CA1274033A - Cathodic electrocoating compositions including alkyl carbamate-containing cross-linking agents and method of making coatings therefrom - Google Patents

Abstract

CATHODIC ELECTROCOATING COMPOSITIONS INCLUDING
ALKYL CARBAMATE-CONTAINING CROSS-LINKING
AGENTS AND METHOD OF MAKING COATINGS THEREFROM
ABSTRACT

A cathodic electrocoating composition comprises a hydrophobic cross-linking agent having at least two carba-mate groups selected from either hydroxyalkyl carbamate groups or alkyl carbamate groups obtained by capping the reaction product of a cyclic carbonate and a polyamine, a water-insoluble and hydrophobic amino group-containing polymer, and an acid disperser. A crosslinking catalyst is optionally included. The components are stable at ambient temperature and may be electrodeposited onto a substrate and heated thereon to be cured to provide a thermoset coating.

Description

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BACKGROU~ID OF THE INVENTION
The present invention is concerned with a multi-component cathodic electrocoating composition comprising a cross-linking agent, a polymer, an acid disperser and, optionally, a cross-linking catalyst. The composition of the invention finds utility in the preparation of coatings on conductive substrate and the present invention also concerns methods for electrodepositing the com-position on a substrate and heating the deposited coating to cure it to form a thermoset coating.
- - Electrodepositable resin compositions are of course well known in the art. For example, U.S. Patent 4,031,050 discloses cationic electrodepositable compositions of blocked organic polyisocyanates and an amine adduct of an epoxy resin. As disclosed in this patent, electrodeposition of such compounds, which may optionally contain a catalyst for urethane formation, can be carried out to provide coatings on a conductive substrate, which coatings have desirable properties. In this regard, see also U.S. Patents 3,984,299 and 4,031,050. ~owever, isocyanate compounds are toxic and highly reactive, requiring suitable precautions in handling and storing the same.
U.S. Patent 4,017,438 discloses an epoxy resin-derived, cati~nic electrodepositable resin enhanced by the incorporation of primary amine groups into the resin molecule, by reacting certaln polyamine compounds having primary amine groups blocked by ketimine. The ketimime groups when contacted with water, will decompose to provide primary amine functionality as disclosed in ~hls patent. Capp~d isocyanates are disclosed in combination with ~ 274~

the amine-resin adduc~ to provide, together with a suitable catalyst, a cationically electrodepositable resin system. The electro-deposited coating, upon being heated to an elevaeed temperature, us~ally in the presence of a cross-linking catalyst, undergoes cross-linking through reaction of hydroxy and amino groups with blocked isocyanate groups.
As well known, the "capped" or "blocked" isocyanates react with hydroxy groups and amino groups under conditions of elevated temperature to for~ urethane and urea cross-linkages.
Numerous literature references exist showing the reactions of primary and secondary amines with, for example, propylene carbonate to yield corresponding hydroxypropyl carbamates (Compt.
rend. 1142, 1954). The reaction of cyclic carbonates and aromatic amines in the presence of certain zinc, tin or cobalt catalysts to provide carbamate compounds is shown by U.S. Patent 4,268,684, with uses of the resulting carbamates disclosed in U.S. Patents 3,919,279; 3,919,280 and 3,962,302. The literature also shows that bishydroxyalkyl carbamates derived from corresponding diamines have been further self-condensed, or transesterified with other diols, to produce linear thermoplastic polyurethanes. For example, see the article "The Preparation oE Polymeric and Cyclic Urethans and Ureas from Ethylene Carbonate and Amines'` by Elizabeth Dyer and Harvey Scott, J.A.C.S. (1956? pp 672 - 675. See also the report "Polyurethane elastomers obtained without the use oE
diisocyanates'` by L. Ya. Rappoport, G.N. Pe~rov, I.I. T~ostyanskaya and O.P. Gavrilova in Interna ~ cience and Technolo~, ~, N~. 1, 1981 and an ar~icle by Richard D. Cowell entitled:

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"Thermoplastic Polyurethane Elastomers: Chemistry Properties and Processing for the 80's" in the Journal of Elastomers and Plastics, Vol. 14, (October, 1982) pages 195 - 203.
SU~MARY OF THE INVENTION
In accordance with the present invention there is provided a cathodic electrocoating composition comprising (a) a hydrophobic cross-linking agent having at least two carbamate groups selected from the class consisting of one or both of (i) hydroxyalkyl carbamate groups, and (ii) alkyl carbamate groups obtained by capping the reaction product of a cyclic carbonate tsuch as ethylene carbonate or propylene carbonate) and a polyamine; (b) a water-insoluble and hydrophobic amino group-containing polymer; and (c) an acid disperser (such as an inorganic acid or hydrophilic organic acid) effective ~o provide cationic groups in the polymer (b) whereby the polymer is rendered water-dispersible; and (d) optionally, a cross-linking catalyst; the cross-linking agent (a) and the polymer (b) being stable relative to each other in the composition while at ambient temperature, and reactive wi~h each other at elevated temperature.
In accordance with one aspect of the invention the cross-linking catalyst is selected from the class consisting of metal-containing catalysts, quaternary compounds and ternary compounts, preferably Çrom the class consisting of one or more of tin, ~inc, and titanium compounds and/or Çrom the class consisting of quaternary ammonium, phosphonium and arsonium compounds and ternary sulfonium compounds.

, ~, '. :' ~ ~ 7~)33 In one aspect of the invention, the cross-linking agent (a), the polymer (b), the acid disperser tc), and, when present, the catalyst (d) are present in weight proportion, per 100 parts by weight of the solids of (a), tb), tc), and (d), of at least about 5, preferably from about 5 to about 50 parts (a), at least about 40, preferably from about 40 to about 90, parts (b), at least about 1, preferably from about 1 to about 10, parts (c), and, when present, at least about 0.1 to 10, preferably from about 1 to about 5, parts (d).
In another aspect of the invention, the polymer (b) contains one or more functional groups which are reactive at elevated temperature with the hydroxyalkyl carbamate groups of the cross-linking agent (a). These functional groups may comprise one or more of amino, amide, hydroxy and ester functional groups, preferably one or both of amino and hydroxy groups. The polymer (b) may com-prise from about 0.25 to about 30~ by weight a~ino groups and from about 0.5 to about 20~ by weight hydroxy groups, based on the weight of polymer (b) solids.
One aspect of the invention provides that the hydrophobic cross-linking agent (a) contains one or more hydroxyalkYl car-bamate ~roups or alkyl carbamate groups capped by a moiety selected from the class consisting of ester, urethane, thiocarbamate, sulfonic ester, sulfona~ate ester, and ether groups.
In accordance with the present invention there is further provided a method Oe forming a cross-linked coating on a substrate comprisin8 immersing the substrate in an alectrodeposition bath comprlsing the composition (a), (b), (c~ and, optionally, ~d~

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above, cathodically èlectrodepositing a coating of the composltion from the bath onto the substrate, removing the coated substrate from the bath, and heating the coated substrate at an elevated temperature and for a time sufficient to cure the deposited coating.
In one aspect of the invention, the catalyst (d) is employed in the bath. In another aspect of the invention, the method includes heating the coated substrate at an elevated temperature of from about 200 to about 400F (about 93 to 204C).
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The compositions of the invention comprise three essential and one optional component which may be present in a composition which has good bath stability at ambient temperature and which may be cathodically electrodeposited upon a substrat~ by conventional techniques and the deposited coating then heated to an elevated temperature for a time sufficient to cure it by a cross-linking reaction between components of the composition.
As mentioned above, the essential components of the electrodepositable composition, which is diluted in water to comPris& an electrodeposition bath, are (a) a capped or uncapped hydroxyalkyl carbamate cross-linking agent, (b) a cationically-charged, non-gelled polymer and (c) an acid solubilizer ar disperser to render the polymer water-dispersible. The optional compenent is (d), a cross-linking catalyst.
The Hydroxyalky~--arbamate Cross-LinkinR Agent Cyclic carbonates such as ethylene or propylene carbonate react with amines to form hydroxyalkyl carbamates, according to the following typical example, in which Ra i5 assu~ed to be hydrogen:

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(1) R1~
a Ib _ CH R ~ N - C - O - CH CH 2 OH

R2~ ~ b ~N - C - O - CH CHOH

d where Rb is hydrogen for ethylene carbonate and methyl for propylene carbonate. The reaction may be run with or without solvent and, if so desired, protic solvenes such as water or alcohols may be used.
h~en either Rc or Rd is hydrogen, as in an unhindered primary amine, the reaction takes place at room or slightly elevated tem-peratures whereas secondary or hindered primary amines usually require heating and/or the use of catalysts for significant reaction.
Hydroxyalkyl carbamate-containing compounds as illustrated in equation (1) above are useful in this invention if they are sufficiently hydrophobic to be co-electrodeposited with a cationic polymer by conventional techniques. In some cases, in order to attain the requisite degree of hydrophobicity of the cross-linking agent, the hydroxy groups may be reacted with other, hydrophobic capping agents to incorporate the latter into the cross-linking agent.
Numerous polyamines, including, for example~ 4,4'-diamino-dicyclohexyl methane, 4,4'-diaminodicyclohexyl propane, and hexamethylene diamine may be used for the formation of carbamate ~: ' ". , , ,: :; : ' ` ; ;

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cross-linking agents by reaction with cyclic carbonates. Suitable polyamines include, by way of example and not limitation, simple diamines such as those of the formula

(2) RlHN-R2-NHR3 where Rl is independently H, CH3 or C2 to C20 al~yl, R2 is independently -CH2 or C2 to C20 alkyl fragments which may con-tain aromatic or saturated rings and wherein ~1~ R2, and R3 may also contain other functional groups which do not interfere with the amine-carbonate reaction, including, for example, esters, am`ides, nitriles, ethers, hydroxys, phenolics, ~etones, etc., and R3 is independently H, CH3 or C2 to C20 alkyl.
A suitable class of monomers/polymers usable to react with a cyclic carbonate to form a carbamate-containing cross-linking agent comprises vi~yls/polyvinyls, acrylicslpolyacrylics, methacrylics/
polymethacrylics, esters/polyesters, amides/polyamides, imides/
polyimides, ethers/polyeehers, or mixtures or capolymers oÇ these which contain an average of two or more pendant amine groups per molecule.
As indicated above, the a~ines utilized in accordance with the present invention to react with one or more cyclic carbonates to provide hydro~yalkyl carbamate-containing cross-linking agents may be any one oÇ a lar~e number oÇ compounds and, generally, may comprise polyflmines containing straight chain or branched alkyl, cycloalkyl or allcyl aromatic moieties? most preferably Cl to C20 : " ~. ~:.
.: "~" ., . -'','- : ::
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alkyl, cycl`oalkyl or alkyl aro~atic moieties and such moieties containing, in addition to at least one carbon atom, one or more heteroatoms. Such moieties containing one or more heteroatoms include, for example, those containing thio groups and organo-silicon moieties, in addition to the groups mentioned above in connection with formula (2).
As will be appreciated by those skilled in the art, a certain degree of hydrophobicity is required of a cathodically electro-depositable material such as the cross-linking agent employed in this invention. Therefore, it is preferred that the polyamines (as used herein and in the claims, the term "polyamines" is deemed to include diamines) utilized be selected so that after reaction with the cylic carbonates the resulting carbamate cross-linking agents are water insoluble or only partly water soluble. However, water soluble carbamate cross-linking agents, otherwise suitable~
may be ~odified to render them water insoluble or par~ly water soluble. This may be accomplished by capping or blocking the hydroxyalkyl carbamate groups by reacting them with a suitable capping agent which, when the deposited composition is heated to cure, will enter into the cross-linking reaction. Generally, ehe capping agents may be any suitable reagen~s which will react with the hydroxy groups of the hydroxyalkyl carbamate moiety to form an ester, urethane, thiocarbamate, sul~onic ester, sulfonamate ester, ether, or the like, whereby the cross-linking agent is rendered water-lnsoluble. Among suitable cappin~
agentS are the clas5eg o~ compounds set forth in the ~ollowing list, ~7~3~

which also shows the class of the moiety resulting from capping the hydroxy moiety of the hydroxyalkyl group of the hydroxyalkyl carbamate.
Cappin~ Agent Resultant Capping Moiety 1. Aliphatic and aromatic carboxylic acids Esters 2. Aliphatic and aromatic carboxylic acid halides Esters

3. Aliphatic and aromatic carboxylic acid anhydrides Esters

4. Aliphatic and aromatic carboxylic esters Esters

5. Isoalkylenyl Esters (e.g., isopropenyl acetate, etc.) Esters

6. Ketenes (e.g., ketene, mono or disubstituted ketenes, etc.) . Esters

7. Ureas (e.g., urea, mono-,di-, or tri-substituted ureas, etc.) Urethanes

8. Aliphatic and aromatic isocyanates Urethanes

9. Cyanic Acid Urethanes

10. Aliphatic and aromatic isothiocyanates Thiocarb~mates

11. Aliphatic and aromatic sulfonyl halides Sulfonic Esters

12. Aliphatic and aromatic sulfamoyl halides Sulfonamate Esters

13. Aliphatic and Alkyl aromatic alkyl halides Esters . ~ , .
"" ~' " ' ' ~

The above list of capping agents is merely illustrative and not limiting, as will be appreciated by those .skilled in the art. For e~ample, alcohols, including diols and polyols (see Example 4, below), mercaptans, amines and polyamines may also be employed as capping agents to render the hydroxyalkyl carbamate cross-linking agent water-insoluble. By way of example, capping the hydroxyalkyl carbamate moiety of the cross linking agent with a polyol is illustrated by the following reaction.

R O H
~3) 3HOCH2CHoc-N-Rl + R2(OH)3 ~, R O H H O R
11 l I li I
[ HOCH2CHOC-N-Rl-N-C-0] 3-R2 ~ 3HOCH2CHoH

In the above reaction r~l must also contain the following hydroxyalkyl carbamate group.

HOCH2CHO~
R O H

As shown by reaction (3), three moles of a biscarbamate pr~pared by reacting 1,6-hexanediamine and propylene carbonate per reaction (1) above, are condensed with one mole of trimethylol propane to prepare a liquid, organic solvent-soluble, trifunctional cross-linker suitable for use in a cationic electrocoating co~-positlon in accordance with the present invention. The starting biscarb3mate is a water soluble, difunctional, crystalline material. Its water solubility prevents its use in cationic electrocoating because it will not codeposit with the resin. The capping of the bi5carba~ate with the polyol provides a hydrophobic ,,~',",:,. "' : ,. ' ' ;

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composition well suited for use in the present invention.
The cyclic carbonates which are to be reacted with the amines may comprise any suitable cyclic carbonate, including bis-carbonates, which are reactive with one or more of the amine groups of a multi-functional amine. Generally, five-me~ber ring organic carbonates are preferred as compared to six-member ring organic carbonates because the latter are relatively morP expensive and difficult to prepare. Accordingly, a preferred cyclic carbonate utilizable in the present invention has the formula shown in the equation (1) above, - wherein R and Rb may be the same or dif~erent, and each may comprise H, or a Cl to C8 aliphat~c, cycloaliphatic, aromatic or heterocyclic compound. Ethylene carbonate and propylene carbonate are readily available and have been successfully employed and to this extent are preferred reactants.
The Amino Group-Containing ~olvmer The amino group-containing polymer is a water-dispersible, non-gelled polymeric material carrying a cationic charge. The polymeric material may con~ain several dif~erent types o~ functio~al groups. For example, the presence of hydroxy groups in the poly-meric material is hlghly desirable for reac~ion with the carbamate cross-lin~ing agents. However, the carbamate-conCaining cross-linking agents will also cross-link through amine groups~ The ..~: .: . . . .

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~ ;~7~3 -- 12 - 611~9-7362 presence of amino groups is essentlal, however~ to impart cationic character to the polymer and to obtain stable dispersion in water in the presence of an acid solubilizer or disperser.
A wide variety of amino group-containing polymers may be utilized in the composition of the present invention. Polymers suitable for use in the present invention are the amine adducts of epoxy group-containing resins as disclosed in U.S. Patent 4,031,050 of Robert D. Jerabek.
A large number and variety of amino group-containing polymeric mater-lals are suitable for use as the cationic polymeric component of the invention, so long as such materials are non-gelled, water-dispersible, polymeric in na-ture, and capable of carrying a cationic charge. It is also necessary that these polymeric materials co-deposit with the carbamate-containing cross-link-ing agent and when used, the optional cross-linking catalyst on the metal sur-face upon passage of an electric current between a cathode comprising the sur-face and an anode immersed in the electrodeposition bath. In this way, the electrodeposited composition can be converted to the cross-linked state by the application of heat. Cationic polymeric materials such as those identiEied as cationic Polymeric Materials A through F in U~S. Patent 4,026~855 may be utilized as the amino group-containing polymers of the present ~7~3~3 invention. Generally, in addition to bisphenol-A based epoxy cationic materials, novalac epoxy based cationic materials may be utilized.
The Acid Solubilizer The acid solubilizer or disperser may comprise one or more organic or inorganic acids which are water soluble or at least water dispersible and which will convert the amino group-containing polymer to a weter-dispersible material carrying a cationic charge.
The acid solubilizer is a water soluble (or at least water disper-sible) material, so that the counterion formed when the acid is added to the cationic polymer facilitates the water dispersion or solubilization of the cationic polymer. Generally, the acid solubilizer may be any suitable acid which will impart a cationic charge to the polymer and will not interfere with the stability or cross-linking reaction of the composition.
Among suitable acid solubilizers are inorganic acids such as;
hydrohalic acids, nitric, sulfuric, phosphoric, carboxylic acids such as acetic, butyric, pentanoic, formic, lactic and citric ac~ds or the like, or polycarboxylic acids such as: adipic, oxalic, malonic, succinic, maleic, or fumaric acids or the like.
The Cross-Linkin~ Catalyst The optional componenc of the composition of the present invention is a catalyst effective to lower the cure temperature of the other components of the composition after they have been electrodeposited upon a substrate. The catalyst accordin~ly must co-electrodepo9it with the other ingredients in the cathodic electrodeposition process. ~yplcally, a suitable cross-linking :, ., . '', -. .

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, ~274~ 3

-14-catalyst will lower the cure temperature of the electrodeposieed materials from about 400 to 600F (about 204 to 316C), the cure temperature without the catalyst, to about 200 to 400F
(about 93 to 204C). In order to attain sufficient co-deposition of the cross-linking catalysts with the other components of the electrodeposition composition, the cross-linking catalysts are preferably water insoluble or, at most, only partially soluble in water. Further, in order to insure efficient co-deposition of the catalyst, it is preferably at least partially soluble in the cross-linking a~ent and in the amino group-containing polymer.
Typical catalysts include organo tin compounds such as dibutyltin-dilaurate, organo zinc compounds, organo titanium compounds, quaternary ammonium compounds and the like, including quaternary phosphonium and arsonium compounds and ternary sulfonium compounds.
Other suitable catalysts include organo tin compounds such as dialkytin compounds, e.g., dibutyltindilaurate, organo ~inc com-pounds such as zinc octoate, zinc bu~yrate, etc., some organo titanium compounds, tetraalkyl ammonium compounds where the alkyl groups are selected so that quaternary ammonium compounds are water insoluble lor at most, water dispersible~ and co-deposit with the other components of the composition. In general, the catalysts are selected so that they are sufficiently hydrophobic to co-deposit with the carbamate cross-linking agent and amino group -containlng polymer components at least in amounts suficient to reduce the cure temperature o~ the electrodeposited compasltion.
A9 k~own ln the art, the catalygts may be lncorporated into the " ~' ' ' ~7~ 3 backbone of the poly~er (b) during preparation of the polymer.
Usually, sufficient catalyst is co-deposited to reduce the cure temperatu~e from about 400 to about 600F tabout 204 to 316C) to from about 200 to about 400F tabout 93 to 204C) or even less, e.g., from about 200 to about 250F tabout 93 to 121C).
The efficacy of the specific embodiments of the invention is illustrated by the following Examples, in which Examples 1-4 illustrate the preparation of suitable carbamate-containing cross-linking agents.
EXAMPLE
Carbamate Cross-Linkin~ Agent I
To a suitably equipped flask under a nitrogen atmosphere was charged 436.8 grams (2.1 moles) of 4,4'-diaminodicyclohexyl methane (mixture of isomers), 435.4 grams (4.3 moles) of propylene carbonate, and 262 grams of tert-butyl alcohol. The ~ixture was brought ~o reflux and the progress of the reaction was followed by titrating ~he remaining amine with O.lN HCl using phenol red indicator. After 3 days at reflux 95% conversion was reached and the mixture was cooled to 50C and 500 ml of acetone was added. After cooling to room tel~perature the mixture converted to a slurry of white crystals. The mixture was then warmed to 60C and fil~ered. To the filtrate was added small portions of e~hylacetate-heptane (2 to 1 by volume) until no more solid separated. Refiltration, combining the collected solid with that obtained previously, and drying at 40qC overnlght afforded 125 grams ~14.5%) of high melting "", '":. '~" ' . . . ' .: : . ' ' ' ',; ., .;.

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-16- 61109~7362 (19Z to 198C) isomers of bis(2-hydroxy-1-methylethyl~ (methylenedi -4,1-cyclohexanediyl)biscarbamate, herein referred to as "Carbamate Cross-Linking A~ent I" which gave satisfactory spectral analyses but were not deemed suitable for use in cathodic electro-coating compositions due to their high melting range. Accordingly, to the clear filtrate was added enough cationic exchange resin (Dowex SOW-X~ manufactured by Dow Chemical Co.) to remove all residual free amine as determined by checking with phenol red indicator from time to time. After all free amine had been removed, the ion exchange resin was filtered off and the solvents were vacuum distilled with steam bath heating, the last traces of which were removed at 5 mm of pressure. The resulting clear, light yellow, low me:Lting semi-solid gave satisfactory spectral analyses for a mixture of isomers of Carbamate Cross-Linking Agent I.
The yield of Carbamate Cross-Linking Agent I was 683.1 grams (80%
of theory; the total yield of all dicarbamates was 93.7% of theory).
E~A~PLE 2 Carbamate Cross-Linkin~ A~ent II
To a suitable reactor under a nitrogen atmosphere was charged 95.36 grams (0.4 moles) of 2,2'-~is(4-amino cyclohexyl) propane, 83.72 grams (0.82 moles) of propylene carbonate, and 53.72 grams of tert-butyl alcohol and the whole was brought to reflu~. The progress of the reaction was followed by titrating the remaining amine with O.lN HCl using phenol red indicator. 95% conversion was obtained after three days of refluxing after which the viscous reactlon mixture was c`oclecl to SOQC and 54 grams of methanol was added. ~nou~h o~ the same ca~ionic exchan~e resin as used in ~xample * 7'rqr~Q M~l rl~

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7~3~3 1 was added to remove ~ree amine and the solution was filtered.
Evaporation of all solvents under vacuum using steam bath heating afforded 163 grams (91% of theory~ of a mixture of isomers of bis(2-hydroxy-1-methylethyl), [~l-methylethylidene)di-4,1-cyclohexanediyl]biscarbamate, herein referred to as "Carbamate Cross-Linking Agent III'. The structure was confirmed by spectral analyses. Carbamate Cross-Linking Agent II softens by about 60C
and begins to melt at about 80C.

Hexane-1,6-bis(hydroxypropyl~carbamate as a starting material for Cathodic Electrocoating Compositions Hexane-1,6-bis(hydroxypropyl) carbamate is completely water soluble and cherefore unsuitabie as a carbamate cross-linking agent for cathodic electrocoating. Hexane-1,6-bis(hydroxypropyl) carbamate was prepared as described in the literature (Na;er, ~1., Chabrier, P., and Guidicelli, R., Compt. rend. 238 690 tl9S4)~ by the reaction of hexamethylene diamine, and propylene carbonate and subsequently fully purified. This bishydroxypropyl carbamate was then chemically modified by "capping" or "blocking" the hydroxyalkyl carbamate groups in order to produce wa~er insoluble carbamate cross-linking agents for cathodic electrocoating as described below.
~X~ E 3 . Carbamate Cross-Linking A~ent III
. _ _ To a suitable reactor under a nitrogen atmosphere was charged 50.0 grams o~ dry pyridine and 8.72 grams tO.04 moles) of hexane-1,6-bis-(h~droxypropyl~ carbamate prepared as described above. The well stirred solutian was then caoled to a 3C and ace~ic anhydride t8.98 Brams; 0.88 moles~ was slowly added keeping the temperature :. .:. . , ~ ' - .

3~

below 10C while efficiently stirring. After complete addition the mixture was stirred overnight at room temperature. At this point thin layer chromatography (TLC-Analtech precoated Silica Gel GF 250 micron plates 2.5 x lOcm; eluent 10/90 V~V MeOH/CHC13 followed by oven drying at 105C for 30 minutes to remove pyridine and pyridine acetate; visualization with iodine) showed only one product spot at Rf 0.73 (pure hexane-1,6-bis(hydroxypropyl) carbamate has Rf 0.53 under the same conditions. Most of ehe solvent pyridine was then removed at aboutlO mm of pressure with a flask temperature of 40 to 80C. The reaction residue containing product was then dissolved in CHC13 ~100 ml) and washed with three 25 ml portions of 25% w/w NH4Cl solution, then with two25:ml portions of water, followed by a25 ml portion of brine. The CHCl3 solution of product was then dried (Na2S04), filtered, and evaporated under vacuum to afford 10.77 grams (99%) of a light yellow liquid which solidified to a low melting solid on standing. This product was insoluble in water, homogeneous by TLC and gave IR and PMR spectra consistent with the diacetate of hexane-1,6-bis(hydroxypropyl) carbamate,. hereinafter referred to as "Carbamate Cross-Linking Agent III".
EXAMPL~ 4 Carbamate Cross-Linking Agene IV
In a suitably equipped flast was charged Trimethylol propane (13.4 grams) hexane-1,6-bis(hydroxyprQpyl)~carbamate prepared as descrlbed above (96 grams)~ and dibutyltindilaurate catalyst (0.6 grams). Th~ reaction mixture was stirred and heated under : ;

4 [)~

reduced pressure (approximately 20 mm of Hg) to 175 to 190C Eor a perlod of about one hour. During this period about 10 grams oE distillate was collected which by GPC proved to mostly propylene glycol. The clear resinous product in the Elask was soluble in alcohol, Cellosolve, and insoluble in water. The resulting condensation product of hexane-1,6-bis(hydroxypropyl)carbamate with trimethylol propane is herein referred to as "Carbamate Cross-Linking A~ent IV". The product was diluted with 20 grams of Cellosolve to 77% solids.
The following Examples 5-7 illustrate the preparation of cationic polymers usable in the composition of the invention.

Cationic P~ol'ymeric'Mat'erial V
Cationic polymeric material V is prepared by reacting n-butyl acrylate, sty-rene, N,N-dimethyl amino ethyl methacrylate, 2-hydroxyethylacrylate, the reac-t:lon product oE acrylic acid and a methoxypolyethyleneglycol having a molecular weight oE 550, N-dodecyl mercaptan, and azobisisobutyronitrile in the amounts and according to the procedure described in U.S. Patent 4,026,855 Eor the pre-paration of the material therein described as "Polymeric Material E". The final reæin is about 71% solids and has an hydroxy number oE about 90 and an amine number of about 45.
EXAMPLE'6 Cationi'c Polymeric Mat'_ial VI
Catlonic polymerlc material VI, a cationic epoxy resin, was prepared by reacting EPON* 1004 (a product of Shell Chemical Co.

*Trade-mark ......

~-Z~74~333 -~ 20 - 61109-7362 comprising the reaction produce of bisphenol-A and epichlorohydrin) with the diketimine of t~e diethylenetriamine (prepared as described in U.S. Patent 3,523,925) and diethyla~ine according to the procedure described in U.S. Patent 3,984,299 Eor the preparation of the material therein described as adduct C.
The final cationic resin was 75% solids. The analysis o~ the resin corrected to 100% solids showed the following: t-amine: 1 meq per gram, primary amine (after hydrolysis): 0.2 meq per gram, and calculated hydroxy content 3.7 to 4 meq per gram.

Cationlc`Polymeric Material VII
Cationic Polymeric Material VII, an epoxy material, was prepared from the ingredients and processes described below:
Pa~rts`by Weight Equivalents EPON 1004* 1017.0 1.0 ~ethyl isobutyl ketone 176.0 --(MIBK) Diketimine 69.4 0.~6 Diethylamlne 57.5 0.79 Propa80l P** 163.0 --*Shell Chemical Co. reaction product of epichlorohydrin and bisphenol-A
**Union Carbide Corp, trade mark for propoxypropanol The EPON 1004 and MIBK were charged to a suitable reactor under nitrogen havlng a decantlng trap in the dlstillate return line. The mixture was heated to reflux with stlrring in order to remo~e any water .~
.

~L274~

present. After cooling to 80C the Propasol P was added followed by the diketi~ine (derived from one mole of diethylenetriamine and 2 moles oE MIBK as described in U.S. Patent 3,523,925). The mixture was held at 80C for one hour and then cooled to 60C and the diethylamine was slowly added keeping the temperature below 65C
(exotherm) so that no diethylamine was lost by volatilization.
After complete addition the mixture was refluxed for one hour and then 100 parts more of Propasol P was added. The same amount of Propasol P was then removed by two vacuum distillations at 100 to 125C in order to remove any residual free diethylamine. The final cationic resin was 78~ solids. The analysis of the resin corrected to 100% solids showed the following: t-amine: 0.84 meq per gram;
primary amine (after hydrolysis): 0.45 meq per gram and calculated hydroxy content: 3.6 to 3.8 meq per gram.
The following Examples 8-12 illustrate the preparation and use of cathodic electrocoating baths in accordance with specific embodiments of the present invention. All references in the following Examples to "parts" means parts by weight.
EXA~PL~ 8 A cathodic electrocoating bath is prepased by combining 50 parts of the Cationic Polymeric Material V, lS parts of t~e Carbamate.
Cross-Linking Agent I, 1.7 parts of 88% lactic acid, and 1.5 parts of dibutyltindilaurate in a suitable mixing vessel equipped with a Cowels stirrer. These ingredients are rapidly mixed while 466 parts of the deioni~ed water is slowly added to produce a bath ~ rP~

1~7~

contalning approxim~tely lO,' solids. The final cathodic elec~ro-oating bath has a pH of 4.8. Af~cr a~in~ the b~th overni~ht, electrodeposition of the composition on aluminum panels serving as the cathode at lOOV for 60 seconds afforded, after rinsing and curing at 175C for 20 minutes, cured films which are glossy, smooth, and have very good solven~ resistance and mechanical propèreies.
EX~YoeLE 9 The procedure of Example 8 was repeated in all essential respects using the following ingredients:
Parts by Weight Cationic Polymeric ~aterial VII 49.0 Carbamace Cross-Linking Agent I 14.4 Hexyl Cellosolve* (1) 5.0 Butyl Cellosolve** 5.0 Lactic Acid (88%) 2.8 Dibutyltindilaurate 1.2 Deionized Water 485.0 *Monohexyl ether of ethylene glycol - a flowing agent **Monobutyl ether of ethylene glycol - a co-solvent The final cathodic electrocoating bath was lOZo solids and had a pH
of 5.8 and a conductivity of 700 micro mho cm 1. APter aging the bath cvernight, electrodeposition of the composition on aluminum panels serving as a cathode at 75V for 20 seconds produced, after rinsing and then curing at 175aC for 20 minutes, films with thick-nesses oP 0.2 to 0.25 mil. All panels were smooth, glossy, had 4H
pencil hardness, passed 40 in-lb impact tests, znd resisted greater ~harl 200 methyl ethyl ke~orle doub~le rubs. rhis cachodic electro-~ 1 ~ r Q '~ J ~ Q m ~

,~,,. ., ~,~

t~

coating bath proved stable for greater than 3 months.
EYA~LE lO
The procedure of Example 8 and the ingredients of Example 9 were repeated, except that 15.3 parts of the Carbamate Cross-Linking Agent II was substituted in place of the 14.4 parts of Carbamate Cross-Linking Agent I. The resulting cathodic electrocoating bath had a pH of 5.8, a conductivity of 700 micro mho cm , and was approximately lO~ solids. Aging the bath overnight followed by electrodeposition on aluminum panels serving as the cathode at 75V for 20 seconds afforded, after rinsing and curing at 175C for 20 minutes, film builds of 0.2 to 0.5 mil. The coatings on all panels were smooth, glossy, had 4H pencil hardness, passed 40 in-lb impact tests and resisted greater than 200 methyl ethyl ketone double rubs. The electrocoating bath was stable for more than three months in storage at ambient temperatures.
EXA~PLE ll The procedure of Example 8 and the ingredients of Example 9 were repeated except that 9.4 parts of Carbamate Cross-Linking Agent III
was substituted for Carbamate Cross-Linking Agent I and 440 parts of deionized water was used. The resulting cathodic electrocoating bath was 10~ solids, had a pH of 5.5, and a conductivity of 780 micro mho cm l The bath was then aged overnight and aluminum panels servlng as the cathode were electrocoated at 75V for 20 seconds. The electrocoated panels were then rinsed and cured at 175~C Eor 20 minutes. The cured ~ilms were 0.2 to 0.25 mil thick, had 4~ pencil hardness, passed 40 in-lb impact tests, were smooth and '''~ . '`' :

~L27~ 3 glossy, and resisted greater than 200 methyl ethyl ketone double rubs. The bath ~as still stable after three months aging at ambient temperature.

Using the mixing procedure of Example 8, 47 parts of Cationic Polymeric Material VI, 19.5 parts of Carbamate Cross-Linking Agent IV, 3 parts of hexyl Cellosolve, 1.2 parts of dibutyltindilaurate, and 3.6 parts of 88~ lactic acid were emulsified to 10% solids with 470 parts of deionized water. A milky white emulsion was obtained having a pH of 5.8 and a conductivity of 1225 micro mho cm . After aging the cathodic electrocoating bath overnight, aluminum panels serving as the cathode were electrocoated at 50V and lOOV for 30 seconds. The electrocoated panels were rinsed with water and then cured at 175C for 20 minutes. After the cure, the electrocoated films were solvent resistant, had thickness of 0.6 to 0.7 ~il, passed 40 in-lb impact tests, and had pencil hardness of 4H to 5H.
Generally reference herein and in the claims to hydroxyalkyl carbamates and compounds containing the same, including structural formulas of the same, is intended to include the various isomeric species thereof, if any.
While the invention has been described with respect to specific preferred embodiments, it will be apparent to one skilled in the art that numerous variations may be made to the embodiments without departing from the spirit and scope of the invention.

Claims (22)

The Claims What is claimed is:

1. A cathodic electrocoating composition comprising:
(a) a hydrophobic cross-linking agent having at least two carbamate groups selected from the class consisting of one or both of (i) hydroxyalkyl carbamate groups, and (ii) alkyl carbamate groups obtained by capping the reaction product of a cyclic carbonate and a polyamine;
(b) a water-insoluble and hydrophobic amino group-containing polymer; and (c) an acid disperser effective to provide cationic groups in the polymer (b) whereby the polymer is rendered water-dispersible;
and (d) optionally, a cross-linking catalyst;
the cross-linking agent (a) and the polymer (b) being stable relative to each other in the composition while at ambient temperature, and reactive with each other at elevated temperature.

2. The composition of claim 1 wherein the cross-linking cata-lyst is selected from the class consisting of metal-containing catalysts, quaternary compounds and ternary compounds.

3. The composition of claim 1 wherein the cross-linking cata-lyst is selected from the class consisting of one or more of tin, zinc, and titanium compounds.

4. The composition of claim 1 wherein the cross-linking catalyst is selected from the class consisting of quaternary ammonium, phosphonium and arsonium compounds and ternary sulfonium compounds.

5. The composition of claim 1 wherein the cyclic carbonate is selected from the class consisting of ethylene carbonate and propylene carbonate.

6. The composition of claim 1 wherein the acid disperser is an inorganic or hydrophilic organic acid.

7. The composition of claim 1 wherein the cross-linking agent (a), the polymer (b), the acid disperser (c), and, when present, the catalyst (d) are present in weight proportion, per 100 parts by weight of the solids of (a), (b), (c), and (d), of at least about 5 parts (a), at least about 40 parts (b), at least about 1 part (c), and, when present, from about 0.1 to about 10 parts (d).

8. The composition of claim 7 wherein the ingredients are present in weight proportions of from about 5 to about 50 parts (a), from about 40 to about 90 parts (b), from about 1 to about 10 parts (c) and, when present, from about 1 to about 5 parts (d).

9. The composition of claim 1 wherein the polymer (b) con-tains one or more functional groups which are reactive at ele-vated temperature with the carbamate groups of the cross-linking agent (a).

10. The composition of claim 9 wherein the functional groups of the polymer (b) comprise one or more of amino, amide, hydroxy and ester functional groups.

11. The composition of claim 1 wherein the polymer (b) contains functional groups comprising one or more of amino and hydroxy groups.

12. The composition of claim 1 wherein the polymer (b) com-prises from about 0.25 to about 30% by weight amino groups and from about 0.5 to about 20% by weight hydroxy groups, based on the weight of polymer (b) solids.

13. The composition of claim 1 wherein the hydrophobic cross-linking agent (a) contains one or more alkyl carbamate groups (ii) capped by a moiety selected from the class consisting of one or more of ester, urethane, thiocarbamate, sulfonic ester, sulfonamate esters and ether groups.

14. The composition of claim 13 wherein the cyclic carbonate is selected from the class consisting of one or both of ethylene carbonate and propylene carbonate.

15. A method of forming a cross-linked coating on a substrate comprises:
(a) immersing the substrate in an electrodeposition bath containing a composition comprising (1) a hydrophobic cross-linking agent containing at least two carbamate groups selected from the class consisting of one or both of (i) hydroxyalkyl carbamate groups and (ii) alkyl carbamate groups obtained by capping the reaction product of a cyclic carbonate and a polyamine; and (2) a water-insoluble and hydrophobic amino group containing polymer; and (3) an acid disperser effective to provide cationic groups in the polymer (2) whereby the polymer is rendered water-dispersible; and (4) optionally, a cross-linking catalyst;
the cross-linking agent (1) and the polymer (2) being stable relative to each other in the bath while at ambient temperature, and reactive with each other at elevated temperature;
(b) cathodically electrodepositing a coating of the composition from the bath onto the substrate;
(c) removing the coated substrate from the bath; and (d) heating the coated substrate at an elevated temper-ature, and for a time sufficient to cure the deposited coating.

16. The method of claim 15 wherein the bath includes the cross-linking catalyst (4).

17. The method of claim 15 including heating the coated sub-strate at an elevated temperature of from about 200 to about 400°F
(about 93 to 204°C).

18. The method of claim 16 wherein the catalyst (d) is selected from the class consisting of metal compound catalysts, quaternary compounds and ternary compounds.

19. The method of claim 16 wherein the catalyst is selected from the class consisting of tin, zinc, and titanium compounds.

20. The method of claim 16 wherein the catalyst is selected from the class consisting of quaternary ammonium, phosphonium and arsonium compounds and ternary sulfonium compounds.

21. The method of claim 15 wherein the hydrophobic cross-linking agent (1) contains one or more alkyl carbamate groups (ii) capped by a moiety selected from the class consisting of one or more of ester, urethane, thiocarbamate, sulfonic ester, sulfonamate ester and ether groups.

22. The method of claim 21 wherein the cyclic carbonate is selected from the class consisting of one or both of ethylene carbonate and propylene carbonate.