WO2025065133A1

WO2025065133A1 - Aqueous antimicrobial coating composition

Info

Publication number: WO2025065133A1
Application number: PCT/CN2023/120992
Authority: WO
Inventors: Yingzhou XIAO; Han Liu; Wei Cui; Jianming Xu
Original assignee: Dow Global Technologies LLC; Rohm and Haas Co
Current assignee: Dow Global Technologies LLC; Rohm and Haas Co
Priority date: 2023-09-25
Filing date: 2023-09-25
Publication date: 2025-04-03
Anticipated expiration: 2026-03-25

Abstract

An aqueous antimicrobial coating composition containing: (A) a specific multistage polymer bearing specific heterocyclic pendant groups and comprising a first-stage polymer and a second-stage polymer; (B) 1 to 1000 parts per million, by weight based on the weight of the aqueous antimicrobial coating composition, of silver ions; where the molar ratio of heterocyclic groups in the multistage polymer to silver ions in the coating composition is 10: 1 or higher; (C) from 0.04%to 1.0%of zinc oxide, by weight based on the weight of the aqueous antimicrobial coating composition; and (D) a pigment.

Description

AQUEOUS ANTIMICROBIAL COATING COMPOSITION

FIELD

The present invention relates to an aqueous antimicrobial coating composition and a method of preparing the same.

INTRODUCTION

Silver ion or silver element is widely used in coating compositions to provide antimicrobial properties. The higher the silver content is in the compositions, the better the antimicrobial properties. However, coatings (dry coating films) made from coating compositions containing inorganic microbiocides on which metal ions are supported often undergo conspicuous changes in coloration upon exposure to sun light. Accordingly, the use of these mierobioeides is effectively limited to systems for which such changes in coloration can be tolerated. Discoloration of coatings can be improved by incorporating counter ions into coating compositions to form more stable silver salts, such as silver chloride (AgCl) in wet state, however, the antimierobial efficacy of the coatings is usually compromised. Incorporation of silver complexed with polymers bearing imidazole pendant groups as antimicrobial additives into polymer binders may improve discoloration of the polymer binders in wet state when the polymer binders have good compatibility with the antimierobial additives, but the discoloration issues of coatings made therefrom still exists when exposed to light.

Recently, some paint manufacturers are seeking solutions for paints that can not only afford antibacterial properties but antiviral properties which usually require even higher silver content, thus making the discoloration issue of coatings even worse when exposure to sun light. Simply increasing the content of imidazole monomers used in preparing polymer binders may be helpful in improving coloration stability of silver-containing antimicrobial coating compositions comprising such polymer binders, but the polymerization process for preparing such polymer binders tends to be unstable and thus a large amount of eoagulum formed during the polymerization process (e.g., more than 520 parts per million (ppm) of coagulum relative to polymer binder weight) . It is therefore desirable to provide an aqueous antimicrobial coating composition that affords coatings made therefrom with improved coloration stability property when exposure to sun light and improved antimicrobial efficacy.

SUMMARY

The present invention solves the problem of discovering an aqueous antimicrobial coating composition without the aforementioned problems. The aqueous antimicrobial coating composition (hereinafter also referred to as “coating composition” ) of the present invention comprises a novel combination of a specific multistage polymer bearing specific heterocyclic pendant groups (such as imidazole groups) , silver ions, zinc oxide, and a pigment. The coating composition affords coating films (i.e., coatings) made therefrom with good coloration stability when exposure to sun light, as indicated by a whiteness change of no more than 10 units and a final whiteness of 75 or higher after two-week exposure to sun light. In the meanwhile, such coating composition can provide coatings or coated surfaces with antimicrobial properties, as indicated by antimicrobial activity against bacteria of 2.0 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 antimicrobial coating composition comprising:

(A) a multistage polymer comprising, by weight based on the weight of the multistage polymer, from 78%to 97%ofa first-stage polymer and from 3%to 22%of a second-stage polymer;

wherein the first-stage polymer comprises: (1a) zero to 0.9%of structural units of a monomer containing at least one heterocyclic group selected from the group consisting of imidazole, benzotriazole, and benzimidazole, by weight based on the weight of the first-stage polymer; (1b) structural units of a C₁-C₄-alkyl (meth) acrylate; and (1c) structural units of a monoethylenically unsaturated functional monomer carrying at lcast one functional group sclcctcd from a carboxyl, carboxylic anhydridc, sulfonic acid, amidc, sulfonatc, phosphoric acid, phosphonate, phosphate, or hydroxyl group; a salt thereof; or combinations thereof; and

wherein the second-stage polymer comprises: (2a) structural units of a monomer containing at least one heterocyclic group selected from the group consisting ofimidazole, benzotriazole, and benzimidazole; and (2b) structural units ofa C₁-C₄-alkyl (meth) acrylate;

wherein the combined concentration of structural units of the monomer containing at least one heterocyclic group in the multistage polymer is from 0.1%to 0.65%, by weight based on the weight of the multistage polymer; and

wherein the multistage polymer comprises, by weight based on the weight of the multistage polymer, from zero to less than 5%of structural units of a cycloalkyl (meth) acrylate, a C₆-C₁₀-alkyl (meth) acrylate, or mixtures thereof;

(B) 1 to 1000 parts per million, by weight based on the weight of the aqueous antimicrobial coating composition, of silver ions; wherein the molar ratio of heterocyclic groups in the multistage polymer to silver ions in the coating composition is 10∶1 or higher;

(C) from 0.04%to 1.0%of zinc oxide, by weight based on the weight of the aqueous antimicrobial coating composition; and

(D) a pigment.

In a second aspect, the present invention is a process for preparing the aqueous antimicrobial coating composition of the first aspect. The process comprises: admixing the multistage polymer (A) with the silver ions (B) , the zinc oxide (C) , and the pigment (D) .

In a third aspect, the present invention is a method of providing a coating. The method comprises: a) applying the aqueous antimicrobial coating composition of the first aspect to a substrate, and b) drying, or allowing to dry, the applied antimicrobial coating composition.

DETAILED DESCRIPTION

Test methods refer to the most recent test method as of the priority date of this document when a date is not indicated with the test method number. References to test methods contain both a reference to the testing society and the test method number. The following test method abbreviations and identifiers apply herein: ASTM refers to ASTM International methods, JIS refers to Japanese Industrial Standard, and T/CNCIA refers to Social Organization Standard issued by China National Coatings Industry Association.

Products identified by their tradename refer to the compositions available under those tradenames on the priority date of this document. “And/or” means “and, or as an alternative” . All ranges include endpoints unless otherwise indicated.

“Antimicrobial coating composition” refers to a composition which can destroy, or prevent the growth of, microorganisms such as bacteria, fungi, and virus, including, for example, the inhibition of the growth and thc killing of bacteria or other microbes in the composition, or on surface of an article coated by the composition.

“Aqueous” composition herein means that polymer particles dispersed in an aqueous medium. By “aqueous medium” herein is meant 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, or mixtures thcrcof.

“Structural units” , also known as “polymerized units” , of the named monomer, refers to the remnant of the monomer after polymerization, that is, polymerized monomer or the monomer in polymerized form. For example, a structural unit of methyl methacrylate is as illustrated: where the dotted lines represent the points of attachment of the structural unit to the polymer backbone.

“Nonionic monomer” herein refers to a monomer that does not bear an ionic charge between pH=1-14.

Throughout this document, the word fragment “ (meth) acryl” refers to both “methacryl” and “acryl” . 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.

“Glass transition temperature” or “T_g” as used herein can be calculated by using a Fox equation (T.G. Fox, Bull. Am. Physics Soc., Volume 1, Issue No. 3, page 123 (1956) ) below. For example, for calculating the T_g of a copolymer ofmonomers M₁ and M₂,

where T_g (calc. ) is the glass transition temperature calculated for the copolymer, w (M₁) is the weight fraction of monomer M₁ in the copolymer, w (M₂) is the weight fraction of monomer M₂ in the copolymer, T_g (M₁) is the glass transition temperature of the homopolymer of monomer M₁, and T_g (M₂) is the glass transition temperature of the homopolymer of monomer M₂, all temperatures being in K. The glass transition temperatures of the homopolymers may be found, for example, in “Polymer Handbook” , edited by J. Brandrup and E.H. Immergut, Interscience Publishers.

“Multistage polymer” herein means a polymer prepared by sequential addition of two or more different monomer compositions including the first monomer mixture and the second monomer mixture, which, after polymerization, form a first-stage polymer and a second-stage polymer, respectively. That is, the multistage polymer comprises at least two polymers, i.e., the first-stage polymer and the second-stage polymer. By “first-stage polymer” (interchangeable with “first polymer” ) and “second-stage polymer” (interchangeable with “second polymer” ) mean these polymers having different compositions and formed in different stages of multistage free-radical polymerization in preparing the multistage polymer. Each stage is sequentially polymerized and different from the immediately proceeding and/or immediately subsequent stage by a difference in monomer composition. By “second-stage polymer” herein is meant a polymer which is formed in the presence of the “first-stage polymer. ” However, the first-stage polymer may be formed in the presence of a previously formed dispersed polymer at a concentration of 0 to 10%by weight, based on the weight of the first-stage polymer, sometimes known as a seed polymer, of a composition that is the same as that of the first-stage polymer. When the seed polymer is used, the weight the seed polymer is counted into the first-stage polymer. “Weight of multistage polymer” in the present invention refers to the dry or solids weight of the aqueous dispersion of multistage polymer.

The coating composition of the present invention comprises (A) a multistage polymer. The multistage polymer can bear pendant heterocyclic groups that are derived from a monomer containing at least one heterocyclic group selected from thc group consisting of an imidazolc group, a benzotriazole group, and a benzimidazole group via polymerization. Desirably, the heterocyclic group is an imidazole group. The multistage polymer comprises a first-stage polymer and a second-stage polymer.

The second-stage polymer in the multistage polymer comprises (2a) structural units of a monomer containing at least one heterocyclic group selected from an imidazole group, a benzotriazole group, and a benzimidazole group (hereinafter also referred to “heterocyclic monomer” ) . The heterocyclic monomer useful in the present invention can be an imidazole group-containing monomer, a benzotriazole group-containing monomer, a benzimidazole group-containing monomer, or mixtures thereof. Suitable heterocyclic monomers may comprise, for example, 1-vinyl imidazole, vinyl benzotriazole, vinyl methyl benzotriazole, vinyl benzothiazole, vinylmethylbenzothiazole, vinyl benzimidazole, vinyl methyl benzimidazole, or mixtures thereof. Desirably, the heterocyclic monomer is 1-vinyl imidazole. The concentration of structural units of the heterocyclic monomer in the second-stage polymer is, by weight based on the weight of the second-stage polymer, from 0.4%to 22%, and can be 0.4%or more, 0.5%or more, 0.6%or more, 0.8%or more, 1.0%or more, 1.2%or more, 1.4%or more, 1.6%or more, 1.8%or more, 2%or more, 2.5%or more, 3.0%or more, 3.5%or more, even 3.75%or more while at the same time is generally 22%or less, 20%or less, and can be 18%or less, 16%or less, 15%or less, 14%or less, 13%or less, or even 12%or less, and desirably from 3.0%to 14%, more desirably from 3.5%to 13%, most desirably from 3.75%to 12%.

The first-stage polymer in the multistage polymer may comprise or be free of (la) structural units of the heterocyclic monomer described above. The heterocyclic monomer for the first-stage polymer and second-stage polymer can be thc same or difference. Structural units of the heterocyclic monomer in the first polymer may be present, by weight based on the weight of the first-stage polymer, at a concentration of from zero to 0.9%, and can be less than 0.9%, less than 0.8%, less than 0.6%, less than 0.4%, less than 0.2%, less than 0.1%, or even zero.

The combined concentration of structural units of the heterocyclic monomer in the multistage polymer (i.e., total concentration of structural units (2a) in the second-stage polymer and structural units (1a) in the first-stage polymer if present) is, by weight based on the weight of the multistage polymer, from 0.1%to 0.65%, and can be 0.1%or more, 0.2%or more, 0.3%or more, 0.4%or more, even 0.5%or more while at the same time is 0.65%or less, and can be 0.6%or less, 0.58%or less, 0.56%or less, less than 0.54%, or even 0.52%or less, desirably from 0.2%to 0.6%. Desirably, from 60%to 100%of structural units of the heterocyclic monomer of the multistage polymer are present in the second-stage polymer, and can be 65%or more, 70%or more, 75%or more, 80%or more, 85%or more, 90%or more, 95%or more, or even 100%ofstructural units of the heterocyclic monomer are present in the second-stage polymer.

The first-stage polymer and second-stage polymer in the multistage polymer each independently comprise structural units of one or more C₁-C₄-alkyl (meth) acrylate, that is, an alkyl ester of (meth) acrylic acid, containing a linear or branched alkyl having 1 to 4 carbon atoms. The C₁-C₄-alkyl (meth) acrylate for the first-stage polymer and the second-stage polymer can be the same or different. The C₁-C₄-alkyl (meth) acrylate can be methyl acrylate (MA) , methyl methacrylate (MMA) , butyl methacrylate (BMA) , ethyl methacrylate (EMA) , butyl acrylate (BA) , ethyl acrylate (EA) , or mixtures thereof. Desirably, the first-stage polymer comprise structural units of the C₁-C₄-alkyl (mcth) acrylatc sclcctcd from the group consisting of butyl acrylate and methyl methacrylate. Desirably, the C₁-C₄-alkyl (meth) acrylate for forming the second-stage polymer is a C₁-C₄-alkyl acrylate, more desirably, butyl acrylate (BA) , ethyl acrylate (EA) , or mixtures thereof.

The first-stage polymer itn the multistage polymer comprises (lb) structural units of the C₁-C₄-alkyl (meth) acrylate. The concentration of structural units of the C₁-C₄-alkyl (meth) acrylate (lb) in the first-stage polymer may be, by weight based on the weight of the first-stage polymer, from 85%to 99%, and can bc greater than 88%, 90%or more, 91%or more, 92%or more, even 93%or more, while at the same time is generally 99%or less, and can be 98%or less, 97%or less, or even 96%or less, desirably 92%to 96%.

The second-stage polymer in the multistage polymer comprises (2b) structural units of the C₁-C₄-alkyl (meth) acrylate. The concentration of structural units of the C₁-C₄-alkyl (meth) acrylate in the second-stage polymer may be, by weight based on the weight of the second-stage polymer, from 75%to 99%, and can be 78%or more, 81%or more, 84%or more, 87%or more, 89%or more, even 90%or more while at the same time is generally 99%or less, 98%or less, 97%or less, 96%or less, or even 95%or less, desirably 87%to 98%, more desirably 90%to 95%.

The first-stage polymer in the multistage polymer also comprises (lc) structural units of one or more monoethylenically unsaturated functional monomers carrying at least one functional group selected from a carboxyl, carboxylic anhydride, sulfonic acid, amide, sulfonatc, phosphoric acid, phosphonatc, phosphate, or hydroxyl group; a salt thereof; or combinations thereof (hereinafter referred to as “monoethylenically unsaturated functional monomer” ) . Examples of suitable monoethylenically unsaturated functional monomers include α, β-ethylenically unsaturated carboxylic acids including an acid-bearing monomer such as methacrylic acid, acrylic acid, itaconic acid, maleic acid, or fumaric acid; or a monomer bearing an acid-forming group which yields or is subsequently convertible to, such an acid group such as anhydride, (meth) acrylic anhydride, or maleic anhydride; sodium styrene sulfonate (SSS) , sodium vinyl sulfonate (SVS) , 2-acrylamido-2-methylpropanesulfonic acid (AMPS) , sodium salt of 2-acrylamido-2-methyl-1-propanesulfonic acid, ammonium salt of 2-acrylamido-2-methyl-1-propane sulfonic acid; sodium salt of allyl ether sulfonate; acrylamide, methacrylamide, monosubstituted (meth) acrylamide, N-methylacrylamide, N-ethylacrylamide, N-isopropylacrylamide, N-butylacrylamide, N-tertiary butylacrylamide, N-2-ethylhexylacrylamide, N, N-dimethylacrylamide, N, N-diethylacrylamide; hydroxy-functional (meth) acrylic acid alkyl ester such as hydroxyethyl methacrylate and hydroxypropyl methacrylate; phosphoalkyl (meth) acrylates such as phosphoethyl (meth) acrylate, phosphopropyl (meth) acrylate, phosphobutyl (meth) acrylate, salts thereof, and mixtures thereof; CH₂=C (R_p1) -C (O) -O- (R_p2O) _p-P (O) (OH) ₂, wherein R_p1=H or CH₃, R_p2=alkyl and p=1-10, such as SIPOMER PAM-100, SIPOMER PAM-200, and SIPOMER PAM-300 all available from Solvay; phosphoalkoxy (meth) acrylates such as phospho ethylene glycol (meth) acrylate, phospho di-ethylene glycol (meth) acrylate, phospho tri-ethylene glycol (meth) acrylate, phospho propylene glycol (meth) acrylate, phospho di-propylene glycol (meth) acrylate, phospho tri-propylene glycol (meth) acrylate, allyl ether phosphate, vinyl phosphonic acid, salts thereof; or mixtures thereof. Desirably, the monoethylenically unsaturated functional monomer is selected from phosphoethyl methacrylate (PEM) , acrylic acid (AA) , acrylamide (AM) , methacrylic acid (MAA) , or mixtures thereof. More desirably, the monoethylenically unsaturated functional monomer is AA, AM, or a mixture of AA and AM. The concentration of (lc) structural units of the monocthylcnically unsaturated functional monomer in the first-stage polymer may be, by weight based on the weight of the first-stage polymer, from 0.1%to 15%, and can be 0.1%or more, and can be 0.3%or more, 0.5%or more, 0.8%or more, 0.9%or more, 1.0%or more, 1.1%or more 1.2%or more, 1.5%or more, even 1.8%or more, while at the same time is generally 15%or less, and can be 12%or less, 10%or less, 8%or less, 5%or less, 3%or less, 3.2%or less, or even 2.8%or less, desirably from 0.1%to 10%, from 1.2%to 3.2%, or from 1.5%to 2.8%.

The second-stage polymer in the multistage polymer may comprise or be free of (2c) structural units of the monoethylenically unsaturated functional monomer as described above in the first-stage polymer section. The monoethylenically unsaturated functional monomer for the first-stage polymer and the second-stage polymer can be the same or different. The concentration of (2c) structural units of the monoethylenically unsaturated functional monomer in the second-stage polymer may be in an amount sufficient to provide a combined concentration of (1c) and (2c) in the multistage polymer of zero to less than 15%, and can be less than 10%, less than 8%, less than 6%, less than 5%, less than 4%, less than 3%, less than 2%, less than 1%, or even zero, by weight based on the weight of the multistage polymer.

The first-stage polymer and/or second-stage polymer in the multistage polymer may each independently comprise, or be free of, structural units of an additional monoethylenically unsaturated nonionic monomer that is other than the monoethylenically unsaturated functional monomer described above. The additional monoethylenically unsaturated nonionic monomer may include an ethylenically unsaturated acetoacetyl functional monomer, a C₆-C₁₀-alkyl (meth) acrylate, a cycloalkyl (meth) acrylate, a silane monomer, a vinyl aromatic monomer such as styrene and substituted styrene, or mixtures thereof. Suitable ethylenically unsaturated acetoacetyl functional monomers may include, for example, acetoacetoxyalkyl (meth) acrylates such as acetoacetoxyethyl methacrylate (AAEM) , acetoacetoxyethyl acrylate, acetoacetoxypropyl methacrylate, acetoacetoxybutyl methacrylate, and 2, 3-di (acetoacetoxy) propyl methacrylate; allyl acetoacetate; acetoacetamidoalkyl (meth) acrylates such as acetoacetamidoethyl methacrylate and acetoacetamidoethyl acrylate; or combinations thereof. Suitable cycloalkyl (meth) acrylates may include, for example, cyclohexyl (meth) acrylate, methcyclohexyl (meth) acrylate, dihydrodicyclopentadienyl (meth) acrylate, trimethylcyclohexyl (meth) acrylate, t-butyl cyclohexyl (meth) acrylate, or mixtures thereof. The C₆-C₁₀-alkyl (meth) acrylates refer to alkyl ester of acrylic acid or methacrylic acid containing a linear or branched alkyl with from 6 to 10 carbon atoms, desirably, from 6 to 8 carbon atoms. Examples of suitable C₆-C₁₀-alkyl (meth) acrylates include 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, or mixtures thereof. Suitable silane monomers may include, for example, alkylvinyldialkoxysilanes; vinyltrialkoxysilanes such as vinyltriethoxysilane and vinyltrimethoxysilane; (meth) acryl functional silanes including, for example, (meth) acryloxyalkyltrialkoxysilanes such as gamma-methacryloxypropyltrimethoxysilane and methacryloxypropyltriethoxysilane; 3-methacryloxypropylmethyldimethoxysilane; 3-methacryloxypropyltrimethoxysilane; 3-methacryloxypropyltriethoxysilane; or mixtures thereof. Desirably, the additional monoethylenically unsaturated nonionic monomer comprises or consists of the monoethylenically unsaturated nonionic monomer such as AAEM. The first-stage polymer and/or second-stage polymer may each independently comprise structural units of the additional monoethylenically unsaturated nonionic monomer at a concentration of from zero to 15%, from 0.1%to 10%, from 0.2%to 8%, from 0.3%to 6%, from 0.4%to 5%, by weight based on the weight of the first-stage polymer and second-stage polymer, respectively. Particularly, the additional monoethylenically unsaturated nonionic monomer for the first-stage polymer and/or the second stage polymer may each independently comprise, or can consist of, the C₆-C₁₀-alkyl (meth) acrylate, the cycloalkyl (meth) acrylates, or mixtures thereof, provided that the total concentration of structural units of the C₆-C₁₀-alkyl (meth) acrylate, the cycloalkyl (meth) acrylates, or mixtures thereof in the multistage polymer is in a range of from zero to less than 5%, and can be less than 4%, less than 3%, less than 2%, less than 1%, or even zero, by weight based on the weight of the multistage polymer. Desirably, the first-stage polymer and the second-stage polymer each independently comprises from zero to less than 5%, less than 4%, less than 3%, less than 2%, less than 1%, or even zero, of structural units of the C₆-C₁₀-alkyl (meth) acrylate, the cycloalkyl (meth) acrylates, or mixtures thereof (such as 2-ethylhexyl acrylate) , by weight based on the weight of the first-stage polymer and second-stage polymer, respectively. Desirably, the first-stage polymer and/or second-stage polymer each independently are free of structural units of the C₆-C₁₀-alkyl (meth) acrylate, the cycloalkyl (meth) acrylates, or mixtures thereof.

The second-stage polymer in the multistage polymer may comprise or be free of a chain transfer agent, i.e., the second-stage polymer may be prepared in the presence of, or can be in the absence of, a chain transfer agent. Desirably, the second-stage polymer is prepared in the absence of the chain transfer agent. Examples of suitable chain transfer agents include 3-mercaptopropionic acid, methyl mercaptopropionate, butyl mercaptopropionate, n-dodecyl mercaptan (nDDM) , methyl 3-mercaptopropionate (MMP) , butyl 3-mercaptopropionate (BMP) , benzenethiol, azelaic alkyl mercaptan, or mixtures thereof. The chain transfer agent may be used in an effective amount to control the molecular weight of the second-stage polymer. Desirably, the second-stage polymer has a number average molecular weight (Mn) of greater than 30,000 grams per mole (g/mol) , and can be greater than 50,000 g/mol or more, 100,000 g/mol or more, 500,000 g/mol or more, or even 1,000,000 g/mol or more. Mn herein refers to a calculated Mn according to the following equation:
Mn= (W_CTA+W_Monomer) / (W_CTA/M_CTA)

where W_CTA is the weight of the chain transfer agent, M_CTA is the molecular weight of the chain transfer agent, and W_Monomer is the total weight of monomers used for preparing the polymer. Ifno chain transfer agent is used, the calculated Mn of the polymer is taken as 1,000,000 g/mol.

The multistage polymer of the present invention may comprise or be free of structural units of one or more multiethylenically unsaturated monomers, which may be present in the first-stage polymer, the second-stage polymer, or combinations thereof, desirably in the first-stage polymer. Suitable multiethylenically unsaturated monomers may include, for example, butadiene, allyl (meth) acrylate, divinyl benzene, ethylene glycol dimethacrylate, butylene glycol dimethacrylate, or mixtures thereof. The multistage polymer may comprise, by weight based on the weight of the multistage polymer, from zero to 3.0%, from 0.05%to 0.8%, or from 0.1%to 0.5%of structural units of the multiethylenically unsaturated monomers.

The first-stage polymer in the multistage polymer may comprise, or can consist of, , by weight based on the weight of the first-stage polymer, from zero to 0.9%of structural units of the monomer containing at lcast onc hctcrocyclic group; from 85%to 99%of structural units of thc C₁-C₄-alkyl (mcth) acrylatc; and from 0.1%to 15%of structural units of the monoethylenically unsaturated functional monomer, the salt thereof, or combinations thereof. Desirably, the first-stage polymer comprises or consists of, by weight based on the weight of the first-stage polymer, from zero to 0.5%of structural units of 1-vinyl imidazole, from 92%to 96%of structural units of the C₁-C₄-alkyl (meth) acrylate (e.g., MMA, BA, and mixtures thereof) , from 1.2%to 3.2%structural units of the monoethylenically unsaturated functional monomer, , and from zero to 5%of the additional monoethylenically unsaturated nonionic monomer. More desirably, the first-stage polymer is free of structural units of 1-vinyl imidazole.

Desirably, the second-stage polymer in the multistage polymer comprises or consists of structural units of 1-vinyl imidazole and structural units of the C₁-C₄-alkyl acrylate such as BA, EA, and mixtures thereof. For example, the second-stage polymer in the multistage polymer may comprise, or can consist of, by weight based on the weight of the second-stage polymer, from 0.4%to 22%of structural units of 1-vinyl imidazole and from 75%to 99%of structural units of butyl acrylate, ethyl acrylate, or mixtures thereof. More desirably, the second-stage polymer comprises, by weight based on the weight of the second-stage polymer, from 5%to 12%of structural units of 1-vinyl imidazole and from 90%to 95%of structural units of the C₁-C₄-alkyl acrylate such as BA, EA or mixtures thereof.

The multistage polymer of the present invention comprises, by weight based on the weight of the multistage polymer, from 78%to 97%of the first-stage polymer and from 3%to 22%of the second-stage polymer, for example, 80%to 96%of the first-stage polymer and 4%to 20%of the second-stage polymer, alternatively 82%to 95%of the first-stage polymer and 5%to 18%of the second-stage polymer, alternatively 83%to 94%of the first-stage polymer and 6%to 17%of the second-stage polymer, alternatively 85%to 95%of the first-stage polymer and 5%to 15%of the second-stage polymer, alternatively 85%to 93%of the first-stage polymer and 7%to 15%of the second-stage polymer, alternatively 88%to 92%of the first-stage polymer and 8%to 12%of the second-stage polymer, alternatively 85%to 90%of the first-stage polymer and 10%to 15%of the second-stage polymer, Desirably, the multistage polymer comprises 85%to 95%of the first-stage polymer and 5%to 15%of the second-stage polymer, by weight based on the weight of the multistage polymer.

The multistage polymer may comprise or be free of a minor amount of a third-stage polymer that can be formed after the second-stage polymer, for example, less than 10%by weight of the multistage polymer, without compromising the desired properties. Desirably, the total amount of the first-stage polymer and the second-stage polymer is from 90%to 100%of the multistage polymer, from 92%to 100%, from 95%to 100%, from 98%to 100%, or from 99%to 100%, by weight based on the weight of the multistage polymer. Total concentration of the structural units of monomers described above in the multistage polymer is equal to 100%, by weight based on the weight of the multistage polymer. Total concentration of the structural units of monomers described above in the first-and second-stage polymer, respectively, is equal to 100%, by weight based on the weight of the first-and second-stage polymer, respectively.

Types and levels of the monomers described above may be chosen to provide the multistage polymer with a Tg suitable for different applications, for example, in the range of from -30 to 50 ℃, and can be greater than -30 ℃, -20 ℃ or more, -16 ℃ or more, -10 ℃ or more, -5 ℃ or more, or even greater than 0 ℃, while at thc same time is generally 50 ℃ or lcss, and can bc 40 ℃ or lcss, 30 ℃ or less, 25 ℃ or less, 20 ℃ or less, or even 15 ℃ or less. Tg values herein can be calculated by the Fox equation.

Without being bounded by a theory, the multistage polymer may comprise multiple different phases (layers or domains) formed by at least the first-stage polymer and the second-stage polymer. Suitable morphologies for the multistage polymer particles may include core-shell polymer particles in which one polymer phase forms a shell that fully encapsulates a core formed from the other polymer phase; and acorn-type polymer particles in which one polymer phase forms a shell that does not fully encapsulate a core formed from the other polymer phase. The core may be the first-stage polymer phase with the shell formed from the second-stage polymer phase.

The multistage polymer of the present invention may have a particle size of from 50 nanometers (nm) to 500 nm, and can be 50 nm or more, 60 nm or more, 100 nm or more, greater than 100 nm, even 105 nm or more while at the same time is generally 500 nm or less, and can be 300 nm, 200 nm or less, 190 nm or less, or even 180 nm or less. The particle size refers to the number average particle size as measured by a Brookhaven BI-90 Plus Particle Size Analyzer.

The multistage polymer can be prepared by a multistage free-radical polymerization process that comprises at least two stages -a stage of forming the first-stage polymer and a stage of forming the second-stage polymer in the presence of the first-stage polymer, thereby forming the multistage polymer comprising at least the first-stage polymer and the second-stage polymer. Optionally, different stages can be formed in different reactors. Each of the stages is sequentially polymerized and different from the immediately preceding and/or immediately subsequent stage by a difference in monomer compositions. The process for preparing the multistage polymer may include: (i) forming the first-stage polymer by polymerization of a first monomer mixture, preferably in an aqueous medium, and (ii) forming the second-stage polymer by polymerization ofa second monomer mixture in the presence of the first-stage polymer obtained from step (i) . The first-stage polymer obtained from step (i) may be neutralized before the second monomer mixture is added. Alternatively, the multistage free-radical polymerization process is free of a step of neutralization of the first-stage polymer prior to step (ii) (i.e., polymerization of the second monomer mixture) . Each stage of the free-radical polymerization can be conducted by polymerization techniques well known in the art such as suspension polymerization or emulsion polymerization of monomers such as the first and second monomer mixtures. Emulsion polymerization is a preferred process. The first and second monomer mixtures may each independently comprise the monomers described above for forming the structural units of the first-stage polymer and the second-stage polymer, respectively. For example, the first monomer mixture comprises, by weight based on the total weight of monomers in the first monomer mixture, zero to 0.9%of the heterocyclic monomer; the C₁-C₄-alkyl (meth) acrylate, the monoethylenically unsaturated functional monomer, and optionally the additional monoethylenically unsaturated nonionic monomer; and the second monomer mixture comprises the heterocyclic monomer and the C₁-C₄-alkyl (meth) acrylate; where the combined concentration of the heterocyclic monomer, by weight based on the total weight of monomers in the first and second monomer mixtures, is from 0.1%to 0.65%; and the total concentration of the cycloalkyl (meth) acrylate, the C₆-C₁₀-alkyl (meth) acrylate, or mixtures thereof, by weight based on the total weight of monomers in the first and second monomer mixtures, is in a range of from zero to less than 5%. For each monomer, thc wcight concentration of such monomer relative to the total weight of monomers used in preparing a polymer (e.g., the first-stage polymer) is the same as the above described weight concentration of structural units of such monomer in such polymer (e.g., the first-stage polymer) as described above. For example, the weight concentration of each monomer in the first monomer mixture relative to the total weight of monomers in the first monomer mixture is the same as the weight concentration of structural units of such monomer in the first-stage polymer relative to the weight of the first-stage polymer. Total weight concentration of the monomers in the first monomer mixture for preparing the first-stage polymer is equal to 100%relative to the total weight of monomers in the first monomer mixture. Total weight concentration of the monomers in the second monomer mixture is equal to 100%relative to the total weight of monomers in the second monomer mixture. The first and second monomer mixtures for preparing the first-stage polymer and the second-stage polymer, respectively, may be added neat or as an emulsion in water; or added in one or more addition or continuously, linearly or nonlinearly, over the reaction period of preparing the first-stage polymer, the second-stage polymer, respectively, or combinations thereof. Temperature suitable for emulsion polymerization processes may be lower than 100 ℃, in a range of from 30 to 95 ℃, or in a range of from 50 to 90 ℃.

In the process for preparing the multistage polymer, a free radical initiator may be used in each stage. The polymerization process may be thermally initiated or redox initiated emulsion polymerization. Examples of suitable free radical initiators include hydrogen peroxide, t-butyl hydroperoxide, cumene hydroperoxide, ammonium persulfate, alkali metal persulfates such as sodium persulfate, sodium perborate, perphosphoric acid, and salts thereof; potassium permanganate, and ammonium or alkali metal salts ofperoxydisulfuric acid, or mixtures thereof. Desirably, the free radical initiator is ammonium persulfate, sodium persulfate, or mixtures thereof. Desirably, the free radical initiator is free of an azo compound such as 2, 2’-azobis (isobutyronitrile) (AIBN) . The free radical initiators may be used typically at a level of 0.01 to 3.0%by weight, based on the total weight of monomers used for preparing the multistage polymer. Redox systems comprising the above described initiators coupled with a suitable reductant may be used in the polymerization process. Examples of suitable reductants 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, formadinesulfinic acid, acetone bisulfite, glycolic acid, hydroxymethanesulfonic acid, glyoxylic acid hydrate, lactic acid, glyceric acid, malic acid, tartaric acid and salts of the preceding acids. Chelating agents for the metals may optionally be used.

In the process for preparing the multistage polymer, a surfactant may be used in the one or more stage (e.g., the first and/or second stage) of the multistage free-radical polymerization process. The surfactant may be added prior to or during the polymerization of the monomers, or combinations thereof. A portion of the surfactant can also be added after the polymerization. The surfactant may be selected from the group consisting of an anionic surfactant and a nonionic surfactant. Examples of suitable surfactants include alkali metal or ammonium salts of alkyl, aryl, or alkylaryl sulfates, sulfonates or phosphates; alkyl sulfonic acids; sulfosuccinate salts; fatty acids; ethylenically unsaturated surfactant monomers; and ethoxylated alcohols or phenols. The surfactant may be used in an amount of from 0.1%to 5%, from 0.15%to 4%, from 0.2%to 3%, or fro m 0.2%to 2%, by weight based on the total wcight of monomcrs uscd for prcparing the multistagc polymer. Thus, the resulting aqueous dispersion may comprise the surfactant at a concentration of from 0.1%to 5%, from 0.15%to 4%, from 0.2%to 3%, or from 0.2%to 2%, by weight based on the weight of the multistage polymer.

In the process for preparing the multistage polymer, a chain transfer agent (e.g., the alkyl thiol) may be present or absent in one or more than one stage of the multistage free-radical polymerization process, such as the first stage and/or the second stage. Desirably, the first monomer mixture and the second monomer mixture are each independently free of the chain transfer agent. The chain transfer agent may be present independently in the first monomer mixture and second monomer mixture, respectively, in an amount of from zero to 5%, and can be zero or more while at the same time is generally 5%or less, 4%or less, 3%or less, 2%or less, 1.7%or less, 1.5%or less, 1%or less, 0.9%or less, 0.8%or less, 0.7%or less, 0.6%or less, 0.5%or less, 0.2%or less, less than 0.15%, 0.1%or less, less than 0.08%, or even zero, by weight based on the total weight of monomers in the first monomer mixture and in the second monomer mixture respectively. When the chain transfer agent comprises an alkyl thiol, the alky thiol in the second monomer mixture may be present in an amount of from zero to less than 0.5%, and can be less than 0.4%, less than 0.3%, less than 0.2%, less than 0.15%, less than 0.1%or less, less than 0.08%, or even zero or less, by weight based on the total weight of monomers in the second monomer mixture. Desirably, the second monomer mixture used for preparing the second-stage polymer is free of a chain transfer agent, particularly, free of tan alkyl thiol such as an alkyl thiol having a linear or branched alkyl group.

The obtained aqueous dispersion comprising the multistage polymer may be neutralized by adding one or more base to a pH value of 7.5 or more, and can be from 7.7 to 10, from 7.9 to 9.8, from 8.0 to 9.5, or from 8.5 to 9.2. Neutralization in the present invention, including, for example, neutralization of the first-stage polymer and/or the multistage polymer, may be conducted by adding one or more base which may lead to partial or complete neutralization of the ionic or latently ionic groups of the first-stage polymer and/or the multistage polymer. Examples of 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, or aluminum hydroxide; organic amines including, for example, primary, secondary, and tertiary amines, such as triethyl amine, ethylamine, propylamine, monoisopropylamine, monobutylamine, hexylamine, ethanolamine, diethyl amine, dimethyl amine, 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, or 2-amino-2-methyl-1-propanol; or mixtures thereof. Desirably, the base is selected from ammonia, 2-amino-2-methyl-1-propanol, or mixtures thereof.

The process for preparing the multistage polymer can reduce coagulum formation in the multistage free-radical polymerization process (that is, good process stability) , for example, the dry coagulum content of the resulting aqueous dispersion of the multistage polymer composition can be 520 parts per million (ppm) or less. The multistage polymer is typically present in an aqueous dispersion. The aqueous dispersion of the multistage polymer can have a reduced coagulum content, such as less than 500 ppm, and can bc less than 200 ppm, less than 150 ppm, or even 100 ppm or less, ofcoagulum, after sieving with 325 mesh (44 micrometers) , by weight based on the weight of the aqueous dispersion (further details provided below under Coagulum Content test) .

The coating composition of the present invention may comprise the multistage polymer at a concentration of from 1%to 80%, from 3%to 70%, or from 5%to 60%, by weight based on the dry weight of the coating composition.

The coating composition of the present invention also comprises (B) silver ions. The silver ions typically form a silver complexed with the multistage polymer. The term “silver complexed with polymer” herein refers to silver ions which is complexed with a polymer via coordination bonds. The term “silver ions” include silver ions, or a compound which can release silver ions when it is incorporated into the coating composition of the present invention. Silver ions may be added to the antibacterial composition in the form of a silver solution such as silver nitrate in water. Aside from water, other liquid mediums can also be used in the silver solution, such as aqueous buffered solutions and organic solutions such as polyethers or alcohols. Other sources of silver for forming silver solutions include silver acetate, silver nitrate, silver sulfate, Tollens' Reagent, silver carboxylates, or mixtures thereof. The concentration of silver in these solutions can vary from the concentration required to add a known quantity of silver to the antibacterial composition to a saturated silver solution.

The coating composition of the present invention comprises from 1 part per million (ppm) to 1000 ppm of the silver ions, by weight based on the weight of the coating composition, and can be 5 ppm or more, 6 ppm or more, 7 ppm or more, 8 ppm or more, 9 ppm or more, 10 ppm or more, 11 ppm or more, even 12 ppm or more while at the same time is 1000 ppm or less, and can be 900 ppm or less, 800 ppm or less, 700 ppm or less, 600 ppm or less, 500 ppm or less, 400 ppm or less, 300 ppm or less, 100 ppm or less, 80 ppm or less, 60 ppm or less, or even 50 ppm or less, desirably 10 to 500 ppm, more desirably 12 to 300 ppm, most desirably 12 to 60 ppm, of the silver ions. Surprisingly, the aqueous antimicrobial coating composition can achieve the required antibacterial activity described below at a low concentration of silver ions, for example, 120 ppm or less, 100 ppm or less, or even 60 ppm or less. Alternatively, the silver ions can be in an amount sufficient to provide a molar ratio of heterocyclic groups (such as imidazole groups) in the multistage polymer to the silver ions in the coating composition is 10∶1 or higher. Alternatively, the molar ratio of heterocyclic groups in the multistage polymer to the silver ions in the coating composition can be 11∶1 or higher, 12∶1 or higher, 13∶1 or higher, 14∶1 or higher, 15∶1 or higher, even 20∶1 or higher while at the same time can be 50∶1 or lower, and can be 48∶1 or lower, 45∶1 or lower, , 40∶1 or lower, 35∶1 or lower, or even 30∶1 or lower, desirably from 14∶1 to 35∶1, more desirably from 14∶1 to 30∶1.

The coating composition of the present invention also comprises (C) zinc oxide. The zinc oxide can be regular zinc oxide particles with a D90 of from greater than 100 nm to 10 micrometers (μm) and can be from greater than 100 nm to 1 μm; nano zinc oxide particles with a D90 of from 1 nm to 100 nm and can be from 20 nm to 100 nm; or mixtures thereof. D90 means that 90%of the total particles are smaller than this size by number distribution, as measured using Malvern Mastersizer 2000 with Hydro 2000SM dispersion unit. The concentration of zinc oxide may be, by weight based on thc weight of thc aqueous antimicrobial coating composition, in a range of 0.04%to 1.0%, and can be 0.04%or more, 0.05%or more, 0.08%or more, 0.1%or more, 0.12%or more, 0.15%or more, even 0.16%or more while at the same time is 1.0%or less, and can be 0.95%or less, 0.9%or less, 0.85%or less, 0.8%or less, 0.7%or less, 0.6%or less, 0.5%or less, 0.4%or less, 0.3%or less, 0.2%or less, 0.18%or less, or even 0.16%or less, desirably from 0.04%to 0.8%.

The coating composition of the present invention comprises (D) a pigment that is other than the zinc oxide described above. “Pigment” herein refers to a particulate inorganic material which is capable of materially contributing to the opacity or hiding capability of a coating. Such materials typically have a refractive index greater than 1.8. The pigments may include, for example, titanium dioxide (TiO₂) , iron oxide, barium sulfate, barium carbonate, or mixtures thereof. Desirably, the pigment is TiO₂. TiO₂ typically exists in two crystal forms, anastase and rutile. TiO₂ may be also available in concentrated dispersion form.

The coating composition of the present invention may comprise or be free of one or more extenders. “Extender” herein refers to a particulate material having a refractive index of less than or equal to 1.8 and greater than 1.3. Examples of suitable extenders include calcium carbonate, clay, calcium sulfate, aluminosilicates, silicates, zeolites, mica, diatomaceous earth, solid or hollow glass, ceramic beads, nepheline syenite, feldspar, diatomaceous earth, calcined diatomaceous earth, talc (hydrated magnesium silicate) , silica, alumina, kaolin, pyrophyllite, perlite, baryte, wollastonite, opaque polymers such as ROPAQUE^TM Ultra E polymer available from The Dow Chemical Company (ROPAQUE is a trademark of The Dow Chemical Company) , or mixtures thereof. The coating composition may have a pigment volume concentration (PVC) of from zero to 90%, from 10%to 80%, from 20%to 70%, or from 30%to 60%. PVC may be determined by the equation:
PVC= [Volume _{(Zinc Oxide+Pigment+Extender)} /Volume _{(Zinc Oxide+Pigment+Extender+Binder)} ] ×100%.

The coating composition of the present invention may comprise or be free of one or more defoamers. “Defoamers” herein refer to chemical additives that reduce and hinder the formation of foam. Defoamers may be silicone-based defoamers, mineral oil-based defoamers, ethylene oxide/propylene oxide-based defoamers, alkyl polyacrylates, or mixtures thereof. Suitable commercially available defoamers include, for example, TEGO Airex 902 W and TEGO Foamex 1488 polyether siloxane copolymer emulsions both available from TEGO, BYK-024 silicone deformer available from BYK, Nopco NXZ deformer available from Nopco, or mixtures thereof. The defoamer may be present at a concentration of from zero to 1.0%, from 0.1%to 0.6%, or from 0.2%to 0.4%, by weight based on the total dry weight of the aqueous antimicrobial coating composition.

The coating composition of the present invention may comprise or be free of one or more thickeners. The thickeners may include polyvinyl alcohol (PVA) , clay materials, acid derivatives, acid copolymers, urethane associate thickeners (UAT) , polyether urea polyurethanes (PEUPU) , polyether polyurethanes (PEPU) , or mixtures thereof. Examples of suitable thickeners include alkali swellable emulsions (ASE) such as sodium or ammonium neutralized acrylic acid polymers; hydrophobically modified alkali swellable emulsions (HASE) such as hydrophobically modified acrylic acid copolymers; associative thickeners such as hydrophobically modified ethoxylated urethanes (HEUR) ; and cellulosic thickeners such as methyl cellulose ethers, hydroxymcthyl ccllulosc (HMC) , hydroxycthyl ccllulosc (HEC) , hydrophobically-modificd hydroxy cthyl cellulose (HMHEC) , sodium carboxymethyl cellulose (SCMC) , sodium carboxymethyl 2-hydroxyethyl cellulose, 2-hydroxypropyl methyl cellulose, 2-hydroxyethyl methyl cellulose, 2-hydroxybutyl methyl cellulose, 2-hydroxyethyl ethyl cellulose, and 2-hydoxypropyl cellulose. Desirably, the thickener is a hydrophobically-modified hydroxy ethyl cellulose (HMHEC) . The thickener may be present at a concentration of from zero to 5.0%, from 0.2%to 4.0%, or from 0.3%to 3%, by dry weight based on the total dry weight of the coating composition.

The coating composition of the present invention may comprise or be free of one or more wetting agents. “Wetting agents” herein refer to chemical additives that reduce the surface tension of a coating composition, causing the coating composition to more easily spread across or penetrate the surface of a substrate. Wetting agents may be polycarboxylates, anionic, zwitterionic, or non-ionic. The wetting agent may be present at a concentration of from zero to 5.0%, from 0.2%to 4.0%, or from 0.3%to 3.0%, by weight based on the total dry weight of the coating composition.

The coating composition of the present invention may comprise or be free of one or more dispersants. The dispersants may include nonionic, anionic, or cationic dispersants such as polyacids with suitable molecular weight, 2-amino-2-methyl-1-propanol (AMP) , dimethyl amino ethanol (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., weight average molecular weight ranging from 1,000 to less than 50,000 as measured by gel permeation chromatography (GPC) ) , including those that have been hydrophobically-or hydrophilically-modified, e.g., 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 of thereof; or mixtures thereof. The dispersant may be present at a concentration of from zero to 10%, from 0.2%to 5.0%, or from 0.5%to 3.0%, by dry weight based on the total dry weight of the coating composition.

The coating composition of the present invention may comprise or be free one or more coalescents. “Coalescents” herein refer to slow-evaporating solvents that fuse polymer particles into a continuous film under ambient condition. Examples of suitable coalescents include 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, dipropylene glycol n-propyl ether, n-butyl ether, or mixtures thereof. Preferred coalescents include dipropylene glycol n-butyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, n-butyl ether, or mixtures thereof. The coalescent may be present at a concentration of from zero to 35%, from 0.1%to 30%, or from 0.2%to 25%, by weight based on the weight of the multistage polymer.

The coating composition of the present invention may also comprise water. Water may be present, by weight based on the weight of the coating composition, from 10%to 90%or from 20%to 80%.

In addition to the components described above, the coating composition of the present invention may further comprise any one or combination of the following additives: buffers, anti-freezing agents, humectants, mildcwcidcs, biocidcs, anti-skinning agents, colorants, flowing agents, antioxidants, plasticizers, leveling agents, thixotropic agents, adhesion promoters, and grind vehicles. These additives may be present in a combined amount of from zero to 20%, from 0.5%to 15%, or from 1.0%to 10%, by weight based on the dry weight of coating composition.

The present invention also relates to a process for preparing the aqueous antimicrobial coating composition. The process comprises admixing the multistage polymer (A) with the silver ions (B) , the zinc oxide (C) , and the pigment (D) . Components in the coating composition may be mixed in any order to provide the coating composition of the present invention. Any of the above-mentioned optional components may also be added to the composition during or prior to the mixing to form the coating composition. Silver ions can be mixed with the aqueous dispersion of the multistage polymer first, and then further mixed with other components such as the zinc oxide (C) and the pigment (D) . Desirably, the pigment and/or zinc oxide powder and other optional components (such as a dispersant, thickener, or neutralizer) are first mixed. The obtained admixture may be then subjected to shearing in a grinding or milling device as is well known in the pigment dispersion art. Such grinding or milling devices include roller mills, ball mills, bead mills, attrittor mills and include mills in which the admixture is continuously recirculated. The shearing of the admixture is continued for a time sufficient to disperse the pigment. The time sufficient to disperse the pigment typically depends on the nature of the pigment, the dispersant and the grinding or milling device which is used and will be determined by the skilled practitioner. The obtained grinds can be further added the multistage polymer and silver ions, and/or zinc oxide dispersed in an aqueous dispersion, thereby forming the coating composition.

The present invention also provides a method of providing an antimicrobial coating or a coated substrate. The method comprises the steps of: a) applying the coating composition to a substrate, and b) drying, or allowing to dry, the applied antimicrobial coating composition, thereby forming the antimierobial coating (hereinafter also referred to as “coating” ) or the coating substrate. The coating composition can be applied to a substrate by incumbent means including brushing, dipping, rolling and spraying. Desirably, the coating composition is applied by spraying. The standard spray techniques and equipment for spraying such as air-atomized spray, air spray, airless spray, high volume low pressure spray, and electrostatic spray such as electrostatic bell application, and either manual or automatic methods can be used. After The coating composition has been applied to a substrate, The coating composition can dry, or allow to dry, to form a fi lm (this is, coating or paint) at room temperature (20-25 degrees Celsius (℃) ) , or at an elevated temperature, for example, from 35 to 60 ℃. The antimicrobial coating obtained therefrom (that is, a film) or the coated substrate shows desired antimicrobial properties, as indicated by antibacterial activity of 2.0 or higher in 2 hours, according to the Antibacterial Activity Test described in the Examples section below. At the same time, such coating or paint also shows good coloration stability upon exposure to light, as indicated by a final whiteness of 75 or higher (≥ 75) and the change of whiteness no more than 10 units (≤ 10) , after exposure for two weeks (further details provided in the Paint Coloration Stability Test described herein below) .

The coating composition of the present invention can be applied to, and adhered to, various substrates. Examples of suitable substrates include concrete, cementious substrates, wood, metals, stones, elastomeric substrates, glass or fabrics, and preferably, wood. The coating composition can be used as is suitable for various applications whcrc antimicrobial propcrtics such as anti-viral propcrtics arc dcsircd, including, for cxamplc, wood coatings, metal protective coatings, architecture coatings, traffic paints, marine and protective coatings, automotive coatings, wood coatings, joinery coatings, floor coatings, coil coatings, traffic paints, and civil engineering coatings. The coating composition can be used alone, or in combination with other coatings to form multi-layer coatings.

EXAMPLES

Some embodiments of the invention will now be described in the following Examples, wherein all parts and percentages are weight percentages relative to composition, unless otherwise specified. The materials used in the examples and their abbreviations are given below. Particle size of zinc oxide is measured using Malvern Mastersizer 2000 with Hydro 2000SM dispersion unit. TERGITOL, TRITON, and ACRYSOL are all trademarks of The Dow Chemical Company.

Butyl acrylate (BA) , methyl methacrylate (MMA) , 2-ethylhexyl acrylate (2-EHA) , ethyl acrylate (EA) and methacrylic acid (MAA) are available from Shanghai LangYuan Chemical Co., Ltd.

Acetoacetoxy ethyl methacrylate (AAEM) is available from The Dow Chemical Company.

DISPONIL^TM FES 32 Surfactant, available from BASF, is a sodium salt of fatty alcohol ether sulphate.

Rhodafac^TM RS-610 S25 Surfactant ( “RS-610 S25” ) , available from Solvay, is a sodium salt of polyethylene glycol monotridecyl ether phosphate.

Rhodafac^TM RS-610 A25 Surfactant ( “RS-610 A25” ) , available from Solvay, is an ammonia salt of polyethylene glycol monotridecyl ether phosphate.

ABS-15 Surfactant, available from Shanghai Honesty Fine Chemical Co., Ltd., is sodium dodecyl benzene sulfonate.

Silquest^TM A-174 ( “A-174” ) , available from Momentive, is 3-Methacryloxypropyltrimethoxysilane.

Acrylamide (AM, 40%active) , imidazole (IMI) , and 1-vinyl imidazole (VI) are available from Shanghai Chemical Reagent Co., Ltd.

BRUGGOLITE^TM FF6, available from Bruggemann Chemical, is a 2-hydroxy-2-sulfinatoacetic acid disodium salt and reducing agent.

Ammonia persulfate (APS) , tert-Butyl hydroperoxide (t-BHP) , and hydrogen peroxide (H₂O₂) used as initiators; ferrous sulfate (FeSO₄) and ethylene diamine tetra acetic acid (EDTA) sodium salt used as promoters; isoascorbic acid (IAA) used as an activator, sodium carbonate (Na₂CO₃) , mono ethanol amine (MEA) , sodium hydroxide (NaOH) used as neutralizers; and silver nitrate (AgNO₃) , and regular zinc oxide (D90 particle size: greater than 100 nm to 10 μm) are all available from Shanghai Chemical Reagent Co., Ltd.

Nano zinc oxide (D90 particle size: ＜ 100 nm) is available from Zhongxing (Guangzhou) of China.

OROTAN^TM Kuai Yi^TM dispersant, TERGITOL^TM EF-406 surfactant, ACRYSOL^TM RM-2020 NPR thickener, and ACRYSOL^TM RM-8W thickener are all available from The Dow Chemical Company.

Nopco NXZ defoamer is available from SAN NOPCO.

Ti-Pure^TM R-706, available form DuPont, is titanium dioxide and used as a pigment.

DB-80 extender (aluminum silicate hydroxide) , CC-1000 extender (CaCO₃) , and CELITE^TM 499 matting agent (flux calcined diatomite) are all available from Guangfu Building Materials Group (China) .

JMAC^TM LP10 prcscrvativc, availablc from Clariant, is a slurry of silvcr chloridc (AgCl) prccipitatcd on titanium dioxide (TiO₂) .

ACTICIDE^TM OTW preservative is available from THOR.

Natrosol^TM 250 HBR thickener is available from Ashland.

The following standard analytical equipment and methods are used in the Examples.

Coagulum Content

Weigh a 325 mesh (44 μm) screen on an analytical balance and record the weight of the screen to 4 decimal places, denoted as “W1” . Fix the screen between plastic rings in a screen apparatus. Weigh 200 grams (g) of an aqueous composition into a container. Pour the aqueous dispersion through the screen. Rinse the container until it is clean and pour the water through the screen. Remove the screen from the plastic rings and place the screen in an oven at 150 ℃ for 5±1 minutes (min) . Remove the screen from the oven, allow it to cool down for 1 min, and then weigh the screen on the analytical balance and record the weight to 4 decimal places, denoted as “W2” . Then the dry coagulum content in part per million (ppm) is calculated by (W2-W1) *5000. The lower the coagulum content, the more stable polymerization process in preparing the aqueous composition.

Paint Coloration Stability Test

Whiteness is measured according to ASTM E131-20 (Standard Practice for Calculating Yellowness and Whiteness Indices from Instrumentally Measured Color Coordinates using Datacolor 500UV) . The higher value of whiteness, the closer to the ideal white.

A coating composition (i.e., paint formulation) sample was let down on a vinyl chart using a 200 μm film applicator and then placed into an oven at 50 ℃ overnight to give a coated panel. The initial whiteness of the resulting coating film on the coated panel was measured by putting the coated panel closely attached to the window of a detector after standardization using D65 as light source, denoted as “Initial W” . Then the coated panel was placed in a glass cabinet on the roof for exposure under sun light. After exposure for two weeks, the whiteness of the coated panel after exposure was measured, denoted as “Final W” . The change of the whiteness, delta W, is then calculated by (Initial W-Final W) . The less delta W, the better coloration stability. Acceptable coloration stability requires delta W equal to or less than 10 units (≤ 10 units) and Final W of 75 or more (≥75) after two-week exposure. Otherwise, if delta W ＞ 10 units and/or Final W ＜75 after two-week exposure, the sample fails the coloration stability test.

Antibacterial Activity Test

Modified JIS Z 2801 (Antimicrobial products -Test for antimicrobial activity and efficacy) was followed for determining antimicrobial activities of samples against Escherichia coli bacteria ( “E. coli” ) (Strain number ATCC 8739 from American Type Culture Collection) in 2 hours at 25 ℃ and 90%relative humidity (RH) .

A coating composition sample ( “test sample” ) was applied onto a plastic chart with a 100 μm film applicator. A blank plastic chart was used as an untreated control sample ( “control sample” ) . The suspension of microorganism was diluted in a nutritive broth at 10⁶ Colony Forming Unit per milliliter (CFU/ml) . Surfaces of the control and test samples were inoculated with the diluted microbial suspension (0.3 mL) , and then covered with a thin, sterile film to ensure the diluted microbial suspension close contact with the sample surfaccs. Microbial conccntrations on thc control samplc and tcst samplc surfaccs wcrc dctcrmincd at “timc zero” by elution followed by dilution and plating, denoted as “V_0-control” and “V_0-test” , respectively. After the suspension of microorganism contacted with the sample surfaces, the covered control sample and test sample were allowed to incubate undisturbed at 25 ℃ and 90%RH for 2 hours. After incubation, residual microbial concentrations on the test sample ( “V_Test” ) and control sample ( “V_Control” ) were determined by colony count (using diluted plates and dilution ratios) .

The antimicrobial activity is calculated as logarithm reduction of colony count in the test sample comparing with the control sample as below:

Antimicrobial activity = log [ (V_Control/V_0-control) / (V_Test/V_0-test) ]

The higher value of the antimicrobial activity, the higher antimicrobial efficacy of the test sample. The acceptable antimicrobial activity is 2.0 or higher, indicating 99%or higher bacteria can be killed in 2 hours.

Antiviral Activity Test

Antiviral efficacy properties against enveloped Influenza Virus H3N2 and non-enveloped virus Enterovirus 71, respectively, are determined according to Chinese CNCIA 03002-2020 (Test method for determining antiviral activity of coating) , which includes sample preparation and antiviral activity test procedure. Details are provided below:

A coating composition sample ( “test sample” ) was applied onto Aluminum carriers with a 50 μm film applicator, after drying, applied again with 50 micrometers (μm) film applicator. A paint without any biocidal components was used as an untreated control sample ( “control sample” ) . The virus of enveloped Influenza Virus H3N2 and non-enveloped virus Enterovirus 71, respectively, were inoculated on both test sample and control sample, then covered with a thin, sterile film to ensure the virus suspension close contact with the samplc surfaces and incubated for 24 hours at 25 ℃ and 90%relative humidity (RH) . The virus titcrs (TCID₅₀/ml) on both control sample and test sample surfaces were determined at “time zero” , denoted as “V_0- _control” and “V_0-test” , respectively. After the virus suspension contacted with the sample surfaces, the covered control sample and test sample were allowed to incubate undisturbed at 25 ℃ and 90%RH for 24 hours. After incubation, residual virus titers on the test sample ( “V_Test” ) and control sample ( “V_Control” ) were determined. The antiviral activity is calculated as logarithm reduction of virus titer in the test sample comparing with the control sample as below:

Antiviral activity = log [ (V_Control/V_0-control) / (V_Test/V_0-test) ]

If the antiviral activity (i.e., logarithm reduction of virus titer) is equal to or greater than 2.0 (≥2.0) for enveloped virus Influenza Virus H3N2 and equal to or greater than 0.82 (≥0.82) for non-enveloped Enterovirus 71 in 24 hours, the sample passes the antiviral activity test. Otherwise, the sample fails the antiviral activity test.

Synthesis of Polymer Dispersion ( “PD” ) -1 (PD-1)

Firstly, a monomer emulsion 1# (ME1) was prepared by mixing deionized (DI) water (329.16 g) , AM (21.19 g, 40%) , MAA (25.82 g) , BA (1022.12 g) , MMA (475.55 g) , AAEM (50.85 g) and RS-610 S25 surfactant (98.41 g, 25%) . A monomer mix 2# (MM2) was prepared by mixing BA (110.73 g) and VI (8.56 g) .

Secondly, in a one-gallon vessel equipped with a reflux condenser and a stirrer, DI water (940 g) was addcd at an agitation ratc of 130 rcvolutions pcr minutc (rpm) . Mcanwhilc, thc tcmpcraturc of thc rcaction vessel was raised to 91℃. Then FES-32 surfactant (5.40 g, 31%) and a buffer solution of sodium carbonate (Na₂CO₃) (3.41 g in 31.37 g DI water) was introduced into the reaction vessel.

Thirdly, the ME1 (93.13 g) and an initiator solution of APS (3.40 g in 28 g DI water) were injected into the reaction vessel. The reaction mixture was held at a temperature between 80 and 95℃ for 5 min. Thereafter, the remainder of ME1 was added into the reaction vessel over the span of 100 min. After completing the feed of ME1, MM2 was added into the reaction vessel over the span of 10 min. During the addition of ME1 and MM2, another shot of an initiator solution consisting of APS (1.55 g) and DI water (167.33 g) were co-fed into the reaction vessel over the span of 120 min. The reaction temperature was being held at somewhere between 84 to 86 ℃. After the above mixing steps were completed, the reaction vessel was cooled down. While cooling the contents of the reaction vessel to room temperature, an initial reductant solution consisting of ferrous sulfate (0.0091 g) , EDTA sodium salt (0.0549 g) and DI water (10 g) , a secondary reductant solution consisting of BRUGGOLITE FF6 (1.05 g) and DI water (50 g) , and an initiator solution consisting of 70%aqueous solution t-BHP (1.03 g) , 35%aqueous solution H₂O₂ (0.45 g) and DI water (50 g) , were injected into the reaction vessel when the temperature had dropped to 70 ℃. Then a H₂O₂ and t-BHP solution (6.55 g 35%aqueous solution H₂O₂, 6.45 g 70%aqueous solution t-BHP in 40 g H₂O) was added into the reaction vessel when the temperature was over 50℃. Then a neutralizer solution comprising 15 g of MEA, 17.5 g of TERGITOL^TM 15-S-40 (70%) and 32.50 g H₂O was added into the reaction vessel. Thus, a dispersion containing a multistage polymer was obtained. Finally, a silver nitrate solution (0.51 g silver nitrate in 53.35 g H₂O) was added to obtain silver ion-containing polymer dispersion for use in preparation of coating composition samples described below.

Synthesis of PD-1A

An aqueous polymer dispersion of PD-1A was prepared based on substantially the same procedure as PD-1, except no silver nitrate solution was added in the final step.

Synthesis of PD-2

An aqueous polymer dispersion of PD-2 was prepared based on substantially the same procedure as PD-1, except the ME1 and MM2 used are given below and no silver nitrate solution was added in the final step.

ME1 was prepared by mixing DI water (329.16 g) , AM (21.19 g, 40%) , MAA (25.82 g) , BA (1013.62 g) , MMA (471.31 g) , AAEM (63.56 g) and RS-610 S25 surfactant (98.41 g, 25%) . MM2 was prepared by BA (119.24 g) .

Synthesis of PD-3

An aqueous polymer dispersion of PD-3 was prepared based on substantially the same procedure as PD-1, except the ME1 and MM2 used are as follows,

ME1 was prepared by mixing DI water (329.16 g) , AM (21.19 g, 40%) , MAA (25.82 g) , BA (885.86 g) , MMA (475.55 g) , AAEM (50.85 g) and RS-610 S25 surfactant (98.41 g, 25%) . MM2 was prepared by mixing BA (247.02 g) and VI (8.56 g) .

Synthesis of PD-4

An aqueous polymer dispersion of PD-4 was prepared based on substantially the same procedure as PD-1, cxccpt ME1 and MM2 uscd arc as follows:

ME1 was prepared by mixing DI water (329.16 g) , AM (21.19 g, 40%) , MAA (25.82 g) , BA (885.86 g) , MMA (475.55 g) , AAEM (50.85 g) and RS-610 S25 surfactant (98.41 g, 25%) . MM2 was prepared by mixing BA (242.76 g) and VI (12.84 g) .

Synthesis of PD-5

Firstly, a monomer emulsion (ME) was prepared by mixing DI water (324.79 g) , AM (18.75 g, 40%) , MAA (30.48 g) , BA (693.89 g) , MMA (767 g) , VI (7.58 g) , and RS-610 S25 surfactant (98.41 g, 25%) .

Secondly, in a one-gallon vessel equipped with a reflux condenser and a stirrer, DI water (818 g) was added at an agitation rate of 130 RPM. Meanwhile, the temperature of the reaction vessel was raised to 91 ℃. Then FES-32 surfactant (7.26 g, 31%) and a buffer solution of sodium carbonate (Na₂CO₃) (3.02 g in 27.78 g DI water) was introduced into the reaction vessel.

Thirdly, the ME (82.4 g) and an initiator solution of APS (3.01 g in 24.08 g DI water) were injected into the reaction vessel. The reaction mixture was held at a temperature between 80 and 95℃ for 5 min. Thereafter, the remainder of ME was added into the reaction vessel over the span of 120 min. During the addition of ME, another shot of an initiator solution consisting of APS (1.37 g) and DI water (148.17 g) were co-fed into the reaction vessel over the span of 120 min. The reaction temperature was being held at somewhere between 84 to 86 ℃. After the above mixing steps were completed, the reaction vessel was cooled down. While cooling the contents of the reaction vessel to room temperature, an initial reductant solution consisting of ferrous sulfate (0.0091 g) , EDTA sodium salt (0.0549 g) and DI water (10 g) , a secondary reductant solution consisting of IAA (0.84 g) and DI water (40.75 g) , and an initiator solution consisting of 70%aqueous solution t-BHP (0.91 g) , 35%aqueous solution H₂O₂ (0.4 g) and DI water (38.89 g) , were injected into the reaction vessel when the temperature had dropped to 70 ℃. Then a H₂O₂ solution (2.69 g 35%aqueous solution H₂O₂ in 5.67 g H₂O) was added into the reaction vessel when the temperature was over 50℃. Finally, a silver nitrate solution (0.51 g silver nitrate in 53.35 g H₂O) was added to obtain silver ion-containing polymer dispersion for use in preparation of coating composition samples described below. Thus, PD-5 containing one-sage polymer was obtained.

Synthesis of PD-6

An aqueous polymer dispersion of PD-6 was prepared based on substantially the same procedure as PD-1, except the ME1 and MM2 used are as follows,

ME1 was prepared by mixing DI water (329.16 g) , AM (21.19 g, 40%) , MAA (25.82 g) , BA (1013.6 g) , MMA (475.55 g) , AAEM (50.85 g) , VI (8.56 g) and RS-610 S25 surfactant (98.41 g, 25%) . MM2 was prepared by BA (119.25 g) .

Synthesis of PD-7

An aqueous polymer dispersion of PD-7 was prepared based on substantially the same procedure as PD-1, except the ME1 and MM2 used arc as follows:

ME1 was prepared by mixing DI water (329.16 g) , AM (21.19 g, 40%) , MAA (25.82 g) , BA (1056.22 g) , MMA (475.55 g) , AAEM (50.85 g) and RS-610 S25 surfactant (98.41 g, 25%) . MM2 was prepared by mixing BA (76.66 g) and VI (8.56 g) .

Synthcsis of PD-8

An aqueous polymer dispersion of PD-8 was prepared based on substantially the same procedure as PD-1, except the ME1 and MM2 used arc as follows,

ME1 was prepared by mixing DI water (329.16 g) , AM (21.19 g, 40%) , MAA (25.82 g) , BA (971.04 g) , MMA (475.55 g) , AAEM (50.85 g) and RS-610 S25 surfactant (98.41 g, 25%) . MM2 was prepared by mixing BA (161.84 g) and VI (8.56 g) .

Synthesis of PD-8A

An aqueous polymer dispersion of PD-8A was prepared based on substantially the same procedure as PD-1, except the ME1, MM2, and silver nitrate solution used arc as follows:

ME1 was prepared by mixing DI water (329.16 g) , AM (21.19 g, 40%) , MAA (25.82 g) , BA (971.04 g) , MMA (475.55 g) , AAEM (50.85 g) and RS-610 S25 surfactant (98.41 g, 25%) . MM2 was prepared by mixing BA (161.84 g) and VI (8.56 g) . 1.02 g of silver nitrate in 53.35 g H₂O was added in the final step.

Synthesis of PD-8B

An aqueous polymer dispersion of PD-8B was prepared based on substantially the same procedure as PD-1, except the ME1, MM2, and silver nitrate solution used arc as follows:

ME1 was prepared by mixing DI water (329.16 g) , AM (21.19 g, 40%) , MAA (25.82 g) , BA (971.04 g) , MMA (475.55 g) , AAEM (50.85 g) and RS-610 S25 surfactant (98.41 g, 25%) . MM2 was prepared by mixing BA (161.84 g) and VI (8.56 g) . 1.78 g silver nitrate in 53.35 g H₂O was added in the final step.

Synthesis of PD-9

An aqueous polymer dispersion of PD-9 was prepared based on substantially the same procedure as PD-1, except the ME1 and MM2 used arc as follows,

ME1 was prepared by mixing DI water (329.16 g) , AM (21.19 g, 40%) , MAA (25.82 g) , BA (800.68 g) , MMA (475.55 g) , AAEM (50.85 g) and RS-610 S25 surfactant (98.41 g, 25%) . MM2 was prepared by mixing BA (332.2 g) and VI (8.56 g) .

Synthesis of PD-10

Firstly, a monomer emulsion 1# (ME1) was prepared by mixing DI water (278 g) , AM (28.78 g, 40%) , MAA (29.69 g) , n-DDM (1.28 g) , MMA (834.26 g) , BA (304.63 g) , 2-EHA (102.52 g) , and ABS-15 surfactant (58.73 g, 16.33%) . A monomer emulsion 2# (ME2) was prepared by mixing Dl water (67.52 g) , BA (170.31 g) , 2-EHA (25.63 g) , MMA (115.33 g) , VI (8.00 g) , A-174 (1.60 g) , ABS-15 surfactant (9.80 g, 16.33%) , and RS-610 A25 surfactant (19.17 g, 25%) .

Secondly, in a one-gallon vessel equipped with a reflux condenser and a stirrer, DI water (837.61 g) was added at an agitation rate of 130 rpm. Meanwhile, the temperature of the reaction vessel was raised to 91℃. Then ABS-15 surfactant (14.12 g, 16.33%) and a buffer solution of sodium carbonate (Na2CO3) (2.08 g in 12.82 g DI water) was introduced into the reaction vessel.

Thirdly, ME1 (51.7 g) , and an initiator solution of APS (3.41 g in 17.09 g DI water) were injected into the reaction vessel. The reaction mixture was being held at a temperature between 80 and 95℃ for 5 min. Thereafter, the remainder of MEl was added into the reaction vessel over the span of 72 min. After completing the feed of ME l, ME2 was added into the reaction vessel over the span of 18 min. During the addition o f ME1 and ME2, anothcr shot of an initiator solution of APS (1.45 g in 100 g DI watcr) and a buffcr solution of Na₂CO₃ (0.79 g in 100 g D1 water) were co-fed into the reaction vessel over the span of 90 min. The reaction temperature vas being held at somewhere between 87 to 89℃. After the above mixing steps were completed, the reaction vessel was cooled down. While cooling the contents of the reaction vessel to room temperature, an initial reductant solution (0.0164 g ferrous sulfate and 0.0164g EDTA sodium salt in 6.78 g DI water) , a secondary reductant solution (0.62 g IAA in 18.8 g DI water) , and an initiator solution of t-BHP (1.12 g 70%aqueous solution in 18.8 g DI water) , were injected into the reaction vessel when the temperature had dropped to 70℃. Finally, an adjustable amount of ammonia solution was added to the resultant dispersion to keep the pH between 7.5 and 8.5 when the temperature had reached 50℃. Thus, PD-10 was obtained.

Synthesis of PD-11

An aqueous polymer dispersion of PD-11 was prepared based on substantially the same procedure as PD-1, except the ME1 and MM2 used are as follows,

ME 1 was prepared by mixing DI water (329.16 g) , AM (21.19 g, 40%) , MAA (25.82 g) , BA (1039.18 g) , MMA (407.61 g) , AAEM (50.85 g) and RS-610 S25 surfactant (98.41 g, 25%) . MM2 was prepared by mixing BA (93.7 g) , EA (67.94 g) and VI (8.56 g) .

Synthesis of PD-12

An aqueous polymer dispersion of PD-12 was prepared based on substantially the same procedure as PD-1, except the ME1 and MM2 used are as follows,

ME 1 was prepared by mixing DI water (329.16 g) , AM (21.19 g, 40%) , MAA (25.82 g) , BA (1039.18 g) , MMA (407.61 g) , AAEM (50.85 g) and RS-610 S25 surfactant (98.41 g, 25%) . MM2 was prepared by mixing BA (93.7 g) , MMA (67.94 g) and VI (8.56 g) .

Synthesis of PD-14

An aqueous polymer dispersion of PD-14 was prepared based on substantially the same procedure as PD-1, except the ME1 and MM2 used for preparing an emulsion polymer are as follows,

ME1 was prepared by mixing DI water (329.16 g) , AM (21.19 g, 40%) , MAA (25.82 g) , BA (885.86 g) , MMA (475.55 g) , AAEM (50.85 g) and RS-610 S25 surfactant (98.41 g, 25%) . MM2 was prepared by mixing BA (245.32 g) and VI (10.27 g) .

Synthesis of PD-15

An aqueous polymer dispersion of PD-15 was prepared based on substantially the same procedure as PD-1, except the ME1 and MM2 used are as follows,

ME1 was prepared by mixing DI water (329.16 g) , AM (21.19 g, 40%) , MAA (25.82 g) , BA (1056.22 g) , MMA (475.55 g) , AAEM (50.85 g) and RS-610 S25 surfactant (98.41 g, 25%) . MM2 was prepared by mixing BA (80.07 g) and VI (5.14 g) .

The obtained polymer dispersions (solids contents between 44%-48%) were characterized and results of propcrties are shown in Table 1. As shown in Table l, polymer dispersions PDs 1 to 3, PDs 6 to 9, and PDs 11 to 15 all met the requirement for process stability (dry coagulum content ＜ 520 ppm) , some of which even showed a dry coagulum content ＜ 200 ppm. All the obtained polymer dispersions were used as binders in coating composition samples described below.

Table 1 Charactcrization of Polymer Dispcrsions

“Particle size” of polymer particles in PDs was measured by Brookhaven BI-90 Plus Particle , Size Analyzer.

“Coagulum content” of PDs was measured according to the Coagulum Content Test above.

Inventive Examples (IEs) 1-11 and Comparative Examples (CEs) A-D and F-L Coating Composition Samples

Typical formulations for these samples are in Table 2, with the amount of each component reported in grams (g) . The samples wcrc prepared through a two-stage process. Firstly, all components in the grind stage were added sequentially and mixed using a high-speed disperser at 1, 000 rpm for 30 min to get a well dispersed slurry. Then components in the letdown stage werc added sequentially into the slurry and stirred for 30 min at 300 rpm, thereby forming the coating composition samples. Types of binders (i.e., the as prepared PDs) , zinc oxide, and silver used for each sample arc given in Table 4. The obtained samples each had a PVC of 53%and weight solids of 59%.

Table 2 Typical coating compositions

The obtained coating composition samples were characterized for coloration stability according to the Coloration Stability Test and antibacterial efficacy according to the Antibacterial Activity Test and characterization results are given in Table 4. IE 1 and CE A samples were also evaluated for antiviral efficacy according to the Antiviral Activity Test and characterization results arc given in Table 3.

As shown in Table 4, all IEs 1-11 coating composition samples comprising at least the multistage polymer (A) , silver ions (B) , and zinc oxide (C) showed good coloration stability properties, as indicated by whiteness change ( “delta W” ) ≤10 units and final whiteness after 2-week exposure ( “Final W” ) to sun light ≥ 75. In the meanwhile, all IEs samples provided coatings with antimicrobial activity against E. coli higher than 2.0, indicating 99%bacteria can be killed in 2 hours.

In contrast, CE A sample that contains the multistage polymer as claimed and silver ions but no ZnO showed poor coloration stability after exposure to sun light (delia W＞12 units) and insufficient antimicrobial efficacy (antimicrobial activity against E. coli at 0.8) . CE B sample that contains a multistage polymer and ZnO but free of silver ions showed insufficient antimicrobial efficacy (antimicrobial activity against E. coli at 0.6) . It indicates that, in combination of a multistage polymer, silver ions or zinc oxide alone can't achieve the requirements for both antimicrobial efficacy and coloration stability. CE C sample that contains a silver additive Clariant JMAC^TM LP10 (AgCl) , zinc oxide, and a conventional binder other than the specific multistage polymer (A) as claimed showed insufficient antimicrobial efficacy (antimicrobial activity against E. coli at 1.1) . CE D sample that contains 546 ppm of free imidazole (by weight based on the weight of the coating composition sample) , silver ions, zinc oxide and a multistage polymer binder free of heterocyclic groups (PD-2) showed poor coloration stability after exposure to sun light. CE F sample containing PD-4 as the binder showed insufficient antimicrobial efficacy. The PD-4 prepared by multistage polymerization using 0.75%VI (based on total monomer weight for preparing the multistage polymer) also showed an undesirably high coagulum content. CE H and CE G samples containing PD-5 as the binder (with or without ZnO) both showed poor coloration stability upon exposure to sun light, as indicated by delta W greater than 17 units. PD-5 containing 0.5%structural units of VI was prepared by one-stage polymerization, which showed an undesirably high coagulum content. CE I sample that contains a multistage polymer binder prepared in the presence of 0.54%VI in the first stage (based on the first monomer mixture weight) while not in the second stage provided the obtained paint films with insufficient antimicrobial efficacy. CE J sample that contains a multistage polymer binder prepared by using 8%EHA (based on total monomer weight) failed the coloration stability test when exposure to sun light. CE K sample that contains a multistage polymer binder and silver ions at a molar ratio of VI to silver ions of less than 10 provided paint films with poor coloration stability after exposure to sun light. CE L sample with too high zinc oxide loading provided paint films made thereof with thc final whiteness after exposure to sun light of less than 73, indicating the paint films turned into dark.

As shown in Table 3, IE 1 sample passed the antiviral activity test with an antiviral activity higher than 2.0 for enveloped virus Influenza Virus H3N2 and higher than 0.82 for non-enveloped Enterovirus 71 in 24 hours. In contrast, CE A sample failed the antiviral activity test.

Table 3 Antiviral activity of coating composition samples

Table 4 Formulations and characterization results for coating composition samples

“Wt% VI” refers to weight percentage of structural units of vinyl imidazole monomer relative to polymer weight in each PD (i.e., one-stage polymer weight for PD-5 and multistage polymer weight for other PDs).

“VI (or IMI)/Ag molar ratio” refers to the molar ratio of imidazole groups from a polymer (e.g., one-stage polymer for PD-5 and multistage polymer for other PDs) or free imidazole (IMI in CE D) to silver ions for the coating composition sample.

“Wt% ZnO” refers to weight percentage of ZnO relative to the total weight of the coating composition sample.“Silver ion content” refers to part per million of silver ions by weight relative to the total weight of the coating composition sample.

“Antibacterial Activity” was measured according to the Antibacterial Activity Test described above.

N.A.-Not Applicable.

Claims

An aqueous antimicrobial coating composition comprising:

(A) a multistage polymer comprising, by weight based on the weight of the multistage polymer, from 78%to 97%of a first-stage polymer and from 3%to 22%of a second-stage polymer;

wherein the first-stage polymer comprises:

(1a) zero to 0.9%of structural units of a monomer containing at least one heterocyclic group selected from the group consisting of imidazole, benzotriazole, and benzimidazole, by weight based on the weight of the first-stage polymer;

(1b) structural units of a C₁-C₄-alkyl (meth) acrylate; and

(1c) structural units of a monoethylenically unsaturated functional monomer carrying at least one functional group selected from a carboxyl, carboxylic anhydride, sulfonic acid, amide, sulfonate, phosphoric acid, phosphonate, phosphate, or hydroxyl group; a salt thereof; or combinations thereof; and

wherein the second-stage polymer comprises:

(2a) structural units of a monomer containing at least one heterocyclic group selected from the group consisting of imidazole, benzotriazole, and benzimidazole; and

(2b) structural units of a C₁-C₄-alkyl (meth) acrylate;

wherein the combined concentration of structural units of the monomer containing at least one heterocyclic group in the multistage polymer is from 0.1%to 0.65%, by weight based on the weight of the multistage polymer; and

wherein the multistage polymer comprises, by weight based on the weight of the multistage polymer, from zero to less than 5%of structural units of a cycloalkyl (meth) acrylate, a C₆-C₁₀-alkyl (meth) acrylate, or mixtures thereof;

(B) 1 to 1000 parts per million, by weight based on the weight of the aqueous antimicrobial coating composition, of silver ions; wherein the molar ratio of heterocyclic groups in the multistage polymer to silver ions in the coating composition is 10: 1 or higher;

(C) from 0.04%to 1.0%of zinc oxide, by weight based on the weight of the aqueous antimicrobial coating composition; and

(D) a pigment.
The aqueous antimicrobial coating composition of claim 1, wherein the C₁-C₄-alkyl (meth) acrylate for the second-stage polymer is selected from the group consisting of butyl acrylate, ethyl acrylate, and mixtures thereof.
The aqueous antimicrobial coating composition of claim 1 or 2, wherein the first-stage polymer comprises, by weight based on the weight of the first-stage polymer, from 0 to 0.9%of structural units of the monomer containing at least one heterocyclic group; from 0.1%to 15%of structural units of the monoethylenically unsaturated functional monomer, the salt thereof, or combinations thereof; and from 85%to 99%of structural units of the C₁-C₄-alkyl (meth) acrylate.
The aqueous antimicrobial coating composition of any one of claims 1-3, wherein the monomer containing at least one heterocyclic group is 1-vinyl imidazole.
The aqueous antimicrobial coating composition of any one of claims 1-4, wherein the second-stage polymer comprises, by weight based on the weight of the second-stage polymer, from 0.4%to 22%of structural units of 1-vinyl imidazole and from 75%to 99%of structural units of butyl acrylate, ethyl acrylate, or mixtures thereof.
The aqueous antimicrobial coating composition of any one of claims 1-5, wherein the molar ratio of heterocyclic groups in the multistage polymer to silver ions in the coating composition is in a range of from 14: 1 to 35: 1.
The aqueous antimicrobial coating composition of any one of claims 1-6, wherein the second-stage polymer has a number average molecular weight of greater than 30000 grams per mole.
A process for preparing the aqueous antimicrobial coating composition of any one of claims 1-7, comprising: admixing the multistage polymer (A) with the silver ions (B) , the zinc oxide (C) , and the pigment (D) .
A method of providing an antimicrobial coating, comprising:

a) applying the aqueous antimicrobial coating composition of any one of claims 1-7 to a substrate; and b) drying, or allowing to dry, the applied antimicrobial coating composition.