HK1149043A - Coatings including pigments comprising substrate particles with ultrafine metal oxide particles deposited thereon - Google Patents

Description

Coating comprising pigment comprising substrate particles and ultrafine metal oxide particles deposited thereon

Technical Field

The present invention relates to colored coatings, and more particularly to coatings comprising inorganic pigments comprising substrate particles and ultrafine metal oxide particles deposited on the surface of the substrate particles.

Background information

Many types of pigments are used in various coating applications. For example, inorganic pigments such as TiO₂、Fe₂O₃、Al₂O₃MgO, CaO, ZnO, carbon black and aluminum silicates are often used in paints and other coatings. These inorganic pigments typically have particle sizes of about 0.5 to about 30 microns and are prepared by processes such as flame processes, plasma processes, solution processes, and sol-gel processes. For example, most commercial TiO₂Using TiCl₄Prepared as starting materials. Pure TiCl₄Reacts with oxygen in an exothermic reaction to form titanium dioxide and gives off chlorine, which is recycled to the chlorination stage. The high temperature ensures that only the rutile crystalline form is produced. After cooling, the gaseous stream is passed through a separator to collect the pigment particles, which are treated to remove adsorbed chlorine from the pigment.

Summary of The Invention

In certain aspects, the present invention relates to a coating composition comprising a base coating material and a pigment dispersed in the base coating material, wherein the pigment comprises substrate particles and ultrafine metal oxide particles deposited on the substrate particles.

In other aspects, the invention relates to a method of preparing a coating composition comprising mixing a pigment and a base coating material, wherein the pigment comprises substrate particles and ultrafine metal oxide particles deposited on the substrate particles.

In other aspects, the present invention relates to pigments comprising substrate particles and ultrafine partially oxidized metal oxide particles deposited on the substrate particles.

In other aspects, the invention relates to a method of making a pigment comprising introducing a substrate particle precursor and an ultrafine metal oxide particle precursor to a plasma, heating the precursors by the plasma to form pigment particles comprising the substrate particles and the ultrafine partially oxidized metal oxide particles deposited thereon, and collecting the pigment particles.

Brief Description of Drawings

FIG. 1 illustrates pigment particles comprising substrate particles and ultrafine metal oxide particles deposited thereon according to certain aspects of the present invention.

FIG. 2 is a flow chart depicting steps of certain methods of the present invention.

Fig. 3 is a partial schematic cross-sectional view of an apparatus for preparing pigment particles comprising ultrafine metal oxide particles deposited on substrate particles, including a precursor feed tube and a plasma chamber, according to certain embodiments of the present invention.

Fig. 4 is a partial schematic cross-sectional view of an apparatus for preparing pigment particles comprising ultrafine metal oxide particles deposited on substrate particles, including a precursor feed tube and a plasma chamber, according to certain embodiments of the present invention.

FIG. 5 is a plot of reflected light intensity versus wavelength for two pigment samples of the present invention.

Detailed description of the invention

For purposes of the following detailed description, it is to be understood that the invention may assume various alternative variations and step sequences, except where expressly specified to the contrary. Moreover, other than in any operating examples, or where otherwise indicated, all numbers expressing, for example, quantities of ingredients used in the specification and claims are to be understood as being modified in all instances by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

In addition, it should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of "1 to 10" is intended to include all sub-ranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, i.e., all sub-ranges having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10.

In this application, the use of the singular includes the plural and plural encompasses singular, unless specifically stated otherwise. Also in this application, the use of "or" means "and/or" unless specifically stated otherwise, although "and/or" may be explicitly used in certain instances.

The term "average particle size" as used herein refers to a particle size determined by: a micrograph of a transmission electron microscopy ("TEM") image is visually inspected, the diameter of the particles in the image is measured, and the average particle size of the measured particles is calculated based on the magnification of the TEM image. One of ordinary skill in the art will understand how to make such TEM images and determine the average particle size based on magnification. Particle size refers to the smallest diameter sphere that will completely encapsulate an individual particle.

The term "b.e.t. specific surface area" as used herein refers to the specific surface area as determined by nitrogen adsorption according to astm d 3663-78 standard based on the Brunauer-Emmett-Teller method described in the journal of the American Chemical Society ", 60, 309 (1938). As will be appreciated by those skilled in the art, the calculated equivalent spherical diameter can be determined from the b.e.t. specific surface area according to the following equation:

diameter (nm) 6000/[ BET (m)²G). rho (g/cm)³)]

The term "pigment" as used herein refers to a material that changes the color of light it reflects as a result of selective color absorption. Pigments have a high tinctorial strength relative to the material they are pigmented. Pigments are stable in solid form at ambient temperature and are insoluble in the carrier in which they are suspended.

Fig. 1 schematically illustrates a pigment particle 10 according to an embodiment of the present invention. The pigment particles 10 comprise substrate particles 11 and a plurality of ultrafine metal oxide particles 12 deposited on the surface of the substrate particles. As described more fully below, during the formation of pigment particles in a plasma system, relatively large substrate particles 11 are formed first, followed by heterogeneous nucleation and deposition of ultrafine metal oxide particles 12 on the surface of the previously formed substrate particles 11. Although the ultrafine metal oxide particles 12 may form a monolayer on the substrate particles 11 in which adjacent ultrafine particles contact each other as shown in fig. 1, the deposited ultrafine particles may not contact each other in some embodiments, for example, when there is a lower proportion or concentration of ultrafine oxide particles 12 as compared to the substrate particles 11.

In certain embodiments, the substrate particles 11 have an average particle size of no more than 1,000 nanometers, in some cases no more than 500 nanometers, or in other cases no more than 300 or 400 nanometers. In certain embodiments, the substrate particles have an average particle size of not less than 20 nanometers, and in some cases not less than 50 nanometers. For example, the substrate particles may have an average particle size of about 100 to about 300 nanometers.

The substrate particles may comprise oxides, mixed oxides and/or nitrides. In certain embodimentsThe substrate particles comprise SiO₂、Al₂O₃、Bi₂O₃、Al₂SiO₅、BN、AlN、Si₃N₄And the like. In a particular embodiment, the substrate particles comprise SiO₂。

In certain embodiments in which the pigment particles 10 are mixed into a coating composition, the substrate particles 11 have a refractive index that substantially matches the refractive index of the base material of the coating composition in which the pigment particles are mixed. In this embodiment, by substantially matching the refractive index of the substrate particles 11 to the refractive index of the base material of the coating composition, the substrate particles 11 appear substantially colorless and provide the desired color characteristics to the pigment particles 10 by virtue of the deposited ultrafine metal oxide particles 12. In certain embodiments, the refractive index of the substrate particles 11 may be from about 1.4 to about 1.6, and in some cases from about 1.48 to about 1.54.

The ultrafine metal oxide particles 12 typically have an average particle size of no more than 20 nanometers, such as no more than 10 nanometers. In certain embodiments, the ultrafine metal oxide particles have an average particle size of 1 to 5 nanometers, and in some cases 2 to 4 nanometers.

In certain embodiments, the ratio of the average particle size of the substrate particles 11 to the average particle size of the ultrafine metal oxide particles 12 is greater than 2: 1, and in some cases greater than 5: 1. For example, the average particle size ratio can be from about 10: 1 to about 1,000: 1, and in some cases from about 20: 1 to about 500: 1.

The metal of the ultrafine metal oxide particles 12 may include at least one metal selected from Cu, Al, Si, Ti, V, Mn, Fe, Co, Mo, Sn, Ce, and the like.

According to certain embodiments of the present invention, the ultrafine metal oxide particles 12 are partially oxidized. The term "partially oxidized" as used herein means that the metal oxide is not in its highest oxidation state. For example, copper oxide in its fully oxidized state has the formula CuO, while partially oxidized copper oxide has lower oxygenAtomic ratio, for example, 0 to less than 1. As a specific example, the partially oxidized copper oxide may include Cu₂And O. As another example, although the fully oxidized titanium oxide has the formula TiO₂However, the partially oxidized titanium oxide may have the formula Ti₃O₄. In certain embodiments, the partially oxidized ultrafine metal oxide particles may include AlO, SiO, Ti₃O₄、V₂O₃、VO、MnO、Mn₂O₃、Fe₃O₄、Co₃O₄、Cu₂O、MoO₂SnO and/or Ce₂O₃. Partial oxidation may result from the use of partially oxidized feed materials such as those described above. Further, partial oxidation may result from the use of an inert atmosphere during the plasma formation process according to certain embodiments of the present invention. For example, a substantially oxygen-free carrier gas may be introduced into the plasma, as described more fully below.

In certain embodiments, Cu₂Ultrafine metal oxide particles in which O is partially oxidized are formed on substrate particles such as SiO₂The above. The use of the substrate particles allows Cu₂SiO where O is first formed during the plasma treatment process₂Nucleation on the substrate particles is heterogeneous. Cu without prior formation of the base particles₂O does not form particles small enough, i.e. less than 10nm, but grows to a much larger particle size.

FIG. 2 is a flow chart depicting certain embodiments of the process of the present invention. A substrate precursor material and a metal oxide precursor material are provided as feeds. In the embodiment shown in fig. 1, the precursors are provided from separate sources. However, a single source of a mixture comprising the precursors may be used.

In certain embodiments, the substrate precursor material is provided in the form of solid particles. The particles may be suspended in a suitable fluid such as a carrier gas or liquid. The particulate substrate precursor feed typically has an average particle size of greater than 0.1 microns, in some cases from about 0.3 to about 200 microns.

The ultrafine metal oxide precursor feed may be provided in particulate form. The particles may be suspended in a fluid, such as a carrier gas or a liquid. The particulate ultrafine metal oxide precursor feed typically has an average particle size of greater than 0.5 microns, in some cases from about 10 to about 200 microns.

According to certain embodiments, the ultrafine metal oxide precursor material has different reflective properties than the pigment particles prepared by the plasma process. For example, the ultrafine metal oxide particles deposited on the surface of the substrate particles as a result of the plasma process may have a different color than the starting particulate ultrafine metal oxide precursor material. For example, when Cu is used₂When O is fed as an ultra-fine metal oxide precursor, it may be provided in the form of a powder having a red color. However, after plasma treatment, ultra-fine Cu is deposited on the substrate particles₂The O particles may provide a pigment having a green color. In this case, changing from red to green represents moving from the longer reflection wavelength to the shorter reflection wavelength.

As shown in fig. 2, according to certain methods of the present invention, the precursor is contacted with a support. The carrier may be a gas for suspending or atomizing the precursor in the gas and thereby generating a gaseous stream (gaseous stream) in which the precursor is entrained. In certain embodiments, the carrier gas is inert and substantially free of oxygen to maintain partial oxidation of the ultrafine metal oxide particles formed during the plasma process. Suitable carrier gases include, but are not limited to, argon, helium, nitrogen, hydrogen, or combinations thereof.

Next, according to certain embodiments of the present invention, the precursors are heated by a plasma system, for example, as entrained precursors flow into a plasma chamber, resulting in gaseous streams of the precursors and/or their gasification or thermal decomposition products and/or their reaction products. In certain embodiments, the precursor is heated to a temperature of 1,500-20,000 deg.C, such as 1,700-8,000 deg.C.

In certain embodiments, the gaseous stream may be contacted with other reactants or a dopant may be injected into the plasma chamber or it may be introduced as part of the precursor. Suitable additional reactant materials include, but are not limited to, hydrogen, nitrogen, methane, and/or silane.

In certain methods of the invention, after the gaseous stream is generated, it is contacted with one or more quench streams injected into the plasma chamber through at least one quench stream injection port. For example, the quench streams are injected at a flow rate and injection angle such that the quench streams collide with each other within the gaseous stream. The material used for the quench stream is not limited so long as it cools the gaseous stream sufficiently to promote the formation of or control the particle size of the substrate particles and the ultrafine metal oxide particles deposited on the surface of the substrate particles, as well as maintain the desired particle composition. Suitable materials for use in the quench stream include, but are not limited to, inert gases such as argon, helium, nitrogen, carbon dioxide, hydrogen, ammonia, mono-, di-, and polyhydric alcohols, hydrocarbons, amines, and/or carboxylic acids.

In certain embodiments, the particular flow rate and angle of injection of the individual quench streams may vary so long as they impinge one another within the gaseous stream such that the gaseous stream is rapidly cooled. For example, before, during, and/or after particle formation, the quench stream may cool the gaseous stream primarily by dilution rather than adiabatic expansion, as described below, prior to passing the particles into and through a converging element, such as a converging-diverging nozzle, thereby causing rapid quenching of the gaseous stream.

In certain embodiments of the invention, after the gaseous product stream is contacted with the quench stream to produce particles, the particles may be passed through a converging element, wherein the plasma system is designed to minimize fouling thereof. In certain embodiments, the converging element comprises a converging-diverging (De Laval) nozzle. In these embodiments, while a converging-diverging nozzle may be used to cool the product stream to some extent, the quench stream performs a substantial amount of cooling such that a significant amount of particles are formed upstream of the nozzle. In these embodiments, the converging-diverging nozzle may act primarily as a choke point (chokenose) that allows the reactor to operate at higher pressures, thereby increasing the residence time of the material therein.

As seen in fig. 2, in certain embodiments of the present method, the pigment particles are collected after they exit the plasma system. Any suitable means may be used to separate the particles from the gas stream (gas flow), such as bag filters, cyclones or deposition on a substrate. The collected ultra-fine particles are then mixed with a base coating material composition comprising a binder or resin, a liquid medium and additives conventionally used in coating compositions.

Fig. 3 is a partial schematic cross-sectional view of an apparatus for preparing pigment particles according to certain embodiments of the present invention. A plasma chamber 20 is provided that includes a feed inlet 50 for introducing a mixture of substrate particle precursors and ultra-fine metal oxide particle precursors into the plasma chamber 20 in the embodiment shown in fig. 3. In another embodiment, feed inlet 50 may be replaced with a separate inlet (not shown) for a different precursor. At least one carrier gas feed inlet 14 is also provided through which a carrier gas flows into the plasma chamber 20 in the direction of arrow 30. A carrier gas may be used to suspend or atomize the precursor in the gas, thereby generating a gaseous stream with entrained precursor that flows to the plasma 29. Numerals 23 and 25 denote cooling inlets and outlets, respectively, which may be present for the double-walled plasma chamber 20. In these embodiments, the coolant flow is represented by arrows 32 and 34.

In the embodiment depicted by fig. 3, a plasma torch 21 is provided. The torch 21 may thermally decompose or vaporize the precursor within or near the plasma 29 as the stream is conveyed through the inlet of the plasma chamber 20, thereby generating a gaseous stream. As seen in fig. 2, in certain embodiments, the precursor is injected downstream of the location where the arc is connected to the annular anode 13 of the plasma generator or torch.

The plasma is a high temperature luminescent gas that is at least partially (1-100%) ionized. The plasma is composed of gas atoms, gas ions, and electrons. By passing a gas through an arc, a thermal plasma may be generated. The arc will heat the gas rapidly within microseconds through the arc by resistive and radiative heating to very high temperatures. The plasma generally emits light at temperatures above 9,000K.

The plasma may be generated with any of a number of gases. This may provide excellent control over any chemical reaction that takes place in the plasma, as the gas may be inert, such as argon, helium or neon, reducing, such as hydrogen, methane, ammonia and carbon monoxide, or oxidising, such as oxygen, nitrogen and carbon dioxide. According to the invention, the pigment particles can be prepared using inert or reducing gas mixtures. In fig. 3, the plasma gas feed inlet is depicted at 31.

As the gaseous product stream exits the plasma 29, it proceeds toward the outlet of the plasma chamber 20. As previously described, additional reactants may optionally be injected into the reaction chamber prior to injecting the quench stream. The supply inlet for the further reactants is shown at 33 in figure 3.

As seen in fig. 3, in certain embodiments of the present invention, the gaseous stream is contacted with a plurality of quench streams entering the plasma chamber 20 through a plurality of quench stream injection ports 40 disposed along the periphery of the plasma chamber 20 in the direction of arrows 41. As previously mentioned, the particular flow rate and angle of injection of the quench streams are not limited as long as they cause the quench streams 41 to collide with each other within the gaseous stream, in some cases at or near the center of the gaseous stream, thereby causing the gaseous stream to rapidly cool to control the particle size of the substrate particles and the ultra-fine metallic particles deposited thereon. This may allow the gaseous stream to be quenched by dilution.

In certain processes of the present invention, contacting the gaseous stream with the quench stream can result in the formation of particles and/or control of particle size of the particles, which are then passed into and through a converging element. The term "converging element" as used herein refers to a device that restricts the passage of fluid therethrough, thereby controlling the residence time of the fluid in the plasma chamber due to the pressure differential upstream and downstream of the converging element.

In certain embodiments, the converging element comprises a converging-diverging (De Laval) nozzle, such as described in fig. 3, disposed within the outlet of the plasma chamber 20. The converging or upstream portion of the nozzle (i.e., the converging element) restricts the passage of gases and controls the residence time of the material within the plasma chamber 20. It is believed that the constriction in the cross-sectional dimension of the stream as it passes through the converging portion of the nozzle 22 changes the motion of at least some of the fluid from a random direction (including rotational and vibrational motion) to a linear motion parallel to the axis of the plasma chamber. In certain embodiments, the dimensions of the plasma chamber 20 and material flow are selected to achieve sonic velocity at the restricted nozzle throat.

As the restricted stream of fluid enters the diverging or downstream portion of the nozzle 22, it experiences an ultra-rapid decrease in pressure due to the gradual increase in volume along the conical wall of the nozzle outlet. By proper selection of nozzle size, the plasma chamber 20 can be operated at atmospheric pressure or slightly less than atmospheric pressure or in some cases under pressurized conditions to achieve the desired residence time, while the chamber 26 downstream of the nozzle 22 is maintained at vacuum pressure by operating vacuum generating equipment, such as a vacuum pump 60. After passing through the nozzle 22, the pigment particles may then enter a cooling chamber 26.

Although the nozzle shown in FIG. 2 includes a converging portion and a downstream diverging portion, other nozzle configurations may be used. For example, the downstream diverging portion may be replaced with a straight portion. The quench stream may be introduced at or near the transition from the converging portion to the straight portion.

As is evident from fig. 3, in certain embodiments of the invention, the pigment particles may flow from the cooling chamber 26 to the collection station 27 through a cooling section 45, which cooling section 45 may comprise, for example, jacketed cooling tubes. In certain embodiments, the collection station 27 comprises a bag filter or other collection means. If desired, a downstream scrubber 28 may be used to condense and collect material within the fluid before it enters the vacuum pump 60.

Fig. 4 is a partial schematic view of an apparatus for preparing pigment particles according to certain embodiments of the present invention. A plasma chamber 120 is provided that includes a precursor feed inlet 150. At least one carrier gas feed inlet 114 is also provided through which carrier gas flows into the plasma chamber 120 in the direction of arrow 130. As previously described, the carrier gas acts to suspend the precursor in the gas, thereby creating a gaseous stream suspension of the precursor flowing to the plasma 129. Numerals 123 and 125 denote cooling inlets and outlets, respectively, which may be present for the double-walled plasma chamber 120. In these embodiments, the flow of coolant is represented by arrows 132 and 134.

In the embodiment depicted by fig. 4, a plasma torch 121 is provided. As the stream is conveyed through the inlet of the plasma chamber 120, the torch 121 thermally decomposes the incoming precursor gaseous stream suspension within the resulting plasma 129, thereby generating a gaseous product stream. As seen in fig. 4, in certain embodiments, the precursor is injected downstream of the location where the arc is connected to the annular anode 113 of the plasma generator or torch.

In fig. 4, the plasma gas feed inlet is depicted at 131. As the gaseous product stream exits the plasma 129, it proceeds toward the outlet of the plasma chamber 120. Obviously, as previously described, the reactants may be injected into the reaction chamber prior to the injection of the quench stream. The supply outlet for the reactants is shown at 133 in fig. 4.

As seen in fig. 4, in certain embodiments of the invention, the gaseous product stream is contacted with a plurality of quench streams that enter the plasma chamber 120 in the direction of arrows 141 through a plurality of quench stream injection ports 140 disposed along the periphery of the plasma chamber 120. As previously mentioned, the particular flow rate and angle of injection of the quench streams are not limited as long as they cause the quench streams 141 to collide with one another within, and in some cases at or near the center of, the gaseous product stream, thereby causing the gaseous product stream to rapidly cool to produce ultrafine metal oxide particles on the substrate particles. This allows the gaseous product stream to be quenched by dilution to form ultrafine particles.

In certain embodiments of the invention, such as described in fig. 4, one or more sheath streams (sheath streams) are injected into the plasma chamber upstream of the focusing element. The term "sheath flow" as used herein refers to a gaseous stream that is injected before a converging element and injected at a flow rate and injection angle that results in an obstruction separating the gaseous product stream from the plasma chamber wall (including the converging portion of the converging element). There is no limitation on the material used for the sheath flow, so long as the flow acts as an obstacle between the gaseous product stream and the converging portion of the converging element, as exemplified by preventing (at least to a significant extent) material from adhering to the inner surface of the plasma chamber wall (including the converging element). For example, materials suitable for use in the sheath stream include, but are not limited to, those materials described above with respect to the quench stream. The feed inlet for sheath flow is shown at 170 in fig. 4 and the direction of flow is indicated by numeral 171.

By appropriate selection of the size of the converging element, the plasma chamber 120 may be operated at atmospheric pressure or slightly less than atmospheric pressure, or in some cases under pressurized conditions to achieve the desired residence time, while the chamber 126 downstream of the converging element 122 is maintained at vacuum pressure by operating a vacuum generating device, such as a vacuum pump 160. After the pigment particles are produced, they may then enter the cooling chamber 26.

As is evident from fig. 4, in certain embodiments of the invention, the pigment particles may flow from the cooling chamber 126 to the collection station 127 through a cooling section 145, which cooling section 145 may comprise, for example, jacketed cooling tubes. In certain embodiments, the collection station 127 comprises a bag filter or other collection means. If desired, a downstream scrubber 128 may be used to condense and collect material within the fluid before the fluid enters the vacuum pump 160.

The precursor may be injected through an orifice under pressure (e.g., 1-100psi) to achieve a sufficient flow rate to permeate and mix with the plasma. In addition, the injected precursor flow is injected perpendicular (90 ° angle) to the flow of the plasma gas in many cases. In some cases, it may be desirable to deviate plus or minus 90 ° by as much as 30 °.

The high temperature of the plasma can rapidly decompose and/or vaporize the precursor. There may be significant differences in temperature gradients and gas flow patterns along the length of the plasma chamber 20. It is believed that at the plasma arc inlet, the flow is turbulent and there is a high temperature gradient from about 20,000K at the chamber axis to about 375K at the chamber wall. It is believed that at the nozzle throat, the flow is laminar and there is a very low temperature gradient across its restricted open area.

The plasma chamber is typically constructed of water-cooled stainless steel, nickel, titanium, copper, aluminum, or other suitable material. The plasma chamber may also be constructed of ceramic materials to withstand the harsh chemical and thermal environments.

The plasma chamber walls can be internally heated by a combination of radiation, convection, and conduction. In certain embodiments, cooling of the plasma chamber walls prevents unwanted melting and/or corrosion at their surfaces. The system for controlling this cooling should maintain the walls at a temperature as high as can be allowed by the wall material selected, which is generally inert to the materials within the plasma chamber at the desired wall temperature. The same is true for the nozzle wall, which can be heated by convection and conduction.

The length of the plasma chamber is often determined experimentally by: first, an elongated tube is used in which a user can set a target critical temperature. The plasma chamber can then be designed to be long enough so that the material has sufficient residence time at the high temperature to reach equilibrium and complete the formation of the desired end product.

The inner diameter of the plasma chamber may be determined by the fluid properties of the plasma and the moving gaseous stream. It should be large enough to allow the necessary gas flow, but not so large that a circulating vortex or quiescent zone is formed along the chamber walls. This detrimental flow pattern can cause premature cooling of the gas and precipitation of undesirable products. In many cases, the inner diameter of the plasma chamber exceeds 100% of the plasma diameter at the inlet end of the plasma chamber.

In certain embodiments, the converging portion of the nozzle has a high aspect ratio change in diameter that maintains a smooth transition to a first steep angle (e.g., > 45 °) and then to a smaller angle (e.g., < 45 °) leading to the nozzle throat. The purpose of the nozzle throat is generally to compress the gas and achieve sonic velocity in the fluid. The velocity achieved in the throat of the nozzle and in the downstream diverging portion of the nozzle is controlled by the pressure difference between the plasma chamber and the section located downstream of the diverging portion of the nozzle. For this purpose, a negative pressure can be applied downstream or a positive pressure can be applied upstream. Converging-diverging nozzles of the type suitable for use in the present invention are described in U.S. patent No. re37,8539, column 65, line 11, line 32, the incorporated sections of which are incorporated herein by reference.

In certain embodiments, the pigments of the present invention are used in coatings. Such coatings may contain base materials such as binders, liquid media, and additives. Some examples of water-based coatings include a mixture of latex, water, biocide, fumed silica, and titanium dioxide. Some examples of oil-based coatings include alumina, titanium dioxide, epoxy, alcohols, and fumed silica. Other coating types include mixtures of polyurethane, water, fumed silica, and clay. The pigments of the present invention may be added to the coating composition in an amount of from about 0.1 to about 20 weight percent of the total coating composition. Conventional mixing techniques may be used to mix the ultrafine pigment particles with the base material of the coating composition.

The following examples are intended to illustrate certain embodiments of the invention and are not intended to limit the scope of the invention.

Example 1

Particles were prepared using a DC thermal plasma system. The plasma system included a DC plasma torch (model SG-100 plasma torch commercially available from Praxair Technology, inc., Danbury, Connecticut) operated with 60 standard liters/minute of argon carrier gas and 16 kilowatts of power delivered to the torch. Solid precursor feed compositions comprising the materials and amounts listed in table 1 were prepared and fed into the reactor at a rate of about 1 gram/minute by a gas-assisted powder feeder (model 1264 commercially available from Praxair Technology) located at the outlet of the plasma torch. In the powder feeder, 2.5 standard liters per minute of argon was delivered as a carrier gas. Argon gas was delivered at 5 standard liters per minute through two 1/8 inch diameter nozzles located 180 ° apart 0.69 inches downstream of the powder injection port. After the 9.7 inch long reactor section, a plurality of quench stream injection ports were provided, including 6 1/8 inch diameter nozzles spaced 60 ° apart in the radial direction. A 7 mm diameter converging-diverging nozzle of the type described in U.S. patent No. re37,853E was positioned 3 inches downstream of the quench stream injection port. Argon quench gas was injected through multiple quench stream injection ports at a rate of 145 standard liters per minute.

TABLE 1

Substance(s)	Measurement of
		Cu1	10 g
Silicon dioxide2	90 g

¹Commercially available from Alfa Aes r co, Ward Hill, MA.

²Commercially available under the trademark WB-10 from PPG Industries, Inc., Pittsburgh, Pa.

The resulting granules had a theoretical composition of 10 wt% copper and 90 wt% silica. The measured b.e.t. specific surface area using a Gemini model 2360 analyzer was 346 square meters per gram and the calculated equivalent spherical diameter was 6 nanometers for the combination of copper and silica.

Example 2

The apparatus and conditions indicated in example 1 were used to prepare particles from solid precursor except that the feeds and amounts are listed in table 2.

TABLE 2

Substance(s)	Measurement of
		Cu2O3	11.3 g
Silicon dioxide2	88.7 g

³Commercially available from Sigma Aldrich co, St Louis, Missouri.

The resulting particles had a theoretical composition of 11.3 wt% copper oxide and 88.7 wt% silica. The measured b.e.t. specific surface area using a Gemini model 2360 analyzer was 202 square meters per gram and the calculated equivalent spherical diameter for the combination of copper oxide and silica was 11 nanometers.

To obtain UV-visible spectra, ball mill sized particle samples (10% Cu/90% silica and 11.3% Cu) were prepared₂O/88.7% silica). Dispersant (Solsperse 32500) and n-butyl acetate solvent were used in the milling. After grinding, the cloudy material was removed using a centrifugal separation technique.

To see the peaks from the absorption/scattering measurements, the spectra were normalized to their extinction value at 400nm and subtracted from the normalized Solsperse spectra from the other two spectra. This results in a "corrected" spectrum as shown in fig. 5, which is a plot of reflected light intensity versus wavelength for pigment particles prepared according to the previous example. SiO of example 1₂the/Cu particles have a reflection peak in the green region of the spectrum, whereas the SiO of example 2₂/Cu₂The O particles exhibit reflection in the red region of the spectrum.

While specific embodiments of the invention have been described above for purposes of illustration, it will be apparent to those skilled in the art that numerous variations of the details of the invention may be made without departing from the invention as defined in the appended claims.

Claims (26)

1. A coating composition comprising:

a base coating material; and

a pigment dispersed in a base coating material, wherein the pigment comprises substrate particles and ultrafine metal oxide particles deposited on the substrate particles.

2. The coating composition of claim 1, wherein the pigment comprises from about 0.1 to about 20 weight percent of the coating composition.

3. The coating composition of claim 1, wherein the substrate particles have a refractive index that substantially matches a refractive index of the base coating material.

4. The coating composition of claim 3, wherein the refractive index of the substrate particles is from about 1.4 to about 1.6.

5. The coating composition of claim 1, wherein the substrate particles comprise oxides, mixed oxides and/or nitrides.

6. The coating composition of claim 1, wherein the substrate particles comprise SiO₂、Al₂O₃、Bi₂O₃、Al₂SiO₅BN, AlN and/or Si₃N₄。

7. The coating composition of claim 1, wherein the substrate particles comprise SiO₂。

8. The coating composition of claim 1, wherein the substrate particles have an average size of less than 1,000 nm.

9. The coating composition of claim 1, wherein the substrate particles have an average size of about 20 to about 500 nm.

10. The coating composition of claim 1, wherein the substrate particles have an average size of about 50nm to about 400 nm.

11. The coating composition of claim 1, wherein the metal of the ultrafine metal oxide particles comprises Al, Si, Ti, V, Mn, Fe, Co, Cu, Mo, Sn, and/or Ce.

12. The coating composition of claim 1, wherein the ultrafine metal oxide particles are partially oxidized.

13. The coating composition of claim 12, wherein the partially oxidized metal oxide comprises AlO, SiO, Ti₃O₄、V₂O₃、VO、MnO、Mn₂O₃、Fe₃O₄、Co₃O₄、Cu₂O、MoO₂SnO and/or Ce₂O₃。

14. The coating composition of claim 1, wherein the ultrafine metal oxide particles comprise partially oxidized copper oxide.

15. The coating composition of claim 14, wherein the partially oxidized copper oxide comprises Cu₂O。

16. The coating composition of claim 14, wherein the pigment is green.

17. The coating composition of claim 1, wherein the ultrafine metal oxide particles comprise partially oxidized titanium oxide.

18. The coating composition of claim 17, wherein the partially oxidized titanium oxide comprises Ti₃O₄。

19. The coating composition of claim 1, wherein the ultrafine metal oxide particles have an average size of less than about 10 nm.

20. The coating composition of claim 1, wherein the ultrafine metal oxide particles have an average size of about 1 to about 5 nm.

21. The coating composition of claim 1, wherein the base coating material comprises latex, acrylic, epoxy, and/or polyurethane.

22. The coating composition of claim 21, wherein the substrate particles comprise SiO₂And the ultrafine metal oxide particles comprise partially oxidized metal oxide.

23. A method of preparing a coating composition comprising mixing a pigment and a base coating material, wherein the pigment comprises substrate particles and ultrafine metal oxide particles deposited on the substrate particles.

24. A pigment, comprising:

substrate particles; and

ultrafine partially oxidized metal oxide particles deposited on the substrate particles.

25. A method of preparing a pigment comprising:

introducing a substrate particle precursor and an ultrafine metal oxide particle precursor into the plasma;

heating the precursor by plasma to form pigment particles comprising substrate particles and ultrafine partially oxidized metal oxide particles deposited thereon; and

collecting the pigment particles.

26. The method of claim 25, further comprising introducing an inert carrier gas substantially free of oxygen into the plasma.