Aqueous dispersion of polymer particles and organic opacifying pigment particles

Abstract

The present invention relates to a composition comprising coprising a) water; b) film-forming polymer particles having a z-average particles size in the range of from 50 nm to 300 nm; c) organic opacifying pigment particles having a z-average particle size in the range of from 200 nm to 650 nm; and d) an extender; wherein the weight-to-weight ratio of the film forming polymer particles to the organic opacifying pigment particles is in the range of from 7:3 to 1:1; and wherein the composition comprises not more than 4 weight percent TiO2, based on the weight of the composition. The composition of the present invention is useful for road markings.

Description

[0001] Aqueous Dispersion of Polymer Particles and Organic Opacifying Pigment Particles Background of the Invention The present invention relates to an aqueous dispersion of polymer particles and organic opacifying pigment particles (opaque polymers), more particularly, dispersions suitable for road marking formulations such as traffic paints. Titanium oxide (TiO2) is the mostly commonly used opacifying pigment in the paint industry due to its very high refractive index. Nevertheless, TiO2, is the most expensive component in paint; moreover, its manufacture requires high energy consumption and poses potential environmental hazardous risks. As regulatory agencies around the world are promoting legislation designed to place warning labels on products containing TiO2, an additional urgency for greatly reducing the concentration of TiO2in paints. Paints suitable for road markings typically require TiO2 at a concentration between 5 and 10 weight percent. It is desirable to reduce or even eliminate TiO2 in road marking formulations, yet maintain key performance properties such as contrast ratio and film-formation. Summary of the Invention The present invention addresses a need in the art by providing a composition comprising a) water; b) film-forming polymer particles having a z-average particles size in the range of from 50 nm to 300 nm; c) organic opacifying pigment particles having a z-average particle size in the range of from 200 nm to 650 nm; and d) an extender; wherein the organic opacifying pigment particles have i) a water-occluded core comprising from 20 to 60 weight percent structural units of a salt of a carboxylic acid monomer and from 40 to 80 weight percent structural units of a nonionic monoethylenically unsaturated monomer; and ii) a polymeric shell having a Tg in the range of from 60 ºC and 120 ºC; wherein the weight-to-weight ratio of the film forming polymer particles to the organic opacifying pigment particles is in the range of from 7:3 to 1:1; and wherein, based on the weight of the composition, the concentration of the sum of the film forming polymer particles and the opacifying pigment particles is in the range of from 10 to 30 weight percent; the concentration of the extender is in the range of from 45 to 65 percent; and wherein the composition comprises not more than 4 weight percent TiO2, based on the weight of the composition. The composition of the present invention is useful as road marking formulation with reduced levels of TiO2. Detailed Description of the Invention The present invention is a composition comprising a) water; b) film-forming polymer particles having a z-average particles size in the range of from 50 nm to 300 nm; c) organic opacifying pigment particles having a z-average particle size in the range of from 200 nm to 650 nm; and d) an extender; wherein the organic opacifying pigment particles have i) a water-occluded core comprising from 20 to 60 weight percent structural units of a salt of a carboxylic acid monomer and from 40 to 80 weight percent structural units of a nonionic monoethylenically unsaturated monomer; and ii) a polymeric shell having a Tgin the range of from 60 ºC and 120 ºC; wherein the weight-to-weight ratio of the film forming polymer particles to the organic opacifying pigment particles is in the range of from 7:3 to 1:1; and wherein, based on the weight of the composition, the concentration of the sum of the film forming polymer particles and the opacifying pigment particles is in the range of from 10 to 30 weight percent; the concentration of the extender is in the range of from 45 to 65 percent; and wherein the composition comprises not more than 4 weight percent TiO2, based on the weight of the composition. The film-forming polymer particles have a z-average particle size in the range of 50 nm or from 75 nm to 300 nm or to 250 nm, where z-average particle size is measured by dynamic light scattering. The glass transition temperature (Tg) of the film-forming polymer particles, as calculated by the Fox equation, is preferably in the range of from -20 °C, more preferably from -10 °C, and most preferably from 0 °C, to preferably 60 °C, more preferably to 40 °C, and most preferably to 25 °C. Examples of suitable film-forming polymer particles are acrylic, styrene-acrylic, vinyl ester, and vinyl ester-ethylene polymer particles. Preferred film-forming polymer particles are acrylic- based polymer particles, especially polymer particles comprising at least 30 weight percent, preferably at least 50 weight percent, and more preferably at least 70 percent, based on the weight of the polymer particles, structural units of one or more acrylate or methacrylate monomers such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, ethyl acrylate, n-butyl acrylate, 2-propylheptyl acrylate, 2-octyl acrylate, and 2-ethylhexyl acrylate. As used herein, the term “structural units” refers to the remnant of the recited monomer after polymerization. For example, a structural unit of methyl methacrylate is as illustrated: where the dotted lines represent the points of attachment of the structural unit to the polymer backbone. The film-forming polymer particles advantageously comprise from about 0.5 to 8 weight percent, based on the weight of the film-forming polymer particles, structural units of an ethylenically unsaturated acid monomer or a salt thereof, such as methacrylic acid, acrylic acid, itaconic acid, and 2-phosphoethyl methacrylate, and salts thereof. The term “film-forming” refers to the formation, by visual inspection, of a continuous film of a latex (optionally in the presence of a coalescent) applied to a Leneta chart at ambient temperature. The film-forming polymer particles may also comprise structural units of other non-acrylate or methacrylate monomers such as styrene and vinyl acetate, as well as structural units of one or more ancillary monomers such as ureido methacrylate, acetoacetoxyethyl methacrylate (AAEM), diacetone acrylamide (DAAM), 2-(dimethylamino)ethyl methacrylate (DMAEMA), typically at a concentration not greater than 15 weight percent, based on the weight of the polymer particles. The molecular weight of the particles may be controlled with the addition of a chain transfer agent such as n-dodecylmercaptan (n-DDM). Preferably, at least 80 weight percent, and more preferably at least 90 weight percent of the film- forming polymer particles comprise structural units of methyl methacrylate (MMA), n-butyl acrylate (BA), and methacrylic acid (MAA) or acrylic acid (AA). The organic opacifying pigment particles (also known as opaque polymers) have a z-average particle size as measured by dynamic light scattering in the range of from 200 nm or from 300 nm or from 350 nm, to 650 or to 550 nm or to 450 nm. These pigment particles comprise a water-occluded core and a shell. The Tg of the shell, as calculated by the Fox equation, is preferably in the range of from 80 °C, more preferably from 90 °C, and most preferably from 95 °C, to preferably 115 °C, and most preferably to 110 °C. The water-occluded core comprises from 20, preferably from 25, more preferably from 30, and most preferably from 32 weight percent, to 60, preferably to 50, more preferably to 40, and most preferably 36 weight percent structural units of a salt of a carboxylic acid monomer based on the weight of structural units of monomers in the core. Examples of suitable carboxylic acid monomers include acrylic acid, methacrylic acid, itaconic acid, and maleic acid. The water-occluded core further comprises from 40, preferably from 50, more preferably from 55, more preferably from 60, and most preferably from 64 weight percent to 80, preferably to 75, more preferably to 70, and most preferably to 68 weight percent structural units of a nonionic monoethylenically unsaturated monomer based on the weight of structural units of monomers in the core. Examples of nonionic monoethylenically unsaturated monomers include acrylates and methacrylates such as methyl acrylate, ethyl acrylate, n-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, 2-octyl acrylate, methyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, isobutyl methacrylate, isobornyl methacrylate, lauryl methacrylate, and cyclohexyl methacrylate; and one or more monoethylenically unsaturated aromatic compounds such as styrene, α-methylstyrene, and 4-t-butylstyrene. A preferred nonionic monoethylenically unsaturated monomer is methyl methacrylate. The shell preferably comprises structural units of methyl methacrylate, styrene, α-methylstyrene, isobornyl methacrylate, lauryl methacrylate, or cyclohexyl methacrylate. In one embodiment, the shell comprises at least 80, more preferably at least 90, and most preferably at least 95 weight percent structural units of styrene. In another embodiment, the shell comprises from 89 to 93 weight percent structural units of styrene and from 7 to 11 weight percent structural units of any or all of methyl methacrylate (4 to 5 weight percent), cyclohexyl methacrylate (0.9 to 2 weight percent), methacrylic acid (2 to 3 weight percent), and the multiethylenically unsaturated monomer, allyl methacrylate (ALMA, 0.1 to 0.5 weight percent). The polymeric shells may also further comprise structural units of other multiethylenically unsaturated monomers such as divinyl benzene (DVB), trimethylolpropane trimethacrylate (TMPTMA), or trimethylolpropane triacrylate (TMPTA). An example of a commercially available opaque polymer is ROPAQUE™ ULTRA Opaque Polymers. (A trademark of The Dow Chemical Company or its Affiliates.) The weight-to-weight ratio of the film-forming polymer particles to the organic opacifying pigment particles is in the range of from 70:30, preferably from 2.2:1, more preferably from 2.1:1, and most preferably from 2.0:1 to 1:1. Extenders are filler materials used to control the gloss, texture, pigment volume concentration, and viscosity of the composition. The term “an extender” refers to one or more extenders. Examples of suitable extenders include silicates and aluminosilicates such as talc, clay, and mica; calcium carbonate; nepheline syenite; feldspar; wollastonite; kaolinite; dicalcium phosphate; and diatomaceous earth. The concentration of the extender is in the range of from 45, and preferably from 50 weight percent, to 65, and preferably to 60 weight percent, based on the weight of the composition. A preferred extender is calcium carbonate. The composition advantageously further comprises a polyamine and a volatile base. The polyamine is present at a concentration preferably in the range of from 0.02 or from 0.05 weight percent, to 2 or to 1 weight percent dry polyamines, based on the weight of the composition. Examples of suitable polyamines are homopolymers and copolymers comprising structural units of the following monomers and hydrolysis products thereof: oxazolidinoethyl methacrylate; oxazolidinoethyl acrylate; 3-(γ-methacryloxypropyl)-tetrahydro-1,3- oxazine; 3-(β-methacryloxyethyl)-2,2-pentamethylene oxazolidine; 3-(β-methacryloxyethyl-2-methyl-2- propyloxazolidine; N-2-(2-acryloxyethoxy)ethyl oxazolidine; N-2-(2-methacryloxyethoxy)ethyl oxazolidine; N-2-(2-methacryloxyethoxy)ethyl-5-methyl oxazolidine; N-2-(2- acryloxyethoxy)ethyl-5-methyl oxazolidine; 3-2-(2-methacryloxyethoxy) ethyl)-2,2-penta- methylene-oxazolidine; 3-2-(2-methacryloxyethoxy) ethyl)-2,2-dimethyl oxazolidine; and 3-2-(methacryloxyethoxy)ethyl)-2-phenyl-oxazolidine. Homopolymers and copolymers comprising structural units of dimethylaminoethyl methacrylate (DMAEMA) and dimethylaminoethyl acrylate are also suitable polyamines. Preferred polyamines are aqueous dispersions of homopolymers of oxazolidinoethyl methacrylate (poly(OXEMA)) and copolymers of DMAEMA as described, for example, in US 5,861,188. Examples of suitable volatile bases are ammonia and C1-C6-alkylamines and C1-C6-alkanol amines including n-butylamine, n-propylamine, ethylamine, ethylenediamine, trimethylamine, triethylamine, diethylamine, diethanolamine, ethanolamine, 2-methylaminoethanol, 2-dimethylaminoethanol, morpholine, and N-methylmorpholine. Preferably, the volatile base is ammonia, or an admixture of ammonia and nonvolatile bases. The composition preferably comprises one or more rheology modifiers such as a hydrophobically modified ethylene oxide urethane polymer (HEUR), a hydroxyethyl cellulose (HEC), an alkali-soluble or alkali-swellable emulsion (ASE), or a hydrophobically modified alkali-soluble or alkali-swellable emulsion. Also, the composition may further comprise additional components including dispersants, surfactants, solvents, coalescents, and defoamers. The composition optionally comprises TiO2 up to 4 weight percent, based on the weight of the composition; in another aspect, the composition comprises from 0.1 or from 0.5 or from 1 or from 2 weight percent, to 4 weight percent TiO2, based on the weight of the composition. It has been discovered that contrast ratios of at least 0.87 can be achieved for 5-mil film thick road marking formulation coatings that contain no TiO2, and that contrast ratios of at least 0.95 can be achieved using TiO2concentrations at about 3 weight percent, based on the weight of the road marking formulation. Examples Measurement of Contrast Ratios The aqueous coating compositions were drawn down on opacity charts (Form 3B, The Leneta Company, Inc.) using a 0.20-mm (8-mil) opening film caster to apply a 0.12-mm (5-mil) wet film thickness. The charts were air dried in a horizontal position overnight in a room kept at 23 °C + / - 2.0 °C and 50% + / - 10% relative humidity. A spectro2go spectrophotometer (BYK- Gardner GmbH) with a d:8° geometry was used to measure the Y component of light reflectance of the XYZ color scale. The Y component reflectance was measured over the white and the black portions of the coated opacity charts. The contrast ratio was determined by dividing the Y reflectance over the black section by the Y reflectance over the white section. Two paint formulations (Comparative Paint 1 and Example Paint 1) were prepared by mixing the following ingredients in a mixing vessel in the order listed in Table 1. TAMOL is a trademark of The Dow Chemical Company or its Affiliates. The acrylic latex had a solids content 50.4 wt%, a z-average particle size of ~200 nm, and a calculated Tgof 25 °C.

[0002] Table 1 – Paint Formulations and Contrast Ratios of Coatings Material Comp.1 (g) Ex.1 (g) Acrylic polymer: 41.2 BA / 57.5 MMA / 1.3 MAA / / 1.25 nDDM 206.94 129.33 6 9 2 3 7 0 3 4 4 1 3 :1 7

[0003] Comparative Paint 2 and Example Paints 2-4 were prepared by blending Comparative Paint 1 and Example Paint 1 for 5 min. The relative amounts of Comparative Paint 1 and Example Paint 1, as well as the resulting ratios of acrylic polymer to opaque polymer shown in Table 2. The contrast ratio was once again measured at a film thickness of 5 mil (0.12 mm). Table 2 – Contrast Ratios for Coatings Different Ratios of Latex and Opaque Polymers Comp.1 (g) Ex.1 (g) Comp.1:Ex.1 Example No. Contrast Ratio 1275 225 755:245 Comp 2 082 Coatings f ios (> 0.89) even at 0% concentrations of TiO2. By comparison, a paint formulation containing 0 wt.% opaque polymer and 7 wt.% TiO2 had a contrast ratio of 0.96, which was the same as the contrast ratio measured for the Example 2 paint containing 3 wt% TiO2.

Claims

Claims:

1. A composition comprising a) water; b) film-forming polymer particles having a z-average particles size in the range of from 50 nm to 300 nm; c) organic opacifying pigment particles having a z-average particle size in the range of from 200 nm to 650 nm; and d) an extender; wherein the organic opacifying pigment particles have i) a water-occluded core comprising from 20 to 60 weight percent structural units of a salt of a carboxylic acid monomer and from 40 to 80 weight percent structural units of a nonionic monoethylenically unsaturated monomer; and ii) a polymeric shell having a Tgin the range of from 60 ºC and 120 ºC; wherein the weight-to-weight ratio of the film forming polymer particles to the organic opacifying pigment particles is in the range of from 7:3 to 1:1; and wherein, based on the weight of the composition, the concentration of the sum of the film forming polymer particles and the opacifying pigment particles is in the range of from 10 to 30 weight percent; the concentration of the extender is in the range of from 45 to 65 percent; and wherein the composition comprises not more than 4 weight percent TiO2, based on the weight of the composition.

2. The composition of Claim 2 wherein the film-forming polymer particles have a calculated Tg in the range of from -20 °C to 60 °C; and comprise at least 50 weight percent, based on the weight of the film-forming polymer particles, of structural units of one or more acrylate or methacrylate monomers.

3. The composition of Claim 2 wherein film-forming polymer particles have a calculated Tg in the range of from -10 °C to 40 °C; wherein at least 70 weight percent of the film-forming polymer particles comprise structural units of one or more acrylate or methacrylate monomers selected from the group consisting of methyl methacrylate, ethyl methacrylate, butyl methacrylate, ethyl acrylate, n-butyl acrylate, 2-propylheptyl acrylate, 2-octyl acrylate, and 2-ethylhexyl acrylate; and wherein the film-forming polymer particles further comprise from 0.5 to 8 weight percent, based on the weight of the film-forming polymer particles, structural units of an ethylenically unsaturated acid monomer or a salt thereof selected from the group consisting of methacrylic acid, acrylic acid, itaconic acid, and 2-phosphoethyl methacrylate, and salts thereof.

4. The composition of Claim 3 wherein the water-occluded core of the organic opacifying pigment particles comprise from 30 to 50 weight percent structural units of a salt of a carboxylic acid monomer selected from the group consisting of acrylic acid, methacrylic acid, and itaconic acid; and from 50 to 70 weight percent structural units of a nonionic monoethylenically unsaturated monomer selected from the group consisting of methyl acrylate, ethyl acrylate, n-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, 2-octyl acrylate, methyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, isobutyl methacrylate, isobornyl methacrylate, lauryl methacrylate, and cyclohexyl methacrylate; wherein the polymeric shell of the organic opacifying pigment particles has a calculated Tg in the range of from 90 ºC and 110 ºC and comprises structural units of one or more monomers selected from the groups consisting of methyl methacrylate, styrene, α-methylstyrene, isobornyl methacrylate, lauryl methacrylate, or cyclohexyl methacrylate.

5. The composition of Claim 4 wherein the water-occluded core of the organic opacifying pigment particles comprise from 32 to 36 weight percent structural units of a salt of methacrylic acid, and from 64 to 68 weight percent structural units of methyl methacrylate; at least 90 weight percent of the shell comprises structural units of styrene; at least 80 weight percent of the film-forming polymer particles comprise structural units of methyl methacrylate, n-butyl acrylate, and methacrylic acid or acrylic acid; wherein the weight-to-weight ratio of the film-forming polymer particles to the opacifying pigment particles is in the range of from 2.2:1 to 1:

1.

6. The composition of Claim 4 wherein the extender is one or more extenders selected from the group consisting of talc, clay, and mica; carbonate; nepheline syenite; feldspar; wollastonite; kaolinite; dicalcium phosphate; and diatomaceous earth.

7. The composition of Claim 5 wherein the extender is calcium carbonate at a concentration in the range of from 50 to 60 weight percent, based on the weight of the composition.

8. The composition of any of Claims 1 to 7 which further comprises a polyamine at a concentration in the range of from 0.02 to 2 weight percent, based on the weight of the composition, wherein the polyfunctional amine is a polymer or copolymer comprising structural units of one or more monomers selected from the group consisting of oxazolidinoethyl methacrylate; oxazolidinoethyl acrylate; 3-(γ-methacryloxypropyl)-tetrahydro-1,3- oxazine; 3-(β-methacryloxyethyl)-2,2-pentamethylene oxazolidine; 3-(β-methacryloxyethyl-2-methyl-2-propyloxazolidine; N-2-(2-acryloxyethoxy)ethyl oxazolidine; N-2-(2-methacryloxyethoxy)ethyl oxazolidine; N-2-(2-methacryloxyethoxy)ethyl-5-methyl oxazolidine; N-2-(2- acryloxyethoxy)ethyl-5-methyl oxazolidine; 3-2-(2-methacryloxyethoxy) ethyl)-2,2-penta- methylene-oxazolidine; 3-2-(2-methacryloxyethoxy) ethyl)-2,2-dimethyl oxazolidine; and 3-2-(methacryloxyethoxy)ethyl)-2-phenyl-oxazolidine; and wherein the composition further comprises a volatile base selected from the group consisting of ammonia, C1-C6-alkylamines and C1-C6-alkanol amines.

9. The composition of Claim 8 wherein the polyamine is a homopolymer oxazolidinoethyl methacrylate or a copolymer comprising structural units of dimethylaminoethyl methacrylate.

10. The composition of Claim 8 which further comprises a rheology modifier, a dispersant, and a surfactant; wherein the polyamine is a homopolymer oxazolidinoethyl methacrylate or a copolymer comprising structural units of dimethylaminoethyl methacrylate.

11. The composition of Claim 10 which further comprises a coalescent and a defoamer.

12. The composition of Claim 10 which comprises 0 weight percent TiO2.

13. The composition of Claim 10 which comprises from 0.1 to 4 weight percent TiO2, based on the weight of the composition.

14. The composition of Claim 10 which comprises from 2 to 4 weight percent TiO2, based on the weight of the composition.

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