Treated inorganic particles and process of making with improved rheology

Abstract

The present invention relates to a treated inorganic oxide particle having an IEP of about 6.5-8.0 having an inorganic oxide particle and a mixed surface treatment. The particles are made by a. providing inorganic oxide particles having inorganic oxide and alumina and / or silica; b. contacting the inorganic oxide particles with citric acid at a pH of about 5.0 to about 8.0; c. contacting the citric acid-treated inorganic oxide particles with an alkaline aluminum compound and compound selected from sulfuric acid, sulfate salt, phosphoric acid, or phosphate salt at a pH of about 6.5 to about 8.0; d. maintaining the pH for a period of time; and e. washing the alumina-treated inorganic oxide particles with water to form treated inorganic oxide particles, where the mixed surface treatment has about 0.20-5.00% by weight alumina (Al2O3), about 0.03-0.83% by weight citric acid, and about 0.02-0.50% by weight SO4 2- or PO4 3- in the same treatment layer.

Description

TI0015-W001TITLE OF THE INVENTIONTREATED INORGANIC PARTICLES AND PROCESS OF MAKING WITH IMPROVED RHEOLOGYCROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority of U.S. Provisional Application No. 63 / 716,781 filed November 6, 2024, claims the benefit of priority of U.S. Provisional Application No. 63 / 842,274 filed July 11 , 2025, 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 a treated inorganic oxide particle having improved rheology performance during processing. The process involves incorporating citric acid, an aluminum compound, and a compound selected from sulfuric acid, phosphoric acid, and / or salts thereof into a mixed surface treatment at a designated pH. The treated inorganic oxide particles can be further treated with organic treatments and dispersed into thermoplastics.BACKGROUND OF THE INVENTION

[0003] The rheology of TiO2 aqueous suspensions is a key factor in many application fields. Maintaining certain rheological properties during processing is critical to increasing speed and yield during filtration. One way to achieve this effect is by slurry dilution; however, this implies larger processing volumes and the need for larger equipment to maintain the production levels of TiO2 particles, causing an increase in needed materials and in operating and capital expenditures.

[0004] To minimize water use or to avoid the need to recover the process water for reuse, the TiO2 suspension should be as concentrated as possible. These modifications lead to variations of the electrostatic inter-particle interactions, thus influencing the suspension’s viscoelastic behavior, especially with adjustment in slurry pH used in some TiO2 particle designs. TiO2 suspensions were firstly formulated in water by adjusting the pH close to the isoelectric point of the TiO2 particles. The influence of the solids amount and pH are coupled to produce rheological properties of aqueous suspensions.TI0015-W001

[0005] Flocculated suspensions with a significant viscosity and a high yield stress are most often not desirable. Quite frequently, inventions are tuned to avoid this occurrence, such as in US Patent 6,558,464.

[0006] Several examples of high solids TiOs aqueous suspensions have been shown (US 5,653,793, US 6,558,464, or US 6,569,920). However, the treatment conditions adopted and the precipitation of a composite layer of alumina, sulfate, and citrate salt layer are not disclosed and do not demonstrate improved rheological properties during filtration.

[0007] US Patent 5,976,237 describes the production of TiO2 pigment with good dispersibility and optical properties for use in plastics and paint compositions. Three layers of coatings are described. The first coating is made of silica or alumina, an optional second coating is made of zirconia; tin oxide; ceria; or titania, and the third coating is made of alumina. The alumina treatment is conducted at a different pH. Sodium aluminate is added to an acidic slurry and the pH is adjusted to 3.5 and maintained under digestion, then to 5.75 and maintained under digestion, then to 6.5 and maintained under digestion, and finally to 7.0 and maintained under digestion. The pH adjustment at each step is done using NaOH, but the treatment conditions adopted and the precipitation of a composite layer of alumina sulfate, and citrate salt layer are not disclosed.

[0008] US Patent 6,656,261 describes substantially sulfate-free titanium dioxide pigments with improved gloss and / or durability and comprising alumina, zirconia, and optionally, phosphate compounds. Methods of making these pigments are also described. These pigments are useful in the manufacture of paints and plastics. This patent describes a method comprising wet treating titanium dioxide with, first, an alumina compound to form an alumina layer, followed sequentially by wet treatment with a zirconia compound to form a zirconia layer. The treatment conditions adopted and the precipitation of a composite layer of aluminum sulfate, and citrate salt layer are not disclosed and do not demonstrate improved rheological properties.

[0009] US Patent 7,135,065 describes a post-treatment of TiO2 to obtain weatherresistant pigment with good optical properties. The pigment is coated sequentially with hydrous tin and zirconium. At least one other component from silicon and titanium is additionally precipitated on the pigment particle surface. Then, a finalTI0015-W001 layer of alumina is precipitated. The post treatment components are added to the aqueous TiO2. Suspension occurs at either an acidic pH range (pH 3.0) or in an alkaline pH range (pH 10.0). The pH value is subsequently set to 6.0 to 8.0 before sodium aluminate / aluminum sulphate addition. However, the treatment conditions adopted and the precipitation of a composite layer of alumina sulfate, and citrate salt layer are not disclosed and do not demonstrate improved rheological properties.

[0010] US Patent 7,238,231 describes a zirconia-treated TiO2 pigment in which the zirconia treatment is performed after re-dispersing a washed semisolid filter cake of silica and alumina-treated TiC>2 pigment using ammonium zirconyl carbonate. The resultant pigment is then spray dried. However, the treatment conditions adopted and the precipitation of a composite layer of alumina sulfate, and citrate salt layer are not disclosed and do not demonstrate improved rheological properties.

[0011] US Patent 8, 105,432 describes a method for making high-durability and easily dispersed pigment by adding citric acid to stabilize amorphous alumina. The combination of silica and citric acid-stabilized alumina is described as the cause of improved dispersion and durability. The precipitation of silica and alumina is done at various controlled pH levels by using either NaOH or HCI at 95°C. However, the treatment conditions adopted and the precipitation of a composite layer of alumina sulfate, and citrate salt layer are not disclosed and do not demonstrate improved rheological properties.SUMMARY OF THE INVENTION

[0012] Despite prior references targeting the optimization of high solids content TiO2 suspensions, sometimes by using alumina stabilized by organic acid, further improvements are continually being sought. In none of the aforementioned references are the benefits to optimize rheological properties taught.

[0013] The present invention shows that with proper elemental surface design on a TiO2 particle, rheological properties, isoelectric point (I EP), and Nujol yellowing can be refined. The processing of high solids slurries is possible only if the rheology or the nature of surface forces operating between particles can be controlled effectively. A second feature of this invention is providing an innovative elemental surface composition to induce a flocculated suspension without the use of organic dispersant additives or organic solvents.TI0015-W001

[0014] The process described herein provides improved processing rheology by adjusting elemental composition of the surface treatments. The present invention relates to a process of producing a treated inorganic oxide particle comprising: a. providing inorganic oxide particles in aqueous suspension at a pH of about 5.0 to about 8.0, where the inorganic oxide particles comprise an inorganic oxide and either alumina or a mixture of alumina and silica; b. contacting the inorganic oxide particles with citric acid to form citric acid- treated inorganic oxide particles at a pH of about 5.0 to about 8.0; c. contacting the citric acid-treated inorganic oxide particles with an alkaline aluminum compound and a compound selected from sulfuric acid, sulfate salt, phosphoric acid, or phosphate salt at a pH of about 6.5 to about 8.0, alternatively about 6.5 to about 7.5, to form alumina-treated inorganic oxide particles; d. maintaining the pH to about 6.5 to about 8.0, alternatively about 6.5 to about 7.5, for a period of time; and e. washing the alumina-treated inorganic oxide particles with water to form treated inorganic oxide particles having an isoelectric point (I EP) of about 6.5- 8.0 and comprising a mixed surface treatment, where the mixed surface treatment comprises about 0.20-5.00% by weight alumina (AI2O3), about 0.03-0.83% by weight citric acid, and about 0.02-0.50% by weight SO42- or PO43; alternatively about 0.04-0.05% by weight) SO2-or PO43; all based on the total weight of the treated inorganic oxide particle, in the same treatment layer.

[0015] The present invention further relates to a treated inorganic oxide particle having an IEP of about 6.5-8.0 comprising an inorganic oxide particle and a mixed surface treatment, where the inorganic oxide particles comprise an inorganic oxide and either alumina or a mixture of alumina and silica; and the mixed surface treatment comprises about 0.20-5.00% by weight alumina (AI2O3), about 0.03-0.83% by weight citric acid, and about 0.02-0.50% by weight SO42' or PO43; alternatively about 0.04-0.50% by weight SC2-or PO43; all based on the total weight of the treated inorganic oxide particle, in the same treatment layer.

[0016] The treated inorganic oxide particle can further be treated with an organic treatment to aid in dispersibility. Thus, the present invention further relates to anTI0015-W001 organic-treated inorganic oxide particle having an IEP of about 6.5-8.0 comprising an inorganic oxide particle, a mixed surface treatment, and an organic surface treatment, where the inorganic oxide particles comprise an inorganic oxide and either alumina or a mixture of alumina and silica; the mixed surface treatment is on the surface of the inorganic oxide particle; the organic surface treatment is on the surface of the mixed surface treatment; and the mixed surface treatment comprises about 0.20-5.00% by weight alumina (AI2O3), about 0.03-0.83% by weight citric acid, and about 0.02-0.50% by weight SO2' or P3; alternatively about 0.04-0.50% by weight SO42' or PC3', all based on the total weight of the treated inorganic oxide particle, in the same treatment layer.DETAILED DESCRIPTION OF THE INVENTION

[0017] The process described herein provides improved processing rheology by adjusting elemental composition of the surface treatments. The present invention relates to a process of producing a treated inorganic oxide particle comprising: a. providing inorganic oxide particles in aqueous suspension at a pH of about 5.0 to about 8.0, where the inorganic oxide particles comprise an inorganic oxide and either alumina or a mixture of alumina and silica; b. contacting the inorganic oxide particles with citric acid to form citric acid- treated inorganic oxide particles at a pH of about 5.0 to about 8.0; c. contacting the citric acid-treated inorganic oxide particles with an alkaline aluminum compound and a compound selected from sulfuric acid, sulfate salt, phosphoric acid, or phosphate salt at a pH of about 6.5 to about 8.0, alternatively about 6.5 to about 7.5, to form alumina-treated inorganic oxide particles; d. maintaining the pH to about 6.5 to about 8.0, alternatively about 6.5 to about 7.5, for a period of time; and e. washing the alumina-treated inorganic oxide particles with water to form treated inorganic oxide particles having an isoelectric point (IEP) of about 6.5- 8.0 and comprising a mixed surface treatment, where the mixed surface treatment comprises about 0.20-5.00% by weight alumina (AI2O3), about 0.03-0.83% by weight citric acid, and about 0.02-0.50% by weight SO42' or PO43, alternatively about 0.04-0.05% by weight) SC>42' or PC>43', all basedTI0015-W001 on the total weight of the treated inorganic oxide particle, in the same treatment layer.

[0018] 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 TiCh, AI2O3, ZnO, CuO, Fe2O3, MnO, MnsCM, Mn2O3, MnC>2, MnOs, Mn2O?, or SiCh. Blends or mixtures of inorganic oxides may also be used. Such compounds may be in any particle form. For example, TO2 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.

[0019] The inorganic oxide particle of step a has one or more additional inorganic oxides present, which are produced prior to being introduced in step a. This additional inorganic oxide comprises alumina or mixtures of silica and alumina, formed as part of the core inorganic oxide particle by any suitable method, including by oxidation of metal chloride or by condensed phase aqueous oxide. In one aspect, the additional inorganic oxide is formed by oxidation of metal chloride or by condensed phase aqueous oxide of an alumina-forming compound or by a mixture of silica- and alumina-forming compounds. In one aspect, the additional inorganic oxide is formed with the formation of the core particle, such as by oxidizing TiCk with AICI3 and / or SiCk Such a method would form a pyrogenic inorganic oxide of alumina or pyrogenic mixed silica and alumina.

[0020] In one aspect, a mixture of alumina and silica is present in a weight ratio of at least about 2:1 alumina:silica; in another aspect, at least about 3:1 ; in another aspect, at least about 4:1 ; and in another aspect, at least about 5:1 . In one aspect, aTI0015-W001 mixture of alumina and silica is present in a weight ratio of at most about 20:1 alumina:silica; in another aspect, at most about 18: 1 ; in another aspect, at most about 15:1 ; and in another aspect, at most about 12:1. In one aspect, the alumina is present in the form of AI2O3 in the inorganic oxide particle of step a in at least about 0.5% by weight; in another aspect, at least 0.7% by weight; and in another aspect, at least 0.9% by weight. In one aspect, the alumina is present in the form of AI2O3 in the inorganic oxide particle of step a in at most about 2.0% by weight; in another aspect, at most 1 .5% by weight; and in another aspect, at most 1 .4% by weight. In one aspect, the silica is present in the form of SiC>2 in the inorganic oxide particle of step a in at least about 0.05% by weight; in another aspect, at least 0.10% by weight; and in another aspect, at least 0.15% by weight. In one aspect, the silica is present in the form of SiO2 in the inorganic oxide particle of step a in at most about 0.50% by weight; in another aspect, at most 0.30% by weight; and in another aspect, at most 0.25% by weight.

[0021] The inorganic oxide particle of step a may have additional inorganic oxide treatments on the surface of the core inorganic oxide particle prior to being introduced in step b. Typical oxide include oxides of Ti, Al, Zn, Cu, Fe, Mn, or Si, such as TiO2, AI2O3, ZnO, CuO, Fe2Os, MnO, MnsC , Mn2O3, MnC , MnOs, Mn2O?, or SiC>2. 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.

[0022] The inorganic oxide particles of step a are provided as an aqueous suspension at a pH of about 5.0 to about 8.0. After forming the inorganic oxide particles, they may be introduced into an aqueous suspension by any means, such as by mixing with water. 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, or 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). Shear may be used and varied to achieve the desired suspension properties. In one aspect, theTI0015-W001 pH is adjusted with acid or base to achieve the desired pH. In one aspect, the pH is about 6.5 to about 7.5.

[0023] The inorganic oxide particles are contacted in step b with citric acid at a pH of about 5.0 to about 8.0 to form citric acid-treated inorganic oxide particles. In one aspect, the pH in step b is from about 5.0 to about 7.5; in another aspect, the pH in step b is from about 6.0 to about 7.5; and in another aspect, the pH in step b is about 6.5 to about 7.5. When adding the citric acid, the pH may drop below the range of 5.0 to 8.0, and a base, such as NaOH, may be used to increase the pH before moving to the next addition. An elevated temperature may be used to aid in mixing and coating. In one aspect, step b is performed at a temperature of at most about 95 °C; in another aspect, at most about 70 °C; in another aspect, at most about 65 °C; in another aspect, at most about 60 °C; and in another aspect, at most about 55 °C. In one aspect, step b is performed at a temperature of at least about 20 °C; in another aspect, at least about 25 °C; in another aspect, at least about 30 °C; and in another aspect, at least about 40 °C. In some aspects, additives such as fluoride compounds are used during this step. In one aspect, no fluoride compounds are used in any part of the process for making the treated inorganic oxide particles, such that the end product would have no detectable fluoride content.

[0024] Following step b, the citric acid-treated inorganic oxide particles are contacted with an alkaline aluminum compound and a compound selected from sulfuric acid, sulfate salt, phosphoric acid, or phosphate salt at a pH of about 6.5 to about 8.0, alternatively about 6.5 to about 7.5; to form alumina-treated inorganic oxide particles (step c). More than one alkaline aluminum compound may be used if desired. The alkaline aluminum compound yields an inorganic oxide layer and can be selected from any alkaline compound capable of forming alumina under the pH conditions, including but not limited to alkali metal aluminum salts. Because of the use of citric acid with sulfuric acid, sulfate salts, phosphoric acid, or phosphate salts, the inorganic oxide layer formed is a mixed surface treatment layer containing citric acid, SO42' or PC3', and alumina AI2O3. The sulfate salts may be any salt capable of forming SO42-on the particle surface, including but not limited to alkali sulfates or bisulfates, alkaline earth sulfates, or aluminum sulfates. The phosphate salts may be any salt capable of forming PC>43' on the particle surface, including but not limited to alkali phosphates, alkaline earth phosphates, or aluminum phosphates. An elevatedTI0015-W001 temperature may be used to aid in mixing and coating. In one aspect, step c is performed at a temperature of at most about 95 °C; in another aspect, at most about 70 °C; in another aspect, at most about 65 °C; in another aspect, at most about 60 °C; and in another aspect, at most about 55 °C. In one aspect, step c is performed at a temperature of at least about 20 °C; in another aspect, at least about 25 °C; in another aspect, at least about 30 °C; and in another aspect, at least about 40 °C.

[0025] The pH is maintained at about 6.5 to about 8.0, alternatively about 6.5 to about 7.5, for a period of time in step d to set and cure the mixed surface treatment. An elevated temperature may be used to aid in this process. In one aspect, step d is performed at a temperature of at most about 95 °C; in another aspect, at most about 70 °C; in another aspect, at most about 65 °C; in another aspect, at most about 60 °C; and in another aspect, at most about 55 °C. In one aspect, step d is performed at a temperature of at least about 20 °C; in another aspect, at least about 25 °C; in another aspect, at least about 30 °C; and in another aspect, at least about 40 °C. The period of time may be any time suitable to set and cure the mixed surface treatment. In one aspect, step d is performed for a at least about 10 minutes; in another aspect, step d is performed for at least about 15 minutes; in another aspect, step d is performed for at least about 20 minutes; in another aspect, step d is performed for at least about 30 minutes; in another aspect, step d is performed for at least about 40 minutes; in another aspect, step d is performed for at least about 45 minutes. The conditions of mixed surface treatment formation and curing provide particles having an I EP of at least about 6.5 and in another aspect, at least about 7.0. The IEP is at most about 8.0.

[0026] The alumina-treated inorganic oxide particles resulting from step d are then washed with water in step e. In one aspect, 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 e include those added in step c 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 e has a conductivity of at most about 500 microSiemens; and in another aspect, the washed slurry has a conductivity of at most about 250 microSiemens.TI0015-W001Such conductivity may be measured by a conductivity probe according to the Test Method described below.

[0027] Any suitable mechanical means of washing the alumina-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 may have a solids content of at least about 25% by weight; in another aspect, at least about 30% by weight; and in another aspect at least about 35% by weight treated inorganic oxide particles in water, based on the weight of total treated inorganic oxide particles in water. In one aspect, the treated inorganic oxide particles may have a solids content of at most about 75% by weight; in another aspect, at most about 65% by weight treated inorganic oxide particles in water, on the weight of total treated inorganic oxide particles in water; in another aspect, at most about 50% by weight treated inorganic oxide particles in water, on the weight of total treated inorganic oxide particles in water; and in another aspect, at most about 45% by weight treated inorganic oxide particles in water, on the weight of total treated inorganic oxide particles in water.

[0028] In one aspect, step e is performed at a temperature of at most about 95 °C; in another aspect, at most about 70 °C; in another aspect, at most about 65 °C; in another aspect, at most about 60 °C; and in another aspect, at most about 55 °C. In one aspect, step e is performed at a temperature of at least about 20 °C; in another aspect, at least about 25 °C; in another aspect, at least about 30 °C; and in another aspect, at least about 40 °C. In one aspect, steps b-e are all performed at a temperature of at most about 95 °C; in another aspect, at most about 70 °C; in another aspect, at most about 65 °C; in another aspect, at most about 60 °C; and in another aspect, at most about 55 °C. In one aspect, steps b-e are all performed at a temperature of at least about 20 °C; in another aspect, at least about 25 °C; in another aspect, at least about 30 °C; and in another aspect, at least about 40 °C.

[0029] The resulting treated inorganic oxide particles have a mixed surface treatment that comprises about 0.20-5.00% by weight alumina (AI2O3), about 0.03-TI0015-W0010.83% by weight citric acid, and about 0.02-0.50% by weight SO42' or PO43all based on the total weight of the treated inorganic oxide particle, in the same treatment layer. In one aspect, the mixed surface treatment comprises about 0.20- 5.00% by weight alumina (AI2O3), about 0.03-0.83% by weight citric acid, and about 0.04-0.50% by weight SO42' or PC>43', all based on the total weight of the treated inorganic oxide particle, in the same treatment layer. In one aspect, the mixed surface treatment comprises about 0.50-3.00% by weight alumina (AI2O3), about 0.08-0.50% by weight citric acid, and at least one of about 0.04-0.24% by weight SO42- or 0.04 to 0.30% by weight PC3', all based on the total weight of the treated inorganic oxide particle, in the same treatment layer; and in another aspect, the mixed surface treatment comprises about 1.00-2.50% by weight alumina (AI2O3), about 0.15-0.42% by weight citric acid, and at least one of about 0.08-0.20% by weight SO42- or PCU3', all based on the total weight of the treated inorganic oxide particle, in the same treatment layer. In one aspect, the mixed surface treatment comprises about 0.50-3.00% by weight alumina (AI2O3), about 0.08-0.50% by weight citric acid, and at least one of about 0.02-0.24% by weight SCU2' or 0.04 to 0.30% by weight PO43; all based on the total weight of the treated inorganic oxide particle, in the same treatment layer; and in another aspect, the mixed surface treatment comprises about 1 .00-2.50% by weight alumina (AI2O3), about 0.15-0.42% by weight citric acid, and at least one of about 0.04-0.20% by weight SO42' or PC3', all based on the total weight of the treated inorganic oxide particle, in the same treatment layer.

[0030] One or more additional wet treatments may be applied to the treated inorganic oxide particles before or after washing step e. 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 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 3.5-8.0; in another aspect, 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.TI0015-W001

[0031] In one aspect, the process further comprises step f: contacting the treated inorganic particles with an alkaline or acidic sulfate compound to form further treated inorganic particles. This step would form additional sulfate content on the particle. In one aspect, step f is performed at a pH of about 6.5 to about 8.0; alternatively, about 6.5 to about 7.5. In one aspect, the further treated inorganic oxide particle in step f comprises about 0.01-0.5% by weight further inorganic oxide treatment layer resulting from the treatment of step f, based on the total weight of the inorganic oxide particle; in another aspect, comprises about 0.05-0.3% inorganic oxide treatment layer resulting from the treatment of step f, based on the total weight of the inorganic oxide particle; and in a further aspect, comprises about 0.01-0.02% inorganic oxide treatment layer resulting from the treatment of step f, based on the total weight of the inorganic oxide particle.

[0032] The inorganic metal salt may be a compound containing Al, Si, Zr, Ba, Mg, or Zn. Such compounds can be used under certain conditions to precipitate inorganic oxides onto a particle. Sulfate compounds may include metal sulfates, alkali sulfates, or alkaline earth metal sulfates. Other 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, magnesium sulfate, or aluminum sulfate salts such as sodium aluminum sulfate or potassium aluminum sulfate; or metal halides and nitrates, such as aluminum chloride or nitrate. The further treated inorganic oxide particles may be washed according to the description above.

[0033] In one aspect, the process further comprises step g: drying the treated inorganic particles or further treated inorganic particles to form dried inorganic particles having a weight loss by TGA of less than 5.0% at 116 °C. 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 inorganic particles produced from the drying step have a water content of less than about 5% by weight; in another aspect, the dried inorganic particles have a water content of less than about 3% by weight; in another aspect, the dried inorganic particles have a water content of less than about 1 % by weight; and in another aspect, the dried inorganic particles have a water content of less than about 0.7% by weight, all based on the total weight of the dried inorganic particles.TI0015-W001

[0034] An organic treatment may also be applied to aid the dispersibility of the final product in different media. The organic treatment may be applied at any point after washing step e. In one aspect, the process further comprises step h: treating the treated inorganic particles, further treated inorganic particles, or dried inorganic particles with an organic compound to form organic-treated inorganic particles. The organic treatment may be applied by any means, such as by mixing the organic compound with the treated inorganic oxide particles in aqueous or dried forms. Following the organic treatment, the organic-treated inorganic particles may be dried and / or milled. In one aspect, the process further comprises step hi : drying the organic-treated inorganic particles to form dried organic-treated inorganic particles.

[0035] The organic compound may be any compound used in inorganic particle and pigment technologies as an organic treatment. The organic compound includes, but is not limited to, polyols, siliconates, carboxylic acids or carboxylic acid esters or salts thereof, alkanolamines, silanes, siloxanes, phosphonic acids, phosphates, phosphonates, phosphinic acids, sulfonic compounds, polyolefins, hydrocarbon amides, hydrocarbon waxes, or mixtures thereof. More specifically, the organic compound may include an organo-silane, an organo-siloxane, a fluoro-silane, an organo-phosphonate, an organo-acid phosphate, an organo-pyrophosphate, an organo-polyphosphate, an organo-metaphosphate, an organo-phosphonate, an organo-sulfonic compound, a hydrocarbon-based carboxylic acid, an associated ester of a hydrocarbon-based carboxylic acid, a derivative of a hydrocarbon-based carboxylic acid, a hydrocarbon-based amide, a low molecular weight hydrocarbon wax, a low molecular weight polyolefin, a co-polymer of a low molecular weight polyolefin, a hydrocarbon-based polyol, a derivative of a hydrocarbon-based polyol, an alkanolamine, a derivative of an alkanolamine, or an organic dispersing agent. The organic treatment may be present in an amount of at least about 0.01 % by weight; in another aspect, at least about 0.1% by weight; and in another aspect, at least about 0.5% by weight, all based on the total weight of the treated inorganic oxide particle. The organic treatment may be present in an amount of at most about 20% by weight; in another aspect, at least about 12% by weight; and in another aspect, at least about 10% by weight, all based on the total weight of the treated inorganic oxide particle.TI0015-W001

[0036] Examples of polyols include trimethylolpropane, trimethylolethane, glycerol, polyglycerol, triethylene glycol, diglycerol, propylene glycol, erythritol, pentaerythritol, mannitol, xylitol, or combinations thereof. For example, the polyol may include a diol with or without an alkyl branch, a triol with or without an alkyl branch, or a tetraol with or without an alkyl branch, such as those falling in the formula H-(O-CH2CH2)n-OH and / or C(H)x(OH)y(R1OH)z , wherein n =1 -4, x=0-1 , y=0-1 , z=2-4, such that x+y+z=4, and R1=CI-C3 alkyl. Examples of siliconates include alkali metal salts of alkyl and / or aryl siliconates, or mixtures thereof. The siliconate may comprise R2-Si(OM)3, wherein M is independently alkali metal or H, R2is linear or branched C1-C18 alkyl or aryl, and at least one M comprises alkali metal. The siliconate may be a sodium and / or potassium salt of alkyl and / or aryl siliconates. For example, the siliconate may be sodium methyl siliconate, potassium methyl siliconate, potassium ethyl siliconate, sodium ethyl siliconate, potassium propyl siliconate, potassium benzyl siliconate, or combinations thereof. Carboxylic acids useful as an organic treatment include monocarboxylic acids, dicarboxylic acids, hydroxycarboxylic acids, or salts thereof. Mixtures may also be employed. Specific examples of carboxylic acids include benzoic acid, adipic acid, propionic acid, citric acid, lactic acid, tartaric acid, or salts thereof. Alkanolamines include hydroxylamines, triisopropanolamine, triethanolamine, tris(hydroxymethyl)aminomethane, or mixtures thereof. Useful siloxanes include polydimethylsiloxane, n-octyltriethoxysilane, silicone alkylpolyethers, silicone polyether carboxylates, or mixtures thereof. Phosphonic acids include n-octylphosphonic acid, decylphosphonic acid, dodecylphosphonic acid, octylphosphonic acid, esters of phosphonic acids, salts of phosphonic acids, and combinations thereof; and phosphinic acids include bis(2,4, 4, -trimethylpentyl) phosphinic acid, bis (2-ethylhexyl phosphinic acid), oleyl phosphinic acid, n- octadecyl phosphinic acid, esters of phosphinic acids, and combinations thereof.

[0037] The treated inorganic oxide particles, further treated inorganic particles, dried inorganic particles, organic-treated inorganic particles, or dried organic-treated particles may be milled to reduce the particle size of the treated inorganic oxide particles and to form a milled slurry. The milling step may occur at any point after washing step e, including at multiple points along the 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. In oneTI0015-W001 aspect, the process further comprises step i: milling the treated inorganic particles, further treated inorganic particles, dried inorganic particles, organic-treated inorganic particles, or dried organic-treated particles. Any suitable wet or dry milling method may be used, including but not limited to milling by fluid energy mill, media mill, sand mill, immersion mill, or basket mill. The desired milled particle size may vary based on particle composition and end use application. The milled slurry may be dried to form milled dried particles.

[0038] In one aspect, the milling step includes adding a processing aid, 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 ™.

[0039] The milled slurry may be subjected to a water removal step to form a dewatered filter cake having 60-85% by weight treated inorganic oxide particles in water. 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 butTI0015-W001 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.

[0040] The final treated inorganic oxide particles may be used in several applications, including in coatings such as architectural coatings, as additives in thermoplastics or other materials, or in paper and paper laminates. In one application, the treated inorganic oxide particles or organ ic-treated inorganic particles are combined with thermoplastic to form a thermoplastic composite.

[0041] Thermoplastic polymers useful in this disclosure are high molecular weight melt processable polymers. By “high molecular weight” it is meant to describe polymers having a melt index value of 0.01 to 50, typically from 2 to 10 as measured by ASTM method D1238-98. By “melt-processable,” it is meant a polymer that can be extruded or otherwise converted into shaped articles through a stage that involves obtaining the polymer in a molten state. The thermoplastic polymers may include traditional thermoplastic materials or thermoelastomers, which include natural and synthetic rubbers, and also rubber blends. Thus generally, the present invention is useful for any such white-pigmented plastic or elastomeric compositions (collectively referred to herein as a white-pigmented polymers).

[0042] Thermoplastic materials include, but are not limited to, polyolefins including polyethylene, polyethylene copolymers including copolymers with C4-C10 alphaolefins, copolymers with vinyl acetate, PET, PETG, polypropylene, polypropylene copolymers, polybutylene and polybutylene copolymers; vinyl polymers including polyvinyl chloride; polyvinyl esters including polyvinyl acetate; phenolics; alkyds; amino resins; epoxy resins; phenoxy resins; polysulfones; polyfluoroolefins; polycarbonates; acrylic homopolymers and copolymers; styrene homopolymers and copolymers; acrylonitrile homopolymers and copolymers including ABS; polyesters and chlorinated polyesters; polyethers including polyoxyethylenes; acetal resins; polyimides; polybenzimidazole; polylactic acids; polyamides and polyamideTI0015-W001 copolymers; polyurethanes; polyphenylene oxides; polyaryletherketones; polyphenylene sulfides; silicones; and blends thereof.

[0043] Polymers suitable for use in the present disclosure also include various rubbers and / or elastomers, either natural or synthetic polymers based on copolymerization, grafting, or physical blending of various diene monomers with the above-mentioned polymers. Thermoelastomers include, but are not limited to, isoprene polymers and copolymers, butadiene polymers and copolymers, chloroprene polymers and copolymers, or silicone polymers or copolymers.Important conjugated dienes used in synthetic rubbers include isoprene (2-methyl- 1 ,3-butadiene), 1 ,3-butadiene, and chloroprene (2-chloro-1 ,3-butadiene).Polymerized 1 ,3-butadiene is mostly referred to simply as polybutadiene. In a number of cases, monomers which are not dienes are also used for certain types of synthetic rubber, often copolymerized with dienes. Some of the most commercially important addition polymers are the copolymers. These are polymers made by polymerizing a mixture of two or more monomers. An example is styrene-butadiene rubber (SBR), which is a copolymer of 1 ,3-butadiene and styrene mixed in a 3:1 ratio, respectively. Nitrile rubber is copolymerized from butadiene and acrylonitrile (H2C=CH-CN). Butyl rubber is copolymerized from isobutylene (H2C=C(CH3)2) and a small percentage of isoprene. Silicone rubber and other compounds, chemically called polysiloxanes, are not from conjugated dienes but have repeating units like - O-SiR2- where R is some organic radical group like methyl.EXAMPLESFilter Cake Quality

[0044] Filter cake quality was ranked on a scale of 1 -5, with 1 having poor quality and 5 being the best quality for processing. The poorest quality filter cakes were difficult to handle, leaving a sticky residue on the filter cloth and liquifying (i.e. , exhibiting shear-thinning or thixotropic behavior) upon discharge. The best quality filter cakes were processed without difficulty, being easily discharged from the filter cloth and exhibiting no shear-thinning behavior. Intermediate quality filter cakes left a sticky residue but did not liquify upon discharge.TI0015-W001Surface Treatment Composition (XRF)

[0045] Percentages of surface compounds were reported on a weight basis. They were analyzed by X-ray fluorescence spectroscopy (XRF) based on oxide compound content. Oxide content of titanium dioxide powder samples was measured using an x-ray wavelength dispersive spectrometer with flow and scintillation detectors, such as the Malvern Panalytical Zetium Spectrometer. Pellet specimens for analysis were formed in a Carver Model C3912 pellet press with a 35mm inner diameter steel mold. A Somarfilm was placed into the mold and enough sample to completely cover the film circle was added (1 -4g), followed with enough reagent grade boric acid on top of the sample to fill the mold. Pellets were then formed using 10,000 to 20,000 psig, held for 10-30 seconds. The Somar film was removed after pressing. Matrix matched calibration standards were employed to establish calibration curves for measurement of AI2O3 and SiO2. Measurement of %SC>3 was conducted using the Omnian Calibration Set produced by Malvern Panalytical for standardless analysis, utilizing the Compton factors to detect uncalibrated elements. %SO3 values were then converted to %SO42-. Amounts in weight % of the inorganic oxide particle components (AI2O3 and SiO2) and mixed surface treatment (MST) components (AI2O3, citric acid, and SO42' I PO43') were reported. MST AI2O3 was calculated by subtracting the original inorganic oxide particle AI2O3 content from the total AI2O3 content.Conductivity

[0046] 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 (10.0 g) were mixed at room temperature with deionized water (50.0 g) and mixed vigorously for 24 hours. A calibrated conductivity probe (VWR model 545, multi-purpose cell (Pt)) connected to a conductivity meter (Amber Science Model 1056) was immersed in the mixture, and the measured conductivity was recorded.TI0015-W001Isoelectric Point (I EP) Using the ZetaProbe (Colloidal Dynamics)

[0047] A 3.94% solids slurry of the particle was prepared by adding 6.9 g of inorganic oxide particles to 168.1 g 0.001 N KNOs. The mixture was stirred at least 5 mins and then sonicated for 15 seconds. The electrokinetic sonic amplitude (ESA) probe and pH probe were submerged into the agitated particle suspension. Subsequent titration of the stirred suspension was accomplished using 0.2 N KOH as base and 0.2 N HNO3 as acid titrants. Machine parameters were chosen so that the acid-bearing leg was titrated down to pH 5 and the base-bearing leg was titrated up to pH 9. The zeta potential was determined from the particle dynamic mobility spectrum which was measured using the ESA technique described by O'Brian, et. al*. The particle isoelectric point was typically determined by interpolating where the zeta potential equals zero along the pH / zeta potential curve. *O'Brien R. W., Cannon D. W., Rowlands W. N. J. Colloid Interface Sci. 173, 406-418 (1995). O'Brien R. W., Jones A., Rowlands W. N. Colloids and Surfaces A 218, 89-101 (2003).Nujol Yellowing

[0048] A mixture of 100.0 + / - 0.25 grams of dry, moisture free, Mineral Oil; 2.00 + / - 0.01 grams of butylated hydroxy toluene (BHT); and 2.00 + / - 0.01 grams of Tinuvin® 770 (Ciba-Geigy Corp) was prepared and allowed to stir at ambient temperature. Petrolatum (10.0 + / - 0.1 g) was added to the mixture with stirring until completely dissolved.

[0049] A pipette was used to transfer 1 .20 + / - 0.05 mL of the mixture prepared above onto a Muller apparatus (Hoover Corp, Model M-5) and 0.64 + / - 0.01 g of inorganic oxide particles were mixed in with a spatula. The mixture was mulled for 20 revolutions, drawn together with a spatula, and then mulled for another 20 revolutions. The mixture was then gathered with a spatula drawn down onto a microscope slide using a 10 mil Bird film applicator. A spectrocolorimeter (such as Labscan Model LS-5100 or LS-6000), warmed up for at least one hour, calibrated and set up to use D65 / 10 degree (illuminant / observer), was used to measure the L*a*b* of the film. The slide was placed into a light booth with 6 black-light-blue (BLB) UV Lamps at a distance of approximately 60 cm. The slide was exposed to the UV light for a total exposure time of 24 hours.TI0015-W001

[0050] After exposure, the spectrocolorimeter was used to measure the L*a*b* of the exposed film. The change in b* (A b*) upon exposure was calculated as the difference between the final and initial b*, and used as a measure of the photochemical activity of the titanium dioxide powder.BET Surface Area

[0051] The surface areas of powders and solids were calculated using the adsorption of nitrogen at its boiling point via the BET method, S. Brunauer, P. H. Emmett, and E. Teller, JACS 60, 309 (1938). A MICROMERITICS ASAP 2405 (a trademark of Micromeritics, Inc., Atlanta, GA) adsorption apparatus was used to measure the amount of nitrogen sorbed; the BET equation was used to calculate the amount of nitrogen corresponding to a monolayer for a given sample. Using an area of 16.2 A2per nitrogen molecule under the sorption conditions, the surface area per gram of solid was calculated. Surface area standards from the National Institute of Standards & Technology were run to insure that the reported values were accurate to within a few percent. For non-porous solids (nearly spherical or cubical), the BET surface area can be compared with the size obtained from another technique (e.g. microscopic or particle size analysis). The relationship iswhere SA is the surface area in m2 / g, p the density in g / cc, and D the diameter in microns (pm). This relationship is exact for spheres and cubes. Therefore, the higher the surface area, the smaller the particle size.Dryness (% by weight H2O)

[0052] Dryness was confirmed by Thermogravimetric Analysis (TGA) and reported as % by weight H2O, based on the total weight of the particles. TGA is a thermal analysis method frequently utilized to measure sample weight loss over time under pre-specified gas and heating conditions. Samples were loaded (up to 1g per pan) in tared platinum pans by the TA Discovery TGA 5500 where an autosampler transferred and encapsulated the sample in an oven to stabilize before heating. For the examples, the stabilization consisted of a 2 minute isotherm at 30°C with subsequent ramp of 20 °C per minute to 700 °C under an air flow rate of 25 mL / min.TI0015-W001The resulting weight loss curve was used to determine characteristic weight loss within the specific temperature range from 30 to 116 °C.Inorganic Oxide Particle Preparation 1

[0053] A TiO2 base material was formed with 1 .30% by weight alumina and 0.17% by weight silica, based on the weight of the particle, by mixing and oxidizing TiCk, AlCh, and SiCk, to form inorganic oxide particles having both alumina and silica inside the crystal lattice. The resulting particles were made into an aqueous suspension having a TiOs solids content of 29% by weight. The suspension was neutralized with NaOH.Inorganic Oxide Particle Preparation 2

[0054] Preparation 1 was performed, except the alumina content was 1.26% by weight, and the silica content was 0.07% by weight. The resulting particles were made into an aqueous suspension having a TiO2 solids content of 29% by weight. The suspension was neutralized with NaOH.Inorganic Oxide Particle Preparation 3

[0055] Preparation 1 was performed, except the alumina content was 1.17% by weight, and the silica content was 0.18% by weight. The resulting particles were made into an aqueous suspension having a TiO2 concentration of 296 grams of dry particles per liter of water.Inorganic Oxide Particle Preparation 4

[0056] Preparation 1 was performed, except the alumina content was 1.29% by weight, and the silica content was 0.04% by weight. The resulting particles were made into an aqueous suspension having a TiC>2 concentration of 29% by weight, based on the total weight of the aqueous suspension.Example 1

[0057] The initial pH of the inorganic oxide particle suspension (Preparation 1) measured as 8.3 at 21 °C. After heating to 44 °C, the suspension pH was adjusted with 1 .61 g of 93% H2SO4 to 7.1 . A solution of 50% citric acid (13.86 g, target 0.50TI0015-W001 wt.% based on titanium dioxide) was added and the pH after mixing was 4.3. The pH was then adjusted to 7.0 with 14.05 g of 20% NaOH solution.

[0058] Then, 93% H2SO4 (36.29 g) and sodium aluminate solution (94.21 g) were added simultaneously over the course of about 5 minutes, maintaining pH in the range of 6-8. After this step, the pH was 7.1 and the temperature was 47 °C. The mixture was stirred for 60 minutes while maintaining a pH of 7.0 + / - 0.2 and temperature of 50 + / - 5°C for the cure step. The mixture was observed for filter cake quality within 1 -2 hours of the final cure.

[0059] The treated slurry was filtered and washed with about 7 liters of deionized water to conductance <500 micro Siemens. The filter cake was vacuum dried for about 15 minutes. The cake was transferred to an Al pan and the handling characteristics were noted (i.e., sticky or thixotropic). The bulk cake material was dried at 125 °C in a convection oven overnight to a water content of 0.63% by weight. The dried material was ground through a 35 mesh sieve and tested according to the Test Methods above.Example 2

[0060] The initial pH of the suspension (Preparation 1 ) measured as 6.3 at 22 °C. After heating to 49°C, the suspension pH was adjusted with 2.23 g of 20% NaOH to 6.9. A solution of 50% citric acid (6.01 g, target 0.25 wt.% based on titanium dioxide) was added and the pH after mixing was 4.2. The pH was then adjusted to 7.0 with 5.97 g of 20% NaOH solution.

[0061] Then, 93% H2SO4 (31 .30 g) and sodium aluminate solution (81 .75 g) were added simultaneously over the course of about 5 minutes, maintaining pH in the range of 6-8. After this step, the pH was 7.0 and the temperature was 50 °C. The mixture was stirred for 60 minutes while maintaining a pH of 7.0 + / - 0.2 and temperature of 50 + / - 5°C for the cure step. The mixture was observed for filter cake quality within 1 -2 hours of the final cure. The treated slurry was washed, dried to a water content of 0.50% by weight, and tested as in Example 1 .Example 3

[0062] The initial pH of the suspension (Preparation 1 ) measured as 6.2 at 21 °C. After heating to 49°C, the suspension pH was adjusted with 2.63 g of 20% NaOH toTI0015-W0016.9. A solution of 50% citric acid (3.43 g, target 0.15 wt.% based on titanium dioxide) was added and the pH after mixing was 4.9. The pH was then adjusted to 7.0 with 4.03 g of 20% NaOH solution.

[0063] Then, 93% H2SO4 (29.83 g) and sodium aluminate solution (77.75 g) were added simultaneously over the course of about 5 minutes, maintaining pH in the range of 6-8. After this step, the pH was 7.0 and the temperature was 50 °C. The mixture was stirred for 60 minutes while maintaining a pH of 7.0 + / - 0.2 and temperature of 50 + / - 5°C for the cure step. The mixture was observed for filter cake quality within 1 -2 hours of the final cure. The treated slurry was washed, dried to a water content of 0.43% by weight, and tested as in Example 1 .Comparative Example A

[0064] The initial pH of the suspension (Preparation 2) measured as 9.42 at 21 °C. After heating to 43°C, the suspension pH was adjusted with 2.15 g of 93% H2SO4 to 7.0. Then, 93% H2SO4 (36.1 g) and sodium aluminate solution (92.99 g) were added simultaneously over the course of about 5 minutes, maintaining pH in the range of 6- 8. After this step, the pH was 7.0 and the temperature was 50 °C. The mixture was stirred for 60 minutes while maintaining a pH of 7.0 + / - 0.2 and temperature of 50 + / - 5°C for the cure step. The mixture was observed for filter cake quality within 1-2 hours of the final cure. The treated slurry was washed, dried to a water content of 0.23% by weight, and tested as in Example 1.Comparative Example B

[0065] The initial pH of the suspension (Preparation 2) measured as 9.4 at 21 °C. After heating to 48 °C, the suspension pH was adjusted with 9.2 g of 20% HCI to 7.0. A solution of 50% citric acid (13.8 g, target 0.50 wt.% based on titanium dioxide) was added and the pH after mixing was 5.2. The pH was then adjusted to 7.0 with 13.62 g of 20% NaOH solution.

[0066] Then, 20% HCI (151.27 g) and sodium aluminate solution (93.52 g) were added simultaneously over the course of about 5 minutes, maintaining pH in the range of 6-8. After this step, the pH was 7.0 and the temperature was 47 °C. The mixture was stirred for 60 minutes while maintaining a pH of 7.0 + / - 0.2 and temperature of 50 + / - 5°C for the cure step. The mixture was observed for filter cakeTI0015-W001 quality within 1 -2 hours of the final cure. The treated slurry was washed, dried to a water content of 0.35% by weight, and tested as in Example 1 . Though no sulfuric acid was intentionally added, trace sulfate content appeared in the XRF data, possibly from one of the reagents.Comparative Example C

[0067] The initial pH of the suspension (Preparation 2) measured as 9.3 at 21 °C. After heating to 48 °C, the suspension pH was adjusted with 9.48 g of 20% HCI to 7.0. A solution of 50% citric acid (6.81 g, target 0.25 wt.% based on titanium dioxide) was added and the pH after mixing was 6.0. The pH was then adjusted to 7.0 with6.61 g of 20% NaOH solution.

[0068] Then, 20% HCI (143.62 g) and sodium aluminate solution (92.62 g) were added simultaneously over the course of about 5 minutes, maintaining pH in the range of 6-8. After this step, the pH was 7.0 and the temperature was 50 °C. The mixture was stirred for 60 minutes while maintaining a pH of 7.0 + / - 0.2 and temperature of 50 + / - 5°C for the cure step. The mixture was observed for filter cake quality within 1 -2 hours of the final cure. The treated slurry was washed, dried to a water content of 0.24% by weight, and tested as in Example 1 . Though no sulfuric acid was intentionally added, trace sulfate content appeared in the XRF data, possibly from one of the reagents.Comparative Example D

[0069] The initial pH of the suspension (Preparation 2) measured as 9.3 at 21 °C. After heating to 49 °C, the suspension pH was adjusted with 8.83 g of 20% HCI to 7.0. A solution of 50% citric acid (4.08 g, target 0.15 wt.% based on titanium dioxide) was added and the pH after mixing was 6.3. The pH was then adjusted to 7.0 with3.61 g of 20% NaOH solution.

[0070] Then, 20% HCI (142.45 g) and sodium aluminate solution (92.41 g) were added simultaneously over the course of about 5 minutes, maintaining pH in the range of 6-8. After this step, the pH was 7.0 and the temperature was 47 °C. The mixture was stirred for 60 minutes while maintaining a pH of 7.0 + / - 0.2 and temperature of 50 + / - 5°C for the cure step. The mixture was observed for filter cake quality within 1 -2 hours of the final cure. The treated slurry was washed, dried to aTI0015-W001 water content of 0.26% by weight, and tested as in Example 1 . Though no sulfuric acid was intentionally added, trace sulfate content appeared in the XRF data, possibly from one of the reagents.Comparative Example E

[0071] The initial pH of the suspension (Preparation 2) measured as 9.4 at 21 °C. After heating to 45°C, the suspension pH was adjusted with 9.75 g of 20% HOI to 7.0. Then, 20% HCI (141 .27 g) and sodium aluminate solution (93.05 g) were added simultaneously over the course of about 5 minutes, maintaining pH in the range of 6- 8. After this step, the pH was 7.0 and the temperature was 49 °C. The mixture was stirred for 60 minutes while maintaining a pH of 7.0 + / - 0.2 and temperature of 50 + / - 5°C for the cure step. The mixture was observed for filter cake quality within 1-2 hours of the final cure. The treated slurry was washed, dried to a water content of 0.14% by weight, and tested as in Example 1. Though no sulfuric acid was intentionally added, trace sulfate content appeared in the XRF data, possibly from one of the reagents.Table 1. Performance Data for Examples 1-3 and Comparative Examples A-E

[0072] As seen in Table 1 , sulfuric acid I sulfate content leads to improved filter cake quality of the particles during filtration. Furthermore, yellowing decreases with increased amounts of citric acid. Overall particle properties are optimized when particle composition is modified to have these two components.Example 4

[0073] The suspension pH (Preparation 3) was adjusted to 6.93 and heated to 45 °C. After achieving the target temperature, citric acid (0.25% by weight of particles) and NaOH were added to the suspension to obtain a final pH of 6.85. TheTI0015-W001 suspension was stirred for 10 minutes. Thereafter, sodium aluminate (23% AI2O3 solution, 1 .57% by weight of particles) and sulfuric acid (93% H2SO4, 0.15% SO2-by weight of particles) were added at a pH of 7.16. The suspension was stirred for thirty minutes, and pH was adjusted to 7.06. The suspension was then filtered and washed until the wash water had a conductivity no greater than 500 micro Siemens, and the aqueous suspension was concentrated to approximately 600 grams of dry particles gram / liter by removing water. The filter cake was dried and tested according to the Test Methods above.Example 5

[0074] Example 4 was repeated, except the concentrated filter cake (100 g) was mixed with MgSO4-7H2O (0.117 g, 0.27% SC2-by weight of particles). The cake was dried and tested according to the Test Methods above.Example 6

[0075] Example 4 was repeated, except the concentrated filter cake (100 g) was mixed with KAI(SO4)2-12H2O (0.111 g, SC>42'0.27% by weight of particles). The cake was dried and tested according to the Test Methods above.Example 7

[0076] Example 4 was repeated, except the concentrated filter cake (100 g) was mixed with Al2(SO4)3-18H2O (0.108 g, SC>42' 0.27% by weight of particles). The cake was dried and tested according to the Test Methods above.Table 2. Performance Data for Examples 4-7

[0077] As can be seen in Table 2, additional sulfate content serves to further reduce the yellowing of the overall particle.TI0015-W001Comparative Example F

[0078] Example 2 was repeated, except the inorganic oxide particles of Preparation 4 were used. The initial pH of the suspension was 6.91 , and the samples were adjusted to a pH of 5.5 in steps b, c, and d.Example 8

[0079] Example 2 was repeated, except the inorganic oxide particles of Preparation 4 were used. The initial pH of the suspension was 6.91 , and the samples were adjusted to a pH of 8.0 in steps b, c, and d.Example 9

[0080] Example 2 was repeated, except the inorganic oxide particles of Preparation 4 were used, the initial pH of the suspension was 6.91 , and sodium aluminate was added in an amount to achieve 0.57% alumina in the surface treatment, based on the total weight of the treated inorganic oxide particle.Table 3. Performance Data for Examples 8-9 and Comparative Example F

[0081] As seen in Table 3, the example with low pH yielded a low value in the Nujol Yellowing test but poor filter cake quality performance. The treatments conducted at high pH or lower alumina addition gave good filter cake quality, but the Nujol Yellowing test performance was not as strong. Overall particle properties are optimized when the treatment process includes appropriate pH conditions, sulfuric acid / sulfate, and alumina content.

Claims

TI0015-W001CLAIMSWhat is claimed is:

1. A process of producing a treated inorganic oxide particle comprising: a. providing inorganic oxide particles in aqueous suspension at a pH of about 5 to about 8, where the inorganic oxide particles comprise an inorganic oxide and either alumina or a mixture of alumina and silica; b. contacting the inorganic oxide particles with citric acid to form citric acid-treated inorganic oxide particles at a pH of about 5 to about 8; c. contacting the citric acid-treated inorganic oxide particles with an alkaline aluminum compound and a compound selected from sulfuric acid, sulfate salt, phosphoric acid, or phosphate salt at a pH of about 6.5 to about 7.5 to form alumina-treated inorganic oxide particles; d. maintaining the pH to about 6.5 to about 7.5 for a period of time; and e. washing the alumina-treated inorganic oxide particles with water to form treated inorganic oxide particles having an isoelectric point (I EP) of about 6.5-8.0 and comprising a mixed surface treatment, where the mixed surface treatment comprises about 0.20-5.00% by weight alumina (AI2O3), about 0.03-0.83% by weight citric acid, and about 0.04-0.50% by weight SC>42' or PO43; all based on the total weight of the treated inorganic oxide particle, in the same treatment layer.

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

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

4. The process of claims 1-3, where the alkaline aluminum compound is selected from alkali metal aluminum salts.

5. The process of claims 1-4, where the inorganic oxide particles comprise a mixture of alumina and silica.

6. The process of claim 5, where the weight ratio of alumina to silica in the inorganic oxide particle is from about 2: 1 to about 20: 1 .TI0015-W0017. The process of claims 1-6, further comprising the step of forming the alumina or mixture of alumina and silica of the inorganic oxide particle prior to step a by pyrogenic methods.

8. The process of claims 1-7, where the mixed surface treatment comprises about 0.50-3.00% by weight alumina (AI2O3), about 0.08-0.50% by weight citric acid, and at least one of about 0.04-0.24% by weight SO42-or 0.04 to 0.30 % by weight PO43; all based on the total weight of the treated inorganic oxide particle, in the same treatment layer.

9. The process of claims 1-8, where the pH in step a is from about 6.5 to about7.5.

10. The process of claims 1 -9, where the pH in step b is from about 6.5 to about7.5.11 . The process of claims 1-10, where the IEP is about 7.0-8.0.

12. The process of claims 1-11 , where the solids content of the treated inorganic particles is greater than about 25% by weight.

13. The process of claim 12, where the solids content is about 35 to about 75% by weight.

14. The process of claims 1-13, where the temperature in steps b-e is at most about 70 °C.

15. The process of claims 1-14, further comprising: f. contacting the treated inorganic particles with an alkaline or acidic sulfate compound to form further treated inorganic particles.

16. The process of claim 15, where the pH of step f is about 6.5 to about 7.5.

17. The process of claims 1-16, further comprising: g. drying the treated inorganic particles or further treated inorganic particles to form dried inorganic particles having a weight loss by TGA of less than 5.0% at 116 °C.TI0015-W00118. The process of claims 1-17, further comprising: h. treating the treated inorganic particles, further treated inorganic particles, or dried inorganic particles with an organic compound to form organic- treated inorganic particles.

19. The process of claim 18, further comprising: hi . drying the organ ic-treated inorganic particles to form dried organic- treated inorganic particles.

20. The process of claims 18-19, where the organic compound is selected from polyols, siliconates, carboxylic acids or carboxylic acid esters or salts thereof, alkanolamines, silanes, siloxanes, phosphonic acids, phosphates, phosphonates, phosphinic acids, sulfonic compounds, polyolefins, hydrocarbon amides, hydrocarbon waxes, or mixtures thereof.21 . The process of claims 1 -20, further comprising: i. milling the treated inorganic particles, further treated inorganic particles, dried inorganic particles, organ ic-treated inorganic particles, or dried organic-treated particles.

22. A treated inorganic oxide particle having an IEP of about 6.5-8.0 comprising an inorganic oxide particle and a mixed surface treatment, where the inorganic oxide particles comprise an inorganic oxide and either alumina or a mixture of alumina and silica; and the mixed surface treatment comprises about 0.20-5.00% by weight alumina (AI2O3), about 0.03-0.83% by weight citric acid, and about 0.04-0.50% by weight SO42- or PC3; all based on the total weight of the treated inorganic oxide particle, in the same treatment layer.

23. The treated inorganic oxide particle of claim 22, where the inorganic oxide is selected from oxides of Ti, Al, Zn, Cu, Fe, Mn, or Si.

24. The treated inorganic oxide particle of claim 23, where the inorganic oxide is TiO2.

25. The treated inorganic oxide particle of claims 22-24, where the inorganic oxide particles comprise a mixture of alumina and silica.TI0015-W00126. The treated inorganic oxide particle of claim 25, where the weight ratio of alumina to silica in the inorganic oxide particle is from about 2: 1 to about 20: 1 .

27. The treated inorganic oxide particle of claims 22-26, where the alumina of the inorganic oxide particle is pyrogenic alumina, and the mixture of alumina and silica of the inorganic oxide particle is pyrogenic silica and alumina.

28. The treated inorganic oxide particle of claims 22-27, where the mixed surface treatment comprises about 0.50-3.00% by weight alumina (AI2O3), about 0.08- 0.50% by weight citric acid, and at least one of about 0.04-0.24% by weight SO42- or 0.04 to 0.30 % by weight PO43; all based on the total weight of the treated inorganic oxide particle, in the same treatment layer.

29. The treated inorganic oxide particle of claims 22-28, where the IEP is about 7.0- 8.0.

30. A treated inorganic oxide particle made by the process of claims 1-21 .31 . A thermoplastic composite comprising a thermoplastic and the treated inorganic oxide particles made by the process of claims 1-21.

32. An organ ic-treated inorganic oxide particle having an IEP of about 6.5-8.0 comprising an inorganic oxide particle, a mixed surface treatment, and an organic surface treatment, where the inorganic oxide particles comprise an inorganic oxide and either alumina or a mixture of alumina and silica; the mixed surface treatment is on the surface of the inorganic oxide particle; the organic surface treatment is on the surface of the mixed surface treatment; and the mixed surface treatment comprises about 0.20-5.00% by weight alumina (AI2O3), about 0.03-0.83% by weight citric acid, and about 0.04-0.50% by weight SO42- or PO43all based on the total weight of the treated inorganic oxide particle, in the same treatment layer.

33. The organic-treated inorganic oxide particle of claim 32, where the inorganic oxide is selected from oxides of Ti, Al, Zn, Cu, Fe, Mn, or Si.TI0015-W00134. The organic-treated inorganic oxide particle of claim 33, where the inorganic oxide is TiO2.

35. The organic-treated inorganic oxide particle of claims 32-34, where the inorganic oxide particles comprise a mixture of alumina and silica.

36. The organic-treated inorganic oxide particle of claim 35, where the weight ratio of alumina to silica in the inorganic oxide particle is from about 2:1 to about 20:1.

37. The organic-treated inorganic oxide particle of claims 32-36, where the alumina of the inorganic oxide particle is pyrogenic alumina, and the mixture of alumina and silica of the inorganic oxide particle is pyrogenic silica and alumina.

38. The organic-treated inorganic oxide particle of claims 32-37, where the mixed surface treatment comprises about 0.50-3.00% by weight alumina (AI2O3), about 0.08-0.50% by weight citric acid, and at least one of about 0.04-0.24% by weight SO42- or 0.04 to 0.30 % by weight PO43all based on the total weight of the treated inorganic oxide particle, in the same treatment layer.

39. The organic-treated inorganic oxide particle of claims 32-38, where the organic treatment is selected from polyols, siliconates, carboxylic acids or carboxylic acid esters or salts thereof, alkanolamines, silanes, siloxanes, phosphonic acids, phosphates, phosphonates, phosphinic acids, sulfonic compounds, polyolefins, hydrocarbon amides, hydrocarbon waxes, or mixtures thereof.

40. The organic-treated inorganic oxide particle of claims 32-39, where the I EP is about 7.0-8.0.41 . A thermoplastic composite comprising a thermoplastic and the organic-treated inorganic oxide particle of claims 32-40.

42. A process of producing a treated inorganic oxide particle comprising: a. providing inorganic oxide particles in aqueous suspension at a pH of about 5.0 to about 8.0, where the inorganic oxide particles comprise an inorganic oxide and either alumina or a mixture of alumina and silica; b. contacting the inorganic oxide particles with citric acid to form citric acid-treated inorganic oxide particles at a pH of about 5.0 to about 8.0;TI0015-W001 c. contacting the citric acid-treated inorganic oxide particles with an alkaline aluminum compound and a compound selected from sulfuric acid, sulfate salt, phosphoric acid, or phosphate salt at a pH of about 6.5 to about 8.0 to form alumina-treated inorganic oxide particles; d. maintaining the pH to about 6.5 to about 8.0 for a period of time; and e. washing the alumina-treated inorganic oxide particles with water to form treated inorganic oxide particles having an isoelectric point (I EP) of about 6.5-8.0 and comprising a mixed surface treatment, where the mixed surface treatment comprises about 0.20-5.00% by weight alumina (AI2O3), about 0.03-0.83% by weight citric acid, and about 0.02-0.50% by weight SC2' or PO43; all based on the total weight of the treated inorganic oxide particle, in the same treatment layer.

43. The process of claim 42, where the inorganic oxide is selected from oxides of Ti, Al, Zn, Cu, Fe, Mn, or Si.

44. The process of claim 43, where the inorganic oxide is TiO2.

45. The process of claims 42-44, where the alkaline aluminum compound is selected from alkali metal aluminum salts.

46. The process of claims 42-45, where the inorganic oxide particles comprise a mixture of alumina and silica.

47. The process of claim 46, where the weight ratio of alumina to silica in the inorganic oxide particle is from about 2: 1 to about 20: 1 .

48. The process of claims 42-47, further comprising the step of forming the alumina or mixture of alumina and silica of the inorganic oxide particle prior to step a by pyrogenic methods.

49. The process of claims 42-48, where the mixed surface treatment comprises about 0.50-3.00% by weight alumina (AI2O3), about 0.08-0.50% by weight citric acid, and about 0.02-0.24% by weight SC>42' or 0.04 to 0.30 % by weight PO43; all based on the total weight of the treated inorganic oxide particle, in the same treatment layer.TI0015-W00150. The process of claims 42-49, where the pH in step a is from about 6.5 to about7.5.51 . The process of claims 42-50, where the pH in step b is from about 6.5 to about7.5.

52. The process of claims 42-51 , where the IEP is about 7.0-8.0.

53. The process of claims 42-52, where the solids content of the treated inorganic particles is greater than about 25% by weight.

54. The process of claim 53, where the solids content is about 35 to about 75% by weight.

55. The process of claims 42-54, where the temperature in steps b-e is at most about 70 °C.

56. The process of claims 42-55, further comprising: f. contacting the treated inorganic particles with an alkaline or acidic sulfate compound to form further treated inorganic particles.

57. The process of claim 56, where the pH of step f is about 6.5 to about 8.0.

58. The process of claims 42-57, further comprising: g. drying the treated inorganic particles or further treated inorganic particles to form dried inorganic particles having a weight loss by TGA of less than 5.0% at 116 °C.

59. The process of claims 42-58, further comprising: h. treating the treated inorganic particles, further treated inorganic particles, or dried inorganic particles with an organic compound to form organic- treated inorganic particles.

60. The process of claim 59, further comprising: hi . drying the organ ic-treated inorganic particles to form dried organic- treated inorganic particles.61 . The process of claims 59-60, where the organic compound is selected from polyols, siliconates, carboxylic acids or carboxylic acid esters or salts thereof,TI0015-W001 alkanolamines, silanes, siloxanes, phosphonic acids, phosphates, phosphonates, phosphinic acids, sulfonic compounds, polyolefins, hydrocarbon amides, hydrocarbon waxes, or mixtures thereof.

62. The process of claims 42-61 , further comprising: i. milling the treated inorganic particles, further treated inorganic particles, dried inorganic particles, organic-treated inorganic particles, or dried organic-treated particles.

63. A treated inorganic oxide particle having an IEP of about 6.5-8.0 comprising an inorganic oxide particle and a mixed surface treatment, where the inorganic oxide particles comprise an inorganic oxide and either alumina or a mixture of alumina and silica; and the mixed surface treatment comprises about 0.20-5.00% by weight alumina (AI2O3), about 0.03-0.83% by weight citric acid, and about 0.02-0.50% by weight SO42- or PO43; all based on the total weight of the treated inorganic oxide particle, in the same treatment layer.

64. The treated inorganic oxide particle of claim 63, where the inorganic oxide is selected from oxides of Ti, Al, Zn, Cu, Fe, Mn, or Si.

65. The treated inorganic oxide particle of claim 64, where the inorganic oxide is TiO2.

66. The treated inorganic oxide particle of claims 63-65, where the inorganic oxide particles comprise a mixture of alumina and silica.

67. The treated inorganic oxide particle of claim 66, where the weight ratio of alumina to silica in the inorganic oxide particle is from about 2: 1 to about 20: 1 .

68. The treated inorganic oxide particle of claims 63-67, where the alumina of the inorganic oxide particle is pyrogenic alumina, and the mixture of alumina and silica of the inorganic oxide particle is pyrogenic silica and alumina.

69. The treated inorganic oxide particle of claims 63-68, where the mixed surface treatment comprises about 0.50-3.00% by weight alumina (AI2O3), about 0.08- 0.50% by weight citric acid, and about 0.02-0.24% by weight SC>42' or 0.04 toTI0015-W0010.30 % by weight PO43all based on the total weight of the treated inorganic oxide particle, in the same treatment layer.

70. The treated inorganic oxide particle of claims 63-69, where the IEP is about 7.0- 8.0.71 . A treated inorganic oxide particle made by the process of claims 42-62.

72. A thermoplastic composite comprising a thermoplastic and the treated inorganic oxide particles made by the process of claims 42-62.

73. An organ ic-treated inorganic oxide particle having an IEP of about 6.5-8.0 comprising an inorganic oxide particle, a mixed surface treatment, and an organic surface treatment, where the inorganic oxide particles comprise an inorganic oxide and either alumina or a mixture of alumina and silica; the mixed surface treatment is on the surface of the inorganic oxide particle; the organic surface treatment is on the surface of the mixed surface treatment; and the mixed surface treatment comprises about 0.20-5.00% by weight alumina (AI2O3), about 0.03-0.83% by weight citric acid, and about 0.02-0.50% by weight SO42- or PO43all based on the total weight of the treated inorganic oxide particle, in the same treatment layer.

74. The organic-treated inorganic oxide particle of claim 73, where the inorganic oxide is selected from oxides of Ti, Al, Zn, Cu, Fe, Mn, or Si.

75. The organic-treated inorganic oxide particle of claim 74, where the inorganic oxide is TiOs.

76. The organic-treated inorganic oxide particle of claims 73-75, where the inorganic oxide particles comprise a mixture of alumina and silica.

77. The organic-treated inorganic oxide particle of claim 76, where the weight ratio of alumina to silica in the inorganic oxide particle is from about 2:1 to about 20:1.TI0015-W00178. The organic-treated inorganic oxide particle of claims 73-77, where the alumina of the inorganic oxide particle is pyrogenic alumina, and the mixture of alumina and silica of the inorganic oxide particle is pyrogenic silica and alumina.

79. The organic-treated inorganic oxide particle of claims 73-78, where the mixed surface treatment comprises about 0.50-3.00% by weight alumina (AI2O3), about 0.08-0.50% by weight citric acid, and about 0.02-0.24% by weight SO42-or 0.04 to 0.30 % by weight PO43; all based on the total weight of the treated inorganic oxide particle, in the same treatment layer.

80. The organic-treated inorganic oxide particle of claims 73-79, where the organic treatment is selected from polyols, siliconates, carboxylic acids or carboxylic acid esters or salts thereof, alkanolamines, silanes, siloxanes, phosphonic acids, phosphates, phosphonates, phosphinic acids, sulfonic compounds, polyolefins, hydrocarbon amides, hydrocarbon waxes, or mixtures thereof.81 . The organic-treated inorganic oxide particle of claims 73-80, where the I EP is about 7.0-8.0.

82. A thermoplastic composite comprising a thermoplastic and the organic-treated inorganic oxide particle of claims 73-81 .

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