CA1119331A

CA1119331A - Water-borne thermosetting coating composition based on nitrogen resin containing epoxy and amine groups

Info

Publication number: CA1119331A
Application number: CA000296642A
Authority: CA
Inventors: Eugene G. Sommerfeld
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1978-02-08
Filing date: 1978-02-08
Publication date: 1982-03-02

Abstract

ABSTRACT OF THE DISCLOSURE
A waker-borne thermosetting coating composition comprising a stable dispersion or solution of:
(A) an epoxy polymer which is either terminally functional or which contains randomly distributed epoxy groups, said resins being reacted with a tertiary amine; and (B) a nitrogen resin is provided. Such composition is useful for spray-. flow-, dip-, roller-, electro- coating metal and paper substrates and provides coatings of improved properties, including high degree of flexibility during machining and stamping of the coated articles, corrosion resistance, gloss, hydrolytic stability, and nonadulter-ating of foods and beverages in contact therewith.

Description

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.
BACKGROUND OF THE INVENTION
Thls lnventlon is related to a water-borne ~oating compositlon of general utility ln coatlng metallic substrates, ~or example in automotlve and coil coatlngs applications.
Nore particularly, the coating composition ls use~ul as an interior and exterior can coating.
The can coating industry utillzes a varlety of thermosetting coating compositions designed to ful~ill various requirements dictated by the intended use. Cans are usually coated on their interior by a thin coating designed to protect the metal walls from attac~ by food or beverage,and vice versa, to be stored therein. Such coatings should have among other properties good adhesion to the metal walls, low extractables and sorption to prevent taste adulteration, and a rapid cure rate ~or an economical manufacturing process.
The coatings of the prior art are thermosetting compositions often dissolved or dispersed in organic solvents.
Among commonly utilized thermosetting compositions are those based on epoxy resins crosslinked with nitrogen resins, usually in an acid catalyzed process.
Increased awareness of the environmental hazards of allowing organic solvent vapors to enter the atmosphere, the desirabllity o~ a single system that can be applied not only by the more conventional techniques of spray, roller or flow co~ting but also by electrodeposition, and the economy resulting from the substitutlon Or water for some or all of the solvents in a coating composition, are all factors mitleating ln favor of water-borne coating compositions.
Unlted States Patent 2,676,166, issued April 20, 1954 to V. J. Webers,~hows the conversion, through the use of 3~

tertiary amines, of some random low molecular weight hydrophilic copolymers of oxirane containing monomers with other ethylenically unstaurated monomers into water soluble materials. These polymers contain a large number of hydroxyl and quaternary ammonium groups per molecule.
In United States Patent 3,839,252 issued October 1, 1974 to J.E. Bosso et al., there are des~ribed water dispersible products of epoxy resins with amine salts.
These products are designed to contain at least one unreacted 1,2-epoxy group per m~lecule and also contain in the resin quaternary ammonium salt groups.
The composition of this invention is an aqueous solu-tion or dispersion of the reaction product of a terminally functional epoxy resin with a tertiary amine and a nitrogen resin cross linking agent. These aqueous solutions or disper-sions of the resinous quaternary ammonium hydroxide and a nitro-ge~ resin are stable both unca~alyzed or catalyzed and can be applied to metallic substrates by spray, roller, dip or flow coating or by electrodeposition at the cathode and to paper.
SUMMARY OF THE INVENTION
According to the present invention there is provided a water-borne thermosetting coating composition consisting essentially of:
(A) 50-97 parts by weight, based on the weight of components (A) plus (B) of (1) an epoxy polymer containing, on the average, either (a) two terminal 1,2-epoxy groups per molecule and having a weight average molecular weight, determined by gel permeation chroma-30tography using a polystyrene standard, of : .

1000-5000, or (b~ 10~150 rarldomly dist~lb~rted 1,2~poxy group~ per molecule and ha~ng a ~reigh~ average molecular weight of 25,000-75,000; said epoxy ~olymer reacted to ~ub~tan-tiallg co~plete consu~pt'lon of the epoxy groy?~
with

(2) ~ agueous ~olu1;ion of about 1-1.25 equival~n~s, per equivalent o~ e~ox~ group of saia epoxy polymer o~ (1), o~ a tertiary ~m~ ne selected from the group cowisting Or RlR2R3N, p9~dine, N~neth~lpyrrole, ~ethyl pyrrolidine, N~nethgl mo~pholine, ~d mixt~re~ ther~of and where Rl ana R2 are h~dro~r~ tit~ted or un~ubstituted mono~alent; alkyl group~ containlng o:ne or two carbon atoms and R3 i~ a hydroxy-s~ tituted or un~ tituted monovalent a~yl gro~p con-taining 1-4 carbon atoms; and (B) 3-50 parts by ~ ht, based on the ~eigh~ o~ COD~pO-nents (A) plus (B), o~ a ~lly alkylated amine-alde~de resin, a par;lally a~cylated amine-aldehyle resin or mixttlre thereof;
wheroln component~ (A) plus (B) co~prise pre~rably about 0.1_50% by weight of the coating composition and the r~m~tnder is co~pri6ed o~ water and orga~ic liguid(s) in a ratio of ~r~m 70:30 t~ 90:10 and said coating composition having a pH of 7.5 or above.
The pres~n~ in~ention also provide~ a thermosettin4 cQa~lng eomposition, ~hich i$ ln~initely dilu~able with water, ch~racterized by conæ~ting e~sentially Or:

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.
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(A~ 50-97 parts by weight, ba~ed on the we~ght o~
con~poneNts (A) plw (B) . of (1) an epoxy poly~er containing, on the a~erageJ
e1ther (a) two te~mi~al 1,2~oxy gro~ps per r~olecule and having a weigh~ average molecu-lar weieht, determined by gel penneation chromatogr~phy u~ing a poly~tyrene s~ dard, of 1000-5000, or (b~ 10~ randomly distrib-u~;e~ 1,2-epoxy grot~p8 per molecul~ and ha~lng a weight average moleeular w0ight of 25J000 to 7~9000; rea¢ted to the slibstantially con~plete con~ ptio~ of the epox~ gro~pe with ~-(2) an aqueou~ solution Or about; }-1.25 equlva-le~, per equi~alent oi epoxy group of said epo:x;y polymer o~ (1), of a te~tiary a~ine ~elected from the gro~p consi~ting o~ Rl~R3N.
pyridine, N-methylpyrrole, N-methyl pyrrolidine, N~neth~ pholine, and m~xtures thereo~ and ~ere P~l and R2 are hydr~xy-s~b~tltuted or u~s~ibst~t~ed monovalen~ alkyl groups contain-ing one or two carbon atom~ and R3 is a hydroxy-s~ tituted or unsubstitu~ea mono~alent alkyl grou~ containlng 1 ~I ca~bon atoms, and ) 3-50 parts by weight, ba3ed on the weight of coD~ponents (A) plu~ (~), o~ a ~ully alkylated ~nine-aldeh~rde re~ln, a part~all~ alkyla~ed amlne-ald~ resin or mixture~ thereoi.
Dl;~CRIPTIO~i OF THE I~V~TION
The ~ater-bor~e thermosetting coating coD~position of this invention i8 a solution or di~persion of a nitrogen 3o re~in cros~linking agent and the reactlon product of a te~tiary amine and an epoxy re~in or polymer ~ch either :

has terminally functional epoxy groups or which contains randomly distributed epoxy groups. By utilizing aqueous solutions of highly specific tertiary amines such as dimethyl ethanol amine and epoxy polymers such as the epichlorohydrin-bisphenol "A"-type epoxides or the poly-glycidyl ethers of novolac resins or other polymers con-taining pendent 1,2-epoxy groups, a stable water soluble or dispersible polymeric quaternary ammonium hydroxide results.
Addition of a nitrogen-resin crosslinking agent, acting also as a solubilizing agent, affords a solution or dispersion which is stable at room temperature and is infinitely dilu-table with water.
Whether the coating composition is a solution or a dispersion is largely dependent on the nature of the parti-cular nitrogen resin and amine used. Even when the composi-tion is opaque some of the resinous components may be dissolved and when the composition appears to be a clear solution it is possible that small amounts of the components are in a dis-persed state. For sake of simplicity hereafter the term "dispersion" will be used to denote the water-borne coating composition. ` -The dispersion as pxepared has a pH of above 10 and a non-volatile content of up to 50~ by weight. It has excel-lent wetting properties when applied to metal substrates and, upon curing, a glossy, highly solvent resistant coating is obtained. It is also useful as a coating for paper.
~ he low molecular weight epoxy resins to be utilized in the present invention to obtain terminally functional 1,2-epoxy groups are commonly known in the art.
3Q One class of such resins has the generalized formula tt~

~ )CH2~ H2 wherein R is an al~ylene grou;p of 1-4 carbon atoms and n i5 an integer from 1-12. The epoxy resin~ utilized in this inYen-ti0n contain ~ average of tw~ term~nal 1,2-epoxy group~ per molecule and are in the molecular wei~ht range Or 3~3-5,000.
q~ey ca~ als0 conta~n ~ubstitu~ed arc~tic rings.
One such preferred epoxy resin i8 hl?O~* 1004 where R 18 i~opropylidene, the a~erage value Or n 1~ 5, and has an epoxy equlvalent of 875-1,025. The epoxy equivalent i8 de~ined a8 the gram8 0~ resin containing 1 gram-oquivalent of epoxlde as mea#ured by ASTM-D-1652. The coating co~posi-tion containing EPON 1004 affords a glo~sy, ~lexib~e, che~icallg reæi~tant film. Another preferred epoxy resin ig EPON 1007 where R iæ i~propyl~dene, the average value of n is ll, has an epoxy equivalent of 2,000 2,500. The coating compo~itlon contaln~ng EPON 1007 af~ords glo8sy, tough, flex$ble films upon cure.
~ he epoxy polymers to be u~llized in the present in~entlon to produce randomly distributed epoxy group8 are also comm~nly known ln the art. One Cla8S of such polymers ha~ the generalized fo~mula R

wherein R is a hydrogen atom or a glycidyl gro~p and the average value of n is 2-11; the molecular weight range is 470-2,000 and iæ known in the art as polyglycidyl ethers Or * denotes trade mE~rk - 6 -: , . . ~` .
, :

novolac rex~ns.
One such pre~err~d epoxy polymer i~ EPON 15~
(available from Shell Chemical Company) where n>2, has an epoxy equlvalent of 176-181, and haæ a Brookfield viscoæity at 52C
of 3,500-7,000 centipoiæeæ (Spindle ~o~ 3, 20 re~olutionæ per minute). The epoxy equivalent i8 defined as the gxams of polymer containing l gram-equlvalent of ~poxide as measured by ASTM-D-1652. The coating compo~ition containing ~2ON 154 affords a glossy, flexible, chemlcally re~istant film.
Another preferred epoxy polymer i5 5156* (available ~r~m the Celanese Corporation), having an epoxy equiv31ent o~
185 and a Brookfield viæcosity o~ 52C o~ lOO,OOO centi-poi~e~. The coating composition containing "5156"
afford~ glossy, tough, flexible films upon cure.
Another suitable no~olac-based epoxy resin is QX-2174* (product o~ the Dow Chemical Company), havlng an epoxy equi~alent of 226 238 and a Durran~s melting point of Still another use~ul polymer is QX-2174-1*
(also ~rom Dow Chemlcal Gompany), epoxy equivalent 230-245, Durran~ mel~ing point 65-75C.
~et a ~urther example of the use~ul polyglycidyl ethers of the phenol/formaldehyde novolacs 18 ERR-OlOO*
(a product of the Un1on Carbide Plastlcs Corporation), where n=5, the epoxy equivalent is 190-220, and the Durran's melt-ing point is 85-100C.
Another c1~3s of polymers that can be u~ilized in the pre~ent invention comprises polymer~ prepared from varlous ethylenically unæatu~ated monomers and epoxy-functional monomers such aæ glycidyl esters o~ acrylic acid, methacrylic * denote~ tr~de ma~k ., 33~

acid, the mono-and/or diglycidyl estexs of maleic acid, fumari~ acid, and itaconic acid, allyl glycidyl ethex~ vinyl glycidyl ether, and the like. Amon~ the useful ethylenically unsaturated monomers are the alkyl- and hydroxyalkyl esters of acrylic and methacrylic acids, the vinyl aromatic monomers, the vinyl esters, (meth)acrylonitrile, (meth)acrylamide, (meth)acrylic acid, itaconic acid, and mixtures thereof.
These polymers are in the 25,000-7S,000 numb.er average molecular weight range (as determined by gel permea-tion chromatography using a polystyrene standard), haye anepoxy equivalent of 500-2,500, and contain, on the average, 10-150 1,2-epoxy groups per m~lecule.
A preferred class of these polymers is styrene/alkyl (meth)acrylate/hydroxyalkyl (meth)acrylate/glycidyl (meth)acrylate, in the weight ratios of 20-60/60-20/0-10/10-20.
Generally, the acrylic esters contain an alkyl group of 1-8 carbon atoms, the methacrylic esters contain an alkyl group of 2-8 carbon atoms, and the hydroxy-alkyl (meth)acrylate can be hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate or hydroxypropyl methacrylate.
For example, a polymer, having the approximate composition by weight, of styrene/ethyl acrylate~hydroxyethyl acrylate/
gylcidyl methacrylate/39/33/8/14, an approximate weight average molecular weight of 25,000, and an approximate epoxy e.~uiva-lent of 1,000, is useful in a can coating composition, Another preferred class is styrene and~or methyl methacrylate/alkyl (meth)acrylate/hydroxyalkyl (meth)acrylate~
gycidyl (meth)acrylate, in the weight ratios of 20-60~60-20/
0-10/10-20. Generally the acrylic esters contain an alkyl group of 1-8 car~on atoms, the methacrylic esters contain an

3~
alkyl group of 2-8 carbon atoms, and the hydroxyalkyl (meth)acrylate can be hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate or hydroxypropyl meth-acrylate. For example, a polymer, having the approximate composition by weight of methyl methacrylate/butyl acrylate/
hydroxyethyl acrylate/glycidyl methacrylate/39/39/8/14, an approximate weight average molecular weight of 25,000, and an approximate epoxy equivalent of l,000, is useful in an automotive coating composition.
These polymers can be prepared by conventional polymerization techniques, for example, in solution, using azo- or peroxy-initiators and conventional solvents.
The epoxy polymer comprises 50-97 parts by weight of the film-forming components of the coating composition and preferably 65-85 parts. One preferred composition con-tains 75 parts of an epoxy polymer.
During the preparation of the coating composition of this invention a solution of an epoxy polymer in organic liquid(s) is brought in contact with an aqueous solution of 20 a tertiary amine. A wide variety of organic liquids can be used to dissolve the epoxy polymers. Among the most commonly used solvents are alcohols such as isopropanol, the butyl alcohols, 2-hydroxy-4-methylpentane, 2-ethylhexyl alcohol, cyclohexanol, glycols such as ethylene glycol, diethylene glycol, 1,3-butylene glycol, ether alcohols such as ethylene glycol mono-ethyl ether, ethylene glycol mono-butyl ether, diethylene glycol mono-methyl ether, mixtures thereof, and many aliphatic and aromatic hydrocarbons if used admixed with at least one of the above.
The reaction of tertiary amines with materials .

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containing epoxy groups, to yield adducts containing quater-nary ammonium groups, is known. Such reaction, when carried out in presence of water, can afford a product that contains both a hydroxyl group and a quaternary ammonium hydroxide.
The reaction can be represented schematically as follows:

,>~<
+ R3N + H20~

While most tertiary amines react with epoxy polymers to form quaternary ammonium hydroxides, the preparation of the quater-nary ammonium hydroxides to be utilized in the water-borne coating composition of this invention is carried out utilizing at least one tertiary amine selected from the group: RlR2R3N, N-methyl morpholine, N-methyl pyrrolidine, pyridine, N-methyl pyrrole, and mixtures thereof and wherein Rl and R2 are sub-stituted or unsubstituted monovalent alkyl groups containing one or two carbon atoms in the alkyl portion and R3 is a substituted or unsubstituted monovalent alkyl group containing 1-4 carbon atoms, Some examples of RlR2R3N are: trimethyl amine, dimethyl ethanol amine, diethyl methyl amine, methyl diethanol amine, ethyl methyl ethanol amine, dimethyl ethyl amine, dimethyl propyl amine, dimethyl 3-hydroxy-1-propyl amine dimethyl benzyl amine, dimethyl 2-hydroxy-1-propyl amine, dimethyl l-hydroxy-2-propyl amine, and mix-tures thereof. Most preferably trimethyl amine or di-methyl ethanol amine is used.
While the exact mode of the reaction is not fully understood, it is believed that the efficiency of the amines 30 utilized is related to steric factors. The amount of tertiary '~

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amine used is determined by the epoxy equivalent of the parti-cular epoxy polymers employed and is at least 0.75 equivalent, and preferably between 0.9 and 1.1 equivalents, per epoxy group. At lower levels of amine use the residual epoxy groups of the epoxy polymers are subject to further reaction in the highly basic reaction medium. Such further reaction can lead to a crosslinked system prior to the addition of the nitrogen resin crosslinking agent or it can lead to storage instability and premature gelation of the coating composition. In a pre-ferred embodiment equivalent amounts of epoxy polymer andteritiary amine are used resulting in substantially complete consumption of the epoxy groups. Such a reaction, when the starting epoxy polymer contains an average of more than two epoxy groups, affords a polymeric quaternary ammonium hydroxide having more than two such groups and the same number of hydroxyl groups.
The teritiary amine and water are admixed with a solution of the epoxy polymers. The exact ratio of the amine and water is not critical but one preferred ratio of amine to water is approximately 1:2 by weight. At the end of the reaction period between the epoxy polymer and the teritiary amine the product is a solution at the reaction temperature.
The reaction can be carried out between room temperature and below the boiling point of the reaction medium, preferably between 50-95C, and most preferably between 70-80C. In this temperature range there is a rapid rate of reaction without complicating side reactions.
Further dilution with water of the solution of the epoxy polymer - tertiary amine adduct, at the reaction temperature, can be carried out. In one embodiment a $.
quaternary ammonium hydroxide remains in solution at about 75C in a liquid medium comprising an approximately 75:25 weight ratio of organic liquid and water Such a solution, however, has a tendency to separate into two phases upon cooling to room temperature. In another embodiment, using trimethyl amine, the solution remains in a single phase even at room temperature, The water-borne thermosettin~ coating composition of this invention is a stable solution or dispersion, even at room temperature, and comprises a nitrogen resin cross-linking agent together with a polymeric quaternary ammonium hydroxide.
The nitrogen resins are well known. They are the alkylated products of amino-resins prepared by the condensa-tions of at least one aldehyde with at least one of urea, N,N'-ethyleneurea, dicyandiamide, and aminotriazines such as melamines and guanamines. Among the aldehydes that are suitable are formaldehyde, revertible polymers thereof such as paraformaldehyde, acetaldehyde, crotonaldehyde, and acrolein. Preferred are formaldehyde and revertible polymers thereof. The amino-resins are alkylated with at least one and up to and including six alkanol molecules containing 1-6 carbon atoms. The alkanols can be straight chain, branched or cyclic.
Among the preferred nitrogen resins are partially methylated melamines, partially butylated melamines, hexa-ethoxymethylmelamine, hexamethoxymethylmelamine, dimethoxy-tetraethoxymethylmelamine, dibutoxytetramethosymethylmelamine, butylated benzoguanamine, partially methylated urea, fully methylated urea, fully butylated urea, hexabutoxymethylmelamine, ;

and mixtures thereof. In one preferred embodiment, utilizing a partially methylated melamine, the composition of this invention has excellent wetting properties on metals such as aluminum or tin-free steel. The cured coatings based on this composition are glossy, show little or no cratering, and are resistant to solvent.
The nitrogen resin crosslinking agents help to solubilize the polymeric quaternary ammonium hydroxide adducts and help to stabilize the resulting water-borne coating 10 composition. These nitrogen resins comprise 3-50 parts by weight of the film-forming components of the coating composi-tion of this invention and preferably 15-35 parts. One preferred embodiment contains the product of 75 parts of an epoxy polymer with an equivalent amount of a tertiary amine and 25 parts of a nitrogen resin.
The water-borne composition of this invention is stable and is a dispersion or, depending on the particular nitrogen resin utilized, a substantially clear solution.
When hexabutoxymethylmelamine is used the coating composi-20 tion is a stable dispersion capable of being applied by anyof the conventional techniques such as spray or roller coat-ing or by electrodeposition. When a partially methylated melamine or hexamethoxymethylmelamine is used the coating composition is a clear solution even at room temperature and is also capable of being applied by a variety of techniques.
The coating compositions of this invention can be cured thermally. After the composition has been applied to the substrate, baking at elevated temperatures brings about the desired crosslinking. Temperatures of 150C to 260C

~' `;-for 0.1 to 30 minutes, are typical baking schedules utilized.
Optionally non-volatile acid catalysts are included in the coating composition to increase the rate of cure. By non-volatile acid catalyst is meant an acid catalyst that remains in the cured film. The acid catalyst can be parti-cularly important when a fully alkylated nitrogen resin cross-linking agent such as hexamethoxymethylmelamine is utilized.
Among useful acid catalysts are phosphoric acid, its mono-and di- esters formed with aliphatic, cycloaliphatic, and aromatic alcohols, citric acid, and para-toluenesulfonic acid.
Mixtures of these can also be used. The final pH of the coat-ing composition is determined by the concentration of the acid used and is determined on the basis of the rate of cure desired and the type of nitrogen resin crosslinking agent used.
The pH of the thermosetting coating composition is above 10 as prepared. The composition can be cured at this pH if desired. A particular advantage resulting from this ability to cure films, resulting from a liquid coating composi-tion of high pH values, is the improved wetting of the water-borne system on metal substrates under many practical appli-cation conditions such as when unclean, oily surfaces are coated.
When acid catalysts are added to the coating composi-tion the final pH of the system is lowered in accordance with the needs of the components of the system, the lower pH being necessary for the more fully alkylated nitrogen resins. When a completely alkylated crosslinking agent is used the final pH of the coating composition is adjusted to between 7.5 and 12l preferably to between 9 and 10. Utilizing a coating composition of this invention there is no need to lower the pH of the system to the acid side, unless very rapid cure is -- 1~ --..

3~.
required. Corrosion, often common to acidic coating composi-tions, can be thereby avoided.
The water-borne composition can be applied by a variety of techniques and to a variety of substrates known in industry. For example, the coating composition of this invention can be utilized in the can manufacturing industry which utilizes mainly metallic cans, many of them cylindrical, made from aluminum, tin-free steel, electrolytic tin-plate, and quality-as-rolled steel, among others. Cans utilized for packaging and shipping food and beer or other beverages are mostly of the three-piece or the two-piece drawn-and-ironed (D and I) variety. Cans constructed from three pieces (body, top, and bottom) can be roller coated before the metallic sheet is formed into the body of the can or can be spray coated after partial fabrication. The D and I cans, where the metal sheet is stamped to form a cylindrical body closed at one end, are generally spray coated.
The thermosetting coating composition of this invention can also be electrocoated. In the electrodeposition process the water-borne composition is placed in contact with an electrically conductive cathode and an electrically con-ductive anode, with the surface to be coated being the cathode.
During the process an adherent film of the coating composition is deposited on the cathode. The nitrogen resin crosslinking agent also migrates, in a possible physical entanglement with the polymeric quaternary ammonium hydroxide, to the cathode.
The conditions under which the electrocoating is carried out are similar to those used in the electrodeposition of other types of coatings. The applied voltage can be ,J!~
.

varied, can range from 1 to 1000 volts, and is typically between 25 and 500 volts. The current density is usually between about 1 milliampere and 100 milliamperes per square centimeter. The current density tends to decrease during the coating process as the coating thickness increases. The coating time can vary from 1 to 120 seconds or longer and is typically between 1 and 5 seconds for coating cans.
The concentration of the coating composition depends upon the process parameters to be used and is not generally critical. Ordinarily the film-forming components comprise 0.1-50 and preferably 5-30~ for conventional coating methods and 1-20% for electrodeposition of the total, the remainder being water and organic liquid(s). The latter are present in a ratio of from 90:10 to 70:30.
The freshly deposited films are capable of being immediately crosslinked without regard to the method of coat-ing used to obtain them.
The water-borne thermosetting coating composition of this invention is useful in a variety of applications.
This coating composition finds particular utility in the can industry where the composition can be applied to the interior of two-piece drawn-and-ironed and three-piece beer and beverage cans, to the exterior of three-piece beer and beverage cans, to the interior and/or exterior ends of two- or three-piece cans or two- or three-piece sanitary cans. When the coating composition of this invention is applied to the interior of food and beer or beverage cans by spray-coating, a thin uniform film is deposited which, after curing, corre-sponds to a coating weight of 0.3 to 1.3 milligrams per square centimeter (2-8 milligrams per square inch).

. :

3 ~, The composition can also be used as a paper coating.
A glossy coating results when the pH of the coating composi-tion is adjusted to approximately six and the coated substrate is baked for 5-10 seconds at 150C.
The water-borne composition also has utility in automotive, appliance and coil coating applications, the final coated articles having especially desirable corrosion, salt-spray, acid, base, stain, and detergent resistance properties.
The coating composition can also be used as a primer lofor metallic substrates. A wide variety of topcoats can be used after the primer has been partially or completely cured.
Among the useful topcoats are polyvinyl chloride, vinyl chloride copolymerized with one or more of the following:
fumaric acid and/or its methyl, ethyl, butyl or octyl ester, a hydroxy-modified vinyl chloride/vinyl acetate copolymer post-reacted with trimellitic anhydride, and acrylic polymers.
After application and curing the coating composition of this invention can be tested, among other properties, for flexibility, adhesion, for pasteurization and processing 20 resistance, for resistance to boiling water and solvents, and for its effect on taste.
The following are convenient procedures for carrying out the various tests. The tests can be carried out on paper, test panels or finished cans, coated and cured in a 205-216C/
1-10 minute or 150C/5-10 second cure cycle.
Pasteurization Resistance: A sample of a coated panel is immersed in water at 66C for 30 minutes. For a coating to be acceptable there must be no blistering, softening, "blush" or loss of adhesion.
Boiling Water Resistance: A coated panel is immersed ~L~

~ :g :~33 ~.

in boiling water for 30 minutes. Again, no blistering, softening or loss of adhesion is permitted and no "blush"
is allowed.
Flexibility: A coated panel is subjected to 180 degree bending. No cracking of the film or loss of adhesion should take place for the coating to be acceptable. No crack-ing or loss of adhesion is permissible during the fabrication of can ends.
Solvent Resistance: A sample coated panel is 10 mechanically rubbed 100 times with cloth soaked in methyl ethyl ketone. A passing sample will show no dissolution of, delamination of, or penetration through, the film by the solvent after 100 strokes.
Taste Test: A simulated coated panel (aluminum foil), representing the interior surface area of a can, is inserted into a twelve-ounce soda bottle filled with spring water and the bottle is capped. The contents of the bottle are pasteurized at 66C for thirty minutes and stored in a 40C
oven for five days. The bottle is cooled to room temperature 20 and the contents are tested by a taste panel comparing to water stored without a coated panel. An acceptable coating will give no taste to the water.
Extractables: This test is carried out according to guideline extraction methods as specified in the 1966 Supplement to the Code of Federal Regulations, issued by the Food and Drug Administration (see Title 21, Section 121.2514).
Processing Resistance: A coated panel or a coated fabricated end is placed in a partially water-filled pressure cooker for ninety minutes at approximately 120C. No blister-30 ing, softening or loss of adhesion is permitted after this .

:~ :

~ .33 ~;
period. ~o "bluæh" ~ 8 allowed.
The invention can be further understood by re~erring to the following examples in which parks and percentages are by weight, unless otherwise indlcated. Example 1-17 illus-trate embodiments of the invention utillzing terminal epoxy group~ and exam~les 18-20 illustrate embodiments of the ln~ention utiliæing randomly distribu~ed 1-2, epoxy groups.
EXA~LE 1 Into a 500~mi11~1iter, three-necked~ round-bottomed flask, equipped with a thermometer, stirrer, and conden~or, are placed EPON 1004 (available ~rom Shell Chemlcal Company), B2.5 grams; 2-butoxy-1-ethanol, 28.9 grams, and dlethylene gylcol mono-butyl ether, 28.9 grams. The contents are heated to 70C to obtain a clear ~olution. To this 801u-tion is added a mixture of dimethyl ethanol amine, 8.5 grams and water, ~7.0 grams. The reaction temperature i~ maintained between 70 and 75C for ~ifteen minutes, after which time a partially methylated melami~e, 80% ~olids in iso~propanol, (avQilable from the Monsanto P~lymers and Petroch~mical~
~o Company under the trade mark of RESIMENE 731) 25.8 grams, is a~ed. To the con~ents now between 60 an~ 65C is added 200.5 grams o~ water o~er a thir~y~m~nute period. A clear, Yi8CoU8 ~olution re~ults ha~ing a Gardner-Holdt viscosity o~ Z6 and a pH o~ 12.2. The product ha~ a solid~ content, determined at 204¢ ~r ten minutesJ o~ 27.2%. ThiQ ~olution is roller coated onto an aluminum panel and ls cured at approYim~tely 204C for ten minutes. Tho resultant coating is glossy, tough, flexible, an~ pa~ses the abo~e-descrlbed te~ts. ~he coating weight i8 0.7 millier~un per ~quare centimeter.
3o - 19 _ .

~ t~,3.^~.

Into a 100-gallon reaetor are ch~rged 2~buto~y-l-eth~.nol, 63.1 pound~, and diethylene glycol mono-butyl ether, 63.1 pounds. The reactor i8 heated to 70C and EPON 100~, 187.1 poundR, i8 added slowly wlth agitatlon. The contents are held between 70 and 75C until all of the epoxy resln is dissolved. A mix~ure of dimethyl ethanol amine, 19.4 pounds, and water, 38.8 pound~, iB then added over a ~ifteen~minute period. After an additional ~ifteen~minute period of agita-tion, hexamethoxymethyl~elamlne, 33.1 pounds, iB addod andthe reaction temperature iæ now between 60 and 70C~ Maintain-ing the batch temperature between 55 and 60C, water, 398 pOUnaS, i8 add~d over a o~e-hour pçriod, followed by a 801u-tion o~ phosphoric acid, 8.3 pounds, in a 3:1 by weight mix-ture o~ water and diethylene glycol mono-butyl ether, 47 pound~. This ~tep is followed by the addition of a partially methylated mela~ine (RESIMENE 731), 17.2 pounds. The content~ o~ the ve~el are allowed to cool to room tempera-ture. ~he ~inal clear 801ution has a Gardner-~oldt ~iscosity ~ Z4~ P~ o~ 9.5, and a solids content, d~termdned at 204C
rOr ten mhnutes, o~ 30.4~. The solution iæ roller coated onto a tin-~ree steel panel and iæ cured at approximately 204C ~or ten manutes. The reæulta~t coating i8 glossy, tough, rlexible, and pa~es the above-de~cribed tests. The coating weigh~ i8 0.7 milligram per s~uare centimeter.
EXAMP~E 3 The procedure o~ E2ample 2 18 repea~ed u~ing the following qua~tities: 2-~utoxy-1-ethanolJ 58.9 pound~;
diethylene glycol mono-butyl ether, 58.9 poundæ; EPON 1004, 182.5 pounds3 dlmethyl ethanol amine, 18.8 pounds, dissol~ed 73 ;3 ~.~
in ~ter, 37.7 pounds; a partially methylated mela~ne, 89%
solids in iso~propanol, (a~railable ~rom Mon~anto Polgmer~ a~
Petrochemical Company, known as RESIMEN~ X-740) 51.3 pounds;
413 pounds of water; 8.1 pounds o~ phosphoric acid disæolved in a 3:1 by weight m~xture of water and diethylene glycol mono-butyl ether, 45.8 pounds. The re~ulting clear æolution ha8 a Ga~dner-Holdt viscosity at room temperature of Z2~ p~
of 9.5~ and solids con~ent, deter~i~ed at 204~ for ten minutes~ o~ 27.8%. ~hi~ ~olution can be applied to variou~
10 sub~trates as i8 or, in order to ~ncrease its rate of cure, the amount o~ nitrogen-resin cr~slinking agent can be increas-ed as follows: to 875 pounds of the total ba~ch as prepared above are added the f~llowing: 2-bu~oxy~ thanol, 27.6 pounds; diethylene glycol mono-bu~yl ether, 29.3 pounds3 and 16.8 pounds of RESIMENE X-740. The resultlng solution h~
a Gardner-Holdt viscoslty of T, pH of 9.5, and a ~olid8 con-tent as determined abo~e of 27.4%. Thi8 solutiQn i8 roller coated on~o quality-as-rolled steel or on tin-free steel, baked at 205C for six minutes. The re#ulting ~ilm i~ clear, glosay, tough, and passe~ the above described teæts.

The procedure of Example 2 ~s repeated using the followlng quan~ities: 2-bu~oxy-1-ethanol, 52.4 pounds;
diethylene glycol mono~butyl ether, 155.1 pound~3 EPON 1004, 181.9 pound~; dimethyl ethanol am$ne, 18.8 pound~, dissolved in water, 37.5 pound~; a mixture of nitrogen reBins: di-butoxytetr~methoxyme~hylmelamine, 39.1 pounds and a partially methylated mela~ine ~CYMEL* 370, ava$1able from the American Cyanamid aompany) 44.4 pound~; wQter, 647.6 pounds, phosphoric 3o acid, 10.2 pounds, di~solved ~n 58.1 pounds o~ a 75:18.5:6.5 denotes trade mark by w~ight mixture of water, diethylene glycol mono~butyl eth~r~
and 2-bu~oxy-1-ethanol. The resulti~g clear solu~ion has a Gardner-Holdt viscosity of G~, pH of 8.o, and a sol~ds content, determlned at 204C for ten minutes, of 20.6~. The 301ution i3 applied with an airless gpray ~pplicator and baked at 204C for 110 ~econds. Satisfacto~y cure can also be obtained if the bakin~ time is reduced to 55 seconds. The coatlngæ so obt~ined paæs all the tests above described.
EXAMP~E 5 A ~olution i~ prepared ~or electrodeposition as ~ollowg. The follo~lng i~gredient~ are mlxed and hea~ed to 75C until dis~olved: EPON 1004, 275.9 grams; 2~butoxy-1-ethanol, 90.4 gram~, and methyl ethyl ketone, 10.1 gram~. To this solution is added over a 5iminute period dimethyl ethanol ~mine, 28.6 gramSJ dis~olved in 48.4 grams of water and the reaction temperature is malntained at 70 to 75C for 30 minutes. Over the next 30iminute period at 60 to 65C is added 405.2 grams of water. The reaction mixture at this point is a two phaEe system. To this mixt~re are added a partially methylated melamine, 80% solids in ~so-propanol, (RESIMENE 7313, 95.8 grams, and water, 334.8 grams, o~er a l-hour period ~hile the temperature i~ maintained at approxi-mately 70C. The resulting clear amber solution has a Gardner-~oldt vi~co~ity o~ 0, p~ of 12.3, and a solids content, determined at 204C for 10 minutes, o~ 23.0%. me solution has a conductivity of 1,350 micromho per centimeter.
A 287.2 gram portion o~ this solution is dilu~ed to 8.o weight percent ~olid~ content by adding 538.6 grams of water. The pH
now is 11.5. Thi~ dispersion 1~ placed in a 1-liter coating tank ~nd a 10 centimeter by 10 centimeter aluminum can end-~ J

stock i8 placed into the solution. When the panel polarity ls ~3uch that it is the cathode then, at an applied vol~age of 100 volts and in a co~ting time o~ 2 seconds, the panel iæ
~ow!ld to have a smooth coating on its ~urface upon baking at 204C for 5 minutes. When the panel is æet to be the anode, no ~lm ls depo~ited at all.
EXA~IiE:S ~ - 14 Coating composition~ are prepared as in Ex~mple 2 by substituting a ~eries of nitrogen resin cros81inking agents 10 ~or the partially methylated mela~ine (RESIME~E 731). In each oi the exe~pleæ, ~ee list below, a 60~3ram porti~n of the compo~ition i~ diluted with 15 grams of a 3:1:1 mixture o~ water:2-bu~oxy-1-ethanol:diethylene glycol mono-butyl ether. Each sa~ple then is cast onto alumi~um, the films bake~ at 204C for 10 minute~, and the samples tested for boiling wator re~istance, I'blu~h", adhesion, and flexlbiLity at the dolible seam of a can a~ter processing. All ~a~ples pa88 thes~ tests.
Exan~le 6 - hexamethoxymethy~melamine.
33~ ple 7 - butyla~ed mela~ne fo~maldehyde (P~5S64 E~mple 8 ~ utoxytetramethoxymethy~nelamine .
Example 9 - partially methylated melamine (C~L 350).
Ex~ple 10- partially methylated melamine (C~EL 370).
E$a~le 11- partially methy~ted ~e~mine (C~EL 373).
Exan~le 12- butylated melPm~ne-~o~ldehyde (C~L 1156).
Exan~le 13- pa~tially ~ethylated melamine (C~EL 735).
Ex~ple 14- bu~ylated benzogu~amine (~ES:CMENE X-7~).

Into a 1-liter, r~und ;bottomed, three-necked flask, 3 equi.pped a~ in Exa~le 1, are plaeed EPON 10û7, 18~.5 grams, :1 f~

2-butoxy-l-ethanol, 74.5 gramB; and diethylene glycol mono-butyl ether, 74.5 grams. The contentæ of the reactor are heat-ed in a nitr~gen a~mosphere to 50C until the solu~ion becQmes clear. To thi~ solution iæ added tr~methyl amine, 5.4 grams, di~olved ~n 16.2 gram8 of water. To the still clear solutlon there i8 added a partially methyla~ed melamine, 89% solids in i~o~ panol, (RES~OENE X-740), 68.4 gram~, and the reactlon mix~ure is maintalned at 70C for 10 minute~. Wa~er, 469.4 gram~ then added over a 30~minute period while the tempera-ture of the reaction mixture i~ raised to 90C. At the end ofthi~ period the ~inal product iæ a clear, dark amber solu~ion.
The product ha8 a Gardner-Holdt viscosity of A and a pH of 10.
A film cast ~ro~ this ~olution onto an electrolytic tin plate panel and baked for 4.5 minutes at 204C has high gloss, iB
hard, and pa~se~ ~5 rubs with methyl ethyl ketone in ~he sol~ent resistance test. For comparison, to a 415-gram por-tion of the above prepared ~olution i~ added 0.5 gram of phosphoric acid dissolved in 10.4 grams o~ a 75:18.5:6.5 weight r~tio m~xture of water:diethylene glycol mono-butyl ether:2-butoxy-1-ethanol. The pH of this solution i8 4 and ha8 a Gardner-Holdt ~iscosity o~ B. A film ca~t from thlæ
solu~on and baked a8 deseribed above i8 hard, has high gloss, and surpas~e~ 100 methyl ethyl ketone rub8.

To a 5~0-gram portion o~ the thermosetting composi-tion prepared i~ Example 3 i8 added 22 gram~ of phosphorlc acid. A film of thi~ solu~ion i~ cast on paper with a number 13 wire-wound rod and cured ~t 150C ~or 10 seconds.
The resulting coating ha8 fair to good gloss, excellent hold-30 out over print¢d and unprinted areas of the paper~ and ~how~

- 2~ -r~o blocking when tested for block resistance in a heat-sealer for 0.5 second at 150C under ~0 pounds per square inches pre~ure. The coating passed 12 rubs o~ me~hyl ethyl ketone ~olvent resistance3 7 rlib8 13r hi~her are con~idered satis-factory for such applic~t~on.
EXA~IE 17 To 500 grams of the ther~osetting ~on~position des-cribed in Exa~le 3 are added 20 grams o~ phosphoric acid and 5~ gram~ of a partially meth~lated melamine, 805~ solidæ cc~ntent, 10 (a~ailable ~rom American Cyana~d Co~pan~ as C~rREZ~ 933). me ~olution is applied and cured as descrlbed ln Exa~ le 16, result~ng in a coa~ing having good glo~s and excellent hold-out and is non-blocking. It pasæes 16 rubs with methyl ethyl ketone.
~XAMPLE 18 (a) Into a suitably equipped reaction ves~el are charged the follow1ng ingredien~s: styrene, 78 grams; ethyl-acrylate, 78 grams; hydroxyethyl acr~late, 16 grams; glycidyl methacrylate, 28 gram6; 2-butoxy l-ethanol, 162 grams; and ditertiary~bu~yl peroxide, 1 grAm. The contents of the vessel are brsug~t to reflux temperature and maintained at thi~
te~perature for 1.5 hours. After this perlod an additional 1 gram Or ditertiary~butyl peroxide i8 added and heating i~
continued ~or 1 hour, af~er which time a further 1 gram of dltertiary~butyl peroxide is adaed and refluxing i~ maintained ~or ~n aaditior~l 1.5 hours. One skilled in the ar~ e~ects the product o~ this polymerization to be a styrene/ethyl ac~late/hydroxyethyl acrylate/glycidyl met~acrg~te//
39/39/8/14 (by weight), 55~ solids content.
3 (b) Eeat ~ 335-g~m portion o~ the polymer, as * denotes trade mark . :....

prepared in (a) above to between 65 and 70C. Add a solution of dimethyl-ethanol amine, 18.4 grams, in water, 36.7 grams.
Maintain temperature at 70 to 75C for 15 minutes followed by t:he addition of a partially methylated melamine (89% solids in iso-propanol, available from the Monsanto Polymers and Petrochemicals Company under the trade name of RESIMENE 740), 69.4 grams. After 15 minutes at 60 to 70 C, water, 491 grams, is added over a 30-minute period. The final solution has a 26.0% solids content as determined at 204C for 10 minutes and a pH of 12.3. A film drawn with a Number 20 wire-sound rod on an aluminum sheet and cured at 204C for 10 minutes is expected to be tough, glossy, and to pass 50 + strokes methyl ethyl ketone solvent resistance test.

To a 475-gram portion of the solution of Example 18b is added phosphoric acid, 4 grams, dissolved in a 3:1 by weight mixture of water and 2-butoxy-1-ethanol, 22.7 grams.
The pH of this solution is 9.3 and the solids content is 25.4~, determined as above. Casting and curing affords a film that passes 100 plus strokes with methyl ethyl ketone.

To a molten mass of a polyglycidyl ether of a novolac resin (EPON 154), 209.3 grams, and diethylene glycol monobutyl ether, 26.2 grams, at 65 to 70C, is added a solu-tion of dimethyl ethanol amine, 104.1 grams, in water, 208.2 grams. An exothermic reaction ensues with a concomitant temperature rise to 90C within 4 minutes. The resultant clear solution is cooled to 70C and dibutoxytetramethoxymethyl-melamine, 89.7 grams, is added over a 15-minute period, follow-~'i `

9"

ed by a 30-minute additlon of water, 307 grams. The pH of the solution ls ad~usted by the addition of phosphoric acid, 50.5 grams; water 161.7 grams; and diethylene glycol monobutyl ether, 40.4 grams. m e solution has a 29.1% solids content and a pH of 9Ø Casting the solutlon and curing at 204C for 10 mlnutes results in a glossy, tough film.

- 27 _

Claims

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:

1. A water-borne thermosetting coating composition characterized by consisting essentially of:
(A) 50-97 parts by weight, based on the weight of components (A) plus (B), of (1) an epoxy polymer containing, on the average, either (a) two terminal 1,2-epoxy groups per molecule and having a weight average molecu-lar weight, determined by gel permeation chromatography using a polystyrene standard, of 1000-5000, or (b) 10-150 randomly distrib-uted 1,2-epoxy groups per molecule and having a weight average molecular weight of 25,000 to 75,000; said epoxy polymer reacted to sub-stantially complete consumption of the epoxy groups with (2) an aqueous solution of about 1-1.25 equivalents, per equivalent of epoxy group of said epoxy polymer of (1), of a tertiary amine selected from the group consisting of R1R2R3N, pyridine, N-methylpyrrole, N-methyl pyrrolidine, N-methyl morpholine, and mixtures thereof and where R1 and R2 are hydroxy-substituted or unsubstituted monovalent alkyl groups containing one or two carbon atoms and R3 is a hydroxy-substituted or unsubstituted monovalent alkyl group containing 1-4 carbon atoms; and (B) 3-50 parts by weight, based on the weight of components (A) plus (B), of a fully alkylated amine-aldehyde resin, a partially alkylated amine-aldehyde resin or mixtures thereof;
dissolved or dispersed in a liquid selected from the group consisting of water and an organic liquid, and mixtures thereof.

2. The composition of Claim 1 wherein components (A) and (B) are dissolved or dispersed in a liquid selected from the group consisting of water, an organic liquid and a mixture of water and an organic liquid in a ratio of from 70:30 to 90:10.

3. The composition of Claim 2 wherein components (A) plus (B) comprise about 0.1-50% by weight of the coating composition.

4. The composition of Claim 3 wherein (A) comprises 65-85 parts by weight and (B) 15-35 parts by weight based on the combined weights of these two components.

5. The composition of Claim 2 containing the epoxy polymer of (A)(1)(a).

6. The composition of Claim 5 wherein the epoxy polymer has a molecular weight of 1000-2500.

7. The composition of Claim 2 containing the epoxy polymer of (A)(1)(b).

8. The composition of Claim 2 wherein the tertiary amine R1R2R3N is selected from the group consisting of:
trimethyl amine, dimethyl ethanol amine, methyl diethanol amine, diethyl methyl amine, ethyl methyl ethanol amine, dimethyl benzyl amine, dimethyl propyl amine, dimethyl ethyl amine, dimethyl 3-hydroxy-1-propyl amine, dimethyl 2-hydroxy-1-propyl amine, dimethyl 1-hydroxy-2-propyl amine, and mixtures thereof.

9. The composition of Claim 3 wherein said tertiary amine is trimethyl amine, dimethyl ethanol amine or mixtures thereof.

10. The composition of Claim 4 wherein said tertiary amine is selected from the group consisting of: trimethyl amine, dimethyl ethanol amine, methyl diethanol amine, ethyl methyl ethanol amine, dimethyl propyl amine, dimethyl 3-hydroxy-1-propyl amine, dimethyl 2-hydroxy-1-propyl amine, dimethyl 1-hydroxy-2-propyl amine, diethyl methyl amine, and mixtures thereof.

11. The composition of Claim 3 wherein the alkylated amine-aldehyde resin is hexamethylol melamine alkylated with 1-6 alkanol molecules containing 1-6 carbon atoms.

12. The composition of Claim 2 wherein said epoxy polymer is a polymer of an epoxy-functional monomer selected from the group consisting of glycidyl acrylate, glycidyl meth-acrylate, and alkyl glycidyl ether and at least one alpha, beta-ethylenically unsaturated monomer selected from the group consisting of styrene, C1-C8 alkyl acrylate, C1-C8 alkyl meth-acrylate, vinyl acetate, and mixtures of one or more of these alpha, beta-ethylenically unsaturated monomers with at least one of: acrylonitrile, methacrylonitrile, acrylamide, meth-acrylamide, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, acrylic acid, methacrylic acid, and itaconic acid.

13. The composition of Claim 12 wherein said epoxy polymer has the composition of styrene/methyl methacrylate/
C1-C8 alkyl acrylate or C2-C8 alkyl methacrylate/hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate or hydroxypropyl methacrylate/glycidyl methacrylate or hydroxypropyl methacrylate/glycidyl methacrylate in the weight ratios, based on the polymer, of 30-50/20-30/30-50/5-10/5-30%.

14. The composition of Claim 13 wherein said epoxy polymer has an epoxy equivalent of 750-1250.

15. The composition of Claim 14 wherein the pH is in the range of 6-8.

16. The composition of Claim 14 wherein the pH is in the range of 7.5-10.

17. A water-borne thermosetting coating composition characterized by consisting essentially of:
(A) 50-97 parts by weight, based on the weight of components (A) plus (B), of (1) an epoxy polymer containing, on the average, either (a) two terminal 1,2-epoxy groups per molecule and having a weight average molecu-lar weight, determined by gel permeation chromatography using a polystyrene standard, of 1000-5000, or (b) 10-150 randomly distrib-uted 1,2-epoxy groups per molecule and having a weight average molecular weight of 25,000 to 75,000; said epoxy polymer reacted to sub-stantially complete consumption of the epoxy groups with (2) an aqueous solution of about 1-1.25 equivalents, per equivalent of epoxy group of said epoxy polymer of (1), of a tertiary amine selected from the group consisting of R1R2R3N, pyridine, N-methylpyrrole, N-methyl pyrrolidine, N-methyl morpholine, and mixtures thereof and where R1 and R2 are hydroxy-substituted or unsubstituted monovalent alkyl groups containing one or two carbon atoms and R3 is a hydroxy-substituted or unsubstituted monovalent alkyl group containing 1-4 carbon atoms; and (B) 3-50 parts by weight, based on the weight of components (A) plus (B), of a fully alkylated amine-aldehyde resin, a partially alkylated amine-aldehyde resin or mixtures thereof;
dissolved or dispersed in a liquid selected from the group consisting of water and an organic liquid, said coating compo-sition also containing an acid catalyst selected from the group consisting of: phosphoric acid, its mono- and di-esters formed with aliphatic, cycloaliphatic, and aromatic alcohols, citric acid, para-toluene-sulfonic acid, and mixtures thereof, in a quantity sufficient to lower the pH of the composition to between 7.5 and 12.

18. The composition of Claim 17 wherein components (A) and (B) are dissolved or dispersed in a liquid selected from the group consisting of water, an organic liquid and a mixture of water and an organic liquid in a ratio of from 70:30 to 90:10.

19. The composition of Claim 17 wherein components (A) plus (B) comprise about 0.1-50% by weight of the coating composition.

20. The composition of Claim 17 wherein (A) comprises 65-85 parts by weight and (B) 15-35 parts by weight based on the combined weights of these two components.

21. The composition of Claim 17 containing the epoxy polymer of (A)(1)(a).

22. The composition of Claim 17 wherein the epoxy polymer has a molecular weight of 1000-2500.

23. The composition of Claim 17 containing the epoxy polymer of (A)(1)(b).

24. The composition of Claim 17 wherein the tertiary amine R1R2R3N is selected from the group consisting of:

trimethyl amine, dimethyl ethanol amine, methyl diethanol amine, diethyl methyl amine, ethyl methyl ethanol amine, dimethyl benzyl amine, dimethyl propyl amine, dimethyl ethyl amine, dimethyl 3-hydroxy-1-propyl amine, dimethyl 2-hydroxy-1-propyl amine, dimethyl 1-hydroxy-2-propyl amine, and mixtures thereof.

25. The composition of Claim 17 wherein said tertiary amine is trimethyl amine, dimethyl ethanol amine or mixtures thereof.

26. The composition of Claim 17 wherein said tertiary amine is selected from the group consisting of: trimethyl amine, dimethyl ethanol amine, methyl diethanol amine, ethyl methyl ethanol amine, dimethyl propyl amine, dimethyl 3-hydroxy-1-propyl amine, dimethyl 2-hydroxy-1-propyl amine, dimethyl 1-hydroxy-2-propyl amine, diethyl methyl amine, and mixtures thereof.

27. The composition of Claim 17 wherein the alkylated amine-aldehyde resin is hexamethylol melamine alkylated with 1-6 alkanol molecules containing 1-6 carbon atoms.

28. The composition of Claim 17 wherein said epoxy polymer is a polymer of an epoxy-functional monomer selected from the group consisting of glycidyl acrylate, glycidyl meth-acrylate, and alkyl glycidyl ether and at least one alpha, beta-ethylenically unsaturated monomer selected from the group consisting of styrene, C1-C8 alkyl acrylate, C1-C8 alkyl meth-acrylate, vinyl acetate, and mixtures of one or more of these alpha, beta-ethylenically unsaturated monomers with at least one of: acrylonitrile, methacrylonitrile, acrylamide, meth-acrylamide, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, acrylic acid, methacrylic acid, and itaconic acid.

29. The composition of Claim 17 wherein said epoxy polymer has the composition of styrene/methyl methacrylate/
C1-C8 alkyl acrylate or C2-C8 alkyl methacrylate/hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate or hydroxypropyl methacrylate/glycidyl methacrylate or hydroxypropyl methacrylate/glycidyl methacrylate in the weight ratios, based on the polymer, of 30-50/20-30/30-50/5-10/5-30%.

30. The composition of Claim 17 wherein said epoxy polymer has an epoxy equivalent of 750-1250.

31. The composition of Claim 17 wherein the pH is in the range of 6-8.

32. The composition of Claim 17 wherein the pH is in the range of 7.5-10.

33. A thermosetting coating composition, which is infinitely dilutable with water, characterized by consisting essentially of:
(A) 50-97 parts by weight, based on the weight of components (A) plus (B), of (1) an epoxy polymer containing, on the average, either (a) two terminal 1,2-epoxy groups per molecule and having a weight average molecu-lar weight, determined by gel permeation chromatography using a polystyrene standard, of 1000-5000, or (b) 10-150 randomly distrib-uted 1,2-epoxy groups per molecule and having a weight average molecular weight of 25,000 to 75,000; reacted to the substantially complete consumption of the epoxy groups with (2) an aqueous solution of about 1-1.25 equivalents, per equivalent of epoxy group of said epoxy polymer of (1), of a tertiary amine selected from the group consisting of R1R2R3N, pyridine, N-methylpyrrole, N-methyl pyrrolidine, N-methyl morpholine, and mixtures thereof and where R1 and R2 are hydroxy-substituted or unsubstituted monovalent alkyl groups containing one or two carbon atoms and R3 is a hydroxy-substituted or unsubstituted monovalent alkyl group containing 1-4 carbon atoms; and (B) 3-50 parts by weight, based on the weight of components (A) plus (B), of a fully alkylated amine-aldehyde resin, a partially alkylated amine-aldehyde resin or mixtures thereof.