylene
imine. Difunctional amines also can be reacted with reactive pendant carboxyl
groups on the polymer.
Blocked amines also can be attached to the polymer and, if desired,
subsequently transformed into primary amine groups by an appropriate reaction
which will be outlined in detail later herein. Such blocked amine groups can
be attached to epoxy resins or acrylic resins having pendant oxirane groups by
reacting a ketimine blocked diethylene triamine, formed from reacting diethylene
triamine with an excess of methyl ethyl ketone, with the polymer. Other similar
blocked dialkyltriamines also can be employed to attach the blocked amine groups.
The amine groups are pendantly attached to the polymer. For purposes
of this application, pendant amine groups include terminal amine groups. By
pendantly attached is meant that such amine groups are attached to the polymer
chain or to a pendant side chain of the polymer. The polymer containing

~31 1.S~
pendant amine groups should contain at least about 5% by weight of such
pendant amine groups, and up to about 50% is d0sired.
Representative polymers containing pendant amine groups can be
derived from epoxy and epoxy-modified diglycidyl ethers of bis-phenol A
structures, various aliphatic polyethylene or polypropylene glycol (diglycidyl
ether) adducts, and glycidyl ethers of phenolic resins, such epoxy resins
being commercially available and commonly used in the electrocoating field.
Other useful polymers containing pendant amine groups include polyamide resins,
for example, condensation products of dimerized fatty acids coreacted with
difunctional amine, such as ethylene diamine. Polyamide resins generally
are between about 500 and about 5,000 molecular weight. Further useful
electrocoating polymers containing pendant amine groups include acrylic
resins having molecular weight of about 1,000 to about 100,000, polyester
re~sins and polyurethane resins both having a molecular weight range of about
SOO to about 5,000, vinyl resins, and amine resins. Various other useful
electrocoating polymers containing pendant amine groups can be advantageously
employed in the composition of this application as will be apparent to those
skilled in the art.
The cross-linking agent is an alpha-, beta-ethylenically unsaturated
carbonyl having alpha-, beta-ethylenic unsaturation capable of being reactive
to cross-link the polymer. The unsaturated cross linking agent has at least
two pendantly attached alpha-, beta-ethylenically unsaturated carbonyl groups
of the following general structure:
o
C - CH CH2
~ach unsaturated carbonyl group is pendantly attached to a radical selected
from the group consisting of an alkyl3 an aryl, an alkyl-aryl, and polymers
having a molecular weight up to about 3,000. Pendantly attached unsaturated

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carbonyl groups are attached to the radical chain or to a said chain of the
radical.
Preferably, the unsaturated carbonyl groups are attached to an
oxygen molecule and are represented by the following general structure:
0 C - CH C~2
A preferred unsaturated cross-linking agent then is a multi-acrylate having
at least two pendant acrylate groups. Specific preferred cross-linking
agents which are particularly suited to the precepts of this invention can be
selected from the group consisting of: ethylene glycol diacrylate, ethylene
glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, bisphenol A
dimethacrylate, diethylene glycol diacrylate, pentaerythritol triacrylate,
pentaerythritol tetraacrylate, trimethylolpropane triacrylate, triethylene
glycol dimethacrylate, tetraethylene glycol dimethacrylate, tetraethylene
glycol diacrylate, 1,6-hexanedioldiacrylate, melamine acrylate, ethoxylated
bisphenol A dimethacrylate, pentaerythTitol tetramethacrylate, and polyethylene
glycol dimethacrylate.
The preferred unsaturated cross-linking agents can be synthesi7ed
by various methods, such as reacting hydroxyl-containing compounds with acrylyl
chlorides or methacrylyl chlorides, direct esterification of hydroxyl-con-
taining compounds with ethylmethacrylate, methylmethacrylate and the like.The preferred unsaturated cross-linking agents also can be produced by the
transesterification of esters or polyesters with 2-hydroxyethylacrylate,
2-hydroxyethylmethacrylate, hydroxypropylmethacrylate and the like. The
preferred unsaturated cross-linking agents can be produced additionally by
reacting diisocyanates, polyisocyanates, or isocyanate-terminated polymers
and prepolymers with hydroxyl-containing acrylic and methacrylic esters such
as, for example, 2-hydroxyethylacrylate or hydroxypropylmethacrylate; by

1~ 15~5~
reacting epoxy polymers with acrylic acids or methacrylic acids; and by
reacting carb~xyl-containing compounds with glycidyl acrylates or glycidyl
methacrylates. Further useful unsaturated cross-linking agents include
acrylamides, vinyl ketones, and the like.
The unsaturated cross-linking agent cross-links the polymer upon
irradiation of the electrocoated cathode substrate with ultraviolet radiation
in the presence of a photosensitizer. The reaction mechanism is a free
radical addition polymerization involving the linking of the unsaturation of
the cross-linking agent with the alpha carbons of the pendant amine groups
of the polymer. By alpha carbon of the pendant amine groups is meant the
carbon in the alpha position relative to the amine group and to which the
pendant amine group is attached.
The UV sensitizers are c-ombined with the electrocoating composition
and are adapted to be simultaneously co-deposited with the composition onto
the cathode substrate during the electrodeposition process. The UV
sensitizers are added to the electrocoating composition in amounts of at
least about 0.5% and preferably between about 1% and 5% by weight of the
polymer.
Useful UV sensitizers of photosensitizers include halogenated
polynuclear ketones as disclosed in United States Patent ~,039,41~
and United States patent 3,827,957. Other suitable UV sensitizers
include organic carbonyl compounds selected from alkylphenones, benzophenone~"
and tricyclic fused ring compounds as disclosed in United States patent
3,759,807. Purther useful UV sensitizers include carbonylated phenyl nuclear
sulfonyl chlorides such as set forth in United States patent 3,827,959.
Additional useful photosensitizer combinations particularly suitable for
pigmented coatings are a combination of sensitizers comprising aromatic
carbonyl compounds, aromatic aldehydes or aromatic ketones, and a synergistic
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sensitizer of about 0.05% to 3% of 2,2'-dithiobis-~benzotKiazole~ as more
particularly set forth in United States patent 3,847,7710 At least about
0.5% by weight of ultraviolet sensitizer and preferably about 1% to 5%
sensitizer is added to the polymer and thoroughly mixed or otherwise dis-
persed in the polymer phase prior to solubilizing the polymer in an aqueous
solution.
In practicing this invention, the polymer is rendered water dis-
persible by adding sufficient acid to the polymer to completely neutralize
the polymer. Appropriate acids are, for example, proton-donating acids such
as phosphoric, sulfuric, hydrochloric, acetic, formic, lactic, and other
proton donating organic and inorganic acids. Water solubility is achieved
by the protonating of all amine groups of the polymer by the acid. The
protonating of the amine groups of the polymer also renders the polymer
positively charged so that during electrodeposition the polymer can migrate
to the cathode substrate and be deposited thereon
The neutralized polymer and UV sensitizer are blended with at
least about 5% of the cross-linking agent by weight of the polymer and up to
about 25% if desired. The blend then is dispersed in water to form the
electrocoating bath of from about 5 to 20% non-volatile dispersion. The bath
is generally about 50 to about 125F., with about 70 to about 95F. being
preferred.
The neutralized (protonated)polymer and cross-linking agent are
both stable in the bath. The cathode substrate to be electrocoated then
is immcrscd in the electrocoating bath while an electric potential is
maintained therethrough as disclosed in United States 3,169,398. During
electrodeposition the positively charged polymer along with cross-linking
agent and the UV sensitizer migrate to the cathode substrate. The protonated
amine groups of the polymer become de-protonated (lose protons) due to the
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electric potential applied. The polymer, the cross-linker, and the W sensitizer
are co-deposited on the cathode substrate. The electric potential applied to the
bath is generally between about 20 and about 500 volts, with about 50 to about
300 volts being preferred. The coated substrate is removed from the bath and
can be washed with water to remove excess coating. The electrodeposited coating
on the cathode substrate is cured with ultraviolet radiation in the presence of
the ultraviolet (W) sensitizer or photosensitizer.
Typical sources of ultraviolet energy ordinarily produce wavelengths
i~ the ultraviolet spectrum that are transmitted through a quartz and such wave-
o o
lengths are usually between about 1,000 A and 4,000 A. Suitable ultraviolet
emittors include various electric arc lamps, plasma arc torch, such as described
in United States Patent 3,364,487, and laser having a lasing output in the ultra-
violet spectrum. Other suitable sources of actinic light include quartz mercury
larnps, ultraviolet quartz lamps, and high flash lamps. Details of ultraviolet
radiation curing the instant electrocoating composition can be as practiced in
United States Patent 4,039,414.
The cathode substrate is an electrically conductive metal such as
iron, steel, aluminum, copper, galvanized steel, zinc, and the like. The cathode
substrate can be in the shape of bars, sheets, irregularly shaped forms with
rounded or sharp edges, and like shapes. The electrocoating composition can
contain opacifying pigments and inert extenders such as, for example, titaniurn
dioxide, zinc oxide, clays such as kaolinite clays, silica, talc, and the like.
Ihe following examples show how the instant invention can be prac-
ticcd, but should not be construed as limiting the invention. In the specifica-
tion all parts are parts by weight, all percentages are weight
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percentages, and all temperatures are in clegrees Fahrenheit, unless
otherwise expressly indicated.
EXAMPLE
A solution acrylic polymer was conventionally prepared by reacting
methyl methacrylate ~290 parts per weight, ppw), ethyl acrylate (230 ppw),
butyl methacrylate (320 ppw), 2-hydroxyethylacrylate (20 ppw), and diethyl-
B amine-ethylmethacrylate (140 ppw) in 2-butoxy ethanol-l solvent (500 ppw)
for six hours in the presence of benzoyl peroxide and VAZO 64 catalysts.
The resulting acrylic polymer having pendant amine groups was
blended with 2-chlorothiozanthone photosensitizer and 20% of pentaerythri-
toltriacrylate cross-linking agent. The blend was neutralized with acetic
acid and dispersed in deionized water to form a 10% non-volatile electro-
coating bath.
The resulting electrocoating composition was cathodically electro-
deposited onto a s1eel panel at 100 volts for 30 to 60 seconds, removed from
the bath, and washed ~ith water. The electrocoated panel then was covered
with a thin polyethylene sheet, placed under an 800 watt medium pressure
mercury lamp (ultraviolet radiation souTce), and irradiated for 30 minutes.
A hard, flexible, solvent-resistant coating covered the panel.
EXAMPLE 2
One mole of an epoxy resin (DER 664, epoxy equivalent weight of
900, Dow Epoxy Resin, Dow Chemical Company) was reacted at 60 C. with two
moles of ketimine blocked diethylene triamine represented by the following
structure:
CH2CH2N = C C CH3
/ CH2 3
HN
\ CH2CH2N = C C CH3
C 2 3'
1r~ ~ DÆ /~ t~ - 8 -

completely neutralized with 4 moles of lactic acid, and blended with 20%
melamine acrylate ~acrylate functionality of 2.7) cross-linking agent with
10% benzophenone photosensitizer. The blend was added to 2-butoxy ethanol-l
and deionized water to form a 7% non-volatile (solids) dispersion.
This electrocoating composition was cathodically electrodeposited
at 100 volts for one minute onto a steel panel, removed from the bath, and
washed with water.
The coating then was heated at 200F., for 10 minutes to flow-out
the coatingO Some cure of the coating resulted due to the pendant amine
groups of the polymer linking with the cross-linking agent.
Full cure of the coating was obtained by placing a thin film of
polyethylene over the coated panel and irradiating the coated panel for ]0
minutes under an 800 watt medium pressure mercury lamp.
EXAMPLE 3
The cathodic electrocoating compositionsoof Examples 1 and 2 each
were prepared again, except that the ultraviolet photosensitizer system used
for each was 1% Michler's Ketone, 5% benzophenone, and 3% 2,2'-dithiobis
(benzothiazole).
Each composition was cathodically electrocoated and cured by
exposure to ultraviolet irradiation in the same manner as described in Examples
1 and 2 above. A fully cured, hard, flexible, solvent-resistant coating resulted
upon curing.