CA1100654A - Cathodic electrocoating composition and process - Google Patents

Abstract

Abstract of the Disclosure A cathodic electrocoating composition containing polymer having pendant amine groups, mercaptan groups and/or combinations thereof, and a bis-maleimide cross-linking agent. Specific electrocoating compositions can be owned by heat, electron beam, or ultraviolet radiation in the presence of an ultraviolet photosensitizer.

Description

~ ~a6~

This invention relates to electrodepositlon of water-dispersed polymers onto a cathode substrate and more particularly to cross-linking of the polymers with a reactive bis-maleimide cross-linking agent.
Several processes foT electrodeposition of heat-curable electro-coating polymers onto a cathode substrate disposed in an aqueous electro-coating bath have been suggested. For example, United States Patent 3,617,~58 discloses an electrocoating epoxy polymer having pendant amine groups which are neutralized with an inorganic acid to render the polymer wa-ter soluble.
The epoxy polymer also contains pendant carboxyl groups which cross-link with the epoxide (oxirane) group of an epoxy resin upon heating to form a cured coating on a cathode substrate. Others have similarly suggested solu-bilizing through amine groups.
It has now been found that a bis-maleimide cross-linking agent cures a coating which has been electrodeposited onto a cathode substrate.
The polymers contain tertiary amine groups, mercaptan groups and/or combina-tions thereof and specific polymers can be cured by heating, exposure to electron beams (ionizing radiation) 3 or ultraviolet irradiation in the pre-sence of an ultraviolet photosensitizer.
According to the invention, there is provided a process for the electrodeposition of an electrocoating composition in aqueous dispersion onto a cathode substrate disposed within an aqueous electrocoating bath to form a curable coating on said cathode substrate which comprises: catho-dically 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 groups selected from tertiary amine groups, mercaptan groups, and combinations thereof, and ~b) at least about 5% by weight of said polymer of bis-maleimide as a cross-linking agentJ and curing said curable coating o-n said cathode substrateJ said cross-linking agent cross-linking said polymer by additional polymerization to form a cured coating on said cathode provided that when said polymer contains amine .

6~

groups the electrocoating coJnposition also contains at least about 0.5%
by weight of said polymer o:E an ultraviolet photosensitizer and said curing is by ultraviolet radiation.
A preferred embodiment of the invention provides a process for electrodeposition of an electrocoating composition dispersed within an aqueous electrocoating bath onto a cathode substrate disposed within said bath to form an electrodeposited coating on said cathode substrate, which comprises: cathodically electrodepositing said e:Lectrocoating composition onto said cathode substrate under cathodic electrocoating conditions, said electrocoating composition comprising: (a) a water-dispersed electro-coating polymer having at least about 1% by weight pendant mercaptan groups;
~b) a water-dispersed electrocoating polymer having at least about 1% by weight pendant tertiary amine groups, each said amine group being attached to an alpha carbon of said polymer; (c) at least about 5% by weight of said polymers of bis-maleimide as a cross-lin~ing agent, and (d) at least about 0.5% ultraviolet photosensitizer by weight of said polymers, said pendant tertiary amine groups and said pendant mercaptan groups together comprising at least about 5% by weight of both said polymers; and curing said electro-deposited coating on said cathode substrate by heating said electrodeposited coating on said cathode substrate to cross-link said polymer having pendant mercaptan groups with said cross-linking agent to partially cure saicl coat-ing, followed by irradiating with ultraviolet radiation said partially cured coating to cross-link with said alpha carbon oE said polymer having pendant ter~iary amine groups with said cross-linking agent to fully cure said coating on said cathode substrate.
The present invention also provides a cathodic electrocoating composition dispersed in an aqueous electrocoating bath for electro-deposition onto a cathode substrate disposed with said bath for forming a curable electrodeposited coating on said cathode substrate, comprising:
(a) a water-dispersed electrocoating polymer having at least about 5~ by weight pendant groups selected from tertiary amine groups,

- 2 -mercap~an groups and combinations thereof; and ~ b) at least about 5% by weight of said polym~r of bis-maleimide as a cross-linking agen~; provided tha~ when said polymer only contains tertiary amine groups the compositlon also contains at least about 0.5% by weight of said polymer of an ultraviolet photosenslti~er for curing the composition by ultraviolet radiation.
The electrocoating composition contains electrocoating polymer or polymers selected according to final use from a wide variety of polymers known in ~he elec~rocoating art.
Representative polymers can be derived from epoxy and epoxy-modified diglycidyl ethers of bis-phenol A structures, various aliphatic poly-ethylene or polypropylene glycol (diglycidal ether) adducts, and glycidyl ethers o phenolic resins, such epoxy resins being commercially available and co~monly used in the electrocoating field. Other useful polymers include polyamide resins generally having a molecular weight of between about 500 and about 5,000; acrylic resins haYing molecular weight of about 1,0~0 to about 100,000; polyester resins and polyurethane resins each haYing a molecular weight range of about 500 to about 5,000; vinyl resins; and aniine resins. Various other useful electrocoating polymers can be advantageously employed in the electrocoating composition of this application as will be apparent to those skilled in the art.
T~le polymers can contain pendant mercaptan groups. Mercaptan groups can be attached ~o the polymer by esterification of free hydroxyl groups on the polymer (for example, a polyester) with a mercaptan~terminated acid, such as mercaptopropionic acid. SimilaTly, mercaptan groups can be in~roduced into the polymer by reacting pendant primary or secondary amine groups on the polymer with a mercaptan-terminated acid or by reacting the free isocyanate group on a monoisocyanate-terl~inated polym0r with a mercaptan-terminated ester having at least two pendant mercaptan groups. Mercaptan - 2a ~

groups can be introduced into the polymer by numerous other me-thods which are well known in the art. The mercap-tan groups are pendantly at-tached to the polymer, which for present purposes is meant -to include terminal mercaptan groups. The polymer containing pendant mercap-tan groups should contain at least 5% by weight of such pendant mercaptan groups and up to about 50% if desired. The polymer containing pendant mercaptan groups is rendered wa-ter dispersible by conventional techniques such as by adding acid and halogen or alkyl halide, such as, for example, methyliodide, -to the electrocoating poly-mer to form a sulfonium ion (the sulfonium ion, for example, can be formed from a minor proportion of the mercap-tan groups or al-terna-tively from avail-able thioethers in the polymer backbone). The mercaptan-containing polymer also can contain minor amounts of pendant amine groups which aid in solubiliz-ing the polymer in the aqueous bath when pro-tonated with a proton-donating acid.
Referring now to the polymer containing pendant tertiary amine groups, tertiary amine groups can be attached to the polymer by reacting free secondary amine groups with any polymer containing oxirane functionality such as, for example, an epoxy resin or a glycidyl-functional acrylic resin.
Similarly, tertiary alkanolamines can be reacted with isocyanate-terminated polymers or esterified onto carboxyl-functional polyester polymers in order to attach the tertiary-amine groups to the polymer. Primary and secondary amine groups can be attached to the polymer by reacting free carboxyl groups on a polymer (polyester, acrylic, ure-thane, etc.) containing available carboxyl groups which can be reacted with alkyleneimine or substituted alkyleneimine, as proposed in United States 3,679,564 and United States 3,617,458.
Similarly, such amine groups can be introduced into the polymer by react-ing pendant carboxylic acid groups on a polymer with ethylene imine or de-rivatives of ethylene imine. Difunctional amines also can be reacted with reactive pendant carboxyl grou-ps on the polymer. Blocked amines also can be attached to the polymer and subsequently transform-~ 3 --5~

ed into primary amine groups by an appropriate reaction which will be outlinedin detail later herein. Such blocked ~line 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. Similar blocked dialkyl triamines also can be employed to attach the blocked ~nine groups as above set forth. The amine groups are pendantly attached to the polymer as herein-before described~ The polymer containing pendant amine groups should contain at least about 1% by weight of such pendant amine groups and up to about 50%
if desired.
In a preferred specific embodiment of the present invention, the cathodic electrocoating composition comprises a polymer containing pendant tertiary-amine groups, a polymer containing pendant mercaptan groups, bis-maleimide cross-linking agent, and an ultraviolet photosensitizerO This com-position is cured by a combination of light heating followed by exposure to ultraviolet radiation (herein described as "dual curing"). Similarly, a single polymer can contain both the tertiary-amine groups and the mercaptan groups. In this embodiment of the present invention, the polymer containing pendant mercaptan groups should contain at least about 1% by weight of such pendant mercaptan groups, and up to about 30% if desired. Advantageously, the proportion of mercaptan groups will be at least about 1% less by weight than the proportion of cross-linker and, preferably, the mercaptan groups will range rom about 1% to abou~ ~% by weight of the polymer to which they are attached. Generally, only a minor amount of mercaptan groups need be present in the electrocoating composition in order to obtain partial cure of the electrocoating composition by heatingO Partial curing of the electrocoating builds molecular weight ~viscosity~of the electrocoating composition which permits shorter ultraviolet radiation times and/or less energy expenditure during ultraviolet radiation of the electrocoating. If a major amount of the mercaptan groups are present in the electrocoating composition, then the light 36~4 heating step i5 practiced at a temperature and for a time such that only par-tial curing of the electrocoating results by such heating. The polymer con-taining pendant tertiary-amine groups in this embodiment, then, should contain at least about 1~ by weight of such pendant amine groups and up to about 50%
if desired. The amine groups and mercaptan groups together comprise at least about 5% by weight of both polymers.
In the dual-curing embodiment of this invention, the electro-coating composition also can contain a resin or polymer having multiple ethylenic unsaturation ~free radical reactors) such as multi-functional allylic unsaturated polymers, acrylics and methacrylics, acrylamides, unsaturated oils, and alkyds. Such ethylenically unsaturated compounds can polymerize into the electrocoating composition for obtaining good properties of the coat-ing. The ethylenic unsaturation of allylic and vinyl unsaturated compounds is not activated ~by a carbonyl group~ and, thus, such unsaturated compounds do not participate in the Michael-type partial cure of the electrocoating by the heating step, but are linked into the electrocoating by the subsequent ultraviolet radiation curing step. Ethylenically unsaturated compounds in-clude, for example, diallyl phthalate, triallyl borate, triallyl amine, di-allyl maleate, diallyl chlorendate, diallyl amine adducts of epoxy resins, and triallyl cyanurate. Additional unsaturated compounds include allylic un-saturated acrylics, epoxies, urethanes, and polyester polymers. Further ethy-lenically unsaturated compounds include alkyds, synthesized with for example, trimethylol propane, pentaerythritol, phthalic anhydride, soybean oil, linseed oil, tung oil, and the like.
The cross-linking agent is a bis-maleimide having alpha-, beta-ethylenic unsaturation capable of being reactive to cross-link the electro-coating polymer. Bis-maleimides can be represented by ~he following general structure:

o o where R is aliphatic, aromatic, aliphatic-aromatic, or polymers having a molecular weight up to about 3,000.
Alkylene-, aryl-bis-maleimides and combinations thereof are par-ticu~Larly usefu~L as the cross-linking agent of -this invention. Specific bis-maleimides which are particularly suited to the precepts of -this invention can be selected from the group consisting of dime-thylenedimaleimide, -tri-methylenedimaleimide, tetramethylenedimaleimide, te-traethylenedimaleimide, pentamethylenedimaleimide, hexamethylenedimaleimide, heptamethylenedimale-imide, decamethylenedimaleimide, 4,4'-methylene-bis (orthoc'hloroani:Line), 4,4'-methylene-dianiline, 4,4'-methylenebis (3-nitroaniline), I~-aminophenyle-ther, N,N'-ortho-phenylenedimaleimide, ~,N'-para-phenylenedimaleimide, and N,N'-meta-phenylenedimaleimide.
Bis-maleimides can be synthesized by various methods such as are disclosed in United States patent 2,444,536. Generally, a dilu-ted ether so-lution of diamine is added to a similar diluted ether solution of maleic an-hydride which results in a maleamic acid. The maleamic acid can be disposed in acetic anhydride and converted into -the corresponding bis-maLeimide in the presence of' potassium acetate.
Referring now to the polymer containing pendant mercaptan groups, such mercaptan groups can be cross-linked through the unsaturation of the bis-maleimide cross-linking agent upon heating of the cathodically electrocoated substrate as hereinbefore described. The electrodeposited coating on -the cathode substrate also can be cured by exposure thereof to ionizing radiation (elec-tron beam curing) as disclosed in United States patents 3~501,390 and

3,501,391, the same being incorporated expressly herein by reference. Fur-ther, the electrodeposited coating of' the ca-thode substrate can 'be cured with ~'10~54 ~.

ultraviolet radiation in the presence of an ultraviolet (W) sensitizer or photosensitizer. The W sensitizers are combined with the eleetroco2ting composition and are adapted to be simultaneously co-deposited with the composition onto the cathode substrate du~ing 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 or photosensitizers include halogenated polynuclear ketones as disclosed in llnited States Serial No. 480,738. Other suitable UV sensitizers include org~nic carbonyl compounds selected from alkylphenones, benzophenones, and tricyclic fused ring compounds as disclosed in United States patent No. 3,759,807. Further use for UV sensitizers include carbonylated phenyl nuclear sulfonyl chloride such as set ~orth in United States Patent No. 3~827J959. Additional useful photosensitizer combinations particularly suitable for pigmented coatings or com~ination of sensitizers comprising aromatic carbonyl compounds, aromatic aldehyde or aromatic ketones, and a synergistic sensitizer of about 0.05% to about 3% of 2,2'-dithiobis-~benzothiazole) as ~ore particularly set forth in United States paten~ No. 3,847,771.
Typical sources of ultraviolet energy ordinarily produce wave-lengths in the ultraviolet spectru~ that are transmitted through a quartz and such wavelengths are usually ~etween about 1,600 ~ and about 4,000 R. Suit-able ultraviolet emitters include various electric arc lamps, plasma arc torch, such as described in United States patent No. 3,364,387, and lasers having a lasing output in the ultra~iolet spectrum. Other suitable sources of actinic light include quartz mercury lamps, ultraviolet quartz lamps, and high flash lamps.

Referring now to polymers containing primary, secondary, tertiary amine groups and combinations thereof, cathodic electrocoating compositions containing such polymers can be combined with the bis-maleimide cross-linker and W photosensitizer. Such compositloll is ultraviolet radiation curable as above described. In this embodiment, though, the amine groups are attached to an alpha-carbon. By alpha-carbon of the c~mine group is meant the carbon in the alpha-positio~ rela*ive to the amine group into which the pendant amine group is attached. Upon exposure of the electrodeposited coating to ultraviolet radiation, the alpha-carbon of the amine groups links with the unsaturation of the bis-maleimide cross-linker ~o provide a cured coating on the cathode substrate.
Referring now to the dual curing embodiment of this invention the elec~rodeposlted coating on the cathode substrate is dual cured wi~h li~ht heating followed by ultraviolet irradiation in the presence of UV sensitizer.
Light hea~ing of the electrocoating film on the subst~ate is done at temperatures of abou~ 180 to about 400~. for about 1 to ~0 mimltes. Such light heating flows out the coating and partially cures the electrocoating by the linking of the unsaturation of the bis-maleimide cross-linking agent with the pendant mercaptan groups o~ the polymer containing the mercaptan groups in a ~lichael-type addition reaction or addition polymerization. The par~ially cured electrocoating then is fully cured by ultraviolet irradiation thereof as previously described.
The following exa~ples show how the above-described embodiments of the present invention can be practiced, but should no~ be construed as limiting the invention. In this application, all parts are parts by weight~
all percentages are weight percentages, and all temperatures are in degrees 6~g Fahrenhelt unless otherwise expressly :indicated.

A solution acrylic polymer was conventionally prepared by react-ing methyl methacrylate (290 par~s per weight, ppw), ethyl acrylate 1230 ppw~, . ~ butyl methacrylate (320 ppw), 2-hydroxyeth lacrylat~ (20 ppw), and diethyl- !
aminoethylmethacrylate (140 ppw) in butyl ee~e~ e 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 5% of 2-chlorothioxanthone photosensitizer and 20~ of hexa-methylenedimaleimide cross-linking agent. The blend was neutralized with acetic acid and dispersed in deionized water to form a 10% non-volatile elec-trocoating bath.
Th0 resulting electrocoating composition was cathodically electro-deposited onto a steel panel at 100 volts for 30 to 60 seconds, removed from the bath, and washed with water. The electrocoated panel, then, was covered with a thin polyethylene sheet, placed under an 800 watt medium pressure mercury lamp (ultraviolet radiation source~, and irradiated for 30 minutes.
A hard, flexible, solvent-~esistant coating covered the panel.

One mole of an epoxy resin (DER 664, epoxy equivalent weight of 900, Dow Epoxy Resin, Dow Chemical Compan~) was reacted at 60C, with two moles of a ketimine blocked diethylene triamine represented by ~he following structure:

~ CH2CH2N = C

HN

\ / CH3 CH2CH3, 65~

completely ne-ltralized with 4 moles of lactic acid, and blended with 20% N,N'-para-phenylenedimaleimide cross~linking agent and 10% benzophenone photo-sensitizer. The blend was added to butyl cellosolve 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 coa*ing. 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 ~or 20 minutes under an 800 watt medium pressure mercury lamp.

The cathodic electrocoating compositions of 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 benzo-thiazole.
Each composition was cathodically electrocoated and cured by exposure to ultraviolet irradiation in the same manner as described in Ex-amples 1 and 2 above. A fully cured, hard, flexible, solvent-resistant coat-ing resulted upon curing.
EXAMPLE ~
A hydroxyl-rich polyester was formulated by the reaction of two moles o succinic anhydride with three moles of propylene glycol. This resin was reacted ~urther with an excess (based on the free hydroxyl content of the polyester resin) o 3-mercaptopropionic acid in order to attach mercaptan groups to the resin. ~ne h~mdred grams of this mercaptan-terminated resin was acidified with three moles of acetic acid and me~hyl iodide, and blended with 30 grams of N,N'-para-phenylenedimaleimide cross-linking agent. The blend 5gL

was dispersed in water to form an ~% non-volatile dispersion (electrocoating bath).
A steel panel was immersed in the bath as the cathode and the electrocoating composition was electrodeposited therein at 60 volts fGr two minutes. The coated panel was removed from the ba~h, washed ~ith water, and baked at 360F. for 15 minutes. A solvent-resistant coating with no mercaptan odor covered the panel indicating that curing had taken place.

An amine-terminated polyamide resin was formulated by the reaction of t~o moles of 1,6-hexylamine with one mole of adipic acid. This resin was reacted with two moles of ~ mercaptopropionic acid to produce a mercaptan-terminated polyamide resin. One hundred grams of the mercaptan-terminated polyamide resin was acidified with an excess of lactic acid and methyl iodide, blended with 20 gr~ms of 1,6-hexamethylene-bis-maleimide cross-linking agent, and added to water to form a 10% non-volatile dispersion.
The electrocoating composition in the electrocoating bath was cathodically electrodeposited onto a steel panel at 100 volts for one min~lte.
The coated panel was removed from the bath, washed with water, and ~aked at 250F. or 40 minutes. A fully cured coating having no mercaptan odor covered the panel.

_ Two moles of toluenediisocyanate was reacted with one mole of poly~tetramethylene ether glycol), having a molecular weight of 2,000, follow-ed by a further reaction with one mole of propanol to pToduce a monoisocyanate-terminated urcthane resin. This resin was reacted with one mole of the tri-ester of 3-mercaptopropionic acid with trimethylolpropane to produce a di-functional mercaptan-terminated urethane polymer. One hundred grams of said mercaptan-teTminated urethane polymer was neutralized with acetic acid and methyl iodide, blended with 20 grams of N,N-orthophenylene-dimaleimide cross-linking agent. The blend then was added to water to form an 8% non-volatile . .

~ ..

~a~s~

dispersion.
The electrocoating composition in the electrocoating bath was cathodically electrodeposi~ed onto steel panels in a manner similar to the previous Examples, washed with water, and baked at 400F~ for 25 minutes. A
fully cured coating co~ered the panels.

One mole of 1,6-hexanediamine was reacted with one mo:Le of adipic acid to form an amine-terminated polyamide resinO This resin then was reacted with one mole of 3-mercaptopropionic acid to form a polyamide resin having pendant mercaptan and amine groups. Pendant amine groups on the mercaptan-functional polymers aid in dispersing the polymers in the aqueous electro-coating bath.
The electrocoating polymer was a blend of 50% by weigh~ each of the above polyamide resin and the urethane polymer of Example 6. A polymer-bis-maleimide cross-linking agent was formulated by reacting two moles of succinic anhydride with one mole of polyoxyethylene glycol ~molecular weight of 1540)~ which reaction product was reacted further with two moles of hexa-methylene diamine. This polymer-diamine was dissolved in tetrahydrofuran ~10%
solution by weight) and then added to a solution of two moles of maleic anhydride (10% solution by weight in tetrahydrofuran) to form a polyether-bis-maleimide compound in the presence of acetic anhydride and potassi~ml acetate.
The electrocoating polymer was neutralized with acetic acid and blended with the polyether-bis-maleimide cross-linking agent in water to form a 20% non-volatile dispersion. This blend was cathodically electrodeposited onto a steel panel at 100 volts Eor two minutes, washed with water, and baked at 400Fo for 35 minutes. A hard, flexible, solvent-resistant coating covered the panel.

One mole of an epoxy resin CDER 664, epoxy equivalcnt weight of 900, DO~ Epoxy Resin, Dow Chemical Company) was reacted with one mole of ., ;

methyl ethanol amine ollowed by a further reaction with trimethylolpropane tri-(beta-mercaptopropionate) to produce a mercapt~m-functional epoxy resin~
This resin was neutrali~ed with lactic acid and methyl iodide, blended ~Yith 20% of N,NI-paraphenylenedimaleimide, and the blend added to water to form an 8% non~volatile dispersion.
The electrocoating composition was cathodically eleetrodeposited onto a steel panel in a manner similar to the previous Examples, removed from the bath9 and washed with water. The coated panel then was heated a-t a suf-ficiently low temperature ~about 150F.) to effect only a flow-out of the coating on the panel and not a curing of the coating.
The "flowed-out" panel then was subjected to electron beam irradiation from an electrocurtain ~laboratory model, Fnergy Sciences, Inc.) under the following conditions: the terminal voltage was 150 kilovolts~ the current was 10 milliamperes, the dose was 10 megarad, and the linespeed of the panel was 10 feet per minute. Upon said electron beam irradiation, a fully cured coating covered the panel.

To the electrocoating bath of Example 8, ten grams of benzophenone (ultraviolet sensitizer) was added. A steel panel was cathodically electro-coated cmd the coating "flowed-out~' in the manner of Example 8.
The"flowed-out" panel was exposed for ten seconds to ultraviolet radiation at a distance of three inches from a 3-bulb Ashdee ultraviolet cur-ing unit, each bulb producing 200 watts per inch on its surfaceO Upon said ultraviolet irradiation, a fully cured coating covered the panel.
EXA~IPLE 10 Two moles of toluene diisocyanate were reacted with one mole of poly~tetramethylene ether glycol), having a molecular weight of 2,000, follow-ed by a urther reaction with one mole of dimethyl ethanol amine to produce a urethane resin having mono-isocyanate terminal functionality. The resin was reacted with one mole of trimethylolpropane tri-(beta-mercaptopropionate) in order to pendantly attach a mercaptan group to the resinO
This resin can be blended wi~h any of the bis-maleimide cross-linking agents of thls application, ca~hodically electrodeposited onto a metal substrate, and cured to form a fully cured coating on the subs-trateO

An acrylic copolymer was synthesized by the solution polymeriza-tion of one mole of butyl acrylate and one mole of methylmethacrylate. This reaction was run under stan~ard solution polymerization conditions using 2-butoxy ethanol-l as the solvent and one mole of thiolacetic acid as a chain transfer agent. This resin was hydrolyzed (with an appropriate acid or base) in order to convert the thiolacetic ester linkages into pendant, f~mctional mercaptan groups.
This resin additionally can be blended with a bis-maleimide cross-linking agent for cathodic electrodeposition onto a metal substrate with subsequent curing of the coating in a manner similar to the above Examples.
The cathode substrate is an electrically conductive metal such as iron, steel, aluminum, copper, galvaniæed steel, zinc and like metals. 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 opaci~ying pigments and inert extenders such as, for example, titanium dioxide, zinc oxide, clays such as kaolinite clays, silica, talc, and the like.
The follo~ing examples further illustrate the invention.

One mole ~1,800 grams) of DER 664 epo~y resin ~Dow Epoxy Resin, epoxide equivalent weight of 875-9759 Dow Chemical Company) was reacted with /ve~
1.2 moles of methyl ethanol amine in butyl6e~s~ solvent ~50% by weight solution) in order to attach pendant tertiary amines to the epoxy polymer.

The polymer having pendant mercaptan groups was commercially available Celanese Epicure 861 ~equivalent weight of 163, Celanese Chemical Corp.). One `6S~

hundred fifty C15Q) grams of the Epicure polymer was dispersed in the solution containing the amine-functional epoxy polymer and the polymers completely neutralized with 5 moles of acetic acid.
The electrocoating bath comprised an 8% non-volatile solids blend of the neutralized polymers, 200 grams of 1,6-hexamethylene-bis-male-imide cross-linker, and a UV sensitizer system comprising 5% benzophenone, 1%
Michler's ketone, and 3% of 2,2'-dithiobis (benzothiazole)~ The blend (elec-trocoating composition) was cathodically electrodeposited onto a steel panel (cathode substrate) at 60 volts for 30 seconds.
The electrocoating covering the panel was lightly heated at 200C.
for 5 minutes to flow-out the electrocoatingO The heated electrocoating dis-played some solvent resistance, indicating that a partial cure of the electro-coating had taken place during the heating step. Full cure of the electro-coating was obtained by irradiating the partially cured electrocoating with ultraviolet radiation from an 800 watt medium pressure mercury lamp (ultra-violet radiation source) for 20 minutes.

The electrocoating composition was the same as the elec~rocoating composition of Example 12, except that the polymer having pendant mercaptan 20 ~ Z groups, Celanese Epicure 861, was reacted with the amine-functional epoxy polymer to yield a single polymer having both pendant tertiary amine groups and pendant mercaptan groups.
This electrocoating composition was dispersed în the bath, elec-trodeposited onto a steel panel~ and dual cured in the same manner as describ-ed in Exc~nple 12. A fully cured electrocoating covered the panel upon dual curing thereof.

The procedures of Examples 12 and 13 were repeated except that the pol~ner having pendant mercaptan groups was trimethylolethane tri-(3-mercapto-propionate). Again, a fully cured electrocoating covered the panel upon the 36S~

dual curing thereof.
EXAMPLE lS
Example 12 was repeated, except that 15% of triallyl cyanurate was added to the bath. Triallyl cyanurate contains a multiplicity of ethy-lenically unsaturated carbon-to-carbon groups~ but such unsaturation is not ac~ivated (by a carbonyl group)O The triallyl cyanurate linked into the electrocoating upon the W irracliation o the electrocoating (subsequent to - flowing-out of the electrocoating) to yield a fully cured electrocoated film on the panel.

A polyester polymer was prepared by reacting one mole of phthalic anhydride, one mole of succinic anhydride, and one mole of propylene glycol.
This reaction was performed in toluene with azeotropic distillation of the water of reaction. This reaction product, an acid-terminated polyester, then was reacted with two moles of N9N-diethyl-1,4-pentanediamine (with the water of reaction being removed) in order to attach pendant tertiary amine groups to the polyester polymer.
The polymer containing pendant mercaptan groups was a mercaptan-terminated polyurethane polymer prepared by reacting 2 moles of toluene di-isocyanate with one mole of poly-~tetramethylene ether-glycol) (molecular weight of about 2,000), followed by a further reverse addition reaction with 2 ~oles of trimethylolpropane tri-(beta-mercaptopropionate).
The diamine-terminated polyester polymer and the mercaptan-terminated polyurethane polymer were completely neutralized with 6 moles of acetic acid, and blended with 20% by weight of meta-phenylene-bis-maleimide ~cross-linking agent~ and 10% by weight of the UV sensitizer system of benzo phenone/acetophenone ~1:1 weight ratio). The blend was dispersed in de-mineralized water to form an electrocoa*ing ba*h of 10% non-volatile solids.
A s~eel panel was cathodically electrocoated with the electro-coating composition, washed with wa~er to remove excess coating, and dual 36~ 4 cured in a manner similar to that described in Example 12. A fully cured electrocoating covered the panel upon the dual curing thereof.
EXAMPLE l7 Example 16 was repeated, except that to the electrocoating com-position (blend) was added 20% by weight of an unsaturated alkyd compound which was the reaction product of 60 parts refined soybean oil, 16 parts tri methylolpropane, 24 par~s phthalic anhydride, and 2 parts pentaerythritol-triacrylate ~all parts are parts by weight~. The alkyd compound polymerized into the electrocoating upon dual CUTing of ~he electrocoating ~o yield a fully cured electrodeposited coating covering the panelO

-One mole of a polypropylene oxide polymer ~PPG 1025, molecular weight of about 1,000, Union Carbide CorpO) was reacted with 2 moles of F~ Ce //~
toluene diisocyanate ~molecular weight of 17~.16) in dry butylc~h3~e~e to form a diisocyanate-terminated prepolymer. Pendant tertiary ~nine groups were attached to the prepolymer by reacting the prepolymer with 1.943 moles of N,N-dimethylethanolamine ~molecular weight of 89.1~). Pendant mercaptan groups also were attached to the prepolymer by reac~ing the amine-~unctional pre-polymer with 0.057 moles of the reaction product of neopentylglycol and mer-captopropionic acid (the reaction product being neopentylglycol dimercapto-propionate, molecular weight o-f 280.~0). The polymer contained about 11% pen-dant te~tiary amine groups and about 1% pendant mercaptan groups ~based on the weight of the polymer).
The polymer was neutralized with acetic acid and blended with 20% by weight of 1,6-hexamethylene-bis-maleimide cross-linker and a UV photo-sensitizer system comprising 5% benzophenone, 1% Michler's ketone, and 3%
2,2'-dithiobis-(benzothiazole). The blend (or electrocoating composition) was let down in deionized water to form an electrocoating bath of 8% non-volatile solids and cathodically electrodeposi~ed onto a steel panel at 60 volts for 30 seconds.

The coated panel was heated at 300Fo for 10 minutes to flow-out the coating. This heating resulted in a partial cure of the electrocoating (indicated by its moderate resistance to solvents) with attendant molecular weight incr~ase. The flowed-out coating then was fully cured by subjecting the coating to W irradiation from an 800 watt medium pressure mercury lamp for 20 minutes.
E _~PLE 19 An advantage of dual cure as practiced in this invention is the advantageous molecular weight build-up obtained by the heating or flowing-out step which permits shorter UV irradiation times~ To demonstrate ~his advan-tage, an electrocoating bath was prepared in the manner set forth in F.xample 18, except that the mercaptan-functional polymer ~neopentylglycol dimercapto-propionate) was omitted from the electrocoating composition. A panel was cathodically electrocoated and flowed-out in the same manner as described in Example 180 The electrocoating displayed no solvent resistance after its heating, indicating that no cure of the electrocoating had taken place. Full cure of the electrocoating was obtained after 30 minutes of W irradiation of the electrocoating, or 10 minutes UV irradiation exposure time longer than the inventive electrocoating composition of Example 18 containing only 1% mercap-tan groups.

The procedure of Example 18 was repeated except that 15% tri-allylcyanurate was added to the electrocoating composition. Dual cure of the `; electrocoating resulted in a fully cured coating covering the panel, indicating that the ethylenically unsaturated compound, triallylcyanurate, had linked into the coating system.

The procedure of Example 18 was repeated, except that the blend also contained 30% by weight of an unsaturated alkyd compound which was the reaction product of 60 parts refined soybean oil, 16 parts trimethylolpropane, ,, 10 parts maleic anhydride, 14 parts phthalic anhydride, and 2 parts pentaery-thritoltriacrylate (all parts are weight parts). A fully cured coating cover-ed the panel upon dual cure of the electrod0positecl coating.
EXA~tPLE 22 The procedure of Example 18 was repeated, except the polymer hav-ing pendan~ mercaptan groups was trimethylolpropane tri-~beta-mercaptopropion~
ate). A fully cured coating covered the panel up on dual curing of the elec~rodeposited coating.
EXA~tPLE 23 The epox~ resin of Example 12 ~DER 664) was reacted with one mole of methylethanolamine in butyl cellosolve ~in order to attach pendant tertiary amine groups) followed by a further reaction with 0.5 moles of trimethylol-propane-tri-~beta-mercaptopropionate) (in order ~o attach pendant mercaptan groups).
The resulting polymer was neutralized with acetic acid and blend-ed with 20% by weight of N,N'-paraphenylene-dimaleimide and a W sensitizer system composed of 5% benzophenone, 1% Michler's ketone, and 3% of 2,2'-di-thiobis-(benzothiazole). The blend was added to water to form an electro-coating bath of 10% non-volatiles.
~ steel panel was immersed in the bath and cathodically electro-coated at 60 volts for 30 seconds. The coated panel then was dual cured in the same manner as described in Example 18.
EXA~tPLE 24 ~; An acrylic polymer was fo-~mulated by the solution polymerization of 40% styrene, 40% butyl acrylate, and 20% glycidyl methacrylate in butyl cellosolve wi~h azeotropic distillation of the water of reaction. Pendant tertiar~ amine groups and pendant mercaptan groups were attached to the poly-mer by reacting the acrylic polymer with 10% of diallylamine and 5% of neo-pentylglycol dimercaptopropionate, respectively.
The cross-lînking agent was 20% by weight of 1,6-hexamethylene-_ 19 -S~ .

bis-maleimide. The UV sensitizer system was 5% benzophenone, 1% Michler's ketone, and 3% 2,2'-dithiobis-~benzothiazole). The bath was formed, a panel cathodically eLectrocoated~ and the resulting electrocoating dual cured in the same manner as described in Example 18. A fully cured, solvent-resistant coating resulted from the dual cure of the electrodeposited coating.

.:.- .
':
."5:;

.` ' , ' ' ' ~ .
; ~ 20 -

Claims (9)

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 composi-tion in aqueous dispersion onto a cathode substrate disposed within an aqueous electrocoating bath to form a curable coating on said cathode sub-strate which comprises: cathodically electrodepositing said electrocoating composition onto said cathode substrate under cathodic electrocoating con-ditions, said electrocoating composition comprising:
(a) a water-dispersed electrocoating polymer having at least about 5% by weight pendant groups selected from tertiary amine groups, mercaptan groups, and combinations thereof, and (b) at least about 5% by weight of said polymer of bis-maleimide as a cross-linking agent, and curing said curable coating on said cathode substrate, said cross-linking agent cross-linking said polymer by addition polymerization to form a cured coating on said cathode provided that when said polymer contains amine groups the electrocoating composition also con-tains at least about 0.5% by weight of said polymer of an ultraviolet photo-sensitizer and said curing is by ultraviolet radiation.

2. The process of claim 1 wherein said pendant groups are mercaptan groups and said curing is by heating.

3. The process of claim 1 wherein said curing is by ionizing radi-ation.

4. A process for electrodeposition of an electrocoating composition dispersed within an aqueous electrocoating bath onto a cathode substrate disposed within said bath to form an 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 1% by weight pendant mercaptan groups;

(b) a water-dispersed electrocoating polymer having at least about 1% by weight pendant tertiary amine groups each said amine group being attached to an alpha carbon of said polymer;
(c) at least about 5% by weight of said polymers of bis-maleimide as a cross-linking agent, and (d) at least about 0.5% ultraviolet photosensitizer by weight of said polymers, said pendant tertiary amine groups and said pendant mercaptan groups together comprising at least about 5% by weight of both said polymers; and curing said electrodeposited coating on said cathode substrate by heating said electro-deposited coating on said cathode substrate to cross-link said polymer having pendant mercaptan groups with said cross-linking agent to partially cure said coating, followed by irradiating with ultraviolet radiation said partially cured coating to cross-link with said alpha carbon of said polymer having pendant tertiary amine groups with said cross-linking agent to fully cure said coating on said cathode substrate.

5. A cathodic electrocoating composition dispersed in an aqueous elec-trocoating bath for electrodeposition onto a cathode substrate disposed with said bath for forming a curable electrodeposited coating on said cathode substrate, comprising:
(a) a water-dispersed electrocoating polymer having at least about 5% by weight pendant groups selected from tertiary amine groups, mercaptan groups, and combinations thereof; and (b) at least about 5% by weight of said polymer of bis-maleimide as a cross-linking agent; provided that when said polymer only contains ter-tiary amine groups the composition also contains at least about 0.5% by weight of said polymer of an ultraviolet photosensitizer for curing the com-position by ultraviolet radiation.

6. The cathodic electrocoating composition of claim 5 wherein said pendant groups are mercaptan groups and said composition is heat curable.

7. The cathodic electrocoating composition of claim 5 wherein said pendant groups are mercaptan groups and said electrodeposited coating on said cathode substrate is ionizing radiation curable.

8. The cathodic electrocoating composition of claim 5 wherein said composition additionally contains at least about 0.5% by weight of said poly-mer of an ultraviolet photosensitizer and said electrodeposited coating on said cathode substrate is ultraviolet radiation curable.

9. The cathodic electrocoating composition of claim 5 comprising:
(a) a water-dispersed electrocoating polymer having at least about 1% by weight pendant mercaptan groups;
(b) a water-dispersed electrocoating polymer having at least about 1% by weight pendant tertiary amine groups, each said amine group being at-tached to an alpha carbon of said polymer;
(c) at least about 5% by weight of said polymers of bis-maleimide as a cross-linking agent; and (d) at least about 0.5% ultraviolet photosensitizer by weight of said polymers;
said pendant tertiary amine groups and said pendant mercaptan groups together comprising at least about 5% by weight of said polymers, said electrodeposi-ted coating of said electrocoating composition being adapted to cure by heat-ing said electrodeposited coating on said cathode substrate to cross-link said mercaptan groups with said cross-linking agent to partially cure said coating followed by irradiating with ultraviolet radiation said partially cured coating to cross-link said alpha carbon of said polymer having said pendant tertiary amine groups with said cross-linking agent to fully cure said coat-ing on said cathode substrate.