CA2156468A1 - Aqueous coating composition - Google Patents

Abstract

An aqueous coating composition containing dispersed acrylic grafted epoxy-ester copolymer produced by first forming a carboxyl functional epoxy-ester by esterifying a low molecular weight epoxy resin with a low molecular weight, unsaturated, carboxyl terminated polyester, followed by in-situ copolymerizing ethylenic monomers in the presence of water-dispersed epoxy-ester.

Description

,~I 50120 -- 21~

AQUEOUS COATING COMPOSITION
This invention relates to protective coatings containing zero or very low levels of volatile organic compounds (VOC), and more particular' y to aqueous dispersed epoxy-ester acrylic-graft polymeric binders particularly useful 15 for coating interior substrates of beer and beverage containers ( cans ) .
Protective surface coatings are organic compositions applied to substrates to form continuous films w~ich are 20 cured or otherwise hardened to provide protection as well as a decorative appearance to the substrate. Protective surface coatings ordinaril~ comprise an organic polymeric binder, pigments, inert fillers and other additives, where:
the polyl[leric binder acts as a fluid vehicle for the 25 pigments and imparts rheological properties to the f luid paint coating. Upon curing, the polymeric binder hardens and functions as a binder for the pigments and provides adhesion of the dried paint film to the substra e. The plgments may be organic or inorganic and functionally 30 contribute to opacity and colour in addition to durabiLity and hardness, although sor~.e paint coatings contain little or no opacifying pigments and are described as clear coatings. The manufacture of paint coatings involves the preparation of a polyrr,eric binder, mixing of component 35= materials, grinding of plgments in the polymeri~ binder, and thinning to co~[l}[Lercial standards.

~156~68 Epoxy resins are particularly desirable for use in surface coating materials as a vehicle or polymeric binder to advantageously provide toughness, flexibility, adhesion, and chemical resistance to the applied coating film. Hence 5 water-dispersed coating cornpositions containing epoxy resins are highly desirable for can coating compositions.
Coatings for soft drink and beer cans, for instance, are critical due to taste sensitivity and must not alter the taste of canned beverages. Taste problems can occur in a 10 variety of ways such as by leaching of coating components into the beverage, or by adsorption of flavour by the coating, or sometimes by chemical reaction, or by some combination thereof.
lS In our US Patent No. 4 212 781, a process is disclosed for modifying epoxy resin by reacting the epoxy resin with addition polymerizable ethylenic monomer in the presence of at least 3% by weight of benzoyl peroxide (or the free radical initiating equivalent thereof ) based on monomer at 20 a suitable reaction temperature to produce a reaction mixture comprising an epoxy-acrylic polymer, and associatively-formed ungrafted addition polymer. The in-situ polymerized monomers include acid functional monomers to provide acid functionality in the reaction 25 mixture sufficiently high to effect stable dispersion of the resulting reaction product in a basic aqueous medium.
Similarly, our ~S Patent No. 3 552 961 relates to a mixture of polymers comprising a self-curing emulsion polymer (latex), an epoxy-acrylic graft copolymer, and preferably a 30 phosphate additive. Related patents are US Patent Nos. 4 2~5 ~47 and 4 399 241, and 5 212 241. Most prior art water-dispersed epoxy coatings utilise relatively high levels of organic solvent to assist processing of the epoxy resin. Although epoxy containing coatings have long been 35 the standard of excellence in the interiors of beverage cans, such coatings cannot be prepared without significant 21~6~ -amounts of solvent, where typically 50~ to lOOï volatile organic solvent is required based on solids (about 2 . 5 to lbs./gal. or about 0.3 to 5Kg/l) . Recent environmental concerns and legislative pressure have created the need for 5 a zero or near zero VOC Gan coating.
It now has been found that high quality aqueous dispersed epoxy coatings can be produced with no organic solvent by esterifying low molecular weight epoxy resin 10 with low molecular weight carboxyl functional polyester to produce a carboxyl functional low molecular weight epoxy-ester, mixing the epoxy-ester with ethylene monomers and dispersing the mixture into water, and then copolymerizing the ethylenically unsaturated monomers to produce a 15 crQsslinked emulsion polyc.er useful as a polymeric binder .
In particular, it has bee~l found that aqueous emulsion dispersions of the crosslinked epoxy-ester copolymer can be prepared and maintained dispersed in water without conventional surfactants and by ammonia neutralisation of 20 the epQxy-ester carboxyl groups without the need for any volatile organic solven~ s. Copolymerization of the ethylenic monomers produces a stable small particle size polymeric dispersion.
It has been found that low molecular weight epoxy resins are eas~ily processable at lower temperatures and viscosities while low molecular weight oligomeric carboxyl functional polyesters lower the overall viscosity of the mixture ar,d provides considerably improved processability.
Temperature control during the formation of the epoxy ester advantageously avoids unwanted molecular weight advancement while the liquid ethylenic monomers serve as a temporary solvent for the epoxy-ester which in turn facilitates the si~ple dispersion of the organic mixture into water. Once epoxy resin is reacted with a low molecular weight, acid ~-unctional polyester oligomer in 4 2156~G8 accordance with the invention, the resultant epoxy-ester can be dissolved in acrylic monomer and dispersed into water with very low levels of ammonia. The epoxy-ester is water dispersed and becomes addition grafted and 5 crosslinked with the copolymerized ethylenic monomers to form a very small particle microgel stably dispersed in water. Grafting of the epoxy-ester with ethylenic monomers in water produces very small size crosslinked microgel particles, a physical property particularly 10 useful for producing tough but resilient and flexible coatings .
According to the present invention there is provided an aqueous dispersed, protective coating composition 15 substantially free of volatile organic compounds and containing a polymeric binder dispersed into water, the polymeric binder comprising a crosslinked epoxy-ester copolymer containing by weight:
a) between 1% and 70~ low molecular weight epoxy resin having a number average molecular weight between 100 and 1, 000;
b) between 1% and 70~ low molecular weight, carboxyl functional, unsaturated polyester oligomer having an acid number between 30 and 500 and a number average molecular weiqht between 200 and 3, OOOi and c) between 1% and 90% addition copolymer made of copolymerized ethylenic monomer;
where the crosslinked epo:~y-ester copolymer is produced by esterifying the carboxyl functional polyester oligomer with epoxy resin to produce a carboxyl functional, unsaturated epoxy-ester having an acid number between 30 and 200 and then copolymerizing the ethylenic monomers in the presence 5 ~ 46~ :
of the epoxy-ester dispersed in water to produce internally crosslinked emulsion microgel particles of an epoxy-ester copolymer crosslinked with ethylenic monomer having an acid number between 25 and 150, where the crosslinked microgel 5 particles have an average particle size less than 0 . 02 microns, and where said microgel particles are stably dispersed into water free of surfactant.
This invention incorporates the advantages of epoxy lO chemistry providing good barrier properties and excellent resistance to flavour absorption along with a synthesis technique that eliminates the need for organic solvents, organic amines and surfactants. Baked paint films utilising the resulting polymeric binder are clear, glossy, 15 solvent resistant, and water resistant.
Briefly, the zero VOC protective coating composition of this invention is substantially free of volatile organic compounds and surfactants and is based on an aqueous 20 dispersed polymeric binder comprising an epoxy-ester polymer binder grafted with ethylenic monomers to produce a crosslinked epoxy-ester emulsion copolymer. The copolymer is produced by copolymerizing an aqueous dispersed mixture of carboxyl functional epoxy-ester and ethylenically 25 unsaturated monomers to produce very small particle microgel particles comprising a stable aqueous dispersed crosslinked epoxy-ester copolymer binder.
The epoxy-ester comprises the esterification reaction 30 product of an epoxy resin esterified with a carboxylic acid functional, low molecular weight polyester oligomer. A
useful epoxy-ester can be produced, for example, by reacting a monofunctional or difunctional epoxy resin with a carboxylic acid functional polyester oligomer to produce 35 a carboxyl functional epoxy-ester copolymer.
, 6 215~6~ ~l Epoxy resins are characterised by the three-membered ether group:
resin - CH - CH
O
5 where any one of the hydrogens can be replaced with a lower alkyl group, where said three-membered ring is commonly referred to an epoxy or oxirane group and such groups typically terminate epoxy backbone chain and/or branched chains. Epoxy-ester groups are formed by esterification of 10 an epoxy group with a carboxyl functional polyester oligomer to produce a carboxyl functional epoxy ester.
Useful epoxy resin comprise conventional bisphenol epoxy resins, glycidyl functional resins, epoxy novalac resins, and alkylene oxide resins. Bisphenol epoxies are 15 preferred and are predominantly linear chain molecules comprising the coreaction product of polynuclear dihydroxy phenols or bisphenols with hal ohydrins to produce epoxy resins containing at least one and preferably two epoxy groups per molecule. The most common bisphenols 20 are bisphenol-A, bisphenol-F, bisphenol-S, and 4, 4' -dihydroxy bisphenol, with the most preferred being bisphenol-A. Halohydrins include epichlorohydrin, dichlorohydrin, and 1, 2-dichloro-3-hydroxypropane with the most preferred being epichlorohydrin. Preferred epoxy 25 resins comprise the coreaction product of excess molar equivalents of epichlorohydrin with bisphenol-A to produce pr~nmin~ntly an epoxy group terminated linear molecular chain of repeating units of diglycidyl ether of bisphenol-A
containing between 2 and 25 repeating copolymerized units 30 of diglycidyl ether of bisphenol-A. In practice, an excess molar equivalent of epichlorohydrin is reacted with bisphenol-A to produce epoxy resins where up to two moles of epichlorohydrin coreact with one mole of bisphenol-A, although less than complete reaction can produce 35 difunctional epoxy resin along with monoepoxide chains terminated at the other end with a bisphenol-A unit. The 21~6S
most preferred linear epoxy resins are polyglycidyl ethers of bisphenol-A having terminating 1,2-epoxide groups.
Commercially available Lower molecular weight resins include Dow Chemical epoxy resins identified by trade 5 number and average molecular weights as follows: DER 333 (380); DER 6~1 (525); while Shell Chemical epoxy resins are EPON 1007 F (4000); and Ciba-Geigy linear epoxy resins GT-7013 (1400); GT-7014 (1500); GT 7074 (2000); and GT-259 (1200)~ Particularly preferred lower molecular weight epoxy resins include EPON 828, EPON 1001, DER 333, and DER 661 having a number average molecular weight less than 1, 000 and preferably between 300 and 500, measured by gel permeation chromatography (GPC) according to AST~I
methods such as D3536-76, D3593-80, or D3016-78. Preferred epoxy resins ~ ~ve an equivalent weight between 180 and 500 .
High equivale~t weight epoxy resins form a viscous melt when combined with acid functional polyester oligomers causing mixing problems, although epoxy blends containing minor amounts of high molecular weight epoxy resins are 20 workable.
Epoxy resins further include non-aqueous alkylene oxide resins which are epoxide functional resins comprising an alkylene oxide adduct of a bisphenol compound. The 25 alkylene oxide is an aliphatic alkyl derivative having up to about 26 carbon atoms although preferred oxides are lower alkyl oxides such as ethylene, propylene, and butylene oxides. Bisphenol compounds include bisphenol-A, bisphenol-F and bissulfone or sulfides. Typically two or 30 more moles of alkyl oxide are coreacted with one mole of bisphenol compound. Preferred compositions are 2 :1 molar reactions while suitable molecular weight range of alkylene oxide resins is between 200 and l, 000 as measured by GPC.
35 Useful polyester oligomers comprise the esterification products of glycols, diols, or polyols with excess * ~ 46~
equivalents of dicarboxylic acid anhydrides or polycarboxylic acids, where the polyester ~ligomers are unsaturated polyesters containing ethylenic unsaturation.
Linear aliphatic glycols are esterified with greater molar 5 amounts of aromatic dicarboxylic acid and/or linear dicarboxylic acid having between 2 and 36 linear carbon atoms such as adipic, azelaic, succinic, glutaric, pimelic, suberic or sebacic acid, as well as unsaturated dicarboxylic acids such as maleic, fumaric or itaconic acid 10 to produced low molecular weight, unsaturated polyesters.
Although not preferred, minor amounts or monocarboxylic unsaturated acid such as acrylic, rnethacrylic or ethacrylic acid can be esterified. Preferred and commercially available linear saturated dicarboxylic acids are 15 dodecanedioic acid, dimer fatty acids, or azelaic acid, while preferred unsaturated acid are maleic and fumaric.
Aromatic dicarboxylic acids (anhydrides) include phthalic, isophthalic, terephthalic, and tetrahydrophthalic. Minor amounts of polyfunctional acids such as tri~ell~tic acids 20 can be added. Suitable glycols include linear aliphatic glycols havi~g 2 to 16 carbon atoms such as 1, 3- or 1, 4-butylene glycol, 1, 6-hexane diol, neopentyl glycol, propylene gly-col, ethylene glycol and diethylene glycol, propylene, and dipropylene glycol, and similar linear 25 glycols. Preferred glycols are hydrophobic glycols such as hydrogenated Bisphenol A, neopentyl glycol and 1, 6-hexane diol. although not desirable, minor amounts of polyols can be used such as glycerol, pentaerythritol, dipentaerythritol, or trimethylol ethane or propane. The 30 molar excess of the dicarboxylic acid over glycol is between about 1~ and 50~ and preferably between about 20%
and 50%, where at least 1 molar % and preferably between 20% and 100~ molar percent of the carboxylic acid components comprises ethylenically unsaturated mono or 35 dicarboxylic acid. ~he polyester oligomer contains considerable excess unreacted carboxylic groups. The -9 215~
carboxyl functional polyester oligomer preferably has an acid number between 100 and 300 rL~illigrams of KOH per gram epoxy ester. The molecular weight of useful polyester oligomer is preferably between 300 and 1, 500.

Acid functional polyester oligomers can be prepared by esterification of the common diacids with dihydroxyl compounds. Useful glycols include for instance ethylene glycol, propylene glycol, butanediols, diethylene glycol, 10 dipropylene glycol, triethylene glycol, hexane diol, and similar glycols. Preferred glycols such as p_opylene, butylene, diethylene glycol and the like can be reacted with diacids such as maleic, adipic, isophthalic acid and the like at an excess of acid to hydroxyl functionality, to 15 produce a carboxylic acid functional polyester having a preferred molecular weight about 300 to 1, 500 . ~ufficient acid functionality in the polyester oligomer needs to be present to allow reaction with the epoxy resin, and then dispersion into water.
Small quantities of monofunctional acids and alco~.~ls (such as benzoic acid, 2-ethylhexanoic acid, benzyl a~' cohol and the like) can be used to modify the polyester str-_~ture, as can polyfunctional acids and alcohols (such as t-imellitic 25 anhydride, trimethylol propane, and the like).
Polyfunctional alcohols and acids can serve t~ provide higher acid contents to the polyesters, which can render the resultant epoxy-esters more water dispersible.
Polyester oligomers containing unsaturated diacids (fumaric 30 and maleic) are preferred, as the unsaturation provides grafting crosslinking functionality for the acrylic monomer .
The polyester component can be synthesised by bulk 35 polymerization, where the raw materials are charged in bulk and esterified at temperatures typically betwee-l 1~0~C -o lo 21~6~68 240~C, although moderately higher or lower temperatures can be utilised satisfactorily. An esterification catalyst can be used, typically an organic tin compound at less than 1%
levels based on weight of the charge.
The acid number of the epoxy-ester resin (the reaction product of the acid functional polyester oligomer and the epoxy resin) is preferably between 50 and 150 mg KOH per gram of epoxy ester. The epoxy-ester preferably has a number average molecular weight between 500 and 4, 000 and more preferably between 600 and 2, 000.
Epoxy-esters are formed by the reaction of the epoxy resins with the preformed acid functional polyester oligomers.
15 Although considerable levels of free diacid may be present in the polyester oligomers, any unreacted carboxylic material ordinarily reacts with epoxy groups without substantially affecting the properties of the epoxy-ester.
Nucleophilic compound such as tertiary amines are excellent 20 catalysts for this epoxy acid reaction, which can be carried out at about 30 to 1203C, but pre~erably from about 70~ to 110aC. ~emperatures higher than about 120'C should be avoided, as resin viscosity can rise c~uickly, and gelation can result. Hence, epoxy polyester mixtures which 25 are fluid, and can be easily mixed at about 100~C are preferred. ~referred epoxy-esters contain from abut 10% to 90% by weight epoxy resin with the remaining weight being oligomer polyester and dicarboxylic acid if any. Epoxies will react with carboxyl polyester oligomers at 100 to 30 140~C without a catalyst, but the reaction proceeds quicker and at preferred lower temperatures in the presence of a suitable nucleophile, such as tertiary amine. Good reaction rates in the presence of about 0.1~ benzyldimethyl amine occur at about 70~C to 100~C.

11 215~6~
The crosslinked epoxy-ester copolymer can be produced by first mixing the epoxy-ester with ethylenic monomers to reduce the resin viscosity to render the epoxy-ester more easily dispersible in water, and then dispersing the 5 mixture into water and copolymerising the monomerS.
Alternatively, the crosslinked epoxy-ester copolymer can be produced by dispersing lower viscosity, low molecular weight epoxy-esters directly into water without the addition of monomer, and then adding the ethylenic monomers 10 to the epoxy-ester aqueous dispersion. ~he epoxy-ester is dispersed by neutralising it at least partially with ammonia and forming a small particle size dispersion in water. ~he epoxy-ester is then copolymerized in water with the ethylenic monomers to produce internally crosslinked 15 microdispersions of crosslinked epoxy-ester.
According to the present invention there is also provided a process for producing an aqueous dispersed, protective coating composition substantially free of volatile organic 20 compounds and containing a polymeric binder dispersed into water, the polymeric binder being emulsion polymerised microgel polymer particles, the process comprising:
esterifying by weight between 1~ and 70% low ~lecular 25 weight epoxy resin having a number average molecul~r weight between 100 and 1, 000 with between 1~ and 70~ low molecular weight, carboxyl functional, unsaturated polyester oligomer having an acid number between 30 and 500 and a number average molecular weight between 200 and 3, 000 30 to form a carboxyl functional unsaturated epoxy-ester having an acid number between 30 and 200i dispersing the carboxyl functional epoxy-ester into water by at least partially neutralising the carboxyl functional 35 epoxy-ester with ammonia;

i2 2~6~
copolymerizing, by emulsion polymerisation at least 1% by weight ethylenic monomer ln the presence of the epoxy-ester dispersed into water to produce internally crosslinked emulsion microgel polymer particles of a copolymer of 5 emulsion polymerised ethylenic monomer crosslinked with the epoxy-ester by addition copolymerisation crosslinking, the emulsion microgel polymer particles having an acid number between 25 and 150, where the emulsion crosslinked microgel particles have an average particle size less than 0 . 02 10 microns, and where said microgel particles are stably dispersed into water without surfactant.
Copolymerizable ethylenic monomers useful for reacting with the epoxy-ester polymer are monomers containing carbon-to-15 carbon, ethylenic unsaturation and include vinyl monomers,acrylic monomers, allylic monomers, acrylamide monomers, and mono- and dicarboxylic unsaturated acids. Vinyl esters include vinyl acetate, vinyl propionate, vinyl butyrates, vinyl benzoates, vinyl isopropyl acetates and similar 20 vinyl esters. Vinyl halides include vinyl chloride, vinyl fluoride, and vinylidene chloride. Vinyl aromatic hydrocarbons include styrene, methyl styrenes and similar lower alkyl styrenes, chlorostyrene, vinyl toluene, vinyl naphthalene, divinyl benzoate, and cyclohexene. Vinyl 25 aliphatic hydrocarbon monomers include alpha olefins such as ethylene, propylene, isobutylene, and cyclohexene as well as coniugated dienes such as 1, 3 butadiene, methyl-2-butadiene, 1, 3-piperylene, 2, 3-dimethyl butadiene, isoprene, cyclopentadiene, and dicyclopentadiene. Vinyl 30 alkyl ether include methyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, and isobutyl vinyl ether.
Acrylic monomers include monomers such as lower alkyl esters of acrylic or methacrylic acid having an alkyl ester portion containing between 1 to 12 carbon atoms as well as 35 aromatic derivatives of ~ acrylic and methacrylic acid.
Useful acrylic monomer include, for example, acrylic and 13 21~6~
methacrylic acid, methyl acrylate and methacrylate, ethyl acrylate and methacrylate, butyl acrylate and methacrylate, propyl acrylate and methacrylate, 2-ethyl hexyl acrylate and methacrylate, cyclohexyl acrylate and methacrylate, 5decyl acrylate and methacrylate, isodecylacrylate and methacrylate, benzyl acrylate and methacrylate, and various reaction products such as butyl, phenyl and cresyl glycidyl ethers reacted with acrylic and methacrylic acids, hydroxyl alkyl acrylates and methacrylates such 10as hydroxyethyl and hydroxy propyl acrylates and methacrylates, as well as amino acrylates and methacrylates. Carboxylic acid functional monomers can be included if desired. Carboxylic acid monomers include 3 acrylic and methacrylic acids. Acrylic acids include 15acrylic and methacrylic acid, ethacrylic acid, alpha-chloracrylic acids, alpha-cyanoacrylic acid, crotonic acid, and beta-acryloxy propionic acid. Ethylenic monomer mixtures of acrylic and/or methacrylic esters with styrene are preferred. Styrene copolymerized very efficiently with 20the double bond unsaturation in the epoxy-ester. On a weight basis of total ethylenic monomers, the ethylenic monomers preferably comprise between 0~ and 100~ styrene monomers, and preferably between 20~ and 80~ styrene monomer, with the balance being other ethylenic monomers.
On a weight basis, the crosslinked epoxy-ester copolymer contains preferably between 25~ and 70% addition polymer component of copolymerized ~onomers based on the total weight of the crosslinked epoxy-ester copolymer with the 30balance being the epoxy-ester polymer component. The crosslinked epoxy-ester copolymer preferably contains between 1% and 50% epoxy resin, more preferably 10 to 40~.
The crosslinked epoxy-ester copolymer preferably comprises between 1% and 50% polyester oligomer, more preferably 10 35to 4Q%. These compositions are preferably free o~ volatile ~ 14 21a~G~
organic compounds in these ranges. The balance of the copolymer is copolymerized èthylenic monomers.
The number average molecular weight of the crosslinked 5 epoxy-ester copolymer is aoove about 50, 000 and typically the crosslinked microgel particles of epoxy-ester mollecular weight readily exceeds and is typically well over l, OOo, ooo 10 In accordance with this invention, the epoxy-ester solution in monomer can be easily dispersed into water by simple mixing with water containing sufficient ammonia to neutralise a substantial portion of the acid groups available in the epoxy-ester . About 0 . 5 to 5~ by weight 15 ammonia as NH? on polymeric solids is typical. Aqueous dispersion pH' s close to 7 are preferred to eliminate the possibility of polyester hydrolysis. Acrylic monomers can be polymerized and initiated with any of the common free radical initiators, such as the peroxides, persulfates, 20 peresters, and the azo initiators. Peroxide and perester redox initiation is preferred with systems such as Na formaldehyde sulfoxylate/Fe/persulfale, and ascorbic acid/
Fe/t-butyl perbenzoate.
25 The resulting crosslinked epoxy-ester copolymers comprise very small micro-dispersion, crosslinked microgel polymer particles having an average microgel particle si~e belo~
0.2 microns, preferably below 0.02 microns, most preferably between 0.02 and 0.06 microns. The microgel particles 30 produced by ethylenic monomer crosslinking of the water dispersed, linear epoxy-ester polymer surprisingly provides highly crosslinked copolymers in the forrn of a stable aqueous microdispersion of extraordinarily small internally crosslinked microgel polymer particles wl~hout the need 35 for, and particularly without, external surfactants.
Excellent protective film formations on substrates are 21-~4~8 achieved without surfactants and even though the microgel particles are intPrn~l ly highly crosslinked. E~ence, the quality coatings for the interior of beverage cans can be produced with crosslinked epoxy-ester copolymer microgel 5 particles. Aqueous dispersions of these blended resins can be prepared in water with ammonia neutralisation without the use of a~y volatile solvent. The acid functional epoxy-esters (dissolved in acrylic monomer) can be easily dispersed into water with low to moderate shear.
10 Polymerization of the acrylic monomers produces the polymer blend in the ~orm of ver-t~ small particles size microgel crosslinked polymer particles in dispersion form. cured films exhibit excellent water resistance, and good clarity and gloss.
The merits of this inventi~n are further illustrated upon referring to the following illustrative examples.

~ 16 21~68 An acid functional polyester oligomer and epoxy ester was prepared as follows: :
Grams 180.2 1, 3-butylene glycol 392 maleic anhydride 0 . 5 piperidine (maleic to fumaric isomerization catalyst) 10 The aboue raw materials were warmed with, good stirring to about 120~C, held for 2 hou~s, and then cooled. Titration gave an acid Number of 133 and equivalent weight (143 theoretical). 266 g of the above unsaturated polyester was combined with 188 grams DER 333 epoxy (epoxy equivalent 15 weight 190 Dow Chemical). The mixture was warmed while controlling exotherm and limiting the reaction mixture temperature to 100~C to produce an ep~xy-ester having an acid number of 120 and a n~ber average molecular weight of about 1, 0 0 0 .

An epoxy ester acrylic copolymer resin dispersion was prepared as follows:
Grams a) 554 epoxy ester from Example (1) 3 4 0 s tyrene 114 butyl acrylate b) 900 water 121 ammonia (28~) c) 1605 water d) 9 . 0 t-butyl perbenzoate e) 9 . 0 ascorbic acid f) 5 ml FeSO~ solution, 1000 ppm Epoxy ester of Example 1 was mixed in monomers to form 35 liquid mix (a), and then dispersed into (b) which had been purged with nitrogen at 20~C for two hours. The mixture 17 21~6~
was mixed with a paddle stirrer at about 300 - 500 rpm for about 2 minutes, and then (c) was added, which has also was purged with nitrogen at 20 C for 2 hours. Components (d), ~e), and (f) were added se~Llentially to the dispersion, and 5 the reaction mixture was insulated such that the temperature rose to about 50~C. The mixture was held for 2 hours, and then 1 g additional t-butyl perbenzoate was added .

10 A polyester oligomer and an epoxy ester was prepared as in Example (1), but using 27.5 g maleic anhydride, 155.8 g diethylene glycol, 1. 0 g piperidine, and 278 . 7 g DER 333 .
Then 0 . 5 g triethylene diamine was added to the epoxy ester after 2 hours at 95~C, held for 2 ~ore hours prior to 15 cooling. Then 181 grams styrene were added during the cool down to cut viscosity.

An epoxy ester acrylic blended resin dispersion was prepared as follows:
2 0 Grams a) 125 epoxy ester in styrene from example (3) styrene (additional) t-butyl perbenzoate b) 200 water 12 ammonia, 28 c) 400 water d) 2.0 ascorbic 2cid (10% in water at pH 6.5) e) 2 FeSO~ solution, lO00 ppm 30 Solution (a) was poured into (b) with 500 rpm paddle agitation, and then (c) was added. Ammonia was added dropwise to give pH 6 . 5 . Then (d) and (e) were added in sequence. Both (b) and (c) were previously purged for 2 hours with nitrogen. ~xotherm was immediate, rising to 50~C in about 15 minutes. Then 1 g additional t-butyl perbenzoate was added after 2 hours.

~ 18 215~4G8 Example (4) was repeated but included 75 g of the epoxy ester solution in styrene, and the addition of an 5 additional 125 g styrene.
RESULTS
Resin dispersions of Examples 2, 4 and 5 were all free from 10 grit, shear stable, and very small in particle size (<0.1 micron) .
Draw down sa~ples of resins in Examples 2, 4 and 5 on aluminum sheet with a ~28 wire wound bar were baked at 184-C ~390~F) for 2 minutes to provide the following cured film properties:
Sample Gloss Cl arity Water Resistance 2 high good no blush noted 4 high good no blush noted high good no blush noted Resin Example 2 was exposed to 70~C ~180~F) water for 30 minute~, while samples 4 and 5 were exposed to boiling 25 water for 5 ~inutes.
The foregoing description and representative examples illustrate the merits of this invention but are not intended to be limiting except as def ined by the appended 30 claims.

Claims (13)

1. An aqueous dispersed, protective coating composition substantially free of volatile organic compounds and containing a polymeric binder dispersed into water, the polymeric binder comprising a crosslinked epoxy-ester copolymer containing by weight:
a) between 1% and 70% low molecular weight epoxy resin having a number average molecular weight between 100 and 1, 000;
b) between 1% and 70% low molecular weight, carboxyl functional, unsaturated. polyester oligomer having an acid number between 30 and 500 and a number average molecular weight between 200 and 3,000; and c) between 1% and 90% addition copolymer made of copolymerized ethylenic monomer;
where the crosslinked epoxy-ester copolymer is produced by esterifying the carboxyl functional polyester oligomer with epoxy resin to produce a carboxyl functional, unsaturated epoxy-ester having an acid number between 30 and 200 and then copolymerizing the ethylenical monomers in the presence of the epoxy-ester dispersed into water to produce internally crosslinked emulsion microgel particles of a copolymer of ethylenic monomer crosslinked epoxy-ester having an acid number between 25 and 150, where the crosslinked microgel particles have an average particle size less than 0.02 microns, and where said microgel particles are stably dispersed into water free of surfactant.

2. The coating composition of claim 1 where the crosslinked epoxy-ester copolymer contains between 1% and 50% by weight of the epoxy resin.

3. The coating composition of claim 1 or Claim 2 where the crosslinked epoxy-ester-acrylic contains between 10%
and 40% by weight of epoxy resin of equivalent weight between 180 and 500.

4. The coating composition of any of claims 1 to 3 where the crosslinked epoxy-ester copolymer contains between 1%
and 50% by weight of the polyester oligomer.

5. The coating composition of claim 4 where the crosslinked epoxy-ester copolymer contains between 10% and 40% polyester oligomer.

6. The coating composition of any of claims 1 to 5 where the crosslinked epoxy-ester copolymer contains between 25%
and 70% by weight of the addition copolymer.

7. The coating composition of claim 1 where the crosslinked epoxy-ester copolymer contains by weight between 1% and 50% of the epoxy resin and between 1% and 50% by weight of the polyester oligomer whereby the coating composition is free of volatile organic compounds.

8. The coating composition of any of claims 1 to 7 where the epoxy-ester has an acid number between 50 and 150mgKOH/g.

9. The coating composition of any of claims 1 to 8 where the carboxyl functional unsaturated polyester oligomer is produced by esterifying between 1% and 50% molar excess dicarboxylic acid with glycol.

10. The coating composition of claim 9 where the molar excess of dicarboxylic acid is between 20% and 50%.

11. The coating composition of claim 1 where the crosslinked epoxy-ester copolymer is produced by first mixing the epoxy-ester with the ethylenic monomers and then dispersing the mixture into water and copolymerizing the monomers.

12. The coating composition of claim 1 where the crosslinked epoxy-ester copolymer is produced by first dispersing the epoxy-ester into water and then copolymerizing the ethylenic monomers upon adding the monomers to the epoxy-ester aqueous dispersion.

13. A process for producing an aqueous dispersed, protective coating composition substantially free of volatile organic compounds and containing a polymeric binder dispersed into water, the polymeric binder being emulsion polymerised microgel polymer particles, the process comprising:
esterifying by weight between 1% and 70% low molecular weight epoxy resin having a number average molecular weight between 100 and 1,000 with between 1% and 70% low molecular weight, carboxyl functional, unsaturated polyester oligomer having an acid number between 30 and 500 and a number average molecular weight between 200 and 3,000 to form a carboxyl functional unsaturated epoxy-ester having an acid number between 30 and 200;
dispersing the carboxyl functional epoxy-ester into water by at least partially neutralising the carboxyl functional epoxy-ester with ammonia;

copolymerizing, by emulsion polymerisation at least 1% by weight ethylenic monomer in the presence of the epoxy-ester dispersed into water to produce internally crosslinked emulsion microgel polymer particles of a copolymer of emulsion polymerised ethylenic monomer crosslinked with the epoxy-ester by addition copolymerisation crosslinking, the emulsion microgel polymer particles having an acid number between 25 and 150, where the emulsion crosslinked microgel particles have an average particle size less than 0.02 microns, and where said microgel particles are stably dispersed into water without surfactant.