REFERENCE TO RELATED APPLICATION

This Application is a continuation in part of U.S. Patent Application Serial No. 08/148,045, filed on November 5, 1993, in the name of Howard Wayne Jacobson, and entitled "Iightfast Titanium Oxide Pigment"; the entire disclosure of which is hereby incorporated by reference.

Field Of The Invention The present invention relates to Iightfast titanium oxide particles which are suitable for use in paints, plastics, paper laminates, synthetic fibers, cosmetic compositions, among many other applications.

Background Of The Invention Several methods are known for making Tiθ2 pigments. One such pigment is prepared by calcining one or more hydrous oxides.

Other known methods for making pigments are disclosed in the following U.S. Patent Nos. 3,513,007, 4,052,223, 4,239,548, and 4,461,810; the disclosure of which is hereby incorporated by reference. Typically, known Tiθ2 pigments are suitable for use only in specific product applications, e.g., rutile ΗO2 is acceptable for use in paper laminates whereas anatase Tiθ2 is conventionally unacceptable. There is a need for a new class of ΗO2 pigments which has wide application such as paints, plastics, paper laminates, synthetic fibers, among many other applications.

Summary Of The Invention The titanium oxide product of the present invention is Iightfast and overcomes the problems associated with conventional pigments. Broadly, the invention relates to pigments comprising or consisting essentially of titanium oxide particles, e.g., rutile, anatase, fumed titania, among others, which have a surface coating comprising cerium radicals which can be combined with phosphorus radicals and an additional coating comprising zirconium oxide that can also be combined with phosphorus radicals. In some cases, the additional coating comprises

alumina. Such pigments can be used in many applications requiring lightfastness, e.g., coatings, plastics, glass paper laminates, clear protective coatings for use on automobiles or wood, synthetic fibers, cosmetics such as sun screen formulations, among many other applications.

The titanium oxide particles or pigments, which are used in the invention, may comprise silica shells that have a surface coating comprising titania, e.g., anatase and/or rutile. Such particles are particularly useful in cosmetic applications.

In one aspect, the invention can overcome problems associated with conventional manufacturing methods by obviating the need for an expensive calcining step to establish lightfastness.

Polymeric or synthetic fibers, e.g., nylon, spandex, among others, typically incorporate pigments that impart whiteness or function as a delustrant. If the pigment lacks sufficient lightfastness, then plastics and polymeric fibers, e.g., nylon, have a tendency to undergo discoloration when exposed to ultra-violet light. While anatase is less abrasive than rutile, anatase has failed to become an acceptable delustrant in many applications because anatase is conventionally known to be highly photoactive. The present invention improves the Iightfast characteristics of anatase such that anatase can be used effectively as a delustrant.

Detailed Description

Paniculate rutile, anatase, and/or fumed titama that is used in the invention can be produced by any suitable method. For example, conventional chloride or sulfate processes can be used for making suitable Tiθ2 particles.

The present invention relates to coated titama particles that can be produced by precipitating compounds comprising or consisting essentially of one or more of cerium that can be combined with hypophosphite and/or hypophosphate, or phosphite and/or phosphate; and zirconium that can be combined with hypophosphite and/or hypophosphate, or phosphate and/or phosphite, in an aqueous solution onto dispersed titania particles. The zirconium can be mixed with or substituted by an aluminum containing material. While a phosphite and phosphate can be employed together, the "hypo" forms typically cannot be effectively generated in the presence of phosphate or phosphite. One aspect of the invention relates to coated titania particles comprising: (a) a first or an inner layer comprising about 0.05 to at least

about 1.0 percent by weight, based on the weight of the titania, of cerium radicals (calculated as Ce) which may be combined with phosphite and/or phosphate, or hypophosphite and/or hypophosphate radicals, (b) a second or an outer layer comprising about 1 to at least about 8 percent by weight, based on the weight of the titania, of hydrous zirconia (calculated as Zrθ2) which may be combined with hypophosphite and/or hypophosphate, or phosphite and/or phosphate radicals, wherein the total weight of phosphorus is usually equivalent to about 0.05 to at least about 2 percent P2O5, based on the weight of the titania, and the total weight of the layers being about 2 to about 9 percent of that of the titania.

Another aspect of the invention relates to a process for making Iightfast titania particles comprising:

(a) contacting particulate titania in an aqueous medium, which has a pH of about 2 to about 5, with Ce cations or radicals typically in an amount of about 0.05 to at least about 1.0 percent by weight, based on the weight of the titania,

(b) contacting the product of step (a), while at a pH about 2 to about 8, simultaneously with (i) hypophosphite and/or hypophosphate, or phosphite and/or phosphate and ions in the amount of about 1 to about 4 percent by weight, and (ϋ) hydrous zirconia in the amount of about 1 to 8 weight percent, both based on the weight of the titania,

(c) curing the product of step (b) for a period of typically about 30 to minutes,

(d) adjusting the pH of the medium to about 7.0 to 8.0,

(e) curing further for a period of time of about 15 to 30 minutes, and;

(f) filtering, washing, and drying.

If desired, the previously described hydrous zirconia can be mixed with or substituted by an alumina precursor or source. By substituting at least some of the hydrous zirconia with alumina, the instant invention can produce a Iightfast titania that is particularly useful as a cosmetic additive, e.g., as a sun-screen or block. An outer layer of alumina enhances the cost effectiveness of the cosmetic additive without adversely affecting its utility as a cosmetic additive. Such a cosmetic additive can be substituted for the titania that is employed in conventional cosmetic

formulations, e.g., lotions, creams, among other cosmetics. Examples of conventional cosmetic formulations and methods for making such formulations can be found in "Formulating With A Physical Sun Block", Damns, Cosmetics & Toiletries, Vol. 107, October 1992, Pages 133 to 143; the disclosure of which is hereby incorporated by reference. In yet another aspect of the invention, amorphous silica coated with titania crystallites, or particles of Siθ2/Tiθ2 are coprecipitated and then coated by using at least one of the previously identified processes.

In all of the above aspects of the invention, the titanium oxide can comprise silica shells which have an exterior titania coating, e.g., crystallites of titania upon amorphous silica shells. Such coated particles are particularly useful in cosmetic applications.

The paniculate concentration of the titama or coated silica shell dispersion to be coated for lightfastness is not a critical aspect of the invention. The concentration of titama particles typically ranges from about 10-600, normally about 50-500, and usually about 200-500 grams of titama per liter. The titama particles are normally about 0.01 to 1 micron in size; but, the coating can be applied to any titania particle that can be dispersed in water.

In the case of fumed titania, any suitable commercially available fumed titama can be employed when preparing the dispersion of particles that are coated using the process of the invention. One example of a commercially available fumed titania comprises "Grade P-25" which is sold by Degussa Company. Fumed or microfine titania typically has a surface area 50 - 150 m^/gm.

The dispersed titania particles are normally first exposed to a source of cerium wherein the cerium is typically in the trivalent state, and then simultaneously to a second source containing hypophosphite and/or hypophosphate, or phosphate and/or phosphite, and zirconium compounds. Aluminum compounds may be used to replace a part, if not all, of the zirconium compounds. After treating with phosphorus and zirconium and/or aluminum compounds, the pH of the dispersion is typically adjusted, e.g., to about 7.0, and the dispersion is cured. The previously described sequence of process steps can form titania particles which have a first or an inner layer comprising cerium radicals associated with hypophosphite and/or hypophosphate, or phosphite and/or phosphate radicals, and an outer or a second layer comprising hydrous zirconium and/or aluminum oxide associated with hypophosphate and/or hypophosphite, or phosphite and/or phosphate radicals. The pH of the aqueous medium that is used for coating the

dispersed titania particles will generally be in the range of about 2-9, and can be adjusted as necessary to cause the desired compound to precipitate onto the titania particles. For example, the pH of the aqueous medium can be adjusted by using a solution comprising sodium hydroxide or hydrochloric acid. The cerium addition step can be carried out at a pH of about 3.0, and normally about 1 to 5. The zirconia/phosphorus addition is typically performed over the pH range of about 3-9. For example, the hypophosphite (and/or hypophosphate)/ zirconia oxychloride addition can be made over the pH range of about 3-9; normally about 3-5. Alternatively, the hypophosphite (and/or hypophosphate)/sodium aluminate addition can be made over a pH range of about 5-9; normally about 7-8. Generally, the temperature used during the coating process ranges from about 25 to 100 degrees C, normally about 25-80 degrees C, and usually about 40-80 degrees C.

After the particulate titania has been coated by precipitating cerium, phosphorus and zirconium and/or aluminum compounds, the coated titania particles can be cured by stirring until the desired deposition and/or reaction are completed. Typically, suitable coating or precipitation process times will range from about 0.5 to 120 minutes, and normally about 15 to 60 minutes.

The cured coated titania particles can be separated from the dispersion by using any suitable method such as Buchner filter. The filtered particles are normally washed with deionized water to be substantially free from salts, e.g., containing less than about 10 ppm of salt. In some cases, the washed particles are dried in air at a temperature of about 120 degrees to about 150 degrees C. The drying step converts the hydrous zirconia into zirconium oxide.

The source of cerium for the inner coating of the titania particles can be supplied, for example, by at least one water soluble cerium salt having a valence of 3 such as cerous chloride. A sufficient quantity of at least one cerium source can be used to provide a coating on the titania particles that contains about 0.05 to at least about 1.0 percent, and normally about 0.1 to about 0.4 percent, by weight of cerium, based on the weight of titania. The source of zirconium for the outer coating can be supplied, for example, by a water soluble zirconium salt such as zirconium oxychloride, zirconium acetate or nitrate, among others. A sufficient quantity of at least one zirconium salt can be used to provide about 0.5 to 6 percent, and normally about 1-4 percent, by weight of zirconium, based on the weight of titania. The precursor or source of alumina for the outer coating, which is

mixed with or replaces the zirconium, can be supplied, for example, by at least one water soluble aluminum salt such as sodium aluminate, aluminum chloride, among others. A sufficient quantity of at least one aluminum salt can be used to provide about 0.5 to about 6 percent, and normally about 3, by weight aluminum, based on the weight of titania. Both the inner and outer coatings can contain phosphorus which is supphed by at least one source comprising, for example, a water soluble hydrophosphite such as sodium hypophosphite, sodium hydrogen phosphate, phosphoric or phosphors acid, among others. The quantity of at least one suitable phosphorus compound should be sufficient to combine with the cerium radicals as well as with a portion of the hydrous zirconia and/or alumina.

After titania particles have been coated and washed and dried, the coated particles may be deagglomerated or comminuted by any suitable means such as in a fluid energy mill, e.g., a steam micronizer. In some cases, the titania particles are admixed with a micronizing or milling aid prior to being deagglomerated or comminuted. The micronizing aid functions to maximize particle dispersion. The micronizing aid can be added to the micronizer as a pure material, normally at approximately 0.25 weight percent. Examples of suitable micronizing aids comprise at least one member from the group consisting of triethanolamine, trimethanol propane, dioctyl azelate, among others. One aspect of the inventive process relates to obviating a calcining step to obtain a Tiθ2 pigment that is highly photostable. While the particles can be calcined whenever it is desirable, calcination is not a necessary step to obtain useful Iightfast coated Tiθ2 particles. Should it be desirable to calcine the particles, typical calcination temperatures range from about 150 degrees C to about 300 degrees C.

The coated particles may be used in any conventional application that requires a pigment which imparts lightfastness or photostability, e.g., in paper laminates, cosmetics, exterior paints, synthetic fibers, among other applications. By "lightfastness" it is meant that the semiconductor behavior of Tiθ2 when radiated with ultraviolet light is minimized, if not eliminated, thereby improving the photostability of the titania pigment. In cosmetic applications, substituting the Iightfast titania of the invention for conventionally used Tiθ2 causes a reduction in the tendency of the cosmetics to destabilize or discolor when exposed to natural or artificial sources of ultra-violet light. Without wishing to be bound by any theory or explanation, it is believed that the

Iightfast pigments of the claimed invention provide electron/hole recombination centers thereby prohibiting the ultraviolet radiation absorbed by the Tiθ2 from forming radicals that can decompose, e.g., discolor, the cosmetic formulation.

When the Iightfast particles of the invention are incorporated, for example, into nylon or spandex fibers, the resultant fibers have an enhanced photostability when exposed to UV light. Further, the invention permits using less abrasive Iightfast anatase particles thereby reducing wear to fiber producing machinery. Normally, these particles are incorporated into such fibers by adding the particles to the nylon melt or the polyurethane which is used for manufacturing or spinning the fibers. While any suitable manufacturing process can be used for making such fibers, the methods disclosed in U.S. Patent Nos. 5,194,578, 4,810,737, WO 92/08827 (which corresponds to U. S. Patent Application Serial No. 07/616,126), and U.S. Patent Application Serial No. 08/042,965 are particularly effective; the disclosure of the previously identified documents is hereby incorporated by reference. Processes for wet or dry spinning spandex are well known in the art. The quantity of coated titania particles, which is added to the fiber, is dependent upon the properties that are desired in the fiber. Typically, the quantity of coated titania particles ranges from 0.3 to 5.0% based on the weight of fiber.

The previously discussed titania particles may comprise a silica shell which has been coated with Tiθ2- While the silica shells may be obtained by any suitable method, the process described in U.S Patent No. 5,024,826 to Linton is particularly desirable; the entire disclosure of which is hereby incorporated by reference. After obtaining a suitable silica shell, a coating comprising Tiθ2 crystallites is deposited by any suitable process. An example of a suitable process is described in copending and commonly assigned U.S. Patent Application Serial no. 07/979,122, filed on November 20, 1992, entitled 'Titania Coated Silica Shells"; the disclosure of which is hereby incorporated by reference. If desired, the Tiθ2 crystallites supported on silica shell discussed in Serial No. 07/979,122, can be rendered Iightfast by employing the compositions described herein. Lightfast titania coated silica shells can be added to any well known cosmetic or sun screen formulation. Without wishing to be bound by any theory of explanation, it is believed that adding the titania coated silica shell causes the formulation to absorb ultraviolet radiation thereby acting as a sun screen. While the quantity of coated silica shell which is added to the sun screen will depend upon the degree of UV absorption desired, the quantity normally ranges from about 2-8% by wt.

In some cases, a film forming composition is used for obtaining a paper laminate which comprises paper and the coated titania particles within a rigid polymer matrix. A film forming composition can also be used for coating automobiles, wood, e.g., a preservative, incorporated within or upon vinyl materials, e.g., vinyl building siding, among many other uses. Such a film imparts enhanced photostability to the coated substrate when exposed to UV light.

The Iightfast properties of the inventive pigments can be characterized by an improved catalytic activity coefficient (CAC). CAC measures the photostability of the pigments in comparison to unstabilized Tiθ2 pigments. Typically, the pigments of the invention will have a relatively low CAC value that ranges from about 0.1 to about 0.4. In other words, a decreasing CAC value corresponds to an increasing lightfastness or photostability. By having such a CAC value, the pigments reduce the tendency of plastics and polymeric fibers to discolor, e.g., yellow when compared to unstabilized ΗO2 pigments.

While the above description places particular emphasis upon coating titania particles by using a certain series of process steps, the titama particles can be coated with a plurality of layers having chemically similar or distinct layers. In some cases, at least one layer of the coating can be tailored by including more than one constituent. Further, the characteristics of the pigment can be tailored by using a mixture of powders having chemically and/or physically distinct properties. The following examples are provided to illustrate, but not limit the scope of this invention as defined in the appended claims. Examples 1 to 10 relate to methods for making titania pigments for plastics and paint systems, and Examples 11 to 17 relate to methods for making a titania containing particle which is useful as a cosmetic additive.

Example 1 A slurry containing about 200 grams of rutile Tiθ2 (produced by oxidation of TiC-4), in approximately 1800 ml of deionized water was heated to a temperature of about 75 degrees C. The pH of the slurry was adjusted to about 3.0 by adding a 20% HC1 solution. Approximately 4 grams of commercially available CeCl3 7H2O (supplied by G.F.S. Chemicals, Powell, Ohio), were added to the slurry, and the slurry was stirred by using a stirring paddle for about 5 minutes.

The following two solutions were prepared: (A) approximately 8 grams of commercially available sodium

hypophosphite (supplied by J.T. Baker, Philhpsburg, N.J.), were dissolved into about 200 ml of deionized water.

(B) approximately 22 grams of commercially available ZrOCl2 (supplied as a 20% Zrθ2 solution by Harshaw Chemical, Cleveland, Ohio) which contained the equivalent of about 20 weight percent Zrθ2, was diluted into about 200 ml of water.

Solutions (A) and (B) were added simultaneously to the slurry, while maintaining the pH at about 3.0, over a period of about 1 hour period. The slurry was cured for about 30 minutes. The pH of the slurry was adjusted to about 7.2 by adding 20% NaOH solution. The slurry was cured for about 30 minutes. The cured slurry was filtered by using a Buchner filter and washed with 50 degrees C H2O to be substantially free of soluble salts, and dried overnight in air at a temperature of about 120 degrees C.

Example 2 Example 1 was substantially repeated with the exception that hypophosphite was omitted.

Example 3 A slurry comprising approximately 12 pounds of anatase Tiθ2 (sold under the trademark "LOCR-SU", by Sachtleben Chemie, Germany), in about 12 liters of deionized water was prepared, and heated to a temperature of about 75 degree C.

The pH of the slurry was adjusted to about 3.0 by adding 20% hydrochloric acid. Approximately 65.5 grams of CeC j 7H2O were added to the slurry, and the slurry was stirred by using a stirring paddle for about 5 minutes. The following two solutions were prepared: (A) approximately 211.2 grams of commercially available sodium hypophosphite, were dissolved into about 1 liter of deionized water, and; (B) approximately 580.8 grams of ZrOCl2 solution, which contained the equivalent of about 20 weight percent Zrθ2, were diluted into about 1 liter of deionized water.

Solutions (A) and (B) were added simultaneously to the slurry, while maintaining the pH at about 3.0, over a period of about 2.5 hours. The slurry was cured for about 20 minutes.

The pH of the slurry was adjusted to about 7.2 by adding caustic soda solution. The slurry was cured again for about 30 minutes.

The slurry was filtered by using a Buchner filter, washed with 50 degrees C water to be substantially free of soluble salts. The washed slurry was dried overnight in a drying oven at a temperature of about 120 degrees C. The dried pigment was micronized in an 8" steam micronizer using 3 lbs. of steam per pound of pigment.

Example 4 A slurry comprising approximately 12 pounds of rutile Tiθ2 (sold under the trademark "R-101" by the DuPont Company), and about 12 liters of deionized water was prepared, and heated to a temperature of about 75 degrees C. The pH of the slurry was adjusted to about 3.0 by adding a 20% hydrochloric acid solution.

Approximately 96.45 grams of commercially available were added to the slurry, and the slurry was stirred by using a stirring paddle for about 30 minutes.

The following two solutions were prepared: (A) approximately 211.2 grams of commercially available sodium hypophosphite, were dissolved into about 1 liter of deionized water, and; (B) approximately 580.8 grams of commercially available ZrOCl2, which contained the equivalent of about 20 weight percent Zrθ2, was diluted into about 1 liter of deionized water.

Solutions (A) and (B) were added simultaneously to the slurry, while maintaining the pH at about 3.0 by adding, over a period of about 2.4 hours. The slurry was cured for about 30 minutes at a pH of about 3.0 and a temperature of about 75 degrees C. The pH was adjusted to about 7.2 by adding a 20% NaOH solution, and the slurry was cured again for about 30 minutes. The slurry was filtered by using Buchner filter, washed with 50 degrees C water to be substantially free of soluble salts. The washed pigment was dried overnight in a drying oven at a temperature of about 120 degrees C.

The dried pigment was micronized in an 8" steam micronizer at a steam/pigment ratio of 3.

Example 5

A slurry comprising about 8.0 pounds of rutile Tiθ2 (produced by the oxidation of ΗCI4) into about 12 liters of water was prepared, and heated to a temperature of about 75 degrees C.

The pH of the slurry was adjusted to about 3.0 by adding hydrochloric acid. Approximately 70.4 grams of CeCl3 H2θ, were added to the slurry, and the slurry was stirred for a period of about 5 minutes.

The following two solutions were prepared: (A) approximately 140.8 grams of commercially available NaH2Pθ3.H2θ, were dissolved into about 1 liter of water, and; (B) approximately 387.2 grams of commercially available ZrOCl2, which contained the equivalent of 20 weight percent Tiθ2, was diluted into about 1 liter with water.

Solutions (A) and (B) were added simultaneously to the slurry, while maintaining the pH at about 3.0, over a period of 2.5 hours. The slurry was cured for a period of about 30 minutes at a temperature of about 75 degrees C. The pH of the slurry was raised to about 7.2 by adding a caustic soda solution. The slurry was cured for a about 30 minutes at a temperature of about 75 degrees C. The slurry was filtered by using a Buchner filter, washed with deionized water to be substantially free of soluble salts. The filtered pigment was dried overnight in a drying oven at a temperature of about 120 degrees C.

Approximately 15 grams of trimethanol propane (TMP) was dissolved in about 100 ml of water, and mixed with the pigment in a commercially available V-blender. The resultant mixture was dried in a drying over at a temperature of about 120 degrees C, sieved through a 20 mesh screen, and micronized in a 8" steam micronizer at a steam/pigment ratio of 3. The surface area of the micronized pigment was measured by using a BET, and was determined to be about 14.8 square meters per gram.

Example 6 A slurry comprising approximately 10 pounds of rutile ΗO2 (sold under the trademark "R-101" by the DuPont Company) into about 12 liters of water was prepared, and heated to a temperature of about 75 degrees C.

The pH of the slurry was adjusted to about 3.0 by adding hydrochloric acid. Approximately 40.2 grams of CeCl3 H2θ were added to the slurry, and the slurry was stύred with a stirring paddle for a period of about 5 minutes.

The following two solutions were prepared as follows:

(A) approximately 176 grams of sodium hypophosphite were dissolved into about 1 liter of water, and;

(B) approximately 484 grams of ZrOCl2 solution, containing the equivalent of 20 weight percent Zrθ2, was dissolved into about 1 liter of water. Solutions (A) and (B) were added simultaneously to the previously formed slurry, while maintaining the pH at about 3.0, over a period of 2.5 hours. The slurry was cured for a period of about 30 minutes while maintaining the pH at about 3.0 and the temperature at about 75 degrees C.

After curing the slurry, the pH was slowly raised to about 7.2 by adding dilute caustic soda solution, and the slurry was cured again for a period of about 30 minutes and at a temperature of about 75 degrees C.

The slurry was filtered by a Buchner Filter Funnel, washed with deionized water to be substantially free of chloride ions, and dried overnight in a drying oven at a temperature of about 120 degrees C. A solution was prepared by dissolving approximately 15 grams of trimethanol propane into about 100 ml of water. The trimethanol propane solution was mixed with dried Tiθ2 containing pigment in a commercially available V- blender. This mixture was dried overnight at a temperature of about 120 degrees C, sieved through a 20 mesh screen, and steam micronized in an 8 inch steam micronizer at a steam/pigment ratio of about 3.

Example 7 A slurry comprising approximately 3100 grams of rutile Tiθ2 pigment (produced by the oxidation of ΗCI4), in 12 liters of water was prepared and heated to a temperature of about 75 degrees C. The pH of the slurry was adjusted to about 3.0 by adding hydrochloric acid. Approximately 27 grams of cerous chloride (CeCl3 H2θ) was added to the slurry, and the slurry stirred by using a stirring paddle for a period of about 5 minutes.

The following two solutions were prepared as follows: (A) approximately 118 grams of sodium hypophosphite (NaF.2PO2.H2O) were dissolved into about 670 ml of water, and;

(B) approximately 324 grams of ZrOCl2 solution, which contained the equivalent of about 20 weight percent Zrθ2, was diluted into about 670 ml of water. Solutions (A) and (B) were added simultaneously to the slurry, while maintaining the pH of the slurry at about 3.0, over a period of about 2.5 hours. The

slurry was then cured for 30 minutes at a pH of about 3.0 and at a temperature of about 75 degrees C.

The pH of the slurry was raised to about 7.2, over a period of about 45 minutes, by adding a caustic soda solution. The slurry was cured again for a period of about 30 minutes at a temperature of about 75 degrees C. The slurry was filtered by using a Buchner Filter Funnel, washed with deionized water to be substantially free of chloride ions, and dried overnight in a drying oven at a temperature of about 120 degrees C.

The dried pigment was sieved through a 20 mesh screen, and approximately 1% weight percent dioctyl azelate (DOA) was added as a micronizing aid. The pigment was steam micronized in an 8 inch steam micronizer at a steam/pigment ratio of about 3.

Example 8 Example 7 was substantially repeated with the exception that about 0.5 weight percent of trimethanol propane (TMP) was added as a micronizing aid.

Example 9 A slurry comprising approximately 3,000 grams of rutile ΗO2 pigment (grade RG, supphed by SCM Chemicals) and about 9 liters of water was prepared, and heated to a temperature of about 75 degrees C. The pH of the slurry was adjusted to about 3.0 by adding hydrochloric acid. Approximately 27 grams of cerous chloride were added to the slurry, and the slurry stirred by using a stirring paddle for a period of about 5 minutes.

The following two solutions were prepared as follows: (A) approximately 118 grams of sodium hypophosphite (NaH2Pθ2-H2θ) were dissolved into about 670 ml of water, and;

(B) approximately 324 grams of ZrOCl2 solution, which contained the equivalent of about 20 weight percent Zrθ2, was diluted into about 670 ml of water. Solutions (A) and (B) were added simultaneously to the slurry, while maintaining the pH at about 3.0, over a period of about 2.5 hours. The slurry was cured for about 30 minutes at a pH about 3.0 and a temperature of about 75 degrees C.

The pH of the slurry was adjusted to about 7.2 by adding caustic soda solution, and the slurry was cured again for a period of abut 30 minutes. The cured slurry was filtered by using a Buchner Filter Funnel,

washed with deionized water at 50 degrees C to be substantially free of chloride ions, and dried overnight in a drying oven at a temperature of about 120 degrees C. The dried pigment was sieved through a 20 mesh screen, and about 1 weight percent commercially available dioctyl azelate (DO A) was added as a micronizing aid. The pigment was steam micronized in an 8 inch steam micronizer at a steam/pigment ratio of about 3.

Example 10 Example 9 was substantially repeated with the exception that about 0.5 weight percent of trimethanol propane (TMP) was added as a micronizing aid. A sample of each of the pigments produced in Examples 1-10 were analyzed by using conventional X-ray fluorescence techniques. The results of the analysis, in weight percent, are shown in Table I.

TABLE I

Example Ti0 ₂ Ce Zr0 ₂ P2Q5 AJ2Q3 Si0 ₂

1 96.6 0.33 2.29 0.08 0.89 0.02

2 96.6 0.36 2.30 0 0.82 0

3 88.8 0.31 2.37 0.73 1.85 5.34

4 96.1 0.29 2.18 0.30 1.01 0.03

5 96.6 0.25 1.85 0.25 0.87 0.03

6 96.7 0.15 2.15 0.32 1.03 0

7 96.4 0.16 2.38 0.16 0.96 0

8 96.9 0.16 2.39 0.15 1.00 0

9 97.5 0.19 2.27 0.31 0 0

The Iightfast properties of samples taken from pigments formed substantially in accordance with the above-identified Examples were evaluated using the following tests.

I. Catalytic Activity Coefficients (CAC)

The durability of a pigment is usually measured as resistance to chalking in a long-term (e.g. 2 years) outdoor exposure test of a paint containing the pigment. Chalk/fade degradation of exterior paints containing Tiθ2 pigments is at least partly attributed to a catalytic activity which causes the surface of Tiθ2 pigments to oxidize in situ while in the presence of ultraviolet radiation, oxygen, and/or water vapor. The mechanisms of the degradation are described in greater detail by H. B. Clark, 'Titanium Dioxide Pigments", Treatise on Coatings, Vol. 3, Pigments, Marcel Dekker, 1975; the entire disclosure of which is hereby incorporated by reference. The ultraviolet reactivity of ΗO2 pigments made substantially in accordance with Examples 1-6 was measured in a test which determines the ΗO2 catalyzed reduction of lead carbonate to metal in an organic medium. An air-sealed dispersion of relatively non-durable ΗO2 and lead carbonate in an organic medium turns from white to almost black when exposed to ultraviolet light. In contrast, when a dispersion contains relatively durable ΗO2 pigments the paste turns light gray.

The Tiθ2-catalyzed reduction of lead carbonate is determined by placing a drop of paste (approximately 0.5 gm) containing lead carbonate, glycerol, fumed silica, and the Tiθ2 pigment being tested between two glass microscope slides. The drop was exposed to ultraviolet light for a period of about five hours. The color of the exposed slides was compared to so-called conventional "Munsell" chips, so that the Catalytic Activity Coefficient ( CAC ) values could be determined. The lower the CAC value the more photostable or "Iightfast" the Tiθ2 pigment. The pigments of the invention possess a CAC value which normally ranges from less than about 0.05 to about 0.4. CAC values for samples of pigments produced in accordance with

Examples 1 to 6 are shown in TABLE II. Values for commercially available Tiθ2 pigments are also shown for comparison.

TABLE π

Example CAC

1 0.06

2 0.10

3 0.19

4 0.05

5 0.13

6 0.11

R-900* 0.60

R-902* 0.10

R-960* 0.04

* A commercially available ΗO2 pigment sold by the DuPont Company, Wilmington, Delaware, U.S.A..

π. Nujol Yellowing Test Pigment that was made substantially in accordance with Examples 7 to 10 was subjected to a Nujol Yellowing Test for determining the resistance of such pigments to yellowing, i.e., another measure of photostability. A master batch of test medium is made by compounding the approximate amounts of the following components: 100 grams of Nujol (a mineral oil supplied by Aldrich, Milwaukee, WI), 2 grams of butylated hydroxyl toluene (BHT) 2 grams of Tinuvin 770, a commercial hindered amine antioxidant, and 10 grams of petroleum gel (sold under the trademark Vaseline).

Approximately 1.2 grams of masterbatch was mulled with about 0.64 grams of the Tiθ2 pigment for a period of about 5 minutes thereby forming a smooth dispersion. A doctor blade was used to form a thin film of the masterbatch/pigment composite on a microscope slide.

The color components L*, a*, and b*, respectively, of the film were measured in a conventional method by using a Lab-Scan spectrocolorimeter. The film was exposed to ultra violet radiation for a period of about 24 hours while being housed in a temperature-controlled box. After being exposed to the ultra-violet radiation, the color components are then measured. The change or delta in the b* color component was used as a measure of stability against yellowing. The lower the value of delta b* the more photostable the pigment. Delta b* values for pigment samples produced substantially in accordance with Examples 7 to 10 are shown in Table III. The pigments of the invention possess delta b* values which

typically range from less than about 3.1 to about zero. Values for commercial Tiθ2 pigments are shown for comparison.

TABLE m

Example Delta b

7 1.04

8 0.13

9 3.07

10 -0.46

R-960* 6.27

CR-80* 1.78

WPD-703* 0.45

R-101* 21.04

*A commercially available pigment sold by the DuPont Company, Wilmington, Delaware, U.S.A..

HI. Photostability in Nylon Fiber

Anatase ΗO2 pigment, which was made substantially in accordance with Example 3, was used as a delustrant in 6,6 nylon yarn. The nylon yarn was then exposed to 225 kilojoules of UV light for deteπr-ining the photostability of the Nylon Fiber. The yarn was fabricated substantially in accordance with the conventional process disclosed in U. S. Patent No. 5,194,578, e.g., refer to Example 2; which is hereby incorporated by reference.

Delta E, a measure of color stability, was calculated by using conventional methods from observations that were made with Hunterlab LabScan spectrocolorimeter. Delta E represents the change in color reflectivity after having been exposed to about 225 kilojoules of UV light. The lower the value the more photostable the pigment. The measured Delta E was about 0.50 in comparison to a value of about 0.98 for a control 66 nylon fiber which was prepared by using a standard alumina coated rutile pigment. Normally, the Delta E ranges from about 2 to about 3.

IV. Photostability of pigment in Spandex Fiber

A rutile Tiθ2 pigment, which was made substantially in accordance with Example 6, was used as a delustrant in dry-spun 70 denier spandex yarn. The concentration of pigment was about 2 wt%, based on the weight of the polymer.

The spandex yarn was formed substantially in accordance with the method disclosed in U.S. Patent No. 5,028,642, e.g., refer to Col. 6, Line 67 through Col. 7, Line 17, that was followed by conventional dry spinning; the entire disclosure of the previously identified patent is hereby incorporated by reference.

The yarn contained approximately 1.5 wt% (based on the weight of the spandex polymer) of "Cyanox" 1790, a hindered phenolic antioxidant sold by American Cyanimid Co. and 0.5% methacrolS, a DuPont Z4-62B. The pigment containing spandex yarn was exposed to an aqueous scour and boil at a pH of about 5.

A test sample of the spandex yarn was used for measuring resistance to (a) ultraviolet (UV) hght, and (b) ultraviolet light and nitrogen dioxide fumes. The procedures for performing the tests are described in U.S. Patent Nos. 5,166,234 and 5,059,647; the entire disclosure of which is hereby incorporated by reference. The test sample was prepared by winding the spandex yarn onto approximately 7.6 by 10.7 by 0.16 cm. aluminum plates to form a layer about 3 mm. thick. For the ultra violet light test, the sample was exposed for a period of about 40 hours, while in the presence of water, to silica-filtered light from a carbon arc. When being exposed to the UV hght, the test sample was housed in an Atlas Series C "Weather- o-meter" made by Atlas Electric Devices Co. of Chicago, Illinois.

For the ultraviolet light and nitrogen dioxide test, a Scott Controlled Atmosphere tester was used for housing the test sample. Nitrogen containing about 200 ppm nitrogen dioxide was introduced into the Scott Controlled Atmosphere and exposed to the test sample. Ultra violet hght was supphed to the tester by eight "daylight" and four "black" fluorescent tubes. The fluorescent tubes were type F30T8 and FT038BL which were sold by the General Electric Co. Discoloration of the test samples was determined as a change in b* color component or a delta b* which was measured by using a differential colorimeter, model D-25-3, made by Hunter Associates Laboratory, Inc., of Reston, Virginia. The lower the value of delta b, the more photostable the pigment in the fiber. A method for measuring discoloration is described in U.S. Patent No. 5,059,647; the entire disclosure of which is hereby incorporated by reference.

The results of the photostability study are shown in TABLE IV. For purposes of comparison, TABLE IV also show the results which were obtained by using a control sample or a fiber containing R-902 (a Tiθ2 pigment made by the DuPont Company).

TABLE IV

Delta b

UV UV/N02

Example 6 3.8 4.1 Control 5.6 6.4

The following Examples 11-15 illustrate certain aspects of the invention which relate to forming a coating comprising ΗO2 crystalhtes on at least a portion of a silica surface. The silica surfaces or shells can be produced in accordance with the method disclosed in U.S. Patent No. 5,024,826 to linton; the entire disclosure of which has been incorporated by reference. The ΗO2 crystallites typically range in size from about 2 to 50 nanometers. The surface area measurements, which are given in the following Examples, were obtained by using the conventional BET method.

Example 11

A. Preparing Amorphous Silica Shells Coated with Anatase ΗO2.

Approximately 2,000 grams of CaCθ3 were mixed into about 9 liters of stirred deionized water, which was maintained at a temperature of about 80 degrees C, in a 12 in. x 12 in. pyrex jar. The pH of the mixture was adjusted to about 9.5 by adding a solution comprising about 20 weight percent NaOH solution. A solution comprising approximately 2,000 grams of K2Siθ3 dissolved into about 2 liters of deionized water was added to the mixture over a period of about 2 hours, while maintaining the pH at about 9.5 by adding a solution comprising about 20 weight percent hydrochloric acid. Simultaneously with the addition of the K2Siθ3 solution, and over the same 2 hour period, a solution comprising approximately 5 grams of CaCl2 mixed into about 100 milliliters of deionized water was also added to the mixture. The resultant mixture comprised CaCθ3 particles which have been coated with silica.

The pH of the mixture was decreased to about 8.5, and the mixture was cured and stirred, for a period of about 30 minutes.

The pH of the mixture was then decreased further to about 2.0, over a 2 hour period, by adding concentrated hydrochloric acid. By reducing the pH, the CaCθ3 core particle is removed thereby forming silica shells.

Approximately 500 milliliters of ΗCI4 were added to about 2000 grams of ice.

The ΗCI4 solution was added to the silica shell mixture, over a period of about 2 hours, while maintaining the pH at about 2.0 by adding a solution comprising about 50 weight percent NaOH. A composition comprising Tiθ2 coated sihca shells was produced.

The coated shell composition was cured and stirred for a period of about 30 minutes, while maintaining the pH at about 2.0 and the temperature at about 80 degrees C. The cured composition was then filtered, and the recovered solids were washed with 50 degrees C deionized water to be substantially free of chloride ions. The solids were dried in a drying oven at a temperature of about 120 degrees C, and then calcined, an optional step, for a period of about 2 hours at a temperature of about 550 degrees C. The calcined product weighed about 870 grams and had a surface area of about 166 square meters per gram.

B. Preparing Iightfast Titania Coated Amorphous Silica Shells.

Approximately 100 grams of silica shells coated with anatase Tiθ2, which were formed substantially in accordance with Example 11 A above, were added into a 4 liter container that housed about 2 liters of stirred deionized water at a temperature of about 75 degrees C. The pH of the titanium dioxide and sihca shell composition was adjusted to about 3.0 by adding a solution containing about 20 weight percent hydrochloric acid Approximately 2.7 grams of cerous chloride (CeC j 7H2O) were added to the mixture, and stirred for about 5 minutes.

The following two solutions were prepared: (A) Approximately 11.8 grams of sodium hypophosphite (NaH2Pθ2-H2θ) were dissolved into about 100 ml of deionized water, and (B) Approximately 32.4 grams of ZrOCl2 solution, which contained the equivalent of about 20 weight percent Z >2, was diluted into about 100 ml of deionized water.

The two previously described solutions, were placed into separate burets. These two solution were then added at the same rate, over a 2 hour period, to the previously described silica shell slurry, while maintaining the pH at about 3.0 by adding a solution comprising 20 weight percent NaOH.

The resultant slurry was then cured for a period of about 30 minutes at pH of about 3.0 and at a temperature of about 75 degrees C. The pH of the slurry was raised to about 7.2 by adding a solution comprising about 20 weight percent NaOH, and the slurry was cured for a period of about 30 minutes at pH of about 7.2

and at a temperature of about 75 degrees C.

The slurry was filtered by using Buchner Filter Funnel, and the recovered sohds were washed with 50 degrees C deionized water to be substantially free of chloride ions. The washed sohds were dried in a drying oven at a temperature of about 120 degrees C. The dried solids comprised Iightfast Tiθ2 coated silica shells which weighed about 117 grams, and had a surface area of about 106 square meters per gram.

Example 12 A. Preparing Amorphous Silica Shells Coated with Anatase ΗO2 and

Trace Amounts of Rutile.

Approximately 2000 grams of CaCθ3 were admixed with about 8 liters of stirred deionized water, which had a temperature of about 80 degrees C, that was housed in a 12 in. x 12 in. pyrex jar. The pH of mixture was adjusted to about 9.5 by adding a solution comprising about 20 weight percent NaOH solution. A solution comprising about 2000 grams of K2Siθ3 diluted into about 2 liters of deionized water was added to the previously described mixture over a 2 hour period, while maintaining the pH at about 9.5 by adding a solution comprising about 20 weight percent hydrochloric acid. Subsequently, the pH was decreased to about 8.5, and the mixture was cured and stirred, for a period of about 30 minutes. The pH was decreased further to about 2.0, over a 2 hour period, by adding concentrated hydrochloric acid. The HC1 functioned to extract the CaCθ3 that had been silica coated, thus leaving sihca shell particles. The SnCl4 solution and ΗCI4 solution were mixed and added to the shells. Thereafter, the mixture was stirred and reheated to a temperature of about 80 degrees C. A solution comprising 100 ml of SnCLj. solution which contained the equivalent of about 0.445 gm Snθ2 per ml was added to the slurry of silica shells over a thirty minute period while maintaining the pH at about 2.0 by adding 20% NaOH solution. The tin oxide coated sihca shells and the slurry contents were cured for 30 minutes.

Approximately 500 ml of the prepared aqueous ΗCI4 solution was added to the stirred silica shells coated with Snθ2 over a 2 hour period while maintaining the pH at approximately 2.0 by adding 20% NaOH solution.

The resultant composition was cured and stirred, for a period of about 30 minutes, while maintaining the pH at about 2.0 and the temperature at about 80

degrees C.

The composition was then filtered by using a Buchner Filter Funnel, and the recovered solids were washed with 50 degrees C deionized water to be substantially free of chloride ions.

The recovered solids were then dried in a drying oven in air at a temperature of about 120 degrees C, and calcined for about 2 hours at a temperature of about 800 degrees C.

The calcined product weighed about 905 grams. The calcined product had a surface area of about 93 square meters per gram.

B. Preparing Iightfast Titania Coated Amorphous Silica Shells.

Substantially the same procedure was used as for Example 11B, with exception that the Tiθ2 on Siθ2 shells were prepared substantially in accordance with Example 12A.

The Snθ2/Tiθ2 on Siθ2 shells is the material from Ex 12A, 111 grams of Ex 12A was used, and had a surface area of about 97 square meters per grams.

Example 13

A. Coprecipitation of Amorphous Sihca and Anatase Tiθ2- A stock solution of soluble titanium chloride solution was prepared by adding approximately 2000 ml. of ΗCI4 to about 8000 grams of ice. About 8000 ml of the stock ΗCI4 solution was added to 5000 ml deionized water stirred at a temperature of 80 degrees C along with 100 grams K2Siθ3 is 2 liter of deionized water and sufficient 50% NaOH to control the pH at 2 over a six hour period. The precipitate formed (a mixture of sihca/titania) was then cured for an approximately 30 minute period at a pH of about 2-3 and a temperature of about 80 degrees C.

The precipitate was then filtered in a Buchner Filter Funnel and washed substantially free of soluble salts. The filtered and washed precipitate was dried at a temperature of about 120 degrees C for about six hours and then calcined for about two hours at a temperature of about 550 degrees C in a calcining oven. The recovered product weighed approximately 1300 grams and had a surface area of 70 square meters per gram.

B. Coating Coprecipitated Amorphous Sihca and Anatase Tiθ2- Approximately 200 grams of the calcined Tiθ2-Siθ2 powder from

Example 13A above, were added to about 2 liters of stirred deionized water which had a temperature of about 75 degrees C that were housed in a 4 liter beaker.

The pH of the water was adjusted to about 3.0 by adding a solution comprising about 20 weight percent hydrochloric acid.

Approximately 5.4 grams of cerous chloride (CeCl3 7H2O) were added to the water, and the slurry was stirred for about 5 minutes. The following two solutions were prepared:

(a) Approximately 23.6 grams of sodium hypophosphite (NaH2Pθ2-H2θ) were dissolved into about 150 ml of deionized water, and;

(b) Approximately 64.8 grams of ZrOCl2 solution, which contained the equivalent of about 20 weight Z >2, was diluted into 150 ml of deionized water.

Solutions (a) and (b) were placed into separate burets, and were added at the same rate, over a 2 hour period, to the above slurry, while maintaining the pH at about 3.0 by adding a solution comprising about 20 weight percent NaOH.

The resultant slurry was cured and stirred for a period of about 30 minutes, at a pH of about 3.0 and a temperature of about 75 degrees C. The pH was increased over a period of about (5 minutes) to about 7.2, by adding a solution comprising about 20 weight percent NaOH.

The slurry was cured and stirred, for a period of about 30 minutes while at a temperature of about 75 degrees C. The slurry was filtered by using a Buchner Filter Funnel, washed with deionized water to be substantially free of chloride ions, and dried in a drying oven at a temperature of about 120 degrees

C.

The dried product weighed about 218 grams and had a surface area of

77 square meters per gram. The dried product comprised a cerium containing Tiθ2-Siθ2 Iightfast pigment.

Example 14 This Example describes a process for coprecipitating Siθ2-Tiθ2 particles without calcining prior to being coated for lightfastness. Approximately 1000 grams of CaCθ3 was added to about 8 liters of stirred deionized water at a temperature of about 80 degrees C that was housed in a 12 in. x 12 in. pyrex jar.

The pH of the deionized water was adjusted to about 9.5 by adding a solution comprising about 20 weight percent NaOH solution. A solution comprising approximately 1000 grams of K2Siθ3

dissolved into about 2 liters of deionized water was added to the previously described carbonate containing solution over a 2 hour period, while maintaining the pH at about 9.5 by adding a solution comprising about 20 weight percent hydrochloric acid.

Simultaneously with the addition of the K2Siθ3 solution, and over the same 2 hour period, a solution comprising about 2.5 grams of CaCl2 dissolved into about 50 ml of deionized water was also added to the carbonate containing solution. The pH of the resultant mixture was decreased to about 8.5 with diluted HC1 solution, and the mixture was cured and stirred, for a period of about 30 minutes to extract the CaCθ3. The pH of the mixture was decreased to about 1.0 over a 2 hour period by adding concentrated hydrochloric acid. After the pH of the mixture was stabilized at about 1.0, the mixture was allowed to cool. When the temperature of the mixture reached about 60 degrees C the stirrer was turned off, and the mixture, which contains sihca shells stood overnight undisturbed. Next day, the sihca shells slurry was heated to a temperature of about 80 degrees C, and stirred.

Approximately 1000 ml of a mixture, which was made by adding ΗCI4 to ice in the proportion of 500 ml of ΗCI4 : 2000 grams of ice, was added to the sihca shells. The pH was controlled at about 2-3 by adding a 20% NaOH solution.

The resultant mixture was cured for about 30 minutes at a pH of about 2.0 and a temperature of about 80 degrees C. The cured mixture was filtered with a Buchner Filter Funnel. The resultant filter cake was added to about 9 liters of deionized water at a temperature of about 75 degrees C that was housed in a 12 in. x 12 in. pyrex jar. The deionized water was stirred until substantially all the cake was dispersed. The pH was adjusted to 3 with dilute HC1. Approximately 17.55 grams of cerous chloride (CeQ j ^O) were added to the slurried filter cake and the slurry was stirred for about 5 minutes. The following two solutions were prepared: (A) approximately 76.7 grams of sodium hypophosphite (NaH2Pθ2-H2θ) were dissolved into about 500 ml of deionized water, and; (B) approximately 210.6 grams of ZrOCl2 solution, which contained the equivalent of about 20 weight percent Zrθ2, were diluted into about 500 ml of deionized water.

Solutions (A) and (B) were placed into separate burets. These two solutions were added at the same rate, over a 2 hour period, to the slurry, while maintaining the pH at about 3.0 by adding about 20 weight percent NaOH.

The slurry was then cured for about 30 minutes at a pH of about 3.0 and a temperature of about 75 degrees C.

The pH of the cured slurry was increased to about 7.2, by adding a solution comprising about 20 weight percent NaOH, and the slurry was cured again for a period of about 30 minutes. The slurry was filtered by using Buchner Filter Funnel, washed with deionized water to be substantially free of chloride ions, and dried in a drying oven at a temperature of about 120 degrees C.

The dried product weighed 477 grams and possessed a surface area of about 150 square meters per gram.

Example 15 This Example describes a process for coprecipitating Tiθ2-Siθ2 particles without calcining prior to being coated.

Approximately 2260 ml of a solution, which was made by adding ΗCI4 to ice in the proportion of 500 ml of ΗCI4 : 2000 grams of ice, were added over about 2 hour period to about 9 liters of stirred deionized water at a temperature of about 80 degrees C that was housed in a 12 in. x 12 in. pyrex jar. The pH of the deionized water was maintained at about 2 by adding a solution comprising about 50 weight percent NaOH. Simultaneous with the addition of the ΗCI4 containing solution, a second solution was added, comprising about 28 grams of K-2Siθ3 was dissolved into about 840 ml of deionized water, thereby forming a a precipitate of Tiθ2/silica. The slurry was cured for a period of about 30 minutes at a pH of about 2 and a temperature of about 80 degrees C. Approximately 8.1 grams of cerous chloride (CeCl3 H2θ) were added to the slurry, and the slurry was stirred for about 5 minutes. The following two solutions were prepared: (A) approximately 35.4 grams of sodium hypophosphite (NaH2Pθ2-H2θ) were dissolved into about 225 ml of deionized water. (B) approximately 97.2 grams of ZrOCl2 solution , which contained the equivalent of about 20 weight percent Zrθ2, was diluted into about 225 ml of deionized water.

The solution (A) and (B) were placed into separate burets. These two solutions were added at the same rate, over about 1.5 hours, to the slurry, while maintaining the pH at about 3.0 by adding a solution comprising about 20 weight

percent NaOH.

The slurry was cured and stirred for a period of about 30 minutes at a pH of about 3.0 and a temperature of about 75 degrees C.

The pH of the cured slurry was raised to about 7.2, by adding a solution comprising about 20 weight percent NaOH, and then the slurry was cured and stirred, for a period of about 30 minutes at a temperature of about 75 degrees C.

The resultant slurry was filtered with a Buchner Filter funnel, washed with deionized water to be substantially free of chloride ions, and dried in a drying oven at a temperature of about 120 degrees C. The dried product weighed about 401 grams and its surface area was

181 square meters per gram. A chemical analyses of the materials produced in accordance with Examples 11-15 is shown in Table V.

TABLE V

Weight percent

Example 11A 11B 12A 12B 13A 13B

Si0 ₂ 67.7 61.6 56.1 59.7 2.3 2.2 τιo ₂ 30.3 28.2 38.3 28.0 95.1 86.7

Zr0 ₂ < 5.8 < 6.0 < 7.3

P2O5 0.73 0.75 0.67 0.68 < 0.35

Ce ₂ 0 ₃ < N.D. < 0.75 < 0.72

Sn0 ₂ < < 3.2 2.6 < <

Na ₂ 0 0.14 1.6 0.13 0.88 0.58 0.54

MgO 0.14 0.13 0.15 0.15 0.27 0.29

AI2O3 0.12 0.11 0.01 0.10 0.04 0.04

CaO 0.19 0.18 0.27 0.21 < <

Fe2θ3 0.10 0.07 0.13 0.06 0.03 < ₂ o 0.02 0.02 0.03 0.02 < <

< = less than 100 ppm

The CAC values for coated particles produced substantially in accordance with Examples 11-15 are shown in Table VI. Values for commercially available ΗO2 pigments are also shown for comparison.

TABLE VI

Example CAC

11A 0.60

11B 0.15

12A 0.60

12B 0.15

13A 0.55

13B 0.10

14 0.18

15 0.15

R-900* 0.60

R-902* 0.10

R-960* 0.04

* A commercially available Tiθ2 material sold by the DuPont Company, Wilmington, Delaware, U.S.A..

EXAMPLE 16 This example used cerium hypophosphite as an inner coating and an outer coating of zirconia combined with hypophosphite on fumed titania (supphed by DeGussa as Grade P-25, microfine titania).

Approximately 1000 grams of DeGussa fumed titania, Grade P-25, was added to a 12" x 12" pyrex jar containing about 10 liters of deionized water. The jar was equipped with a paddle stirrer and mounted on an electric heating pad. The bath and contents were heated to a temperature of about 80° C. The pH of the bath was adjusted to about 3.0 by using a 20% HC1 solution. Following the pH adjustment, about 31.0 grams of cerous chloride (CeCkj 7H2O supplied by G.F. Smith, P.O. Box 23214, Columbus Ohio), was added to the bath and allowed to dissolve. Approximately 67.7 grams of NaH2Pθ2 (supplied by J.T. Baker, Inc., Philhpsburg, NJ 08865) was dissolved in to about 350 ml deionized water and approximately 185.8 grams of ZrOCl2 solution (20% Zrθ2 supplied by Harshaw chemical) was added to the 350 mis of deionized water.

The sodium hypophosphite solution and the zirconium oxychloride solution were added to the bath from burettes over an approximately 1.5 hour period. A solution of 20% NaOH was added to control the pH at about 3.0. Following the previous addition, the coated titania was stirred for about 30 minutes at a pH of about 3.0 and a temperature of about 80° C to cure. The pH was then increased to about 1.2 by adding a 20% NaOH solution. The system was stirred at a pH of about 7.2 and a temperature of about 80° C for about 30 minutes to cure. The coated fumed titania was recovered by filtering on a Buchner funnel. The coated filtered titania was washed substantially free of soluble salts with deionized water, then dried at about 120° C overnight.

The coated and dried product was passed through a hammermill that utilized a #20 screen.

The hammermilled product had a CAC value of about 0.13 and a surface area about 45.8 m^/gr.

EXAMPLE 17

This example used cerium phosphate as an inner coating and alumina combined with phosphate as an outer coating on fumed titania (supphed by DeGussa as Grade P-25).

Approximately 1000 grams of DeGussa fumed titania, Grade P-25 was added to a 12" x 12" pyrex jar containing 10 hters of deionized water. The jar was equipped with a paddle stirrer and mounted on an electric heating plate. The bath and contents were heated to a temperature of about 45° C.

The pH was adjusted to about 2.0 by using a 20% sulfuric acid solution. Following the pH adjustment, about 7.5 mis of eerie nitrate solution (260 gm Ceθ2/lit supphed by G.F. Smith, P.O. Box 23214, Columbus, Ohio) was added to the bath over an approximately 2 minute period. After about 5 minutes stirring, approximately 17.6 mis of 85% phosphoric acid was added to the bath over a 2 min. period. The resultant system was stirred for a period of about ten minutes.

While continuing stirring, the pH was increased to about 7.2 with a 20% NaOH solution, and the temperature raised to about 55° C. Approximately 100 mis of sodium aluminate solution (supphed by Vinings VSA 38, Vinings Industries, Inc., 1654 West Oak Dr., Marietta, GA 30062) was added to the bath while controlling the pH at about 7.2 with 20% sulfuric acid over a period of about 2 hours. The contents were then cured while stirring at a pH of about 7.2 and a temperature of about 55° C.

The coated titania was then recovered by filtering on a Buchner funnel. The coated titania was washed substantially free of soluble salts with deionized water, then dried at about 120° C overnight.

The coated and dried product was passed through a hammermill that utilized a #20 screen.

The hammermilled product had a CAC value of about 0.15 and a surface area of about 42 m^/gr.

While a few aspects of the invention have been described in detail one of ordinary skill would recognize that other embodiments and variations are encompassed by the appended claims.