Patent Description:
Opaque polymers are well known as additives in pigmented coating formulations such as paints and are used to improve hiding of coated substrates. Opaque polymers are used to reduce the load of the comparatively expensive TiO<NUM> in formulations without sacrificing hiding, or to maintain the same levels of TiO<NUM> to improve hiding. Opaque polymers can be prepared, for example, as described in <CIT>.

<CIT> discloses a multistage emulsion polymer including, as copolymerized units: from <NUM>% to <NUM>%, by weight P-acid monomer, based on the weight of the emulsion polymer; from <NUM>% to <NUM>% by weight multiethylenically unsaturated monomer, based on the weight of the emulsion polymer; and at least one second monoethylenically unsaturated monomer; the emulsion polymer having a calculated Tg of from -<NUM> to <NUM>; the emulsion polymer is formed by the "pulsed" addition of <NUM>% to <NUM>% of the P-acid monomer during a stage including from <NUM>% to <NUM>% of the total monomer weight, preferably added during the relatively early stages of the polymerization.

<CIT> discloses an organic-inorganic composite particle containing an inorganic particle having a plurality of polymer particles attached to the inorganic particle and a polymer layer encapsulating the attached polymer particles.

<CIT> discloses processes for chemically-modifying the surface of an emulsion polymer particle which include providing an aqueous emulsion polymer, a monomer at a level of at least <NUM>% by weight based on the weight of the emulsion polymer and a surface-modifying chemical capable of bonding with the monomer, under conditions where there is no substantial polymerization of the monomer, and then reducing the level of the monomer by at least <NUM>%.

It would be an advance in the field of pigmented coating compositions to discover an additive with improved hiding capability.

The present invention addresses a need in the art by providing a method INSERT CLAIM <NUM>.

The phosphorus acid functionalized core-shell polymer particles are useful in forming composite with TiO<NUM> particles, which composites improve hiding efficiency in paint formulations.

The present invention is INSERT CLAIM <NUM>.

The first monomer emulsion comprises from <NUM>, preferably from <NUM>, more preferably from <NUM> weight percent, to <NUM>, more preferably to <NUM>, and most preferably to <NUM> weight percent of a phosphorus acid monomer, based on the weight of monomers in the first monomer emulsion. The first monomer emulsion further comprises, based on the weight of monomers in the first monomer emulsion, from <NUM>, more preferably from <NUM>, and most preferably from <NUM> weight percent, to <NUM>, and more preferably to <NUM> weight percent of a first nonionic ethylenically unsaturated monomer. The first nonionic ethylenically unsaturated monomer preferably has a refractive index (Rf) of at least <NUM>.

Examples of suitable phosphorus acid monomers include phosphonates and dihydrogen phosphate esters of an alcohol in which the alcohol contains or is substituted with a polymerizable vinyl or olefinic group. Preferred dihydrogen phosphate esters are phosphates of hydroxyalkyl methacrylates, including phosphoethyl methacrylate and phosphopropyl methacrylates, with phosphoethyl methacrylate being especially preferred. "Phosphoethyl methacrylate" (PEM) is used herein to refer to the following structure:
<CHM>.

The first nonionic ethylenically unsaturated monomers include styrene, methyl methacrylate, acrylonitrile, or t-butyl acrylate, as well as combinations thereof. Styrene or a combination of styrene and acrylonitrile are preferred monomers. When styrene and acrylonitrile are both used, the preferred w/w ratio of styrene to acrylonitrile is from <NUM>:<NUM> to <NUM>:<NUM>.

The first monomer emulsion further comprises from <NUM>, preferably from <NUM>, and more preferably from <NUM> weight percent, to <NUM>, more preferably to <NUM>, and most preferably to <NUM> weight percent of a carboxylic acid functionalized monomer, based on the weight of the monomers in the first monomer emulsion. Examples of suitable carboxylic acid functionalized monomers include acrylic acid, methacrylic acid, maleic acid, fumaric acid, and itaconic acid, with acrylic acid or methacrylic acid being preferred.

The first monomer emulsion may include other monomers. For example, the first monomer emulsion may include a polyethylenically unsaturated monomer at a concentration from <NUM>, more preferably from <NUM>, to preferably <NUM>, more preferably to <NUM>, more preferably to <NUM>, and most preferably to <NUM> weight percent, based on the weight of monomers in the first monomer emulsion. Preferred polyethylenically unsaturated monomers are diethylenically unsaturated monomers and triethylenically unsaturated monomers such as allyl methacrylate (ALMA), divinyl benzene (DVB), ethylene glycol diacrylate (EGDA), ethylene glycol dimethacrylate (EGDMA), trimethylolpropane triacrylate (TMPTA), and trimethylolpropane trimethacrylate (TMPTMA).

The acid functionalized polymer particles comprise a) preferably from <NUM>, and more preferably from <NUM> weight percent, to <NUM>, preferably to <NUM>, and more preferably to <NUM> weight percent structural units of a carboxylic acid monomer, preferably acrylic acid or methacrylic acid, based on the weight of the polymer particles; and b) preferably from <NUM>, and more preferably from <NUM> weight percent, to preferably to <NUM>, and more preferably to <NUM> weight percent structural units of a second nonionic ethylenically unsaturated monomer, based on the weight of the acid functionalized polymer particles. Examples of preferred second nonionic ethylenically unsaturated monomers include methyl methacrylate and styrene, with methyl methacrylate being more preferred. The acid functionalized polymer particles preferably have an average diameter of from <NUM>, more preferably from <NUM> to preferably <NUM>, more preferably to <NUM>, and most preferably to <NUM>, as determined by a BI90 Plus Particle Size Analyzer.

The first monomer emulsion and the aqueous dispersion of acid functionalized polymer particles are contacted together under emulsion polymerization conditions to form an aqueous dispersion of core-shell polymer particles. Preferably, the phosphorus acid monomer portion of the first monomer emulsion is added to a vessel containing the aqueous dispersion of polymer particles in a staged fashion such that all of the phosphorus added monomer is added to the reaction vessel over a shorter period of time than the other monomers of the monomer emulsion. More preferably, the phosphorus acid monomer is added over a period that is less than <NUM>%, of the total monomer emulsion time of addition. Most preferably, the phosphorus acid monomer addition is delayed until <NUM>% to <NUM>% of the monomer emulsion, absent the phosphorus acid monomer, is added to the reaction vessel. It has been surprisingly discovered that staging of the addition of the phosphorus acid monomer has a marked effect on the extent of composite formation, which, in turn advantageously impacts the hiding observed in the final coated product.

The polymerization is allowed to proceed to a desired degree of conversion of monomer in the first monomer emulsion, preferably at least <NUM>%, more preferably at least <NUM>%, and most preferably at least <NUM>% conversion of monomers; once the desired degree of conversion is achieved, the reaction is preferably inhibited to stop or substantially stop the polymerization of unreacted residual monomer. Inhibition is preferably carried out using an inhibitor or a redox pair. Examples of suitable inhibitors include <NUM>-hydroxy-<NUM>,<NUM>,<NUM>,<NUM>-tetramethylpiperidin-<NUM>-oxyl, (<NUM>-hydroxy-TEMPO), <NUM>,<NUM>,<NUM>,<NUM>-tetramethylpiperidin-<NUM>-oxyl (TEMPO), monomethyl ether hydroquinone (MEHQ), and <NUM>-t-butyl catechol. Examples of suitable redox pairs include combinations of an oxidant such as t-butyl hydroperoxide (t-BHP); t-amyl hydroperoxide (t-AHP), sodium persulfate (NaPS), ammonium persulfate (APS), and hydrogen peroxide, with a reductant such as isoascorbic acid (IAA), sodium bisulfite, and sodium sulfate. It is also possible, though not necessarily preferable, to stop or substantially stop polymerization by allowing the reaction to run to completion or substantial completion.

A polymerizable plasticizing agent is then contacted with the phosphorus acid functionalized core-shell polymer particles to plasticize the shell, thereby providing a means for the subsequently added aqueous base to penetrate the shell (with concomitant swelling of the polymer particles) and fill the core with water neutralized to a pH of at least <NUM>, more preferably at least <NUM>, to <NUM> more preferably to <NUM>. Examples of suitable bases include alkali metal hydroxides, alkaline earth metal hydroxides, alkali metal carbonates, alkaline earth metal carbonates, amines, and NH<NUM>OH, with NaOH, KOH, and NH<NUM>OH being particularly preferred bases.

The polymerizable plasticizing agent can be any ethylenically unsaturated monomer but is preferably either a monomer having a Tg of greater than <NUM> (that is, the homopolymer of the monomer has a Tg of greater than <NUM> as calculated by the Fox equation) or a low Tg monomer copolymerized with a crosslinking agent. Examples of preferred polymerizable plasticizing agents include styrene or methyl methacrylate, or a combination of butyl acrylate and divinyl benzene or allyl methacrylate.

The polymerizable plasticizing agent is used at a concentration of preferably from <NUM>, and more preferably from <NUM> weight percent, to preferably to <NUM>, and more preferably to <NUM> weight percent, based on the weight of the core-shell polymer particles. It is understood that the polymerizable plasticizing agent may include unreacted monomer from the first monomer emulsion; although not preferred, it is possible that the polymerizable plasticizing agent arises entirely from unreacted monomer. It is preferred however, that additional polymerizable plasticizing agent be contacted with the aqueous dispersion of core-shell polymer particles.

Once the polymer particles have swollen to their desired levels, the polymerizable plasticizing agent is then polymerized. It is preferred that less than <NUM>%, more preferably less than <NUM>%, and most preferably less than <NUM>% of residual polymerizable plasticizing agent remains after this polymerization step.

The phosphorus acid functionalized polymer particles are advantageously admixed with pigment particles such as an aqueous slurry of TiO<NUM> particles - especially TiO<NUM> particles surface-treated with silane or alumina - to form composites that are useful in providing opacity in coating compositions such as paint formulations, paper coatings, ink jet coatings, printing inks, sunscreens, nail polish, and wood coatings.

The formulation may also include any of a variety of other materials such as fillers; binders; rheology modifiers; dispersants, surfactants; defoamers; preservatives; flow agents; leveling agents; and neutralizing agents. It has been discovered that the composites confer additional hiding benefits for the formulation as compared with non-composite forming aqueous blends of opaque polymer and pigment particles.

The present invention discloses a composite comprising an aqueous dispersion of phosphorus acid functionalized core-shell polymer particles adsorbed to TiO<NUM> particles, wherein the core comprises water having a pH of at least <NUM> and not more than <NUM>; wherein the average diameter of the core is from <NUM> to <NUM>, and the average diameter of the core-shell particles is from <NUM> to <NUM>; wherein the shell comprises a) from <NUM> to <NUM>% of a polymer or a copolymer of one or more monomers selected from the group consisting of styrene, methyl methacrylate, acrylonitrile, and t-butyl acrylate ; and b) from <NUM> to <NUM> weight percent structural units of a phosphorus acid monomer.

The phosphorus acid functionalized core-shell polymer particles have a preferred final core diameter in the range of from <NUM>, and more preferably from <NUM>, to preferably <NUM>, more preferably to <NUM>, and most preferably to <NUM>, as determined by void fraction measurement described in the Examples Section. The diameter of the final core-shell polymer particles is preferably in the range of from <NUM>, more preferably from <NUM>, and most preferably from <NUM>, to preferably <NUM>, more preferably to <NUM>, and most preferably to <NUM>, as determined using a BI90 Plus Particle Size Analyzer. The void fraction of the final core-shell polymer particles (that is, the volume of the final core to the total volume of the final core-shell polymer particles) is preferably in the range of from <NUM>%, more preferably from <NUM>%, and most preferably from <NUM>%, to preferably <NUM>%, more preferably to <NUM>%, and most preferably to <NUM>%.

To a <NUM>-liter, four necked round bottom flask was equipped with paddle stirrer, thermometer, nitrogen inlet, and reflux condenser was added DI water (<NUM>) under N<NUM>. The contents were heated <NUM>, whereupon NaPS (<NUM>) dissolved in DI water (<NUM>) was added followed immediately by the addition of <NUM> MMA/<NUM> MAA seed material prepared substantially as described in <CIT>, Examples <NUM>-<NUM> (<NUM>, <NUM>% solids, PS = <NUM>, by BI90 Plus Particle Size Analyzer).

A first monomer emulsion (ME I), which was prepared by mixing DI water (<NUM>), SDS (<NUM>), STY (<NUM>), AN (<NUM>), and linseed oil fatty acid (<NUM>) was added to the kettle at a rate of <NUM>/min at a temperature of <NUM>. Two minutes after the start of the ME I addition, a solution of AA (<NUM>) mixed with DI water (<NUM>) was added to the kettle. After <NUM> from the start of the ME I addition, the feed rate was increased to <NUM>/min, and a mixture of sodium persulfate (<NUM>) dissolved in DI water (<NUM>) was co-fed to the kettle at a rate of <NUM>/min. The temperature of the reaction mixture was then allowed to increase to <NUM>. After <NUM> from the start of the ME I addition, the feed rate was increased to <NUM>/min and the temperature was allowed to increase to <NUM>. After <NUM> from the start of the ME I addition, the feed rate was increased to <NUM>/min. Upon completion of the ME I and co-feed additions, a solution of ferrous sulfate (<NUM>) dissolved in DI water (<NUM>) was mixed with a solution of EDTA (<NUM>) dissolved in two g of DI water. This mixture was added to the kettle along with a separate solution of IAA (<NUM>) dissolved in DI water (<NUM>). The batch was then held at <NUM> for <NUM>; a second monomer emulsion (ME II), which was prepared by mixing DI water (<NUM>), SDS (<NUM>), BA (<NUM>), DVB (<NUM>) and <NUM>-hydroxy TEMPO (<NUM>) was added to the kettle at a rate of <NUM>/min along with hot DI water (<NUM>). A solution of ammonium hydroxide (<NUM>, <NUM>% aq) in DI water (<NUM>) of was then added to the kettle over <NUM>. The batch was then held for five min at <NUM>, after which time a solution t-BHP (<NUM>) mixed with DI water (<NUM>) and a solution of IAA (<NUM>) mixed with DI water (<NUM>) was co-feed to the kettle at a rate of <NUM>/min. After completion of the t-BHP and IAA co-feed, the batch was cooled to room temperature and filtered to remove any coagulum formed. The final latex had a solids content of <NUM>%.

The Examples were prepared by the procedure of Comparative Example <NUM> except that for Examples <NUM>-<NUM>, PEM was added to the ME1tank after <NUM>% of ME1 was added to the kettle; for Examples <NUM>-<NUM>, PEM was added to the ME I tank after <NUM>% of ME1 was added to the kettle.

Void fraction of the opaque polymers was determined using three separate bulking cup weight measurements. For the first measurement, a triethylene glycol (TEG)-water blank is prepared by placing TEG (<NUM>) and water (<NUM>) in a <NUM>-oz jar. The TEG and water were stirred to form a thoroughly dispersed mixture, which was poured into a tared bulking cup. The weight of this mixture (the blank, designated BL for ensuing calculations) was obtained. The second measurement was obtained by pouring the opaque polymer emulsion into a tared bulking cup and obtaining the weight of the opaque polymer emulsion (designated OP for ensuing calculations). For the third measurement, a mixture of TEG and opaque polymer emulsion was prepared by placing TEG (<NUM>) with stirring into a <NUM>-oz jar. Opaque polymer emulsion was added to the jar that was calculated to be equal to the amount of emulsion that contains <NUM> of water. Within <NUM> of adding the aliquot of opaque polymer emulsion to the TEG, the mixture was poured into a tared bulking cup and the weight (the weight of the OP/TEG mixture, designated "OP-A" for ensuing calculations) was obtained.

Void fractions of the opaque polymers were in accordance with the below equations. In addition to the values obtained through the bulking cup measurements, the solids content of the opaque polymer emulsion also must be known ("Solids"). The result of the calculations is the void fraction (%VF) of the opaque polymer.

<MAT> wherein, <MAT> <MAT> <MAT> <MAT> <MAT>.

The void diameter of the opaque polymer can be calculated using the particle size of the opaque polymer particle and the void fraction of the opaque polymer particle. The void diameter was calculated as follows: <MAT>.

Table <NUM> Stage ratio refers to the ratio of the Core to the Inner Shell (ME I) to the Outer Shell (ME II).

The opaque polymers were formulated into paints in accordance with Table <NUM>. (ACRYSOL and RHOPLEX are Trademarks of The Dow Chemical Company or its Affiliates.

Four draw-downs were prepared on Black Release Charts (Leneta Form RC-BC) for each paint using a <NUM>-mil Bird draw down bar and the charts allowed to dry overnight. Using a template, <NUM>" x <NUM>" rectangles were cut out on each chart. The Y-reflectance was measured using a X-Rite Color i7 Spectrophotometer in each of the scribed areas five times and the average Y-reflectance recorded. A thick film draw down was prepared for each paint on the Black Release Charts using a <NUM>", <NUM>-mil block draw down bar and the charts were allowed to dry overnight. The Y-reflectance was measured in five different areas of the draw down and the average Y-reflectance recorded. Kubelka-Munk hiding value S is given by Equation <NUM>: <MAT> where X is the average film thickness, R is the average reflectance of the thick film and RB is the average reflectance over black of the thin film. X can be calculated from the weight of the paint film (Wpf), the density (D) of the dry film; and the film area (A). Film area for a <NUM>" x <NUM>" template was <NUM> in<NUM>.

The Hiding (S/mil) data for Paint Examples and Comparative Example are summarized in Table <NUM>.

Claim 1:
A method for preparing an aqueous dispersion of phosphorus acid functionalized core-shell polymer particles comprising the steps of a) contacting under emulsion polymerization conditions i) a first monomer emulsion with ii) an aqueous dispersion of acid functionalized polymer particles having an average particle size of from <NUM> to <NUM> to form an aqueous dispersion of core-shell polymer particles; then b) plasticizing the shell portion of the core-shell polymer particles with a polymerizable plasticizing agent; then c) contacting the core-shell polymer particles with an aqueous base to swell the core without substantially polymerizing the plasticizing agent; then d) polymerizing the plasticizing agent;
wherein the first monomer emulsion comprises a) from <NUM> to <NUM> weight percent of a phosphorus acid monomer, based on the weight of the monomers in the first monomer emulsion; and b) at least <NUM> weight percent of a first nonionic ethylenically unsaturated monomer selected from the group consisting of styrene, methyl methacrylate, acrylonitrile, and t-butyl acrylate, and a combination thereof; and c) from <NUM> to <NUM> weight percent of a carboxylic acid functionalized monomer;
wherein the acid functionalized polymer particles comprise from <NUM> to <NUM> weight percent structural units of a carboxylic acid monomer, based on the weight of the polymer particles; and <NUM> to <NUM> weight percent of structural units of a second nonionic ethylenically unsaturated monomer;
wherein the plasticizing agent comprises from <NUM> to <NUM> percent of a third nonionic ethylenically unsaturated monomer based on the weight of the phosphorus acid functionalized core-shell polymer particles;
wherein the phosphorus acid functionalized core-shell polymer particles have a average particle size after step d) in the range of <NUM> to <NUM> as determined using a BI90 Plus Particle Size Analyzer.