CA1059674A - Rheologically modified metal decorating and aqueous coating composition comprising water-soluble copolymer and aminoplast - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

An aqueous alkaline thermosettable composition is disclosed comprising (A) as to 65 parts of a water-soluble tertiary amine salt of a water-insoluble copolymer of (C1 to C16) alkyl(meth)-acrylate, an unsaturated acid, and a hydroxy ester of an unsaturated acid having a molecular weight of about 20,000 to 200,000,(B) 15 to 35 party of a water soluble urea- or triazine-formaldehyde reaction product or methanol or ethanol ethers thereof or mixtures thereof, (C) 1 to 5 parts of a water-soluble polyethylene glycol, or poly(ethylene oxide) as a rheology modifier having an average molecular weight from about 400 to about 100,000,wherein the total parts of (A) and (B) is 100. These compositions can be direct-roll or mandrel coated onto substrates, which can be subsequently mechanically formed.
When thus applied, the position exhibits good flow and leveling characteristics.

Description

( --~0596~7~

. .~
SPECIFICATION
This invention concerns metal decorating and thermo- ~.
setting coating compositions which are applied from aqueous media to the surfaces to be coated. By "mstal decorating" is meant coating a metal sheet with a suitable coating co~position and then subiecting the sheet to various mechanical forming _processes. Examples of metal decorated items which are in common use are beer cans, beverage cans~ vegetable cans, scre~- cap jars and aerosol containers. The coatings for such items must be able to withstand a variety of ~abricatio treatments without cracking or chipping of the coating. These i~
fabrication treatments range from very mild treatments (e.g., the formation of can bodies) to extremely severe ~e.g., the fabrication of aerosol domes). m e compositions can also be applied to previously shaped articles such as mandrel-formed `~
two piece can bodies, toothpaste tubes~ etc.
In a typical process for the formation of a finished metal decorated item~ a pigme~ted base white coating compositior;
is roller-coated onto a metallic substrate and the coated substrate is subjected to a baking operation. A decorative printing is then applied over the base white coat and, while the ink is still wet 9 a clear over~print varnish is roller-coated over the ink to protect it. The coated metallic -sheet is then subjected to a baking operation to develop final hardness. The ~inished coated metal sheets may then be stacXed and stored for various time periods prior to fabricating into the final product. It is essential that ;-~

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~5g674 the coating have good hot stack resistance to prevent the metal sheets from adhering one to another since this results in marring of the coatings. The coated sheets are finally fabricated into various forms. The fabrication requirements will vary depending upon the end use of the sheet material~ , e.g., whether it is to be fabricated into cans, lids~ screw caps, etc. In addition to withstanding the various fabri-cating operations performed on the sheet metal, many end uses require processing or sterilization operations which in-volve high temperature conditions. In such instances, the ;~
coating must possess good overbake properties.
In order to obtain maximum hot stacking properties f~r coatings, it is desirable to use a thermosetting coa'~ing composition which results in a high degree of crosslinking when cured. However, the cured coating must also possess sufficient flexibility to permit the fabrication treatment to which it will be subjected. If the coated sheet is to be ~ ;
sub~ected to severe fabricating operations, a "soft" thermo-setting resin should be used, i.e.~ a resin which is thermo set with an aminoplast having a low crosslinking density.
Whereas, if the coated sheet is to be subjec-ted to relatively mild fabricating conditions, a "hard" thermosetting resin may be employed.
Heretofore, metal decorating has involved the ap-plication of primers comprising certain corrosion-protective pigments in non-aqueous vehicles based on a drying oil, such as linseed oil, a fast-drying varnish base comprising natural resins~ or a mixture of natural and synthetic resins, or an alkyd base modified wi-th a urea-, melamine-, or phenol-for-maldehyde resin! Such coating compositions are usually .

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~ 59 ~7 ~

supplied in high-boillng solven-ts to insure good flow and leveling in the thin films applied during a rollèr-coating operation. The solvents are frequently of an in~lammable character and often are the type which give off noxious fumes during the coating operation. To cope with the fire and health hazards, protection is usually provided by way of solvent recovery systems. Moreover9 recent interest in air pollution control has been aimed at reducing or eliminating ;;
organic solvent emission to the atmosphere.
There has long been a demand for thermosetting coating c~mpositions which can be applied from an aqueous medium to avoid air pollution~ fire hazards and other prob-lems which attend the use of organic solvent coating com-positions. However, earlier aqueous coating systems 7 such as shown in U.S- Patent Nos. 2~760~886 to Prentiss~ et al;

2,918~391 to Hornibrook, et al; and 3~033~811 to Brown~ a~
al, havè not proved fully satisfactory for coating metals for uses according to the present invention by direct-roller ~ -coating machinery because they tend to dry on the roller causing difficulties in clean up or blister when the wet products are put directly in an oven, or are not amenable to post-forming operations because of brittleness or to handling because of softness. The greatest difficulty with water based systems is to obtain rheological properties suitable for direct-roll coating of the system. Thus~ a composition is required which possesses flow and leveling properties such t~at when applied by a direct-r~ll coater~
it will form a uniform and smooth surface which does not contain striations. Tlle deficiency of aqueous emulsions from the standpoint of flow and leveling is well recognized , . . .

~ 67 ~
in the metal coating industry, see Pai~ntr__nd Varrnish Pr duc- i tion~ February, 1964, pages 28-33. The flow and leveling of the pigmented base coat is most critical since~pigmentation noticeably reduces flow in aqueous systems.
Our Canadian Patent No. 980, 475, issued December 23, 1975, de-scribes a thermosetting aqueous coating compbsition which can be applied by direct-roller processes to metals to pro-vide films with good appearance which can be post-formed and which provide~ after baking~ clear or pigmented coatings possessing excellent water- and solvent-resistance~ excellent adhesion to a variety of substrates, and high gloss, and can be advantageously used in connection with direct-roll ccaters wherein the rollers are of lcw Durometer hardness, e.~., about 12. However~ since soft rubber rolls do not have good wear characteristics a it iS desirable to provide a thermo-setting resin coating composition which can be applied by a .
mandrel-coater or a direct-roll coater wherein the rolls are of high Durometer har~ness, e.g.a about 20-50 without sacrificing flow and leveling properties. This invention provides such a coating composition.
The coating compositions of this invention comprise an alkaline aqueous blend having a binder consisting essen-tially of:
A. A water-soluble salt of a tertiary amine -wi-th a water-insoluble7 addition copolymer, having a molecular weight of about 20~000 to 200~000 of a mixture of copolymerizable monomers con-sisting essentially of:
~1) at least one ester of a (Cl-C16)-alcohol and an a~-unsaturated carboxylic acid, .. . . ... .
. .

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(2) 1 to ~ percent by weight of an olefin.i.-cally unsaturated carboxylic acid~and ..

(3) about 3 to 20 percent by w~iglnt of ~t .:
least one compound selected from the group consisting of hydroxy(C2-C~)-alkyl ;: :
esters of an acid of the formula:
H2C=l-(CH2)n-l H
COOH l;
in which n is an integer having a value ~.
of 1 to 2, and (Cl-C2)-alkyl esters of ;
alpha methylol acryiic acid, B. a water-soluble condensation product of urea or a triazine with formaldehyde or a water~
soluble methanol or ethanol ether thereof~
C. said composition containing from 1 to 5 per- :~
cent by weight of a polyethylene glycol or a as poly(ethylene oxide) / a water-soluble rheology modifier havlng a number average molecular weight of from about ~00 to`100,000~ the per-- centage being based on the total weight of :
(A) and (B) on a solids basis, :
.the weight ratio of A to B on a solids basis being from 85:15 to 65:35, the minimum film-forming temperature of the composition being no higher than about 25 C., the solids .
content of the composition being between 30 and 80 percent by weight.
Desirably?: B is the reaction product of a uraa-formaldehyde adduct with mathano~ the mole ratio of urea:
formaldehyde:methanol being in the range o~ 1/1.75-3/2-3.5;

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- ~95~674 ' :.
or a melamine~frmaldehYde adduct with metha~ol, the mole ratio o~ melamine:formaldehyde:methanol being in the range of 1/7-10il2-17, or a mixture thereof. In copolymer A, (1) is ~.-~; pre~erably an ester of acrylic acid and an alkanol having from about 2 to 12 carbon atoms; ~2) is methacrylic acid;
and (3) is at least o~e of hydroxyethyl acrylate or meth-acrylate or hydroxypropyl acry]ate or methacrylate.
If the coated metal is to be subjected to severe fabrication treatments, such as the fabrication of aerosol domes or bottle caps~ then the copolymer should be a "soft"
copolymer. The Tg of the "soft" copolymer should be below 0 C. and5 preferably, below -15 C. For best results, the COati!lg composition should contain a volàtile base, a i tertiary amîne being preferred, and should have a minimum ~15 film-forming temperature no higher than about 15 C~ When the coated sheet is to be subjected to mild fabrication treatments such as formed into can bodies~ either a l'so~t"
or "hard" copolymer may be used.
The most preferred copolymer is a copolymer of ,0 ethyl acrylate~ hydroxypropyl methacrylate~ methacrylic acid and methyl methacrylate.
. ~ .
One of the monomers utilized in a substantial pro-portion to prepare the addition copolymer is a flexibilizing l`
or "sof$" monomer which may be represented by the following !:
~5 formula ~ 1l H2C=C-c_oRl wherein R is H or alkyl having 1 to 4 carbon atoms and Rl is the straight chain or branched chaiQ radical of a primary or secondary alkanol, alkoxyal~anol or alkylthiaalkanol~ the ~3 .'' , . .~

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~59674 allcanol having from 2 to about L4 carbon atoms9 examples being ethyl, methylpropyl, n-butyl, 2-ethylhexyl, heptyl, hexyl~ oc~yl, propyl~ 2-methylbutyl, l-methylburyl, butoxy- `
butyl, 2-methylpentyl, methoxymethyl, ethoxyethyl, cyclohexyl, n-hexyl, isobutyl, ethylthiaethyl, methylthiaethyl, ethyl-thiapropyl, n-octyl, 6-methylnonyl, decyl, dodecyl~ and the - like. When R is alkyl and Rl is alkyl, Rl should have from abo~t 6 to about 14 carbon atoms and when R is H and Rl is alkyl, Rl should have from 2 to about 12 carbon atoms, in order to qualify as a "soft" monomer.
Important properties of the copolymer are its toughness and flexibility, as well as its influence upon the minimum film-forming temperature ~NFT) of the coating composition. The glass transition temperature (Tg) of the lS copolymer and consequently the selection of monomers and proportions thereof depends upon their influence on the Tg.
"Tgl' is a conventional criterion of polymer hardness and is ~
described by Flory, "Principles of Polymer Chemistry", pp. -`
56 and 57~ (1953~, Cor~ell University Press. While actual measurement of the Tg is preferred~ it may be calculated as described by FQX, BU11. Am~ Physics Soc. 1, 3~ p. 123 (1956). ~ -Examples of the Tg Qf homopolymers and the inherent ~g thereof which permits such calculations are as follows:
Homopolymer of ~
. .
n-octyl acrylate -80 C.
n~decyl methacrylate ~60 C~
2.ethylhexyl acrylate -70 C.
octyl methacrylate -2~ C.
n-tetradecyl methacrylate - 9 CO ;
methyl acrylate 9 C.
n-tetradecyl acrylate 20 C.
methyl methacrylate 105 C.
acrylic acid 106 G.
These or other monomers are blended to give the desired Tg of the copolymer. As is known~ for a given - 8 _ 1~59g j~

number of carl~on atoms in the al~ohol moiety, the extent and type o branching markedly influences the ~g, the straight chain products giving the lower ~g.
The coating composition of this invention similarly has a maximum MFT. MFT is determined-by the method described in Resin Review, Vol. 16, No. 2 (19663. This is influenced not only by the Tg of the addition copolymer~ but by the plasticizers or coalescing agerts used and their amounts.
At MFT values appreciably above this maximum~ difficulties in obtaining a uniform coating film and lack of film in-tegrity during deformation of the metal are encountered.
In addition to the f1exibilizing monomer, the other essential monomers are the "toughening" or "hard" ~, ; monomers, including the unsaturated acid monomer, and the hydroxyalkyl methacrylates. The hardness or softness of the acid and other functional monomers is not critical because of the small amounts used.
The copolymers used in the present invention should l~
have a molecular weight from about 20~000 to 200,000~ pre-ferably in this range by viscosity average determination.
In order to render the acid copolymers soluble in aqueous ! -media for the purposes of the present invention, they are neutralized with a tertiary amine such as 2-(dimethylamino)-ethanol. The copolymers may be prepared in a wide variety of ways. For example, they may be prepared by polymerization of the appropriate monomers in solution, or in aqueous media - ending up in the latter case as a stable latex or dispersion.
; In some cases~ it may be necessary to employ a chain-regulator in order to provide a molecular weight in the range desired.
This is particularly the case when polymerizing in aqueous .' - ` . .
_ 9 _ ~oS~74 media. Examples of chain-regula~ors that may be employed include lo~g-chain alkyl mercaptans~ e . g . ~ tertiary-dodecyl mercaptan of the formula:
H3cc~cH3)2cH2c(cH3)2cH2c(cH3)2sH ;
isopropanol, isobutanol, long-chain alcohols, e.g.~ lauryl alcohol, tertiary-octyl alcohol~ cumene~ CCl~1 C2Cl~ and CBrC13. The amount of chain regulator that may be used : depends upon the particular system and the conditions and may vary from 0 to 2 percent b~sed on the weight of monomers.
Generally, the use of 0.1 to 1 percent of bromotrichloromethane serves to provide as wide a range of molecular weigh-ts in aqueous media as is required.
While in the formation of the copolymer by emulsion copolymerization any suitabie dispersant or emulsifier may be employed~ it is preferable to use a salt obtained from a previously prepared batch as the dispersant in the system so that the coating composition is essentially uniform in character. The amount of such a dispersant that is used in such a latex polymerization may vary from about 1/2 percent to 6 percent on the weight of monomers. Commonly employed water-soluble free-radical initiators, such as the persul-fates of ammonium, sodium, or potassium, or redox systems using tertiary-butyl hydroperoxide with a reducing agent such ;~
as isoascorbic acid7 may be employed.
The presence of certain water-miscible solvents in the final special amine copolymer salt solution has been - found to markedly improve the stability of aqueous solu~ions of the amine salts, to improve the gloss of coatings obtained therefrom and to make it possible to use a wider variety of 3o comonomers for special purposes as mentioned abo~e. The .

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:
1~59674 useful solven~s which are herein called "cosolvent~" are soluble in water but ~t to such an extent that they remain essentially in the water phase to the substantial exclusion of entry into the polymer micelle. The useful cosolvents enter extensively into the polymer micelle and; as a result, they show a noticeable thickening action which does not occur when the solvent remains practically entirely in the water phase.
The cosolvent should be volatil~ so that it leaves the film or coating on air-drying and is practically all removed before baking to avoid blistering on baking. The volatility should not be so high that the flash point of the aqueous composi- ~
tions is undesirably low. Suitable cGsolvents are 2-butoxy- -ethanol~ 2-ethylhexyl alcohol, tertiary butanol, n-butanol, isopropanol~ isophorone~ butoxyethyl acetate, bwtoxyethoxy-ethyl acetate~ ethoxyethoxyethyl acetate and triethanolamine.
If the polymer is prepared in other types of organic solvent, such as acetone, ethanol, or 2-ethoxyethanol, which are in-capable of serving as cbsolvents, the solvent used in pre-paration of the polymer may be removed before the acid polymer is neutralized with the amine to form the salt~ since this type of solvent usually contributes no particular ad~
vantage or benefit to the final aqueous copolymer salt com-position.
In order to form the salt of the acid copolymer, the acid copolymer is intrQduced into water, the amine is added, and then the mixture may be heated with agitation at a temper~ture of about ~0 to 80o C. for a period of about 15 minutes to 15 ho~rs. Preferably9 a temperature of 50 to 75 C. is used. How~verg in some cases and particularly with the low molecular weight polymers in finely-dlvided condition, ~ , " , , ' ' " , ` . ' ' ' ~I `

l~S9674 the reaction wi-th the amine requires no heat and is virtually instantaneous. <~ ) If the acid copolymer has b~n pre~ared in an aqueous medium, the amine may be added directly to the aqueous ,~
dispersion of the copolymer. However, in this case, it is often desirable to eliminate ionic constituents such as by treatment with an ion-exchange resin or by dialysis before . . .~
adding the amine. Preferably, ths copolymer is of reduced particle size to facilitate the reaction with the amine in forming the salt. When the copolymer has been produced by a solution method, it may be isolated from the solution before ~-it is introduced into the water. However, in general~ it has been found that the solvent need not be eliminated before introduction of the copolymer into the water. When ~-the solvent used in the polymerization is one of the co-solvents mentioned~ it improves the clarity and stability (against mechanical action and on storage under normal con-ditions) of the aqueous solution obtained with the amine when used in the appropriate amount and improves the gloss of the films or coatings obtained.
The unsaturated carboxylic acid may be a simple monocarboxylic acid~ or may be a half ester or half amide of an a~-unsaturated dicarboxylic acid, and salts thereof with a volatile base such as ammonia, or with a volatile water-soluble amine such as dimethylamine, dimethylethanolamine, triethylamine, triethanolamine, morpholine, N-meth~l mor-pholine, picoline, and the like. Examples of copolymerizable ethylenically unsaturated monocarboxylic or polycarboxylic acids are sorbic, cinnamic, vinyl furoic~ a-chlorosorbic, 3 p-vinylbenzoic, acrylic, methacrylic~ maleic~ fumaric, aconitic~ atropic, crotonic~ and itaconic acid~ or mixtures thereof, with itaconic acid and the a,~-unsatura~ed mono-carboxylic acids, particularly methac ylic acid and acrylic acid, being preferred. Other copolymerizable acid monomers include the alkyl half esters or partial estérs of unsaturated polycarboxylic acids such as of itaconic acid~ maleic acid, and f~maric acid, or the partial amides thereof. Preferred half esters are the lower alkyl (Cl to C6) esters such as methyl acid itaconate, butyl acid itaconate~ methyl acid ; fumarate, butyl acid fumarate, methyl acid maleate, and butyl acid maleate Such partial esters and partial amides are considered to be "a,~-unsaturated monocarboxylic acids,"
and the term as used herein includes such esters and amid~s.
The hydroxyl-containing monomers may be hydroxyethyl, hy-droxypropyl or hydroxybutyl acrylate or methacrylate, or ethyl or methyl ~ -methylol acrylate.
Other ethylenically lmsaturated copolymerizable monomers optionally present are useful in combinations with !`
the above mentioned flexibilizing monomers and toughening monomers provided they do not adversely affect the desired properties of the copolymer (e.g~, unduly raise the overall Tg). These may be represented by the formula:
R Q
H2C=C-~-OR

where~n R is as above. R2 is preferably alkyl and is methyl or alkyl having from about 13 to about 20 carbon atoms when R is H~ and is alkyl of from 1 to about 5 carbon atoms or -alkyl of from about 15 to about 20 carbon atoms when R is methyl. It can be seen from above that for alkyl acrylates I and alkyl methacrylates the Tg at first decreases with an ':" ` ' . ' ~`.,. . ' , ' . 1 ' : ' : . ~

105967~

increased chain length of the alkyl group and then the Tg again increases; i.e., both hard and soft ~.onomers are known to occur in each group of monomers. Examples of these hard monomers and other hard monomers include: vinyl aromatics such as styrene and vinyl toluerle~ vinyl chloride~ vinyl acetat~
nitriles such as acrylonitrile, methyl acrylate~ tetradecyl acrylate, pentadecyl acrylate~ methyl methacrylate~ e~hyl methacrylate, t-butyl acrylate, butyl methacrylate, and pentadecyl methacrylate. For this purpose, the cosol~Jent, tertiary-butanol may be used in an amount of about 5 to 10 ;~
percent based on the total weigh-t of solution.
The proportion of amine used may be about 1 to 6 equivalents of amine per equivalent of acid in the copolymer.
Generally~ a minimum of one equivalent of amine is needed and ordinarily, a maximum of 2 or 3 equivalents is most suitable.
A typical composition may be composed of 150 to 500 parts of water per 100 parts of polymer, about 10 to 50 parts of co-solvent per 100 parts of polymer, and 1 to 2 equivalents of the amine, based on the content of acid component in the copolymer.
The acid cop~lymers contain certain units in certain proportions as previously defined. The content of 1 to 4 percent acid-containing units and from 3 to 20 percent of hydroxyl-containing units both apparently cooperate in the solubilization by treatment with the dimethylaminoethanol.
In general, after solubilization the pH of the aqueous system containing the solubilized copolymer has a pH in the range of 8.5 to 9.5. If insufficient amine is added to raise the pH to about 8.5 the shelf life of the composition becomes relatively short. Whereas, if an excessive amount of amine is added whereby the pH of the system is raised above 9.5~

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1~59~74 the visccsity becomes excessive for systems having solids concentrati~n~ that are most suitable for coating and im-i pregnating applications. By providin~ a relatively low propor-~ion of acid groups in the copolymer along with a sub-stantial proportion of hydroxyl-containing groups thersin, the conversion of the copolymers into water-soluble salt molecules or micel].es of colloidal dimensions is accomplished without encolmtering excessive viscosity.
The preparation of water-soluble salts of a tertiary amine with a water-insoluble~ addit1on copolymer is exempli-fied in U.S. Patent No. 3~2~5~932.
The water-soluble, heat-cor~ertible condensation products of urea or triazine (e.g., melamine) with formalde- ~ -hyde and/or their derivatives obtained by reaction with ethanol or methanol can be prepared according to one of the - following schemes: (1) control of reaction conditions so -.that the degree of polymerization is kept very low, even to the monomeric stage~ and (2) introduction of hydrophilic groups into the molecules of the polymeric condensates.
. 20 Thus~ they can be made by careful control of reaction con- ~;~
ditions as set forth in Schildknecht~ "Polymer Processes,"
. .
Vol. X~ page 295 et seq. (Interscience Press~ 1956). The preparation of another class of compounds suitable in the present invention~ such as N~N'-bis(methoxymethyl)urea is set forth in Bull. Chem. Soc. Japan, Vol. XI, No. 3~239 (1936). In a preferred embodiment of this invention~ a mixture of a urea-formaldehyde adduct with methanol and a melamine-formaldehyde adduct with methanol is employed in the coating composition.
3 The coating composition of thls invention preferably '.

~ 15 ~5~6t74 contains a material designated as a "coalescent" or a "cosolvent". These rnaterials aid fusion of the film duringJ
air-drying prior to baking and promot~ the flow of the coating composition during the baking cycle. However, be-cause they are volatile they do not form a part of the finished coating. They are characterized by being low in water-so~ubility, good solvents for the uncured polymer mixture~ less volatile than water so that they remain in the film after the water has evaporated, sufficiently volatile so that they are removed from the film before the end of the baking cycle and not susceptible to hydrolysis in alkaline media either at ambient or elevated temperatures. They also serve to lower the surface tension of the aqueous system, maklng it eas1er to wet the metal substrate. Typical examples include those coalescents previously mentioned as well as diacetone alcohol~ dimethyl formamide, alkyl ethers of ethylene glycol and propylene glycol, and tributyl phosphate. The coalescent is preferably present in the !~
coating composition in an amount of from 10 to 20 percent by weight based on the weight of the solids. The water-soluble condensation product of urea or triazine with formaldehyde is usually supplied as an 80 percent solids solution in iso- ~`
propanol or an equal volume mixture of isopropanol and butanol which are coalescent. Moreover~ the water-soluble copolymer salt is preferably supplied in a mixture of water and a coalescent. Therefore~ the coating composition will normally contain a coalescent even without additional cosolvent being added.
The rheology ~odifiers which may be used in the 3o practice of this invention are materials which are well known ' .: ' .~ .

~S9674 in the art. Polyethylene glycols are sold rommercially under the trademark "Carbowax". Their preparation is described by Fordyce in J. Am. Chem. Soc., Vol. 61, pages 1905, 1910 (1939)o Preferably, a polyethylene glycol is used having a molecular weight Or from about 400 ~o 20,000. Poly(ethylene oxide) is a polyether obtained by polymerizing ethylene oxide.
Such materials are sold under the commercial designation "Polyox"*. They may be prepared, for example, by processes as described in U.S. Patent Nos. 3,365~09; 3,167~519;
3~251~78~; and 3,~4~102. It is preferred that the poly-(ethylene oxide) have a molecular weight which does nct exceed about 100,000. It may be necessary to use conventional methr,ds to depolymerize product~ produced according to these patents to obtain this molecular weight or lower ones. Such 0 depolymerized products are commercially available. m e rheology modifier may be added to the coating system at any stage of preparation--i.e.~ it may be added to the-thermo~
setting resin emulsion during or after its preparation, it may be added to the composition at the time of mixing with the condensation product of urea or triazine ~Jith formaldehyde, etc.
Both the "Polyox" and "Carbowax" products are essentially polyoxyethylene polymers having linear chains and having terminal hydroxyl groups. The terminal groups can be varied to include ester groups, ether groups, epoxy groups, or other groups and herein wherever "polyethylene glycols" are referred to~ the functionally equivalent linear polyethers having terminal groups other than hydroxyls are intended to be included. Such terminal groups other than hydroxyl should have no more than about two carbon atoms. ;
*Trademark ;., ' . ~, . . ~ . , . -. . . .. , .. :

~S~674 With products having the molecular wei~hts; o~ the invention, the nature of the end groups on the linear chain have essentially no effect upon the rheology-impartin~ properties of the polymer. The "Carbowax" type of polyethylene glycols are understood to be prepared by starting with water or athylene glycol and ethylene oxide and polymerizing in the presence of an alkaline catalyst. The "Polyox" polyethylene -~
glycols are understood to be prepared by polymerization of polyethylene oxide using a different catalyst and in the absence of water or a starter such as a glycol. The latter products may have a molecular weight of several million, - having a relatively broad molecular weight distribution as compared with the lower molecular weight polyethylene glycols prepared with a starter. The water-soluble polyethylene oxide materials useful in the invention may be obtained by depolymerizing the products having molecular weight of several ;
million. As suggested above, the polyethylene glycols made with a starter generally have a very narrow molecular weight distribution. These facts show that the molecular weight distribution of the polyether is not particularly critical, and where a molecular weight is given, it is to be understood -~
that this is a number average molecular weight. ;
The exact mechanism by which the polyethylene glycols and poly(ethylene oxides) act to modify the rheo-logical properties of the coating composition is not known.
. . .
- In the amounts used, they do not act as thickeners for the ;. ,:
- composition~ but actually lower the viscosity of the com-positions. It is believed that these compounds may complex with the aminoplast--i.e.~ the urea- or triazine-formaldehyde condensation product, thereby decreasing the normal rapid - 18 - , 10596i~
:
increase in viscosity which occurs with a relatively small increase in solids encountered with the coating compositions in the absence of the rheology modifier. Thus, while the -coating composition without the rheology modifier may set up very fast resulting in striations in the ~inal coating, the coating compositions con-taining the rheology modifiers flow into a smooth coating before setting up. By the practice of this invention, there is obtained a synergistic effect between the urea- or triazine~formaldehyde condensation -~
product and the rheology modifier to give improved flow.
That ,s, the improvement in flow is considerably greater ~- than can be attributed to the additive effect of the con-densation product and the rheology modifier each by itself.
Since it is desired to have the mixture of the water-soluble salt of the water-insoluble copolymer and the aminoplast stable on prolonged storage, and since the amino-plast is reactive under acid conditions, the mixture must be made alkaline. A volatile base, such as ammonia or a tertiary amine~ is used to make -the system alkaline because tertiary amines will not react with the formaldehyde associated with the aminoplast. The tertiary amines also function as corrosion ir~ibitors when the coating compositions of the present invention are used for coating metal. The tertiary s amine must be sufficiently volatile that it will be driven from the film durirlg the baking operation. However 7 it must not be so volatile that it "flashes" from the film or gasifies if the coating composition is applied by spraying. Particu-larly preferred because of the balance of properties~ avail-ability and economy is triethylamine. The pH of the mixture should be mair~tained in the range of 9 to 11 in order to 1()59~i74 ensu~e good storage stabili-t~J. However? it is apparent that initial pH control alone is not sufficient tc insure adequate stability and retention of properties since samples neutra-lized to the desired pH range with a~monia have inadequate stability on prolonged storage, although satisfactory films are obtained if the ammonia-neutralized compositions are used shortly after preparation. However~ if the tertiary amine is the predominant nitrogen base present~ small amounts of ammonia can be used without deleterious effects. The amounts of amine used will vary depending on the specific composition employed but will be in the range of 1 to 5 "
-- parts by weight per 100 parts by weight of coating com- `
position (solids basis). A preferred embodiment employs two parts by weight per 100 parts by weight of the coating com- -position (solids basis).
While a dispersant may be used when employing pigments~ it is not essential due to the presence of the -~
acid moieties in the colloidal dispersion. A wide variety of dispersants will satisfactorily disperse pigments~ the effect of the dispersant on the properties of the final film must be considered. Many dispersing agents remain in the final film unchanged, thus seriously impairing the water- ;~
resistance of the film. Other dispersing agents will adversely affect the stabilities of the systems into which they are in-corporated.
A preferred embodiment employs as dispersants the ammonium and lower amine salts of polymeric carboxylic acids.
Thus, the ammonium and lower amine salts of polyacrylic and polymethacrylic acids and similar salts of the polymeric acid 3o obtained by copolymerizing methyl vinyl ether with maleic ;

3 ~967~ 1~
, .
anhydride are suitable. A particularly preferred embodiment employs the a~nonium half amide salt or the diammonium salt -~
of a diisobutylene-maleic a~-lydride copolymer having a number average molecular weight of from about 2,000 -to about L~oO0.
The an~ount of dispersant employed will vary lepending on the amount and nature of the pigments used and the amount and nature of the composition employed as binder. Generally, however~ from about 0.3 to about 3.5 parts by weight (solids basis) per 100 parts by weight of pigment~ will prove to be effective for dispersing the pigment.
It appears that the dispersants of the type herein-~ before described decompose at the temperatures employed in t~e baking cycle to liberate ammonia or lower amine which is then volatilized. It is further postulated that the carboxylic residuals react either with the amide group of the copolymer or with the aminoplast or both to become insoluble. Regard-less of the mechanism involved, the fact that it is observed ~ that this particular class of dispersants~ when employed as; set forth hereinbefore, do not detract from the excellent ,, , water-resistance and other highly desirable properties of the films proves that such catalysis does occur. It has been proven that even clears which contain a small amount of such ~! dispersants exhibit better water- and solvent-resistances ;`
than do the same compositions without dispersant, both samples being cured under exactly the same conditions. The amount of dispersant employed in clears varies depending on the amount of aminoplast employed. From about 0.1 to about 1.0 part by weight dispersant per 100 parts by weight (solids basis) of the coating composition will effect the desired - 30 catalysis.

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l~S9674 ~ he coating compositions of the present invention may be employed as clears, i.e., non-pigmented clear top coatings, or as pigmented coatings.
In the latter applications, the coatings can also be left in a "varnishless" condition, i.e., they can be left on the substrate without an additional clear varnish overprint coating.
If pigmented, the ratio of pigments to coating solids may be varied widely, depending on the pigment employed and the specific application involved. Thus, the ratio of pigment to coating solids may vary from 1 to 20 to 20 to 1. Preferably, the weight ratio of pigment to coating solids (i.e. components A and B, as defined hereinabove in pages 5 and 6) ranges from 5:95 to 60:40, the total being 100. The clears are particularly ~i`
useful as "overcoats", i.e., the ;sd-called overprint coatings `~
which are used to protect decorakive undercoats without detract-ing from the decorative effect. Because the clear coatings of i the present invention exhibit good clarity, high gloss, excel-lent solvent- and water-resistance, and high adhesion to a `~
variety of surraces, they are admirably suited for use as over- ;~
print finishes.
m e coating compositions of this invention can ba applied to a variety of substrates, the only restriction being the ability of the substrate to withstand the baking cycle which is essential in the processing of said coating compositions.
Metals are particularly suitable, whether prime-coated or unprimed. Thus, iron, steel, chrome-plated steel, tin-plated steel, aluminum, copper, bronze, or brass surfaces, particularly in sheet or coil form with thicknesses of 0~05 to 0~20 inc~es, prove to be excellent as substrates for the coating compositions of the present invention. Ceramic surfaces and, in some instances, wood surfaces, are also suitable as substrates. For roller coating such as reverse roll coating, the thickness is from 0.05 to 5 mils 11:1 S9674 in thickness, preferably 0.2 to 1.5 mils in thickness wher not cured. ' A wide variety of pigments can be employed with the coating compositions of the present invention. The pigments employed, however~ must be stable and non-reactive under alkaline conditions, i.e., a pH from about 9 to about 11. Typical pigments which are suitable include titani~m dioxide, iron oxide, calcium carbonate~ barytes and numerous types of clays.
The coating compositions of this invention are particularly suitable for application by a direct-roll coater or a mandrel coater although they may be applied by other means such as a reverse-roll coater or a spray gl~n.
As is well known in the art, a sing]e roll coater applies ¦
the coating to the substrate while the applicator roll .
rotates in a pool of the coating composition. The coatings are then baked at a temperature of from about 250O F. to 350 F. for from about 1/2 to 10 minutes. The baking or curing operation volatilizes all the volatile material in the film including any remaining water, traces of monomer~ ;
coalescents, and the tertiary amine. It is particularly important that the tertiary amine be volatilized since it inhibits the cure of the aminoplast. The baking operation effects the decomposition of the ammonium or amine salts of -the polymeric carboxylic acids, apparently releasing the acid ~ -j;. . .
form of the copolymer which may then react with the other components to become insolublë. The baking operation causes the cure of the aminoplast ~hich crosslinks and insolub~lizes the entire film.
The following examples illustrate the best modes " ~ vi~

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~ 05967~
contemplated for carrying out this invention:

A water-soluble salt of 2-~dimethylamino)-ethanol with a water-insoluble copolymer of ethyl acrylate/hydroxy-propyl methacrylate/methacrylic acid/methyl methacrylate in ~.
the weight ratios of ~6/5/3/46 (30-32 percent by weight ..
total solids in a mixture of 90 percent water and 10 percent t-butyl alcohol) is blended with a water-soluble melamine-formaldehyde adduct modified by reaction with methanol~ the 10 ~ mole ratio of melamine/formaldehyde/methanol being 1:7:12-, ~80 p~Qrcent total solids in an equal volu~e mixture of iso- ;~
propanol and butanol) and 1.3 percent based on the weight of total solids of a polyethylene glycol havlng à molecular weight o~ about 20700Q ("Carbowax" 20M). m e weight ratio of :
the copolymer to the adduct in the mixture is 75:25. ~he resultant composition has a pH of 8.6, a viscosity of about . ~.
75 cps and a total solids content of 36% by weight. The ..
weight ratio of water to alcohol in the system is 87:13.
m e composition is direct-roll coated on 90 pound tin-p'ated . steel as a clear over-print varnish for can bodies a~ 150 feet per minute with a urethane roll of durometer 20. The flow and leveling of the composition is very good. m e coated panels are baked at 3250 F. for 10 minutes to obtain ~.
a uniformly smooth, hard coating having good mar resistance.
The flow characteristics of the coating compositlon of this Example are improved slightly by the addition of 5 percent by weight of Butyl Cellosolve"*, based on the weight of the total solids.

A ball mill grind ls prepared by ball-milling 250 *Trademark. Butyl "Cellosolve" is ethylene glycol monobutyl ether.

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parts by w~ight of the composition of Example 1~ 2~0 parts by weight titanium dioxide pigment (DuP~nt "TiPure R900"*) and 1 part by weight of a defoaming agent ("Nopco NDW"**). After this composition has been ball-milled for 16 hours~ 150 parts by weight are mixed with 133.5 parts by weight of the composition of Example 1 and an equal volume mixture of water and dimethylaminoethanGl in an amount sufficient to give a viscosity of 60 to 70 seconds with a ~ 2 Zahn cup. The final composition has a total solids content of about 53% by weight. The weight ratio of water to cosolvent in the mixture is 87:13. The pigmented coating is applied by a ~-~
direct-roll coater having urethane rolls of high Durometer rubber (20 Duromete~) onto 90 pound tin plated steel as a base white coat for can bodies at 150 feet per minute. The flow and leveling characteristics of the coating composition are very good. The coated panels are baked for 10 minutes at 325 F. Uniformly white, smooth coatings are thus obtained. ~he composition of this example may also be ap- ;
plied by a mandrel coater.
2C . When each of these examples is repeated omitting the "~arbowax", the composition does not exhibit acceptable flow and leveling characteristics.

*Trademark **Trademark ~ t - - - . ., .. . . . .
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Claims (14)

WE CLAIM:

1. A pigmented or unpigmented thermosettable composition adapted for direct-roller coating and mandrel coating of metals comprising an alkaline aqueous blend having a binder consisting essentially of:
A. a water-soluble salt of a tertiary amine with a water-insoluble. addition copolymer, having a molecular weight of about 20,000 to 200,000, of a mixture of copolymerizable monomers consisting essentially of:
(1) at least one (C1-C16)-alkyl acrylate or methacrylate, (2) 1 to 2 percent by weight of an olefini-cally unsaturated carboxylic acid, and (3) about 3 to 20 percent by weight of at least one compound selected from the group consisting of hydroxy(C2-C4)-alkyl esters of an acid of the formula:

in which n is an integer having a value of 1 to 2, and (C1-C2)-alkyl esters of alpha methylol acrylic acid, B. a water-soluble condensation product of urea or a triazine with formaldehyde or a water-soluble methanol or ethanol ether thereof, C. said composition containing from 1 to 5 per-cent by weight of a polyethylene glycol or a poly(ethylene oxide) as a water-soluble rheology modifier having a number overage molecular weight of from about 400 to 100,000, the percentage being based on the total weight of (A) and (B) on a solids basis, the weight ratio of A to B on a solids basis being from 85:15 to 65:35, the minimum film-forming temperature of the composition being no higher than about 25° C. J the solids content of the composition being between 30 and 80 percent by weight.

2. The composition of Claim 1 wherein said tertiary amine is 2-(dimethylamino)-ethanol.

3. The composition of Claim 1 in which B is a urea-formaldehyde reaction product or a melamine-formaldehyde reaction product, or a mixture thereof.

4. The composition of Claim 1 in which B is the reaction product of a urea-formaldehyde adduct with methanol, the mole ratio of urea:formaldehyde:methanol being in the range of 1/1.75-3/2-3.5; or a melamine-formaldehyde adduct with methanol, the mole ratio of melamine:formaldehyde methanol being in the range of 1/7-10/12-17, or a mixture thereof.

5. The composition of Claim 2 in which (1) is an ester of acrylic acid and an alkanol having from about 2 to 12 carbon atoms, (b) is methacrylic acid and (c) is at least one of hydroxyethyl acrylate or methacrylate, or hydroxypropyl acrylate or methacrylate.

6. The composition of Claim 5 wherein said co polymer contains methyl methacrylate.

7. The composition of Claim 6 wherein said co-polymer is a polymer of ethyl acrylate, hydroxypropylmeth-acrylate, methacrylic acid and methyl methacrylate.

8. The composition of Claim 6 in which the rheology modifier is a polyethylene glycol having a molecular weight of from about 400 to 20,000.

9. The composition of Claim 6 in which the rheology modifier is a poly(ethylene oxide).

10. The composition of Claim 6 containing from 10 to 20 percent by weight of the solids in the composition of an organic solvent for the uncured polymer mixture.

11. The composition of Claim 6 containing a pig-ment, the relative weight of pigment to A plus B being from 5:95 to 60:40, the total being 100.

12. A method of decorating a substrate comprising the steps of direct-roller coating or mandrel coating said substrate with the composition of Claim 1, in an amount to provide a final cured layer of 0.05 to 5 mils in thickness, and heating the coating until it is thermoset.

13. The method of Claim 10 in which the substrate is a metal sheet, and it is mechanically shaped after the coating is cured.

14. A method of coating and decorating a metal sheet comprising the steps of coating said sheet with the composition of Claim 5, in an amount to provide a final cured layer of 0.05 to 5 mils in thickness, heating the coating until it is thermoset, and mechanically shaping the sheet.