CN105377999B

CN105377999B - Polymer-coated pigment particles

Info

Publication number: CN105377999B
Application number: CN201480040853.6A
Authority: CN
Inventors: 詹森·尼斯; 李海波
Original assignee: Xuanwei Investment Management Co ltd
Current assignee: Industrial Solution Co; Xuanwei Headquarters Co; Xuanwei Investment Management Co ltd; Sherwin Williams Co; Valspar Corp
Priority date: 2013-07-19
Filing date: 2014-07-18
Publication date: 2021-05-07
Anticipated expiration: 2034-07-18
Also published as: CN105377999A; EP3022261A1; WO2015010016A1; AU2014290450B2; EP3022261A4; AU2014290450A1

Abstract

The polymer-coated pigment dispersion is prepared from a mixture of: (a) a carrier; (b) pigment particles; and (c) a polymeric dispersant having a polymer backbone and zwitterionic polymer side chains comprising anionic and cationic groups. The dispersants can provide effective pigment wetting and dispersion with relatively low and therefore economical pigment amounts, and have good opacity and good hiding characteristics, especially in titanium dioxide-containing coating compositions.

Description

Polymer-coated pigment particles

FIELD

The present invention relates to pigment wetting and dispersing agents, pigment grind dispersions, pigment coated dispersions, and to pigmented paints and other coating compositions.

Background

Titanium dioxide is a widely used but increasingly expensive pigment in paints and other coating compositions. In many paint formulations, titanium dioxide represents the most expensive single raw material. Various techniques and ingredients have been proposed to reduce the amount of titanium dioxide in the coating composition formulation while still providing acceptable light scattering or opacity. One such ingredient is EVOQUE supplied by the Dow Chemical Company^TMPre-compounding the polymer. Four grades of EVOQUE products (EVOQUE 1140, EVOQUE 1180, EXP-4340 and EXP-4463) are currently available which are said to have varying degrees of reactivity towards titanium dioxide. EVOQUE Pre-composite Polymer "with TiO" according to its supplier's name₂And combined to form a polymer-pigment composite that improves both the wet and dry hiding efficiency of the pigment. Paints or other coating compositions made from the composites can have somewhat reduced levels of titanium dioxide pigmentA given degree of pigment coverage, or a certain degree of increased pigment coverage at a given titanium dioxide pigment level, is achieved. However, the potential savings in titanium dioxide feedstock cost and potential benefits in pigment hiding efficiency are offset by EVOQUE product cost.

A variety of other polymers have been proposed for use in pigments, for example as pigment dispersants. The synthesis of some of these polymers requires expensive starting monomers or complex synthetic schemes. In other cases, the polymers have high viscosity, limited pigment dispersion properties, or other disadvantages.

As can be appreciated from the foregoing, there remains a need in the art for improved pigmented coating compositions having even lower raw material costs, even higher pigment hiding efficiency, or both lower cost and higher efficiency. Such compositions and components and methods for their preparation are disclosed and claimed herein.

Disclosure of Invention

In one aspect, the present specification provides a pigment grind dispersion comprising a mixture of a carrier, pigment particles, and a polymeric dispersant having a polymeric backbone and zwitterionic polymeric side chains comprising anionic and cationic groups.

In another aspect, the present specification provides a pigment-coated polymer dispersion comprising a mixture of a carrier, pigment particles, and a polymeric dispersant, wherein the particles are at least partially coated with at least one polymer layer, and the polymeric dispersant has a polymer backbone and zwitterionic polymeric side chains comprising anionic groups and cationic groups.

In another aspect, the present description provides a method of making a pigment grind dispersion. The method comprises the following steps: the carrier, pigment particles, and polymeric dispersant are mixed, the polymeric dispersant having a polymeric backbone and zwitterionic polymeric side chains comprising anionic and cationic groups.

In another aspect, the present description provides a method of making a pigment-coated polymer dispersion. The method comprises the following steps: a dispersion of a carrier, pigment particles, and a polymeric dispersant having a polymer backbone and zwitterionic polymer side chains comprising anionic and cationic groups is formed. In one embodiment, a free radical initiator and one or more ethylenically unsaturated monomers are then included in or added to the dispersion, and the ethylenically unsaturated monomers are polymerized to at least partially coat the pigment particles with the at least one polymer layer.

In another aspect, the present description provides a coating composition comprising a dispersion of a carrier, pigment particles, and a polymeric dispersant, wherein the pigment particles are at least partially coated with at least one polymer layer, and the polymeric dispersant has a polymer backbone and zwitterionic polymer side chains comprising anionic groups and cationic groups. In addition, the composition further comprises one or all of the following two substances: a film-forming binder comprising a polymer different from the encapsulating polymer; or one or more of the standard paint formulation additives.

The disclosed dispersions, methods, and coating compositions can comprise, consist essentially of, or consist of the recited ingredients. In an exemplary preferred embodiment, the carrier comprises water, the pigment particles comprise titanium dioxide particles, the polymer backbone comprises a vinyl chain-growth polymer, the anionic groups comprise sulfonic acid groups, the cationic groups comprise quaternary ammonium groups, and the at least partially coated pigment particles self-coalesce at room temperature without the presence of a film-forming binder comprising a polymer other than a chain-growth polymer. The disclosed polymeric dispersants can provide effective pigment wetting and dispersion with relatively low and therefore economical raw material amounts (e.g., amounts of pigment, polymeric dispersant, and chain growth polymer). Preferred embodiments of the disclosed dispersions, methods and coating compositions desirably provide good pigment particle wetting and improved pigment dispersion in the final dried film, especially in latex paints containing silica, where the improved dispersion results in increased pigment hiding efficiency.

Detailed Description

Unless the context indicates otherwise, the following terms shall have the following meanings and apply to the singular and plural:

the terms "a", "an", "at least one" and "one or more" and the instances where quantitative terms are not used, are used interchangeably. Thus, for example, a coating composition comprising "a" carrier or "an" optional surfactant means: the coating composition may comprise "one or more" carriers and "one or more" optional surfactants.

The term "anionic group" when used in reference to a monomer or polymer side chain means: organic groups having a net negative charge, preferably a pH dependent net negative charge, when dissolved or dispersed in an aqueous carrier.

The term "binder" when used with respect to a liquid coating composition means: film-forming natural or synthetic polymers suitable for use in such compositions (with suitable coalescents, if desired).

The term "bulk polymer" means: polymers formed from homogeneous reaction mixtures made by dissolving a suitable initiator in one or more reactive monomers and which can be polymerized without the presence of a solvent.

The term "carrier" when used with respect to a pigment grind dispersion or coating composition means: a volatile dispersant or other vehicle for the dispersion or the remaining components of the composition.

The term "cationic group" when used in reference to a monomer or polymer side chain means: organic groups having a net positive charge, preferably a pH dependent net positive charge, when dissolved or dispersed in an aqueous carrier.

The term "emulsion polymer" means: a polymer formed from a heterogeneous reaction mixture that is initially in the form of an emulsion comprising water, an emulsifier (e.g., a surfactant), and one or more monomers. As used herein, the term "pigment-coated polymer dispersion" refers to pigment particles that are at least partially coated with a polymer layer. The term is used interchangeably with "polymer-encapsulated pigment dispersion".

The term "film-forming" when used with respect to a water-insoluble polymer means that an aqueous dispersion of the polymer (along with a suitable coalescing agent, if desired) can be formed on a suitable substrate or support, coated into a thin wet layer (e.g., a wet layer of about 25 μm thickness, and at a temperature above room temperature, if desired), and dried or otherwise hardened to form a substantially continuous coating on the substrate or support.

The term "contrast ratio" means the value determined by casting a 51 μm (2 mil) dry thickness coating film on a black and white portion of a Leneta co.form 3B opacity shrink sheet (draw down chart, from BYK-Gardner USA), as defined in ASTM International Standards on Color and application Measurement, 8 th edition, and dividing the L value measured on the black portion by the L value measured on the white portion.

The term "functional group" when used in reference to an organic group in a monomer or polymer refers to a group that enables such monomer or polymer to participate in a chemical reaction or to aid in the suspension or dispersion of the pigment in the vehicle.

The terms "group" and "fragment" are used to distinguish between chemical species that are permissive for substitution or that may be substituted and those that are not permissive or that cannot be so substituted. Thus, when the term "group" is used to describe a chemical substituent, the substituent described includes unsubstituted groups and groups having O, N, Si or S atoms (e.g., in the chain (e.g., as in an alkoxy group)) as well as groups having carbonyl groups or other conventional substituents. When the term "fragment" is used to describe a chemical compound or substituent, it is intended to include only the unsubstituted chemical species or substituent. For example, the phrase "alkyl" is intended to include not only pure open-chain saturated hydrocarbon alkyl substituents (e.g., methyl, ethyl, propyl, t-butyl, and the like), but also alkyl substituents bearing additional substituents known in the art (e.g., hydroxy, alkoxy, alkylsulfonyl, halogen atoms, cyano, nitro, amino, carboxyl, and the like). Thus, "alkyl group" includes ether groups, haloalkyl groups, nitroalkyl groups, carboxyalkyl groups, hydroxyalkyl groups, sulfoalkyl groups, and the like. On the other hand, the phrase "alkyl moiety" is limited to inclusion of pure open chain saturated hydrocarbon alkyl substituents, such as methyl, ethyl, propyl, t-butyl, and the like. The term "alkyl group" encompasses the term "alkyl fragment," and the disclosure of any particular group is also intended to explicitly disclose the corresponding fragment of that particular group.

The term "intermediate" when used in reference to the number of atoms between two organofunctional groups refers to the number of atoms in the shortest path between the groups, without counting the atoms of the groups.

The term "latex" when used in reference to a polymer means an emulsion of polymer particles in water, wherein the polymer itself cannot be dispersed in water; in contrast, latex polymers require a second emulsifier (e.g., a surfactant) to form the emulsion. The term is synonymous with the term "aqueous polymer dispersion" and is used interchangeably.

The term "low VOC" when used with respect to paints and other coating compositions means: the coating composition contains less than about 1 wt% volatile organic compounds, preferably less than about 0.5 wt% volatile organic compounds, more preferably less than about 0.05 wt% volatile organic compounds and most preferably less than about 0.005 wt% volatile organic compounds, based on the total weight of the coating composition.

The term "monomer" means: if desired in the presence of a suitable initiator or comonomer, may be reacted to form a polymer comprising 3 or more repeat units derived from the monomer or comonomer.

The term "multistage" when used with respect to a latex means that the latex polymer is made by dispersing (discrete) addition of two or more monomers, or by continuously varying addition of two or more monomers. Typically, a multistage latex will not exhibit a single Tg inflection point when measured using DSC. For example, a DSC curve of a multi-stage latex made with dispersed addition of two or more monomers may exhibit two or more Tg inflection points. Further, the DSC curve of a multistage latex prepared with continuously varying additions of two or more monomers may exhibit no Tg inflection points. By way of further explanation, the DSC curve of a single stage latex prepared with one monomer addition or with two or more monomers unchanged may exhibit only one Tg inflection point. Occasionally, when only one Tg inflection point is observed, it may be difficult to judge whether the latex represents a multi-stage latex. In this case, a lower Tg inflection point can sometimes be detected after a more precise examination, or the synthesis protocol used to make the latex can be examined to determine if it is expected to produce a multi-stage latex.

The term "pigment" when used in reference to a coating composition or pigment grind dispersion means a particulate material that imparts one or more colors (including white or black), or other visual or performance effects to the composition or dispersion. The term "pigment" includes, but is not limited to, extender pigments, opacifying pigments, coloring pigments, and the like. As used herein, the term "extender pigment" or "filler" refers to an inert (usually colorless and translucent) pigment used in coating compositions to enhance and reduce the overall cost. By "opacifying pigment" is meant one or more pigments added to a paint composition to make it opaque. As used herein, the term "opaque" means: the contrast ratio of the dry film of the coating composition at a dry film thickness of 51 μm (2 mils) is higher than 95%. Typically, the refractive index of the extender pigment is assumed to be less than about 1.8, while the refractive index of the opacifying pigment is assumed to be greater than about 1.8.

The term "pigment volume concentration" or "PVC" when used in reference to a coating composition means the total percentage of the dry coating volume occupied by all pigment species in the coating. The PVC can be calculated according to the following equation: PVC ═ pigment volume/(pigment volume + non-pigment volume).

The term "polymer" includes both homopolymers and copolymers (i.e., polymers of two or more different monomers) that contain two or more repeat units and have a weight average molecular weight (Mw) of at least 500 as measured using gel permeation chromatography and polystyrene standards.

The terms "preferred" and "preferably" refer to embodiments of the invention that may provide certain benefits under certain circumstances. However, other embodiments may also be preferred under the same or other circumstances. Furthermore, recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the invention.

The term "substantially free", when used with respect to components that may be found in a coating composition or pigment grind dispersion, means: less than about 1 wt% of the component is included, based on the weight of the coating composition or pigment grind dispersion.

The term "vinyl", when used in reference to a monomer, denotes a site of ethylenic unsaturation (preferably, terminal ethylenic unsaturation) having the formula-CH ═ CH 2-.

The term "water-based" when used with respect to a coating composition or pigment grind dispersion means that the primary carrier is water.

The term "solvent-borne" when used with respect to a pigment grind dispersion or coating composition means that the primary vehicle is a non-aqueous or a mixture of non-aqueous solvents.

The term "water-dispersible" when used with respect to a polymer means: the polymer itself can be dispersed in water without the use of a separate surfactant, or water can be added to the polymer to form an aqueous dispersion. The water dispersible polymer may include nonionic or ionic functional groups on the polymer to help render the polymer water dispersible. For such polymers, an external acid or base is typically required for ion stabilization, but this is not the case in all cases. For example, water-soluble compositions (i.e., highly hydrophilic polymer compositions or systems) do not require such stabilization. However, these external acids are not secondary emulsifiers (e.g., surfactants), such as those used to form latex polymer emulsions.

The term "zwitterionic" when used in reference to a monomer or polymer side chain means that the monomer or polymer side chain has at least one anionic group and at least one cationic group.

The recitation of numerical ranges by endpoints includes all numbers subsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4,5, etc.).

A variety of pigment particles can be used in the disclosed dispersions, methods, and coating compositions. The particles provide light scattering sites in the disclosed dry film coating compositions and impart hiding or opacity to the dry film. The light scattering ability of a pigment is described by its refractive index. Thus, in one aspect, the pigment particles described herein have a wide range of refractive indices, from about 1.2 to about 2.7. Without being limited by theory, the refractive index of the extender pigment will generally be less than about 1.8, while the refractive index of the opacifying pigment will be greater than about 1.8.

Exemplary pigment particles include opacifying pigment particles such as treated or untreated inorganic pigments or mixtures thereof, for example, metal oxides including titanium dioxide, iron oxides of various colors (including black); other oxides include zinc oxide, antimony oxide, zirconium oxide, chromium oxide, and lead oxide; sulfates, sulfides, and mixtures thereof, including barium sulfate, zinc sulfide, and lithopone; and metal flakes (flake) such as aluminum flakes, pearlescent flakes, and the like. Representative pigments can have a variety of forms, in the case of titanium dioxide pigments, such as rutile, anatase, and brookite forms. The pigment particles can have a variety of shapes and sizes, but desirably scatter photons having wavelengths in the spectral region of about 300nm to about 1000nm (e.g., in the infrared region of about 700nm to about 1000nm, in the visible spectral region of about 380nm to about 700nm, or portions or combinations thereof). Suitable shapes for the pigment particles include spherical shapes, such as regular spherical, oblate spherical, prolate spherical, and irregular spherical shapes; cubic shapes such as regular cubes and rhombuses; plate-like shapes including flat, concave and convex; and irregular shapes. Particles having a spherical shape desirably have an average diameter of about 5nm to about 5000nm, for example about 10nm to about 1000nm, about 100nm to about 500nm, about 200nm to about 300nm, or about 220nm to about 280 nm. Particles having a non-spherical shape desirably have a maximum diameter of up to about 1 micron, for example up to about 500nm or up to about 300 nm. The pigment particles may include one or more coatings or surface treatments, e.g. inorganic or organic coatings or surfacesTreatments such as silica, alumina, zirconia, hydrous titania, tin oxide, zinc oxide, cerium oxide, phosphates, nitrates, polyols, amines, amine salts, silicones, siloxanes, and combinations thereof (e.g., silica coatings and alumina coatings). The pigment particles may be uncoated and untreated, but may be sufficiently coated as described herein that the coated pigment particles can be used in an exterior coating while requiring reduced levels of UV absorbers, antioxidants, or other weathering additives as compared to coatings made from pigment particles that are not so coated. Suitable pigments are commercially available from a variety of suppliers including BASF, LANXESS Inorganic Pigment Business Unit of Bayer Corp., Cabot Corp, Ciba Specialty Chemicals, Clariant, Ferro Corporation, Shepherd Color Company, Sun Chemical and Tomatec America, Inc. Titanium dioxide pigment particles are preferred, including those prepared by the chloride process, those prepared by the sulfide process, and those prepared in slurry or dry form. Exemplary titanium dioxide pigment particles include Kronos from Kronos, inc^TM1071. 2020, 2044, 2090, 2101, 2102, 2131, 2160, 2210, 2310, 4102, 4310 and 4311, TIONA from Millennium Specialty Chemicals Inc^TM595 and 596i, TIPURE from E.I. duPont de Nemours and Company^TMTS-6200, R-706, R-741, R-746, R-900, R-902+, R-931, and R-960, TRONOX from Tronox Corporation^TMCR-813, CR-813S, CR-826, CR-826S, CR-828, CR-834, and CR-880, as well as products from other suppliers including Bluestar New Chemical Materials Co., Ltd., Hebei Chuang Hui Chemical Co., Ltd.), Henan Billions Chemical Co., Ltd., Ishihara Sangyo Kaisha, Ltd., Nanjing Henan Hengsman Chemical Co., Ltd., Panzhi Titanium Industrial Co., Panzhi Titanium Co., Ltd., Shanggang Titanium Industrial Co., Ltd., Qigdao Graceco., Ltd., Lzhang Chemical Co., Shang Titanium Industrial Co., Ltd., Shang Titanium product Yo Co., Ltd., Yan Titanium product, Jian product Co., Ltd., Yan Titanium product, Shang Titanium product Co., Shang Titanium product Co., Ltd., Yoghe product, Yan Chemical product Co., Ltd., Yan Ha Chemical product, Shang Titanium product Co., Ltd., Yan Ha product, Shang Titanium product Co., You product, Yan Chemical product, Yoghe Co., Ltdhijiazhuang Kelichuangxin Chemicals co., Ltd.), xu zhou Chemical co.

The disclosed pigment grind dispersions may also contain a variety of extender pigments or filler materials including talc, china clay, barytes, carbonates, silicates, and mixtures thereof. Exemplary such materials include magnesium silicate, calcium carbonate, aluminum silicate, silicon dioxide, and various clays.

The disclosed pigment grind dispersions may, if desired, contain other pigments, including dyes, treated or untreated organic pigments, glass, and mixtures thereof. Exemplary such materials include various carbon blacks, azo pigments, benzimidazolones, carbazoles (e.g., carbazole violet), indanthrones, isoindolinones, isoindolines (isoindolols), perylenes, phthalocyanines, quinacridones, thioindigo reds; organic pigments include plastic pigments such as solid bead pigments (e.g., polystyrene or polyvinyl chloride beads), and microsphere pigments comprising one or more voids and vesiculated polymer particles (e.g., those described in U.S. Pat. nos. 4,427,835, 4,920,160, 4,594,363, 4,469,825, 4,468,498, 4,880,842, 4,985,064, 5,5157,084, 5,041,464, 5,036,109, 5,409,776, and 5,510,422). Other exemplary materials of this type include EXPANCEL^TM551DE20 Acrylonitrile/vinyl chloride foamed particles (from Expancel Inc.), SIL-CEL^TM43 glass microporous Filler (from Silbrico Corporation), FILLITE^TM100 ceramic spherical particles (from Trelleborg Fillite Inc.), SPHERICEL^TMHollow glass spheres (from Potter Industries Inc.), 3M ceramic microspheres including G-200, G-400, G-600, G-800, W-210, W-410 and W-610 grades (from 3M), 3M hollow microspheres including 3M Performance Additives iM30K (also from 3M), INHANCE^TMUH 1900 polyethylene particles (from Fluoro-Seal Inc.) and BIPHOR aluminum phosphate (from Bunge fertilizates s.a., Brazil).

The pigment is used in an amount sufficient to provide a suitably pigmented, if desired opaque, cured coating composition at the desired coating thickness level, for example to a Pigment Volume Concentration (PVC) of about 0.25 to about 95 volume percent. At a variety of desired PVC values, the pigment particles can improve the opacity or hiding of the formulated coating composition. Preferably, the disclosed coating compositions have a PVC of about 5% to about 85%, and more preferably about 10% to about 60%.

The disclosed pigment grind dispersions can be made by blending together the disclosed pigment particles, polymeric dispersant, carrier, and optional surfactant. Without wishing to be bound by any theory, the milling process may include loosening the pigment particles (e.g., caused by shear or other stresses in the agitated pigment mill dispersion), and the polymeric dispersant may help wet out newly exposed pigment surface areas, electrostatically (or otherwise) stabilize the loosened particles, and prevent or inhibit them from re-agglomerating. Thus, the polymeric dispersant can facilitate more efficient use of the pigment particles and increase the degree to which the particles refract light and make the disclosed coating compositions opaque. The polymeric dispersant may, for example, be a bulk polymer, a solution polymer or a water-dispersible polymer, or an aqueous polymer dispersion, and may, for example, be made by polymerizing a mixture of ethylenically unsaturated monomers, and ethylenically unsaturated zwitterionic monomers, in a suitable carrier, in the presence of an initiator. The polymeric dispersant may, for example, comprise at least about 0.1 wt%, at least about 0.2 wt%, at least about 0.3 wt%, or at least about 0.5 wt%, and up to about 25 wt%, up to about 10 wt%, up to about 5 wt%, or up to about 2 wt% of the opacifying pigment particle weight.

A variety of ethylenically unsaturated zwitterionic monomers can be used to form the disclosed polymeric dispersants. The ethylenically unsaturated zwitterionic monomer may comprise one or more (and preferably, one) ethylenically unsaturated groups, preferably terminal vinyl groups. The ethylenically unsaturated zwitterionic monomer may also comprise one or more (and preferably one) anionic groups and one or more (and preferably one) cationic groups. The anionic groups and the cationic groups provide side chains to the zwitterionic polymer, wherein each side chain comprises an anionic group and a cationic group in the polymeric dispersant; and can be assisted as described aboveAid in wetting and stabilization of the polymeric dispersant. In the presence of water, exemplary anionic groups form anions. Non-limiting examples of anionic groups include neutralized acid or anhydride groups, sulfate groups (e.g., -OSO₃ ^-) Sulfonic acid groups (e.g., -SO)₂O^-) Phosphoric acid groups (e.g., -PO)₄ ^2-) Phosphinic acid groups (e.g., -POO)^-) Phosphonic acid groups (e.g., -PO)₃ ^-) Or carboxylic acid groups (e.g., -COO^-). In the presence of water, exemplary cationic groups form cations. Non-limiting examples of cationic groups include quaternary ammonium groups (e.g., -NH)³⁺、-NH₂R1+ or-NHR 1R²⁺Wherein R1 and R2 are organic groups), quaternary phosphonium groups (e.g., -PR 1R 2R³⁺Wherein R1, R2 and R3 are organic radicals) or tertiary (tertiary) sulfuric acid groups (e.g., -SR1R²⁺Wherein R1 and R2 are organic groups). The addition of water to the amine group containing monomer will not generally convert the amine group to a quaternary ammonium cation, and thus monomers containing only cations and such amine groups will not be considered zwitterionic monomers. Exemplary ethylenically unsaturated zwitterionic monomers include sulfobetaine (meth) acrylate, phosphate betaine (meth) acrylate, and carboxylic betaine (meth) acrylate, including sulfobetaine methacrylate (CAS number 3637-26-1; also known as 3-dimethyl (methacryloyloxyethyl) aminopropane sulfonate, N- (3-sulfopropyl) -N- (methacryloyloxyethyl) -N, N-dimethyl amino betaine), or [2- (methacryloyloxy) ethyl ] ethyl]Dimethyl- (3-sulfopropyl) amino hydroxylate)), 2-methacryloyloxyethyl phosphorylcholine (CAS number 67881-98-5), and monomers having betaine groups such as those described in U.S. patent application publication No. US 2011/0137001 Al (Prat et Al), including commercially available monomers from Raschig

MER SPE、

MER SPP、

MER SPDA and

MER SPV. Mixtures of ethylenically unsaturated zwitterionic monomers can also be utilized. The ethylenically unsaturated zwitterionic monomer can, for example, constitute at least about 0.5 wt.% and up to about 99.5 wt.% of the disclosed polymeric dispersant.

In one embodiment, the disclosed polymeric dispersants may be formed from a variety of monomers, including hydrophobic or hydrophilic monomers. A variety of ethylenically unsaturated hydrophobic monomers can be used to form the disclosed polymeric dispersants. The ethylenically unsaturated hydrophobic monomer may comprise one or more (and preferably, one) ethylenically unsaturated groups, preferably terminal vinyl groups. The ethylenically unsaturated hydrophobic monomers also comprise one or more (and preferably one) hydrophobic groups, which preferably do not comprise hydrophilic groups. The hydrophobic groups provide hydrophobic polymeric side chains in the polymeric dispersant. Exemplary hydrophobic groups include alkyl groups having 3 or more carbon atoms, aryl groups, fatty acid residues, fluorocarbons, and silicone compounds. Exemplary ethylenically unsaturated hydrophobic monomers include n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, isodecyl methacrylate, styrene, substituted styrenes (e.g., vinyltoluene, α -methylstyrene, p-t-butylstyrene, and divinylbenzene), allyl compounds (e.g., diallyl phthalate and 2, 4, 6-triallyl-1, 3, 5-triazine), lauryl methacrylate, stearyl methacrylate, behenyl methacrylate, trimethylcyclohexyl methacrylate, cyclohexyl methacrylate, t-butylcyclohexyl methacrylate, tert-butylcyclohexyl methacrylate, and mixtures thereof, Isobornyl methacrylate, t-butylcyclohexyl methacrylate, phenyl methacrylate, benzyl methacrylate, their acrylate counterparts, and mixtures thereof. The ethylenically unsaturated hydrophobic monomers can, for example, constitute at least about 0.5% and up to about 99.5% by weight of the disclosed polymeric dispersants.

A variety of ethylenically unsaturated hydrophilic monomers can be used to form the disclosed polymeric dispersants. The ethylenically unsaturated hydrophilic monomer may comprise one or more (and preferably, one) ethylenically unsaturated groups, preferably terminal vinyl groups. The ethylenically unsaturated hydrophilic monomers also comprise one or more (and preferably one) hydrophilic groups, such as an acidic group, an amino group or an ethylene oxide group. The hydrophilic group provides a hydrophilic polymer side chain in the polymeric dispersant and may increase the water solubility of the polymeric dispersant or may assist in the wetting and stabilization of the polymeric dispersant as described above. Exemplary acidic hydrophilic groups include carboxyl (e.g., -COOH), sulfonyl (e.g., -S (═ O) OH), and organophosphorus (e.g., -P (═ O) OH2) groups, and salts and esters thereof. Exemplary ethylenically unsaturated acidic monomers include acrylic acid, methacrylic acid, itaconic acid, 2-sulfoethyl (meth) acrylate, sulfopropyl (meth) acrylate, styrene sulfonic acid, vinyl sulfonic acid, and salts and esters thereof. Exemplary esters of unsaturated acidic monomers can be formed by reacting an unsaturated acid with a linear, cyclic or aromatic alcohol or polyol having 1 or more (e.g., 1 to 18) carbon atoms or derivatives thereof, or by reacting an unsaturated alcohol with a linear, cyclic or aromatic carboxylic or polyacid having 1 or more (e.g., 1 to 18) carbon atoms or derivatives thereof. Exemplary salts of unsaturated acidic monomers include alkali metal and ammonium salts. Exemplary amide groups include acrylamide (e.g., -C (═ O) NH2) groups. Exemplary ethylenically unsaturated amide monomers include 2- (meth) acrylamide-2-methylpropanesulfonic acid, methacrylamide, methoxymmethacrylamide, methoxymethyl methacrylamide and n-butoxymethyl methacrylamide. Mixtures of ethylenically unsaturated hydrophilic monomers may also be used. The ethylenically unsaturated hydrophilic monomers can, for example, comprise from about 0% to about 90% by weight of the disclosed polymeric dispersant.

If desired, the polymeric dispersant can be formed using the appropriate amounts of other ethylenically unsaturated monomers (e.g., acrylonitrile, vinyl ethers, and other monomers familiar to those of ordinary skill in the art). The disclosed polymeric dispersants may also be formed using monomers that do not provide polymeric side chains as discussed above, provided that the monomers comprise precursor units that can be modified by post-polymerization to provide polymeric side chains as discussed above. For example, the above-mentioned U.S. patent application publication No. us 2011/0137001 Al describes a post-polymerization betalain that can be used to provide the pendant groups of the polymer to be obtained, which utilizes the above-mentioned zwitterionic monomers. Other post-polymerization reactions for providing the other polymer side chain groups discussed above will be apparent to those of ordinary skill in the art.

The polymeric dispersant may be formed in the presence of one or more optional chain growth polymerization initiators (i.e., catalysts). Exemplary initiators include hydroperoxides, persulfates, peroxy and azo derivatives, and other initiators familiar to those of ordinary skill in the art. Exemplary hydroperoxide initiators include, but are not limited to, cumene hydroperoxide, t-butyl hydroperoxide, hydrogen peroxide, and the like. Exemplary persulfate initiators include, but are not limited to, sodium persulfate, potassium persulfate, ammonium persulfate, and the like. Exemplary peroxy initiators include t-butyl peroxy 2-ethylhexanoate, di-t-butyl peroxide, di-cumyl peroxide, t-amyl peroxide, cumyl hydroperoxide, di-n-propyl peroxydicarbonate, t-amyl peracetate, and the like. Exemplary azo initiators include 2, 2-azobis (2-methyl isobutyronitrile), 2-azobis (2-methylbutyronitrile), 2-azobis (2, 4-dimethyl valeronitrile), 2-azobis (2, 4-dimethyl-4-ethoxyvaleronitrile), and the like.

The polymeric dispersant may be prepared by copolymerizing ethylenically unsaturated zwitterionic and non-zwitterionic monomers using techniques familiar to those of ordinary skill in the art. The amount of each monomer can be adjusted to provide desired properties and other characteristics, with polymeric dispersants at least partially derived from one or more of styrene, acrylates or methacrylates being preferred. The polymeric dispersant is typically formed in (or may be combined with) one or more solvents or carriers. Exemplary solvents or carriers include esters, such as ethyl acetate and butyl acetate; ketones such as methyl ethyl ketone, methyl isobutyl ketone, methyl n-amyl ketone and acetone; alcohols such as methanol, ethanol, isopropanol, and butanol; glycols, such as ethylene glycol and propylene glycol; ethers such as tetrahydrofuran, ethylene glycol monobutyl ether, and propylene glycol methyl ether; and mixed ether acetates such as propylene glycol methyl ether acetate, ethylene glycol monobutyl ether acetate, and the like. In one aspect, when the polymeric dispersant comprises an aqueous polymer dispersion or water-soluble polymer dispersion, the carrier or solvent may be water. In some pigment grind dispersion embodiments (e.g., in some solvent-based embodiments), the polymeric dispersant is a solution polymer having an acid number, for example, greater than about 2, greater than about 5, greater than about 10, or greater than about 20. In other pigment grind dispersion embodiments (e.g., in some water-based embodiments), the polymeric dispersant is water-dispersible (as is or by addition of an appropriate neutralizing agent) and can have an acid number of, for example, 0 or greater than about 20, greater than about 30, greater than about 50, or greater than about 100. The acid number may also be, for example, up to about 700, less than about 500, or less than about 300. Polymeric dispersants can also be made into solution polymers and then used in waterborne coating compositions by: replacing the polymerization solvent with water after completion of the solution polymerization to facilitate subsequent mixing of the polymeric dispersant and pigment particles in the aqueous carrier; or by: the polymer is separated from the polymerization solvent using techniques familiar to those skilled in the art (e.g., precipitating the polymer in a non-solvent and then redissolving the precipitate in an aqueous carrier).

The polymeric dispersant can have a variety of molecular weights. Preferably, the molecular weight is sufficiently low so that the polymer has low viscosity and good pigment wetting characteristics. The polymeric dispersant may have a weight average molecular weight (measured using coacervation permeation chromatography and polystyrene standards) of, for example, greater than about 500, greater than about 2000, greater than about 5000, or greater than about 7000. The weight average molecular weight may also be, for example, less than about 200000, less than about 50000, less than about 20000, less than about 10000, or less than about 8000. Expressed on a weight basis, the pigment grind dispersion may, for example, comprise from about 5% to about 80% by weight pigment, from about 0.01% to about 10% by weight polymeric dispersant, and from about 10% to about 70% by weight carrier. However, these amounts depend on a variety of factors including the type of pigment, density, surface area, and oil absorption value.

Techniques familiar to those of ordinary skill in the art can be used to combine the pigment particles and the polymeric dispersant. Preferably, they are combined in a carrier, which will become the final carrier for the finished coating composition, in a mixture commonly referred to as a "mill grind". If desired, the mill grind may contain grinding media and other components or ingredients that facilitate size reduction and dispersion of the pigment. The mill may optionally contain one or more monomers that will ultimately be used to coat the dispersed pigment particles, or such monomers may be added after the pigment particles have been dispersed in the mill grind.

Once the appropriate pigment particle size and degree of dispersion is achieved, the pigment particles are then at least partially coated with one or more of the disclosed polymer layers. In one aspect, the one or more polymer layers may be chain-growth polymer layers. In another aspect, the one or more polymer layers may be step-growth polymer layers.

In one embodiment, when the polymer layer is a chain-growth polymer, the partial coating may be conveniently carried out by including or adding one or more ethylenically unsaturated monomers (e.g., the monomers discussed above) and a free radical initiator (e.g., the initiators discussed above) and, if desired, additional or other carriers (e.g., the carriers discussed above) to the pigment grind dispersion to form a dispersion of coated pigment. Exemplary ethylenically unsaturated monomers for forming the one or more chain-growth polymer layers include styrene, acrylates and methacrylates, such as, but not limited to, styrene, substituted styrenes (e.g., vinyl toluene, alpha-methyl styrene, p-t-butyl styrene, divinyl benzene, and the like), Methyl Methacrylate (MMA), ethyl methacrylate, 2-hydroxyethyl methacrylate (2-HEMA), methacryloyloxyethyl phosphate, sulfoethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, 2-hydroxypropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, 4-hydroxybutyl methacrylate, 2-ethylhexyl methacrylate, divinyl benzene, and the like), Methyl Methacrylate (MMA), ethyl methacrylate, 2-hydroxyethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, 2-hydroxypropyl methacrylate, n-butyl methacrylate, 4-hydroxybutyl methacrylate, 2-ethylhexyl, Isodecyl methacrylate, lauryl methacrylate, stearyl methacrylate, behenyl methacrylate, Ethylene Glycol Dimethacrylate (EGDMA), triethylene glycol dimethacrylate (TEGDMA), polypropylene glycol dimethacrylate (PPGDMA), dipropylene glycol dimethacrylate, 1, 3-and 1, 4-butylene glycol dimethacrylate (1, 4-butylene glycol dimethacrylate), polyethylene glycol dimethacrylate (PEGDMA), 1, 3-butylene glycol dimethacrylate (1, 3-butylene glycol dimethacrylate), 1, 6-hexanediol dimethacrylate (HDDMA), trimethylolpropane trimethacrylate (TMPTMA), tetramethylolpropane trimethacrylate, acetoacetoxyethyl methacrylate (AAEM), Glycidyl Methacrylate (GMA), Trimethylcyclohexyl methacrylate, cyclohexyl methacrylate, t-butylcyclohexyl methacrylate, isobornyl methacrylate, t-butylcyclohexyl methacrylate, phenyl methacrylate, methacryl benzyl ester, their acrylate counterparts, and mixtures thereof. Additional exemplary ethylenically unsaturated monomers include acrylamides and acrylonitriles such as, for example, methacrylamide, methoxymethylacrylamide, methoxymethylmethacrylamide, n-butoxymethylmethacrylamide, methacrylonitrile, and the like. In some embodiments, desirably, the chain-growth polymer layer is at least partially derived from one or more fatty acid (meth) acrylates, such as up to about 25 weight percent of the one or more fatty acid (meth) acrylates based on the starting ethylenically unsaturated monomers. Preferably, the chain growth polymer layer is a latex polymer (e.g., a single-stage or multi-stage latex polymer).

In one embodiment, when the polymer layer is a step-growth polymer, the partial coating may be conveniently carried out by including or adding one or more highly functional reactive monomers or oligomers capable of forming a polymer by step-growth into the pigment grind dispersion to provide a dispersion of coated pigment. Exemplary polymers formed by step growth as described herein include, but are not limited to, the reaction products of one or more dibasic acids, such as succinic acid, adipic acid, sebacic acid, dimer acids, maleic anhydride, phthalic anhydride, isophthalic acid, terephthalic acid, and the like, and one or more polyhydric alcohols (e.g., diols, triols, tetraols, and the like), such as, but not limited to, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, 1, 2-propanediol, 1, 3-propanediol, 1, 2-butanediol, 1, 3-butanediol, 1, 4-butanediol, 2, 3-butanediol, 2-methyl-1, 2-propanediol, 1, 5-pentanediol, 2-methyl-2, 3-butanediol, 1, 6-hexanediol, 1, 2-hexanediol, 2, 5-hexanediol, 2-methyl-2, 4-pentanediol, 2, 3-dimethyl-2, 3-butanediol, 2-ethyl-hexanediol, 1, 2-octanediol, 1, 2-decanediol, 2, 4-trimethylpentanediol, 2-butyl-2-ethyl-1, 3-propanediol, 2-diethyl-1, 3-propanediol, glycerol, trimethylolpropane, pentaerythritol, and the like. These polymers formed by step growth may be further modified by reaction with one or more aromatic diisocyanates, aliphatic or cycloaliphatic diisocyanates, polyisocyanates derived therefrom, and the like.

In a preferred embodiment, at least one of the polymer layers formed as described herein is a film-forming binder and the at least partially encapsulated pigment particles self-coalesce at room temperature without the presence of another film-forming binder and without a coalescing aid containing an undesirable (objectionable) amount of VOCs.

The layers may be formed using a variety of methods, including those described in U.S. patent No.5,171,772(Hoy et al). The calculated thickness of the one or more polymer layers may be, for example, from about 10nm to about 400nm, and the desired spacing will depend to some extent on the pigment particle size. For example, for titanium dioxide particles having an average particle size of 250nm, it is desirable that the thickness of the coating polymer layer be about 100nm to maintain spacing between the titanium dioxide particles of at least about one-half of the lowest wavelength of visible light (i.e., a minimum of about 200 nm).

The resulting dispersion of coated pigments can be optionally combined with one or more binders or one or more coating adjuvants (e.g., thickeners, rheology modifiers, surfactants, or coalescing agents) to form a finished coating. Exemplary binders are well known to those of ordinary skill in the art and may take a variety of forms, including latex polymers and solution polymers, such as acrylic copolymers, styrene/acrylic copolymers, vinyl acetate/acrylic copolymers, vinyl versatate/acrylic copolymers, ethylene/vinyl acetate copolymers, styrene/butadiene copolymers, alkyds, polyesters, polyester urethanes, drying oil modified polymers such as drying oil modified polyesters and polyurethanes, polyethers, polyamides, epoxy esters, polyureas, polyurethanes, polysiloxanes, silicones, fluorinated copolymers such as vinylidene fluoride, and blends of any of the foregoing polymeric binders. The adhesive may comprise one or more components of a multi-component (e.g., two-component) reaction system, such as, for example, an isocyanate-polyamine, an isocyanate-polyol, an epoxy-polyamine, a carbodiimide-polyacid, an aziridine-polyacid, a melamine-polyol, or a component of a urea-formaldehyde-polyol coating system. The binder may, for example, comprise from about 5% to about 99% by volume of the dry coating volume. The volumetric solids content is defined as the volume fraction of dry ingredients in the supplied coating composition, which may, for example, constitute from about 5% to about 80% by volume of the coating composition. Pigment volume concentration is defined as the volume fraction of pigment in the dry coating, which may, for example, comprise from about 0.1% to about 95% by volume of the base coating. In some embodiments, the pigment volume concentration is desirably from about 0.1% to about 30%, from about 0.5% to about 25%, or from about 1% to about 25% by volume. The glass transition temperature of the polymeric binder may be, for example, from about-130 ℃ to about 350 ℃, preferably from about-20 ℃ to about 150 ℃, more preferably from about-10 ℃ to about 100 ℃. Using BROOKFIELD^TMViscometer and RTV Spindle No.4 operating at 20rpmThe measured viscosity of the coating composition at 25 ℃ may, for example, be about 10 to 100000 cps.

Such thickeners, rheology modifiers, surfactants, and coalescents are well known to those of ordinary skill in the art. Exemplary thickeners or rheology modifiers include precipitation inhibitors, Hydrophobic Ethoxylated Urethane Resin (HEUR) thickeners, hydrophobically modified, alkali soluble or alkali swellable emulsion (HASE) thickeners, cellulosic thickeners, polysaccharide thickeners and mixtures thereof. Exemplary commercially available rheology modifiers include NATROSOL from Ashland^TM250 and AQUAFLOW^TMSeries, ATTAGEL from BASF Corp^TM50 CELLOSIZE from Dow Chemical Co^TMSeries and UCAR POLYPHOBE^TMT-900 and T-901, Bentone from Elementis Specialties^TMAD and BENTONE EW, LATTICE from FMC Biopolymer^TMNTC-61, and all from Rohm&ACRYSOL by Haas^TMRM-6, ACRYSOL RM-8, ACRYSOL RM-12W, and ACRYSOL RM-2020 NPR. When present, the disclosed coating compositions preferably comprise from about 0.1 wt.% to about 10 wt.%, or from about 0.5 wt.% to about 3 wt.% of the thickener or rheology modifier, based on the weight of the final coating composition.

Exemplary surfactants include anionic, amphoteric and nonionic surfactants. Commercially available surfactants or dispersants include TAMOL from Dow Chemical Co^TMSeries of nonyl and octyl phenol ethoxylates from Dow Chemical Co (e.g., TRITON)^TMX-45, TRITON X-100, TRITON X-114, TRITON X-165, TRITON X-305 and TRITON X-405) and nonyl and octyl phenol ethoxylates from other suppliers (e.g., the T-DET N series from Harcross Chemicals), alkylphenol ethoxylate (APE) alternatives from Dow Chemical Co., Elementis Specialties, Inc., and other suppliers, SURFYNOL from Air Products and Chemicals, Inc.)^TMIndividual members of the series (e.g., SURFYNOL 104A, SURFYNOL 104BC, SURFYNOL 104DPM, SURFYNOL 104E, SURFYNOL 104H, SURFYNOL 104PA, SURFYNOL 104PG50, SURFYNOL 104S, SURFYNOL 104C, SURFYNOL,SURFYNOL 2502, SURFYNOL 420, SURFYNOL 440, SURFYNOL 465, SURFYNOL 485W, SURFYNOL 82, SURFYNOL CT-211, SURFYNOL CT-221, SURFYNOL OP-340, SURFYNOL PSA204, SURFYNOL PSA216, SURFYNOL PSA336, SURFYNOL SE and SURFYNOL-F), various fluorocarbon surfactants from 3M, e.i. dupont de Nemours and co. When present, the disclosed coating compositions preferably comprise from about 0.1 wt.% to about 10 wt.% and more preferably from about 1 wt.% to about 3 wt.% surfactant, based on the total composition weight.

The coalescing agent can help to coalesce the coated pigment particles or optional other film-forming polymers into a continuous film. Exemplary coalescents include benzoates such as alkyl benzoates, monobenzoates, and dibenzoates; hexanoic acid esters, e.g. OPTIFILM from Eastman Chemical co^TM400 tris (ethylene glycol) bis (2-ethylhexanoate); dioctyl maleate; propylene glycol oleate, e.g. EDENOL from Cognis^TMEFC-100 having the formula HOCH (CH)₃)CH₂OC(O)(CH₂(CH＝CH(CH₂)₇CH₃) (ii) a UCAR film ffiT, UCAR n-propyl propionate, UCAR n-butyl propionate, and UCAR n-pentyl propionate from DOW Chemical co; and TEXANOL from Eastman Chemical Co^TMAn ester alcohol; materials discussed in U.S. Pat. Nos. 6,762,230B 2, 7,812,079B 2, and 8,110,624B 2 (collectively Brandenburger et Al) and in U.S. Pat. Nos. 8,106,239B 2(Zhou et Al) and 8,394,496B 2(Foster et Al), U.S. published patent application No. US 2009/0149591 Al (Yang et Al); mixtures thereof and the like. Other coalescents that may be added to the aqueous type embodiment include VOCs including glycol ethers, organic esters, aromatics, and ethylene glycol or propylene glycol. When present, the disclosed coating compositions preferably comprise from about 0.05 wt.% to about 10 wt.%, or from about 0.05 wt.% to about 5 wt.% coalescing agent, based on the weight of the final coating composition.

The disclosed coating compositions may comprise a variety of materials familiar to those skilled in the artAnd (3) other adjuvants. Representative adjuvants are described in Koleske et al, Paint and Coatings Industry, 4 months 2003, pages 12 to 86. Exemplary adjuvants and commercial examples thereof include adhesion promoters; an anti-cratering agent; an antioxidant; biocides, fungicides, mildewcides, and preservatives (e.g., BUSAN from Buckman Laboratories, Inc.)^TM1292. NOPCOCIDE from Cognis^TMN-40D from Rohm&Kathon of Haas^TMLX and POLYPHASE from Troy Corporation^TM663. POLYPHASE 678 and POLYPHASE PW-40); a buffering agent; a cure indicator; defoaming agents; a heat stabilizer; a humectant; a leveling agent; light stabilizers (e.g., hindered amine light stabilizers such as TINUVIN from Ciba Specialty Chemicals^TM123-DW and TINUVIN 292 HP); an optical brightener; pearling agents (pearlescent); a plasticizer; a polymeric additive; a reactive diluent; a tackifier; ultraviolet light absorbers (e.g., TINUVIN 234 and TINUVIN 1130 from Ciba Specialty Chemicals); waxes (e.g., AQUACER from Altana)^TM593. HYDROCER FROM SHAmrock Technologies, Inc^TM303 and MICHEM from Michelman, inc^TMEmulsion 32535); wetting agents (e.g., BYK from Altana)^TM346 and BYK 348, PENTEX from Rhodia^TM99 and TROYSOL LAC from Troy corporation^TM) And the like. The type and amount of these and other adjuvants are typically selected empirically.

The dispersions of the coated pigments are preferably conventional dispersions whose vehicle and other ingredients make them suitable for use in solvent-borne and water-borne coating compositions. The dispersion of the coated pigment can be used to form or can be added to a variety of coating compositions including primers, surfacers, topcoats (including monocoats), and basecoats for clear/base coat finishes. These coating compositions may contain crosslinking agents including blocked isocyanates, alkylated melamines, polyisocyanates, epoxies, etc., and may be either solvent borne or waterborne. A variety of vehicles or carriers can be used in either solvent-borne or water-borne embodiments. Exemplary solvents and carriers include those described above. The disclosed coating compositions are preferably low VOC dispersions comprising, based on total liquid composition weight, from 0.01 to less than 5 weight% VOC, more preferably from 0.01 to less than 2.5 weight% VOC, most preferably from 0.01 to less than 0.5 weight% VOC.

The disclosed coatings can be applied to a variety of substrates. Exemplary substrates include cement, cement fiberboard, concrete, metal, plastic, and wood (including monolithic, composite, and plywood wood). Dried or hardened paints and stains can be evaluated using a variety of measurements including adhesion (e.g., as measured using ASTM D3359-07), block resistance (e.g., as measured using ASTM D4946-89, 2003 review), chalking (e.g., as measured using ASTM D4214-07), cracking (e.g., as measured using ASTM D661-93), contrast ratio (CR, as measured above), plate out (e.g., as measured using ASTM D3719-00), discoloration or discoloration (e.g., as measured using ASTM D2244-11), gloss or gloss loss (e.g., as measured using ASTM D523-08), impact resistance (e.g., as measured using ASTM D2794-93, 2010 review), low temperature coalescence (LTC, e.g., as measured using ASTM D3793-06), pendulum hardness (e.g., as measured using ASTM D4366-95), Scrub tests (e.g., as measured using ASTM D2486-06), actual washability (e.g., as measured using ASTM D4828-94), tint strength (TS, e.g., as measured using ASTM D2066-07), water resistance (e.g., as measured using ASTM D870-09), or collected measurement standards (e.g., those described in ASTM D3730-10 and ASTM D5324-10).

The invention is further described in the following examples in which all parts and percentages are by weight unless otherwise indicated.

Abbreviations

BA n-butyl acrylate

MMA methyl methacrylate

MAA methacrylic acid

AA acrylic acid

AAm acrylamide

DMAEMA dimethylaminoethyl methacrylate

BzCl benzyl chloride

SBMA sulfobetaine methacrylate

DMAEMA-BzCl dimethylaminoethyl methacrylate benzyl chloride quaternary amine

APS ammonium persulfate

MEK methyl Ethyl Ketone

NVM non-volatiles by mass (percent solids)

2ME 2-mercaptoethanol

tBHP tert-butyl hydroperoxide (70% aqueous solution)

FF6 BRUGGOLITE^TMFF6 (from Bruggemann Chemical)

Preparatory example 1

Preparation of aqueous dispersions of zwitterionic copolymer dispersants

An aliquot of 173.92g of deionized water and 1.94g of Rhodacal DS-4 was added to a four-necked 2L flask equipped with a condenser, mechanical stirring blade, nitrogen purge adapter and thermocouple and heated to 82 ℃. At this temperature and with stirring under nitrogen, 28.93g of a monomer pre-emulsion comprising 49.61g deionized water, 8.01g Rhodacal DS-4, 72.78g BA, 121.29g SBMA, 36.39g MAA and 1.21g 2ME was added to the reaction flask. After 2 minutes, a pre-mix of 10.0g deionized water and 2.43g APS was added to the flask. The contents of the flask were stirred at 81-82 ℃ for 20 minutes and then the remaining monomer pre-emulsion was added to the reaction vessel at a uniform rate over the course of 62 minutes. After the monomer pre-emulsion feed was complete, the monomer pre-emulsion beaker and feed tube were rinsed with 10.0g of deionized water. Then, the temperature of the contents of the reaction flask was maintained for 18 minutes while stirring. Next, 0.33g of tBHP was added to the reaction flask followed by a pre-mix of 10.0g deionized water and 0.25g FF 6. 17 minutes after the last addition, the batch was allowed to cool. The NVM of the resulting product was determined to be 48.1%.

Preparatory example 2

Zwitterionic monomer sulfobetaine methacrylate (SBMA)

In a 200mL LERLenmeyer flask, 30.01g DMAEMA and 30.03g MEK were combined at room temperature. The resulting solution was cooled in an ice bath for 10 minutes, followed by the addition of 23.27g of 1, 3-propane sultone in one portion. The reaction was cooled in an ice bath for an additional 20 minutes and then allowed to gradually warm to room temperature. The reaction flask was kept open. After 2 hours, the product had precipitated and was then collected by filter paper. The product SBMA was transferred to an aluminum foil boat and dried.

Preparatory example 3

Hydrophobic water-soluble monomer DMAEMA-BzCI

In a 200mL Erlenmeyer flask, 40.03g DMAEMA, 32.27g BzCl and 40.07g MEK were combined in one portion. The resulting mixture was stirred and heated to about 40-50 ℃ for 2 hours, then left at room temperature overnight. The precipitated product DMAEMA-BzCl was collected on a filter and dried.

Preparatory example 4

Preparation of zwitterionic copolymer dispersant in Water

A portion of 100.45g of deionized water was charged to a four-necked 1L kettle equipped with a condenser, mechanical stirring blade, nitrogen purge adapter, and 2-hole rubber septum. The kettle was purged with nitrogen at 91 ℃ for 30 minutes. At this temperature and with mechanical stirring, a monomer solution made of 6.01g DMAEMA-BzCl, 10.00g SBMA, 3.03g MAA, 0.10g 2ME, 0.20g APS and 50.04g deionized water was added over 31 minutes. A chaser solution made of 0.15g APS and 9.89g deionized water was added over 11 minutes. The reaction mixture was kept at 90 ℃ for another 100 minutes to remove excess initiator. The NVM was determined to be 11.30%.

Example 1

Preparation of titanium dioxide dispersions

A titanium dioxide dispersion was prepared as follows: to the stirred aqueous solution was gradually added over 5 minutes 500.0g of TI-PURE^TMR706 titanium dioxide, the aqueous solution containing 21.8g of the zwitterionic copolymer dispersant aqueous dispersion of preparative example 1 diluted with 125.3g of deionized water. The mixture was stirred at high speed for an additional 30 minutes,it was then diluted to 73% NVM with 51.5g of deionized water to produce a titanium dioxide slurry containing 71.57 wt% titanium dioxide and 1.43 wt% copolymer dispersant.

Example 2

Preparation of titanium dioxide dispersions

A titanium dioxide mill dispersion was prepared as follows: 750.30g of TI-PURE were gradually added to the stirred aqueous solution over a period of 5 minutes^TMR706 titanium dioxide, the aqueous solution containing 109.49g of the polymer dispersant solution of preparative example 4 diluted with 191.55g of deionized water. The mixture was stirred at high speed for an additional 60 minutes to produce a titanium dioxide slurry containing 71.4 wt% titanium dioxide and 1.14 wt% polymeric dispersant.

Example 3

Formation of coated titanium dioxide latex

470.53g of the titanium dioxide slurry prepared in example 1 were transferred to a 2L tank and treated with 189.77g deionized water and 25.65g of RHODA CAL^TMAnd (4) diluting with a DS-4 surfactant. The kettle was heated to 50 ℃ and then 0.18g of tBHP and 0.15g of a 7% solution of sodium edetate were added. Next, a first monomer emulsion containing 11.74g deionized water, 37.69g BMA, 25.96g MMA, 1.36g MAA, 0.90g tBHP, and 12.83g Rhodacal DS-4 surfactant was added over 20 minutes and the concurrent reducing agent mixture was added over 120 minutes. The reducing agent mixture contained 2.49g of FF6 reducing agent in 81.25g of deionized water. The first monomer emulsion was rinsed with 10.0g of deionized water, followed by the addition of a second monomer emulsion comprising 150.77g BA, 106.53g MMA, 2.71g MAA, 49.07g Rhodacal DS-4, 51.46g deionized water, and 3.61g tBHP. The second monomer feed was added over 84 minutes and rinsed with 15.0g of deionized water. The pH of the product was adjusted to about 8.2 by addition of aqueous ammonia hydroxide solution. The reaction product was a coated titanium dioxide latex containing 55.7% NVM with little coagulum or reactor fouling.

Example 4

Formation of coated titanium dioxide latex

939.55g of the titanium dioxide slurry prepared in example 2 were transferred to a 3L kettle and charged with 382g of deionized water and 51.29g of sulfuric acid fromRHODACAL of Solvay^TMAnd (4) diluting with a DS-4 surfactant. The kettle was heated to 50 ℃ followed by 200g of the first monomer emulsion containing 45.65g of deionized water, followed by the addition of a monomer mixture containing 58%/40%/2% BA/MMA/MAA and 25.65g of RHODACAL DS-4 surfactant over 20 minutes and the concurrent redox initiator mixture over 126 minutes. Following the first monomer emulsion and redox initiator feeds, 750g of a second monomer emulsion containing 58%/41%/l 1% BA/MMA/MAA feed was added over 70 minutes. The volume ratio of the first monomer emulsion to the second monomer emulsion was 20: 8, and the redox initiator feed comprised 1.0 wt.% tBHP and 0.76 wt.% FF6, based on the total weight of monomers. The pH of the product was adjusted to about 9 by adding aqueous ammonia hydroxide solution. The reaction product was a coated titanium dioxide latex containing 55.5% NVM and having a monomodal particle size distribution with an average particle size of 470 nm.

Having thus described the preferred embodiments of the present invention, those skilled in the art will readily appreciate that: the teachings herein may be applied to other embodiments within the scope of the claims appended hereto. The complete disclosures of all patents, patent documents, and publications are incorporated by reference herein, as if individually incorporated.

Claims

1. A polymer-encapsulated pigment dispersion comprising a mixture of:

a) a carrier;

b) pigment particles, said particles being at least partially coated with at least one polymer layer, said polymer layer having a calculated thickness of from 10nm to 400 nm; and

c) a polymeric dispersant having:

i) a polymer backbone; and

ii) zwitterionic polymer side chains comprising anionic and cationic groups.

2. A method of making the polymer-encapsulated pigment dispersion of claim 1, the method comprising:

a) forming a dispersion of a carrier, pigment particles, and a polymeric dispersant, wherein the polymeric dispersant has:

i) a polymer backbone; and

ii) zwitterionic polymer side chains comprising anionic and cationic groups;

b) allowing the dispersion to comprise or add to the dispersion a free radical initiator and one or more ethylenically unsaturated monomers; and

c) polymerizing the ethylenically unsaturated monomers so that the pigment particles are at least partially coated with at least one polymer layer having a calculated thickness of from 10nm to 400 nm.

3. A coating composition comprising a dispersion of:

a) the polymer-coated pigment dispersion of claim 1;

b) one or two of the following:

i) a film-forming binder comprising a polymer different from the polymeric dispersant backbone polymer; or

ii) one or more of a thickener, rheology modifier, surfactant or coalescent.

4. The dispersion of claim 1, the method of claim 2, or the coating composition of claim 3, wherein the pigment particles are opacifying pigment particles having a refractive index of at least 1.8.

5. The dispersion of claim 1, the method of claim 2, or the coating composition of claim 3, wherein the pigment particles are extender pigment particles having a refractive index of less than 1.8.

6. The dispersion of claim 1, the method of claim 2, or the coating composition of claim 3, wherein the carrier comprises water.

7. The dispersion of claim 1, the method of claim 2, or the coating composition of claim 3, wherein the pigment particles comprise titanium dioxide particles.

8. The dispersion of claim 1, the method of claim 2, or the coating composition of claim 3, wherein the polymer backbone for encapsulation comprises a vinyl chain growth polymer.

9. The dispersion, method, or coating composition of claim 8, wherein the at least partially coated pigment particles self-coalesce at room temperature without the presence of a film-forming binder comprising a polymer different from the vinyl chain growth polymer.

10. The dispersion of claim 1 or the coating composition of claim 3, wherein the polymer backbone for encapsulation comprises a step-growth polymer.

11. The dispersion of claim 1, the method of claim 2, or the coating composition of claim 3, wherein the anionic groups comprise sulfonic acid groups.

12. The dispersion of claim 1, the method of claim 2, or the coating composition of claim 3, wherein the cationic group comprises a quaternary ammonium group.

13. The dispersion of claim 1, the method of claim 2, or the coating composition of claim 3, wherein the polymeric dispersant is formed from a hydrophobic monomer.

14. The dispersion of claim 1, the method of claim 2, or the coating composition of claim 3, wherein the polymeric dispersant is formed from a hydrophilic monomer.