Coated titanium dioxide pigments and processes for production and use

ES 2 379 650 T3

DESCRIPTION

Coated Titanium Dioxide Pigments and Production and Use Processes

This application claims the benefit of US Provisional Application No. 60/201576, filed May 1, 2000 and entitled "Titania Pigment Having Sequential Multiple Layer Hydrous Oxide Deposits Exhibiting Improved Gloss and Durability and Processes For Production and Use", whose The full description is hereby incorporated by reference into the present disclosure.

Field of the invention

The invention relates to titanium dioxide pigments coated with a first layer of a phosphate compound, a layer of silica or a zirconia compound, a second layer of a phosphate compound and a layer of alumina. The titanium dioxide pigments of the present invention are easily dispersible and retain their gloss and durability.

Background

Titanium dioxides, in the forms of either rutile or anatase, are well known as opacifying pigments due to their high refractive index: they are among the compounds that when prepared in a size range of from about 0, 2 to about 0.4 microns diffuse light as well or better than any other known compound. However, titanium dioxide (TiO2) is a semiconductor and will convert UV radiation (e.g. from UV light) into low-energy β particles (electrons) that can ultimately initiate the degradation of many organic-based materials in pigment is used, such as paints, plastics and other organic-based compositions, through the production of various radical species.

One method of limiting the effects of light on the titanium dioxide pigment is to coat the pigment with inorganic compounds such as oxides and hydroxides of alumina, silica, zirconium, or phosphate. Such coatings can result in a more durable product that is resistant to UV light-induced degradation. However, some coatings cause the formation of agglomerates that lead to difficulties in dispersing pigments in various organic-based compositions, thereby reducing opacity and gloss.

In general, it is desirable to use phosphate coatings because they have good profitability. However, the conventional prior art teaches that phosphate coatings greater than 0.5% tend to cause pigments to agglomerate causing a reduction in dispersibility and therefore opacity of the final product, as well as gloss. Accordingly, prior art phosphate coatings on titanium dioxide particles have typically been limited to phosphate contents ranging from 0.1% to 0.5% by weight based on the basis weight of titanium dioxide. titanium.

US 5,851,652 A to Jacobson et al. discloses coated rutile-type TiO2 pigment particles, however it does not disclose a second phosphate deposit between the silica and alumina deposits.

WO 89/09801 A by Kerr-McGee Chemical Company discloses a durable titania pigment with improved optical properties having a layer stack of silica, alumina and silica.

FR 2758826 A by Rhodia Chimie discloses a titania pigment comprising a first coating of zirconium hydroxide, an additional layer of hydrated titanium hydroxide, followed by a layer of a mixed compound of silica and a phosphate and a coating alumina exterior.

Based on the foregoing, there is still a need for phosphate coated titanium dioxide pigments which are easily dispersible and exhibit excellent gloss and durability. Such coated pigments are useful in the manufacture of paints and other coating systems.

Summary of the invention

The present invention provides titanium dioxide pigments coated with at least two layers of a phosphate compound. Preferably, a layer of silica or zirconia separates the two phosphate layers. The pigments of the present invention are readily dispersible and maintain a gloss and durability comparable to so-called "super durable" pigments (eg, pigments having up to 6% silica).

In one embodiment, the present invention provides a coated titanium dioxide pigment, which includes a base titanium dioxide particle; a first deposit of a phosphate compound contiguous to the base TiO2 particle; a deposit of a dense silica compound contiguous to the phosphate deposit; a second deposit of a phosphate compound contiguous with the dense silica compound; and a reservoir of a contiguous alumina compound

ES 2 379 650 T3 to the second phosphate reservoir.

In a second embodiment, the present invention provides a process for preparing coated titanium dioxide pigment, comprising the steps of: a) preparing an aqueous suspension of titanium dioxide base, b) adding a first phosphate compound to the suspension to form a first phosphate compound coating, c) adding a silica compound to the suspension to form a compound coating silica, d) adding a second phosphate compound to the suspension e) adding an alumina compound to the suspension to form an alumina compound coating, thereby forming the coated titanium dioxide pigment.

In another embodiment, the present invention provides a process for preparing coated titanium dioxide pigment comprising the steps of: a) preparing an aqueous suspension of titanium dioxide base, b) adding a first phosphate compound to the suspension to form a first phosphate deposit, c) increasing the pH of the suspension to about 7.0, d) heating the suspension to a temperature of about 80 ° C to about 95 ° C, e) adding a silica compound to the suspension over a period of about 30 minutes, f) aging the suspension for about 20 minutes, g) adjusting the pH of the suspension to about 6.5 over a period of about 60 minutes, h) adding a second phosphate compound to the suspension, i) adding an alumina compound to the suspension under conditions such that the pH of the suspension is maintained at approximately 6.5, j) aging the suspension for approximately 30 minutes, k) adjusting the pH of the suspension to approximately 5.3 and, l) discharge and filter the coated titanium dioxide pigment.

In yet another embodiment, the present invention provides a process for preparing coated titanium dioxide pigment, comprising the steps of: a) preparing an aqueous suspension of titanium dioxide base, b) adding a first phosphate compound to the suspension to form a first phosphate compound coating, c) adding a silica or zirconia compound or combination thereof to the suspension to form a coating comprising silica or zirconia or a combination thereof, d) adding a second phosphate compound to the suspension to form a second phosphate compound coating, e) adding an alumina compound to the suspension to form an alumina compound coating, thereby forming the coated titanium dioxide pigment.

For a better understanding of the present invention together with other and additional embodiments, reference is made to the following description taken in conjunction with the examples, the scope of which is set forth in the appended claims.

Detailed description of the invention

In preparing the preferred embodiments of the present invention, various alternatives may be used to facilitate the objectives of the invention. These embodiments are presented to aid in an understanding of the invention and are not intended, and should not be construed, to limit the invention in any way. All equivalents, alternatives, and modifications that may be obvious to those of ordinary skill in the art upon reading the present disclosure are included within the spirit and scope of the present invention.

This description is not a manual on the manufacture of titanium dioxide pigments, basic concepts known to those skilled in the art have not been discussed in detail.

Coated Titanium Dioxide Pigments

The coated titanium dioxide pigments of the present invention include base titanium dioxide particles, either of the rutile type or of the anatase type. The titanium dioxide base particle suitable for use in the present invention has a particle size range of less than about 1.0 microns, and more preferably from about 0.1 microns to about 0.5 microns, and most preferably from about 0.1 microns to about 0.35 microns.

The titanium dioxide base particle is coated with a first layer of a phosphate compound by depositing the phosphate compound on the TiU2 base particle. Preferably, the phosphate compound is a water soluble phosphate compound, such as, for example, tetrapotassium pyrophosphate, sodium polyphosphate, tetrasodium pyrophosphate (Tetron ™), sodium tripolyphosphate, potassium tripolyphosphate, sodium hexametaphosphate (Calgon ™ ), phosphoric acid and the like. Most preferably, the water soluble phosphate compound is sodium hexametaphosphate. The percentage by weight of the phosphate compound can vary depending on the layer deposited on the titanium dioxide base. It is not necessary for the phosphate compound to coat each titanium dioxide particle, only that a certain amount of phosphate be deposited on the particle. Preferably, the phosphate compound in the first layer is deposited in an amount of from about 0.05% to about 1.0%, more preferably from about 0.05% to about 0.75% and most preferably, from about 0.05% to about 0.5% based on the basis weight of titanium dioxide.

ES 2 379 650 T3

The titanium dioxide particles of the present invention are optionally coated with a silica compound. Preferably, the silica coating is dense and contiguous with the first phosphate compound. The silica content in weight percent can vary depending on the layer deposited on the first phosphate layer. Suitable silica compounds for use in the present invention include water soluble alkali metal silicates. Preferred alkali metal silicates include sodium silicate, potassium silicate, and the like. Most preferably the silica compound is sodium silicate. Preferably, the silica compound is deposited in an amount of from about 0.5% to about 5.0% by weight of silica based on the total weight of the titanium dioxide base. More preferably, from about 1% to about 5%, and most preferably, the silica content is about 2.5% based on the weight of the titanium dioxide base.

In an alternative embodiment of the present invention, the titanium dioxide particles of the present invention can be coated with a zirconia compound. Preferably, the zirconia coating is contiguous with the first phosphate compound. The weight percent of zirconia can vary depending on the layer deposited on the first phosphate layer. Suitable zirconia compounds for use in the present invention include the acidic zirconia salts such as zirconium oxychloride, zirconyl sulfate, and the like. Most preferably, the zirconia compound is zirconium oxychloride or zirconyl sulfate. Preferably, the zirconia compound is deposited in an amount of from about 0.1% to about 5.0% by weight of zirconia based on the total weight of the titanium dioxide base. More preferably, from about 0.5% to about 2%, and most preferably, the weight percent of zirconia is from about 0.5 to about 1.0% based on the weight of the dioxide base. titanium.

In another embodiment of the present invention, the titanium dioxide particles of the present invention are optionally coated with a combination of a silica compound and a zirconia compound as defined above. Preferably, this combination is contiguous with the first phosphate layer.

The titanium dioxide particles of the present invention are coated with a second layer of a phosphate compound. The weight percent of the second phosphate compound can vary depending on the layer deposited on the silica or zirconia layer. Preferably, the second phosphate coating is contiguous with the silica or zirconia layer. Suitable phosphate compounds for use in the present invention include water soluble phosphate compounds, such as, for example, tetrapotassium pyrophosphate, sodium polyphosphate, tetrasodium pyrophosphate (Tetron ™), sodium tripolyphosphate, potassium tripolyphosphate, hexametaphosphate sodium (Calgon ™), phosphoric acid and the like. Most preferably, the water soluble phosphate compound is sodium hexametaphosphate.

Those skilled in the art will understand that the phosphate compound used in the first layer can be the same phosphate compound or a different one than that used in the second phosphate layer. Preferably, the phosphate compound in the second phosphate layer is deposited in an amount of from about 0.05% to about 1.0%, more preferably from about 0.08% to about 0.75%, and most preferably, from about 0.05% to about 0.5% based on the basis weight of titanium dioxide.

The total phosphate content of the pigments of the present invention including both phosphate layers is preferably not less than about 0.1% and not more than about 2% of the total weight of the titanium base. Phosphate content greater than about 2% based on the total weight of the titanium dioxide base tends to cause agglomeration by reducing pigment dispersibility, coating system opacity, and ultimately gloss.

After the deposition of the second phosphate compound, the titanium dioxide particle is coated with an alumina compound. Preferably, the alumina compound is contiguous with the second phosphate layer. Suitable alumina compounds for use in the present invention include aluminates, such as, for example, sodium or potassium aluminate, aluminum sulfate, aluminum chloride, and the like. Most preferably, the water soluble alumina compound is sodium aluminate. The weight percent of the alumina compound can vary depending on the layer of alumina deposited on the second phosphate layer. The alumina compound preferably comprises from about 1.0% to about 5.0% by weight, and more preferably, from about 2.0% to about 3.0% by weight, and most preferably, about 2.0% by weight of the alumina compound based on the total weight of the titanium dioxide base.

In the most preferred embodiment of the present invention, it has been unexpectedly discovered that dividing the phosphate addition into at least two separate tanks, with an intermediate silica layer of about 2.5% (based on the pigment weight of TiO2) , and a final deposit of alumina in the range of about 1% to about 3% (based on the weight of the titanium dioxide pigment), a level of pigment durability is achieved that approaches or exceeds that of some of the super durable quality pigments. Some super durable pigments are known in the art to incorporate up to six percent by weight of dense silica and alumina in the pigment to enhance durability. Unlike these super durable pigments, the pigments of the present invention can have less silica content, maintain equal durability and

ES 2 379 650 T3, while exhibiting improved gloss and dispersibility.

Preparation of coated titanium dioxide pigments

The coated titanium dioxide pigments of the present invention can be prepared starting from titanium dioxide base particles. Titanium dioxide base particles are commercially produced in two crystalline forms, namely the rutile form that is commonly produced by the chloride and sulfate processes and the anatase form that is commonly produced by the sulfate process. These two well-known processes are generally described in US Pat. Nos.^you RE 27,818 and 2,559,638 and those basic descriptions are incorporated herein by reference. The present invention is applicable to both rutile and anatase forms of the TiO2 pigment.

Generally, the TiO2 base particles are subjected to wet milling or milling by methods known in the art to provide a base of substantially uniform particle size. Preferably, the base particle has a size range of less than about 1.0 microns, and more preferably, between about 0.1 microns and about 0.5 microns, and most preferably between about 0.1 microns and about 0, 35 micrometers.

Coated pigments of the present invention are prepared by forming an initial aqueous suspension of the base titanium oxide. Titanium dioxide base suspensions can be prepared by methods known in the art. Preferably, the suspension has a TiO2 solids content of greater than about 5%, more preferably, less than about 75%, and most preferably, the TiO2 suspension has a TiO2 solids content of about 30%.

Optionally, a water soluble dispersing agent can be added to the suspension to maintain the pigment in a highly dispersed state. Suitable dispersing agents are well known in the art.

Typically, the pH of the initial suspension can be determined by those skilled in the art and adjusted to a desired pH range using methods known in the art. For example, if adjustment of the pH of the suspension becomes necessary, such adjustments can be made simply by adding a suitable acid or a suitable base. Suitable acids include water soluble acids such as hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, and the like. Preferably, the pH of the initial suspension is at least about 3.5. Suitable bases include water-soluble alkaline bases such as ammonia, sodium hydroxide, or other suitable alkali compounds.

The temperature of the suspension can be kept in a range that will facilitate the deposition of the phosphate, silica or zirconium and alumina layers on the titanium dioxide base. Preferably, the suspension is heated to a temperature range of from about 30 ° C to about 100 ° C depending on the specific deposition step. The temperature of the suspension can be adjusted or maintained throughout the process through the use of conventional heating means known to those skilled in the art, such as, for example, steam.

In the most preferred embodiment of the present invention, the titanium dioxide is surface treated with the first and second phosphate compounds, the silica or zirconia compound, and the alumina compound. A particularly preferred surface treatment is wet treatment. Wet treatment methods are well known to those skilled in the art.

First phosphate addition

After formation of the initial suspension, a phosphate compound is added to the suspension while the temperature of the suspension is preferably less than about 35 ° C. For the purposes of the present invention, any water soluble phosphate compound that can provide phosphate for deposition on the basis of titanium dioxide can be employed under the operating conditions of the process. Suitable phosphate compounds for use in the present invention include water soluble phosphate compounds, such as, for example, tetrapotassium pyrophosphate, sodium polyphosphate, tetrasodium pyrophosphate, sodium tripolyphosphate, potassium tripolyphosphate, sodium hexametaphosphate, acid phosphoric and the like. Most preferably, the water soluble phosphate compound is sodium hexametaphosphate.

The weight percent of the phosphate compound can vary depending on the phosphate layer produced. It is not necessary for the phosphate compound to coat each titanium dioxide particle, only that a certain amount of phosphate be deposited on the particle. Preferably, the phosphate coating is continuous rather than discontinuous. In one embodiment of the present invention, the phosphate compound is added to the suspension in an amount of preferably from about 0.05% to about 0.5%, more preferably from about 0.1% to about 0 , 3% and most preferably from about 0.1% to about 0.2% based on the total weight of the titanium dioxide pigment.

ES 2 379 650 T3

Typically, the phosphate compound is added to the suspension with stirring, such as for example by an in-line mixer or other suitable means, over a period of preferably from about 5 minutes to 120 minutes. More preferably, the phosphate compound is added to the suspension over a period of from about 10 minutes to about 60 minutes and most preferably from about 10 minutes to 20 minutes.

The pH of the suspension is adjusted before, during or after the addition of the phosphate compound. Those skilled in the art can determine the specific pH and adjust it to a desired pH range used by methods known in the art. For example, if adjustment of the pH of the suspension becomes necessary, such adjustments can be made by adding a suitable acid or a suitable base as discussed above. Preferably, the pH is adjusted to above about 6.0, more preferably to a range of from about 6.0 to about 7.0, and most preferably the pH is adjusted to the range of from about 6.5 to about 7.0.

Silica or zirconia additions

After the deposition of the first phosphate compound on the base titanium dioxide, optionally, a silica compound is added to the suspension. Preferably, the temperature of the suspension is raised to above about 70 ° C, more preferably from about 70 ° C to about 100 ° C, and most preferably, from about 86 ° C to about 95 ° C. For the purposes of the present invention, any water soluble silica compound can be employed which can provide silica for deposition on the titanium dioxide particle under the operating conditions of the process of the present invention. Suitable silica compounds for use in the present invention include water soluble alkali metal silicates. Preferred water soluble alkali metal silicates include sodium silicate, potassium silicate, and the like. Most preferably the silica compound is sodium silicate.

The weight percent of the silica compound can vary depending on the dense silica layer produced. Preferably, the silica coating is dense and continuous rather than porous and discontinuous. As used herein, aging or curing refers to maintaining the suspension in such a way that the suspension achieves physical and chemical equilibrium. The aging time of the silica is preferably at least about 5 minutes, more preferably from about 5 minutes to about 120 minutes, and most preferably, from about 5 to about 10 minutes. Preferably, the silica compound is deposited in an amount of from about 0.5% to about 5.0% by weight of silica, more preferably from about 1% to about 5%, and most preferably, the content on silica it is approximately 2.5% based on the total weight of the titanium dioxide base.

Preferably, the silica compound is added to the suspension with stirring, such as for example by an in-line mixer or other suitable means, over a period of at least about 5 minutes to 120 minutes, more preferably, from about 10 minutes. minutes to about 60 minutes and most preferably, from about 20 minutes to about 30 minutes depending on the process selected (ie, continuous or batch).

As with the first phosphate layer, the pH of the suspension can be adjusted during or after addition of the silica compound to produce a dense, silica compound coating on the titanium dioxide particle. Those skilled in the art can determine the specific pH and adjust it to a desired pH range used by methods known in the art. For example, if adjustment of the pH of the suspension becomes necessary, such adjustments can be made by adding a suitable acid or a suitable base as discussed above. Most preferably, the pH is adjusted to the range of from about 5.0 to about 8.0 over a period of from about 20 minutes to about 60 minutes after the silica compound is added depending on the selected process. .

Optionally, instead of a silica compound, after deposition of the phosphate compound on the base titanium dioxide, a zirconia compound can be added to the suspension. Preferably, the temperature of the suspension is about room temperature, 15-25 ° C, or higher when the zirconia compound is added. For the purposes of the present invention, any water soluble zirconia compound can be employed which can provide zirconia for deposition on the titanium dioxide particle under the operating conditions of the process of the present invention. Suitable zirconia compounds for use in the present invention include acid salts such as zirconium oxychloride, zirconyl sulfate, and the like. Most preferably, the zirconia compound is zirconium oxychloride or zirconyl sulfate.

The weight percent of the zirconia compound can vary depending on the layer produced. Preferably, the zirconia coating is continuous rather than discontinuous. The time for aging of the zirconia is preferably at least about 5 minutes, more preferably from about 5 minutes to about 120 minutes, and most preferably, from about 5 to about 10 minutes. Preferably, the zirconia compound is deposited in an amount of from about

ES 2 379 650 T3

0.1% to about 5.0% by weight of zirconia based on the total weight of the titanium dioxide base. More preferably, from about 0.5% to about 2%, and most preferably, the weight percent of zirconia is about 0.5-1.0% based on the weight of the titanium dioxide base.

Preferably, the zirconia compound is added to the suspension with stirring, such as for example by an in-line mixer or other suitable means, over a period of at least about 5 minutes to 120 minutes, more preferably, from about 10 minutes. minutes to about 60 minutes and most preferably, from about 20 minutes to about 30 minutes depending on the process selected (ie, continuous or batch).

As with the first phosphate layer, the pH of the suspension can be adjusted, during or after the addition of the zirconia compound to produce a coating on the titanium dioxide particle. Those skilled in the art can determine the specific pH and adjust it to a desired pH range used by methods known in the art. For example, if adjustment of the pH of the suspension becomes necessary, such adjustments can be made by adding a suitable acid or a suitable base as discussed above. Most preferably, the pH is adjusted to the range of from about 3.0 to about 8.0 over a period of from about 20 minutes to about 60 minutes after the silica compound is added depending on the selected process. (ie continuous or bath).

Optionally, after the deposition of the first phosphate compound on the titanium dioxide base, a combination of silica or zirconia can be added to the suspension. Suitable zirconia and silica compounds were described above.

The present invention also contemplates splitting the phosphate addition into at least two separate deposits on the titanium dioxide, with an interlayer of phosphate-free hydrated oxide between the phosphate deposits. Suitable intermediate non-phosphate compounds for use in the present invention include silica or zirconia and the like.

Second phosphate addition

After the deposition of the silica or zirconia compound on the titanium dioxide particle, a second phosphate compound is added to the suspension while the temperature of the suspension is kept above about 30 ° C. For the purposes of the present invention, any water soluble phosphate compound that can provide phosphate can be employed for deposition on the titanium dioxide pigment under process operating conditions. Such phosphate compounds can be the same or different phosphate compounds as used in the first phosphate layers. Suitable phosphate compounds for use in the present invention include water soluble phosphate compounds, such as, for example, tetrapotassium pyrophosphate, sodium polyphosphate, tetrasodium pyrophosphate, sodium tripolyphosphate, potassium tripolyphosphate, sodium hexametaphosphate, acid phosphoric and the like. Most preferably, the water soluble phosphate compound is sodium hexametaphosphate.

The weight percent concentration of the phosphate compound can vary depending on the phosphate layer produced. Preferably, the phosphate coating is continuous with silica deposition, rather than discontinuous. The phosphate compound is added to the suspension in an amount of preferably from about 0.05% to about 0.5%, more preferably from about 0.1% to about 0.3%, and most preferably from about 0.1% to about 0.2% based on the total weight of the titanium dioxide base.

As with the first phosphate addition, the second phosphate compound in this layer is added to the suspension with stirring, such as for example by an in-line mixer or other suitable means, over a period of preferably from about 5 minutes up to 120 minutes, more preferably from about 10 minutes to about 60 minutes, and most preferably, more than about 10 minutes to about 20 minutes.

The temperature of the suspension can be maintained in a range that will facilitate the deposition of the second phosphate compound on the titanium dioxide pigment. Preferably, the suspension is maintained at a temperature range of from about 30 ° C to about 100 ° C.

Alumina addition

After the addition of the second phosphate compound to the suspension, an alumina compound is added to the suspension while the suspension is kept at a temperature above preferably 50 ° C. Suitable alumina compounds for use in the present invention include water soluble alkali metal aluminates, such as for example sodium or potassium aluminate, or acid salts such as aluminum sulfate or aluminum chloride. Most preferably, the water soluble alumina compound is aluminate

ES 2 379 650 T3 sodium.

The weight percent of the alumina compound can vary depending on the alumina layer deposited with the phosphate layer. The alumina compound preferably comprises from about 1.0% to about 5.0% and more preferably from about 2.0% to about 3.0% and most preferably about 2.0% by weight based in the total weight of the titanium dioxide pigment.

As with other additions, preferably, the alumina compound is added to the suspension with stirring, over a period of preferably from about 5 minutes to 120 minutes, more preferably from about 10 minutes to about 60 minutes, and most preferably from more than about 10 minutes to about 20 minutes depending on the process selected (ie, continuous or batch).

The pH of the suspension is adjusted during the addition of the alumina compound to deposit the alumina compound on the titanium dioxide base. Those skilled in the art can determine the specific pH and adjust it to a desired pH range used by methods known in the art. For example, such adjustments can be made simply by adding a suitable acid or a suitable base as discussed above. Preferably the pH is adjusted to the range of from about 7.8 to about 4.0, more preferably from about 7.0 to about 5.0, and most preferably from about 6.5 to about 5.3.

The temperature of the suspension can be maintained in a range that will facilitate the deposition of the alumina compound on the titanium dioxide pigment. Preferably, the suspension is heated to a temperature range of from about 30 ° C to about 100 ° C.

After completion of the addition of the alumina compound, the pH of the suspension is adjusted to preferably about 4.0 to 8.0. The resulting titanium dioxide pigment coated with a first layer of phosphate, a layer of silica or zirconia, a second layer of phosphate and a layer of alumina is recovered by filtration, washed until substantially free of soluble salts that adhere to the pigment, dried and then subjected to a final milling using liquid energy milling techniques known in the art. Preferably, the washed and dried pigment is micronized in a steam micronizer at intensities known to those skilled in the art.

Optionally, a polyol such as, for example, trimethylolpropane (TMP), trimethylolethane (TME) or pentaerythritol and the like, can be added to the pigment during steam micronization. In the most preferred embodiment, TMP is added in an amount of from about 0.2% to 0.4% based on the weight of the titanium dioxide pigment.

Continuous and discontinuous processes

Those skilled in the art will understand that the process of the present invention can be performed by a batch process or a continuous process and combinations thereof. Preferably, continuous processes involve continuous feed lines with cascade treatment tanks with separate addition points for phosphate, silica and alumina compounds, pH adjusters, and other additives. Continuous processes typically involve residence times less than about 120 minutes, preferably from about 5 minutes to about 120 minutes, more preferably from about 10 minutes to 60 minutes, and most preferably from about 10 minutes to about 30 minutes for the individual deposition. of phosphate, silica, zirconia and alumina on the titanium dioxide pigment.

Batch processes generally involve longer pigment processing times with an addition point for phosphate, silica and alumina compounds, pH adjusters, and other additives. Typically, batch processes typically involve residence times generally greater than about 10 minutes for the deposition of phosphate, silica, zirconia, and alumina on the titanium dioxide particle. Regardless of the process used (batch or continuous), the coated pigments of the present invention are suitable for use in paints, plastics and coatings, where both durability and gloss are needed.

Dispersibility, gloss and durability

Coated pigments produced by the methods of the present invention have been unexpectedly found to have good dispersibility, gloss, or durability. Dispersibility is determined by methods known in the art. For example, the coated titanium dioxide pigments of the present invention can be mixed into a plastic or paint and the distribution of the pigment particles measured. A uniform distribution of the pigment throughout the paint or plastic indicates good dispersibility, while the formation of agglomerates would indicate poor dispersibility of the pigment. Some methods of determination

ES 2 379 650 T3 of dispersibility known in the art include dyeing power, Q proof and the like.

Gloss is determined by methods known in the art. Preferably, the gloss is determined by incorporating the pigment into paint and measuring the gloss using a gloss meter. In the most preferred method, pigments prepared by methods of the present invention are incorporated into acrylic-based paints with a CPV (pigment concentration by volume) of 40% and the gloss is measured at 20 °.

The durability of the pigments of the present invention can be determined by methods known in the art. Some durability measurement methods include measurement of the photocatalytic activity of the pigment, the acid solubility of the titanium dioxide base, weatherometer tests, and natural exposure. Most preferably, durability is measured by natural exposure or aging chamber tests.

Aging chamber testing involves incorporating the pigments into, for example, paint and subjecting the paint to exposure in an Atlas Weatherometer aging chamber and then comparing pigments coated with two layers of phosphate versus coated pigments produced with one or neither. phosphate layer. Pigments are then rated for durability.

The invention having now generally been described, the same may be more readily understood by the following reference to the following examples, which are provided by way of illustration and are not intended to limit the present invention unless specified.

Examples

The following examples are presented to aid an understanding of the present invention and are not intended, and should not be construed, to limit the invention in any way. All equivalents, alternatives, and modifications that may be obvious to those of ordinary skill in the art upon reading the present disclosure are included within the spirit and scope of the present invention.

Example 1

To an aqueous suspension with vigorous stirring of a TiO base₂ Rutile type, having a mean diameter from about 0.15 microns to about 0.35 microns, a 0.2% P2O5 (phosphate) was added as an aqueous solution of Calgon- ™ (sodium hexametaphosphate) on a basis weight of TiO2. The suspension was heated to between about 85 ° C and 90 ° C and then the pH of the suspension was increased to about 7.0 using a sodium hydroxide solution. A sodium silicate solution, (2.5% by weight of SiO2 based on the basis weight of TiO2) was added to the titania pigment particles, the addition being made over a period of about twenty minutes. Subsequently, the suspension was aged (or cured) for a period of about 5 to 10 minutes. The pH was adjusted back to about 6.5 using HCl over about 60 minutes and followed by a second addition of a 0.2% P2O5 (phosphate) such as Calgon- ™ (sodium hexametaphosphate).

Next, 2% by weight of alumina was added to the suspension as sodium aluminate solution while maintaining the pH at about 6.5 using HCl over a period of about 20 minutes. This addition was followed by an aging or curing period of approximately 10 minutes, in which the pH was adjusted to approximately 5.3 with HCl. The pH was rechecked periodically and adjusted again if necessary. After stabilizing the pH, the pigment was discharged onto a filter and washed. The filter cake was dried and washed and micronized in a steam micronizer with the addition of from about 0.2% to 0.4% trimethylolpropane (TMP).

Example 2

Example 2 is a comparative example based on Example 1 except that the entire amount of phosphate was added in a single treatment step.

Example 3

Example 3 repeats the treatment of example 1, however the base pigment was TiO₂ sulfate-based rutile type. The dried product was micronized at two different intensities using a ratio of vapor to pigment of either 2.0 or 2.5.

Example 4

Example 2 was repeated, but the base pigment was rutile type titanium dioxide from a sulfate process.

ES 2 379 650 T3

Pigment durability and retention test methods

Pigments were prepared in an air-dried acrylic paint with a CPV (pigment concentration by volume) of 15% using Synocryl-9122X ™ resin. Subsequently, these paints were spread on aluminum test panels and allowed to dry for 24 hours before applying a second coat of approximately 100 pm. The panels were dried until there was no apparent tack.

The initial baseline gloss was read with a Glossgard II-TM gloss meter to establish baseline levels. The panels were then exposed to an Atlas Ci65A Weatherometer camera. The panels are then checked for gloss and spray at approximately 300 hour intervals. Gloss was measured as gloss units with the calibrated gloss meter using a calibrated gloss tile (Sheen Instruments Inc., UK).

Spraying was determined by comparing the intensity of whiteness of pigment particles that adhere to a strip of masking tape that is adhered to and subsequently removed from a test paint panel under constant pressure conditions and compared against a set of standards (available from Paint Research Institute, TNO). The spray rating was adjusted to a scale between 0 and 10, with a higher number indicating a greater amount of loose pigment particles, or more advanced spraying, and thus more paint deterioration.

40% CPV Acrylic Paint Gloss Test Method at 20 Degree

Pigment was incorporated into an acrylic paint with a CPV (pigment concentration by volume) of 40% using a Synocryl 9122X resin. The prepared paint was spread on glass panels using an automatic spreading device incorporating a doctor blade. The painted panel was allowed to dry in a dust free booth for a minimum of 5 hours before reading 20 degree gloss values ​​from a Glossgard II gloss meter. Typically, up to 5 measurements from each panel were recorded and the average result was tallied.

Table I illustrates gloss in air-dried acrylic systems using the example pigments.

Table I.

20 degree gloss test for 40% CPV on an acrylic paint system

Example 1^er set 2 ° set 3^er set

48 50 49

45 45 45

The results illustrate the systematic repeatability of the tests. In addition, Table I illustrates the 20 degree gloss gain using a split phosphate treatment (Example 1) in the acrylic paint system test with 40% pigment concentration by volume (CPV) versus single addition. phosphate (example 2).

Table II.

Gloss at 20 degrees for 40% CPV in an acrylic paint system

Micronization intensity

Example Low intensity High intensity

55 61

51 55

Table II illustrates the systematic improvement by up to ten percent of the gloss of acrylic paint with a CPV of 40% with the treatment with divided phosphate (example 3) versus the single addition of phosphate (example 4) in pigments based on sulfate. The results show a ten percent improvement in gloss that is difficult to achieve in super durable pigments (incorporating up to 6% by weight dense silica) that have this level of gloss.

Comparative durability tests

The pigments produced according to Examples 1 and 2 were subjected to durability tests in air dried acrylic paint systems together with a super durable pigment containing from four to six percent by weight of silica.

The gloss values ​​referred to in Tables III and Tables IV were measured at 20 degrees relative to perpendicular to the sample surface. The values ​​for total gloss and total spraying refer to

ES 2 379 650 T3 the sums of all individual gloss and spray values ​​respectively, recorded at regular exposure intervals of about 300 hours.

Table III.

First series after a 6994 hour exposure on an Atlas Weatherometer camera

<td>Pigment</td><td>Surface treatment</td><td>Total brightness</td><td>Full brightness / Initial brightness</td><td>Total spraying</td>

<td>Ex. 1.</td><td>2.5% SiO2</td><td> 642</td><td> 10,0</td><td> 9</td>

<td>Ex. 2.</td><td>2.5% SiO2</td><td> 581</td><td> 9,5</td><td> 12</td>

<td>Eg com. 1.</td><td>4.5% SiO2</td><td> 538</td><td> 9,0</td><td> 9</td>

<td>Eg com. 2.</td><td>3.0% SiO2</td><td> 471</td><td> 7,5</td><td> 14</td>

<td>Eg com. 3.</td><td>3.0% SiO2</td><td> 520</td><td> 8,0</td><td> 15</td>

Table IV.

8,519 hour exposure to Atlas Weatherometer

<td>Pigment</td><td>Treatment</td><td>Total brightness</td><td>Total brightness / Initial brightness</td><td>Total spraying</td>

<td>Ex. 1</td><td>2.5% SiO2</td><td> 550</td><td> 9,1</td><td> 12</td>

<td>Ex. 2</td><td>2.5% SiO2</td><td> 498</td><td> 8,3</td><td> 12</td>

<td>Ex. 3</td><td>4.5% SiO2</td><td> 438</td><td> 7,7</td><td> 12</td>

<td>Ex. 5</td><td>8.0% SiO2</td><td> 406</td><td> 8,1</td><td> 12</td>

<td>Ex. 6</td><td>5.0% SiO2</td><td> 435</td><td> 7,3</td><td> 12</td>

<td>Eg com. 1</td><td>3.0% SiO2</td><td> 405</td><td> 6,1</td><td> 16</td>

<td>Eg com. 2</td><td>3.0% SiO2</td><td> 499</td><td> 8,3</td><td> 12</td>

Table III illustrates that the divided sulfate-treated samples (Example 1) consistently performed better than the single-phase phosphate-added products (Example 2) and the competitive products in gloss retention (Ex. Com.1, Ex com 2 and / or ex com 3). The spray resistance of the split phosphate treated pigments is equal to or better than both the single phase phosphate treated sample and the three competing products.

Table IV illustrates gloss and spray values ​​for various competitive samples using different levels of silica coatings compared to embodiments of the present invention. Table IV shows that the gloss and spray values ​​of the coated pigments of the present invention are at least comparable to, if not better than, those of super durable pigments.