CA1195036A - Water-borne coating composition made from epoxy resin, first polymeric acid, tertiary amine and second polymeric acid - Google Patents

Abstract

TITLE
Water-Borne Coating Composition Made From Epoxy Resin, First Polymeric Acid, Tertiary Amine And Second Polymeric Acid ABSTRACT OF TEE DISCLOSURE
Water-borne reaction products of (a) carboxyl-functional polymers; (b) polyepoxides; and (c) tertiary amines are blended with (d) carboxyl-functional polymers having an acid number dissimilar to that of (a). The resulting products are useful as film-forming components of coating compositions which can be spray-, flow-, dip-, roller-, or electro-coated and are especially useful for spray coating the inside of two-pieces tin-plated steel cans of beverages and food. The coating compositions are useful as such or can be crosslinked with crosslinking agents such as a nitrogen resin.

Description

3~

TI~LE
Water-Borne Coating Composition ~ade From Epoxy Resin, Fi.rst Polymeric Acid, Textiary Amine and Second Polymeric Acid This invention relates to coating compositions based on a water-borne reaction product of carboxyl-functi.onal polymers, an epoxide, and a tertiary amine, having general utility in coating metallic substrates. It is more particularly directed to coating composi~ions useful as can coatings.
Coatings of the prior art are 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.
Aqueous epoxy-acrylic amine coating compositi.ons of other investigators are less stable than desired or lack advantages of the present i~vention, especially for applications to steel cans including tin-plated steel cans.
The present application is directed to an improvement over U..S. Patent 4,2~7,439 - Matthews and 2S Sommerfeld, g.ranted January 27, 1981.
SUMMARY_OF THE INVENTION
According to the present invention, there i.s provided a water-borne coating composition based`on polymeric quaternary salts of polymeric acids which are the reaction product of:
(A) 50 90%, based on the weight of (A) plus (B), preferably 65-90%, most preferably about 78%, of an epoxy resin containing, on -the ~2 ~
average, about 1 1/2 to 2, preferably about

2, terminal 1,2-epoxy group~ per molecule and having an epoxy equivalent wei.ght of 750-5Q00, preferably 2bout 150C-4000, most preferably about 3000;
(B) a carboxyl-func~ional polymer in an amount sufficient to provide at least 1.25/
preferably at least about 1. 75, and not more than 6~0/ equivalents of carboxyl groups, when the source of the carboxyl g~oup is a mono-protic acid, and at least 2.0 equivalents o~ carboxyl groups, when the source of such groups is a diprotic acid~
per equivalent o 1,2-epoxy groups in the epoxy resin of (A), said polymer having a weight average molecular weight (determined by light scatteriny~ of 10,000 160,000, preferably about 10,000-~0,000, most preferably about 13,000~18,000, and an acid number o 100 500, pre~erably about 150~350 J
most preferably about 300, and (C) at least 1.~5, preferably at least about 1.75, most preferably a~out 3.0, equivalents t preferably as an aqueous solution, of a tertiary amine per eq-livalent of 1,2-epoxy groups in the epoxy resin of (A), said tertiary amine being selected from the group consisting of RlR2R3N, pyridine, N~methyl pyrrole, N~methyl piperidine~ N-methyl pyrrolidine, M-methyl morpholine~ an~ mixtures thereo~ and wherein Rl and R2 are substituted or unsubstituted monovalent alkyl groups containing one or two carbon atoms in the alkyl portioll and ~ is a substitu~ed or O

. ~ .

3~

unsuhstituted monovalent alkyl sroup containing 1~4 carbon atoms, preferably dimethyl ethanol amine; and (D) optionally, 10-90% of the amount required for stoichiometric reaction with the caxboxyl = functional polymer o (133 of at least one primary, secondary or tertiary amine or monofunctional quaternary ammonium hydroxide~ and wher~in for increasin~ ratios of carboxyl groups to 1,2-epoxy group~, the amount of amine is increased to keep the carboxyl-functional polymer water dispersible;
(E) said second carboxyl-functional polymer lS being blended in an amount of S to ~00 parts by weight per 100 parts by weight of ~A) plus (B) and having a weight average molecular weight ~determined by light scattering) of about 10,000-160,000 and an acid number of 50-500, said acid number being at least 50 units different than the acid number of said first carboxyl-functional polymer, sa.id second reaction product containing not less than 30% by we.ight of epoxy resin (A) based on the total of (A), (B) and (E).
Preferably the ~irst carboxyl~functiona7 polymer has an acid number oE at least 100 un.its higher than tha~ of said second carboxyl-unctional polymer. The second carboxyl-functional polymer (E) can be neutralized with an amine beEore it is bler.ded with the first reaction product. Preferably the first reaction produc. is prepared in organic solvents using an aqueous solution of tertiary amine (c)~ then the second carboxyl~functional polymer (~) 3~

4' is blended with the first reaction product, and the~
the combined xeaction product is inverted into water by blending with water in sufficlent quantity so that the continuous phase is aqueous.
Preferably, components (A), (B), (C) and (E) are capable of :forming hydrogel structures wi~h components 5A~ ), (C) and (E) c:omprising abou ~ 50~ of the coa~in~ composition and the remainder compr ising water and~ optionally, organic li~uid (s) 10 in a volume ratio of rom 70:30 to all water, sometim2s preferably 80: 20 .
(Percen~ages, propor~ions and ratios herein are by welght except where indicated otherwise~) The water-borne coating composi~ion can be crosslinked without the addition of a crosslinking ag~nt or) op~ionally, it can contain crosslinking agents such as a nitr~gen resin or a phenolic resin, as well a~ additives commonly utilized in soating c:omposi~ions such as pigments, ~illers, W absorbers, and the like.
~ESCRIPTION OF THE INVENl'~ON
The preferred water~b~rne coatislg compos ition of t~e invention is a solution or dispersion o~ the reaction products of an epoxy resin, a tertiary amine, and two carboxyl~functional polymers~ By mixing the~e componen~s in a de~ined manrler and utili~ing aqueous solutions of specific te.rtiary amines such as dimethyl ethanol amine, a stable~ water soluble or dispersible salt of a polymeric quaternary ammonium hydrox.ide and at least two carboxyl-fuslctional polymers results wllich can be crosslinked without the additional of external crosslinking agents~ The optional addition of exter~al crosslinking asents, such as phenollc or nitrogen resins, also affords a crossllnkable .~ y .. ~, .

~s~

5' solution or dispersion which is stable at room temperature. Both compositions, the salt and the solution or dispersion containing an external -` crosslinking asent~ are infinitely dilutable with water~
Whether the coating composition is a solution or a dispersion is largely dependent on the nature of ~he particular amine used, ~he stoichiometry of the system, and the epoxy equivalent weight. Even when ~he composltion is opaque some of the resinous comporlents may be dissolved, and when the composition appears to be a clear solution it i5 possible that small amounts of the components are in a dispersed state. For sake of simplicity, hereater 15 the term "dispersion" will be used to denote the water~borne coating composition.
The dispersion, with or without an external crosslinking agent, as prepared, usually has a pH of about 7-8 and a nonvolatile content oE up to 50~D
2Q IJpon drying, a hard, solvent-resistant fllm having excellent resistance to acids, bases, hot water, and detergent resultsO
Preparation of First Reaction Product The low molecular weight epox~ resins to be utilized in the present invention are commonly known in the artO One class of such resins has the generalized formula 3~ CH2CHCH2~ ~ C~2~--{} ~ ~ ~ ~2C~O~C~

wherein R is an al.'~ylene srcup of 1~ carbcn atoms and n i5 an integer from 1-12. The epoxy resins utilized in this invention contain an average of at least about one and a half and up to ~wo ~erminal 192-epoxy groups per molecule and are in the epoxy equivalent weight range of 750 5000, preferably 1500-4000. They can al~o contain substitute~
aromatic ring~O
One such preferred epoxy resin is Epon*
1004 where R is isopropylidene, the average value of n is 5, having an epoxy e~uivalent weight of 875 1025, with an average of about 950 50~ The epoxy equivalent weight is defined as the grams of resin containing 1 gram-equivalent of epoxide as measured by ASTM~D-1652~ The coating composltion containing ~J "Epon 1004" a~fords a glossy, 1exible, chemically~resistant film. Another preferred epoxy resin is "Epon 1007" where R is isopropylidene, the average v~lue of n is 11, havinq an epoxy equivalent weight of 2000~250~, with an average of about 2175~500 The coating composition containing "Epon 1007N affords glossy, tou~ht flexible films upon cure. Another preferred epoxy is an analog of '~ pon 1009" with an average epoxy equivalent weight of 3000 made by chain extending "Epon 829" (EW 195~ with bisphenol A. The Epon products are made by Shell Chemial CompanyO
The quantity of the epoxy resin to he utilixed in the coating composition of this invention is determined in relation to the amount cf carb~xyl--functional pol~mer and the relative amounts 30 are dependent on the end use application of the coating but there must be at least 50%, prefer2bly in the range of 65-90%, of epoxy resin present. There must be9 rurthermore, al least 1.25, preferably at least 1.75, a~d most preferably about ~6, 3~ equivalents of carboxyl groups per equivale~ of *de~otes trade mark 3~

1,2~epoxy groups in the epoxy resin~ This minimum equivalent requirement is valid for those carboxyl-functional pol~ners which contain monoprotic acids derived from alpha,beta-ethylenically S unsaturated acid monomers such as acrylic acid, methacrylic acid, monoesters of alkanols having 1-8 carbon atoms with diacids, such as maleic acid5 - itaconic acid, fumaric acid, mesaconic acid, citraconic acid and the like, and mixtures thereofO
For tho~e carboxyl-functional polymers which contain : diprotic acids derived from diacids such as maleic acid, itacorlic acid, fumaric acid, mesaconic acid, citraconic acid, and mixtures th*reof, ~he minimum requirement is ~.0 equivalents, preferably a~ least 205 ~quivalent8, of carboxyl group per 1~2-epoxy groups. Usually, no more than 10.0~ and preferably no more than 600~ equivalents of carboxyl groups~ per equivalent of 1,2-epoxy group~, will be present.
The carboxyl-functional polymers utilized in ; zo this invention are prepared by conventional free radical polymerization techniques from at least one ethylenically unsaturated monomer and at least one ethylenically unsaturated acid monomer. The choice of the alpha,beta-unsaturated monomer(s) is dictated by the intended end use of the coatin~ compos.ition and is practically unlimited. A variety of acid monomers can be used; their selection i5 dependent on the desired final polymer properties.
Thi~ acid monomer can be an ethylenically 30 unsat~rated acid, mono-plotic or diprotic, ~nhydride or monoester oE a dibasic acid, which is copolymerizable wi~h the other monomer (s) used to prepare the polymer.

t~3~

lllustrative monobasic aci.ds are those represented by the structure R
5CH2 = C - ~OG)EI

where R is hydrogen or an alkyl rad ical of 1-6 carhon atoms .
Suitable dibasic acids are those represented by the formula HOOC \ ~ R~
~C z C

Rl~ /R2 C -- C
HOOC COO~
or 2Q R2 ~ ~ COOH

Rl / R3COOH
where RL and R2 are hydrogen, an alkyl radical of 25 1^n8 carbon atoms, halogen~ cycloalkyl of 3-7 carbon akoms or phenyl ~ and X3 is an alkylene rad ical of 1-6 carbon atom~ ~Ia3.f-esters of these acids with alkanols o:E l~a carbon atoms are al so suitable .
The most preferre~ acid monomers are acrylic 30 ~cid, methacrylic acid, and itaconic acid.
The acid number of the polymers is 100-500, which corresponds to concentrations of about 1~77~
of the acid monomers by weight of the polymer~ The acid number is the number o~ mili~rams of potassium hydroxide required to neutralize one gram of ~he 9~
polymer. For purposes of illus~ration, an acid number of 100 corresponds to the presence in the polymer of either 12.8% acrylic acid, 15.3~ of methacrylic acid, 11.5% of itaconic acidt or 10.3~ of 5 maleic or fumaric aeid. An acid number of 500 corresponds to 64~ of acrylic acid~ 76.5~ of methacrylic acid, 57~5~ of itaconic acid, or Sl.5% of maleic or fumaric acid in the polymer. Preferred acid numher values are 150-350.
Vinyl aromatic monomers are commonly utilized to be copolymerized with the ac.id monomers.
They are represented by the ~tructure-Rl ~ ~2 1~ C - C

~ ~3 where R, Rl, R2, and R3 ~re hydrogen or an alkyl radical of 1-5 carbon atomsO Illustrative of these monomexs are styrene, ~-methyl styrene, v.inyl tolu~ne, and the like. The best polymers, in terms of final film properties, are those in which this type of monomer is styrene. The vinyl aromatic mon~mers can be presen~ from 0-80g of the carboxyl-func~ional polymer, preferably from 40-80%, most preferably from 40-70%, and specifically at concentrations of about 42, 53, and 66%. For some purposes 10-45% may be prefexred and, in some applications, the polymer contains no such monomer.
Other commonly utilized monomers are t'ne unsaturated nitriles represented by the stru~ture:

\ ,2 C =
Rl ~

3~

where R and ~1 are hydroger., an alkyl ra~ical of 1-18 carbon atoms, tolyl, benz~fl or phenyl, and R2 is hydrogen or methyl. Most commonly utilized are acrylonitrile and methacrylonitrile. The nitrile monomer can be present ~rom 0-40~ based on the carboxyl-functional polymer. The polymers pr~ferably contain 10-30~ and more p~eferably 18-22% of the polymer, of ~he ni~.rile monomer. For certain purposes it may be desirable to use 5-10~ of the 10. nitrile monomer and in some cases no such monomer is included in the polymers.
Other suitable monomers are esters of acrylic acid, methacrylic acid o~ mixtures thereo~
with Cl~C16 alkanols~ Preferred ~sters are the methy}, ethyl, propyl, n~butyl isobutyll and ~-ethylhexyl esters of acrylic acid or methacrylic acid or mixtures of such esters~ The~e ester~ can be present in concentrations of 0-97.
One can also utilize hydroxyalkyl 2~ (meth)acrylate monomers such as hydroxyethyl acrylatef hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxyprop~fl methacrylate or mixtures thereof~ Up to 20% of such ester(s) ean be incorporated .
~s It may be desirable, for certain uses, to include in the polyme.r acrylamide, methacrylamide or an N-alkoxymethyl (meth)acrylamide such as N-isobutoxymethyl (meth)acrylamide. Alternatively, a polymer containing copolymeriæed acrylamide or methacrylamide can be post-reacted with formaldehyde and an alkanol to produce an ~-alkoxymethylated polymer.
The carboxyl~functional polymers can be prepared by polymerizing su1table monomersf in proper 3; amounts, in an organic liquid medium. In general~

.

3~
- 1~
thi~ liquid i5 an organic liquid capable of medium hydrogen bonding, OE a combination sf this liquid with less than about 50~ of an organic liquid capable of strong hydrogen bonding.
Preerably~ the li~uid medium for the polymerization is an alcohol mixture~ generally 62 butanol and 38~ of ethylene glycol monobutyl ether.
Other media which could be used include either water-soluble or insoluble ketone. Optionally, the ketone can also contain less than a~out 50~ of an ethylene glycol- or diethylene glycol monoalkyl ether twh~re the ~lkyl group contains 1=4 carbon atoms), or diacetone alcohol, and/or an a~kanol of 1-4 carbon atoms or an alkanediol of 1-7 carbon atoms. A
prefe~red medium is methyl ethyl ketone used by itselfO Another preferred medium for the polymerization is a mixture of methyl ethyl ketone and ethylene glycol monobutyl ether.
R c~alyst or polymerization initiator is ordinarily used in the polymerization of the carboxyl-functional pol~mers, in the usual amounts.
This can be any free radical initiator that decomposes with a half-life of 0.5 to 2~5 hours at the reflux temperature of the organic li~uid medium be:ing used. Tertiary butyl perbenzoate, tertiary butyl peroxypivalate~ and tertiary butyl peroxyisobutyrate are preferred.
l'he polymer~ utilize~ in the water~borne coating composition of thi~ invention have a weight average molecular weight, as determined by l:Lght scattering or, more conveniently, gel. permeation chromatography, using a poLystyrene standard, cali.brated by light scattering methods of about 10~000 l~O~OOOo The pref2rred weiyht avera~e molecular weight ra~ge is 10,000-80,000. For some applications a 13sO00~18~000 molecular weight is pre~erred.
During the preparation of the coating composition of this invention, an aqueous solution of S a tertiary amine, ~pecified below, is brought in contact with a solution of an epo~y resin in organic li~uid(s) or with a solution of an e~oxy resin and a carboxyl functional polymer. A wide variety of organic liquids can be used to dissolve the epoxy resins and the carboxyl-functional polymers. ~mong the most commonly used solve~ts are alcohols such as isopropanol, the butyl alcohols, 2-hydroxy-4-methyl-pentane, 2-ethylhexyl alcohol, cyclohexanol, glycols such as ethylene glycol, diethylene glycol, 1,3-butylene glycol, ether alco~ols 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.
While the exact mode of the reaction is not fully understood, it i9 believed that the tertiary amine irst reacts with the carboxyl-functional polymer to foxm the corresponding salt which, in turn, can dissociate to allow the amine to react with the 1,2-epoxy groups of the epoxy resin. I~ is al~o possible, however, that the tertiary amine reacts directly with the 1,2-epoxy groups~ In either case, the resulting quaternary ammonium hydroxide can react 30 with the carbox~l-functional polymer to yield a polymeric quaternary ammonium~amine mixed salt o~ a polymeric acid.
The reaction of tertiary amines with materials containing epoxy groups, to yield addllcts containing quaternary ammonium groups, is known.

5~3~

Such reaction, when carried out ln presence of water or other suitable proton donors7 such as certain alcohols or carboxylic acids, can afford a product that contalns bo-th a hydroxyl group and a quaternary ammonium hydroxide. The reaction c-~n be represented schematically as follows:

~0 ~ ~ R3N + H~0 ~
L0 OH NR3~0 While most tertiary amines react with epoxy resins to form quaternary ammonium hydroxides, the preparation of the water borne ~oating compo~ition of ~his I5 inventiorl is carried out utilizin~ at least one tertiary amine selected from the gro-lpo R1R~R3~, N-methyl pyrrolidine, N~methyl morpholine, pyridine, N methyl pyrroleD N-methyl piperidine, and mixtures thereof, wherein Rl and R2 are substituted or unsubs~i~u~ed monovalent alkyl groups containing one or two carbon atoms in the allsyl por~ion and R3 is a ~ubstitu~ed or unsuh5tituted monovalent alkyl group containing 1-4 carbon akoms. Some examples of ~lR2R3N are:
trimethyl amine, dimethyl ethanol amin~ (also known as dimethyl amino ethanol~ methyl diethanol amine, et.hyl methyl ethanol amine, dimethy1 ~thyl amine, dîmethyl. propyl amine, dimethyl 3-hydroxy-1-propy1 amine, dimethylbenzy1 amine, dimethyl 2-h~yd.roxy~l-propyl ami.ne, diethyl methyl amine, dimethyl l~hydroxy 2~propyl amine, and mi~tures thereof~ .Most preferabiy trimethyl amine or dimethyl ethanol amine is usecl.
The generation of a polymeric quaternary 3S ammonium hydroxide which is water soluble or ;`~ 3~

disperible when in presence of a nitrogen resin cro s~ inking agent is described in U.S. Patent 4~076~676J granted ~ebruary 28, 1978~
The amount of tertiary amine needed in the 5 preparation of the water-borne coating composition of this invention is determined by two factors. As a minlmum, there is reguired at least 1. 25 eq~iv~lents of tertiary amine per equivalent of 1,2-epoxy ~roups, preferably a~ lea~ 75 equivalents, more preferably 10 3,.0, for the forn~ation o~ stable dispersions~ As ~he ratio of the number of carboxyl groups in the carboxyl-functiona~. polyrlser to the number of 1,2-epoxy groups in the epoxy resin increases, the amount of amine is also increased ~o keep ~he 15 carboxyl-functional polymer water dispersible~ This excess amine is believed to form 2 salt with some c:r all of the excess carboxyl groups of the polymer . I t is pre~erred that no excess amine, over the total number of eql~ivalen~,:s of carboxyl groups, be used in 20 the coating composition of this invention~ The amine utilized in excess of 'che l o 25 equivalerlts of the highly specific tertiary amine per eq~ivalent of 1, 2-epoxy ~roups need not be the s2me as, nor does i t nec~essarlly have to be selected ~rom ~he ~roup of, 25 the highly specific tertiary amines, Any primary, secondary or tert:iary amine or monofunctiorlal quaternary ammonium hydroxide can be utilized in n~utralizing carboxyl groups of the carboxyl-functiorlal polyrl~er which are not already 30 neutralizedO Among such tertiary arnines are included: trieth~l amine, diethyl ethanol am.irle, dimethyl cyclohexyl amine, triethanol ~mlne, tributyl amine, dimethyl n-butyl amine, tripro~yl .. ... . .

amine, dimethyl lauryl amine, and ~-picoline.
Primary and secondary amines preferably should not be used along with tertiary amines in the neutralization of the epoxies because unwant.ed covalent bon~s.coul-3 S be formed, and this can interfere with the desired hydrogel formation.
The first reaction product can be prepared without regard to the sequence of addition of the variou~ componen~s. It is preferred, however, to first dissolve the epoxy resin in suitable organic liquids and then add the carboxyl functional polymer which has been partially neutralized wi~h a suitable tertiary amine, usually dissolved in water~
Addit.ional water can then be added to achieve the final volume ratio of water and organic liquid of from 70,30 preferably to 90~10. Additional amine can also be added to in~ure dispersibility.
A preferred ratio of tertiary amine to water - i~ approximately 1:3 by weight.
The reaction can be carried out between room temperature and below the boiling point of the reaction medium, preferably between 50-100C9 most preferably ~0-L00e. In this temperature range there is a rapid rate of reaction.
In another preferred method of preparation of the ~oating composition, an epoxy resin is dissolved in a suitable or~anic liquid such as the mono-butyl ether of ethylene glycol or cliethylene glycol, followed by the addition of a suitable t~rtiary amine. Afte.r the formation of the polymeric quaternary ammonium hydroxide is substantiall~
complete, a carboxyl-functional polymer9 dissolved in a suitable orgarlic liquid is mixed with it with agitation. This latter solution can also contain any additional primary9 ~econdar~s or tertiary amine, dissolved in water, necessary ~or dispersibili~y of the coating composition. Mixing with any additional desired water of the components completes the preparation of the water-borne coatin~ composition. This sequence of steps can also be carried out between room temperature and temperatures below the boiling point of ~e reaction media.
Alternatively, the first reac~ion product of this inven~ion can be prepare~ by first dissolving the epoxy resin in the carboxyl-functional pol.ymer, in the presence of suitable organic liquids.
~ddition of a suitable tertiary amin~, usually dissolved in wa~er, completes the prepara~ion of th~ pol~meric quaternary ammonium salt of a polymeric ac.id. Additional water can then be added to achieve the inal volume ratio of water and organic liquid of from 70:30 preferably to 90 :10 . Additional amine can also be add~d to insure dispersibility.
The polymeric quaternar~ ammonium~amine mixed salt of the carboxyl-functional polymer of the water-borne coating composition of this inverltion pxeferab1y is a complex hydrogel structure. It is the generation~ during the epoxy/carboxyl/amine : reaction, of such a hydrogel structure which affo.rds the solubility or dispersibility, ~nd stabi.lization, in water of the coaking composition. A possible schematic formula is showrl by the formula below. The exact nature of the bonding is not known. The number of carhoxyl groups in the schematic~lly shown polymer molecules and of the relative portion o free acid groups to the amine salt groups are determined by the stoichiometry employed during the preparation of the coating composi'ion. The schematlc representation is ;, . . . .

3~

shown to further the understanding o~ the nature of the invention:

~ OH OH
CH2 - CY~-~C~ CH~

--cooQ ~ N0- ~ -l l 10 ~ ~ . --Coo3 M~
O~I OH
CH2 ~ CH~C~2 --~co9 _~
- .
CH-COO~ M~
~ ~ ~ CH2 -C~

where ~ is hydrogen or a protonated primary, secondary or tertiary amine or a monofunctional quaternary ammonium group and - ~ - is formed from a tertiary amine selected ~rom the group:
RlR2R3N, N-methyl pyrrolidine~ N-methyl morpholine, pyridine, N~methyl pyrrole, N-methyl pipericline, and mixtures thereof, wherein Rl and R~ are sub5tituted or unsubstituted monovalent alkyl groups containing one or two carbon atoms in the allcyl portion and R~ is a substituted or unsubstituted monovalent alkyl gxoup containing 1-4 carbon a~oms~

~5~3Çi It has been found that desirable versatile rheological characteristics can be obtained in compositions o~ the invention i~ the second S polymeric-acid-contain-rng polymer (typically an acrylic) i5 added af~er the first reaction product is formed, typically of epoxy and acrylic resins and tertiary amines~ Although the invention can be useful if the second acrylic is added after inversion, better dispersion stabili~y i5 generally obtained if the second ac:rylic pol~ner is added before the first reaction product has been inverted into or diluted with water to a substantial extent~
such as up to the full water content that will be in the finished product.
The first and second acrylics should have signif.icantly dissimilar acid numbers, as defined.
For reason~ not clearly understood, this gives better results than if the composition is made with a single acrylic resin having an acid numbe.r ~hich i5 the average o~ the two acrylics used, or if both acrylic resins are present for the initial epoxy amine reactions~
One hypothesis for the unusual rheological behavior observed is that the ionic bonds between the in-situ formed quaternary structure and the carboxyl groups on the acrylic resin present in.itially are not completely lablle and do not arrive at an equilibrium or statistical distrihution of ionic charges with the carboxyl groups on the acrylic resin added in the second stage. Another hypothesis along the same lines relates to the formation of hydrogel structures formed ~y ionic bonding of uaternary structures and carboxyls from the acrylic resin present initially~.
35 T'nis hydrogel structure may effectively remove some 1~

~ .

3~

species frQm a continuous phase~ again res~ricting equilibrium dis~ribution of ionic charges~

The water-bcrne coating composition of this S invention is a stable solution or dispersion and can be used as prepared. It can be crosslinked without the addition of an external crosslinking agent and can also be crosslinked with external crosslinking agents such as phenol formaldehyde resins or, preferably, nitrogen resins.
The nitrogen resins are well known. They are the alkylated products of amino~resins prepared by tbe condensations of at least one aldehyde with at least one of urea, N,N?~ethyleneurea, dicyandiamide, and aminotrlazines such as melamines and guanamines.
~mong the aldehydes that are suitable are formaldehyde~ revertible polymers thereof such as paraformaldehyde, acetaldehyde, crotonaldehyde, and acrolein. Pr~ferred are formaldehyde and revertible polymer~ 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 re~lns are partially methylated melamines~ partially butylated melamines, hexaethoxymethylmelamine, hexamethoxy-methylmelamine, dimethoxytetraethoxymethylmelamine, dibutyoxyte~ramethoxymethylmelamine, butylated ben~oguanamin~, partially methylated urea, fully methylated urea, ful.ly butylated urea, hexabutoxymethylmelamine~ and mix~ures ~hereof.
These nitrogen resin~ can be blended directly into the coating compositions at the completion of the preparation or before final 2b dilution with water, either a5 a ~olid or as a solution in some miscible organic li~uido The nitrogen resins are ordinarily added to the composition of the invention at concentrations S ranging from S to 3S%, preferably 8 to ~0%~ even more pr~ferably 10 to 15~. The exact amount will be dictated primarily by the final proper~ies desired of the composition and can be determined by ~ne skilled in this artO
In the claims~ the term 'iconsisting essentially of" means not includii-lg other in~redients ii~ amounts which change the basic and novel characteristics of the invention, including providinq an a~ueous acid-polymer-modified epoxy coating composition that can form a hydrogel and is useful as a~ interior coating for cans. Other corn~only utilized additives such as coalescing aids, flow-control a~ents, pigments and the like can be added, in the usual amounts, if this appears nece~ssary or desirable, The water-borne composition can be applied by a variety of techniques and to a variety of substrates known in industry. For example, the coatiny composition of this invention can be utillzed 25 in the can manufacturing industry which uti.li.zes mainly metallic cans, many s:)f them cylindr ical ~ made frolil alumin~m7 tin free qteel, electrolytic ~in-pl.ate~ and quality-as-rolled steel, amons others. Cans utilized for paclcaging and shipping 30 food and beer or other bevera~es are mostly of the t~ree-piece or the two-piece drawn-and-ironed (D and I) variety. Cans constructed from three pieces ~body, top and bottom) can be roller coatea before the ~etallic sheet is formed into the body of the can 35 or can l~e spray coated a~ter partial ~abrication.

~0 .

3~ 1 The D and I cans, where ~he metal sneet is stamped ~o form a cylindrical body closed at one end, are generally spraY coated.
The coating composi~ion of this invention 5 can also be applied by electrodeposition, preferably by techniques described in U.S. Patent 4~247~439/
of Matthews and So~merfeld, grant~d 1981 January 27 and in U.S. Patent 4,303,488 of Seiler and Sommerfeld, gran~ed 1981 December 1.
. The concentratlon or ~ne coating composition .
depends upon~the process paraMeters to be used and is not g~nerally criticalO Ordinarily the film-forming components comprise O~l-50~ and preferably 5 30~, for conventional eoating method~, and 1~20%, for 1~ electxodeposition, of the total composltion, the remainder being water and organic liguid (s~ . The latter ~s:e present in a volume ratio of ~rom 90 :lO
prefera~ly to 70 :30 .
The ~reshly dep~s i ted f i lms are capa~le o~
2û being inunediately dried and/or crosslinked, withou~
regard to the method of coating used to obtain them.
The coating compositions of this inverltion can be d.ried tc useful fil~s as is or can be cured thermally as i8 or when containing, for example, a ~5 nitrogen resin crosslir~king ag~nt. After the composition has been applied to .the substrate, bakin~
at ~levated ~emperatures br ings abou~ the des ire2 crosslinkiny. Temperatures of 150C to 260t~C, for a . l to 30 minutes, are ~ypical baking schedules utilized.
The water borne C02 ting composition of this invention is useful in a variety of applications~
Thi~ coating composition finds particular utili~y in the can industry where the composition can be ap~lied to the interior of two-piece dra-~n-and~i~oned an~

three-piece beer and beverage cans, to the exter.ior of three-piece beer and beverage cans, to the interior and/or ex~erior ends o~ 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 ~nd beer or beverage cans by spray-coating/ a thin uniform film is deposited which, a~er curing, corresponds to a coating weight of 0.3 to 1~3 milligrams per squ re centimeter (2-8 ~illigrams per square inch). Coatings utilized as an interior enamel have excellent taste and odor characteristios~ that is to say, low extractables and sorption to prevent taste adulteration~
The water~borne composition also has lS utility, expecially when crosslinked with a nitrogen resin, in automotive primerS appliance finish, and coil coating applications, the final coated articles having especially desirable hardness and acid, base, solvent, and detergent resistance properties. The cured coatings are also resistant to s~lt spray and "processing"0 This latter property is tested in a steam~pressure cooker at approximately 120C.
The following examples gave compositions with adequate stability defined as no significant ~5 change i~ viscosity, solution/dispersion appearance (settling, creaming, ~yneresis) or ilm propert:ies of curecl coatings after the liquld has been stored for four weeks at 49C or s.ix months at room ternperature.
They also had acceptable taste performance, meaning they showed no addit.ion to, or substraction of, 1avor bodies of contents packe~ in a can li.ned with this material after invervals of storage ranging from four weeks to a year.
Although most of the emphasis in this application has been on can CQatingS~ such compositions can also be ~sed as coatings in a variety of other applications. The invention is further illus~ra~ed by the following examples.
PRELIMINARY EXAMPLE A
.. . .
, 5 ACRYLIC RESIN X
_ _ . . _ _ _ _ _ _ _ _ _ _ _ _ Into a suitably equipped kettle, inerted with nitrogen, are added the followin~, expressed in parts by weight:
~onobutyl ether of ethylene glycvl 91.567 Normal butanol 320503 Ethyl acrylate 14.453 Tertiary butyl perbenzoate 0.026 ln a separate vessel, the follow.ing are added and mixed:
Ethyl acrylate 54.764 Methacrylic acid 122.060 5tyrene 72.919 Normal butanol 2.050 Tertiary butyl perbenzoate 2.351 The reactor is heated to reflux and the monomer mixture is added evenly to the refluxing reactor over a two-hour period. Then 7.932 parts of monobutyl ether of ethylene glycol are added as a rinse for the monomer feed lines, Re1ux is maintained for one hour, at which point 55.500 parts of normal butanol is added. Reflux temperatures ~re maintained for one hour, at whlch point the heat is turned off and 72. 623 parts of normal butanol are added, followed by 82.312 parts of dimethyl ethanol amine and 246.940 parts of deionized water. ~he product is a solution of a styrene/ ethyl acrylate/methacrylic acid//2706/26~2/4602 pclymer at 30.8% solids ln solvent, water and amineO The acid number of the product is 300 before neutralizaticnO
: 35 5¢~

PRELIMINARY EXAMPLE B
YLIC ~ESIN Y
Into a suitably equipped kettle, inerted with nitrogen, are added the following, in parts by weight.
Monobutyl ether of ethylene glycol 1828 . 36 Normal butanol 649 O 17 Ethyl acrylate 466 . 06 Ter~iary butyl perbenzoate 0.60 In a separate vessell the followins are added and mixed:
~thyl acrylate 1765.~1 Methacl:ylic acid 807 . 24 S ~yxene 2236 . S0 Normal butanol 41. 03 Tertiary butyl perbenzoate47.06 The reactor is heated to reflux and the monomer mixture is added evenly to the refluxing reactor over a two hour period. Then 158.37 parts of 20 normal butanol are added as a rinse for the monomer eed linesO Reflux is continued for two additional hours at which time the heat is turned off and the batch cool~d. The product is a solution of a styrer.e/~thyl acrylate~methacrylic acid a 4~.4/42.3/1503 polymer at 6b% ~olids i.n solventO The acid number o the polymer is lO0~
PRELI lNARY EXAMæLE C
AC~YLIC RESIN Z
Into a suitably equipped Icettle, iner~ed 30 with nitxogen, are added the following parts by weigh~:

~ ~5~3~

Monobutyl ether of ethylene ~l~col 1828.00 : Normal bu~anol 649.60 Ethyl acrylate 465.33 Tertiary butyl perben20ate 0.60 In a separate vessel, the following are ;, added and mixed:
Ethyl acrylate 1561,15 Methacrylic acid 1~13.79 Styre~e 2037 D 05 ~ormal bu~anol 41~07 Tertiary butyl perbenzoate47,20 The reactor is heated to reflux and the monomer mixture is added evenly to the refluxing reactor over a two-hour period~ Then 156.28.parts of norm-ai butanol are added as a rinse for the monomer feed lines. Reflux is continued for two additional hours at which time the heat is turned of~ and the batch cooled. The product is a solution oE a styre~e~ethyl acrylate~methacr~ylic acid =
,20 38~6/38,4/23.0 polymer at 66~ solids in solventO The acid number of the polymer is lS0.

To a suitable reactor 3 the following parts by weight are charged:
Epon 829 ~product of Shell 873.9 Chem.ical Co D ) Bisphenol A 464.
Monobutyl ether of ethylene gl.ycol 84.0 The charge is heated to 130~140C a~d allowed to exotherm to about 200C. Tem~erature is maintained above 165C for two hours after peak exotherm i~ reached. The Epon 829 has an epoxy equivalent weight of about 195, and it is chain extended by the bisphenol A to an epoxy equivalent - 3S weight of about 3000. 56.6 additional parts of 3 ~

monobutyl ether of ethylene glycol and 273 D 7 parts of normal butanol are added an~ the batch is cooled to 100C. 1211.3 parts of acrylic resin X is added and the batch is heated to reflux and held for 25 minutes. 370.3 parts of acrylic resin Y is added and mixed for 10 minutes. 23Z~9 parts of normal hutanol is added next. 6203 parts of deionized water are added evenly over a one-hour period. The resulting product contains 77,8~ epoxy resin and 22.2~ acrylic . 10 resin .in the first stage. Then 1~.5 parts of acrylic resin Y are added to 100 parts of the above acrylic/epoxy reaction product (not counting the weight contribution of the amine because it is fugitive on curin~), and the overall ratio is 68~
epoxy and 32~ acrylic. The product is ready to spray at 20.15~ solids and has an ICI viscosity of 26 centipoises and a low shear viscosity of 28 sec in a Ford number 4 cup. It is vexy responsive to pH
adjustment and addition of 0.1~ dimethyl ethanol amine will increa~e the ICI vis~osity to 32 centipoi~es and the Ford #4 visc05ity to 6~". When ~pplied by airless spray to drawn and ironed cans of Stee1D or of treated or untreated aluminumr the product has very good coverage, very good adhesion, and good blister resistance.

'rO a suitable reactor, the following parts by weight are charged Epon 829 25004 3isphenol A 12~06 Normal butanol 1.77 The char~e is heated to 130-140C and allowed to exotherm to about 200C~ Temperature is maintalned above 165'~C for two hours after exotherm is reachedO The Epon 829 has an epoxy equivalent 3~

weight o~ about 195, and it is chain extended by the bisphenol A to an epoxy equivalent weight of about ~000 . 5 . 99 parts o~ normal butanol are added and the batch is cooled tv 100C. 29 . 06 parts of acrylic 5 resin X are added and the batch is heated to reflux and held for 25 minutes . 40 ~ 71 parts of acrylic resin Y are added and mixed for 10 minutes. llol parts of normal butanol are added . 234 . 52 parts of deionized water are added evenly over a one-hour period. The resul~ing product contains 80% epoxy resin and 20~ acryIic resin in the first stage. Then 59.5 parts of acrylic resin Y are added to 100 parts of-the above acrylic/epoxy reaction product, and the overall ratio is 50% epoxy resin and 50% acrylic resin. The product is ready to ~pray at 20O22~
solids and has an XCI VisC05ity of 25 centipoises and a low she3r viscoslty of 17 sec ïn a Ford number 4 cup. It is very responsive to pH adjustment and addition o~ 0.1~ dimethylethanol amine will increase the I~I viscosity to 46 centipoises and the Ford number 4 cup viscosity to 90 ~ec. When applied by airless spray to drawn and ironed cans of steel or of treated or untreated aluminum, the product has very good coverage, very good blisker resistance and excellent adhesion.

To a suitable reactor, the following parts by weight are charged:
Epon 1009 7440 Normal b~tanol 177.4 The charge îs heated to about 115C and mixed until the epoxy resin is dissolved. Epon 1009 has an average epoxy equivalent weight of 3250. The batch is cooled to 100C and 604.0 parts of acr~lic resin X are added and the batch is heated to reflux ~ l~S~D3~ ~`

; 2~
and held for 25 min. 408.9 parts of acrylic resin Y
are added and mixed until uniform. 232.2 parts of normal butanol are added. 2065.8 parts of deionized : water are added uniformly over a one-hr period. An ~- additional 1767.3 part~ of deionized water are added.
T~e resulting produc~ con~ains 80~ epoxy resin and 20~ acrylic resin from the first stage. Then 29 parts of acrylic resin Y are added to 100 parts of the above acrylic/epoxy reaction product, and the overall ratio is 62% epoxy resin and 38~ acrylic res~n. The product is r~ady to spray at 20% solids and has an ICI viscosi~y of 19 centipoise~ and a low shear viscosity o 16 sec in a Ford number 4 cup. It is responsive to pH adjustment and addit.ion of 001%
dimethylethanol ami~e increases the ICI viscosity to 26 centipoises and the Ford number 4 cup viscosity to 23 sec. When applied by airless spray to drawn and ironed cans o~ steel or of treated or untreated aluminum, the product has very good coverage~ good blister resistance and excellent adhesion.
EX~PPLE 4 To a suitable reactor, the following parts by we.i~ht are charged:
Epon 1007 672~0 Normal butanol 160.3 The charge is heated to about 115C and mixed until the epoxy resin is dissolved~ Eporl 1007 has an average epoxy equivalent weight of abou~ 2000. The batch is cooled to 100C and 545.1 parts of acrylic resin X are added and the batch is heated to reflux and held for 25 minutes. 545.5 parts of acryllc resin Z are added and mixed until uniform. 232.2 ~arts of normal butanol are added. 2077.2 parts of deionized water are added uniformly over a one-hour period. ~n additional 1767.9 part~ of deionized water are added.

2~

. . ~.

The resul~ing product contains 80~ ep9xy resin and 2~% acryli~ resin fro~ the fixst stageO Then 42.8 parts of acrylic resin Z ar@ added to 100 parts cf the above acrylic/epoxy reaction produc~, and the S overail ratio is 5~% epoxy resin and 44~ acrylic resinO The product is ready to spray at 20% 501id5.
The product has an ICI viscosity of ~7 centipoises and a low shear viscosity of 16 sec in 3 Ford number 4 cup. It is very responsive ~o the p~
a~justmentr-and the addition of 0.1~ ~imethyl-e~hanol.
- -amine will i-ncre~e ~he-I~I viscosi-ty to 3~ ~ ~
centipsises and the Ford number 4 viscosi.y to 27 sec. When applied by airless spray ~o drawn and ironed cans of steel, treated or untreated aluminum, the product has very good overage, excellent adhesion and good .bli~ter resistance.
EX~PLE 5 3800 parts of ExampLe 2 7~ part~ o~ Cymel 373 (product of American Cyanamid CoO) Mix well. This acts as an external cro~slinker to aid in curing coated ~ilms. C~mel 378 is a parti211y alkylated melamine formaldehyde resin wh.ich is 85% solids in water~
E~MPLE 6 3800 parts of Example 2 3~ pa.rt:s of Cymel 373 38 parts of Methylon* resin 75L08 Mix well. These additives are both external 30 c~os51inkers 'co aid in cur ing coated f il~ns . Methylon resin 7510B is a co~ting intermediate consisting of a mixture of the allyl ethers of morlo-, di- and tri~methylol phenols, produced by General ~ilectric Company .
*denotes trade mark ~ 5~3~

To a suitable reactor, the following parts by weight are charged:
Epon 829 358O9 Bisphenol A 190.7 Monobutyl ether of ethylene glycol 34.5 The charge is heated to l30-140C and allowed to exotherm to abou~ 200C. Te~perature is maintained above 165C for two hours after peak exoth~rm is reached. Epon 82~ has an epoxy equivalent weight of about 195~ and it is chain extended by bisphenol A to an epoxy equivalen~ weight of about 3000. 27.4 parts of monobutyl ether of ethylene ~lycol and 112 7 4 parts of normal butanol are added, and the batch is cooled to 100C. 497.5 parts of acrylic resin X is added and the batch i5 heated to reflux and held for 25 minutesO 2183 parts of deionized water are added over a one hour period and then 9~.7 parts of normal butanol are added. 104O3 parts of deionized water are added. A premix is made o~ 124.9 parts of acrylic resin Y, 20.5 parts of deioniz~d water and 1.~ parts o dime~hyl ethanol amine. This premix is added to the above dispersion. This gives a final dispersion where the solids portiGn is 60% epoxy and 40% acrylic resin.
The product i5 ready to spray at 21S solids, and has an ICI v:iscosity Gf 36 centipoises and a lcw s~ear viscosity in a Ford number 4 of 38 sec. When applied by airless spray to drawn and ironed cans of steel, treated or untreated aluminum, the product nas good coverage, good blister resistance and very good adhesion. This particular sam~le has acceptable stability after 4 weeks at 50C, although the stabilit~ varies and other similar samples have been 3s less stable and not always acceptable.

Claims (45)

CLAIMS:

1. A water-borne coating composition consisting essentially of liquid carrier and a second reaction product made by blending a second carboxyl-functional polymer with a first reaction product, wherein said first reaction product is the product of the reaction in an organic media of:
(A) 50-90% by weight, based on the weight of (A) plus (B), of an epoxy resin containing, on the average, about 1 1/2 to 2 terminal 1.2-epoxy groups per molecule and having an epoxy equivalent weight of 750-5000;
(B) a first carboxyl functional polymer in an amount sufficient to provide at least 1.25 equivalents of carboxyl groups, when the source of the carboxyl group is a mono-protic acid, and at least 2.0 equivalents of carboxyl groups, when the source of such groups is a diprotic acid, per equivalent of 1,2-epoxy groups in the epoxy resin, said polymer having a weight average molecular weight (determined by light scattering) of about 10000-160000 and an acid number of 100-500;
(C) at least 1.25 equivalents of a tertiary amine per equivalent of 1,2-epoxy groups in the epoxy resin, said tertiary amine being selected from the group consisting of R1R2R3N, pyridine, N-methylpyrrole, N-methyl piperidine, N methyl pyrrolidine, N-methyl morpholine, and mixtures thereof and wherein R1 and R2 are substituted 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;
(D) 0-90% of the amount required for stoichiometric reaction with the carboxyl-functional polymer of (B) of at least one primary, secondary or tertiary amine or monofunctional quaternary ammonium hydroxide;
wherein for increasing ratios of carboxyl groups to 1,2-epoxy groups, the amount of amine is increased to keep the carboxyl-functional polymer water dispersible;
(E) said second carboxyl-functional polymer being blended in an amount of 5 to 200 parts by weight per 100 parts by weight of (A) plus (B) and having a weight average molecular weight (determined by light scattering) of about 10,000-160,000 and an acid number of 50-500, said acid number being at least 50 units different than the acid number of said first carboxyl-functional polymer, said second reaction product containing not less than 30% by weight of epoxy resin (A) based on the total of (A), (B) and (E).

2. The composition of claim 1 wherein water is blended with the first reaction product in sufficient quantity in that the continuous phase is aqueous, and then (E) is blended with the first reaction product.

3. The composition of claim 1 wherein (E) is blended with the first reaction product to make the second reaction product and then water is blended with the second reaction product in sufficient quantity so that the continuous phase is aqueous.

4. The composition of claim 2 wherein the second carboxyl-functional polymer (E) is neutralized with an amine before (E) is blended with the first reaction product.

5. The composition of claim 3 wherein the second carboxyl-functional polymer (E) is neutralized with an amine before (E) is blended with the first reaction product.

6. The composition of claim 1 wherein tertiary amine (C) is provided as an aqueous solution.

7. The composition of claim 1 wherein said first carboxyl-functional polymer has an acid number at least 100 units higher than that of said second carboxyl-functional polymer.

8. The composition of claim 1 wherein components (A), (B), (C), (D) and (E) comprise about 0.1-50% by weight of the coating composition and the remainder is comprised of the liquid carrier which is water and, optionally, organic liquid in a volume ratio of from 70:30 to all water.

9. The composition of claim 1 wherein components (A), (B), (C), (D) and (E) comprise about 0.1-50% by weight of the coating composition and the remainder is comprised of the liquid carrier which is water and organic liquid in a volume ratio of from 70:30 to all water.

10. The composition of claim 1 wherein said first carboxyl-functional polymer is present in an amount sufficient to provide at least 1.75 equivalent of carboxyl groups, when the source of the carboxyl groups is a mono-protic acid, and at least 2.5 equivalents of carboxyl groups, when the source of such groups is a diprotic acid, per equivalent of 1,2-epoxy groups in the epoxy resin.

11. The composition of claim 10 where m the source of said carboxyl groups is a mono-protic acid and said first carboxyl-functional polymer is present in an amount sufficient to provide 1.5-2.5 equivalents of carboxyl groups per equiva-lent of 1,2-epoxy groups and said tertiary amine of (C) is present in the amount of 2.0-2.5 equivalents per equivalent of 1,2-epoxy groups.

12. The composition of claim 1 wherein said first carboxyl-functional polymer is present in an amount sufficient to provide no more than 6.0 equivalents of carboxyl groups per equivalent of 1,2-epoxy groups in the epoxy resin.

13. The composition of claim 1 wherein said epoxy resin has an epoxy equivalent weight of 1500-4000.

14. The composition of claim 1 wherein said first and second carboxyl-functional polymers are polymers of the same monomers or different monomers, including at least one .alpha.,.beta. -ethylenically unsaturated monomer and at least one .alpha.,.beta. -ethylenically unsaturated acid.

15. The composition of claim 14 wherein said .alpha.,.beta. -ethylenically unsaturated acid is represented by the structures:

or wherein R is hydrogen or an alkyl radical of 1-6 carbon atoms, R1 and R2 are hydrogen, an alkyl radical of 1-8 carbon atoms, halogen, cycloalkyl of 3-7 carbon atoms or phenyl, and R3 is an alkylene radical of 1-6 carbon atoms; or half-esters thereof with alkanols of 1-8 carbon atoms.

16. The composition of claim 15 wherein said .alpha.,.beta.-ethylenically unsaturated acid is selected from the group consisting of acrylic acid, methacrylic acid, and itaconic acid.

17. The composition of claim 14 wherein said first carboxyl-functional polymer has an acid number of 150-350 and said second carboxyl-functional polymer has an acid number of 50-150.

18. The composition of claim 14 wherein said .alpha.,.beta. -ethylenically unsaturated monomer is at least one selected from the group consisting of (a) where R, R1, R2 and R3 are hydrogen or an alkyl radical of 1-5 carbon atoms;
(b) where R and R1 are hydrogen an alkyl radical of 1-18 carbon atoms, tolyl, benzyl or phenyl, and R2 is hydrogen or methyl;
(c) esters of acrylic acid, methacrylic acid or mixtures thereof with alkanols of 1-16 carbon atoms;
(d) a mixture of up to 20% of said polymer, of hydroxyalkyl (meth)acrylate with at least one of (a), (b) and (c); and (e) a mixture of up to 20% of said polymer of (meth)acrylamide or N-alkoxymethyl (meth)acrylamide with at least one of (a), (b) and (c).

19. The composition of claim 18 wherein the .alpha.,.beta.-ethylenically unsaturated acid is selected from the group consisting of acrylic acid, methacrylic acid, and itaconic acid.

20. The composition of claim 2 wherein the tertiary amine of (C) 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.

21. The composition of claim 20 wherein the tertiary amine of (C) is dimethyl ethanol amine.

22. The composition of claim 1 consisting essentially of liquid carrier and the reaction product of:
(A) 65-90% by weight, based on the weight of (A) plus (B), of an epoxy resin containing , on the average, two terminal 1,2-epoxy groups per molecule and having an epoxy equivalent weight of about 1500-4000;
(b) a carboxyl-functional polymer in an amount sufficient to provide at least about 1,75 equivalents of carboxyl groups, when the source of the carboxyl group is a mono-protic acid, and at least 2.0 equivalents of carboxyl groups, when the source of such groups is a diprotic acid, per equivalent of 1,2-epoxy groups in the epoxy resin, said polymer having a weight average molecular weight (determined by light scattering) of about 10000-80000 and an acid number of about 150-350;
(C) an aqueous solution of at least about 1.75 equivalents of a tertiary amine per equivalent of 1,2-epoxy groups in the epoxy resin, said tertiary amine being selected from the group consisting of R1R2R3N, pyridine, N-methylpyrrole, N-methyl piperidine, N-methyl pyrrolidine, N-methyl morpholine, and mixtures thereof and wherein R1 and R2 are substituted 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;
(D) 0-90% of the amount required for stiochiometric reaction with the carboxyl-functional polymer of (B) of at least one primary, secondary or tertiary amine or monofunctional quaternary ammonium hydroxide;
wherein for increasing ratios of carboxyl groups to 1,2-epoxy groups, the amount of amine is increased to keep the carboxyl-functional polymer water dispersible;
(E) said second carboxyl-functional polymer being blended in an amount of 5 to 200 parts by weight per 100 parts by weight of (A) plus (B) and having a weight average molecular weight (determined by light scattering) of about 10,000-160,000 and an acid number of 50-500, said acid number being at least 50 units different than the acid number of said first carboxyl-functional polymer, said second reaction product containing not less than 30% by weight of epoxy resin (A) based on the total of (A), (B) and (E).

23. The composition of claim 22 wherein components (A), (B), (C), (D) and (E) comprise about 0.1-50% by weight of the coating composition and the remainder is comprised of the liquid carrier which is water and, optionally, organic liquid in a volume ratio of from 70:30 to all water.

24. The composition of claim 23 wherein the liquid carrier is water and organic liquid in a volume ratio of about 80:20.

25. The composition of claim 1 or 22 additionally containing a crosslinking agent which is at least one of a phenol formaldehyde resin and a nitrogen resin.

26. The composition of claim 1 or 22 additionally containing diethoxytetramethoxymethylmelamine.

27. An article coated with a cured coating based on the composition of claim 1.

28. An article coated with 2 cured coating based on the composition of claim 1 additionally containing a nitrogen resin crosslinking agent.

29. A coating composition of claim 1 or 22 wherein components (A), (B), (C) and (E) are capable of forming a hydrogel structure.

30, A method of making the composition of claim 1 wherein a first reaction mixture is made by dissolving the epoxy resin of (A) and the first caroxyl-functional polymer of (B) in an organic liquid, then the tertiary amine of (C) is added to the first reaction mixture, to make a second solution, then a third reaction mixture is made by adding a second carboxyl-functional polymer of (E) to said second reaction mixture, then water is mixed with the third reaction mixture, if needed, to achieve a volume ratio of water to organic liquid between 70:30 and 90:10.

31. A method of making the composition of claim 1 wherein a first reaction mixture is made by dissolving the epoxy resin of (A) and the first carboxy-functional polymer of (B) in an organic liquid, then the tertiary amine of (C) is added to the first reaction mixture to make a second solution, then water is mixed with the second reaction mixture, then a third reaction mixture is made by adding a second carboxyl-functional polymer of (E) to said second reaction mixture, then water is mixed with the third reaction mixture, if needed, to achieve a volume ratio of water to organic liquid between 70:30 and 90:10.

32. A method of making the composition of claim 1 wherein a first solution is made by dissolving the epoxy resin of (A) in an organic liquid, then the tertiary amine of (C) is added to the first solution to form a polymeric quaternary ammonim hydroxide in an organic liquid, then the carboxyl-functional polymer of (B), dissolved in an organic liquid, is mixed with the polymeric quaternary ammonium hydroxide with agitation to form a second solution, then a third reaction mixture is made by adding a second carboxyl-functional polymer of (E) to said second reaction mixture, then water is mixed with the second solution, if needed, to achieve a weight ratio of water to organic liquid between 70:30 and 90:10.

33. A method of making the composition of claim 1 wherein a first solution is made by dissolving the epoxy resin of (A) in an organic liquid, then the tertiary amine of (C) is added to the first solution to form a polymeric guaternary ammonium hydroxide in an organic liquid, then the carboxyl-functional polymer of (B), dissolved in an organic liquid, is mixed with the polymeric guaternary ammonium hydroxide with agitation to form a second solution, then water is mixed with the second reaction mixture, then a third reaction mixture is made by adding a second carboxyl-functional polymer of (E) to said second reaction mixture, then water is mixed with the second solution, if needed, to achieve a weight ratio of water to organic liquid between 70:30 and 90:10.

34. The method of claim 32 wherein the carboxyl-functional polymer of (B) is pre-reacted to 10-90% of stoichiometry with at least one primary secondary or tertiary amine or monofunctional quaternary ammonium hydroxide (D) before being mixed with the polymeric quaternary ammonium hydroxide.

35. The method of claim 33 wherein the carboxyl-functional polymer of (B) is pre-reacted to 10-90% of stoichiometry with at least one primary, secondary or tertiary amine or monofunctional quaternary ammonium hydroxide (D) before being mixed with the polymeric quaternary ammonium hydroxide.

36. A method of making the composition of claim 1 where in a first solution is made by dissolving the carboxyl-functional polymer of (B) in an organic liquid, then an aqueous solution of a tertiary amine of (C) is mixed with the first solution to form a second solution, then the epoxy resin of (A) is mixed with the second solution to form a third solution, then a third reaction mixture is made by adding a second carboxyl-functional polymer of (E) to said second reaction mixture, then water is mixed with the third solution if needed, to achieve a volume ratio of water to organic liquid between 70:30 and 90:10.

37. A method of making the composition of claim 1 wherein a first solution is made by dissolving the carboxyl-functional polymer of (B) in an organic liquid, then an aqueous solution of a tertiary amine of (C) is mixed with the first solution to form a second solution-then the epoxy resin of (A) is mixed with the second solution to form a third solution, then water is mixed with the second reaction mixture, then a third reaction mixture is made by adding a second carboxyl-functional polymer of (E) to said second reaction mixture, then water is mixed with the third solution, if needed, to achieve a volume ratio of water to organic liquid between 70:30 and 90:10.

38. The method of any one of claim 30, claim 31, and claim 32 wherein the resulting mixture of (A), (B) and (C) is heated between 50° and 95°C, to react (A), (B) and (C).

39. The method of any one of claim 33, claim 34 and claim 35 wherein the resulting mixture of (A), (B) and (C) is heated between 50° and 95°C, to react (A), (B) and (C).

40. The method of claim 36 or claim 37 wherein the resulting mixture of (A) (B) and (C) is heated between 50° and 95°C, to react to (A), (B) and (C) .

41. The method of any one of claim 30, claim 31 and claim 32 wherein the resulting mixture of (A), (B) and (C) is heated between 70° and 80°C, to react (A), (3) and (C).

42. The method of any one of claim 33, claim 34 and claim 35 wherein the resulting mixture of (A), (B) and (C) is heated between 70° and 80°C, to react (A), (B) and (C).

43. The method of claim 36 or claim 37 wherein the resulting mixture of (A), (B) and (C) is heated between 70° and 80°C, to react (A), (B) and (C).

44. The method of any one of claim 21, claim 31 and claim 32 wherein the mixed ingredients of said claim are allowed to react to produce a reaction product and then at least one primary, secondary or tertiary amine or monofunctional quaternary ammonium hydroxide of (D) is mixed with the reaction product.

45. The method of any one of claim 33, claim 36 and claim 37 wherein the mixed ingredients of said claim are allowed to react to produce a reaction product and then at least one primary, secondary or tertiary amine or monofunctional quaternary ammonium hydroxide of (D) is mixed with the reaction product.