CA1067232A - Method for producing solvent free water based enamels - Google Patents

Abstract

METHOD FOR PRODUCING SOLVENT-FREE WATER-BASED ENAMELS

ABSTRACT OF THE DISCLOSURE
The formation of solvent-free water-based enamels is described. The paint is made up of a mixture of (a) an amino resin cross-linking agent, (b) a mixture of at least two copolymers of acrylic monomers and (c) an amine.
The mixture of copolymers includes an emulsion copolymer and a solution copolymer which is prepared by emulsion polymerization.

Description

1067Z3'~

This invention relates to the formation of water-based paints. This application is a division of copending ~anadian application Serial No. 228,423 filed May 30, 1975.
Water-based paints of the prior art have included "solution paints" and "emulsion (or latex) paints" with distinction being made with reference to the manner in which the sole or principal binder polymer is dispersed within the aqueous medium.
In those paints wherein the sole or principal binder polymer is soluble in the aqueous medium, the polymer is ordinarily of low molecular weight. These paints can be formulated to provide coatings of very high gloss. They tend to be slow drying and prone to sagging during application and to solvent popping during baking under high humidity conditions.
Application solids are much lower than comparable latex paints.
The emulsion or latex paints have employed as their sole or principal binder polymer a polymer of very high molecular weight, i.e., in the range of about 100,000 to about 1,000,000 or higher. Such paints have been characterized by rapid drying and comparatively low gloss relative to paints based on water-soluble polymers.
Water-soluble polymers of high molecular weight have been added to latex paints as thickeners. Characteris-tically, such thickener polymers are used in very small amounts, e.g., of the order of one percent.
It has been discovered that water-based paints having a superior combination of physical properties and application characteristics can be obtained by using certain novel combinations of solution polymers and emulsion polymers.
The coatings obtained from these hybrid compositions exhibit - 1~67Z3Z

~ligll gloss and generally excellent appearance.
In accordance with the present invention, there is provided an improvement in a method for producing an aqueous dispersion of paint in which a carboxy-functional polymer is at least partially neutralized with a water-soluble amine and dispersed with an amino resin cross-linking agent selected from melamine-formaldehyde resins and urea-formal-dehyde resins in an aqueous solution of water and water-soluble amine, wherein the carboxy functional polymer, amino resln cross-linking agent and water~soluble amine constitute about 30 to 50% by weight of the continuous aqueous phase of the paint with the balance of the continu-ous aqueous phase being water or a mixture of water and an organic solvent, the water soluble amine is present in an amount sufficient to provide an aqueous phase pH of about 7.1 to about 8.5, and said water or mixture of water and organic solvent constitutes about 50 to about 65% by weight o the paint.
The improvement is that the aqueous dispersion is produced essentially free of organic solvents by intimately dispersing with the water, the amino resin cross-linking agent and the water soluble amine: I. an aqueous emulsion consisting essentially of water, water-soluble amine, and about 50 to about 95 parts by weight of an emulsion polymer having functionality selected from carboxy functionality and hydroxy functionality and is a copolymer of acrylic monomers that:
(a) is essentially insoluble in the aqueous solution; (b) has average molecular weight (Mn) in the range of about 3,000 to about 20,000, and (c) has Tg in the range of -15C to 50C and II. about 5 to about 50 parts by weight of a sol-ution polymer which is a carboxy functional copolymer of IJ

1~)67Z32 acrylic monomers th~t: (a) is at ].east partially neutralized with water-soluble amine. (b) is soluble in the aqueous solution; (c) has average molecular weight (Mn) in the range of about 3,000 to about 20,000, (d) has Tg in the range of -15C to 50C,and (e) has been prepared by emulsion poly-merization in water of about 5 to about 25 mole percent of an alpha-beta olefinically unsaturated monocarboxylic acid selected from acrylic and methacrylic acid and 75 to 95 mole percent of other monoethylenically unsaturated monomers consisting of monomers selected from the group consisting of monoacrylates, monomethacrylates and monovinyl - 3a -~3 1(;~67Z32 hydrocarbons at a temperature between about 45~C. and the reflux temperature of the reaction mixture and subsequently at least partially neutralized with water-soluble amine in the water in which it is formed, the amino resin cross-linking agent being present in an amount in the range of about 15 to about 35 weight percent of the sum of the weights of the solution polymer and the emulsion polymer.
The term "parts" when used herein without further designation shall mean "parts by weight".
The term "acrylic monomer" shall mean acrylic acid, methacrylic acid, esters of acrylic acid and a Cl - C8 monohydric alcohol, e.g., ethyl acrylate butyl acrylate, hexyl acrylate and 2-ethylhexyl acrylate, esters of methacrylic acid and a Cl - C8 monohydric alcohol, e.g., methyl methacrylate, butyl methacrylate, hexyl methacrylate and 2-ethylhexyl methacrylate, hydroxyalkYl acrylates, e.g., hydroxyethyl acrylate and hydroxypropyl acrylate, hydroxyalkyl methacrylates, e.g., hydroxyethyl methacrylate and hydroxypropyl methacrylate, acrylamide, methacrylamide, methylolacrylamides, e.g., n-methylolacrylamide, methylol-methacrylamides, e.g., N-methylDlmethacrylamide, alkyl ethers of methylolacrylamides, e.g., N-isobutoxymethylolacrylamide, and alkyl ethers of methylolmethacrylamides, e.g., N-isobutoxy-methylolmethacrylamide.
The term "copolymer of acrylic monomers" shall mean a polymer of at least two different monoethylenically unsaturated monomers of which more than S0 mole percent are acrylic monomers.
The hybrid, water-based, paint compositions formed in this invention employ in combination a low molecular weight emulsion polymer and a low molecular weight solution polymer )6~232 with the latter being present in an ~mount sufficient to contribute significantly to the composition of the polymeric binder, i.e., at least about 5 weight percent of this polymeric combination. Thus, they differ from the conventional emulsion type paints employing a water-soluble thickener polymer in at least three compositional respects irrespective of chemical functionality, namely (1) the emulsion polymers of the instant paints have significantly lower molecular weights, (2) the solution polymers of the instant paints have significantly lower molecular weights, and (3) the solution polymers of the instant paints are employed in significantly higher concentrations than are the water-soluble thickener polymers.
More specifically, the hybrid paint compositions formed in this invention, exclusive of optional components such as pigments, particulate fillers and catalysts, have a liquid continuous aqueous phase. About 30 to about 50% by weight of this phase, exclusive of the aforecited optional components, is made up of a mixture of (a) an amino resin cross-linking agent; (b) a mixture of at least two copolymers of acrylic monomers; and (c) an amine. The balance is water or, in certain embodiments, water and an organic solvent.
The mixture of copolymers preferably comprises about 10 to about 30 parts by weight of the solution polymer and about 60 to about 90 parts by weight of the 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.

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.

" 1067232 In the present invention both the solution polymer i and the emulsion polymer are prepared by emulsioll polymerization in water. The paints thus prepared are prepared without organic solvents and thus employed free of same. Organic solvents may be added to the dispersion, if desired, preferably in the range of about 10 to about 20 volume percent of the volatile phase. In carrying out one or both, preferably both, of the emulsion polymerizations the surfactant may be replaced by a solution polymer, as claimed in our copending Canadian application Serial No. 251,35~ filed concurrently herewith.
The solution polymer used to form the paints in this invention has carboxy functionality and may also have hydroxy functionality and/or amide functionality. These polymers usually 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 0 and about 30, preferably 0 to 15, mole percent of such polymer. In the embodiment wherein the solution polymer has both carboxy functionality and hydroxy functionality, the copolymer usually contains about 5 to about 25 mole percent of acrylic or methacrylic acid, about 5 to about 25 mole percent of a hydroxyalkylacrylate or methacrylate, e.g., hydroxylethyl acrylate, hydroxypropyl acrylate, hydroxyethyl 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 usually contains about 5 to about 25 mole percent acrylic acid or methacrylic acid, about 5 to about 25 mole percent of acrylamide, methacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, or the alkyl ether or a methylolacrylamide or a methylolmethacrylamide, e.g., N-isobutoxymethylolacrylamide, with the remainder of the same monofunctional monomers as set forth above for the solely carboxy-functional polymer~ A portion of the amide functional monomer may be replaced with an equimolar amount of one of the aforementioned hydroxyacrylates or hydroxymeth-acrylates.
Other monomers not heretofore mentioned may be used in these polymers if used in limited concentrations. These include 2-acrylamido-2-methylpropanesulfonic acid and methacryloyloxyethylphosphate, which may comprise up to about 3~ of such polymer.
The emsulsion polymer used to form the paints in this invention has carboxy functionality, hydroxy functionality or carboxy and hydroxy functionality. These polymers 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 ~hat are copoly-merizable 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 dis-tribution range as those heretofore disclosed for the solution polymer with the exception of the acid monomer content above noted.
In those embodiments, wherein both the solution polymer and the emulsion polymer have hydroxy functionaltiy 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 con-centration of the hydroxy functionality on the emulsion polymer relative to the solution polymer.
Thus, the combinations involved include (a) a carboxy-functional solution polymer and a hydroxy-functional emulsion polymer, (b) a carboxy-functional solution polymer and a carboxy-functional emulsion polymer, (c) a carboxy-functional solution polymer and a carboxy-functional, hydroxy-functional emulsion polymer, (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-functional 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 polymer, (i) a carboxy-functional, hydroxy-functional, and amide-functional solution polymer and a hydroxy-functional emulsion polymer, (j) a carboxy-functional, hydroxy-functional, amide-functional solution 1067Z3;~

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 functionality 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 modified amide functionality, e.g., N-methylol-acrylamide.
The amino resin cross-link~ng agent, may be and is hereafter illustrated as a conventional amino resin cross-linking agent o~ the type long in use as a cross-linking agent in acrylic enamels, e.g., melamine-formaldehyde resins and urea-formaldehyde resins.
In the formation of water-based paints, in accor-dance with this invention, the following procedure may be adopted.
In the preparation of the solution polymer emulsion polymerization is used. The functional monomers are mixed and reacted by conventional free-radical initiated polymerization in aqueous emulsion to obtain the copolymer desired. The resulting acid-functional copolymer latex is converted to a polymer solution by the addition of an appropriate 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 micelle-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 group, alkali metal or ammonium carboxylate groups, phosphate or sulfate partial ester groups, sulfonate groups, or a polyether chain.

_ g _ 1~67232 Exemplary emulsifying agents include alkali metal sulfonates of styrene, naphthalene, decyl benzene and dodecyl benzene;
sodium dodecyl sulfate; sodium stearate; sodium oleate, the sodium alkyl aryl polyether or sulfates and phosphates; the ethylene oxide condensates of long chain fatty acids, alcohols, 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 in the art.
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 conversion to solution polymers, polymers prepared by emulsion polymerization for use as a solution polymer ordinarily contain a higher concen-tration of carboxyl groups and a lower concentration of decidedly hydrophobic monomers, e.g., 2-ethylhexyl acrylate, relative to the corresponding concentrations in the polymers prepared for use as emulsion polymers. Further, when preparing the latter, an alkali metal or ammonium persulfate is used either as the sole polymerization initiator or as one constituent of a mixed initiator system to avoid coagulum formation through time and under a variety of pH conditions, solvent environment, etc. 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., s~lfate ions, in the paint formulation is reduced. A chain trar,sfer agent or mixture of chain transfer agents may be added to the reaction medium to limit the molecular weight of the polymer, such chain transfer agents are generally mercaptans such as dodecanethiol, benzenethiol, l-octanethiol, pentanethiol and butanethiol. These are conventional materials employed in a conventional manner. The polymeriza-tion initiator is composed of one or more water-soluble, free-radical-generating species such as hydrogen peroxide or the sodium, potassium or ammonium persulfates, perborates, peracetates, percarbonates and the like. As is well known in the art, these initiators may be associated with activating systems such as redox system which may incorporate mild reducing agents, such as sulfites and thiosulfites and redox reaction promoters such as transition metal ions.
However, it is desirable to maintain a low concentration of non-polymeric ionic species in the finished paint formulation in order that the cured paint film may have optimum resistance to water. Hence, it is preferred to use a minimum concentra-tion of such optional inorganic salts as ferrous sulfate, sodium bisulfite, 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 of acceptable cured paint film properties.
The polymerization is carried out at a temperature between about 45C and the reflux temperature of the reaction mixture.
The resultant acid-functional copolymer latex is converted to a polymer solution by the addition of an appropriate base, usually ammonia or an organic amine.

10~7Z3Z
In preparing ~he 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 micelle-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 carboxylate groups, sulfonate groupsr phosphate or sulfate partial ester groups, or a polyether chain. Exemplary emulsifying agents include alkali metal sulfonates of styrene, naphthalene, decyl benzene, and dodecyl benzene; sodium dodecyl sulfate; sodium stearate; sodium oleate; the sodium alkyl aryl polyether sulfates and phos-phates; the ethylene oxide condensates of long chain fatty acids, alcohols, 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 in the art. A chain transfer agent or mixture of chain transfer agents may be added to the reaction medium to limit the molecular weight of the copolymer; such chain trans~er agents are generally mercaptans such as dodecanethiol, benzenethiol, l-octanethiol, pentanethiol, and butanethiol.
These are conventional materials and are employed in a conventional manner. The polymerization initiator is composed of one or more water-soluble, free-radical-generating species such as hydrogen peroxide or the sodium, potassium, or ammonium persulfates, perborates, peracetates, percarbonates and the like. The polymerization is carried out at a 1~6723Z
tomperature between about 45C. and the reflux temperature of the reaction mixture. As is well known in the art, these initiators may be associated with activating systems such as redox systems which may incorporate mild reducing agents, such as sulfites and thiosulfites, and redox reaction promoters such as transition metal ions, and that these allow the polymerization to be carried out at a lower temperature, e.g., 0C or below. As, however, it is desirable to maintain a low concentration of non-polymeric ionic species in the finished paint formulation in order that the cured paint film may have optimum resistance to water, it is preferred to use a minimum concentration of such optional inorganic salts as ferrous sulfate, sodium bisulfite, 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 of acceptable cured paint film properties.
There are 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 as described above to a solution polymer and used as such. These needs should be taken into consideration in the preparation procedure.
In the use of 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, after the polymer goes into solution upon neutralization. To facilitate such conversion to solution polymers, polymers prepared by emulsion polymerization for ~067Z32 use as solution polymers ordinarily contain a higher concentration of carboxyl groups and a lower concentration of decidedly 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 pH
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 which conventional surfactants are used, it is pre~erred to use a plurality of surfactants, more specifically a combination of anionic and nonionic surfactants, to obtain a more stable latex. Such surfactant mixtures are well known in the art.
The polymer solution and the polymer latex prepared according to the aforedescribed procedures are subsequently converted into a paint using conventional paint formulation techniques. Typically, a mill base is prepared which comprises the bulk of the pigment and/or particulate filler of the paint formulation. The mill base is "let down" i.e., blended with the remaining polymeric and liquid constituents of the final formulation. A mill base, prepared by conventional sand grinding, ball milling, 3~ or pebble milling generally comprises all or a part of the water soluble resin, pigments, organic cosolvents, and may also comprise a quantity of amine in excess of that required to solubilize the solution polymer. To complete the paint, the polymer latex 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, cross-linking agent, and mi11 ~ase are added slowly with agitation. Additional quantities of pigment may ~e added subsequently as slurries in organic solvents or as separate mill bases to adjust the colour as desired. The viscosity of the finished paint is determined and adjusted as required to obtain desired application properties.
Alternately, all or a portion of the (preferably neutralized) polymer latex, water, organic cosolvent, and amine may be added to the solution polymer and pigments prior to ball milling, sand grinding, or pebble milling.
This procedure is advantageously employed to reduce the viscosity of mill bases prepared using the solution polymers of relatively high molecular weight.
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 pH of the finished paint formulation above about 7, e.g., in the range of 7 to 10, preferably between 7 and 9.5, and with certain pigments such as aluminum flakes preferably between 7 and 9, to prevent premature reaction of the functional groups on the acrylic copolymer with the amino resin cross-linking 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 pH range for application and later adjusted to the desired p~ shortly before it is applied.

A portion of the amine, e.g., 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. Advangageously, 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 tbe mill base is not subjected to the low pH environment of the polymer latex (pH about 2.5).
Suitable amines are amines (1) which are soluble in the aqueous medium of the paint, (2) that ionize sufficiently in such aqueous medium to solubilize the solution polymer, (3) that ionize sufficiently in such aqueous 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 (cross-linking agent) negligible prior to curing, and (4) that allow for rapid curing of the enamel upon heating. Suitable amines include alkyl, alkanol and aryl primary, secondary and tertiary amines. Preferred are secon-dary and tertiaryalkyl and alkanol amines having a boiling point within the range of 80 to 200C. By way of example, these include N,N-dimethyl ethanolamine, N,N-diethylethanol-amine, isopropanolamine, morpholine, N-methylmorpholine, N-ethylmorpholine, N-methylethanolamine, 2,6-dimethylmorpholine, methoxypropylamine, and 2-amino-2-methyl-1-propanol.
Catalysts for the curing of resins described herein are not normally required to obtain satisfactory film properties. If desired, however, for purposes of lowering the film baking temperature or of further improving cured film properties, strong acid catalysts can be employed in an amount not in excess of 3% by weight of the total finished paint formulation. Said strong acid catalysts may be introduced either as copolymerizable species incorporated in one or both acrylic copolymers, e.g., 2-acrylamide-2-methylpropanesulfonic acid, or as a non-polymerizable additive, e.g., p-toluenesulfonic acid. It is generally preferred not to add such catalysts, however, as they may tend to increase the water sensitivity of the cured film and may deleteriously affect storage stability of the liquid paint.

This invention will be more fully understood from the following illustrative examples:
EXAMPLE I
Step I P~paration of the Solution Polymer - An acrylic copolymer soluble in the aaeous phase of the water-based paint of which it later becomes a part is prepared from the following materials in the manner hereinafter described: ~~
Materials Parts by Weight methyl methacrylate 45.0 methacrylic acid 15.0 butylacrylate 40.0 water go.o "TRITON" (Trade Mark) X-200(1) 1.15 Triton X-305( ) 3.58 Potassium persulfate 0.4 l-octanethiol 1.5 Reactor Charge water 60.0 Triton X-200( ) 1.67 potassium persulfate 0.1 (1) an anionic surfactant containing 28% active component described as the sodium salt of an alkyl aryl polyether ,ulfonate and solid by Rohm and EIaas Company.

(2) a nonionic surfactant containing 70% active component described as an alkylaryl polyether alcohol averaging 30 ethylene oxide units per molecule and sold by Rohm and Hass Company.
The reactor charge is heated quickly to boiling and cooled to 95C. A monomer emulsion is formed from the above by mixing and stirring. The monomer emulsion is added to the hot reactor charge over a two-hour period. The temperature is maintained at 90 + 5C throughout the monomer addition period and for two hours after addition is complete. The 2-(dimethylamino)ethanol is added in an amount equivalent to the acid monomer incorporated in the polymer and the solids content is reduced with water to 30~ by weight. The polymer (Mn) is about 5,000 and the Tg is calculated to be 25C.
Step II Pre~aration of the Emulsion Polymer An emulsion polymer is prepared following the procedure of Step I from the following reactant monomers, initiator and chain transfer agent.
Materials Parts by Weight methyl methacrylate48.0 methacrylic acid 7.0 ethyl acrylate 35.0 butyl acrylate 10.0 l-octanethiol 0.4 t-butylperoctoate 3.5 The average molecular weight of this copolymer is about 10,000 and it has a Tg of about 40C.
Step III Formulation of Paint (free of organic solvent) A mill base is prepared by pebble milling together the following materials:

~ 106723Z

MaterialsParts by Weight polymer solution from Step I 18.4 "CYMEL" (Trade ~lark) 300(1) 6.7 titanium dioxide pigment 16.5 water 8.3 (I) a commercial grade of hexamethoxymeth~ylmelamine - sold by American Cyanamid Company.
An enamel is formulated by blending together the following materials:
Materials Parts by Weight latex from Step II 46.0 10~ a~ueous 2-(dimethylamino)ethanol 3.3 10% aqueous p-toluene sulfonic acid 0.8 (neutralized with 2-(dimethylamino) ethanol mill base 49.9 The viscosity of the paint is adjusted to 17-20 seconds (No. 4 Ford Cup), and sprayed on primed steel panels.
- The panels are baked 25 minutes. The baking temperature at the beginning is 80C. This is increased gradually to 180C
and maintained at 180C over a ten-minute period. The resultant panels have a coating of excellent gloss and organic so]vent resistance (one minute xylene exposure). Appearance and hardness do not noticeably change when water soaked at 32C.
EXAMPLE II
The procedures of Example I are repeated with the following differences: (1) the reactant monomers and the chain transfer agent used in the monomer emulsion of Step II
are as follows:

B

~067232 Reactant Monomers and Chain Parts by Weight Transfer Agent methyl methacrylate 49.0 methacrylic acid 5.0 butyl acrylate 30.0 ethyl acrylate 16.0 l-octanethiol 0.1 and ~2) the reactor charge is heated up to 55 + 5C with nitrogen purging. The emulsifie~ monomers are added for a period of four hours. Reaction is continued for another two hours with the temperature maintained at 55 + 5C. The latex thus obtained is cooled, filtered, and used in the formulation of a water-based enamel as in Example I.
EXAMPLE III
. .
A series of water dilutable polymers are prepared as in Step I of Example I and employed in place of the water dilutable polymer of Step I, Example I in the water-based paint described in Example I. The procedures of prepar-ation are the same as used in Step I of Example I. The materials employed in preparing these "solution polymers" and the molecular weights and glass transition temperatures of the resultant copolymers are set forth below:

` lQ67Z32 Materials Polymer Designation A B C D E
styrene 25 methyl methacrylate 50 45 35 35 methacrylic acid 10 15 15 15 15 butyl acrylate 30 25 40 50 50 ethyl acrylate 10 butyl methacrylate 35 Triton X-200 2.8 2.8 Triton X-305 3.6 3.6 3.6 3.6 . 3.6 Aerosol 22( ) 2.4 2.4 2.4 l-octanethiol 1 1.5 2 1.5 Properties of Polymer (Mn) 7500 5400 4000 5400 7500 !
Tg, C -8 16 25 8 8 (I) Aerosol 22 is a product of American Cyanamlc Comp.any.
EXAMPLE IV
A series of emulsion polymers are prepared as in Step II of Example I and employed in place of the emulsion polymer of Step II, Example I. The procedures are the same as used in Step II of Example I. The materials employed in preparing these "emulsion polymers" and the molecular weights and glass transition temperatures of the resultant copolymers are set forth in the following Table:

a~ ~D 00 H N ,~ ~ ~ O O

~ ~ In N ,~ U) ~I N ~ O o U~

a~ ~D 1`
C~ O O O CO N ~ O ~
o~ .

O ' E4 11~ 0 N ~ O O U~

~D ~
. O t~ O ~ N ~ O O N

P

14 ~ O t~ ~ It~ ~1 ~ O O
. ~
C~ N N N ~r o N
U~
~`7 . ~D 'I
m "~ O u~ o ~) N ~ o ~
I`

N N N N o ~

u o U~ o;

o ~ o ~ O O rl IJ rl 0 ~ ~ O rl N t~) ~ h ~3 1 I N
:E: ~ ~ ~ Q. ~d X X
o ~ o o h ~ ~ ~ O

~XAMPLE V
~ater-based enamel is prepared by mixing the follow-ing materials:
Mate-ials Parts by Weight Mill base (prepared by pebble milling) polymer (solution polymer)18.8 from Step I, Example I
Cymel 300(I) 4.6 10 . titanium dioxide pigment16.~
water 7~3 (1) defined in Example I.
Other materials (to let down) ... . . ~
polymer (emulsion polymer from 47.0 Example II
i 10% aqueous 2(dimethylamino)ethanol 4.4 - 10% aqueous p-toluene sulfonic acid 1.0 (neutralized with 2-(dimethylamino) ethanol) The above enamel is sprayed on primed steel panels and baked for 25 minutes. The initial temperature of the bake is 80C and this is raised gradually to 180C where the latter temperature is maintained for 10 minutes. The appearance of the baked panel and the properties of the baked coating are essentially the same as those obtained in Example I.
EXAMPLE VI
A water-based enamel is prepared by mixing the following materials:

Mill Base (Prepared bv ball millin~) Parts bY Weight polymer "D" of Example III (solution 18.5 polymer) Cymel 301 ) 7.6 titanium dioxide pigment 16.5 water 8.4 Other Materials (to let down) polymer "G" of Example IV (emulsion 46.1 polymer 10% aqueous 2-(dimethylamino)ethanol 2.9 (1) a product of American Cyanamid Company, and a commercial grade of hexamethoxymethylmelamine.
This enamel is adjusted to a viscosity of 17-20 seconds (No. 4 Ford Cup), by adding water and sprayed over primed steel panels. The coated steel panels are baked at 160C for 25 minutes. The baked coatings exhibit good gloss, good solvent resistance and retained their gloss and hardness after soaking in water at 32C for 240 hours.
EXAMPLE VII

_ _ _ A water-based enamel is prepared by mixing the - following materials:
Mill Base (pre~ared by ball milling) Parts by Weight polymer "A" of Example III (solution 14.8 polymer~
Cymel 300(1) 4.5 titanium dioxide pigment 17.7 water 9 Other Materials (to let down) polymer "A" of Example IV (emulsion 49.4 polymer) 10% aqueous 2(dimethylamino)ethanol 3.6 10% aqueous p-toluene sulfonic acid 11 (1) defined in Example I

106~232 This enamel is adjusted to a viscosity of 20 seconds (No. 4 Ford Cup) by adding water, and sprayed over primed steel panels. These coatings are baked for 25 minutes.
The initial baking temperature is 80C and this is gradually raised to 180C where it is maintained for at least 10 minutes. These coatings exhibit good physical properties.
EXAMPLE VIII
A water-based enamel is prepared by mixing the following materials:
Mill Base (prepared by ball milling) Parts by Weight Polymer "B" of Example III (solution 12.4 polymer) titanium dioxide pigment 16.3 Cymel 301(1) 8.3 water 8.3 (1) defined in Example VI.
Other Materials (to let down) Polymer "IN of Example IV (emulsion 45.6 polymer) 10% 2-(dimethylamino)ethanol9.1 This enamel is adjusted to a viscosity of 20 seconds (No. 4 Ford Cup) by adding water and sprayed on primed steel panels. The coated panels are baked at 160C
- for 25 minutes. The coatings thus obtained exhibit excellent gloss 80 at 20 and good solvent resistance.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a method for producing an aqueous dispersion of paint in which a carboxy-functional polymer is at least partially neutralized with a water-soluble amine and dispersed with an amino resin cross-linking agent selected from melamine-formaldehyde resins and ure-formaldehyde resins in an aqueous solution of water and water-soluble amine, wherein said carboxy functional polymer, amino resin cross-linking agent and water-soluble amine constitutes about 30 to 50% by weight of the continuous aqueous phase of the paint with the balance of the continuous aqueous phase being water or a mixture of water and an organic solvent, said water-soluble amine is present in an amount sufficient to provide an aqueous phase pH of about 7.1 to about 8.5 and said water or mixture of water and organic solvent constitute about 50 to about 65% by weight of the paint, the improvement wherein the aqueous dispersion is produced essentially free of organic solvents by intimately dispersing with said water, said amino resin cross-linking agent and said water soluble-amine:
I. an aqueous emulsion consistent essentially of water, water-soluble amine, and about 50 to about 95 parts by weight of an emulsion polymer having functionality selected from carboxy functionality and hydroxy functionality and is a copolymer of acrylic monomers 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 II. about 5 to about 50 parts by weight of a solution polymer which is a carboxy-functional copolymer of acrylic monomers that:
(a) is at least partially neutralized with water-soluble amine, (b) is soluble in said aqueous solution;
(c) has average molecular weight (Mn) in the range of about 3,000 to about 20,000, (d) has Tg in the range of -15°C to 50°C, and (e) has been prepared by emulsion polymerization in water of about 5 to about 25 mole percent of an alpha-beta olefinically unsaturated monocarboxylic acid selected from acrylic and methacrylic acid and 75 to 95 mole percent of other monoethylenically unsaturated monomers consisting essentially of monomers selected from the group consisting of monoacrylates, monomethacrylates and monovinyl hydrocarbons at a temperature between about 45°C and the reflux temperature of the reaction mixture and subsequently at least partially neutralized with water-soluble amine in the water in which it is formed, said amino resin cross-linking agent being present in an amount in the range of about 15 to about 35 weight percent of the sum of the weights of said solution polymer and said emulsion polymer.