CA1076283A - Water-based paint with corrosion inhibitor i - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Water-based paints contain about 500 to about 2500 parts by weight barium nitrite per million parts by weight paint formulation including water by excluding pigment. The disclosure relates to their composition and method preparation.

Description

~ 3 Water-based paints of the prior art ha~e included "solution paints" and "emulsion (or latex) paints" with distinction being made with reference to the manner in which the sole or principal binder is dispersed within the aqueous medium. ~Iybrid, water-based paints are now available which include both a solution polymer and a latex.
Many conventional water-based industrial paints, especially those based on synthetic polymer latexes, are corrosive to mild steel. Introduction of these paints into automotive assembly plants currently requires that existing mild steel paint handling facilities be replaced by stainless steel, plastic or other corrosion resistant materials.
Obviously, the development of a non-corrosive, water-based paint is a more attractive alternative than replacing such equipment but formulation of a non-corrosive, water-based paint, especially an emulsion or hybrid paint, presents pro-blems without any obvious solution.
Ideally, a water-based paint should be formulated to provide first the paint desired and this formulation supplemented with an additive that (l) will render the form-ulation non-corrosive, (2) will not coagulate the latex, and (3) will not affect any property of the paint deleteriously either before during or after its application to a substrate ~r require reformulation.
The corrosion of mild steel depends on the ratio of aggressive ion concentration to inhibitor ion concentration.
Dependiny on this ratio, three conditions may exist: general corrosion; localized corrosion in the form of pitting or crevice corrosion, and complete immunity, i.e., no corrosion.

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~- ~ai76283 Immunity can be achieved by decreasing the aggressive ion concentration and by increasing inhibitor ion concentration.
In ~h~ water-based enamels based on synthetic polymer latexes, the most significant aggressive ions are usually free sulfate ions. The sulfate ion is present in the latex as one of the decomposition products o~ the commonly used persulfate initiator, or as a residue from addition oE FeS04 as one component of an activated initiator system.
There are a great many corrosion inhibiting additives for aqueous systems. The details of the mechanisms of pro~
tection and the classification of corrosion inhibitors are described in detail in "Corrosion Inhibitors", edited by C.C.
Nathan, National Association o~ Corrosion Engineers, Houston, Texas (1973) and in "Electrodeposition and CorrOsiQn Processes", by J. M. West, D. Van Nostrand Co., Ltd., London, England (1965).
It has been found, however, that conventional add-itive approaches to control of paint corrosivity are not sat-isfactory in application to water-based enamels, and specific-ally in application to hybrid, water-based enamels. Con-ven$ional additives which have been tried and found wanting for this purpose include ben20ate, silicate, chromate, phosphate r : : .
nitrite, bicarbonate, and sulfite salts, organic amines, polyols, benzotriazole and related heterocyclic compounds, and mixtures of these and various other known inh:ibitors.
Even when incorporated at the 0.5 weight percent level~ adsorptive inhibitors such as hexamethylene diamine and morpholine do not stop the corrosion of mild steel in a typical hybrid enamel formulation. Cathodic inhibitors such as bicarbonates have been found simîlarly ineffective.
Anodic inhibitors such as sodium nitrite and potassium chromate inhibit corrosion but are not acceptable as paint additives. Both of these inhibit the cure of a thermosetting . :. : : '-~ 6283 paint. Potassium chromate cannot be used in paints because of the resultant colorin~.
Ammonium nitrite does not inhibit paint cure and does inhibit corrosion but it is unstable in solution and soon decomposes to form water and nitrogen gas.
Amine nitrites are also unsuitable when used alone~
For example, dicyclohexylaminenitrite, at the 0.5 weight per-cent level, inhibits corrosion but interferes with cure and - causes white paints to turn yellow. The latter problems are avoided at lower concentrations, but the corrosion protection afforded is not adequate when the concentration drops to a level where the others are obtained.
It now has been discovered that limited amounts of barium nitrite, unlike other nitrites, effectively inhibit corrosion from water-based paints of the type comprising a dispersion of crosslinkable organic polymers in a solution of water and organic amine, to which they are added without significant effect on curing or other properties of the paint. Barium nitrite may be used advantageously in com-bination with amine nitrites. These additives may be usedwith any of the principal types of water-based industrial paints, i.e., resin solutions, resin emulsions and resin emulsion-resin solution hybrids although the corrosion problem is most severe and the value of the additive is greatest with the emulsions and emulsion-solutions that they customarily contain corrosion inducing sulfate ions.
Barium nitrite is not fugitive from solution in the manner of ammonium nitrite. The corrosion protection pro-vided by barium nitrite is equivalent to that afforded by 3G alkali metal nitrites. ~nlike the alkali metal nitrites, barium nitrite does not inhibit crosslinking of the paint ' .. .. ' ; ~'~

;2133 film in the curing ovenO
sarium nitrite is employed in an amount that will provide a concentration of NO2 in the paint formulation in the range between 200 parts per million, hereinafter referred to as ppm, and 1000 ppm (basis paint formulation weight excluding any pigment but including water - this basis is used through-out this specification wherever the term ppm appears). This is equivalent to about 500 to about 2500 ppm of Ba(NO2)2.
In a pre~erred embodiment about 1000 to about 2500 ppm, Ba(NO2)2 are used~
This invention is applicable to any water-based paints but its advantages are most pronounced with emulsion (synthetic latex) paints, i.e., solely emulsion paints and emulsion-solution hybrid paints, which are prepared usin~
persulfate initiators or initiator systems which include sulfate ion yielding components, e.g., FeSO4.
To avoid endless and useless repetition, this inven-tion will be illustrated by its use in emulsion-solution hybrid enamels. The preferred water-hased enamels are those disclosed in U.K. Patent No. 1,496,198.
The hybrid, water-based paint compositions preferred for use in this invention employ in combination a low mole-cular weight emulsion polymer and a low molecular weight solution polymer with the latter being present in an amount sufficient to contribute significantly to the composition of the polymeric binder, i.e., at least about 5 weight percent of , .,~ :, .: ~:
this polymeric combination. They differ from the conventional emul8ion type paints employing a water-soluble thickener poly-mer in at least three compositional respects irrespective of chemical functionality, namely (1) the emulsion polymers have significantly lower molecular weights, (2) the solution ..' E~ - ~
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1~7~2~33 polymers have significantly lower molecular weights, and (3) the solution polymers are employed in significantly higher concentrations than are the water-soluble thickener polymers.
More specifically, the hybrid paint compositions us~d in thîs invention, exclusive of optional components such as pi~ments, particulate ~illers and catalysts, have a li~uid continuous aqueous phase. About 30 to about 50% by weight of this phase, exclusive of the a~orecited optional com-ponents, is made up of a mixture of (a) an amino resin crosslinking agent; (b) a mixture of at least two copolymers of acxylic monome~s; and (cl an amine. The balance is water or, in certain embodiments, water and an organic solvent.
The mixture of copolymers comprises (1) about 5 to about 95, preferably about 5 to about 50, and most preferably about 10 to about 30,lparts by weight of a "solution polymer", i.e., a carboxy-functioIlal copolymer of acrylic monomers that ~i) is at least partially neutralized with an ~mine, (ii) is soluble in said aqueous phase, (iii) has average molecular weight (Mn) in the range of about 3,000 to about 20,000 and (iv) has Tg in the range of -15 to 50C., and (2) .
about 5 to about 95, pxeferably abo ut 50 to about 95 and most preerably about 50 to about 70 parts by weight of an "emu]sion polymer", i.e., a copolymer of acrylic monomers have carboxy, hydroxy or carboxy and hydroxy ~unctionality that (i) is essentially insoluble in ~aid continuolls phase, (ii3 has average molecular weight (Mn) in the range of about 2,000 to about 20,000 and (iii) has Tg of -15 to 50C. The amino resin cross~inking agent is present in an amount in the range o~ about 15 to about 35 weigh~ percent .
of the sum of the weighk of solution polymer and the weight ~.

1~762~33 of emulsion polymer. The amine is a water~soluble amine and is present in an amount sufficient to solubilize the solution polymer in the aqueous phase at a pH range of about 7.1 to about 8.5. In certain embodiments, herein a~ter illustrated, these hybrid compositions include organic cosolvents while in other embodiments such solvents are not presentO

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When applied to the substrate to be coated by spraying, these water-based paints including pigments, particulate fillers, and catalysts, if any, contain between about 50 and about 65% by weight water or in those embodiments wherein such solvents are used, water and organic cosolvents.

_reparation of Water-Based Paint A number of methods can be used to prepare the water-based paints preferred for use in this invention.
In a first general method, at least one of -the polymers, usually the solution polymer, is polymerized in solution in a water miscible or dilutable organic solvent while the other polymer, usually the emulsion polymer, is prepared by an emulsion polymerization in water. The resultant water-based paint will contain a conventional, essentially non-reactive, water-miscible or dilutable organic paint solvent. The concentration of organic solvent in such paints will be at least about 5% by volume of the volatile phase, i.e., organic solvent and water, and preferably in the range of about 10 to about 20 volume percent of the ~olatile phase.
In a second general method both the solution polymer and the emulsion polymer are prepared by emulsion polymerization in water. The paints thus prepared are prepared without organic solvents~and thus employed free of same. Organic solvents in the amounts used in the first general method may be added to the dispersion, i desired.
A third general method is the same as the first general method except for the difference that in carrying out the emulsion polymerization the suractant, i.e., surface active agent or emulsifier, is replaced by a solutlon polymer hereinafter more fully described.

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3L~76i~83 A fourth general method is the same as the second general method except for the difference that in carrying out one or both, preferably both, of the emulsion polymeriza-tions the surfactant is replaced by a solution polymer hereinafter more fully described.
The advantage provided by the third and fourth general methods is that elimination of the conventional surfactant eliminates the problem o~ incompatibility and water sensitivity associated with the use of surfactants.

Polymer Composition Water-Based Paints (A) The solution polymer in these paints has carboxy functionality and may also have hydroxy functionality and/or amide functionality. These polymers contain about 5 -' to about 30 mole percent of acrylic or methacrylic acid and 70 to 95 mole percent of olefinically unsaturated monomers copolymerizable with such acid component. Preferably, these other olefinically unsaturated monomers are monoacrylates or ~',''' ' monomethacrylates. In the embodiment wherein the,primary solution polymer has only carboxy functionality, these are preferably esters of acrylic acid or methacrylic acid and a -Cl - C8 monohydric alcohol. ~C8 - C12 monovinyl hydrocarbons such as styrene, alpha methyl styrene, t-butyl styrene, and vinyl toluene may comprise up to about 30 mole percent of such polymer. Vinyl monomers such as vinyl chloride, acrylonitrile, methacrylonitrile and vinyl acetate may be, included in the copolymer as modifying monomers. However, when employed, these modifying monomers should constitute only between about O and about 33, preferably 0 to about 15, mole percent of such polymer. In the embodiment wherein the , ' , solution polymer has both carboxy functionality and hydroxy functionality, the copolymer contalns about 5 to about 25 mole percent of acrylic or methacrylic acid, about 5 to about , 25 mole percent of a hydroxyalkylacrylate or methacrylate, .
, ~ L~7~2~3 e.g., hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxy-ethyl methacrylate or hydroxypropyl methacrylate, and a remainder of the same monofunctional monomers as set forth above for the solely carboxy-functional polymer. In still another embodiment, the polymer has amide functionality in addition to carboxy functionality. Such-a polymer contains about 5 to about 25 mole percent acrylic acid or methacrylic acid, about 5 to about 25 mole percent of acrylamide, meth- -acrylamide~ N-methylolacrylamide, N-methylolmethacrylamide, or the alkyl ether of a me~hylolacrylamide or a methylolmeth-acrylamide, e.g.~ N~isobutoxymethylolacrylamide, with the remainder of the same monofunctional monomers as set forth above for the solely carboxy-~unctional polymer. A portion o~ the amide functional monomers may be replaced with an equimolar amount of one of the aforementioned hydroxyacrylates or hydroxy-methacrylates.
Other monomers not heretofore mentioned may be used in these polymers if used in limited concentrations. These include 2-acrylamide-2-methylpropanesulfonic acid and methacryloyloxyethylphosphate, which may comprise up to about 3% of such polymer.
(B) The emulsion polymer in these paints has caxboxy functionality, hydroxy functionality or carboxy and hydroxy functionality. These polym~rs contain 0 to 15 mole percent acrylic acid or methacrylic acid, preferably 0 to 10 mole percent, and 85 to 100 mole percent of other olefinically unsaturated monomers that are copolymerizable with each other and with the acid component when the latter is used. Such other olefinically unsaturated monomers are the same in type and of the same percentage distribution range as those hereto-fore disclosed for the solution polymer with the exception of the acid monomers content above noted.

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~7~83 In -those embodiments, wherein both the solution polymer and the emulsion polymer have hydroxy funtionality and carboxy functionality, it is preferred to have a greater concentration of carboxy functionality on the solution polymer relative to the emulsion polymer and a greater concentration of the hydroxy functionality on ~he emulsion polymer relative to the solution polymer.
Thus, the combinations involved include ~a) a carhoxy-functional solution polymer and a hydroxy-functional emulsion polymer, (b) a carboxy-functional solution polymer and a car~oxy-functional emulsion polymer, (c) a carboxy-functional solution polymer and a carboxy-functional, hydroxy-functional emulsion polymer r (d) a carboxy-functional and hydroxy-functional solution polymer and a hydroxy-functional emulsion polymer, (e) a carboxy-functional, hydroxy-functional solution polymer and a carboxy-funct:ional and hydroxy-functional emulsion polymer, (f) a carboxy-functional and amide-functional solution polymer and a hydroxy-functional emulsion polymer, (g) a carboxy-functional and amide- ```
functional solution polymer and a carboxy-functional emulsion polymer, (h) a carboxy-functional and amide-functional solution polymer and a carboxy-functional and hydroxy-functional emulsion polymeir, (i) a carboxy-functional, hydroxy-functional, and amide-functional solution polymer and a hydroxy-functional emulsion polymer, (j) a carbox~-functional, hydroxy-functional, amide-functional solution polymer and a carboxy-functional emulsion polymer, and (k) a carboxy-functional, hydroxy-functional, amide-functional solution polymer and a carboxy-functional, hydroxy-functional emulsion polymer. Amide functlonality may also be incorporated into the emulsion polymer but this is more difficult to achieve efficiently than in the solution polymer, particularly in the case of modi~ied amide functionality, e.g., N-methylolacrylamide .

(C) The amino resin crosslinking agent, may be and is hereafter illustra-ted as a conventional amino resin crosslinking agent of the type long in use as a crosslinking agent in acrylic enamels, e.g., melamine-formaldehyde resins and urea-formaldehyde resins.

Detailed Description o~ First General Method ~or Preparing Water-Based Paints Described Herein A. Preparation of Solution Copolymer In preparing the water-soluble copolymer, the ~unctional monomers and the remaining monoethylenically unsaturated monomers are mixed and reacted ~y conven-tional free radical initiated polymerization in such proportions as to obtain the copolymer desired. A large number of free radical initiators are known to the art and are suitable for this purpose. These include benzoyl peroxide;
t-butyl peroctoate; t-butyl perbenzoate; lauryl peroxide;
t-butyl-hydroxy peroxide; acetylcyclohexane sulfonyl peroxide;
diisobutyryl peroxide; di-(2-ethylhexyl) peroxydicarbonate;
diisopropyl peroxydicarbonate; t-butylperoxypivalate; decanoyl peroxide; azobis(2-methyl propionitrile); e~c. ~he polymer-ization is carried out in solution using a solvent which is miscible or dilutable with water. The solvent concentration at this stage is ordinarily about 30 to 60 weight percent o~
the polymerization solution. The polymeri~ation is carried ~out at a temperature between about 45C. and the reflux temperature of the reaction mixture. Included among the suitable solvents are n-propyl alcohol, isopropyl alcohol, dioxane, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene 3~ glycol monobutyl ether, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, etc. The copolymer , 1Q17~ii;Z 83 thus obtained is neutralized with amine to a pH of about 6 to 10 and diluted to desired ~iscosity with water or organic solvent.
B. Preparation of Emulsion Copolymer In preparing the emulsion copolymer, the functional monomers are mixed and reacted by conventional free-radical initiated polymerization in aqueous emulsion to obtain the copolymer desired.
Conventional surfactants, chain transfer agents, and initiators are employed in the emulsion polymerization. The monomer charge is usually emulsified by one or more micello-forming compounds composed of a hydrophobic part, such as a hydrocarbon group containing six or more carbon atoms, and a hydrophilic part, such as hydroxyl groups, alkali metal, ammonium c~rboxylate groups, sulfonate groups, phosphate or sulfate partial ester groups, or a polyether chain. Exemplary emulsifying agents include alkali metal sulfonates of styrene, naphthalene, decyl benzene, and dodecyl benæene; sodium dodecyl sulfate; sodium stearate; sodium oleate; the sodium alkyl aryl polyether sulfates and phosphates; the ethylene oxide condensates of long chain fatty acids, alcohols, and mercapta~s, and the alkali metal salts of resin acids. These materials a~d the techni~les of their employment in emulsion polymerization are well known.

As will be disclosed later herein, the solution polymer may also be prepared by emulsion polymerization. In such preparation, the resultant acid~~unctional copolymer latex is converted to a polymer solution by the addition of an appropriate b~ase, usually ammonia or an organic amine.
There are, however, different needs involved in the after-preparation employment of the emulsion polymer that is used as such in formulation of paint and the solution polymer which :
although prepared by emulsion polymerization is subsequently converted to a solution polymer and used as such. These needs --__ .

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should be taken into consideration in the preparation procedure.
In the use ~f emulsion polymerization to produce a solution polymer, there is no need for the resulting latex to be stable under conditions different from those ensuing at the end of the polymerization process since the latex no longer exists, as such, a~ter the polymer goes into solution - upon neutralization. To facilitate such conversion to solution polymers, polymers prepared by emulsion polymerization for use as solution polymers ordinarily contain a higher concentration of carboxyl groups and a lower concentration of deci~ed1y hydrophobic monomers, e.g., 2-ethylhexyl acrylate, relative to the corresponding concentrations in the polymers prepared by emulsion polymerization for use as such.
In contrast, latices which are used as such in the formulation of paint are required to remain essentially as stable latices throughout the processes of polymerization, paint formulation, and product distribution and use. This implies a requirement of stability, i.e., freedom from coagulum formation through time and under a variety of pM
conditions, solvent environment, etc. These requirements are best met, and hence it is preferred to use, an alkali metal or ammonium persulfate either as the sole polymerization initiator, or as one constituent of a mixed initiator system.
In those embodiments in ~hich con~entional surfactants, are used, a combination of anionic and nonionic surfactants provide a more stable latex. Such surfactant mixtures are well known in the art.
C; Formulation of Paint The polymer solution and th0 polymer late~ pre-pared according to the aforedescribed procedures are subse~-uently conyerted into a paint using conventional paint form-ulation techniques. Typically, a mill base is prepared which .
comprise~ the bulk of the pigment and/or particulate filler . . .
- 1 5, - ' ., . ~ ' - ~; .: .. , , , . . . . . . .. , . ,. .. . :

-o~ the paint formulation. The mill ~ase is "let down" i.e., blended with the remaining polymeric and liquid constituents of the final formulation. ~ mill base, prepared by con-ventional sand grinding, ball milling, or pebble milling generally comprises all or a part of the water soluble resin, pigments, organic cosolvents/ and ~ay also comprise a quantity of amine in excess of that required to solubilize the solution polymer. To complete the paint, the polymer late~ which has been neutralized to a pH range of 5.0 to 10, preferably 5 to 9, is added with mild agitation to the balance of the water required in the total formulation. The balance of the water-soluble resin, crosslinking agent, and millbase are added slowly with agitation. Additional quantities of pigment may be added subsequently as slurries in organic solvents or as separate mill bases to adjust the color as desired. The viscosity of the finished paint is determined and adjusted as required to obtain desired application properties. I -Alternately, all or a portion of the (preferably neutralize~ polymer latex, water, organic cosolvent, and -amine may be added to the solution polymer and pigments prior to ball milling r sand grinding, or pebble milling. This pro~
ceaure is advantayeo~sly employed to reduce the viscosity of mill bases prepared using the solution polymers o~ relatively high moIecular weight.
The water-based paints used as transparent overcoats in the process of this invention are formulated in the same way as the pigmented basecoats, save only for the omission of pigments or substantial reduction in the quantity thereof~ -D. Use of Organic Amines Organic amines are used to neutralize carboxyl groups on the solution polymer and hence to render it soluble in the aqueous dispersion. They are also used to maintain the p~ of the finished paint formulation above about 7, e.g., in the range o~ 7-10, preferably between 7 and 9.5, and with -~

~762~33 certain pigments such as aluminum flakes preferably bet~leen 7 and 9, to pr:event premature reaction of the functional groups on the acrylic copolymer with the amino resin crosslinking agent. Those skilled in the art will be aware that in certain embodiments the paint dispersion can be made up at a pH
outside the p~ range for application and later adjusted to the desired pH shortly before it is applied. A portion oE the amine, e.gO, preferably between about 60 and 100% of the amount chemically equivalent to the carboxyl functionality of the polymer is added to the solution polymer directly. Ad-vantageously, a small additional portion of amine is used to raise the pH of the emulsion polymer to about 5 to about 10, preferably 5 to 9, prior to finishing the paint formulation so that the mill base is not subjected to the low pH environ-ment of the polymer latex ~pH about 2.5). Suitable amine~
are amines (1) which are soluble in the aqueous medium of the paint, (2) that ionize suficiently in such aqueous medium to solubilize the solution polymer, (3) that ionize sufficiently in such a~ueous medium when employed in suitable amounts -to provide the paint dispersion with a pH of at least about 7, preferably 7.2 or higher, and thereby keep the rate of reaction between reactive groups of the amino resin (crosslinking agent) negligihle prior to curing and (4) that allow Eor rapid curing of the enamel upon heating~ Suitable amines include alkyl, alkanol and aryl primary, secondary and tertiary amines.
Preferred are secondary and tertiaryalkyl and alkanol amines having a boiling point within the range of 80 - 200C. By way of example, these include N,N-dimethyl ethanolamine, ~ -N,N-diethylethanolamine, isopropanolamine, morpholine, N-meth-ylmorpholine, N-ethylmorpholine, N-methylethanolamine, 2,6-dimethylmorpholine, methoxypropylamine, and 2-amino-2-methyl-l-propanol.
E. Catalysts Catalysts for the curing of resins described herein ~62~33 are not norinally required to obtain satisfactory film prop-erties. If desired, however, for purposes of lowering the film baking temperature or of further improving cured film propertles, strong acid catalysts can be employed in an amount not in excess o~ 3~ by weight of the total ~inished paint formulation. Said strong acid catalysts may be intro-duced either as copolymerizable species incorporated in one or both acrylic copolymers, e.g., 2-acrylamide-2-methyl-propanesulfonic acid, or as a non-polymerizable additive, - e.g~, p-toluenesulfonic acid. It is generally preferred not to add such catalysts, however, as th~y may tend to increase the water sensitivity of the cured film and may deleteriously affect storage stability of the liquid paint.
F. Cosolvents In those embodiments wherein a volatile organic solvent is employed as a cosolvent, i.e., solution of the solution polymer also being affected by the use of a water-soluble amine, the following solvents are suitable for this use include: n-propyl alcohol, isopropyl alcohol, butanol,

2-butoxyethanol, 2(2-butoxy)ethoxyethanol, n-octyl alcohol, dioxane, ethylene glycol monomethyl ether, ethylene ~lycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-butyl ether, ethylene ~lycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, etc.
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Detailed Description of Second General Method For Preparing Water-Based Paints Described ~Ierein A. Preparation of Solution Polymer In this method, the water-soluble copolymer is produced by emulsion polymerization. The functional monomers are mixed and reacted by conventional free-radical initiated polymerization in aqueous emulsion to obtain the copolymer ;Zg33 desired. The resulting acid-functional copolymer latex is converted to a polymer solution by the addition of an app-ropriate base, usually ammonia or an organic amine.
Conventional surfactants, chain transfer agents, and initiators are employed in the emulsion polymerization.
The monomer charge is usually emulsified by one or more micel-leforming compounds composed of a hydrophobic part, such as a hydrocarbon group containing six or more carbon atoms, and a ~ydrophilic part, such as hydroxyl group, alkali metal or ammonium carboxylate groups, phosphate or sulfate partial ester groups, sulfonate groups, or a polyether chain. Ex-emplary emulsifying agents include alkali metal sulfonates of styrene, naphthalene, decyl benzene and dodecyl benzene;
sodium dodecyl sulfate; sodium stearate; sodium oleate, the t sodium alkyl aryl polyether or sul~ates and phosphates; the ethylene oxide condensates of long chain fatty acids, alco-hols, and mercaptans, and the alkali metal salts of rosin acids. These materials and the techniques of their employment in emulsion formation and maintenance are well known. As previously pointed out, however, when emulsion polymerization is used to produce a solution polymer, there is no need for the resulting latex to be stable under conditions different from those ensuing at the end of the polymerization process since the latex no longer exists as such after the polymer goes into solution upon neutralization. To facilitate such con-version to solution polymers, polymers prepared by emulsion polymerization for use as a solution polymer ordinarily contain a higher concentration of carboxyl groups and a lower con-centration of decidedly hydrophilic monomers, e.g., 2~ethylhexyl acrylate, relative to the corresponding con-centrations in the polymexs prepared for use as emulsion poly-mers. Further, the teaching hereinbefore set forth with respect to the choice of initiators when preparing the latter, i.e., using an alkali metal or ammonium persulfate either as the sole polymerization initiator or as one constituent of a ~1~76Z~33 mixed initiator s~s-tem -to avoid coaglum formation through time and under a variety of pH conditions, solven-t environment, etc., is applicable where -the polymer is to be converted to a solution polymer. Such initiators may be used when preparing the solution polymer by emulsion polymerization but conventional peroxide initiators are quite suitable for this. Hence, this method offers an advantage, in this respect, in that the concentration of ionic inorganic contaminants, e.g., sulfate ions, in the paint formulation is reduced. A chain transfer agent or mixture of chain transfer agents may be added to the ~eaction medium to limit the molecular weight of the polymer, such chain trans~er agents are generally mercaptans such as dodecanothiol, benzene-thiol, l-octanethiol, pentanethiol and butanethiol. These are conventional materials employed in a conventional manner. The polymerization initiator is composed of one or more water-soluble, free-radical-generating species such as hydrogen pero~ide or the sodium, potassium or ammonium ~ -persulfates, perbo~rates, peracetates, percarbonates and the like.
As is well known in the art, these initiators may be associated with activating systems such as re~ox system which may in-corporate mild reducing agents, such as sulfites and thio-sul~ites and redox reaction promoters such as transition metal ions. ~s hereinbefore mentioned, however, it is desira~le to maintain a low concentration of non-polymeric ionic species in the finished paint formulation in order that the cured paint film may have optimium resistance to water. Hence it is preferred to use a minimum concentration of such optional inor~anic salts as ferrous sulfate, sodium bisulfate, and the like. Those skilled in the art will be aware that other emulsifying agents, polymerization initiators and chain transfer agents may be used which are compatible with the polymerization system herein required and with the attainment ~6;Z~3 of acceptable curecl paint film properties.

B. Preparation o~ Emulsion Copolymer The emulsion copolymer may be prepared using the same procedures hereinbefore recited for preparation of the emulsion copolymer in part ~. of the first general method.

C. Formulation of Paint The polymer solution and the polymer latex prepared according to the aforedescribed procedures may be subsequently converted into a paint using the same procedures hereinbefore recited for formulation of paint in part C. of the first general method. ~

D. Use of Organic ~mines .
The use of organic amines and amines which are suitable for such use are the same for this general method as hereinbefore described in detail in part D. of the first general method.

E. Catalysts ~.
The use of catalysts and catalysts which are suitable for curing the reslns hereinbefore described and hereinafter illustrated are the same for this general method as hereinbefore described in detail in part D. of the first general method.

F. Cosolvents ..
The use and choice of cosolvents for use with this general method ma~ be the same as hereinbefore described in part F. of the first yeneral method.

Detailed Description o~ Third General M~thod For Preparing Water-Based Paints Described Herein .
The third general method for preparing the paints disclosed herein is identical with the first general method hereinbefore described in detail except for the difference that al~ or a part of the surfactant, i.e., surface active , ' :

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1~7~283 a~ent or emulsifier, employed in preparing the emulsion polymer, is replaced with a stabilizer polymer, that is id-entical with or similar to, the solution polymer heretofore described in the first and second general methods and employed as a primary constituent of the paints described herein.
The stabilizer polymer of the third and fourth general methods is carboxy functional and soluble in the aqueous phase of these paint dispersions and is either the same as the primary solution polymer, heretofore discussed, or similar to such solution polymer and compati~le with the system. The average molecular weight (Mn) of the stabilizer polymer may be the same as that of the primary solution polymer, i.e., between 3,000 and 20,000 but advisedly is of lower molecular weight than the primary solution polymer.
Preerably, the average molecular weight o this third co-polymer is in the range of about 3,000 to about 8,000. Its Tg is in the range of -15 - 50C. When the stabilizer polymer is used in lieu of the surfactant to prepare either the solution polymer or the emulsion polymer, it is present in a concentration in the range of about 0~2 to about 10, preerably about 0.5 to about ~, weight percent based on the wei~ht of polymer to be prepared.
The stabilizer polymer may be prepared by any o several methods, including (1) the method used to prepare the solution polymer of the first general method of paint pre-paration, i.e., polymerization in solution in a water miscible or dilutable or~anic solvent; (2) the method used to prepare the solution polymer or the second general method of paint preparation, i.e., emulsion polymerization using an emulsifier or auractant; (3) emulsion polymerization using in lieu of a surfactant a small amount o the intended polymer rom a previous preparation; and (4) a method of emulsion polymeri-zation described hereinafter which employs neither surfactant :.
. . -~(~7~ 33 nor a water soluble polymer in lieu thereof. In the latter, conventional chain transfer agents and polymerization in-iators are used as described hereinbefore for the preparation of a solution'polymer by emulsion polymerization. A mixture of monomers includin~ carboxyfunctional monomers and a chain transfer agent is added slowly to a stir-red mixture of in-itiator and water maintained at a suitable reaction temp-erature, e.g., between 45 and 95C. It is preferred to add simultaneously with the monomer mixture an additional quantity of polymerization initiator to sustain a sufficient initiator concentration throughout the polymerization. The polymer latex so obtained is filtered and neutrali~ed with ammonia or water-soluble amine to render it water soluble.

Detailed Description of Fourth General Method For Preparing Paints Described Herein The fourth general method for preparin~ the paints disclosed herein is identical wi.th the second general method hereinbefore described in detail except for the difference that all or a part of the surfactant used to prepare the .
solution polymer, the emulsion polymer or, preferab~y, both the solution polymer and the emulsion polymer is replaced by a stabilizer polymer, such as heretofore described in detail ' in the description of the third ~eneral method.
This invention will be more fully understoocl from the following illustrative examples:

Example 1 A, Preparation of hybrid water-based enamel.
A heat curable coating composition suitable for automotive topcoat application is prepared from an aqueous acrylic copolymer latex, an aqueous solution of a second acrylic copolymer, and an amino resin crosslinking agent, here a melamine resin, in the manner hereinafter set forth:

~ 23 -- .. . ., . ........ , . . ,, : . : ~ . - -- . . . : , 1~7~ 3 Step I - Preparation of Acry]ic Copolymer Latex Monomers and AdditivesParts by Weight methylmethacrylate 5 styrene 25 2-ethylhexylacrylate 20 butylmethacrylate 30 hydroxypropylmethacrylate 18 acrylic acid 2 l-octane thiol 0.5 Triton(trademark)X-200~
Triton X-305 3 water 70 potassium persulfate 0.5 Reactor Charge water 50 Triton X-200 1 potassium persulfate U.l (1) a product of Rohm and EIaas Company, character-ized as an anioni~ surfactant containing 28~ active component described as the sodium salt of an alkyl aryl polyether sulfonate.
(2) a product of Rohm and Haas Company, character-ized as a nonionic surfactant containing 70% active component described as an alkyl aryl-polyether alcohol averaging 30 ethylene oxide units per molecule.
The reactor charge is heated to 95 C. in a reaction vessel equippea with a stirrer, reflux conde~ser, addition funnel and thermometer. The monomer mixture and listed additives are mixed and an emulsion is formed by stirring.

The monomer mixture is added to the reactor over a one-hour period; temperature is maintained at g5C. for two hours following completion of monomer mixture addition. The latex .

, . :
..
: .... : :

~L~37~Z~3 so obt.ained is :Eormulated into paint as hereinafter described~
Step II. Preparation of water soluble polymer.
_ nomers and Il~itiator Parts by Weiyht styrene 25 2-ethylhexylacrylate 20 butyl methacrylate 37 acryli.c acid 8 hydroxy propylmethacrylate 10 t-butyl perbenzoate 3 lOReactor Charge 2(2 butoxyethoxy) ethanol 35 A mixture of monomers and initiator as listed is added to the reactor (which is maintained at 130C.) over a 90-minute period. The temperature is maintained at 130 C.
for an additional 2.5 hours. (The entire polym~rization is carried out under a nitrogen atmosphere.) The polymer solution is cooled to room temperature, neutraliæed with 90~ of the calculated equivalent weight ~based on acid functional comonomer) of N,N-dimethylethanolamine, and re-duced to 60% solids with water.

Step III. Formulation of Paint An enamel is prepared from the descri~ed latex and solution polymer according to the ormula:

Parts by Wei~ht Component water 7.6 latex from Step I 57.5 colorant mill bases (l) and -~
aluminum flake pigment paste 6.9 2(2-butoxyethoxy)ethanol l.9 ~ ~
polymer soluti.on from S'tep II 13.2 ~-"~esimene" (Trademark) 740( ) 12.9 (l) colorant mill bases are prepared from con~
ventional p.igments using the polymer solution from Step II.

~6~Z~3 ~2) a product o~ Monsan~o Company and a w~ter reducible methylated melamine resin.
The enamel so obtained is adjusted to pH 7.8 using, N,N-dimethylethanol amine; viscosity is adjusted ko 25 sec.
Fo~d cup No. 4 by addition of wa-ter.
B. Evaluation of Paint Corrosivity.
I. Static immersion test Mild steel coupons are cut to size 1.3 x 8 cm.
decreased with trichloroethylene, and immersed halfway in a 20g. sample of the enamel prepared in part A of this example.
After 30 days immersion, the test coupons are removed, rinsed with distilled water, and inspected for evidence of corrosion below, above and ak the liquid level of the paint. There is substantial deposit of paint solids coagulated by corrosion products at the paint liquid level and along the edges of the test coupons. There is scattered rusting oE the test coupon above the paint liquid level.

II. Circulating System Test.
A pilot scale circulating s~stem comprising about 200 ft. of 1.5 in. mild steel pipe joined with standard fittings (malleable cast iron, steel seated unions) is used in further evaluation of corrosivity. Other components oE
the system are constructed of corrosion resistant materials (stainless steel, nylon, Mylar, Teflon, and the like). A
flow of 5 gpm with approximately 6 psi back pressure is mainta:ined in the system. Circulation is continued for 8 weeks. Pipe and union sections are removed, sectioned lengthwise, and examined for evidence of corrosion. Corrosion deposits are removed using a commercial stripper ~Stauffer Chemical Company Surfclean) to allow inspection of the under-lying pipe for evidence of localized pitting corrosion. The enamel prepared in part A of this example is found to corrode - -~6~762~33 the mild steel pipe badly, leaving a heavy deposit of coag-ulated paint solids mixed with corrosion products. Severe pitting of the pipe is observed.
C. Evaluation of Corrosion Inhibitors I. Barium nitrite Paint samples are prepared (using enamel from part A of this example) containing 250,500, 1000, and 2000 and 3000 ppm Ba(NO2)2, corresponding approximately to 100,200, 400, 800 and 1200 ppm NO2. These samples are evaluated for corrosivity using the static immersion test method pre-scribed under part B(I) of this example. Addition of 500 ppm BatNO2)2 or more reduces corrosivity of the paint;
addition of 1000 ppm Ba(NO2)2 or more effectively eliminate attack on mild steel in these tests. Addition of 2000 ppm or more Ba(NO2)2 tends to impair solvent resistance (the film softens when exposed to xylene); the paint tends to coagulate upon addition of 3000 ppm Ba(NO2)2.
II. Other nltrites By comparison with the results in part G(I) of this example, sodium and potassium nitrite are equally as ~;
effective in terms of corrosion inhibition when added in amounts calculated to yield the same concentration of NO2 in the paint. Both sodium and potassium nitrite interere with cure (solvent resistance) at all levels effective for corrosion inhihition.
~mmonium nitrite is similarly effective as a corrosion inhibitor and does not inhibit cure. The pro-tec-tion is shortlived, however. ~t 450 ppm NO2, for example, NH4NO2 provides effective inhibition for two to three weeks; ;
Ba(NO2) 2' tested under identical conditions, provides pro-tection for at least 4 to 6 weeks.
N,N-dimethylethanolamine nitrite is not as effective as Ba(NO2)2 (evaluated at equal levels ~f NO2 ' ~Q7~'~83 .
under identical conditions~) At 400 ppm NO2, the organic amine nitrite allows the mild steel test coupon to corrode freely while sa(NO2)2, as noted above, eEfectively stops the corrosion.

III. Combination of Ba(NO2)2 with organic amine nitrite.
A paint sample is prepared (using -the enamel from part A of this example) containing 250 ppm Ba(NO2)2 and 900 ppm N,N-dimethylethanolamine nitrite. This sample is evaluated for corrosivity, solvent resistance and settling and coagulation as hereinbefore discussed. It is essentially non-corrosive to mild steel in the static immersion test, is equivalent in solvent resistance to unmodified paint, and does not exhibit coagulation or undue settling. A pilot scale circulating test on this paint system indicates sub-stantial reduction in corrosivity. A liyht deposit of corrosion products and coagulated paint is formed. Some pitting of the pipe is observed, but its severity is greatly reduced in comparison with unmodified paint.
...
Example 2 .
A. Preparation of Hybrid Water Based Enamel The procedures set forth in part A of Example 1 are followed with the differences that: in Step I, pre-paration of acrylic copolymer latex, the monoMer composition is altered by the replacement of methylmethacrylate and 2-ethylhexylacrylate hy a mixture of 5 parts by weight styrene and 20 parts by weight butylmethacrylate; in Step 2, the preparation of water-soluble polymer, the polymer solution in neutralized with 60% of the calculated equivalent weight (based on acid functional comonomer) of N,N-dimethyle-thanolamine; and in Step 3, formulation of paint, the form-: ' . ' .

~7~ii;283 ulation comprises 11.9 parts by w~ight water, 47.1 parts latex, 20.9 parts polymer solution, 12.9 parts Resimene 740, 0.3 parts 2(2-butoxyethoxy)ethanol, the balance being colorant mill bases and aluminum flake plgment paste.
B. Evaluation of Corrosivity The paint prepared in Part A of this example is tested according to the static immersion test set forth in Example 1. The paint actively corrodes mild steel as evidenced by formation of a heavy deposit of coagulated paint and corrosion products at the paint liquid level.

C. Evaluation of Corrosion Inhibitors To the paint prepared in Part A of this example is added 250 ppm Ba(N02)2 and 900 ppm, N,N-dimethylethanolamine nitrite. The modified paint does not corrode mild steel in the static immersion test.

Example 3 The procedures of Example 2 are repeated with equivalent results using, in the formulation of paint, a latex prepared from 30 parts by weight styrene, 20 parts by weight ethyl acrylate, 30 parts by weight butyl methacrylate, 18 parts by weight hydroxypropyl methacrylate, and 2 parts by weight acrylic acid; ammonium persulfate is substituted for potassium persulfate. The remainder of the paint com-position is prepared as previously set forth.
Example 4 The procedures of Rxample 2 are repeated with equivalent results usin~, in the formulation of paint,Cymel (Trademark) 301, a product of American Cyanamid and a water dispersible methylated melamlne resin, in place of Resimene 740.

_amp]e 5 The procedures of Examp]e 4 are repeated with equivalent results using, in the formulation of paint, a polymer solution neutralized with 75% (based on khe acid functional monomer) of the calculated equivalent weight of N,N-dimethylethanolamine.

Example 6 The procedures of Example S are repeated with the difference that the corrosion inhibitor added is Ba(NO2)2 and i~s concentration is 1000 ppm. No corrosive attack is observed on mild steel in the static immersion test.

Example 7 A. Preparation of Hybrid Water-Based Enamel A heat-curable coating composition suitable for automotive topcoat application is prepared from an aqueous acrylic copolymer latex, an aqueous solution of a second `
acrylic copolymer, and an amino resin crosslinking agent, here a melamine resin, in the manner hereinafter set forth:

Step I. Preparation of Acrylic Copolymer Latex Monomers and Additives Parts by Weight methyl methacrylate 41 methacrylic acid 4 ethyl acrylate 35 butyl acrylate 20 `
l-octanethiol Triton X-200(1) 1 r~riton X-305(2) ` 4 5 Water 70 potassium persulfate 0.4 Reactor Charge Water 30 .

Momomers and Additives 1~7~Z83 Parts by Weight -Triton X-200 2 potassium persulfate 0.1 (1) a product of ~ohm and Haas Company, characterized as an anionic surfactant containing 28~
active componen~ described as the sodium salt of an alkyl aryl polyether sulfonate.
(2~ a product of Rohm and Haas Company, character-ized as a noniOnic suractant containing 70% active component described as an alkylarylpolyether alcohol averaging 30 ethylene oxide units per molecule.
The reactor charge is heated to 50C. in a reaction :.
vessel equipped with a stirrer, reflux condenser, nitrogen inlet type, addition funnel and thermometer. The monomer mixture is mixed with the listed additives and an emul.sion .
is ormed by stirring. The monomer emulsion is added over a four and one-hal~ hour period. The temperature is main-tained at 50 5C. throughout the monomer addition and or ::
2 hours ~hereafter. A nitrogen sparge is maintainecl through-out. The latex so formed is cooled to room temperature, filtered, and formulated into paint as hereinafter described.
1'he molecul.ar weight of th.e polymer so prepared (Mn) is about 6000. Its glass transition temperature, Tg, is akout 14C~ ~calculated from the monomeric composition without regard to moleculax weight as are all Tg values herein given).

Step II. Preparation of Water Soluble Acrylic Polymer Monomer Mixture and Initicltor Parts ~ ..
methacrylic acid 15.0 methyl~.nethacrylate 15.0 . -. 30 styrene 20.0 , , . ' ' , ~ .
~ 31 ~L~7~Z~33 Monomer Mixture and_IhitiatorParts by Wei~ht butyl acrylate 40.0 butyl methacrylate 10.0 t-butylperoctoate 3.5 Reactor Cha _ isopropyl alcohol 45 A mixture of the monomers and initiator listed is added to refluxing isopropyl alcohol over a 90-minute period.
An additional initiator chanye - 0.2 parts t-bu-tylperoctoate in 5 parts isopropyl alcohol - is added 30 minukes aftex completion of the monomer addition. The reaction mix-ture is main-tained at reflux an additional 2 hours, cooled to room temperature, neutralized with 90% o~ the calculated equivalent weight (based on acid functional comonomer) of dimethylethanolamine, and reduced to 60% by weight solids ~ith water. The polymer thus prepared has molecular weight ~Mn) of abou-t 9200. The glass transition temperature of this polymer is about 18C.
' Step XII. Formulation of Paint A mill base is prepared by pebble milling together the following materials.

onents Parts b~ Weigh polymer solution from Step 2 5.5 titanium dioxide pigment 13.8 water 3,3 An enamel i9 then prepared by blending this mill base with the following materials:

Components Parts by Weight latex from Step I 42~5 water 19.0 isopropanol 1.0 propylene glycol 5.1 , ., . , ~ . -. . .

~L~7~;Z133 Components Parts by We ght melamine c~slinking agent, Cymel 30~ 4.6 10~ aqueous N,N-dimethylethanolamine 1.4 10% aqueous p-toluenesulfonic acid(2) 3.8 (1) a product of American Cyanamid Company, and a commercial ~rade of hexamethoxymethylmelamine.
(2) the solution is adjusted to pH 8 by addition of dimethylaminoethanol.
B. Evaluation of Corrosivity The enamel prepared in Part-A of this example is evaluated for corrosivity following the static immersion test procedure described in Example 1. The enamel actively corrodes mild steel as evidenced by a heavy deposit of rust and coagulated paint at the paint liquid level.

C. Evaluation of Corrosion Inhibitor To the enamel is added lr)O ppm Ba(NO2)2 and 1500 ppm N,N-dimethylethanolamine nitrite. Corrosive attack on mild steel in the static immersion test is greatly reduced. The additives have no effect on solvent resistance of the cured paint films.
' ' .
. Preparati.on of Enamel Step I. Preparation of Stabilizer Polymer -There is charged to a reactor 200 parts of water.

The reactor charye is heated to boiling and then cooled to 95C. To the reactor charge is added Solution A, a solution of 0.1 parts of ammonium persulfate in 0.8 parts of water.

A solution hereinafter termed Solution B, is prepared from O.4 parts of ammonium persulfate in 2.5 parts water. A

reactant monomer and chain transfer agent mix-ture is formed from the following materials:

, _ 33 7~'~83 Ma-terials Parts by Wei~ht methyl methacry]ate 35 methacrylic acid 15 butyl acrylate 50 l-octanethiol 2 The monomer mixture and Solution B are sirnul-taneously charged to the reactor by incremental addition over a two-hour period. The temperature of the reaction mixture is maintained for 3 hours after addition of the last of th~ reactants. The latex so obtained is cooled to room temperature and filtered. The polymer thus obtained, hereinafter termed stabilizer polymer I, is then neutralized with N,N-dimethylethanolamine in an amount equivalent to the acid monomer content of the polymer.
A clear solution is obtained.

Step II Preparation of Emulsion'Polym~r An emulsion polymer is produced by first preparing the following: (1) there is charged to the reactor 200 parts of water and 4.25 parts of the stabilizer polymer from Z0 Step I; (2) the following materials are thoroughly mixed:

Matexials Parts b~ Weight st~rene 20.0 methacrylic acid 15.0 butyl acrylate 55.0 butyl methacrylate 10.0 l-octanethiol (3~ there are dissolved in 0.5 parts of ammonium persulfate and one part of 2-acrylamide-2methylpropanesulfonic acid in 2.5 parts of water; and (4) there is dissolved 0.2 parts of ammonium persulfate in 5 parts of water. After these are prepared the emulsion polymer is prepared using the procedure and conditions used to prepare the stabili2er polymer of Step I. In such, the order of addition of the four above

- 3~ -listed components is as follows: (4) îs added to (1) in the reactor and (2) and (3) are added simultaneously to the mixture of (1) and (4).

Step III. Preparation of the Solution Polymer The procedures and steps of Step II of this example are repeated with the following employment of reactant monomers:

Materials Parts by Weight . .
methyl methacrylate 35 methacrylic acid 15 ~:.
butyl acrylate 50 l-octanethiol After this latex is cooled and filtered, it is neutralized with N,N-dimethylethanolamine to the amount ..
equ.ivalent to the methacrylic acid constituent of the polymer.
...
Step IV. Formulation of Water-Based Enamel .. ... .
Materials Parts by Weight solution polymer from Step III14.1 Cymel 300 6.5 titanium dioxide . 16.1 water " . 6.4 The above materials are ball milled for 16 hours and mixed (let down~ with the following materials:

Materials Parts by Weight -latex from Step II (includes both emulsion polymer and stabilizer polymer I) 47.3 10% aqueous N,N-dimethylethanolamine 9.6 .:, .
- . .

~'7~

B. Evaluation of Corrosivity The enamel so prepared is tested in accordance with the procedures set forth in Example 1 - static immersion test. The enamel actively corrodes onto steel as evidenced by a heavy deposit of rust a~d coagulated paint at the paint liquid level.

C. Evaluation o~ Corrosion Inhibitor To the enamel is added 800 ppm Ba(NO2)2 and 900 ppm N,N-dimethylethanolamine nitrite. Corrosive attack on mild steel in the static immersion test is greatly reduced. The additives have no effect on solvent resistance of cured paint films.

Exam~
The procedures of Example 2 are repeated wi-th equivalent results using triethylamine nitrite in place of N,N-dimethylaminoethanol nitrite.

, ~e ~
The procedures of Example 2 are repeated using morpholine nitrite in place of dimethylethanolamine nitrite.
Results are equivalent.
The term "acrylic monomer" as used herein means a compound selected from the group consisting of glycidyl acrylate, glycidyl methacrylate, acrylic acid, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, esters of acrylic acid and a Cl - C~ monohydric alcohol, and esters of methacrylic acid and a Cl - C8 monohydric alcohol.

The term "acrylic copolymer" means a copolymer of monoethylenically unsaturated compounds at least a major portion of which are acrylic monomers. -~
:
' ~76~1 33 The term "major portion" means in excess of sn weight percent of the entity referred to.
The term "minor portion" means less than 50 wei~ht percent of the entity referred to.
Many modific~tions of -the foregoing examples will be apparent to those skilled in the art i.n view of this specification. It is intended that al.l such modifications which fall within the scope of this invention as defined in the claims shall be considered to be a part of this invent.ion.

Claims (7)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
1. In a paint formulation which comprises a dispersion of crosslinkable organic polymers in a solution of water and organic amine the improvement wherein said paint formulation contains about 500 to about 2500 parts by weight barium nitrite per million parts by weight of said paint formulation.
2. In a paint formulation which consists essentially of a dispersion of thermosetting paint binder in an aqueous solution of organic amine which consists essentially of:
A. 100 parts by weight paint binder resins con-sisting essentially of

1. about 5 to about 95 parts by weight of a solution polymer which is a carboxy-function-al acrylic copolymer that (a) is at least partially neutralized with said aqueous solution of organic amine, (b) is soluble in said aqueous solution, (c) has average molecular weight (?n) in the range of about 3,000 to about 20,000 and (d) has Tg in the range of -15°C to 50°C, and

2. about 5 to about 95 parts by weight of an emulsion polymer having functionality selected from carboxy functionality and hydroxy func-tionality and is an acrylic copolymer that (a) is essentially insoluble in said aqueous solution, (b) has average molecular weight (?n) in the range of about 3,000 to about 20,000 and (c) has Tg in the range of -15°C to 50°C, and B. about 15 to about 35 parts by weight of an amino resin crosslinking agent for said solution polymer and said emulsion polymer, the improvement wherein said paint formulation contains about 500 to about 2500 parts by weight barium nitrite per million parts by weight of said paint formulation.

3. The paint formulation of claim 1 or 2, which contains 1000 to 2500 parts by weight barium nitrite per million parts of said paint formulation.

4. The paint formulation of Claim 2, wherein 50 to 65 weight percent of said paint formulation is water and said dispersion has a pH between 7 and 10.

5. The paint formulation of Claim 2, wherein an equal volume of an essentially non-ionizable organic solvent for said solution polymer is substituted for about 5 to about 20 volume percent of said water.

6. The paint formulation of Claim 5, wherein said organic solvent is an alcohol.

7. In a method of preparing a paint formulation com-prising a dispersion of crosslinkable organic polymers in a solution of water and organic amine, the improvement which comprises the addition of barium nitrite in an amount providing in said paint formulation a barium nitrite con-centration in the range of about 500 to about 2500 parts by weight barium nitrite per million parts by weight of said paint formulation including water.