Method of manufacturing titanium dioxide pigment particles with an organic coating

Abstract

A method of manufacturing titanium dioxide (TiO2) pigment particles with an organic oil coating includes heating a mixer containing a charge of TiO2 pigment particles to an elevated temperature sufficient to lower the viscosity of the organic oil to close to the viscosity of water Organic oil is injected into the heated mixer through two-phase atomizer nozzle(s) while mixing the TiO2 pigment particles with the agitator. While mixing with the agitator, the heated TiO2 pigment particles and the injected organic oil are simultaneously chopped with the chopper to break up agglomerates formed by the mixture of the organic oil and the TiO2 particles. The mixer may then be cooled to a preselected temperature at which agglomeration of coated pigment particles substantially ceases while continuing to mix and chop the homogeneous mixture. The chopper is stopped when the mixer reaches the preselected temperature.

Description

FIELD OF THE INVENTION

[0001] The present invention relates generally to a method of manufacturing titanium dioxide pigment particles with an organic coating and a mixing apparatus for implementing the method. BACKGROUND

[0002] Titanium dioxide (TiO2) pigment particles are sometimes coated with organic coatings when used in various products, such as cosmetics. Typically, these coated pigment particles are formed by simply mixing the TiO2 particles with the organic coating and the final end product. However, coated pigment particles produced in this typical manner regularly have either a rather thick coating or are not homogeneously coated if a reduced amount of organic compound is used for coating, either of which conditions may have undesirable effects on the final end product. In addition, this typical method can cause undesirable agglomeration of the pigment particles, which can reduce the visual quality of the final product. Furthermore, coated pigment particles produced by this typical method often have inferior dispersing properties leading to decreased tinting strength of the final cosmetic product. Therefore, it would be desirable to have a system and method of manufacturing titanium dioxide pigment particles for use in cosmetics that reduces the formation of agglomerates and / or have a relatively thin homogenous organic coating to provide for a superior pigment for cosmetics products. SUMMARY OF THE INVENTION

[0003] It is a technical object of the invention to provide a method and apparatus manufacturing titanium dioxide pigment particles with an organic oil coating that overcomes one or more of the above problems. This object is achieved by the method(s) and / or apparatus of the present invention that provides an improved way to manufacture TiO2 pigment particles that are coated with organic coatings, such as soybean oil or other biobased organic oils and / or glycerin or other organic oils.

[0004] In one aspect of the invention, a method of manufacturing titanium dioxide (TiO2) pigment particles with an organic oil coating is provided. The method includes loading a charge of TiO2 pigment particles into a mixer. The mixer has at least one two-phase atomizer nozzle for injecting an organic oil into the mixer, at least one agitator for mixing components inside the mixer, and at least one chopper for deagglomerating the components inside the mixer. The mixer and the charge of TiO2 pigment particles may be heated to an elevated temperature sufficient to lower the viscosity of the organic oil. Optionally, the elevated temperature is sufficient to lower the viscosity of the organic oil to about to the viscosity of water at room temperature in order to allow for formation of very fine atomized or aerosolized droplets of the organic oil by the two-phase atomizer nozzle(s). A selected amount of organic oil may be injected into the heated mixer through the two-phase atomizer nozzle(s). While injecting the selected amount of organic oil, the heated TiO2 pigment particles inside the mixer may be mixed with the agitator to form a homogeneous mixture of the TiO2 pigment particles coated with the organic oil. While mixing with the agitator, the heated TiO2 pigment particles and the injected organic oil may be chopped with the chopper to break up agglomerates formed by the mixture of the organic oil and the TiO2 particles, thereby forming a homogeneous mixture of de-agglomerated coated TiO2 particles. The chopping can be ended after the mixer reaches a preselected temperature at which agglomeration of the organic oil and the TiO2 pigment particles substantially ceases.

[0005] In some optional configurations, the elevated temperature may be above about 70 °C and / or may be between about 70 °C and about 110 °C. If the organic oil is primarily soybean oil and the elevated temperature may be between about 70° C and about 85° C, for example about 80° C. The amount of soybean oil injected into the mixer may be between about 0.1 weight % and about 1 weight %, preferably about 0.35 weight %, relative to the TiO2 pigment particles. If the organic oil is primarily glycerin, the elevated temperature may be between about 90° C and about 110° C, for example about 100° C. The amount of glycerin injected into the mixer may be between about 0.1 weight % and about 1 weight %, preferably about 0.55 weight %, relative to the TiO2 pigment particles.

[0006] In some optional configurations, the agitator and the chopper may continue to simultaneously mix and chop the homogeneous mixture until the mixer cools to the preselected temperature. The preselected temperature at which the chopping is ended may be between about 30 °C and about 50 °C, preferably about 40 °C, to prevent significant agglomeration of the coated pigment particles. When the organic oil is comprised primarily of soybean oil, the preselected temperature at which the chopping is ended is preferably about 40 °C or lower. The mixer and the homogeneous mixture contained therein may be actively cooled, for example by an active cooling system, or passively cooled, after injecting the selected amount of organic oil into the mixer.

[0007] In some optional configurations, the agitator may form a cloud of suspended TiO2 pigment particles inside the mixer. The two-phase nozzles may be configured to inject the organic oil as an atomized spray (e.g., an aerosolized spray) into the cloud of suspended TiO2pigment particles.

[0008] In some optional configurations, the mixer may be electrically grounding to prevent buildup of electrostatic charge in the TiO2 pigment particles during the mixing. For example, the mixer may be electrically grounded continually from the time the charge of TiO2 pigment is loaded into the mixer until the homogeneous mixture is removed from the mixer.

[0009] In some optional configurations, the de-agglomerated coated TiO2 particles may be sieved to obtain a preselected size of the de-agglomerated coated TiO2 particles. For example, such sizing may occur after the mixer has cooled to below the selected temperature and both the mixing and the chopping has ended. The sieving may occur outside of the mixer, for example after unloading the de-agglomerated coated TiO2 particles from the mixer.

[0010] In another aspect of the invention, a mixing apparatus for coating TiO2 pigment particles with an organic oil in accordance with the methods described herein is provided. The mixing apparatus may include a mixer having at least one agitator and at least one chopper disposed inside a mixing tank configured to receive a batch of the TiO2 pigment particles, at least one two-phase atomizer nozzle configured to spray the organic oil into the mixing tank, and one or more heating units configured to heat the mixing tank and the and the two-phase atomizer nozzles to at least about 70 °C.

[0011] In some optional configurations, the mixing tank may have a horizontally elongate cylindrical body. The choppers may be disposed along an interior sidewall of the mixing tank between a bottom and a horizontal centerline of the horizontally elongate cylindrical body. The mixer may be grounded to prevent buildup of electrostatic charges in the mixer.

[0012] In some optional configurations, the agitator(s) may be a mixing shaft with mixing elements, such as a plurality of ploughshare blades. For example, the agitator may have four ploughshare blades extending from a rotating shaft. The agitator may be aligned to create a cloud of suspended pigment particles in the top region of the mixing chamber in the mixing tank. For example, the rotating shaft may be aligned horizontally along the horizontal axis of the mixing tank.

[0013] In some optional configurations, the atomizer nozzle(s) is / are positioned at the top of the mixing tank, for example to spray downwardly into the cloud of suspended pigment particles in the top region of the mixing chamber. There may be four atomizer nozzles. The atomizer nozzles may provide for internal mixing of a propellant gas and the organic oil before emitting an atomized spray of a mixture of the propellant gas and the organic oil.

[0014] In some optional configurations, the heating unit(s) may be configured to heat the mixing tank to a first elevated temperature between about 70 °C and about 110 °C, for example about 90 °C. The heating unit(s) may be configured to separately heat the atomizer nozzles to a second elevated temperature between about 70 °C and about 110 °C, such as about 80 °C. One or more cooling units may be provided for actively cooling the mixing tank and / or the atomizer nozzle(s). The heating unit(s) and / or the cooling unit(s) may have water heating and / or water cooling systems.

[0015] Coating TiO2 pigment particles in this manner typically provides a coated TiO2 pigment particle having a relatively thin, homogeneous organic coating, which are typically particularly well suited for use as pigments in decorative cosmetics and personal care products. These and other advantages, uses, and / or characteristics will become apparent upon review of the following detailed description and the drawings in which: BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 represents certain steps in a non-limiting example method of coating TiO2 pigment particles with an organic coating according to certain principles of the invention;

[0017] FIG. 2 is a schematic side perspective view of a mixer according to certain nonlimiting aspects of the invention for use in the method of FIG. 1;

[0018] FIG. 3 is a schematic end elevational view of the mixer; and

[0019] FIG. 4 is a schematic partial cross-sectional view of a two-phase atomizing nozzle used in the mixer. DETAILED DESCRIPTION

[0020] The following description is meant to describe what is shown in the drawings and / or to various contemplated embodiments shown and / or related to what is shown in the drawings. The embodiment(s) shown in the drawings and / or described herein are nonlimiting examples and do not themselves define the invention. Any of the features shown and / or described in relation to one embodiment may be combined with any one or more features shown and / or described relative to another embodiment in any suitable combination. Any dimensions shown in the drawings are exemplary only and are not intended to limit the scope of the invention. Numerical ranges stated in the format "from x to y" or "from about x to y" include the mentioned values and the values that are within the respective measuring accuracy as known to the skilled person. If several preferred numerical ranges are stated in this format, all ranges formed by the combination of the various end points are also included.

[0021] FIG. 1 represents a nonlimiting example of a method 100 of manufacturing titanium dioxide (TiO2) pigment particles with an organic oil coating according to certain aspects of the invention. At 102, a mixer is loaded with dry and / or powdered TiO2 pigment particles that have been manufactured according to any suitable process, such as the well known sulfate and / or chlorination processes. The mixer preferably includes both an agitator for mixing the pigment particles and a chopper for breaking apart agglomerated particles disposed inside a mixing tank. The mixer also may include one or more two-phase atomization nozzles for injecting the organic oil into the mixing tank. The mixer also may include one or more heating systems for heating the mixing tank as well as the atomization nozzles. One nonlimiting example of a mixer suitable for use in the process is illustrated in FIGS. 2-4, which are described in more detail hereinafter; however, other types and / or arrangements of mixers could be used. To reduce the risk of sparking and possible ignition during operation, the mixer may be grounded during the entire filling, mixing, and unloading cycle.

[0022] Preferably, the TiO2 pigment particles being loaded into the mixer have an average particle size, that is, the mass-related median d50 (hereinafter, d50), of between about 0.1 pm and about 1 pm, and more preferably between about 50 nm and about 500 nm, even more preferably between about 200 nm and about 400 nm, as determined by disc centrifuge. Optionally, the TiO2 pigment particles may have an “almost spherical” form, i.e., that closely approach, but do not necessarily precisely attain, a perfect spherical shape. While such approximately spherical form shares some characteristics with a sphere, such as a rounded appearance, smooth contours, and a lack of sharp edges, there may be slight deviations or irregularities in its form. The term "almost spherical" is a descriptive term conveying that the particles resemble a sphere to a high degree but may exhibit minor variations or imperfections. The term "almost spherical" excludes flake like structures. In one embodiment, the TiO2 pigment particles may be purified rutile TiO2 particles, either with or without one or more additional surface coatings of other metal oxides and a TiO2 content of at least 98% wt.%, preferably 99 wt.% or more rutile. One preferred possible TiO2 pigment particle may be, by way of nonlimiting example, the KRONOS™ 2071 grade purified pigment particles available from Kronos International; however, other TiO2 pigment particles could be used.

[0023] At 104, the mixer is heated to an elevated temperature above room temperature to heat the TiO2 pigment particles. Preferably, the elevated temperature is a temperature at which the which the organic oil has a viscosity close to the viscosity of water at about room temperature (between about 15-25 °C, more typically about 21 °C), for example, a viscosity within about 25% of the viscosity of water, preferably a viscosity within about 10% of the viscosity of water. The mixer can be heated to the elevated temperature before and / or after the TiO2 pigment particles are loaded into the mixer. In one nonlimiting example, the mixer is heated to a selected mixing temperature between about 70 °C and about 110 °C, more preferably to between about 80 °C and about 100 °C, depending on the type of organic oil to be used. The mixer may be heated prior to being loaded or after being loaded. For example, the mixer may be pre-heated after being loaded with the TiO2 pigment particles to the selected mixing temperature and prior to introducing the organic oil to ensure that all components of the mixer are already heated to the mixing temperature when the organic oil is introduced to the contents inside the mixer.

[0024] At 106, the heated TiO2 pigment particles are mixed with the agitator. The agitator may be turned on prior to loading the TiO2 pigment particles into the mixer or after the TiO2 pigment particles are loaded. For example, the agitator may be operated at a first slow speed, such as about 5 Hz while the TiO2 pigment particles are being loaded, and after the TiO2 pigment particles the speed of the agitator may be increased to increase aeration and movement of the TiO2 pigment particles inside the mixing tank, for example to about 20 Hz, so that at least an upper portion of the pigment particles are temporarily suspended in the air in the upper region of the mixing chamber 24. The agitator is preferably a low-shear mixer, such as a plough- or paddle-type mixer, that that can throw the upper pigment particles into the air in the upper region of the mixing chamber to temporarily suspend at least some of the pigment particles in the upper region of the mixing chamber, but does not create enough shear in the particulate contents being mixed to break the particulate contents apart.

[0025] At 108, organic oil is introduced into the heated mixing tank through the atomizing nozzles. Preferably, the organic oil is introduced while the agitator continues to mix the contents of the mixer. For example, the organic oil may be sprayed as an atomized mist directly into the cloud of suspended TiO2 pigment particles formed by the agitator. In some nonlimiting examples, the organic oil is a bio-based oil made of pure or substantially all soybean oil, although other bio-based oils, such as sesame oil, moringa oil, avocado oil, or rice seed oil. A bio-based oil is a type of oil that is derived from renewable biological sources, such as plants, algae, or other organic materials. Unlike traditional petroleumbased oils, which are derived from fossil fuels, bio-based oils are produced from biomass through processes like extraction, fermentation, or other bioconversion methods. Those biobased oils are typically environmentally sustainable and reduce the carbon footprint associated with their production. In other embodiments, the organic oil may be composed substantially of glycerin. The atomizing nozzles may also be heated to lower the oil’s viscosity to about the viscosity of water and improve atomization of the oil through the atomizing nozzles. The atomizing nozzles may be heated to either the same temperature or a different temperature than the rest of the mixer. For example, the atomizing nozzles may be heated to a temperature between about 70 °C and about 110 °C, more preferably to between about 80 °C and about 100 °C, although other temperatures may be used. The atomizing nozzles preferably heat the organic oil to a temperature to lower its viscosity to a viscosity that enables the two-phase atomizing nozzles to inject an atomized spray (e.g., an aerosolized mist) of the organic oil into the mixing tank to mix with the TiO2 pigment particles. For typical two-phase atomizing nozzles, this desired viscosity is typically about the same as the viscosity of water at room temperature.

[0026] Obtaining a homogenous coating of the TiO2 pigment particles with low amounts of oil is highly desirable when the coated pigment particles are to be used in cosmetics, for example for dispersing the pigments in a cosmetic formulation. If there is too much of the organic oil on the surfaces of the pigment particles, then these particles are not desirable for use for cosmetic purposes as the carbon content would be too high and the loss on drying and loss on ignition would be too high. On the other hand, not completely covering the pigment particles also can cause undesirable results when used in cosmetics, for example, by hindering proper dispersion in the cosmetic formulation. Therefore, having a relatively thin, even layer of the organic oil completely coating all the pigment particles homogeneously without having excess oil is desirable. To accomplish this, particularly at the industrial level, using the atomizing nozzles 18 to atomize (e.g., aerosolize) the organic oil into a spray or mist of very fine droplets that is slowly injected into the cloud of the suspended particles in the upper region of the mixing chamber caused by the agitator helps obtain the desired relatively thin, even, and substantially complete homogeneous coating of the organic oil on the outer surfaces of all the pigment particles in the mixing chamber. Maintaining the temperature of the contents of the mixer while mixing the contents at the elevated temperature also helps the oil to spread evenly across the surfaces of the individual pigment particles.

[0027] To further help ensure obtaining a thin, homogeneous coating of all the particles without having an excess of the organic oil, the amount of organic oil introduced into the mixer preferably is selected to be sufficient to substantially completely coat all the TiO2 pigment particles loaded into the mixer, but not so much as to have a significant excess of the oil or have a coating that is thicker than desired. For example, if the organic oil is soybean oil, the amount of soybean oil added to the load of TiO2 pigment particles is preferably between approximately 0.1 weight % and 1 wt.% (weight % measured relative to the weight of the TiO2 pigment particles), more preferably between approximately 0.3 wt.% and 0.4 wt.%, and even more preferably about 0.35 wt.%. In another example, if the organic oil is glycerin, the amount of glycerin added is preferably between approximately 0.1 weight % and 1 wt.% (weight % measured relative to the weight of the TiO2 pigment particles), more preferably between approximately 0.4 wt.% and 0.6 wt.%, and even more preferably about 0.55 wt.%. When the desired amount of the organic oil has been delivered into the mixing tank, the nozzles are turned off so that no additional organic oil is added to the mixture in order to prevent excess organic oil from being introduced into the batch.

[0028] At 110, with both the heated TiO2 pigment particles and the heated organic oil in the mixing tank, the mixture continues to be mixed with the agitator in order to form a homogeneous mixture of the TiO2 pigment particles coated relatively evenly and completely (homogenously) with the organic oil. This continued mixing may last as long as necessary to homogenize the mixture and the coating.

[0029] The process of mixing and coating the heated TiO2 pigment particles with the heated organic oil typically causes the coated TiO2 pigment particles to agglomerate together into agglomerates having sized larger than desired in the final product. Therefore, at 112, while the heated TiO2 pigment particles and the heated organic oil are being mixed with the agitator, the mixture of heated TiO2 pigment particles and the heated organic oil are also simultaneously de-agglomerated using the chopper(s). Preferably, the chopper(s) are turned on immediately prior to dosing the heated organic oil into the mixing tank; however, the choppers may be turned on after the heated organic oil is sprayed into the mixing tank. In either case, operating both the agitator and the chopper(s) at the same time results in breaking up agglomerates of the coated TiO2 pigment particles while the mixing is occurring, which may also help ensure full and / or even coating of all the de-agglomerated TiO2 pigment particles. The simultaneous mixing and chopping can be continued as long as desired to homogenize the mixture and / or break up agglomerated particles. In one example, the simultaneous mixing and chopping is continued for approximately 60 minutes, during which both the agitator and the chopper(s) are operating; however, other lengths of time may be implemented as desired or needed to achieve a desired level of coating, consistency of coating, and / or level of homogenization.

[0030] At 114, the mixer and the contents therein are cooled down to allow for subsequent packaging and / or processing, for example, preferably back to about room temperature. The cooling may be accomplished passively, for example by simply turning off the heating components used to heat the mixer and / or the atomizing nozzles, and / or the cooling may be accomplished actively with a cooling system to cool the mixer and the contents therein faster. In either case, the mixing and chopping preferably continue during this cooling down period, at least until the homogenized coated TiO2 pigment particles cool down to a temperature sufficient to prevent significant further agglomeration of the coated particles. For example, when the organic oil is soybean oil, the choppers may be turned off when the contents (and typically also the mixer) have cooled to a temperature of about 40 °C or less. It is evident that the processes of cooling and of simultaneously mixing and deagglomerating the contents may begin at essentially any time after the organic oil has been introduced into the TiO2 pigment particles in the mixer and may take almost any length of time desired to ensure suitably complete and / or even coating of the TiO2 pigment particles with the organic oil. For example, the agitator(s) and the chopper(s) may be both turned on to simultaneously mix, coat, and de-agglomerate the pigment particles during while the organic oil is being injected, and the cooling process may begin as soon as the desired amount of organic oil has been injected (e.g., atomized and sprayed) into the loaded mixer.

[0031] After the mixer has cooled sufficiently to turn off the choppers, the contents, that is the homogenous mixture of TiO2 pigment particles having a homogeneous coating of organic oil, (or simply the “coated TiO2 pigment particles”) may be removed from the mixer for packaging and / or further processing.

[0032] FIGS. 2-4 show a mixer 10 suitable for implementing many of the steps in the process 100. The mixer includes a mixing tank 12 defining a mixing chamber 24 therein, an agitator 14 disposed in the mixing chamber, at least one chopper 16 disposed in the mixing chamber, and at least one two-phase atomizer nozzle 18 for injecting a spray of atomized fluid into the mixing chamber. In addition, the mixer includes one or more heating units 20 for heating the mixing tank 12 and the nozzles 18. The mixing tank 12 may be in the form of an elongate cylindrical tank that is oriented horizontally along its axis, as illustrated in FIG. 2. The agitator is configured to thoroughly mix contents in the mixing chamber by agitating and / or stirring the contents, preferably at speeds slow enough so as not to damage the TiO2 pigment particles or de-agglomerate agglomerated particles and fast enough to temporarily suspend at least some of the particles up in the air. For example, the agitator may rotate at any speed up to about 2000 rpm, including, for example speeds from 0 to 200 rpm, to 300 rpm (5 Hz), to 1200 rpm (20 Hz), on up to 2000 rpm, as well as any speed therebetween. The agitator 14 may be of the type having a rotatable shaft and mixing elements extending from the rotatable shaft. For example, the agitator 14 may include a plurality of ploughshare blades 22 extending radially outwardly from a central axle extending substantially horizontally along the central axis of the mixing tank 12. One preferred mixer is the Lbdige ploughshare mixer by Gebruder Lbdige Maschinenbau GmbH with an agitator 14 having four ploughshare blades; however other types and configurations of mixers could be used.

[0033] Preferably, several choppers 16 are provided inside the tank for de-agglomerating agglomerated coated TiO2 particles. In this example, four choppers 16 are disposed on the interior wall of the mixing chamber 24. Preferably, the choppers 16 are disposed below the horizonal centerline / axis of the mixing tank 12 and above the bottom of the mixing chamber. Additional or fewer choppers 16 and different locations may be used in other configurations. The choppers 16 are preferably high-shear / high-speed choppers with knife blades that rotate at speeds and produce shears high enough to break up agglomerated oil / TiO2 agglomerate clusters back into un-agglomerated particles. Typical rotation speeds for choppers are typically about 2500 rpm to about 3600 rpm, although other speeds may be used depending on the design of the knife blades. The choppers may be, for example, four-knife blade type choppers with a 4 kW power input, although other types and numbers of choppers may be used.

[0034] As schematically illustrated in FIG. 4, the atomizer nozzles 18 are two-phase nozzles that vigorously mix a first flow of the organic oil with a second flow of a propellant gas in an internal mixing chamber before forcefully ejecting the mixed oil and propellant out of an outlet orifice in an atomized spray configuration into the mixing chamber 24 of the mixing tank 12. The atomizer nozzles 18 may be disposed at the top of the mixing chamber 24 so as to spray an atomized mist of the organic oil down into any contents being mixed in the mixing chamber by the agitator 14. In the shown example, three atomizing nozzles 18 are spaced apart along the horizontal length of the mixing tank 12 along the top of the mixing tank; however, more or fewer atomizing nozzles could be used.

[0035] The heating units 20a and 20b are configured to heat the mixing tank 12 and the atomizing nozzles 18. Preferably, the heating units 20a are arranged on the mixing tank 12 so as to substantially evenly heat the entire mixing tank. The heating units 20b are arranged so as to heat each atomizing nozzle 18. The heating units 20a and 20b may be integral heating units or they may be separate heating units. Preferably, the heating units 20a and 20b are configured to be able to heat the mixing tank 12 independently from the atomizing nozzles 18 so that the mixing tank can be heated at a different time and to a different temperature than the atomizing nozzles. The heating units 20a and 20b may also optionally include the capability of actively cooling the mixing tank 12 and / or the atomizing nozzles 18. In one example, the heating units 20a and 20b are water heating and / or cooling systems that can circulate heated and / or chilled water; however other types of heating systems, such as electric or gas fired heating systems could be used. The heating system 20a is preferably configured to be able to heat the mixing tank 12, as well as all contents and components held inside the tank, to temperatures ranging from at least 70 °C to at least 110 °C within a period of 30 minutes to 6 hours. The heating system 20b is preferably configured to be able to heat each mixing nozzle 18 to a separate temperature ranging from at least 70 °C to at least 110 °C within a similar or less time period of time.

[0036] The mixer may optionally include temperature measurement sensors for monitoring the temperature of the mixer 10 and / or any of the various components and / or contents inside the mixing chamber 24. Of course, suitable doors may be provided at any suitable locations along the mixing tank 12 to allow for loading and / or unloading of the TiO2 pigment particles into and out of the mixing tank.

[0037] Preferably, the mixer may be grounded to reduce the risk of sparking during operation, for example from electrostatic charge buildup due to the loading and / or mixing operations. Such grounding may or may not be permanent, but preferably is continual during the entire filling, mixing, and unloading cycle.

[0038] Next, a nonlimiting example of a process conducted according to principles of the present invention using the mixer 10 is provided.

[0039] In a first step, a Lodige 3000 Mixer configured as describe for mixer 10 is filled with 1250 kg TiO2 piment particles (KRONOS 2071 grade pigment particles) with the agitator 14 turned on at about 5 Hz.

[0040] In a second step, the mixer 10 is closed and the agitator speed is adjusted to about 20 Hz. At the same time, the mixer is pre-heated by the heating unit(s) 20a up to about 75°C over a period of about 4-5 hours.

[0041] In a third step, the knife choppers are tuned on and the inlet temperature of the heating unit(s) 20b are turned on to about 90 °C.

[0042] In a fourth step, the atomizer nizzles 18 are heated to about 80°C, and dosing stations for supplying soybean oil to the atomizer nozzles 18 are filed.

[0043] In a fifth step, the soybean oil is sprayed through the heated atomizer nozzles 18 at a pressure of about 0.2 barg and 3 barg of nitrogen (as a propellant) for a time period of about 2-3 hours to provide approximately 0.3-0.4 wt% of soybean oil in the mixing chamber 24 with the TiO2 pigment particles.

[0044] In a sixth step, the heating is turned off and the simultaneous mixing (agitating) with the agitator 14 and chopping / de-agglomerating with the knife choppers 16 continues for about 60 minutes after turning off the heat, and then, in a seventh step, the cooling system is turned on.

[0045] In an eighth step, when the temperature of the mixing tank 12 is lower than 40 °C (after about 75 minutes), the choppers 16 are turned off. Thereafter, the homogenized, organic-oil-coated TiO2 particles are removed from the mixing tank the lower mixer outlet and filled directly into storage bags for subsequent storage, transportation, and / or other processing, such as sieving in a sieve mill.

[0046] The process and equipment provide a homogeneous coating of the TiO2 particles and also reduces the amount and / or size of agglomerated particles, which can provide improved characteristics when use din cosmetics. By heating the nozzles, and subsequently the organic oil, smaller droplets can be produced, which helps provide a more homogeneous 5 and / or even coating on the TiO2 particles being swirled around with high turbulence during the mixing. In addition heating the entre mixing chamber and the TiO2 particles also helps the organic oil can to spread more easily across the surfaces of the TiO2 particles (almost like water). Under these conditions, the fixation by adhesions forces is much higher in comparison to a standard pigment liquid mixing processes. TiO2 pigment particles coated 10 with organic oils in accordance with the teachings of the present invention can provide a significant improvement in the dispersion quality in cosmetics, such as an all-day-long foundation formulation. The pigment particles coated in with this process also provide improved brightness in cosmetics over other pigment particles.

Claims

1. A method of manufacturing titanium dioxide (TiO2) pigment particles with an organic coating, the method comprising:loading a charge of TiO2 pigment particles into a mixer, wherein the mixer comprises at least one two-phase atomizer nozzle for injecting an organic oil into the mixer, at least one agitator for mixing components inside the mixer, and at least one chopper for deagglomerating the components inside the mixer;heating the mixer and the charge of TiO2 pigment particles to an elevated temperature sufficient to lower the viscosity of the organic oil;injecting a selected amount of organic oil into the heated mixer through the two-phase atomizer nozzle(s);while injecting the selected amount of organic oil, mixing the heated TiO2 pigment particles inside the mixer with the agitator to form a homogeneous mixture of the TiO2 pigment particles coated with the organic oil;while mixing with the agitator, chopping the heated TiO2 pigment particles and the injected organic oil with the chopper to break up agglomerates formed by the mixture of the organic oil and the TiO2 particles, thereby forming a homogeneous mixture of deagglomerated coated TiO2 particles; andending the chopping after the mixer reaches a preselected temperature at which agglomeration of the organic oil and the TiO2 pigment particles substantially ceases.

2. The method of claim 1, further comprising;cooling the mixer and the homogeneous mixture contained therein after injecting the selected amount of organic oil into the mixer; andcontinuing to simultaneously mix and chop the homogeneous mixture with the agitator and the chopper until the mixer cools to the preselected temperature.

3. The method of claim 1, wherein the elevated temperature is above about 70° C, preferably between about 70° C and about 110° C.

4. The method of any one of the previous claims, wherein the organic oil iscomprised primarily of soybean oil and the elevated temperature is between about 70° C and about 85° C, preferably about 80° C, and optionally wherein the selected amount of soybean oil injected into the mixer is between about 0.1 weight % and about 1 weight %, preferably about 0.35 weight %, relative to the charge of TiO2 pigment particles.

5. The method of any one of claims 1-3, wherein the organic oil is comprised primarily of glycerin and the elevated temperature is between about 90° C and about 110° C, preferably about 100° C, and optionally wherein the amount of glycerin injected into the mixer is between about 0.1 weight % and about 1 weight %, preferably about 0.55 weight %, relative to the charge of TiO2 pigment particles.

6. The method of any one of the previous claims, wherein the agitator forms a cloud of suspended TiO2 pigment particles inside the mixer, and optionally wherein the two-phase nozzles inject the organic oil as an atomized spray into the cloud of suspended TiO2 pigment particles.

7. The method of any one of the previous claims, further comprising:sieving the de-agglomerated coated TiO2 particles to obtain a preselected size of the de-agglomerated coated TiO2 particles.

8. The method of any one of the previous claims, further comprising:electrically grounding the mixer to prevent buildup of electrostatic charge in the TiO2 pigment particles during the mixing, and optionally wherein the mixer is electrically grounded continually from the time the charge of TiO2 pigment is loaded into the mixer until the deagglomerated coated TiO2 particles are removed from the mixer.

9. The method of any one of the previous claims, wherein the preselected temperature at which the chopping is ended is between about 30 °C and about 50 °C, preferably about 40 °C.

10. The method of claim 1, wherein the preselected temperature at which the chopping is ended is about 40 °C or lower when the organic oil is comprised primarily ofsoybean oil.

11. A mixing apparatus for coating TiO2 pigment particles with an organic oil in accordance with the method of any one of the previous claims, the mixing apparatus comprising:a mixer (10) comprising at least one agitator (14) and at least one chopper (16) disposed inside a mixing tank (12) configured to receive a batch of the TiO2 pigment particles;at least one two-phase atomizer nozzle (18) configured to spray the organic oil into the mixing tank; andone or more heating units (20a, 20b) configured to heat the mixing tank and the and the two-phase atomizer nozzles to at least about 70 °C.

12. The mixing apparatus of claim 11, wherein the at least one agitator (14) comprises a plurality of ploughshare blades (22), preferably four ploughshare blades.

13. The mixing apparatus of any one of claims 11-12, wherein the mixing tank (12) comprises a horizontally elongate cylindrical body and the choppers are disposed along an interior sidewall of the mixing tank between a bottom and a horizontal centerline of the horizontally elongate cylindrical body, and wherein optionally the mixer is grounded to prevent buildup of electrostatic charges in the mixer.

14. The mixing apparatus of any one of claims 11-13, wherein the at least one atomizer nozzle (18) is positioned at a top of the mixing tank, and optionally wherein there are four atomizer nozzles, and optionally wherein the atomizer nozzles provide for internal mixing of a propellant gas and the organic oil before emitting an atomized spray of a mixture of the propellant gas and the organic oil.

15. The mixing apparatus of any one of claims 1 -14, wherein the one or more heating units (20a) are configured to heat the mixing tank (12) to a first elevated temperature between about 70 °C and about 110 °C, preferably about 90 °C, and the one or more heating units (20b)are configured to separately heat the atomizer nozzles (18) to a second elevated temperature between about 70 °C and about 110 °C, preferably about 80 °C, and optionally one or more cooling units for actively cooling the mixing tank and / or the atomizernozzles, and optionally wherein the one or more heating units and the one or more cooling units comprise water heating and water cooling systems.

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