Coating composition and method for preparing a coating composition

Abstract

A coating composition containing, based on the weight of the coating composition, (a) from 20% to 38.5% by dry weight of an aqueous dispersion of an acrylic (co) polymer; (b) 0.5% to 2.9% by dry weight of a water soluble alkali metal silicate; (c) an aqueous solution comprising a water-soluble non-alkali metal salt of non-alkali metal ions; and (d) 0 to 2% by dry weight of a microfiller; wherein the aqueous solution of the non-alkali metal salt is present in an amount that provides a dry weight ratio of the non-alkali metal ions to the acrylic (co) polymer in the range of 0.13% to 3.3% and a dry weight ratio of the non-alkali metal ions to the water-soluble alkali metal silicate in the range of 1.4% to 42%. A process for preparing the coating composition, the process comprising the steps of: (i) blending the aqueous dispersion of the acrylic (co) polymer with the aqueous solution of the water-soluble non-alkali metal salt, thereby forming a blend; (ii) further blending the blend obtained from step (i) with the water-soluble alkali metal silicate and, if present, the microfiller; and optionally, before step (ii), adding 0.06% to 0.52% by weight, based on the total weight of the coating composition, of ethylenediamine tetraacetic acid, a salt thereof or a mixture thereof to the blend obtained from step (i).

Description

Technical Field

[0001] The present invention relates to a coating composition and a method for preparing the same. Background Art

[0002] Waterborne or water-based coating compositions are becoming increasingly more important than solvent-based coating compositions due to fewer environmental problems. A matte coating film is a coating film having a low glossiness, typically having a level lower than 50 on the 60° Gardner glossiness scale. In the wood coating industry, it is more desirable to provide substrates having an even lower gloss finish. Adding micro-fillers such as conventional matting agents and pigments to the coating composition can reduce the glossiness of the coating film made therefrom. To obtain the desired low glossiness, typically 2-3% by dry weight of a matting agent is used based on the solid weight of the coating composition. However, such a high dosage of micro-fillers usually produces a coating film having an undesired low transparency, with a haze value equal to or greater than 33, and sometimes even impairs the hardness of the coating film, which is usually F or harder for topcoats. The coating composition also needs to be stable, otherwise, the grit formed in the coating composition tends to cause defects in the resulting coating film and impair properties such as water resistance.

[0003] Therefore, there is a desire to provide a coating composition that provides a coating film having balanced properties of low glossiness and high transparency without impairing hardness. Summary of the Invention

[0004] The present invention solves the above problems by discovering a novel coating composition. The coating composition of the present invention can provide a coating film having low glossiness, high transparency, and desired hardness. Such a coating composition is a novel combination of: (a) an aqueous dispersion of an acrylic (co)polymer; (b) a water-soluble alkali metal silicate; and (c) an aqueous solution of a water-soluble non-alkali metal salt containing a specified content and ratio of non-alkali metal ions. The coating composition of the present invention provides a matte coating film without the need to use conventional micro-fillers (e.g., matting agents). The coating film exhibits a gloss level less than 50 on the 60° Gardner glossiness scale, a haze value less than 33, and a hardness of F or harder. As indicated by a fineness of less than 40 micrometers (μm), the coating composition is also stable at room temperature (20 - 25 degrees Celsius (°C)). Desirably, the coating composition provides a coating film having good water resistance with a rating greater than 3. These properties can be determined according to the test methods described in the Examples section below.

[0005] In a first aspect, the present invention is a coating composition that, based on the total weight of the coating composition, comprises:

[0006] (a) 20% to 38.5% by dry weight of an aqueous dispersion of an acrylic (co)polymer;

[0007] (b) 0.5% to 2.9% by dry weight of a water-soluble alkali metal silicate;

[0008] (c) an aqueous solution of a water-soluble non-alkali metal salt containing non-alkali metal ions; and

[0009] (d) 0 to 2% by dry weight of a micro filler;

[0010] wherein the aqueous solution of the non-alkali metal salt is present in an amount to provide a dry weight ratio of these non-alkali metal ions to the acrylic (co) polymer in the range of 0.13% to 3.3% and a dry weight ratio of these non-alkali metal ions to the water-soluble alkali metal silicate in the range of 1.4% to 42%.

[0011] In a second aspect, the present invention is a method for preparing the coating composition of the first aspect. The method includes:

[0012] (i) admixing the aqueous dispersion of the acrylic (co) polymer with the aqueous solution of the water-soluble non-alkali metal salt to form an admixture;

[0013] (ii) further admixing the admixture obtained from step (i) with the water-soluble alkali metal silicate and, if present, the micro filler; and optionally,

[0014] adding 0.06% to 0.52% by weight, based on the total weight of the coating composition, of ethylenediaminetetraacetic acid, its salts, or mixtures thereof to the admixture obtained from step (i) before step (ii). Detailed Description

[0015] When not designated by a test method number, the test method refers to the latest test method as of the priority date of this document. References to test methods include references to both the test society and the test method number. The following test method abbreviations and identifiers apply herein: ASTM refers to ASTM International methods, GB / T refers to the national standards of China, and EN refers to European standards.

[0016] Products identified by their trade names refer to the compositions that could be obtained under those trade names as of the priority date of this document. "And / or" means "and, or as an alternative form". Unless otherwise specified, all ranges include the endpoints.

[0017] The "structural unit" (also referred to as "polymeric unit") of a named monomer refers to the residue of the monomer after polymerization, i.e., the polymerized monomer or the monomer in polymerized form. For example, the structural unit of methyl methacrylate is shown below: where the dashed line indicates the attachment point of the structural unit to the polymer backbone.

[0018] As used herein, "nonionic monomer" refers to a monomer that does not carry an ionic charge between pH = 1 - 14.

[0019] As used herein, the "glass transition temperature" or "Tg" can be calculated using the following Fox equation (T.G. Fox, Bull. Am. Physics Soc., Vol. 1, No. 3, p. 123 (1956)). For example, for calculating the Tg of a copolymer of monomers M1 and M2,

[0020]

[0021] where T g (calculated) 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, and 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 are in K. The glass transition temperatures of homopolymers can be found in, for example, "Polymer Handbook" edited by J. Brandrup and E.H. Immergut, Interscience Publishers.

[0022] The coating composition of the present invention comprises an aqueous dispersion of an acrylic (co)polymer that can be used as a binder. As used herein, an "aqueous" dispersion refers to particles dispersed in an aqueous medium. As used herein, "aqueous medium" means water and water-miscible compounds in an amount of 0% to 30% by weight based on the weight of the medium, such as, for example, alcohols, diols, diol ethers, diol esters, or mixtures thereof. Mixtures of two or more acrylic (co)polymers can be used. "Acrylic (co)polymer" as used herein refers to a homopolymer of acrylic monomers or a copolymer comprising structural units of acrylic monomers and one or more additional monomers. "Acrylic" in the present invention includes (meth)acrylic acid, (meth)acrylic acid alkyl esters, (meth)acrylamide, (meth)acrylonitrile, and modified forms thereof, such as (meth)acrylic acid hydroxyalkyl esters. Throughout this document, the word fragment "(meth)acryloyl" refers to both "methacryloyl" and "acryloyl". For example, (meth)acrylic acid refers to both methacrylic acid and acrylic acid, and (meth)acrylic acid methyl ester refers to both methyl methacrylate and methyl acrylate. Specific examples of acrylic (co)polymers include acrylic homopolymers, styrene-acrylic copolymers, or mixtures thereof.

[0023] The acrylic (co)polymers useful in the present invention may comprise structural units of one or more ethylenically unsaturated acid monomers, their salts, or mixtures thereof. The acid monomer and / or its salt may include α,β-ethylenically unsaturated carboxylic acids, which include monomers bearing an acid, such as methacrylic acid (MAA), acrylic acid (AA), itaconic acid, maleic acid, or fumaric acid; or monomers bearing an acid-forming group that gives rise to or can subsequently be converted into such acid groups (such as acid anhydrides, (meth)acrylic anhydride, or maleic anhydride); phosphorus-containing monomers such as vinylphosphonic acid, allylphosphonic acid, (meth)acrylic acid phosphate alkyl esters such as ethyl (meth)acrylate phosphate, propyl (meth)acrylate phosphate, butyl (meth)acrylate phosphate, SIPOMER PAM-100, SIPOMER PAM-200, and SIPOMER PAM-300, all available from Solvay; (meth)acrylic acid phosphonoalkoxy esters such as ethylene glycol (meth)acrylate phosphate, diethylene glycol (meth)acrylate phosphate, triethylene glycol (meth)acrylate phosphate, propylene glycol (meth)acrylate phosphate, dipropylene glycol (meth)acrylate phosphate, tripropylene glycol (meth)acrylate phosphate; sulfonic acid monomers and their salts, including, for example, 2-acrylamido-2-methyl-1-propanesulfonic acid; the sodium salt of 2-acrylamido-2-methyl-1-propanesulfonic acid; and the ammonium salt of 2-acrylamido-2-methyl-1-propanesulfonic acid; sodium p-styrenesulfonate (SSS); sodium vinylsulfonate (SVS); the sodium salt of allyl ether sulfonic acid; their salts; and esters of mixtures thereof. Desirably, the acid monomer is an α,β-ethylenically unsaturated carboxylic acid. More desirably, the acid monomer includes acrylic acid, methacrylic acid, SSS, or mixtures thereof, and more desirably, the acid monomer is MAA. Based on the weight of the acrylic (co)polymer, the acrylic (co)polymer may contain the structural units of the acid monomer at a concentration of 0.1 wt% to 20 wt%, and may be 0.1 wt% to 15 wt%, 0.3 wt% to 12 wt%, 0.5 wt% to 10 wt%, or 0.7 wt% to 8 wt%.

[0024] The acrylic (co)polymers useful in the present invention may or may not contain structural units of one or more ethylenically unsaturated monomers bearing at least one functional group selected from amide, ureido, carbonyl or silyl groups or combinations thereof (hereinafter referred to as "functional monomers"). Suitable functional monomers may include, for example, carbonyl-containing functional monomers such as ethyl acetoacetoxyethyl methacrylate (AAEM) and diacetone acrylamide (DAAM), acrylamide, methacrylamide, vinyl trialkoxysilanes such as vinyltrimethoxysilane, (meth)acryloyloxyalkyltrialkoxysilanes such as (meth)acryloyloxyethyltrimethoxysilane and (meth)acryloyloxypropyltrimethoxysilane or mixtures thereof. Desirably, the functional monomers include acrylamide, DAAM, ureido-containing monomers or mixtures thereof. Based on the weight of the acrylic (co)polymer, the acrylic (co)polymer may contain structural units of the functional monomers and their salts at a concentration of 0.1 wt% to 20 wt%, and may be 0.1 wt% to 15 wt%, 0.3 wt% to 12 wt%, 0.5 wt% to 10 wt%, or 0.7 wt% to 8 wt%.

[0025] The acrylic (co)polymers useful in the present invention may or may not contain structural units of one or more ethylenically unsaturated nonionic monomers in addition to the above-mentioned functional monomers. The term "nonionic monomer" refers to a monomer that does not carry an ionic charge between pH = 1 - 14. Suitable ethylenically unsaturated nonionic monomers may include alkyl esters of (meth)acrylic acid; hydroxy-functional alkyl esters of (meth)acrylic acid; cycloalkyl esters of (meth)acrylic acid such as cyclohexyl (meth)acrylate, vinyl aromatic monomers such as styrene and substituted styrenes (including, for example, α-methylstyrene, p-methylstyrene, tert-butylstyrene, vinyltoluene); glycidyl (meth)acrylate; α-olefins, such as ethylene, propylene and 1-decene; vinyl, vinyl butyrate, vinyl versatate and other vinyl esters; nitrile-containing monomers, such as acrylonitrile (AN); or mixtures thereof. "Alkyl" means a straight-chain or branched-chain alkyl group. The alkyl esters of (meth)acrylic acid may be selected from C1-C2-alkyl esters of (meth)acrylic acid, C4-C 20 -alkyl esters of (meth)acrylic acid or mixtures thereof. The C4-C 20 -alkyl esters of (meth)acrylic acid refer to alkyl esters of (meth)acrylic acid containing an alkyl group having 4 to 20 carbon atoms or 4 to 18 carbon atoms. The C4-C 20Examples of -alkyl esters include butyl (meth)acrylate, isobutyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (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 or mixtures thereof. Desirably, (meth)acrylic acid C4-C 20- The alkyl esters are selected from 2-ethylhexyl acrylate (EHA), butyl (meth)acrylate or mixtures thereof. Suitable C1-C2-alkyl (meth)acrylates may include methyl (meth)acrylate, ethyl (meth)acrylate or mixtures thereof. Suitable hydroxy-functional (meth)acrylic acid alkyl esters may include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 3-hydroxy-2-ethylhexyl (meth)acrylate or mixtures thereof. Desirably, the hydroxy-functional (meth)acrylic acid alkyl esters are selected from the group consisting of 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate (HEMA), 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl acrylate, 3-hydroxypropyl methacrylate and mixtures thereof. Desirably, the ethylenically unsaturated nonionic monomers are selected from styrene, HEMA, acrylonitrile, methyl (meth)acrylate, cyclohexyl (meth)acrylate, ethyl (meth)acrylate, butyl methacrylate, butyl acrylate (BA), EHA or mixtures thereof. Desirably, based on the weight of the acrylic (co)polymer, the acrylic (co)polymer contains structural units of hydroxy-functional (meth)acrylic acid alkyl esters, which are usually present in an amount of 0.1 wt% to 45 wt%, and may be 0.1 wt% or more, 0.5 wt% or more, 1 wt% or more, 2 wt% or more, 5 wt% or more, 7 wt% or more, 10 wt% or more, even 12 wt% or more, while being 45 wt% or less, and may be 40 wt% or less, 35 wt% or less, 33 wt% or less or even 30 wt% or less, and more desirably, 1 wt% to 33 wt%. Alternatively, based on the weight of the acrylic (co)polymer, the acrylic (co)polymer may contain structural units of acrylonitrile in a concentration of 0.5 wt% to 40 wt%, and may be 1 wt% to 35 wt%, 2 wt% to 33 wt%, 5 wt% to 30 wt%, 10 wt% to 28 wt%, 15 wt% to 27 wt% or 19 wt% to 25 wt%. Alternatively, based on the weight of the acrylic (co)polymer, the acrylic (co)polymer may contain structural units of styrene in a concentration of 0 wt% to 60 wt%, and may be 5 wt% to 55 wt%, 10 wt% to 50 wt% or 20 wt% to 45 wt%. Based on the weight of the acrylic (co)polymer, the acrylic (co)polymer may contain 20 wt% to 99.8 wt% of structural units of alkyl esters of (meth)acrylic acid, and may be 25 wt% to 99.5 wt%, 30 wt% to 98 wt%, 50 wt% to 95 wt%, 55 wt% to 90 wt% or 60 wt% to 90 wt%.The acrylic (co)polymer may or may not contain structural units of polyfunctional nonionic monomers such as butadiene, divinylbenzene, and allyl (meth)acrylate, usually at a concentration of 0 wt% to 5 wt% based on the weight of the acrylic (co)polymer, and may be 0 wt% to 2 wt%, 0.1 wt% to 1 wt%, or 0.1 wt% to 0.5 wt%. Based on the weight of the acrylic (co)polymer, the acrylic (co)polymer may contain structural units of ethylenically unsaturated nonionic monomers at a total concentration of 80 wt% to 99.9 wt%, and may be 85 wt% to 99.5 wt%, 88 wt% to 98 wt%, 90 wt% to 97.5 wt%, or 90 wt% to 95 wt%.

[0026] The acrylic (co)polymer may be a multi-stage acrylic (co)polymer containing polymer A and polymer B, where the Tg difference between polymer A and polymer B is 40 °C or higher, and may be 45 °C or higher, 50 °C or higher, 55 °C or higher, 60 °C or higher, 65 °C or higher, 70 °C or higher, or even 75 °C or higher. The weight ratio of polymer A to polymer B may be in the range of 20:80 to 80:20, and may be 22:78 to 78:22, 25:75 to 75:25, 30:70 to 70:30, 35:65 to 65:35, 38:62 to 60:40, or 40:46 to 55:45, and desirably, 22:78 to 78:22 or 38:62 to 55:45.

[0027] Desirably, the acrylic (co)polymer is a multi-stage acrylic (co)polymer having a Tg in the range of 0 °C to 80 °C and containing polymer A and polymer B, where the weight ratio of polymer A to polymer B is in the range of 78:22 to 22:78,

[0028] where the Tg difference between polymer A and polymer B is 40 °C or greater, and

[0029] where based on the weight of the multi-stage acrylic (co)polymer, the multi-stage acrylic (co)polymer contains

[0030] 10 wt% to 40 wt% of structural units of cycloalkyl (meth)acrylate, such as cyclohexyl methacrylate;

[0031] 40 wt% to 85 wt% of C4-C 20 -alkyl (meth)acrylate, vinyl aromatic monomer, or a mixture thereof, such as BA, EHA, styrene, or a mixture thereof; and

[0032] Structural units of 0.5 wt% to 10 wt% of an acid monomer, its salt, or a mixture thereof.

[0033] Alternatively, the acrylic (co)polymer can be a multi-stage acrylic (co)polymer comprising Polymer A and Polymer B, wherein Polymer A has a number average molecular weight (Mn) of 3,000 to 50,000 and, based on the weight of Polymer A, comprises

[0034] (a1) Structural units of 2.1 wt% to 10 wt% of a carbonyl-functional monomer (such as DAAM);

[0035] (a2) Structural units of 5 wt% to 15 wt% of an acid monomer, its salt, or a mixture thereof;

[0036] [[ID=1--12]]And

[0037] (a3) Structural units of 75 wt% to 92 wt% of methyl (meth)acrylate, ethyl (meth)acrylate, or a mixture thereof; and

[0038] wherein, based on the weight of Polymer B, Polymer B comprises, as polymerization units,

[0039] (b1) Structural units of 0.8 wt% to 10 wt% of a carbonyl-functional monomer (such as DAAM); and

[0040] (b2) Structural units of 90 wt% to 99.2 wt% of an ethylenically unsaturated nonionic monomer;

[0041] wherein the glass transition temperature of Polymer B is at least 40 °C lower than the glass transition temperature of Polymer A, and the weight ratio of Polymer A to Polymer B is 38:62 to 55:45.

[0042] Polymer A in the multi-stage polymer can have an Mn of 3,000 or greater, and can be 4,500 or greater, even 5,000 or greater, while being 50,000 or less, and can be 30,000 or less, 20,000 or less, or even 10,000 or less. Mn can be determined by gel permeation chromatography (GPC) analysis using polystyrene as a standard or calculated as follows:

[0043] Mn = [W(monomer) + W(CTA)] / mole(CTA),

[0044] where W(monomer) is the total weight of the monomers used to prepare Polymer A, W(CTA) is the weight of the chain transfer agent used to prepare Polymer A, and mole(CTA) is the number of moles of the chain transfer agent used to prepare Polymer A.

[0045] The coating composition of the present invention may comprise, by dry weight based on the weight of the coating composition, an aqueous dispersion of an acrylic (co)polymer in an amount of 20% to 38.5%, and by dry weight, may be 20.5% or greater, 21% or greater, 22% or greater, 22.5% or greater, even 23% or greater, while being 38.5% or less, and by dry weight, may be 35% or less, 32% or less, 30% or less, less than 30%, 28% or less or even 27% or less, and by dry weight, desirably, less than 30%, 21% to 30% or 23% to 27%.

[0046] The acrylic (co)polymer useful in the present invention can be prepared by free radical polymerization, desirably emulsion polymerization, of the above monomers. The total weight concentration of the structural units of the acrylic (co)polymer is equal to 100% relative to the weight of the acrylic (co)polymer. A single-stage or multi-stage free radical polymerization can be used. When the acrylic (co)polymer is a multi-stage acrylic (co)polymer prepared by multi-stage free radical polymerization, the multi-stage free radical polymerization involves at least two stages (e.g., a first stage and a second stage) formed in sequence, and generally results in the formation of a multi-stage acrylic (co)polymer comprising at least two polymer compositions (i.e., polymer A and polymer B). The total weight concentration of the structural units in polymer A and polymer B is respectively equal to 100% relative to the weight of polymer A and the weight of polymer B.

[0047] Emulsion polymerization can be carried out under conventional conditions, including using free radical initiators, surfactants, chain transfer agents, or combinations thereof. Surfactants can be added before or during monomer polymerization or a combination thereof. A portion of the surfactant can also be added after polymerization. Based on the weight of the total monomers used to prepare the acrylic (co)polymer, these surfactants can include anionic and / or non-ionic emulsifiers at a typical concentration of 0.1 wt% to 6% or 0.3 wt% to 1.5 wt%. Examples of suitable chain transfer agents include 3-mercaptopropionic acid, dodecyl mercaptan, methyl 3-mercaptopropionate, butyl 3-mercaptopropionate, benzenethiol, alkanethiol azelate, or mixtures thereof. When preparing a multi-stage acrylic (co)polymer, the chain transfer agent can be added in an effective amount in the first stage of the multi-stage polymerization to control the molecular weight of the first stage polymer (e.g., polymer A), for example, at a concentration greater than 1.2 wt% based on the total weight of the monomers used in the first stage of the multi-stage polymerization, and can be 1.3 wt% or greater, 1.4 wt% or greater, 1.5 wt% or greater, 1.6 wt% or greater, 1.7 wt% or greater, 1.8 wt% or greater, or even 1.9 wt% or greater, while typically being 10 wt% or less, 9 wt% or less, 8 wt% or less, 7 wt% or less, 6 wt% or less, 5 wt% or less, or even 4 wt% or less. After completion of the polymerization process, the obtained acrylic (co)polymer can be controlled to a pH value of at least 6, such as 6 to 11 or 7 to 10, by neutralization using one or more bases, which can cause partial or complete neutralization of the ionic or potentially ionic groups of the acrylic (co)polymer. Commercially available aqueous acrylic (co)polymer dispersions can include, for example, ROSHIELD, PR-600, ROSHIELD TM , P200, RHOPLEX TM , WL-91, and MAINCOTE TM , HG-54C emulsion, or mixtures thereof (ROSHIELD, RHOPLEX, and MAINCOTE are trademarks of The Dow Chemical Company). TM PR-600, ROSHIELD TM P200, RHOPLEX TM WL-91 and MAINCOTE TM HG-54C emulsion, or mixtures thereof (ROSHIELD, RHOPLEX, and MAINCOTE are trademarks of The Dow Chemical Company).

[0048] The acrylic (co)polymer particles in the aqueous dispersion can have a particle size of 30 nanometers (nm) or greater, and can be 80 nm or greater, 90 nm or greater, 100 nm or greater, greater than 100 nm, 105 nm or greater, or even 110 nm or greater, while typically being 500 nm or less, and can be 300 nm or less, or even 200 nm or less, or even 150 nm or less. The particle size herein refers to the number average particle size and can be measured by a Brookhaven BI-90Plus particle size analyzer.

[0049] The aqueous dispersion of the acrylic (co) polymer useful in the present invention further contains water. Based on the total weight of the aqueous dispersion, water can be present in an amount of 30% by weight or more, and can be 40% by weight or more, even 50% by weight or more, while generally being 90% by weight or less, and can be 85% by weight or less or even 80% by weight or less. Based on the weight of the coating composition, the coating composition can contain 47% to 89% by weight of the aqueous dispersion of the acrylic (co) polymer, and can be 50% to 80%, 50.5% to 77%, 51% to 75%, 52% to 70% or 53% to 66%, and desirably 54% to 62%.

[0050] The coating composition of the present invention may or may not contain a polyfunctional carboxylic acid hydrazide containing at least two hydrazide groups per molecule, especially when the acrylic (co) polymer contains a structural unit of a carbonyl-containing functional monomer. The polyfunctional carboxylic acid hydrazide can act as a crosslinking agent and can be selected from the group consisting of: adipic dihydrazide, oxalic dihydrazide, isophthalic dihydrazide and polyacrylic hydrazide. When present, based on the weight of the acrylic (co) polymer, the concentration of the polyfunctional carboxylic acid hydrazide can be 0.5% by weight to 10% by weight or 1% by weight to 5% by weight.

[0051] The coating composition of the present invention may also contain or not contain an aqueous polyurethane dispersion that can be used as a binder, which is generally present in an amount of 0 to 15% by dry weight based on the weight of the coating composition, and can be 0 or more, 1% or more, 2% or more, even 5% or more, while being 15% or less, and can be 12.5% or less or even 10.5% or less.

[0052] The coating composition of the present invention further comprises a water-soluble alkali metal silicate. The alkali metal silicate may be sodium silicate, potassium silicate, lithium silicate or a combination thereof. Suitable alkali metal silicates may be any silicate of the general formula M2O·xSiO2, where M represents an alkali metal, including lithium, sodium, potassium and combinations thereof; and x represents the molar ratio of silicon dioxide (SiO2) to metal oxide (M2O). Sodium silicate (Na2O·xSiO2) typically has a molar ratio of Na2O to SiO2 in the range of 1:4 to 2:1. Suitable sodium silicates may include, for example, orthosodium silicate (Na4SiO4), sodium metasilicate (Na2SiO3), disodium silicate (Na2Si2O5), tetrasodium silicate (Na2Si4O9), sodium pyrosilicate (Na6Si2O7), other polysodium silicates or mixtures thereof. Potassium silicate (K2O·xSiO2) typically has a molar ratio of K2O to SiO2 of 0.2 to 1. Potassium silicates with all variable compositions from K2Si2O5 to K2Si3O7 can be used. Lithium silicate (Li2O·xSiO2) typically has a molar ratio of Li2O to SiO2 of 0.3 to 8. Mixtures of two or more water-soluble alkali metal silicates with different solubilities can be used. Mixed water-soluble alkali metal silicates such as potassium sodium silicate, potassium lithium silicate or mixtures thereof can be used. Preferably, the water-soluble alkali metal silicate is potassium lithium silicate.

[0053] Based on the weight of the coating composition, the coating composition of the present invention may comprise 0.5% to 2.9% by dry weight of the water-soluble alkali metal silicate, and may be 0.5% or greater, 0.55% or greater, 0.6% or greater, 0.65% or greater, 0.7% or greater, higher than 0.75%, 0.8% or greater, 0.9% or greater, even 1% or greater, while being 2.9% or less, and may be 2.85% or less, 2.8% or less, 2.7% or less, 2.6% or less, 2.5% or less, 2.4% or less, 2.3% or less, 2.2% or less, 2.1% or less, 2% or less, 1.8% or less, 1.5% or less, 1.2% or less or even 1% or less. Desirably, based on the weight of the coating composition, the coating composition comprises 0.9% to 2.7% or 1% to 2.5% by dry weight of the water-soluble alkali metal silicate.

[0054] The water-soluble alkali metal silicate can be provided as an aqueous solution which, based on the weight of the aqueous solution, typically contains 5% to 80%, 10% to 70% or 15% to 60% by dry weight of the water-soluble alkali metal silicate. Based on the weight of the coating composition, the aqueous solution of the water-soluble alkali metal silicate can be present in an amount of 2% to 27.5% by wet weight and can be 2% or greater, 2.25% or greater, 2.5% or greater, 2.75% or greater, 3% or greater, 3.5% or greater, even 4% or greater while being 27.5% or less and can be 25% or less, 22.5% or less, 20% or less, 18% or less, 15% or less or even 12% or less.

[0055] The coating composition of the present invention further comprises an aqueous solution of a water-soluble non-alkali metal salt which contains non-alkali metal ions. The water-soluble non-alkali metal salt can include, for example, zinc ammonium complex salts, aluminum salts, zirconium salts or mixtures thereof. Such water containing the non-alkali metal salt (thus forming an aqueous solution) can provide polyvalent cations. Such an aqueous solution can contain zinc ions (Zn 2+ ), aluminum ions (Al 3+ ), zirconium ions (Zr 4+ ) or mixtures thereof.

[0056] The non-alkali metal salt useful in the present invention can comprise or consist of a zinc ammonium complex salt. The zinc ammonium complex salt is water-soluble. The zinc ammonium complex salt can be selected from ammonium zinc bicarbonate, ammonium zinc nitrate, ammonium zinc acetate or mixtures thereof, and desirably is ammonium zinc carbonate. The zinc ammonium complex salt can be prepared by mixing one or more zinc salts and / or zinc oxide, ammonia and optionally a water-soluble carbonate such as ammonium bicarbonate. Ammonia is added in an amount sufficient to provide an aqueous solution of the zinc ammonium complex salt having a pH higher than 9, desirably higher than 9.5. Ammonia forms a zinc ammonium complex in the presence of an excess equivalent. Examples of the zinc salt include zinc carbonate, zinc acetate, zinc chloride, zinc nitrate or mixtures thereof. The aqueous solution of the zinc ammonium complex salt contains zinc ions and ammonium ions.

[0057] The non-alkali metal salt useful in the present invention can include or consist of one or more water-soluble aluminum salts. An aqueous solution of an aluminum chloride salt can be prepared by dissolving aluminum chloride powder in water. The aluminum salt can include aluminum chloride (AlCl3), aluminum nitrate or mixtures thereof.

[0058] An aqueous solution of a non-alkali metal salt may be present in an amount sufficient to provide a dry weight ratio of non-alkali metal ions to the acrylic (co)polymer of from 0.13% to 3.3%, and may be 0.13% or greater, 0.14% or greater, 0.15% or greater, 0.2% or greater, 0.3% or greater, 0.4% or greater, 0.5% or greater, 0.65% or greater, 0.7% or greater, 0.8% or greater or even 1.0% or greater, while being 3.3% or less, and may be 3.2% or less, 3.1% or less, 3% or less, 2.9% or less, 2.5% or less, 2.4% or less, 2% or less, 1.5% or less, 1.3% or less, 1.2% or less or even 1.1% or less. Desirably, the dry weight ratio of non-alkali metal ions to the acrylic (co)polymer is in the range of 0.5% to 2.5%, 0.7% to 2% or 0.8% to 1.2%. At the same time, the amount of the aqueous solution of the non-alkali metal salt may provide a dry weight ratio of non-alkali metal ions to the water-soluble alkali metal silicate in the range of 1.4% to 42%, and may be 1.4% or greater, 1.5% or greater, 2% or greater, 5% or greater, 7.5% or greater, 10% or greater, 13% or greater, 14% or greater, even 20% or greater, while being 42% or less, and may be 41% or less, 40.5% or less, 38% or less, 35% or less, 33% or less, 30% or less, 28% or less, 27% or less, 25% or less, 22% or less or even 21% or less. Desirably, the dry weight ratio of non-alkali metal ions to the water-soluble alkali metal silicate is in the range of 5% to 35%, or 7.5% to 33% or 10% to 30%.

[0059] The coating composition of the present invention may contain or not contain ethylenediaminetetraacetic acid (EDTA), its salts (such as sodium ethylenediaminetetraacetate) or mixtures thereof. Adding EDTA and / or EDTA salts can be used to further increase the stability of the coating composition, especially when using an aqueous acrylic (co)polymer dispersion having an adhesion of less than 0.975 in the coating composition. "Adhesion" refers to the ability of an aqueous dispersion of an acrylic (co)polymer to capture non-alkali metal ions, as measured by centrifugation of a mixture containing the aqueous acrylic (co)polymer dispersion and non-alkali metal ions. The adhesion is calculated as the weight percentage of non-alkali metal ions in the precipitate after centrifugation of the mixture relative to the total non-alkali metal ions in the mixture before centrifugation (further details can be found in the adhesion test in the Examples section below).

[0060] Based on the weight of the coating composition, the coating composition may contain ethylenediaminetetraacetic acid and / or its salts at the following concentrations: 0 wt% to 0.52 wt%, and may be greater than 0 wt%, 0.06 wt% or greater, 0.07 wt% or greater, even 0.09 wt% or greater, while typically being 0.52 wt% or less, and may be 0.4 wt% or less or even 0.35% or less, and desirably 0.07 wt% to 0.4 wt% or 0.09 wt% to 0.35 wt%.

[0061] The coating composition of the present invention may contain or not contain microfillers. "Microfillers" refer to any organic or inorganic particles having a d50 particle size of 0.5 μm to 40 μm according to the ASTM E2651-10 method, and typically having a d50 particle size of 0.5 μm to 30 μm, 1 μm to 20 μm or 1 μm to 10 μm. Examples of microfillers include matting agents, pigments, extenders, fillers or mixtures thereof. In the present context, a "matting agent" refers to any inorganic or organic particles that provide a matte effect. The matting agent may be silica, polyurea, polyacrylate polyethylene or polytetrafluoroethylene matting agent or a mixture thereof. The matting agent may be in the form of a powder or an emulsion. Based on the weight of the coating composition, the coating composition may contain microfillers at a concentration of 0 to 2% by dry weight, and may be 2% or less, 1.5% or less, 1% or less, less than 1%, 0.5% or less, 0.1% or less, less than 0.1% or even 0.

[0062] The coating composition of the present invention may also contain or not contain one or more defoamers. A "defoamer" in the present context refers to a chemical additive that reduces and hinders foam formation. The defoamer may be a silicone-based defoamer, a mineral oil-based defoamer, an ethoxylated / propoxylated defoamer, an alkyl polyacrylate or a mixture thereof. Based on the weight of the coating composition, the defoamer may be present at the following concentrations: 0 wt% to 2 wt%, 0.1 wt% to 1 wt% or 0.2 wt% to 0.5 wt%.

[0063] The coating composition of the present invention may contain or not contain one or more thickeners (also known as "rheology modifiers"). Thickeners may include polyvinyl alcohol (PVA), clay materials, acid derivatives, acid copolymers, urethane associative 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 polymers; hydrophobically modified alkali-swellable emulsions (HASE), such as hydrophobically modified acrylic copolymers; associative thickeners, such as hydrophobically modified ethoxylated urethanes (HEUR); and cellulose thickeners, such as methyl cellulose ether, hydroxymethyl cellulose (HMC), hydroxyethyl cellulose (HEC), hydrophobically modified hydroxyethyl 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-hydroxypropyl cellulose, and preferably HEUR. Based on the weight of the coating composition, the thickener may be present in the following concentrations: 0 wt% to 2 wt%, 0.02 wt% to 1 wt%, or 0.04 wt% to 0.5 wt%.

[0064] The coating composition of the present invention may contain or not contain one or more wetting agents. The "wetting agent" herein refers to a chemical additive that reduces the surface tension of the coating composition, thereby making it easier for the coating composition to spread across the surface of the substrate or penetrate the surface of the substrate. The wetting agent may be anionic, zwitterionic, or nonionic polycarboxylate esters. Based on the weight of the coating composition, the wetting agent may be present in the following concentrations: 0 wt% to 2 wt%, 0.05 wt% to 1 wt%, or 0.1 wt% to 0.5 wt%.

[0065] The coating composition of the present invention may contain or not contain one or more coalescing agents. The "coalescing agent" herein refers to a slowly evaporating solvent that causes polymer particles to fuse into a continuous film under ambient conditions. Examples of suitable coalescing agents 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 coalescing agents include dipropylene glycol n-butyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, n-butyl ether, or mixtures thereof. Based on the weight of the coating composition, the coalescing agent may be present in the following concentrations: 0 wt% to 20 wt%, 0.5 wt% to 15 wt%, or 1 wt% to 10 wt%.

[0066] The coating composition of the present invention is generally an aqueous coating composition containing water, and water is generally present in a concentration of 20% to 90%, 40% to 85%, or 50% to 80% by weight based on the weight of the coating composition.

[0067] In addition to the components described above, the coating composition of the present invention may further contain any one or combination of the following additives: buffering agents, neutralizing agents, dispersants, wetting agents, biocides, anti-skinning agents, colorants, flow agents, antioxidants, plasticizers, freeze / thaw additives, leveling agents, thixotropic agents, tackifiers, anti-scratch additives, and grinding media. Based on the weight of the coating composition, these additives may be present in a total concentration of 0% to 5%, 0.001% to 3%, or 0.1% to 2%.

[0068] The pH value of the coating composition of the present invention is generally higher than 7, and may be 7.5 to 11 or 8.5 to 10.

[0069] The present invention also relates to a method for preparing the coating composition of the present invention. The method may include the following steps: (i) blending an aqueous dispersion of an acrylic (co)polymer with an aqueous solution of a water-soluble non-alkali metal salt to form a blend; and (ii) further blending the blend obtained from step (i) with a water-soluble alkali metal silicate and, if present, a micro filler. Before step (ii), optional components such as the above-mentioned ethylenediaminetetraacetic acid and / or its salts may be added to the blend obtained from step (i). Desirably, the method further includes adjusting the pH value of the blend obtained from step (i) to 9 or higher or even 9.5 or higher, for example, by an ammonia solution, before blending with the aqueous solution of the water-soluble alkali metal silicate. Any of the other above-mentioned optional components, such as the micro filler, may also be added to the composition together with the water-soluble alkali metal silicate or after step (ii).

[0070] The present invention also provides a method for preparing a coating. The method may include: forming the coating composition of the present invention; applying the coating composition onto a substrate; and drying or allowing to dry the applied coating composition to form a coating. The coating composition can be used alone or in combination with other coatings to form a multi-layer coating. The coating composition can be applied onto the substrate by existing methods including brushing, dipping, roll coating, and spraying. Desirably, the coating composition is applied by spraying. Standard spraying techniques and spraying equipment such as air atomizing spraying, air spraying, airless spraying, high volume low pressure spraying, and electrostatic spraying (such as electrostatic bell application) and manual or automatic methods can be used. After applying the coating composition of the present invention onto the substrate, the coating composition can be dried or allowed to dry at room temperature or at a high temperature (e.g., 35°C to 60°C) to form a film (i.e., a coating). The coating composition can be applied and adhered to various substrates, especially wood. The coating composition is particularly suitable for furniture coatings, joinery coatings, and floor coatings. The coating on the substrate generally has a dry film thickness of 30 μm to 80 μm.

[0071] The coating prepared from the coating composition of the present invention exhibits low gloss, high transparency, and achieves a pencil hardness grade of F or harder as measured according to GB / T 6739-2006. "Low gloss" means a gloss less than 50 on the 60° Gardner gloss scale, and desirably less than 30, as determined by using a BYK Micro-Tri-Gloss meter according to ASTM D523. "High transparency" means a haze value less than 33 as measured by a BYK Haze-gard dual haze meter. Desirably, the coating further shows good water resistance with a grade of 4 or higher, as measured according to EN 12720-2009. Further details for measuring these properties are provided in the Examples section below. The coating composition of the present invention is particularly suitable for preparing transparent coatings.

[0072] Example

[0073] Some embodiments of the present invention will now be described in the following examples, where percentages (%) are weight percentages relative to the weight of the composition, unless otherwise specified. The materials for the coating composition of the samples are described below. ROSHIELD, RHOPLEX, MAINCOTE, DOWANOL, and OPTI-MATT are trademarks of The Dow Chemical Company.

[0074] Table 1

[0075]

[0076]

[0077] The following standard analytical equipment and methods are used for the examples and to determine the properties and characteristics described herein:

[0078] Preparation of Coated Panels

[0079] 1) Coated Wood Board

[0080] Three coats are applied to the wood substrate by, for each coat, applying the test coating composition at 80 - 90 grams per square meter (g / m 2 ) to the wood panels. After applying the first coat of the coating composition, the panel is left at room temperature for 4 hours and then sanded. Then, the second coat of the coating composition is applied, dried, and sanded using the same procedure as for the first coat. After applying the third coat of the coating composition, the coated wood panel is dried at room temperature for 4 hours and then placed in an oven at 50 °C for 48 hours before testing.

[0081] 2) Coated Glass Plate

[0082] The test coating composition is applied by knife coating to the glass substrate at a wet thickness of 150 μm. Only one coat of the coating composition is applied. Before testing, the coating on the glass is dried at room temperature for 4 hours and then placed in an oven at 50 °C for 48 hours.

[0083] 3) Coated Vinyl Cardboard

[0084] The test coating composition is applied by knife coating to the vinyl sticker at a wet thickness of 150 μm. Only one coat of the coating composition is applied. Before testing, the coating on the vinyl sticker is dried at room temperature for 4 hours and then placed in an oven at 50 °C for 48 hours.

[0085] Water Resistance Test

[0086] Water resistance and alcohol resistance are determined according to EN 12720 - 2009.

[0087] For the water resistance test, first, a disk filter paper is saturated with deionized water, placed on the coated wood panel prepared above, and covered with a lid to reduce evaporation. After 24 hours, the lid is removed. The test area is wiped with a wet paper towel and allowed to dry at room temperature for 2 hours to observe the degree of damage defined as follows. The degree of damage for water resistance is rated on a scale of 0 - 5 according to EN 12720 - 2009, where 0 is the worst and 5 is the best, as follows:

[0088] 5 - No change: The test area cannot be distinguished from the adjacent surrounding area;

[0089] 4 - Slight change: The test area can be distinguished from the adjacent surrounding area only when the light source shines on the test surface and reflects towards the observer's eyes. Minor changes may include some slight discoloration and gloss changes, but there are no changes in the surface structure such as swelling, fiber bulging, cracking, and / or blistering;

[0090] 3 - Moderate change: The test area can be distinguished from the adjacent surrounding area and is visible in several observation directions, such as discoloration; changes in gloss and color; but there are no changes in the surface structure such as swelling, fiber bulging, cracking, and / or blistering;

[0091] 2 - Significant change: The test area is clearly distinguishable from the adjacent surrounding area and is visible in all observation directions, such as discoloration; changes in gloss and color; and / or slight changes in the surface structure such as swelling, fiber bulging, cracking, and / or blistering.

[0092] 1 - Strong change: The surface structure is significantly changed and / or discolored, the gloss and color are changed, and / or the surface material is completely or partially removed, and / or the filter paper adheres to the surface.

[0093] The higher the grade, the better the water resistance.

[0094] Pencil Hardness

[0095] The pencil hardness of the coating film on the prepared coated glass plate was determined according to GB / T 23999 - 2009 "Water based Coating for Woodenware for Indoor Decorating and Refurbishing" (hardness part - GB / T 6739). The hardness of the hardest pencil lead that did not leave a mark on the coating film was recorded as the pencil hardness. A pencil hardness of F or harder is acceptable.

[0096] Glossiness

[0097] The glossiness of the coating film on the prepared coated vinyl paper was measured using a BYK Micro - Tri - Gloss meter according to ASTM D523. An acceptable glossiness on the 60° Gardner glossiness scale is <50.

[0098] Haze

[0099] The haze of the coating film on the prepared coated glass plate was measured using a BYK Haze - gard dual - haze meter according to ASTM D1003. A haze value <33 indicates acceptable transparency. The lower the haze value, the higher the clarity.

[0100] Fineness

[0101] According to ASTM D1210-96, at room temperature, the fineness of the coating composition was tested using a QXD 100 scraping fineness gauge (Shanghai Modern Environment Engineering Technique Co., Ltd., detection limit: 10 - 100 μm). A coating composition with a fineness less than 40 μm is acceptable and is considered a stable coating composition.

[0102] Adhesion

[0103] An aqueous acrylic (co)polymer dispersion (also known as "latex") (10.7 g by dry weight), 2.5 g of the above-prepared Zn / ammonia solution (containing 6.57% Zn 2+ ) and water were mixed to form a mixture (100 g). The mixture was left at room temperature for 1 week. Then 1 g of the mixture was taken out of the container and centrifuged at 80,000 revolutions per minute (RPM) for 10 minutes. The obtained supernatant was analyzed by inductively coupled plasma optical emission spectrometry (ICP-OES) Agilent 5800. The weight of Zn ions in the obtained supernatant per gram of supernatant was reported as W (μg / g). The adhesion of the latex was calculated by the following equation:

[0104]

[0105] Coating Composition

[0106] Tables 2 - 4 list the components used to prepare the IE and CE coating composition samples, and the amount of each component is reported in grams (g) unless otherwise specified.

[0107] IE1-11 and CE1, 4-9, 11-12 and 14 Coating Composition Samples :

[0108] First, an aqueous solution of a non-alkali metal complex or salt (the above-prepared zinc / ammonia solution or AlCl3 solution) was added to the latex binder, and mixed at a speed of 200 - 500 RPM using a disperser to form a homogeneous blend, and the pH value of the obtained blend was adjusted to 9.5 using an ammonia solution. The potassium lithium silicate solution (CB-956) was first diluted with the amounts of water listed in Tables 2 and 3, and then added to the above blend. The remaining components, such as defoamers, wetting agents, coalescing agents, and thickeners (if present), were further added and mixed at a speed of 200 - 1,000 RPM for 10 minutes until a homogeneous coating composition was obtained. The obtained coating composition samples were characterized according to the above test methods, and the characterization results are given in Tables 2 and 3.

[0109] CE2, 3, 10, 13, 15 and 16 Coating Composition Samples :

[0110] Based on the formulations listed in Table 3, water, an antifoaming agent, a wetting agent, and a coalescing agent are first added to the latex binder in sequence and mixed using a disperser at a speed of 200 - 500 RPM to form a homogeneous blend. According to the formulations in Table 3, OPTI-MATT AB-2, TS100, and magnesium silicate (Mg) (zinc powder or zinc phosphate) are added to the blend and mixed at a speed higher than 1200 RPM for 10 minutes. Finally, a thickening agent is added and mixed at a speed of 200 - 500 RPM until a homogeneous coating composition is obtained. The resulting coating composition samples are characterized according to the above test method, and the characterization results are given in Table 3.

[0111] As shown in Tables 2 and 3, all IE 1 - 11 coating composition samples provide a coating film having a good matting effect (gloss at 60° < 50), desired hardness (> HB), and high transparency (haze value < 33). Compared with CE 1 which contains neither zinc / ammonia solution nor water-soluble silicate solution, IE 1 and 2 provide a coating film with a significantly reduced gloss (indicating that a matting effect is achieved) and enhanced hardness.

[0112] All IE coating compositions show a higher matting efficiency than CE 3 (i.e., a greater gloss reduction is achieved when using a lower concentration of soluble silicate and non-alkali metal ion salt relative to the weight of the coating composition), and also achieve a higher hardness than CE 2 and 3 containing conventional matting agents.

[0113] Coating compositions (CE 7 and 9) having a dry non-alkali metal ion / dry silicate ratio outside the claimed range provide a coating film with a higher gloss (insufficient matting effect).

[0114] The coating composition sample of CE 4 having a high non-alkali metal ion / latex binder ratio (by dry weight) is unstable. CE 8 provides a coating film with an undesirably low hardness due to an insufficient amount of non-alkali metal ions and cannot provide a matting effect.

[0115] When the amount of the latex binder exceeds the claimed range, the coating composition provides a high haze value (CE 5) or an undesirably high gloss (CE 6). Without being bound by theory, the latex content is important for stabilizing the mixture of non-alkali metal ions and water-soluble alkali metal silicate before the coating composition is dried.

[0116] CE 10, which essentially replicates Example 2 of US7652087B2 and contains 40.98% soluble silicate and 10.25% insoluble zinc phosphate (by weight based on the weight of the coating composition), fails to provide a clear coating film as indicated by the high haze values.

[0117] Using only a zinc / ammonia solution in the absence of a water-soluble silicate (CE 11) or incorporating only a water-soluble alkali metal silicate in the absence of non-alkali metal ions (CE 12) resulted in coating films with undesirably high gloss. Furthermore, incorporating an insoluble silicate (e.g., magnesium silicate) in the absence of non-alkali metal ions produced a matte film but resulted in undesirably high haze values (CE 13). When the dry weight ratio of non-alkali metal ions to alkali metal silicate was too high (CE 14), the coating composition was unstable, as indicated by a fineness greater than 40. Adding zinc powder (a solid filler) to a latex binder in the absence of a water-soluble alkali metal silicate resulted in sediment (CE 15), making it impossible to prepare a paint. The coating composition of CE 16, which contained 3% zinc phosphate (an insoluble zinc filler) based on the weight of the coating composition, exhibited poor clarity.

[0118] Table 2. IE Coating Compositions and Characterization

[0119]

[0120] IE 12-16 Coating Composition Samples

[0121] Based on the formulations given in Table 4, coating composition samples of IEs 12-16 were prepared according to the same procedure as IE 1, except that EDTA was further added after the zinc / ammine complex salt solution was incorporated. The resulting coating composition samples were characterized according to the test methods described above, and the characterization results are given in Table 4. As shown in Table 4, the latex binder having a bond strength of less than 0.975 in combination with EDTA all provided stable coating compositions, as indicated by low fineness (<40 μm). At the same time, these coating compositions all provided coating films with balanced properties, including a gloss of <50 at 60°, a hardness of F or harder, and good clarity (haze value <33), as well as surprisingly good water resistance (rating >3).

[0122] Table 4 IE Coating Compositions and Characterization

[0123]

[0124] *The adhesion of ROSHIELD 500 and MAINCOTE HG-54C latex adhesives were 0.577 and 0.972, respectively, as measured according to the Adhesion Test Method described above.

[0125] The EDTA content refers to the ratio of the weight of EDTA to the weight of the coating composition.

[0126]

[0127] Wet latex / wet coating = (weight of latex binder) / (weight of coating composition) × 100%;

[0128] Dry latex / wet coating = (weight of latex × latex solids content) / (weight of coating composition) × 100%;

[0129] Dry silicate / wet coating = (weight of alkali metal silicate solution × silicate solution solids content) / (weight of coating composition) × 100%;

[0130] Wet silicate / wet coating = (weight of alkali metal silicate solution) / (weight of coating composition) × 100%;

[0131] Insoluble filler / wet coating = (weight of insoluble filler) / (weight of coating composition) × 100%;

[0132] The adhesion forces of ROSHIELD PR-600 and P200 latex binders are 0.998 and 0.991 respectively, as measured according to the above adhesion test method.

Claims

1. A coating composition, based on the weight of the coating composition, the coating composition comprises (a) an aqueous dispersion of an acrylic (co)polymer in an amount of 20% to 38.5% by dry weight; (b) a water-soluble alkali metal silicate in an amount of 0.5% to 2.9% by dry weight; (c) an aqueous solution of a water-soluble non-alkali metal salt containing non-alkali metal ions; and (d) a micro filler in an amount of 0 to 2% by dry weight; wherein the aqueous solution of the non-alkali metal salt is present in an amount to provide a ratio of the non-alkali metal ions to the dry weight of the acrylic (co)polymer in the range of 0.13% to 3.3% and a ratio of the non-alkali metal ions to the dry weight of the water-soluble alkali metal silicate in the range of 1.4% to 42%.

2. The coating composition according to claim 1, wherein the non-alkali metal ions include zinc ions, aluminum ions, zirconium ions or a mixture thereof.

3. The coating composition according to claim 1 or 2, wherein the alkali metal silicate is lithium potassium silicate.

4. The coating composition according to any one of claims 1 to 3, wherein the acrylic (co)polymer is a multi-stage acrylic (co)polymer having a Tg in the range of 0 °C to 80 °C and comprising polymer A and polymer B, and the weight ratio of polymer A to polymer B is in the range of 78:22 to 22:78, wherein the difference in Tg between polymer A and polymer B is 40 °C or greater, and wherein, based on the weight of the multi-stage acrylic (co)polymer, the multi-stage acrylic (co)polymer comprises structural units of (meth)acrylic cycloalkyl ester in an amount of 10% to 40% by weight; 40% to 85% by weight of structural units of C4-C 20 -alkyl (meth)acrylate, vinyl aromatic monomer or a mixture thereof; and structural units of an acid monomer, its salt or a mixture thereof in an amount of 0.5% to 10% by weight.

5. The coating composition according to any one of claims 1 to 3, wherein the acrylic (co)polymer is a multi-stage acrylic (co)polymer comprising polymer A and polymer B, wherein polymer A has a number average molecular weight of 3,000 to 50,000 and, based on the weight of polymer A, comprises (a1) structural units of a carbonyl group-containing functional monomer in an amount of 2.1% to 10% by weight; (a2) structural units of an acid monomer, its salt or a mixture thereof in an amount of 5% to 15% by weight; and (a3) structural units of (meth)acrylic acid methyl ester, (meth)acrylic acid ethyl ester or a mixture thereof in an amount of 75% to 92% by weight; and wherein, based on the weight of polymer B, polymer B comprises (b1) structural units of a carbonyl group-containing functional monomer in an amount of 0.8% to 10% by weight; and (b2) structural units of additional ethylenically unsaturated non-ionic monomers in an amount of 90% to 99.2% by weight; wherein the glass transition temperature of polymer B is at least 40 °C lower than the glass transition temperature of polymer A, and the weight ratio of polymer A to polymer B is 38:62 to 55:

45.

6. The coating composition according to any one of claims 1 to 3, wherein based on the weight of the acrylic (co)polymer, the acrylic (co)polymer comprises structural units of a hydroxy-functional (meth)acrylic acid alkyl ester in an amount of 1% to 33% by weight.

7. The coating composition according to any one of claims 1 to 6, based on the weight of the coating composition, the coating composition further comprises 0.06% to 0.52% by weight of ethylenediaminetetraacetic acid, its salts, or mixtures thereof.

8. The coating composition according to any one of claims 1 to 7, wherein based on the weight of the coating composition, the coating composition comprises an aqueous dispersion of the acrylic (co)polymer in an amount of less than 30% by dry weight.

9. The coating composition according to any one of claims 1 to 8, based on the weight of the coating composition, the coating composition comprises 0.9% or more of the water-soluble alkali metal silicate by dry weight.

10. A method for preparing the coating composition according to any one of claims 1 to 9, the method comprising: (i) admixing the aqueous dispersion of the acrylic (co)polymer with the aqueous solution of the water-soluble non-alkali metal salt to form an admixture; (ii) further admixing the admixture obtained from step (i) with the water-soluble alkali metal silicate and, if present, the microfillers; and optionally, adding 0.06% to 0.52% by weight of ethylenediaminetetraacetic acid, its salts, or mixtures thereof, based on the total weight of the coating composition, to the admixture obtained from step (i) before step (ii).

Images