Inorganic oxide particle process with improved energy efficiency

Abstract

The present invention relates to a treated inorganic oxide slurry and process of making including: a. treating an inorganic oxide particle with aqueous inorganic metal salt; b. washing the treated inorganic oxide particle with water and removing aqueous inorganic metal salt to form a washed slurry having 30-60% by weight treated inorganic oxide particles in water; c. milling the washed slurry to reduce the particle size of the treated inorganic oxide particles using a wet milling process to form a milled slurry having a PSD 0.509 of less than 50%; d. drying the milled slurry to form a dried particle; and e. contacting the dried particle with water and dispersant to form a product slurry. The process uses less energy and water compared with prior art processes that include jet milling steps and full drying steps, while maintaining performance. The slurries can be used in applications including coatings and paper.

Description

TI0013-W001TITLE OF THE INVENTIONINORGANIC OXIDE PARTICLE PROCESS WITH IMPROVED ENERGY EFFICIENCYCROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority of U.S. Provisional Application No. 63 / 707,786 filed October 16, 2024, the disclosures of which are incorporated herein by reference in its entirety.FIELD OF THE INVENTION

[0002] The present invention relates to a process for producing an inorganic oxide particle slurry including wet milling the slurry, drying the milled slurry, and combining with water and dispersant to form a final product slurry. The process uses less energy and water compared with prior art processes that include jet milling, while maintaining performance.BACKGROUND OF THE INVENTION

[0003] Current processes for producing inorganic oxide particles employ jet milling and drying techniques between washing the particles and milling the particles, such as in US 9,505,022, US 6,395,081 , or US 5,730,795. However, jet milling requires a large amount of energy due to heating and use of high-pressure gases.

[0004] Previous methods to avoid drying and jet milling the particles have been demonstrated; however, those processes did not allow for an aqueous treatment step, which presents unique issues. Salts generated in an aqueous treatment step harm particle properties and must be removed from the finished product.SUMMARY OF THE INVENTION

[0005] The process described herein avoids the jet milling step while maintaining the performance integrity of the particles. The present invention relates to a process of producing a treated inorganic oxide slurry comprising: a. treating an inorganic oxide particle with at least one aqueous inorganic metal salt to form a treated inorganic oxide particle; b. washing the treated inorganic oxide particle with water and removing aqueous inorganic metal salt to form a washed slurry having 30-60% by weight treated inorganic oxide particles in water;TI0013-W001 c. milling the washed slurry to reduce the particle size of the treated inorganic oxide particles using a wet milling process to form a milled slurry having a particle size distribution (PSD) 0.509 of less than 50%; d. drying the milled slurry to form a dried particle; and e. contacting the dried particle with water and dispersant to form a product slurry.The present invention further relates to a treated aqueous inorganic oxide particle slurry made by the process. The present invention further relates to a treated aqueous inorganic oxide particle slurry comprising about 60-85% by weight treated inorganic oxide particles in water, based on the total slurry weight, where the treated aqueous inorganic particle slurry has a viscosity of at most 700 cP and at most 5.00 cm deflection.BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FIG. 1 shows a flow diagram of the inventive process, including optional steps.

[0007] FIG. 2 shows comparative process flow diagram, including jet milling that is not part of the present invention.DETAILED DESCRIPTION OF THE INVENTION

[0008] The present invention relates to a process of producing a treated inorganic oxide slurry comprising: a. treating an inorganic oxide particle with at least one aqueous inorganic metal salt to form a treated inorganic oxide particle; b. washing the treated inorganic oxide particle with water and removing aqueous inorganic metal salt to form a washed slurry having 30-60% by weight treated inorganic oxide particles in water; c. milling the washed slurry to reduce the particle size of the treated inorganic oxide particles using a wet milling process to form a milled slurry having a PSD 0.509 of less than 50%; d. drying the milled slurry to form a dried particle; and e. contacting the dried particle with water and dispersant to form a product slurry.TI0013-W001

[0009] The inorganic oxide particle of step a may be any suitable particle, including but not limited to oxides of Ti, Al, Zn, Cu, Fe, Mn, or Si, such as TiO2, AI2O3, ZnO, CuO, Fe2O3, MnO, MnsC , Mn2Os, MnC>2, MnOs, I O?, or SiC . Blends or mixtures of inorganic oxides may also be used. Such compounds may be in any particle form. For example, TiC particles may be in rutile or anatase form, and they may be made by the chloride process or sulfate process. Particles may be a pigment or nanoparticle. By “pigment” it is meant that the primary particles have an average particle size of less than 1 pm; in another aspect, the particles have an average particle size of about 0.020 to about 0.95 pm; in another aspect, about 0.050 to about 0.75 pm; and in another aspect, about 0.075 to about 0.50 pm. By “nanoparticle” it is meant that the primary particles typically have an average particle size diameter of less than about 100 nm as determined by dynamic light scattering that measures the particle size distribution of particles in liquid suspension. The nanoparticles are typically agglomerates that may range from about 3 nm to about 6000 nm. The inorganic oxide particle serves as a “core particle” for the further treatments described herein.

[0010] The inorganic oxide particle of step a may have inorganic oxide treatments on the surface of the core inorganic oxide particle prior to being introduced in step a. Typical oxide include oxides of Ti, Al, Zn, Cu, Fe, Mn, or Si, such as Tit , AI2O3, ZnO, CuO, Fe2Os, MnO, MnsO4, Mn2O3, MnO2, MnOs, Mn2O?, or SiO2. Mixtures of inorganic oxides may also be applied, and the treatment oxide may be the same or different than the oxide of the core inorganic oxide particle. Such oxides may be formed on the core inorganic oxide particle by any suitable method, including aqueous treatment, by oxidation of metal chloride, or by condensed phase aqueous oxide. In one aspect, the inorganic oxide particle is TiO2 having a surface treatment of SiO2 or AI2O3.

[0011] The inorganic oxide particles are treated in step a with at least one aqueous inorganic metal salt to form a treated inorganic oxide particle, such that the aqueous inorganic metal salt yields an inorganic oxide layer on the core inorganic oxide particle. Such a process may be performed by any suitable aqueous treatment process. For example, an inorganic metal salt may be combined with water and the inorganic oxide particle, in any order, to form a slurry. The slurry may comprise the inorganic oxide particle in any suitable amount, such as about 1-35% by weight, orTI0013-W001 about 25-35% by weight, or about 30% by weight, all based on the total slurry weight (the weight of the treated inorganic oxide particles in water). The mixture may be heated, such as to a temperature of 30-95 °C, 30-90 °C, 35-90 °C, 40-90 °C, or 45- 90 °C, and the pH may be adjusted to the appropriate conditions to precipitate the inorganic metal salt onto the inorganic oxide particle. For basic inorganic metal salts, the pH range may be about 3.5-7.5; or in another aspect, about 5.0-6.5. For acidic inorganic metal salts, the pH range may be about 7.0-10.0; or in another aspect, about 8.5-9.5.

[0012] The inorganic metal salt may be a compound containing Al, Si, Zr, Ba, or Zn. Such compounds can be used under certain conditions to precipitate inorganic oxides onto a particle. These inorganic metal salt compounds include, but are not limited to, alkali metal salts, such as sodium or potassium silicate, sodium or potassium aluminate; metal sulfates, such as aluminum sulfate; or metal halides, such as aluminum chloride. In one aspect, the treated inorganic oxide particle in step a comprises about 1 .0-20.0% by weight inorganic oxide treatment layer resulting from the treatment of step a, based on the total weight of the inorganic oxide particle; in another aspect, comprises about 4.0-8.0% inorganic oxide treatment layer resulting from the treatment of step a, based on the total weight of the inorganic oxide particle; and in a further aspect, comprises about 5.0-7.5% inorganic oxide treatment layer resulting from the treatment of step a, based on the total weight of the inorganic oxide particle.

[0013] The treated inorganic oxide particles resulting from step a are then washed with water in step b, and the water is at least partially removed with aqueous inorganic metal salts dissolved therein, thus removing the residual inorganic metal salt. Aqueous inorganic metal salts that are removed in step b include those added in step a but may also include aqueous inorganic metal salts that are present from inorganic oxide particle production. Aqueous inorganic metal salts include, for example, alkali metal salts, metal halides or chlorides, metal sulfates, metal nitrates, or metal fluorides. In one aspect, the washed slurry resulting from step b has a resistance of at least about 2 kOhms-s; in another aspect, the washed slurry has a resistance of at least about 4 kOhms-s; and in another aspect, the washed slurry has a resistance of at least 6 kOhms-s.TI0013-W001

[0014] Any suitable mechanical means of washing the treated inorganic oxide particles may be used, as long as the salts are removed from the mixture. Removal of water with aqueous inorganic metal salts can be performed by filtration, for example, by rotary vacuum filter, belt filter, or filter press. Although some temperature control may be used, it is less preferred to heat the slurry since energy efficiency is desired. After removal of aqueous inorganic metal salts, the treated inorganic oxide particles form a washed slurry having a solids content of 30-60% by weight treated inorganic oxide particles in water; in another aspect, the washed slurry has 30-50% by weight treated inorganic oxide particles in water; and in another aspect, the washed slurry has 35-45% by weight treated inorganic oxide particles in water, all based on the total washed slurry weight.

[0015] The washed slurry, having the solids content specified above, is then milled to reduce the particle size of the treated inorganic oxide particles and to form a milled slurry having a Particle Size Distribution - PSD 0.509 - of less than 50%. The solids content and order of operations are important in this process. If milling is performed before or during the washing step, for example, the washing step is less efficient due to difficulties with removing water and dissolved solids from small particles. The removal process is slower, and the dissolved solids may remain on the particle surfaces. Any suitable wet milling method may be used, including but not limited to milling by media mill, sand mill, immersion mill, or basket mill. The desired milled particle size may vary based on particle composition and end use application.

[0016] The Particle Size Distribution (PSD) of the milled slurry is important to reducing the viscosity of the final product slurry. PSD D50 represents the particle size with a cumulative mass % greater than 50%, commonly referred to as the median. PSD 0.509 represents the cumulative mass % that is greater than 0.509 microns. “PSD 0.509 of less than 50%” can also be written as “PSD greater than 0.509 microns of less than 50%”. Both can be measured by a particle size analyzer. The milled slurry has a PSD 0.509 of less than 50%, such that the dried particles used in slurry step e also have a PSD 0.509 of less than 50%. In another aspect, the milled slurry has a PSD 0.509 of less than 45%, and / or the dried particles used in slurry step e have a PSD 0.509 of less than 45%; and in another aspect, the milled slurry has a PSD 0.509 of less than 40%, and / or the dried particles used in slurry step e have a PSD 0.509 of less than 40%. In one aspect, the milled slurry has aTI0013-W001PSD D50 of less than 0.509, and / or the dried particles used in slurry step e have a PSD D50 of less than 0.509. In another aspect, the milled slurry has a PSD D50 of less than 0.475, and / or the dried particles used in slurry step e have a PSD D50 of less than 0.475; and in another aspect, the milled slurry has a PSD D50 of less than 0.450, and / or the dried particles used in slurry step e have a PSD D50 of less than 0.450.

[0017] In one aspect, the washed slurry contains a processing aid that may be added during the washing step or after washing but before the milling step. Such a processing aid may help with the grinding step, such as to lower viscosity or increase solids content, or it may be added at this stage to aid processing after the milling step. Processing aids often are used to impart stabilization of the small-sized particles making up the slurry. Dispersants, for example, may be added prior to milling to achieve milled slurries having higher solids contents. Examples of processing aids include but are not limited to dispersants, surfactants, or pigment stabilizers; more specific examples include inorganic processing aids, including but not limited to silicates or alkali metal phosphates; small organic molecule processing aids; or polymeric processing aids, including but not limited to those having carboxylic acid groups for anchoring or those having molecular weights between 1 ,000 and 10,000. Specific examples of inorganic processing aids include but are not limited to sodium pyrophosphate or sodium hexametaphosphate; and specific examples of small organic processing aids include but are not limited to citric acid. Specific examples of polymeric processing aids include but are not limited to dispersants sold by Dow Chemical under the Tamol™ brand, such as Tamol-851 ™, Tamol-1124™, Tamol-731 A™, or Tamol-165A™; dispersants sold by Arkema under the Coadis™ brand, such as Coadis 144A™; and dispersants sold by Byk under the Disperbyk™ brand, such as Disperbyk 191 ™.

[0018] The milled slurry is then dried to form dried particles in step d. Any suitable means for drying may be used, including but not limited to flash drying, spray drying, or oven drying. In one aspect, the dried particles produced from the drying step have a water content of less than about 5% by weight; in another aspect, the dried particles have a water content of less than about 3% by weight; in another aspect, the dried particles have a water content of less than about 1 % by weight; and inTI0013-W001 another aspect, the dried particles have a water content of less than about 0.7% by weight, all based on the total weight of the dried particles.

[0019] Drying the milled slurry is important to the process to provide a product slurry with lower viscosity compared to the same milled slurry without the drying step. The drying step can also produce slurries with higher coating tint strength and hiding power. It is important that the slurry step e is performed with dried particles rather than wet particles. In one aspect, at least 50% by weight of the particles in slurry step e are dried particles; in another aspect, at least 60% by weight of the particles in slurry step e are dried particles; and in another aspect, at least 70% by weight of the particles in slurry step e are dried particles.

[0020] The dried particles are then contacted with water and dispersant to form a product slurry in step e. In one aspect, the invention relates to a treated aqueous inorganic oxide particle slurry comprising about 60-85% by weight treated inorganic oxide particle in water, based on the total slurry weight, where the treated aqueous inorganic particle slurry has a viscosity of at most 700 cP and at most 5.00 cm deflection. The treated aqueous inorganic oxide particle slurry can also be referred to as a product slurry.

[0021] In one aspect, the product slurry contains 60-85% by weight treated inorganic oxide particles; in another aspect, the product slurry has 65-85% by weight treated inorganic oxide particles; and in another aspect, the product slurry has 70- 85% by weight treated inorganic oxide particles, all based on the total product slurry weight. Even at such high solids, the product slurry has a viscosity of at most 700 cP and / or 5.00 cm deflection; in another aspect, the product slurry has a viscosity of at most 600 cP and / or 4.50 cm deflection; in another aspect, the product slurry has a viscosity of at most 500 cP and / or 4.00 cm deflection; an in another aspect, the product slurry has a viscosity of at most 400 cP and / or 3.50 cm deflection.

[0022] The dispersant added to the dried particles includes but is not limited to silicates or alkali metal phosphates; small organic molecule processing aids; or polymeric processing aids, including but not limited to those having carboxylic acid groups for anchoring or those having molecular weights between 1 ,000 and 10,000. Specific examples of inorganic processing aids include but are not limited to sodium pyrophosphate or sodium hexametaphosphate; and specific examples of smallTI0013-W001 organic processing aids include but are not limited to citric acid. Specific examples of polymeric processing aids include but are not limited to dispersants sold by Dow Chemical under the Tamol™ brand, such as Tamol-851 ™, Tamol-1124™, Tamol- 731 A™, or Tamol-165A™; dispersants sold by Arkema under the Coadis™ brand, such as Coadis 144A™; and dispersants sold by Byk under the Disperbyk™ brand, such as Disperbyk 191 ™.

[0023] In another aspect, treated inorganic oxide particles or other inorganic particles from other sources may be introduced into the process at any step, including to the aqueous treatment step a, the washing step b, the milling step c, or the dewatering step c2. In one aspect, the treated inorganic particles from other sources may be in the form of dry particles; in another aspect the treated inorganic particles from other sources may be in the form of a particle slurry in water. Other inorganic particles may include, but are not limited to, clays, calcium carbonate, or fumed silicas.

[0024] The introduction of dry treated inorganic oxide particles serves to maximize yield of treated inorganic oxide particles from separate sources, reduce waste, and / or serve to increase solids when needed. In one aspect, the dry treated inorganic oxide particles come from other sources. By “treated”, it is meant that the inorganic oxide particles have been contacted with an inorganic metal salt as described above. By “other sources” is meant that the treated inorganic particles come from a separate process or production line. Dry particles may be sourced, for example, from a finished dry particle product or from an intermediate step of another process, such as the output of a dryer discharge.

[0025] Treated inorganic particles or other inorganic particles may be added at up to about 50% of the weight of the milled slurry of step c, and more preferably, less than about 25% of the weight of the milled slurry.

[0026] For some applications, it may be desired to have even smaller particle sizes or a specific particle size distribution. In this case, it may be useful to further mill the milled slurry of step c or the dewatered filter cake of step c2. In one aspect, the process comprises secondary milling step c1 : milling the milled slurry to form a milled product slurry. The milling step d may be performed by the same processes used in step c. In one aspect, step c1 is performed by media mill, sand mill,TI0013-W001 immersion mill, or basket mill. In one aspect, the milling process components are selected to further reduce the particle size D50 of the treated inorganic particles. For example, in a media mill, the media may be selected to be different than the media of step c, such that a smaller particle size is achieved.

[0027] The milled slurry from step c, or the further milled slurry from step c1 , is optionally subjected to a water removal step to form a dewatered filter cake having 60-85% by weight treated inorganic oxide particles in water (c2). If a water removal step is employed, it occurs prior to the contacting step d, such that step d is performed on the dewatered filter cake taking the form of the milled slurry. Water removal is performed by any suitable mechanical means, as opposed to drying by heat treatment, to optimize energy efficiency. For example, water may be removed by filtration or centrifuge methods, where filtration includes but is not limited to filtration by filter press, cross-flow filter, or belt filter. Water is partially but not completely removed in this step. In one aspect, the dewatered filter cake contains 65-85% by weight treated inorganic oxide particles in water; in another aspect, the dewatered filter cake has 70-85% by weight treated inorganic oxide particles in water; and in another aspect, the dewatered filter cake has 75-81 % by weight treated inorganic oxide particles in water, all based on the total dewatered filter cake weight.

[0028] Because mechanical means are used to remove water, treated inorganic oxide particles may be present in the water that is removed from the milled slurry in step c2. In one aspect, the water removed from the milled slurry in step c2 may contain 5-100 g / L of treated inorganic oxide particles in water; in another aspect, the water removed from the milled slurry has 5-90 g / L treated inorganic oxide particles in water; and in another aspect, the water removed from the milled slurry has 10-75 g / L treated inorganic oxide particles in water, all based on the total removed water weight. This water removed from the milled slurry may be reintroduced into the process at any step, including to the initial slurry make-up of inorganic oxide particles, the aqueous treatment step a, the washing step b, the milling step c, or the dewatering step c2. This reintroduction step would serve to maximize yield of the treated inorganic oxide particles, reduce waste, and / or reduce total water usage. In one aspect, the water removed from the milled slurry in step c2 is recycled and combined with the treated inorganic oxide particles during the washing step b. In one aspect of this process, the water removed from the milled slurry may be combinedTI0013-W001 with a separate water source to form the water for washing the treated inorganic oxide particles in washing step b.

[0029] In one aspect, a processing aid is added to the dewatered filter cake or product slurry. Such a processing aid may be added during the dewatering or contacting step or after the dewatering or contacting step but before an additional milling step. In some cases, the processing aid may be the same dispersant of step d. Such a processing aid may help with further milling or may help with general processing and handling of the slurry, such as to lower viscosity or increase solids content. Examples of processing aids include but are not limited to dispersants, surfactants, or pigment stabilizers; more specific examples include inorganic processing aids, including but not limited to silicates or alkali metal phosphates; small organic molecule processing aids; or polymeric processing aids, including but not limited to those having carboxylic acid groups for anchoring orthose having molecular weights between 1 ,000 and 10,000. Specific examples of inorganic processing aids include but are not limited to sodium pyrophosphate or sodium hexametaphosphate; and specific examples of small organic processing aids include but are not limited to citric acid. Specific examples of polymeric processing aids include but are not limited to dispersants sold by Dow Chemical under the Tamol™ brand, such as Tamol-851 ™, Tamol-1124™, Tamol-731A™, or Tamol-165A™; dispersants sold by Arkema under the Coadis™ brand, such as Coadis 144A™; and dispersants sold by Byk under the Disperbyk™ brand, such as Disperbyk 191 ™.

[0030] For some applications, it may be desired to have even smaller particle sizes or a specific particle size distribution. In this case, it may be useful to further mill the product slurry. In one aspect, the process comprises step f: milling the product slurry to form a milled product slurry. The milling step f may be performed by the same processes used in step c. In one aspect, step f is performed by media mill, sand mill, immersion mill, or basket mill. In one aspect, the milling process components of step f are selected to further reduce the particle size D50 of the treated inorganic particles. For example, in a media mill, the media may be selected to be different than the media of step c or d , such that a smaller particle size is achieved. In one aspect, the process comprises at least one of step c1 or step f.

[0031] The process of the current invention results in a treated inorganic oxide particle slurry, where water is the carrier medium for the slurry. In one aspect, theTI0013-W001 process of the current invention excludes the step of jet milling the inorganic particles in any form. Jet milling, or fluid-energy milling, uses super-heated air or steam to grind the particles at high velocity, which requires a lot of energy. Because of the lack of jet milling used in this process, the process and resulting treated inorganic oxide particle slurry have a low carbon dioxide emission (CC e) value. In one aspect, the process steps a-d have a CC e value of less than 0.4 tons CC e per ton inorganic oxide according to Equation A-1 in 40 CFR Part 98 of the US Environmental Protection Agency. In another aspect, the process steps a-e have a CCtee value of less than 0.2 tons CChe per ton inorganic oxide according to Equation A-1 in 40 CFR Part 98 of the US Environmental Protection Agency.

[0032] The final treated inorganic oxide particle slurry may be used in several applications, including in coatings such as architectural coatings, where it is combined with a coating base to form a pigmented coating; or it may be used in paper or paper slurry products, where it is combined with a paper slurry to form a paper or pigmented paper slurry. Preferred architectural coatings include emulsion paints where water is the liquid carrier, including but not limited to exterior paint, interior paint, or specialty paints. Drying the final slurry may result in dry pigment that can be used in still further applications.EXAMPLES

[0033] Tamol™ 1 124 is a dispersant product having a solids content of 50% by weight, available from Dow, Midland, Ml.

[0034] ZirPro ER-120S ceramic beads were used, having a size of 0.8-1 .0 mm, available from Saint-Gobain, Malvern, PA.Viscosity

[0035] Viscosity (cP) was measured using a Brookfield viscometer using spindle 3 at a shear rate of 100 rpm.

[0036] Viscosity (cm deflection) was measured using a Hercules Hi-Shear Viscometer using an “A” bob and 50,000 dyne cm / cm spring set at a shear rate of 500 rpm.TI0013-W001Particle Size Distribution (PSD)

[0037] A dispersing solution of 0.4 g / L tetrapotassium pyrophosphate was mixed. The samples were mixed with the dispersing solution to form a mixture at 2.4% by weight solids. Samples were sonicated, and PSD was measured and calculated using a particle size analyzer, HORIBA LA-300 analyzer.Relative Tint Strength (RTS)

[0038] Tint Strength is a function of the light scattering of a pigment. A paint base was mixed with 2.2 lbs inorganic oxide particles per gallon of paint base, and a colorant was added to give approximately 55% ± 5 reflectance. The samples were mixed using a Speedmixer® DAC 1100.1 FVZ-HV (Hauschild, Farmington Hills, Ml) and drawn down onto a 5.5-in x 11.25-in Leneta Form WM card using a drawdown blade with 0.006 in clearance. The paint films were allowed to dry for at least 2 hours, and the reflectance of the samples were recorded as R°° using a Labscan® XE optical instrument (HunterLab, Reston, VA). The reported R°° was an average of 3 readings from the top, middle, and bottom of each sample. The R°° readings were used to calculate K / S values according to the equation: (100 - / ?oo)2200 X Rco

[0039] A control sample is measured to use in the calculation. RTS is then calculated as:K / S of controlRTS=_ x 100K / S of sampleHiding Power

[0040] Hiding Power is another function of the light scattering of a pigment. A paint base was mixed with a recorded amount of inorganic oxide particles per gallon of paint base. The samples were mixed using a Speedmixer® DAC 1100.1 FVZ-HV (Hauschild, Farmington Hills, Ml) and drawn down onto a tared Leneta Opacity Form 14H card using a drawdown blade with at most 0.006 in clearance. The paint films were allowed to dry overnight in an oven, and the reflectances Y of the samples were recorded in both the center of the white and black sections of the chart using a Labscan® XE optical instrument (HunterLab, Reston, VA). The wet film thickness inTI0013-W001 mils was calculated from the paint density, area of the drawdown, and tare weight of wet sample drawdown. The substrate reflectance Rg, white section reflectance R, and black section reflectance Ro were used to calculate Hiding Power s in units of 1 / mil using the Kubelka-Munk equations.Conductivity

[0041] Conductivity gives an indication of the amount of inorganic metal salts present in the mixture. A high conductivity indicates higher concentration of inorganic metal salts, while a lower conductivity indicates a lower concentration. Inorganic oxide particles (50 g) were mixed at room temperature with 250 ml_ of distilled water. A conductivity probe (Horiba DS-71 , Kyoto, Japan) was immersed in the mixture, and the measured conductivity was recorded.Preparation of Dried Particles

[0042] TiO2 particles containing about 1% by weight AI2O3 and 4% by weight NaCI were slurried with water to produce a mixture having about 25% solids. The slurry was treated with aqueous sodium silicate, sodium aluminate, and HCI to produce a TiO2 core particle with about 3% by weight SiC>2 and 2.7% by weight AI2O3 on the surface. The treated slurry was washed, milled in a media mill, and filtered on a rotary vacuum filter yielding a solids content of 40% by weight. The slurry was dried to form dried particles. The dried particles were analyzed for PSD and found to have PSD D50 of 0.526 microns and PSD 0.509 of 52.33%.Preparation of Milled Slurry

[0043] TiC>2 particles containing about 1% by weight AI2O3 and 4% by weight NaCI were slurried with water to produce a mixture having about 25% solids. The slurry was treated with aqueous sodium silicate, sodium aluminate, and HCI to produce a TiO2 core particle with about 3% by weight SiC>2 and 2.7% by weight AI2O3 on the surface. The treated slurry was washed, milled in a media mill, and filtered on a rotary vacuum filter yielding a milled slurry with a solids content of 40% by weight. The milled slurry was analyzed for PSD and found to have PSD D50 of 0.445 microns and PSD 0.509 of 38.33%.TI0013-W001Comparative Example A

[0044] A vessel was charged with Tamol 1124 (3.15 g), water (174 g), and 2- amino-2-methyl-1 -propanol (AMP, 1.1 g) and placed on a Dispermat™ fitted with a 60-mm diameter cowles blade. The mixture was set to grind at 2000 rpm while the dried particles (750 g) were slowly added. The mixture was stirred at 2000 rpm for 10 minutes, then water (51.9 g) was added while stirring at 1000 rpm. The mixture was screened (No. 325, 45 pm) before an antimicrobial (0.75 g) was added, resulting in a product slurry. The product slurry was tested according to the Test Methods above. This example represents a process, where the washing step followed the milling step.Example 1

[0045] The dried particles (200 g) were further washed by placing in a 500-mL plastic bottle with water (200 g) and shaking by hand. The resulting slurry was centrifuged at 9000 rpm for 20 minutes, and the amount of water that was removed was replaced with the same amount of clean water. The slurry was shaken again by hand and centrifuged a second time at 9000 rpm for 20 minutes to yield an inorganic oxide particle dewatered filter cake. The filter cake had a PSD D50 of 0.489 and PSD 0.509 of 46.7. The filter cake was dried overnight at 110 °C.

[0046] A vessel was charged with Tamol 1124 (3.15 g), water (174 g), and AMP (1.1 g) and placed on a Dispermat™ fitted with a 60-mm diameter cowles blade. The mixture was stirred at 2000 rpm while the dried particles of the filter cake (750 g) were slowly added. The mixture was stirred at 2000 rpm for 10 minutes, then water (51.9 g) was added while stirring at 1000 rpm. The mixture was screened (No. 325, 45 pm) before an antimicrobial (0.75 g) was added, resulting in a product slurry. The product slurry was tested according to the Test Methods above.Comparative Example B

[0047] The dried particles (200 g) were further washed by placing in a 500-mL plastic bottle with water (200 g) and shaking by hand. The resulting slurry was centrifuged at 9000 rpm for 20 minutes, and the amount of water that was removed was replaced with the same amount of clean water. The slurry was shaken again by hand and centrifuged a second time at 9000 rpm for 20 minutes to yield an inorganicTI0013-W001 oxide particle dewatered filter cake. The filter cake had a PSD D50 of 0.489 and PSD 0.509 of 46.7.

[0048] A vessel was charged with the dewatered filter cake (708.4 g), Tamol 1124 (3.15 g), and AMP (1.1 g) and placed on a Dispermat™ fitted with a 60-mm diameter cowles blade. The mixture was set to stir at 2000 rpm while the dried particles (215.8 g) were slowly added. The mixture was stirred at 2000 rpm for 10 minutes, then water (51 .9 g) was added while stirring at 1000 rpm. The mixture was screened (No. 325, 45 pm) before an antimicrobial (0.75 g) was added, resulting in a product slurry. The product slurry was tested according to the Test Methods above. This example represents a process, where the washing step followed the milling step and slurry step e was performed using wet particles rather than dried particles.Example 2

[0049] The milled slurry (400 g) was further washed by placing in a 500-mL plastic bottle and shaking by hand. The resulting slurry was centrifuged at 9000 rpm for 20 minutes, and the amount of water that was removed was replaced with the same amount of clean water. The slurry was shaken again by hand and centrifuged a second time at 9000 rpm for 20 minutes to yield an inorganic oxide particle dewatered filter cake. The filter cake had a PSD D50 of 0.432 and PSD 0.509 of 35.24. The filter cake was dried overnight at 110 °C.

[0050] A vessel was charged with Tamol 1124 (3.15 g), water (174 g), and AMP (1.1 g) and placed on a Dispermat™ fitted with a 60-mm diameter cowles blade. The mixture was stirred at 2000 rpm while the dried particles of the filter cake (750 g) were slowly added. The mixture was stirred at 2000 rpm for 10 minutes, then water (51.9 g) was added while stirring at 1000 rpm. The mixture was screened (No. 325, 45 pm) before an antimicrobial (0.75 g) was added, resulting in a product slurry. The product slurry was tested according to the Test Methods above.Comparative Example C

[0051] The milled slurry (400 g) was further washed by placing in a 500-mL plastic bottle and shaking by hand. The resulting slurry was centrifuged at 9000 rpm for 20 minutes, and the amount of water that was removed was replaced with the same amount of clean water. The slurry was shaken again by hand and centrifuged aTI0013-W001 second time at 9000 rpm for 20 minutes to yield an inorganic oxide particle dewatered filter cake. The filter cake had a PSD D50 of 0.432 and PSD 0.509 of 35.24.

[0052] A vessel was charged with the dewatered filter cake (693.3 g), Tamol 1124 (3.15 g), and AMP (1.1 g) and placed on a Dispermat™ fitted with a 60-mm diameter cowles blade. The mixture was set to stir at 2000 rpm while the dried particles (218.3 g) were slowly added. The mixture was stirred at 2000 rpm for 10 minutes, then water (51 .9 g) was added while stirring at 1000 rpm. The mixture was screened (No. 325, 45 pm) before an antimicrobial (0.75 g) was added, resulting in a product slurry. The product slurry was tested according to the Test Methods above. This example represents a process, where no drying step or further milling was performed.Example 3

[0053] The dried particles (200 g) were further milled by placing in a 500-mL plastic bottle with water (200 g) and ceramic beads (1 .15 x total mass), and the mixture was shaken for 2 hours on a Red Devil paint shaker. The resulting slurry was screened twice (No. 35, 500 pm followed by No 325, 45 pm) and centrifuged at 9000 rpm for 20 minutes. The filter cake had a PSD D50 of 0.388 and PSD 0.509 of 24.04. The dewatered filter cake was dried overnight at 110 °C.

[0054] A vessel was charged with Tamol 1124 (2.49 g), water (137.3 g), and AMP (0.87 g) and placed on a Dispermat™ fitted with a 60-mm diameter cowles blade.The mixture was stirred at 2000 rpm while the dried particles of the filter cake (592 g) were slowly added. The mixture was stirred at 2000 rpm for 10 minutes, then water (41 g) was added while stirring at 1000 rpm. The mixture was screened (No. 325, 45 pm) before an antimicrobial (0.59 g) was added, resulting in a final slurry. The final slurry was tested according to the Test Methods above.Comparative Example D

[0055] The dried particles (200 g) were further milled by placing in a 500-mL plastic bottle with water (200 g) and ceramic beads (1 .15 x total mass), and the mixture was shaken for 2 hours on a Red Devil paint shaker. The resulting slurry was screened twice (No. 35, 500 pm followed by No 325, 45 pm) and centrifuged at 9000 rpm for 20 minutes to yield an inorganic oxide particle dewatered filter cake having aTI0013-W001 solids content of 77.67% by weight. The filter cake had a PSD D50 of 0.388 and PSD 0.509 of 24.04.

[0056] A vessel was charged with the dewatered filter cake (801.4 g), Tamol 1124 (3.24 g), and AMP (1.13 g) and placed on a Dispermat™ fitted with a 60-mm diameter cowles blade. The mixture was set to stir at 2000 rpm while additional dried particles (149 g) was slowly added. The mixture was stirred at 2000 rpm for 10 minutes, then water (53.4 g) was added while stirring at 1000 rpm. The mixture was screened (No. 325, 45 pm) before an antimicrobial (0.77 g) was added, resulting in a product slurry. The product slurry was tested according to the Test Methods above. This example represents a process, where the washing step followed the milling step and the slurry step e was performed using wet particles rather than dried particles.Example 4

[0057] The milled slurry (400 g) was further milled by placing in a 500-mL plastic bottle with ceramic beads (1 .15 x total mass), and the mixture was shaken for 2 hours on a Red Devil paint shaker. The resulting slurry was screened twice (No. 35, 500 pm followed by No 325, 45 pm) and centrifuged at 9000 rpm for 20 minutes. The filter cake had a PSD D50 of 0.366 and PSD 0.509 of 17.40. The dewatered filter cake was dried overnight at 110 °C.

[0058] A vessel was charged with Tamol 1124 (3.2 g), water (174 g), and AMP (1.1 g) and placed on a Dispermat™ fitted with a 60-mm diameter cowles blade. The mixture was stirred at 2000 rpm while the dried particles of the filter cake (592 g) were slowly added. The mixture was stirred at 2000 rpm for 10 minutes, then water (41 g) was added while stirring at 1000 rpm. The mixture was screened (No. 325, 45 pm) before an antimicrobial (0.59 g) was added, resulting in a final slurry having 76.56% solids by weight. The final slurry was tested according to the Test Methods above.Comparative Example E

[0059] The milled slurry (400 g) was further milled by placing in a 500-mL plastic bottle with ceramic beads (1 .15 x total mass), and the mixture was shaken for 2 hours on a Red Devil paint shaker. The resulting slurry was screened twice (No. 35, 500 pm followed by No 325, 45 pm) and centrifuged at 9000 rpm for 20 minutes toTI0013-W001 yield an inorganic oxide particle dewatered filter cake having a solids content of 77.67% by weight. The filter cake had a PSD D50 of 0.388 and PSD 0.509 of 24.04.

[0060] A vessel was charged with the dewatered filter cake (696 g), Tamol 1124 (3.2 g), and AMP (1.1 g) and placed on a Dispermat™ fitted with a 60-mm diameter cowles blade. The mixture was set to stir at 2000 rpm while additional dried particles (279.6 g) was slowly added. The mixture was stirred at 2000 rpm for 10 minutes, then water (51 .9 g) was added while stirring at 1000 rpm. The mixture was screened (No. 325, 45 pm) before an antimicrobial (0.75 g) was added, resulting in a product slurry having 76.58% solids by weight. The product slurry was tested according to the Test Methods above. This example represents a process, where no drying step was performed.Example 5

[0061] Example 3 was repeated, except the milled slurry mixture was shaken for 4.5 hours on a Red Devil paint shaker. The filter cake had a PSD D50 of 0.349 and PSD 0.509 of 12.97. The product slurry was tested according to the Test Methods above.Comparative Example F

[0062] Comparative Example D was repeated, except the dried particles were shaken for 4.5 hours on a Red Devil paint shaker. The filter cake had a PSD D50 of 0.349 and PSD 0.509 of 12.97. The inorganic oxide particle dewatered filter cake had a solids content of 74.94% by weight.

[0063] A vessel was charged with the dewatered filter cake (694.33 g), Tamol 1124 (3.15 g), and AMP (1.1 g) and placed on a Dispermat™ fitted with a 60-mm diameter cowles blade. The mixture was set to stir at 2000 rpm while additional dried particles (229.7 g) and water (15 g) were slowly added. The mixture was stirred at 2000 rpm for 10 minutes, then water (36.9 g) was added while stirring at 1000 rpm. The mixture was screened (No. 325, 45 pm) before an antimicrobial (0.75 g) was added. The product slurry was tested according to the Test Methods above. This example represents a process, where the washing step followed the milling step and slurry step e was performed using wet particles rather than dried particles.TI0013-W001Example 6

[0064] Example 4 was repeated, except the milled slurry mixture was shaken for 4.5 hours on a Red Devil paint shaker. The filter cake had a PSD D50 of 0.341 and PSD 0.509 of 10.97. The product slurry was tested according to the Test Methods above.Comparative Example G

[0065] Comparative Example E was repeated, except the milled slurry mixture was shaken for 4.5 hours on a Red Devil paint shaker. The filter cake had a PSD D50 of 0.341 and PSD 0.509 of 10.97. The inorganic oxide particle dewatered filter cake had a solids content of 74.94% by weight.

[0066] A vessel was charged with the dewatered filter cake (623.77 g), water (20.6 g), Tamol 1124 (3.2 g), and AMP (1 .1 g) and placed on a Dispermat™ fitted with a 60-mm diameter cowles blade. The mixture was set to stir at 2000 rpm while additional dried particles (279.6 g) were slowly added. The mixture was stirred at 2000 rpm for 10 minutes, then water (36.9 g) was added while stirring at 1000 rpm. The mixture was screened (No. 325, 45 pm) before an antimicrobial (0.75 g) was added. The product slurry was tested according to the Test Methods above. This example represents a process, where no drying step was performed.Table 1. Performance Data for Examples 1-3 and Comparative Examples A-D

[0067] The performance data in Table 1 demonstrates that the drying step just prior to the slurry step (e) is essential to reducing viscosity of the product slurry while also maintaining high solids, tint strength, and hiding power. The high viscosity ofTI0013-W001Comparative Example A indicates the significance of having a PSD 0.509 <50% entering slurry step e. As can be seen in Comparative Example F, the additional long milling step does reduce the viscosity to some degree, but the addition of the drying step shows an even further reduction (Examples 5 and 6). It can also be seen that having a lower PSD 0.509 before slurry step (e), such as lower than 50%, reduces viscosity as well.Preparation Example 1

[0068] TiO2 particles containing about 1% by weight AI2O3 and 4% by weight NaCI were slurried with water to produce a mixture having about 25% solids. The slurry was treated with aqueous sodium silicate, sodium aluminate, and HCI to produce a TiO2 core particle with about 3% by weight SiC>2 and 2.7% by weight AI2O3 on the surface. The treated slurry was filtered on a rotary vacuum filter yielding a solids content of 40% by weight. The slurry was milled in a media mill to yield a milled slurry. The milled slurry (175 g) was further washed by placing in a 500-mL plastic bottle with water (175 g) and shaking by hand for 5 minutes. The resulting slurry was centrifuged at 9000 rpm for 20 minutes, and the removed water (104 g) was tested for conductivity. The conductivity was found to be 0.129 mS / cm.

[0069] Another portion of water (104 g) was added to the slurry, mixed, and the sample was centrifuged again at 9000 rpm for 20 minutes. The decanted water was tested for conductivity and found to be 0.07 mS / cm. This indicates the importance of washing steps to reduce residual salt content.Preparation Example 2

[0070] TiC>2 particles containing about 1% by weight AI2O3 and 4% by weight NaCI were slurried with water to produce a mixture having about 25% solids. The slurry was treated with aqueous sodium silicate, sodium aluminate, and HCI to produce a TiO2 core particle with about 3% by weight SiC>2 and 2.7% by weight AI2O3 on the surface. The treated slurry was filtered on a rotary vacuum filter yielding a solids content of 40% by weight. The slurry was milled in a media mill to yield a milled slurry. The milled slurry (350 g) was further washed by placing in a 500-mL plastic bottle with water (175 g) and shaking by hand for 5 minutes. The resulting slurry was centrifuged at 9000 rpm for 20 minutes, and the removed water (216 g) was tested for conductivity. The conductivity was found to be 0.159 mS / cm.TI0013-W001

[0071] Another portion of water (216 g) was added to the slurry, mixed, and the sample was centrifuged again at 9000 rpm for 20 minutes. The decanted water was tested for conductivity and found to be 0.03 mS / cm. This indicates the importance of washing steps to reduce residual salt content.

Claims

TI0013-W001CLAIMSWhat is claimed is:

1. A process of producing a treated inorganic oxide slurry comprising: a. treating an inorganic oxide particle with at least one aqueous inorganic metal salt to form a treated inorganic oxide particle; b. washing the treated inorganic oxide particle with water and removing aqueous inorganic metal salt to form a washed slurry having 30-60% by weight treated inorganic oxide particles in water; c. milling the washed slurry to reduce the particle size of the treated inorganic oxide particles using a wet milling process to form a milled slurry having a PSD 0.509 of less than 50%; d. drying the milled slurry to form a dried particle; and e. contacting the dried particle with water and dispersant to form a product slurry.

2. The process of claim 1 , where the inorganic oxide particle is selected from oxides of Ti, Al, Zn, Cu, Fe, Mn, or Si.

3. The process of claim 1 , where the inorganic oxide particle is TiC>2.

4. The process of claims 1-3, where the aqueous inorganic metal salt is a compound containing Al, Si, Zr, Ba, orZn.

5. The process of claims 1-4, where the removing aqueous inorganic metal salt step in washing step b includes using rotary vacuum filter, belt filter, or filter press.

6. The process of claims 1-5, where the milling step c is performed by media mill, sand mill, immersion mill, or basket mill.

7. The process of claims 1-6, where the washed slurry or milled slurry further comprises a processing aid.

8. The process of claim 7, where the processing aid is selected from a dispersant, surfactant, or pigment stabilizer.TI0013-W0019. The process of claims 1-8, further comprising step c2 of removing water from the milled slurry to form a dewatered filter cake having 60-85% by weight treated inorganic oxide particles in water, where step d is performed on the dewatered filter cake.

10. The process of claim 9, where the water removal step c2 is performed by filtration or centrifuge.11 . The process of claim 10, where the water removal step c2 is performed by filter press, cross-flow filter, or belt filter.

12. The process of claims 9-11 , where the water removed from the milled slurry in step c2 is recycled and combined with the treated inorganic oxide particles during the washing step b, and wherein the water removed from the milled slurry in step c2 contains treated inorganic oxide particles.

13. The process of claims 1-12, further comprising the step: f. milling the product slurry of step e to form a milled product slurry.

14. The process of claim 13, where the milling step f is performed by media mill, sand mill, immersion mill, or basket mill.

15. The process of claims 1-14, where the treated inorganic oxide particle of treatment step a is in an aqueous mixture having 1-35% by weight treated inorganic oxide particles in water.

16. The process of claims 1-15, where the process excludes jet milling.

17. The process of claims 1-16, where the process of steps a-d have a carbon dioxide equivalent (CC e) of less than 0.4 tons CC e per ton inorganic oxide according to Equation A-1 in 40 CFR Part 98 of the US Environmental Protection Agency.

18. The process of claims 1-17, further comprising a secondary milling step c1 , where the milled slurry of step c is further milled.

19. The process of claim 18, where secondary milling step c1 is performed by media mill, sand mill, immersion mill, or basket mill.TI0013-W00120. The process of claims 1-19, where at least one additional milling step of step c1 or step f is performed.21 . The process of claims 1-20, where the product slurry has a viscosity of at most 900 cP and at most 5.00 cm deflection.

22. A treated aqueous inorganic oxide particle slurry produced by the process of claims 1-21 .

23. The process of claims 1 -21 , further comprising combining the product slurry or milled product slurry with a coating base to form a pigmented coating.

24. The process of claims 1 -21 , further comprising combining the product slurry or milled product slurry with a paper slurry to form a pigmented paper slurry.

25. A pigmented coating formed by the process of claim 23.

26. A paper slurry or paper formed by the process of claim 24.

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