AQUEOUS DISPERSION OF POLYMERIC PARTICLES

Abstract

An aqueous dispersion of polymeric particles comprising a specific emulsion polymer and a hydroxyl-terminated polysiloxane, and an aqueous coating composition comprising the aqueous dispersion providing coatings manufactured therefrom with improved water resistance, anti-corrosion, and water-repellent properties.

Description

AQUEOUS DISPERSION OF POLYMERIC PARTICLES FIELD OF INVENTION The present invention relates to an aqueous dispersion of polymeric particles and an aqueous coating composition comprising this. BRIEF DESCRIPTION OF THE INVENTION Solvent-based coating compositions comprising epoxy, polyurethane, or alkyd resins are widely used in protective metal coatings due to their anti-corrosion performance, mechanical properties, and appearance. Aqueous or water-based coating compositions are becoming increasingly important compared to solvent-based coating compositions because they pose fewer environmental problems. For some coating applications, such as general industrial finishes and coatings for agricultural construction equipment, coatings with improved anti-corrosion performance are typically required to withstand at least 240 hours of salt spray testing at a dry film thickness of approximately 45–55 µm or even less.In addition, it is desired that water-based coatings in many applications have sufficient water resistance and water repellency properties to meet industry requirements. Ref. 332071 Therefore, there remains a need to provide an aqueous dispersion that provides the anti-corrosive properties described above, as well as other convenient properties. SUMMARY OF THE INVENTION The present invention provides a novel, stable aqueous dispersion of polymer particles prepared by incorporating a hydroxyl-terminated polysiloxane into the polymerization process of a specific emulsion polymer. An aqueous coating composition comprising such an aqueous dispersion can provide coatings made therefrom with improved corrosion resistance, improved water resistance, and / or improved water repellency compared to the same coating compositions, except that the aqueous dispersion is free of either or both the hydroxyl-terminated polysiloxane and the specific emulsion polymer. In a first aspect, the present invention is an aqueous dispersion of polymeric particles comprising an emulsion polymer and a hydroxyl-terminated polysiloxane, wherein the emulsion polymer comprises, by weight based on the weight of the emulsion polymer, more than 0.5% to 1.8% of structural units of an ethylene-unsaturated phosphorous acid monomer, one of its salts or mixtures thereof; and from zero to 5.0% of structural units of a monomer QQpznn / zznz / E / YiAi functional unsaturated with ethylene carrying at least one functional group selected from an amide, carboxyl, carboxylic anhydride, sulfonic acid, sulfonate, sulfuric acid or sulfate group; wherein the hydroxyl-terminated polysiloxane with the polymer particles is present in an amount of 0.1% to 10%, by weight based on the weight of the emulsion polymer. In a second aspect, the present invention is a process for preparing the aqueous dispersion of polymeric particles from the first aspect. The process may comprise: Polymerization of monomers in an aqueous medium in the presence of a hydroxyl-terminated polysiloxane to obtain the aqueous dispersion of polymeric particles, wherein the monomers comprise, by weight based on the total weight of the monomers, more than 0.5% to 1.8% of an ethylene-unsaturated phosphorous acid monomer, one of its salts or mixtures thereof; and from zero to 5.0% of an ethylene-unsaturated functional monomer carrying at least one functional group selected from an amide, carboxyl, carboxylic anhydride, sulfonic acid, sulfonate, sulfuric acid or sulfate group; and wherein the hydroxyl-terminated polysiloxane with the polymeric particles is present in an amount of 0.1% to 10%, by weight based on the weight of the emulsion polymer. In a third aspect, the present invention is an aqueous coating composition comprising the dispersion QQpznn / zznz / E / YiAi of polymeric particles of the first aspect. Qocznn / zznz / E / YiAi DETAILED DESCRIPTION OF THE INVENTION Acrylic in the present invention includes (meth)acrylic acid, alkyl (meth)acrylate, (meth)acrylamide, (meth)acrylonitrile, and their modified forms, such as hydroxyalkyl (meth)acrylate. Throughout this document, the phrase (meth)acrylate refers to both methacrylate and acrylate. For example, (meth)acrylic acid refers to both methacrylic acid and acrylic acid, and (meth)acrylate refers to both methyl methacrylate and methyl acrylate. Aqueous dispersion in the present invention means polymeric particles dispersed in an aqueous medium. Aqueous medium in the present invention means water and from 0 to 30%, by weight based on the weight of the medium, of water-miscible compound(s) such as, for example, alcohols, glycols, glycol ethers, glycol esters, and the like. Structural units, also known as polymerized units, of the named monomer refer to the remainder of the monomer after polymerization; that is, the polymerized monomer or the monomer in its polymerized form. For example, a structural unit of methyl methacrylate is as illustrated: , where the dotted lines represent the attachment points of the structural unit to the main polymer chain. The aqueous dispersion of polymeric particles comprising an emulsion polymer and a hydroxyl-terminated polysiloxane can be prepared by polymerization, e.g., emulsion polymerization, of monomers in an aqueous medium in the presence of one or more hydroxyl-terminated polysiloxanes. The emulsion polymer useful in the present invention may comprise structural units of one or more ethylene-unsaturated phosphorous acid monomers, salts thereof, or mixtures thereof. The ethylene-unsaturated phosphorous acid monomers may be dihydrogen phosphate esters of an alcohol wherein the alcohol contains or is substituted with a polymerizable vinyl or olefinic group.Ethylene-unsaturated phosphorous acid monomers and salts thereof may include phosphoalkyl (meth)acrylates such as phosphoethyl (meth)acrylate, phosphopropyl (meth)acrylate, phosphobutyl (meth)acrylate, salts thereof and mixtures thereof; CH2=C (R)-C (O)-O-(RPO) nP (O) (OH) 2, wherein R=H or CH3, Rp=alkylene and n=l-10, such as SIPOMER PAM-100, SIPOMER PAM200 and SIPOMER PAM-300, all available from Solvay; Phosphoalkoxy (meth)acrylates such as phosphoethylene glycol (meth)acrylate, phosphodiethylene glycol (meth)acrylate, phosphotriethylene glycol (meth)acrylate, phosphopropylene glycol (meth)acrylate, phosphodipropylene glycol (meth)acrylate,. QQpznn / zznz / E / YiAi phosphotripropylene glycol (meth)acrylate, salts thereof and mixtures thereof. The preferred ethylene-unsaturated phosphorous acid monomers and salts thereof are selected from the group consisting of phosphoethyl (meth)acrylate, phosphopropyl (meth)acrylate, phosphobutyl (meth)acrylate, and salts thereof, and mixtures thereof; most preferably, phosphoethyl methacrylate (PEM). The emulsion polymer may comprise, by weight based on the weight of the emulsion polymer, more than 0.5% of structural units of the ethylene-unsaturated phosphorous acid monomer and / or salts thereof, for example, 0.55% or more, 0.6% or more, 0.65% or more, 0.7% or more, 0.75% or more, 0.8% or more, 0.85% or more, 0.90% or more, 0.95% or more, or even 1.0% or more, and at the same time, 1.8% or less, 1.75% or less, 1.7% or less, 1.65% or less, 1.6% or less, 1.55% or less, 1.50% or less, 1.45% or less, or even 1.40% or less.The weight of the polymer in emulsion described in the present description, in the present invention, refers to the dry weight or weight of solids of the polymer in emulsion. The emulsion polymer useful in the present invention may comprise structural units of one or more ethylene-unsaturated functional monomers bearing at least one functional group selected from an amide, carboxyl, carboxylic anhydride, sulfonic acid, sulfonate, sulfuric acid, or sulfate group. The ethylene-unsaturated functional monomers Suitable ethylene monomers may include, for example, β-unsaturated carboxylic acids with ethylene or anhydrides thereof such as (meth)acrylic acid, fumaric acid, (meth)acrylic anhydride, maleic anhydride, or mixtures thereof; sodium styrenesulfonate (SSS), sodium vinylsulfonate (SVS), 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and salts of AMPS, methacrylamide, acrylamide, or mixtures thereof. Preferred ethylene-unsaturated functional monomers include acrylic acid, methylacrylic acid, sodium styrenesulfonate, or mixtures thereof. The emulsion polymer may comprise, by weight based on the weight of the emulsion polymer, zero or more, 0.1% or more, 0.2% or more, 0.3% or more, 0.4% or more, 0.5% or more, and at the same time 5.0% or less, 4.5% or less, 4.0% or less, 3.5% or less, 3.0% or less, 2.5% or less, 2.0% or less, 1.5% or less, 1.2% or less, or even 1.0% or less, of structural units of unsaturated monomer with ethylene carrying at least one functional group. The emulsion polymer useful in the present invention may comprise structural units of one or more ethylene monounsaturated nonionic monomers that are different from the monomers described above. The term "nonionic monomers" in this description refers to monomers that do not contain an ionic charge between pH 1 and 14. The ethylene monounsaturated nonionic monomers may include alkyl esters of (methyl)acrylic acids with an alkyl group having 1 to 20 carbon atoms, 1 to 10 carbon atoms, or 1 to 8 carbon atoms. Examples of suitable ethylene monounsaturated nonionic monomers include methyl acrylate, methyl methacrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, decyl acrylate, lauryl acrylate, methyl methacrylate, butyl methacrylate, isodecyl methacrylate, lauryl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, or combinations thereof;(meth)acrylonitrile; ureidofunctional monomers such as hydroxyethyl ethylene urea methacrylate; monomers bearing acetoacetate functional groups such as acetoacetoxyethyl methacrylate (AAEM); monomers bearing carbonyl-containing groups such as diacetone acrylamide (DAAM); vinylaromatic monomers including styrene and substituted styrene such as α-methylstyrene, p-methylstyrene, t-butylstyrene, vinyltoluene, or mixtures thereof; butadiene; α-olefins such as ethylene, propylene, and 1-decene; vinyl acetate, vinyl butyrate, vinyl versatate, and other vinyl esters; glycidyl (meth)acrylate;or combinations thereof. The preferred ethylene monounsaturated nonionic monomers are selected from the group consisting of methyl methacrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, styrene, or mixtures thereof. The emulsion polymer may comprise, by weight based on the dry weight of the emulsion polymer, 88% or more, 89% or more, 90% or more, 91% or more, or even 92% or more, and at the same time, 99.5% or less, 99% or less, 98.5% or less, or even 98% or less of structural units of ethylene monounsaturated nonionic monomers. The emulsion polymer useful in the present invention may further comprise structural units of one or more ethylene multiunsaturated monomers. Suitable ethylene multiunsaturated monomers may include alkylene glycol diacrylates and dimethacrylates such as, for example, ethylene glycol di(meth)acrylate, butylene glycol di(meth)acrylate, 1,1,1-trimethylolpropane di(meth)acrylate, or pentaerythritol trimethacrylate; divinylbenzene, vinyl (meth)acrylate; allyl (meth)acrylate, N,N-methylenebisacrylamide, and the like; or mixtures thereof. The emulsion polymer may comprise, by weight based on the weight of the emulsion polymer, zero or more, 0.01% or more, 0.05% or more, or even 0.1% or more, and at the same time 5% or less, 3% or less, or even 1% or less, of structural units of the multi-unsaturated monomer with ethylene. The total weight concentration of the structural units described above in the emulsion polymer can be equal to 100. The types and levels of the monomers described above can be selected to give the resulting emulsion polymer a glass transition temperature (Tg) suitable for different applications. The emulsion polymer can have a measured Tg in the range of -20 °C or higher, -15 °C or higher, -10 °C or higher, 5 °C or higher, 0 °C or higher, or even 5 °C or higher, and at the same time, 80 °C or lower, 70 °C or lower, 60 °C or lower, 50 °C or lower, 40 °C or lower, or even 30 °C or lower. By measured Tg, as used herein, is meant the glass transition temperature determined by differential scanning calorimetry (DSC) in accordance with the test method described in the Examples section below. The polymeric particles in the aqueous dispersion also comprise one or more hydroxyl-terminated polysiloxanes. Hydroxyl-terminated polysiloxane in the present description refers to a polysiloxane with two terminal hydroxyl groups. The hydroxyl-terminated polysiloxane useful in the present invention may have the structure represented by formula (I). QQpznn / zznz / E / YiAi where p is an integer from 2 to 100,000, and Ri and R2 can be the same or different and are selected independently of the group consisting of a substituted or unsubstituted alkyl group having from one to 18 carbon atoms, a substituted or unsubstituted alkenyl group having from 2 to 14 carbon atoms, a substituted or unsubstituted aryl group having from 5 to 14 carbon atoms, a fluorinated alkyl group having from one to 14 carbon atoms, and a substituted or unsubstituted aralkyl group having from 6 to 24 carbon atoms. The value of p can be 2 or higher, 3 or higher, 4 or higher, 5 or higher, 10 or higher, 15 or higher, or even 20 or higher, and at the same time, 100,000 or less, 1,000 or less, 400 or less, 120 or less, 100 or less, 75 or less, or even 50 or less.The Rio R2 groups can be, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, dodecyl, vinyl, allyl, phenyl, naphthyl, tolyl, 3,3,3-trifluoropropyl, benzyl, or phenylethyl. Preferably, Ri and R2 are independently methyl, ethyl, propyl, or phenyl. Ri and R2 can be the same. Preferably, Ri and R2 are independently methyl or ethyl. More preferably, Ri and R2 are both methyl. Suitable examples of hydroxyl-terminated polysiloxanes include, for example, hydroxyl-terminated polydimethylsiloxanes. The hydroxyl-terminated polysiloxane useful in the present invention may have a weight average molecular weight of 400 grams per mole (g / mol) or more, 600 g / mol or more, 800 g / mol or more, or even 1000 g / mol or more, at the same time, 1,000,000 g / mol or less, 500,000 g / mol or less, 100,000 g / mol or less, 80,000 g / mol or less, 60,000 g / mol or less, 50,000 g / mol or less, 40,000 g / mol or less, 30,000 g / mol or less, 20,000 g / mol or less, 10,000 g / mol or less, 8000 g / mol or less, 7000 g / mol QQpznn / zznz / E / YiAi or less, or even 6000 g / mol or less. The weight average molecular weight can be determined by gel filtration chromatography (GPC) as described in the Examples section below. The hydroxyl-terminated polysiloxane with the polymer particles may be present in an amount of 0.1% or more, 0.2% or more, 0.3% or more, 0.4% or more, 0.5% or more, 0.6% or more, 0.7% or more, 0.8% or more, 0.9% or more, 1.0% or more, 1.2% or more, 1.5% or more, 1.8% or more, 2.0% or more, 2.2% or more, or even 2.5% or more, and at the same time, 10.0% or less, 9.5% or less, 9.0% or less, 8.5% or less, 8.0% or less, 7.5% or less, 7.0% or less, 6.5% or less, 6.0% or less, 5.5% or less, or even 5% or less, by weight based on the weight of the polymer in emulsion. Hydroxyl-terminated polysiloxane with polymer particles refers in this description to hydroxyl-terminated polysiloxane bonded to the surface of the polymer particles (i.e., on the polymer particles) or embedded in the polymer particles.The hydroxyl-terminated polysiloxane content with the polymer particles can be determined by 1H NMR analysis as described in the Examples section below. The polymeric particles in the aqueous dispersion can have a particle size in the range of 50 to 500 nanometers (nm), 80 to 300 nm, or 100 to 200 nm. The particle size in this description refers to the average size Z and can be measured using a Brookhaven BI-90 Plus particle size analyzer. The aqueous polymer particle dispersion of the present invention can be prepared by polymerization, preferably emulsion polymerization, of the monomers described above in an aqueous medium in the presence of the hydroxyl-terminated polysiloxane. The monomers suitable for preparing the emulsion polymer may include the ethylene-unsaturated phosphorous acid monomer, its salt, or mixtures thereof; the ethylene-monounsaturated nonionic monomer; and optionally, the ethylene-unsaturated functional monomer; and the ethylene-multiunsaturated monomer. In some embodiments, the monomers comprise the ethylene-monounsaturated nonionic monomer, plus 0.5% to 1.8% of the ethylene-unsaturated phosphorous acid monomer, its salt, or mixtures thereof, and zero to 5.0% structural units of the ethylene-unsaturated functional monomer, by weight based on the total weight of the monomers.The monomers for preparing the emulsion polymer may be added pure or as an emulsion in water; or added in one or more additions or continuously, linearly or non-linearly, throughout the reaction period for preparing the polymer particles. The total weight concentration of the monomers for preparing the emulsion polymer may be equal to 100%. The content of each monomer based on the total weight of the monomers may be the same as the content of the monomer as structural units in the emulsion polymer described above, by weight based on the weight of the emulsion polymer; for example, the monomers comprise, by weight based on the total weight of the monomers, more than 0.5% to 1.8%, preferably 0.6% to 1.6%, of the ethylene-unsaturated phosphorous acid monomer, its salt, or mixtures thereof. The hydroxyl-terminated polysiloxane, preferably in an amount of 0.From 1% to 10% by weight, based on the total weight of the monomers (i.e., the weight of the emulsion polymer), may be added before or during the polymerization of the monomers or their combinations. The hydroxyl-terminated polysiloxane may be added to the monomers, added to a polymer seed (e.g., a polystyrene seed) for injection into a reactor, or dispersed in the monomers. In one embodiment, the hydroxyl-terminated polysiloxane is mixed with the monomers before the monomers polymerize. The polymer particles formed after emulsion polymerization are typically hybrid particles of emulsion polymer / hydroxyl-terminated polysiloxane. Not tied to any theory, after the polymerization process, all or most of the hydroxyl-terminated polysiloxanes are with the polymer particles (i.e., in or on the polymer particles). QQpznn / zznz / E / YiAi means that the aqueous medium of the aqueous dispersion of the present invention comprises a substantial absence of hydroxyl-terminated polysiloxane. As used herein, a substantial absence of hydroxyl-terminated polysiloxane means less than 5%, less than 3%, less than 2%, or less than 0% of the total weight of hydroxyl-terminated polysiloxane in the aqueous dispersion (i.e., the total weight of hydroxyl-terminated polysiloxane with the polymer particles and in the aqueous medium of the aqueous dispersion). The hydroxyl-terminated polysiloxane content in the aqueous medium of the aqueous dispersion can be determined by extraction of the aqueous dispersion through hexane according to 1H NMR analysis as described in the Examples section below. The suitable temperature for polymerization of the monomers can be less than 100 °C, in the range of 30 to 95 °C, or in the range of 50 to 92 °C. Multi-stage emulsion polymerization can be used with the monomers described above, where at least two stages are formed sequentially, usually resulting in the formation of a multi-stage polymer comprising at least two polymer compositions. Free radical initiators can be used in the polymerization process. The polymerization process can be thermally initiated or emulsion polymerization with redox initiation. Examples of suitable free radical initiators include hydrogen peroxide, tert-butyl hydroperoxide, eumene hydroperoxide, ammonium and / or alkali metal persulfates, sodium perborate, perphosphoric acid and its salts, potassium permanganate, and ammonium or alkali metal salts of peroxydisulfuric acid. Free radical initiators can typically be used at a level of 0.01 to 3.0 wt%, based on the total weight of the monomers. Redox systems comprising the initiators described above, along with a suitable reducing agent, can be used in the polymerization process.Examples of suitable reducing agents include sodium sulfoxylate formaldehyde, ascorbic acid, isoascorbic acid, alkali metal salts, and ammonium compounds of sulfur-containing acids, such as sodium sulfite, bisulfite, thiosulfate, hydrosulfite, sulfide, hydrosulfide, or dithionite, formadinasulfinic acid, acetone bisulfite, glycolic acid, hydroxymethanesulfonic acid, glyoxylic acid hydrate, lactic acid, glyceric acid, malic acid, tartaric acid, and salts of the above acids. Metal salts of iron, copper, manganese, silver, platinum, vanadium, nickel, chromium, palladium, or cobalt can be used to catalyze the redox reaction. Optionally, chelating agents can be used for the metals. One or more surfactants may be used in the polymerization process. The surfactant may be added before or during the polymerization of the monomers or their combinations. A portion of the surfactant may also be added after polymerization. These surfactants may include anionic and / or nonionic emulsifiers. The surfactants may be reactive surfactants, for example, polymerizable surfactants. Examples of suitable surfactants include alkali metal salts or ammonium salts of alkyl, aryl, or alkylaryl sulfates, sulfonates, or phosphates; alkylsulfonic acids; sulfosuccinate salts; fatty acids; and ethoxylated alcohols or phenols. Preferably, alkali metal salts or ammonium salts of alkyl, aryl, or alkylaryl sulfates are used. The surfactant used is generally from zero to 10%, from 0.5% to 3% by weight, or from 0.8% to 1.5% by weight based on the total weight of the monomers. One or more chain transfer agents can be used in the polymerization process. Examples of suitable chain transfer agents include 3-mercaptopropionic acid, n-dodecyl mercaptan, methyl 3-mercaptopropionate, butyl 3-mercaptopropionate, benzenethiol, alkyl azelaic mercaptan, or mixtures thereof. The chain transfer agent can be used in an amount effective in controlling the molecular weight of the emulsion polymer. The chain transfer agent can be used in QQpznn / zznz / E / YiAi an amount of zero to 5%, from 0.05% to 1%, or from 0.1% to 0.3% by weight, based on the total weight of the monomers. After the polymerization process is complete, the resulting aqueous dispersion can be neutralized by one or more bases as neutralizers to a pH value, for example, at least 7, from 7 to 10, or from 8 to 9.Examples of suitable bases include ammonia; alkali or alkaline earth metal compounds such as sodium hydroxide, potassium hydroxide, calcium hydroxide, zinc oxide, magnesium oxide, sodium carbonate; primary, secondary and tertiary amines, such as triethylamine, ethylamine, propylamine, monoisopropylamine, monobutylamine, hexylamine, ethanolamine, diethylamine, dimethylamine, di-n-propylamine, tributylamine, triethanolamine, dimethoxyethylamine, 2-ethoxyethylamine, 3-ethoxypropylamine, dimethylethanolamine, diisopropanolamine, morpholine, ethylenediamine, 2-diethylaminoethylamine, 2,3-diaminopropane, 1,2-propylenediamine, neopentanediamine, dimethylaminopropylamine, hexamethylenediamine, 4,9-dioxadodecane-1,12-diamine, polyethyleneimine or polyvinylamine; aluminum hydroxide; or mixtures thereof. The aqueous dispersion of the present invention may have a solids content of 20% to 70% by weight or 40% to 60% by weight. The aqueous dispersion of the present invention is a stable aqueous dispersion, as indicated by the absence of phase separation or visible oil-like droplets. QQpznn / zznz / E / YiAi float on the surface after storage at room temperature (23 ± 2 °C) for 1 month or more, 2 months or more, or even 6 months or more. The aqueous dispersion of polymeric particles of the present invention is useful for use in many applications, for example, coatings, adhesives, and inks. The present invention also relates to an aqueous coating composition comprising an aqueous dispersion of polymeric particles. The aqueous dispersion of polymeric particles may be present, by weight based on the total weight of the aqueous coating composition, in an amount of 10% to 80%, 20% to 70%, or 30% to 60%. The aqueous coating composition of the present invention may also comprise one or more pigments. As used herein, the term pigment refers to a particulate inorganic material capable of substantially contributing to the opacity or hiding power of a coating. The materials typically have a refractive index greater than 1.8 and include both inorganic and organic pigments. Examples of suitable inorganic pigments include titanium dioxide (TiO2), zinc oxide, zinc sulfide, iron oxide, barium sulfate, barium carbonate, or mixtures thereof. The preferred pigment used in the present invention is TiO2. TiO2 may also be available in the form of a concentrated dispersion. The aqueous coating composition may also comprise one or more extenders. The term extender refers to a particulate inorganic material having a refractive index less than or equal to 1.8 and greater than 1.3. Examples of suitable extenders include calcium carbonate, aluminum oxide (Al₂O₃), clay, calcium sulfate, aluminosilicate, silicate, zeolite, mica, diatomaceous earth, solid or hollow glass, ceramic microspheres, and opaque polymers such as ROPAQUE™ Ultra E available from The Dow Chemical Company (ROPAQUE is a trademark of The Dow Chemical Company), or mixtures thereof. The aqueous coating composition may have a pigment (PVC) concentration by volume of 10% to 60%, 12% to 55%, 15% to 50%, or 17% to 45%. The PVC of a coating composition may be determined according to the following equation: PVC = [Volume (pigment + extender) / Volume (pigment + extender + binder)] x 100%. The aqueous coating composition of the present invention may comprise one or more coalescing agents. Coalescing agent, in this description, means a compound that can assist dispersed polymer particles to form a homogeneous coating film by lowering the film-forming temperature of the polymer. The coalescing agent typically has a molecular weight of less than 410. Examples of suitable coalescing agents include ethylene glycol ethyl ether, ethylene glycol propyl ether, and ethylene glycol butyl ether. QQpznn / zznz / E / YiAi ether, ethylene glycol hexyl ether, diethylene glycol methyl ether, diethylene glycol ethyl ether, diethylene glycol butyl ether, diethylene glycol hexyl ether, propylene glycol n-butyl ether, dipropylene glycol n-butyl ether, dipropylene glycol methylene ether, tripropylene glycol methyl ether, propylene glycol phenyl ether, propylene glycol tert-butyl ether, 2,2,4-thymethyl-1,3-pentanediol monoisobutyrate, 4-trimethyl-1,3-pentanediol 2,2,diisobutyrate, or mixtures thereof. Commercially available coalescing agents may include, for example, Texanol ester alcohol, OE-300 and OE-400 coalescing agents, all from Eastman Chemical Company, COASOL coalescing agents from Chemoxy International, or mixtures thereof. The coalescing agent may be present in an amount of 0 to 10.0%, 0.2% to 5.0%, 0.4% to 3.0%, 0.6% to 2.0%, or 0.8% to 1.5%, by weight based on the total weight of the aqueous coating composition. The aqueous coating composition of the present invention may comprise one or more matting agents. Mating agents in this description refer to any inorganic or organic particles that provide a matting effect. The matting agents may be selected from silica matting agents, diatomaceous earth matting agents, polyurea, polyacrylate, polyethylene, polytetrafluoroethylene, or mixtures thereof. The matting agent may be present, by weight of solids based on the total weight of the aqueous coating composition, in an amount of 0 to 10%, 0.1% to 8%, or 0.5% to 5%. The aqueous coating composition of the present invention may further comprise one or more defoamers. Defoamers herein refer to chemical additives that reduce and prevent foam formation. The defoamers may be silicone defoamers, mineral oil defoamers, ethylene oxide / propylene oxide defoamers, alkyl polyacrylates, or mixtures thereof. The defoamer may be present, by weight based on the total weight of the aqueous coating composition, in an amount of 0 to 1.0%, 0.05% to 0.8%, 0.1% to 0.6%, or 0.2% to 0.4%. The aqueous coating composition of the present invention may further comprise one or more thickeners (also known as rheology modifiers). The thickeners may include polyvinyl alcohol (EVA), clay materials, acid derivatives, acid copolymers, urethane-associated thickeners (UAT), polyether urea polyurethanes (PEUPU), polyether polyurethanes (PEPU), or mixtures thereof.Examples of suitable thickeners include alkali swellable emulsions (ASEs) such as sodium- or ammonium-neutralized acrylic acid polymers; hydrophobically modified alkali swellable emulsions (HASEs) such as hydrophobically modified acrylic acid copolymers; associative thickeners such as hydrophobically modified ethoxylated urethanes (HEURs); and cellulosic thickeners such as methylcellulose ethers, hydroxymethylcellulose (HMC), hydroxyethylcellulose (HEC), hydrophobically modified hydroxyethylcellulose (HMHEC), sodium carboxymethylcellulose (SCMC), sodium carboxymethyl 2-hydroxyethylcellulose, 2-hydroxypropyl methylcellulose, 2-hydroxyethyl methylcellulose, 2-hydroxybutyl methylcellulose, 2-hydroxyethyl ethylcellulose, and 2-hydroxypropylcellulose. The preferred thickener is based on HEUR. The thickener may be present, by weight based on the total weight of the aqueous coating composition, in an amount of zero to 5%, from 0.1% to 4%, from 0.2% to 4%, or from 0.3% to 3%. The aqueous coating composition of the present invention may further comprise one or more dispersants. The dispersants may include nonionic, anionic, and cationic dispersants such as polyacids of suitable molecular weight, 2-amino-2-methyl-L-propanol (AMR), dimethylaminoethanol (DMAE), potassium tripolyphosphate (KTPP), trisodium polyphosphate (TSPP), citric acid, and other carboxylic acids. The polyacids used may include homopolymers and copolymers based on polycarboxylic acids (e.g., molecular weight between 1,000 and 50,000 as measured by GPC), including those that have been modified hydrophobically or hydrofilamentously, for example, QQpznn / zznz / E / YiAi polyacrylic acid or polymethacrylic acid or maleic anhydride with various monomers such as styrene, acrylate or methacrylate esters, diisobutylene and other hydrophilic or hydrophobic comonomers; salts thereof; or mixtures thereof. The dispersant may be present, by weight based on the total weight of the aqueous coating composition, in an amount of zero to 10%, 0.2% to 5.0%, or 0.5% to 1.5%. The aqueous coating composition of the present invention may further comprise water. The concentration of water may be, by weight based on the total weight of the aqueous coating composition, from 30% to 90%, from 35% to 80%, or from 40% to 70%. In addition to the components described above, the aqueous coating composition of the present invention may further comprise any or a combination of the following additives: buffers, neutralizers, wetting agents, anti-mold agents, biocides, anti-scaling agents, colorants, flow agents, antioxidants, leveling agents, adhesion promoters, anti-scratch additives, rapid anti-oxidation additives, anti-corrosion additives, cosolvents, and grinding media. These additives may be present in a combined amount of 0 to 40%, 0.5% to 30%, 1.0% to 20%, or 2.0% to 10%, by weight based on the total weight of the composition. QQpznn / zznz / E / YiAi aqueous coating. The aqueous coating composition of the present invention can be prepared using techniques known in the art of coatings. The process of preparing the aqueous coating composition may comprise mixing the aqueous dispersion of polymer particles with other optional components, for example, pigments and / or other extenders as described above. The components in the aqueous coating composition can be mixed in any order to provide the aqueous coating composition of the present invention. Any of the optional components mentioned above can also be added to the composition during or before mixing to form the aqueous coating composition. When the aqueous coating composition comprises pigments and / or extenders, the pigments and / or extenders are preferably mixed with the dispersant to form a pigment and / or extender suspension. The present invention also provides a method for providing a coating on a corrosion-susceptible substrate, such as a metal, comprising: applying the aqueous coating composition to the substrate and drying, or allowing to dry, the aqueous coating composition to form the coating. The aqueous coating composition can provide the coating with improved corrosion resistance, for example, a blister rating of 6M or QQpznn / zznz / E / YiAi better and an oxidized surface rating of 7P or better, for a coating with a thickness of 45–55 µm after exposure to salt spray for at least 240 hours. The aqueous coating composition may also provide the coating with improved water resistance, for example, a blister rating of 5 or higher, preferably 6 or higher, more preferably 7 or higher; and an oxide rating of 6 or higher. The aqueous coating composition may also provide the coating with good water repellency (also as a droplet effect), as indicated by a droplet score of 3 or higher, or even 4 or higher. These properties are measured according to the test methods described in the Examples section below. The aqueous coating composition of the present invention can be applied to, and adhere to, various substrates. Examples of suitable substrates include wood, metals, plastics, foams, stones, elastomeric substrates, glass, fabrics, concrete, or cementitious substrates. The aqueous coating composition, which preferably comprises the pigment, is suitable for various applications such as marine protective coatings, general industrial finishes, protective metal coatings, automotive coatings, traffic paint, and finishing systems. QQpznn / zznz / E / YiAi Exterior Insulation and Finish System (EIFS), wood coatings, coil coatings, plastic coatings, can coatings, architectural coatings, and civil engineering coatings. The aqueous coating composition is particularly suitable for protective metal coatings. The aqueous coating composition can be used as a primer, topcoat, as a single-coat coating, directly onto metal, or in combination with other coatings to form multi-coat coatings. The aqueous coating composition of the present invention can be applied to a substrate by current means including brushing, dip enameling, laminating, and spraying. Preferably, the aqueous composition is applied by spraying. Standard spraying techniques and equipment can be used for spraying, such as air atomization spraying, air spraying, airless spraying, low-pressure high-volume spraying, and electrostatic spraying, such as electrostatic hood application, and manual or automatic methods. After the aqueous coating composition of the present invention has been applied to a substrate, the aqueous coating composition can be dried, or allowed to dry, to form a film (i.e., a coating) at room temperature, or at an elevated temperature, for example, from 25 to 80°C. EXAMPLES Some embodiments of the invention will be described below in the following Examples, where all parts and percentages are by weight, unless otherwise specified. Styrene (ST), butyl acrylate (BA), and methacrylic acid (MIA) are available from Shanghai Lang Yuan Chemical Co., Ltd. Sodium p-styrene sulfonate (SSS) (90.5% active) is available from Shanghai Chemical Reagent Co., Ltd. Phosphoethyl methacrylate (PEM) is available from Solvay. PDMS-1, available from The Dow Chemical Company, is a hydroxyl-terminated polydimethylsiloxane with a weight average molecular weight of approximately 5,600 g / mol and a hydroxyl (OH) group weight equivalent of 1.2%. PDMS-2, available from The Dow Chemical Company, is a hydroxyl-terminated polydimethylsiloxane with a weight-average molecular weight of approximately 1,800 g / mol and an OH weight equivalent of 4.8%. The surfactant Disponil FES-32 (solids: 31%), available from Cognis, is a sodium salt of fatty alcohol ether sulfate. AMP-95 (solids: 95%), available from Angus Chemical QQpznn / zznz / E / YiAi Company, is 2-amino-2-methyl-l-propanol and is used as a neutralizer. TAMOL™ 681 dispersant (a hydrophobic copolymer pigment dispersant), OROTAN™ CA-2500 dispersant (a hydrophobic copolymer pigment dispersant), and ROPAQUE™ ULTRA E opaque polymer are available from The Dow Chemical Company. The ACRYSOL™ RM-12W, ACRYSOL RM8W and ACRYSOL RM-2020 NPR rheology modifiers, available from The Dow Chemical Company, are hydrophobically modified ethylene oxide urethane (HEUR) nonionic rheology modifiers. Tego Foamex 825 antifoam is available from Evonik Industry Co., Ltd. Nopco NXZ antifoam is available from Japan Nopco. The coalescing agent TEXANOL is available from The Eastman Chemical Company. Ti-Pure R-706 titanium dioxide as a pigment is available from The Chemous Company. Calcium dioxide CC-1500, available from Huangtian Chengxin Calcium Carbonate Powder Company, is used as a diluent. Natrosol 250 HBR water-soluble hydroxyethylcellulose is available from Ashland Specialty Chemical Company. TAMOL, ACRYSOL and OROTAN are trademarks of The Dow Chemical Company. The following equipment and methods are used in the Examples QQpznn / zznz / E / YiAi standard analytical. Measured glass transition temperature (Tg) The glass transition temperature (Tg) was measured by DSC. A 510-milligram (mg) sample was analyzed on a sealed aluminum tray using a TA DSC Q2000 instrument equipped with an automatic sample loader under a nitrogen (N2) atmosphere. Tg was measured by DSC with three cycles: 60 to 1500 °C, 10 °C / min (1st cycle, then held for 5 minutes to clear the sample's thermal history); 150 to -60 °C, 10 °C / min (2nd cycle); and -60 to 150 °C, 10 °C / min (3rd cycle). Tg was obtained from the 3rd cycle using the mean height method. 1H NMR analysis Five grams of each aqueous dispersion to be tested were mixed with 15 mL of hexane. The resulting mixture was stirred overnight. The hexane phase was then separated and dried under a nitrogen atmosphere. The dried residue of the hexane phase was sent for 1H NMR analysis. An 1H NMR measurement was performed to quantify the amount of polydimethylsiloxane (PDMS) in the extracted hexane phase (i.e., the amount of PDMS in the aqueous medium of the aqueous dispersion). Triphenylphosphine (PPh3) was selected as the internal standard. A mixture of 50 mg of PPh3 and 51 mg of PDMS-1 was used as the standard sample for the aqueous dispersions of Examples 6, 7, and 9. Chloroform-DL was used as the solvent. The hydroxyl-terminated polysiloxane content with the polymer particles was reported, by weight based on the weight of the polymer in emulsion. The PDMS extraction ratio was also reported.The PDMS extraction ratio represents the PDMS content present in the aqueous medium of an aqueous dispersion, by weight based on the total weight of PDMS in the aqueous dispersion (i.e., the total weight of PDMS with the polymeric particles and in the aqueous medium). GPC Analysis The molecular weights of a hydroxyl-terminated polysiloxane sample (e.g., PDMS-1 or PDMS-2) were measured by GPC analysis using an Agilent 1200. The sample was dissolved in 30 mL of tetrahydrofuran (THF) / formic acid (FA) (95:5 v / v) at a concentration of 2 mg / mL, stirred for 1 hour, and allowed to stand overnight. It was then filtered through a 0.45 µm polytetrafluoroethylene (PTFE) filter prior to GPC analysis. The GPC analysis was performed using the following instrumental conditions: Columns: one PLgel GUARD column (10 pm, 50x7.5 mm) (132#), two Mixed B columns (7.8x300 mm) in succession (114#,115#); column temperature: 40 °C; mobile phase: THF / FA (5%); flow rate: 1.0 ml / min; injection volume: 100 pl; detector: Agilent refractive index detector, 40 °C; and calibration curve: narrow polystyrene PL standards with molecular weights in the range of 2,329,000 to 580 QQpznn / zznz / E / YiAi g / mol, using a polynomial fit 3. Water resistance The coated panels were prepared by applying a test coating composition to a steel sheet using an applicator to form two layers of coating films with a wet film thickness of 120 µm for the first layer and 80 µm for the second layer. The resulting films were then allowed to dry at room temperature for 24 hours. The coated panels were immersed in water for 10 days before recording the degree of rust and blistering. The surface of the panels was then graded for rust and blistering, respectively, according to the evaluation criteria provided in Table A below. For the water resistance test, the acceptable blistering grade is 5 or higher, and the acceptable rust grade is 6 or higher. Table A. Classification criteria for blisters / oxide QQpznn / zznz / E / YiAi Blistered Surface / Percentage Oxidation Classification Less than or equal to 0.01 percent 10 Greater than 0.01 percent and up to 0.05 percent 9 Greater than 0.05 percent and up to 0.1 percent 8 Greater than 0.1 percent and up to 1.0 percent 7 Greater than 1.0 percent and up to 2.0 percent 6 Greater than 2.0 percent and up to 5.0 percent 5 Greater than 5.0 percent and up to 10.0 percent 4 Greater than 10.0 percent and up to 20.0 percent 3 Greater than 20.0 percent and up to 30.0 percent 2 Greater than 30.0 percent and up to 50.0 percent 1 Greater than 50.0 percent 0 Salt spray resistance test The coated panels were prepared by applying a test coating composition to a steel sheet using an applicator to form two layers of coating films with a wet film thickness of 120 µm for the first layer and 80 µm for the second layer. The coated panels were then allowed to dry at room temperature for 7 days to obtain dry films with a total thickness of approximately 50 µm. Salt spray resistance properties were tested by exposing the prepared coated panels to a salt spray environment (5% sodium chloride spray) in accordance with ASTM B117-2011. The exposed cold-rolled steel was covered with tape (3M #471 plastic tape) prior to exposure. A cut mark was made with a razor blade on the lower half of the panels immediately before exposure.The panels were exposed to a salt spray environment for 240 hours and then removed from the salt spray environment. The surface of the panels was then classified for blistering and rust. The results are presented as blister / rust ratings. Blister ratings were performed in accordance with ASTM D714-02 (2010) and consisted of a number and / or one or more letters, as shown. Qocznn / zznz / E / YiAi in Table B. The letters F, M, MD, or D are a qualitative representation of blister density. The number refers to blister size, where 2 is the largest, 8 is the smallest, and 10 is no blisters. The larger the number, the smaller the blister size. Rust classifications are determined by ASTM D610-2001, as shown in Tables C and D. For the 240-hour salt spray test, the acceptable blister classification is 6M or better, and the acceptable rust classification is 7P or better. Table B. Blister classification criteria QQpznn / zznz / E / YiAi Blister Density Abbreviation Blister Size Classification Low F Very large blister 2 Medium M Large blister 4 Medium density MD Small to medium blister 6 Dense D Smallest blister visible to the naked eye 8 No blister 10 Table C. Oxidation index by degree of oxidation Degree of oxidation Classification In spots S General G In points P Table D. Oxidation classification by percentage of oxidized surface Qocznn / zznz / E / YiAi Oxidized Surface Classification Less than or equal to 0.01 percent 10 Greater than 0.01 percent and up to 0.03 percent 9 Greater than 0.03 percent and up to 0.1 percent 8 Greater than 0.1 percent and up to 0.3 percent 7 Greater than 0.3 percent and up to 1.0 percent 6 Greater than 1.0 percent and up to 3.0 percent 5 Greater than 3.0 percent and up to 10.0 percent 4 Greater than 10.0 percent and up to 16.0 percent 3 Greater than 16.0 percent and up to 33.0 percent 2 Greater than 33.0 percent and up to 50.0 percent 1 Greater than 50.0 percent 0 Water repellency Water repellency (also known as beading effect) represents the difficulty water has in wetting the coating surface. A coating composition was poured onto a Leneta black scrubbable test panel (P121-10N) using a 100 µm film caster, starting from the secured end of the panel. The panel was then air-dried horizontally at 25°C for 7 days in a constant temperature room (CTR). The resulting panel was held vertically so that water droplets could flow from the top to the bottom of the panel. Water repellency was visually observed and rated using beading scores as shown in Table E below. A beading score of 3 or higher indicates good water repellency (i.e., good beading effect).Otherwise, if the droplet formation score is less than 3 (<3), it indicates poor water repellency (i.e., no droplet formation effect). Table E. Standard water repellency rating Droplet Formation Score Description 5 No wetting or adhesion of water droplets is observed on the coating surface 4 Wetting is observed by small, individual, circular or elliptical water droplets on the coating surface 3 Wetting is observed by large, individual water droplets on the coating surface 2 Wetting is observed along the discrete trail of water on the coating surface 1 Wetting is observed along the thinnest trail of water on the coating surface 0 Wetting is observed along the entire path of water on the coating surface Example (Ex.) 1 First, a monomer emulsion was prepared by mixing deionized water (DI) (487.42 g), surfactant FES32 (31%, 57.93 g), SSS (90.5%, 5.68 g), BA (964.02 g), ST (721.80 g), MAA (3.48 g), PEM (23.64 g), and PDMS-1 (85.5 g). An initial charge of water was added to a one-gallon vessel equipped with a reflux condenser, addition funnels, and a stirrer, with stirring at 130 rpm. The reaction vessel was heated to 88 °C. Surfactant FES-32 (31%, 4.20 g) was then added to the vessel. A portion of the monomer emulsion (110.74 g) and an ammonium persulfate (APS) solution (6.18 g of APS dissolved in 17.73 g of DI water) were loaded into the reaction vessel. The reaction mixture was maintained for 5 minutes for seed formation at 82–88 °C. The remainder of the monomer emulsion was added over a period of 120 minutes at a temperature between 85 °C and 87 °C. After the addition of the monomer mixture was complete, an APS solution (2.47 g of APS dissolved in 67.18 g of water (DI) and a sodium bisulfate (NaBS) solution (2.62 g of NaBS (solids: 99.8%) dissolved in 66.28 g of water DI), the contents of the reaction vessel were cooled to room temperature. During cooling, a mixture of 4.04 g of tere-butyl hydroperoxide (t-BHP) (solids: 70%) in 28.65 g of water DI and 2.08 g of isoascorbic acid (IAA) in 28.87 g of water DI was added when the temperature reached 65 °C. When the temperature of the vessel reached 50 °C or less, AMP-95 (95%, 27.50 g) was added to adjust the pH of the resulting polymer dispersion above 7. Example 2 The aqueous dispersion of Example 2 was prepared as in Example 1 except that 85.5 g of PDMS-2 was used in the monomer emulsion instead of 85.5 g of PDMS-1. Example 3 The aqueous dispersion of Example 3 was prepared as in Example 1 except that the dosage of PDMS-1 in the monomer emulsion was 8.55 g. Example 4 The aqueous dispersion of Example 4 was prepared as in Example 1 except that the dosage of PDMS-1 in the monomer emulsion was 17.10 g. Example 5 The aqueous dispersion of Example 5 was prepared as in Example 1 except that the dosage of PDMS-1 in the monomer emulsion was 42.75 g. Example 6 The aqueous dispersion of Example 6 was prepared as in Example 1 except that the dosage of PDMS-1 in the monomer emulsion was 25.65 g. The resulting polymer dispersion was analyzed by 1H NMR analysis as described above, and the PDMS extraction ratio was 1.18. Example 7 The aqueous dispersion of Example 7 was prepared as in Example 1, except that the dosage of PDMS-1 in the monomer emulsion was 136.80 g. The resulting polymer dispersion was analyzed by 1H NMR analysis as described above, and the PDMS extraction ratio was 2.76%. Example 8 The aqueous dispersion of Example 8 was prepared as in Example 1 except that the dosage of PDMS-1 in the monomer emulsion was 181.00 g. QQpznn / zznz / E / YiAi Example 9 The aqueous dispersion of Example 9 was prepared as in Example 1 except that the doses of PEM and ST in the monomer emulsion were 10.26 g and 735.13 g, respectively. The resulting polymer dispersion was analyzed by ^-H NMR analysis as described above, and the PDMS extraction ratio was 1.74%. Example 10 The aqueous dispersion of Example 10 was prepared as in Example 1 except that the doses of PEM and ST in the monomer mixture were 27.71 g and 717.57 g, respectively. Comparative Example (Comp) 1 First, a monomer mixture was prepared by mixing DI water (487.42 g), FES-32 surfactant (31%, 57.93 g), SSS (90.5%, 5.68 g), BA (964.02 g), ST (706.05 g), and MAA (42.88 g). An initial charge of water was added to a one-gallon vessel equipped with a reflux condenser, addition funnels, and a stirrer, with stirring at 130 rpm. The reaction vessel was heated to 88 °C. FES-32 surfactant (31%, 4.20 g) was added to the vessel. A portion of the monomer emulsion (110.74 g) and an APS solution (6.18 g of APS dissolved in 17.73 g of DI water) were then charged into the reaction vessel. The reaction mixture was held for 5 minutes for seed formation at 82-88 °C. The remainder of the monomer emulsion was QQpznn / zznz / E / YiAi was added over a period of 120 minutes at a temperature between 85 °C and 87 °C. After the addition of the monomer emulsion, an APS solution (2.47 g of APS dissolved in 67.18 g of water) and a NaBS solution (2.62 g of NaBS (solids: 99.8%) dissolved in 66.28 g of water) were completed, and the contents of the reaction vessel were cooled to room temperature. During cooling, a mixture of 4.04 g of t-BHP (solids: 70%) in 28.65 g of water and 2.08 g of IAA in 28.87 g of water was added when the temperature was 65 °C. When the temperature of the container reached 50 °C or less, AMP-95 (95%, 27.50 g) was added to adjust the pH of the resulting polymer dispersion above 7. Example Comp 2 The aqueous dispersion of Example Comp 2 was prepared as in Example 1 except that the monomer emulsion was prepared by mixing DI water (487.42 g), FES-32 surfactant (31%, 57.93 g), SSS (90.5%, 5.68 g), BA (964.02 g), ST (721.80 g), MAA (3.48 g) and PEM (23.64 g). Example Comp 3 The aqueous dispersion of Example Comp 3 was prepared as in Example Comp 1 except that the monomer emulsion was prepared by mixing DI water (487.42 g), surfactant FES-32 (31%, 57.93 g), SSS (90.5%, 5.68 g), BA (964.02 g), ST (706.05 g), MAA (42.88 g) and PDMS-1 (85.5 g). QQpznn / zznz / E / YiAi Example Comp 4 The aqueous dispersion of Example Comp 4 was prepared as in Example Comp 1 except that the monomer emulsion was prepared by mixing DI water (487.42 g), surfactant FES-32 (31%, 57.93 g), SSS (90.5%, 5.68 g), BA (964.02 g), ST (742.88 g), MAA (3.48 g), PEM (2.57 g), and PDMS-1 (85.5 g). Example Comp 5 The aqueous dispersion of Example Comp 5 was prepared as in Example Comp 1 except that the monomer emulsion was prepared by mixing DI water (487.42 g), surfactant FES-32 (31%, 57.93 g), SSS (90.5%, 5.68 g), BA (964.02 g), ST (715.84 g), PEM (32.84 g) and PDMS-1 (85.5 g). Example Comp. 6 PDMS-1 (23.2 g) was added to 1000 g of the aqueous dispersion from Example Comp 1 at room temperature with stirring for 24 hours. The appearance of the resulting mixture was then evaluated by visual inspection. Many oil-like droplets were observed floating on the surface, indicating that cold mixing is not an efficient way to create a homogeneous and stable paint or binder system. In contrast, all the aqueous dispersions in Examples 1-10 were homogeneous and stable, showing no phase separation and no oil-like droplets floating on the surface, after storage at room temperature for 6 months or after QQpznn / zznz / E / YiAi thermal aging at 50 °C for 10 days. Indicates that the aqueous dispersions of the present invention have better stability than Example Comp 6. The properties of the aqueous dispersions obtained above are shown in Tables 1 and 2. These dispersions were used as binders to prepare coating compositions. Table 1. Physical properties of aqueous dispersions Aqueous Dispersion pH Particle Size1 (nm) Solids Content2, % Viscosity3, cP Tg4, °C Example Comp 1 8.86 118 48.21 196 10.0 Example Comp 2 7.37 128 47.62 86 9.5 Example Comp 3 9.03 122 48.88 186 10.0 Example Comp 4 8.17 118 48.54 339 10.0 Example Comp 5 8.29 123 48.81 343 10.0 Example 1 7.21 125 49.18 149 10.0 Example 2 6.52 120 49.10 130 10.0 Example 3 7.27 125 48.1 131 10.0 Example 4 7.2 128 48.13 122 10.0 Example 5 7.18 124 48.61 142 10.0 Example 6 7.33 118 48.38 316 10.0 Example 7 7.57 121 49.71 125 10.0 Example 8 7.72 117 50.15 160 10.0 Example 9 8.15 115 48.47 335 10.0 Example 10 7.5 119 49.15 107 10.0 ^Particle size was measured using a Brookhaven BI-90 Plus particle size analyzer;2E1 Solids content was measured by weighing 0.7±0.1 g of an aqueous dispersion sample (wet sample weight denoted as W1), placing the sample in an aluminum tray (weight of aluminum tray denoted as W2) in an oven at 150 °C for 25 min, and then cooling and weighing the aluminum tray with the dry sample with the total weight denoted as W3. Solids content is calculated by (W3-W2) / W1*100%;3Viscosity in centipoises (cP) was measured using the BROOK FIELD LVDV-1 Prime viscosity detector at room temperature (spindle no. 2, 60 rpm);4Tg of the aqueous dispersions was measured by DSC. Coating compositions (Coatings Comp 1-5 and Coatings Comp 1-10) The coating compositions for Coatings Comp 1-5 and Coatings Comp 1-10 were prepared through a two-stage process. First, all the grinding stage ingredients, consisting of water (39.3 g), propylene glycol (22.6 g), TAMOL 681 (11.3 g), Tego Foamex 825 (1.1 g), Ti-Pure R-706 (237.7 g), and water (8.4 g), were added sequentially and mixed using a high-speed disperser at 1000 revolutions per minute (rpm) for 30 minutes to obtain a well-dispersed suspension. Next, the ingredients in the downsizing stage, consisting of a binder (610.0 g), Tego Foamex 825 (1.7 g), AMP-95 (95%, 2.0 g), Texanol (14.8 g), ACRYSOL RM-12W (0.6 g), ACRYSOL RM-8W (1.0 g), water (46.4 g), and 15% NaNO2 (13.0 g), were sequentially added to the suspension. The types of binders (i.e., the prepared aqueous dispersions) used for each coating composition are given in Table 2.Each of the coating compositions obtained had a PVC of. QQpznn / zznz / E / YiAi 17.24%, volume solids of 42.33% and weight solids of 53.69%. The resulting coating compositions were evaluated for water resistance and salt spray resistance properties according to the test methods described above and the results are provided in Table 2. As shown in Table 2, the binders prepared in the absence of PEM and PDMS (Example Comp 1), or in the absence of PEM (Example Comp 3), both provided coatings with poor oxidation resistance performance, scoring 2–3 in the water resistance test and 1S in the salt spray resistance test (Coatings Comp 1 and 3). The binder in Example Comp 2, comprising the emulsion polymer having PEM structural units but free of PDMS, provided coatings with poor blistering resistance in the water resistance test, scoring only 2. In contrast, all the binders in Examples 1–10, comprising emulsion polymers prepared in the presence of a specific amount of PEM and PDMS, provided coatings with improved water resistance and salt spray resistance properties.It is believed that there is a synergy between PDMS and PEM in improving water resistance and durability. QQpznn / zznz / E / YiAi to salt spray. Table 2. Water resistance and anti-corrosion properties QQpznn / zznz / E / YiAi (resistance to salt fog) Coating Composition Binder (Aqueous Dispersion) Water Resistance Salt Spray Resistance Blisters Oxide Blisters Oxide Coating Comp 1 Example Comp 1 7 3 6D 1S Coating Comp 2 Example Comp 2 2 7 6M 5G Coating Comp 3 Example Comp 3 7 2 6D 1S Coating Comp 4 Example Comp 4 2 3 6D OS Coating Comp 5 Example Comp 5 1 6 6F 7G Coating 1 Example 1 7 9 8F 9P Coating 2 Example 2 8 9 10F 9P Coating 3 Example 3 6 7 6F 8P Coating 4 Example 4 7 8 6M 7P Coating 5 Example 5 8 9 8F 9P Coating 6 Example 6 8 9 10F 9P Coating 7 Example 7 7 9 9F 9P Coating 8 Example 8 7 9 9F 9P Coating 9 Example 9 5 9 8F 8P Coating 10 Example 10 6 9 8F 8P Coating compositions (Coatings Comp 6-10 and Coatings Comp 11-20) The coating compositions for Coatings Comp 6-10 and Coatings Comp 11-20 were prepared according to the same procedure as for preparing Coating 1 above. First, all the ingredients in the milling stage, consisting of water (180.0 g), Natrosol 250 HBR (1.0 g), Nopco NXZ (2.0 g), OROTAN CA-2500 (13.0 g), AMP-95 (95%, 1.0 g), Ti-Pure R-706 (230.0 g), and CC-1500 (95.0 g), were added sequentially and mixed with a high-speed disperser at 1000 revolutions per minute (rpm) for 30 minutes to obtain a well-dispersed suspension. Then, the ingredients in the reduction stage consisting of a binder (330.0 g), propylene glycol (15.0 g), Texanol (8.0 g), ROPAQUE Ultra E (50.0 g), Nopco NXZ (1.0 g), ACRYSOL RM-8W (1.5 g), ACRYSOL RM-2020 NPR_ (1.0 g) and water (71.5 g) were added sequentially to the suspension.The types of binders (i.e., the prepared aqueous dispersions) used to prepare each coating composition are given in Table 4. Each of the resulting coating compositions had a PVC content of 45.96%, volume solids of 34.50%, and weight solids of 49.97%. The resulting coating compositions were evaluated for droplet formation properties according to the test methods described above, and the results are provided in Table 3. As shown in Table 3, Coatings Comp 6 and 7 provided a droplet formation score of 0, indicating no droplet formation effect. Coatings Comp 8-10 provided poor water repellency properties with droplet formation scores of 2. In contrast, Coatings 11-20 of the present invention provided a clear improvement in water repellency performance as indicated by droplet formation scores of 3 or higher, indicating a good droplet formation effect. QQpznn / zznz / E / YiAi Table 3. Water repellency properties Coating Composition Binder (Aqueous Dispersion) PDMS* (%) PEM* (%) Droplet Formation Score Coating Comp 6 Example Comp 1 0 0 0 Coating Comp 7 Example Comp 2 0 1.4 0 Coating Comp 8 Example Comp 3 5.0 0 2 Coating Comp 9 Example Comp 4 5.0 0.15 2 Coating Comp 10 Example Comp 5 5.0 1.9 2 Coating 11 Example 1 5.0 1.4 4 Coating 12 Example 2 5.0 1.4 4 Coating 13 Example 3 0.5 1.4 3 Coating 14 Example 4 1.0 1.4 4 Coating 15 Example 5 2.5 1.4 4 Coating 16 Example 6 1.5 1.4 4 Coating 17 Example 7 8.0 1.4 4 Coating 18 Example 8 10.0 1.4 4 Coating 19 Example 9 5.0 0.6 3 Coating 20 Example 10 5.0 1.6 3 *by weight based on the weight of the polymer in emulsion. Coating Comp Composition 21 To the previous coating composition of Coating Comp 2, PDMS-1 was added at a rate of 5 wt% based on the binder solids (Example Comp 2) in the coating composition of Coating Comp 2. The resulting coating composition was stored overnight and then plotted on a black and white Leneta chart with a wet film thickness of 100 µm. The resulting coating film immediately exhibited severe shrinkage cavities and was not qualified for further performance evaluation. In contrast, all coating compositions of Coatings 1–20 were visually homogeneous and stable. The coating films manufactured from these compositions showed good appearance, and no cavities were observed on the surface of the coating films. It is hereby stated that, as of this date, the best method known to the applicant for putting the aforementioned invention into practice is the one that is clear from the present description of the invention.

Claims

CLAIMS Having described the invention as above, the following claims are claimed as property:

1. An aqueous dispersion of polymeric particles, characterized in that it comprises an emulsion polymer and a hydroxyl-terminated polysiloxane, wherein the emulsion polymer comprises, by weight based on the weight of the emulsion polymer, more than 0.5% to 1.8% of structural units of an ethylene-unsaturated phosphorous acid monomer, a salt thereof, or mixtures thereof; and from zero to 5.0% of structural units of an ethylene-unsaturated functional monomer carrying at least one functional group selected from an amide, carboxyl, carboxylic anhydride, sulfonic acid, sulfonate, sulfuric acid, or sulfate group; wherein the hydroxyl-terminated polysiloxane with the polymeric particles is present in an amount of 0.1% to 10%, by weight based on the weight of the emulsion polymer.

2. The aqueous dispersion according to claim 1, characterized in that the ethylene-unsaturated phosphorous acid monomer is selected from the group consisting of phosphoethyl (meth)acrylate, phosphopropyl (meth)acrylate, phosphobutyl (meth)acrylate, and mixtures thereof. QQpznn / zznz / E / YiAi 3. The aqueous dispersion according to claim 1, characterized in that the emulsion polymer comprises, by weight based on the weight of the emulsion polymer, from 0.6% to 1.6% of structural units of the ethylene-unsaturated phosphorous acid monomer, the salt thereof, and mixtures thereof.

4. The aqueous dispersion according to claim 1, characterized in that the hydroxyl-terminated polysiloxane has a weight average molecular weight of 400 to 1,000,000 g / mol.

5. The aqueous dispersion according to claim 1, characterized in that the hydroxyl-terminated polysiloxane is hydroxyl-terminated polydimethylsiloxane.

6. The aqueous dispersion according to claim 1, characterized in that the polymeric particles have a particle size of 50 to 500 nm.

7. The aqueous dispersion according to claim 1, characterized in that the polymeric particles are formed by emulsion polymerization in an aqueous medium in the presence of the hydroxyl-terminated polysiloxane.

8. The aqueous dispersion according to claim 1, characterized in that the emulsion polymer comprises, by weight based on the weight of the emulsion polymer, QQpznn / zznz / E / YiAi from 0.1% to 3% of structural units of the ethylene-unsaturated functional monomer.

9. The aqueous dispersion according to claim 1, characterized in that the aqueous medium of the aqueous dispersion comprises less than 5% of the hydroxyl-terminated polysiloxane, by weight based on the total weight of the hydroxyl-terminated polysiloxane in the aqueous dispersion.

10. The aqueous dispersion according to claim 1, characterized in that the hydroxyl-terminated polysiloxane with the polymer particles is present in an amount of 0.5% to 10%, by weight based on the weight of the polymer in emulsion.

11. A process for preparing an aqueous polymer particle dispersion according to any of claims 1-10, characterized in that it comprises: the polymerization of monomers in an aqueous medium in the presence of a hydroxyl-terminated polysiloxane to obtain the aqueous polymer particle dispersion, wherein the monomers comprise, by weight based on the total weight of the monomers, more than 0.5% to 1.8% of an ethylene-unsaturated phosphorous acid monomer, a salt thereof, or mixtures thereof; and from zero to 5.0% of an ethylene-unsaturated functional monomer carrying at least one functional group selected from an amide, carboxyl, carboxylic anhydride, sulfonic acid, sulfonate, sulfuric acid, or sulfate group; and wherein the hydroxyl-terminated polysiloxane with the polymer particles is present in an amount of 0.1% to 10%, by weight based on the weight of the emulsion polymer.

12. An aqueous coating composition, characterized in that it comprises the aqueous dispersion of polymeric particles according to any of claims 1-10.