AQUEOUS DISPERSION OF MULTI-STAGE POLYMERIC PARTICLES AND PROCESS FOR ITS PREPARATION

Abstract

An aqueous dispersion of multi-stage polymer particles comprising at least two polymers, a process for preparing the aqueous dispersion of multi-stage polymer particles; and an aqueous coating composition comprising such an aqueous dispersion of multi-stage polymer particles that provides coatings with heat resistance, alcohol resistance, alkali resistance, and acetic acid resistance.

Description

AQUEOUS DISPERSION OF MULTI-STAGE POLYMERIC PARTICLES AND PROCESS FOR ITS PREPARATION FIELD OF INVENTION The present invention relates to a multi-stage aqueous dispersion of polymeric particles and to a process for its preparation. BACKGROUND OF THE INVENTION Water-based or aqueous coating compositions are widely used in industrial and architectural applications because they contribute fewer volatile organic compounds (VOCs), but they still suffer from limitations such as insufficient water and chemical resistance, including resistance to alcohol, acetic acid, and alkali, compared to solvent-based coating compositions. It is particularly challenging for water-based coating compositions, including one- and two-component water-based compositions, to produce coatings with hot water resistance. For example, some applications, such as coatings for kitchen furniture and dining tables, require coatings that resist damage after exposure to hot water (i.e., water at 70 degrees Celsius (°C) or higher), particularly boiling water. J / UUUl Ref. 341571 Therefore, it is preferred to provide an aqueous polymer dispersion, particularly suitable for use in aqueous coating compositions that can provide coatings with hot water resistance while achieving more than good chemical resistance to alcohol, acetic acid and alkali. BRIEF DESCRIPTION OF THE INVENTION The present invention provides a novel aqueous dispersion of multi-stage polymer particles that is particularly suitable for coating applications. An aqueous coating composition comprising such an aqueous dispersion of multi-stage polymer particles provides coatings prepared therefrom with excellent heat resistance rated 4 or higher, while also achieving good chemical resistance, including alcohol resistance rated 4 or higher, alkali resistance rated 4 or higher, and acetic acid resistance rated 3 or higher. These properties can be measured according to the test methods described in the Examples section below. In a first aspect, the present invention is an aqueous dispersion of multi-stage polymer particles, wherein the multi-stage polymer particles comprise, by weight based on the weight of the multi-stage polymer particles, from 38% to 58% of a polymer A having a glass transition temperature of more than 47 °C and 42% to 62% of a polymer B having a glass transition temperature of 40 °C or less, wherein polymer A comprises, by weight based on the weight of polymer A, structural units of a multifunctional monomer containing two or more different ethylenically unsaturated polymerizable groups, from zero to 6% of diacetone (meth)acrylamide structural units, monoethylenically unsaturated nonionic monomer structural units; and optionally, structural units of an acid monomer and / or a salt thereof selected from the group consisting of methacrylic acid, a phosphorous-containing acid monomer or a salt thereof, or mixtures thereof; and wherein polymer B comprises, by weight based on the weight of polymer B, 1.1% to 15% of diacetone (meth)acrylamide structural units, structural units of an acid monomer and / or a salt thereof selected from the group consisting of methacrylic acid, a phosphorous-containing acid monomer or a salt thereof, or mixtures thereof, and structural units of a monoethylenically unsaturated nonionic monomer; and wherein the multi-step polymer particles comprise, by weight based on the weight of the multi-step polymer particles, structural units of the acid monomer and salt thereof in a total amount of 0.1% a. 3.9% and structural units of the multifunctional monomer in a total amount of more than 1.5% to 5%. In a second aspect, the present invention is a process for preparing the aqueous dispersion of multi-step polymer particles by multi-step free-radical polymerization, comprising at least one polymerization step forming a polymer A and at least one polymerization step forming a polymer B to form the multi-step polymer particles. In a third aspect, the present invention is an aqueous coating composition comprising the aqueous dispersion of the first aspect. 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 methyl (meth)acrylate refers to both methyl methacrylate and methyl acrylate. As used herein, the term structural units, also known as polymerized units, of the named monomer refers to the remainder of the monomer after polymerization, or the monomer in its polymerized form. For example, a structural unit of methyl methacrylate is as illustrated: , where the dashed lines represent the attachment points of the structural unit to the polymer backbone. Aqueous composition or dispersion means herein that the particles were dispersed in an aqueous medium. Aqueous medium herein means water and 0 to 30% by weight, based on the weight of the medium, of water-miscible compounds such as alcohols, glycols, glycol ethers, glycol esters, and the like. The glass transition temperature (Tg) in the present invention can be measured by various techniques including, for example, differential scanning calorimetry (DSC) or calculation using the following equation, for example, to calculate the Tg of a copolymer of monomers Ma, Mb and Mc, Tg = Wa* Tga+Wb* Tgb+Wc* Tgcen where Tg is the calculated glass transition temperature for the copolymer, Wa is the weight fraction of monomer Ma in the copolymer, Wb is the weight fraction of monomer Mb in the copolymer, Wc is the weight fraction of monomer Mc in the copolymer, Tga is the glass transition temperature of the homopolymer of monomer Ma, Tgb is the glass transition temperature of the homopolymer of monomer Mb, and Tg is the glass transition temperature of the homopolymer of monomer Mc; all temperatures are in °C. The linear Tg values ​​of some commonly used monomers are summarized in the following table: J / UUUl Monomer Tg of homopolymer (°C) Methyl methacrylate 83 Butyl acrylate -45 Butyl methacrylate 20 2-Ethylhexyl acrylate -65 Styrene 83 Methacrylic acid 155 Acrylic acid 110 Phosphoethyl methacrylate 100 Diacecone acrylamide 85* Allyl methacrylate 94** * Macromolecules. 1983, 16(10), pages 1561-1563; A thesis submitted to the Graduate School of Natural and Applied Sciences of Middle East Technical University, Tugba Vardareli, Polymerization and Characterization of Allyl Methacrylate, 2006 Multi-stage polymer particles in the present description means polymer particles prepared by the sequential addition of two or more different monomer compositions, comprising at least two polymers including a polymer A and a polymer B. By polymer A (also as first-stage polymer) and polymer B (also as second-stage polymer) we refer to these polymers having different compositions and formed in different stages of multi-stage free-radical polymerization to prepare the multi-stage polymer particles. Polymer A and / or polymer B in multi-step polymer particles, preferably polymer B, may each independently comprise structural units of one or more acid monomers, a salt thereof, or mixtures thereof. The acid monomer and / or salt thereof is selected from the group consisting of methacrylic acid, a phosphorous-containing acid monomer or a salt thereof, or mixtures thereof. The phosphorous-containing acid monomers may be monomers containing ethylenically unsaturated phosphorous acid, including, for example, dihydrogen phosphate esters of an alcohol in which the alcohol contains or is substituted with a polymerizable vinyl or olefinic group.Suitable phosphorous acid-containing monomers and salts thereof may include, for example, phosphoalkyl (meth)acrylates such as phosphoethyl (meth)acrylate, phosphopropyl (meth)acrylate, phosphobutyl (meth)acrylate, salts of phosphoalkyl (meth)acrylates, or mixtures thereof; 0H2=0 (R)-0 (O)-O-(RPO)nP (O) (OH) 2, wherein R=H or CH3 and Rp=alkyl, n is from 1 to 20, such as SIPOMER PAM-100, SIPOMER PAM-200, SIPOMER PAM-300, and SIPOMER PAM-4000, all available from Solvay; phosphoalkoxy (meth)acrylates such as phosphoethylene glycol (meth)acrylate, (meth)acrylate of. J / UUUl phosphodiethylene glycol, phosphotriethylene glycol (meth)acrylate, phosphopropylene glycol (meth)acrylate, phosphodipropylene glycol (meth)acrylate, phosphotripropylene glycol (meth)acrylate, allyl ether phosphate, salts thereof, or mixtures thereof. The preferred ethylenically unsaturated phosphorous acid-containing monomers and salts thereof are selected from the group consisting of phosphoethyl (meth)acrylate, phosphopropyl (meth)acrylate, phosphobutyl (meth)acrylate, salts thereof, or mixtures thereof; most preferably, phosphoethyl methacrylate (PEM). Multi-step polymer particles may comprise structural units of the acid monomer and salt thereof in a total 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, 1.1% or more, 1.2% or more, 1.3% or more, 1.4% or more, or even 1.5% or more, and at the same time, 3.9% or less, 3.8% or less, 3.7% or less, 3.6% or less, 3.5% or less, 3.4% or less, 3.3% or less, 3.2% or less, 3.1% or less, or even 3.0% or less, by weight based on the weight of multi-stage polymer particles. Polymer A in multi-stage polymer particles may comprise structural units of the acid monomer and its salt in amounts of zero or more, 0.1% or more, 0.2% or more, 0.5% or more, 0.8% or more, 1.2% or more, 1.5% or more, or even 1.8% or more, and at the same time, 3% or less, 2.8% or less, 2.5% or less, 2.3% or less, 2.1% or less, or even 2.0% or less, by weight based on the weight of polymer A. Polymer B in multi-stage polymer particles may comprise structural units of the acid monomer and its salt in amounts of 0.2% or more, 0.5% or more, 0.8% 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, 2.5% or more, 2.8% or more, or even 3.0% or more, and at the same time, 5.5% or less, 5.2% or less, 5.0% or less, 4.8% or less, 4.5% or less, 4.3% or less, or even 4.0% or less, by weight based on the weight of polymer B. Polymer A and / or polymer B in multi-stage polymeric particles, preferably polymer B, may each independently comprise structural units of diacetone (meth)acrylamide, preferably diacetone acrylamide (DAAM). Polymer A may optionally comprise diacetone (meth)acrylamide structural units in amounts of zero or more, 0.1% or more, 0.2% or more, 0.3% or more, or even 0.5% or more, and at the same time, 6% or less, 5% or less, 4% or less, 3% or less, 2% or less, 1.5% or less, 1.1% or less, or even 1% or less, by weight based on the weight of polymer A. Polymer B may comprise diacetone (meth)acrylamide structural units in amounts of 1.1% or more, 1.2% or more, 1.3% or more, 1.4% or more, 1.5% or more, 1.6% or more, 1.7% or more, 1.8% or more, 1.9% or more, 2.0% or more, 2.2% or more, or 2.4%. or more, 2.5% or more, 2.8% or more, 3.0% or more, 3.2% or less, 3.5% or more, 3.8% or more, J / UUUl % or more, 4.2 % or more, 4.5 % or more, 4.8 % or more, or even 5 % or more, at the same time, 15 % or less, 14 % or less, 13 % or less, 12 % or less, 11 % or less, 10 % or less, 9 % or less, 8 % or less, 7 % or less, 6 % or less, by weight based on the weight of polymer B. Diacetone (meth)acrylamide structural units may be present in multi-step polymer particles in a total amount of more than 0.6%, for example, 0.7 % or more, 0.8 % or more, 1.0 % or more, 1.2 % or more, 1.5 % or more, 1.8 % or more, 2.0 % or more, or even 2.2 % or more, and at the same time, 10 % or less, 9 % or less, 8% or less, 7% or less, 6% or less, 5% or less, 4% or less, or even 3.5% or less, by weight based on the weight of multi-stage particles. Polymer A and / or polymer B in multi-step polymer particles, preferably polymer A, may each independently comprise structural units of one or more multifunctional monomers containing two or more different ethylenically unsaturated polymerizable groups. The two or more different ethylenically unsaturated polymerizable groups typically have different reactivity. Each of the ethylenically unsaturated polymerizable groups may be selected from one of three different categories: (i), (ii), (iii), and (iv): (i) an acryl group, (ii) a methacryl group, (iii) an allyl group (H₂C=CH₂CH₂-), and (iv) an additional ethylenically unsaturated group other than (i), (ii), and (iii). The acryl group may be an acryloxy group or an acrylamino group. The methacryl group may include a methacryloxy group or a methacrylamino group.The additional ethylenically unsaturated group may include a vinyl group, a maleate group, a crotyl group, or a dicyclopentenyl group. Preferably, the multifunctional monomer contains at least one allyl group and at least one acrylate or methacrylate group. Suitable multifunctional monomers may include, for example, allyl (meth)acrylate, allyl (meth)acrylamide, allyloxyethyl (meth)acrylate, crotyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenylethyl (meth)acrylate, diallyl maleate, or mixtures thereof. Multi-stage polymer particles may comprise structural units of the multifunctional monomer in a total amount of more than 1.5%, for example, 1.6% or more, 1.7% or more, 1.8% or more, 1.9% or more, 2.0% or more, 2.1% or more, 2.2% or more, 2.3% or more, 2.4% or more, or even 2.5% or more, and at the same time, 5% or less, 4.9% or less, 4.8% or less, 4.7% or less, 4.6% or less, 4.5% or less, 4.4% or less, 4.3% or less, 4.2% or less, 4.1% or less, 4% or less, 3.9% or less, 3.8% or less, 3.7% or less, 3.6% or less, 3.5% or less, 3.4% or less, 3.3% or less, 3.2% or less, 3.1% or less, or even 3.0% or less, by weight based on the weight of multi-stage polymer particles. Polymer A may comprise structural units of the multifunctional monomer in an amount of 3.1% or more, 3.2% or more, 3.3% or more, 3.4% or more, 3.5% or more, 3.6% or more, 3.8% or more, 4.0% or more, 4.2% or more, or even 4.5% or more, and at the same time, 12% or less, 11% or less, 10% or less, 9% or less, 8% or less, 7% or less, 6.5% or less, 6% or less, 5.5% or less, or even 5% or less, by weight based on the weight of polymer A. Polymer B may comprise structural units of the multifunctional monomer in an amount from zero to 2.0%, for example, less than 1.5%, less than 1.2%, less than 1.0%, less than 0.8%, less than 0.5%, less than 0.3%, less than 0.2%, less than 0.1%, less than 0.08%, less than 0.0.5%, less than 0.04%, less than 0.02%, less than 0.01%, or even zero, by weight based on the weight of polymer B. The multi-stage polymer particles of the present invention may also comprise structural units of one or more monoethylenically unsaturated nonionic monomers other than diacetone (meth)acrylamide. The monoethylenically unsaturated nonionic monomer structural units may be present in polymer A, polymer B, or both polymers A and B. As used herein, the term nonionic monomer refers to a monomer that does not carry an ionic charge between pH 1 and 14.The monoethylenically unsaturated nonionic monomer may comprise any one or any combination of more than one type of monomer selected from alkyl esters of (meth)acrylic acids, aromatic vinyl monomers such as styrene and substituted styrene, vinyl esters of carboxylic acids, (meth)acrylamide, ethylenically unsaturated nitriles such as (meth)acrylonitrile, functional silanes of (meth)acryl such as (meth)acryloxyalkyltrialkoxysilanes, vinyl silanes such as vinyltrialkoxysilanes, or mixtures thereof.The alkyl esters of (meth)acrylic acids useful in the present invention may be C1-C20, CiC10 or Ci-Cs alkyl esters of (meth)acrylic acids including, for example, methyl acrylate, methyl methacrylate, ethyl acrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, isobutyl (meth)acrylate, hexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, oleyl (meth)acrylate, palmityl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, octadecyl (meth)acrylate, hydroxyethyl (meth)acrylate, or hydroxypropyl (meth)acrylate, or mixtures thereof.The vinyl silanes useful in the present invention may comprise any one or any combination of more than one type of monomer selected from alkylvinyldialkoxysilanes, vinyltriethoxysilane, vinyltrimethoxysilane, or mixtures thereof. The (meth)acrylate functional silanes useful in the present invention may comprise any one or any combination of more than one type of monomer selected from gamma-methacryloxypropyltrimethoxysilane, methacryloxypropyltriethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, or mixtures thereof. Preferably, the monoethylenically unsaturated nonionic monomer is selected from the group consisting of methyl methacrylate, methacrylate, ethyl acrylate, butyl methacrylate, butyl acrylate, 2-ethylhexyl acrylate, styrene, or mixtures thereof.Multi-step polymer particles may comprise structural units of the monoethylenically unsaturated nonionic monomer in a total amount of 80% or more, 82% or more, 85% or more, 87% or more, 89% or more, or even 89.5% or more, and at the same time, 97.8% or less, 96% or less, 95% or less, 94% or less, or even 93.5% or less, by weight based on the weight of the multi-step polymer particles. Preferably, polymer A in the multi-stage polymer particles comprises structural units of the acid monomer and / or salt thereof, structural units of the multifunctional monomer, such as J / UUUl methacrylate of aillo, structural units of the monoethylenically unsaturated nonionic monomer, and optionally, structural units of diacetone (meth)acrylamide. More preferably, polymer A comprises, by weight based on the weight of polymer A, 1% to 3% of structural units of the acid monomer and salt thereof, 4% to 6% of structural units of the multifunctional monomer, 89% to 95% of structural units of the monoethylenically unsaturated nonionic monomer, and 0% to 2% of structural units of diacetone (meth)acrylamide. Preferably, polymer B in the multi-step polymer particles comprises structural units of the acid monomer and / or its salt, structural units of the monoethylenically unsaturated nonionic monomer, and structural units of diacetone (meth)acrylamide. More preferably, polymer B comprises, by weight based on the weight of polymer B, 3% to 5% of structural units of the acid monomer and its salt, 87% to 94% of structural units of the monoethylenically unsaturated nonionic monomer, and 3% to 8% of structural units of diacetone (meth)acrylamide. The multi-stage polymeric particles of the present invention may comprise, by weight based on the weight of the multi-stage polymeric particles, from 2% to 3.5% of structural units of the acid monomer and salt thereof, from 1.5% to 3.5% of structural units of diacetone (meth)acrylamide, from 2.0% to 3.0% of structural units of the multifunctional monomer, and from 90% to 94.5% of structural units of the monoethylenically unsaturated nonionic monomer. The multi-stage polymer particles of the present invention comprise polymer A and polymer B. Polymer A in the multi-stage polymer particles may be present in an amount of 38% or more, 38.5% or more, 39% or more, 39.5% or more, 40% or more, 41% or more, 42% or more, 43% or more, 44% or more, or even 45% or more, and at the same time, 58% or less, 57% or less, 56% or less, 55% or less, 54% or less, 53% or less, 52% or less, 51% or less, or even 50% or less, by weight based on the weight of the multi-stage polymer particles. Polymer B in the multi-step polymer particles may be present in an amount of 42% or more, 43% or more, 44% or more, 45% or more, 46% or more, 47% or more, 48% or more, 49% or more, or even 50% or more, and at the same time, 62% or less, 61.5% or less, 61% or less, 60.5% or less, 60% or less, 59% or less, 58% or less, 57% or less, 56% or less, or even 55% or less, by weight based on the total weight of the multi-stage polymer particles. The multi-stage polymer particles may be two-stage polymer particles, where the total weight concentration of polymer A and polymer B in the multi-stage polymer particles is equal to 100%. The multi-stage polymer particles of the present invention may comprise multiple different phases or layers, which are formed by at least polymer A and polymer B. The multi-stage polymer particles may comprise two layers such as an inner layer of polymer A and an outer layer of polymer B. The types and concentrations of monomers described above can be selected to give multi-stage polymer particles a Tg suitable for different applications. Multi-stage polymer particles can have a Tg of 0 °C or higher, 2 °C or higher, 5 °C or higher, 8 °C or higher, 10 °C or higher, 12 °C or higher, 15 °C or higher, 18 °C or higher, 20 °C or higher, 22 °C or higher, 25 °C or higher, or even 30 °C or higher, and at the same time, 70 °C or lower, 68 °C or lower, 65 °C or lower, 62 °C or lower, 60 °C or lower, 58 °C or lower, 55 °C or lower, 50 °C or lower, or even 45 °C or lower. The polymer A in the multi-stage polymer particles may have a Tg of 47 °C or more, for example, 48 °C or more, 49 °C or more, 50 °C or more, 51 °C or more, or even 52 °C or more, and at the same time, 100 °C or less, 95 °C or less, 90 °C or less, 85 °C or less, 80 °C or less, 75 °C or less, 72 °C or less, 70 °C or less, 68 °C or less, 67 °C or less, 65 °C or less, 62 °C or less, or even 60 °C or less.Polymer B in the polymer particles. A multi-stage J / UUU1 can have a Tg of 40 °C or less, for example, 38 °C or less, 35 °C or less, 32 °C or less, 30 °C or less, 28 °C or less, or even 25 °C or less, and at the same time, -10 °C or more, -9 °C or more, -8 °C or more, -7 °C or more, -6 °C or more, -5 °C or more, -4 °C or more, -3 °C or more, -2 °C or more, -1 °C or more, 0 °C or more, 1 °C or more, 2 °C or more, 3 °C or more, 4 °C or more, 5 °C or more, 6 °C or more, 7 °C or more, 8 °C or more, 9 °C or more, or even 10 °C or more. The Tg values ​​are calculated using the equation described above. The multi-stage polymeric particles in the aqueous dispersion of the present invention may have an average particle size of 50 nanometers (nm) or more, 80 nm or more, 90 nm or more, and at the same time, 500 nm or less, 300 nm or less, or even 200 nm or less. The particle size herein refers to the average particle size and can be measured by a Brookhaven BI-90 Plus particle size analyzer. In addition to the multi-stage polymer particles, the aqueous dispersion of the present invention may further comprise one or more polyfunctional carboxylic hydrazides containing at least two hydrazide groups per molecule. The polyfunctional carboxylic hydrazide may act as a crosslinking agent and may be selected from the group consisting of adipic dihydrazide, oxalic dihydrazide, isophthalic dihydrazide, polyacrylic polyhydrazides, or mixtures thereof. The polyfunctional carboxylic hydrazide may be present in an amount of zero or more, 0.05% or more, 0.1% or more, 0.2% or more, or even 0.5% or more, and at the same time, 10% or less, 7% or less, 5% or less, 2% or less, or even 1% or less, by weight based on the weight of the multi-stage polymer particles. The multi-stage aqueous polymer particle dispersion of the present invention further comprises water. The water may be present in an amount of 30% or more, 40% or more, or even 50% or more, and at the same time, 90% or less, 85% or less, or even 80% or less, by weight based on the total weight of the aqueous dispersion. The present invention also relates to a process for preparing an aqueous dispersion comprising multi-stage polymer particles by multi-stage free-radical polymerization, comprising at least one polymerization stage forming polymer A and at least one polymerization stage forming polymer B. In multi-stage free-radical polymerization, at least two stages are formed sequentially, usually resulting in the formation of multi-stage polymer particles comprising at least two polymer compositions such as polymer A and polymer B; optionally, different stages may be formed in different reactors. Each stage polymerizes sequentially and differs from the immediately preceding and / or immediately following stage by a difference in monomer composition.Multi-step free-radical polymerization may include at least one step of forming polymer A by polymerizing a mixture of monomers A in the first step, followed by the formation of polymer B by polymerizing a mixture of monomers B in the second step in the presence of polymer A obtained from the first step. Alternatively, multi-step free-radical polymerization may include forming polymer B by polymerizing the mixture of monomers B in the first step, followed by the formation of polymer A by polymerizing the mixture of monomers A in the second step in the presence of the previously formed polymer B. Each step of the free-radical polymerization may be carried out using well-known polymerization techniques such as suspension polymerization or emulsion polymerization of monomers such as mixtures of monomers A and B.Emulsion polymerization is a preferred process. Monomer composition A and monomer composition B may each independently include the monomers described above to form the structural units of polymer A and polymer B, respectively. J / UUUl The total concentration of monomers in monomer mixture A for preparing polymer A is equal to 100%. The total concentration of monomers in monomer mixture B is also equal to 100%. For each monomer, the weight concentration of that monomer in the total monomers used in preparing a polymer (e.g., polymer A) is substantially equal to the weight concentration of structural units of that monomer in that polymer (e.g., polymer A). As described above, for example, the weight concentration of each monomer in monomer mixture A (i.e., based on the total weight of monomer mixture A) is equal to the weight concentration of structural units of that monomer in polymer A (i.e., based on the weight of polymer A).The mixtures of monomers A and B for preparing polymer A and polymer B, respectively, may be added pure or as an emulsion in water; or they may be added in one or more additions or continuously, linearly or non-linearly, during the reaction period for preparing polymer A, polymer B, respectively, or combinations thereof. The suitable temperature for emulsion polymerization processes may be less than 100 °C, in the range of 30 to 95 °C, or in the range of 50 to 90 °C. In the multi-stage free-radical polymerization process used to prepare the aqueous dispersion of multi-stage polymer particles, one or more free-radical initiators can be used in each stage. 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 concentration of 0.01 to 3.0 wt%, depending on the total weight of the monomers used to prepare the multi-stage polymer.Redox systems comprising the initiators described above coupled 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 and ammonium salts 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. J / UUUl Optionally, chelating agents can be used for metals. In the multi-stage free-radical polymerization process for preparing the aqueous dispersion of multi-stage polymer particles, one or more surfactants may be used in one or more stages of 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. Surfactants may be used for at least one stage or for all stages in preparing the multi-stage polymer particles. Surfactants may include anionic and / or nonionic emulsifiers. Surfactants may be reactive surfactants such as polymerizable surfactants. Examples of suitable surfactants include ammonium or alkali metal salts of alkyl, aryl, or alkylaryl sulfates, sulfonates, or phosphates; alkylsulfonic acids; sulfosuccinate salts; fatty acids; and ethoxylated alcohols or phenols.Preferably, alkali metal or ammonium salts of alkyl, aryl, or alkylaryl sulfate surfactants are used. The combined amount of surfactant used is generally 0 to 10% or 0.5% to 3% by weight, depending on the weight of total monomers used to prepare the multi-stage polymer. In the multi-stage free-radical polymerization process to prepare the aqueous dispersion of the In multi-stage polymer particles, one or more chain transfer agents may be used in one or more stages of the polymerization process. Examples of suitable chain transfer agents include 3-mercaptopropionic acid, methyl mercaptopropionate, butyl mercaptopropionate, n-dodecyl mercaptan, benzenethiol, azelaic alkyl mercaptan, or mixtures thereof. The chain transfer agent may be used in an amount effective in controlling the molecular weight of the polymers in the multi-stage polymer particles; for example, the chain transfer agent may be used in the polymerization stage forming polymer A, the polymerization stage forming polymer B, or both stages. The chain transfer agent can be used in an amount of zero or more, 0.1% or more, 0.15% or more, or even 0.2% or more, and at the same time, 2% or less, 1% or less, 0.5% or less, or even 0.3% or less, by weight based on the total weight of monomers used to prepare the multi-stage polymer particles. The aqueous dispersion obtained from multi-stage polymer particles can be neutralized to a pH of at least 6, for example, from 6 to 10 or from 7 to 9. Neutralization can be carried out by adding one or more bases, which can lead to partial or complete neutralization of the latent ionic or non-ionic groups of the multi-stage polymer. Examples Suitable bases include ammonia; alkali metal 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, aluminum hydroxide; or mixtures thereof.The process for preparing the aqueous dispersion of the present invention may further comprise the addition of the polyfunctional carboxylic hydrazide containing at least two hydrazide groups per molecule described above for the aqueous dispersion. The aqueous dispersion of multi-stage polymer particles of the present invention exhibits good film-forming properties with a minimum film-forming temperature (MFFT) above 20°C, for example, 25°C or higher, 30°C or higher, 35°C or higher, or even 40°C or higher, and simultaneously, 75°C or lower, 70°C or lower, 67°C or lower, or even 65°C or lower. The MFFT is the lowest temperature at which the polymer particles of the aqueous dispersion will bond together and form a continuous film when the volatile component (e.g., water) evaporates. The MFFT can be determined according to the test method described in the Examples section below. The aqueous dispersion of multi-stage polymer particles is useful in many applications, including, for example, wood coatings, metal coatings, construction coatings, and road marking paints. The present invention also relates to an aqueous coating composition comprising the aqueous dispersion of multi-stage polymer particles. The aqueous coating composition may also comprise one or more pigments. The pigments may include particulate inorganic materials that are capable of contributing significantly to the opacity or covering power of a coating. Such materials typically have a refractive index greater than 1.8. Examples of suitable pigments include titanium dioxide (TiO2), zinc oxide, zinc sulfide, iron oxide, barium sulfate, barium carbonate, or mixtures thereof. The aqueous coating composition may also comprise one or more extenders. The extenders may include particulate inorganic materials that typically have a refractive index less than or equal to 1.8 and greater than 1.5. Examples of suitable extenders include J / UUU1 calcium carbonate, aluminum oxide (Al2O3), clay, calcium sulfate, aluminosilicate, silicate, zeolite, mica, diatomaceous earth, solid or hollow glass, ceramic beads, 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. Pigments and / or extenders may be present in amounts of zero or more, 5% or more, 10% or more, or even 15% or more, and at the same time 40% or less, 30% or less, 25% or less, or even 20% or less, by weight based on the total weight of the aqueous coating composition. The aqueous coating composition of the present invention may further comprise one or more defoamers. Defoamer in this description refers to a chemical additive that reduces and prevents 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 in an amount of zero or more, 0.01% or more, or even 0.1% or more, and at the same time, 2% or less, 1.5% or less, or even 1% or less, by weight based on the total weight of the aqueous coating composition. The aqueous coating composition of the present invention may further comprise one or more thickeners (also known as rheology modifiers). The thickeners J / UUUl may include polyvinyl alcohol (PVA), 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 (BASEs) such as hydrophobically modified acrylic acid copolymers; associative thickeners such as hydrophobically modified ethoxylated urethanes (HEURs); and cellulosic thickeners such as methylcellulose ethers, hydroxymethylcellulose (BMC), hydroxyethylcellulose (HEC), hydrophobically modified hydroxyethylcellulose (BMBEC), 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 in an amount of zero or more, 0.01% or more, or even 0.1% or more, and at the same time, 5% or less, 4% or less, or even 3% or less, by weight based on the total weight of the. J / UUUl aqueous coating composition. The aqueous coating composition of the present invention may further comprise one or more wetting agents. Wetting agent, as described herein, refers to a chemical additive that reduces the surface tension of a coating composition, thereby enabling the aqueous coating composition to penetrate or spread more readily across the surface of a substrate. Wetting agents may be polycarboxylates, anionic, amphoteric, or nonionic. The wetting agent may be present in an amount of zero or more, 0.01% or more, or even 0.1% or more, and at the same time, 5% or less, 4% or less, or even 3% or less, by weight based on the total weight of the aqueous coating composition. The aqueous coating composition of the present invention may further comprise one or more coalescing agents. Coalescing, in this description, refers to a slow-evaporating solvent that fuses polymer particles into a continuous film under ambient conditions. Suitable coalescing agents may include, for example, 2-n-butoxyethanol, dipropylene glycol n-butyl ether, propylene glycol n-butyl ether, dipropylene glycol methyl ether, propylene glycol methyl ether, propylene glycol n-propyl ether, diethylene glycol monobutyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, triethylene glycol monobutyl ether, and dipropylene glycol n-propyl ether. J / UUUl n-butyl ether, or mixtures thereof. Preferred coalescing agents include dipropylene glycol n-butyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, n-butyl ether, or mixtures thereof. The coalescing agent may be present in an amount of zero or more, 0.1% or more, or even 1% or more, and at the same time, 12% or less, 10% or less, or even 9% or less, by weight based on the total weight of the aqueous coating composition. In addition to the components described above, the aqueous coating composition of the present invention may further comprise any one or any combination of more than one type of the following additives: regulators, neutralizers, dispersants, wetting agents, biocides, anti-scaling agents, colorants, flow agents, antioxidants, plasticizers, freeze / thaw additives, leveling agents, thixotropic agents, adhesion promoters, scratch-resistant additives, and grinding media. These additives may be present in an amount of zero or more, 0.001% or more, or even 0.1% or more, and at the same time, 5% or less, 3% or less, or even 2% or less, by weight based on the total weight of the aqueous coating composition. The aqueous coating composition of the present invention can be prepared using techniques known in the coating art, for example, by mixing the aqueous dispersion comprising the multi-stage polymer particles with other optional components 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. The aqueous coating composition can be a one-component, water-based wood coating composition. The present invention also provides a method for preparing a coating. The method may comprise: forming the aqueous coating composition, applying the aqueous coating composition to a substrate, and drying, or allowing to dry, the applied coating composition to form the coating. The aqueous coating composition may be applied to a substrate by traditional means, including brushing, dipping, rolling, and spraying. The aqueous coating composition is preferably applied by spraying. Standard spraying techniques and equipment may 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 Whereas the aqueous coating composition of the present invention has been applied to a substrate, the coating composition can be dried, or allowed to dry, to form a film (i.e., a coating) at room temperature (20-25 °C), or at an elevated temperature, for example, from 35 to 60 °C. The aqueous coating composition can provide the coating obtained therefrom (i.e., the film obtained after drying, or allowing to dry, the aqueous coating composition applied to a substrate) and the coated substrate with excellent resistance to hot water at 70 °C or more, at 80 °C or more, or at temperatures between 90 and 100 °C, with a rating of 4 or more.The coating and the coated substrate may also demonstrate resistance to alcohol (48% aqueous ethanol solution, 1 hour) with a rating of 4 or higher, resistance to alkali (10% aqueous sodium carbonate solution, 16 hours) with a rating of 4 or higher, and resistance to acetic acid (10% aqueous glacial acetic acid solution, 16 hours) with a rating of 3 or higher, or even 4 or higher. These properties can be measured according to the test methods described in the Examples section below. The aqueous coating composition of the present invention can be applied and adhered to various substrates. Examples of suitable substrates include concrete, cementitious substrates, wood, metals, stones, elastomeric substrates, glass, or fabrics; preferably, wood. The aqueous coating composition is suitable for various coating applications, such as construction coatings, marine and protective coatings, automotive coatings, wood coatings including furniture coatings, joinery coatings, and flooring coatings, coil coatings, road marking paints, and civil engineering coatings. The aqueous coating composition can be used alone or in combination with other coatings to form multi-layer coatings. 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. The materials used in the Examples and their abbreviations are given below: Methacrylic acid (MAA), acrylic acid (AA), methyl methacrylate (MMA), butyl acrylate (BA), styrene (ST), 2-ethylhexyl acrylate (2-EHA), divinylbenzene (DVB), and allyl methacrylate (ALMA) are available from Sinoreagent Group. Diacetone acrylamide (DAAM) and adipic acid hydrazide (ADH) are available from Shandong Heda. Acetoacetoxyethyl methacrylate (AAEM) is available from The Dow Chemical Company. Phosphoethyl methacrylate (PEM) is available through Solvay. DOWANOL™ DPnB (dipropylene glycol n-butyl ether) and DOWANOL EB (ethylene glycol monobutyl ether), available from The Dow Chemical Company, are used as coalescing agents. The Tego Airex 902w defoamer and the Tego Glida 410 polyether siloxane copolymer antiblocking additive are both available from Evonik. BYK-346 polyether-modified siloxane, available from BYK, is used as a wetting agent. The ACRYSOL™ RM-8W rheology modifier is available from The Dow Chemical Company. ACRYSOL and DOWANOL are trademarks of The Dow Chemical Company. The following standard analytical equipment and methods are used in the Examples and in the determination of the properties and characteristics set out in this description: MFFT measurement The MFFT was measured using a Coesfeld MFFT instrument by casting a 75 pm wet film of a J / UUUl aqueous dispersion sample on a temperature gradient heating plate. The film was dried and the minimum temperature at which a coherent film formed was recorded as the MFFT. Particle size measurement The particle size of polymer particles in an aqueous dispersion was measured using the Brookhaven BI-90 Plus particle size analyzer, which employs photon correlation spectroscopy (light scattering of sample particles). This method involves diluting 2 drops of the aqueous dispersion to be evaluated in 20 mL of 0.01 M sodium chloride (NaCl) solution and further diluting the resulting mixture in a sample cuvette to achieve the desired count rate (K) (e.g., 250 to 500 counts / s for a diameter in the 10–300 nm range). The particle size of the aqueous polymer dispersion was then measured and reported as an average diameter (Z) multiplied by intensity. Hot water resistance The black wood substrate was coated in two layers, applying 80–90 g / m² of a test coating composition for each layer. After the first coat, the panels were left at room temperature for 4 hours and then sanded with sandpaper. After the second coat, the panels were allowed to dry. J / UUUl at room temperature for 4 hours, then in an oven at 50 °C for 48 hours to obtain coated panels for the hot water resistance test. First, 10–20 ml of boiling water were applied to the surface of the coated panels. Then, a stainless steel beaker filled with 350–500 ml of boiling water was placed on top of the coated panels so that the boiling water was between the bottom of the beaker and the coated panels. After 30 minutes, the beaker was removed, and the water residue was wiped off the coated panels. After 1 hour, the trace remaining on the surface of the coated panels was rated on a scale of 0–5, where 0 is the worst and 5 is the best. - No changes: Test area indistinguishable from the adjacent surrounding area. - Minor change: The test area is distinguishable from the adjacent surrounding area only when the light source is reflected off the test surface and back towards the observer's eye, e.g., discoloration; change in brightness and color; and / or no change in surface structure, such as swelling, fiber elevation, cracking and / or bubble formation. - Moderate change: The test area is distinguishable from the adjacent surrounding area, visible in various viewing directions, e.g., discoloration; change in brightness and color; and / or no change in surface structure, such as swelling, fiber elevation, cracking and / or bubble formation. - Significant change: The test area is clearly distinguishable from the adjacent surrounding area, visible in all viewing directions, for example, discoloration; change in brightness and color; and / or slight changes in surface structure, such as swelling, fiber elevation, cracking and / or bubble formation. - Significant change: The surface structure is clearly modified and / or discolored, the brightness and color change, and / or the surface material is totally or partially removed, and / or the filter paper adheres to the surface. Acceptable resistance to hot water is 4 or higher. Alcohol resistance tests, acetic acid resistance tests, and alkali resistance tests Panel preparation: The panels were prepared by brushing, applying three coats at 80-90 g / m² to each type of wood. After the first coat, the panels were left at room temperature for 4 hours, then sanded with sandpaper. After the second coat, the panels were left to dry at room temperature for 4 hours and then oven-dried at 50 °C for 48 hours before testing. J / UUUl following, respectively. Alcohol resistance test: Filter discs were saturated with an aqueous ethanol solution (48%), placed on the finished panels, and covered with a lid to reduce evaporation. After 1 hour, the lid was removed. The tested areas were wiped with moist disposable wipes and allowed to air dry at room temperature to observe the degree of damage. Acid resistance test: Filter discs were saturated with an aqueous solution of glacial acetic acid (10%), placed on the finished panels, and covered with a lid to reduce evaporation. After 16 hours, the lid was removed. The tested areas were wiped with moist disposable wipes and allowed to dry at room temperature to observe the degree of damage. Alkali resistance test: Filter discs were saturated with an aqueous solution of sodium carbonate (NagCOa) (10%), placed on the finished panels, and covered with a lid to reduce evaporation. After 16 hours, the lid was removed. The tested areas were wiped with moist disposable wipes and allowed to dry at room temperature to observe the degree of damage. The degree of damage for the alcohol resistance, acetic acid resistance, and alkali resistance tests, respectively, is rated on a scale of 0-5, where 0 is J / UUUl is the worst, and 5 is the best, as follows: - No changes: Test area indistinguishable from the adjacent surrounding area; - Minor change: The test area is distinguishable from the adjacent surrounding area only when the light source is directed at the test surface and reflected towards the observer's eye. Minor change could be some slight discoloration and brightness change, but no change in surface structure such as swelling, fiber elevation, cracking and / or bubble formation; - Moderate change: The test area is distinguishable from the adjacent surrounding area, visible in various viewing directions, e.g., discoloration; change in brightness and color; but no change in surface structure, such as swelling, fiber elevation, cracking and / or bubble formation; - Significant change: The test area is clearly distinguishable from the adjacent surrounding area, visible in all viewing directions, for example, discoloration; change in brightness and color; and / or slight changes in surface structure, such as swelling, fiber elevation, cracking and / or bubble formation. - Significant change: The surface structure is clearly modified and / or discolored, the brightness and color change, and / or the surface material is totally or partially removed, and / or the filter paper adheres to the surface. The higher the rating, the better the resistance. Acceptable acetic acid resistance is 3 or higher. Acceptable alkali resistance is 4 or higher. Acceptable alcohol resistance is 3 or higher. Pendulum hardness Pendulum hardness (Konig) was measured on a coated glass panel using a BYK pendulum durometer, in accordance with ASTM D4366-16. Test results were reported in seconds. A test coating composition was applied to a glass panel with a wet film thickness of 120 µm, dried at room temperature for 4 hours, and then placed in an oven at 50 °C for 2 days to form the coated glass panel for pendulum hardness measurement. Flexibility test A conical flexibility test was performed to evaluate the ability of a coating film to resist cracking in accordance with GB / T 1731-1993. A test coating composition was spread on the tin plate with a wet film thickness of 120 µm and then dried at 50 °C for 2 days before the test. Impact resistance The impact resistance of a coating film The J / UUUl test was performed in accordance with ASTM 2974. A test coating composition was spread directly onto the tin plate with a wet film thickness of 120 µm and then dried at 50 °C for 2 days prior to testing. Examples (Ejs.) 1-3 and 5 and comparative Ejs. (comp.) 1-4 and 6 of multi-stage (MP) polymer dispersions Preparation of the monomer emulsion 1 (ME1): The surfactant SLS (14.25 g, 25% active) was dissolved in deionized water (DI) (181.4 g), with stirring, and then the monomers listed in Table 1 or 2 were slowly added to the stirred solution to obtain ME1. Preparation of the monomer emulsion 2 (ME2): The surfactant SLS (14.38 g, 25% active) was dissolved in DI water (171.96 g), with stirring, and then the monomers listed in Table 1 or 2 were slowly added to the stirred solution to obtain ME2. A solution containing SLS surfactant (23.87 g, 25% active) and DI water (630.7 g) was placed in a 5-liter, four-necked round-bottom flask equipped with a thermocouple, a cooling condenser, and a stirrer, and heated to 85 °C in nitrogen. An aqueous sodium carbonate solution (1.84 g of sodium carbonate in 61.20 g of DI water) and an aqueous ammonium persulfate (APS) initiator solution (1.84 g of J / UUUl APS in 23.8 g of water (DI) and 5% of ME1 were added to the flask. In approximately 5 minutes, the start of polymerization was confirmed by a 3 °C temperature increase and a change in the external appearance of the reaction mixture. After the heat generation was complete, the remaining ME1 was gradually added to the flask over a period of 45 minutes, with stirring. Simultaneously, an aqueous solution of APS (0.9 g APS in 67.30 g of water DI) was gradually added to the flask over 45 minutes. The polymerization reaction temperature was maintained at 84–86 °C. After the addition was complete, the container holding ME1 and the feed lines leading to the flask were rinsed with water DI (20.4 g), and the rinse water was added back to the flask. The reaction mixture was then maintained at 82–86 °C for 30 minutes. Next, ME2 was added in the same manner as ME1 for 45 minutes. Simultaneously, an aqueous solution of APS (0.9 g APS in 67.30 g DI water) was gradually added to the flask over a period of 45 minutes. After the addition was complete, the reaction mixture was held at 70 °C for 60 minutes. Then, an aqueous solution of t-BHP (1.63 g, 70% active) in 27.2 g DI water and an aqueous solution of IAA (0.82 g in 30.6 g DI water) were added to the flask. The reaction was cooled to 50 °C and then neutralized to a pH of 7.0–8.0 with ammonia (25%). The reaction mixture was held at 45–50 °C for 10 minutes. A suspension of ADH (15.00 g in 28 g of DI water) was then added at 40 °C for 10 minutes and held for 20 minutes. The resulting dispersion was cooled to room temperature and filtered to obtain the aqueous polymer dispersion. MP Dispersion of Ex. 4 Preparation of the monomer emulsion 1 (ME1): The surfactant SLS (11.40 g, 25% active) was dissolved in DI water (129.12 g), with stirring, and then the monomers listed in Table 1 were slowly added to the stirred solution to obtain ME1. Preparation of the monomer emulsion 2 (ME2): The surfactant SLS (17.24 g, 25% active) was dissolved in DI water (206.18 g), with stirring, and then the monomers listed in Table 1 were slowly added to the stirred solution to obtain ME2. A solution containing SLS surfactant (23.87 g, 25% active) and DI water (630.7 g) was placed in a 5-liter, four-necked round-bottom flask equipped with a thermocouple, a cooling condenser, and a stirrer, and heated to 85 °C in nitrogen. An aqueous sodium carbonate solution (1.84 g sodium carbonate in 61.20 g DI water), an APS initiator solution (1.84 g APS in 23.8 g DI water), and 5% of ME1 were added to the flask. The initiation of polymerization was confirmed by a 3 °C temperature increase and a change in the external appearance of the reaction mixture after approximately 5 minutes. Once heating was complete, the remaining ME1 was gradually added to the flask over 36 minutes with stirring. Simultaneously, an aqueous solution of APS (0.68 g of APS in 53.86 g of DI water) was gradually added to the flask over a period of 36 minutes. The polymerization reaction temperature was maintained at 84 to 86 °C.Once the addition was complete, the container holding ME1 and the feed tubing leading to the flask were rinsed with 20.4 g of DI water, and the rinse was added back to the flask. The reaction mixture was then held at 8286 °C for 30 minutes. Next, ME2 was added in the same manner as ME1 for 54 minutes. Simultaneously, an aqueous solution of APS (1.02 g APS in 80.78 g of water) was gradually added to the flask over a period of 54 minutes. After the addition was complete, the reaction mixture was held at 70 °C for 60 minutes. Then, an aqueous solution of t-BHP (1.63 g, 70% active) in 27.2 g of water and an aqueous solution of IAA (0.82 g in 30.6 g of water) were added to the flask. The reaction was cooled to 50 °C and then neutralized to a pH of 7.0–8.0 with ammonia (25%). The reaction mixture was held at 45–50 °C for 10 minutes. A suspension of ADH (17.90 g in 28 g of DI water) was then added at 40 °C for 10 minutes and held for 20 minutes. The resulting dispersion was cooled to room temperature and J / UUUl filtered to obtain the aqueous polymer dispersion. MP Dispersion of Example 6 Preparation of the monomer emulsion 1 (ME1): The surfactant SLS (15.68 g, 25% active) was dissolved in DI water (177.54 g), with stirring, and then the monomers listed in Table 1 were slowly added to the stirred solution to obtain ME1. Preparation of the monomer emulsion 2 (ME2): The surfactant SLS (12.94 g, 25% active) was dissolved in DI water (154.76 g), with stirring, and then the monomers listed in Table 1 were slowly added to the stirred solution to obtain ME2. A solution containing SLS surfactant (23.87 g, 25% active) and DI water (630.7 g) was placed in a 5-liter, four-necked round-bottom flask equipped with a thermocouple, a cooling condenser, and a stirrer, and heated to 85 °C in nitrogen. An aqueous sodium carbonate solution (1.84 g sodium carbonate in 61.20 g DI water), an APS initiator solution (1.84 g APS in 23.8 g DI water), and 5% of ME1 were added to the flask. The initiation of polymerization was confirmed by a 3 °C temperature increase and a change in the external appearance of the reaction mixture after approximately 5 minutes. Once heating was complete, the remaining ME1 was gradually added to the flask over 50 minutes with stirring. Simultaneously, an aqueous solution of APS (0.95 g of APS in 74.80 g of DI water) was gradually added to the flask over a period of 50 minutes. The polymerization reaction temperature was maintained at 84 to 86 °C.Once the addition was complete, the container holding ME1 and the feed tubing leading to the flask were rinsed with 20.4 g of DI water, and the rinse was added back to the flask. The reaction mixture was then held at 8286 °C for 30 minutes. Next, ME2 was added in the same manner as ME1 for 40 minutes. Simultaneously, an aqueous solution of APS (0.76 g APS in 59.84 g of water) was gradually added to the flask over a period of 40 minutes. After the addition was complete, the reaction mixture was held at 70 °C for 60 minutes. Then, an aqueous solution of t-BHP (1.63 g, 70% active) in 27.2 g of water and an aqueous solution of IAA (0.82 g in 30.6 g of water) were added to the flask. The reaction was cooled to 50 °C and then neutralized to a pH of 7.0–8.0 with ammonia (25%). The reaction mixture was held at 45–50 °C for 10 minutes. A suspension of ADH (13.43 g in 28 g of DI water) was then added at 40 °C for 10 minutes and held for 20 minutes. The resulting dispersion was cooled to room temperature and filtered to obtain the aqueous polymer dispersion. MP dispersion of the comp. Ej. 5 Ex. comp. 5 was prepared substantially the same as the Example 5 of US20020013405A1: Preparation of the monomer emulsion 1 (ME1): The surfactant SLS (9.50 g, 25% active) was dissolved in DI water (114.67 g), with stirring, and then EHA (42.85 g), MMA (352.26 g), DVB (4.77 g) and AA (4.77 g) were slowly added to the stirred solution to obtain ME1. Preparation of the monomer emulsion 2 (ME2): The surfactant SLS (9.50 g, 25% active) was dissolved in DI water (114.67 g), with stirring, and then MMA (292.74 g), EHA (107.10 g) and AA (4.77 g) were slowly added to obtain ME2. Preparation of the monomer emulsion (ME3): The surfactant SLS (9.50 g, 25% active) was dissolved in DI water (114.67 g), with stirring, and then MMA (107.12 g), EHA (233.25 g), DAAM (35.72 g) and AA (4.76 g) were slowly added to the stirred solution to obtain ME3. A solution containing SLS surfactant (23.87 g, 25% active) and DI water (630.7 g) was placed in a 5-liter, four-necked round-bottom flask equipped with a thermocouple, a cooling condenser, and a stirrer, and heated to 85 °C in nitrogen. An aqueous sodium carbonate solution (1.84 g sodium carbonate in 61.20 g DI water), an APS initiator solution (1.84 g APS in 23.8 g DI water), and 5% of ME1 were added to the flask. In approximately 5 minutes, the initiation of polymerization was confirmed by a 3 °C temperature increase and a change in the external appearance of the reaction mixture. After heating was complete, the remaining ME1 was gradually added to the flask over 30 minutes with stirring. Simultaneously, an aqueous solution of APS (0.57 g of APS in 44.88 g of DI water) was gradually added to the flask over a period of 30 minutes. The polymerization reaction temperature was maintained at 84–86 °C.Once the addition was complete, the container holding ME1 and the feed tubing leading to the flask were rinsed with DI water (20.4 g), and the rinse was added back to the flask. After that, ME2 was added in the same manner as ME1 for 30 minutes. Simultaneously, an aqueous solution of APS (0.57 g of APS in 44.88 g of DI water) was gradually added to the flask over a period of 30 minutes. Once the addition was complete, the container holding ME2 and the feed tubing leading to the flask were rinsed with DI water (20.4 g), and the rinse was added back to the flask. After that, ME3 was added in the same manner as ME1 for 30 minutes. Simultaneously, an aqueous solution of APS (0.57 g of APS in 44.88 g of DI water) was gradually added to the flask over a period of 30 minutes. After the addition was completed, the reaction mixture was kept at 70 °C for 60 minutes.An aqueous solution of t-BHP (1.63 g, 70% active) in DI water (27.2 g) and an aqueous solution of IAA (0.82 g in 30.6 g of DI water) were then added to the flask. The reaction was cooled to 50 °C and then neutralized to a pH of 7.0–8.0 with ammonia (25%). The reaction mixture was held at 45–50 °C for 10 minutes. An ADH suspension (17.86 g in 28 g of DI water) was then added at 40 °C for 10 minutes and held for 20 minutes. The resulting dispersion was cooled to room temperature and filtered to obtain the aqueous polymer dispersion (Tgs for polymer of each stage: 67.5 / / 44.1 / / -7.1 °C, MFFT: 56.7 °C, average particle size: 80 nm, and solids: 45.3%). MP dispersion of the comp. Ej. 7 Ex. comp. 7 was prepared as Ex. 1, except that the ADH dose was 29.85 g in 28 g of DI water, based on the monomer compositions provided in Table 2. MP dispersion of the comp. Ej. 8 Preparation of the monomer emulsion 1 (ME1): The surfactant SLS (17.10 g, 25% active) was dissolved in DI water (193.68 g), with stirring, and then the monomers listed in Table 2 were slowly added to the stirred solution to obtain ME1. Preparation of the monomer emulsion 2 (ME2): The surfactant SLS (11.49 g, 25% active) was dissolved in DI water (137.40 g), with stirring, and then the monomers listed in Table 2 were slowly added to the stirred solution to obtain ME2. A solution containing SLS surfactant (23.87 g, 25% active) and DI water (630.7 g) was placed in a bottom flask A 5-liter, four-necked round-bottom flask equipped with a thermocouple, a cooling condenser, and a stirrer was heated to 85 °C in nitrogen. An aqueous sodium carbonate solution (1.84 g sodium carbonate in 61.20 g water), an APS initiator solution (1.84 g APS in 23.8 g water), and 5% of ME1 were added to the flask. The start of polymerization was confirmed by a 3 °C temperature increase and a change in the external appearance of the reaction mixture after approximately 5 minutes. Once heating was complete, the remaining ME1 was gradually added to the flask over 54 minutes with stirring. Simultaneously, an aqueous APS solution (1.02 g APS in 80.78 g water) was gradually added to the flask over another 54 minutes. The polymerization reaction temperature was maintained at 84 to 86 °C.Once the addition was complete, the container holding ME1 and the feed tubing leading to the flask were rinsed with 20.4 g of DI water, and the rinse was added back to the flask. The reaction mixture was then held at 82–86 °C for 30 minutes. Next, ME2 was added in the same manner as ME1 for 36 minutes. Simultaneously, an aqueous solution of APS (0.68 g APS in 53.86 g of water) was gradually added to the flask over a period of 36 minutes. After the addition was complete, the reaction mixture was held at 70 °C for 60 minutes. Then, an aqueous solution of t-BHP (1.63 g, 70% active) in 27.2 g of water and an aqueous solution of IAA (0.82 g in 30.6 g of water) were added to the flask. The reaction was cooled to 50 °C and then neutralized to a pH of 7.0–8.0 with ammonia (25%). The reaction mixture was held at 45–50 °C for 10 minutes. A suspension of ADH (11.93 g in 28 g of DI water) was then added at 40 °C for 10 minutes and held for 20 minutes. The resulting dispersion was cooled to room temperature and filtered to obtain the aqueous polymer dispersion. The properties of the MP dispersions prepared above were provided in Tables 1 and 2. Table 1. Monomer compositions and properties for J / UUU1 the MP dispersions of Ex. 1-6 Dispersion of MP Ex.1 Ex.2 Ex.3 Ex.4 Ex.5 Ex.6 ME1 to prepare polymer A (Composition of monomers A), gram MMA 422.45 416.8 428.31 337.96 422.45 464.7 ALMA 29.55 29.55 29.55 23.64 29.55 32.51 DVB 0 0 0 0 0 0 MAA 11.72 11.72 0 9.38 11.72 12.89 DAAM 0 5.65 0 0 0 0 AA 0 0 0 0 0 0 BA 130.65 130.65 130.65 104.52 130.65 143.72 PEM 0 0 5.86 0 0 0 ME2 to prepare polymer B (Monomer Composition B), gram MMA 262.05 262.05 273.82 314.2 232.26 235.85 EHA 280.21 280.21 280.21 335.97 280.21 252.19 DAAM 29.85 29.85 29.85 35.79 59.7 26.87 MAA 23.54 23.54 0 28.23 23.54 21.19 AAEM 0 0 0 0 0 0 PEM 0 0 11.77 0 0 0 AA 0 0 0 0 0 0 Properties Tg of polymer A / Tg of polymer 56.8 / / 56.9 / / 55.6 / / 56.8 / / 56.8 / / 56.8 / / B, °C 16.3 16.3 13.7 16.3 16.4 16.3 MFFT, °C 58.5 60 61 44 64 67 Average PS, nm 97 99 172 96 98 94 Solids, % 44.6 44.95 44.48 44.97 44.54 44.54 The solids content was measured by weighing 0.7 ± 0.1 g of a sample ML / a / ZUZ J / UUU1 (the wet weight of the sample is indicated as Wl), placing the sample in an aluminum tray (the weight of the aluminum tray is indicated as W2) in an oven at 150 °C for 25 min, and then, after cooling, weighing the aluminum tray with the dry sample, with a total weight indicated as W3. W3-W2 refers to the dry or solids weight of the sample. The solids content is calculated by (W3-W2) / Wl*100%. Average PS: The average particle size was measured using the Brookhaven BI-90 Plus particle size analyzer Table 2. Monomer compositions and properties for comparative MP dispersions MP dispersion Comp. Ex. 1 Comp. Ex. 2 Ex. comp. 3 Ex. comp. 4 Ex. comp. 6 Ex. comp. 7 Ex. comp. 8 ME1 to prepare polymer A (Composition of monomers A), gram MMA 422.45 422.45 422.45 422.45 422.45 433.9 506.94 ALMA 29.55 29.55 29.55 29.55 0 17.83 35.46 DVB 0 0 0 0 29.55 0 0 MAA 11.72 11.72 11.72 0 11.72 11.72 14.07 DAAM 0 0 0 0 0 0 0 AA 0 0 0 11.72 0 0 0 BA 130.65 130.65 130.65 130.65 130.65 130.65 156.78 PEM 0 0 0 0 0 0 0 ME2 to prepare polymer B (Monomer Composition B), gram MMA 273.59 247.13 244.22 262.05 262.05 232.26 209.38 EHA 292.55 265.29 285.92 280.21 280.21 280.21 223.89 DAAM 5.97 0 29.85 29.85 29.85 59.7 23.85 MAA 23.54 23.54 35.74 0 23.54 23.54 18.81 AAEM 0 59.7 0 0 0 0 0 PEM 0 0 0 0 0 0 0 AA 0 0 0 23.54 0 0 0 Properties Tg of polymer A / Tg of polymer B, °C 56.8 / / 13.2 56.8 / / 12 56.8 / / 16.4 55.9 / / 14.5 56.8 / / 16.3 56.6 / / 16.4 56.8 / / 16.3 MFFT, °C 57 55 59 43.8 53 59 66 Average PS, nm 94 100 100 135 79 90 97 Solids, % 44.6 44.7 44.5 45.42 45.13 45.25 45.15 Coating compositions The previously obtained multi-stage aqueous polymer dispersions were used as binders to prepare coating compositions based on the compositions provided in Table 3. The binder, coalescing agent DOWANOL EB, DPnB, wetting agent BYK346, defoamer Tego Airex 902W, rheology modifier ACRYSOL RM-8W, and water were mixed and stirred at 600 rpm / min to form the coating compositions. The resulting coating compositions were evaluated according to the test methods described above, and the property results are shown in Table 4. Table 3. Coating compositions Coating Composition Coating 1 and Coating Comp. 14 Coating 2 CoatingS Coating 4 Coatings Coating 6 Coating Comp. 5 Coating Comp. 6 Coating Comp. 7 Coating Comp. 8 Binder (MP dispersion) Ex. 1 and Coating Comp. 1-4 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. comp. 5 Ex. comp. 6 Ex.comp.7 Ex.comp.8 Binder Dosage 70 70 70 70 70 70 70 70 70 70 Water 22.6 19.6 19.5 22.1 19.1 18.6 20.6 20.6 19.6 18.6 EB 3.5 4.5 4.6 3 5 5 4 4 4.5 5 DPnB 3 5 5 4 5 5.5 4.5 4.5 5 5.5 Tego-902w 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 BYK346 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 RM-8W 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 Total 100 100 100 100 100 100 100 100 100 100 Solid 31.5 31.7 31.7 31.7 31.1 31.1 31.5 31.7 31.7 31.7 Cn As shown in Table 4, the coating compositions comprising the binders of the invention from the multi-stage polymer dispersions of Ex. 1-6 provided coatings with surprisingly good hot water resistance (rating >4) as well as good alcohol resistance, alkali resistance, and acetic acid resistance, and acceptable pendulum hardness, impact resistance, and flexibility. Compared to the binder of the multi-stage polymer dispersion of Ex. 1, the binders of Ex. 1, 3-6, and 8 provided coatings with poor hot water resistance, and even poor acetic acid resistance (Ex. 1) or alkali resistance (Ex. 4 and 5). Compared to the binder of Ex. 5, the binder of Ex. 3-6... 2 using AAEM that replaces DAAM showed lower resistance to acetic acid and the binder of the Ej. comp.7 provided less resistance to hot water. J / UUUl Table 4. Coating properties Coating Composition Binder Type Pendulum Hardness Impact Resistance Flexibility Alcohol Resistance Alkali Resistance Acetic Acid Resistance Hot Water Resistance Coating 1 Ex. 1 143 <5cm >15 mm 4 5 3 5 Coating 2 Ex. 2 109 5cm 10 mm 4 4 4 5 Coatings Ex. 3 120 15cm 2mm 4 4 3 4 Coating 4 Ex. 4 111 5cm <1 mm 4 4 4 5 Coatings Ex. 5 141 5cm 5mm 4 4 4 4 Coatings Ex. 6 95 5cm >15 mm 4 4 4 4 Coating comp. 1 Ex. comp. 1 112 <5cm >15 mm 4 5 2 2 Coating of comp. 2 Ex. comp. 2 118 <5cm >15 mm 4 4 2 4 Compound coating Ex. comp. 3 130 <5cm >15 mm 4 3 3 3 Compound coating 4 Ex. comp. 4 118 5cm 10 mm 4 3 4 3 Compound coating 5 Ex. comp. 5 114 10 cm 3mm 4 3 4 1 Compound coating 6 Ex. comp. 6 111 5cm 2mm 4 4 4 1 Compound coating 7 Ex. comp. 7 136 10 cm <1 4 4 4 2 Compound coating 8 Ex. comp. 8 115 5cm 10 4 4 4 2 U1 OΊ It is noted that with regard to this date, the method known to the applicant to carry out the aforementioned invention is the one that is clear from the description of the invention.

Claims

1. An aqueous dispersion, characterized in that it comprises multi-stage polymeric particles, wherein the multi-stage polymeric particles comprise, by weight based on the weight of the multi-stage polymeric particles, from 38% to 58% of a polymer A having a glass transition temperature greater than 47°C and from 42% to 62% of a polymer B having a glass transition temperature of 40°C or lower, wherein the polymer A comprises, by weight based on the weight of polymer A, structural units of a multifunctional monomer containing two or more different ethylenically unsaturated polymerizable groups, from zero to 6% of diacetone (meth)acrylamide structural units, structural units of a monoethylenically unsaturated nonionic monomer, and optionally structural units of an acid monomer and / or a salt thereof selected from the group consisting of methacrylic acid, a phosphorous-containing acid monomer, or a salt thereof,or mixtures thereof; wherein polymer B comprises, by weight based on the weight of polymer B, from 1.1% to 15% of diacetone (meth)acrylamide structural units, structural units of an acid monomer and / or a salt thereof selected from the group consisting of methacrylic acid, a phosphorus-containing acid monomer or a salt thereof, or mixtures thereof, and structural units of a monoethylenically unsaturated nonionic monomer; and wherein the multi-stage polymer particles comprise, by weight based on the weight of the multi-stage polymer particles, structural units of the acid monomer and salt thereof in a total amount of 0.1% to 3.9%, and structural units of the multifunctional monomer in a total amount greater than 1.5% to 5%; wherein the aqueous dispersion further comprises a polyfunctional carboxylic hydrazide containing at least two hydrazide groups per molecule.

2. The aqueous dispersion according to claim 1, characterized in that the multi-stage polymer particles comprise diacetone (meth)acrylamide structural units in a total amount of 1.5% to 6% by weight based on the weight of the multi-stage polymer particles.

3. The aqueous dispersion according to claim 1 or 2, characterized in that polymer B comprises, by weight based on the weight of polymer B, from 3% to 12% of diacetone (meth)acrylamide structural units.

4. The aqueous dispersion according to any of claims 1-3, characterized in that polymer A comprises, by weight based on the weight of polymer A, from 3.1% to 12% of multifunctional monomer structural units.

5. The aqueous dispersion according to any of claims 1-4, characterized in that the multifunctional monomer is selected from the group consisting of allyl (meth)acrylate, allyl (meth)acrylamide, allyloxyethyl (meth)acrylate, crotyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenylethyl (meth)acrylate, diallyl maleate, or mixtures thereof.

6. The aqueous dispersion according to any of claims 1-5, characterized in that the polyfunctional carboxylic hydrazide is selected from the group consisting of adipic dihydrazide, oxalic dihydrazide, isophthalic dihydrazide, polyacrylic polyhydrazides, or mixtures thereof.

7. The aqueous dispersion according to any of claims 1-6, characterized in that polymer B comprises, by weight based on the weight of polymer B, from 0.2% to 5.5% of structural units of the acid monomer and salt thereof.

8. The aqueous dispersion according to any of claims 1-7, characterized in that polymer A comprises, by weight based on the weight of polymer A, from 0.1% to 3% of structural units of the acid monomer and salt thereof.

9. The aqueous dispersion according to any of claims 1-8, characterized in that the acid monomer is methacrylic acid, phosphoethyl methacrylate, or a mixture thereof.

10. The aqueous dispersion according to any of claims 1-9, characterized in that the multi-stage polymer particles have a glass transition temperature in the range of 0 to 70 °C.

11. The aqueous dispersion according to any of claims 1-10, characterized in that it has a minimum film formation temperature of 20 to 75 °C.

12. A process for preparing the aqueous dispersion according to any of claims 1-11, characterized in that it comprises: forming the multi-step polymer particles by multi-step free-radical polymerization comprising at least one polymerization step forming polymer A and at least one polymerization step forming polymer B, and further adding the polyfunctional carboxylic hydrazide containing at least two hydrazide groups per molecule.

13. An aqueous coating composition, characterized in that it comprises the aqueous dispersion according to any of claims 1-11.