Background of the Invention

The present invention relates to a composition comprising an aqueous dispersion of polymer-encapsulated TiO2 composite particles and an organic matting agent, as well as a method for making the composition.

Paints sold in retail outlets are typically produced in bulk by a batch process that includes grinding pigment and extender particles to form a solid dispersion, then combining this dispersion in a so-called letdown stage with binder, thickeners, and other additives. The batch process produces paint bases of different concentrations of pigment and extender that are transported to the retail outlet where colorant is added to the paint to meet the demands of the consumer. This base system model of paint production requires substantial inventory and is further disadvantaged by using a fixed amount of TiCh where the flexibility to adjust TiCh levels would be desirable. For example, where a colorant requires lower amounts TiCh than present in the untinted paint to achieve the desired tint, excess colorant would need to be added to balance the excess TiCh. The unnecessary costs associated with the use of excess TiCh and colorant as well as the additional time required to prepare the final paint are examples of inefficiencies in the base system model that need to be addressed.

An alternative to the base system model is a point-of-sale model where cans of paint are made by concurrent dispensing of binder, pigment, and extender components from separate holding tanks into a paint container, then mixing the contents of the container. (See US 2003/0110101, para [0027] and [0028].) Although this point-of-sale model is an improvement on the base system model, it is still a labor and cost intensive batch process that relies on both the speed of dispensing the materials into a container and the time it takes to mix the materials in the container and to stabilize the viscosity of the final paint.

Accordingly, it would be advantageous to make cans of paint by a more efficient and versatile process. Summary of the Invention

The present invention addresses a need in the art by providing a composition comprising polymer-encapsulated TiO composite particles, an organic matting agent, and a rheology modifier.

Brief Description of Drawings

FIG. 1 is a schematic of an apparatus used to make a paint by the process of the present invention.

Detailed Description of the Invention

The present invention is a composition comprising polymer-encapsulated TiO composite particles, an organic matting agent, and a rheology modifier.

Fig. 1 illustrates an example of a preferred apparatus for carrying out the process of the present invention. In a first example of a process for preparing the composition of the present invention, an aqueous dispersion of polymer-encapsulated TiO composite particles and rheology modifier stored in pre-paint storage tank (1) and an aqueous dispersion of organic matting agent and rheology modifier stored in pre-paint storage tank (2) are fed through valves (13) and (12) respectively into mixing chamber (6) fitted with mixing baffles (7) and mixed to form an aqueous dispersion of the polymer-encapsulated TiO composite particles and the organic matting agent. Mixing chamber (6) is preferably an in-line continuous flow mixer, more preferably an in-line static mixer. The pre-paints in storage tanks (1) and (2) are each blended with a suitable rheology modifier. For example, pre-paint storage tank (1) advantageously contains an ICI builder or an alkali swellable emulsion (ASE), and pre-paint storage tank (2) advantageously contains an ASE), examples of which include a polyacrylic acid, or a hydrophobically modified alkali swellable emulsion (HASE) or a hydroxyethyl cellulose (HEC). A commercial example of an ICI builder is ACRYSOL™ RM-2020 NPR HEUR Rheology Modifier (a Trademark of The Dow Chemical Company or Its Affiliates). In a second example of a process for preparing a composition of the present invention, the aqueous dispersion of polymer-encapsulated TiCh composite particles and rheology modifier stored in pre-paint storage tank (1), the aqueous dispersion of the organic matting agent and rheology modifier stored in pre-paint storage tank (2), and an aqueous dispersion of opacifying pigment-binder hybrid particles and rheology modifier stored in pre-paint storage tank (3) are concurrently fed into mixing chamber (6) and mixed to form an aqueous dispersion of the polymer-encapsulated TiCb composite particles, the organic matting agent, and the opacifying pigment-binder hybrid particles.

Preferably, the opacifying pigment particles are TiCb particles. Pre-paint storage tank (3) optionally comprises a water-soluble dispersant such as a polymer comprising structural units of a sulfonic acid monomer or a salt thereof and less than 30 weight percent structural units of acrylic acid or methacrylic acid, based on the weight of the dispersant. More particularly, the water-soluble dispersant comprises from 50% to 80% by weight structural units of a sulfonic acid monomer or a salt thereof, wherein the sulfonic acid monomer is 2-acrylamido-2- methylpropane sulfonic acid or a salt thereof, vinyl sulfonic acid or a salt thereof, 2-sulfoethyl acrylate, 2-sulfoethyl methacrylate, 3-sulfopropyl acrylate, 3-sulfopropyl methacrylate, sodium styrene sulfonate, or 2-propene-l-sulfonic acid or a salt thereof.

Additional materials such as surfactants, dispersants, defoamers, coalescents, additional thickeners, organic opacifying pigments, block additives, photoinitiators, and solvents may be fed from any or all of pre-paint storage tanks (5) into mixing chamber (6) through any or all of valves (14), (16), and (17). Alternatively, it may be desirable to include one or more of a defoamer, a surfactant, and a coalescent in any of the pre-paints.

Colorants are a special class of additives that require special care. For tinted paints, one or more aqueous solutions or dispersions of colorants from colorant addition system (8) is fed into mixing chamber (6) through valve (19), the final paint is formed and then directed into paint container (9).

The aqueous dispersion of polymer-encapsulated TiCb composite particles can be prepared by methods known in the art, for example, US 7,579,081, US 8,283,404, US 9,234,084, and US 9,371,466. The z-average particle size of the polymer-encapsulated TiCb composite particles, as measured by dynamic light scattering, is typically in the range of from 200 nm to 500 nm. The weight-to-weight ratio of the polymer to the TiO in the polymer-encapsulated TiCh composite particles is generally in the range of from 0.4:1 to 3:1.

As used herein, the term “aqueous dispersion of opacifying pigment-binder hybrid particles” refers to an aqueous dispersion of a) multistage polymer particles comprising 1) 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; 2) a polymeric shell having a T _g in the range of from 60 °C and 120 °C; and 3) a polymeric binder layer superposing the shell, wherein the polymeric binder layer has a T _g of not greater than 35 °C and comprises structural units of at least one monoethylenically unsaturated monomer. Examples of suitable polymeric binder materials include acrylic, styrene- acrylic, vinyl esters such as vinyl acetate and vinyl versatates, and vinyl ester-ethylene polymeric binders. Acrylic binders comprising structural units of methyl methacrylate and structural units of one or more acrylates such as methyl acrylate, ethyl acrylate, n-butyl acrylate, or 2-ethylhexyl acrylate, are especially preferred, as are styrene- acrylic binders.

The z-average particle size of the opacifying pigment-binder hybrid particles, as measured by dynamic light scattering, is typically in the range of from 300 nm, or from 400 nm, or from 450 nm, to 750 nm, or to 700 nm, or to 600 nm, or to 550 nm. The aqueous dispersion of opacifying pigment-binder hybrid particles can be prepared as described in US 7,691,942.

Suitable opacifying pigments include inorganic opacifying pigments having a refractive index of greater than 1.90. TiCb and ZnO are examples of inorganic opacifying pigments, with TiCb being preferred. Other opacifying pigments include organic opacifying pigments such as opaque polymers (other than opacifying pigment-binder hybrid particles), which could be fed into the mixer from a pre-paint to mix specifically with the polymer encapsulated TiO2 composite particles. Although an organic opacifying pigment may be used as a substitute for an inorganic opacifying pigment, it is more desirable to use the organic opacifying pigment as a supplement to augment the efficiency of the inorganic opacifying pigment. The organic opacifying pigment can be added to the mixing chamber from a separate additives tank. ROPAQUE™ ULTRA Opaque Polymers and AQACell HIDE 6299 Opaque Polymers are commercial examples of opaque polymers.

As used herein, the term “organic matting agent” refers to non-film-forming polymeric microspheres having a median weight average particle size (Dso) in the range of from 0.7 pm, or from 1 pm, and or from 2 |im, and or from 4 |im, to 30 |im, or to 20 |im, or to 13 |im, as measured using a Disc Centrifuge Photosedimentometer (DCP). These organic polymeric microspheres preferably have a crosslinked low T _g core, that is, a crosslinked core having a T _g , as calculated by the Fox equation, of not greater than 25 °C, or not greater than 15 °C, or not greater than 10 °C.

The crosslinked core of the organic polymeric microspheres preferably comprises structural units of one or more monoethylenically unsaturated monomers whose homopolymers have a T _g of not greater than 20 °C (low T _g monomers) such as methyl acrylate, ethyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate. Preferably, the crosslinked low T _g core comprises, based on the weight of the core, from 50, or from 70, or from 80, or from 90 weight percent, to 99, or to 97.5 weight percent structural units of a low T _g monoethylenically unsaturated monomer, n- Butyl acrylate, and 2-ethylhexyl acrylate are preferred low T _g monoethylenically unsaturated monomers used to prepare the low T _g core.

The crosslinked core further comprises structural units of a multiethylenically unsaturated monomer, examples of which include allyl methacrylate, allyl acrylate, divinyl benzene, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, butylene glycol (1,3) dimethacrylate, butylene glycol (1,3) diacrylate, ethylene glycol dimethacrylate, and ethylene glycol diacrylate. The concentration of structural units of the multiethylenically unsaturated monomer in the crosslinked microspheres is typically in the range of from 1, or from 2 weight percent, to 9, or to 8, or to 6 weight percent, based on the weight of the core.

The crosslinked polymeric core is preferably clad with high a T _g shell, that is, a shell having a T _g of at least 50 °C, or at least 70 °C, or at least 90 °C. The shell preferably comprises structural units of monomers whose homopolymers have a T _g greater than 70 °C (high T _g monomers), such as methyl methacrylate, styrene, isobornyl methacrylate, cyclohexyl methacrylate, and /-butyl methacrylate. The high T _g shell preferably comprises at least 90 weight percent structural units of methyl methacrylate.

The concentration of polymer-encapsulated TiCh composite particles in the composition is typically in the range of from 10, or from 40, or from 60, to 85, or to 80 weight percent; and the concentration of the organic matting agent is typically in the range of from 5, or from 10, to 76, or to 40 weight percent, based on the weight of the polymer-encapsulated TiCh composite particles and the organic matting agent. The composition of the present invention may further comprise an inorganic matting agent, which may be fed into the mixer from one or more separate storage tanks. Examples of inorganic matting agents include talc, clay, mica, and sericite; CaCCh; nepheline syenite; feldspar; wollastonite; kaolinite; dicalcium phosphate; and diatomaceous earth.

The composition of the present invention may also further comprise additional film- forming polymer particles not encapsulating TiCh particles. These polymer particles, which typically have a z-average particle size by dynamic light scattering in the range of from 50 nm to 600 nm, may be fed from a latex pre-paint storage tank into the mixer. Examples of suitable polymeric dispersions include acrylic, styrene-acrylic, urethane, alkyd, vinyl ester (e.g., vinyl acetate and vinyl versatate), and vinyl acetate-ethylene (VAE) polymeric dispersions, and combinations thereof. Acrylic and styrene-acrylic polymeric dispersions typically have a z-average particle size in the range of from 70 nm to 300 nm, while vinyl ester latexes generally have a z-average particle size in the range of from 200 nm to 550 nm as measured using dynamic light scattering. If it is desirable to feed more than one kind of latex into the mixing chamber, the latexes are preferably added from separate latex pre -paint storage tanks.

The concentration and type of rheology modifier included in each pre -paint storage tank is readily predetermined to achieve the desired Brookfield, KU, and ICI viscosity of the final paint. Examples of suitable rheology modifiers include hydrophobically modified ethylene oxide urethane polymers (HEURs); hydrophobically modified alkali swellable emulsion (HASEs); alkali swellable emulsions (ASEs); and hydroxy ethyl cellulosics (HECs), and hydrophobically modified hydroxy ethyl cellulosic (HMHECs); and combinations thereof.

The composition of the present invention may be prepared by the in-line mixing process described hereinabove as well as by standard mixing methods well known in the art. The in-line mixing process provides a way of making a wide variety of paints quickly with minimal cleanup between runs. Significantly, no further mixing is required after the in-line mixed pre-paints are dispensed into the paint container. Examples

The aqueous dispersion of TiC -encapsulated polymer particles (aqueous dispersion of composite particles) was prepared substantially as described in US 7,579,081, Example 1; the aqueous dispersion of the organic matting agent was prepared substantially as described in EP 2 586 835 Bl, Example 12. Table 1 illustrates paint formulations with and without the composition of the present invention (Examples 1-3 and Comparative Examples 1-3, respectively). In the table, Composite _Pig ment refers to the portion of the composite particles attributed to Ti-Pure R-706 TiCb; Compositebinder refers to the portion of the composite particles attributed to binder; Composite _to tai refers to the total weight of composite particles and water; TiCh slurry refers to Ti-Pure R-746 TiCh slurry; Latex refers to RHOPLEX™ VSR- 1050 Acrylic Latex (49.5 wt% solids); Coalescent refers to Texanol coalescent; HEUR refers to ACRYSOL RM-8W Rheology Modifier; and Beads refers to the aqueous dispersion of microspheres as prepared above. (RHOPLEX and ACRYSOL are Trademarks of The Dow Chemical Company or Its Affiliates.) All weights are in kg and the total volume of each paint is 100 L.

Table 1 - Paint Formulations Metal mark testing procedure:

Draw-downs were prepared on Leneta form 5C opacity charts for each paint using a 1.5-mil Bird draw-down bar, then the paints were allowed to dry overnight. A 3.5-cm x 11 -cm swatch of the coated chart was removed and placed on a Rub Fastness Tester (model 421, Satra Footware Technology Centre). The surface of the coating was rubbed using an Al foil covered Veslic pad (Ar N° 701 pads, Swissatest corporation, St Gallen, CH) and 0.5 kg of weight for 1 to 2 cycles. The coating surfaces were visually evaluated for metal transfer transferred to the coating and given a rating of 1 to 10, where a rating of 1 indicates a substantial transference of Al to the coating and a rating of 10 indicates no metal transference. Table 2 illustrates the results of the metal mark tests.

Table 2 - Metal Mark Test Results

The data show a marked improvement in mar resistance for paints formulated with the compositions of the present invention.