CA1108332A

CA1108332A - Aqueous acrylic interpolymeric emulsion for coating metal

Info

Publication number: CA1108332A
Application number: CA284,457A
Authority: CA
Inventors: Sergio E. Balatan
Original assignee: Whittaker Corp
Current assignee: Whittaker Corp
Priority date: 1976-08-17
Filing date: 1977-08-10
Publication date: 1981-09-01
Also published as: GB1566942A; JPS5324386A

Abstract

ABSTRACT OF THE DISCLOSURE
The invontion relates to a novel method of preparing aqueous polymeric colloids comprising the steps of (a) polymerization in organic solvent at high concentration of monomers consisting of 15 to 60% of aromatic vinyl monomer 20 to 50% of a 1ong chain acrylate ester monomer 3 to 30% of at least one compound having the formula wherein R1 is hydrogen or methyl, R2 is amino or hydroxyalkoxy and R3 is alkoxyalkyl or hydrogen, and 0 to 12% of unsaturated cnrboxylic acid monomer, said acid producing a water insolubte polymer (b) emulsification of the resultant polymer solution in water using small proportion of surfactant.
The pH of the resulting solution is adjustedd to 6.5 to 10 with amines. The structure of the polymers in the present invention is highly hydrophobic so that, even at full neutralization of the carboxylic acid groups with amines, it would not producs an aqueous solution. In the absence of surfactant, a stable colloidal emulsion cannot be attained. The product is useful as an aqueous coating composition for tho interior and/or exterior coating of food, beer, beverage and other metal containers. The emulsions can be easily applied by spraying or direct roller coating and baked to give films of outstanding properties.

Description

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The present lnvention relates to aqueous polymeric colloids particularly suitable as metal conta:iner coatings.
ln the prior art, coating compositions used as interior linings for ~ood, beer and beverage metal containers, generally epoxy and vinyl chloride - vinyl acetate copolymers, were applied from organic solvents.
However, due to air pollution regulations and solvent shortage problems~
effort is being expended towards developing new coating compositions which can be applied from water containing blends which have satisfactory per-formance as interior linings :Eor food, beer and beverage metal containers.
The amount of volatile organic solvent in the blend should be no more than 20~ by volume.
Accordingly, the principal objectives of the present invention are to ~ 1) Provide such new coating compositions;
~2) Provide a new method o:E preparing such coating compositions which overcomes certain deficiencies of aqueous polymeric colloids made by two general methods known in the art as follows:
Method I
Highly carboxylic polymers, synthesized in organic solvents, are transferred in water by partial or full neutralizatioD of the carboxylic groups. Colloidal emulsions are produced by partially neutralizing the acid groups with amines. In order to obtain adequate dispersibility and emulsion stability, the general practice is to incorporate a high percentage of carboxylic . -- 1 -- .

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acid groups in the polymer. Substantial ~mount of amines i5 required to neutralize the acid groups. The amine can retard the rate of cure of the film, thereby adversely affecting the quality of the cured film If sufficient amount of amine is 1 added to fully neutralize the carboxyl groups, an aqueous solution is obtained. This system is generally not~d for bubbling or i foaming during application, especially with the use of roller coater or airless spray equipment. To suppress the foam, special i defoamers such as silicones are incorporated. ~Iowever, the use ll of such additive could produce undesirable side effects such as I! poor adhesion between multiple coatings or~poor recoatability of the coated surface. Moreover, over a period of time, the additive ' could migrate through suraces with which the coating is in I contact. The subsequent contamination of the surface can cause i prohlems such as eyehollng, cratering and the like.
t ll Method II
I Polymers synthesized in an aqueous medium in the I presence of surfactants by the well known method of emulsion 1~ polymerlzation. ~e surfactants and other additives used for 1l s~abilization of the resultan~ polymeri~ colloid tend to reduce water or blush resistance of the cured film. This can be , observed when the coated substrate is pasteurized in beer or in water at 160F for 1/2 hour. The blush is the degree of I milkiness or whitening which occurs in the coating.
¦ In the present invention,~the foregolng problems characteristic of the prior art are avoided. The polymers synthesized in organic solvents can be made more hydrophobic than in Method I butr nevertheless, can yield a polymeric colloid .,~. ,:

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in t~ater by surfactant ad(lition. The structure of the polymer in the present inYentiQIl is h;.ghly hydrophobic so that, even at full neutralizati.on of the carboxylic aci.d grollp with amines, it would not produce a true solution in water. Furthermore, i.n the absence of surfactant, a stable coIloidal emul-sion cannot be attai.ned.
In accordance with the present invention, there is provided a ~ -composition including a copolymer having a glass transition temperature of about -6C to about -~30C, and contalning by wei.ght:
lS to 60% of an aromatic vi.nyl monomer 20 to 50% of a long chain acrylate ester monomer 3 to 30% of at least one compound having the formula .
Rl R3 - C = C - C
R2 :
wherein Rl is hydrogen or methyl, R2 is amino or hydroxyalkoxy and R3 is alkoxyalkyl or hydrogen, and 0 to 12% of unsaturated carboxylic acid monomer, said acid forming a water insoluble polymer .. ~ ~ . .
and an effective amount of a surfactant for producing a stable emulsion when water is added to the copolymer. ~ ;~
In another aspect, the invention comprises a method of~preparing a composition including a hydrophobic:copolymer comprising the steps of (a) polymerizing monomers in organic solvent in the presence of about 0.5%
to about 6% by weight of a free radical initiator based on the weight of the monomers and in which the total weight of the monomers is atsout 60% to about ~:~
80% by weight of the ttstal charge, said monomers consisti.ng of 15 to 60% of aromatic vinyl monomer 20 to 50% of a long chain acrylate ester monomer 3 to 30% of at least one compound having the formula .:

R3 - C = C - C~

: . . . : : ~ : . ~

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wherein Rl ls hydrogen or methyl, R2 is amino or hydroxyalkoxy and is alkoxyalkyl or hydrogen~ and ~-o to 12% of unsaturated carboxylic acid monomer, said acid producing a water insoluble polymer and by adcling an effective amount of a surfactant sufficient to produce a stable emulsion in water. -The invention also comprises a method of preparing an aqueous coating composltioll comprising steps of emulsiying the above defined composition in water using about 0.25% to about 3~ by weight of surfactant based on the weight of the copolymer and adjusting p~l of the resulting emulsion with amines to about 6.5 to 10.
For subsequent emulsification of the polymer solution in water, only a small proportion of emulsifier is required. Although the basic structure ~ -of the polymer is highly hydrophobic, the resulting emulsion does not require any post addition of additives usually required by aqueous polymeric colloids prepared by Method II.
Therefore, the unique advantage of the present method to prepare a polymeric colloid in water is that the structure of the copolymers can be made more hydrophobic than those of Method I~ and the amount of surfactant - ~-required to produce an emulslon is less than in Method II. Thus, the present novel method of coating preparation is better suited for container coatings than aqueous coatings made in the prior art.
In connection with the emulsification of the polymer solution, the surfactant used are preferably anionic and/or nonionic emulsifiers such as octylphenoxyethanol, nonylphenoxyethanol amine polyglycol condensate, ammonium or sodium salt of alkyl aryl polyether sulfate, ammonium or sodium salt of sulfated alkyl phenoxYethaDol and the like. The proportion of emulsifier based on the weight of the polymer is preferably 0.25% to 3% by weight.

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The emulsion can be easily applied by spraying or direct roller coating, and the film can be cured by heating at ~empera-tures of approximately 300F to 450F for 2 to 10 minutes. Such ¦I brief heatin~ to produce an insoluble film is adequate for coat-ll ings prepared from Type I and Type III polymers described below.
However, aqueous compositions of Type II polymers must be prepared , with conventional external crosslinkers such as phenolic and amine resins in order to produce an insoluble film under the afore-l mentioned conditions.
I
Description of the Preferred Embodiments The polymers of the present invention have glass transition temperature of about -6C to about +30C. The three different types of polymeric structures embodied in this invention Il are defined by their contents of monomers as follows:
1l Type I - Self Reactive Copolymers. Will cure to an insoluble film upon heating.
Composition, by~weight ~
I 15 to 60 percent of aromatlc vinyl monomer preferably ¦ styrene.
1 20 to 50 pexcent of any long chain acrylat~ es~er monomer can be used; nButyl acrylate, isobutylacrylate and 2 ethyt ~exyl acrylate are preferred.
3 to 30 percent o~ alkoxyalkyl(meth)acrylamide such as isobutyoxy methy~ acrylamide~
0 to 12 percent of unsaturated carboxylic acid monomer such as acrylic acid a.nd ~ methacrylic acid :-' ~

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monomer. The amount of acid incorporated is adjusted to produce an insoluble polymer in water even at full neutralization o~ the earboxyl groups with amines. The polymer requixes the addition of surfactant to produee a stable emulsion~
Type II - Potentially Reactive Copolymers. Require the addition of external crosslinker such as phenolie and amine resinsO
Composition, by weight 15 to ~0 pereent of aromatic vinyl monomer preferably styrene~
25 to 50 percent of any long ehain aerylate ester moncmer can be used; nButyl acrylate, isobutylacrylate and 2 ethyl hexyl aerylate are preferred. ~ , 3 to 30 pereent oE hydroxy alkyl ester of an unsaturat-ed~earboxylie aei~ sueh as 2-hydroxyethyl aerylate, 2 hydroxyethyl methaerylate, hydroxy propyl acrylate and h~droxy propyl methaerylate 0 to 12 pereent of unsaturated earboxylie acid monomer such as aerylic aeid and methaerylic aeid monomer. The amount of acid ineorporated is adjusted to produee an insoluhle~polymer in water even at full neutralization of the carboxyl groups with amines. The polymer requires the addition of surfaetant to produee ¦¦ a stable emulsion, I!

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Type III - Hybrid o Type I and Type II Copolymers. May or may not require external crosslinking depending on the design o the specific polymer composition.
Composition, by weight 15 to 60 percent of aromatic vinyl monomer preferably styrene.
25 to 50 percent of any long chain acrylate ester monomer can be used; nButyl acrylate, isobutylacrylate and 2 ethyl hexyl acrylate are preferred, 3 to 30 percent of alkoxy alkyl(meth)acrylamide such as isobutoxy methyl acrylamide~
3 to 30 percent of hydroxy alkyl ester of an unsaturat-ed carboxylic acid monomer such as

2-hydroxyethyl acrylate, 2 hydroxyethyl methacrylate, hydroxy propyl acrylate and hydroxy propyl methacrylate.
0 to 12 percent of unsaturated carboxylic acid monomer such as acrylic acid and methacrylic acid ~0 monomer. The amount of acid incorporated is adjusted to produce an insoluble polymer in water even at ~ull neutralization of the carboxyl groups with amines. The polymer requires the addition of surfactant to produce a stable emulsion.
The free radical initiator for the polymerization is any , ~ ~e~t ~`
I conventional one such as benzoyl peroxide ~e~-butyl perbenzoate, ¦~e~
~e~-bu~yl peracetate, cumene hydroperoxide ana the like~
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Il 1 Solvents preferred ~or use in the invention are hydrophobic ones such as ketones t hydrocarbons, esters and long chain monohydric aliphatic alcohols. A combination of hydrophobic !and hydrophilic solvents is also satisfactory.
The polymerization is carried out in the desired solvent ¦or solvent combination and at high monomer concentration, preer-ably about 60 percent to about 80 percent by weight based on the total weight of polymerization solution. The proportion of the iifree radic~al initiator is abou~ 0.5 percent to about 6 percent llby weight based on the total weight of the monomers.
Emulsification is carried out by mixing the resultant polymer solution wi'th water and small proportion of surfactant !I to produce an oil in water emulsion system. The p~ of the l,resulting emulsion is adjusted to 6.5 to 10 with amines.
~1 The invention is illustrated by the following examples, ~which are given for purposes of illustration only and not to be construed as limiting its scope. Parts or percentages are being ~given on weight basis: ' ~ ~ .,, ~Example I
IA. Preparation or the Polymer Constituents Parts Primary Amyl Acetate 25.55 NButanol 4.50 Benzoyl Peroxide1.00 Styrene 33.10 2 Ethyl Hex,yl Acrylate ' 30.34 Isobutoxy Methyl Acrylamide 4~65 ¦ Methacrylic Acid0.86 .' 1 100.00 Procedure il Charge solvents to reaction vessel equipped with thermometer ii inert gas sparge, total condenser, addition funnel and glass ii or stalnless steel agitator. Sparge with inert gas and i~ preheat solvents tc 95C. Mix monomers and benzoyl peroxide initiator together in separate container. Add the premixed items -to the reactor vessel with agitation over a period of ; approximately ~ hours. Continue to react for five additional `, hours or until convexsion to polymer is complete. Cool i, rapidly to 60C. Fill of~ into lined containers.
~ Viscosity of Polymer Solution = 35,000 cps at 80F
~, .

IB. Preparation of the Emulsion Constituents Parts Polymer Solution Prepared i in Part IA 100~0 Anionic Emulsi~ier 0.3 Deionized Water 140.2 Di Methyl Ethanol Amine 0.5 I
241.0 Procedure ; . i Charge first 2 items into stainless steel container. Mix for ten minutes. Add deionized water gradually to the container with moderate agitation until conversion occurs. ¦
At this point, the remainder o the water is rapidly added, -~ Adjust pH with di methyl ethanol amine.
Physical Constants: pH = 8.8 Viscosity = 20 secs. at 80F I ;~
#4 Ford Cup Total 5Olids = 29,8~ by weight ~ Water/Orqanic Solvent = 80/20 ; by volume ., ' 333~2 1 Example 2 2A. Preparation of the Polymer Constituents Parts . Butyl Cellosolve Acetàte 15.00 Xylene 9.00 . Butanol 6.00 Benzoyl Peroxide1.00 Styrene 36.50 . nBu~yl Acrylate30.50 Isobu-tyl Methyl Acrylamide 2.00 I00.00 Use the sam~ poIymerization as in Formula IA. :
~1 ' . . . ~ :
11 ~' ' ,.
; 2B. Emulsification of the Polymer :~. .
Ii Cons:tituents ~ Parts ~! Polymer Solutio~
¦¦ Prepared:in Part 2A 10~0,0 Il Anionic Emulslfier Ø6 Il Deionlzed`Water 140.4 !I D.i Methyl Ethanol Amine O.S
~ 141.5 Use tile same emulsification :procedure as in Formula IB.
~¦ Physical Constants: pH = 9.2 ~¦ -visc05ity = 1~ ~ secs. at 80C~F
~ : #4;Ford Cup !¦ Total Solids =~30.1% by weight Water/Or~anic Solvent = 80/20 ~ by volume ;
il * Trade Mark for mono- and dialkyl ethers of ethylene glycol i! and their deri.vati.ves. .
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3~. Preparation o~ the Polymer :
Cons-tituents Parts !, Xylene 10.0 ~I Butyl Carbitol Acetate 20.0 ; Test Butyl Perbenzoate 1.0 ~i Styrcne 27~3 ~l 2 Ethyl Hexyl Acrylate 30.4 l, 2 Hydroxy E-thyl Methacrylate 10.7 ' ~crylic Acid 9.8 '~I 100. 0 ; Follow the same pol.ymerization procedure as in Example IA.
. ,.
3B . Emulsificat;lon of the Polymer with Amine Resin added as Crosslinker : ¦
Constituents Parts i Polymer Solution Prepared ~ in Par~ 3A100~0 : Amine Crosslinker :(60% solids)3.0 Nonionic Emulsifier~ 2.0 .
Deionized Water .140.0 ' Di Methyl Ethanol Amine 0~5 250.5 rrocedure , Charg~ first 3 items into stainless steel container. Mix for 10 minutes. Add gradually the deionized water with agitation,' until conversion occurs. At this point, the remainder o.f the - water is rapidly added.
Physical Constants pH - 9.5 Total Solids - 30.3% by weigh , Viscosity = 19 secs. at 80F
- : #4 Ford Cup `, Water/Organic Solvent = 80~20 !, by volum~
. * Trade Mark for mono- and diàlkyl ethers oE diethylene glycol and their derivatives.
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1. 3C~ Emulsification of ~he Polymer with Phenolic Resin added .ll as Crosslinker 1~ Constituents Parts I Polymer Solution Prepared ¦ in Part 3A 100.0 ,i Phenvlic Resin (50~ solids) 10.0 ¦1~ Anionic Emulsifier 0.6 Deionized Watex 150.4 Il Di Methyl Ethanol Amine0.5 101l 261,5 s, U~e the same emulsification procedure as in Example 3B~
1' Physica~. Constants: pH = 9.2 j! Viscosity = 18 secs. at 80F
¦¦ . #4 Ford Cup 15j~ Total Solids = 30.5% by weight ¦i Water/Organic Solvent -- 80/20 ji ~ by volume I5 :~
~ Example 4 : ~ I
$ ~
4A. Prepaxation of the Polymer 20 ~ Constituents : Part~
1~ Methyl Amyl Alcohol2i.20 ~3 j~ Butanol 4.45 D ~ ~es~ Butyl Peracetate s~ (75% active)1~40 l$
~:
25!` styrene 310 03 2 Ethyl Hexyl Acrylate 27.58 !s 2 Hydroxy Ethyl A:crylate 4.83 ~ ;
s"Isobutoxy Methyl Acrylamide ; 4~13 ~.
~,Methacrylic Acid 1.38 301'. 100.00 ':' ~ . . ;~

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1 4B. Emulsification of the Polymer t' Constituents Parts ,i PolymPr Solution Prepared l in Part 4A 100.0 Anionic Emulsifier 0~3 Deionized Water 135.2 ~t~ Di Methyl Ethanol Amine 0.5 236 . O
~i Use the same emulsification procedure as in Example ~B.
'~
!
4C. Emulsification of the Polymer with Amine Resin added as Crosslinker `. Constituents Parts ,' Polymer Solution Prepared ¦~
I in Part 4A 100.Q
i Urea-Formaldehyde Condensate (60~ solids) 6.0 Monionic Emulsifier 2.0 t Deionized Water 14000 ~I Di Methyl Ethanol Amine0.5 ,~ 248O5 Use the same emulsification procedure as in Example 3B.
` Physical Constants: pH = 9.5 ;t : Viscosit~ ~ 20 secs. at 8GP
i ~4 Fo~d Cup !'l Water/Organic Volatile = 80/20 , by volume .1 i '!
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33z _valuation of the F,mulsions The pxeceding aqueous coating compositions were i subjected to the following standard tests generally used to , evaluate perfo~mance of metal container coatings~ A commercial solvent based vinyl chloride - vinyl acetate copolymer was use~
! as control.
1. Intercoat Adhesion !I The coating variable is applied on a piece of commercially ! primed tin free steel at approximately 4 to 5 milligrams ~1 per square inch and baked at 320F for 5 minutesO The cured coating was scored with a knife edge and the score i5 then covered with a scot~h tape. The area proximate to the score is then examined to detexmine the amount of ~' coating material which is removed with the scotch tapeD
~I The amount of coating material which comes off with the scotch tape is indicative~of the adhesion.
' 2. Blush Resistance ~ ~ I
The coated sub~trate i8 placed in beer or in water having a temperature of 160F for one hal hour. The blush of the ~ coating is measured by the degree GE milkiness and/or loss of gloss of the film.
3. Flavor Test ' The test is designed to~determine any~change in flavor i which may be impar~ed by the sub~ect coating. It is carried out by placing into a bottle of beer strips of aluminum foil l coated on both sides by;the coating variable. The bottle ,' is sealed tightly and stosed at predetermined temperatuxes I ;
~ over a period of time and tasted by a flavor panel. The . !

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!i total amount of coating applied on about 40 square i w h aluminum ~il is usually approximately 200 milligrams and 1~ baked at 320F for 5 minutes.
,j 4. Turbidity Test 1l The test ~easures any change in clarity of the beer which , may be imparted by the coating variable. Test specimens , are prepared in the same manner as in flavor test. Turbidity is measured using a Mach Turbidity Meter and is expressed in ~ Formazin ~urbi~ity Units (FTU). A value of 15 to 30 FTU is ~j normal or an acceptable bottle of beer.
i. :
Results are s~mmariæed in the following table.
~1 .
Turbidity ~ata Flavor Intercoat Blush Coatinq Varia~le 3 Weeks at 100F Test Adhesion Resistance __ _ Example No. lB 20 - 30 FTU OK OK~ OK
lSExample No. 2B 20 - 30 FTU OR OK OK
Example No. 3B 20 - 30 FTU OK OR OK
` Example No. 3C 20 - 30 FTU OK OK OK
Example No. 4~ 20 - 30 FTU OK OR OK
Example No. 4C 20 - 30 FTU OK OK OK
20~ Vinyl Control 20 - 30 FTU OK OK OK

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A composition including a copolymer having a glass transition temperature of about -6°C to about +30°C, and containing by weight:
15 to 60% of an aromatic vinyl monomer 20 to 50% of a long chain acrylate ester monomer 3 to 30% of at least one compound having the formula wherein R1 is hydrogen or methyl, R2 is amino or hydroxyalkoxy and R3 is alkoxyalkyl or hydrogen, and 0 to 12% of unsaturated carboxylic acid monomer, said acid forming a water insoluble polymer, and an effective amount of a surfactant for producing a stable emulsion when water is added to the copolymer.

2. A composition according to claim 1 having a glass transition temperature of about -6°C to about +30°C, and containing by weight:
15 to 60% of an aromatic vinyl monomer 25 to 50% of a long chain acrylate ester monomer 3 to 30% of alkoxyalkyl(meth)acrylamide 0 to 12% of unsaturated carboxylic acid monomer and an effcctive amount of a surfactant to produce a stable emulsion.

3. A composition according to claim 1 having a glass transition temperature of about -6°C to about +30°C, containing by weight:
15 to 60% of an aromatic vinyl monomer 25 to 50% of a long chain acrylate ester monomer 3 to 30% of hydroxyalkyl ester of an unsaturated carboxylic acid selected from the group consisting of 2-hydroxy ethyl acrylate, 2 hydroxy ethyl methacrylate, hydroxy propyl acrylate and hydroxy propyl methacrylate 0 to 12% of unsaturated carboxyllc acid monomer and an effective amount of a surfactant to produce a stable emulsion.

4. A composition according to claim 1 having a glass transition temperature of about -6°C to about +30°C. containing by weight:
15 to 60% of aromatic vinyl monomer 25 to 50% of a long chain acrylate ester monomer 3 to 30% of an hydroxyalkyl ester of an unsaturated carboxylic acid monomer 3 to 30% of alkoxyalkyl(meth)acrylamide 0 to 12% of unsaturated carboxylic acid monomer, said acid producing an insoluble polymer in water, and an amount of surfactant to produce a stable emulsion.

5. A method of preparing a composition including a hydrophobic copolymer having a glass transition temperature of about -6°C to about +30°C comprising the steps of (a) polymerizing monomers in organic solvent in the presence of about 0.5%
to about 6% by weight of a free radical initiator based on the weight of the monomers and in which the total weight of the monomers is about 60% to about 80% by weight of the total charge, said monomers consisting of 15 to 60% of aromatic vinyl monomer 20 to 50% of a long chain acrylate ester monomer 3 to 30% of at least one compound having the formula wherein R1 is hydrogen or methyl, R2 is amino or hydroxyalkoxy and R3 is alkoxyalkyl or hydrogen, and 0 to 12% of unsaturated carboxylic acid monomer, said acid producing a water insoluble polymer and by adding an effective amount of a surfactant sufficient to produce a stable emulsion in water.

6. A method of preparing an aqueous coating composition comprising steps of emulsifying the composition of claim 1 in water using about 0.25%
to about 3% by weight of surfactant based on the weight of the copolymer and adjusting pH of the resulting emulsion with amines to about 6.5 to 10.

7. A method according to claim 5 in which the organic solvent comprises at least one member of the group consisting of ketones, hydrocarbons, esters, long chain aliphatic monohydric alcohols and glycol ethers.

8. A method according to claim 5 in which the free radical initiator is selected from the group consisting of benzyol peroxide, azobisisobuty-ronitrile, tert-butyl perbenzoate and tert butyl peracetate and cumene hydroperoxide.

9. A method according to claim 6 in which the surfactant used is a nonionic and/or an anionic emulsifier selected from the group consisting of octylphenoxyethanol, nonylphenoxyethanol, amine polyglycol condensate, ammonium or sodium alkyl aryl polyether sulfonate ammonium or sodium salt of sulfated alkylphenoxyethanol.

10. A method or preparing an aqueous coating composition according to claim 6 of hydrophobic copolymers comprising the steps of (a) polymerizing monomers in organic solvent in the presence of about 0.5% to about 6% by weight of free radical initiator based on the weight of the monomers and in which the total weight of the monomers is about 60% to about 80% by weight of the total charge, said monomers consisting of 15 to 60% of aromatic vinyl monomer 25 to 50% of a long chain acrylate ester monomer 3 to 30% of hydroxy alkyl ester of an unsaturated carboxylic acid 0 to 12% of unsaturated carboxylic acid monomer, said acid forming a water insoluble polymer (b) emulsification of the resultant polymer solution and an external cross-linker in water using about 0.25% to about 3% by weight of surfactant based on the weight of the copolymer and external crosslinker and adjusting the pH
of the resulting emulsion to 6.5 to 10 with amines.

11. A method according to claim 10 in which the organic solvent comprises at least one member of the group consisting of ketones, hydrocarbons, esters, long chain aliphatic monohydric alcohols and glycol ethers.

12. A method according to claim 10 in which the free radical initiator is selected from the group consisting of benzoyl peroxide, tert butyl per-benzoate, tert butyl peracetate and cumene hydroperoxide.

13. A method according to claim 10 in which the external crosslinker is an amine-formaldehyde condensate or a phenol-formaldehyde condensate.

14. A method according to claim 10 in which the surfactant is a nonionic or an anionic emulsifier.

15. A method of preparing aqueous coating composition according to claim 6 of hydrophobic copolymers comprising the steps of (a) polymerizing monomers in organic solvent in the presence of about 0.5%
to about 6% by weight of free radical initiator based on the weight of the monomers and in which the total weight of the monomers is about 65% to about 80% by weight of the total charge, said monomers consisting of 15 to 60% of aromatic vinyl monomer 25 to 50% of a long chain acrylate ester monomer 3 to 30% of an alkoxy alkyl(methy) acrylamide 3 to 30% of hydroxy alkyl ester of an unsaturated carboxylic acid monomer 0 to 12% of unsaturated carboxylic acid monomer, said acid forming a water insoluble polymer (b) emulsification of the resultant polymer solution in water using about 0.25% to about 3% by weight of surfactant based on the weight of the copolymer and adjusting the pH of the resulting emulsion with amines to about 6.5 to 10.

16. A method according to claim 15 in which the organic solvent com-prises at least one member of the group consisting of ketones, hydrocarbons, esters, long chain aliphatic monohydric alcohols and glycol ethers.

17. A method according to claim 15 in which the free radical initiator is selected from the group consisting of benzoyl peroxide, tert-butyl per-benzoate, tert butyl peracetate and cumene hydroperoxide.

18. A method according to claim 15 in which the surfactant is a nonionic or an anionic emulsifier.

19. A method of preparing an aqueous coating composition according to claim 6 of hydrophobic copolymers comprising the steps of (a) polymerizing monomers in organic solvent in the presence of about 0.5%
to about 6% by weight of free radical initiator based on the weight of the monomers and in which the total weight of the monomers is about 60% to about 80% of the total charge, said monomers consisting of 15 to 60% of aromatic vinyl monomer 25 to 50% of a long chain acrylate ester monomer 3 to 30% of an alkoxy alkyl(meth)acrylamide 3 to 30% of hydroxy alkyl ester of an unsaturated carboxylic acid monomer 0 to 12% of an unsaturated carboxylic acid monomer, said acid forming a water insoluble polymer (b) emulsification of the resultant polymer solution and an external cross-linker in water using about 0.25% to about 3% by weight of surfactant based on the weight of the copolymer and external crosslinker and adjusting the pH
of the resulting emulsion to about 6.5 to 10 with amines.

20. A method according to claim 19 in which the organic solvent is selected from the groups consisting of ketones, hydrocarbons, long chain aliphatic monohyclric alochols, glycol ethers and esters.

21. A method according to claim 19 in which the free radical initiator is selected from the group consisting of benzoyl peroxide, tert butyl perbenzoate, tert butyl peracetate, cumene hydroperoxide and azobis iso-butyronitrile.

22. A method according to claim 19 in which the external crosslinker is an amine-formaldehyde condensate or a phenol-formaldehyde condensate.

23. A method according to claim 19 in which the surfactant is a nonionic or an anionic emulsifier.

24. A metal container having a surface coated with a resinous composition which includes a copolymer having a glass transition temperature of about -6°C
to about +30°C and containing by weight, 15 to 60% of aromatic vinyl monomer 25 to 50% of a long chain acrylate ester monomer 3 to 30% of at least one compound having the formula wherein R1 is hydrogen or methyl, R2 is amino or hydroxyalkoxy and R3 is alkoxyalkyl or hydrogen, and 0 to 12% of unsaturated carboxylic acid monomer, said acid producing a water insoluble polymer.

25. A metal container according to clalm 24 having a surface coated with a resinous composition of, by weight, 15 to 60% of aromatic vinyl monomer 20 to 50% of a long chain acrylate ester monomer 3 to 30% of alkoxyalkyl(meth)acrylamide 0 to 12% of unsaturated carboxylic acid monomer said acid forming a water insoluble polymer.

26. A metal contai.ner according to claim 24 having a surface coated with a resinous comyosition of, by weight, 15 to 60% of aromatic vinyl monomer 25 to 50% of a long chain acrylate ester monomer 3 to 30% of hydroxy alkyl ester of an unsaturated carboxylic acid selected from the group consisting of 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, hydroxy propyl acrylate and hydroxy propyl methacrylate 0 to 12% of an unsaturated carboxylic acid monomer said acid forming a water insoluble polymer.

27. A metal container according to claim 24 having a surface coated with a resinous composition of, by weight, 15 to 60% of aromatic vinyl monomer 25 to 50% of a long chain acrylate ester monomer 3 to 30% of hydroxyalkyl ester of unsaturated carboxylic acid monomer 3 to 30% of alkoxyalkyl(meth)acrylamide 0 to 12% of unsaturated carboxylic acid monomer, said acid producing an insoluble polymer in water.