MX2007013050A - Method to incorporate pigment into paint by formation of resin beads - Google Patents

Abstract

A coating composition is prepared by polymerizing an addition polymer with a Tg of at least about 60°C in the presence of a particulate pigment having substantially primary aggregate particles to form encapsulated pigment particles, isolating and drying the encapsulated pigment product, and combining the dried encapsulated pigment product with a coating vehicle.

Description

METHOD FOR INCORPORATING PIGMENT IN PAINT THROUGH THE FORMATION OF RESIN BEADS FIELD OF THE INVENTION The present invention relates to processes for pigmenting coating compositions and for preparing coated articles. BACKGROUND OF THE INVENTION A wide variety of pigments are used in coating compositions. and painting, each with its own structure and unique properties. Accordingly, each different pigment tends to behave slightly differently in the coating compositions. The different behaviors of the pigments, such as their effects on the rheology and the viscosity of the coating composition, require special consideration in the formulation and manufacture of the coating composition. In addition, care must be taken to maintain a stable dispersion of the pigment in the coating composition to prevent settling and color deterioration. In general, industrial and automotive coatings are pigmented using dry pigments that have been pre-dispersed in a liquid pigment dispersion. Pigment dispersions are prepared by cutting or shearing the dry pigment, agglomerated in a system resin liquid to separate the pigment agglomerates to the primary particles in pigment aggregates and to intimately associate the resin with the surface of the pigment particles These actions are necessary for the proper development of the color of the pigment in the coating. These pigment dispersions may still exhibit certain problems, including sedimentation and seeding during storage and interactions that affect the physical properties of the paint such as rheology and viscosity. Dispersions of encapsulated pigments have been suggested for certain uses. GB 1 156 653, for example, describes dispersions of pigment coated particles prepared by the steps of grinding or grinding the pigment in a polymer solution and stabilizer, modifying the dispersion to change the organic liquid to a non-solvent, and subsequently encapsulating the dispersed particles by a polymer formed by dispersion polymerization of a second polymer that is insoluble in the organic liquid. The change of the organic liquid can be carried out by adding a liquid that is a non-solvent for the polymer or, if the liquid is a mixture of solvent and non-solvents, removing part of the solvent component, for example, by evaporation or partition. The process described in GB 1 156 653 is difficult and complicated. The change in the liquid medium from an organic solvent to an organic non-solvent is not only a stage where the pigment can be destabilized if the conditions are not carefully controlled, but the stage uses a large amount of organic liquids. Thus, the process does not lend itself to modern coatings that limit organic liquids through high solids coatings or waterborne coatings formulations. While the contemporary coatings of GB 1 156 653 in the mid-1960s may have had 83 to 85% by weight of the volatile organic compounds, today's coatings generally have less than 30% by weight of volatile organic compounds. Finally, using the pigment dispersed in the organic liquid to pigment the coatings introduces storage and manufacturing problems that the traditional pigment pastes do not have, in the least, of which is the storage of a much larger amount of organic liquid with the pigment and the introduction of this large amount of organic liquid into the coating composition together with the pigment. U.S. Patent No. 3,849,152 describes the encapsulation of certain inorganic pigments by the dispersion of the pigments in an organic solvent, polymerizing a polysiloxane polymer in the solvent, and then spray drying the dispersion to obtain the encapsulated pigment particles. The inorganic pigment may have hydroxyl groups reactive with the polysiloxane polymer. US Patent No. 3,826,670 describes the preparation of an encapsulated organic pigment with an intermediate layer of an ionically crosslinked polymer salt, such as a polyvalent metal salt of a polymer of an acid. unsaturated, β-ethylenically, and an outer layer of an amorphous, dense, hydrated, silicon, zirconium, or titanium oxide. The encapsulated pigment is reported as chemically inert with excellent dispersibility. US Patent No. 4,771,086 describes the suspension in the aqueous medium of a pigment (eg, Ti02), water insoluble monomer, and water-soluble, non-ionic surfactant. The monomer is further polymerized using an initiator. The encapsulated pigment suspension can be used as a paint with improved hiding power and color compared to conventional latex paints. US Patent No. 3,849,152 describes the pigment suspended in, for example, acetone, hexane, or trichlorethylene, the pigment being completely covered with a liquid of polysiloxane which is then polymerized to a solid form to encapsulate the pigment. The pigment preferably has hydroxyl groups reactive with the polysiloxane. The suspension is spray dried and the pigment coated particles are collected in a standard cyclone collector and dry air at 100 ° C to complete the cure of the encapsulating polysiloxane film. The abstract of O 01/92359 discloses polymerically microencapsulated pigments for coatings prepared from a particle having an average diameter of 10 nm to 1 mm with a surface first reacted with a compound containing reactive groups of phosphoric acid, phosphonic acid, sulphonic acid sulfonate, carboxylate or amino groups, then the active groups bound to the surface are reacted with an initiator containing a leaving group, and, finally, the ATRP graft polymerization is carried out on the initiator with at least one monomer not olefinically saturated. The encapsulated pigments have been manufactured for use in ink jet inks. US Patent No. 6,057,384 discloses an aqueous ink jet inking that includes a colorant associated with the core-shell polymers. The monomers of a first polymer are selected to improve the adhesion to the dye, while the monomers of a second polymer are selected to confer film-forming capacity during drying and a durable film after drying. The polymers are associated with the dye by direct grinding in a liquid phase, as in the Examples in columns 26-35 or by a process of "hot stirring" with the polymer and solvent of the first polymer and grinding in one phase liquid with the second polymer. The ground pigments are diluted with water to prepare the final ink. JP 2000 281951 describes the dissolution or dispersion of a dye in an oil-soluble solvent, then emulsifying it in water. The emulsion and a resin are dissolved in a water-insoluble organic solvent and are in inverted phase with respect to an aqueous emulsion, providing the dye, a surfactant with ethylene oxide chains, and particles containing cationic resin with an average particle size of 0.01 to 2.0 microns. The ink gives an image resistant to scratches, markers and water. JP1111 6881 discloses ink jet inking containing the pigment encapsulated in a hydrophilic resin that can be emulsified in water and a hydrophobic resin that can not be emulsified in water. The ink does not clog the ink jet nozzles and is resistant to time and water. U.S. Patent Application No. 2003/097961 describes grinding together a polymer dissolved in organic solvent with a pigment, adding a crosslinker, emulsifying the mixture in water, removing the organic solvent, and, in the emulsified phase, crosslinking the polymer with the crosslinker. The product is said to be a pigment emulsion encased in a cross-linked polymer. An ink is prepared by gradually adding an aqueous medium containing additional ink components to the dye dispersion. These inkjet inking publications, however, do not address many problems that arise in industrial and automotive coatings, including the problems of forming a continuous protective coating layer, the smoothness of the coating layer, the complex rheological behavior required during the application and curing of the coating composition, and manufacturing interests. Thus, a need remains for a method that would create an intermediate form of a dye that would equalize or neutralize the effects of different pigments on the properties of the coating material. This allows the use of an intermediate with better handling and storage characteristics, capable of reducing the number of process steps required in the manufacture of the paint.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides a method for preparing a thermosetting coating composition that includes a step of incorporating into the thermosetting coating composition a particulate pigment, solid, encapsulated in an addition polymer having a glass transition temperature of at least about 60. ° C. The pigment particles are substantially primary particles in aggregates. A primary aggregate size refers to a pigment particle that is approximately the smallest aggregate size that can be achieved through traditional pigment dispersion techniques, such as milling. The typical average particle sizes for the primary pigment aggregates used in the coatings are from about 0.05 microns to about 2.0 microns. The solid particulate pigment encapsulated in the addition polymer may have an average particle size preferably from about 2 to about 5 microns. The invention further provides a method for coating a substrate with the thermosetting coating composition of the invention and forming a continuous, cured coating layer of the applied composition. In In one embodiment, the encapsulating addition copolymer reacts during curing with another vehicle component of the coating composition. "Vehicle" refers to the resins and polymers that form films, along with any solvent and / or dispersion liquid in the coating composition. The present invention allows to achieve the manufacture of paints and coatings with a better process for the incorporation of the pigments in other dyes and to achieve a more uniform behavior, especially with respect to the rheology and viscosity, between the coating compositions that vary only in its pigment content. An aspect of the present invention is that the pigments and dyes are captured in an account or particle form, approaching a spherical shape. Such particles allow long-term shelf stability and help reduce or eliminate physical and chemical interactions within the paint system during the manufacture and application of coatings. This allows the preparation of pigments in volume for incorporation into the coatings, and allows a more accurate and / or dosed assortment of dyes in the coatings, thus reducing or eliminating the inking operations. The products created by the process according to the present invention they will allow the delivery of the dyes in a paint or coating in wet or dry form depending on the desired process used for the manufacture of the coating paint. Such beads containing colored pigment can be manufactured from a variety of processes and materials. Preferred examples include, but are not limited to, thermoset resins, thermoplastic resins, or UV cured resins. Different formulations may account for differing physical properties such as homogeneity in the paint system, resistance to chemical interactions, and other properties that may benefit coating integrity, durability, or color. The present invention allows the possible design of a resin, or combination of resins used to encapsulate a pigment exhibiting a variety of properties designed to be compatible with the paint system. Such properties include the variation from close to dissolving within a paint system to tough and very hard chemical resins. For example, resistant, very hard chemical resins for the formation of the account would offer the best properties for handling and storage of the intermediate material.

The incorporation of the pigment in the resin according to the present invention, is carried out through a variety of processes, including normal dispersion, and other processes designed to take advantage of the dye manufacturing process, or other types of energy, dilutions, distillations, or stresses such as heat. The advantages of the process according to the present invention in the area of painting manufacture include, among others, making all the dyes have the same neutral effect on the properties of the paint, allowing the color to be made, by dosing by volume or dosage by weight of the colorants, pre-manufacture of the colorant in larger volumes, better quality control, longer shelf life stability, greater versatility of the colorants to be used in a variety of paint technologies with the same coloristic and physical properties. In one aspect of the present invention, the encapsulated pigment could be poured in a dry state. Such pigments could be specifically ordered by particle size, and packaged and handled better than current forms of colored pigments "A" and "an" as used herein indicates that "at least one" of the elements is present, a plurality of such Elements can be present, when possible.

"Approximately" when applied to the values, indicates that the calculation or measurement allows some slight inaccuracy in the value (with some approximation to the accuracy in the value, approximately or reasonably close to the value, closely). If, for some reason, the inaccuracy provided by "approximately" is not otherwise understood in the art with this ordinary meaning, then "approximately" as used herein indicates a possible variation of up to 5% in value. In addition, the areas of applicability of the present invention will be apparent from the detailed description provided below. It should be understood that the detailed description and the specific examples, insofar as they indicate the preferred embodiment of the invention, are presented only for purposes of illustration and are not intended to limit the scope of the invention DETAILED DESCRIPTION OF THE PREFERRED MODALITIES The following description of the ( s) preferred mode (s) is merely exemplary in nature and in no way intended to limit the invention, its application, or uses. A thermosetting coating composition is prepared by combining a thermosetting carrier and at least one solid pigment particle encapsulated in an addition polymer having a transition temperature vitrea of at least approximately 60 ° C. The average particle size of the encapsulated pigment particle product is preferably from about 2 microns to about 5 microns. The pigment contained in the encapsulated particle is preferably a primary pigment aggregate, and may be from about 0.5 to about 2 microns. The pigments used can be inorganic pigments, including metal oxides, chromates, molybdates, phosphates, and silicates. Examples of inorganic pigments and fillers that could be used are titanium dioxide, barium sulfate, carbon black, ocher, sienna, um hematite, limonite, red iron oxide, transparent red iron oxide, black iron oxide, brown iron oxide, chromium oxide green, strontium chromate, zinc phosphate, silicas such as fumed silica, calcium carbonate, talc, barites, ferric ammonium ferrocyanide (Prussian blue), ultramarine, lead chromate, molybdate of lead, and pigments of mica flakes. The method is used particularly beneficially with organic pigments. Examples of useful organic pigments are metallized and unmetallized azo reds, quinacridone reds and violets, perylene reds, copper phthalocyanine blue and green, carbazole violet, yellows of monoarylide and diarylide, benzimidazolone yellows, tolyl orange, naphthol orange, and the like. The addition polymer has a glass transition temperature of at least about 60 ° C, preferably at least about 100 ° C. In particular, the glass transition temperature of the addition polymer is selected to prevent sintering of the encapsulated, solid pigment during storage. The encapsulated pigment can preferably be used as a free-flowing particulate material. For this reason, it is also generally advantageous to avoid the functionalities of the addition polymer which would cause strong interactions causing the binding of the encapsulated pigment. On the other hand, the polymer must have good pigment wetting characteristics. In a preferred method, the encapsulating addition polymer can be formed by emulsifying the addition polymerizable monomer into an aqueous pigment dispersion that has been deagglomerated, preferably reduced to its primary aggregate particle size, and then carrying out the emulsion polymerization of the monomer The encapsulated pigment particles can be separated from the aqueous medium by an appropriate method, such as by air drying or filtration. The particulate product of encapsulated pigment preferably it has an average diameter of about 2 to about 5 microns. The emulsion polymer preferably includes crosslinkable functionality such as, without limitation, active hydrogen groups, oxirane groups, carbodiimide groups, and acetoacetoxy groups. The emulsion polymer can be polymerized from a mixture of monomers that includes a functional monomer with active hydrogen and, when the functional monomer with active hydrogen is not an acidic functional monomer, preferably also includes an acid-functional monomer. Examples of functional monomers with active hydrogen include, without limitation, hydroxyl functional monomers such as hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylates, and hydroxybutyl methacrylates, acid functional monomers including acrylic acid, methacrylic acid, and crotonic acid, and functional monomers with urea and carbamate or monomers with functional groups that are converted to carbamate or urea groups after polymerization such as, without limitation, those described in U.S. Patent 5,866,259, " First Coating Compositions Containing Carbamate-Functional Acrylic Polymers ", the full description of which is incorporated here for reference. Examples of other monomers that can be used to provide the crosslinkable functionality include, without limitation, glycidyl acrylate, glycidyl methacrylate, acetoacetoxybutyl methacrylate, acetoacetoxyethyl acrylate, and carbodiimide methacrylate. Preferably, a sufficient amount of functional monomer is included with active hydrogen to produce an equivalent weight of 1000 or less grams per equivalent, more preferably 800 or less grams per equivalent, and even more preferably 600 or less grams per equivalent In a preferred embodiment, the emulsion polymer forms an anionic dispersion. Examples of suitable functional acid monomers include, without limitation, α, β-ethylenically unsaturated monocarboxylic acid containing 3 to 5 carbon atoms, α, β-ethylenically unsaturated dicarboxylic acids containing 4 to 6 carbon atoms, and anhydrides and monoesters thereof. Examples include, without limitation, acrylic acid, methacrylic acid, crotonic acid, maleic acid or maleic anhydride, itaconic acid or itaconic anhydride, and so on. A sufficient amount of functional monomer is included with acid to produce an emulsion polymer with a number of acids of at least about 1, and preferably the polymer in emulsion has a number of acids of about 1 to about 10. In addition to one or more polymerizable esters of the glycidyl esters of tertiary acids, one or more other ethylenically unsaturated monomers are used as comonomers in the formation of the emulsion polymers of the invention. Examples of such copolymerizable monomers include, without limitation, derivatives of unsaturated α, β-ethylenically unsaturated monocarboxylic acid containing 3 to 5 carbon atoms, including the esters, nitriles, or amides of those acids; diesters of unsaturated dicarboxylic acid, β-ethylenically containing 4 to 6 carbon atoms; vinyl esters, vinyl ethers, vinyl ketones, vinyl amides, and aromatic heterocyclic aliphatic vinyl compounds. Representative examples of amides of methacrylic and acrylic acid and aminoalkyl amides include, without limitation, such compounds as acrylamide, N- (1, 1-dimethyl-3-oxobutyl) -acrylamide, N-alkoxy amides such as methylolamides; N-alkoxy acrylamides such as n-butoxy acrylamide; N-aminoalkyl acrylamides or methacrylamides such as aminomethylacrylamide, l-aminoethyl-2-acrylamide, 1-aminopropyl-2-acrylamide, l-aminopropyl-2-methacrylamide, Nl- (N-butylamino) propyl- (3) -acrylamide and 1-aminohexyl- (6) -acrylamide and 1- (N, N-dimethylamino) -ethyl- (2) -methacrylamide, 1- (?,?, -dimethylamino) -propyl- (3) -acrylamide and 1- (N, N-dimethylamino) -hexyl- (6) -methacrylamide. Representative examples of esters of acrylic, methacrylic, and crotonic acids include, without limitation, those esters of the reaction with saturated cycloaliphatic and aliphatic alcohols containing 1 to 20 carbon atoms, such as methyl, ethyl, propyl, isopropyl, -butyl, isobutyl, tert-butyl, 2-ethylhexyl, lauryl, stearyl, cyclohexyl, trimethylcyclohexyl, tetrahydrofurfuryl, stearyl, sulfoethyl, and isobornyl acrylates, methacrylates, and crotonates, and polyalkylene glycol acrylates and methacrylates.

Representative examples of vinyl monomers that can be copolymerized include, without limitation, such components as vinyl acetate, vinyl propionate, vinyl ethers such as vinyl ethyl ether, vinyl and vinylidene halides, and vinyl ethyl ketone. Representative examples of heterocyclic or aromatic aliphatic vinyl compounds include, without limitation, such components as styrene, α-methyl styrene, vinyl toluene, tert-butyl styrene, and 2-vinyl pyrrolidone. Representative examples of other polymerizable ethylenically unsaturated monomers include, without limitation, such compounds as fumaric, maleic, and itaconic anhydrides (which would provide the acid functionality in the emulsion polymer), monoesters (also provide acid functionality), and diesters. Polyfunctional monomers may also be included to provide a partially crosslinked dispersion. Examples of polyfunctional compounds include, without limitation, ethylene glycol diacrylate, ethylene glycol dimethacrylate, triethylene glycol diacrylate, tetraethylene glycol dimethacrylate, 1,4-butanediol diacrylate, dimethacrylate, 1,6-hexanediol diacrylate and dimethacrylate, Trinylolpropane divinylbenzene, triacrylate and trimethacrylate, pentaerythritol tetaacrylate and tetramethacrylate, and so on. In one embodiment, the encapsulating polymer is a styrene homopolymer or copolymer. The monomers can be polymerized in emulsion in a one-stage or two-stage polymerization according to well-known methods. In a two-stage polymerization, the monomers of the first stage are they add and polymerize first in the aqueous medium, followed by the addition and polymerization of the monomers of the second stage. The aqueous medium may contain a portion of organic solvent, but preferably less than about 5% of the aqueous medium is organic solvent, and preferably no organic solvent is included in the aqueous medium. The appropriate examples of Water-miscible organic solvent include, without limitation, esters, alkylene glycol ethers, alkylene glycol ether esters, lower molecular weight aliphatic alcohols, and so on, Preferably ionic or amphoteric surfactants, such as lauryl sulfate, are included. of sodium, non-ionic surfactants based on polyethoxylated alcohols or block copolymers of polyethoxy-polyalkoxy, polyoxyethylenenonylphenyl ether, polyoxyethylenealkylalkyl ether sulfuric acid esters, alkaline and amino salts of dodecylbenzenesulfonic acid such as the dimethylethanolamine salt of dodecylbenzenesulfonic acid and sodium dodecylbenzenesulfonic acid, and sodium dioctyl sulfosuccinate. The reactor is charged with water and a surfactant. It is preferred to load from about 0.08% by weight to about 0.5% by weight, preferably from about 0.15% by weight to about 0.35% by weight, based on the total weight of the monomers polymerized in the first and second stages, of an anionic surfactant . The combination of monomers to be polymerized in each step can be pre-emulsified in water and 1% to 5% by weight of surfactant, based on the weight of the monomer, before it is added to the reactor. The emulsion polymerization is preferably carried out in the presence of a nonionic surfactant or an anionic surfactant. Suitable surfactants include, without limitation, polyoxyethylenenonylphenyl ether, polyoxyethylene alkylaryl ether sulfuric acid ester, alkaline and amino salts of dodecylbenzenesulfonic acid such as the dimethylethanolamine salt of dodecylbenzenesulfonic acid and sodium dodecylbenzenesulfonic acid, and sodium dioctylsulfosuccinate. In general, the polymerization is carried out at temperatures from about 30 ° C to about 95 ° C, preferably from about 50 ° C to about 90 ° C. A suitable initiator capable of producing free radicals in the polymerization is used. Examples of suitable initiators include, without limitation, azo compounds and peroxy compounds such as azodiisobutyronitrile, 4,4-azobis (4-cyanovaleric acid), benzoyl peroxide, lauroyl peroxide, diisopropyldicarbonate, t-butyl-2-ethylhexanoate. butyl, peroxyisopivalate, persulphate initiators such as ammonium persulfate, potassium persulfate, and sodium persulfate, and alkali metal peroxydiphosphates, in some cases in combination with reducing agents such as sodium disulfite, hydrazine, hydroxylamine and catalytic amounts of accelerators such as salts of iron, cobalt, cerium, and vanadyl, preferably peroxydisulfates of alkali metals or ammonium. Chain transfer agents may be added, if desired, to control molecular weight. Typical chain transfer agents include, without limitation, mercaptan components such as alkyl mercaptans, for example, octyl mercaptan and dodecyl mercaptan, mercaptopropionic acid, and mercaptopropionic acid esters. Polymerization typically proceeds by the polymerization of free radicals. The source of free radicals is typically provided by a redox initiator or by an organic peroxide or azo compound. Useful initiators include, without limitation, ammonium peroxydisulfate, potassium peroxydisulfate, sodium metabisulfite, hydrogen peroxide, t-butyl hydroperoxide, dilauryl peroxide, t-butyl peroxybenzoate, 2,2'-azobis (isobutyronitrile), and redox initiators such as ammonium peroxydisulfate and sodium metabisulfite with ferrous ammonium sulfate. Optionally, a chain transfer agent can be used. Typical chain transfer agents include mercaptans such as octyl mercaptan, n- or tert-dodecyl mercaptan, thiosalicylic acid, mercaptoacetic acid, and mercaptoethanol; halogenated compounds, and alpha-methyl dimer styrene.

The weight ratio of encapsulating polymer to pigment can vary considerably for the encapsulated pigment product. For example, the black pigment may have an extremely small primary aggregate size of less than 0.02 microns, but an encapsulated pigment product having an average particle size of less than about 2 microns would be more difficult to handle. Because of this, an encapsulated black pigment can be made with a relatively high proportion of encapsulating addition polymer. In contrast, the titanium dioxide pigment would most likely have a primary aggregate particle size of about 1 miera, then an encapsulated titanium dioxide product having an average particle size of about 2 microns would include a lower proportion of the polymer of the titanium dioxide. Addition The emulsion polymer can typically have the average molecular weight of about 5,000 to about 1,000,000. In certain embodiments, the emulsion polymer has a weight average molecular weight of from about 10,000 to about 100,000. The theoretical vitreous transition temperature of the emulsion polymer can be adjusted according to methods well known in the art through the selection and distribution of the comonomers. The encapsulating polymer is selected to provide adequate shelf life for the encapsulated pigment material. The encapsulating polymer must have a glass transition temperature or softening point that is high enough so that the encapsulated pigment material does not sinter significantly during storage. In general, the encapsulating polymer should have a glass transition temperature or softening point above the storage temperature, preferably at least about 60 ° C, more preferably at least about 100 ° C. The encapsulating polymer may or may not coalesce in the coating film during curing or cooking of an applied coating layer. The amount of encapsulated pigment added to a coating composition can vary considerably, depending on the desired color properties. The encapsulated pigments can be used in the coating compositions in amounts typically up to 40% by weight of the pigment, based on the total weight of the coating composition. The addition polymer that encapsulates the particulate pigment preferably does not dissolve in the solvent coating medium. In some embodiments of the invention, however, some partial or complete dissolution of the encapsulating addition polymer can provide the desirable color properties in the coating layer prepared from the coating composition. Additional agents may be incorporated into the coating composition, for example hindered amine light stabilizers, ultraviolet light absorbers, antioxidants, surfactants, stabilizers, wetting agents, rheology control agents, dispersing agents, adhesion promoters, etc. . Such additives are well known and can be included in amounts typically used for coating compositions. The coating compositions may be coated on the article by any of several techniques well known in the art. These include, for example, spray coating, dip coating, roller coating, curtain coating and the like. For automotive body panels, spray coating is preferred. The coating composition can be applied on many different substrates, including metal substrates such as bare steel, phosphatized steel, galvanized steel, or aluminum, and non-metallic substrates, such as plastics and composites. The substrate can also be any of these materials that already have a layer in it of another coating, such as a layer of an electrodeposited primer, or priming primer. The coating composition can be applied in one or more steps to provide a film thickness after cure of typically from about 20 to about 100 microns. After the application of the pigmented coating composition to the substrate, the applied coating layer can be overcoated with a layer of a clear coating composition, before or after curing of the pigmented layer, but preferably before with the coating layer. pigmented coating and the transparent coating layer that is cured at the same time in the industry standard "wet wet" method. The coating is cured, preferably by heating at a temperature and for a length of time sufficient to cause the reactants to form an insoluble polymer network. The cure temperature is usually from about 105 ° C to about 175 ° C, and the length of the cure is usually about 15 minutes to about 60 minutes. Preferably, the coating is cured at about 120 ° C to about 150 ° C for about 20 a approximately 30 minutes. The heating can be done, for example, in convection and / or infrared ovens. The invention is further described in the following examples. The examples are merely illustrative and in no way limit the scope of the invention as described and claimed. All parts are parts by weight unless otherwise indicated. Example A suspension is prepared by mixing 100 grams of titanium dioxide in 400 grams of deionized water. The suspension is mixed in a Cowles disperser for about 30 minutes, until the particles in the suspension are less than 10 microns. 20 grams of a monomer mixture (20% by weight of styrene, 30% by weight of hydroxyethyl methacrylate, 45% by weight of butyl methacrylate, and 5% by weight of acrylic acid) are polymerized to the suspension. emulsion, it is stabilized with ABEX EP 110 (anionic surfactant available from Rhodia). The polymerization reaction is initiated by ammonium persulfate. The emulsion polymer is formed on the surfaces of the pigment particle. The suspension of the product is filtered to isolate the pigment. The pigment is rinsed with de-ionized water and dried to produce the encapsulated pigment product A coating is prepared using the encapsulated pigment product. With rapid stirring, 20 parts by weight of a non-pigmented coating mixture (30% solids, comprising as a solid binder 70% an anionic acrylic and 30% hexa (methoxymethyl) melamine) and 10 parts by weight of a dispersion of pigment (prepared by suspending 6 parts by weight of the encapsulated pigment product in a combination of 2 parts by weight of polyester resin and 2 parts by weight of n-propyl ether of propylene glycol, subsequently adding 0.44 parts by weight of an aqueous solution to the 20% amine). Stirring is continued for approximately thirty minutes. The pigment in the resulting coating composition is stable. The coating composition is applied by spraying on a metal substrate (pre-primed). The applied coating is cured by cooking the coated substrate for 20 minutes at 129.44 ° C (265 ° F). The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the essential point of the invention are intended to be within the scope of the invention. Such variations will not be considered as a deviation from the spirit and scope of the invention.

Claims (6)

1. CLAIMS: 1. A method for preparing a coating composition, characterized in that it comprises: (a) preparing a mixture of water, a portion of monomer or polymerizable addition monomers, and a particulate pigment having substantially primary particles in aggregates, ( b) emulsion polymerizing the portion of the polymerizable addition monomer or monomers to produce an addition polymer, wherein the portion of polymerizable monomer or addition monomers is selected such that the addition polymer has a glass transition temperature of at least about 60 ° C and at least substantially encapsulates the pigment particles to form the encapsulated pigment particles, (c) removing the encapsulated pigment particles from the water to form a particulate, encapsulated pigment product, and (d) combining the pigment product with a vehicle comprising at least one resin, at least one reticulum for the resin, and at least one member selected from the group consisting of water and organic liquids to form a coating composition.
2. 2. A method according to claim 1, characterized in that the pigment particles have an average particle size of about 0.1 microns to about 5 microns.
3. 3. A method according to claim 1, characterized in that the addition polymer has a glass transition temperature of at least about 100 ° C.
4. 4. A method according to claim 1, characterized in that the addition polymer is a styrene homopolymer or copolymer. A method according to claim 1, characterized in that when the coating composition is applied to a substrate and cured to form a coating film, the addition polymer forms a part of the coating film. 6. A method according to claim 5, characterized in that the addition polymer reacts with a vehicle component when the composition applied to the substrate is cured.