Color-neutral rutile pigment particles

Abstract

The present invention relates to color-neutral rutile pigment particles, a method for obtaining said pigment particles, and compositions comprising said rutile pigment particles. Finally, the present invention relates to the use of the rutile pigment particles in various applications.

Description

[Technical field]

[0001] The present invention relates to color-neutral rutile pigment particles, a method for obtaining said pigment particles, and compositions comprising said rutile pigment particles. Finally, the present invention relates to the use of the rutile pigment particles in various applications. [Background technology]

[0002] Titanium dioxide, also called titania, is a white pigment for high-end applications and exists as two important polymorphs: stable rutile and metastable anatase. As a pigment, titanium dioxide pigment imparts a white color and provides the opacity necessary to conceal the substrate to which it is applied. The sulfate and chloride processes are well-established routes for producing titanium dioxide. Depending on the end use, the chloride route is preferred over the sulfate route. In contrast to the sulfate process, the chloride process is more energy- and waste-efficient, since the chlorine is recycled and the resulting waste is less invasive to the environment. However, the sulfate route requires a lower purity starting material, such as ilmenite ore. In this regard, the higher the level of ilmenite availability, the more attractive the sulfate route becomes. In general, rutile can be produced by both the chloride and sulfate processes.

[0003] Depending on the end use, rutile is chosen over anatase due to its higher refractive index and Mohs hardness. Compared to anatase, rutile has a yellowish appearance, which is due to the different adsorption edges of both polymorphs. Furthermore, further elements such as iron, manganese and chromium, derived from the ilmenite used as starting material, can amplify the yellowness. These elements cannot be easily removed and remain as traces in the titanium dioxide.

[0004] In some end uses, a more yellowish appearance is desired. However, in many applications, a more neutral color appearance is preferred. Thus, when used in a matrix such as a paint or lacquer, the matrix will inevitably have a yellowish appearance, which is undesirable. This applies to both white and colorful applications. The latter first uses a neutral or white paint as a base layer, on which the colorful paint is applied.

[0005] In summary, there is a need in the art to have rutile pigment particles that are neutral in color, i.e., do not have a yellowish appearance. Summary of the Invention [Problem to be solved by the invention]

[0006] A technical object of the present invention is to provide rutile pigment particles that are color neutral. [Means for solving the problem]

[0007] This object is achieved by a color-neutral rutile pigment particle comprising rutile particles and at least one coating applied onto said rutile particles, said coating being doped with a blue pigment.Furthermore, this object is achieved by a method for obtaining same, a composition comprising said particles, as well as the use of the rutile pigment particles described herein.

[0008] The inventors have surprisingly found that color-neutral rutile pigment particles, comprising rutile particles and at least one coating applied on the rutile particles, suppress the inherent yellowish hue of rutile. As a consequence, when applying colorful compositions, the color of the composition must not be adapted to compensate for the yellowish hue. When the color-neutral pigment particles according to the present invention are used in white applications, the appearance is neutral and not yellowish.

[0009] Thus, in a first aspect, the present invention refers to a color-neutral rutile pigment particle comprising rutile particles and at least one coating applied onto said rutile particles, characterized in that the coating is doped with a blue pigment.

[0010] In another aspect, the present invention provides a method for producing a pharmaceutical composition comprising the steps of: a) providing an aqueous suspension of rutile pigment particles; b) adding a coating precursor to the aqueous suspension; c) adding a blue pigment or a precursor thereof to said aqueous suspension; d) forming a coating on the rutile pigment particles from the blue pigment doped coating precursor to obtain color neutral rutile pigment particles; The present invention relates to a method for obtaining color-neutral rutile pigment particles, comprising:

[0011] In yet another aspect, the present invention relates to a composition comprising color neutral rutile pigment particles as disclosed herein.

[0012] In a final aspect, the present invention relates to the use of color-neutral rutile pigment particles according to any one of claims 1 to 7 for coloring coatings, lacquers, paints, plastics, paper, coated paper or textiles. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] These and other aspects, features and advantages of the present invention will become apparent to those skilled in the art upon review of the following detailed description and claims. Each feature from one aspect of the present invention can be used in any other aspect of the present invention. Numerical ranges described in the format "from x to y" include the stated values ​​and values ​​within the respective measurement precision known to those skilled in the art. When several preferred numerical ranges are described in this format, it goes without saying that all ranges formed by combining the various endpoints are also included.

[0014] The color-neutral rutile pigment particles according to the present invention comprise rutile pigment particles and at least one coating applied onto said rutile particles, the coating being doped with a blue pigment. As used herein, "rutile pigment particles" refers to titanium dioxide in the rutile polymorph obtained by the sulfate or chloride process, optionally milled. Preferably, said pigment particles consist of at least 98% by weight, preferably at least 99% by weight, rutile based on the total weight of said pigment particles.

[0015] The color-neutral rutile pigment particles further include at least one coating. Precursors and techniques for forming such at least one coating are known in the art. The at least one coating is doped with a blue pigment. Any blue pigment known in the art that imparts a blue color can be used.

[0016] Within the scope of the present invention, rutile pigment particles ideally have a primary size such that they scatter visible light at a high rate. The particle size is the mass-related median d50 (hereinafter d50) between 200 nm and 400 nm as measured by disc centrifugation.

[0017] Preferably, a further coating is applied over at least one coating applied onto the color-neutral rutile pigment particles.

[0018] At least one coating and further coating are independently selected from the group consisting of silicon dioxide, aluminum oxide, tin oxide, zirconium oxide, cerium oxide, phosphorus oxide or mixtures thereof. It should be noted that the oxides also include their respective hydroxides, oxyhydroxides and water-containing phases. Among these, silicon dioxide and aluminum oxide are particularly preferred.

[0019] Furthermore, the color-neutral pigment particles preferably include a final coating. The "final coating" as defined herein is the outermost coating of the color-neutral rutile pigment particles. Such compounds can be selected from siloxanes, especially polydimethylsiloxane (PDMS), silanes, and alcohols, such as commercially available Tegomer DA 640, trimethylolpropane (TMP), octyltrichlorosilane (OCTCS), octyltriethoxysilane (OCTEO) or etidronic acid. The techniques of forming post-treatments are known in the art.

[0020] In a particular embodiment of the present invention, at least one coating is silicon dioxide and the further coating is aluminum oxide. This coating sequence is particularly preferred because the silicon dioxide coating suppresses the natural photocatalytic activity of rutile, and the aluminum oxide contributes to good dispersion of the color-neutral rutile pigment particles. Furthermore, the aluminum oxide covers the blue pigment so that it cannot interact with other components to which it may be exposed, for example in paints.

[0021] In another embodiment, the further coating is also doped with a blue pigment.

[0022] In a preferred embodiment, the blue pigment is selected from the group consisting of neodymium oxide, neodymium hydroxide, neodymium phosphate, Prussian blue, Egyptian blue, azurite, copper hydroxide, cobalt oxide, and mixtures thereof. As used herein, "Prussian blue" refers to the compound iron(II,III) hexacyanoferrate(II,III), and "Egyptian blue" refers to calcium copper silicate (CaCuSiO 10 As used herein, "azurite" refers to a mineral having the formula Cu2CO3(OH)2. Even more preferably, the blue pigment is selected from neodymium oxide, neodymium hydroxide, neodymium phosphate, or mixtures thereof.

[0023] In particular, at least one coating and the further coating are independently doped with 100 ppm to 100,000 ppm, preferably 500 ppm to 12,000 ppm, of the blue pigment.

[0024] The pigment particles according to the invention have a b value in the CIELAB color space standardized by EN ISO 11664-4 between +2.5 and -2.0, more preferably between +1.5 and -1.0, even more preferably between +0.75 and -0.5. * It has a value.

[0025] In a further aspect, the present invention provides a method for producing a pharmaceutical composition comprising the steps of: a) providing an aqueous suspension of rutile pigment particles; b) adding a coating precursor to the aqueous suspension; c) adding a blue pigment or a precursor thereof to said aqueous suspension; d) forming a coating on the rutile particles from the blue pigment doped coating precursor to obtain color neutral rutile pigment particles. The present invention relates to a method for obtaining pigment particles which are neutral in color, comprising the steps of:

[0026] The coating formed in step d) is either at least one coating applied directly to the rutile pigment particles or a further coating applied over the at least one coating.

[0027] The blue pigment can be selected from the group disclosed herein. Preferably, the blue pigment is added in an amount such that the coating of the color-neutral pigment particles is doped with 100 ppm to 100,000 ppm, more preferably 500 ppm to 12,000 ppm of blue pigment.

[0028] In a preferred embodiment, after step d), a further coating is formed on at least one coating of step e).The further coating can be selected from the group consisting of silicon dioxide, aluminum oxide, tin oxide, zirconium oxide, cerium oxide, phosphorus oxide or mixtures thereof.It should be noted that said oxides also include the respective hydroxides, oxyhydroxides and the respective water-containing phases.Among these, silicon dioxide and aluminum are particularly preferred.

[0029] The method steps described herein are performed in the following order: a), b), c), and d). However, the method can also be performed in the following order: a), c), b), and d). Steps b) and c) can be performed simultaneously.

[0030] Preferably, at least one coating is silicon dioxide and a further coating is aluminum oxide.

[0031] Neodymium oxide, neodymium phosphate, Egyptian blue and cobalt oxide can be used as solid compounds and can be added as blue pigments in step c). Optionally, they can be ground before being used as blue pigments. The particle size of the blue pigment is preferably less than 1,000 nm, more preferably less than 200 nm, and even more preferably less than 100 nm. The particle size is the mass-related median d50 (hereinafter d50) measured by disc centrifugation.

[0032] Neodymium hydroxide can be precipitated at an alkaline pH range above 8, preferably between 9 and 12.

[0033] Prussian blue is conventionally produced by reacting iron ions with potassium ferrocyanide in an aqueous solution having a neutral or acidic pH value, preferably a pH range of 0-8, preferably 1-4. It can be added to the suspension in step b) or can be obtained in situ by reacting the aforementioned precursors. Preferably, Prussian blue is produced in situ. This is particularly suitable when the formation of at least one coating and / or further coating in steps d) and / or e) is also achieved by lowering the pH value to an acidic pH value, such as 1-4. Silicon dioxide is also precipitated, for example, by preparing an aqueous water glass solution, preferably with a weakly to strongly alkaline pH value, and then lowering the pH to an acidic pH value, such as 1-4. As a result, Prussian blue is obtained while silicon dioxide is precipitated and a coating doped with Prussian blue is formed on the rutile pigment particles. This approach can be used for all blue pigments that can be formed in situ at acidic pH values.

[0034] Azurite can be produced by precipitation from an aqueous solution containing CuSO4 and Na2CO3, or CuSO4 and NaHCO3, at a pH value of 6.0-7.0, preferably 6.5.

[0035] Copper hydroxide can be obtained by reacting copper with water in the presence of oxygen or air. Alternatively, it can be produced by reacting sodium hydroxide with a solution of copper sulfate, preferably in the presence of ammonium chloride, to obtain a purer product.

[0036] In a further aspect, the present invention refers to a composition comprising colour-neutral rutile pigment particles according to any one of claims 1 to 7. The composition may be selected from the group consisting of coatings, lacquers, paints, plastics, paper, in particular coated paper, and fibres.

[0037] As plastic, any plastic known in the art and suitable for the purpose according to the invention can be used. As used herein, "plastic" refers to a material containing at least 50.0% by weight of a polymer, based on the total weight of the plastic. The polymer may be a homopolymer, a copolymer or a grafted polymer. Furthermore, the polymer may be an atactic, isotactic or syndiotactic polymer. Furthermore, the plastic is a thermoplastic, an elastomer, a thermoset or a thermoplastic elastomer, preferably a thermoplastic. Without being limited thereto, the polymer is selected from the group consisting of polyolefins, polystyrenes, polyamides, polyketones, polyesters, polyurethanes, poly(meth)acrylates, and mixtures thereof. Without being limited thereto, the polyolefins are selected from the group consisting of polyethylenes, polypropylenes, polybutylenes, and mixtures thereof. The color pigment particles can be incorporated into the plastic by known techniques and methods, for example by extrusion. The color pigment particles are processed into the plastic in the usual amounts. The resulting plastics therefore contain from 0.1 to 30.0% by weight, preferably from 1.0 to 25.0% by weight, of the agent according to the invention, based on the total weight of the plastic.

[0038] The use of color-neutral rutile pigment particles for coloring coatings, lacquers, paints, plastics, paper, coated paper, or textiles. EXAMPLES

[0039] Preparation of color-neutral rutile pigment particles Example 1a: Preparation of Color-Neutral Rutile Pigment Particles with Nd2O3 Rutile pigment particles (200 g) were mixed with water (1 l) to obtain an aqueous suspension. The suspension was then heated to 60° C. and the pH value was adjusted to 9.7. Zirconium sulfate was then added under stirring over a period of 15 minutes in an amount that resulted in a 0.4% by weight coating of zirconium dioxide, based on the total weight of the color-neutral rutile pigment particles. The suspension thus obtained was aged for about 30 minutes. The pH value was then reduced to about 1.

[0040] An aqueous suspension of neodymium oxide (20 ml, 5% by weight based on the weight of water) was added to the rutile pigment particle suspension over a period of 10 minutes.

[0041] Sodium aluminate was then added over a period of 40 minutes in an amount to provide a 2.4 wt. % aluminum oxide coating based on the total weight of the color-neutral rutile pigment particles. The pH was then adjusted to a value of about 7 to terminate the coating formation. The color-neutral pigment particles were filtered, washed, and dried.

[0042] Example 1b: Preparation of Color-Neutral Rutile Pigment Particles with Nd2O3 The protocol of Example 1a was followed, except that 40 ml of aqueous neodymium oxide solution was used to obtain color-neutral rutile pigment particles.

[0043] Example 1c: Preparation of Color-Neutral Rutile Pigment Particles with Nd2O3 The protocol of Example 1a was followed, except that 80 ml of aqueous neodymium oxide solution was used to obtain color-neutral rutile pigment particles.

[0044] Example 1d: Preparation of Color-Neutral Rutile Pigment Particles with Nd2O3 The protocol of Example 1d was followed, except that 160 ml of aqueous neodymium oxide solution was used to obtain color-neutral rutile pigment particles.

[0045] Test Methods and Results CIELAB Determination Color tones of Examples 1a to 1d (b *) was determined as follows: Color-neutral rutile pigment particles were pressed in the form of a powder pellet having a matte surface. An X-Rite VS450 colorimeter was used to measure the reflectance data.

[0046] The results were compared to standard rutile pigment particles. * The shifts are summarized in the table below. [Table 1]

[0047] The amount of dopant is b * It can be seen that the shift in the value of the desired b * The values ​​can be adjusted to obtain color neutral rutile pigment particles. Particle size measurement

[0048] The size of the titanium dioxide particles was measured using a CPS disc centrifuge, Model DC 20000, available from CPS Instrument, Inc., Florida, USA. The samples were prepared by mixing 2 g of dry pigment particles with 80 g of sodium hexametaphosphate solution (0.06% by weight in water) to obtain a first premix. Sodium hexametaphosphate is commercially available under the name Calgon N from BK Giulini GmbH, Ledenburg, Germany, until the first premix was homogenized. 2 g of this first premix was then added to the sodium hexametaphosphate solution (0.06% by weight in water) and mixed again to obtain a second premix. 100 μl of this second premix was used as the sample for determining the particle size. The centrifuge was operated at 3,000 rpm. The calibration standard parameters were as follows: Particle density: 1.385g / mL Peak diameter: 1.27μL Peak half-width: 0.08μL

[0049] The fluid parameters were as follows: Fluid density: 1.045g / mL Fluid refractive index: 1.344 Fluid viscosity: 1.2cps

Claims

1. 1. A color-neutral rutile pigment particle comprising: rutile pigment particles; and at least one coating applied onto said rutile particles, Color-neutral rutile pigment particles, said coating being doped with a blue pigment.

2. 10. The color-neutral rutile pigment particles of claim 1, wherein an additional coating is applied over the at least one coating applied to the rutile pigment particles.

3. the at least one coating and the further coating are independently selected from the group consisting of silicon dioxide, aluminum oxide, tin oxide, zirconium oxide, cerium oxide, phosphorus oxide, or mixtures thereof; and / or 3. The color-neutral rutile pigment particle of claim 2, wherein said at least one coating is silicon dioxide and said additional coating is aluminum oxide.

4. 3. The color-neutral rutile pigment particle of claim 2, wherein said further coating is doped with a blue pigment.

5. 10. The color-neutral rutile pigment particle of claim 1, wherein the blue pigment is selected from the group consisting of neodymium oxide, neodymium hydroxide, neodymium phosphate, Prussian blue, Egyptian blue, azurite, copper hydroxide, cobalt oxide, and mixtures thereof.

6. 6. The color-neutral rutile pigment particles of claim 5, wherein the blue pigment is neodymium oxide, neodymium hydroxide, neodymium phosphate, or a mixture thereof.

7. 3. The color-neutral rutile pigment particle of claim 2, wherein said at least one coating and said further coating are independently doped with 100 ppm to 100,000 ppm, preferably 500 ppm to 12,000 ppm, of said blue pigment.

8. The following steps: a) providing an aqueous suspension of rutile pigment particles; b) adding a coating precursor to the aqueous suspension; c) adding a blue pigment or a precursor thereof to said aqueous suspension; d) forming a coating on said rutile pigment particles from said blue pigment-doped coating precursor to obtain said color-neutral rutile pigment particles.

9. 9. The method of claim 8, wherein the coating formed in step d) is either at least one coating applied directly to the rutile pigment particles or an additional coating applied to the at least one coating.

10. 9. The method of claim 8, wherein the blue pigment is selected from the group consisting of neodymium oxide, neodymium hydroxide, Prussian blue, Egyptian blue, azurite, copper hydroxide, cobalt oxide, and mixtures thereof.

11. 9. The method of claim 8, wherein the blue pigment is added in an amount such that the coating of the color-neutral rutile pigment particles is doped with 100 ppm to 100,000 ppm, preferably 500 ppm to 12,000 ppm of the blue pigment.

12. A composition comprising the color-neutral rutile pigment particles of any one of claims 1 to 7.

13. 13. The composition of claim 12, wherein the composition is selected from the group consisting of a coating, a lacquer, a paint, a plastic, paper, coated paper, or a fiber.

14. 8. Use of the color-neutral rutile pigment particles according to any one of claims 1 to 7 for coloring coatings, lacquers, paints, plastics, paper, coated paper, or textiles.