Low-VOC coalescent for coatings

Abstract

A glycerol ether compound that has a boiling point of more than 250℃ can function as a low-VOC coalescent in aqueous coating formulations.

Description

[0001] LOW-VOC COALESCENT FOR COATINGS FIELD This invention relates to the field of aqueous coating formulations. INTRODUCTION Aqueous coating formulations include paints, varnishes and clear coats that are applied to solid substrates such as walls, ceilings, floors, cabinets, furniture and other objects. They contain the following components dispersed in an aqueous solvent: • A film-forming polymer that is insoluble in water, which is commonly called a binder; and • Optionally, water-insoluble pigments, extenders and fillers; and • Optionally, other additives. The term “aqueous solvent” does not imply that components of the coating formulation dissolve in the solvent. Typically, the binder, the pigments, extenders and fillers and many of the other additives are solid, insoluble particles and are dispersed in the aqueous solvent in a stable or quasi-stable dispersion. Paints contain water-insoluble pigments, extenders and / or fillers. Common pigments in paints include inorganic powders such as titanium dioxide, antimony white, carbon black, cobalt blue, chrome green, cobalt yellow, and yellow ochre. Common extenders and fillers in paints include calcium carbonate, aluminum trihydrate, aluminosilicates and silica. However, the dividing line between pigments, extenders and fillers is not always clear. Materials that are considered pigments in some applications may be treated as extenders or fillers in other applications, and similar cross-over happens for materials considered extenders or fillers. Varnishes and clear-coats often contain fewer pigments, extenders and fillers than paints and may sometimes omit them entirely. Common additives include coalescents, thickeners, dispersants, wetting agents, emulsifiers, levelling agents, open-time extenders, antioxidants, light stabilizers and drying agents. The film-forming polymer, the pigments, extenders, fillers and other solid additives are referred to as “solid components” or “solids”. The quantity of aqueous solvent is typically high enough to fully wet the solid components and to provide a homogeneous coating composition whose viscosity is suitable to apply by ordinary means such as spraying, brushing, or rolling. The quantity of aqueous solvent is typically low enough that the coating formulation can dry quickly to leave a solid coating. To coat a substrate, the coating formulation is applied to the substrate. As the aqueous solvent evaporates, particles of the film-forming polymer come into contact and coalesce to form a smooth, continuous coating adhered to the substrate, and harden. Film-forming polymers typically have a minimum film forming temperature (MFFT), below which they do not effectively coalesce. Coalescent additives are added to the coating composition to reduce the MFFT and to assist coalescence above the MFFT. Many coalescents are volatile organic compounds (VOC). Aqueous coating formulations are used to minimize release of VOCs into the air, and so it is desirable to identify low-VOC coalescents. The regulatory definition of what is a VOC and what is low-VOC varies from country to country. Generally, a coalescent is not required to be completely non-volatile to be treated as low-VOC. Instead, low-VOC coalescents may volatilize slowly over time, so that the coalescent remains in low concentrations in air and minimizes exposure to the coalescent. SUMMARY One aspect of this invention is an aqueous coating formulation that comprises the following components dispersed in an aqueous solvent: (a) A film forming organic polymer; (b) Optionally, water-insoluble pigments, extenders and fillers; and (c) A glycerol ether compound that has a boiling point of more than 250℃ and is present in a concentration suitable to enhance the coalescence of the film forming organic polymer. A second aspect of this invention is a process to apply a coating to a substrate comprising the steps of (1) applying a coating formulation as described in the first aspect of the invention directly or indirectly onto the substrate; and (2) allowing the coating formulation to dry on the substrate. A coating on a substrate, which coating comprises: (a) A solid continuous film of film forming organic polymer adhered directly or indirectly to the substrate; (b) Optionally, water-insoluble pigments, extenders and fillers adhered to the continuous film of film forming organic polymer; and (c) a glycerol ether compound that has a boiling point of more than 250℃, in a ratio from 1 to 20 weight percent of the weight of the film forming organic polymer. The glycerol ether compounds in this invention are low-VOC compounds and can effectively depress the minimum film forming temperature of common binder polymers used in aqueous paints. DETAILED DESCRIPTION The invention relates to aqueous coating formulation that contains a high-boiling low-VOC coalescent. Solid components dispersed in the aqueous coating formulation include a film forming organic polymer, optionally water-insoluble pigments, extenders and fillers, and optionally other additives aside from the coalescent. Binder The film forming organic polymer is commonly referred to as a binder. Binders and aqueous dispersions that contain binders are known, and they are commercially available. They are described in publications such as “Paints” published by Department of Chemistry, University of York at https: / / www.essentialchemicalindustry.org / materials-and-applications / paints.html (March 18, 2013). Examples of known aqueous binders include acrylic polymers, vinyl ester copolymers and polyurethane binders. “Film-forming” means that the binder is capable of forming a film upon application to a solid surface. The ability of polymers and their solutions or dispersions to be film-forming is known and described in publications such as: P.A. Steward et al., “An Overview of Polymer Latex Film Formation and Properties”, 86 Advances in Colloid and Interface Science at 195-267 (2000) and J. Guerts et al., “New Waterborne Acrylic Binders for Zero VOC Paints”, 5 J. Coating Technol. Res. at 57-63 (2008). Film-forming polymer latexes generally contain colloidal particles that coalesce as they dry. Coalescence can arise from individual particles compacting, deforming, adhering to each other and / or having polymer chains diffuse with each other. Commonly, the film-forming ability of polymers increases with lower molecular weight and / or lower Tg and decreases with higher molecular weight and / or higher Tg. In some embodiments, polymers in the coalesced film cross-link to add further strength and water-resistance to the coating. In some embodiments, the binder comprises an acrylic polymer. An acrylic polymer is a homopolymer or copolymer that contains repeating units derived from acrylic monomers. Exemplary acrylic monomers include acrylic acid, methacrylic acid, and their esters. Exemplary esters used in acrylic monomers include alkyl esters, such as alkyl groups containing from 1 to 8 carbon atoms or from 1 to 4 carbon atoms or in some cases methyl groups or ethyl groups. Examples of useful acrylic monomers are acrylic acid, methacrylic acid, butyl acrylate, 2-ethylhexyl acrylate, methyl acrylate, ethyl acrylate, methyl methacrylate and ethyl methacrylate. Exemplary acrylic polymer binders may contain at least 70 weight percent repeating units derived from acrylic monomers, or at least 80 weight percent or at least 90 weight percent or at least 95 weight percent. Exemplary acrylic polymer binders may contain up to 100 percent repeating units derived from acrylic monomers. Some exemplary acrylic polymer binders are copolymers containing units derived from two or more acrylic monomers, such as copolymers of butyl acrylate with methyl methacrylate and / or methacrylic acid. Some exemplary acrylic polymer binders may contain a crosslinking monomer. For example, acetoacetoxyethyl methacrylate (AAEM), which is sold under the trademark: Eastman AAEM, can be incorporated in the acrylic polymer chain and reacts with dihydrazides or diamines to form cross-links. Alternatively, hydroxyl-functional monomers such as (hydroxyethyl)methacrylate can provide pendant hydroxyl groups that react readily with the isocyanate cross-linker to form cross-links. The crosslinking monomer enables the acrylic polymer binder to crosslink as it sets when applied as a coating. In some embodiments, no more than 10 mole percent of repeating units in the acrylic polymer binder are derived from crosslinking acrylic monomers or no more than 5 mole percent or no more than 3 mole percent or no more than 2 mole percent or no more than 1 mole percent. In some embodiments, 0 mole percent of repeating units in the acrylic polymer binder are derived from crosslinking acrylic monomers or at least 0.1 mole percent or at least 0.5 mole percent or at least 1 mole percent. An example of a suitable acrylic polymer binder containing a crosslinking acrylic monomer is sold as RHOPLEX™ VSR 1065. Some exemplary acrylic polymer binders may contain repeating units derived from non-acrylic ethylenically unsaturated comonomers, such as ethylene, vinyl esters (such as vinyl acetate) or styrene. In some embodiments, the comonomer is an ethylene monomer. Suitable acrylic polymer binders and their aqueous dispersions are commercially available from the Dow Chemical Company under the ROVACE™, RHOPLEX™ and PRIMAL™ trademarks. Other acrylic polymer binders can be made by emulsion polymerization of suitable monomers in the presence of suitable dispersants. Emulsion polymerization processes are well-known and described in numerous publications, such as Emulsion Polymerization of Acrylic Monomers, published by Rohm and Haas Company (1966); Lovell et al, Fundamentals of Emulsion Polymerization, 21 Biomacromolecules 4396−4441 (2020); and Juaregui, Thesis: Synthesis and Optimization of Emulsion Polymers, published by California Polytechnic State University, San Luis Obispo (2016). In some embodiments, the binder comprises a vinyl ester copolymer. Vinyl ester copolymers contain repeating units derived from one or more vinyl ester monomers, such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl 2-ethylhexanoate, vinyl laurate, 1-methylvinyl acetate, vinyl pivalate, and vinyl esters of C-branched monocarboxylic acids having 9 to 11 carbon atoms, such as vinyl versatate or vinyl neodecanoate. In some embodiments, the vinyl ester copolymer comprises vinyl acetate. In some embodiments, the vinyl ester copolymer comprises both vinyl acetate and vinyl esters of higher molecular weight monocarboxylic acids, such as vinyl versatate or vinyl neodecanoate; examples of such polymers are commercially available under the trademark VeoVa. In some embodiments, the vinyl ester copolymer further comprises repeating units derived from ethylene. For example, some vinyl ester-ethylene copolymers may contain at least 1 weight percent repeating units derived from ethylene or at least 5 weight percent or at least 10 weight percent, and some vinyl ester-ethylene copolymers may contain at most 60 weight percent repeating units derived from ethylene or at most 50 weight percent. In some embodiments, the vinyl ester copolymer further comprises repeating units derived from an acrylic or methacrylic ester such as n-butyl acrylate or 2-ethyl hexyl acrylate. For example, some vinyl ester-acrylic ester copolymers may contain 30 to 90 weight percent repeating units derived from vinyl ester, 1 to 60 weight percent repeating units derived from acrylic ester and 1 to 40 weight percent repeating units derived from ethylene. In some embodiments, the vinyl ester copolymer comprises no measurable quantity of acrylic or methacrylic ester. Examples of suitable vinyl ester copolymers are described in US Patent 6,890,975. In some embodiments, the vinyl ester copolymer is a vinyl acetate-ethylene (VAE) copolymer. In some embodiments, the vinyl ester copolymer is a vinyl ester of versatic acid (VeoVa) copolymer. Suitable vinyl ester polymer binders and their dispersions are commercially available under the Vinnipas, EcoVae and Encor trademarks. Other vinyl ester copolymers can be produced by aqueous emulsion polymerization of vinyl ester monomers and ethylene at temperatures below 100°C and ethylene pressure between 20 and 120 bar. Water-based polyurethane dispersions are known for a variety of coating applications. Some water-based polyurethane dispersions can be made from a di-isocyanate and a polyol by a two-stage process. In the first stage, a di-isocyanate, such as methylene-bis(phenyl isocyanate) (MDI), toluene diisocyanate (TDI), and hexamethylene diisocyanate (HDI), and a polyol that contains an acid moiety, such as 2-2 dimethylolproprionic acid, react together in the presence of a tin catalyst to form a prepolymer. In the second stage, the acid is neutralized with an amine, the prepolymer is dispersed in water, and the prepolymer further reacts with a polyol or diamine to extend the polyurethane polymer and form an aqueous dispersion of the polymer. Exemplary water-based polyurethane dispersions are commercially available from Lubrizol Corporation, Lanxess and UBE Corporation. Other polyurethane dispersions can be made as described in Joseph et al., PCT Publication WO 2022 / 066320 A1 (31 March 2022). In some embodiments, the minimum film forming temperature (MFFT) of the binder polymer is at least 5℃ or at least 7℃ or at least 9℃ or at least 11℃ or at least 12℃ or at least 13℃ or at least 15℃ or at least 17℃ or at least 19℃. In some embodiments, the minimum film forming temperature (MFFT) of the binder polymer is at most 30℃ or at most 27℃ or at most 25℃ or at most 23℃ or at most 21℃ or at most 19℃ or at most 18℃ or at most 17℃. The binder may desirably remain flexible at temperatures that the dried coating may be exposed to. In some embodiments, the binder has a glass transition temperature (Tg) of at most 40℃ or 35℃ or 25℃ or 15℃ or 5 or 0°C or -10°C or -20°C or -30°C. There is no minimum desirable Tg, but Tg below -60°C are seldom necessary. The binder may also need to remain non-molten at temperatures that the dried coating may be exposed to. In some embodiments, the binder has a melting temperature of at least 60°C or at least 75°C or at least 80°C or at least 95°C or at least 110°C. There is no maximum desirable melting temperature, but melting temperatures above 200°C are seldom necessary. It is known to adjust the glass transition temperature and melting temperature of binder polymers by adjusting the selection and ratio of monomers. For example, in acrylic polymers certain monomers, such as methyl methacrylate, increase Tg and melting point of the resulting polymer, and other monomers, such as butyl acrylate, reduce Tg and melting point of the resulting polymer. In some embodiments, an acrylic polymer binder contains at least 7 weight percent units derived from methyl methacrylate or at least 10 weight percent or at least 12 weight percent. In some embodiments, an acrylic polymer binder contains at most 50 weight percent units derived from methyl methacrylate or at most 45 weight percent or at most 40 weight percent. In some embodiments, an acrylic polymer binder contains at least 50 weight percent units derived from butyl acrylate or at least 55 weight percent or at least 60 weight percent. In some embodiments, an acrylic polymer binder contains at most 93 weight percent units derived from butyl acrylate or at most 90 weight percent or at most 88 weight percent. Likewise, in vinyl acetate-ethylene copolymers, increasing levels of ethylene reduce Tg and melting point of the resulting polymer, whereas increasing levels of vinyl acetate increase Tg and melting point of the resulting polymer. The binder is in the form of particles that are dispersed in the aqueous solvent. In some embodiments, the binder has an average particle diameter of at least 30 nm or of at least 50 nm or at least 100 nm or at least 150 nm or at least 200 nm or at least 250 nm or at least 300 nm. In some embodiments, the binder has an average particle diameter of at most 700 nm or at most 650 nm or at most 600 nm or at most 550 nm or at most 500 nm or at most 450 nm or at most 400 nm. In many embodiments, the binder particles are dispersed in the aqueous solvent using dispersants, which are usually surfactants. In some embodiments, the dispersants are anionic surfactants, and in some embodiments the dispersants are non-ionic surfactants. Examples of suitable dispersants are sodium dodecylbenzenesulfonate and sodium lauryl sulfate. Examples of suitable dispersants are available under the DOWFAX™, TRITON™, TERGITOL™, ECOSURF™, and Polystep trademarks. The binder concentration should be high enough to effectively form a continuous film on the substrate. In some embodiments, the binder makes up at least 10 weight percent of the solid components in the coating formulation, or at least 15 weight percent or at least 20 weight percent or at least 25 weight percent or at least 28 weight percent or at least 30 weight percent or at least 32 weight percent or at least 34 weight percent or at least 36 weight percent or at least 38 weight percent or at least 40 weight percent. In some embodiments, the binder makes up at most 95 weight percent of the solid components in the coating formulation, or at most 90 weight percent or most 85 weight percent. • In coating compositions that do not contain pigments, extenders and fillers, the concentration of binder may be higher than coating compositions that contain pigments, extenders and fillers. In some embodiments, the binder makes up at most 80 weight percent of the solid components in the coating formulation, or at most 75 or at most 70 or at most 60. For example, the binder can make up from 30 to 75 weight percent of the solid components in the coating formulation, or from 35 to 70 weight percent or from 40 to 60 weight percent. • In coating compositions that contain pigments, extenders and fillers, the concentration of binder may be lower than in compositions that do not contain pigments, extenders and fillers. In some embodiments, binder makes up at most 60 weight percent of the solid components in the coating formulation, or at most 55 weight percent or at most 50 weight percent. For example, binder can make up from 20 to 60 weight percent of the solid components in the coating formulation, or from 25 to 55 weight percent or from 30 to 50weight percent. In some embodiments, the binder is added to the aqueous coating formulation as an aqueous dispersion. For clarity, the weight percentages listed above refer to the weight of the binder only, excluding the weight of water in the dispersion that contains the binder. In some embodiments, the aqueous dispersion contains at least 30 weight percent binder or at least 40 weight percent and at most 70 weight percent binder or at most 60 weight percent or at most 50 weight percent. In some embodiments, the aqueous dispersion contains at least 30 weight percent water or at least 40 weight percent or at least 50 weight percent and at most 70 weight percent water or at most 60 weight percent. Pigments, Extenders and Fillers Some embodiments of the coating formulation contain pigments, extenders and fillers. Inorganic pigments are known and commercially available. In some embodiments, the inorganic pigments include oxides and salts of metals such as cobalt, chromium, cadmium, titanium, zinc, copper and iron. Examples of common inorganic pigments include titanium dioxide, carbon black, cerulean blue (Co2SnO4), chrome green (Cr2O3), cobalt violet (Co3(PO4)2), cadmium orange (Cd2SSe), titanium white (TiO2), antimony white (Sb2O3), zinc white (ZnO), ultramarine blue, Prussian blue (Fe7(CN)18), cobalt blue (CoAl2O4), viridian green (hydrated Cr2O3), cadmium yellow (CdS), chrome yellow (PbCrO4), zinc yellow (ZnCrO4), cadmium red (CdSe) and red ochre (Fe2O3). See, for example, G. Buxbaum, Industrial Inorganic Pigments, 2ndEd. (1998), published by Wiley-VCH. These and other suitable inorganic pigments are commercially available. Fillers and extenders for coatings are known and commercially available. In some embodiments, the inorganic fillers and extenders include oxides, carbonates and sulfates of silicon, calcium, titanium and / or aluminum. Examples of common inorganic fillers and extenders include silica and silicates, calcium carbonate, quartz, dolomite, kaolin, barium sulfate, wollastonite, mica, talc, feldspar, diatomaceous earth, glass powder and microspheres and aluminum hydroxide. Fillers and extenders and their production and use are described in publications such as: Gysau, Fillers for Paints (3rd Ed.), Vincentz Network GmbH & Co.(2017). In some embodiments, such as in clear coating formulations, organic materials such as polymers and waxes may also be considered as fillers. It is known in the coatings arts to select pigments, extenders and fillers that have a particle size suitable for the coating formulation. In some embodiments, pigments, extenders and fillers have a minimum (D10) particle size of at least 0.01 microns or at least 0.03 microns or at least 0.05 microns or at least 0.07 microns or at least 0.1 microns. In some embodiments, pigments, extenders and fillers have a maximum (D90) particle size of at most 100 microns or at most 80 microns or at most 70 microns or at most 60 microns or at most 50 microns or at most 40 microns or at most 30 microns. Selections within this range influence the stability of the coating formulation dispersion and the appearance of the resulting coating, in ways that are known. See for example, “Gloss Control and the Role of Particle Size”, published at www.pcimag.com / articles / 83141-gloss-control-and-the-role-of-particle-size; “Titanium Dioxide Kumar et al., “Size Dependent Reflective Properties of TiO2Nanoparticles and Reflectors Made Thereof”, Vol.7, No.2 Digest Journal of Nanomaterials and Biostructures, 607 – 619 (2012). In some embodiments, pigments and extenders have a median particle size of at least 0.1 micron or at least 0.2 micron or at least 0.3 micron. In some embodiments, the pigments and extenders have a median particle size of at most 10 micron or at most 8 micron or at most 6 micron or at most 4 micron or at most 2 micron or at most 1 micron. In some embodiments, fillers and extenders have a median particle size of no more than 50 microns or no more than 40 microns or no more than 30 microns or no more than 25 microns or no more than 20 microns or no more than 15 microns or no more than 12 microns. In some embodiments, fillers and extenders have a median particle size of at least 1 micron or at least 3 microns or at least 5 microns or at least 8 microns. The pigments, extenders and fillers are typically insoluble in water. Dispersing and wetting agents may help to maintain a stable dispersion. Suitable dispersing and wetting agents are known and commercially available, such as under the following trademarks: TAMOL™, ACUMER™, OROTAN™, Calgon, and Dispex. In some embodiments, the dispersant may be a polycarboxylate, a polyphosphate or a block copolymer having blocks that interact with water and blocks that interact with the pigments, extenders and fillers. In some embodiments, a wetting agent is a surfactant such as a salt of a fatty acid, a poly (ethylene oxide) surfactant or a silicone-based surfactant. In some embodiments, the coating formulation contains 0 weight percent of pigments, extenders and fillers, based on the weight of solid components excluding solvent, or at least 10 weight percent or at least 20 weight percent or at least 25 weight percent or at least 30 weight percent or at least 35 weight percent or at least 40 weight percent. In some embodiments, the coating formulation contains at most 80 weight percent of pigments, extenders and fillers, based on the weight of solid components excluding solvent, or at most 70 weight percent or at most 65 weight percent or at most 60 weight percent or at most 55 weight percent or at most 50 weight percent. For example, the coating formulation may contain from 35 to 70 weight percent of pigments, extenders and fillers, based on solid components excluding solvent, or from 40 to 60 weight percent. Concentration of pigments, extenders and fillers are often defined based on pigment volume concentration (PVC), which is the volume percentage of pigments, extenders and fillers in the solids of coating formulation calculated according to Formula 2: Ve is the dry volume of extenders and filler and Vb dry is the dry volume of binder. In some embodiments, the PVC of the coating formulation is at least 0 percent or at least 10 percent or at least 20 percent or at least 25 percent or at least 30 percent. In some embodiments, the PVC of the coating formulation is at most 75 percent or at most 75 percent or at most 70 percent or at most 65 percent or at most 60 percent. Optimum PVC depends on the desired properties of the coating. High gloss paints typically have PVC of at least 15 percent and at most 25 percent. Semigloss paints typically have PVC of at least 20 percent and at most 40 percent. Eggshell paints typically have PVC of at least 30 percent and at most 45 percent. Flat paints typically have PVC of at least 50 percent and at most 80 percent. Low-VOC Coalescents The coating formulation contains a coalescent, which is a glycerol ether compound with a boiling point greater than 250℃. In some embodiments, the glycerol ether compound has a boiling point of at least 255℃ or at least 260℃ or at least 270℃ or at least 280℃ or at least 290℃ or at least 300℃ or at least 310℃ or at least 320℃ or at least 330℃. In some embodiments, the glycerol ether compound has a boiling point of at most 600℃ or at most 550℃ or at most 500℃ or at most 475℃ or at most 450℃ or at most 440℃ or at most 440℃ or at most 430℃ or at most 420℃. Glycerol ethers are represented by Formula 1: or an organic moiety selected su1 2 ch that at least one of R , R and R3is an organic moiety. In some embodiments, organic moieties in R1, R2and R3are selected such that the organic moieties have low polarity, and the glycerol ether interacts preferentially with the binder over the aqueous solvent. In some embodiments, the organic moieties are each independently hydrocarbyl. In some embodiments, at least one or all of the organic moieties in R1, R2and R3are aliphatic. In some embodiments, at least one or all the organic moieties are independently selected from alkyl, aryl and alkaryl groups. In some embodiments, at least one or all of the organic moieties in R1, R2and R3are alkyl groups. In some embodiments, at least one or all of the organic moieties in R1, R2and R3are aryl groups. In some embodiments, at least one or all of the organic moieties in R1, R2and R3are alkaryl groups, such as benzyl, 2-phenylethyl, tolyl and cumenyl groups. Examples of suitable organic moieties in R1, R2and R3include linear and branched alkyl groups that contain from 1 to 12 carbon atoms, phenyl, and benzyl, 2-phenylethyl, tolyl and cumenyl groups. In some embodiments, the organic moieties are selected such that R1, R2and R3collectively contain at least 4 carbon atoms or at least 5 carbon atoms or at least 6 carbon atoms or at least 7 carbon atoms or at least 8 carbon atoms. In some embodiments, the organic moieties are selected such that R1, R2and R3collectively contain at most 30 carbon atoms or at most 25 carbon atoms or at most 20 carbon atoms or at most 18 carbon atoms or at most 17 carbon atoms or at most 16 carbon atoms or at most 15 carbon atoms or at most 14 carbon atoms. The glycerol ethers contain at least 1 organic moiety per molecule in R1, R2and R3, and no more than 3 organic moieties per molecule in R1, R2and R3. In some embodiments, the glycerol ethers contain on average at least 1.1 organic moieties per molecule in R1, R2and R3or at least 1.2 organic moieties per molecule or at least 1.4 organic moieties per molecule or at least 1.6 organic moieties per molecule or at least 1.8 organic moieties per molecule or at least 2.0 organic moieties per molecule. In some embodiments, the glycerol ethers contain on average at most 2.9 organic moieties per molecule in R1, R2and R3or at most 2.7 organic moieties per molecule or at most 2.5 organic moieties per molecule or at most 2.3 organic moieties per molecule or at most 2.1 organic moieties per molecule or at most 2.0 organic moieties per molecule. In some embodiments, R1is an organic moiety, and R2and R3are hydrogen (a monoether). In some embodiments, R1and R2are organic moieties, and R3is hydrogen (a diether). In some embodiments, R1and R3are organic moieties, and R2is hydrogen (a diether). In some embodiments, R1, R2and R3are organic moieties (a triether). In some embodiments, the vapor pressure of the glycerol ether at 293.15°K is less than 0.01 KPa or no more than 0.005 KPa or no more than 0.001 KPa or no more than 0.0005 KPa or no more than 0.0001 Kpa. Examples of suitable glycerol ethers include 1,3-di(benzyloxy)-2-propanol; 3-benzyloxy-1,2- propanediol; n-pentyl glyceryl ether; 1,3-di-n-butoxy-2-propanol; chimyl alcohol; glycerin 1,3-bis-(2- ethylhexyl) ether; 2,3-di((2-ethylhexyl)oxy)-1-propanol; and 2,3-dibenzyl-sn-glycerol. Many suitable glycerol ethers are commercially available, such as from the Millipore Sigma division of Merck KGaA. Others can be made by known procedures, as described in Griese et al., US Patent 8,901,056 B2 (2 Dec 2014), col 2, lines 55-68. For example, • Reacting glycerol, alkyl alcohol and etherification catalyst in an etherification reactor to obtain a reaction product comprising alkyl glycerol ethers. See Arredondo et al., US Patent Publication 2007 / 0238905 A1 (11 Oct 2007). • Reacting cyclic carbonate that has a pendant hydroxyl or ether group with an alcohol in the presence of an acid catalyst. See Mignani et al., US Patent Publication 2015 / 0080613 A1 (19 Mar 2015). In some embodiments, the ratio of glycerol ether to binder (excluding solvent) is at least 1 weight percent, or at least 2 weight percent or at least 3 weight percent or at least 4 weight percent or at least 5 weight percent or at least 6 weight percent or at least 7 weight percent. In some embodiments, the ratio of glycerol ether to binder (excluding solvents) is at most 20 weight percent or at most 18 weight percent or at most 15 weight percent or at most 14 weight percent or at most 13 weight percent or at most 12 weight percent or at most 11 weight percent or at most 10 weight percent or at most 9 weight percent or at most 8 weight percent. For example, ratio of glycerol ether to binder (excluding solvents) may be from 1 to 15 weight percent or from 3 to 12 weight percent or from 7 to 11 weight percent or from 8 to 10 weight percent. In some embodiments, the selection and concentration of the glycerol ethers reduces the MFFT of the binder by at least 1℃ or at least 2℃ or at least 3℃ or at least 4℃ or at least 5℃ or at least 6℃ or at least 7℃ or at least 8℃ or at least 9℃ or at least 10℃. In some embodiments, the selection and concentration of the glycerol ethers reduces the MFFT of the binder by no more than 30℃ or no more than 25℃ or no more than 20℃ or no more than 18℃ or no more than 16℃ or no more than 14℃ or no more than 12℃ or no more than 11℃ or no more than 10℃ or no more than 9℃. Other Additives Coating formulations may optionally contain other additives that are appropriate for aqueous coating formulations. Many such components are described in the publication Johan Bieleman (ed.), Additives for Coatings, published by WILEY-VCH Verlag GmbH (2000). Some examples of common additives are listed below. All of the additives listed below are commercially available. The coating formulation may optionally contain thickeners to make it easier to handle and apply. Examples of thickeners include inorganic materials such as certain clays and polymer thickeners, such as certain cellulose derivatives, starches, and acrylic polymers. The coating formulation may optionally contain surfactants for a number of purposes. Some surfactants are emulsifiers, wetting agents and dispersants. Some surfactants are antifoaming agents. Some surfactants can promote adhesion of the binder to the substrate. The coating formulation may optionally contain hydrophobic additives to improve its ability resist water infiltration. Examples of hydrophobic components may include waxes and polymers such as polypropylene. The coating formulation may optionally contain levelling agents to provide complete coverage and a smooth surface on the roof. Examples of levelling additives include certain polyacrylate polymers, which have a low glass-transition temperature such as -20°C or lower. The coating formulation may optionally contain antioxidants. Antioxidants may include a primary antioxidant such as certain amines or sterically-hindered phenols and / or a secondary antioxidant such as certain organophosphates or thioesters. The coating formulation may optionally contain light and ultraviolet (UV) stabilizers. Examples of light and ultraviolet (UV) stabilizers may include: • UV absorbers such as benzotriazoles and other compounds having coordinated double bonds; and • Sterically hindered amines such as compounds containing a 2,2,6,6-tetramethylpiperidine group; The coating formulation may optionally contain antifouling additives, such as 4,5-dichloro-2- octyl-4-isothiazolin-3-one (DCOIT), 2-n-octyl-4-isothiazolin-3-one (OIT) and zinc pyrithione (ZPT). The coating formulation may optionally contain dirt pickup resistance additives, such as benzophenone. In some embodiments, the coating formulation contains at most 10 weight percent additives (other than the glycerol ether), based on the weight of solids excluding solvent, or at most 8 weight percent or at most 6 weight percent or at most 5 weight percent or at most 4 weight percent or at most 3 weight percent. In some embodiments, the coating formulation contains 0 weight percent additives (other than the glycerol ether), based on the weight of solids excluding solvent, or at least 0.1 weight percent or at least 0.5 weight percent or at least 0,8 weight percent or at least 1 weight percent or at least 2 weight percent. Aqueous Solvent The coating formulation contains an aqueous solvent. The aqueous solvent contains primarily water, but may contain a minor amount of other solvents that are miscible with water, such as ethanol. In some embodiments, the aqueous solvent contains at least 70 weight percent water or at least 80 weight percent water or at least 90 weight percent water or at least 95 weight percent water or at least 98 weight percent water. In some embodiments, the aqueous solvent may contain up to 100 percent water. (The weight percentages of water in the solvent are based on the weight of solvents, excluding solid components). In some embodiments, the aqueous solvent has a pH of at least 5.5 or at least 6.0 or at least 6.5 or at least 7.0 or at least 7.5 or at least 8.0 or at least 8.5. In some embodiments, the solvent has a pH of at most 10.0 or at most 9.5 or at most 9.3 or at most 9.0 or at most 8.8 or at most 8.5. Correct selection of pH may influence the stability of the coating formulation suspension. The coating formulation has sufficient aqueous solvent to wet the solid components and form a homogeneous suspension that has a viscosity which makes it practical to apply. In many embodiments, its viscosity is low enough to apply evenly by brush, roller or spray and high enough to minimize running and dripping after the coating formulation is applied. In some embodiments, the quantity of water is minimized in order to minimize the time needed for the coating formulation to dry. In some embodiments, the coating formulations contain at least 40 weight percent solid components or at least 45 weight percent or at least 50 weight percent or at least 55 weight percent or at least 60 weight percent. In some embodiments, the coating formulations contain at most 75 weight percent solid components or at most 70 weight percent or at most 65 weight percent. In some embodiments, the coating formulations contain at least 25 weight percent aqueous solvent or at least 30 weight percent or at least 35 weight percent. In some embodiments, the coating formulations contain at most 60 weight percent aqueous solvent or at most 55 weight percent or at most 50 weight percent or at most 45 weight percent or at most 40 weight percent. In some embodiments, the coating formulation has a viscosity at 25℃ of at least 50 KU when it is first mixed, or at least 60 KU or at least 70 KU or at least 85 KU or at least 90 KU. In some embodiments, the coating formulation has a viscosity at 25℃ of at most 150 KU when it is first mixed, or at most 145 KU or at most 141 KU or at most 135 KU or at most 130 KU or at most 125 KU or at most 120 KU. In some embodiments, the viscosity of coating formulation increases by no more than 30 percent after storage for 10 days at 25℃, or no more than 25 percent or no more than 20 percent or no more than 18 percent or no more than 16 percent or no more than 14 percent or no more than 12 percent or no more than 10 percent. In some embodiments, the viscosity of coating formulation increases by 0 percent after storage for 10 days at 25℃, or at least 2 percent or at least 5 percent. In some embodiments, the dispersion of solid components in coating formulation is stable for at least 1 day, or at least 1 week or at least 1 month or at least 2 months or at least 3 months or at least 4 months or at least 6 months or at least 8 months or at least 10 months or at least 1 year. In some embodiments, the dispersion of solid components in the coating formulation is stable indefinitely. In some embodiments, the dispersion of solid components in the coating formulation is a latex. Process and Coated Substrate In the process of this invention, the coating formulation is applied directly or indirectly onto a substrate. In some embodiments, the substrate is part of a building, such as a wall, ceiling, floor, roof or molding. In some embodiments, the substrate is a solid object, such as furniture, equipment or a vehicle. In some embodiments, the substrate is a paved surface. Examples of substrate materials include wood, drywall, concrete, brick, metal and polymers. In some embodiments, the coating formulation is applied directly onto the substrate. In some embodiments, the coating formulation is applied onto an intervening layer that is adhered to the substrate. For example, a primer or tie layer may be applied to the substrate first, or a face sheet or membrane may be adhered to the substrate first. The coating formulation may be applied to the substrate by known means such as spraying, rolling, brushing or dipping. Application may be done before or after the substrate is fixed in position for its intended use. In most cases, the coating formulation would be applied under dry conditions with a temperature high enough for the aqueous solvent to evaporate quickly leaving the dry coating behind. In some embodiments, the temperature is at least 0℃ or 5℃ or 10℃ or at least 15℃. Maximum temperature is not usually critical, but temperature is commonly below 50℃ or 45℃ or 40℃. The coating formulation is allowed to dry, leaving behind a solid dried coating on the substrate. During drying, particles of binder in the coating formulation coalesce to form a continuous film adhered to the substrate, and the film hardens trapping other solid components in and on the film. Drying time may vary depending on many factors, such as the contents of the coating formulation, temperature, humidity and air flow / wind. In some embodiments, at a temperature of 25℃ and relative humidity of no more than 50 percent, the coating dries to the touch in no more than 24 hours or no more than 12 hours or no more than 6 hours or no more than 4 hours or no more than 2 hours. In some embodiments, at a temperature of 25℃ and relative humidity of no more than 50 percent, the coating dries to the touch in at least 5 minutes or at least 10 minutes or at least 15 minutes or at least 20 minutes or at least 30 minutes. The coating formulation may be applied as a single coat, or two or more coats may be applied with each coat permitted to substantially dry before the next coat is applied. The contents of the dry coating are essentially the same as the solid components of the coating formulation in the same proportions as in the coating formulation. The dried coating typically contains: (a) A solid continuous film of film forming organic polymer adhered to the solid object; (b) Optionally, water-insoluble pigments, extenders and fillers adhered to the continuous film of film forming organic polymer; and (c) a glycerol ether compound that has a boiling point of more than 250℃, in a ratio from 1 to 20 weight percent of the weight of the film forming organic polymer. In some embodiments, the dry coating comprises no more than 5 weight percent water, or no more than 3 weight percent or no more than 1 weight percent or no more than 0.5 weight percent. There is no required content of water in the coating but in some cases, it may be impractical to remove solvent to a content below 0.01 weight percent. In some embodiments, the average thickness of the coating is at least 10 mil (250 micron) or at least 20 mil (500 micron) or at least 25 mil (760 micron). In some embodiments, the average thickness of the coating is at most 120 mil (3000 micron) or 100 mil (2500 micron) or 75 mil (1900 micron) or 50 mil (1300 micron) or 45 mil (1200 micron). In some embodiments, the dried coating has a scrub resistance of at least 300 strokes or at least 350 strokes or at least 375 strokes or at least 400 strokes or at least 410 strokes or at least 420 strokes or at least 430 strokes or at least 440 strokes. There is no maximum desired scrub resistance, but in some cases scrub resistance greater than 1000 strokes or 800 strokes or 600 strokes may be unnecessary. Test Methods Unless stated otherwise, measurements listed in this application are made using the following test methods: Parameter Test Measured usin laser diffraction with a Beckman Coulter LS13320XR Surfactant Leaching A paint colorant is added at 8 wt% concentration to paint samples that contain coalescent. The mixture is mechanically stirred until the color is homogeneous. The paint is applied on black Leneta PVC substrates with a 3 mils applicator and left to dry in a horizontal position at 25 °C and 60% relative humidity. Two hours after the application, two drops of approximately 0.2 mL of deionized water are placed on the painted surface and left at rest for 10 minutes. Then the painted surface is changed to a vertical position. The procedure is repeated 4 hours and 24 hours after paint application on the film. The degree of surfactant leaching after 2 hours, 4 hours and 24 hours is evaluated by comparing the differences in color and gloss of the paint film in the regions where the droplets of water were applied, according to these criteria: 1 - Visible color change, color leak; 2 - Visible color change; 3 - Subtle color change; 4 - No color change, gloss change; 5 - No visible change. Examples The following examples illustrate specific embodiments of the invention, but do not limit the broadest scope of the invention. Table 1 lists binders and coalescents that are used for the Examples. Table 1 Binders Solids a) Preparation of Paint 1 A grind phase of the ingredients shown in Table 2 is blended until homogeneous. Table 2: Grind Components Component Parts by Weight Water 23.51 OROTAN™ 731A disersant 073 geneous. Table 3: Let-Down Components Component Parts by Weight Binder 1 31.32 T e seecton and proporton o coaescent n t e et-down pase components or each Example is shown in Table 6. The let-down phase is added to the grind phase, and they are stirred until homogeneous.

[0002] Preparation of Paint 2 A grind phase of the ingredients shown in Table 4 is blended until homogeneous. Table 4: Grind components Component Parts by weight Water 17.6 1 2 2 7 6 5 6 2 6 .8 2 9 ogeneous. Table 5: Let-Down Components Component Parts by weight ROPAQUE™ ULTRA opaque polymer dispersion 5.3 3 4 1 w .1 2 3 .2 .1 The selection and proportion of coalescent in the let-down phase components for each Example is shown in Table 6. The let-down phase is added to the grind phase, and they are stirred until homogeneous. Paint Compositions with Coalescent CE1 through CE18 are comparative examples. IE1 through IE24 are inventive examples. • The viscosity of chosen samples is measured immediately after addition of the coalescents, after 1 day and after 10 days; each result is shown in Table 7. • The pH of chosen samples is measured immediately after addition of the coalescents, after 1 day and after 10 days; each result is shown in Table 8. • Each sample is tested for minimum film formation temperature. Chosen samples are tested for scrub resistance and surfactant leaching. Results are shown in Table 6. • Chosen samples are tested for stain removal, and results are shown in Table 9. Table 6 Coalescent Scrub Dispersion Coalescent MFFT R Surfactant wt % of binder (℃) esistance (strokes) Leaching Table 7: Viscosity Stability Coalescent Initial viscosity 24 h viscosity 10 days viscosity @ 25 °C (KU) @ 25 °C (KU) @ 25 °C (KU) CE5 909 908 913 Table 8: Dispersion pH Stability CoalescentInitial pHInitial pH pH after 24 h pH after 24 h pH after 10 pH after 10 (25°C) (50°C) (25 °C) (50 °C) days (25°C) days (50°C) Table 9: Stain Removal Stain CE5 CE9 IE4 IE8 Pencil 3 3 5 6

Claims

CLAIMS: We claim:

1. An aqueous coating formulation that comprises the following components dispersed in an aqueous solvent: : (a) A film forming organic polymer; (b) Optionally, water-insoluble pigments, extenders and fillers; and; and (c) A glycerol ether compound that has a boiling point of more than 250℃ and is present in a concentration suitable to enhance the coalescence of the film forming organic polymer.

2. The aqueous coating formulation of Claim 1 wherein the glycerol ether compound has a boiling point from 300℃ to 500℃.

3. The aqueous coating formulation of Claim 1 wherein the vapor pressure of the glycerol ether compound at 293.15°K is less than 0.01 KPa .

4. The aqueous coating formulation of Claim 1 wherein the glycerol ether compound meets Formula 1:or an organic moiety selected such that at least one of R1, R2and R3is an organic moiety and such that R1, R2and R3collectively contain from 4 to 30 carbon atoms.

5. The aqueous coating formulation of Claim 4 wherein organic moieties in R1, R2and R3are each independently hydrocarbyl groups.

6. The aqueous coating formulation of Claim 4 wherein organic moieties in R1, R2and R3are each independently alkyl, aryl or alkaryl groups.

7. The aqueous coating formulation of Claim 6 wherein R1is an organic moiety and R2and R3are each hydrogen.

8. The aqueous coating formulation of Claim 6 wherein R1and R3are each an organic moiety and R2is hydrogen.

9. The aqueous coating formulation of Claim 4 wherein R1, R2and R3collectively contain from 6 to 20 carbon atoms.

10. The aqueous coating formulation of Claim 1 wherein the ratio of glycerol ether compound to film forming organic polymer in the coating formulation is of from 3 to 12 weight percent.

11. The aqueous coating formulation of Claim 4 wherein: (a) the ratio of glycerol ether compound to film forming organic polymer in the coating formulation is from 3 to 12 weight percent; and(b) organic moieties in R1, R2and R3are each independently alkyl, aryl or alkaryl groups selected such that R1, R2and R3collectively contain from 6 to 20 carbon atoms; and (c) the glycerol ether compound has a boiling point from 300℃ to 500℃.

12. The aqueous coating formulation of Claim 1 wherein the glycerol ether compound is selected from the group consisting of 1,3-dibenzyloxy-2-propanol; 3-benzyloxy-1,2-propanediol; n-pentyl glyceryl ether; 1,3-di-n-butoxy-2-propanol and chimyl alcohol.

13. The aqueous coating formulation of Claim 1 wherein the minimum film forming temperature of the film forming organic polymer in the aqueous coating formulation is at least 2℃ below the minimum film forming temperature of the film forming organic polymer in a similar formulation without the glycerol ether compound.

14. The aqueous coating formulation as described in any one of Claims 1 through 13 wherein the film forming organic polymer comprises an acrylic polymer, a vinyl ester copolymer or a polyurethane polymer which has a minimum film forming temperature from 5℃ to 30℃ in the aqueous coating formulation.

15. The aqueous coating formulation of Claim 14 wherein the aqueous coating formulation has a pigment volume concentration from 10 percent to 80 percent.

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